Access the latest research conducted by Lowell Observatory astronomers, partners, and visiting scientists.

Research involving Lowell Observatory staff, 2016 to Present

This is a work ever in progress.

(Pulled from ADS by sel on 2021-06-17)


We are grateful for all the effort that went into making The SAO/NASA Astrophysics Data System (ADS) possible. The ADS is operated by the Smithsonian Astrophysical Observatory under NASA Cooperative Agreement NNX16AC86A and can be found at:

If you notice references that are missing, or ones that do not belong, please let us know (send email to sel .at. lowell plus edu).

For missing articles, please send either the ADS bibcode, or a standard short form journal citation.

Years: 2021 2020 2019 2018 2017 2016 Bottom


    1. Fayolle, M., Quirico, E., Schmitt, B., et al., 2021, Icar, 367, 114574, Testing tholins as analogues of the dark reddish material covering Pluto’s Cthulhu region

      Pluto’s fly-by by the New Horizons spacecraft in July 2015 has revealed a dark reddish equatorial region, named Cthulhu, covered by a dark, non-icy material whose origin and composition have yet to be determined. It has been suggested that this material could form from the sedimentation of photochemical aerosols, originating from dissociation and ionisation processes in Pluto’s high atmosphere (similarly to aerosols forming Titan’s haze). This hypothesis is here further investigated by comparing New Horizons spectra collected both in the visible and the near-infrared to laboratory reflectance measurements of analogues of Pluto’s aerosols (Pluto tholins). These aerosols were synthesised in conditions mimicking Pluto’s atmosphere, and their optical and reflectance properties were determined, before being used in Hapke models. In particular, the single scattering albedo and phase function of Pluto tholins were retrieved through Hapke model inversion, performed from laboratory reflectance spectra collected under various geometries. From reconstructed reflectance spectra and direct comparison with New Horizons data, some of these tholins are shown to reproduce the photometric level (i.e. reflectance continuum) reasonably well in the near-infrared. Nevertheless, a misfit of the red visible slope still remains and tholins absorption bands present in the modelled spectra are absent in those collected by the New Horizons instruments. Several hypotheses are considered to explain the absence of these absorption features in LEISA data, namely high porosity effects or GCR irradiation. The formation of highly porous structures, which is currently our preferred scenario, could be promoted by either sublimation of ices initially mixed with the aerosols, or gentle deposition under Pluto’s weak gravity.

    2. Jenniskens, Peter, Lauretta, Dante S., Towner, Martin C., et al., 2021, Icar, 365, 114469, Meteor showers from known long-period comets

      What long-period comets with orbital periods >250 years cause detectable meteor showers on Earth? Low-light video cameras are used to track the motion of +4 to -5 magnitude meteors in our atmosphere by triangulation and calculate the meteoroid orbit in space. In recent years, the CAMS (Cameras for Allsky Meteor Surveillance) low-light video camera network was greatly expanded and, together with other video networks, now has increased the total video meteoroid orbit database to over 2.2 million orbits. Here, we searched this database for meteor showers associated with known long-period comets. Previously, five associations were known. Now, we find 14, as well as six uncertain but likely associations. These showers show a change of longitude of perihelion with node that is a strong function of inclination. Showers of longer duration show a steeper magnitude distribution index, presumably due to aging of the meteoroid population. Showers are generally detected only if the orbital period of the comet is less than 4000 years and the Earth-Comet orbital miss distance is 0.10 AU. The lack of an associated meteor shower sets lower limits on the orbital period of poorly observed comets.

    3. Linscott, I. R., Bird, M. K., Hinson, D. P., et al., 2021, Icar, 363, 114430, High-resolution radiometry of Pluto at 4.2 cm with New Horizons

      The radio thermal emission from Pluto was observed from the New Horizons spacecraft at a wavelength of 4.2 cm along two scans across the planetary disk shortly after closest approach to Pluto on 14 July 2015. The measurements were performed as part of the New Horizons Radio Science Experiment (REX) using the 2.1 m High Gain Antenna (HGA) and the spacecraft’s X-Band receiver. The HGA boresight first scanned along a diametric chord across the Pluto disk and then reversed direction to traverse a chord that crossed close to Pluto’s winter pole. The diametric scan reveals a “hot spot” on the Pluto nightside associated with an optically bright region centered roughly at the planetocentric coordinates 280 E, 55 S, imaged in 2002-03 with the Hubble Space Telescope. The nightside was also found to be warmer than the dayside during the polar scan. The highest emission was not observed at the maximum southern latitude, however, but rather near the outbound Pluto limb at lower latitude. The REX emission profile from the polar scan is qualitatively consistent with a bright U-shaped polar cap observed on Pluto’s Charon-facing hemisphere during the recurring Pluto/Charon mutual events in the late 1980’s. The REX radiometer measurements show distinct variations in microwave brightness that constrain volatile transport models and provide unique information on the thermal structure and composition on the regions in winter night during the New Horizons encounter at Pluto.

    4. Stahl, Asa G., Tang, Shih-Yun, Johns-Krull, Christopher M., et al., 2021, AJ, 161, 283, IGRINS RV: A Precision Radial Velocity Pipeline for IGRINS Using Modified Forward Modeling in the Near-infrared

      Application of the radial velocity (RV) technique in the near-infrared is valuable because of the diminished impact of stellar activity at longer wavelengths, making it particularly advantageous for the study of late-type stars but also for solar-type objects. In this paper, we present the IGRINS RV open-source python pipeline for computing infrared RV measurements from reduced spectra taken with IGRINS, an R / 45,000 spectrograph with simultaneous coverage of the H band (1.49-1.80 m) and K band (1.96-2.46 m). Using a modified forward-modeling technique, we construct high-resolution telluric templates from A0 standard observations on a nightly basis to provide a source of common-path wavelength calibration while mitigating the need to mask or correct for telluric absorption. Telluric standard observations are also used to model the variations in instrumental resolution across the detector, including a yearlong period when the K band was defocused. Without any additional instrument hardware, such as a gas cell or laser frequency comb, we are able to achieve precisions of 26.8 m s-1 in the K band and 31.1 m s-1 in the H band for narrow-line hosts. These precisions are empirically determined by a monitoring campaign of two RV standard stars, as well as the successful retrieval of planet-induced RV signals for both HD 189733 and Boo A; furthermore, our results affirm the presence of the Rossiter-McLaughlin effect for HD 189733. The IGRINS RV pipeline extends another important science capability to IGRINS, with publicly available software designed for widespread use. *

    5. Benedict, G. Fritz, Franz, Otto G., Horch, Elliott P., et al., 2021, AJ, 161, 285, Dissecting the Quadruple Binary Hyad vA 351 Masses for Three M Dwarfs and a White Dwarf

      We extend results first announced by Franz et al., that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, $P=2.70\,\mathrm{yr}$ and total mass 2.1 ${{ \mathcal M }}_{\odot }$ . With ground-based radial velocities from the McDonald Observatory Otto Struve 2.1 m Telescope Sandiford Spectrograph, and Center for Astrophysics Digital Speedometers, spanning 37 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period ( ${P}_{\mathrm{BC}}=0.749$ days), having a mass ratio ${{ \mathcal M }}_{{\rm{C}}}$ / ${{ \mathcal M }}_{{\rm{B}}}$ = 0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher-mass component. The quadruple system consists of three M dwarfs (A, B, C) and one white dwarf (D). We determine individual M dwarf masses ${{ \mathcal M }}_{{\rm{A}}}$ = 0.53 0.10 ${{ \mathcal M }}_{\odot }$ , ${{ \mathcal M }}_{{\rm{B}}}$ = 0.43 0.04 ${{ \mathcal M }}_{\odot }$ , and ${{ \mathcal M }}_{{\rm{C}}}$ = 0.41 0.04 ${{ \mathcal M }}_{\odot }$ . The white dwarf mass, 0.54 0.04 ${{ \mathcal M }}_{\odot }$ , comes from cooling models, an assumed Hyades age of 670 Myr, and consistency with all previous and derived astrometric, photometric, and radial velocity results. Velocities from H and He I emission lines confirm the BC period derived from absorption lines, with similar (He I) and higher (H) velocity amplitudes. We ascribe the larger H amplitude to emission from a region each component shadows from the other, depending on the line of sight. * We dedicate this paper to John Stauffer, who died on 2021 January 29, in honor of his many contributions to the field.

    6. Horch, Elliott P., Broderick, Kyle G., Casetti-Dinescu, Dana I., et al., 2021, AJ, 161, 295, Observations with the Differential Speckle Survey Instrument. X. Preliminary Orbits of K-dwarf Binaries and Other Stars

      This paper details speckle observations of binary stars taken at the Lowell Discovery Telescope, the WIYN telescope, and the Gemini telescopes between 2016 January and 2019 September. The observations taken at Gemini and Lowell were done with the Differential Speckle Survey Instrument (DSSI), and those done at WIYN were taken with the successor instrument to DSSI at that site, the NN-EXPLORE Exoplanet Star and Speckle Imager (NESSI). In total, we present 378 observations of 178 systems, and we show that the uncertainty in the measurement precision for the combined data set is 2 mas in separation, 1-2 in position angle depending on the separation, and 0.1 mag in magnitude difference. Together with data already in the literature, these new results permit 25 visual orbits and one spectroscopic-visual orbit to be calculated for the first time. In the case of the spectroscopic-visual analysis, which is done on the ternary star HD 173093, we calculate masses with a precision of better than 1% for all three stars in that system. Twenty-one of the visual orbits calculated have a K dwarf as the primary star; we add these to the known orbits of K-dwarf primary stars and discuss the basic orbital properties of these stars at this stage. Although incomplete, the data that exist so far indicate that binaries with K-dwarf primaries tend not to have low-eccentricity orbits at separations of one to a few tens of astronomical units, that is, on solar system scales.

    7. Sevilla-Noarbe, I., Bechtol, K., Carrasco Kind, M., et al., 2021, ApJS, 254, 24, Dark Energy Survey Year 3 Results: Photometric Data Set for Cosmology

      We describe the Dark Energy Survey (DES) photometric data set assembled from the first three years of science operations to support DES Year 3 cosmologic analyses, and provide usage notes aimed at the broad astrophysics community. Y3 GOLD improves on previous releases from DES, Y1 GOLD, and Data Release 1 (DES DR1), presenting an expanded and curated data set that incorporates algorithmic developments in image detrending and processing, photometric calibration, and object classification. Y3 GOLD comprises nearly 5000 deg2 of grizY imaging in the south Galactic cap, including nearly 390 million objects, with depth reaching a signal-to-noise ratio 10 for extended objects up to iAB 23.0, and top-of-the-atmosphere photometric uniformity <3 mmag. Compared to DR1, photometric residuals with respect to Gaia are reduced by 50%, and per-object chromatic corrections are introduced. Y3 GOLD augments DES DR1 with simultaneous fits to multi-epoch photometry for more robust galactic color measurements and corresponding photometric redshift estimates. Y3 GOLD features improved morphological star-galaxy classification with efficiency >98% and purity >99% for galaxies with 19 < iAB < 22.5. Additionally, it includes per-object quality information, and accompanying maps of the footprint coverage, masked regions, imaging depth, survey conditions, and astrophysical foregrounds that are used to select the cosmologic analysis samples.

    8. Tang, Shih-Yun, Stahl, Asa, Johns-Krull, Christopher, et al., 2021, JOSS, 6, 3095, IGRINS RV: A Python Package for Precision Radial Velocities with Near-Infrared Spectra
    9. Grandis, S., Mohr, J. J., Costanzi, M., et al., 2021, MNRAS, 504, 1253, Exploring the contamination of the DES-Y1 cluster sample with SPT-SZ selected clusters

      We perform a cross validation of the cluster catalogue selected by the red-sequence Matched-filter Probabilistic Percolation algorithm (redMaPPer) in Dark Energy Survey year 1 (DES-Y1) data by matching it with the Sunyaev-Zel’dovich effect (SZE) selected cluster catalogue from the South Pole Telescope SPT-SZ survey. Of the 1005 redMaPPer selected clusters with measured richness \hat > 40 in the joint footprint, 207 are confirmed by SPT-SZ. Using the mass information from the SZE signal, we calibrate the richness-mass relation using a Bayesian cluster population model. We find a mass trend MB consistent with a linear relation (B 1), no significant redshift evolution and an intrinsic scatter in richness of = 0.22 0.06. By considering two error models, we explore the impact of projection effects on the richness-mass modelling, confirming that such effects are not detectable at the current level of systematic uncertainties. At low richness SPT-SZ confirms fewer redMaPPer clusters than expected. We interpret this richness dependent deficit in confirmed systems as due to the increased presence at low richness of low-mass objects not correctly accounted for by our richness-mass scatter model, which we call contaminants. At a richness \hat = 40, this population makes up > 12 per cent (97.5 percentile) of the total population. Extrapolating this to a measured richness \hat = 20 yields > 22 per cent (97.5 percentile). With these contamination fractions, the predicted redMaPPer number counts in different plausible cosmologies are compatible with the measured abundance. The presence of such a population is also a plausible explanation for the different mass trends (B 0.75) obtained from mass calibration using purely optically selected clusters. The mean mass from stacked weak lensing (WL) measurements suggests that these low-mass contaminants are galaxy groups with masses 3-5 1013 M which are beyond the sensitivity of current SZE and X-ray surveys but a natural target for SPT-3G and eROSITA.

    10. Inserra, C., Sullivan, M., Angus, C. R., et al., 2021, MNRAS, 504, 2535, The first Hubble diagram and cosmological constraints using superluminous supernovae

      We present the first Hubble diagram of superluminous supernovae (SLSNe) out to a redshift of two, together with constraints on the matter density, M, and the dark energy equation-of-state parameter, w(p/). We build a sample of 20 cosmologically useful SLSNe I based on light curve and spectroscopy quality cuts. We confirm the robustness of the peak-decline SLSN I standardization relation with a larger data set and improved fitting techniques than previous works. We then solve the SLSN model based on the above standardization via minimization of the 2 computed from a covariance matrix that includes statistical and systematic uncertainties. For a spatially flat cold dark matter (CDM) cosmological model, we find M = 0.38-0.19+0.24, with an rms of 0.27 mag for the residuals of the distance moduli. For a w0waCDM cosmological model, the addition of SLSNe I to a ‘baseline’ measurement consisting of Planck temperature together with Type Ia supernovae, results in a small improvement in the constraints of w0 and wa of 4 per cent. We present simulations of future surveys with 868 and 492 SLSNe I (depending on the configuration used) and show that such a sample can deliver cosmological constraints in a flat CDM model with the same precision (considering only statistical uncertainties) as current surveys that use Type Ia supernovae, while providing a factor of 2-3 improvement in the precision of the constraints on the time variation of dark energy, w0 and wa. This paper represents the proof of concept for superluminous supernova cosmology, and demonstrates they can provide an independent test of cosmology in the high-redshift (z > 1) universe.

    11. Knight, Matthew M., Schleicher, David G., Farnham, Tony L., 2021, PSJ, 2, 104, Narrowband Observations of Comet 46P/Wirtanen during Its Exceptional Apparition of 2018/19. II. Photometry, Jet Morphology, and Modeling Results

      We report on our extensive photometry and imaging of comet 46P/Wirtanen during its 2018/19 apparition and use these data to constrain the modeling of Wirtanen’s activity. Narrowband photometry was obtained in 9 epochs from 2018 October through 2019 March as well as 10 epochs during the 1991, 1997, and 2008 apparitions. The ensemble photometry reveals a typical composition and a secular decrease in activity since 1991. Production rates were roughly symmetric around perihelion for the carbon-bearing species (CN, C3, and C2), but steeper for OH and NH outbound. Our imaging program emphasized CN, whose coma morphology and lightcurve yielded rotation periods reported in a companion paper (Farnham et al. 2021). Here, we compare the gas and dust morphology on the 18 nights for which observations of additional species were obtained. The carbon-bearing species exhibited similar morphology that varied with rotation. OH and NH had broad, hemispheric brightness enhancements in the tailward direction that did not change significantly with rotation, which we attribute to their originating from a substantial icy grain component. We constructed a Monte Carlo model that replicates the shape, motion, and brightness distribution of the CN coma throughout the apparition with a single, self-consistent solution in principal axis rotation. Our model yields a pole having (R.A., decl.) = 319, -5 (pole obliquity of 70) and two large sources (radii of 50 and 40) centered at near-equatorial latitudes and separated in longitude by 160. Applications of the model to explain observed behaviors are discussed.

    12. Levine, Stephen E., Zuluaga, Carlos A., Person, Michael J., et al., 2021, AJ, 161, 210, Occultation of a Large Star by the Large Plutino (28978) Ixion on 2020 October 13 UTC

      We observed the occultation of the star Gaia DR2 4056440205544338944 by (28978) Ixion. The event was observed from two Lowell Observatory sites, using the 4.3 m Lowell Discovery Telescope (LDT), near Happy Jack, AZ, USA, and a 0.32 m telescope co-mounted with the Titan Monitoring telescope on Lowell’s Mars Hill campus in Flagstaff, AZ. The LDT chord, at 44.86 s, was roughly 30% longer than the longest predicted possible chord. Under the assumption of a spherical body, Ixion’s fitted diameter D = 709.6 0.2 km. The LDT light-curve profile was used to place an upper limit on the surface pressure P < 2 bar on any possible atmosphere of Ixion. At the distance of Ixion, the occulted star had a fitted projected diameter of 19.25 0.3 km assuming uniform disk illumination, giving a stellar angular diameter of 0.675 0.010 mas. Using the Gaia EDR3 parallax of 0.565 mas, the stellar radius is ${130}_{-17}^{+20}\,{R}_{\odot }$ <!– –> . The measured size is consistent with prior spectral classification of this star as a reddened mid-M giant. This is one of only a modest number of M5 III stars to have a directly measured diameter, and is more distant than most.

    13. Holler, Bryan, Milam, Stefanie N., Bauer, James M., et al., 2021, BAAS, 53, 030, Minor Body Science with the Nancy Grace Roman Space Telescope

      There is a long history of solar system observations with space telescopes. The Nancy Grace Roman Space Telescope will have a larger aperture, larger field of view, and more sensitive instrumentation than its predecessors. The prospects for solar system science are substantial, particularly in the area of surveys for the detection of minor bodies.

    14. Brown, Adrian, Videen, Gorden, Byrne, Shane, et al., 2021, BAAS, 53, 036, The case for a multi-channel polarization sensitive LIDAR for investigation of insolation-driven ices and atmospheres

      All LIDAR instruments are not the same, and advancement of LIDAR technology requires an ongoing interest and demand from the community to foster further development of the required components. The purpose of this white paper is to make the decadal survey panel aware of the need for further technical development, and the potential payoff of LIDARs.

    15. Rivera-Valentin, Edgard, Martinez, German, Filiberto, Justin, et al., 2021, BAAS, 53, 091, Resolving the water cycle on a salty Mars: Planetary science and astrobiology exploration strategies for the next decade

      Atmosphere-regolith water vapor exchange processes are an important aspect of the Martian water cycle. Hygroscopic salts in the regolith furthers its role because salts lead to temperature- and humidity-dependent exchange processes. Here, we identify knowledge gaps in these processes and recommend strategies to resolve the Martian water cycle.

    16. MacKenzie, Shannon, Birch, Sam, Horst, Sarah, et al., 2021, BAAS, 53, 124, Titan: Earth-like on the Outside, Ocean World on the Inside

      As the organic-rich endmember of the Ocean World spectrum and host of the most Earth-like atmosphere-surface interactions, the exploration of Titan is essential to a successful Ocean Worlds program and the study of terrestrial bodies, atmospheres, and exoplanets. Dragonfly will revolutionize our understanding but global questions will remain.

    17. Fayolle, Edith, Barge, Laurie, Cable, Morgan, et al., 2021, BAAS, 53, 170, Critical Laboratory Studies to Advance Planetary Science and Support Missions

      Laboratory studies are crucial to interpret observations and mission data, are key incubators for mission and instrument development, and are needed to assess habitability and search for life beyond Earth. Here we present an overview of the planetary science areas where laboratory studies are critically needed and make recommendations accordingly.

    18. Smith, Isaac, Calvin, W. M., Smith, D. E., et al., 2021, BAAS, 53, 301, Solar-System-Wide Significance of Mars Polar Science

      Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

    19. Barnes, Jason W., Hayes, Alexander G., Soderblom, Jason M., et al., 2021, BAAS, 53, 317, New Frontiers Titan Orbiter

      As one of two planetary objects (other than Earth) that have solid surfaces, thick atmospheres, and astrobiological significance, Titan, like Mars, merits ongoing study with multiple spacecraft. We propose that a Titan orbiter dedicated to geophysics, geology, and atmospheric science be added to the New Frontiers menu for the coming decade.

    20. Brisset, Julie, Fernandez-Valenzuela, Estela, Sickafoose, Amanda, et al., 2021, BAAS, 53, 335, Understanding the Formation and Evolution of the Kuiper Belt by Exploring the Haumea System

      The in-situ observation and data collection at the dwarf planet Haumea would provide for invaluable insight into the history of the Kuiper Belt and the Solar System I as well as the on-going processes that lead to high spin rates, rings, and satellite systems. In this white paper, we will make a case for an exploration mission to the Haumea system.

    21. van Belle, Gerard, Kugler, Justin, Moskovitz, Nick, et al., 2021, BAAS, 53, 338, LightBeam: Flyby-Like Imaging Without The Flyby

      The LightBeam spacecraft is a mission concept for a facility providing milliarcsecond-class imaging of solar system objects, from NEOs to the main belt to Jupiter Trojans. LightBeam achieves this via innovative in-space manufacturing techniques which enable a long-baseline optical interferometer to be flown in a cost-effective smallsat package.

    22. Smith, Isaac, Hayne, Paul O., Byrne, Shane, et al., 2021, BAAS, 53, 378, Unlocking the Climate Record Stored within Mars’ Polar Layered Deposits

      We present the science drivers and a mission concept for a polar lander that would enable a future reading of the past few million years of the Martian climate record.

    23. Scipioni, F., White, O., Cook, J. C., et al., 2021, Icar, 359, 114303, Pluto’s Sputnik Planitia: Composition of geological units from infrared spectroscopy

      We have compared spectroscopic data of Sputnik Planitia on Pluto, as acquired by New Horizons’ Linear Etalon Imaging Spectral Array (LEISA) instrument, to the geomorphology as mapped by White et al. (2017) using visible and panchromatic imaging acquired by the LOng-Range Reconnaissance Imager (LORRI) and the Multi-spectral Visible Imaging Camera (MVIC). We have focused on 13 of the geologic units identified by White et al. (2017), which include the plains and mountain units contained within the Sputnik basin. We divided the map of Sputnik Planitia into 15 provinces, each containing one or more geologic units, and we use LEISA to calculate the average spectra of the units inside the 15 provinces. Hapke-based modeling was then applied to the average spectra of the units to infer their surface composition, and to determine if the composition resulting from the modeling of LEISA spectra reflects the geomorphologic analyses of LORRI data, and if areas classified as being the same geologically, but which are geographically separated, share a similar composition. We investigated the spatial distribution of the most abundant ices on Pluto’s surface – CH4, N2, CO, H2O, and a non-ice component presumed to be a macromolecular carbon-rich material, termed a tholin, that imparts a positive spectral slope in the visible spectral region and a negative spectral slope longward of ~1.1 m. Because the exact nature of the non-ice component is still debated and because the negative spectral slope of the available tholins in the near infrared does not perfectly match the Pluto data, for spectral modeling purposes we reference it generically as the negative spectral slope endmember (NSS endmember). We created maps of variations in the integrated band depth (from LEISA data) and areal mass fraction (from the modeling) of the components. The analysis of correlations between the occurrences of the endmembers in the geologic units led to the observation of an anomalous suppression of the strong CH4 absorption bands in units with compositions that are dominated by H2O ice and the NSS endmember. Exploring the mutual variation of the CH4 and N2 integrated band depths with the abundance of crystalline H2O and NSS endmember revealed that the NSS endmember is primarily responsible for the suppression of CH4 absorptions in mountainous units located along the western edge of Sputnik Planitia. Our spectroscopic analyses have provided additional insight into the geological processes that have shaped Sputnik Planitia. A general increase in volatile abundance from the north to the south of Sputnik Planitia is observed. Such an increase first observed and interpreted by Protopapa et al., 2017 and later confirmed by climate modeling (Bertrand et al., 2018) is expressed geomorphologically in the form of preferential deposition of N2 ice in the upland and mountainous regions bordering the plains of southern Sputnik Planitia. Relatively high amounts of pure CH4 are seen at the southern Tenzing Montes, which are a natural site for CH4 deposition owing to their great elevation and the lower insolation they are presently receiving. The NSS endmember correlates the existence of tholins within certain units, mostly those coating the low-latitude mountain ranges that are co-latitudinal with the tholin-covered Cthulhu Macula. The spectral analysis has also revealed compositional differences between the handful of occurrences of northern non-cellular plains and the surrounding cellular plains, all of which are located within the portion of Sputnik Planitia that is presently experiencing net sublimation of volatiles, and which do not therefore exhibit a surface layer of bright, freshly-deposited N2 ice. The compositional differences between the cellular and non-cellular plains here hint at the effectiveness of convection in entraining and trapping tholins within the body of the cellular plains, while preventing the spread of such tholins to abutting non-cellular plains.

    24. Scheirich, P., Pravec, P., Kusnirak, P., et al., 2021, Icar, 360, 114321, A satellite orbit drift in binary near-Earth asteroids (66391) 1999 KW4 and (88710) 2001 SL9 – Indication of the BYORP effect

      We obtained thorough photometric observations of two binary near-Earth asteroids (66391) Moshup = 1999 KW4 and (88710) 2001 SL9 taken from 2000 to 2019. We modeled the data and derived physical and dynamical properties of the binary systems. For (66391) 1999 KW4, we derived its mutual orbit’s pole, semimajor axis and eccentricity that are in agreement with radar-derived values (Ostro et al., 2006. Science, 314, 1276-1280). However, we found that the data are inconsistent with a constant orbital period and we obtained unique solution with a quadratic drift of the mean anomaly of the satellite of -0.65 0.16 deg./yr2 (all quoted uncertainties correspond to 3). This means that the semimajor axis of the mutual orbit of the components of this binary system, determined a = 2.548 0.015 km by Ostro et al. (2006), increases in time with a mean rate of 1.2 0.3 cm/yr.


      For (88710) 2001 SL9, we determined that the mutual orbit has a pole within 10 of (L, B) = (302, -73) (ecliptic coordinates), and is close to circular (eccentricity < 0.07). The data for this system are also inconsistent with a constant orbital period and we obtained two solutions for the quadratic drift of the mean anomaly: 2.8 0.2 and 5.2 0.2 deg./yr2, implying that the semimajor axis of the mutual orbit of the components (estimated a ~ 1.6 km) decreases in time with a mean rate of -2.8 0.2 or -5.1 0.2 cm/yr for the two solutions, respectively.

      The expanding orbit of (66391) 1999 KW4 may be explained by mutual tides interplaying with binary YORP (BYORP) effect (McMahon and Scheeres, 2010a. Icarus 209, 494-509). However, a modeling of the BYORP drift using radar-derived shapes of the binary components predicted a much higher value of the orbital drift than the observed one. It suggests that either the radar-derived shape model of the secondary is inadequate for computing the BYORP effect, or the present theory of BYORP overestimates it. It is possible that the BYORP coefficient has instead an opposite sign than predicted; in that case, the system may be moving into an equilibrium between the BYORP and the tides.

      In the case of (88710) 2001 SL9, the BYORP effect is the only known physical mechanism that can cause the inward drift of its mutual orbit.

      Together with the binary (175706) 1996 FG3 which has a mean anomaly drift consistent with zero, implying a stable equilibrium between the BYORP effect and mutual body tides (Scheirich et al., 2015. Icarus 245, 56-63), we now have three distinct cases of well observed binary asteroid systems with their long-term dynamical models inferred. They indicate a presence of all the three states of the mutual orbit evolution – equilibrium, expanding and contracting – in the population of near-Earth binary asteroids.

    25. Doux, C., Baxter, E., Lemos, P., et al., 2021, MNRAS, 503, 2688, Dark energy survey internal consistency tests of the joint cosmological probes analysis with posterior predictive distributions

      Beyond CDM, physics or systematic errors may cause subsets of a cosmological data set to appear inconsistent when analysed assuming CDM. We present an application of internal consistency tests to measurements from the Dark Energy Survey Year 1 (DES Y1) joint probes analysis. Our analysis relies on computing the posterior predictive distribution (PPD) for these data under the assumption of CDM. We find that the DES Y1 data have an acceptable goodness of fit to CDM, with a probability of finding a worse fit by random chance of p = 0.046. Using numerical PPD tests, supplemented by graphical checks, we show that most of the data vector appears completely consistent with expectations, although we observe a small tension between large- and small-scale measurements. A small part (roughly 1.5 per cent) of the data vector shows an unusually large departure from expectations; excluding this part of the data has negligible impact on cosmological constraints, but does significantly improve the p-value to 0.10. The methodology developed here will be applied to test the consistency of DES Year 3 joint probes data sets.

    26. Hillier, D. John, Aadland, Erin, Massey, Philip, et al., 2021, MNRAS, 503, 2726, BAT99-9 – a WC4 Wolf-Rayet star with nitrogen emission: evidence for binary evolution?

      An analysis of the Large Magellanic Cloud (LMC) WC4 star BAT99-9 (HD 32125, FD 4, Brey 7, WS 3) shows that the star still contains photospheric nitrogen. Three N emission features (N V 1238, 1242, N IV 1719, and N IV 3479-3485) are unambiguously identified in the spectrum. CMFGEN models of the star yield an N/C ratio of 0.004 0.002 (by number) and a C/He ratio of $0.15_{-0.05}^{+0.10}$ . Due to the similarity of BAT99-9 to other WC4 stars, and the good fit achieved by CMFGEN to both the classic WC4 spectrum and the N lines, we argue that the N lines are intrinsic to BAT99-9. An examination of a limited set of rotating models for single-star evolution at LMC and Galactic metallicities shows that a model with a Galactic metallicity (z = 0.014) and a progenitor mass of around 50 M can have an N/C ratio similar to, or larger than, what we observe for a significant fraction of its lifetime. However, the LMC models (z = 0.006) are inconsistent with the observations. Both the single and binary BPASS models predict that many WC stars can have an N/C ratio similar to, or larger than, what we observe for a significant fraction of their lifetime. While the binary models cover a wider range of luminosities and provide a somewhat better match to BAT99-9, it is not currently possible to rule out BAT99-9 being formed through single-star evolution, given the uncertainties in mass-loss rates, and the treatment of convection and mixing processes.

    27. Doux, C., Chang, C., Jain, B., et al., 2021, MNRAS, 503, 3796, Consistency of cosmic shear analyses in harmonic and real space

      Recent cosmic shear studies have reported discrepancies of up to 1 on the parameter ${S_{8}=\sigma _{8}\sqrt{{\Omega _{\rm m}}/0.3}}$ between the analysis of shear power spectra and two-point correlation functions, derived from the same shear catalogues. It is not a priori clear whether the measured discrepancies are consistent with statistical fluctuations. In this paper, we investigate this issue in the context of the forthcoming analyses from the third year data of the Dark Energy Survey (DES Y3). We analyse DES Y3 mock catalogues from Gaussian simulations with a fast and accurate importance sampling pipeline. We show that the methodology for determining matching scale cuts in harmonic and real space is the key factor that contributes to the scatter between constraints derived from the two statistics. We compare the published scales cuts of the KiDS, Subaru-HSC, and DES surveys, and find that the correlation coefficients of posterior means range from over 80 per cent for our proposed cuts, down to 10 per cent for cuts used in the literature. We then study the interaction between scale cuts and systematic uncertainties arising from multiple sources: non-linear power spectrum, baryonic feedback, intrinsic alignments, uncertainties in the point spread function, and redshift distributions. We find that, given DES Y3 characteristics and proposed cuts, these uncertainties affect the two statistics similarly; the differential biases are below a third of the statistical uncertainty, with the largest biases arising from intrinsic alignment and baryonic feedback. While this work is aimed at DES Y3, the tools developed can be applied to Stage-IV surveys where statistical errors will be much smaller.

    28. Devogele, Maxime, Ferrais, Marin, Jehin, Emmanuel, et al., 2021, MNRAS, (6478) Gault: Physical characterization of an active main-belt asteroid

      In December 2018, the main-belt asteroid (6478) Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of P = 2.4929 0.0003 hours with a lightcurve amplitude of 0.06 magnitude. This short rotation period close to the spin barrier limit is consistent with Gault having a density no smaller than = 1.85 g cm-3 and its activity being triggered by the YORP spin-up mechanism. Analysis of the Gault phase curve over phase angles ranging from 0.4 to 23.6 provides an absolute magnitude of H = 14.81 0.04, G1 = 0.25 0.07, and G2 = 0.38 0.04. Model fits to the phase curve find the surface regolith grain size constrained between 100-500 m. Using relations between the phase curve and albedo we determine that the geometrical albedo of Gault is pv = 0.26 0.05 corresponding to an equivalent diameter of D = 2.8-0.2+0.4 km. Our spectroscopic observations are all consistent with an ordinary chondrite-like composition (S, or Q-type in the Bus-DeMeo taxonomic classification). A search through archival photographic plate surveys found previously unidentified detections of Gault dating back to 1957 and 1958. Only the latter had been digitized, which we measured to nearly double the observation arc of Gault. Finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit.

    29. Eisner, N. L., Nicholson, B. A., Barragan, O., et al., 2021, MNRAS, Planet Hunters TESS III: Two transiting planets around the bright G dwarf HD 152843

      We report on the discovery and validation of a two-planet system around a bright (V = 8.85 mag) early G dwarf (1.43 R , 1.15 M , TOI 2319) using data from NASA’s Transiting Exoplanet Survey Satellite (TESS). Three transit events from two planets were detected by citizen scientists in the month-long TESS light curve (sector 25), as part of the Planet Hunters TESS project. Modelling of the transits yields an orbital period of 11.6264-0.0025+0.0022 days and radius of 3.41-0.12+0.14 R for the inner planet, and a period in the range 19.26-35 days and a radius of 5.83-0.14+0.14 R for the outer planet, which was only seen to transit once. Each signal was independently statistically validated, taking into consideration the TESS light curve as well as the ground-based spectroscopic follow-up observations. Radial velocities from HARPS-N and EXPRES yield a tentative detection of planet b, whose mass we estimate to be 11.56-6.14+6.58 M, and allow us to place an upper limit of 27.5 M (99 per cent confidence) on the mass of planet c. Due to the brightness of the host star and the strong likelihood of an extended H/He atmosphere on both planets, this system offers excellent prospects for atmospheric characterisation and comparative planetology.

    30. Claytor, Zachary R., Lucas, Miles, Llama, Joe, 2021, zndo, Butterpy: realistic star spot evolution and light curves in Python

      Generate star spot evolution and light curves following the models of Mackay et al. (2004), Llama et al. (2012), and Aigrain et al. (2015). This software is an open-source version, with some slight modifications, of what was introduced and used by Aigrain et al. (2015). View on GitHub: View on PyPI:

    31. Hunter, Deidre A., Elmegreen, Bruce G., Archer, Haylee, et al., 2021, AJ, 161, 175, A Search for Correlations between Turbulence and Star Formation in LITTLE THINGS Dwarf Irregular Galaxies

      Turbulence has the potential for creating gas density enhancements that initiate cloud and star formation (SF), and it can be generated locally by SF. To study the connection between turbulence and SF, we looked for relationships between SF traced by FUV images, and gas turbulence traced by kinetic energy density (KED) and velocity dispersion (vdisp) in the LITTLE THINGS sample of nearby dIrr galaxies. We performed 2D cross-correlations between FUV and KED images, measured cross-correlations in annuli to produce correlation coefficients as a function of radius, and determined the cumulative distribution function of the cross-correlation value. We also plotted on a pixel-by-pixel basis the locally excess KED, vdisp, and H I mass surface density, HI, as determined from the respective values with the radial profiles subtracted, versus the excess SF rate density SFR, for all regions with positive excess SFR. We found that SFR and KED are poorly correlated. The excess KED associated with SF implies a 0.5% efficiency for supernova energy to pump local H I turbulence on the scale of the resolution here, which is a factor of 2 too small for all of the turbulence on a galactic scale. The excess vdisp in SF regions is also small, only 0.37 km s-1. The local excess in HI corresponding to an excess in SFR is consistent with a H I consumption time of 1.6 Gyr in the inner parts of the galaxies. The similarity between this timescale and the consumption time for CO implies that CO-dark molecular gas has comparable mass to H I in the inner disks.

    32. Stringer, K. M., Drlica-Wagner, A., Macri, L., et al., 2021, ApJ, 911, 109, Identifying RR Lyrae Variable Stars in Six Years of the Dark Energy Survey

      We present a search for RR Lyrae stars using the full six-year data set from the Dark Energy Survey covering 5000 deg2 of the southern sky. Using a multistage multivariate classification and light-curve template-fitting scheme, we identify RR Lyrae candidates with a median of 35 observations per candidate. We detect 6971 RR Lyrae candidates out to 335 kpc, and we estimate that our sample is >70% complete at 150 kpc. We find excellent agreement with other wide-area RR Lyrae catalogs and RR Lyrae studies targeting the Magellanic Clouds and other Milky Way satellite galaxies. We fit the smooth stellar halo density profile using a broken-power-law model with fixed halo flattening (q = 0.7), and we find strong evidence for a break at ${R}_{0}={32.1}_{-0.9}^{+1.1}\,\mathrm{kpc}$ with an inner slope of ${n}_{1}=-{2.54}_{-0.09}^{+0.09}$ and an outer slope of ${n}_{2}=-{5.42}_{-0.14}^{+0.13}$ . We use our catalog to perform a search for Milky Way satellite galaxies with large sizes and low luminosities. Using a set of simulated satellite galaxies, we find that our RR Lyrae-based search is more sensitive than those using resolved stellar populations in the regime of large (rh 500 pc), low-surface-brightness dwarf galaxies. A blind search for large, diffuse satellites yields three candidate substructures. The first can be confidently associated with the dwarf galaxy Eridanus II. The second has a distance and proper motion similar to the ultrafaint dwarf galaxy Tucana II but is separated by 5 deg. The third is close in projection to the globular cluster NGC 1851 but is 10 kpc more distant and appears to differ in proper motion.

    33. Nofi, Larissa A., Johns-Krull, Christopher M., Lopez-Valdivia, Ricardo, et al., 2021, ApJ, 911, 138, Projected Rotational Velocities and Fundamental Properties of Low-mass Pre-main-sequence Stars in the Taurus-Auriga Star-forming Region

      The projected stellar rotational velocity ( $v\sin i$ ) is critical for our understanding of processes related to the evolution of angular momentum in pre-main-sequence stars. We present $v\sin i$ measurements of high-resolution infrared and optical spectroscopy for 70 pre-main-sequence stars in the Taurus-Auriga star-forming region, in addition to effective temperatures measured from line-depth ratios, as well as stellar rotation periods determined from optical photometry. From the literature, we identified the stars in our sample that show evidence of residing in circumstellar disks or multiple systems. The comparison of infrared $v\sin i$ measurements calculated using two techniques shows a residual scatter of 1.8 km s-1, defining a typical error floor for the $v\sin i$ of pre-main-sequence stars from infrared spectra. A comparison of the $v\sin i$ distributions of stars with and without companions shows that binaries/multiples typically have a higher measured $v\sin i$ , which may be caused by contamination by companion lines, shorter disk lifetimes in binary systems, or tidal interactions in hierarchical triples. A comparison of optical and infrared $v\sin i$ values shows no significant difference regardless of whether the star has a disk or not, indicating that CO contamination from the disk does not impact $v\sin i$ measurements above the typical 1.8 km s-1 error floor of our measurements. Finally, we observe a lack of a correlation between the $v\sin i$ , presence of a disk, and H-R diagram position, which indicates a complex interplay between stellar rotation and evolution of pre-main-sequence stars.

    34. Li, Ting S., Koposov, Sergey E., Erkal, Denis, et al., 2021, ApJ, 911, 149, Broken into Pieces: ATLAS and Aliqa Uma as One Single Stream

      We present the first spectroscopic measurements of the ATLAS and Aliqa Uma streams from the Southern Stellar Stream Spectroscopic Survey (S5), in combination with the photometric data from the Dark Energy Survey and astrometric data from Gaia. From the coherence of spectroscopic members in radial velocity and proper motion, we find that these two systems are extremely likely to be one stream with discontinuity in morphology and density on the sky (the “kink” feature). We refer to this entire stream as the ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive exploration of the effect of baryonic substructures and find that only an encounter with the Sagittarius dwarf 0.5 Gyr ago can create a feature similar to the observed “kink.” In addition, we also identify two gaps in the ATLAS component associated with the broadening in the stream width (the “broadening” feature). These gaps have likely been created by small mass perturbers, such as dark matter halos, as the AAU stream is the most distant cold stream known with severe variations in both the stream surface density and the stream track on the sky. With the stream track, stream distance, and kinematic information, we determine the orbit of the AAU stream and find that it has been affected by the Large Magellanic Cloud, resulting in a misalignment between the proper motion and stream track. Together with the Orphan-Chenab Stream, AAU is the second stream pair that has been found to be a single stream separated into two segments by external perturbation.

    35. Drummond, Jack D., Merline, W. J., Carry, B., et al., 2021, Icar, 358, 114275, The orbit of asteroid (317) Roxane’s satellite Olympias from Gemini, Keck, VLT and the SOR, and (22) Kalliope’s Linus from the SOR

      A definitive orbit is derived for asteroid (317) Roxane’s satellite Olympias [S/2009 (317)1] by combining the 2009 discovery images from Gemini North (Merline et al. 2009) with images from Keck and the VLT obtained in 2012, as well as images from its 2016-2017 apparition from the Starfire Optical Range. The orbit is retrograde with respect to the ecliptic but in the same sense as Roxane’s spin. Olympias has a period of P=11.94400.0005 days, a semi-major axis of a=2453 km, and an orbital pole at RA=97, Dec=-71, or ecliptic coordinates =245, =-85, close to the south ecliptic pole. This satellite orbital pole is only 3 from Roxane’s orbital pole (but in a retrograde sense) and restricts all observations of Olympias from Earth to within 4 of the satellite’s orbital plane. By fitting the brightness ratios between Roxane (rotational period of 8.169610.00005 h) and Olympias as a Fourier series, we find a rotational period for Olympias of 8.25870.0001 h, making this an asynchronous wide binary. From the brightness ratios, and with the average infrared modeling diameter found in the literature of 19.160.39 km (error of the mean), we estimate triaxial ellipsoid radii of km for Roxane and km for Olympias. We can then apportion the mass between the two objects and find a density for both (assumed to be the same) of 2.160.18 g/cm3. There are only a few E-type binaries known and this is the first direct determination of E-type density from a binary. We suggest that the system was formed by the Escaping Ejecta Binary (EEB) mechanism of Durda et al. (2004a), probably forming closer together, and then undergoing the complex evolution steps described by Jacobson et al. (2014) involving synchronization, BYORP orbit expansion, loss of tidal lock, and then YORP spinup. Roxane and Olympias may be the only known EEB system to date.


      From the same 2016-2017 apparition the orbit of Linus around asteroid (22) Kalliope is derived from the SOR. This well-observed bright satellite is found to have a circular orbit with a period of P=3.59560.0004 days, in good agreement with the latest elements of Vachier et al. (2012) of P=3.59570.0001 days, and a semi-major axis of a=10996 km, somewhat greater than their a=108211 km for a slightly eccentric orbit (e=0.0070.010). With a diameter for Kalliope of 1616 km (Hanus et al. 2017), we derive a density for Kalliope of 3.720.25 g/cm3 from our one apparition study, the same as Hanus et al. (2017) but greater than the 3.240.16 of Vachier et al. (2012).

    36. Mucesh, S., Hartley, W. G., Palmese, A., et al., 2021, MNRAS, 502, 2770, A machine learning approach to galaxy properties: joint redshift-stellar mass probability distributions with Random Forest

      We demonstrate that highly accurate joint redshift-stellar mass probability distribution functions (PDFs) can be obtained using the Random Forest (RF) machine learning (ML) algorithm, even with few photometric bands available. As an example, we use the Dark Energy Survey (DES), combined with the COSMOS2015 catalogue for redshifts and stellar masses. We build two ML models: one containing deep photometry in the griz bands, and the second reflecting the photometric scatter present in the main DES survey, with carefully constructed representative training data in each case. We validate our joint PDFs for 10 699 test galaxies by utilizing the copula probability integral transform and the Kendall distribution function, and their univariate counterparts to validate the marginals. Benchmarked against a basic set-up of the template-fitting code BAGPIPES, our ML-based method outperforms template fitting on all of our predefined performance metrics. In addition to accuracy, the RF is extremely fast, able to compute joint PDFs for a million galaxies in just under 6 min with consumer computer hardware. Such speed enables PDFs to be derived in real time within analysis codes, solving potential storage issues. As part of this work we have developed GALPRO 1, a highly intuitive and efficient PYTHON package to rapidly generate multivariate PDFs on-the-fly. GALPRO is documented and available for researchers to use in their cosmology and galaxy evolution studies.

    37. Aguena, M., Benoist, C., da Costa, L. N., et al., 2021, MNRAS, 502, 4435, The WaZP galaxy cluster sample of the dark energy survey year 1

      We present a new (2+1)D galaxy cluster finder based on photometric redshifts called Wavelet Z Photometric (WaZP) applied to DES first year (Y1A1) data. The results are compared to clusters detected by the South Pole Telescope (SPT) survey and the redMaPPer cluster finder, the latter based on the same photometric data. WaZP searches for clusters in wavelet-based density maps of galaxies selected in photometric redshift space without any assumption on the cluster galaxy populations. The comparison to other cluster samples was performed with a matching algorithm based on angular proximity and redshift difference of the clusters. It led to the development of a new approach to match two optical cluster samples, following an iterative approach to minimize incorrect associations. The WaZP cluster finder applied to DES Y1A1 galaxy survey (1511.13 deg2 up to mi = 23 mag) led to the detection of 60 547 galaxy clusters with redshifts 0.05 < z < 0.9 and richness Ngals 5. Considering the overlapping regions and redshift ranges between the DES Y1A1 and SPT cluster surveys, all SZ based SPT clusters are recovered by the WaZP sample. The comparison between WaZP and redMaPPer cluster samples showed an excellent overall agreement for clusters with richness Ngals ( for redMaPPer) greater than 25 (20), with 95 per cent recovery on both directions. Based on the cluster cross-match, we explore the relative fragmentation of the two cluster samples and investigate the possible signatures of unmatched clusters.

    38. Huang, Hung-Jin, Eifler, Tim, Mandelbaum, Rachel, et al., 2021, MNRAS, 502, 6010, Dark energy survey year 1 results: Constraining baryonic physics in the Universe

      Measurements of large-scale structure are interpreted using theoretical predictions for the matter distribution, including potential impacts of baryonic physics. We constrain the feedback strength of baryons jointly with cosmology using weak lensing and galaxy clustering observables (3 2pt) of Dark Energy Survey (DES) Year 1 data in combination with external information from baryon acoustic oscillations (BAO) and Planck cosmic microwave background polarization. Our baryon modelling is informed by a set of hydrodynamical simulations that span a variety of baryon scenarios; we span this space via a Principal Component (PC) analysis of the summary statistics extracted from these simulations. We show that at the level of DES Y1 constraining power, one PC is sufficient to describe the variation of baryonic effects in the observables, and the first PC amplitude (Q1) generally reflects the strength of baryon feedback. With the upper limit of Q1 prior being bound by the Illustris feedback scenarios, we reach $\sim 20{{\ \rm per\ cent}}$ improvement in the constraint of $S_8=\sigma _8(\Omega _{\rm m}/0.3)^{0.5}=0.788^{+0.018}_{-0.021}$ compared to the original DES 3 2pt analysis. This gain is driven by the inclusion of small-scale cosmic shear information down to 2.5 arcmin, which was excluded in previous DES analyses that did not model baryonic physics. We obtain $S_8=0.781^{+0.014}_{-0.015}$ for the combined DES Y1+Planck EE+BAO analysis with a non-informative Q1 prior. In terms of the baryon constraints, we measure $Q_1=1.14^{+2.20}_{-2.80}$ for DES Y1 only and $Q_1=1.42^{+1.63}_{-1.48}$ for DESY1+Planck EE+BAO, allowing us to exclude one of the most extreme AGN feedback hydrodynamical scenario at more than 2.

    39. Gregg, Michael D., West, Michael J., Lemaux, Brian C., et al., 2021, MNRAS, Discovery of tidal debris stars from G1/Mayall-II in M31

      The object Mayall II or G1 is the brightest globular cluster belonging to M31. Because of its extreme properties for a globular cluster, it has been speculated that G1 is the remnant nucleus of a dwarf galaxy that has been stripped by the tidal field of M31. Using the Keck DEIMOS spectrograph, we have conducted a survey for tidally stripped stars from G1, obtaining a sample of 351 stellar velocities over 320 sq. arcminutes of sky centered on G1. Thirteen are within $25~{\, \rm km\, s^{-1}\, }$ of the systemic velocity of G1, and exhibit spatial and velocity correlations consistent with being dynamically associated with G1, and all thirteen are well outside the tidal radius of the cluster. These thirteen stars could be either (i) the remnants of an almost completely evaporated stellar envelope, or (ii) G1 member stars lost through tidal interaction with M31. Estimates of the implied mass loss rate based on our data suggest a short dissolution time-scale for G1, thus favouring the stellar envelope hypothesis for the origin of the tidal tail stars, or, at the very least, an advanced stage of cluster dissolution. In either case, G1, and by extension compact stellar systems in general, have likely played a significant role in building the halo of M31.

    40. Napier, K. J., Gerdes, D. W., Lin, Hsing Wen, et al., 2021, PSJ, 2, 59, No Evidence for Orbital Clustering in the Extreme Trans-Neptunian Objects

      The apparent clustering in longitude of perihelion and ascending node of extreme trans-Neptunian objects (ETNOs) has been attributed to the gravitational effects of an unseen 5-10 Earth-mass planet in the outer solar system. To investigate how selection bias may contribute to this clustering, we consider 14 ETNOs discovered by the Dark Energy Survey, the Outer Solar System Origins Survey, and the survey of Sheppard and Trujillo. Using each survey’s published pointing history, depth, and TNO tracking selections, we calculate the joint probability that these objects are consistent with an underlying parent population with uniform distributions in and . We find that the mean scaled longitude of perihelion and orbital poles of the detected ETNOs are consistent with a uniform population at a level between 17% and 94% and thus conclude that this sample provides no evidence for angular clustering.

    41. Hsieh, Henry H., Ishiguro, Masateru, Knight, Matthew M., et al., 2021, PSJ, 2, 62, The Reactivation of Main-belt Comet 259P/Garradd (P/2008 R1)

      We present observations of main-belt comet (MBC) 259P/Garradd from 4 months prior to its 2017 perihelion passage to 5 months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of ${\dot{M}}_{d}=(4.6\pm 0.2)$ kg s-1 (assuming grain densities of = 2500 kg m-3 and a mean effective particle size of ${\bar{a}}_{d}=2$ mm) and a best-fit start date of detectable activity of 2017 April 22 1, when the object was at a heliocentric distance of rh = 1.96 0.03 au and a true anomaly of = 3139 04. We estimate the effective active fraction of 259P’s surface area to be from fact 7 10-3 to fact 6 10-2 (corresponding to effective active areas of Aact 8 103 m2 to Aact 7 104 m2) at the start of its 2017 active period. A comparison of estimated total dust masses measured for 259P in 2008 and 2017 shows no evidence of changes in activity strength between the two active apparitions. The heliocentric distance of 259P’s activity onset point is much smaller than those of other MBCs, suggesting that its ice reservoirs may be located at greater depths than on MBCs farther from the Sun, increasing the time needed for a solar-irradiation-driven thermal wave to reach subsurface ice. We suggest that deeper ice on 259P could be a result of more rapid ice depletion caused by the object’s closer proximity to the Sun compared to other MBCs.

    42. To, C., Krause, E., Rozo, E., et al., 2021, PhRvL, 126, 141301, Dark Energy Survey Year 1 Results: Cosmological Constraints from Cluster Abundances, Weak Lensing, and Galaxy Correlations

      We present the first joint analysis of cluster abundances and auto or cross-correlations of three cosmic tracer fields: galaxy density, weak gravitational lensing shear, and cluster density split by optical richness. From a joint analysis (4 2 pt +N ) of cluster abundances, three cluster cross-correlations, and the auto correlations of the galaxy density measured from the first year data of the Dark Energy Survey, we obtain m=0.30 5-0.038+0.055 and 8=0.78 3-0.054+0.064. This result is consistent with constraints from the DES-Y1 galaxy clustering and weak lensing two-point correlation functions for the flat CDM model. Consequently, we combine cluster abundances and all two-point correlations from across all three cosmic tracer fields (6 2 pt +N ) and find improved constraints on cosmological parameters as well as on the cluster observable-mass scaling relation. This analysis is an important advance in both optical cluster cosmology and multiprobe analyses of upcoming wide imaging surveys.

    43. Carvalho, Adolfo, Johns-Krull, Christopher M., Prato, L., et al., 2021, ApJ, 910, 33, Radial Velocity Monitoring of the Young Star Hubble 4: Disentangling Star-spot Lifetimes from Orbital Motion

      We studied the weak-lined T Tauri star Hubble 4, a known long-period binary, and its star-spot phenomena. We used optical radial velocity (RV) data taken over a span of 14 yr (2004-2010, 2017-2019) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope and single epoch imaging from the Hubble Space Telescope (HST)/Wide Field Camera 3 instrument. The observed and apparent RV variations show contributions, respectively, from the binary motion as well as from a large spot group on one of the stars, presumed to be the primary. Fitting and removing the orbital signal from the RVs, we found the lower bound on the lifetime of a previously identified large spot group on the surface of the star to be at least 5.1 yr. An 5 yr lower limit is a long, but not unprecedented, duration for a single spot group. The later epoch data indicate significant spot evolution has occurred, placing an upper bound on the spot group lifetime at 12 yr. We find that pre-main-sequence evolutionary models for the age of Taurus (2 Myr), combined with component mass estimates from the literature, permit us to reproduce the HST relative photometry and the binary-induced contribution to the apparent RV variations. The long-lived star spot we find on Hubble 4 has significant implications for dynamo models in young stars, as it adds evidence for long lifetimes of magnetic field topologies. There are also significant implications for young star exoplanet searches, as long-lived coherent RV signals may be spot induced and not the result of planetary motion. * This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

    44. Hilton, M., Sifon, C., Naess, S., et al., 2021, ApJS, 253, 3, The Atacama Cosmology Telescope: A Catalog of >4000 SunyaevZeldovich Galaxy Clusters

      We present a catalog of 4195 optically confirmed SunyaevZeldovich (SZ) selected galaxy clusters detected with signal-to-noise ratio >4 in 13,211 deg2 of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multifrequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008 to 2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 < z < 1.91 (median z = 0.52). The catalog contains 222 z > 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ signal versus mass-scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M 500c > 3.8 1014 M , evaluated at z = 0.5, for clusters detected at signal-to-noise ratio >5 in maps filtered at an angular scale of 2.4. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ signal mass-scaling relation, such as the Dark Energy Survey (4566 deg2), the Hyper Suprime-Cam Subaru Strategic Program (469 deg2), and the Kilo Degree Survey (825 deg2). We highlight some noteworthy objects in the sample, including potentially projected systems, clusters with strong lensing features, clusters with active central galaxies or star formation, and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr.

    45. Person, Michael J., Bosh, Amanda S., Zuluaga, Carlos A., et al., 2021, Icar, 356, 113572, Haze in Pluto’s atmosphere: Results from SOFIA and ground-based observations of the 2015 June 29 Pluto occultation

      On UT 29 June 2015, the occultation by Pluto of a bright star (r = 11.9) was observed from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and several ground-based stations in New Zealand and Australia. Pre-event astrometry allowed for an in-flight update to the SOFIA team with the result that SOFIA was deep within the central flash zone (~22 km from center). Analysis of the combined data leads to the result that Pluto’s middle atmosphere is essentially unchanged from 2011 and 2013 (Person et al. 2013; Bosh et al. 2015); there has been no significant expansion or contraction of the atmosphere. Additionally, our multi-wavelength observations allow us to conclude that a haze component in the atmosphere is required to reproduce the light curves obtained. This haze scenario has implications for understanding the photochemistry of Pluto’s atmosphere.

    46. Lewis, Briley L., Stansberry, John A., Holler, Bryan J., et al., 2021, Icar, 356, 113633, Distribution and energy balance of Pluto’s nitrogen ice, as seen by New Horizons in 2015

      Pluto’s surface is geologically complex because of volatile ices that are mobile on seasonal and longer time scales. Here we analyzed New Horizons LEISA spectral data to globally map the nitrogen ice, including nitrogen with methane diluted in it. Our goal was to learn about the seasonal processes influencing ice redistribution, to calculate the globally averaged energy balance, and to place a lower limit on Pluto’s N2 inventory. We present the average latitudinal distribution of nitrogen and investigate the relationship between its distribution and topography on Pluto by using maps that include the shifted bands of methane in solid solution with nitrogen (which are much stronger than the 2.15- m nitrogen band) to more completely map the distribution of the nitrogen ice. We find that the global average bolometric albedo is 0 . 83 0 . 11 , similar to that inferred for Triton, and that a significant fraction of Pluto’s N2 is stored in Sputnik Planitia. We also used the encounter-hemisphere distribution of nitrogen ice to infer the latitudinal distribution of nitrogen over the rest of Pluto, allowing us to calculate the global energy balance. Under the assumption that Pluto’s nitrogen-dominated 11.5 bar atmosphere is in vapor pressure equilibrium with the nitrogen ice, the ice temperature is 36 . 93 0 . 10 K, as measured by New Horizons’ REX instrument. Combined with our global energy balance calculation, this implies that the average bolometric emissivity of Pluto’s nitrogen ice is probably in the range 0.47-0.72. This is consistent with the low emissivities estimated for Triton based on Voyager results, and may have implications for Pluto’s atmospheric seasonal variations, as discussed below. The global pattern of volatile transport at the time of the encounter was from north to south, and the transition between condensation and sublimation within Sputnik Planitia is correlated with changes in the grain size and CH4 concentration derived from the spectral maps. The low emissivity of Pluto’s N2 ice suggests that Pluto’s atmosphere may undergo an extended period of constant pressure even as Pluto recedes from the Sun in its orbit.

    47. Cruikshank, Dale P., Dalle Ore, Cristina M., Scipioni, Francesca, et al., 2021, Icar, 356, 113786, Cryovolcanic flooding in Viking Terra on Pluto

      A prominent fossa trough (Uncama Fossa) and adjacent 28-km diameter impact crater (Hardie) in Pluto’s Viking Terra, as seen in the high-resolution images from the New Horizons spacecraft, show morphological evidence of in-filling with a material of uniform texture and red-brown color. A linear fissure parallel to the trough may be the source of a fountaining event yielding a cryoclastic deposit having the same composition and color properties as is found in the trough and crater. Spectral maps of this region with the New Horizons LEISA instrument reveal the spectral signature of H2O ice in these structures and in distributed patches in the adjacent terrain in Viking Terra. A detailed statistical analysis of the spectral maps shows that the colored H2O ice filling material also carries the 2.2-m signature of an ammoniated component that may be an ammonia hydrate (NH3nH2O) or an ammoniated salt. This paper advances the view that the crater and fossa trough have been flooded by a cryolava debouched from Pluto’s interior along fault lines in the trough and in the floor of the impact crater. The now frozen cryolava consisted of liquid H2O infused with the red-brown pigment presumed to be a tholin, and one or more ammoniated compounds. Although the abundances of the pigment and ammoniated compounds entrained in, or possibly covering, the H2O ice are unknown, the strong spectral bands of the H2O ice are clearly visible. In consideration of the factors in Pluto’s space environment that are known to destroy ammonia and ammonia-water mixtures, the age of the exposure is of order 109 years. Ammoniated salts may be more robust, and laboratory investigations of these compounds are needed.

    48. Gabasova, L. R., Schmitt, B., Grundy, W., et al., 2021, Icar, 356, 113833, Global compositional cartography of Pluto from intensity-based registration of LEISA data

      In 2015 the New Horizons spacecraft reached the Pluto system and returned unprecedentedly detailed measurements of its surface properties. These measurements have already been integrated into global reflectance, topography and narrow-band multispectral surface maps. However, analysis of the hyperspectral data from the Ralph/LEISA infrared spectrometer, which lets us analyse the surface composition, has until now been confined to the high-resolution encounter hemisphere of Pluto. We use an innovative technique – intensity-based registration – to co-register this high-resolution data with lower-resolution measurements taken during the spacecraft’s approach, and present the first global qualitative composition maps for CH<!–l. 82 –>4, N<!–l. 82 –>2 and H<!–l. 82 –>2O ice, and a tholin-like red material. We compare these maps with the other maps produced for Pluto and study the global extent of the previously-described latitudinal distribution of the surface components, which is relatively longitudinally constant with the exception of Sputnik Planitia. We also correlate these compositional components with geological features and propose physical interpretations, which include: CH<!–l. 82 –>4-ice-rich dissected plateaus in high northern latitudes, CH<!–l. 82 –>4-rich eroded terrain with N<!–l. 82 –>2-rich infill in medium northern latitudes, CH<!–l. 82 –>4-rich bladed terrain in low northern latitudes, and a red material belt overlaying H<!–l. 82 –>2O ice in low southern latitudes.

    49. Steckloff, Jordan K., Lisse, Carey M., Safrit, Taylor K., et al., 2021, Icar, 356, 113998, The sublimative evolution of (486958) Arrokoth

      We consider the history of New Horizons target (486958) Arrokoth in the context of its sublimative evolution. Shortly after the Sun’s protoplanetary disk (PPD) cleared, the newly intense sunlight sparked a sublimative period in Arrokoth’s early history that lasted for ~10-100 Myr. Although this sublimation was too weak to significantly alter Arrokoth’s spin state, it could drive mass transport around the surface significant enough to erase topographic features on length scales of ~10-100 m. This includes craters up to ~50-500 m in diameter, which suggests that the majority of Arrokoth’s craters may not be primordial (dating from the merger of Arrokoth’s lobes), but rather could date from after the end of this sublimative period. Thereafter, Arrokoth entered a Quiescent Period (which lasts to the present day), in which volatile production rates are at least 13 orders of magnitude less than the ~1024 molecules/s detection limit of the New Horizons spacecraft (Lisse et al. 2020). This is insufficient to drive either mass transport or sublimative torques. These results suggest that the observed surface of Arrokoth is not primordial, but rather dates from the Quiescent Period. By contrast, the inability of sublimative torques to meaningfully alter Arrokoth’s rotation state suggests that its shape is indeed primordial, and its observed rotation is representative of its spin state after formation.

    50. Lisse, C. M., Young, L. A., Cruikshank, D. P., et al., 2021, Icar, 356, 114072, On the origin & thermal stability of Arrokoth’s and Pluto’s ices

      In this paper we discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt object (KBO) 2014 MU69 (also called Arrokoth; hereafter “MU69“) after its 4.6 Gyr residence in the Edgeworth-Kuiper belt (EKB) as a cold classical object. We compare the upper bounds for the gas production rate (~1024 molecules/s) measured by the New Horizons (NH) spacecraft flyby on 01 Jan 2019 to estimates for the outgassing flux rates from a suite of common cometary and KBO ices at the average ~ 40 K sunlit surface temperature of MU69, but do not find the upper limit very constraining except for the most volatile of species (e.g. CO, N2, CH4). More constraining is the stability versus sublimation into vacuum requirement over Myr to Gyr, and from this we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability), while NH3 and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 108-109 years by nearby supernovae and passing O/B stars. To date the NH team has reported the presence of abundant CH3OH and H2O on MU69‘s surface (Stern et al., 2019; Grundy et al., 2020). NH3 has been searched for, but not found. We predict that future absorption feature detections, if any are ever derived from higher signal-to-noise ratio spectra, will be due to an HCN or poly-H2CO based species. Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to state that it is highly likely that it “formed in the dark”, in an optically thick mid-plane, unable to see the nascent, variable, highly luminous Young Stellar Object (YSO)/TTauri Sun, and that KBOs contain HCN and CH3OH ice phases in addition to the H2O ice phases found in their short period (SP) comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that methanol ice is likely ubiquitous in the outer solar system; that if Pluto isn’t a fully differentiated body, then it must have gained its hypervolatile ices from proto-planetary disk (PPD) sources in the first few Myr of the solar system’s existence; and that hypervolatile rich, highly primordial comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar few Myr timescale.

    51. Showalter, Mark R., Benecchi, Susan D., Buie, Marc W., et al., 2021, Icar, 356, 114098, A statistical review of light curves and the prevalence of contact binaries in the Kuiper Belt

      We investigate what can be learned about a population of distant Kuiper Belt Objects (KBOs) by studying the statistical properties of their light curves. Whereas others have successfully inferred the properties of individual, highly variable KBOs, we show that the fraction of KBOs with low amplitudes also provides fundamental information about a population. Each light curve is primarily the result of two factors: shape and orientation. We consider contact binaries and ellipsoidal shapes, with and without flattening. After developing the mathematical framework, we apply it to the existing body of KBO light curve data. Principal conclusions are as follows. (1) When using absolute magnitude H as a proxy for the sizes of KBOs, it is more accurate to use the maximum of the light curve (minimum H) rather than the mean. (2) Previous investigators have noted that smaller KBOs tend to have higher-amplitude light curves, and have interpreted this as evidence that they are systematically more irregular in shape than larger KBOs; we show that a population of flattened bodies with uniform proportions, independent of size, could also explain this result. (3) Our method of analysis indicates that prior assessments of the fraction of contact binaries in the Kuiper Belt may be artificially low. (4) The pole orientations of some KBOs can be inferred from observed changes in their light curves over time scales of decades; however, we show that these KBOs constitute a biased sample, whose pole orientations are not representative of the population overall. (5) Although surface topography, albedo patterns, limb darkening, and other surface properties can affect individual light curves, they do not have a strong influence on the statistics overall. (6) Photometry from the Outer Solar System Origins Survey (OSSOS) survey is incompatible with previous results and its statistical properties defy easy interpretation. We also discuss the promise of this approach for the analysis of future, much larger data sets such as the one anticipated from the upcoming Vera C. Rubin Observatory.

    52. Singer, Kelsi N., Grundy, William M., White, Oliver L., et al., 2021, Icar, 356, 114269, Introduction to Icarus special issue “Pluto System, Kuiper Belt, and Kuiper Belt Objects”

      The Kuiper belt represents a vast treasure of scientific information. From evolved, planet-sized bodies to relatively primordial smaller bodies, the science that can be done with Kuiper belt data touches many aspects of solar system formation and evolution. These connections along with advancements in telescope and spacecraft technology have created the conditions for a golden age for Kuiper belt science, as exemplified by the breadth and depth of topics in this special issue.

    53. Oszkiewicz, Dagmara, Wilawer, Emil, Podlewska-Gaca, Edyta, et al., 2021, Icar, 357, 114158, First survey of phase curves of V-type asteroids

      The V-type asteroids are of major scientific interest as they may sample multiple differentiated planetesimals. Determination of their physical properties is crucial for understanding the diversity and multiplicity of planetesimals. Previous studies have suggested distinct polarimetric behaviours for the V-type asteroids. Similarly to phase-polarization curves, asteroid phase-magnitude curves (hereinafter called “phase curves”) are also diagnostic of surface and regolith properties, and can be used to unveil a variety of distinct behaviours.


      We present well determined phase curves for ~20 V-type asteroids for the first time. Their phase curve parameters are consistent with those for moderate and high albedo asteroids. The computed median G12 parameter for the V-type asteroids is G12=0.14. We do not find substantial evidence for any clustering into distinct phase curve parameters groups. Only one asteroid (2763) Jeans shows exceptionally high G2 value. The derived median G12 may be used in single parameters fitting of V-type asteroids.

    54. Johnson, Jeffrey R., Grundy, William M., Lemmon, Mark T., et al., 2021, Icar, 357, 114261, Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 4. Final mission observations

      The last sets of Panoramic Camera (Pancam) visible/near-infrared (432-1009 nm) multispectral observations made under varying viewing and illumination geometries by the Mars Exploration Rovers Spirit and Opportunity were examined using radiative transfer models to study the surface scattering and microphysical nature of rock and soil units at both sites. Nearly 12,000 individual measurements were collected for this study of soil, dust, and rock units over phase angles of ~0 to ~150. Images were acquired on sols 1944-1946 (June 2009) at Troy, the final resting place of Spirit on the western side of Home Plate in Gusev crater, and by Opportunity at three locations on the western rim of Endeavour crater in Meridiani Planum between sols 2785 (November 2011) and 3867 (December 2014). Sky models were developed from observations of atmospheric opacity, which enabled corrections for diffuse skylight when combined with surface facet orientations determined from stereo images. Model results were improved by removing data affected by scattered light evident in some high phase angle images (resulting from minor dust contamination on the camera windows). At Troy, relatively dust-free “gray” rock units exhibited narrow, forward scattering behaviors akin to previous analyses of similar gray rock units at Gusev crater. Soils and “red” rocks coated with greater amounts of dust were more backscattering. Red rocks exhibited higher single scattering albedo (w), macroscopic roughness (), and opposition effect width (h) parameters, indicative of rough, low-porosity surfaces perhaps with more uniform grain size distributions. At Meridiani Planum, rubbly soils near Sao Gabriel crater and Cape Tribulation exhibited w values typical of previous soil analyses. However, the large drift “dust” deposits found in depressions on the northern tip of Cape York near Turkey Haven demonstrated elevated w values with a downturn toward 1009 nm, consistent with minor hydration of these materials. The dust deposits were modeled with the lowest values and highest h values of all soil units analyzed during the Opportunity mission, indicative of a smooth surface with homogeneous grain size distribution and/or lower porosity than other units. The dust unit scattering function was dissimilar to those for atmospheric and airfall-deposited dusts, however, suggesting that the originally deposited materials had been modified, perhaps by hydration and ongoing aeolian effects. Analyses of phase curve ratios among the units studied here and from laboratory data of analog soils suggested that surface scattering is a major control on the peak phase angle position of the “arch” in phase curve ratios, alongside the effects of particle-scale roughness.

    55. Kelsey, L., Sullivan, M., Smith, M., et al., 2021, MNRAS, 501, 4861, The effect of environment on Type Ia supernovae in the Dark Energy Survey three-year cosmological sample

      Analyses of Type Ia supernovae (SNe Ia) have found puzzling correlations between their standardized luminosities and host galaxy properties: SNe Ia in high-mass, passive hosts appear brighter than those in lower mass, star-forming hosts. We examine the host galaxies of SNe Ia in the Dark Energy Survey 3-yr spectroscopically confirmed cosmological sample, obtaining photometry in a series of ‘local’ apertures centred on the SN, and for the global host galaxy. We study the differences in these host galaxy properties, such as stellar mass and rest-frame U – R colours, and their correlations with SN Ia parameters including Hubble residuals. We find all Hubble residual steps to be >3 in significance, both for splitting at the traditional environmental property sample median and for the step of maximum significance. For stellar mass, we find a maximal local step of 0.098 0.018 mag; 0.03 mag greater than the largest global stellar mass step in our sample (0.070 0.017 mag). When splitting at the sample median, differences between local and global U – R steps are small, both 0.08 mag, but are more significant than the global stellar mass step (0.057 0.017 mag). We split the data into sub-samples based on SN Ia light-curve parameters: stretch (x1) and colour (c), finding that redder objects (c > 0) have larger Hubble residual steps, for both stellar mass and U – R, for both local and global measurements, of 0.14 mag. Additionally, the bluer (star-forming) local environments host a more homogeneous SN Ia sample, with local U – R rms scatter as low as 0.084 0.017 mag for blue (c < 0) SNe Ia in locally blue U – R environments.

    56. Vega-Ferrero, J., Dominguez Sanchez, H., Bernardi, M., et al., 2021, MNRAS, Pushing automated morphological classifications to their limits with the Dark Energy Survey

      We present morphological classifications of 27 million galaxies from the Dark Energy Survey (DES) Data Release 1 (DR1) using a supervised deep learning algorithm. The classification scheme separates: (a) early-type galaxies (ETGs) from late-types (LTGs), and (b) face-on galaxies from edge-on. Our Convolutional Neural Networks (CNNs) are trained on a small subset of DES objects with previously known classifications. These typically have mr 17.7mag; we model fainter objects to mr < 21.5 mag by simulating what the brighter objects with well determined classifications would look like if they were at higher redshifts. The CNNs reach 97% accuracy to mr < 21.5 on their training sets, suggesting that they are able to recover features more accurately than the human eye. We then used the trained CNNs to classify the vast majority of the other DES images. The final catalog comprises five independent CNN predictions for each classification scheme, helping to determine if the CNN predictions are robust or not. We obtain secure classifications for 87% and 73% of the catalog for the ETG vs. LTG and edge-on vs. face-on models, respectively. Combining the two classifications (a) and (b) helps to increase the purity of the ETG sample and to identify edge-on lenticular galaxies (as ETGs with high ellipticity). Where a comparison is possible, our classifications correlate very well with Sersic index (n), ellipticity () and spectral type, even for the fainter galaxies. This is the largest multi-band catalog of automated galaxy morphologies to date.

    57. Gustafsson, Annika, Moskovitz, Nicholas, Cushing, Michael C., et al., 2021, PASP, 133, 035001, Science Commissioning of NIHTS: The Near-infrared High Throughput Spectrograph on the Lowell Discovery Telescope

      The Near-Infrared High Throughput Spectrograph (NIHTS) is in operation on the 4.3 m Lowell Discovery Telescope (LDT) in Happy Jack, AZ. NIHTS is a low-resolution spectrograph (R 200) that operates from 0.86 to 2.45 microns. NIHTS is fed by a custom dichroic mirror which reflects near-infrared wavelengths to the spectrograph and transmits the visible to enable simultaneous imaging with the Large Monolithic Imager (LMI), an independent visible wavelength camera. The combination of premier tracking and acquisition capabilities of the LDT, a several arcminutes field of view on LMI, and high spectral throughput on NIHTS enables novel studies of a number of astrophysical and planetary objects including Kuiper Belt Objects, asteroids, comets, low mass stars, and exoplanet hosts stars. We present a summary of NIHTS operations, commissioning, data reduction procedures with two approaches for the correction of telluric absorption features, and an overview of select science cases that will be pursued by Lowell Observatory, Northern Arizona University, and LDT partners.

    58. Nadler, E. O., Drlica-Wagner, A., Bechtol, K., et al., 2021, PhRvL, 126, 091101, Constraints on Dark Matter Properties from Observations of Milky Way Satellite Galaxies

      We perform a comprehensive study of Milky Way (MW) satellite galaxies to constrain the fundamental properties of dark matter (DM). This analysis fully incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and marginalizes over uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk. Our results are consistent with the cold, collisionless DM paradigm and yield the strongest cosmological constraints to date on particle models of warm, interacting, and fuzzy dark matter. At 95% confidence, we report limits on (i) the mass of thermal relic warm DM, mWDM>6.5 keV (free-streaming length, fs10 h-1 kpc ), (ii) the velocity-independent DM-proton scattering cross section, 0<8.8 10-29 cm2 for a 100 MeV DM particle mass [DM-proton coupling, cp(0.3 GeV )-2], and (iii) the mass of fuzzy DM, m>2.9 10-21 eV (de Broglie wavelength, dB0.5 kpc ). These constraints are complementary to other observational and laboratory constraints on DM properties.

    59. Benedict, G. Fritz, Franz, Otto, Horch, Elliot, et al., 2021, csss, 29, The Multiple-component Binary Hyad, vA 351

      We extend results first announced by Franz et al. (1998), that identified vA351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, P = 2.70y and total mass 2.1M. With ground-based radial velocities, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (PBC = 0.749 days), having a mass ratio MC/MB=0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher mass component. The quadruple system consists of three M dwarfs (A,B,C) and one white dwarf (D); MA=0.57M, MB=0.48M, and MC=0.45M. The WD mass, 0.53M, comes from cooling models, an assumed Hyades age of 670My, and consistency with all previous and derived astrometric, photometric, and RV results. Velocities from H and He I emission lines confirm the BC period derived from absorption lines, with similar (HeI) and higher (H) velocity amplitudes. We ascribe the larger H amplitude to emission from a region each component shadows from the other, depending on the line of sight.

    60. Coffaro, M., Stelzer, B., Orlando, S., et al., 2021, csss, 38, The Sun as a young star: reproducing the X-ray cycle of Eridani with solar magnetic structures

      Epsilon Eri is a young solar-like star with a ~3 yr X-ray activity cycle, detected by us for the first time in a dedicated XMM-Newton long-term monitoring campaign. The magnetic structures on the Sun are intimately linked to the 11-yr activity cycle and they were spatially and temporally resolved throughout the solar cycle. However, for other stars these structures can not be spatially resolved with present-day X-ray instruments. We have, thus, developed a new technique which allows us to reproduce the stellar X-ray variability in terms of time-variations in the coverage of the corona with the same kind of magnetic structures observed on the Sun: active regions (ARs), cores of active regions (COs) and flares (FLs). This poster presents this new method and the results we obtained for the case of Epsilon Eri. Our approach is to simulate a grid of emission measure distributions (EMDs) derived from the analysis of regions observed in the solar corona to artificially reproduce a solar-like corona with the physical characteristics of Epsilon Eri. The three magnetic structures are allowed to contribute to the total coronal EMD with varying area coverage fraction. Thus, from a comparison between these pseudo-solar EMDs and the observations of Epsilon Eri, we are able to associate to each state of the X-ray activity cycle of Epsilon Eri the percentage of ARs, COs and FLs on the corona of the star. The observed amplitude of the X-ray luminosity in the cycle of Epsilon Eri is much smaller than on the Sun. Our analysis provides a physical explanation for this: the simulated EMDs indicate that in all phases of the X-ray cycle a large portion of the corona of Epsilon Eri is covered by active structures. Therefore, there is little space for adding further magnetic structures in the cycle maximum. In the future, this method will be applied to other stars providing an important contribution to better understand the solar-stellar corona connection.

    61. Stahl, Asa G., Tang, Shih-Yun, Johns-Krull, Christopher M., et al., 2021, csss, 66, IGRINS RV: A Precision RV Pipeline for IGRINS Using Modified Forward-Modeling in the Near-Infrared

      Applications of the radial velocity (RV) technique to the near infrared (NIR) are valuable for their diminished susceptibility to the impact of stellar activity and their suitability for studying late-type stars. In this paper, we present the \texttt{IGRINS RV} open source \texttt{python} pipeline for computing infrared RV measurements from reduced spectra taken with IGRINS, a R$\equiv \lambda/\Delta \lambda \sim$45,000 spectrograph with simultaneous coverage of the H band (1.49–1.80 $\mu$m) and K band (1.96–2.46 $\mu$m). Using a modified forward modeling technique, we construct high resolution telluric templates from A0 standard observations on a nightly basis to provide a source of common-path wavelength calibration while mitigating the need to mask or correct for telluric absorption. A0 standard observations are also used to model the variations in instrumental resolution across the detector, including a yearlong period when the K band was defocused. Without any additional instrument hardware, such as a gas cell or laser frequency comb, we are able to achieve precisions of 26.8 \ms in the K band and 31.1 \ms in the H band for narrow-line hosts. These precisions are validated by a monitoring campaign of two RV standard stars as well as the successful retrieval of planet-induced RV signals for both HD\,189733 and $\tau$\,Boo\,A; furthermore, our results affirm the presence of the Rossiter-McLaughlin effect for HD\,189733. The \texttt{IGRINS RV} pipeline extends another important science capability to IGRINS, with publicly available software designed for widespread use.

    62. Biddle, Lauren, I., Llama, Joe, Cameron, Andrew, et al., 2021, csss, 214, Amplitude Modulation of Short Timescale Variability

      Variability of Classical T Tauri Systems occurs over a range of timescales. A common source of this variability is caused by accretion shocks, which can hamper the detectability of young planets within these systems, further motivating the characterization of accretion signatures. We present analysis of small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of 1 d. Our findings reveal that the amplitude of this stochastic variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same.

    63. Clark, Catherine, van Belle, Gerard, Horch, Elliott, et al., 2021, csss, 236, First Results from the POKEMON Speckle Survey of Nearby M-dwarfs

      We present the first results from the POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey, the largest speckle survey of stellar multiplicity ever produced for the objects that comprise over 70% of the stars in our galaxy: the M-dwarfs. We have conducted a volume-limited survey through M9 that inspected, at diffraction-limited resolution, every M-dwarf out to 15pc, with additional brighter targets to 25pc. POKEMON utilized the Differential Speckle Survey Instrument (DSSI) at the 4.3m Lowell Discovery Telescope, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) on the 3.5-m WIYN telescope. We report the discovery of 30+ new companions to these nearby M-dwarfs. Given the priority these targets have for exoplanet studies with TESS, and in the future JWST and the degree to which initially undetected multiplicity has skewed Kepler results a comprehensive survey of our nearby low-mass neighbors provides a homogeneous, complete catalog of fundamental utility. Prior knowledge of secondary objects or robust non-detections, as captured by this survey immediately clarify the nature of exoplanet transit detections from these current and upcoming missions.

    64. Hartman, Zachary, Lepine, Sebastien, van Belle, Gerard, 2021, csss, 245, Confirming the “Lobster” Diagram: Unresolved Companions in K+K Wide Binaries with TESS and Kepler

      We present an analysis of TESS and Kepler light curves for 4,947 K+K wide binaries from the SUPERWIDE Catalog. We use these systems to examine the usefulness of the “Lobster” diagram, a plot which allows for the identification of over-luminous components in wide binaries using Gaia data alone. These over-luminous components are believed to be unresolved binaries, making the wide binaries a triple (or even quadruple) system. To confirm this, we search through the high cadence light curves from TESS, Kepler and K2 and the data products produced from the MIT Quick Lookup Pipeline for signals from eclipses and from rotational modulation in spotted fast-rotating stars. We identify 64 eclipsing systems and 115 systems showing signs of fast rotation. We highlight the systems containing eclipsing binaries, fast rotators (P<5 days) and rotators (P>5 days) on the “Lobster” diagram. Eclipsing binaries are overwhelmingly found to be in areas that show a component is over-luminous. Fast rotators are also more likely to be found in these areas while stars showing rotation with periods > 5 days are more likely to be found where true wide binaries are believed to be located.

    65. Hunter, Deidre A., Elmegreen, Bruce G., Goldberger, Esther, et al., 2021, AJ, 161, 71, Relationships between the Stellar, Gaseous, and Star Formation Disks in LITTLE THINGS Dwarf Irregular Galaxies: Indirect Evidence for Substantial Fractions of Dark Molecular Gas

      The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We find that the H I radial profiles are generally flatter in the center and fall faster in the outer regions than the V-band profiles, while young stars are more centrally concentrated, especially if the H I is more centrally flat. This pattern suggests that the H I is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt-Schmidt relation, reproduces the relationship between the ratio of the visible to the H I scale length and the H I Sersic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3RD is 23% 17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.

    66. Massey, Philip, Neugent, Kathryn F., Levesque, Emily M., et al., 2021, AJ, 161, 79, The Red Supergiant Content of M31 and M33

      We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of $\mathrm{log}L/{L}_{\odot }=4.0$ . Our archival survey data cover 5 deg2 of M31, and 3 deg2 for M33, and are likely spatially complete for these massive stars. Gaia is used to remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars in the color-magnitude diagram. The photometry is used to derive effective temperatures and bolometric luminosities via MARCS stellar atmosphere models. The resulting H-R diagrams show superb agreement with the evolutionary tracks of the Geneva evolutionary group. Our census includes 6400 RSGs in M31 and 2850 RSGs in M33 within their Holmberg radii; by contrast, only a few hundred RSGs are known so far in the Milky Way. Our catalog serves as the basis for a study of the RSG binary frequency being published separately, as well as future studies relating to the evolution of massive stars. Here we use the matches between the NIR-selected RSGs and their optical counterparts to show that the apparent similarity in the reddening of OB stars in M31 and M33 is the result of Malmquist bias; the average extinction in M31 is likely higher than that of M33. As expected, the distribution of RSGs follows that of the spiral arms, while the much older AGB population is more uniformly spread across each galaxy’s disk.

    67. Tanoglidis, D., Drlica-Wagner, A., Wei, K., et al., 2021, ApJS, 252, 18, Shadows in the Dark: Low-surface-brightness Galaxies Discovered in the Dark Energy Survey

      We present a catalog of 23,790 extended low-surface-brightness galaxies (LSBGs) identified in $\sim 5000\,{\deg }^{2}$ from the first three years of imaging data from the Dark Energy Survey (DES). Based on a single-component Sersic model fit, we define extended LSBGs as galaxies with g-band effective radii ${R}_{\mathrm{eff}}(g)\gt 2\buildrel{\prime\prime}\over{.} 5$ and mean surface brightness ${\bar{\mu }}_{\mathrm{eff}}(g)\gt 24.2\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$ . We find that the distribution of LSBGs is strongly bimodal in (g – r) versus (g – i) color space. We divide our sample into red (g – i 0.60) and blue (g – i < 0.60) galaxies and study the properties of the two populations. Redder LSBGs are more clustered than their blue counterparts and are correlated with the distribution of nearby (z < 0.10) bright galaxies. Red LSBGs constitute 33% of our LSBG sample, and $\sim 30 \% $ of these are located within 1 of low-redshift galaxy groups and clusters (compared to 8% of the blue LSBGs). For nine of the most prominent galaxy groups and clusters, we calculate the physical properties of associated LSBGs assuming a redshift derived from the host system. In these systems, we identify 41 objects that can be classified as ultradiffuse galaxies, defined as LSBGs with projected physical effective radii ${R}_{\mathrm{eff}}\gt 1.5\,\mathrm{kpc}$ and central surface brightness ${\mu }_{0}(g)\gt 24.0\,\mathrm{mag}\,{\mathrm{arcsec}}^{-2}$ . The wide-area sample of LSBGs in DES can be used to test the role of environment on models of LSBG formation and evolution.

    68. Holler, B. J., Grundy, W. M., Buie, M. W., et al., 2021, Icar, 355, 114130, The Eris/Dysnomia system I: The orbit of Dysnomia

      We present new results on the Eris/Dysnomia system including analysis of new images from the WFC3 instrument on the Hubble Space Telescope (HST). Seven HST orbits were awarded to program 15171 in January and February 2018, with the intervals between observations selected to sample Dysnomia over a full orbital period. Using relative astrometry of Eris and Dysnomia, we computed a best-fit Keplerian orbit for Dysnomia. Based on the Keplerian fit, we find an orbital period of 15.7858990.000050days, which is in good agreement with recent work. We report a non-zero eccentricity of 0.0062 at the 6.2- level, despite an estimated eccentricity damping timescale of 17 Myr. Considering the volumes of both Eris and Dysnomia, the new system density was calculated to be 2.430.05g cm-3, a decrease of ~4% from the previous value of 2.520.05g cm-3. The new astrometric measurements were high enough precision to break the degeneracy of the orbit pole orientation, and indicate that Dysnomia orbits in a prograde manner. The obliquity of Dysnomia’s orbit pole with respect to the plane of Eris’ heliocentric orbit was calculated to be 78.290.65 and is in agreement with previous work; the next mutual events season will occur in 2239. The Keplerian orbit fit to all the data considered in this investigation can be excluded at the 6.3- level, but identifying the cause of the deviation was outside the scope of this work.

    69. Jarvis, M., Bernstein, G. M., Amon, A., et al., 2021, MNRAS, 501, 1282, Dark Energy Survey year 3 results: point spread function modelling

      We introduce a new software package for modelling the point spread function (PSF) of astronomical images, called PIFF (PSFs In the Full FOV), which we apply to the first three years (known as Y3) of the Dark Energy Survey (DES) data. We describe the relevant details about the algorithms used by PIFF to model the PSF, including how the PSF model varies across the field of view (FOV). Diagnostic results show that the systematic errors from the PSF modelling are very small over the range of scales that are important for the DES Y3 weak lensing analysis. In particular, the systematic errors from the PSF modelling are significantly smaller than the corresponding results from the DES year one (Y1) analysis. We also briefly describe some planned improvements to PIFF that we expect to further reduce the modelling errors in future analyses.

    70. Sampaio-Santos, H., Zhang, Y., Ogando, R. L. C., et al., 2021, MNRAS, 501, 1300, Is diffuse intracluster light a good tracer of the galaxy cluster matter distribution?

      We explore the relation between diffuse intracluster light (central galaxy included) and the galaxy cluster (baryonic and dark) matter distribution using a sample of 528 clusters at 0.2 z 0.35 found in the Dark Energy Survey (DES) Year 1 data. The surface brightness of the diffuse light shows an increasing dependence on cluster total mass at larger radius, and appears to be self-similar with a universal radial dependence after scaling by cluster radius. We also compare the diffuse light radial profiles to the cluster (baryonic and dark) matter distribution measured through weak lensing and find them to be comparable. The IllustrisTNG galaxy formation simulation, TNG300, offers further insight into the connection between diffuse stellar mass and cluster matter distributions the simulation radial profile of the diffuse stellar component does not have a similar slope with the total cluster matter content, although that of the cluster satellite galaxies does. Regardless of the radial trends, the amount of diffuse stellar mass has a low-scatter scaling relation with cluster’s total mass in the simulation, out-performing the total stellar mass of cluster satellite galaxies. We conclude that there is no consistent evidence yet on whether or not diffuse light is a faithful radial tracer of the cluster matter distribution. Nevertheless, both observational and simulation results reveal that diffuse light is an excellent indicator of the cluster’s total mass.

    71. Shajib, A. J., Birrer, S., Treu, T., et al., 2021, MNRAS, 501, 2833, Erratum: Is every strong lens model unhappy in its own way? Uniform modelling of a sample of 13 quadruply+ imaged quasars
    72. Farnham, Tony L., Knight, Matthew M., Schleicher, David G., et al., 2021, PSJ, 2, 7, Narrowband Observations of Comet 46P/Wirtanen during Its Exceptional Apparition of 2018/19. I. Apparent Rotation Period and Outbursts

      We obtained broad- and narrowband images of the hyperactive comet 46P/Wirtanen on 33 nights during its 2018/2019 apparition, when the comet made a historic close approach to the Earth. With our extensive coverage, we investigated the temporal behavior of the comet on both seasonal and rotational timescales. We used CN observations to explore the coma morphology, revealing that there are two primary active areas that produce spiral structures. The direction of rotation of these structures changes from pre- to postperihelion, indicating that the Earth crossed the comet’s equatorial plane sometime around perihelion. We also used the CN images to create photometric light curves that consistently show two peaks in the activity, confirming the two source regions. We measured the nucleus’s apparent rotation period at a number of epochs using both the morphology and the light curves. These results all show that the rotation period is continuously changing throughout our observation window, increasing from 8.98 hr in early November to 9.14 hr around perihelion and then decreasing again to 8.94 hr in February. Although the geometry changes rapidly around perihelion, the period changes cannot be primarily due to synodic effects. The repetition of structures in the coma, both within a night and from night to night, strongly suggests that the nucleus is in a near-simple rotation state. We also detected two outbursts, one on December 12 and the other on January 28. Using the apparent velocities of the ejecta in these events, 68 5 and 162 15 m s-1, respectively, we derived start times of 2018 December 12 at 00:13 UT 7 minutes and 2019 January 27 at 20:01 UT 30 minutes.

    73. Fernandez-Valenzuela, E., Pinilla-Alonso, N., Stansberry, J., et al., 2021, PSJ, 2, 10, Compositional Study of Trans-Neptunian Objects at > 2.2 m

      Using data from the Infrared Array Camera on the Spitzer Space Telescope, we present photometric observations of a sample of 100 trans-Neptunian objects (TNOs) beyond 2.2 m. These observations, collected with two broadband filters centered at 3.6 and 4.5 m, were done in order to study the surface composition of TNOs, which are too faint to obtain spectroscopic measurements. With this aim, we have developed a method for the identification of different materials that are found on the surfaces of TNOs. In our sample, we detected objects with colors that are consistent with the presence of small amounts of water, and we were able to distinguish between surfaces that are predominantly composed of complex organics and amorphous silicates. We found that 86% of our sample have characteristics that are consistent with a certain amount of water ice, and the most common composition (73% of the objects) is a mixture of water ice, amorphous silicates, and complex organics. Twenty-three percent of our sample may include other ices, such as carbon monoxide, carbon dioxide, methane, or methanol. Additionally, only small objects seem to have surfaces dominated by silicates. This method is a unique tool for the identification of complex organics and to obtain the surface composition of extremely faint objects. Furthermore, this method will be beneficial when using the James Webb Space Telescope for differentiating groups within the trans-Neptunian population.

    74. Safrit, Taylor K., Steckloff, Jordan K., Bosh, Amanda S., et al., 2021, PSJ, 2, 14, The Formation of Bilobate Comet Shapes through Sublimative Torques

      Recent spacecraft and radar observations found that 70% of short-period comet nuclei, mostly Jupiter-family comets (JFCs), have bilobate shapes (two masses connected by a narrow neck). This is in stark contrast to the shapes of asteroids of similar sizes, of which 14% are bilobate. This suggests that a process or mechanism unique to comets is producing these shapes. Here we show that the bilobate shapes of JFC nuclei are a natural byproduct of sublimative activity during their dynamical migration from their trans-Neptunian reservoir, through the Centaur population, and into the Jupiter family. We model the torques resulting from volatile sublimation during this dynamical migration, and find that they tend to spin up these nuclei to disruption. Once disrupted, the rubble pile-like material properties of comet nuclei (tensile strengths of 1-10 Pa and internal friction angles of 35) cause them to reform as bilobate objects. We find that JFCs likely experienced rotational disruption events prior to entering the Jupiter family, which could explain the prevalence of bilobate shapes. These results suggest that the bilobate shapes of observed comets developed recently in their history (within the past 1-10 Myr), rather than during solar system formation or collisions during planet migration and residency in the trans-Neptunian population.

    75. Strauss, Ryder H., Leiva, Rodrigo, Keller, John M., et al., 2021, PSJ, 2, 22, The Sizes and Albedos of Centaurs 2014 YY49 and 2013 NL24 from Stellar Occultation Measurements by RECON

      In 2019, the Research and Education Collaborative Occultation Network (RECON) obtained multiple-chord occultation measurements of two Centaur objects: 2014 YY49 on 2019 January 28 and 2013 NL24 on 2019 September 4. RECON is a citizen-science telescope network designed to observe high-uncertainty occultations by outer solar system objects. Adopting circular models for the object profiles, we derive a radius $r={16}_{-1}^{+2}$ km and a geometric albedo ${p}_{V}={0.13}_{-0.024}^{+0.015}$ for 2014 YY49 and a radius $r={66}_{-5}^{+5}$ km and a geometric albedo ${p}_{V}={0.045}_{-0.008}^{+0.006}$ for 2013 NL24. To the precision of these measurements, no atmosphere or rings are detected for either object. The two objects measured here are among the smallest distant objects measured with the stellar occultation technique. In addition to these geometric constraints, the occultation measurements provide astrometric constraints for these two Centaurs at a higher precision than has been feasible by direct imaging. To supplement the occultation results, we also present an analysis of color photometry from the Pan-STARRS surveys to constrain the rotational light curve amplitudes and spectral colors of these two Centaurs. We recommend that future work focus on photometry to more deliberately constrain the objects’ colors and light curve amplitudes and on follow-on occultation efforts informed by this astrometry.

    76. Ye, Quanzhi, Knight, Matthew M., Kelley, Michael S. P., et al., 2021, PSJ, 2, 23, A Deep Search for Emission from “Rock Comet” (3200) Phaethon at 1 au

      We present a deep imaging and spectroscopic search for emission from (3200) Phaethon, a large near-Earth asteroid that appears to be the parent of the strong Geminid meteoroid stream, using the 4.3 m Lowell Discovery Telescope. Observations were conducted on 2017 December 14-18 when Phaethon passed only 0.07 au from the Earth. We determine the 3 upper level of dust and CN production rates to be 0.007-0.2 kg s-1 and 2.3 1022 molecules s-1 through narrowband imaging. A search in broadband images taken through the SDSS r’ filter shows no 100 m class fragments in Phaethon’s vicinity. A deeper but star-contaminated search also shows no sign of fragments down to 15 m. Optical spectroscopy of Phaethon and comet C/2017 O1 (ASASSN) as a comparison confirms the absence of cometary emission lines from Phaethon and yields 3 upper levels of CN, C2, and C3 of 1024-1025 molecules s-1, 2 orders of magnitude higher than the CN constraint placed by narrowband imaging, due to the much narrower on-sky aperture of the spectrographic slit. We show that narrowband imaging could provide an efficient way to look for weak gas emission from near-extinct bodies near the Earth, though these observations require careful interpretation. Assuming Phaethon’s behavior is unchanged, our analysis shows that the DESTINY+ mission, currently planning to explore Phaethon in 2026, may not be able to directly detect a gas coma.

    77. Nesvorny, David, Li, Rixin, Simon, Jacob B., et al., 2021, PSJ, 2, 27, Binary Planetesimal Formation from Gravitationally Collapsing Pebble Clouds

      Planetesimals are compact astrophysical objects roughly 1-1000 km in size, massive enough to be held together by gravity. They can grow by accreting material to become full-size planets. Planetesimals themselves are thought to form by complex physical processes from small grains in protoplanetary disks. The streaming instability (SI) model states that millimeter/centimeter-sized particles (pebbles) are aerodynamically collected into self-gravitating clouds that then directly collapse into planetesimals. Here we analyze ATHENA simulations of the SI to characterize the initial properties (e.g., rotation) of pebble clouds. Their gravitational collapse is followed with the PKDGRAV N-body code, which has been modified to realistically account for pebble collisions. We find that pebble clouds rapidly collapse into short-lived disk structures from which planetesimals form. The planetesimal properties depend on the cloud’s scaled angular momentum, $l=L/({{MR}}_{{\rm{H}}}^{2}{\rm{\Omega }})$ , where L and M are the angular momentum and mass, RH is the Hill radius, and is the orbital frequency. Low-l pebble clouds produce tight (or contact) binaries and single planetesimals. Compact high-l clouds give birth to binary planetesimals with attributes that closely resemble the equally sized binaries found in the Kuiper Belt. Significantly, the SI-triggered gravitational collapse can explain the angular momentum distribution of known equally sized binariesa result pending verification from studies with improved resolution. About 10% of collapse simulations produce hierarchical systems with two or more large moons. These systems should be found in the Kuiper Belt when observations reach the threshold sensitivity.

    78. Porredon, A., Crocce, M., Fosalba, P., et al., 2021, PhRvD, 103, 043503, Dark Energy Survey Year 3 results: Optimizing the lens sample in a combined galaxy clustering and galaxy-galaxy lensing analysis

      We investigate potential gains in cosmological constraints from the combination of galaxy clustering and galaxy-galaxy lensing by optimizing the lens galaxy sample selection using information from Dark Energy Survey (DES) Year 3 data and assuming the DES Year 1 METACALIBRATION sample for the sources. We explore easily reproducible selections based on magnitude cuts in i -band as a function of (photometric) redshift, zphot, and benchmark the potential gains against those using the well-established REDMAGIC [E. Rozo et al., Mon. Not. R. Astron. Soc. 461, 1431 (2016), 10.1093/mnras/stw1281] sample. We focus on the balance between density and photometric redshift accuracy, while marginalizing over a realistic set of cosmological and systematic parameters. Our optimal selection, the MAGLIM sample, satisfies i <4 zphot+18 and has 30 % wider redshift distributions but 3.5 times more galaxies than REDMAGIC. Assuming a w CDM model (i.e. with a free parameter for the dark energy equation of state) and equivalent scale cuts to mitigate nonlinear effects, this leads to 40% increase in the figure of merit for the pair combinations of m, w , and 8, and gains of 16% in 8, 10% in m, and 12% in w . Similarly, in CDM , we find an improvement of 19% and 27% on 8 and m, respectively. We also explore flux-limited samples with a flat magnitude cut finding that the optimal selection, i <22.2 , has 7 times more galaxies and 20 % wider redshift distributions compared to MAGLIM, but slightly worse constraints. We show that our results are robust with respect to the assumed galaxy bias and photometric redshift uncertainties with only moderate further gains from increased number of tomographic bins or the inclusion of bin cross-correlations, except in the case of the flux-limited sample, for which these gains are more significant.

    79. Costanzi, M., Saro, A., Bocquet, S., et al., 2021, PhRvD, 103, 043522, Cosmological constraints from DES Y1 cluster abundances and SPT multiwavelength data

      We perform a joint analysis of the counts of redMaPPer clusters selected from the Dark Energy Survey (DES) year 1 data and multiwavelength follow-up data collected within the 2500 deg2 South Pole Telescope (SPT) Sunyaev-Zel’dovich (SZ) survey. The SPT follow-up data, calibrating the richness-mass relation of the optically selected redMaPPer catalog, enable the cosmological exploitation of the DES cluster abundance data. To explore possible systematics related to the modeling of projection effects, we consider two calibrations of the observational scatter on richness estimates: a simple Gaussian model which account only for the background contamination (BKG), and a model which further includes contamination and incompleteness due to projection effects (PRJ). Assuming either a CDM +m or w CDM +m cosmology, and for both scatter models, we derive cosmological constraints consistent with multiple cosmological probes of the low and high redshift Universe, and in particular with the SPT cluster abundance data. This result demonstrates that the DES Y1 and SPT cluster counts provide consistent cosmological constraints, if the same mass calibration data set is adopted. It thus supports the conclusion of the DES Y1 cluster cosmology analysis which interprets the tension observed with other cosmological probes in terms of systematics affecting the stacked weak lensing analysis of optically selected low-richness clusters. Finally, we analyze the first combined optically SZ selected cluster catalog obtained by including the SPT sample above the maximum redshift probed by the DES Y1 redMaPPer sample (z =0.65 ). Besides providing a mild improvement of the cosmological constraints, this data combination serves as a stricter test of our scatter models: the PRJ model, providing scaling relations consistent between the two abundance and multiwavelength follow-up data, is favored over the BKG model.

    80. Neugent, K. F., Levesque, E., Massey, P., 2021, AAS, 53, 119.05D, The Red Supergiant Binary Fraction in the Local Group Galaxies

      The binary fraction of massive main-sequence OB stars is thought to be as high as 70% or greater. However, until recently, only around a dozen binary red supergiants (RSGs) had been identified, despite the fact that these stars are the evolved descendants of a large portion of OB stars. My research focuses on searching for these “missing” binary RSGs. As dictated by stellar evolution, binary RSGs will likely have B-type companions and such systems will have unique photometric signatures due to the shape of their spectral energy distributions. After observing candidate RSG+B star binaries spectroscopically in the Local Group galaxies of M31, M33 and the Magellanic Clouds, we’ve discovered over 250 new systems. I’ll discuss how these results have allowed us to place constraints on the binary fraction of RSGs as a function of metallicity and the greater impacts this has on our understanding of massive star evolution, supernovae populations, and the creation of gravitational wave events.

    81. Bodansky, S., Massey, P., Penny, L., 2021, AAS, 53, 133.05, Weighing the Most Massive Binary Known: An Archival Study of NGC 3603-A1

      NGC 3603-A1 is likely the most massive binary star ever “weighed” through its orbital mass. The system is hard to observe, as it is found in the dense core of NGC 3603, with other massive stars within an arcsecond. Analysis of VLT spectroscopy in 2008 found a mass of 116 31 M for the primary and 89 16 M for secondary (Schnurr et al. 2008, MNRAS 389, L38). As an extremely massive, double-lined eclipsing binary, this system provides unique insight into the accuracy of model-dependent methods of determining stellar masses for very high mass stars. We use previously unanalyzed archival spectra and imaging from HST to test the accuracy of the ground-based results and to increase the precision of these masses. From these spectroscopic data, we found a mass ratio of 0.72 0.03, which agrees with the VLT mass ratio of 0.75 0.3. We have also produced a light curve for A1 using HST photometry, which provides a more accurate measurement of the systems inclination. Ultimately we hope to refine the masses of A1 with new observations.


      SB’s work was supported by through the National Science Foundation REU program grant to NAU (awards 1852478 and 1950901), while PM’s efforts were supported in part through AST-1612874.

    82. Castelloe, E., Hunter, D., 2021, AAS, 53, 147.03, Searching for Star Formation in the Outer Disks of Dwarf Galaxies

      The outer disks of dwarf galaxies provide an extreme environment for studies of star formation because of their low gas densities and metallicities. Previous work has found evidence of young star clusters in the outer disks of dwarf galaxies, but it is unclear how these star clusters could have formed there since the gas density is too low to fragment into clouds via gravitational instability. We searched for young star clusters in the outer disks of dwarf galaxies with new deep images of three dwarf galaxies in four filters from the Local Irregulars That Trace Luminosity Extremes, The H I Nearby Galaxy Survey (LITTLE THINGS). We confirmed one young star cluster in the outer disk of DDO 43, which also appeared in H and far ultraviolet images. We found three additional young star cluster candidates, one in the outer disk of DDO 43 and two in the outer disk of DDO 187. We use photometry of the young star cluster and cluster candidates and a model catalog of cluster evolution to estimate the age and mass and measure diameters of the star clusters. We found that the confirmed young star cluster and the candidate cluster in DDO 43 have reasonable masses and diameters but the two cluster candidates in DDO 187 are very small. Our findings suggest that it is possible for stars to form in the outer disks of dwarf galaxies. This research has been supported by NSF awards 1852478 and 1950901 to Northern Arizona University for the 2020 REU program.

    83. Clark, C., van Belle, G., Horch, E., et al., 2021, AAS, 53, 241.02, The optomechanical design of the Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI)

      The Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI) is a new speckle imaging instrument operational on the 4.3-m Lowell Discovery Telescope. QWSSI is built to efficiently make use of collected photons and detector real estate. The instrument images on a single EMCCD at four wavelengths in the optical (577, 658, 808, and 880nm) with 40nm bandpasses. Longward of 1um, two imaging wavelengths in the near-infrared are collected at 1150 and 1570nm on two InGaAs cameras. All remaining non-imaging visible light is sent into a wavefront EMCCD. With simultaneous wavefront sensing, QWSSI characterizes atmospheric aberrations in the wavefront for each speckle frame. This results in additional data that can be utilized during post-processing, enabling advanced techniques such as Multi-Frame Blind Deconvolution. The design philosophy was optimized for an inexpensive, rapid build; virtually all parts were commercial-off-the-shelf, and custom parts were 3D printed. QWSSI’s unique build and capabilities represent a new frontier in civilian high-resolution speckle imaging.

    84. Aadland, E., Hillier, D., Massey, P., et al., 2021, AAS, 53, 330.02, A New Wolf-Rayet Transition Star: A WC with Nitrogen

      We announce the discovery of a new “transition” Wolf-Rayet (WR) star, BAT99-9. WR stars are classified into two different classes, based on their optical spectra: the nitrogen sequence WN-type (show strong emission lines of helium and nitrogen) and the carbon sequence WC-type (show strong emission lines of carbon). WR stars are the evolved He-burning descendants of the most massive O-type stars, with the products of their nuclear fusion brought to the surface. The Large Magellanic Cloud (LMC) WC BAT99-9 is unique as it still has nitrogen in its spectrum, which is unheard of in WC stars! There is a group of stars called WN/C stars, whose spectra are that of WN-type WR stars with the exception of a single carbon line, C IV 5812. It is unclear whether these stars have a higher abundance of carbon than the WNs, as the strength of this line is heavily influenced by other parameters. The model analysis is presented as part of an analysis of three other WC-type stars in the LMC. We found that the WCs’ chemical abundances are in agreement with both binary and single-star evolutionary models. However, for BAT99-9, binary evolution models may better explain the timescales with nitrogen still being on the surface. This work is supported through the NASA Astrophysics Data Analysis Program80NSSC18K0729 as well as a grant from the Space Telescope Science Institute (GO-13781).

    85. Hartman, Z., Lepine, S., van Belle, G., 2021, AAS, 53, 438.03D, A Tale of Nearly 100,000 Wide Binaries as Told by a Lobster, Two Spacecraft and Some Speckles

      Astronomers still do not know how the widest systems with separations larger than 10,000 au form. And yet, these systems have proved invaluable for calibrating metallicity relations and studying Galactic tides. One possible way to gain insight into their formation history is to examine the higher order multiplicity fraction, i.e. how many triples, quadruples, etc. To study this, we present a catalog of 99,203 wide binaries with probabilities greater than 95% of being gravitationally bound pairs. These binaries were identified through a Bayesian analysis of the high proper motion stars (> 40 mas/yr) in the Gaia DR2 catalog, along with supplemental stars from the SUPERBLINK high proper motion survey. Taking advantage of the linearity of the slope of the color-magnitude relationship of the K dwarf main sequence stars, we represent the relative over-luminosity of the components in K+K wide binaries in a plot we call the “Lobster” diagram. This diagram allows us to identify over-luminous components that most likely contain companions unresolved by Gaia DR2. Using this, we place a lower limit on the higher order multiplicity fraction of K+K wide binaries at 39.6%. To further prove that the “lobster” diagram highlights higher order multiples, we use the Lightkurve package in Python to identify eclipsing binary systems in TESS, K2 and Kepler and see where they fall on the diagram. Of the 12 eclipsing binaries identified, 11 were predicted to host an over-luminous component. In addition, we show that the presence of a spot modulation or unperiodic signal in a light curve suggests that system is more likely to show an over-luminous component. Finally, we present the first results of a speckle follow-up campaign examining the widest K+K systems (> 10,000 au) making use of the QWSSI speckle camera for the first time, a new instrument that we built at Lowell Observatory.

    86. Ramiaramanantsoa, T., Bowman, J., Shkolnik, E., et al., 2021, AAS, 53, 515.08, An Automated Onboard Image Integration Control for the Star-Planet Activity Research CubeSat

      M dwarfs are known to possess strong and highly variable ultraviolet (UV) radiation that might play an important role in the habitability and atmospheric loss of their planets. The Star-Planet Activity Research CubeSat (SPARCS) is a dedicated space-based observatory that will photometrically monitor the flaring activity of a sample of M dwarfs of different ages simultaneously at near-UV and the far-UV wavelengths. Hence, the mission adopts a 9-cm reflective telescope to project a 40′ field-of-view onto two back-illuminated delta-doped CCDs with high UV quantum efficiency. To achieve its science objective, the satellite is equipped with a dedicated science payload processor that manages detector thermal control as well as science observations, and performs near-real time image reduction and aperture photometry in order to automatically and actively control subsequent integration times and gains when flaring events are detected. We present the approach adopted for the SPARCS dynamic exposure control loop and its pre-flight tests and performance using synthetic M dwarf light curves and full-frame images in the two SPARCS passbands.


      Acknowledgements: Funding for SPARCS is provided by NASA’s Astrophysics Research and Analysis program, NNH16ZDA001N.

    87. Smith, E. C., Logsdon, S., McLean, I. S., et al., 2021, AAS, 53, 526.04, SOFIA/FLITECAM 3-5.4 micron Spectroscopy of PAHs in Planetary Nebulae

      We present stratospheric observations of the ~3-5.4 micron spectra of young planetary nebulae by the SOFIA instrument FLITECAM. The goals of this study were to characterize the NIR emission of Polycyclic Aromatic Hydrocarbons (PAHs) in planetary nebulae and study the evolution of PAH features within these objects. Using airborne 3-5.4 micron grism spectroscopy of three young, Carbon-rich planetary nebulae: IC 5117, PNG 093.9-00.1, and BD +30 3639, we investigated the spectral variation of the 3.3 micron PAH feature and its associated aliphatic features (3.4-3.6 microns), characterized the weak 5.25 PAH emission feature, and set limits on the theoretical contribution of the 4.4-4.8 micron deuterated-PAH features. All features, including atomic emission lines, were fit with a series of Gaussians to determine their flux. We further characterized the 3.3 micron PAH feature by measuring equivalent width and central wavelength, and by classifying the shape of the emission. We also determined the PAH/Aliphatic ratio for each target. The 3.3 micron PAH emission feature is observed in all three objects, as is PAH emission at 5.25 microns. PNG 093.9-00.1 exhibits NGC 7027-like aliphatic emission in the 3.4-3.6 micron region while aliphatic emission in IC 5117 and BD +30 3639 is weaker, and exhibits less structure.

    88. Dimitrova, T., Neugent, K., Levesque, E., et al., 2021, AAS, 53, 548.08, Locating Red Supergiants in the Galaxy NGC6822

      Using near-IR photometry, we are identifying red supergiants (RSG) in the irregular barred galaxy NGC6822 to compare with stellar evolutionary models. This research is complementary to our previous work, in which we located RSGs in the starburst galaxy IC10. These stars are the coolest of the evolved massive stars and have K and M spectral types and temperatures below 4100 K. Typically, they can be up to a thousand times the radius of the Sun and are therefore highly luminous. To find them in NGC6822, we first used GAIA parallax and proper motion values to filter out foreground red dwarfs before transforming the J and K magnitudes to effective temperatures and luminosities. Then, we used these values to apply RSG temperature and luminosity constraints. Next, we will compare our results to previous spectroscopically confirmed RSGs. Finally, we will use the color magnitude diagram to eliminate lower-mass AGB stars contaminants. Stellar evolutionary theory provides us with the expected quantity of RSG populations. Here, we propose a new sample of RSG candidates in NGC6822 that can be utilized as an observational test of such theory. By comparing our results in IC10 and NGC6822 with the RSG content studies done by our collaborators in M31, M33, and the LMC, our results can be used in further studies to test the effectiveness of RSG population projection methods. Additionally, by locating a population of RSGs in NGC6822, future possibilities for studying these massive stars with direct spectroscopic follow-up are created.

    89. Margon, B., Massey, P., Neugent, K., et al., 2021, AAS, 53, 548.10, The Enigmatic Nature of 2MASS J05073893-6826061: A Hot, H-poor Post-AGB Star?

      We call attention to the very unusual spectrum of the LMC star 2MASS J05073893-6826061, which shows an unprecedented combination of odd properties, including intense UV and IR excesses, no Balmer transitions, weak C II emission, and a dense thicket of narrow, difficult to identify absorption lines. The spectrum of this V = 15.6 star has recently been reported by Margon et al. (ApJ, 898, 85, 2020), where it is referred to as object 233-1. The position of 233-1 on the H-R diagram implies that this star may be a very hot, H-poor post-AGB object, caught in a brief stage of evolution.


      Membership in the LMC seems certain. The object shows weak C II 7231, 7236 emission, with the doublet well resolved, appearing at the LMC velocity, and the Gaia proper motion and parallax data are also compatible with membership. There is no evidence for large amplitude photometric variability or surrounding nebulosity. The most remarkable spectral features are a series of dozens of narrow absorption lines, unresolved at our 1~A resolution, in the 3300-5000 A range. Identification of these features is problematic due to the sheer number of observed transitions, making chance coincidences with common atomic species and ionization states likely. Cross-correlation of atomic line lists with the spectrum does reveal strong evidence for the presence of O II, and less convincing although still substantial evidence for He I, He II, Si III, and N II. Although the late-type, low-mass [WC] stars do share the UV and IR excesses and C II 7231, 7236 emission seen in 233-1, as well as occasional narrow absorption lines, their spectra, dominated by dozens of very strong C II and He I emission lines, are quite different. The combination of the weak C II emission, lack of H, UV and IR excess, and numerous narrow absorption lines in 233-1 seems very unusual. We plan continued monitoring of the object.

      P.M. is grateful for the support of NSF grant AST-1612874 and the Mt. Cuba Astronomical Foundation.

    90. Cabot, Samuel H. C., Roettenbacher, Rachael M., Henry, Gregory W., et al., 2021, AJ, 161, 26, EXPRES. II. Searching for Planets around Active Stars: A Case Study of HD 101501

      By controlling instrumental errors to below 10 cm s-1, the EXtreme PREcision Spectrograph (EXPRES) allows for a more insightful study of photospheric velocities that can mask weak Keplerian signals. Gaussian processes (GP) have become a standard tool for modeling correlated noise in radial velocity data sets. While GPs are constrained and motivated by physical properties of the star, in some cases they are still flexible enough to absorb unresolved Keplerian signals. We apply GP regression to EXPRES radial velocity measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD 101501. We obtain tight constraints on the stellar rotation period and the evolution of spot distributions using 28 seasons of ground-based photometry, as well as recent Transiting Exoplanet Survey Satellite data. Light-curve inversion was carried out on both photometry data sets to reveal the spot distribution and spot evolution timescales on the star. We find that the >5 m s-1 rms radial velocity variations in HD 101501 are well modeled with a GP stellar activity model without planets, yielding a residual rms scatter of 45 cm s-1. We carry out simulations, injecting and recovering signals with the GP framework, to demonstrate that high-cadence observations are required to use GPs most efficiently to detect low-mass planets around active stars like HD 101501. Sparse sampling prevents GPs from learning the correlated noise structure and can allow it to absorb prospective Keplerian signals. We quantify the moderate to high-cadence monitoring that provides the necessary information to disentangle photospheric features using GPs and to detect planets around active stars.

    91. Lauer, Tod R., Postman, Marc, Weaver, Harold A., et al., 2021, ApJ, 906, 77, New Horizons Observations of the Cosmic Optical Background

      We used existing data from the New Horizons Long-range Reconnaissance Imager (LORRI) to measure the optical-band (0.4 0.9 m) sky brightness within seven high-Galactic latitude fields. The average raw level measured while New Horizons was 42-45 au from the Sun is 33.2 0.5 nW m-2 sr-1. This is 10 as dark as the darkest sky accessible to the Hubble Space Telescope, highlighting the utility of New Horizons for detecting the cosmic optical background (COB). Isolating the COB contribution to the raw total required subtracting scattered light from bright stars and galaxies, faint stars below the photometric detection limit within the fields, and diffuse Milky Way light scattered by infrared cirrus. We removed newly identified residual zodiacal light from the IRIS 100 m all-sky maps to generate two different estimates for the diffuse Galactic light. Using these yielded a highly significant detection of the COB in the range 15.9 4.2 (1.8 stat., 3.7 sys.) nW m-2 sr-1 to 18.7 3.8 (1.8 stat., 3.3 sys.) nW m-2 sr-1 at the LORRI pivot wavelength of 0.608 m. Subtraction of the integrated light of galaxies fainter than the photometric detection limit from the total COB level left a diffuse flux component of unknown origin in the range 8.8 4.9 (1.8 stat., 4.5 sys.) nW m-2 sr-1 to 11.9 4.6 (1.8 stat., 4.2 sys.) nW m-2 sr-1. Explaining it with undetected galaxies requires the assumption that the galaxy count faint-end slope steepens markedly at V > 24 or that existing surveys are missing half the galaxies with V < 30.

    92. Biddle, Lauren I., Llama, Joe, Cameron, Andrew, et al., 2021, ApJ, 906, 113, Amplitude Modulation of Short-timescale Hot Spot Variability

      Variability of Classical T Tauri stars (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks, which can occur stochastically, periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present an analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of 1 day. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star (6.6 days) and the orbital period of the planet (9.0 days) known to drive pulsed accretion onto the star.

    93. De Propris, Roberto, West, Michael J., Andrade-Santos, Felipe, et al., 2021, MNRAS, 500, 310, Brightest cluster galaxies: the centre can(not?) hold

      We explore the persistence of the alignment of brightest cluster galaxies (BCGs) with their local environment. We find that a significant fraction of BCGs do not coincide with the centroid of the X-ray gas distribution and/or show peculiar velocities (they are not at rest with respect to the cluster mean). Despite this, we find that BCGs are generally aligned with the cluster mass distribution even when they have significant offsets from the X-ray centre and significant peculiar velocities. The large offsets are not consistent with simple theoretical models. To account for these observations BCGs must undergo mergers preferentially along their major axis, the main infall direction. Such BCGs may be oscillating within the cluster potential after having been displaced by mergers or collisions, or the dark matter halo itself may not yet be relaxed.

    94. Vielzeuf, P., Kovacs, A., Demirbozan, U., et al., 2021, MNRAS, 500, 464, Dark Energy Survey Year 1 results: the lensing imprint of cosmic voids on the cosmic microwave background

      Cosmic voids gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint on degree scales. We use the simulated CMB lensing convergence map from the Marenostrum Institut de Ciencias de l’Espai (MICE) N-body simulation to calibrate our detection strategy for a given void definition and galaxy tracer density. We then identify cosmic voids in Dark Energy Survey (DES) Year 1 data and stack the Planck 2015 lensing convergence map on their locations, probing the consistency of simulated and observed void lensing signals. When fixing the shape of the stacked convergence profile to that calibrated from simulations, we find imprints at the 3 significance level for various analysis choices. The best measurement strategies based on the MICE calibration process yield S/N 4 for DES Y1, and the best-fitting amplitude recovered from the data is consistent with expectations from MICE (A 1). Given these results as well as the agreement between them and N-body simulations, we conclude that the previously reported excess integrated Sachs-Wolfe (ISW) signal associated with cosmic voids in DES Y1 has no counterpart in the Planck CMB lensing map.

    95. Liao, Wei-Ting, Chen, Yu-Ching, Liu, Xin, et al., 2021, MNRAS, 500, 4025, Discovery of a candidate binary supermassive black hole in a periodic quasar from circumbinary accretion variability

      Binary supermassive black holes (BSBHs) are expected to be a generic byproduct from hierarchical galaxy formation. The final coalescence of BSBHs is thought to be the loudest gravitational wave (GW) siren, yet no confirmed BSBH is known in the GW-dominated regime. While periodic quasars have been proposed as BSBH candidates, the physical origin of the periodicity has been largely uncertain. Here, we report discovery of a periodicity (p = 1607 7 d) at 99.95 per cent significance (with a global p value of 10-3 accounting for the look elsewhere effect) in the optical light curves of a redshift 1.53 quasar, SDSS J025214.67-002813.7. Combining archival Sloan Digital Sky Survey data with new, sensitive imaging from the Dark Energy Survey, the total 20-yr time baseline spans 4.6 cycles of the observed 4.4-yr (rest frame 1.7-yr) periodicity. The light curves are best fit by a bursty model predicted by hydrodynamic simulations of circumbinary accretion discs. The periodicity is likely caused by accretion rate modulation by a milli-parsec BSBH emitting GWs, dynamically coupled to the circumbinary accretion disc. A bursty hydrodynamic variability model is statistically preferred over a smooth, sinusoidal model expected from relativistic Doppler boost, a kinematic effect proposed for PG1302-102. Furthermore, the frequency dependence of the variability amplitudes disfavours Doppler boost, lending independent support to the circumbinary accretion variability hypothesis. Given our detection rate of one BSBH candidate from circumbinary accretion variability out of 625 quasars, it suggests that future large, sensitive synoptic surveys such as the Vera C. Rubin Observatory Legacy Survey of Space and Time may be able to detect hundreds to thousands of candidate BSBHs from circumbinary accretion with direct implications for Laser Interferometer Space Antenna.

    96. Henghes, B., Lahav, O., Gerdes, D. W., et al., 2021, PASP, 133, 014501, Machine Learning for Searching the Dark Energy Survey for Trans-Neptunian Objects

      In this paper we investigate how implementing machine learning could improve the efficiency of the search for Trans-Neptunian Objects (TNOs) within Dark Energy Survey (DES) data when used alongside orbit fitting. The discovery of multiple TNOs that appear to show a similarity in their orbital parameters has led to the suggestion that one or more undetected planets, an as yet undiscovered “Planet 9”, may be present in the outer solar system. DES is well placed to detect such a planet and has already been used to discover many other TNOs. Here, we perform tests on eight different supervised machine learning algorithms, using a data set consisting of simulated TNOs buried within real DES noise data. We found that the best performing classifier was the Random Forest which, when optimized, performed well at detecting the rare objects. We achieve an area under the receiver operating characteristic (ROC) curve, (AUC) = 0.996 0.001. After optimizing the decision threshold of the Random Forest, we achieve a recall of 0.96 while maintaining a precision of 0.80. Finally, by using the optimized classifier to pre-select objects, we are able to run the orbit-fitting stage of our detection pipeline five times faster.

    97. Muir, J., Baxter, E., Miranda, V., et al., 2021, PhRvD, 103, 023528, DES Y1 results: Splitting growth and geometry to test CDM

      We analyze Dark Energy Survey (DES) data to constrain a cosmological model where a subset of parametersfocusing on mare split into versions associated with structure growth (e.g., mgrow) and expansion history (e.g., mgeo). Once the parameters have been specified for the CDM cosmological model, which includes general relativity as a theory of gravity, it uniquely predicts the evolution of both geometry (distances) and the growth of structure over cosmic time. Any inconsistency between measurements of geometry and growth could therefore indicate a breakdown of that model. Our growth-geometry split approach therefore serves both as a (largely) model-independent test for beyond- CDM physics, and as a means to characterize how DES observables provide cosmological information. We analyze the same multiprobe DES data as [Phys. Rev. Lett. 122, 171301 (2019), 10.1103/PhysRevLett.122.171301] : DES Year 1 (Y1) galaxy clustering and weak lensing, which are sensitive to both growth and geometry, as well as Y1 BAO and Y3 supernovae, which probe geometry. We additionally include external geometric information from BOSS DR12 BAO and a compressed Planck 2015 likelihood, and external growth information from BOSS DR12 RSD. We find no significant disagreement with mgrow=mgeo. When DES and external data are analyzed separately, degeneracies with neutrino mass and intrinsic alignments limit our ability to measure mgrow, but combining DES with external data allows us to constrain both growth and geometric quantities. We also consider a parametrization where we split both m and w , but find that even our most constraining data combination is unable to separately constrain mgrow and wgrow. Relative to CDM , splitting growth and geometry weakens bounds on 8 but does not alter constraints on h .


    1. Holler, B., Young, L. A., Grundy, W. M., et al., 2020, AGUFM, 2020, P032-0006, Comparative KBOlogy: The Dynamic Surfaces of Pluto and Triton

      Pluto, the largest Kuiper Belt dwarf planet, and Triton, Neptune’s largest satellite and a former Kuiper Belt Object [1], are the largest known objects with rock/ice compositions found at or beyond Neptune’s orbit. The similarities between Pluto and Triton provide a backdrop for the differences and a window into physical processes at work on icy surfaces.


      Seasonal transitions on Pluto and Triton are moving in opposite directions, with surface composition changes observed on both over 10+ years. Pluto is approaching N. hemisphere summer in 2029 while Triton entered S. hemisphere summer in 2000. Volatile N2 and CH4 band depths are decreasing on Pluto [2] and increasing on Triton [3]. This makes sense at first glance, but the reasons for these changes may be different.

      Increasing volatiles on Triton could indicate ongoing deposition or regions of past deposition being revealed in the N. hemisphere. Continued spectral observations of Triton over the coming years will provide clues to evaluate ongoing changes: A decrease in H2O band area would point to deposition, even if volatile band areas remain constant due to volatile transport. It remains to be seen if volatiles will be completely removed from the N. hemisphere of Pluto over the next decade, mimicking the current state of Triton’s S. hemisphere [3]. Yearly observations of Pluto are critical in the coming years, as models predict the complete loss of volatiles from the N. hemisphere by 2030 [4]; “matched pairs” of spectra made at comparable sub-observer latitudes and longitudes will make yearly comparisons possible.

      The same strategy is not as critical for Triton due to the lack of a Sputnik Planitia-like feature that dominates the spectrum (evidence of a depleted volatile inventory compared to Pluto) and because non-volatile H2O absorption is constant with longitude [3]. The difference in volatile inventory between Pluto and Triton, a result of different formation histories [1,5], should play a key role in the magnitude of the band depth changes with time. These differences will be discussed in the context of spacecraft and other ground-based observations.


      [1] Agnor & Hamilton 2006. Nature 441, 192-194. [2] Grundy et al. 2014. Icarus 235, 220-224. [3] Holler et al. 2016. Icarus 267, 255-266. [4] Bertrand & Forget 2016. Nature 540, 86-89. [5] Canup 2011. AJ 141, 35.

    2. Sciamma-O’Brien, E. M., Roush, T. L., Salama, F., et al., 2020, AGUFM, 2020, P068-0001, Determination of the Complex Refractive Indices of Aerosol Analogs Formed at Low Temperatures with the NASA Ames Optical Constants Facility (OCF)

      The NASA Ames COsmic SImulation Chamber (COSmIC) [1] is a unique experimental facility that allows: 1) cooling a gas mixture to low temperature (150 K) in a jet expansion before inducing chemistry by plasma; and 2) controlling the extent of the chemical reactions by employing a pulsed plasma discharge. This enables the study of the early stages of aerosol production, as well as specific chemical pathways in planetary environments (e.g. Titan’s and Pluto’s atmospheres). Both the gas and solid products can be studied. For a decade COSmIC has been used to simulate Titan’s atmospheric chemistry at low, Titan-like temperature [2]. New developments on the COSmIC facility are investigating formation of aerosols in tenuous, or transitory, atmospheres of other icy bodies [3-5], as well as cool exoplanets atmospheres having a hydrocarbon component, that results in formation of hazes and/or surface deposits of refractory materials.


      The new Ames Optical Constants Facility enables determination of the aerosol analogs’ complex refractive indices, n and k, from 0.59 to 200 m [2]. Here we report efforts of determining n and k from ex-situ transmission measurements of solid samples produced from binary N2-CH4 and Ar-CH4, and tertiary N2-CH4-C2H2 and Ar-CH4-C2H2 gas mixtures in COSmIC, and deposited onto various substrates. A computational technique [6] that addresses interference fringes observed in the laboratory transmission data, particularly at wavelengths < 3 m, has been implemented and applied to determine n and k for the samples. At visible and near-infrared wavelengths (0.4-1.6 m) the deposit thickness, and its variation, as well as n and k were determined by a commercial entity. These data provide the ability to compare results, from independent methods, in the region of overlap between the two approaches.


      This research is supported by NASA’s Science Mission Directorate SERA Directed Work Package. The authors acknowledge the outstanding technical support of R. Walker and E. Quigley.

      [1] Salama F. et al., IAU Proc., 13 (S332), 364-369, 2017.

      [2] Sciamma-O’Brien, E. et al., IAU Proc. (S350), 2020.

      [3] Grundy, W. et al. Icarus 314, 232-245, 2018.

      [4] Cook, J. C., et al. Icarus 331, 148-169, 2019.

      [5] Bertrand, T. and Forget, F. Icarus 287, 72-86, 2017.

      [6] Swanepoel, R., J. Phys. E: Sci. Instr., 16, 1214-1222, 1983.

    3. Cartwright, R. J., Beddingfield, C. B., Nordheim, T., et al., 2020, AGUFM, 2020, P074-04, Evidence for ammonia-bearing species on the Uranian satellite Ariel supports recent geologic activity

      The Voyager 2 encounter with the Uranian system revealed that the surface of Ariel exhibits many geologic landforms with unusual morphologies. The morphologies and estimated flow rheologies of these features are consistent with emplacement of ammonia (NH3) rich cryolavas on Ariel. NH3 is an efficient antifreeze agent when mixed with liquid H2O, allowing icy bodies to retain subsurface salty oceans for longer periods of time compared to “pure” H2O oceans. Because Voyager 2 was not equipped with a near-infrared mapping spectrometer, the composition of these geologic features is unknown. Recent ground-based telescope observations have detected spectral hints of a 2.2 m band on Ariel, which has been attributed to NH3-bearing species on other icy bodies, including Pluto and its moons Charon, Nix, and Hydra. However, the spatial distribution and spectral signature of the 2.2-m band on Ariel have not been previously investigated, limiting our ability to interpret its origin.


      We analyzed 32 ground-based telescope spectra of Ariel, spanning a wide range of sub-observer longitudes and latitudes. We measured the area and depth of the 2.2-m band, finding that ten spectra display prominent 2.2-m features (> 2 measurements). We found no discernable spatial trends in the distribution of the 2.2-m band, unlike the distribution of CO2 ice and H2O ice, which display significant hemispherical asymmetries on Ariel. Furthermore, we compared the Ariel spectra displaying the strongest 2.2-m bands to laboratory spectra of different NH3-bearing species, finding that NH3-H2O solutions and NH3-hydrates provide the best match to its spectral signature. We also found evidence for a 2.24-m band in four spectra, with a spectral signature most consistent with NH3 ice.

      The possible presence of NH3 is intriguing given that this constituent should be removed by energetic electrons (~1 MeV) over geologically short timescales. Consequently, the hints of NH3 detected on Ariel might result from geologic activity in the fairly recent past (< 2 Ga, based on regional crater density estimates), perhaps including emplacement of NH3-rich cryolavas. Similar connections have been made between the presence of NH3 and possible cryovolcanic features on Pluto, suggesting that NH3 might be a useful tracer of endogenic activity on some icy bodies.

    4. Smith, M., D’Andrea, C. B., Sullivan, M., et al., 2020, AJ, 160, 267, First Cosmology Results using Supernovae Ia from the Dark Energy Survey: Survey Overview, Performance, and Supernova Spectroscopy

      We present details on the observing strategy, data-processing techniques, and spectroscopic targeting algorithms for the first three years of operation for the Dark Energy Survey Supernova Program (DES-SN). This five-year program using the Dark Energy Camera mounted on the 4 m Blanco telescope in Chile was designed to discover and follow supernovae (SNe) Ia over a wide redshift range (0.05 < z < 1.2) to measure the equation-of-state parameter of dark energy. We describe the SN program in full: strategy, observations, data reduction, spectroscopic follow-up observations, and classification. From three seasons of data, we have discovered 12,015 likely SNe, 308 of which have been spectroscopically confirmed, including 251 SNe Ia over a redshift range of 0.017 < z < 0.85. We determine the effective spectroscopic selection function for our sample and use it to investigate the redshift-dependent bias on the distance moduli of SNe Ia we have classified. The data presented here are used for the first cosmology analysis by DES-SN (“DES-SN3YR”), the results of which are given in Dark Energy Survey Collaboration et al. The 489 spectra that are used to define the DES-SN3YR sample are publicly available at

    5. Fedorets, Grigori, Micheli, Marco, Jedicke, Robert, et al., 2020, AJ, 160, 277, Establishing Earth’s Minimoon Population through Characterization of Asteroid 2020 CD3

      We report on our detailed characterization of Earth’s second known temporary natural satellite, or minimoon, asteroid 2020 CD3. An artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the S or V complex in asteroid taxonomy. The discovery of 2020 CD3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. The estimated diameter of ${1.2}_{-0.2}^{+0.4}$ m and geocentric capture approximately a decade after the first known minimoon, 2006 RH120, are in agreement with theoretical predictions. The capture duration of 2020 CD3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 CD3‘s atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. More discoveries and a detailed characterization of the population can be expected with the forthcoming Vera C. Rubin Observatory Legacy Survey of Space and Time.

    6. Hinkle, Kenneth H., Lebzelter, Thomas, Fekel, Francis C., et al., 2020, ApJ, 904, 143, The M Supergiant High-mass X-Ray Binary 4U 1954+31

      The X-ray binary 4U 1954+31 has been classified as a low-mass X-ray binary containing an M giant and a neutron star (NS). It has also been included in the rare class of X-ray symbiotic binaries. The Gaia parallax, infrared colors, spectral type, abundances, and orbital properties of the M star demonstrate that the cool star in this system is not a low-mass giant but a high-mass M supergiant. Thus, 4U 1954+31 is a high-mass X-ray binary (HMXB) containing a late-type supergiant. It is the only known binary system of this type. The mass of the M I is ${9}_{-2}^{+6}$ M giving an age of this system in the range 1250 Myr with the NS no more than 43 Myr old. The spin period of the NS is one of the longest known, 5 hr. The existence of M I plus NS binary systems is in accord with stellar evolution theory, with this system a more evolved member of the HMXB population.

    7. Neugent, Kathryn F., Levesque, Emily M., Massey, Philip, et al., 2020, ApJ, 905, 83, Erratum: “The Red Supergiant Binary Fraction of the Large Magellanic Cloud” (2020, ApJ, 900, 118)
    8. Chen, Yu-Ching, Liu, Xin, Liao, Wei-Ting, et al., 2020, MNRAS, 499, 2245, Candidate periodically variable quasars from the Dark Energy Survey and the Sloan Digital Sky Survey

      Periodically variable quasars have been suggested as close binary supermassive black holes. We present a systematic search for periodic light curves in 625 spectroscopically confirmed quasars with a median redshift of 1.8 in a 4.6 deg2 overlapping region of the Dark Energy Survey Supernova (DES-SN) fields and the Sloan Digital Sky Survey Stripe 82 (SDSS-S82). Our sample has a unique 20-yr long multicolour (griz) light curve enabled by combining DES-SN Y6 observations with archival SDSS-S82 data. The deep imaging allows us to search for periodic light curves in less luminous quasars (down to r 23.5 mag) powered by less massive black holes (with masses 108.5M) at high redshift for the first time. We find five candidates with significant (at >99.74 per cent single-frequency significance in at least two bands with a global p-value of 7 10-4-3 10-3 accounting for the look-elsewhere effect) periodicity with observed periods of 3-5 yr (i.e. 1-2 yr in rest frame) having 4-6 cycles spanned by the observations. If all five candidates are periodically variable quasars, this translates into a detection rate of ${\sim }0.8^{+0.5}_{-0.3}$ per cent or ${\sim }1.1^{+0.7}_{-0.5}$ quasar per deg2. Our detection rate is 4-80 times larger than those found by previous searches using shallower surveys over larger areas. This discrepancy is likely caused by differences in the quasar populations probed and the survey data qualities. We discuss implications on the future direct detection of low-frequency gravitational waves. Continued photometric monitoring will further assess the robustness and characteristics of these candidate periodic quasars to determine their physical origins.

    9. dal Ponte, M., Santiago, B., Carnero Rosell, A., et al., 2020, MNRAS, 499, 5302, Increasing the census of ultracool dwarfs in wide binary and multiple systems using Dark Energy Survey DR1 and Gaia DR2 data

      We present the discovery of 255 binary and 6 multiple system candidates with wide (> 5 arcsec) separation composed by ultracool dwarfs (UCDs) companions to stars, plus nine double ultracool dwarf systems. These systems were selected based on common distance criteria. About 90 per cent of the total sample has proper motions available and 73 per cent of the systems also satisfy a common proper motion criterion. The sample of ultracool candidates was taken from the Dark Energy Survey (DES) and the candidate stellar primaries are from Gaia DR2 and DES data. We compute chance alignment probabilities in order to assess the physical nature of each pair. We find that 174 candidate pairs with Gaia DR2 primaries and 81 pairs with a DES star as a primary have chance alignment probabilities $\lt 5{{\ \rm per\ cent}}$ . Only nine candidate systems composed of two UCDs were identified. The sample of candidate multiple systems is made up of five triple systems and one quadruple system. The majority of the UCDs found in binaries and multiples are of early L type and the typical wide binary fraction over the L spectral types is $2\!-\!4{{\ \rm per\ cent}}$ . Our sample of candidate wide binaries with UCDs as secondaries constitutes a substantial increase over the known number of such systems, which are very useful to constrain the formation and evolution of UCDs.

    10. Pandey, S., Krause, E., Jain, B., et al., 2020, PhRvD, 102, 123522, Perturbation theory for modeling galaxy bias: Validation with simulations of the Dark Energy Survey

      We describe perturbation theory (PT) models of galaxy bias for applications to photometric galaxy surveys. We model the galaxy-galaxy and galaxy-matter correlation functions in configuration space and validate against measurements from mock catalogs designed for the Dark Energy Survey (DES). We find that an effective PT model with five galaxy bias parameters provides a good description of the 3D correlation functions above scales of 4 Mpc /h and z <1 . Our tests show that at the projected precision of the DES Year 3 analysis, two of the nonlinear bias parameters can be fixed to their coevolution values, and a third (the k2 term for higher derivative bias) set to zero. The agreement is typically at the 2% level over scales of interest, which is the statistical uncertainty of our simulation measurements. To achieve this level of agreement, our fiducial model requires using the full nonlinear matter power spectrum (rather than the one-loop PT one). We also measure the relationship between the nonlinear and linear bias parameters and compare them to their expected coevolution values. We use these tests to motivate the galaxy bias model and scale cuts for the cosmological analysis of the Dark Energy Survey; our conclusions are generally applicable to all photometric surveys.

    11. Scowen, Paul A., Ardila, David, Jensen, Logan, et al., 2020, SPIE, 11444, 114440A, SPARCS payload assembly, integration, and test update

      The Star-Planet Activity Research CubeSat (SPARCS) is a 6U CubeSat under construction that is devoted to the photometric monitoring of M stars in the far-UV (FUV) and near-UV (NUV), to measure the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation. We report on the progress made in the assembly, integration and test of the instrument payload at Arizona State University using a custom TVAC chamber and optical stimulus that provides calibration light sources and the custom contamination control environment that the FUV demands. The payload consists of a custom 90mm clear aperture telescope developed by Hexagon/Sigma Space, combined with a dichroic plate to separate the FUV and NUV beams developed by Teledyne Acton and Materion, married with twin focal plane array cameras separately optimized for their bandpasses as developed by JPL.

    12. Cornelius, Frank, Sweaton, Michael, Hardesty, Ben A., et al., 2020, SPIE, 11445, 114457I, Status and performance of Lowell Observatory’s Lowell Discovery Telescope’s active optical support system

      Lowell Observatory’s Lowell Discovery Telescope (LDT) is a 4.3-m telescope designed and constructed for optical and near infrared astronomical observation. We examine the performance of the primary and secondary mirror support systems during scientific operations, over the first six years of science operations. During that time we have redesigned the sacrificial pins in the primary mirror lateral support system, and developed a method to re-calibrate the load cell sensors used in both the primary and secondary mirror supports.

    13. van Belle, Gerard, Clark, James, Armstrong, J. Thomas, et al., 2020, SPIE, 11446, 1144608, The Navy Precision Optical Interferometer: two years of development towards large-aperture observations

      We have been pursuing a comprehensive program of improving high-resolution imaging at the Navy Precision Optical Interferometer (NPOI) hosted at Lowell Observatory’s Anderson Mesa site, for the purpose of spatially resolved observations of faint objects at scales down to less than 1 milliarcsecond. This activity at NPOI is being implemented with two primary phases. First, the `PALANTIR’ upgrade of NPOI is augmenting the existing telescope array with three 1-meter PlaneWave PW1000 telescopes. These telescopes are housed in mobile domes for rapid relocation around the array, and are being augmented with adaptive optics. Second, we are implementing a `NPOI Plus-Up’ plan which is modernizing the array infrastructure and streamlining its operations. All of these activities are being carried out as our current operations are continuing.

    14. Clark, Catherine A., van Belle, Gerard T., Horch, Elliott P., et al., 2020, SPIE, 11446, 114462A, The optomechanical design of the Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI)

      The Quad-camera Wavefront-sensing Six-channel Speckle Interferometer (QWSSI) is a new speckle imaging instrument available on the 4.3-m Lowell Discovery Telescope (LDT). QWSSI is built to efficiently make use of collected photons and available detector area. The instrument images on a single Electron Multiplying CCD (EMCCD) at four wavelengths in the optical (577, 658, 808, and 880nm) with 40nm bandpasses. Longward of 1m, two imaging wavelengths in the NIR are collected at 1150 and 1570nm on two InGaAs cameras with 50nm bandpasses. All remaining non-imaging visible light is then sent into a wavefront EMCCD. All cameras are operated synchronously via concurrent triggering from a timing module. With the simultaneous wavefront sensing, QWSSI characterizes atmospheric aberrations in the wavefront for each speckle frame. This results in additional data that can be utilized during post-processing, enabling advanced techniques such as Multi-Frame Blind Deconvolution. The design philosophy was optimized for an inexpensive, rapid build; virtually all parts were commercial-off-the-shelf (COTS), and custom parts were fabricated or 3D printed on-site. QWSSI’s unique build and capabilities represent a new frontier in civilian high-resolution speckle imaging.

    15. van Belle, Gerard T., Hillsberry, Dan, Kloske, John, et al., 2020, SPIE, 11446, 114462K, Optimast structurally connected interferometry enabled by in-space robotic manufacturing and assembly

      Future goals for astrophysics at the frontiers of high spatial resolution demand synthetic apertures significantly larger than the current or upcoming generations of single-aperture space observatories. Space-based interferometry enabled by in-space manufacturing delivers cost-effective observation of faint objects at unprecedented levels of angular resolution. Using the Made In Space (MIS) Optimast technology, a simple, two aperture Structurally Connected Interferometer (SCI) can be produced via in-space Additive Manufacturing (AM) technology. Optimast enables the manufacturing and deployment of small interferometric apertures at the tips of two large primary trusses unconstrained by launch loads or volume restrictions that meet science requirements for high angular resolutions, in the milliarcsecond regime. The LightBeam mission concept enabled by this capability has a wide range of ground-breaking science capabilities, including: measuring the sizes, shapes, and surface morphology of single asteroids, and binary asteroid orbits; imaging of young stellar object disk sculpting in the terrestrial planet regime; and probing the inner regions of active galactic nuclei. Space-based deployment of an interferometer unconstrained by the turbulent atmosphere will increase the sensitivity reach of such an instrument relative to its ground-based counterparts by a factor of 1,000 or more.

    16. Lawrence, J., Ben-Ami, S., Braulio, A., et al., 2020, SPIE, 11447, 1144728, The MANIFEST pre-concept design

      MANIFEST is a multi-object fibre positioner for the Giant Magellan Telescope that uses `Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeing-limited instruments, GMACS and GCLEF, offers access to: larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via multiple integral-field-units; increased spectral resolution using image-slicers; the capability for simultaneous observations with multiple instruments; the possibility of a gravity-invariant spectrograph mounting; the potential for OH suppression via fiber systems in the near-infrared; and the versatility of adding new instruments in the future. We have now completed the pre-concept phase for MANIFEST. This phase has focused on developing the science case and requirements, further developing high risk aspects of the instrument design, designing the opto-mechanical interfaces to the GMACS and GCLEF instruments, and detailing the interfaces to the GMT.

    17. Kuehn, Kyler, Kuhlmann, Stephen, Ellis, Simon, et al., 2020, SPIE, 11451, 114516A, Application of atmospheric OH suppression technology to ground-based infrared astronomy

      We seek to advance the capabilities of photonic technologies in support of ground-based infrared astronomy. Currently, observers in this field suffer from an irreducible background generated by emission from OH (hydroxyl) molecules in the upper atmosphere. However, if narrow-band notch filters could be incorporated into the optical path of astronomical instruments prior to any optical elements that would spectrally broaden such emission lines, then this background could be effectively suppressed with very little accompanying loss of signal from the astronomical sources of interest. Micron-scale ring resonators are one technology that provides a promising method of generating such notch filters. Building on our previous efforts in astrophotonic technology development, our current goals are 1) to optimize the design of ring resonators so that the notch filters they create provide greatest suppression at the wavelengths of the most prominent OH lines, and 2) to optimize the coupling of the resonator-equipped silicon devices with the input fibers (from the sky) and output fibers (to the spectrograph and detector) such that the throughput losses do not completely eliminate the signal-to-noise improvement gained from the OH suppression. Theoretical estimates show that suppression (by 20-40dB) of the most prominent OH lines improves the signal to noise of near-IR observations by a factor of 5 or more – this is similar in effect to turning a telescope with a 1m aperture into a telescope with a 5m aperture!

    18. Oszkiewicz, Dagmara, Troianskyi, Volodymyr, Fohring, Dora, et al., 2020, A&A, 643, A117, Spin rates of V-type asteroids

      Context. Basaltic V-type asteroids play a crucial role in studies of Solar System evolution and planetesimal formation. Comprehensive studies of their physical, dynamical, and statistical properties provide insight into these processes. Thanks to wide surveys, currently there are numerous known V-type and putative V-type asteroids, allowing a detailed statistical analysis.
      Aims: Our main goal is to analyze I corrected for US language conventions in this paper the currently available large sample of V-type spin rates, to find signatures of the non-gravitational Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect among the different V-type populations, and to estimate the spin barrier and critical density for V-type asteroids. Our intention is to increase the pool of information about the intriguing V-types.
      Methods: We collected rotational periods from the literature for spectrally confirmed V-types, putative V-types, and Vesta family members. Through spectroscopic observations we confirmed their taxonomic type and verified the high confirmation rates of the putative V-types. We combined the collected periods with periods estimated in this manuscript and produced rotational frequency distributions. We determined the spin barrier in the frequency-light curve amplitude space for V-type asteroids.
      Results: We analyzed rotational periods of 536 asteroids in our sample. As expected, due to the small size of the objects analyzed, the frequency distributions for the Vesta family and the V-types outside the family are inconsistent with a Maxwellian shape. The Vesta family shows an excess of slow-rotators. V-types outside the family show an excess of both slow and fast rotators. Interestingly, we found that the population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. The estimated critical density for V-type asteroids exceeds c = 2.0 g cm-3, which surpasses the previous estimates.
      Conclusions: We demonstrated that V-type asteroids have been influenced by the thermal radiation YORP effect and that their critical spin rate is higher than for C-type asteroids. The population of V-types outside the Vesta family shows a significant excess of fast rotators compared to the Vesta family. We hypothesize that the objects that evolved from the Vesta family though the Yarkovsky drift are also more susceptible to the YORP effect. Objects for which YORP has not yet had enough time to act and those that are more YORP resistant will be left in the family, which explains the relatively small proportion of fast rotators being left. The YORP timescale must thus be similar to the migration timescale for those objects.

    19. Garcia, A., Morgan, R., Herner, K., et al., 2020, ApJ, 903, 75, A DESGW Search for the Electromagnetic Counterpart to the LIGO/Virgo Gravitational-wave Binary Neutron Star Merger Candidate S190510g

      We present the results from a search for the electromagnetic counterpart of the LIGO/Virgo event S190510g using the Dark Energy Camera (DECam). S190510g is a binary neutron star (BNS) merger candidate of moderate significance detected at a distance of 227 92 Mpc and localized within an area of 31 (1166) square degrees at 50% (90%) confidence. While this event was later classified as likely nonastrophysical in nature within 30 hours of the event, our short latency search and discovery pipeline identified 11 counterpart candidates, all of which appear consistent with supernovae following offline analysis and spectroscopy by other instruments. Later reprocessing of the images enabled the recovery of six more candidates. Additionally, we implement our candidate selection procedure on simulated kilonovae and supernovae under DECam observing conditions (e.g., seeing and exposure time) with the intent of quantifying our search efficiency and making informed decisions on observing strategy for future similar events. This is the first BNS counterpart search to employ a comprehensive simulation-based efficiency study. We find that using the current follow-up strategy, there would need to be 19 events similar to S190510g for us to have a 99% chance of detecting an optical counterpart, assuming a GW170817-like kilonova. We further conclude that optimization of observing plans, which should include preference for deeper images over multiple color information, could result in up to a factor of 1.5 reduction in the total number of follow-ups needed for discovery.

    20. Buckley-Geer, E. J., Lin, H., Rusu, C. E., et al., 2020, MNRAS, 498, 3241, STRIDES: Spectroscopic and photometric characterization of the environment and effects of mass along the line of sight to the gravitational lenses DES J0408-5354 and WGD 2038-4008

      In time-delay cosmography, three of the key ingredients are (1) determining the velocity dispersion of the lensing galaxy, (2) identifying galaxies and groups along the line of sight with sufficient proximity and mass to be included in the mass model, and (3) estimating the external convergence ext from less massive structures that are not included in the mass model. We present results on all three of these ingredients for two time-delay lensed quad quasar systems, DES J0408-5354 and WGD 2038-4008 . We use the Gemini, Magellan, and VLT telescopes to obtain spectra to both measure the stellar velocity dispersions of the main lensing galaxies and to identify the line-of-sight galaxies in these systems. Next, we identify 10 groups in DES J0408-5354 and two groups in WGD 2038-4008 using a group-finding algorithm. We then identify the most significant galaxy and galaxy-group perturbers using the ‘flexion shift’ criterion. We determine the probability distribution function of the external convergence ext for both of these systems based on our spectroscopy and on the DES-only multiband wide-field observations. Using weighted galaxy counts, calibrated based on the Millennium Simulation, we find that DES J0408-5354 is located in a significantly underdense environment, leading to a tight (width $\sim 3{{\ \rm per\ cent}}$ ), negative-value ext distribution. On the other hand, WGD 2038-4008 is located in an environment of close to unit density, and its low source redshift results in a much tighter ext of $\sim 1{{\ \rm per\ cent}}$ , as long as no external shear constraints are imposed.

    21. Gatti, M., Chang, C., Friedrich, O., et al., 2020, MNRAS, 498, 4060, Dark Energy Survey Year 3 results: cosmology with moments of weak lensing mass maps – validation on simulations

      We present a simulated cosmology analysis using the second and third moments of the weak lensing mass (convergence) maps. The second moment, or variances, of the convergence as a function of smoothing scale contains information similar to standard shear two-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The analysis is geared towards the third year (Y3) data from the Dark Energy Survey (DES), but the methodology can be applied to other weak lensing data sets. We present the formalism for obtaining the convergence maps from the measured shear and for obtaining the second and third moments of these maps given partial sky coverage. We estimate the covariance matrix from a large suite of numerical simulations. We test our pipeline through a simulated likelihood analyses varying 5 cosmological parameters and 10 nuisance parameters and identify the scales where systematic or modelling uncertainties are not expected to affect the cosmological analysis. Our simulated likelihood analysis shows that the combination of second and third moments provides a 1.5 per cent constraint on S8 8(m/0.3)0.5 for DES Year 3 data. This is 20 per cent better than an analysis using a simulated DES Y3 shear two-point statistics, owing to the non-Gaussian information captured by the inclusion of higher order statistics. This paper validates our methodology for constraining cosmology with DES Year 3 data, which will be presented in a subsequent paper.

    22. Pereira, M. E. S., Palmese, A., Varga, T. N., et al., 2020, MNRAS, 498, 5450, masses: weak-lensing calibration of the Dark Energy Survey Year 1 redMaPPer clusters using stellar masses

      We present the weak-lensing mass calibration of the stellar-mass-based mass proxy for redMaPPer galaxy clusters in the Dark Energy Survey Year 1. For the first time, we are able to perform a calibration of at high redshifts, z > 0.33. In a blinded analysis, we use 6000 clusters split into 12 subsets spanning the ranges 0.1 z < 0.65 and up to ${\sim} 5.5 \times 10^{13} \, \mathrm{M}_{\odot }$ , and infer the average masses of these subsets through modelling of their stacked weak-lensing signal. In our model, we account for the following sources of systematic uncertainty: shear measurement and photometric redshift errors, miscentring, cluster-member contamination of the source sample, deviations from the Navarro-Frenk-White halo profile, halo triaxiality, and projection effects. We use the inferred masses to estimate the joint mass–z scaling relation given by $\langle M_{200c} | \mu _{\star },z \rangle = M_0 (\mu _{\star }/5.16\times 10^{12} \, \mathrm{M_{\odot }})^{F_{\mu _{\star }}} ((1+z)/1.35)^{G_z}$ . We find $M_0= (1.14 \pm 0.07) \times 10^{14} \, \mathrm{M_{\odot }}$ with $F_{\mu _{\star }}= 0.76 \pm 0.06$ and Gz = -1.14 0.37. We discuss the use of as a complementary mass proxy to the well-studied richness for: (i) exploring the regimes of low z, < 20 and high , z 1; and (ii) testing systematics such as projection effects for applications in cluster cosmology.

    23. Herner, K., Annis, J., Brout, D., et al., 2020, A&C, 33, 100425, Optical follow-up of gravitational wave triggers with DECam during the first two LIGO/VIRGO observing runs

      Gravitational wave (GW) events detectable by LIGO and Virgo have several possible progenitors, including black hole mergers, neutron star mergers, black hole-neutron star mergers, supernovae, and cosmic string cusps. A subset of GW events is expected to produce electromagnetic (EM) emission that, once detected, will provide complementary information about their astrophysical context. To that end, the LIGO-Virgo Collaboration (LVC) sends GW candidate alerts to the astronomical community so that searches for their EM counterparts can be pursued. The DESGW group, consisting of members of the Dark Energy Survey (DES), the LVC, and other members of the astronomical community, uses the Dark Energy Camera (DECam) to perform a search and discovery program for optical signatures of LVC GW events. DESGW aims to use a sample of GW events as standard sirens for cosmology. Due to the short decay timescale of the expected EM counterparts and the need to quickly eliminate survey areas with no counterpart candidates, it is critical to complete the initial analysis of each night’s images as quickly as possible. We discuss our search area determination, imaging pipeline, and candidate selection processes. We review results from the DESGW program during the first two LIGO-Virgo observing campaigns and introduce other science applications that our pipeline enables.

    24. Jones, Terry Jay, Kim, Jin-Ah, Dowell, C. Darren, et al., 2020, AJ, 160, 167, HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891

      Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera Plus polarimetry at 154 m is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 $\mathrm{MJy}\,{\mathrm{sr}}^{-1}$ are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891, the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.

    25. Ji, Alexander P., Li, Ting S., Hansen, Terese T., et al., 2020, AJ, 160, 181, The Southern Stellar Stream Spectroscopic Survey (S5): Chemical Abundances of Seven Stellar Streams

      We present high-resolution Magellan/MIKE spectroscopy of 42 red giant stars in seven stellar streams confirmed by the Southern Stellar Stream Spectroscopic Survey (S5): ATLAS, Aliqa Uma, Chenab, Elqui, Indus, Jhelum, and Phoenix. Abundances of 30 elements have been derived from over 10,000 individual line measurements or upper limits using photometric stellar parameters and a standard LTE analysis. This is currently the most extensive set of element abundances for stars in stellar streams. Three streams (ATLAS, Aliqa Uma, and Phoenix) are disrupted metal-poor globular clusters, although only weak evidence is seen for the light-element anticorrelations commonly observed in globular clusters. Four streams (Chenab, Elqui, Indus, and Jhelum) are disrupted dwarf galaxies, and their stars display abundance signatures that suggest progenitors with stellar masses ranging from 106 to 107 M. Extensive description is provided for the analysis methods, including the derivation of a new method for including the effect of stellar parameter correlations on each star’s abundance and uncertainty. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

    26. Rector, T. A., Prato, L., Strom, A. L., 2020, AJ, 160, 189, Herbig-Haro Outflows in Circinus W

      We report the discovery of new Herbig-Haro (HH) outflows in the Western Circinus molecular cloud. They were found using a color-composite imaging method that reveals faint H emission in complex environments. Follow-up observations in [S II] confirmed their classification as HH objects. Nearly half of the newly discovered objects are part of the HH 76 outflow and are associated with a likely young stellar object (YSO) candidate. We also identify the source of a second outflow. Three newly discovered objects are part of a third outflow whose origin is unknown. Four more HH objects are also discovered, each of which has a location and morphology that does not suggest an origin. In total there must be at least five YSOs in the field currently producing outflows. The discovery of new HH objects and associated driving sources in this cloud complex provides more evidence for active star formation and a relatively young age in this seldom-studied region.

    27. Smith, Erin C., Logsdon, Sarah E., McLean, Ian S., et al., 2020, ApJ, 902, 118, A Survey of 3-5.4 m Emission from Planetary Nebulae Using SOFIA/FLITECAM

      Here we present the results of an airborne 3-5.4 m spectroscopic study of three young, carbon-rich planetary nebulae (PNs) IC 5117, PNG 093.9-00.1, and BD +30 3639. These observations were made using the grism spectroscopy mode of the First Light Infrared TEst CAMera (FLITECAM) instrument during airborne science operations on board NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). The goal of this study is to characterize the 3.3 and 5.25 m polycyclic aromatic hydrocarbon (PAH) dust emission in PNs and study the evolution of PAH features within evolved stars before their incorporation into new stellar systems in star-forming regions. Targets were selected from Infrared Astronomical Satellite, Kuiper Airborne Observatory and Infrared Space Observatory source lists, and were previously observed with FLITECAM on the 3 m Shane telescope at Lick Observatory to allow direct comparison between the ground and airborne observations. We measure PAH emission equivalent width and central wavelength, classify the shape of the PAH emission, and determine the PAH/aliphatic ratio for each target. The 3.3 m PAH emission feature is observed in all three objects. PNG 093.9-00.1 exhibits NGC 7027-like aliphatic emission in the 3.4-3.6 m region while IC 5117 and BD +30 3639 exhibit less aliphatic structure. All three PNs additionally exhibit PAH emission at 5.25 m.

    28. Cartwright, Richard J., Nordheim, Tom A., Cruikshank, Dale P., et al., 2020, ApJL, 902, L38, Evidence for Sulfur-bearing Species on Callisto’s Leading Hemisphere: Sourced from Jupiter’s Irregular Satellites or Io?

      We investigated whether sulfur-bearing species are present on the icy Galilean moon Callisto by analyzing eight near-infrared reflectance spectra collected over a wide range of sub-observer longitudes. We measured the band areas and depths of a 4 m feature in these spectra, which has been attributed to sulfur dioxide (SO2), as well as carbonates, in previously collected data sets of this moon. All eight spectra we collected display the 4 m band. The four spectra collected over Callisto’s leading hemisphere display significantly stronger 4 m bands compared to the four trailing hemisphere spectra (>3 difference). We compared the central wavelength position and shape of Callisto’s 4 m band to laboratory spectra of various sulfur-bearing species and carbonates. Our comparison demonstrates that Callisto’s 4 m band has a spectral signature similar to thermally altered sulfur, as well as a 4.025 m feature attributed to disulfanide (HS2). Our analysis therefore supports the presence of S-bearing species on Callisto but is not consistent with the presence of SO2. The significantly stronger 4 m band detected on Callisto’s leading hemisphere could result from collisions with H2S-rich dust grains that originate on Jupiter’s retrograde irregular satellites or implantation of magnetospheric S ions that originate from volcanic activity on Io. Alternatively, S-bearing species could be native to Callisto and are exposed by dust collisions and larger impacts that drive regolith overturn, primarily on its leading side.

    29. Cartwright, R. J., Nordheim, T., Cruikshank, D., et al., 2020, DPS, 52, 106.05, What is the origin and composition of Callisto’s 4-micron band?

      Spectra collected by the Near Infrared Mapping Spectrometer (NIMS) onboard the Galileo spacecraft determined that a variety of near-infrared absorption bands overprint the dominantly ‘dirty’ H2O ice spectral signature of Callisto’s surface. One such absorption band centered near 4 m has been attributed to the presence of SO2 on Callisto, as well as on Europa and Ganymede. This 4-m feature is thought to originate from S-rich species that are erupted from volcanoes on Io, ionized, and subsequently transported in Jupiter’s co-rotating plasma to the three icy Galilean moons. This process can explain the presence of the 4-m feature on the trailing hemispheres of Europa and Ganymede. On Callisto, however, the 4-m band is stronger on its leading hemisphere, hinting at a different origin for this band and/or different contributing species, possibly including carbonates. Complicating matters, the often low signal-to-noise and low resolving power (R ~40200) of spectra collected by NIMS has limited our ability to interpret the origin and composition of the 4-m feature.


      To further investigate Callisto’s 4-m band, we collected new near-infrared spectra with the SpeX spectrograph on NASA’s Infrared Telescope Facility (~1.95.3 m, R ~2500), representing a significant improvement over the quality of the available NIMS spectra. These SpeX spectra show that the 4-m feature is significantly stronger on Callisto’s leading hemisphere, supporting prior analysis of the distribution of the 4-m feature detected by NIMS. The central wavelength position of the feature we detected is shifted to 4.02 m, whereas the SO2 combination band (1 + 3) detected on Io is centered near 4.07 m, casting doubt on SO2 as the primary constituent contributing to Callisto’s 4-m band. Our results are more consistent with other S-bearing species like H2S2 or HS2, which could be formed by charged particle radiolysis of hydrogen sulfide (H2S). Additionally, the spectral signature of carbonates like Na2CO3 can also provide a good match to the 4-m feature. The clear hemispherical asymmetry in the distribution of the 4-m band is consistent with in-falling dust grains from Jupiter’s retrograde irregular satellites, which should contribute material primarily to Callisto’s leading side. Alternatively, the species contributing to Callisto’s 4-m band could be native to this moon and are exposed by dust particle collisions that spur regolith overturn, as well as larger impact events that sample greater depths into its subsurface.

    30. Schleicher, D. G., Knight, M. M., Skiff, B. A., 2020, DPS, 52, 111.05, A Smorgasbord of Recent Comet Narrowband Imaging and Photometry: Results from NEOWISE (C/2020 F3), ATLAS (C/2019 Y4), PanSTARRS (C/2017 T2), and 88P/Howell

      We will report on preliminary results from recent and upcoming narrowband filter imaging and photometry data of four comets obtained from Lowell Observatory in 2020. Comet NEOWISE (C/2020 F3) was the brightest object in more than a decade but only became accessible for us in late July. By that time, water production had decreased to 1.61029 molecules/s, while the dust-to-gas ratio was significantly lower than average as compared to our database. CN imaging exhibits a counter-clockwise spiral rotation with successive outward moving arcs implying a possible period of about 7-8 hr; however, variations in the spacing and brightness of arcs in early August suggests multiple jets might be present, with the actual period perhaps twice the apparent value. The rapidly brightening Comet ATLAS (C/2019 Y4) suffered a major fragmentation event in April, about a month prior to perihelion. Though characterized in the press as having disappeared, we obtained additional photometry and imaging of the remnants in mid-May; the images showed that fragmentation was continuing to take place with the location and brightness of features changing from night-to-night. Furthermore, a CN coma was observed nightly, suggesting that at least one fragment remained active.


      We began our observations of Comet PanSTARRS (C/2017 T2) in early October 2019 at a distance of 3.15 AU. By perihelion (1.61 AU), water production reached 61028 molecules/s, following an r-dependence log-log slope of -4.3, and a steeper slope thus far outbound. Although early imaging showed little in morphological features, CN imaging in June revealed a pair of apparently side-on jets; however, these were no longer evident just a month later. Comet 88P/Howell, the only Jupiter Family object in this group, continues to have relatively unfavorable apparitions though the current one is the best since its discovery. Between mid-May and mid-August, and still approaching perihelion, water production is following an extremely steep r-dependence of -9.1, possibly suggesting that a dominant, isolated source region is rapidly “moving” from winter to summer.

      These and additional results from our observing campaigns will be presented. This work is supported by NASA’s Solar System Observations Program grant 80NSSC18K0856.

    31. Fraser, W. C., Schwamb, M., Bannister, M., et al., 2020, DPS, 52, 203.01, Do less-red KBOs share origins with the C-type asteroids?

      Spectral surveys of the outer Solar System are starting to reveal the signatures of the early dispersal of the protoplanetesimal disk in the compositional-dynamical structure of the current planetesimal populations. The distribution of the known surface types of Kuiper Belt Objects (KBOs) are now being used to infer the compositional structure of the protoplanetesimal disk itself. We present a new idea regarding the compositional properties of KBOs that is predicated on the correlated optical-NIR colours of the two dynamically excited compositional classes. Specifically, we hypothesize that nearly all KBOs belonging to the less-red class share origins with some of the carbonaceous asteroids. We make use of the ugrizJ colours sample acquired by the Colours of the Outer Solar System Origins Survey to probe what compositional components are compatible with that idea. The broad spectral behaviour of the less-red class can be very well accounted for with a C-type spectrum mixed with many laboratory organic materials, such as tholins and other disordered organic ices, and requires the presence of water-ice. Variation of the non-carbonaceous additions can account for the correlated optical-NIR colours of KBOs. Increasing concentrations of the non-carbonaceous materials not only increases the optical spectral slopes, but increasingly masks the presence of the absorption features common to carbonaceous asteroids, which are seen on only the most neutral coloured KBOs, and produce nearly linear spectra like those observed. Within this model, Phoebe occupies a special category, possessing a high concentration of water-ice, and is completely devoid of the reddening agent. If this idea is true, it follows that the less-red class of KBOs are cosmogonically related to certain classes of carbonaceous asteroids, and likely shared a similar origin within the protoplanetesimal disk. As the Kuiper Belt is dominated by mass from the less-red class, our model implies that the majority of KBOs are simply reddened carbonaceous asteroids. Confirmation of this idea will come from the identification of the absorption features common to the C-types, which must also be common to most small KBOs, albeit with a more modest presence.

    32. Thirouin, A., Sheppard, S. S., 2020, DPS, 52, 203.03, Lightcurves of 2:1 Neptune resonant trans-Neptunian objects

      The 2:1 mean motion resonance with Neptune is located at about 47.8 AU and contains more than 85 known trans-Neptunian objects (TNOs). During Neptune’s migration outward in the Solar System, TNOs from various locations were pushed and scattered into the 2:1 resonance giving this population of TNOs a large range of formation locations and surface colors. The 2:1 resonance with Neptune likely contains some TNOs of the dynamically Cold Classical population that show a very-red/ultra-red surface. Previously, we studied the rotational properties of the 3:2 resonance and dynamically Cold Classical TNOs and estimated the fraction of contact binaries in these two different dynamical populations (Thirouin and Sheppard, 2018, 2019). As the 3:2 and 2:1 resonances delimit the reservoir of dynamically Cold Classical TNOs in the main Kuiper belt, we obtain the lightcurves of a number of 2:1 TNOs in order to estimate the number of contact binaries and identify rotational differences between the various different highly evolved resonant populations and the more primitive Cold Classicals. For consistency and to limit observational biases, we designed a survey dedicated to the 2:1 resonant TNOs in the same way we did for the 3:2 and Cold Classical populations, using the Lowell Discovery Telescope and the Magellan telescope for lightcurves and color photometry. Here, we report some preliminary results on our observations of the 2:1 resonant TNOs which correspond to 58 percent of the 2:1 TNOs with a visual magnitude V less than 23.5mag. Sparse and complete lightcurves obtained are used to constrain the shape and rotational frequency distributions. We also compare the properties of the Cold Classicals to the various Neptune resonant populations. Using our results and the literature, we estimate that the 2:1 resonance could likely have fewer contact binaries than the 3:2 resonant population and are more consistent with our estimate for the dynamically Cold Classicals contact binary population. This low estimate for the 2:1 resonance contact binary percentage is not expected based on some binary survival modeling (Nesvorny and Vorouhlicky, 2019).


      This work is supported by the National Science Foundation (NSF), grant number 1734484.

    33. Strauss, R., Leiva, R., Keller, J., et al., 2020, DPS, 52, 203.05, The sizes and albedos of Centaurs 2014 YY49, (342842) 2008 YB3, and 2013 NL24 from stellar occultation

      Trans-Neptunian objects (TNOs) are among our primitive neighbors. Their characterization can provide invaluable clues to understanding the formation and evolution of the early Solar System. Equally interesting to study are Centaurs, a transient population of dynamically unstable objects with orbits between those of the Jupiter and Neptune, understood to consist primarily of objects transitioning between TNOs and Jupiter family comets. Stellar occultation remains one of the most powerful techniques by which to obtain ground-truth measurements of the size and shape of TNOs and Centaurs. In the year 2019, stellar occultation measurements for three Centaurs were obtained by the Research and Education Collaborative Occultation Network (RECON), a citizen science telescope network designed to observe high-uncertainty occultations by these distant bodies. The objects measured, 2014 YY49, (342842) 2008 YB3, and 2013 NL24, are among the smallest objects in the outer Solar System measured by occultation.


      We present the methods and results of these three occultation efforts. We discuss the predictions, observations, and profile modeling techniques for the three centaurs. We will present the results of the modeling and the derived sizes and geometric albedos for each object, and for the brightest of these objects, 2008 YB3, we compare the occultation result with existing radiometric size estimates.

      Funding for RECON was provided by grants from NSF AST-1413287, AST-1413072, AST-1848621, and AST-1212159

    34. Moullet, A., Lellouch, E., Gurwell, M., et al., 2020, DPS, 52, 203.06, Thermal mapping of large KBO systems: putting the equal albedo assumption to the test

      High-resolution optical imaging of Kuiper-Belt objects has revealed that a surprisingly high fraction of objects are in binary or multiple systems, up to 70% in some dynamical populations. Several system formation mechanisms may be at play, such as capture, disruption, co-formation and collision, which are in turn indicative of the dynamical history of the region at large. Detailed studies of a systems’ orbital properties as well as measurements of member sizes’ ratios can help to distinguish across such formation mechanisms. Unfortunately with optical imaging alone, size ratios can only be determined under the unverified assumption of equal albedo across the system.


      The specific contribution of thermal mapping for a KBO system lies in the possibility to determine geometric albedos for each detected system’s member, by using the radiometric method, hence allowing one to break the albedo/size degeneracy. This technique can possibly reveal a different picture of a system’s physical properties than what can be determined from optical imaging alone.

      The Atacama Large Millimeter Array is the only instrument operating in the thermal regime offering sufficient spatial resolution and point source sensitivity to be able to detect and separate Kuiper-Belt multiple systems other than Pluto/Charon. We present the first spatially resolved thermal ALMA observations of three well known Kuiper Belt systems: Varda/Ilmare, Salacia/Actea and Lempo/Hiisi, which belong to different dynamical populations. Our results indicate that in two of these systems, the assumption of equal albedo across the system does not hold, resulting in a significant reassessment of size ratios.

    35. McKinnon, W. B., Stern, S. A., Spencer, J. R., et al., 2020, DPS, 52, 206.02, Evolution of Binary Planetesimals due to Gas Drag in the Protosolar Nebula

      The apparent gentle merger of the two lobes of the cold classical Kuiper belt object (KBO) 486958 Arrokoth, as revealed by New Horizons (Stern et al., Science 364, eaaw9771, 2019; Spencer et al., Science 367, aay3999, 2020; Grundy et al., Science 367, aay3705, 2020), prompts consideration of the physical mechanism(s) that might have driven mergers of originally co-orbiting binaries (which are known to be common in the Kuiper belt today). In McKinnon et al. (Science 367, aay6620, 2020 [M20]) several mechanisms were examined: tides, collisions, Kozai-Lidov cycling, asymmetric radiation effects (YORP and BYORP), and gas drag. Here we examine and update the case for gas drag, both as it might have affected Arrokoth and more generally. The evolution of binaries in a gaseous protoplanetary disk was first considered in detail by Perets & Murray-Clay (Astrophys. J. 733, 56, 2011 [PMC]), who focused on the possibility of differential wind shear causing binaries to become unbound, and secondarily on the possibility that gas drag could cause binary inspiral and merger. The former is not an issue for the relatively massive lobes of Arrokoth, and we derive a new result for the latter. Though the protosolar nebular gas at Arrokoth’s distance is quite dilute and binary motions slow, it is the headwind due to pressure support of the nebula that determines the drag regime, irrespective of the binary’s orientation, and couples to the slower velocity of the co-orbiting binary. As the binary pinwheels in this nebular wind, each of its lobes will alternately feel accelerating and decelerating torques; time averaged the difference does not average to zero. M20 derived a stopping time (e-folding time of the binary’s angular momentum) for Arrokoth as low as 1-2 Myr, based on the classic Whipple-Weidenschilling drag formulae, recognizing that inspiral of an extended binary orbit could take longer than the nominal nebular lifetime of ~5 Myr. Using the standard drag law in PMC, and with a corrected estimate for the Reynolds number, lengthens these time scales further (and all such estimates are subject to the uncertainties in nebular and binary density). Nevertheless, we expect the importance of gas drag to increase for KBO binaries that are smaller, lower density, less inclined, and/or form closer to the Sun.

    36. Spencer, D., Ragozzine, D., Pincock, S., et al., 2020, DPS, 52, 206.03, Non-Keplerian Effects in Kuiper Belt Multiples

      As the number of solar system small body multiple systems (including binaries) grows in number and in observational baseline, advanced dynamical modelling will reveal physical, orbital, and spin properties that are currently poorly understood. For example, among Kuiper Belt Objects (KBOs) beyond Neptune, only a few have well determined obliquities, but observations of orbital precession due to non-spherical shapes can identify spin pole directions and obliquities. The ~50 KBO Binaries with known orbital solutions have only been studied assuming Keplerian motion, but evidence suggests that several of these are beginning to show observationally significant non-Keplerian effects. To study these effects, we have developed and validated an n-quadrupole integrator SPINNY (SPIN + N-bodY) which can include all the dominant non-Keplerian effects relevant within observational precision. SPINNY has been combined with advanced Bayesian model fitting for KBO astrometry in a new modeling tool called MultiMoon. We present MultiMoon along with some potential use cases to demonstrate its value. We also present results on an analysis of the 47171 Lempo (1996 TC36) KBO trinary system using MultiMoon.

    37. Presler-Marshall, B., Schleicher, D. G., Knight, M. M., et al., 2020, DPS, 52, 212.06, Diatomic Sulfur in Jupiter Family Comets

      Diatomic Sulfur in Jupiter Family Comets


      The first astronomical detection of diatomic sulfur (S2) was in comet IRAS-Araki-Alcock in 1983 using the IUE satellite (A’Hearn et al. 1983) and it has since been remotely detected in 3 other comets. All four remote S2 detections have come from objects originating from the Oort cloud, and the only detection in an object originating from the Kuiper Belt was taken in situ by the Rosetta mass spectrometer at 67P/Churyumov-Gerasimenko (Calmonte et al. 2016). As many compositional differences have been observed between Kuiper Belt and Oort Cloud objects, there is no compelling reason to assume that S2 ought to be present in similar abundances in both populations. Observations of three Jupiter Family Comets (252P/LINEAR, 45P/HondaMrkosPajdusakova and 46P/Wirtanen) were conducted using the DeVeny Spectrograph on the Lowell Discovery Telescope (formerly the Discovery Channel Telescope) between 2016 and 2018, ranging from 3000 to 4000 A. Geocentric distances were all under 0.1 AU, yielding a spatial resolution on the order of 60 km/arcsec. S2 is believed to sublimate directly from the surface of the nucleus, and the short lifetime (approximately 450 seconds) prior to photodissociation means that high spatial resolution, and thus a very low geocentric distance, is needed to search for the molecule. The observing geometry is therefore relatively rare, and another similar opportunity will not present itself for nearly another decade. Preliminary results indicate the presence of several unexplained emission features in the spectra of both 46P and 252P. Work is ongoing to ascertain whether those features match those expected by the fluorescence model (Reyle and Boice, 2003) or if another yet-unidentified molecule has been detected.

      This work is supported by NASA’s Solar System Observations Program grant 80NSSC18K0856 and the Marcus Cometary Research Fund.

    38. Parker, A., Benecchi, S., Grundy, W., et al., 2020, DPS, 52, 307.01, Cold Classical Binary KBOs in the Solar System Origins Legacy Survey: Preliminary Results from Complete Survey

      The Solar System Origins Legacy Survey (SSOLS) is a Hubble Space Telescope Treasury Program targeting a very large, well-characterized sample of cold classical Kuiper Belt Objects in an effort to determine the intrinsic properties of the binary systems endemic to that population. Observations for this program were completed in July of 2020, revealing 25 clearly-resolved binary systems and 172 objects currently identified as solitary. Here we will provide an overview of SSOLS, including survey design and motivation, as well as our initial results regarding the intrinsic binary fraction of the cold classical Kuiper Belt. We confirm a very strong trend in apparent binary fraction with system brightness, but also confirm that this can largely be explained as a novel discovery bias. We show that the binary population’s luminosity function is shifted to brighter values with respect to that of solitary objects. The size of this shift can be used to constrain the origin of these binary systems, and the SSOLS preliminary results suggest that this luminosity function shift is approximately 1 magnitude larger than would be expected through origin scenarios involving common formation through collapse of swarms of cm-scale particles. We will discuss this potential tension with leading theories of the origin of the cold classical KBOs, possible alternative scenarios, and our ongoing efforts to leverage the SSOLS Treasury Sample to illuminate the origin and history of the outer solar system.

    39. Benecchi, S., Parker, A., Porter, S., et al., 2020, DPS, 52, 307.02, Correlated Colors of Cold Classical Binary KBOs from the HST Solar System Origins Legacy Survey

      In HST Cycle 26 we successfully observed a treasury sample of 197 cold classical (CC) Kuiper Belt Objects (KBOs), The Solar System Origins Legacy Survey (SSOLS), at optical wavelengths to measure an F606W-F814W color and to look for binaries using the Wide Field Camera 3/UVIS (WFC3/UVIS). Our KBO sample draws on the highly successful, and bias-correctable, ground-based discovery surveys the Canada France Ecliptic Plane Survey (CFEPS), and the Outer Solar System Origins Survey (OSSOS) with the goal of better understanding the binarity and luminosity function of the intrinsic CC KBO population. Here we give an overview of the survey and present the resolved colors for 25 clearly resolved binary cold classical KBOs, and the colors of 172 objects identified as solitary at the limit of HST’s spatial resolution. This large, high-quality sample permits robust testing of previously identified trends in colors. We find evidence supporting a trend of color with system brightness, with fainter objects in the sample being redder. Further, we find that while primaries and secondaries in binary systems have colors similar to one another, secondaries tend to be slightly redder than their primaries, and this shift is consistent with the overall trend of color with brightness in the entire CC KBO population. We will explore these trends and their implications for the origins and evolution for the CC KBO population and the outer solar system as a whole.

    40. Bair, A. N., Schleicher, D. G., Knight, M. M., et al., 2020, DPS, 52, 313.06, The Unusual Chemical Composition of Interstellar Comet 2I/Borisov

      Comet 2I/Borisov, discovered 2019 August 30, is the second interstellar object detected in our solar system, and the first inter-stellar object exhibiting cometary activity. Initial observations of the comet’s composition proved most interesting, with clear detections of CN but comparatively extremely low abundances of C2 and low upper limits for C3. These early observations placed 2I/Borisov firmly in the carbon-chain depleted class of comets as defined by A’Hearn et al. (1995). Our updated database, which builds on the dataset from A’Hearn et al. and now includes 40 years of observations, indicates these early observations place Borisov more specifically into the strongly carbon-chain depleted (i.e. strongly depleted in both C2 and C3) compositional class. When we froze our database in 2016 (Schleicher and Bair 2016), eight of our 114 well-determined comets were grouped into this compositional class, including the prototype depleted comet 21P/Giacobini-Zinner, 73P/Schwassmann-Wachmann 3 and 43P/Wolf-Harrington, among others. Since 2016, we have determined several additional comets are carbon-chain depleted, with 48P/Johnson, 123P/West-Hartley, and 260P/McNaught falling in the strongly carbon-chain depleted class and 114P/Wiseman-Skiff borderline between the strongly and moderately carbon-chain depleted classes. Unlike the other carbon-chain depleted comets we have observed, which show no variation in composition with heliocentric distance, 2I/Borisov became far less depleted as it moved closer to the Sun, and by December exhibited only moderate carbon-chain depletion. A further indication of its unusual composition, 2I/Borisov has a higher NH/OH ratio than any of the 114 objects in our restricted database. We will compare our compositional observations of 2I/Borisov with those obtained by other researchers, and place it into the context of our database, showing that while 2I/Borisov contains the same chemical components as comets originating in our solar system, its composition and behavior with changing temperature appears to be unique. This work is supported by NASA’s Solar System Observations Program grant 80NSSC18K0856.

    41. Noll, K., Brown, M., Weaver, H., et al., 2020, DPS, 52, 401.01, Detection of a Satellite of the Trojan Asteroid (3548) Eurybates A Lucy Mission Target

      We have identified a satellite of the Trojan asteroid (3548) Eurybates in images obtained with the Hubble Space Telescope. The satellite has been detected on four separate epochs, 12 and 14 September 2018, 03 January 2020 and 19 July 2020. The satellite was not detected in observations on 11 and 21 December 2019 and 03 August 2020 when it was presumed to be within 0.4 arcsec of Eurybates where it is too faint to be detected against the scattered light from the primary. The satellite has a brightness consistent with an effective diameter of d2 = 1.20.4 km for a body with the same albedo as Eurybates. The projected separation from Eurybates ranged from s ~ 17002300 km and varied in position. The detections and non-detections are consistent with a range of possible orbits. Eurybates is one of the targets of the Lucy Discovery mission and the early detection of this satellite provides an opportunity for a significant expansion of the scientific return from this encounter.

    42. Pinilla-Alonso, N., Popescu, M., Licandro, J., et al., 2020, DPS, 52, 401.03, The irregular limb of Manoetius South Pole and Improved Orbital Solution (extended analysis)

      In 2033, after a 12-year trip across the Solar System, NASA’s Lucy mission will arrive at the PatroclusMenoetius binary system, in Jupiter’s L5 cloud. On its way, Lucy will visit one asteroid and seven Jupiter Trojans, all of them primitive asteroids. Lucy’s foreseen discoveries about the surface geology, color, and composition of these Trojans, about their interior and bulk properties, and about the presence of satellites or rings, which have the potential of revolutionizing the knowledge of the Solar System and opening new insights into the origins of our Earth. In preparation for that moment, ground-based observations are fundamental to obtain important physical information on these targets, which is needed to plan the operations and the best observational strategy. Furthermore, they provide ground truth of the state-of-the-art analysis techniques used for the study of the whole population, which is essential to better understand the big picture.


      In this work, we present surprising results from a set of 14 lightcurves of 11 mutual events of the PatroclusMenoetius system obtained during the last season, in 20172018. Results based on the first set of seven light curves (corresponding to five different events) has been recently published (Pinilla-Alonso et al. 2020, PSJ, in press) reporting the imprint for a possible crater in the south pole of Menoetius, as deep as a fourth of its radius, and an improved orbit solution for the system. This new analysis, including seven inferior events and seven superior events, provides new details of the shape of both components and a new orbit solution, which is key for the planning of the flyby of the Patroclus and Menoetius system. Figure 1: Artistic representation of the Patroclus-Menoetius system showing a void in the southern limb of Menoetius. The profile of this void was extracted from the analysis of the light curve of an occultation obtained at the Gran Telescopio Canarias (GTC) on December 08, 2017.

    43. Engle, A., Hanley, J., Thompson, G., et al., 2020, DPS, 52, 408.02, Phase Diagram for the Methane-Ethane System at Conditions Relevant to Titan

      On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in the polar lakes and seas. In this study, we have combined molecular dynamics simulations with laboratory work to both create a binary phase diagram at cryogenic temperatures and gain a better understanding of how the system interacts at a molecular level.


      The molecular dynamics (MD) simulations reveal that the methane-ethane system deviates from ideality as the mixing ratio approaches the eutectic point, indicating that the methane-ethane interactions are stronger than the self-interactions of either molecule at the eutectic. Identifying the deviation from ideality was accomplished through comparing the MD simulations to experimental data, focusing on excess volume, density, and temperature vs. mixing ratio of the liquidus line and eutectic point.

      From the laboratory work, we have found that Raman spectroscopy is a reliable means of detecting the liquidus, solidus, and solvus lines, allowing for full characterization of the phase diagram. The liquidus is defined as the first point in which ice forms on cooling or when the last ice disappears on warming. The solidus marks the last point in which liquid occurs on cooling the sample. Lastly, the solvus differentiates between a fully homogeneous system and a structure where one species dominates the crystal structure, with the other as only a minority contaminant.

      The temperatures and mixing ratios at which the solidus and solvus lines occur are mostly below 90 K. This means they likely have a larger impact on processes taking place at deeper parts of the lakes and seas as well as for portions of the atmosphere, as opposed to on the surface. In general, this diagram is not only useful in terms of understanding the methane-ethane system itself, but also as a foundation for creating more complex systems that better exemplify the compositions of Titan’s various lakes and seas.

    44. Hanley, J., Wing, B., Engle, A., et al., 2020, DPS, 52, 408.06, The Effects of Propane on the Liquids of Titan

      The lakes and seas of Titan are composed primarily of methane (CH4) and ethane (C2H6), with the concentration of dissolved nitrogen (N2) depending on the ratio of methane to ethane, the temperature, and pressure. Propane (C3H8) is formed photochemically in the upper atmosphere of Titan, and condenses at the tropopause. The freezing point of pure propane is 85.5 K, meaning that it would be liquid on the surface of Titan, like methane and ethane. We have begun an exploration of the effect of propane on methane, ethane, nitrogen, and their mixtures in the NAU Astrophysical Materials Laboratory. Cryogenic samples are studied via Raman spectroscopy and photography. As nitrogen was added to a binary hydrocarbon mixture of either propane-methane or propane-ethane, it caused the formation of a second liquid. The droplets form at the meniscus and this nitrogen-rich denser liquid falls once enough material has collected to break surface tension. Ice can form under certain conditions. Differences in behavior of the propane-ethane system and the propane-methane system can be attributed to the difference in nitrogen solubility. For further analysis, the phase diagrams at conditions where the second liquids were observed were calculated using CRYOCHEM. We also modeled a homogeneous N2:CH4:C2H6:C3H8 liquid system to understand the breakdown of ideality. In these simulations, real effects are quantified by calculating the binding free energy between each pair of molecules. We found that increasing alkane length results in a decrease in binding strength between N2 and each of the alkanes, which suggests a molecular explanation for the phase behavior observed in the experiments of these systems at lower temperatures. In summary, pure propane should not freeze on the surface of Titan. However, we see propane ice form under certain conditions that might be possible on Titan. We also see that the liquid-liquid system can form with the addition of propane. We continue to explore the effects of propane on methane, ethane and nitrogen, both individually and additively, and constrain the conditions under which interesting phenomena occur.

    45. Gustafsson, A., Moskovitz, N., 2020, DPS, 52, 409.01, Revealing Regolith Properties of Near-Earth Asteroids

      The most common method for estimating surface grain size of asteroids is by determining thermal inertia using thermophysical models. Calculating accurate values of thermal inertia is a difficult process requiring a shape model, thermal-infrared observations obtained over broad viewing geometry, and detailed thermophysical modeling. Nevertheless, thermal inertia is a sensitive probe of surface regolith properties (Christensen et al. 2003), and therefore is of great importance in the design of instrumentation and observing strategies for asteroid missions where knowledge of surface characteristics is critical. Yet, thermal inertia alone cannot uniquely describe the full complexity of asteroid surface properties. This was true for OSIRIS-REx target (101955) Bennu whose thermally derived grain size estimates did not accurately represent the rough, bouldered surface observed by the spacecraft (Dellagiustina et al. 2019).


      Radiative transfer models are some of the most widely used tools for compositional analyses of planetary bodies and have the opportunity to provide a comprehensive understanding of asteroid surface properties when used in conjunction with thermal modeling. In application to silicate-rich asteroids, radiative transfer models have almost exclusively been used to derive olivine to pyroxene abundance ratios. However, new formulas have been developed for deriving mineralogy from visible and near-infrared spectra that display prominent olivine and pyroxene (1 and 2 micron) absorption bands (e.g. Burbine et al. 2007, Reddy et al. 2011). Furthermore, the effects of non-compositional parameters (temperature, phase angle, grain size) have been well characterized, allowing for a more detailed analysis of these parameters with radiative transfer models.

      We present a new implementation of the Hapke radiative transfer model to constrain grain size for unresolved asteroid surfaces. This technique can be applied to a large number of targets including near-Earth and Main Belt asteroids. This model is optimized for investigating S/Q type asteroids whose spectra are dominated by olivine and pyroxene absorption bands. Results from this study compliment thermal grain size estimates, when they exist, and provide standalone constraints on surface properties for a much larger number of near-Earth and Main Belt asteroids.

      We will present a validation of the model against ordinary chondrite meteorites and well-studied near-Earth asteroids (e.g. Eros, Itokawa) with thermal inertia and spacecraft observations.

      This work is supported by the NASA NEOO program, grant number NNX17AH06G.

    46. Kueny, J. K., Chandler, C. O., Devogele, M., et al., 2020, DPS, 52, 415.02, Shape Model, Pole Solution Implications, and Refined Rotational Period of (155140) 2005 UD

      (155140) 2005 UD is a Near-Earth Asteroid in a companion orbit with (3200) Phaethon, an active asteroid in a highly-elliptical orbit thought to be responsible for the Geminid meteor shower. Evidence points to a genetic relationship between these two objects (Devogele et al. 2020), but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Notably, 2005 UD is the extended mission target for the Japanese Aerospace Exploration Agency DESTINY+ mission scheduled to launch in 2024. Presented herein are new observations of 2005 UD using the Lowell Discovery Telescope, Nordic Optical Telescope, and TRAPPIST-North motivated by access to a previously unseen viewing geometry in October-November 2019. Lightcurve inversion using our new data, archival lightcurve data from an advantageous apparition in late 2018, and data from an epoch in late 2005 were used to derive a shape model of 2005 UD. Results pertaining to 2005 UD’s mass loss from additional analyses involving these new data will also be discussed. We also determined a retrograde spin state, largely consistent with a previous thermophysical analysis, and a refined sidereal rotational period of Psid = 5.2338 0.0040 hours. Although a precise shape model is at present infeasible due to remaining gaps in lightcurve data at critical viewing aspects, we were able to leverage our results to help limit the range of formation scenarios and the link to Phaethon in the context of non-gravitational forces and timescales associated with the physical evolution of the system.

    47. Fedorets, G., Micheli, M., Jedicke, R., et al., 2020, DPS, 52, 415.03, Characterization of 2020 CD3, Earth’s Second Minimoon

      Introduction: Small NEOs may become captured temporarily by planets. Theoretical models (Granvik et al. 2012, Fedorets et al. 2017) predict the existence of a steady-state population of these so-called minimoons also in the Earth-Moon system. Only one minimoon, 2006 RH120 has been discovered until recently (Kwiatkowski et al. 2009). Minimoons have been identified as viable targets for in situ exploration of metre-sized asteroids, as test cases for initial steps of asteroid resource utilisation (Granvik et al. 2013, Jedicke et al. 2018), and as constraints for the size-frequency distribution of metre-sized NEOs (Harris & D’Abramo 2015, Granvik et al. 2016, Tricarico 2017, Brown et al. 2002). So far, the observational evidence of the minimoon population has been lacking.


      Observations: The object 2020 CD3 was discovered on February 15th 2020 at the Mt. Lemmon station of the Catalina Sky Survey, and was reported to be on a geocentric orbit the following night. We report the results of the astrometric and photometric observational campaign of 2020 CD3 performed by Gemini North, LDT, NOT, CFHT, CSS, and other telescopes during spring 2020. By investigating the solar radiation pressure signature on the astrometry of 2020 CD3, and broad-band photometry, we present evidence that it is the second temporary natural satellite in the Earth-Moon system. We describe its discovery circumstances, physical characterisation, rotational period, orbital evolution, and possible origin.

      Discussion: We discuss the challenges of discovering minimoons with contemporary surveys. For the first time, we are able to compare the observational evidence of minimoons with the theoretical models. We assess the capture duration and rotation period of 2020 CD3 in context of simulation and similar objects.

      Prospects: The discovery of 2020 CD3, and the comparison to discovery predictions with other surveys (Bolin et al. 2014), assures that the expectation of discovery of tens of minimoons with LSST is realistic (Fedorets et al. 2020). With the anticipated growth of the population of minimoons, the path for further exploration of minimoons is foreseen.

      1: Bolin et al. (2014), Icarus 241, 280 ; 2: Brown et al. (2002), Nature, 420, 294 ; 3: Fedorets et al. (2017) Icarus, 285, 83 ; 4: Fedorets et al. (2020), Icarus, 338, 113517 ; 5: Granvik et al. (2012), Icarus, 218, 262 ; 6: Granvik et al. (2013) in V. Badescu ed. Asteroids: Prospective Energy and Material Resources, 151 ; 7: Granvik et al. (2016), Nature, 530, 303 ; 8: Harris & D’Abramo (2015), Icarus, 257, 302 ; 9: Jedicke et al. (2018) FrASS, 5, A13 ; 10: Kwiatkowski et al. (2009), A&A, 495, 967 ; 11: Tricarico et al. (2017), Icarus, 284, 416

    48. Devogele, M., Virkki, A., Marshall, S. E., et al., 2020, DPS, 52, 415.04, Heterogeneous surface of 1998 OR2

      We report observations of the H=15.8 mag potentially hazardous asteroid 52768 (1998 OR2) obtained during its 2020 apparition. On April 29th 2020, OR2 experienced its closest approach to Earth (16.4 Lunar distance) until 2079. Observations were obtained in polarimetry with the Torino Polarimeter at the Calern observatory (France; MPC 010) in February and April 2020, in radar with the Arecibo Radio telescope (Puerto Rico; MPC 251) Planetary Radar system from April 13th to 23rd 2020, and in photometry with the TRAPPIST-North and the Las Cumbres observatory (LCOGT) network of telescopes. One epoch was obtained by the NEOWISE mission.


      Using the polarimetric albedo-polarization relation [1] we derived a visual albedo pV = 0.16 0.02 corresponding to an equivalent diameter of D=2.3 km based on its measured H=15.8 absolute magnitude. The NEOWISE observation provides other determinations of D=2.5 0.5 km and pV = 0.13 0.04 consistent with the polarimetric data. Radar delay-Doppler images, with a resolution of 7.5 m per pixel in delay and 0.037 Hz in frequency, provide another independent size measurement and display a maximum extent of 2.16 km 0.05 km. Both radar and optical lightcurve observations confirm the rotation period of p=4.112 h [2], with a low amplitude lightcurve varying from single to double peaked, based on the phase angle and aspect angle variation throughout the apparition.

      The polarimetric observations were conducted over more than one rotation period during each night and we observe a consistent phase-locked variation of the polarization. Asteroid polarization is independent of shape and is at first order dependent on the surface albedo. The observed variation of the polarization thus suggests that the surface of OR2 is heterogeneous. Such variation has only previously been observed for 4 Vesta [3], 1943 Anteros [4], and 3200 Phaethon [5,6].

      The radar images of OR2 suggest the presence of a large concavity or crater near the radar sub-latitude (closest point of the object to the observer). Phasing the radar and polarimetric observations, we find that the maximum of polarization occurs when the radar concavity is directly facing the observer. Such correlation suggests that the polarimetric variations could be related to the presence of the concavity and that it possesses lower albedo or different scattering properties than the rest of the surface.

      1: Cellino et al., 2015 MNRAS, 451, 3473 ; 2: Skiff et al, 2019, MPB, 46 ; 3: Cellino et al., 2016, MNRAS, 456, 248 ; 4: Masiero et al., 2010, Icarus, 207, 795 ; 5: Devogele et al., 2018 MNRAS, 465, 4335 ; 6: Borisov et al., 2018 MNRAS, 480, L131

    49. Keane, J. T., Porter, S. B., Beyer, R. A., et al., 2020, DPS, 52, 508.02, Geophysics of (486958) Arrokoth revealed by New Horizons

      On 1 January 2019, NASA’s New Horizons spacecraft performed the first flyby of a small Kuiper Belt Object: (486958) Arrokoth (formerly 2014 MU69). This ~35-km long, bilobed contact binary is a member of the cold classical Kuiper belt populationa dynamically stable reservoir of small bodies that has remained relatively untouched since the earliest epochs of solar system formation. In short, Arrokoth is a relic planetesimala leftover building block of planet formationand by studying its geology and geophysics we can explore the processes and environment that built our solar system. In this work, we present the current state of knowledge of Arrokoth’s shape and geophysical environment, and quantitative comparisons to other small bodies across the solar system. Arrokoth’s flattened, bilobate nature yields an unintuitive physical environment, making geophysical analyses critical to interpreting the observed geology. Several surface features correlate with the modeled geophysical environment. Most notably, bright surface features appear preferentially in geopotential lowslike Arrokoth’s neck and the bright annulus on the encounter hemisphere of the large lobeperhaps indicative of mass-wasting or other geologic processes. While New Horizons was not able to directly measure Arrokoth’s mass, several lines of evidence suggest that it has a very low bulk density. The statistics of surface slopes, required neck strength, and overall configuration of the contact binary suggest a bulk density between 200-500 kg/m3. While this density is low compared to characterized (i.e., larger) Kuiper Belt objects and many comets (e.g., 67P/Churyumov-Gerasimenko density = 532 kg/m3), it is suspiciously similar to some small ring moons of Saturn (e.g., Atlas, Pan, Methone have densities between 300-400 kg/m3). While not conclusive, this supports the hypothesis that Arrokoth formed in a gentle environment (e.g., Stern et al. 2019, Spencer et al. 2020, McKinnon et al. 2020).

    50. Grandis, S., Klein, M., Mohr, J. J., et al., 2020, MNRAS, 498, 771, Validation of selection function, sample contamination and mass calibration in galaxy cluster samples

      We construct and validate the selection function of the MARD-Y3 galaxy cluster sample. This sample was selected through optical follow-up of the 2nd ROSAT faint source catalogue with Dark Energy Survey year 3 data. The selection function is modelled by combining an empirically constructed X-ray selection function with an incompleteness model for the optical follow-up. We validate the joint selection function by testing the consistency of the constraints on the X-ray flux-mass and richness-mass scaling relation parameters derived from different sources of mass information: (1) cross-calibration using South Pole Telescope Sunyaev-Zel’dovich (SPT-SZ) clusters, (2) calibration using number counts in X-ray, in optical and in both X-ray and optical while marginalizing over cosmological parameters, and (3) other published analyses. We find that the constraints on the scaling relation from the number counts and SPT-SZ cross-calibration agree, indicating that our modelling of the selection function is adequate. Furthermore, we apply a largely cosmology independent method to validate selection functions via the computation of the probability of finding each cluster in the SPT-SZ sample in the MARD-Y3 sample and vice versa. This test reveals no clear evidence for MARD-Y3 contamination, SPT-SZ incompleteness or outlier fraction. Finally, we discuss the prospects of the techniques presented here to limit systematic selection effects in future cluster cosmological studies.

    51. Wiseman, P., Pursiainen, M., Childress, M., et al., 2020, MNRAS, 498, 2575, The host galaxies of 106 rapidly evolving transients discovered by the Dark Energy Survey

      Rapidly evolving transients (RETs), also termed fast blue optical transients, are a recently discovered group of astrophysical events that display rapid luminosity evolution. RETs typically rise to peak in less than 10 d and fade within 30, a time-scale unlikely to be compatible with the decay of Nickel-56 that drives conventional supernovae (SNe). Their peak luminosity spans a range of -15 < Mg < -22.5, with some events observed at redshifts greater than 1. Their evolution on fast time-scales has hindered high-quality follow-up observations, and thus their origin and explosion/emission mechanism remains unexplained. In this paper, we present the largest sample of RETs to date, comprising 106 objects discovered by the Dark Energy Survey, and perform the most comprehensive analysis of RET host galaxies. Using deep-stacked photometry and emission lines from OzDES spectroscopy, we derive stellar masses and star formation rates (SFRs) for 49 host galaxies, and metallicities ([O/H]) for 37. We find that RETs explode exclusively in star-forming galaxies and are thus likely associated with massive stars. Comparing RET hosts to samples of host galaxies of other explosive transients as well as field galaxies, we find that RETs prefer galaxies with high specific SFRs (<log (sSFR)> -9.6), indicating a link to young stellar populations, similar to stripped-envelope SNe. RET hosts appear to show a lack of chemical enrichment, their metallicities akin to long-duration gamma-ray bursts and superluminous SN host galaxies (<12 + log (O/H)> 9.4). There are no clear relationships between mass or SFR of the host galaxies and the peak magnitudes or decline rates of the transients themselves.

    52. Bertrand, Tanguy, Forget, Francois, Schmitt, Bernard, et al., 2020, NatCo, 11, 5056, Equatorial mountains on Pluto are covered by methane frosts resulting from a unique atmospheric process

      Pluto is covered by numerous deposits of methane, either diluted in nitrogen or as methane-rich ice. Within the dark equatorial region of Cthulhu, bright frost containing methane is observed coating crater rims and walls as well as mountain tops, providing spectacular resemblance to terrestrial snow-capped mountain chains. However, the origin of these deposits remained enigmatic. Here we report that they are composed of methane-rich ice. We use high-resolution numerical simulations of Pluto’s climate to show that the processes forming them are likely to be completely different to those forming high-altitude snowpack on Earth. The methane deposits may not result from adiabatic cooling in upwardly moving air like on our planet, but from a circulation-induced enrichment of gaseous methane a few kilometres above Pluto’s plains that favours methane condensation at mountain summits. This process could have shaped other methane reservoirs on Pluto and help explain the appearance of the bladed terrain of Tartarus Dorsa.

    53. Leung, Y., Zhang, Y., Yanny, B., et al., 2020, RNAAS, 4, 174, The Diffuse Light Envelope of Luminous Red Galaxies

      We use a stacking method to study the radial light profiles of luminous red galaxies (LRGs) at redshift 0.62 and 0.25, out to a radial range of 200 kpc. We do not find noticeable evolution of the profiles at the two redshifts. The LRG profiles appear to be well approximated by a single Sersic profile, although some excess light can be seen outside 60 kpc. We quantify the excess light by measuring the integrated flux and find that the excess is about 10%a non-dominant but still nonnegligible component.

    54. Neugent, Kathryn F., Levesque, Emily M., Massey, Philip, et al., 2020, ApJ, 900, 118, The Red Supergiant Binary Fraction of the Large Magellanic Cloud

      The binary fraction of unevolved massive stars is thought to be 70%-100% but there are few observational constraints on the binary fraction of the evolved version of a subset of these stars, the red supergiants (RSGs). Here we identify a complete sample of RSGs in the Large Magellanic Cloud (LMC) using new spectroscopic observations and archival UV, IR, and broadband optical photometry. We find 4090 RSGs with $\mathrm{log}L/{L}_{\odot }\gt 3.5$ , with 1820 of them having $\mathrm{log}L/{L}_{\odot }\gt 4$ , which we believe is our completeness limit. We additionally spectroscopically confirmed 38 new RSG + B-star binaries in the LMC, bringing the total known up to 55. We then estimated the binary fraction using a k-nearest neighbors algorithm that classifies stars as single or binary based on photometry with a spectroscopic sample as a training set. We take into account observational biases such as line-of-sight stars and binaries in eclipse while also calculating model-dependent corrections for RSGs with companions that our observations were not designed to detect. Based on our data, we find an initial result of ${13.5}_{-6.67}^{+7.56} \% $ for RSGs with O- or B-type companions. Using the Binary Population and Spectral Synthesis models to correct for unobserved systems, this corresponds to a total RSG binary fraction of ${19.5}_{-6.7}^{+7.6} \% $ . This number is in broad agreement with what we would expect given an initial OB binary distribution of 70%, a predicted merger fraction of 20%-30%, and a binary interaction fraction of 40%-50%.

    55. Zhang, Hong-Xin, Smith, Rory, Oh, Se-Heon, et al., 2020, ApJ, 900, 152, The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging: H I Gas, Star Formation, and Numerical Simulations

      A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA H I emission line mapping, optical imaging, and numerical simulations of VCC 848 in order to examine the effect of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its H I gas concentrated within the central high-surface-brightness star-forming region, while the remaining H I is entrained in outlying tidal features. Particularly, a well-defined tidal arm reaches N(H I) comparable to the galaxy center but lacks SF. The molecular gas mass inferred from the current SF rate (SFR) dominates over the atomic gas mass in the central 1.5 kpc. VCC 848 is consistent with being a main-sequence star-forming galaxy for its current stellar mass and SFR. The H II region luminosity distribution largely agrees with that of normal dwarf irregulars with similar luminosities, except that the brightest H II region is extraordinarily luminous. Our N-body/hydrodynamical simulations imply that VCC 848 is a merger between a gas-dominated primary progenitor and a gas-bearing star-dominated secondary. The progenitors had their first passage on a near-radial noncoplanar orbit more than 1 Gyr ago. The merger did not build up a core as compact as typical compact dwarfs with a centralized starburst, which may be partly ascribed to the star-dominated nature of the secondary and, in a general sense, a negative stellar feedback following intense starbursts triggered at early stages of the merger.

    56. Palmese, A., deVicente, J., Pereira, M. E. S., et al., 2020, ApJL, 900, L33, A Statistical Standard Siren Measurement of the Hubble Constant from the LIGO/Virgo Gravitational Wave Compact Object Merger GW190814 and Dark Energy Survey Galaxies

      We present a measurement of the Hubble constant H0 using the gravitational wave (GW) event GW190814, which resulted from the coalescence of a 23 M black hole with a 2.6 M compact object, as a standard siren. No compelling electromagnetic counterpart has been identified for this event; thus our analysis accounts for thousands of potential host galaxies within a statistical framework. The redshift information is obtained from the photometric redshift (photo-z) catalog from the Dark Energy Survey. The luminosity distance is provided by the LIGO/Virgo gravitational wave sky map. Since this GW event has the second-smallest localization volume after GW170817, GW190814 is likely to provide the best constraint on cosmology from a single standard siren without identifying an electromagnetic counterpart. Our analysis uses photo-z probability distribution functions and corrects for photo-z biases. We also reanalyze the binary black hole GW170814 within this updated framework. We explore how our findings impact the H0 constraints from GW170817, the only GW merger associated with a unique host galaxy. From a combination of GW190814, GW170814, and GW170817, our analysis yields ${H}_{0}={72.0}_{-8.2}^{+12}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ (68% highest-density interval, HDI) for a prior in H0 uniform between $[20\mathrm{and}140]\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ . The addition of GW190814 and GW170814 to GW170817 improves the 68% HDI from GW170817 alone by 18%, showing how well-localized mergers without counterparts can provide a significant contribution to standard siren measurements, provided that a complete galaxy catalog is available at the location of the event.

    57. Morgan, R., Soares-Santos, M., Annis, J., et al., 2020, ApJ, 901, 83, Constraints on the Physical Properties of GW190814 through Simulations Based on DECam Follow-up Observations by the Dark Energy Survey

      On 2019 August 14, the LIGO and Virgo Collaborations detected gravitational waves from a black hole and a 2.6 solar mass compact object, possibly the first neutron star-black hole merger. In search of an optical counterpart, the Dark Energy Survey (DES) obtained deep imaging of the entire 90% confidence level localization area with Blanco/DECam 0, 1, 2, 3, 6, and 16 nights after the merger. Objects with varying brightness were detected by the DES Pipeline, and we systematically reduced the candidate counterparts through catalog matching, light-curve properties, host-galaxy photometric redshifts, Southern Astrophysical Research spectroscopic follow-up observations, and machine-learning-based photometric classification. All candidates were rejected as counterparts to the merger. To quantify the sensitivity of our search, we applied our selection criteria to full light-curve simulations of supernovae and kilonovae as they would appear in the DECam observations. Because the source class of the merger was uncertain, we utilized an agnostic, three-component kilonova model based on tidally disrupted neutron star (NS) ejecta properties to quantify our detection efficiency of a counterpart if the merger included an NS. We find that, if a kilonova occurred during this merger, configurations where the ejected matter is greater than 0.07 solar masses, has lanthanide abundance less than 10-8.56, and has a velocity between 0.18c and 0.21c are disfavored at the 2 level. Furthermore, we estimate that our background reduction methods are capable of associating gravitational wave signals with a detected electromagnetic counterpart at the 4 level in 95% of future follow-up observations.

    58. Buchanan, Laura, Schwamb, Megan, Fraser, Wesley, et al., 2020, EPSC, EPSC2020-185, Col-OSSOS: Probing Ice Line/Colour Transitions within the Kuiper Belt’s Progenitor Populations

      The Colours of the Outer Solar System Origins Survey (Col-OSSOS, Schwamb et al., 2019) has examined the surface compositions of Kuiper Belt Objects (KBOs) by way of broadband g-, r- and J-band photometry, using the Gemini North Hawaii Telescope. This survey showed a bimodal distribution in the colours of the objects surveyed, consistent with previous colour surveys (Tegler et al., 2016). These broadband surface colours can be considered a proxy for surface composition of these KBOs, so this survey allows the frequency of different surface compositions within the outer Solar System to be explored. The bimodality of the observed colours suggests the presence of some sort of surface transition within the Kuiper belt, perhaps due to a volatile ice-line transition in the pristine planetesimal disk that existed before Neptune”s migration. The Outer Solar System Origins Survey (OSSOS, Bannister et al., 2018), from which Col-OSSOS selected objects brighter than 23.6 r-band magnitude, has well characterised and quantified biases, so allowing for comparisons between the observations and numerical models of the Kuiper belt.By applying different colour transitions to the primordial planetesimal disk, in this work we explore the possible positions for ice line/colour transitions within the planetesimal disk that existed before Neptune”s migration. Within Schwamb et al. (2019), a simplified toy model was used to investigate the possible position of this transition. Nesvorny et al. (2020) has investigated the primordial colour fraction, in particular how it can create the inclination distribution that we see in the colours of KBOs today. In this work we use a full dynamical model of the Kuiper belt to more precisely pinpoint the possible location of this transition. We make use of the model by Nesvorny & Vokrouhlicky (2016) of Neptune”s migration from 23 au to 30 au, and the consequent perturbation of the Kuiper belt into its current form. This model allows precise tracking of the objects from their pre-Neptune migration to post-Neptune migration positions, allowing various colour transition positions in the initial disk, an example of which is shown in Figure 1, to be compared with the Col-OSSOS observations of the modern day disk.Figure 1: An example red/neutral transition at 27 au. The left plots show the objects in the primordial disk, while the right plots show the objects post-Neptune migration from the model of Nesvorny & Vokrouhlicky (2016).The OSSOS survey simulator (Lawler et al., 2018) can then be used to calculate which of the simulated objects could have been observed by OSSOS, and so selected by Col-OSSOS for surface colour observations. The colour transition within the initial disk, shown in Figure 1, is moved radially outwards through the disk and the corresponding outputs are compared with the Col-OSSOS colour observations to see which initial disk colour transition positions are consistent with the modern day Kuiper belt. We will present results combing an accurate dynamical model of the Kuiper Belt”s evolution by Nesvorny & Vokrouhlicky (2016) with Col-OSSOS photometry. We will explore multiple radial colour distributions in the primordial planetesimal disk and implications for the the positions of ice line/colour transitions within the Kuiper Belt”s progenitor populations. ReferencesBannister, M. T., Gladman, B. J., Kavelaars, J. J., et al. 2018, ApJS, 236, 18Lawler, S. M., Kavelaars, J. J., Alexandersen, M., et al. 2018, Front. Astron. Space Sci., 5, 14Nesvorny, D., Vokrouhlicky, D., Alexandersen, M., et al. 2020, AJ, in pressNesvorny, D., & Vokrouhlicky, D. 2016, ApJ, 825Schwamb, M. E., Bannister, M. T., Marsset, M., et al. 2019, ApJS, 243, 12Tegler, S. C., Romanishin, W., Consolmagno, G. J., & J., S. 2016, AJ, 152, 210

    59. Fedorets, Grigori, Micheli, Marco, Jedicke, Robert, et al., 2020, EPSC, EPSC2020-658, Characterisation of 2020 CD3, Earth’s second minimoon

      IntroductionSmall solar system objects may occasionally become captured temporarily by planets. Theoretical models (Granvik et al. 2012, Fedorets et al. 2017) predict the existence of a steady-state population of these objects, also known as minimoons, also in the Earth-Moon system. Only one minimoon, 2006 RH120 has been discovered until recently (Kwiatkowski et al. 2009). Since minimoons spend a significant amount of time in Earth”s vicinity, they have been identified as outstanding targets for in situ exploration, or test cases for initial steps of asteroid resource utilisation (Granvik et al. 2013, Chyba et al. 2014, Brelsford et al. 2016, Jedicke et al. 2018). Moreover, not only are minimoons outstanding targets to constrain the size-frequency distribution of metre-sized asteroids (Harris & D”Abramo 2015, Granvik et al. 2016, Tricarico 2017, Brown et al. 2002), but also for studying the structure of the smallest asteroids. However, until now, the observational evidence of the minimoon population has been lacking.ObservationsThe object 2020 CD3 was discovered on February 15th 2020 at the Mt. Lemmon station of the Catalina Sky Survey, and was noticed to be on a geocentric orbit the following night. We report the results of the astrometric and photometric observational campaign to characterise 2020 CD3 performed by Gemini North, LDT, NOT, CFHT, CSS, and other telescopes during spring 2020. By investigating the solar radiation pressure signature on the astrometry of 2020 CD3, and broad-band photometry, we present evidence that 2020 CD3 is indeed the second temporary natural satellite in the Earth-Moon system. We describe its discovery circumstances, physical characterisation, rotational period and orbital evolution.DiscussionUsing 2020 CD3 as an example case, we discuss the challenges of discovering minimoons with contemporary surveys. For the first time, we are able to compare the observational evidence of minimoons with the theoretical models. We also assess the capture duration and rotation period of 2020 CD3 in context of simulation and similar objects. Finally, we compare the origin of minimoons as captured objects from the NEO population against their origin as lunar ejecta, and show why the first mechanism is dominant.ProspectsThe discovery of 2020 CD3, and the comparison to discovery predictions with other surveys (Bolin et al. 2014), assures that the expectation of discovery of tens of minimoons with LSST is realistic (Fedorets et al. 2020). With the anticipated growth of the population of minimoons, the path for further exploration of minimoons is foreseen.ReferencesBolin et al. (2014), Icarus 241, 280Brelsford et al. (2016), PSS, 123, 4.Brown et al. (2002), Nature, 420, 294.Chyba et al. (2014) JIMO, 10(2), 477.Fedorets et al. (2017) Icarus, 285, 83.Fedorets et al. (2020), Icarus, 338, 113517.Granvik et al. (2012), Icarus, 218, 262.Granvik et al. (2013) in V. Badescu ed. Asteroids: Prospective Energy and Material Resources, 151.Granvik et al. (2016), Nature, 530, 303.Harris & D”Abramo (2015), Icarus, 257, 302.Jedicke et al. (2018) FrASS, 5, A13.Kwiatkowski et al. (2009), A&A, 495, 967.Tricarico et al. (2017), Icarus, 284, 416.

    60. Pieres, A., Girardi, L., Balbinot, E., et al., 2020, MNRAS, 497, 1547, Modelling the Milky Way – I. Method and first results fitting the thick disc and halo with DES-Y3 data

      We present a technique to fit the stellar components of the Galaxy by comparing Hess Diagrams (HDs) generated from TRILEGAL models to real data. We apply this technique, which we call MWFITTING, to photometric data from the first 3 yr of the Dark Energy Survey (DES). After removing regions containing known resolved stellar systems such as globular clusters, dwarf galaxies, nearby galaxies, the Large Magellanic Cloud, and the Sagittarius Stream, our main sample spans a total area of 2300 deg2. We further explore a smaller subset (1300 deg2) that excludes all regions with known stellar streams and stellar overdensities. Validation tests on synthetic data possessing similar properties to the DES data show that the method is able to recover input parameters with a precision better than 3 per cent. We fit the DES data with an exponential thick disc model and an oblate double power-law halo model. We find that the best-fitting thick disc model has radial and vertical scale heights of 2.67 0.09 kpc and 925 40 pc, respectively. The stellar halo is fit with a broken power-law density profile with an oblateness of 0.75 0.01, an inner index of 1.82 0.08, an outer index of 4.14 0.05, and a break at 18.52 0.27 kpc from the Galactic centre. Several previously discovered stellar overdensities are recovered in the residual stellar density map, showing the reliability of MWFITTING in determining the Galactic components. Simulations made with the best-fitting parameters are a promising way to predict Milky Way star counts for surveys such as the LSST and Euclid.

    61. Eckert, K., Bernstein, G. M., Amara, A., et al., 2020, MNRAS, 497, 2529, Noise from undetected sources in Dark Energy Survey images

      For ground-based optical imaging with current CCD technology, the Poisson fluctuations in source and sky background photon arrivals dominate the noise budget and are readily estimated. Another component of noise, however, is the signal from the undetected population of stars and galaxies. Using injection of artifical galaxies into images, we demonstrate that the measured variance of galaxy moments (used for weak gravitational lensing measurements) in Dark Energy Survey (DES) images is significantly in excess of the Poisson predictions, by up to 30 per cent, and that the background sky levels are overestimated by current software. By cross-correlating distinct images of ’empty’ sky regions, we establish that there is a significant image noise contribution from undetected static sources (US), which, on average, are mildly resolved at DES resolution. Treating these US as a stationary noise source, we compute a correction to the moment covariance matrix expected from Poisson noise. The corrected covariance matrix matches the moment variances measured on the injected DES images to within 5 per cent. Thus, we have an empirical method to statistically account for US in weak lensing measurements, rather than requiring extremely deep sky simulations. We also find that local sky determinations can remove most of the bias in flux measurements, at a small penalty in additional, but quantifiable, noise.

    62. Steckloff, Jordan K., Soderblom, Jason M., Farnsworth, Kendra K., et al., 2020, PSJ, 1, 26, Stratification Dynamics of Titan’s Lakes via Methane Evaporation

      Saturn’s moon Titan is the only extraterrestrial body known to host stable lakes and a hydrological cycle. Titan’s lakes predominantly contain liquid methane, ethane, and nitrogen, with methane evaporation driving its hydrological cycle. Molecular interactions between these three species lead to nonideal behavior that causes Titan’s lakes to behave differently than Earth’s lakes. Here, we numerically investigate how methane evaporation and nonideal interactions affect the physical properties, structure, dynamics, and evolution of shallow lakes on Titan. We find that, under certain temperature regimes, methane-rich mixtures are denser than relatively ethane-rich mixtures. This allows methane evaporation to stratify Titan’s lakes into ethane-rich upper layers and methane-rich lower layers, separated by a strong compositional gradient. At temperatures above 86 K, lakes remain well mixed and unstratified. Between 84 and 86 K, lakes can stratify episodically. Below 84 K, lakes permanently stratify and develop very methane-depleted epilimnia. Despite small seasonal and diurnal deviations (<5 K) from typical surface temperatures, Titan’s rain-filled ephemeral lakes and “phantom lakes” may nevertheless experience significantly larger temperature fluctuations, resulting in polymictic or even meromictic stratification, which may trigger ethane ice precipitation.

    63. Noll, K. S., Brown, M. E., Weaver, H. A., et al., 2020, PSJ, 1, 44, Detection of a Satellite of the Trojan Asteroid (3548) EurybatesA Lucy Mission Target

      We describe the discovery of a satellite of the Trojan asteroid (3548) Eurybates in images obtained with the Hubble Space Telescope. The satellite was detected on three separate epochs, two in 2018 September and one in 2020 January. The satellite has a brightness in all three epochs consistent with an effective diameter of d2 = 1.2 0.4 km. The projected separation from Eurybates was s 1700-2300 km and varied in position, consistent with a large range of possible orbits. Eurybates is a target of the Lucy Discovery mission and the early detection of a satellite provides an opportunity for a significant expansion of the scientific return from this encounter.

    64. Leiva, Rodrigo, Buie, Marc W., Keller, John M., et al., 2020, PSJ, 1, 48, Stellar Occultation by the Resonant Trans-Neptunian Object (523764) 2014 WC510 Reveals a Close Binary TNO

      We report on the stellar occultation by (523764) 2014 WC510 observed on 2018 December 1 UT. This occultation campaign was part of the Research and Education Collaborative Occultation Network (RECON), a network of small telescopes spread over 2000 km in western USA and Canada. Light curves from six stations revealed three groups of two or more consecutive flux drops correlated in time between adjacent stations. A Bayesian model comparison reveals that a model with a double object occulting a double star is favored over alternative models considered. For the statistically favored model, we determined that the primary component of the object has a diameter dp = 181 16 km and the secondary ds = 138 32 km, assuming identical geometric albedo between the two components. The two components have a projected separation of 349 26 km. Adopting an absolute magnitude for the system of HV = 7.2 from the Minor Planet Center, we derive a geometric albedo of pV = 5.1% 1.7%. This is the smallest resonant object with an occultation size measurement and with a detected secondary from a ground-based stellar occultation, filling a region of the size versus separation parameter space of binary objects that is largely unexplored. The results show the capabilities of the unique design of the RECON experiment sensitive to small objects and close binaries. 2014 WC510 is presently at a low galactic latitude where the high surface density of stars will provide good occultation opportunities in the upcoming years.

    65. Brewer, John M., Fischer, Debra A., Blackman, Ryan T., et al., 2020, AJ, 160, 67, EXPRES. I. HD 3651 as an Ideal RV Benchmark

      The next generation of exoplanet-hunting spectrographs should deliver up to an order of magnitude improvement in radial velocity (RV) precision over the standard 1 ${\rm{m}}\ {{\rm{s}}}^{-1}$ state-of-the-art spectrographs. This advance is critical for enabling the detection of Earth-mass planets around Sun-like stars. New calibration techniques such as laser frequency combs and stabilized etalons ensure that the instrumental stability is well characterized. However, additional sources of error include stellar noise, undetected short-period planets, and telluric contamination. To understand and ultimately mitigate error sources, the contributing terms in the error budget must be isolated to the greatest extent possible. Here, we introduce a new high-cadence RV program, the Extreme Precision Spectrograph (EXPRES) 100 Earths Survey, which aims to identify rocky planets around bright, nearby G and K dwarfs. We also present a benchmark case: the 62 day orbit of a Saturn-mass planet orbiting the chromospherically quiet star, HD 3651. The combination of high eccentricity (0.6) and a moderately long orbital period ensures significant dynamical clearing of any inner planets. Our Keplerian model for this planetary orbit has a residual rms of 58 cm s-1 over a 6 month time baseline. By eliminating significant contributors to the RV error budget, HD 3651 serves as a standard for evaluating the long-term precision of extreme precision RV programs.

    66. Walker, Constance, Hall, Jeffrey, Allen, Lori, et al., 2020, BAAS, 52, 0206, Impact of Satellite Constellations on Optical Astronomy and Recommendations Toward Mitigations

      In May 2019 SpaceX launched its first batch of 60 Starlink communication satellites, which surprised astronomers and laypeople with their appearance in the night sky. Astronomers have only now, a little over a year later, accumulated enough observations of constellation satellites like those being launched by SpaceX and OneWeb, and run computer simulations of their likely impact when fully deployed, to thoroughly understand the magnitude and complexity of the problem. This research informed the discussion at the Satellite Constellations 1 (SATCON1) workshop held virtually 29 June to 2 July 2020 and led to recommendations for observatories and constellation operators. The SATCON1 report concludes that the effects on astronomical research and on the human experience of the night sky range from “negligible” to “extreme.”

    67. Ragozzine, D., Pincock, S., Porter, S., et al., 2020, DDA, 52, 203.04, Non-Keplerian Effects in Kuiper Belt Multiples

      As the number of solar system small body multiple systems (including binaries) grows in number and in observational baseline, advanced dynamical modelling will reveal physical, orbital, and spin properties that are currently poorly understood. For example, among Kuiper Belt Objects (KBOs) beyond Neptune, only a few have well determined obliquities, but observations of orbital precession due to non-spherical shapes can identify spin pole directions and obliquities. The ~50 KBO Binaries with known orbital solutions have been heretofore studied assuming Keplerian motion, but evidence suggests that several of these are beginning to show observationally significant non-Keplerian effects. To study these effects, we have developed and validated an n-quadrupole integrator SPINNY (SPIN + N-bodY) which can include all the dominant non-Keplerian effects relevant within observational precision. SPINNY has been combined with advanced Bayesian model fitting for KBO astrometry in a new modeling tool called MultiMoon. We present MultiMoon along with some potential use cases to demonstrate its value. We also present preliminary results on an analysis of the 47171 Lempo (1996 TC36) KBO trinary system.

    68. Guo, Hengxiao, Burke, Colin J., Liu, Xin, et al., 2020, MNRAS, 496, 3636, Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability

      We report the identification of a low-mass active galactic nucleus (AGN), DES J0218-0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218-0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg II and broad H lines, confirming its nature as a broad-line AGN. Archival XMM-Newton X-ray observations suggest an intrinsic hard X-ray luminosity of $L_{{\rm 2-12\, keV}}\approx 7.6\pm 0.4\times 10^{43}$ erg s-1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H from SDSS spectrum, we estimate a virial black hole (BH) mass of M 106.43-106.72 M (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* 1010.5 0.3 M based on modelling the multiwavelength spectral energy distribution. DES J0218-0430 extends the M-M* relation observed in luminous AGNs at z 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.

    69. Macaulay, E., Bacon, D., Nichol, R. C., et al., 2020, MNRAS, 496, 4051, Weak lensing of Type Ia Supernovae from the Dark Energy Survey

      We consider the effects of weak gravitational lensing on observations of 196 spectroscopically confirmed Type Ia Supernovae (SNe Ia) from years 1 to 3 of the Dark Energy Survey (DES). We simultaneously measure both the angular correlation function and the non-Gaussian skewness caused by weak lensing. This approach has the advantage of being insensitive to the intrinsic dispersion of SNe Ia magnitudes. We model the amplitude of both effects as a function of 8, and find 8 =1.2 $^{+0.9}_{-0.8}$ . We also apply our method to a subsample of 488 SNe from the Joint Light-curve Analysis (JLA; chosen to match the redshift range we use for this work), and find 8 =0.8 $^{+1.1}_{-0.7}$ . The comparable uncertainty in 8 between DES-SN and the larger number of SNe from JLA highlights the benefits of homogeneity of the DES-SN sample, and improvements in the calibration and data analysis.

    70. Hartley, W. G., Chang, C., Samani, S., et al., 2020, MNRAS, 496, 4769, The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys

      Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is to apply weights to a spectroscopic sample, so that their weighted photometry distribution matches the target sample. In this work, we estimate the selection bias in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in Dark Energy Survey (DES) as an example data set but the implications generalize to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of up to z 0.04 in the weighted mean redshift of different redshift intervals (z 0.015 in the case most relevant to DES). To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the z = 0.005-0.05 level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

    71. van Belle, Gerard T., Collins, Michael, Guzman, Giannina, et al., 2020, RNAAS, 4, 148, Improved ASCOM Dome Following

      An improved algorithm for dome following for an altitude-azimuth telescope mount is presented, with a specific implementation in ASCOM.

    72. Schaefer, G. H., Beck, Tracy L., Prato, L., et al., 2020, AJ, 160, 35, Orbital Motion, Variability, and Masses in the T Tauri Triple System

      We present results from adaptive optics imaging of the T Tauri triple system obtained at the Keck and Gemini Observatories in 2015-2019. We fit the orbital motion of T Tau Sb relative to Sa and model the astrometric motion of their center of mass relative to T Tau N. Using the distance measured by Gaia, we derived dynamical masses of ${M}_{\mathrm{Sa}}=2.05\pm 0.14$ M and MSb = 0.43 0.06 ${M}_{\odot }$ . The precision in the masses is expected to improve with continued observations that map the motion through a complete orbital period; this is particularly important as the system approaches periastron passage in 2023. Based on published properties and recent evolutionary tracks, we estimate a mass of 2 M for T Tau N, suggesting that T Tau N is similar in mass to T Tau Sa. Narrowband infrared photometry shows that T Tau N remained relatively constant between late 2017 and early 2019 with an average value of K = 5.54 0.07 mag. Using T Tau N to calibrate relative flux measurements since 2015, we found that T Tau Sa varied dramatically between 7.0 and 8.8 mag in the K band over timescales of a few months, while T Tau Sb faded steadily from 8.5 to 11.1 mag in the K band. Over the 27 yr orbital period of the T Tau S binary, both components have shown 3-4 mag of variability in the K band, relative to T Tau N.

    73. Hansen, T. T., Marshall, J. L., Simon, J. D., et al., 2020, ApJ, 897, 183, Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis

      We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( $\geqslant $ 20 M) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

    74. Margon, Bruce, Massey, Philip, Neugent, Kathryn F., et al., 2020, ApJ, 898, 85, A Survey for C II Emission-line Stars in the Large Magellanic Cloud

      We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the C II 7231, 7236 emission lines in objects as faint as m7400 18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged 50 deg2 using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population.

    75. Cartwright, Richard J., Beddingfield, Chloe B., Nordheim, Tom A., et al., 2020, ApJL, 898, L22, Evidence for Ammonia-bearing Species on the Uranian Satellite Ariel Supports Recent Geologic Activity

      We investigated whether ammonia-rich constituents are present on the surface of the Uranian moon Ariel by analyzing 32 near-infrared reflectance spectra collected over a wide range of sub-observer longitudes and latitudes. We measured the band areas and depths of a 2.2 m feature in these spectra, which has been attributed to ammonia-bearing species on other icy bodies. Ten spectra display prominent 2.2 m features with band areas and depths >2. We determined the longitudinal distribution of the 2.2 m band, finding no statistically meaningful differences between Ariel’s leading and trailing hemispheres, indicating that this band is distributed across Ariel’s surface. We compared the band centers and shapes of the five Ariel spectra displaying the strongest 2.2 m bands to laboratory spectra of various ammonia-bearing and ammonium-bearing species, finding that the spectral signatures of the Ariel spectra are best matched by ammonia-hydrates and flash frozen ammonia-water solutions. Our analysis also revealed that four Ariel spectra display 2.24 m bands (>2 band areas and depths), with band centers and shapes that are best matched by ammonia ice. Because ammonia should be efficiently removed over short timescales by ultraviolet photons, cosmic rays, and charged particles trapped in Uranus’ magnetosphere, the possible presence of this constituent supports geologic activity in the recent past, such as emplacement of ammonia-rich cryolavas and exposure of ammonia-rich deposits by tectonism, impact events, and mass wasting.

    76. Cruikshank, Dale P., Pendleton, Yvonne J., Grundy, William M., 2020, Life, 10, 126, Organic Components of Small Bodies in the Outer Solar System: Some Results of the New Horizons Mission

      The close encounters of the Pluto-Charon system and the Kuiper Belt object Arrokoth (formerly 2014 MU69) by NASA’s New Horizons spacecraft in 2015 and 2019, respectively, have given new perspectives on the most distant planetary bodies yet explored. These bodies are key indicators of the composition, chemistry, and dynamics of the outer regions of the Solar System’s nascent environment. Pluto and Charon reveal characteristics of the largest Kuiper Belt objects formed in the dynamically evolving solar nebula inward of ~30 AU, while the much smaller Arrokoth is a largely undisturbed relic of accretion at ~45 AU. The surfaces of Pluto and Charon are covered with volatile and refractory ices and organic components, and have been shaped by geological activity. On Pluto, N2, CO and CH4 are exchanged between the atmosphere and surface as gaseous and condensed phases on diurnal, seasonal and longer timescales, while Charon’s surface is primarily inert H2O ice with an ammoniated component and a polar region colored with a macromolecular organic deposit. Arrokoth is revealed as a fused binary body in a relatively benign space environment where it originated and has remained for the age of the Solar System. Its surface is a mix of CH3OH ice, a red-orange pigment of presumed complex organic material, and possibly other undetected components.

    77. Wiseman, P., Smith, M., Childress, M., et al., 2020, MNRAS, 495, 4040, Supernova host galaxies in the dark energy survey: I. Deep coadds, photometry, and stellar masses

      The 5-yr Dark Energy Survey Supernova Programme (DES-SN) is one of the largest and deepest transient surveys to date in terms of volume and number of supernovae. Identifying and characterizing the host galaxies of transients plays a key role in their classification, the study of their formation mechanisms, and the cosmological analyses. To derive accurate host galaxy properties, we create depth-optimized coadds using single-epoch DES-SN images that are selected based on sky and atmospheric conditions. For each of the five DES-SN seasons, a separate coadd is made from the other four seasons such that each SN has a corresponding deep coadd with no contaminating SN emission. The coadds reach limiting magnitudes of order 27 in g band, and have a much smaller magnitude uncertainty than the previous DES-SN host templates, particularly for faint objects. We present the resulting multiband photometry of host galaxies for samples of spectroscopically confirmed type Ia (SNe Ia), core-collapse (CCSNe), and superluminous (SLSNe) as well as rapidly evolving transients (RETs) discovered by DES-SN. We derive host galaxy stellar masses and probabilistically compare stellar-mass distributions to samples from other surveys. We find that the DES spectroscopically confirmed sample of SNe Ia selects preferentially fewer high-mass hosts at high-redshift compared to other surveys, while at low redshift the distributions are consistent. DES CCSNe and SLSNe hosts are similar to other samples, while RET hosts are unlike the hosts of any other transients, although these differences have not been disentangled from selection effects.

    78. de Jaeger, T., Galbany, L., Gonzalez-Gaitan, S., et al., 2020, MNRAS, 495, 4860, Studying Type II supernovae as cosmological standard candles using the Dark Energy Survey

      Despite vast improvements in the measurement of the cosmological parameters, the nature of dark energy and an accurate value of the Hubble constant (H0) in the Hubble-Lemaitre law remain unknown. To break the current impasse, it is necessary to develop as many independent techniques as possible, such as the use of Type II supernovae (SNe II). The goal of this paper is to demonstrate the utility of SNe II for deriving accurate extragalactic distances, which will be an asset for the next generation of telescopes where more-distant SNe II will be discovered. More specifically, we present a sample from the Dark Energy Survey Supernova Program (DES-SN) consisting of 15 SNe II with photometric and spectroscopic information spanning a redshift range up to 0.35. Combining our DES SNe with publicly available samples, and using the standard candle method (SCM), we construct the largest available Hubble diagram with SNe II in the Hubble flow (70 SNe II) and find an observed dispersion of 0.27 mag. We demonstrate that adding a colour term to the SN II standardization does not reduce the scatter in the Hubble diagram. Although SNe II are viable as distance indicators, this work points out important issues for improving their utility as independent extragalactic beacons: find new correlations, define a more standard subclass of SNe II, construct new SN II templates, and dedicate more observing time to high-redshift SNe II. Finally, for the first time, we perform simulations to estimate the redshift-dependent distance-modulus bias due to selection effects.

    79. Lidman, C., Tucker, B. E., Davis, T. M., et al., 2020, MNRAS, 496, 19, OzDES multi-object fibre spectroscopy for the Dark Energy Survey: results and second data release

      We present a description of the Australian Dark Energy Survey (OzDES) and summarize the results from its 6 years of operations. Using the 2dF fibre positioner and AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope, OzDES has monitored 771 active galactic nuclei, classified hundreds of supernovae, and obtained redshifts for thousands of galaxies that hosted a transient within the 10 deep fields of the Dark Energy Survey. We also present the second OzDES data release, containing the redshifts of almost 30 000 sources, some as faint as rAB = 24 mag, and 375 000 individual spectra. These data, in combination with the time-series photometry from the Dark Energy Survey, will be used to measure the expansion history of the Universe out to z 1.2 and the masses of hundreds of black holes out to z 4. OzDES is a template for future surveys that combine simultaneous monitoring of targets with wide-field imaging cameras and wide-field multi-object spectrographs.

    80. Gutierrez, C. P., Sullivan, M., Martinez, L., et al., 2020, MNRAS, 496, 95, DES16C3cje: A low-luminosity, long-lived supernova

      We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of 1500 km s-1, and the light curve shows an initial peak that fades after 50 d before slowly rebrightening over a further 100 d to reach an absolute brightness of Mr -15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of 56Co, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either (I) a low explosion energy (0.11 foe) and relatively large 56Ni production of 0.075 M from an 15 M red supergiant progenitor typical of other SNe II, or (II) a relatively compact 40 M star, explosion energy of 1 foe, and 0.08 M of 56Ni. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of 0.5 10-8 M s-1.

    81. Abbott, T. M. C., Aguena, M., Alarcon, A., et al., 2020, PhRvD, 102, 023509, Dark Energy Survey Year 1 Results: Cosmological constraints from cluster abundances and weak lensing

      We perform a joint analysis of the counts and weak lensing signal of redMaPPer clusters selected from the Dark Energy Survey (DES) Year 1 dataset. Our analysis uses the same shear and source photometric redshifts estimates as were used in the DES combined probes analysis. Our analysis results in surprisingly low values for S8=8(m/0.3 )0.5=0.65 0.04 , driven by a low matter density parameter, m=0.17 9-0.038+0.031, with 8m posteriors in 2.4 tension with the DES Y1 3x2pt results, and in 5.6 with the Planck CMB analysis. These results include the impact of post-unblinding changes to the analysis, which did not improve the level of consistency with other data sets compared to the results obtained at the unblinding. The fact that multiple cosmological probes (supernovae, baryon acoustic oscillations, cosmic shear, galaxy clustering and CMB anisotropies), and other galaxy cluster analyses all favor significantly higher matter densities suggests the presence of systematic errors in the data or an incomplete modeling of the relevant physics. Cross checks with x-ray and microwave data, as well as independent constraints on the observable-mass relation from Sunyaev-Zeldovich selected clusters, suggest that the discrepancy resides in our modeling of the weak lensing signal rather than the cluster abundance. Repeating our analysis using a higher richness threshold ( 30 ) significantly reduces the tension with other probes, and points to one or more richness-dependent effects not captured by our model.

    82. Dimitrova, Tzvetelina A., Neugent, Kathryn F., Levesque, Emily M., et al., 2020, RNAAS, 4, 107, Locating Red Supergiants in the Galaxy IC10

      We use archival near-IR photometry to identify red supergiants (RSGs) in the starburst galaxy IC10. RSGs are the coolest of the evolved massive stars and have K and M spectral types and temperatures below 4100 K. Typically, they can be up to a thousand times the radius of the Sun, and are therefore highly luminous. Using archival 2MASS and UKIRT photometry we transformed J and K colors to effective temperatures and luminosities, which allowed us to identify the RSGs. After applying temperature and luminosity constraints and eliminating foreground stars using Gaia, we arrived at our finalized list of 138 RSGs. Of this list, 26 were confirmed RSGs based on Gaia parallaxes, with the remaining 112 being unconfirmed proposed IC10 RSGs.

    83. Flagg, Laura, Shkolnik, Evgenya L., Weinberger, Alycia, et al., 2020, ApJ, 896, 153, ACRONYM IV: Three New, Young, Low-mass Spectroscopic Binaries

      As part of our search for new low-mass members of nearby young moving groups (YMGs), we discovered three low-mass, spectroscopic binaries, two of which are not kinematically associated with any known YMG. Using high-resolution optical spectroscopy, we measure the component and systemic radial velocities of the systems, as well as their lithium absorption and H emission, both spectroscopic indicators of youth. One system (2MASS J02543316-5108313, M2.0+M3.0) we confirm as a member of the 40 Myr old Tuc-Hor moving group, but whose binarity was previously undetected. The second young binary (2MASS J08355977-3042306, K5.5+M1.5) is not a kinematic match to any known YMG, but each component exhibits lithium absorption and strong and wide H emission indicative of active accretion, setting an upper age limit of 15 Myr. The third system (2MASS J10260210-4105537, M1.0+M3.0) has been hypothesized in the literature to be a member of the 10 Myr old TW Hya Association, but our measured systemic velocity shows the binary is in fact not part of any known YMG. This last system also has lithium absorption in each component, and has strong and variable H emission, setting an upper age limit of 15 Myr based on the lithium detection.

    84. Scolnic, D., Smith, M., Massiah, A., et al., 2020, ApJL, 896, L13, Supernova Siblings: Assessing the Consistency of Properties of Type Ia Supernovae that Share the Same Parent Galaxies

      While many studies have shown a correlation between properties of the light curves of SNe Ia and properties of their host galaxies, it remains unclear what is driving these correlations. We introduce a new direct method to study these correlations by analyzing “parent” galaxies that host multiple SNe Ia “siblings.” Here, we search the Dark Energy Survey SN sample, one of the largest samples of discovered SNe, and find eight galaxies that hosted two likely SNe Ia. Comparing the light-curve properties of these SNe and recovered distances from the light curves, we find no better agreement between properties of SNe in the same galaxy as any random pair of galaxies, with the exception of the SN light-curve stretch. We show at 2.8 significance that at least one-half of the intrinsic scatter of SNe Ia distance modulus residuals is not from common host properties. We also discuss the robustness with which we could make this evaluation with LSST, which will find 100 more pairs of galaxies, and pave a new line of study on the consistency of SNe Ia in the same parent galaxies. Finally, we argue that it is unlikely that some of these SNe are actually single, lensed SN with multiple images.

    85. Cowall, D. E., Skiff, B. A., Odell, A. P., 2020, JAVSO, 48, 28, Continued Period Changes in BW Vulpeculae

      BW Vulpeculae (BW Vul) has the largest amplitude of the beta Cephei stars. Over almost 80 years of observations, BW Vul has closely followed a parabolic ephemeris and possibly a light-travel-time effect. This parabola, with excursions on either side, also could be viewed as a sequence of straight lines (constant period) with abrupt period increases. This paradigm predicted a period increase around 2004, which did not occur. A recent observing campaign on this star using the AAVSOnet’s Bright Star Monitor telescopes as well as the 0.7-m Lowell Observatory telescope has been undertaken. A period analysis of our data suggests that the period may have paradoxically decreased beginning around 2009. Further observations are necessary to confirm this analysis.

    86. Pursiainen, M., Gutierrez, C. P., Wiseman, P., et al., 2020, MNRAS, 494, 5576, The mystery of photometric twins DES17X1boj and DES16E2bjy

      We present an analysis of DES17X1boj and DES16E2bjy, two peculiar transients discovered by the Dark Energy Survey (DES). They exhibit nearly identical double-peaked light curves that reach very different maximum luminosities (Mr = -15.4 and -17.9, respectively). The light-curve evolution of these events is highly atypical and has not been reported before. The transients are found in different host environments: DES17X1boj was found near the nucleus of a spiral galaxy, while DES16E2bjy is located in the outskirts of a passive red galaxy. Early photometric data are well fitted with a blackbody and the resulting moderate photospheric expansion velocities (1800 km s-1 for DES17X1boj and 4800 km s-1 for DES16E2bjy) suggest an explosive or eruptive origin. Additionally, a feature identified as high-velocity Ca II absorption ( $v$ 9400 km s-1) in the near-peak spectrum of DES17X1boj may imply that it is a supernova. While similar light-curve evolution suggests a similar physical origin for these two transients, we are not able to identify or characterize the progenitors.

    87. Zenteno, A., Hernandez-Lang, D., Klein, M., et al., 2020, MNRAS, 495, 705, A joint SZ-X-ray-optical analysis of the dynamical state of 288 massive galaxy clusters

      We use imaging from the first three years of the Dark Energy Survey to characterize the dynamical state of 288 galaxy clusters at 0.1 z 0.9 detected in the South Pole Telescope (SPT) Sunyaev-Zeldovich (SZ) effect survey (SPT-SZ). We examine spatial offsets between the position of the brightest cluster galaxy (BCG) and the centre of the gas distribution as traced by the SPT-SZ centroid and by the X-ray centroid/peak position from Chandra and XMM data. We show that the radial distribution of offsets provides no evidence that SPT SZ-selected cluster samples include a higher fraction of mergers than X-ray-selected cluster samples. We use the offsets to classify the dynamical state of the clusters, selecting the 43 most disturbed clusters, with half of those at z 0.5, a region seldom explored previously. We find that Schechter function fits to the galaxy population in disturbed clusters and relaxed clusters differ at z > 0.55 but not at lower redshifts. Disturbed clusters at z > 0.55 have steeper faint-end slopes and brighter characteristic magnitudes. Within the same redshift range, we find that the BCGs in relaxed clusters tend to be brighter than the BCGs in disturbed samples, while in agreement in the lower redshift bin. Possible explanations includes a higher merger rate, and a more efficient dynamical friction at high redshift. The red-sequence population is less affected by the cluster dynamical state than the general galaxy population.

    88. Ragone-Figueroa, C., Granato, G. L., Borgani, S., et al., 2020, MNRAS, 495, 2436, Evolution and role of mergers in the BCG-cluster alignment. A view from cosmological hydrosimulations

      Contradictory results have been reported on the time evolution of the alignment between clusters and their brightest cluster galaxy (BCG). We study this topic by analysing cosmological hydrosimulations of 24 massive clusters with $M_{200}|_{z=0} \gtrsim 10^{15}\, \rm {\, M_{\odot }}$ , plus 5 less massive with $1 \times 10^{14} \lesssim M_{200}|_{z=0} \lesssim 7 \times 10^{14}\, \rm {\, M_{\odot }}$ , which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift z = 0, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20. The BCG alignment with the DM halo is even tighter. The alignment persists up to z 2 with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter (3R200) is already in place at z 4 with a typical angle of 35, before the BCG-cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG-cluster alignment occurs in an outside-in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent major mergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis.

    89. Devogele, Maxime, MacLennan, Eric, Gustafsson, Annika, et al., 2020, PSJ, 1, 15, New Evidence for a Physical Link between Asteroids (155140) 2005 UD and (3200) Phaethon

      In 2018, the near-Earth object (155140) 2005 UD (hereafter UD) experienced a close fly by of the Earth. We present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (07-88). We also analyze archival NEOWISE observations. We report an absolute magnitude of HV = 17.51 0.02 mag and an albedo of pV = 0.10 0.02. UD has been dynamically linked to Phaethon due their similar orbital configurations. Assuming similar surface properties, we derived new estimates for the diameters of Phaethon and UD of D = 5.4 0.5 km and D = 1.3 0.1 km, respectively. Thermophysical modeling of NEOWISE data suggests a surface thermal inertia of ${\rm{\Gamma }}={300}_{-110}^{+120}$ and regolith grain size in the range of 0.9-10 mm for UD and grain sizes of 3-30 mm for Phaethon. The light curve of UD displays a symmetric shape with a reduced amplitude of Am(0) = 0.29 mag and increasing at a linear rate of 0.017 mag/ between phase angles of 0 and 25. Little variation in light-curve morphology was observed throughout the apparition. Using light-curve inversion techniques, we obtained a sidereal rotation period P = 5.235 0.005 hr. A search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of 10% m-1 and 16%, respectively. In this work, we present new evidence that Phaethon and UD are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects. * Partially based on data collected with 2 m RCC telescope at Rozhen National Astronomical Observatory.

    90. Barrows, Robert Scott, Comerford, Julia, Llama, Joe, et al., 2020, hst, 16362, Redshift Evolution of ULXs

      We propose a project to identify and analyze archival HST imaging of ~200 ultra-luminous X-ray source (ULX) candidates out to intermediate redshifts (z~0.25). ULXs are luminous (LX>10^39 erg/s), off-nuclear X-ray sources in galaxies, and at intermediate redshifts they are expected to contribute significantly to the cosmic X-ray background. They are also unique laboratories for studying the physics of super-Eddington accretion or accretion onto massive stars and stellar remnants. Some ULXs may also represent accretion onto intermediate-mass black holes (IMBHs) that have been deposited into the host galaxy following a merger and may be the seed masses of supermassive black holes. HST is the only observational resource with the imaging resolution and sensitivity to detect intermediate redshift ULX stellar counterparts and to resolve their galactic environments. This project will yield the largest sample of ULXs out to intermediate redshifts studied with HST, and we will use it to conduct four tests designed to elucidate their nature: A) test for likely contaminants (background or foreground sources) based on association with external galaxies; B) test the stellar mass origin or IMBH scenarios by measuring stellar counterpart masses or upper limits; C) test if the ULXs reside in galaxies with enhanced star-formation rates; and D) test if the ULXs reside in locally star-forming environments. The results of these tests will enable, for the first time, a comprehensive view of how ULX properties evolve out to intermediate redshifts. The archival approach of this project will eliminate the burden on HST time while maximizing its contribution to the science of ULXs.

    91. Horch, Elliott P., van Belle, Gerard T., Davidson, James W., Jr., et al., 2020, AJ, 159, 233, Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars

      We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument at Lowell Observatory’s Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2 mas, and the relative photometry appears to be uncertain at the 0.1-0.15 mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66 Oph and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD 22451 (YSC 127) and HD 185501 (YSC 135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2 level. We find that HD 22451 consists of an F6V+F7V pair with orbital period of 2401.1 3.2 days and masses of 1.342 0.029 and $1.236\pm 0.026\,{M}_{\odot } . For HD 185501, both stars are G5 dwarfs that orbit one another with a period of 433.94 0.15 days, and the masses are 0.898 0.012 and $0.876\pm 0.012\,{M}_{\odot } . We discuss the details of both the new discoveries and the orbit objects.

    92. Blackman, Ryan T., Fischer, Debra A., Jurgenson, Colby A., et al., 2020, AJ, 159, 238, Performance Verification of the EXtreme PREcision Spectrograph

      The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radial-velocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial-velocity measurement precision of EXPRES, with a focused discussion of individual terms in the instrument error budget. We find that EXPRES can reach a single-measurement instrument calibration precision better than 10 cm s-1, not including photon noise from stellar observations. We also report on the performance of the various environmental, mechanical, and optical subsystems of EXPRES, assessing any contributions to radial-velocity error. For atmospheric and telescope related effects, this includes the fast tip-tilt guiding system, atmospheric dispersion compensation, and the chromatic exposure meter. For instrument calibration, this includes the laser fRequency comb (LFC), flat-field light source, CCD detector, and effects in the optical fibers. Modal noise is mitigated to a negligible level via a chaotic fiber agitator, which is especially important for wavelength calibration with the LFC. Regarding detector effects, we empirically assess the impact on the radial-velocity precision due to pixel-position nonuniformities and charge transfer inefficiency (CTI). EXPRES has begun its science survey to discover exoplanets orbiting G-dwarf and K-dwarf stars, in addition to transit spectroscopy and measurements of the Rossiter-McLaughlin effect.

    93. Burke, Colin J., Baldassare, Vivienne F., Liu, Xin, et al., 2020, ApJL, 894, L5, The Curious Case of PHL 293B: A Long-lived Transient in a Metal-poor Blue Compact Dwarf Galaxy

      We report on small-amplitude optical variability and recent dissipation of the unusually persistent broad emission lines in the blue compact dwarf galaxy PHL 293B. The galaxy’s unusual spectral features (P Cygni-like profiles with 800 km s-1 blueshifted absorption lines) have resulted in conflicting interpretations of the nature of this source in the literature. However, analysis of new Gemini spectroscopy reveals the broad emission has begun to fade after being persistent for over a decade prior. Precise difference imaging light curves constructed with the Sloan Digital Sky Survey and the Dark Energy Survey reveal small-amplitude optical variability of 0.1 mag in the g band offset by 100 21 pc from the brightest pixel of the host. The light curve is well-described by an active galactic nuclei (AGN)-like damped random walk process. However, we conclude that the origin of the optical variability and spectral features of PHL 293B is due to a long-lived stellar transient, likely a Type IIn supernova or nonterminal outburst, mimicking long-term AGN-like variability. This work highlights the challenges of discriminating between scenarios in such extreme environments, relevant to searches for AGNs in dwarf galaxies. This is the second long-lived transient discovered in a blue compact dwarf, after SDSS1133. Our result implies such long-lived stellar transients may be more common in metal-deficient galaxies. Systematic searches for low-level variability in dwarf galaxies will be possible with the upcoming Legacy Survey of Space and Time at the Vera C. Rubin Observatory.

    94. Nord, B., Buckley-Geer, E., Lin, H., et al., 2020, MNRAS, 494, 1308, Observation and confirmation of nine strong-lensing systems in Dark Energy Survey Year 1 data

      We describe the observation and confirmation of nine new strong gravitational lenses discovered in Year 1 data from the Dark Energy Survey (DES). We created candidate lists based on (i) galaxy group and cluster samples, and (ii) photometrically selected galaxy samples. We selected 46 candidates through visual inspection and then used the Gemini Multi-Object Spectrograph (GMOS) at the Gemini South telescope to acquire a spectroscopic follow-up of 21 of these candidates. Through an analysis of these spectroscopic follow-up data, we confirmed nine new lensing systems and rejected two candidates, and the analysis was inconclusive on 10 candidates. For each of the confirmed systems, our report measured spectroscopic properties, estimated source image-lens separations, and estimated enclosed masses as well. The sources that we targeted have an i-band surface brightness range of $i_{\rm SB} \sim 22\!-\!24\, {\rm mag}\,{\rm arcsec}^{-2}$ and a spectroscopic redshift range of zspec 0.8-2.6. The lens galaxies have a photometric redshift range of zlens 0.3-0.7. The lensing systems range in source image-lens separation from 2 to 9 arcsec and in enclosed mass from 1012 to 1013 M.

    95. Gupta, N., Pannella, M., Mohr, J. J., et al., 2020, MNRAS, 494, 1705, Constraining radio mode feedback in galaxy clusters with the cluster radio AGNs properties to z 1

      We study the properties of the Sydney University Molonglo Sky Survey (SUMSS) 843 MHz radio active galactic nuclei (AGNs) population in galaxy clusters from two large catalogues created using the Dark Energy Survey (DES): 11 800 optically selected RM-Y3 and 1000 X-ray selected MARD-Y3 clusters. We show that cluster radio loud AGNs are highly concentrated around cluster centres to $z$ 1. We measure the halo occupation number for cluster radio AGNs above a threshold luminosity, finding that the number of radio AGNs per cluster increases with cluster halo mass as N M1.2 0.1 (N M0.68 0.34) for the RM-Y3 (MARD-Y3) sample. Together, these results indicate that radio mode feedback is favoured in more massive galaxy clusters. Using optical counterparts for these sources, we demonstrate weak redshift evolution in the host broad-band colours and the radio luminosity at fixed host galaxy stellar mass. We use the redshift evolution in radio luminosity to break the degeneracy between density and luminosity evolution scenarios in the redshift trend of the radio AGNs luminosity function (LF). The LF exhibits a redshift trend of the form (1 + $z$ ) in density and luminosity, respectively, of D = 3.0 0.4 and P = 0.21 0.15 in the RM-Y3 sample, and D = 2.6 0.7 and P = 0.31 0.15 in MARD-Y3. We discuss the physical drivers of radio mode feedback in cluster AGNs, and we use the cluster radio galaxy LF to estimate the average radio-mode feedback energy as a function of cluster mass and redshift and compare it to the core (<0.1R500) X-ray radiative losses for clusters at $z$ < 1.

    96. Lemon, C., Auger, M. W., McMahon, R., et al., 2020, MNRAS, 494, 3491, The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2017/2018 follow-up campaign: discovery of 10 lensed quasars and 10 quasar pairs

      We report the results of the STRong lensing Insights into the Dark Energy Survey (STRIDES) follow-up campaign of the late 2017/early 2018 season. We obtained spectra of 65 lensed quasar candidates with ESO Faint Object Spectrograph and Camera 2 on the NTT and Echellette Spectrograph and Imager on Keck, confirming 10 new lensed quasars and 10 quasar pairs. Eight lensed quasars are doubly imaged with source redshifts between 0.99 and 2.90, one is triply imaged (DESJ0345-2545, z = 1.68), and one is quadruply imaged (quad: DESJ0053-2012, z = 3.8). Singular isothermal ellipsoid models for the doubles, based on high-resolution imaging from SAMI on Southern Astrophysical Research Telescope or Near InfraRed Camera 2 on Keck, give total magnifications between 3.2 and 5.6, and Einstein radii between 0.49 and 1.97 arcsec. After spectroscopic follow-up, we extract multi-epoch grizY photometry of confirmed lensed quasars and contaminant quasar + star pairs from DES data using parametric multiband modelling, and compare variability in each system’s components. By measuring the reduced 2 associated with fitting all epochs to the same magnitude, we find a simple cut on the less variable component that retains all confirmed lensed quasars, while removing 94 per cent of contaminant systems. Based on our spectroscopic follow-up, this variability information improves selection of lensed quasars and quasar pairs from 34-45 per cent to 51-70 per cent, with most remaining contaminants being star-forming galaxies. Using mock lensed quasar light curves we demonstrate that selection based only on variability will over-represent the quad fraction by 10 per cent over a complete DES magnitude-limited sample, explained by the magnification bias and hence lower luminosity/more variable sources in quads.

    97. Smith, M., Sullivan, M., Wiseman, P., et al., 2020, MNRAS, 494, 4426, First cosmology results using type Ia supernovae from the Dark Energy Survey: the effect of host galaxy properties on supernova luminosity

      We present improved photometric measurements for the host galaxies of 206 spectroscopically confirmed type Ia supernovae discovered by the Dark Energy Survey Supernova Program (DES-SN) and used in the first DES-SN cosmological analysis. For the DES-SN sample, when considering a 5D (z, x1, c, , ) bias correction, we find evidence of a Hubble residual ‘mass step’, where SNe Ia in high-mass galaxies (>1010M) are intrinsically more luminous (after correction) than their low-mass counterparts by $\gamma =0.040\pm 0.019$ mag. This value is larger by 0.031 mag than the value found in the first DES-SN cosmological analysis. This difference is due to a combination of updated photometric measurements and improved star formation histories and is not from host-galaxy misidentification. When using a 1D (redshift-only) bias correction the inferred mass step is larger, with $\gamma =0.066\pm 0.020$ mag. The 1D-5D difference for DES-SN is $0.026\pm 0.009$ mag. We show that this difference is due to a strong correlation between host galaxy stellar mass and the x1 component of the 5D distance-bias correction. Including an intrinsic correlation between the observed properties of SNe Ia, stretch and colour, and stellar mass in simulated SN Ia samples, we show that a 5D fit recovers with -9 mmag bias compared to a +2 mmag bias for a 1D fit. This difference can explain part of the discrepancy seen in the data. Improvements in modelling correlations between galaxy properties and SN is necessary to ensure unbiased precision estimates of the dark energy equation of state as we enter the era of LSST.

    98. Muir, J., Bernstein, G. M., Huterer, D., et al., 2020, MNRAS, 494, 4454, Blinding multiprobe cosmological experiments

      The goal of blinding is to hide an experiment’s critical results – here the inferred cosmological parameters – until all decisions affecting its analysis have been finalized. This is especially important in the current era of precision cosmology, when the results of any new experiment are closely scrutinized for consistency or tension with previous results. In analyses that combine multiple observational probes, like the combination of galaxy clustering and weak lensing in the Dark Energy Survey (DES), it is challenging to blind the results while retaining the ability to check for (in)consistency between different parts of the data. We propose a simple new blinding transformation, which works by modifying the summary statistics that are input to parameter estimation, such as two-point correlation functions. The transformation shifts the measured statistics to new values that are consistent with (blindly) shifted cosmological parameters while preserving internal (in)consistency. We apply the blinding transformation to simulated data for the projected DES Year 3 galaxy clustering and weak lensing analysis, demonstrating that practical blinding is achieved without significant perturbation of internal-consistency checks, as measured here by degradation of the 2 between the data and best-fitting model. Our blinding method’s performance is expected to improve as experiments evolve to higher precision and accuracy.

    99. Smith, Isaac B., Hayne, Paul O., Byrne, Shane, et al., 2020, P&SS, 184, 104841, The Holy Grail: A road map for unlocking the climate record stored within Mars’ polar layered deposits

      In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to “read” the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet’s climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered.


      During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers.

      The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below.

      In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record.

    100. van Belle, Gerard T., Schaefer, Gail H., von Braun, Kaspar, et al., 2020, PASP, 132, 054201, HST/FGS Trigonometric Parallaxes of M-dwarf Eclipsing Binaries

      Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) trigonometric parallax observations were obtained to directly determine distances to five nearby M-dwarf/M-dwarf eclipsing binary systems. These systems are intrinsically interesting as benchmark systems for establishing basic physical parameters for low-mass stars, such as luminosity L, and radius R. HST/FGS distances are also one of the few direct checks on Gaia trigonometric parallaxes, given the comparable sensitivity in both magnitude limit and determination of parallactic angles. A spectral energy distribution (SED) fit of each system’s blended flux output was carried out, allowing for estimation of the bolometric flux from the primary and secondary components of each system. From the stellar M, L, and R values, the low-mass star relationships between L and M, and R and M, are compared against idealized expectations for such stars. An examination on the inclusion of these close M-dwarf/M-dwarf pairs in higher-order common proper motion (CPM) pairs is analyzed; each of the 5 systems has indications of being part of a CPM system. Unexpected distances on interesting objects found within the grid of parallactic reference stars are also presented, including a nearby M dwarf and a white dwarf.

    101. Massey, Philip Louis, Hillier, D. John, Morrell, Nidia, et al., 2020, hst, 16299, The Nature of a Newly Discovered Wolf-Rayet Binary: Archetype of Stripping?

      Understanding massive star evolution is important for a variety of astrophysical processes, from the formation of the elements to the generation of gravitational waves as their remnants merge. Wolf-Rayet stars are evolved stars, where the hydrogen has been removed from a massive OB star, and its nuclear burning products revealed at the surface. This stripping can occur either by stellar winds or by interactions in close binaries. Although we expect the latter to be an important mechanism, there are few examples where one can argue which mechanism has been responsible, as even a single WR star may have formed through binary interaction, but merged with its companion. Given the large number of massive stars in binaries, we expect stripped remnants to be common. Binary models suggest these should look like WR stars, but they are curiously absent where we most expect to find them. However, the recent discovery of a WR binary in the LMC matches many of the properties expected for a stripped binary WR. We have obtained extensive ground-based photometry and spectroscopy of this object, and have carried the analysis as far as it is possible. The WR component is of WN4-type, but with intrinsic hydrogen and helium absorption lines. The companion is an “impossible” star, with a sub-solar mass and radius but a very high temperature. We suggest that this is the result of an Algol-like system, with both components having been donors and recipients at some point. This could be the archetype of binary-produced WRs, but we need UV spectra to determine CNO abundances, stellar wind properties, and better estimates of the bolometric luminosity. HST is the only way to achieve this.

    102. Coffaro, M., Stelzer, B., Orlando, S., et al., 2020, A&A, 636, A49, An X-ray activity cycle on the young solar-like star Eridani

      Chromospheric Ca II activity cycles are frequently found in late-type stars, but no systematic programs have been created to search for their coronal X-ray counterparts. The typical time scale of Ca II activity cycles ranges from years to decades. Therefore, long-lasting missions are needed to detect the coronal counterparts. The XMM-Newton satellite has so far detected X-ray cycles in five stars. A particularly intriguing question is at what age (and at what activity level) X-ray cycles set in. To this end, in 2015 we started the X-ray monitoring of the young solar-like star Eridani, previously observed on two occasions: in 2003 and in early 2015, both by XMM-Newton. With an age of 440 Myr, it is one of the youngest solar-like stars with a known chromospheric Ca II cycle. We collected the most recent Mount Wilson S-index data available for Eridani, starting from 2002, including previously unpublished data. We found that the Ca II cycle lasts 2.92 0.02 yr, in agreement with past results. From the long-term XMM-Newton lightcurve, we find clear and systematic X-ray variability of our target, consistent with the chromospheric Ca II cycle. The average X-ray luminosity is 2 1028erg s-1, with an amplitude that is only a factor of 2 throughout the cycle. We apply a new method to describe the evolution of the coronal emission measure distribution of Eridani in terms of solar magnetic structures: active regions, cores of active regions, and flares covering the stellar surface at varying filling fractions. Combinations of these three types of magnetic structures can only describe the observed X-ray emission measure of Eridani if the solar flare emission measure distribution is restricted to events in the decay phase. The interpretation is that flares in the corona of Eridani last longer than their solar counterparts. We ascribe this to the lower metallicity of Eridani. Our analysis also revealed that the X-ray cycle of Eridani is strongly dominated by cores of active regions. The coverage fraction of cores throughout the cycle changes by the same factor as the X-ray luminosity. The maxima of the cycle are characterized by a high percentage of covering fraction of the flares, consistent with the fact that flaring events are seen in the corresponding short-term X-ray lightcurves predominately at the cycle maxima. The high X-ray emission throughout the cycle of Eridani is thus explained by the high percentage of magnetic structures on its surface.

    103. Buie, Marc W., Porter, Simon B., Tamblyn, Peter, et al., 2020, AJ, 159, 130, Size and Shape Constraints of (486958) Arrokoth from Stellar Occultations

      We present the results from four stellar occultations by (486958) Arrokoth, the flyby target of the New Horizons extended mission. Three of the four efforts led to positive detections of the body, and all constrained the presence of rings and other debris, finding none. Twenty-five mobile stations were deployed for 2017 June 3 and augmented by fixed telescopes. There were no positive detections from this effort. The event on 2017 July 10 was observed by the Stratospheric Observatory for Infrared Astronomy with one very short chord. Twenty-four deployed stations on 2017 July 17 resulted in five chords that clearly showed a complicated shape consistent with a contact binary with rough dimensions of 20 by 30 km for the overall outline. A visible albedo of 10% was derived from these data. Twenty-two systems were deployed for the fourth event on 2018 August 4 and resulted in two chords. The combination of the occultation data and the flyby results provides a significant refinement of the rotation period, now estimated to be 15.9380 0.0005 hr. The occultation data also provided high-precision astrometric constraints on the position of the object that were crucial for supporting the navigation for the New Horizons flyby. This work demonstrates an effective method for obtaining detailed size and shape information and probing for rings and dust on distant Kuiper Belt objects as well as being an important source of positional data that can aid in spacecraft navigation that is particularly useful for small and distant bodies.

    104. Simon, J. D., Li, T. S., Erkal, D., et al., 2020, ApJ, 892, 137, Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V

      We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of Vhel = 110.0 0.5 km s-1, Vhel = 15.9-1.7+1.8 km s-1, and Vhel=-36.2-2.2+2.5 km s-1 for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of = 4.3-1.0+1.7 km s-1, but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of < 1.9 km s-1, and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below [Fe/H]=-2.1, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of 25-7+6 kpc and orbital eccentricity of 0.45-0.05+0.08. Tuc V likely has an apocenter beyond 100 kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of 25-8+11 kpc and an eccentricity of 0.36-0.06+0.13. However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4 kpc 120 Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain.

    105. Drlica-Wagner, A., Bechtol, K., Mau, S., et al., 2020, ApJ, 893, 47, Milky Way Satellite Census. I. The Observational Selection Function for Milky Way Satellites in DES Y3 and Pan-STARRS DR1

      We report the results of a systematic search for ultra-faint Milky Way satellite galaxies using data from the Dark Energy Survey (DES) and Pan-STARRS1 (PS1). Together, DES and PS1 provide multi-band photometry in optical/near-infrared wavelengths over 80% of the sky. Our search for satellite galaxies targets 25,000 deg2 of the high-Galactic-latitude sky reaching a 10 point-source depth of 22.5 mag in the g and r bands. While satellite galaxy searches have been performed independently on DES and PS1 before, this is the first time that a self-consistent search is performed across both data sets. We do not detect any new high-significance satellite galaxy candidates, recovering the majority of satellites previously detected in surveys of comparable depth. We characterize the sensitivity of our search using a large set of simulated satellites injected into the survey data. We use these simulations to derive both analytic and machine-learning models that accurately predict the detectability of Milky Way satellites as a function of their distance, size, luminosity, and location on the sky. To demonstrate the utility of this observational selection function, we calculate the luminosity function of Milky Way satellite galaxies, assuming that the known population of satellite galaxies is representative of the underlying distribution. We provide access to our observational selection function to facilitate comparisons with cosmological models of galaxy formation and evolution.

    106. Nadler, E. O., Wechsler, R. H., Bechtol, K., et al., 2020, ApJ, 893, 48, Milky Way Satellite Census. II. Galaxy-Halo Connection Constraints Including the Impact of the Large Magellanic Cloud

      The population of Milky Way (MW) satellites contains the faintest known galaxies and thus provides essential insight into galaxy formation and dark matter microphysics. Here we combine a model of the galaxy-halo connection with newly derived observational selection functions based on searches for satellites in photometric surveys over nearly the entire high Galactic latitude sky. In particular, we use cosmological zoom-in simulations of MW-like halos that include realistic Large Magellanic Cloud (LMC) analogs to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC on the MW satellite population due to an estimated 6 2 observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper-motion measurements, confirming the predictions of cold dark matter models for the existence of satellites within satellite halos. Moreover, we infer that the LMC fell into the MW within the last 2 Gyr at high confidence. Based on our detailed full-sky modeling, we find that the faintest observed satellites inhabit halos with peak virial masses below $3.2\times {10}^{8}\ {M}_{\odot }$ at 95% confidence, and we place the first robust constraints on the fraction of halos that host galaxies in this regime. We predict that the faintest detectable satellites occupy halos with peak virial masses above ${10}^{6}\ {M}_{\odot }$ , highlighting the potential for powerful galaxy formation and dark matter constraints from future dwarf galaxy searches.

    107. Nesvorny, David, Vokrouhlicky, David, Bottke, William F., et al., 2020, ApJL, 893, L16, Very Slow Rotators from Tidally Synchronized Binaries

      A recent examination of K2 lightcurves indicates that 15% of Jupiter Trojans have very slow rotation (spin periods Ps > 100 hr). Here we consider the possibility that these bodies formed as equal-size binaries in the massive outer disk at 20-30 au. Prior to their implantation as Jupiter Trojans, tight binaries tidally evolved toward a synchronous state with Ps Pb, where Pb is the binary orbit period. They may have been subsequently dissociated by impacts and planetary encounters with at least one binary component retaining its slow rotation. Surviving binaries on Trojan orbits would continue to evolve by tides and spin-changing impacts over 4.5 Gyr. To explain the observed fraction of slow rotators, we find that at least 15%-20% of outer disk bodies with diameters 15 < D < 50 km would have to form as equal-size binaries with 12 ab/R 30, where ab is the binary semimajor axis and R = D/2. The mechanism proposed here could also explain very slow rotators found in other small-body populations.

    108. Marsset, Michael, DeMeo, Francesca E., Binzel, Richard P., et al., 2020, ApJS, 247, 73, Twenty Years of SpeX: Accuracy Limits of Spectral Slope Measurements in Asteroid Spectroscopy

      We examined two decades of SpeX/NASA Infrared Telescope Facility observations from the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate uncertainties and systematic errors in reflectance spectral slope measurements of asteroids. From 628 spectra of 11 solar analogs used for calibration of the asteroid spectra, we derived an uncertainty of on slope measurements over 0.8-2.4 m. Air mass contributes to -0.92% m-1 per 0.1 unit air mass difference between the asteroid and the solar analog and therefore for an overall 2.8% m-1 slope variability in SMASS and MITHNEOS designed to operate within 1.0-1.3 air mass. No additional observing conditions (including the parallactic angle, seeing, and humidity) were found to contribute systematically to slope change. We discuss implications for asteroid taxonomic classification works. Uncertainties provided in this study should be accounted for in future compositional investigation of small bodies to distinguish intrinsic heterogeneities from possible instrumental effects.

    109. Benson, Conor J., Scheeres, Daniel J., Moskovitz, Nicholas A., 2020, Icar, 340, 113518, Spin state evolution of asteroid (367943) Duende during its 2013 earth flyby

      On February 15, 2013 asteroid (367943) Duende, provisionally named 2012 DA14, experienced an extremely close earth encounter, passing within 27,700 km altitude. An observation campaign was made possible by one year’s notice of the flyby. This campaign, discussed in detail in the companion paper by Moskovitz et al. (2019), yielded visible-wavelength photometry before and after closest approach. Post-flyby Goldstone Doppler-delay radar data were also obtained. These data indicated a roughly 40 m 20 m object in non-principal axis rotation. Leveraging light curve frequency analysis from the Moskovitz et al. companion paper, dynamical and inertia constraints from the rough radar-derived elongations, and simulated photometry, only two post-flyby states were deemed viable. These were a long axis mode (LAM) with long axis convention periods Pbar = 6.36 h and P = 8.73 h and a short axis mode (SAM) with Pbar = 8.71 h and P = 23.7 h (each with nominal long-intermediate and long-short ellipsoid axis ratios of 1.7:1 and 2.3:1 respectively). The SAM solution was more consistent with the post-flyby photometry and radar data. Nevertheless, there were differences between the amplitude and phase of the post-flyby and best-fit simulated SAM light curves at some epochs. These discrepancies may be due to a non-ellipsoidal shape, non-uniform albedo, and/or incorrect spin state solution (attitude, inertias, tumbling periods, or rotation mode).


      Analysis of the sparse pre-flyby photometry by Moskovitz et al. yielded poor Fourier series solutions for all principal axis states and different peaks in the pre and post-flyby WindowCLEAN power spectra. This suggests the asteroid was tumbling before the encounter and that its spin state changed. Propagating the best-fitting LAM and SAM solutions backwards through the flyby with terrestrial tidal torques resulted in significant dispersion of the rotation states. The pre-flyby SAM states coincided with the notable Moskovitz et al. Fourier solution P1 = 8.37 h and P2 = 24.2 h. Overall, we propose Duende was tumbling before the 2013 flyby and that its spin state may have changed during the flyby. Furthermore, our analysis suggests Duende is currently in SAM with P bar = 8 . 71 h and P = 23.7 h with pole J2000 ecliptic longitude and obliquity of roughly 70 and 95 or 245 and 90 respectively. The spin state characterization approach outlined in this paper could be used for future analyses with inertia, dynamical, and observational constraints.

    110. Moskovitz, Nicholas A., Benson, Conor James, Scheeres, Daniel, et al., 2020, Icar, 340, 113519, Observational investigation of the 2013 near-Earth encounter by asteroid (367943) Duende

      On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We present here the results of an extensive, multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby. Our spectral data reveal no changes within systematic uncertainties. Post-flyby lightcurve photometry places strong constraints on the rotation state of Duende, showing that it is in non-principal axis rotation with fundamental periods of P1 = 8.71 0.03 and P2 = 23.7 0.2 h. Multiple lightcurve analysis techniques, coupled with theoretical considerations and delay-Doppler radar imaging, allow us to assign these periods to specific rotational axes of the body. In particular we suggest that Duende is now in a non-principal, short axis mode rotation state with a precessional period equal to P1 and oscillation about the symmetry axis at a rate equal to P2. Temporal and signal-to-noise limitations inherent to the pre-flyby photometric dataset make it difficult to definitively diagnose whether these periods represent a change imparted due to gravitational torques during the flyby. However, based on multiple analysis techniques and a number of plausibility arguments, we suggest that Duende experienced a rotational change during the planetary encounter with an increase in its precessional rotation period. Our preferred interpretation of the available data is that the precession rate increased from 8.4 h prior to the flyby to 8.7 h afterwards. A companion paper by Benson et al. (2019) provides a more detailed dynamical analysis of this event and compares the data to synthetic lightcurves computed from a simple shape model of Duende. The interpretation and results presented in these two works are consistent with one another. The ultimate outcome of this campaign suggests that the analytic tools we employed are sufficient to extract detailed information about solid-body rotation states given data of high enough quality and temporal sampling. As current and future discovery surveys find more near-Earth asteroids, the opportunities to monitor for physical changes during planetary encounters will increase.

    111. Cheng, Ting-Yun, Conselice, Christopher J., Aragon-Salamanca, Alfonso, et al., 2020, MNRAS, 493, 4209, Optimizing automatic morphological classification of galaxies with machine learning and deep learning using Dark Energy Survey imaging

      There are several supervised machine learning methods used for the application of automated morphological classification of galaxies; however, there has not yet been a clear comparison of these different methods using imaging data, or an investigation for maximizing their effectiveness. We carry out a comparison between several common machine learning methods for galaxy classification [Convolutional Neural Network (CNN), K-nearest neighbour, logistic regression, Support Vector Machine, Random Forest, and Neural Networks] by using Dark Energy Survey (DES) data combined with visual classifications from the Galaxy Zoo 1 project (GZ1). Our goal is to determine the optimal machine learning methods when using imaging data for galaxy classification. We show that CNN is the most successful method of these ten methods in our study. Using a sample of 2800 galaxies with visual classification from GZ1, we reach an accuracy of 0.99 for the morphological classification of ellipticals and spirals. The further investigation of the galaxies that have a different ML and visual classification but with high predicted probabilities in our CNN usually reveals the incorrect classification provided by GZ1. We further find the galaxies having a low probability of being either spirals or ellipticals are visually lenticulars (S0), demonstrating that supervised learning is able to rediscover that this class of galaxy is distinct from both ellipticals and spirals. We confirm that 2.5 per cent galaxies are misclassified by GZ1 in our study. After correcting these galaxies’ labels, we improve our CNN performance to an average accuracy of over 0.99 (accuracy of 0.994 is our best result).

    112. Palmese, A., Annis, J., Burgad, J., et al., 2020, MNRAS, 493, 4591, Stellar mass as a galaxy cluster mass proxy: application to the Dark Energy Survey redMaPPer clusters

      We introduce a galaxy cluster mass observable, , based on the stellar masses of cluster members, and we present results for the Dark Energy Survey (DES) Year 1 (Y1) observations. Stellar masses are computed using a Bayesian model averaging method, and are validated for DES data using simulations and COSMOS data. We show that works as a promising mass proxy by comparing our predictions to X-ray measurements. We measure the X-ray temperature- relation for a total of 129 clusters matched between the wide-field DES Y1 redMaPPer catalogue and Chandra and XMM archival observations, spanning the redshift range 0.1 < $z$ < 0.7. For a scaling relation that is linear in logarithmic space, we find a slope of = 0.488 0.043 and a scatter in the X-ray temperature at fixed of $\sigma _{{\rm ln} T_\mathrm{ X}|\mu _\star }= 0.266^{+0.019}_{-0.020}$ for the joint sample. By using the halo mass scaling relations of the X-ray temperature from the Weighing the Giants program, we further derive the -conditioned scatter in mass, finding $\sigma _{{\rm ln} M|\mu _\star }= 0.26^{+ 0.15}_{- 0.10}$ . These results are competitive with well-established cluster mass proxies used for cosmological analyses, showing that can be used as a reliable and physically motivated mass proxy to derive cosmological constraints.

    113. Mawdsley, B., Bacon, D., Chang, C., et al., 2020, MNRAS, 493, 5662, Dark Energy Survey Year 1 Results: Wide-field mass maps via forward fitting in harmonic space

      We present new wide-field weak lensing mass maps for the Year 1 Dark Energy Survey (DES) data, generated via a forward fitting approach. This method of producing maps does not impose any prior constraints on the mass distribution to be reconstructed. The technique is found to improve the map reconstruction on the edges of the field compared to the conventional Kaiser-Squires method, which applies a direct inversion on the data; our approach is in good agreement with the previous direct approach in the central regions of the footprint. The mapping technique is assessed and verified with tests on simulations; together with the Kaiser-Squires method, the technique is then applied to data from the DES Year 1 data and the differences between the two methods are compared. We also produce the first DES measurements of the convergence Minkowski functionals and compare them to those measured in simulations.

    114. Yang, Qian, Shen, Yue, Chen, Yu-Ching, et al., 2020, MNRAS, 493, 5773, Spectral variability of a sample of extreme variability quasars and implications for the Mg II broad-line region

      We present new Gemini/GMOS optical spectroscopy of 16 extreme variability quasars (EVQs) that dimmed by more than 1.5 mag in the g band between the Sloan Digital Sky Survey (SDSS) and the Dark Energy Survey epochs (separated by a few years in the quasar rest frame). These EVQs are selected from quasars in the SDSS Stripe 82 region, covering a redshift range of 0.5 < z < 2.1. Nearly half of these EVQs brightened significantly (by more than 0.5 mag in the g band) in a few years after reaching their previous faintest state, and some EVQs showed rapid (non-blazar) variations of greater than 1-2 mag on time-scales of only months. To increase sample statistics, we use a supplemental sample of 33 EVQs with multi-epoch spectra from SDSS that cover the broad Mg II 2798 line. Leveraging on the large dynamic range in continuum variability between the multi-epoch spectra, we explore the associated variations in the broad Mg II line, whose variability properties have not been well studied before. The broad Mg II flux varies in the same direction as the continuum flux, albeit with a smaller amplitude, which indicates at least some portion of Mg II is reverberating to continuum changes. However, the full width at half-maximum (FWHM) of Mg II does not vary accordingly as continuum changes for most objects in the sample, in contrast to the case of the broad Balmer lines. Using the width of broad Mg II to estimate the black hole mass with single epoch spectra therefore introduces a luminosity-dependent bias.

    115. Levesque, Emily M., Massey, Philip, 2020, ApJL, 891, L37, Betelgeuse Just Is Not That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse

      We present optical spectrophotometry of the red supergiant (RSG) Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way RSGs, we conclude that Betelgeuse has a current effective temperature of 3600 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse’s recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse’s recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution.

    116. Cartwright, Richard J., Emery, Joshua P., Grundy, William M., et al., 2020, Icar, 338, 113513, Probing the regoliths of the classical Uranian satellites: Are their surfaces mantled by a layer of tiny H2O ice grains?

      We investigate whether the surfaces of the classical moons of Uranus are compositionally stratified, with a thin veneer of mostly tiny H2O ice grains (2 m diameters) mantling a lower layer composed of larger grains of H2O ice, dark material, and CO2 ice (~10-50 m diameters). Near-infrared observations (~1-2.5 m) have determined that the H2O ice-rich surfaces of these moons are overprinted by concentrated deposits of CO2 ice, found almost exclusively on their trailing hemispheres. However, best fit spectral models of longer wavelength datasets (~3-5 m) indicate that the spectral signature of CO2 ice is largely absent, and instead, the exposed surfaces of these moons are composed primarily of tiny H2O ice grains. To investigate possible compositional layering of these moons, we have collected new data using the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (~3-5 m). Spectral modeling of these new data is consistent with prior analyses, suggesting that the exposed surfaces of the Uranian moons are primarily composed of tiny H2O ice grains. Furthermore, analysis of these new data reveal that the trailing hemispheres of these moons are brighter than their leading hemispheres over the 3 to 5 m wavelength range, except for Miranda, which displays no hemispherical asymmetries in its IRAC albedos. Our analyses also reveal that the surface of Ariel displays five distinct, regional-scale albedo zones, possibly consistent with the spatial distribution of CO2 ice on this moon. We discuss possible processes that could be enhancing the observed leading/trailing albedo asymmetries exhibited by these moons, as well as processes that could be driving the apparent compositional stratification of their near surfaces.

    117. Bourrier, V., Wheatley, P. J., Lecavelier des Etangs, A., et al., 2020, MNRAS, 493, 559, MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b

      In this third paper of the MOVES (Multiwavelength Observations of an eVaporating Exoplanet and its Star) programme, we combine Hubble Space Telescope far-ultraviolet (FUV) observations with XMM-Newton/Swift X-ray observations to measure the emission of HD 189733 in various FUV lines, and its soft X-ray spectrum. Based on these measurements we characterize the interstellar medium towards HD 189733 and derive semisynthetic XUV spectra of the star, which are used to study the evolution of its high-energy emission at five different epochs. Two flares from HD 189733 are observed, but we propose that the long-term variations in its spectral energy distribution have the most important consequences for the environment of HD 189733b. Reduced coronal and wind activity could favour the formation of a dense population of Si2+ atoms in a bow-shock ahead of the planet, responsible for pre- and in-transit absorption measured in the first two epochs. In-transit absorption signatures are detected in the Lyman line in the second, third, and fifth epochs, which could arise from the extended planetary thermosphere and a tail of stellar wind protons neutralized via charge-exchange with the planetary exosphere. We propose that increases in the X-ray irradiation of the planet, and decreases in its EUV irradiation causing lower photoionization rates of neutral hydrogen, favour the detection of these signatures by sustaining larger densities of H0 atoms in the upper atmosphere and boosting charge-exchanges with the stellar wind. Deeper and broader absorption signatures in the last epoch suggest that the planet entered a different evaporation regime, providing clues as to the link between stellar activity and the structure of the planetary environment.

    118. Schmidt, Carl A., Baumgardner, Jeffrey, Moore, Luke, et al., 2020, PSJ, 1, 4, The Rapid Imaging Planetary Spectrograph: Observations of Mercury’s Sodium Exosphere in Twilight

      Ground-based observations of Mercury’s exosphere are intrinsically difficult due to its proximity to the Sun and must be made in daylight or during brief windows at twilight. While the dimmer twilight background is far preferred, high airmass seeing and haze through Earth’s atmosphere, windshake, and guiding all present formidable challenges toward spatially resolving the exosphere’s structure. This study explores how such effects can be mitigated using results from a new instrument for high cadence spectroscopy, the Rapid Imaging Planetary Spectrograph. While high cadence observations do not significantly improve upon the resolution floor imposed by atmospheric seeing, the method does mitigate obstacles such as telescope tracking inaccuracy, windshake, and flux calibration. Whereas daytime observing has been the predominant methodology in past exosphere studies, the twilight observations performed here easily resolve distinct brightness enhancements near 50-60 latitude, just equatorward of magnetic cusp regions. The exosphere in these locations is diagnostic of space weather effects such as charged particle precipitation. The structure in the sodium exosphere generally appears both more extended and brighter over the southern cusp, which has a broader open magnetic field line region. However, a northern enhancement during one observation confirms that the exosphere responds dynamically to environmental drivers, presumably changes in the solar wind dynamic pressure and/or interplanetary magnetic field.

    119. Mau, S., Cerny, W., Pace, A. B., et al., 2020, ApJ, 890, 136, Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey

      We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={2.3}_{-0.3}^{+0.4}\,\mathrm{arcmin}$ , an age of $\tau \gt 12.85\,\mathrm{Gyr}$ , a metallicity of $Z={0.0002}_{-0.0002}^{+0.0001}$ , and an absolute magnitude of ${M}_{V}=-{5.55}_{-0.11}^{+0.11}\,\mathrm{mag}$ . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\text{}}{D}_{\odot }={19.0}_{-0.6}^{+0.5}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={0.97}_{-0.17}^{+0.24}\,\mathrm{arcmin}$ , an age of $\tau ={12.5}_{-0.7}^{+1.0}\,\mathrm{Gyr}$ , a metallicity of $Z={0.0005}_{-0.0001}^{+0.0002}$ , and an absolute magnitude of ${M}_{V}=-{0.2}_{-0.6}^{+0.8}\,\mathrm{mag}$ , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

    120. Golombek, M., Warner, N. H., Grant, J. A., et al., 2020, NatCo, 11, 1014, Geology of the InSight landing site on Mars

      The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) spacecraft landed successfully on Mars and imaged the surface to characterize the surficial geology. Here we report on the geology and subsurface structure of the landing site to aid in situ geophysical investigations. InSight landed in a degraded impact crater in Elysium Planitia on a smooth sandy, granule- and pebble-rich surface with few rocks. Superposed impact craters are common and eolian bedforms are sparse. During landing, pulsed retrorockets modified the surface to reveal a near surface stratigraphy of surficial dust, over thin unconsolidated sand, underlain by a variable thickness duricrust, with poorly sorted, unconsolidated sand with rocks beneath. Impact, eolian, and mass wasting processes have dominantly modified the surface. Surface observations are consistent with expectations made from remote sensing data prior to landing indicating a surface composed of an impact-fragmented regolith overlying basaltic lava flows.

    121. Jenniskens, Peter, Lyytinen, Esko, Johannink, Carl, et al., 2020, P&SS, 181, 104829, 2019 outburst of 15-Bootids (IAU#923, FBO) and search strategy to find the potentially hazardous comet

      The CAMS BeNeLux and UAE Astronomical Camera Network meteor shower surveys detected a FWHM = 1.8-h wide outburst of 15-Bootids on April 21/22, 2019. Both networks had clear skies throughout the night, but only between 21h28m and 00h13m UTC were meteors from this shower detected. The measured orbit is that of a Halley-type or Long-Period comet. If the shower is an encounter with the 1-revolution dust trail of a Long-Period comet, then that parent comet is a potential impact hazard. The long duration of the outburst suggests comparatively high ejection speeds from, presumably, a large nucleus. The orbit offers guidance for early comet recovery and a search strategy is described. The orbital elements resemble those of bright comet C/539 W1, which may be the parent comet.

    122. Grundy, W. M., Bird, M. K., Britt, D. T., et al., 2020, Sci, 367, aay3705, Color, composition, and thermal environment of Kuiper Belt object (486958) Arrokoth

      The outer Solar System object (486958) Arrokoth (provisional designation 2014 MU69) has been largely undisturbed since its formation. We studied its surface composition using data collected by the New Horizons spacecraft. Methanol ice is present along with organic material, which may have formed through irradiation of simple molecules. Water ice was not detected. This composition indicates hydrogenation of carbon monoxide-rich ice and/or energetic processing of methane condensed on water ice grains in the cold, outer edge of the early Solar System. There are only small regional variations in color and spectra across the surface, which suggests that Arrokoth formed from a homogeneous or well-mixed reservoir of solids. Microwave thermal emission from the winter night side is consistent with a mean brightness temperature of 29 5 kelvin.

    123. Spencer, J. R., Stern, S. A., Moore, J. M., et al., 2020, Sci, 367, aay3999, The geology and geophysics of Kuiper Belt object (486958) Arrokoth

      The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU69). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

    124. McKinnon, W. B., Richardson, D. C., Marohnic, J. C., et al., 2020, Sci, 367, aay6620, The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt

      The New Horizons spacecrafts encounter with the cold classical Kuiper Belt object (486958) Arrokoth (provisional designation 2014 MU69) revealed a contact-binary planetesimal. We investigated how Arrokoth formed and found that it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing cloud of solid particles. The geometric alignment of the lobes indicates that they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly because of dynamical friction and collisions within the cloud or later gas drag. Arrokoths contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper Belt and therefore informs the accretion processes that operated in the early Solar System.

    125. Ramiaramanantsoa, T., Shkolnik, E. L., Ardila, D. R., et al., 2020, AAS, 235, 132.05, M dwarf activity and flaring in the ultraviolet domain with the Star-Planet Activity Research CubeSat (SPARCS)

      With the increasing number of exoplanets discovered in the habitable zones of M dwarfs, the necessity for tighter constraints on the conditions for habitability around cool low-mass stars is rapidly growing. Theoretical studies suggest that the strong and highly variable ultraviolet (UV) radiation of M dwarfs is a key factor influencing the habitability and atmospheric loss of their planets. However, those studies lack sufficient observational constraints. The Star-Planet Activity Research CubeSat (SPARCS) is a NASA-funded mission intended to be inserted into a low-Earth, Sun-synchronous orbit, and will perform photometric monitoring of the chromospheric activity of M stars of various ages, both at far-UV and the near-UV wavelengths. The SPARCS science instrument is composed of a 9-cm Ritchey-Chretien telescope, at the focal plane of which lie two back-illuminated, delta-doped CCDs with high quantum efficiency in UV domain. An active thermal control system will maintain the temperatures of the detectors at -35C to minimize dark-current effects. The detectors’ thermal control will be commanded through a dedicated payload processor, which will also perform onboard image processing and trigger changes in detector gain and exposure time upon flare detection. The mission is currently in its development phase, with finalized designs for the telescope, camera, instrument optical bench and thermal system. Besides its science goals, SPARCS will also serve as a technology demonstration by paving the way for the use of high-sensitivity UV-optimized detectors in missions like LUVOIR or HabEx. Acknowledgements: Funding for SPARCS is provided by NASA’s Astrophysics Research and Analysis program, NNH16ZDA001N.

    126. Osby, E., Ardila, D., Barman, T., et al., 2020, AAS, 235, 150.08, Photometric Color Correction of the Star Planet Activity Research CubeSat (SPARCS)

      The Star Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-ultraviolet (UV) and near-UV (160 and 280 nm respectively), measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. The delta-doped detectors baselined for SPARCS have demonstrated more than five times the in-band quantum efficiency of the detectors of GALEX. Given that red:UV photon emission from cool, low-mass stars can be ~million:one, UV observation of such stars are susceptible to red light contamination. In addition to the high efficiency delta-doped detectors, SPARCS will include red-rejection filters to help minimize red leak. Even so, careful red-rejection and photometric calibration is needed. As was done for GALEX, white dwarfs are used for photometric calibration in the UV. We find that the use of white dwarfs to calibrate the observations of red stars leads to significant errors in the reported flux, due to the differences in white dwarf and red dwarf spectra. Here we discuss the planned SPARCS calibration model and the color correction, and demonstrate the importance of this correction when recording UV measurements of M stars taken by SPARCS. Funding for SPARCS is provided by NASA’s Astrophysics Research and Analysis program, NNH16ZDA001N.

    127. Kuehn, K., S5 Collaboration, 2020, AAS, 235, 156.05, Highlights from the Southern Stellar Stream Spectroscopic Survey

      Stellar streams, produced by the tidal disruption of dwarf galaxies and globular clusters, yield a snapshot of hierarchical structure formation, and are powerful probes of the mass and profile of the Milky Way’s dark matter halo, as well as the formation of its stellar halo. Over the last several years, large imaging surveys have increased the number of known stellar streams to over 60. Spectroscopic follow-up observations are crucial, not only for confirming the nature of the streams, but also for determining their full 6D kinematics, metallicities, orbits, progenitors, and formation histories. The Southern Stellar Stream Spectroscopic Survey (S5) began observing the streams recently discovered by the Dark Energy Survey in 2018, and expanded beyond the DES footprint in 2019. S5 employs the large FoV of AAT and high multiplex of 2dF+AAOmega to obtain kinematic measurements along the spatial extent of the tidal streams. We highlight the most important results from our first observational campaigns, including confirmation of at least seven streams using velocities and metallicities of the members stars. We also report on the serendipitous discovery one of the highest velocity stars in the galaxy, S5-HVS1. This star provides the first direct proof of the Hills Mechanism, in which one star in a binary pair is captured by a supermassive black hole (in this case, Sagittarius A*), while its companion is ejected at extremely high speed.

    128. Kuehn, K., Schindler, K., 2020, AAS, 235, 181.01, The Telescopes of Lowell Observatory: the First 125 Years

      From its founding by Percival Lowell 125 years ago, Lowell Observatory has maintained an impressive suite of scientifically productive telescopes. While Lowell’s original site (and telescopes) on Mars Hill in Flagstaff, AZ, is now primarily used for public education, outreach, and historical preservation, the Observatory has over its lifetime expanded to multiple additional sites, including Anderson Mesa, which houses 31″ and 42″ telescopes as well as the Navy Precision Optical Interferometer, and Happy Jack, which hosts the 4.3m Discovery Channel Telescope, one of the newest and most advanced 4m-class telescopes on the planet. We describe the evolution of Lowell Observatory’s telescopes and accompanying instrumentation, from its beginnings to the present day, and highlight the most impactful discoveries made by the Observatory’s astronomers.

    129. Prato, L., Schindler, K., 2020, AAS, 235, 181.02, Highlights from 125 Years of Lowell Observatory Science: Vera Rubin and the Identification of Dark Matter

      Vera Rubin’s identification of dark matter in the Andromeda galaxy using Lowell Observatory’s Perkins 72-inch and the KPNO 84-inch telescopes with Kent Ford’s image-tube spectrograph represented the culmination and intersection of scientific, technological, collaborative, and managerial interests that spanned the continental United States in the late 1950s and 1960s. Highly sensitive spectroscopic observations were required to detect the redshifts of M31’s HII regions, particularly in the outer more tenuous reaches of the great spiral, and adequately generous allocations of telescope time were needed to map out these motions across the whole spatial extent of Andromeda. Because of the constructive spirit of cooperation between scientific and technical staff at Lowell Observatory, Carnegie DTM, Ohio State, USNO, KPNO, Carnegie Pasadena, and other institutions and players, in 1967, driven by an interest in galactic dynamics and the availability of the image-tube spectrograph, Rubin and Ford began a three-year project, dismissed by some colleagues as not worth doing and as overly time-consuming, which ultimately revealed evidence for Fritz Zwicky’s conjecture that a significant fraction of gravitationally active matter is not luminous. Rubin pioneered work on some of the most fundamental problems in astrophysics and was an inspiration and supporter to scientists, faculty, and staff at universities and observatories around the world. She made rich contributions to the science and culture at Lowell Observatory where she served on the Board of Advisors for many years and was a colleague and role model to many.

    130. Schindler, K., 2020, AAS, 235, 181.03, The 1894 Lowell Expedition and the Origins of Northern Arizona as Center for Scientific Research

      In 1894, Percival Lowell became fascinated with the possibility of life on Mars and planned to build his own astronomical research facility to carry out studies. He chose Arizona Territory (Arizona didn’t achieve statehood until 1912) as site for his observatory and organized an expedition there in order to find an ideal location. He wanted a place removed from eastern U.S. cities, where factory smoke and electric lights blotted out stars and planets. A dry climate and high elevation were also ideal, all characteristics of certain areas in the American Southwest. Lowell himself would not join the expedition. Instead, he hired young astronomer Andrew Douglass to carry out the work. Traveling alone, Douglass performed seeing tests in several locations around the Territory. Based on these observations, Lowell chose Flagstaff as site for his observatory. In looking back at the expedition, Lowell clearly deemed the atmospheric conditions in Flagstaff sufficient for building the observatory there. However, a combination of other factors ensured Flagstaff as the site. Extraordinary community support and politicking by residents certainly helped. Perhaps even a greater factor had to do with timing. Lowell wanted the observatory to be established as quickly as possible. By the time Douglass arrived in Flagstaff, he had been site testing for a month longer than Lowell originally anticipated. The atmospheric conditions in Flagstaff were good, community support was strong, and transportation was adequate, so Lowell, anxious to have telescopes ready for an upcoming Mars opposition, chose Flagstaff. Had Douglass at the time been in another of the locations where conditions were favorable, such as Tombstone, the Observatory quite possibly would have been built there. In any event, Lowell chose Flagstaff and Lowell Observatory became the first permanent scientific institution in Flagstaff. It helped establish the community as a center for scientific research, laying the groundwork for other research facilities in the area such as the Museum of Northern Arizona (1928), U.S. Naval Observatory’s Flagstaff Station (1955), U.S. Geological Survey’s Astrogeology Branch (1963) and others.

    131. van Belle, G. T., 2020, AAS, 235, 181.05, Interferometry and the Development of NPOI

      Lowell Observatory is a partner in the The Navy Precision Optical Interferometer (NPOI) facility, a long-baseline optical interferometer (LBOI) located at Lowell’s Anderson Mesa site near Flagstaff, AZ. NPOI is a modern realization of LBOI efforts, which began in 1919 with the 20-foot beam interferometer that Michelson and Pease bolted to the 100-inch Hooker Telescope. The ensuing colorful century of LBOI, replete with trials and tribulations, visionary and eccentric leaders, and most of all, scientific achievements, is reviewed with an eye towards the promising future of the technique.

    132. Hall, J., 2020, AAS, 235, 181.06, Flagstaff’s Dark Sky Heritage

      Flagstaff, Arizona has a 60-year tradition of dark sky preservation, beginning with a 1958 ordinance to ban advertising searchlights. The current ordinance, enacted in 1989, is the most comprehensive in the world; it specifies not only shielding and maximum illumination requirements, but strict control of the emission spectrum via use of low pressure sodium (LPS) lamps. As of the end of May 2019, LPS lamps have been discontinued by lighting manufacturers, so Flagstaff, like many cities worldwide, will be switching its outdoor street lighting system to LEDs. We have spent several years working with City staff to develop what will again be world-leading standards in outdoor illumination, making extensive use of narrow band amber (NBA) and phosphor-converted amber (PCA) LEDs rather than white LEDs. We have already installed NBA and PCA test fixtures in several areas around town, and retrofit of all 3,700 fixtures in Flagstaff should occur in the next 2-5 years. These standards will set the precedent for other applications such as commercial properties and parking lots (pictured below). In this iPoster, I will review the history of dark sky preservation in Flagstaff, the current state of affairs in outdoor lighting, the types of LEDs available, their impact on the night sky, and how Flagstaff will preserve its exceptionally dark sky in the LED era.

    133. Leger, V. E., Massey, P., Morell, N., et al., 2020, AAS, 235, 204.09, Massive Star Content of OB association Lucke-Hodge 41 (NGC 1910) in the Large Magellanic Cloud

      The Large Magellanic Cloud’s (LMC) rich OB association LH41 (NGC 1910) is home to an abundance of O and B type stars, as well S Doradus, the prototypic Luminous Blue Variable, a surprising number of Wolf-Rayet stars, and interesting evolved supergiants. LH41 is the second most active star forming region in the LMC after the famous 30 Doradus, and like its big cousin, is a hotbed for young, massive stars. We have studied this association with HST UV imaging, B- and V-band ground-based photometry, and Magellan 6.5-m optical spectroscopy to determine the massive star content and age of the association. Spectroscopy and modeling using FASTWIND yielded spectral types and effective temperatures for select O and B stars in LH41. This allowed us to apply bolometric corrections to our photometric data and get luminosities and temperatures of the remaining LH41 stars. We eliminated foreground stars using astrometric data from GAIA DR2. The resulting HR Diagram shows a large age spread of O and B type stars, as well as a significant number of evolved supergiants, indicating that LH41 is not strictly coeval. Our findings challenge the current understanding of OB associations as temporary collections of young, hot stars. This work was supported by the National Science Foundation (AST-1852478 and AST-1612874), and by NASA/Space Telescope Science Institute (GO-14707, GO-12940).

    134. Tafla, L., Hunter, D., Elmegreen, B. G., et al., 2020, AAS, 235, 213.02, Molecular Cloud Structure at Low Metallicity

      Detecting and mapping molecular cloud tracers in gas-rich, low metallicity dwarf irregular galaxies is relevant for the study of star formation in the early universe when metallicities were low. Because of the lower in metallicity it is expected the (giant) molecular clouds to have thicker shells of predominantly H2 and tinier CO cores than GMCs in the Milky Way because there is a commensurate lower abundance of dust to absorb UV light. We identified 47 CO-cores in the Wolf-Lundmark-Melotte (WLM) galaxy from ALMA radio interferometer data using the automated cloud-finding algorithm CLOUDPROPS. We present a study of the CO clouds found in WLM and a review of three other nearby dwarf galaxies with lower abundances than WLM and discuss the upper limits found there. We plotted the CO-cores on FUV and FIR images of WLM to analyze the correlation between CO clouds, HI, and young star clumps in this galaxy. A comparison of the intensity-velocity spectrum of CO-cores and HI is presented. We discuss the relationship between the CO-cores, molecular H2, and young stars. L.T. acknowledges grant AST-1461200 from the National Science Foundation to Northern Arizona University to fund the 2019 REU program and as well as support from the 2019 CAMPARE Scholar program.

    135. Robbins, S. J., Lisse, C., Singer, K., et al., 2020, AAS, 235, 220.04, Comets Sourced by KBOs: Comparison of Cometary Size-Frequency Distributions with Outer Solar System Craters

      The outer solar system is thought to be populated by millions of Kuiper Belt Objects (KBOs) ranging in size from the dwarf planets Pluto and Eris (~1000 km radius) down to objects as small as cometary nuclei (~1 km). Today’s Jupiter-family comets (JFCs) are likely birthed from scattered KBOs that were once in the trans-Neptunian region. One method to probe the evolution of these bodies is through examination of their size-frequency distribution (SFD), for cometary activity drives changes to the nuclei (e.g., sublimative mass loss and fragmentation) on timescales short compared to dynamical lifetimes. There have been many recent attempts to measure the JFC SFD based on telescopic surveys. Most attempts have derived sizes using optical photometry of sunlight scattered by the nucleus and an assumed albedo, but newer work using Spitzer & WISE infrared photometry can directly measure sizes as thermal emissivities vary little. The IR studies demonstrate cometary SFDs are different from inner solar system asteroid and crater SFDs: Asteroid SFDs follow a reasonably constant power-law at diameters from ~10 km to at least ~10 m. By contrast, the JFC SFD appears to have an inflection point to a shallower SFD slope starting ~1-4 km. However, debiasing these surveys based on observational limitations is difficult, and past authors have tended to propose ad hoc mechanisms for removing small nuclei to reconcile the SFDs. A significant finding from New Horizons mission imagery was that Pluto and Charon impact crater SFDs also have an inflection point to shallower slopes at 10 km ( = ~1 km impactor radius). The result is unambiguous on airless Charon. This is in contrast with previous crater population studies of outer solar system moons which showed a potential small object deficit, but with potential observational biases. Preliminary results of possible impact craters on 2014 MU69 similarly can be interpreted to support a shallower small-object slope. In this work, we present a synthesis: Comparing JFC sizes with crater populations. Taken together, they present strong evidence that there truly is an inflection point in the source KBO population, which has important implications for the evolution of these objects.

    136. Adams, D., 2020, AAS, 235, 221.06, Integrating Cultural Astronomy into Public Outreach Programs

      The modern night sky showcases the remains of cultural interactions that span millennia. Greco-Mesopotamian sky pictures are called by Latin constellation names, but their brightest stars are designated with the letters of the Greek alphabet. Some of these stars also have Greek or Roman proper names, but modern astronomers call most by names derived from Arabic. Of these Arabic star names, some describe Greek astronomy, while others describe indigenous Arabian astronomy. Despite this cultural messiness in the night sky, astronomy outreach programs continue to focus on Greek mythology and a decidedly Western view of the night sky. Taking indigenous (non-Greek) Arabian astronomy as a frame of reference, this presentation offers an alternative to the traditional Greek cultural stories that also addresses core astronomical concepts like precession and proper motion. Other indigenous traditions from outside of Arabia can also be used to similar effect. The application of non-Western astronomical traditions to astronomy outreach programs presents something new to observatory guests that inspires awe and activates curiosity.

    137. Clark, C., van Belle, G., Horch, E., et al., 2020, AAS, 235, 256.06, The POKEMON Speckle Survey of Nearby M-dwarfs

      We present results from the POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey, the most exhaustive stellar multiplicity survey every produced of the objects that comprise over 70% of the stars in our galaxy: the M-dwarfs. We have conducted a volume-limited survey through M9 that inspected, at diffraction-limited resolution, every M-dwarf out to 15pc, with additional brighter targets to 25pc. POKEMON utilized Lowell Observatory’s 4.3-m Discovery Channel Telescope with the Differential Speckle Survey Instrument (DSSI @ DCT), along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) on the 3.5-m WIYN telescope, to directly image low-mass companions to these M-dwarfs. Given the priority these targets have for exoplanet studies with TESS, and in the future JWST – and the degree to which initially undetected multiplicity has skewed Kepler results – a comprehensive survey of our nearby low-mass neighbors provides a homogeneous, complete catalog of fundamental utility. Prior knowledge of secondary objects – or robust non-detections, as captured by this survey – immediately clarify the nature of exoplanet transit detections from these current and upcoming missions. We report the discovery of 20+ new companions and identify candidate multi-star systems. We establish the most up-to-date M-dwarf multiplicity rate, and obtain sufficient statistics to determine, for the first time, M-dwarf multiplicity as a function of subtype.

    138. Hartman, Z., Lepine, S., Clark, C., et al., 2020, AAS, 235, 265.03, The Tale of the Lobster: Over-luminous Stars in Wide Binaries and a Search for Higher Order Multiples

      We present a search for higher-order multiples (triples, quadruples, etc.) among K+K and K+M wide binaries identified in the SUPERWIDE all-sky catalog of wide binaries. The SUPERWIDE catalog was assembled from a Bayesian analysis of the high proper motion (> 40 mas/yr) stars in Gaia Data Release 2 (DR2) using their positions, proper motions, and parallaxes. Examining the color-magnitude diagram of the primary and secondary components clearly shows a doubling of the main sequence in the K and early-M dwarf regime, consistent with a normal single star main sequence plus an over-luminous sequence due to some of the components being unresolved binaries. To better identify the over-luminous stars in our wide binaries, we define an over-luminosity factor, which measures the difference between the absolute magnitude of a star and a reference line which runs parallel to the main sequence in the K dwarf region. A “lobster” diagram is then created, which plots the over-luminosity factor of the primary as a function of the over-luminosity factor of the secondary. An examination of this plot reveals that for K+K wide binaries, the higher order multiplicity of the selected sample is at least ~40%. We expand this technique to the lower mass regime (mid-M to late-M) by matching subsets of K+M pairs to the apogee catalog, and by assuming the metallicity of the low-mass secondaries is the same as that of the higher mass primaries. Using the resulting metallicity “tracks”, we determine the shape of the main sequence in the M dwarf regime, which allows us to define a proper reference and identify over-luminous components in the M dwarf range as well. To test if our over-luminous components are caused by binarity rather than other potential sources, we crossmatch our sample with TESS, K2 and Kepler to identify eclipsing systems among the over-luminous components and take speckle imaging results from previous observations and the POKEMON survey.

    139. Huls, C., Prato, L., Wasserman, L., et al., 2020, AAS, 235, 272.05, Orbital Parameters for a Young, Low Mass, Spectroscopic Binary Star in Orion

      We present orbital parameters for the young, low-mass, pre-main sequence, double-lined spectroscopic binary, V562 Ori. To measure radial velocities for each of the components in the binary system, we use high-resolution infrared spectra acquired by IGRINS at the Lowell Observatory 4.3m Discovery Channel Telescope. We use a two-dimensional cross-correlation technique, TODCOR, to correlate our observed spectra against standard star templates. The results from this analysis provide radial velocities, spectral types, vsini values, and flux ratios for both components in the binary system. For V562 Ori, the spectral templates that maximized the cross-correlation coefficient were K5 for the primary and K6 for the secondary, with vsini values of 12 km/s and 10 km/s, respectively. By combining the radial velocities from our infrared observations, we are able to determine the orbital parameters and mass ratio for this system. For V562 Ori, we find an orbital period of P = 11.861 0.002 days, and eccentricity of e = 0.075 0.017, a mass ratio of q = 1.008 0.039, and a center-of-mass velocity of 29.24 0.61 km/s. The results shown here not only increase the small sample of PMS spectroscopic binary stars with known orbital elements, but also describes the effectiveness of infrared spectroscopy for the detection of cool secondary stars. We will compare the results obtained with both observed and synthetic template standard star spectra. This research was funded in part by NSF grant AST-1518081 (to L.P.).

    140. Alvarez, C., Kassis, M., Campbell, R., et al., 2020, AAS, 235, 275.11, Keck/MOSFIRE Imaging and Spectroscopy of the Embedded Star Cluster G018.303-0.392

      Embedded Clusters (ECs) are stellar clusters buried in interstellar gas and dust within molecular clouds. Their members are very young forming stars. These stellar nurseries are fundamental to understanding the early stages of star formation. Dynamical interactions between cluster members in these dense environments can lead to the disruption of circumstellar disks and their planetary progeny (Adams and Myers 2001). The application of data mining techniques on large ground-based Galactic IR surveys such as the UKIDSS Galactic Plane Survey (GPS) and the VISTA Variables in the Via Lactea (VVV) survey, and space-based surveys such as the WISE multi-band Atlas, has recently led to the discovery of hundreds of previously unknown embedded-cluster candidates (Solin et al. 2012 and 2014, Camargo et al. 2015 and 2016). Due to the large column densities of interstellar material in these clusters, deep infrared imaging and spectroscopy are ideal to characterize their stellar population. We present Keck/MOSFIRE JHK imaging and K-band multi-object spectroscopy of the region centered on the EC G018.303-0.392, which was included in the list of cluster candidates by Solin et al. (2012). The photometry is used to create color-color and color-magnitude diagrams of the region, which help spotting the reddest sources. K-band spectra show a wide variety to features, including Brackett gamma in absorption and emission, continuum reddening and CO absorption bands. These data will be used to asses the cluster membership of each individual source and to constrain the general properties of the cluster such as distance and age.

    141. Harvison, B., Thomas, C., Hyden, J., et al., 2020, AAS, 235, 277.06, Spectral Analysis of the Agnia Asteroid Family

      Asteroids are considered the remnants of the early solar system and are prime targets of investigation since they can teach us about the history of the solar system and the evolution of the asteroids themselves since their creation. Asteroid families are of particular interest because these groups of objects with similar orbital elements were once part of a larger body that has since been disrupted. Sunshine et al. (2004) used spectral modeling to identify products of partial differentiation in members of the Agnia asteroid family. The study concluded that the Agnia family objects analyzed were most similar to primitive achondrite meteorites. We performed a visible and near-infrared wavelength spectral survey of Agnia family members to enable a follow-up investigation. Our analysis of spectral parameters is based off of the band parameter analyses of Gaffey et al. (1993) and Lucas et al. (2019). Two of the spectral parameters used were the Band 1 and Band 2 centers (B1C and B2C, respectively), the local minimums of the characteristic 1 and 2 micron absorption features with the continuum removed that are indicative of the composition of olivine and pyroxene. The third band parameter, Band Area Ratio (BAR), was the ratio of the area of the 2 micron band to the 1 micron band which is characteristic of the relative abundances of olivine and pyroxene. Gaffey et al. (1993) used the B1C and the BAR to identify compositional S-subtypes which they connected to specific meteorite analogs. Lucas et al. (2019) used the Band 1 and Band 2 Centers to further separate the spectrally similar H ordinary chondrites and acapulcoite-lodranite primitive achondrite meteorites. Further analysis using principal component values calculated by the Bus-DeMeo online classifier (DeMeo et al. 2009) for our asteroid spectra compared to the calculated values of H ordinary chondrites and primitive achondrites provided an additional approach to connecting asteroids and their meteorite analogs. Based on the combination of these analyses, we conclude that members of the Agnia family are most similar to H ordinary chondrites with the possibility that they are primitive achondrite-like.

    142. Hyden, J., Thomas, C., Harvison, B., et al., 2020, AAS, 235, 277.07, Spectral Analysis of the Massalia Asteroid Family

      Asteroid families are remnants of larger parent bodies that were broken apart in a past collisional event. Due to their common origin, asteroids within the same family tend to exhibit similar spectra to one another. We analyzed data from a visible and near-infrared wavelength spectral survey of Massalia family members to study the composition of the family. The Massalia family consists of S-type asteroids that show broad spectral absorption features at 1 and 2 microns. By analyzing these absorption features, we can determine the composition and most likely meteorite analog for the family. We examine these spectral features, by calculating the Band 1 Center, Band 2 Center, and Band Area Ratio (BAR). The Band Centers are the local minima of the bands after the continuum has been removed and the BAR is the ratio of the area of the 2 micron band to the area of the 1 micron band. The Band Centers are indicative of the mineralogy of the olivine and pyroxene of the asteroid. The BAR shows the relative abundance of olivine and pyroxene on the surface of the object. Gaffey et al. (1993) used Band 1 Center and BAR to identify distinct compositional S-subtypes which have been correlated to potential meteorite analogs. We use the Gaffey et al. regions to determine the best meteorite analog for each member of the Massalia family. We also use the Band 1 Center and Band 2 Center to further distinguish between the spectrally similar H ordinary chondrites and, the Acapulcoite and Lodranite primitive achondrites (Lucas et al. 2019). Through conducting this spectral analysis we conclude that the Massalia family asteroids are most similar to H ordinary chondrites.

    143. Holler, B., Grundy, W., Murray, K., et al., 2020, AAS, 235, 278.06, New Insights into the Eris/Dysnomia System

      The dwarf planet (136199) Eris is known to be the most massive Kuiper Belt Object (KBO) based on the orbit of its large satellite, Dysnomia. At first glance, this system appears to be similar to the Pluto/Charon binary, but there is still much to learn about Eris and Dysnomia. In order to further characterize this system, we used the WFC3 camera onboard the Hubble Space Telescope in early 2018 to observe Dysnomia at roughly evenly spaced intervals over one full orbit. From these data we (1) computed a new orbital fit for Dysnomia, (2) determined the current pole orientation of Eris and characterized its seasons in the present epoch, (3) evaluated the maximum albedo variations across Eris’ surface, (4) constructed a rotational light curve of Dysnomia for comparison to ground-based Palomar P60 data of Eris to determine the tidal state of the system, (5) searched for minor satellites, and (6) constrained the Dysnomia-to-Eris mass ratio. Future work will explore the seasonal cycle of Eris over Myr timescales.

    144. Prato, L., Lindstrom, K., Graham, S., et al., 2020, AAS, 235, 308.14, Young Binaries as Laboratories for Disk Evolution: Angularly Resolved Determinations of Stellar and Circumstellar Characteristics

      Detailed properties of the primordial planet-forming disks and of the stars in young multiple systems provide powerful inputs with which to explore the factors controlling the early stages of disk evolution. Because a large fraction, if not most, stars form in pairs, triples, or higher order configurations, characterizing the properties of these systems that dominate disk evolution is key to development of a broad understanding of planet formation. Using adaptive optics fed high-resolution infrared spectroscopy and imaging, we are studying the individual components in systems with separations of a few to a few hundred AU in a sample of 100+ pre-main sequence binaries in the nearby Taurus, Upper Scorpius / Ophiuchus, and TW Hya associations. We present initial results of this survey, including evidence for more rapid disk evolution in lower mass pairs and a paucity of cool primary stars in wide pairs. The advent of the K2 Taurus and Upper Sco / Oph campaigns, as well as the growing wealth of angularly resolved ALMA imaging of disks in these young systems, provide rich, complementary data sets with which to further interpret our results. Ultimately, our spectra and higher-level products of our analysis will be publicly available to the community at Support for this research was provided in part by NSF award AST-1313399 and by NASA Keck KPDA funding.

    145. Lopez-Valdivia, R., Sokal, K., Mace, G., et al., 2020, AAS, 235, 316.04, Stellar parameters of pre-main sequence stars in Taurus and Auriga

      Young Stellar Objects represent the first stages of stellar evolution, and their characterization tests the initial conditions of planetary evolution. Here we present the simultaneous determination of the effective temperature, surface gravity, magnetic field strength, projected rotational velocity and veiling for about one hundred K and M pre-main sequence stars located in the Taurus-Auriga star forming region. We have employed a Markov Chain Monte Carlo approach to fit synthetic models to high-resolution (R ~ 45,000) infrared spectra (1.45 to 2.45 microns), obtained with the Immersion GRating INfrared Spectrometer (IGRINS). The simultaneous approach is critical for disentangling the spectral effects of various parameters. We discuss preliminary results and how they compare with previous, singly-determined physical parameters. This research is made possible by funding from the National Science Foundation grant AST-1908892.

    146. van Belle, G. T., Moskovitz, N., Patane, S., et al., 2020, AAS, 235, 373.01, Science with Optimast-SCI: New Discovery Frontiers with Sensitive, Millarcsecond Resolution

      The Optimast-SCI (Structurally Connected Interferometry) mission is a NASA-funded SBIR study of the science possibilities enabled by a space-based optical interferometer mission. Optimast-SCI will provide ~2 milliarcsecond spatial resolution with a limiting magnitude of V<12 in a SmallSat package, which even at this small scale is sensitivity performance superior to any ground-based facility by 2-5 magnitudes. A number of scientific opportunities are enabled by this performance. Observation of asteroids can directly measure their sizes, and constrain their albedos; for binary asteroids, orbit mapping can establish masses, and thereby indicate their compositional and structural properties. Observations of young stellar objects will produce results similar to ALMA, but at superior spatial resolution – which corresponds to the terrestrial planet hot-dust regimes, complementary to the gas giant cold-dust regimes of ALMA. At extragalactic distances, Optimast-SCI will have sufficient sensitivity to probe the inner regions of AGNs, constraining the mechanisms that shape the narrow-line region and windy torus. Each one of these areas – and more – are bold new horizons for scientific discovery, from the extreme angular resolution of optical interferometry enabled by space-based sensitivity.

    147. Patane, S., Fagin, M., Riley, D., et al., 2020, AAS, 235, 373.02, Precision In-Space Manufacturing for Structurally-Connected Interferometry

      In-Space Robotic Manufacturing and Assembly (IRMA) enables novel space mission architectures that broaden the toolkit available to mission planners within the astrophysics community. Equipped with these tools, innovative mission architectures rooted in IRMA offer an alternative approach to achieving science requirements at the forefront of high-spatial resolution astrophysics. The Made In Space Optimast Structurally-Connected Interferometry (SCI) technology will produce a two-aperture system at Sun-Earth L2. Matured via extensive ground testing in a relevant, space-like thermal vacuum environment, Optimast-SCI enables the manufacturing and deployment of structural booms unconstrained by launch loads or volumetric limits of standard vehicle fairings. This foundational additive manufacturing process bypasses limitations of traditional deployable structures by enabling boom designs that reduce parasitic mass. Using its proven in-space additive manufacturing capabilities, the Optimast-SCI hardware drives the efficient packaging of a variable, 1-20 m baseline interferometer to achieve an effective angular resolution in the milliarcsecond regime.

    148. Earle, A. M., Olkin, C., Stern, S., et al., 2020, AAS, 235, 419.03, The Color of 2014 MU69

      On January 1, 2019 NASA’s New Horizons spacecraft flew close to the Kuiper Belt Object (486958) 2014 MU69 nicknamed “Ultima Thule” (herein MU69). MU69 is a bi-lobed contact binary with an unusual flattened shape. Based on its orbit, MU69 is considered a member of the Cold Classical Kuiper Belt population. This class of objects is thought to be more or less dynamically undisturbed bodies that formed in situ ~4.5 Gyr ago and have since remained at or close to their current, large heliocentric distances. Since MU69 appears to be well preserved, New Horizons’ observations of it serve as an opportunity to better understand planetesimal accretion and the earliest stages of planetary formation. In this talk we will focus on the color of MU69’s surface, its context as a member of the Kuiper Belt, and the implications its color has for formation scenarios. New Horizons found MU69 to be very red in color (which is consistent with pre-encounter Hubble Telescope observations). Both lobes show basically the same average color. However, subtle color variations exist across the body, for example the less red, higher albedo patches near the “neck” region where the lobes come together. We will explore how these variations correlate with the surface geology of MU69 as well as the insolation and “climate zone” boundaries. We will also consider MU69’s color in the broader context of the Kuiper Belt. This red color is consistent with the rest of the Cold Classical Kuiper Belt population, which it is dynamically a member of. Finally, we will discuss the implications MU69’s color has for constraining and better understanding its possible formation scenarios.

    149. Umurhan, O. M., Keane, J. T., Beyer, R. A., et al., 2020, AAS, 235, 419.05, Thermophysical, Gravitational, and Geomorphology Properties of 2014 MU69

      NASA’s New Horizons spacecraft imaging of 2014 MU69 on January 1, 2019 revealed a ~16-hr rotating bi-lobed object whose constituents, informally referred to as Ultima and Thule (or collectively “UT”), appear nearly spherical with ~9.5 km and ~7.1 km radii (respectively). Ultima and Thule have similar colors with measured albedos ~ 0.06, indicating that UT is a typical member of the Cold Classical Kuiper Belt class of objects. Detailed image analysis and shape modeling (also presented at this meeting) suggests that UT’s obliquity is nearly 99o and Ultima is relatively flattened by comparison to Thule. The surface morphology admits features ranging from small pits, large craters, smooth undifferentiated planes interspersed with scarps possibly derived from sublimation-driven landform evolutionary processes (also discussed at this meeting). Of particular note is the presence of relatively bright materials observed in UT’s neck region. Additionally, the onboard radiometer (“REX”) observed UT on its backlit side and its beam (4cm wavelength, X-band), containing the entirety of UT’s sky projection, measured an approximate brightness temperature of about TB = 29K 5K. However the depth to which the radar beam penetrated UT’s near subsurface was not independently measured and therefore requires theoretical modeling. In this talk we survey the gravitational and thermophysical properties of UT derived from detailed global theoretical modeling of the body based on the most recent shape model developed by Beyer and Porter. We place these results into the context of UT’s observed features. We calculate the body’s geopotential surfaces and local slopes, and based on previous theoretical considerations we conjecture about UT’s average density. Further analysis reveals that both of UT’s lobes are remarkably well-aligned with their principal axes being nearly parallel. Due to self-shadowing we find that the neck region is on average cooler than the rest of the body despite significant surface re-radiation into the zone. Thule’s large deep crater, informally named Maryland, is about 1K warmer than the surrounding regions. We predict that the surface temperature of the unlit side to be about 16K suggesting that the REX beam may have penetrated anywhere from 5-50 cm beneath the surface. We consider these properties in light of UT’s possible evolutionary scenarios.

    150. Singer, K. N., Spencer, J. R., McKinnon, W. B., et al., 2020, AAS, 235, 419.06, Impact craters on 2014 MU69: Implications for Kuiper belt object size-frequency distributions and planetesimal formation

      The size-distribution of small body populations are a signature of solar system formation and evolution processes. Smaller bodies (< ~100 km in diameter) are difficult to observe in the Kuiper belt. The New Horizons flyby of the Pluto-system in July of 2015 provided new data on smaller bodies in the Kuiper belt from observations of impact craters on the surfaces of Pluto and Charon. The new information revealed a previously-unknown deficit of small Kuiper belt objects (KBOs) less than ~1-2 km in diameter (Singer et al., 2019, Science). New Horizons was poised to test this observation 3.5 years later with its next close flyby of the cold classical KBO (486958) 2014 MU69. The images returned by New Horizons in early 2019 show MU69 is only modestly cratered, and potential craters on the surface show a shallow size-frequency distribution (SFD) similar to that of craters on Pluto and Charon (Stern et al. 2019, Science; Singer et al., 2019, EPSC-DPS abstract; Spencer et al. 2019, Science). Both the apparent lack of craters overall, and the shallow SFD slopes, are consistent with a relatively benign collisional environment for MU69 (McKinnon et al., 2019, Science). This deficit of objects smaller than 1 km gives the Kuiper belt population a different shape than the asteroid belt for objects between ~1 km and 200 m in size (the lower end is bound by the smallest impact craters we can see in the New Horizons data). The slope of the Kuiper belt size distribution has a shallow differential power-law slope of approximately -1.8, whereas the Asteroid belt has an average slope closer to -3 in this size range. The shallow slope seen in the Kuiper belt is not representative of a population in traditional collisional equilibrium, and we discuss the implications for formation and evolution of the Kuiper belt and planetesimals in our own solar system, and in other solar systems. Many models assume dust or debris has a collisional size distribution, but the New Horizons data implies there may be more possible outcomes for the size-distribution of evolved planetesimal populations than the traditional collisional equilibrium slope (of approximately -3.5).

    151. Protopapa, S., Olkin, C., Grundy, W., et al., 2020, AAS, 235, 438.03, Titan tholin like materials across the surface of Pluto

      Pluto presents in enhanced visible color images acquired with the New Horizons’ Multi-spectral Visible Imaging Camera (MVIC, Reuter et al. 2008) a wide range of colors from vivid red, brown, to yellow colors, highly correlated with Pluto’s varied underlying geological structures (Stern et al. 2015; Olkin et al. 2017). The color contrast is less obvious in natural-color images. Tholins, which are the refractory residues obtained from the irradiation of gases and ices containing hydrocarbons (Cruikshank 2005), are thought to be present on the surface of Pluto, serving as coloring agents (e.g., Stern et al. 2018). However, the number of distinct types of tholins on the surface of Pluto, and the processes responsible for their formation and distribution remains subject of investigation. We investigate this problem by means of 1) a multi-wavelength, regionally dependent photometric analysis of Pluto’s encounter hemisphere using the color images collected by the Ralph/MVIC instrument on board of New Horizons at four visible wavelengths from 400 nm to 910 nm and 2) analysis, using a multiple-scattering radiative transfer model (Hapke, 2012), of combined MVIC and LEISA (a mapping infrared composition spectrometer covering the wavelength range 1.25-2.50 m) spectra of eastern Cthulhu and Lowell Regio. Cthulhu and Krun Maculae are significantly darker and redder than the rest of the surface. Regions dominated by volatile ices such as the yellow material across Pluto’s north pole observed in enhanced color images present single scattering albedos of 0.98 or higher, and almost neutral across the visible wavelength range. This result indicates a very limited contribution of tholin materials on the optically active surfaces in these regions. We use a tholin material with optical constants very similar to that of Titan tholin by Khare et al. (1984) to reproduce the spectral properties of these two regions with such diverse coloration, compositions, morphologies, and ages. Because a single pigment can be used to account for all of Pluto’s colors and this is consistent with a Titan tholin like material, we concur with the idea suggested first by Grundy et al. (2018) that Pluto’s coloration is the result of photochemical products mostly produced in the atmosphere. Although cosmic rays and ultraviolet photons at wavelengths longer than 145 nm do reach Pluto’s surface, and can be expected to drive chemical processing there, the observations of diverse colors do not require different chemical products to be responsible for the colors in different environments.

    152. Lisse, C. M., Young, L., Cruikshank, D., et al., 2020, AAS, 235, 438.04, Ices in KBO MU69 and Pluto Implications for Their Formation & Evolution

      The New Horizons (NH) mission flyby of 14 July 2015 verified the presence of an extensive surface ice sheet consisting of CO + N2 ice in Sputnik Planitia, and a near-global covering of layered and structured CH4 ice around the planet. Assuming Pluto was aggregated out of billions of icy planetesimals, the prominence of large amounts of N2 ice is in tension with its ~0.2% vs water abundance found in inner system comets. A similar tension results from the ~1.0 % CH4 vs water in comets. Using the results of the 01 Jan 2019 NH flyby of KBO MU69, we infer new constraints on the icy makeup of the smaller KBOs, which differ substantially from the icy makeup of inner system comets in having abundant amorphous hydrogen-bonded ices like H2O, CH3OH, and (maybe) HCN/H2CO. Here we use this new information and new modeling of the thermodynamic properties of MU69’s ices to argue that due to the action of solar insolation, short-lived radioactive isotope decay, micrometeorite bombardment, galactic cosmic rays, passing O/B stars, and nearby supernovae, hypervolatile ices like N2, CO, and CH4 exist today in small icy solar system bodies only as minority species in water ice phases. Only refractory hydrogen-bonded ices should remain after 4.56 Gyrs. Any pure hypervolatile ices that originally condensed “in the dark”, while the solar system’s midplane was optically thick, were lost within 1 Myr of the time of disk clearing. This implies that Pluto either formed very fast, before the time of disk clearing + 1 Myr, or is completely melted and differentiated through and through, allowing the release of all its minority hypervolatiles from trapped water ice phases and their rise to its surface and atmosphere.

    153. Rabinowitz, David L., Benecchi, Susan D., Grundy, William M., et al., 2020, AJ, 159, 27, The Complex Rotational Light Curve of (385446) Manwe-Thorondor, a Multicomponent Eclipsing System in the Kuiper Belt

      Kuiper Belt Object (385446) Manwe-Thorondor is a multiobject system with mutual events predicted to occur from 2014 to 2019. To detect the events, we observed the system at 4 epochs (UT 2016 August 25 and 26, 2017 July 22 and 25, 2017 November 9, and 2018 October 6) in g, r, and VR bands using the 4 m SOAR and the 8.1 m Gemini South telescopes at Cerro Pachon, Chile, and Lowell Observatorys 4.3 m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap the uncertainty range (0.5 day) for four inferior events (Thorondor eclipsing Manwe). We clearly observe variability for the unresolved system with a double-peaked period 11.88190 0.00005 hr and 0.5 mag amplitude together with much longer-term variability. Using a multicomponent model, we simultaneously fit our observations and earlier photometry measured separately for Manwe and Thorondor with the Hubble Space Telescope. Our fit suggests Manwe is bilobed, close to the barbell shape expected for a strengthless body with density 0.8 g cm-3 in hydrostatic equilibrium. For Manwe, we thereby derive maximum width to length ratio 0.30, surface area equivalent to a sphere of diameter 190 km, geometric albedo 0.06, mass 1.4 1018 kg, and spin axis oriented 75 from Earths line of sight. Changes in Thorondors brightness by 0.6 mag with a 300 day period may account for the systems long-term variability. Mutual events with unexpectedly shallow depth and short duration may account for residuals to the fit. The system is complex, providing a challenging puzzle for future modeling efforts.

    154. Lopez-Rodriguez, Enrique, Dowell, C. Darren, Jones, Terry J., et al., 2020, ApJ, 888, 66, SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068

      We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 m polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy’s inner-bar and active galactic nucleus (AGN). We find correlations between the 89 m magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of {16.9}-2.8+2.7\circ and a disk inclination of 48 2. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk (<1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak 3-6 NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized (<1%) at both 53 and 89 m.

    155. Sokal, Kimberly R., Johns-Krull, Christopher M., Mace, Gregory N., et al., 2020, ApJ, 888, 116, The Mean Magnetic Field Strength of CI Tau

      We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5 to 2.5 m observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes a uniform magnetic field) and modeling with SYNTHMAG (which includes a distribution of magnetic field strengths) yield consistent measurements for the mean magnetic field strength of CI Tau is B of 2.2 kG. This value is typical compared with measurements for other young T Tauri stars and provides an important contribution to the existing sample given that it is the only known developed planetary system hosted by a young classical T Tauri star. Moreover, we potentially identify an interesting and suggestive trend when plotting the effective temperature and the mean magnetic field strength of T Tauri stars. While a larger sample is needed for confirmation, this trend only appears for a subset of the sample, which may have implications regarding the magnetic field generation.

    156. Neugent, Kathryn F., Massey, Philip, Georgy, Cyril, et al., 2020, ApJ, 889, 44, The Luminosity Function of Red Supergiants in M31

      The mass-loss rates of red supergiant stars (RSGs) are poorly constrained by direct measurements, and yet the subsequent evolution of these stars depends critically on how much mass is lost during the RSG phase. In 2012 the Geneva evolutionary group updated their mass-loss prescription for RSGs with the result that a 20 M star now loses 10 times more mass during the RSG phase than in the older models. Thus, higher-mass RSGs evolve back through a second yellow supergiant phase rather than exploding as Type II-P supernovae, in accord with recent observations (the so-called “RSG Problem”). Still, even much larger mass-loss rates during the RSG phase cannot be ruled out by direct measurements of their current dust-production rates, as such mass loss is episodic. Here, we test the models by deriving a luminosity function for RSGs in the nearby spiral galaxy, M31, which is sensitive to the total mass loss during the RSG phase. We carefully separate RSGs from asymptotic giant branch stars in the color-magnitude diagram following the recent method exploited by Yang and collaborators in their Small Magellanic Cloud studies. Comparing our resulting luminosity function with that predicted by the evolutionary models shows that the new prescription for RSG mass loss does an excellent job of matching the observations, and we can readily rule out significantly larger values.

    157. Yu, Zhefu, Martini, Paul, Davis, T. M., et al., 2020, ApJS, 246, 16, Quasar Accretion Disk Sizes from Continuum Reverberation Mapping in the DES Standard-star Fields

      Measurements of the physical properties of accretion disks in active galactic nuclei are important for better understanding the growth and evolution of supermassive black holes. We present the accretion disk sizes of 22 quasars from continuum reverberation mapping with data from the Dark Energy Survey (DES) standard-star fields and the supernova C fields. We construct continuum light curves with the griz photometry that span five seasons of DES observations. These data sample the time variability of the quasars with a cadence as short as 1 day, which corresponds to a rest-frame cadence that is a factor of a few higher than most previous work. We derive time lags between bands with both JAVELIN and the interpolated cross-correlation function method and fit for accretion disk sizes using the JAVELIN thin-disk model. These new measurements include disks around black holes with masses as small as 107 M, which have equivalent sizes at 2500 A as small as 0.1 lt-day in the rest frame. We find that most objects have accretion disk sizes consistent with the prediction of the standard thin-disk model when we take disk variability into account. We have also simulated the expected yield of accretion disk measurements under various observational scenarios for the Large Synoptic Survey Telescope Deep Drilling Fields. We find that the number of disk measurements would increase significantly if the default cadence is changed from 3 days to 2 days or 1 day.

    158. Liang, Weigang, Johnson, Jeffrey R., Hayes, Alexander G., et al., 2020, Icar, 335, 113361, Spectrophotometry from Mars Hand Lens Imager goniometer measurements: Kimberley region, Gale crater

      The light-scattering properties of surface materials on Mars are typically modeled using in situ spectrophotometric imaging sequences taken at multiple times of day to provide sufficient phase coverage. Herein, we report analyses of observations acquired at one time of day but under varying emission angles using the Mars Hand Lens Imager (MAHLI) on the robotic arm of the Mars Science Laboratory (MSL) rover as a goniometer. A multiple-viewpoint data set was acquired on Sol 544 by manipulating the arm to provide MAHLI images from 20 arm positions, all centered at the same location and from a near-constant distance of 1 m from the surface, permitting a phase angle coverage from 8 to 100. From these images, we constructed a digital terrain model of the scene, and used it in combination with atmospheric scattering models to remove the diffuse components of radiance from surface units. Radiative transfer models using Hapke theory were conducted using the direct radiance components from specific rock and soil units. Despite the relatively limited number of observations, our modeled Hapke parameters were well-constrained for terrain types such as soils and certain types of rocks that were common within the scene, but the errors increased for rock types with fewer observations. Results from one-term and two-term Henyey-Greenstein phase functions show the soil units to be more backscattering than rocks, consistent with previous photometric studies of martian landing sites. Overall, we find that the MAHLI goniometer sequences can produce reasonable and consistent photometric results, providing a new and efficient means of acquiring spectrophotometric data by arm cameras on rovers such as MSL.

    159. Koposov, Sergey E., Boubert, Douglas, Li, Ting S., et al., 2020, MNRAS, 491, 2465, Discovery of a nearby 1700 km s-1 star ejected from the Milky Way by Sgr A*

      We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a 2.35 M A-type star located at a distance of 9 kpc from the Sun and has a heliocentric radial velocity of 1017 2.7 km s^{-1} without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 50 km s^{-1}. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of 1800 km s^{-1} and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy, = 246.1 5.3 km s^{-1} or position R0 = 8.12 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.

    160. Sickafoose, A. A., Bosh, A. S., Emery, J. P., et al., 2020, MNRAS, 491, 3643, Characterization of material around the centaur (2060) Chiron from a visible and near-infrared stellar occultation in 2011

      The centaur (2060) Chiron exhibits outgassing behaviour and possibly hosts a ring system. On 2011 November 29, Chiron occulted a fairly bright star (R 15 mag) as observed from the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea and the 2-m Faulkes Telescope North (FTN) at Haleakala. Data were taken as visible wavelength images and simultaneous, low-resolution, near-infrared (NIR) spectra. Here, we present a detailed examination of the light-curve features in the optical data and an analysis of the NIR spectra. We place a lower limit on the spherical diameter of Chiron’s nucleus of 160.2 1.3 km. Sharp, narrow dips were observed between 280 and 360 km from the centre (depending on event geometry). For a central chord and assumed ring plane, the separated features are 298.5-302 and 308-310.5 km from the nucleus, with normal optical depth 0.5-0.9, and a gap of 9.1 1.3 km. These features are similar in equivalent depth to Chariklo’s inner ring. The absence of absorbing/scattering material near the nucleus suggests that these sharp dips are more likely to be planar rings than a shell of material. The region of relatively increased transmission is within the 1:2 spin-orbit resonance, consistent with the proposed clearing pattern for a non-axisymmetric nucleus. Characteristics of possible azimuthally incomplete features are presented, which could be transient, as well as a possible shell from 900-1500 km: future observations are needed for confirmation. There are no significant features in the NIR light curves, nor any correlation between optical features and NIR spectral slope.

    161. Liu, P., Kuhlmann, S., Ellis, S. C., et al., 2020, SPIE, 11203, 112030Y, Photonic ring resonator notch filters for astronomical OH line suppression

      Photonic ring resonator arrays used as notch filters are a promising novel solution to improve the signal-to-noise ratio of ground-based astronomical observations by suppressing OH emission lines in the near-infrared (NIR) wavelength range (0.9-2.5 m). We aim to fabricate a series of ring resonators connected by a waveguide, each with its resonance wavelength and full-width-half-maximum (FWHM) matched with one of the OH emission lines.

    162. Pendleton, Y. J., Cruikshank, D. P., Stern, S. A., et al., 2020, IAUS, 350, 91, Kuiper Belt object 2014MU69, Pluto and Phoebe as windows on the composition of the early solar nebula

      The initial chemical composition of a proto-planetary nebula depends upon the degree to which 1) organic and ice components form on dust grains, 2) organic and molecular species form in the gas phase, 3) organics and ices are exchanged between the gas and solid state, and 4) the precursor and newly formed (more complex) materials survive and are modified in the developing planetary system. Infrared and radio observations of star-forming regions reveal that complex chemistry occurs on icy grains, often before stars even form. Additional processing, through the proto-planetary disk (PPD) further modifies most, but not all, of the initial materials. In fact, the modern Solar System still carries a fraction of its interstellar inheritance (Alexander et al. 2017). Here we focus on three examples of small bodies in our Solar System, each containing chemical and dynamical clues to its origin and evolution: the small-cold classical Kuiper Belt object (KBO) 2014 MU69, Pluto, and Saturn’s moon, Phoebe. The New Horizons flyby of 2014 MU69 has given the first view of an unaltered body composed of material originally in the solar nebula at ~45 AU. The spectrum of MU69 reveals methanol ice (not commonly found), a possible detection of water ice, and the noteworthy absence of methane ice (Stern et al. 2019). Pluto’s internal and surface inventory of volatiles and complex organics, together with active geological processes including cryo-volcanism, indicate a surprising level of activity on a body in the outermost region of the Solar System, and the fluid that emerges from subsurface reservoirs may contain material inherited from the solar nebula (Cruikshank et al. 2019). Meanwhile, Saturn’s captured moon, Phoebe, carries high D/H in H2O (Clark et al. 2019) and complex organics (Cruikshank et al. 2008), both consistent with its formation in, and inheritance from, the outer region of the solar nebula. Together, these objects provide windows on the origin and evolution of our Solar System and constraints to be considered in future chemical and physical models of PPDs.

    163. Kavanagh, R. D., Vidotto, A. A., Fionnagain, D. O., et al., 2020, IAUS, 354, 305, Tuning in to the radio environment of HD189733b

      The hot Jupiter HD189733b is expected to be a source of strong radio emission, due to its close proximity to its magnetically active host star. Here, we model the stellar wind of its host star, based on reconstructed surface stellar magnetic field maps. We use the local stellar wind properties at the planetary orbit obtained from our models to compute the expected radio emission from the planet. Our findings show that the planet emits with a peak flux density within the detection capabilities of LOFAR. However, due to absorption by the stellar wind itself, this emission may be attenuated significantly. We show that the best time to observe the system is when the planet is near primary transit of the host star, as the attenuation from the stellar wind is lowest in this region.

    164. Wan, Zhen, Lewis, Geraint F., Li, Ting S., et al., 2020, Natur, 583, 768, The tidal remnant of an unusually metal-poor globular cluster

      Globular clusters are some of the oldest bound stellar structures observed in the Universe1. They are ubiquitous in large galaxies and are believed to trace intense star-formation events and the hierarchical build-up of structure2,3. Observations of globular clusters in the Milky Way, and a wide variety of other galaxies, have found evidence for a `metallicity floor’, whereby no globular clusters are found with chemical (metal) abundances below approximately 0.3 to 0.4 per cent of that of the Sun4-6. The existence of this metallicity floor may reflect a minimum mass and a maximum redshift for surviving globular clusters to formboth critical components for understanding the build-up of mass in the Universe7. Here we report measurements from the Southern Stellar Streams Spectroscopic Survey of the spatially thin, dynamically cold Phoenix stellar stream in the halo of the Milky Way. The properties of the Phoenix stream are consistent with it being the tidally disrupted remains of a globular cluster. However, its metal abundance ([Fe/H] = -2.7) is substantially below the empirical metallicity floor. The Phoenix stream thus represents the debris of the most metal-poor globular clusters discovered so far, and its progenitor is distinct from the present-day globular cluster population in the local Universe. Its existence implies that globular clusters below the metallicity floor have probably existed, but were destroyed during Galactic evolution.


    1. Steckloff, J., Soto, A., Soderblom, J. M., et al., 2019, AGUFM, 2019, P21C-02, Titan’s Bistable Climate and the Origin of its Atmospheric Methane

      Saturn’s largest moon, Titan, hosts a methane-driven hydrological cycle [1-2]. This methane has been in the atmosphere for less than 470 Myr [3]. However, the reservoir that released this methane is poorly understood. Here we show that Titan presently has a bistable climate, and that the atmospheric methane is released during a transition between climatic regimes: from the colder “Slushball Titan” regime (in which all surface methane is sequestered in the depths of a nearly global nitrogen-dominated ocean) to the present warm climatic regime in which nearly all surface methane is atmospheric.


      In the Slushball Titan regime, the lack of atmospheric methane results in frigid surface temperatures, well below 84 K [4-5], the tipping point between regimes. Under these conditions, Titan’s atmosphere partially collapses into a nearly global ~70 m deep nitrogen ocean. Thermodynamics drive nearly all surface methane (whether atmospheric or geologically released) into this ocean.

      We propose that Titan was in a slushball climate until a few hundred Myr ago, until an energetic event (such as a large impact and/or changes in insolation) warmed Titan sufficiently to trigger a transition to the warm Titan climate. This transition would evaporate the nitrogen ocean and release its oceanic methane to the atmosphere. This atmospheric methane would further warm the moon and begin to experience photochemical processing. This scenario is consistent with Titan’s surface cratering age (200-1000 Myr; [6]), the ~50-630 Myr required to form Titan’s dune materials from atmospheric methane [7], and the ~300-1200 Myr required to explain Titan’s global shape via ethane substitution in methane clathrates [8]. This is also consistent with the presence of fluvial features in Titan’s low latitudes [9], the lower crater abundance at lower elevations [10], and the overabundance of small craters, which indicate that Titan’s atmosphere was thinner in the past [6].

      [1] Tomasko et al. 2005. Nature 44, 61

      [2] Tokano et al. 2006. Nature 442, 432

      [3] Mandt et al. 2012. ApJ 749, 160

      [4] Lorenz, 1997. Science 275, 642

      [5] Charnay et al. 2014. Icarus 241, 269

      [6] Neish & Lorenz. 2012. P&SS 60, 26

      [7] Sotin et al. 2012. Icarus 221, 768

      [8] Chokrun & Sotin, 2012. GRL 39, L04201

      [9] Larsson & McKay. 2013. P&SS 78, 22

      [10] Neish & Lorenz. 2014. Icarus 228, 27

    2. Cartwright, R. J., Emery, J. P., Pinilla-Alonso, N., et al., 2019, AGUFM, 2019, P32A-08, Probing the regoliths of the classical Uranian satellites using near-infrared telescope observations: CO2 ice deposits mantled by a veneer of tiny H2O ice grains?

      In the late 1970s and early 1980s, near-infrared (NIR) ground-based observations (~1 – 2.5 m) determined that the surfaces of the large and tidally-locked “classical” moons of Uranus are composed of H2O ice, mixed with a dark, C-rich constituent. In the late 1990s and early 2000s, CO2 ice was detected in NIR spectra of these moons, with spectral properties remarkably similar to the second and third order combination and overtone bands of CO2 ice (between 1.9 to 2.1 m and 1.57 to 1.61 m, respectively). The presence of these relatively weak CO2 bands indicates that the detected CO2 ice is retained in thick deposits (~1 – 100 mm) on the surfaces of these moons. However, over longer NIR wavelengths (~3 – 5 m), the spectral signature of CO2 ice is mostly absent from these moons. Photon penetration depths into H2O-rich particulate surfaces are a steep function of wavelength, with NIR photons between 1 and 2.5 m penetrating deeper (~0.15 – 10 mm depths) than NIR photons between 3 and 5 m (~0.001 – 0.05 mm depths). Thus, we hypothesize that the regoliths of the classical Uranian satellites are compositionally stratified, with thick deposits of CO2 ice retained beneath a veneer of tiny H2O ice grains.


      To test this hypothesis, we have collected data using the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope (spanning ~3 to 5 m). We compared these new IRAC data to an IRAC dataset collected previously, as well as longer NIR spectra, spanning 3 to 4 m. Analysis of these longer NIR datasets indicates that the Uranian moons are relatively bright over the 3 to 5 m range, with enhanced 3.6-m H2O ice peaks. Best fit spectral models of the IRAC datasets are primarily composed of tiny H2O ice grains ( 2 m diameters), with no trace of CO2 ice. Thus, our analyses support compositional stratification of these moons’ regoliths. We explore some of the processes that could generate layered media on the Uranian moons and discuss why the surfaces of icy Jovian and Saturnian moons lack similar veneers of tiny H2O ice grains. Additionally, we discuss how next generation telescopes and future spacecraft missions would revolutionize our understanding of the classical Uranian moons and ice giant planetary systems.

    3. Weaver, H. A., Jr., Porter, S. B., Spencer, J. R., et al., 2019, AGUFM, 2019, P33I-3531, Update on High Resolution Searches for KBO Binaries using New Horizons LORRI

      The New Horizons (NH) spacecraft has been traversing the Kuiper belt for the past four years, enabling observations of known Kuiper belt objects (KBOs) at unique geometries, including at large phase angles not possible from the inner solar system and at ranges that provide higher spatial resolution than available from Earth, or Earth-orbiting, facilities. New Horizons carries a large aperture (20.8 cm) visible light imaging system, the LOng Range Reconnaissance Imager (LORRI), whose resolution (IFOV=1,4 arcsec for 1×1 and 4×4 modes, respectively) permits searches for binaries at finer spatial scales than available from the Hubble Space Telescope (HST). We have already observed 13 KBOs (1 Plutino, 1 Hot Classical, 1 Scattered Disk, and 10 Cold Classicals) that passed within 1 AU of the NH spacecraft, and two more KBOs are scheduled for observations in early September 2019. We are actively searching for additional candidates using ground-based telescopes. Five of the observed KBOs passed within 0.2 AU of the NH spacecraft, including two with ranges of ~0.11 AU (82 km/pix for 1×1 mode). LORRI’s photometric sensitivity for these satellite searches (V~16.3 in 1×1 mode after co-adding ~125 0.5s exposures; V~21 in 4×4 mode after co-adding ~50 30s exposures, and even deeper after implementing 64s exposures in fall 2019) is comparable to, or exceeds, that available from HST. Five of the six highest resolution (1×1 mode) NH KBO satellite searches were performed during the latter half of 2018, and some of those data are scheduled for downlink in Oct-Nov 2019. Here we report on the binary search limits achieved for the 1×1 data that were downlinked by the end of Nov 2019.

    4. Showalter, M., Benecchi, S., Buie, M. W., et al., 2019, AGUFM, 2019, P33I-3532, A Statistical Test for the Population of Contact Binaries in the Kuiper Belt

      New Horizons images of Kuiper Belt object (486958) 2014 MU69 dramatically revealed that it is a contact binary, comprising two flattened lobes attached by a very narrow neck. In spite of its highly elongated shape, MU69 has a rotational light curve with an amplitude that was too small to be measured from Earth or during the approach of the spacecraft in December 2018. This surprising result is, in part, a consequence of MU69’s bilobate shape; in general, contact binaries have light curve amplitudes that are systematically lower than those of equivalent-area ellipsoids.


      The prevalence of contact binaries among the cold classical KBOs (CCKBOs) has been a topic of investigation on several fronts. We find that an important constraint on the answer to this question can be inferred from the statistical distribution of light curve amplitudes among CCKBOs. We have modeled these distributions based on a variety of assumptions, including rough or irregular shapes, albedo variations, degree of flattening, the size of the neck, and the size ratio of the two lobes. We have also explored the dependence on the statistical distribution of KBO orientations, assuming that the rotation poles are either completely random or are preferentially oriented normal to the orbit plane. In all cases, the distribution of light curve amplitudes is predicted to be lower if contact binaries are prevalent among the CCKBOs.

      At this time, the limited available data on CCKBO light curve amplitudes does not permit a definitive answer to the question of how many CCKBOs are contact binaries. However, the statistical test holds promise as more CCKBOs are observed. It would complement the shape determinations based on the direct modeling of KBOs with high-amplitude light curves, combined with further occultation studies of KBO shapes. Needed is a large and an unbiased sample of light curve amplitudes, one which does not focus on the high-amplitude light curves that are often of greatest interest.

    5. Singer, K. N., Spencer, J. R., McKinnon, W. B., et al., 2019, AGUFM, 2019, P33I-3535, Impact craters on 2014 MU69: Implications for Kuiper belt object size-frequency distributions and planetesimal formation

      Impact craters in the Pluto system as observed by New Horizons in July of 2015 revealed a previously-unknown deficit of small Kuiper belt objects (KBOs) less than ~1-2 km in diameter (Singer et al., 2019, Science) . New Horizons was poised to test this observation 3.5 years later with its next KBO close flyby of the cold classical KBO (486958) 2014 MU69 (nicknamed Ultima Thule). The images returned by New Horizons in early 2019 show MU69 is only modestly cratered, and potential craters on the surface show a shallow size-frequency distribution (SFD) similar to that of craters on Pluto and Charon (Stern et al. 2019, Science; Singer et al., 2019, EPSC-DPS; Spencer et al. 2019, Science).


      Some features on MU69 do have multiple morphologic indicators suggesting they are impact craters. There are regions on MU69 with few-to-no craters, even where the lighting is favorable for recognizing topographic features. The ~7-km-diameter depression (informally called Maryland) on the small lobe of MU69 is the largest easily observed feature that is likely to be an impact crater. There are also craters under 1 km in diameter, but no obvious craters between 1 and 7 km in diameter.

      The possible impact craters < ~1 km in diameter were divided into subgroups based on morphology, likelihood of being a crater , lighting geometry, and also into one possible geologic unit. Measurements/ratings were provided by several team members. All subgroups produced shallow-sloped SFDs (differential power-law slope -2) similar to those seen on Pluto and Charon for the same size craters (when scaled for gravity and impact velocity). Whole-sale resurfacing through geologic processes is not expected for MU69. Thus many more craters and at least some heavily cratered terrains would be predicted if the impactor SFD slope were steeper (an average differential slope closer to -3; Greenstreet et al. 2019, ApJ). Both the apparent lack of craters overall, and the shallow SFD slopes, are consistent with a relatively benign collisional environment for MU69 (McKinnon et al., 2019, Science).

    6. Lisse, C. M., Young, L. A., Cruikshank, D. P., et al., 2019, AGUFM, 2019, P33I-3540, On the Stability & Origin of MU69’s and Pluto’s Ices

      In this paper we discuss in a model-independent way the nature of the stable, refractory ices that could be present in Kuiper Belt object (KBO) 2014 MU69 (“Ultima Thule”) after its 4.6 Gyr residence in the Edgeworth-Kuiper belt (EKB) as a cold classical object, and the processes that could affect them, such as short-lived radioactive decay, x-ray/ultraviolet photon (XUV) and galactic cosmic ray (GCR) irradiation, and micrometeorite bombardment. We compare the upper bounds for the gas production rate (~1024molecules/sec) measured by the New Horizons spacecraft flyby on 01 Jan 2019 to estimates for the outgassing flux rates from a suite of common cometary and KBO ices at the average ~40K sunlit surface temperature of UT, but do not find the upper limit very constraining except for the most volatile of species (eg CO, N2, CH4). More constraining is the stability versus sublimation into vacuum requirement over Myr to Gyr, and from this we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability), while NH3and H2CO ices are marginally stable and may be removed by any positive temperature excursions in the EKB, as produced every 108– 109yrs by nearby supernovae (SN) and passing O/B stars. To date the New Horizons (NH) team has reported the presence of abundant CH3OH and H2O on MU69’s surface (Stern+ 2019, Grundy+ 2019). NH3has been searched for, but not found. We predict that future absorption feature detections, if any are ever derived from higher SNR spectra, will be due to an HCN or poly-H2CO based species.


      Consideration of the conditions present in the EKB region during the formation era of MU69 lead us to state that it is highly likely that it “formed in the dark”, unable to see the nascent, variable, highly luminous YSO/TTauri Sun, in an optically thick proto-planetary disk (PPD) mid-plane. Also, that KBOs contain pure CH3OH (and likely HCN) ice phases in addition to the H2O ice and H2O ice clathrates found in their short period (SP) comet descendants. Finally, when we apply our ice thermal stability analysis to bodies/populations related to MU69, we find that that Pluto must have gained its hypervolatiles from PPD sources in the first few Myr of the solar system’s existence, that comet C/2016 R2 was placed onto an Oort Cloud orbit on a similar timescale, and that the O2in comet 67P is not primordial.

    7. Linscott, I., Asmar, S., Bird, M., et al., 2019, AGUFM, 2019, P34A-01, Pluto’s Surface Properties from the New Horizons Uplink Bistatic Radar Experiment

      Exploration of planetary surface properties by scattering radio signals has been carried out via Solar System spacecraft for nearly six decades. During the New Horizons flyby of Pluto on July 14, 2015, an innovative approach reversed the radio path using a high-power uplink transmitted from the Deep Space Network. The uplink illuminated the surface of Pluto, and the scattered signals were recorded onboard the spacecraft by REX the Radioscience instrument, setting a record at 7.6 Bkm for bistatic radar. The high SNR advantage, needed to characterize such a distant object, was nearly three orders of magnitude greater than traditional downlink experiments could have provided.


      The bistatic experiment was performed using a radar transmission at 7.18 GHz, from the NASA’s Deep Space Network 34-m diameter antenna (designated DSS-26) at Goldstone, California. The transmission was CW at 80 kilowatts in right-hand circular polarization (RCP) and was adjusted in frequency to compensate for predicted Doppler shifts to ensure it would fall within REX’s 1.25 kHz bandpass. The received signal’s SNR was 30x, (15 dB), and digitized by REX in both polarizations, and in-phase and quadrature, revealing a polarization ratio of ~1/2, and a surface reflectivity of ~0.3. The radar illumination at Pluto’s specular point subtended an angle of incidence between 40 degrees and 60 degrees, a near-optimal geometry for modelling surface properties. Characterization of Pluto’s surface in the vicinity of the specular point has incorporated Fresnel reflection, as well as electromagnetic scattering models for randomly oriented surface facets as well as subsurface propagation and multidimensional optimization over the distribution of surface slopes and roughness, to obtain both the composition and structure of Pluto’s surface and subsurface.

      These results demonstrate the efficacy of bistatic scattering for planetary surface characterization and suggest that bistatic experiments, if incorporated in future missions to the solar system’s planets, moons, dwarf planets and bodies, will substantially increase and enrich their science return.

    8. White, O. L., Moore, J. M., McKinnon, W. B., et al., 2019, AGUFM, 2019, P42C-01, The Geology and Formation of the Kuiper Belt Object 2014 MU69

      The New Horizons flyby of the small Kuiper Belt Object 2014 MU69 provided the first look at the geology of a member of the Cold Classical Kuiper Belt, the most primitive known population of objects in the solar system. MU69 is a contact binary, composed of two sharply distinct components (nicknamed “Ultima” and “Thule”) that make contact at a bright, narrow, “neck”. Both are flattened, with their smallest axes aligned, and their contact point is close to the longest axis of both bodies. This configuration strongly suggests that the two components formed independently, and orbited each other in a tidally locked configuration before coming gently together. The current rotation period of 15.92 hours is slow enough that, for reasonable densities, the two bodies must have lost significant angular momentum after contacting each other. On both components, the surface is generally smooth, though pits are seen near the terminator, and bright spots away from the terminator may also be bright-floored pits. If impact-generated, these features indicate a surface age dating to the era of planetary accretion.


      Ultima, the larger component, is highly flattened, with approximate dimensions 20.6 19.9 9.4 km. Thule is closer to spherical than Ultima, with approximate dimensions 15.4 13.8 9.8 km. In both cases, the shortest dimension is the least certain. Ultima appears to be divided into several sub-units, distinguished by surface texture and/or separated by linear scarps or bright linear albedo features. Dark features that appear to be low hills and ridges are unevenly distributed across the surface. The sub-units may provide evidence for assembly of Ultima from smaller bodies, though the continuity of some surface texture units across some of the bounding linear features argues for some of the unit boundaries being relatively young rather than primordial.

      Thule is markedly different in appearance. It is dominated by a large depression (nicknamed “Maryland”) that is 7 km across and 0.5-1 km deep, and which is likely to be an impact feature. The rest of the surface is characterized by bright and dark albedo markings that often have strikingly sinuous boundaries, possibly due to sublimation erosion of thin, discrete surface layers.

      This work was supported by the NASA New Horizons project.

    9. Protopapa, S., Grundy, W. M., Cruikshank, D. P., et al., 2019, AGUFM, 2019, P42C-04, Surface compositions and colors of Pluto, its system of moons, and 2014 MU69

      The trans-neptunian population is extremely diverse, with bodies ranging from geologically-active, atmosphere-bearing, volatile-dominated dwarf planets to small primitive planetesimals lacking abundant surface volatile ices (e.g., methane, nitrogen, carbon monoxide)—what we think of as the building blocks of planets. Our understanding of the Kuiper Belt has been limited by the challenges of acquiring high-quality spectroscopy for midsize and small trans-neptunian objects and composition maps of large dwarf planets. NASA’s New Horizons mission represents a breakthrough in our understanding of the trans-neptunian population providing a detailed portrait of objects with very different size scales: the 2400-km-diameter dwarf planet Pluto, the midsize ~1200-km-diameter body Charon, and the much smaller Pluto’s satellites (e.g., Nix and Hydra) and (486958) 2014 MU69 (hereafter MU69), the latter with an 18 km equivalent spherical diameter. This is the result of two successful flybys: that of Pluto and its moons on July 14th, 2015 (Stern, S. A., Bagenal, F., Ennico, K., et al. 2015, Science, 350, aad1815), and that of MU69 on January 1st, 2019 (Stern, S. A., Weaver, H. A., Spencer, J. R., et al. 2019, Science, 364, aaw9771). We will present an overview of the color and composition of these very diverse bodies in terms of size, evolutionary stage, and dynamical class in the broad context of the physical and chemical properties of other trans-neptunian objects. Comparing and contrasting these objects will shed light on the mechanisms at play during the epoch of planet formation in the Third Zone of the Solar System.

    10. McKinnon, W. B., Grundy, W. M., Hamilton, D., et al., 2019, AGUFM, 2019, P42C-05, On the solar nebula origin of (486958) 2014 MU69, a primordial contact binary in the Kuiper belt

      MU69 is a contact binary, and all the data returned from New Horizons are consistent with it being a planetesimal. It is not a product of heliocentric, high-speed collisional evolution. There is no evidence of it having suffered a catastrophic or even a subcatastrophic impact during its lifetime. Nor is there evidence of hierarchical accretion of independent, heliocentric planetesimals, as slow as those collisions may have been in the beginning. Rather, there is strong evidence that its two lobes (“Ultima” and “Thule”) came together at an extremely low velocity, on the order of no more than a couple of m/s and possibly much more slowly. Binary formation is a theoretically predicted common outcome in protoplanetary disks when swarms of locally concentrated solids (“pebble clouds”) collapse under their own gravity, and plausibly explains the high fraction of binaries among cold classical Kuiper belt objects (KBOs). Cold classical KBO binaries exhibit a range of binary orbital separations, down to the observable limit, so there is no physical reason that tight or even contact binaries could not form in a collapsing pebble cloud. The prominence of bilobate shapes among the short-period comets, which are derived from the scattered disk component of the Kuiper belt, suggests (but does not require) that there is a process that collapses or hardens Kuiper belt binaries. The alignment of the principal axes of the Ultima and Thule lobes is also consistent with tidal coupling between two co-orbiting bodies, prior to a final merger. Our examination of various mechanisms to drive binary mergers in the cold classical Kuiper belt (Kozai-Lidov, BYORP, tides, collisions, gas drag) highlights the potential importance of gas drag while the protosolar nebula is still present. We find the process to be surprisingly effective, because in a gas nebula with a radial pressure gradient the velocity of the gas deviates from the heliocentric Keplerian velocity of the binary. The headwind that the binary feels couples to the motion of the binary pair about its own center of mass. The resulting viscous, Stokes-regime gas drag can collapse MU69-scale co-orbiting binariesas well as smaller, cometary-scale binarieswithin the few-Myr lifetime of the protosolar gas nebula.

    11. Schindler, K., Bosh, A. S., Levine, S. E., et al., 2019, AGUFM, 2019, P42C-08, Results from a stellar occultation by KBO Varda

      We present results obtained from a stellar occultation by the classical Kuiper belt object (174567) Varda on 10 September 2018. Varda is a known binary system and among the largest TNOs known today, but has not been studied during an occultation before. Among our collaborators, 24 stations were able to acquire data at the time of the event, of which 15 obtained a clear detection, making this the best-sampled occultation of a TNO to date. As potential stellar duplicity could cause a significant shift of the ground path, we studied the target star in advance through speckle imaging with ‘Alopeke at Gemini North. The reconstructed shape is an ellipsoid, which supports Varda’s status as a dwarf planet candidate. Albeit slightly smaller, the calculated size is in agreement with the radiometric diameter based on Herschel/PACS FIR measurements. Post-event analysis of the dataset obtained at DCT revealed a faint, unresolved companion or background star very close to the target, which was well under the detection limit of our speckle imager data, but had practically no effect on the predicted path. No atmosphere has been detected. The occultation helped to constrain size and albedo, which in turn helps to better constrain Varda’s density.

    12. Dalle Ore, C., Cruikshank, D. P., Grundy, W. M., et al., 2019, AGUFM, 2019, P43C-3486, Pluto Refractory Material

      One of Pluto’s unexpected discoveries has been the variety of terrains that characterize its surface. This bounty of data has given us the opportunity to investigate the composition of the different regions to compare and contrast the non-icy refractory component(s) of Pluto’s surface. The colored materials that are the target of our investigation are thought to originate either from haze deposition, or from ejection from a liquid water sub-crustal reservoir, or from surface irradiation of the hydrocarbon ices. Considering the dynamic nature of Pluto’s surface, continually refreshed and/or renewed, the possibility of a primordial component is remote. We compare the refractory material of different regions of Pluto’s surface and attempt at identifying their origin.

    13. Schenk, P., Grundy, W. M., Hansen, C. J., et al., 2019, AGUFM, 2019, P53D-3492, Triton’s Surface Composition: Reevaluation of Voyager colors from the perspective of New Horizons at Pluto

      New Horizons mapping of Pluto the best known Kuiper Belt Object (KBO), revealed the presence of surface ices (including CO, CH4, N2, and H2O) and their geologic distribution. Triton, the largest moon of Neptune, is very similar in size and bulk density to Pluto and was likely a KBO before capture. Both bodies orbit at comparable distances from the Sun (though Pluto goes further out) and have similar rotation periods. Both have complex obliquity cycles and both may have been or are ocean worlds. Triton is also a priority target for future exploration. Voyager (VGR) color mapping lacked the infrared capabilities of New Horizons (NH), rendering compositional mapping very difficult, but also revealed complex geologic and atmospheric color patterns on the surface of Triton. These include color changes at unit boundaries and equatorial bright and dark regional patterns uncorrelated to geology with very strong UV signatures. Small dark spots that appear wind-blown also have distinct spectral signatures. We have remapped the color data for Triton using updated cartography. VGR did extend into the UV which allows comparisons to Cassini icy moons color mapping. Color filter bandpasses for VGR & NH overlap in the 0.4 and 0.6 micron bands, which allows for a comparison of the brightness and spectral slopes of color units on the two bodies. The presence of CO2 on Triton will produce a distinct spectral signature compared to Pluto. Principle component analysis will be updated using all 6 filters to identify distinctive surface components. Disk integrated color rotational coverage from Earth-based spectra may also permit correlation of specific color units with identified longitudinal concentrations of ice phases.

    14. Singer, K. N., Stern, A., Moore, J. M., et al., 2019, AGUFM, 2019, P54B-09, The New Horizons Mission: Pluto and the Kuiper Belt Up-Close

      In July of 2015 the New Horizons spacecraft flew through the Pluto system, initiating humanity’s close-up exploration of Kuiper belt objects (Stern et al., 2015, Science). Pluto turned out to be a world of remarkable geologic diversity whose terrains display a range of ages and varied compositions, suggesting geologic activity of various forms (both endogenic and exogenic) has persisted for much of Pluto’s history (e.g., Moore et al., 2016, Science). This was a surprise given Pluto’s size and lack of recent tidal energy inputs. Many discoveries were also made about Pluto’s complex atmosphere, including the existence of many haze layers. Pluto’s large moon Charon appears to have had an early large cyrovolcanic resurfacing episode along with large-scale extensional tectonism.


      On January 1 of 2019 New Horizons encountered its second target, a cold classical Kuiper belt object approximately 35 km across at 43 AU (Stern et al., 2019, Science). This is the farthest and most primordial planetary body ever explored in detail. Its flattened, snowperson-like shape and unique surface features are helping us learn about the earliest times in the solar system and how planetary bodies formed (Spencer et al., 2019, Science; McKinnon et al., 2019, Science). No satellites or rings were found. MU69’s surface has the signature of H2O and CH3OH (methanol) and a very red color, indicative of other organics.

      This presentation will highlight some of the unique aspects of the Pluto-system, and give an update on the ongoing work to further unveil its secrets. We will also present an overview of what New Horizons is learning about the Kuiper belt as a whole (from Pluto to MU69 to distant KBO observations) and what new information this gives us about planetesimal and planet formation.

    15. McNeill, A., Mommert, M., Trilling, D. E., et al., 2019, ApJS, 245, 29, Asteroid Photometry from the Transiting Exoplanet Survey Satellite: A Pilot Study

      The Transiting Exoplanet Survey Satellite (TESS) searches for planets transiting bright and nearby stars using high-cadence, large-scale photometric observations. Full frame images provided by the TESS mission include a large number of serendipitously observed main-belt asteroids (MBAs). Due to the cadence of the published full frame images, we are sensitive to periods as long as of order tens of days, a region of phase space that is generally not accessible through traditional observing. This work represents a much less biased measurement of the period distribution in this period range. We have derived rotation periods for 300 MBAs and have partial lightcurves for a further 7277 asteroids, including 43 with periods of P > 100 hr; this large number of slow rotators is predicted by theory. Of these slow rotators we find none requiring significant internal strength to resist rotational reshaping. We find our derived rotation periods to be in excellent agreement with results in the Lightcurve Database for the 55 targets that overlap. Over the nominal two-year lifetime of the mission, we expect the detection of around 85,000 unique asteroids with rotation period solutions for around 6000 asteroids. We project that the systematic analysis of the entire TESS data set will increase the number of known slow-rotating asteroids (period > 100 hr) by a factor of 10. Comparing our new period determinations with previous measurements in the literature, we find that the rotation period of asteroid (2320) Blarney has decreased by at least 20% over the past decade, potentially due to surface activity or subcatastrophic collisions.

    16. Morbidelli, Alessandro, Grundy, William, 2019, Icar, 334, 1, Introduction to Icarus special papers on trans-neptunian solar system

      In March 2018, the international community working on the trans-neptunian small body population met in Coimbra for a one-week scientific meeting. It was the sixth of such meetings, starting with the one in Garching in 1998, just six years after the discovery of the first trans-neptunian object besides Pluto: 1992 QB1 by Jewitt and Luu (1993). This special issue of Icarus contains ten papers which report original research results presented at the meeting. A book of review papers associated to the meeting is under finalization and will be published soon by Elsevier.

    17. Grundy, W. M., Noll, K. S., Buie, M. W., et al., 2019, Icar, 334, 30, The mutual orbit, mass, and density of transneptunian binary Gkun’homdima (229762 2007 UK126)

      We present high spatial resolution images of the binary transneptunian object Gkun’homdima (229762 2007 UK126) obtained with the Hubble Space Telescope and with the Keck observatory on Mauna Kea to determine the orbit of Go’e huGo’e hu, the much smaller and redder satellite. Go’e hu orbits in a prograde sense, on a circular or near-circular orbit with a period of 11.3 days and a semimajor axis of 6000 km. Tidal evolution is expected to be slow, so it is likely that the system formed already in a low-eccentricity configuration, and possibly also with the orbit plane of the satellite in or close to the plane of Gkun’homdima’s equator. From the orbital parameters we can compute the system mass to be 1.4 1020 kg. Combined with estimates of the size of Gkun’homdima from thermal observations and stellar occultations, we can estimate the bulk density as about 1 g cm-3. This low density is indicative of an ice-rich composition, unless there is substantial internal porosity. We consider the hypothesis that the composition is not unusually ice-rich compared with larger TNOs and comet nuclei, and instead the porosity is high, suggesting that mid-sized objects in the 400 to 1000 km diameter range mark the transition between small, porous objects and larger objects that have collapsed their internal void space as a result of their much higher internal pressures and temperatures.

    18. Muller, T., Kiss, Cs., Ali-Lagoa, V., et al., 2019, Icar, 334, 39, Haumea’s thermal emission revisited in the light of the occultation results

      A recent multi-chord occultation measurement of the dwarf planet (136108) Haumea (Ortiz et al., 2017) revealed an elongated shape with the longest axis comparable to Pluto’s mean diameter. The chords also indicate a ring around Haumea’s equatorial plane, where its largest moon, Hi’iaka, is also located. The Haumea occultation size estimate (size of an equal-volume sphere1 Dequ = 1595 km) is larger than previous radiometric solutions (equivalent sizes in the range between 1150 and 1350 km), which lowers the object’s density to about 1.8 g/cm3, a value closer to the densities of other large TNOs. We present unpublished and also reprocessed Herschel and Spitzer mid- and far-infrared measurements. We compare 100 and 160 Am thermal lightcurve amplitudes – originating from Haumea itself – with models of the total measured system fluxes (ring, satellite, Haumea) from 24-350 m. The combination with results derived from the occultation measurements allows us to reinterpret the object’s thermal emission. Our radiometric studies show that Haumea’s crystalline water ice surface must have a thermal inertia of about 5 J K-1 m-2s-1/2 (combined with a root mean square of the surface slopes of 0.2). We also have indications that the satellites (at least Hi’iaka) must have high geometric albedos 0.5, otherwise the derived thermal amplitude would be inconsistent with the total measured system fluxes at 24, 70, 100, 160, 250, and 350 Am. The high albedos imply sizes of about 300 and 150 km for Hi’iaka and Namaka, respectively, indicating unexpectedly high densities > 1.0 g cm-3 for TNOs this small, and the assumed collisional formation from Haumea’s icy crust. We also estimated the thermal emission of the ring for the time period 1980-2030, showing that the contribution during the Spitzer and Herschel epochs was small, but not negligible. Due to the progressive opening of the ring plane, the ring emission will be increasing in the next decade when JWST is operational. In the MIRI 25.5 m band it will also be possible to obtain a very high-quality thermal lightcurve to test the derived Haumea properties.

    19. Grundy, W. M., Noll, K. S., Roe, H. G., et al., 2019, Icar, 334, 62, Mutual orbit orientations of transneptunian binaries

      We present Keplerian orbit solutions for the mutual orbits of 17 transneptunian binary systems (TNBs). For ten of them, the orbit had not previously been known: 60458 2000 CM114, 119979 2002 WC19, 160091 2000 OL67, 160256 2002 PD149, 469514 2003 QA91, 469705 Kagara, 508788 2000 CQ114, 508869 2002 VT130, 1999 RT214, and 2002 XH91. Seven more are systems where the size, shape, and period of the orbit had been published, but new observations have now eliminated the sky plane mirror ambiguity in its orientation: 90482 Orcus, 120347 Salacia-Actaea, 1998 WW31, 1999 OJ4, 2000 QL251, 2001 XR254, and 2003 TJ58. The dynamical masses we obtain from TNB mutual orbits can be combined with estimates of the objects’ sizes from thermal observations or stellar occultations to estimate their bulk densities. The Kagara system is currently undergoing mutual events in which one component casts its shadow upon the other and/or obstructs the view of the other. Such events provide valuable opportunities for further characterization of the system. Combining our new orbits with previously published orbits yields a sample of 35 binary orbits with known orientations that can provide important clues about the environment in which outer solar system planetesimals formed, as well as their subsequent evolutionary history. Among the relatively tight binaries, with semimajor axes less than about 5% of their Hill radii, prograde mutual orbits vastly outnumber retrograde orbits. This imbalance is not attributable to any known observational bias. We suggest that this distribution could be the signature of planetesimal formation through gravitational collapse of local density enhancements such as caused by the streaming instability. Wider binaries, with semimajor axes >5% of their Hill radii, are somewhat more evenly distributed between prograde and retrograde orbits, but with mutual orbits that are aligned or anti-aligned with their heliocentric orbits. This pattern could perhaps result from Kozai-Lidov cycles coupled with tidal evolution eliminating high inclination wide binaries.

    20. Lin, Hsing Wen, Gerdes, David W., Hamilton, Stephanie J., et al., 2019, Icar, 334, 79, Reprint of “Evidence for color dichotomy in the primordial Neptunian Trojan population”

      In the current model of early Solar System evolution, the stable members of the Jovian and Neptunian Trojan populations were captured into resonance from the leftover reservoir of planetesimals during the outward migration of the giant planets. As a result, both Jovian and Neptunian Trojans share a common origin with the primordial disk population, whose other surviving members constitute today’s trans-Neptunian object (TNO) populations. The cold (low inclination and small eccentricity) classical TNOs are ultra-red, while the dynamically excited “hot” (high inclination and larger eccentricity) population of TNOs contains a mixture of ultra-red and blue objects. In contrast, Jovian and Neptunian Trojans are observed to be blue. While the absence of ultra-red Jovian Trojans can be readily explained by the sublimation of volatile material from their surfaces due to the high flux of solar radiation at 5 AU, the lack of ultra-red Neptunian Trojans presents both a puzzle and a challenge to formation models. In this work we report the discovery by the Dark Energy Survey (DES) of two new dynamically stable L4 Neptunian Trojans, 2013 VX30 and 2014 UU240, both with inclinations i > 30, making them the highest-inclination known stable Neptunian Trojans. We have measured the colors of these and three other dynamically stable Neptunian Trojans previously observed by DES, and find that 2013 VX30 is ultra-red, the first such Neptunian Trojan in its class. As such, 2013 VX30 may be a “missing link” between the Trojan and TNO populations. Using a simulation of the DES TNO detection efficiency, we find that there are 162 73 Trojans with Hr < 10 at the L4 Lagrange point of Neptune. Moreover, the blue-to-red Neptunian Trojan population ratio should be higher than 17:1. Based on this result, we discuss the possible origin of the ultra-red Neptunian Trojan population and its implications for the formation history of Neptunian Trojans.

    21. Martinez-Vazquez, C. E., Vivas, A. K., Gurevich, M., et al., 2019, MNRAS, 490, 2183, Search for RR Lyrae stars in DES ultrafaint systems: Grus I, Kim 2, Phoenix II, and Grus II

      This work presents the first search for RR Lyrae stars (RRLs) in four of the ultrafaint systems imaged by the Dark Energy Survey using SOAR/Goodman and Blanco/DECam imagers. We have detected two RRLs in the field of Grus I, none in Kim 2, one in Phoenix II, and four in Grus II. With the detection of these stars, we accurately determine the distance moduli for these ultrafaint dwarf satellite galaxies; 0 = 20.51 0.10 mag (D = 127 6 kpc) for Grus I and 0 = 20.01 0.10 mag (D = 100 5 kpc) for Phoenix II. These measurements are larger than previous estimations by Koposov et al. and Bechtol et al., implying larger physical sizes; 5 per cent for Grus I and 33 per cent for Phoenix II. For Grus II, of the four RRLs detected, one is consistent with being a member of the galactic halo (D = 24 1 kpc, 0 = 16.86 0.10 mag), another is at D = 55 2 kpc (0 = 18.71 0.10 mag), which we associate with Grus II, and the two remaining at D = 43 2 kpc (0 = 18.17 0.10 mag). Moreover, the appearance of a subtle red horizontal branch in the colour-magnitude diagram of Grus II at the same brightness level of the latter two RRLs, which are at the same distance and in the same region, suggests that a more metal-rich system may be located in front of Grus II. The most plausible scenario is the association of these stars with the Chenab/Orphan Stream. Finally, we performed a comprehensive and updated analysis of the number of RRLs in dwarf galaxies. This allows us to predict that the method of finding new ultrafaint dwarf galaxies using two or more clumped RRLs will work only for systems brighter than MV -6 mag.

    22. Farahi, A., Chen, X., Evrard, A. E., et al., 2019, MNRAS, 490, 3341, Mass variance from archival X-ray properties of Dark Energy Survey Year-1 galaxy clusters

      Using archival X-ray observations and a lognormal population model, we estimate constraints on the intrinsic scatter in halo mass at fixed optical richness for a galaxy cluster sample identified in Dark Energy Survey Year-One (DES-Y1) data with the redMaPPer algorithm. We examine the scaling behaviour of X-ray temperatures, TX, with optical richness, RM, for clusters in the redshift range 0.2 < z < 0.7. X-ray temperatures are obtained from Chandra and XMM observations for 58 and 110 redMaPPer systems, respectively. Despite non-uniform sky coverage, the TX measurements are > 50{{ per cent}} complete for clusters with RM > 130. Regression analysis on the two samples produces consistent posterior scaling parameters, from which we derive a combined constraint on the residual scatter, _{ln T | }= 0.275 0.019. Joined with constraints for TX scaling with halo mass from the Weighing the Giants program and richness-temperature covariance estimates from the LoCuSS sample, we derive the richness-conditioned scatter in mass, _{ln M | }= 0.30 0.04 _{(stat)} 0.09 _{(sys)}, at an optical richness of approximately 100. Uncertainties in external parameters, particularly the slope and variance of the TX-mass relation and the covariance of TX and RM at fixed mass, dominate the systematic error. The 95{{ per cent}} confidence region from joint sample analysis is relatively broad, _{ln M | }\in [0.14, 0.55], or a factor 10 in variance.

    23. Li, T. S., Koposov, S. E., Zucker, D. B., et al., 2019, MNRAS, 490, 3508, The southern stellar stream spectroscopic survey (S5): Overview, target selection, data reduction, validation, and early science

      We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9 m Anglo-Australian Telescope’s 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction, and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on S5, including future public data releases, can be found at

    24. Hannon, Stephen, Lee, Janice C., Whitmore, B. C., et al., 2019, MNRAS, 490, 4648, H morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters

      The morphology of H II regions around young star clusters provides insight into the time-scales and physical processes that clear a cluster’s natal gas. We study 700 young clusters (10 Myr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H morphology (concentrated, partially exposed, no-emission) and whether they have neighbouring clusters (which could affect the clearing time-scales). Through visual inspection of the HST images, and analysis of ages, reddenings, and stellar masses from spectral energy distributions fitting, together with the (U- B), (V – I) colours, we find (1) the median ages indicate a progression from concentrated (3 Myr), to partially exposed (4 Myr), to no H emission (>5 Myr), consistent with the expected temporal evolution of H II regions and previous results. However, (2) similarities in the age distributions for clusters with concentrated and partially exposed H morphologies imply a short time-scale for gas clearing (1 Myr). Also, (3) our cluster sample’s median mass is 1000 M, and a significant fraction ( 20{{ per cent}}) contain one or more bright red sources (presumably supergiants), which can mimic reddening effects. Finally, (4) the median E(B – V) values for clusters with concentrated H and those without H emission appear to be more similar than expected (0.18 versus 0.14, respectively), but when accounting for stochastic effects, clusters without H emission are less reddened. To mitigate stochastic effects, we experiment with synthesizing more massive clusters by stacking fluxes of clusters within each H morphological class. Composite isolated clusters also reveal a colour and age progression for H morphological classes, consistent with analysis of the individual clusters.

    25. D’Ammando, F., Raiteri, C. M., Villata, M., et al., 2019, MNRAS, 490, 5300, Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017

      We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi (-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented -ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 63) 10-8 ph cm-2 s-1, corresponding to a luminosity of (2.2 0.1) 1050 erg s-1, was reached on 2016 December 28. These four -ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and -ray activity is found. The -ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This -ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.

    26. Simon, M., Prato, L., 2019, RNAAS, 3, 186, Disk Evolution and Dissipation in the Taurus Star-forming Region
    27. Devogele, Maxime, Moskovitz, Nicholas, Thirouin, Audrey, et al., 2019, AJ, 158, 196, Visible Spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic Dependence on Asteroid Size

      The Mission Accessible Near-Earth Object Survey (MANOS) aims to observe and characterize small (mean absolute magnitude H 25 mag) Near-Earth Objects (NEOs) that are accessible by spacecraft (mean v 5.7 km s-1) and that make close approaches with the Earth (mean Minimum Orbital Intersection Distance MOID 0.03 au). We present here the first results of the MANOS visible spectroscopic survey. The spectra were obtained from August 2013 to March 2018 at Lowell Observatorys Discovery Channel 4.3 m telescope, and both Gemini North and South facilities. In total, 210 NEOs have been observed and taxonomically classified. Our taxonomic distribution shows significant variations with respect to surveys of larger objects. We suspect these to be due to a dependence of Main Belt source regions on object size. Compared to previous surveys of larger objects, we report a lower fraction of S+Q-complex asteroids of 43.8 4.6%. We associate this decrease with a lack of Phocaea family members at very small size. We also report higher fractions of X-complex and A-type asteroids of 23.8 3.3% and 3.8 1.3% respectively due to an increase of Hungaria family objects at small size. We find a strong correlation between the Q/S ratio and perihelion distance. We suggest this correlation is due to planetary close encounters with Venus playing a major role in turning asteroids from S to Q-type. This hypothesis is supported by a similar correlation between the Q/S ratio and Venus MOID.

    28. Shipp, N., Li, T. S., Pace, A. B., et al., 2019, ApJ, 885, 3, Proper Motions of Stellar Streams Discovered in the Dark Energy Survey

      We cross-match high-precision astrometric data from Gaia DR2 with accurate multiband photometry from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar streams in the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana III, and Turranburra. We determine low-confidence proper-motion measurements for four additional stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment between stream tracks and the systemic proper motion of streams that may suggest a systematic gravitational influence from the Large Magellanic Cloud (LMC). These proper motions, when combined with radial velocity measurements, will allow for detailed orbit modeling that can be used to constrain properties of the LMC and its effect on nearby streams, as well as global properties of the Milky Ways gravitational potential.

    29. Moskovitz, Nicholas A., Fatka, Petr, Farnocchia, Davide, et al., 2019, Icar, 333, 165, A common origin for dynamically associated near-Earth asteroid pairs

      Though pairs of dynamically associated asteroids in the Main Belt have been identified and studied for over a decade, very few pair systems have been identified in the near-Earth asteroid population. We present data and analysis that supports the existence of two genetically related pairs in near-Earth space. The members of the individual systems, 2015 EE7 – 2015 FP124 and 2017 SN16 – 2018 RY7, are found to be of the same spectral taxonomic class, and both pairs are interpreted to have volatile-poor compositions. In conjunction with dynamical arguments, this suggests that these two systems formed via YORP spin-up and/or dissociation of a binary precursor. Backwards orbital integrations suggest a separation age of <10 kyr for the pair 2017 SN16 – 2018 RY7, making these objects amongst the youngest multiple asteroid systems known to date. A unique separation age was not realized for 2015 EE7 – 2015 FP124 due to large uncertainties associated with these objects’ orbits. Determining the ages of such young pairs is of great value for testing models of space weathering and asteroid spin-state evolution. As the NEO catalog continues to grow with current and future discovery surveys, it is expected that more NEO pairs will be found, thus providing an ideal laboratory for studying time dependent evolutionary processes that are relevant to asteroids throughout the Solar System.

    30. Pravec, P., Fatka, P., Vokrouhlicky, D., et al., 2019, Icar, 333, 429, Asteroid pairs: A complex picture

      We studied a sample of 93 asteroid pairs, i.e., pairs of genetically related asteroids that are on highly similar heliocentric orbits. We estimated times elapsed since separation of pair members (i.e., pair age) that are between 7 103 yr and a few 106 yr. With photometric observations, we derived the rotation periods P1 for all the primaries (i.e., the larger members of asteroid pairs) and a sample of secondaries (the smaller pair members). We derived the absolute magnitude differences of the studied asteroid pairs that provide their mass ratios q. For a part of the studied pairs, we refined their WISE geometric albedos and collected or estimated their taxonomic classifications. For 17 asteroid pairs, we also determined their pole positions. In two pairs where we obtained the spin poles for both pair components, we saw the same sense of rotation for both components and constrained the angles between their original spin vectors at the time of their separation. We found that the primaries of 13 asteroid pairs in our sample are actually binary or triple systems, i.e., they have one or two bound, orbiting secondaries (satellites). As a by-product, we found also 3 new young asteroid clusters (each of them consisting of three known asteroids on highly similar heliocentric orbits). We compared the obtained asteroid pair data with theoretical predictions and discussed their implications. We found that 86 of the 93 studied asteroid pairs follow the trend of primary rotation period vs mass ratio that was found by Pravec et al. (2010). Of the 7 outliers, 3 appear insignificant (may be due to our uncertain or incomplete knowledge of the three pairs), but 4 are high mass ratio pairs that were unpredicted by the theory of asteroid pair formation by rotational fission. We discuss a (remotely) possible way that they could be created by rotational fission of flattened parent bodies followed by re-shaping of the formed components. The 13 asteroid pairs with binary primaries are particularly interesting systems that place important constraints on formation and evolution of asteroid pairs. We present two hypotheses for their formation: The asteroid pairs having both bound and unbound secondaries could be “failed asteroid clusters”, or they could be formed by a cascade primary spin fission process. Further studies are needed to reveal which of these two hypotheses for formation of the paired binary systems is real.

    31. Salvador, A. I., Sanchez, F. J., Pagul, A., et al., 2019, MNRAS, 482, 1435, Measuring linear and non-linear galaxy bias using counts-in-cells in the Dark Energy Survey Science Verification data

      Non-linear bias measurements require a great level of control of potential systematic effects in galaxy redshift surveys. Our goal is to demonstrate the viability of using counts-in-cells (CiC), a statistical measure of the galaxy distribution, as a competitive method to determine linear and higher-order galaxy bias and assess clustering systematics. We measure the galaxy bias by comparing the first four moments of the galaxy density distribution with those of the dark matter distribution. We use data from the MICE simulation to evaluate the performance of this method, and subsequently perform measurements on the public Science Verification data from the Dark Energy Survey. We find that the linear bias obtained with CiC is consistent with measurements of the bias performed using galaxy-galaxy clustering, galaxy-galaxy lensing, cosmic microwave background lensing, and shear + clustering measurements. Furthermore, we compute the projected (2D) non-linear bias using the expansion _{ g} = \sum _{k=0}3 (bk/k!) k, finding a non-zero value for b2 at the 3 level. We also check a non-local bias model and show that the linear bias measurements are robust to the addition of new parameters. We compare our 2D results to the 3D prediction and find compatibility in the large-scale regime (>30 h-1Mpc).

    32. Samuroff, S., Blazek, J., Troxel, M. A., et al., 2019, MNRAS, 489, 5453, Dark Energy Survey Year 1 results: constraints on intrinsic alignments and their colour dependence from galaxy clustering and weak lensing

      We perform a joint analysis of intrinsic alignments and cosmology using tomographic weak lensing, galaxy clustering, and galaxy-galaxy lensing measurements from Year 1 (Y1) of the Dark Energy Survey. We define early- and late-type subsamples, which are found to pass a series of systematics tests, including for spurious photometric redshift error and point spread function correlations. We analyse these split data alongside the fiducial mixed Y1 sample using a range of intrinsic alignment models. In a fiducial non-linear alignment model analysis, assuming a flat cold dark matter cosmology, we find a significant difference in intrinsic alignment amplitude, with early-type galaxies favouring A_IA = 2.38^{+0.32}_{-0.31} and late-type galaxies consistent with no intrinsic alignments at 0.05^{+0.10}_{-0.09}. The analysis is repeated using a number of extended model spaces, including a physically motivated model that includes both tidal torquing and tidal alignment mechanisms. In multiprobe likelihood chains in which cosmology, intrinsic alignments in both galaxy samples and all other relevant systematics are varied simultaneously, we find the tidal alignment and tidal torquing parts of the intrinsic alignment signal have amplitudes A_1 = 2.66 ^{+0.67}_{-0.66}, A_2=-2.94^{+1.94}_{-1.83}, respectively, for early-type galaxies and A_1 = 0.62 ^{+0.41}_{-0.41}, A_2 = -2.26^{+1.30}_{-1.16} for late-type galaxies. In the full (mixed) Y1 sample the best constraints are A_1 = 0.70 ^{+0.41}_{-0.38}, A_2 = -1.36 ^{+1.08}_{-1.41}. For all galaxy splits and IA models considered, we report cosmological parameter constraints consistent with the results of the main DES Y1 cosmic shear and multiprobe cosmology papers.

    33. Sluse, D., Rusu, C. E., Fassnacht, C. D., et al., 2019, MNRAS, 490, 613, H0LiCOW – X. Spectroscopic/imaging survey and galaxy-group identification around the strong gravitational lens system WFI 2033-4723

      Galaxies and galaxy groups located along the line of sight towards gravitationally lensed quasars produce high-order perturbations of the gravitational potential at the lens position. When these perturbation are too large, they can induce a systematic error on H0 of a few per cent if the lens system is used for cosmological inference and the perturbers are not explicitly accounted for in the lens model. In this work, we present a detailed characterization of the environment of the lens system WFI 2033-4723 (z_src = 1.662, z_lens= 0.6575), one of the core targets of the H0LiCOW project for which we present cosmological inferences in a companion paper. We use the Gemini and ESO-Very Large telescopes to measure the spectroscopic redshifts of the brightest galaxies towards the lens, and use the ESO-MUSE integral field spectrograph to measure the velocity-dispersion of the lens ( _{los}= 250^{+15}_{-21} km s-1) and of several nearby galaxies. In addition, we measure photometric redshifts and stellar masses of all galaxies down to i < 23 mag, mainly based on Dark Energy Survey imaging (DR1). Our new catalogue, complemented with literature data, more than doubles the number of known galaxy spectroscopic redshifts in the direct vicinity of the lens, expanding to 116 (64) the number of spectroscopic redshifts for galaxies separated by less than 3 arcmin (2 arcmin ) from the lens. Using the flexion-shift as a measure of the amplitude of the gravitational perturbation, we identify two galaxy groups and three galaxies that require specific attention in the lens models. The ESO MUSE data enable us to measure the velocity-dispersions of three of these galaxies. These results are essential for the cosmological inference analysis presented in Rusu et al.

    34. Kammer, Joshua A., Becker, Tracy M., Retherford, Kurt D., et al., 2019, AJ, 158, 168, Probing the Hill Sphere of (486958) 2014 MU69. II. Hubble Space Telescope Fine Guidance Sensors Observations during the 2018 August 4 Stellar Occultation

      We observed the 2018 August 4 stellar occultation by the Kuiper Belt object (486958) 2014 MU69, the first close flyby target of the extended New Horizons mission. Rather than capture a solid-body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for one HST orbit during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on of 0.02-0.08 for rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from 1660 to 57,700 km from the main body.

    35. Sullivan, Kendall, Prato, L., Edwards, Suzan, et al., 2019, ApJ, 884, 28, S and VV Corona Australis: Spectroscopic Variability in Two Young Binary Star Systems

      We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1-2 separation systems have optically thick circumstellar disks and high extinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we have determined the spectral types of all of the stars in these two systems for the first time, examined the variable NIR veiling, measured the emission line equivalent widths, and created spectral energy distributions. They have similar spectral types (K7-M1) and are at approximately the same evolutionary stage, allowing for comparison of the four stars in the two systems. We conclude that S CrA and VV CrA are young binary systems of stars bridging the Class I and Class II evolutionary stages, characterized by high accretion luminosities and variable emission lines.

    36. Simon, M., Guilloteau, S., Beck, Tracy L., et al., 2019, ApJ, 884, 42, Masses and Implications for Ages of Low-mass Pre-main-sequence Stars in Taurus and Ophiuchus

      The accuracy of masses of pre-main-sequence stars derived from their locations on the Hertzsprung-Russell diagram (HRD) can be tested by comparison with accurate and precise masses determined independently. We present 29 single stars in the Taurus star-forming region (SFR) and 3 in the Ophiuchus SFR with masses measured dynamically to a precision of at least 10%. Our results include 9 updated mass determinations and 3 that have not had their dynamical masses published before. This list of stars with fundamental, dynamical masses, M dyn, is drawn from a larger list of 39 targets in the Taurus SFR and 6 in the Ophiuchus SFR. Placing the stars with accurate and precise dynamical masses on HRDs that do not include internal magnetic fields underestimates the mass compared to M dyn by about 30%. Placing them on an HRD that does include magnetic fields yields mass estimates in much better agreement with M dyn, with an average difference between M dyn and the estimated track mass of 0.01 0.02 M . The ages of the stars, 3-10 MY on tracks that include magnetic fields, is older than the 1-3 MY indicated by the nonmagnetic models. The older ages of T Tauri stars predicted by the magnetic models increase the time available for evolution of their disks and formation of the giant gas exoplanets. The agreement between our M dyn values and the masses on the magnetic field tracks provides indirect support for these older ages.

    37. Cook, Jason C., Dalle Ore, Cristina M., Protopapa, Silvia, et al., 2019, Icar, 331, 148, The distribution of H2O, CH3OH, and hydrocarbon-ices on Pluto: Analysis of New Horizons spectral images

      On July 14, 2015, the New Horizons spacecraft made its closest approach to Pluto at about 12,000 km from its surface (Stern et al., 2015). Using the LEISA (Linear Etalon Imaging Spectral Array) near-IR imaging spectrometer we obtained two scans across the encounter hemisphere of Pluto at 6-7 km/pixel resolution. By correlating each spectrum with a crystalline H2O-ice model, we find several sites on Pluto’s surface that exhibit the 1.5, 1.65 and 2.0 m absorption bands characteristic of H2O-ice in the crystalline phase. These sites tend to be isolated and small ( 5000 km2 per site). We note a distinct near-IR blue slope over the LEISA wavelength range and asymmetries in the shape of the 2.0 m H2O-ice band in spectra with weak CH4-ice bands and strong H2O-ice bands. These characteristics are indicative of fine-grain (grain diameters < wavelength or 1 m) H2O-ice, like that seen in the spectra of Saturnian rings and satellites. However, the best-fit Hapke models require small mass fractions (10-3) of fine-grained H2O-ice that we can exchange for other refractory materials in the models with little change in 2, which may mean that the observed blue slope is possibly not due to a fine-grained material but an unidentified material with a similar spectral characteristic. We use these spectra to test for the presence of amorphous H2O-ice and estimate crystalline-to-amorphous H2O-ice fractions between 30 and 100%, depending on the location. We also see evidence for heavy hydrocarbons via strong absorption at > 2.3 m. Such heavy hydrocarbons are much less volatile than N2, CH4, and CO at Pluto temperatures. We test for CH3OH, C2H6, C2H4, and C3H8-ices because they have known optical constants and these ices are likely to arise from UV and energetic particle bombardment of the N2, CH4, CO-rich surface and atmosphere. Finally, we attempt to estimate the surface temperature using optical constants of pure CH4, and H2O-ice and best-fit Hapke models. Our standard model gives temperature estimates between 40 and 90 K, while our models including amorphous H2O-ice give lower temperature estimates between 30 and 65 K.

    38. Costanzi, M., Rozo, E., Simet, M., et al., 2019, MNRAS, 488, 4779, Methods for cluster cosmology and application to the SDSS in preparation for DES Year 1 release

      We implement the first blind analysis of cluster abundance data to derive cosmological constraints from the abundance and weak lensing signal of redMaPPer clusters in the Sloan Digital Sky Survey (SDSS). We simultaneously fit for cosmological parameters and the richness-mass relation of the clusters. For a flat cold dark matter cosmological model with massive neutrinos, we find S_8 8( _ m/0.3)^{0.5}=0.79^{+0.05}_{-0.04}. This value is both consistent and competitive with that derived from cluster catalogues selected in different wavelengths. Our result is also consistent with the combined probes analyses by the Dark Energy Survey (DES), the Kilo-Degree Survey (KiDS), and with the cosmic microwave background (CMB) anisotropies as measured by Planck. We demonstrate that the cosmological posteriors are robust against variation of the richness-mass relation model and to systematics associated with the calibration of the selection function. In combination with baryon acoustic oscillation data and big bang nucleosynthesis data (Cooke et al.), we constrain the Hubble rate to be h = 0.66 0.02, independent of the CMB. Future work aimed at improving our understanding of the scatter of the richness-mass relation has the potential to significantly improve the precision of our cosmological posteriors. The methods described in this work were developed for use in the forthcoming analysis of cluster abundances in the DES. Our SDSS analysis constitutes the first part of a staged-unblinding analysis of the full DES data set.

    39. Buchs, R., Davis, C., Gruen, D., et al., 2019, MNRAS, 489, 820, Phenotypic redshifts with self-organizing maps: A novel method to characterize redshift distributions of source galaxies for weak lensing

      Wide-field imaging surveys such as the Dark Energy Survey (DES) rely on coarse measurements of spectral energy distributions in a few filters to estimate the redshift distribution of source galaxies. In this regime, sample variance, shot noise, and selection effects limit the attainable accuracy of redshift calibration and thus of cosmological constraints. We present a new method to combine wide-field, few-filter measurements with catalogues from deep fields with additional filters and sufficiently low photometric noise to break degeneracies in photometric redshifts. The multiband deep field is used as an intermediary between wide-field observations and accurate redshifts, greatly reducing sample variance, shot noise, and selection effects. Our implementation of the method uses self-organizing maps to group galaxies into phenotypes based on their observed fluxes, and is tested using a mock DES catalogue created from N-body simulations. It yields a typical uncertainty on the mean redshift in each of five tomographic bins for an idealized simulation of the DES Year 3 weak-lensing tomographic analysis of z = 0.007, which is a 60 per cent improvement compared to the Year 1 analysis. Although the implementation of the method is tailored to DES, its formalism can be applied to other large photometric surveys with a similar observing strategy.

    40. Varga, T. N., DeRose, J., Gruen, D., et al., 2019, MNRAS, 489, 2511, Dark Energy Survey Year 1 results: validation of weak lensing cluster member contamination estimates from P(z) decomposition

      Weak lensing source galaxy catalogues used in estimating the masses of galaxy clusters can be heavily contaminated by cluster members, prohibiting accurate mass calibration. In this study, we test the performance of an estimator for the extent of cluster member contamination based on decomposing the photometric redshift P(z) of source galaxies into contaminating and background components. We perform a full scale mock analysis on a simulated sky survey approximately mirroring the observational properties of the Dark Energy Survey Year One observations (DES Y1), and find excellent agreement between the true number profile of contaminating cluster member galaxies in the simulation and the estimated one. We further apply the method to estimate the cluster member contamination for the DES Y1 redMaPPer cluster mass calibration analysis, and compare the results to an alternative approach based on the angular correlation of weak lensing source galaxies. We find indications that the correlation based estimates are biased by the selection of the weak lensing sources in the cluster vicinity, which does not strongly impact the P(z) decomposition method. Collectively, these benchmarks demonstrate the strength of the P(z) decomposition method in alleviating membership contamination and enabling highly accurate cluster weak lensing studies without broad exclusion of source galaxies, thereby improving the total constraining power of cluster mass calibration via weak lensing.

    41. Lee, S., Huff, E. M., Ross, A. J., et al., 2019, MNRAS, 489, 2887, Producing a BOSS CMASS sample with DES imaging

      We present a sample of galaxies with the Dark Energy Survey (DES) photometry that replicates the properties of the BOSS CMASS sample. The CMASS galaxy sample has been well characterized by the Sloan Digital Sky Survey (SDSS) collaboration and was used to obtain the most powerful redshift-space galaxy clustering measurements to date. A joint analysis of redshift-space distortions (such as those probed by CMASS from SDSS) and a galaxy-galaxy lensing measurement for an equivalent sample from DES can provide powerful cosmological constraints. Unfortunately, the DES and SDSS-BOSS footprints have only minimal overlap, primarily on the celestial equator near the SDSS Stripe 82 region. Using this overlap, we build a robust Bayesian model to select CMASS-like galaxies in the remainder of the DES footprint. The newly defined DES-CMASS (DMASS) sample consists of 117 293 effective galaxies covering 1244 \deg ^2. Through various validation tests, we show that the DMASS sample selected by this model matches well with the BOSS CMASS sample, specifically in the South Galactic cap (SGC) region that includes Stripe 82. Combining measurements of the angular correlation function and the clustering-z distribution of DMASS, we constrain the difference in mean galaxy bias and mean redshift between the BOSS CMASS and DMASS samples to be b = 0.010^{+0.045}_{-0.052} and z = \left(3.46^{+5.48}_{-5.55} \right) 10^{-3} for the SGC portion of CMASS, and b = 0.044^{+0.044}_{-0.043} and z= (3.51^{+4.93}_{-5.91}) 10^{-3} for the full CMASS sample. These values indicate that the mean bias of galaxies and mean redshift in the DMASS sample are consistent with both CMASS samples within 1.

    42. Gregg, Michael D., West, Michael J., 2019, hst, 16025, Snapshot Survey of the Globular Cluster Populations of Isolated Early Type Galaxies

      We propose WFC3/UVIS snapshot observations of a sample of 75 isolated early type galaxies residing in cosmic voids or extremely low density regions. The primary aim is to use their globular cluster populations to reconstruct their evolutionary history, revealing if, how, and why void ellipticals differ from cluster ellipticals. The galaxies span a range of luminosities, providing a varied sample for comparison with the well-documented globular cluster populations in denser environments. This proposed WFC3 study of isolated early type galaxies breaks new ground by targeting a sample which has thus far received little attention, and, significantly, this will be the first such study with HST. Characterizing early type galaxies in voids and their GC systems promises to increase our understanding of galaxy formation and evolution of galaxies in general because isolated objects are the best approximation to a control sample that we have for understanding the influence of environment on formation and evolution. Whether these isolated objects turn out to be identical to or distinct from counterparts in other regions of the Universe, they will supply insight into the formation and evolution of all galaxies. Parallel ACS imaging will help to characterize the near field environments of the sample.

    43. Santos, Fabio P., Chuss, David T., Dowell, C. Darren, et al., 2019, ApJ, 882, 113, The Far-infrared Polarization Spectrum of Ophiuchi A from HAWC+/SOFIA Observations

      We report on polarimetric maps made with HAWC+/SOFIA toward Oph A, the densest portion of the Ophiuchi molecular complex. We employed HAWC+ bands C (89 m) and D (154 m). The slope of the polarization spectrum was investigated by defining the quantity {{ \mathcal R }}{DC}={p}D/{p}C, where p C and p D represent polarization degrees in bands C and D, respectively. We find a clear correlation between {{ \mathcal R }}{DC} and the molecular hydrogen column density across the cloud. A positive slope ({{ \mathcal R }}{DC} > 1) dominates the lower-density and well-illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope ({{ \mathcal R }}{DC} < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of {{ \mathcal R }}{DC} is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.

    44. Marshall, J. L., Hansen, T., Simon, J. D., et al., 2019, ApJ, 882, 177, Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy

      We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in r-process elements, i.e., they have < [{Eu}/{Fe}]> +0.4 dex. The non-neutron-capture elements generally follow trends seen in other dwarf galaxies, including a metallicity range of 0.44 dex and the expected trend in -elements, i.e., the lower metallicity stars have higher Ca and Ti abundances. Overall, the chemical abundance patterns of these stars suggest that Tucana III was an ultra-faint dwarf galaxy, and not a globular cluster, before being tidally disturbed. As is the case for the one other galaxy dominated by r-process enhanced stars, Reticulum II, Tucana IIIs stellar chemical abundances are consistent with pollution from ejecta produced by a binary neutron star merger, although a different r-process element or dilution gas mass is required to explain the abundances in these two galaxies if a neutron star merger is the sole source of r-process enhancement.


      This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

    45. Alexandersen, Mike, Benecchi, Susan D., Chen, Ying-Tung, et al., 2019, ApJS, 244, 19, OSSOS. XII. Variability Studies of 65 Trans-Neptunian Objects Using the Hyper Suprime-Cam

      We present variability measurements and partial light curves of trans-Neptunian objects (TNOs) from a two-night pilot study using Hyper Suprime-Cam (HSC) on the Subaru Telescope (Maunakea, Hawaii, USA). Subarus large aperture (8 m) and HSCs large field of view (1.77 deg2) allow us to obtain measurements of multiple objects with a range of magnitudes in each telescope pointing. We observed 65 objects with m r = 22.6-25.5 mag in just six pointings, allowing 20-24 visits of each pointing over the two nights. Our sample, all discovered in the recent Outer Solar System Origins Survey (OSSOS), spans absolute magnitudes of H r = 6.2-10.8 mag and thus investigates smaller objects than previous light curve projects have typically studied. Our data supports the existence of a correlation between the light curve amplitude and absolute magnitude seen in other works but does not support a correlation between the amplitude and orbital inclination. Our sample includes a number of objects from different dynamical populations within the trans-Neptunian region, but we do not find any relationship between variability and the dynamical class. We were only able to estimate periods for 12 objects in the sample and found that a longer baseline of observations is required for a reliable period analysis. We find that 31 objects (just under half of our sample) have variability of {{{ }}}mag} greater than 0.4 mag during all of the observations; in smaller 1.25 hr, 1.85 hr, and 2.45 hr windows, the median {{{ }}}mag} is 0.13, 0.16, and 0.19 mag, respectively. The fact that variability on this scale is common for small TNOs has important implications for discovery surveys (such as OSSOS or the Large Synoptic Survey Telescope) and color measurements.


      Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

    46. Levesque, Emily, Prato, Lisa, Sneden, Chris, et al., 2019, BAAS, 51, 26, Key Challenges for AAS Journals in the Next Decade

      The AAS Journals are a vital asset to astronomy, but the page charge model for funding their publication could prove challenging in the open access (OA) era. Discussing alternative models for funding publishing costs must be part of Astro2020. We recommend that the NAS form a task force to address the concerns highlighted in this white paper.

    47. Hall, Jeffrey, Allen, Lori, Arion, Douglas, et al., 2019, BAAS, 51, 97, Light Pollution, Radio Interference, and Space Debris: Threats and Opportunities in the 2020s

      In this white paper, we will outline threats to astronomy in the areas of light pollution, radio interference, and space debris, and we will specify key principles and policy points that the AAS and other advocates can use in mitigating these threats.

    48. van Belle, Gerard, Armstrong, J. Thomas, Baines, Ellyn, et al., 2019, BAAS, 51, 104, The Navy Precision Optical Interferometer

      We outline a plan for NPOI for 2020-2030 that will provide the highest resolution visible-light system on the planet, with multi-km baselines and sub-mas imaging. This capability will resolve the sizes and shapes of stars, resolve AGNs, image protoplanetary disks, and observe the passage of exoplanets across their stellar disks.

    49. Monnier, John, Aarnio, Alicia, Absil, Olivier, et al., 2019, BAAS, 51, 133, Setting the Stage for the Planet Formation Imager

      The Planet Formation Imager (PFI) is a next-generation infrared interferometer designed to image the active phases of planet formation and to take planetary snapshots of young systems. We outline a technology plan to make PFI a reality, identifying a potential breakthrough opportunity for making inexpensive large telescopes available.

    50. Mawet, Dimitri, Fitzgerald, Michael, Konopacky, Quinn, et al., 2019, BAAS, 51, 134, High-resolution Infrared Spectrograph for Exoplanet Characterization with the Keck and Thirty Meter Telescopes

      HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffraction-limited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope.

    51. Monnier, John, Aarnio, Alicia, Absil, Olivier, et al., 2019, BAAS, 51, 153, A Realistic Roadmap to Formation Flying Space Interferometry

      The ultimate astronomical observatory would be a formation flying space interferometer, combining sensitivity and stability with high angular resolution. The smallSat revolution offers a new and maturing prototyping platform for space interferometry and we put forward a realistic plan for achieving first stellar fringes in space by 2030.

    52. Ridgway, Stephen, Armstrong, J. Thomas, Baines, Ellyn K., et al., 2019, BAAS, 51, 157, Revitalizing the Optical/Infrared Interferometry Community in the U.S.

      Long baseline optical/infrared interferometry (LBOI) has produced groundbreaking results in stellar astrophysics and is essential for the future of high-resolution observations. We describe capabilities and recent results, discuss the development of LBOI in the U.S., and make recommendations for the support and growth of U.S. interferometry.

    53. Rinehart, Stephen, Arenberg, J., Baines, E., et al., 2019, BAAS, 51, 222, A Long-Term Vision for Space-Based Interferometry

      A number of important astrophysical questions require observations with angular resolution beyond the capabilities of either existing or proposed facilities. We discuss some of these key science questions and present a potential path to obtaining high angular resolution through the development of space-based interferometers.

    54. Harrington, Joseph, Gommers, Ralf, Gentemann, Chelle, et al., 2019, BAAS, 51, 265, Support the Python Numerical Core

      Open-source software (OSS) promotes reproducibility and efficiency in science. The most popular OSS framework in astrophysics is the Python Numerical Core (PNC), including the NumPy, SciPy, Matplotlib, Pandas, and Scikit-learn packages. With over 5,000,000 users, these projects have grown beyond the volunteer scale and require financial support.

    55. Moore, Jeffrey M., McKinnon, William B., Spencer, John R., et al., 2019, EPSC, 2019, EPSC-DPS2019-50, Scarp Retreat on MU69: Evidence and Implications for Composition and Structure

      Crenulated scarps and other unit boundary patterns are consistent with scarp retreat. If indeed scarps have retreated on MU69 the most likely process is sublimation degradation. This explanation has implications for both original volatile composition and structure (layering) of MU69.

    56. Porter, Simon, Beyer, Ross, Keane, James, et al., 2019, EPSC, 2019, EPSC-DPS2019-311, The Shape and Pole of (486958) 2014 MU69

      NASA’s New Horizons spacecraft flew past the cold classical Kuiper Belt Object (KBO) 2014 MU69, providing the first opportunity to see a KBO up close. We will present our initial results on the shape and pole fitting of MU69, showing its contact-binary shape, highly-inclined pole, and the implications for KBO formation.

    57. McNeill, Andrew, Mommert, Michael, Trilling, David, et al., 2019, EPSC, 2019, EPSC-DPS2019-318, Asteroid Photometry from the Transiting Exoplanet Survey Satellite

      We present photometric measurements for main belt asteroids (MBAs) measured by the Transiting Exoplanet Survey Satellite (TESS). TESS data provides a unique opportunity to measure the how the brightness of thousands of asteroids change continuously for twenty-seven days and is the first data set to allow a probe of long asteroid rotation periods. We present a sample of the 300 constrained rotation periods and 6600 partial light curves obtained from Sectors 1+2 of the TESS Public Data Release, allowing us to learn about the shapes and rotational properties of these objects. We aim to continue this project through the mission lifetime of TESS and expect to obtain 4000 rotation periods and partial data for a further 48000 asteroids.

    58. Sanchez, Juan, Reddy, Vishnu, Thirouin, Audrey, et al., 2019, EPSC, 2019, EPSC-DPS2019-344, Characterization of Active Asteroid (6478) Gault

      Here we report the results from our rotational and spectral characterization of main belt active asteroid (6478) Gault. Based on three nights of observations, we could not confirm the rotation period of 2 h for Gault reported in previous work, as no obvious variability in the lightcurves was found. NIR spectroscopic data obtained with the IRTF showed a spectrum similar to that of S-type asteroids, and a composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and the Phocaea family.

    59. Moskovitz, Nicholas, Schottland, Robert, Burt, Brian, et al., 2019, EPSC, 2019, EPSC-DPS2019-644, Modernizing Lowell Observatory’s astorb Database

      The astorb database is an actively currated catalog of orbits for all known asteroids in the Solar System. The full catalog is downloadable from Lowell Observatory and VizieR. The data in astorb are used to support a number of observational planning tools hosted at Since 2016 we have been funded by NASA to modernize both the underlying database infrastructure and the front-end web applications. We will present an overview of the current astorb ecosystem and plans for future development.

    60. Moskovitz, Nicholas, Fatka, Petr, Farnocchia, Davide, et al., 2019, EPSC, 2019, EPSC-DPS2019-650, A common origin for dynamically associated near-Earth asteroid pairs

      We present analysis that supports the existence of two genetically related asteroid pairs in near-Earth space. This work suggests that these systems formed via radiative spin-up and fission, and/or dissociation of a binary asteroid. Backwards orbital integrations suggest a separation age of <10 kyr for one of these pairs, making it one of the youngest multiple asteroid systems known to date. As the NEO catalog grows with current and future discovery surveys, the known population of NEO pairs will also increase.

    61. Thirouin, Audrey, Sheppard, Scott S., 2019, EPSC, 2019, EPSC-DPS2019-657, Contact binaries in the trans-Neptunian population: location, physical and rotational properties.

      We are searching for and characterizing contact binaries in the trans-Neptunian populations through an extensive survey with the 4.3 m Lowell’s Discovery Channel Telescope and the 6.5 m Magellan-Baade telescope. We aim to derive their rotational and physical properties, to constrain their fractions in several sub-populations of trans-Neptunian objects, understand their formation and evolution as well as improve our knowledge of the binary population and by extension the entire trans-Neptunian belt

    62. Devogele, Maxime, Moskovitz, Nicholas, Thomas, Cristina, et al., 2019, EPSC, 2019, EPSC-DPS2019-694, The Mission Accessible Near-Earth Objects Survey (MANOS): taxonomic distribution of sub-kilometer NEOs

      The Mission Accessible Near-Earth Objects Survey (MANOS) is a new generation of surveys aiming to observe and characterize sub-kilometer newly discovered Near-Earth Objects (NEOs). This survey began in August 2013 and has been collecting astrometry, photometry, and reflectance spectra of this under-studied category of the NEO population. We have determined the taxonomic type of 210 asteroids with a mean size around 60 meters and as small as a few meters. This is the first comprehensive dataset for spectroscopically classified NEOs smaller than 100 meters. In the MANOS dataset, we find the population of small NEOs differ in composition from the population of larger ones. We believed this variation is due to the fact that NEOs originate from different source regions in the Main Belt. Each of these source regions have a different delivery rate efficiency as a function of object size.

    63. Schleicher, David, Knight, Mathew, Farnham, Tony, et al., 2019, EPSC, 2019, EPSC-DPS2019-740, Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19: Photometry, Jet Morphology, and Modeling Results

      An extensive observing campaign was successfully conducted for Comet 46P/Wirtanen during its excellent recent apparition of 2018/19 using several telescopes at Lowell Observatory. Gas and dust production rates were determined throughout the apparition, while narrowband imaging was obtained over a three-month interval. Two CN gas jets were detected, and modeling of these jets is on-going.

    64. Umurhan, Orkan M., Keane, James T., Porter, Simon B., et al., 2019, EPSC, 2019, EPSC-DPS2019-749, Near surface temperature modelling of 2014 MU_69

      New Horizons REX radiometer observed of the small Kuiper Belt Object 2014 MU69 at relatively high phase angle and measured a disk averaged brightness temperature of about 23 K. In this study, we perform a thermophysical analysis of the body to better understand this radio observation. We find for assumed thermophysical parameters, the REX radiometer may have been observing about 0.5 meters beneath MU69’s surface.

    65. Devogele, Maxime, Moskovitz, Nicholas, 2019, EPSC, 2019, EPSC-DPS2019-841, SPECTROSCOPYPIPELINE: multi-instrument python-based pipeline for long-slit asteroid visible spectroscopy reduction

      SPECTROSCOPYPIPELINE (SP) is a pipeline dedicated to the reduction of long-slit visible spectroscopic data. The pipeline can perform reduction of any spectroscopic data, but has been primarily developed and optimized for complete reduction of asteroid spectroscopic observation. It is a python-based open source pipeline intended to be easily portable to any long-slit spectrometer. It currently supports both Gemini North and South GMOS instruments, Lowell Observatory’s 4.3m Discovery Channel Telescope DeVeny spectrograph and the SOAR 4.1m Goodman spectrograph.

    66. Beyer, Ross, Porter, Simon, Schenk, Paul, et al., 2019, EPSC, 2019, EPSC-DPS2019-849, Stereo Topography of KBO (486958) 2014 MU69

      We describe stereo topography of KBO MU69. We detail the New Horizons observations that were used to produce the topography, characteristics of the resulting model, and its relation to the whole body shape model derived by other means.

    67. Fayolle, Marie, Quirico, Eric, Schmitt, Bernard, et al., 2019, EPSC, 2019, EPSC-DPS2019-876, Testing tholins as analogs of the dark reddish material covering the cthulhu region.

      We report on the determination of the optical properties of dusty tholins, which have been used in Hapke models to fit MVIC/LEISA data collected by the New Horizons spacecraft. We show a mismatch between models and observations, which is best explained by the presence of a highly porous organic material.

    68. Delbo, Marco, Walsh, Kevin, Avdellidou, Chrysa, et al., 2019, EPSC, 2019, EPSC-DPS2019-877, The search for the most ancient asteroid collisions reveals the original planetesimals of our solar system

      Hundred years of asteroid family research and new asteroid family identification methods have shed new light on the collisions among asteroids that shaped the main belt. In particular, in the inner portion of the belt – bracketed by the nu6 secular resonance at 2.1 au and by the J:3/1 mean motion resonance at 2.5 au – it is now possible to distinguish those asteroids that formed as collisional fragments from the break up of larger and older parents, and those other that are not fragments. This second population, which constitutes those asteroids that formed as planetsiamals by the accretion of dust in the protoplanetary disk, has a size distribution skewed towards bodies with diameters larger than 50 km. This indicates that planetesimals formed big, as previously suggested.

    69. Spencer, John, Grundy, William, Schmidt, Carl, 2019, EPSC, 2019, EPSC-DPS2019-935, Rapid Temporal Variability of Condensed Oxygen on Europa?

      New visible-wavelength spectroscopy of Europa provides the best view so far of the enigmatic 0.3% deep 5770 A absorption feature due to condensed O2. The band depth is inconsistent in observations of the same longitude on Europa taken a week apart, which if real implies surprisingly rapid temporal variability. Additional observations are being obtained to further test the reality of these rapid changes.

    70. Young, Leslie, Tan, Sugata, Trafton, Lawence, et al., 2019, EPSC, 2019, EPSC-DPS2019-1015, Atmosphere/Surface/Subsurface Interaction at Pluto

      Methane is critical to Pluto’s evolution. The methane in Pluto’s atmosphere, surface, and subsurface is not in equilibrium. If we understand how and why now, we can extrapolate behavior to other epochs.

    71. Knight, Matthew, Farnham, Tony, Schleicher, David, et al., 2019, EPSC, 2019, EPSC-DPS2019-1035, Narrowband Observations of Comet 46P/Wirtanen During its Exceptional Apparition of 2018/19: Gas Jet Morphology and Rotation Period

      An extensive observing campaign was successfully conducted for Comet 46P/Wirtanen during its excellent recent apparition of 2018/19 using several telescopes at Lowell Observatory. Narrowband imaging was obtained over a three-month interval, revealing two CN gas jets throughout the apparition. Their motion and repetition allowed us to determine a rotation period near 9 hr in early November. We continued to obtain sufficient data to constrain the rotation period through early February and detect little to no change. We see no rotational variation in dust images. C3 exhibits a similar morphology to CN, while OH shows a different spatial distribution. Analyses are ongoing and new results will be presented.

    72. Prato, Lisa, Johns-Krull, Christopher, Llama, Joe, et al., 2019, EPSC, 2019, EPSC-DPS2019-1078, Finding the Youngest Exoplanets

      In spite of the diverse wealth of data provided by the identification of thousands of planets spanning a broad parameter space, we know little about young (less than a few Myr old) planets. To advance our understanding of the processes governing planet formation and evolution, we need to find and characterize young planets themselves. Given the extreme activity inherent in young stars, particularly those with active, primordial accretion disks, this is a challenging undertaking. We describe our search for young exoplanets and recent results.

    73. Hanley, Jennifer, Engle, Anna, Dustrud, Shyanne, et al., 2019, EPSC, 2019, EPSC-DPS2019-1146, Understanding the Hydrocarbon Lakes and Seas on Titan

      We have performed laboratory experiments and chemical modeling to understand methane and ethane stability in the presence of a nitrogen atmosphere with respect to surface condition on Titan.

    74. Gustafsson, Annika, Moskovitz, Nicholas, Protopapa, Silvia, et al., 2019, EPSC, 2019, EPSC-DPS2019-1179, Water-Ice Distribution in the Coma of 46P/Wirtanen

      Comet 46P/Wirtanen made a close approach to the Earth in December 2018 (geocentric distance=0.077 au ; heliocentric distance=1.056 au), providing a unique opportunity to collect spatially resolved spectral observations. We created a near-infrared spectral data cube near close approach to better understand the water-ice grain properties of the comet coma.

    75. Gustafsson, Annika, Moskovitz, Nicholas, Roe, Henry, et al., 2019, EPSC, 2019, EPSC-DPS2019-1190, The Near-Infrared High Throughput Spectrograph

      NIHTS is a low resolution near-infrared spectrograph on the Discovery Channel Telescope in Happy Jack, AZ, USA. NIHTS has been fully operational since March of 2018. The instrument will enable many science use cases, including investigations into water-ice in Kuiper Belt Objects and comets, and classification of Near-Earth asteroids and ultracool brown dwarfs.

    76. Fraser, Wesley, Schwamb, Megan, Bannister, Michele, et al., 2019, EPSC, 2019, EPSC-DPS2019-1206, Col-OSSOS: A Compositional Interpretation of Kuiper Belt Spectra

      We propose a new compositional model for Kuiper Belt Objects that can account for many of the observed properties of those bodies, including their colour, and spectral behaviour. This model successfully accounts for the links to other related bodies, including the satellite Phoebe. The model asserts that the majority of KBOs consist of reddened carbonaceous material. If true, this implies that neutral class KBOs share a primordial link with the carbonaceous asteroids, the same bodies that scattered in to become the C-types in the asteroid belt.

    77. Schwamb, Megan, Fraser, Wesley, Bannister, Michele, et al., 2019, EPSC, 2019, EPSC-DPS2019-1271, A Potential New Surface Type in the Kuiper Belt

      Colours of the Outer Solar System Origins Survey (Col-OSSOS) is probing Kuiper belt object (KBO) surface properties via near simultaneous g,r and J photometry from Gemini North with additional u-band imaging from CFHT. We will present the latest results from the survey including the surface properties of two outlier objects from the Col-OSSOS color distribution that may represent a new surface type present within the small KBO population.

    78. Sickafoose, Amanda, Bosh, Amanda, Emery, Joshua, et al., 2019, EPSC, 2019, EPSC-DPS2019-1306, Characterization of material around (2060) Chiron from a 2011 stellar occultation

      We present results from a stellar occultation by the centaur Chiron from observations in 2011. This work places a constraint on the size of Chiron’s nucleus and expands on previous work by analyzing the surrounding material in detail. We find (i) two distinct, thin features that are symmetric around the nucleus and 300 km away; (ii) multiple asymmetric arcs or less-optically-thick material between 200-450 km; and (iii) what is likely a diffuse shell of material extending from 900-1500 km. These results are particularly interesting in the context of the ring system that was discovered around the similarly-sized centaur Chariklo.

    79. Young, Leslie, Porter, Simon, Keeny, Brian, et al., 2019, EPSC, 2019, EPSC-DPS2019-1321, The Gaia-based prediction of the 2019 May 1 occultation of elongated KBO (33128) 1998 BU48

      Gaia should enable the Golden Age of stellar occultations. We planned for an occultation by elongated KBO 1998 BU48, with no positive reported events yet. We will study this example to improve future Gaia-enabled occultations.

    80. Marciniak, Anna, Oszkiewicz, Dagmara, Troianskyi, Volodymyr, et al., 2019, EPSC, 2019, EPSC-DPS2019-1379, Investigating V-type asteroids outside Vesta family

      We are conducting a photometric, spectroscopic, and dynamical study of V-type asteroids outside the Vesta family in the inner main belt. The aim is to find traces of once existing differentiated planetesimals other than Vesta, to provide the missing observational evidence for theories predicting an abundance of such planetesimals in the early solar system.

    81. McKinnon, William B., Keane, James T., Nesvorny, David, et al., 2019, EPSC, 2019, EPSC-DPS2019-1387, On the Origin of the Remarkable Contact Binary (486958) 2014 MU69 (“Ultima Thule”)

      We discuss the remarkable world 2014 MU69, or “Ultima Thule,” as revealed by the recent New Horizons flyby. This body reveals hitherto unimagined details of how the building blocks of planets -planetesimals -were actually assembled.

    82. Bertrand, T., Forget, F., Umurhan, O. M., et al., 2019, Icar, 329, 148, The CH4 cycles on Pluto over seasonal and astronomical timescales

      Pluto’s surface is covered in numerous CH4 ice deposits, that vary in texture and brightness, as revealed by the New Horizons spacecraft as it flew by Pluto in July 2015. These observations suggest that CH4 on Pluto has a complex history, involving reservoirs of different composition, thickness and stability controlled by volatile processes occurring on different timescales. In order to interpret these observations, we use a Pluto volatile transport model able to simulate the cycles of N2 and CH4 ices over millions of years. By assuming fixed solid mixing ratios, we explore how changes in surface albedos, emissivities and thermal inertias impact volatile transport. This work is therefore a direct and natural continuation of the work by Bertrand et al. (2018), which only explored the N2 cycles. Results show that bright CH4 deposits can create cold traps for N2 ice outside Sputnik Planitia, leading to a strong coupling between the N2 and CH4 cycles. Depending on the assumed albedo for CH4 ice, the model predicts CH4 ice accumulation (1) at the same equatorial latitudes where the Bladed Terrain Deposits are observed, supporting the idea that these CH4-rich deposits are massive and perennial, or (2) at mid-latitudes (25- 70), forming a thick mantle which is consistent with New Horizons observations. In our simulations, both CH4 ice reservoirs are not in an equilibrium state and either one can dominate the other over long timescales, depending on the assumptions made for the CH4 albedo. This suggests that long-term volatile transport exists between the observed reservoirs. The model also reproduces the formation of N2 deposits at mid-latitudes and in the equatorial depressions surrounding the Bladed Terrain Deposits, as observed by New Horizons. At the poles, only seasonal CH4 and N2 deposits are obtained in Pluto’s current orbital configuration. Finally, we show that Pluto’s atmosphere always contained, over the last astronomical cycles, enough gaseous CH4 to absorb most of the incoming Lyman- flux.

    83. Cruikshank, Dale P., Umurhan, Orkan M., Beyer, Ross A., et al., 2019, Icar, 330, 155, Recent cryovolcanism in Virgil Fossae on Pluto

      The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae troughs or channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 m of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. Model calculations of NH3 destruction in H2O ice by galactic cosmic rays suggest that the maximum lifetime of NH3 in the uppermost meter of the exposed surface is 109 years, while considerations of Lyman- ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 10000. Thus, 109 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger.


      The red colorant in the ammoniated H2O in Virgil Fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of Pluto’s surface, but probably different in composition and age. Owing to the limited spectral range of the New Horizons imaging spectrometer and the signal precision of the data, apart from the H2O and NH3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on Pluto. We suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. Although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside Pluto.

      A planet-scale stress pattern in Pluto’s lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of Sputnik Planitia, consistent with the structure of Virgil Fossae and similar extensional features. This faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated H2O ice deposits in and around Virgil Fossae. Models of a cryoflow emerging from sources in Virgil Fossae indicate that the lateral extent of the flow can be several km (Umurhan et al., 2019). The deposit over the full length (>200 km) of the main trough in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of 2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for Pluto’s interior. Alternatives to cryovolcanism in producing the observed characteristics of the region around Virgil Fossae are explored in the discussion section of the paper.

    84. Zhang, Y., Miller, C. J., Rooney, P., et al., 2019, MNRAS, 488, 1, Galaxies in X-ray selected clusters and groups in Dark Energy Survey data – II. Hierarchical Bayesian modelling of the red-sequence galaxy luminosity function

      Using 100 X-ray selected clusters in the Dark Energy Survey Science Verification data, we constrain the luminosity function (LF) of cluster red-sequence galaxies as a function of redshift. This is the first homogeneous optical/X-ray sample large enough to constrain the evolution of the LF simultaneously in redshift (0.1 < z < 1.05) and cluster mass (13.5 {log_{10}}(M_{200crit}) < 15.0). We pay particular attention to completeness issues and the detection limit of the galaxy sample. We then apply a hierarchical Bayesian model to fit the cluster galaxy LFs via a Schechter function, including its characteristic break (m*) to a faint end power-law slope (). Our method enables us to avoid known issues in similar analyses based on stacking or binning the clusters. We find weak and statistically insignificant (1.9) evolution in the faint end slope versus redshift. We also find no dependence in or m* with the X-ray inferred cluster masses. However, the amplitude of the LF as a function of cluster mass is constrained to { } 20{{ per cent}} precision. As a by-product of our algorithm, we utilize the correlation between the LF and cluster mass to provide an improved estimate of the individual cluster masses as well as the scatter in true mass given the X-ray inferred masses. This technique can be applied to a larger sample of X-ray or optically selected clusters from the Dark Energy Survey, significantly improving the sensitivity of the analysis.

    85. Klein, M., Grandis, S., Mohr, J. J., et al., 2019, MNRAS, 488, 739, A new RASS galaxy cluster catalogue with low contamination extending to z 1 in the DES overlap region

      We present the MARD-Y3 catalogue of between 1086 and 2171 galaxy clusters (52 per cent and 65 per cent new) produced using multicomponent matched filter (MCMF) follow-up in 5000 deg2 of DES-Y3 optical data of the 20 000 overlapping ROSAT All-Sky Survey source catalogue (2RXS) X-ray sources. Optical counterparts are identified as peaks in galaxy richness as a function of redshift along the line of sight towards each 2RXS source within a search region informed by an X-ray prior. All peaks are assigned a probability fcont of being a random superposition. The clusters lie at 0.02 < z < 1.1 with more than 100 clusters at z > 0.5. Residual contamination is 2.6 per cent and 9.6 per cent for the cuts adopted here. For each cluster we present the optical centre, redshift, rest frame X-ray luminosity, M500 mass, coincidence with NWAY infrared sources, and estimators of dynamical state. About 2 per cent of MARD-Y3 clusters have multiple possible counterparts, the photo-z’s are high quality with z/(1 + z) = 0.0046, and 1 per cent of clusters exhibit evidence of X-ray luminosity boosting from emission by cluster active galactic nuclei. Comparison with other catalogues (MCXC, RM, SPT-SZ, Planck) is performed to test consistency of richness, luminosity, and mass estimates. We measure the MARD-Y3 X-ray luminosity function and compare it to the expectation from a fiducial cosmology and externally calibrated luminosity- and richness-mass relations. Agreement is good, providing evidence that MARD-Y3 has low contamination and can be understood as a simple two step selection – X-ray and then optical – of an underlying cluster population described by the halo mass function.

    86. Torrealba, G., Belokurov, V., Koposov, S. E., et al., 2019, MNRAS, 488, 2743, The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2

      We report the discovery of a Milky Way satellite in the constellation of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic disc at a latitude of b 11 and spans 1.26, which corresponds to 2.9 kpc at its distance of 130 kpc. While similar in spatial extent to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter at MV = -9 mag, making it by far the lowest surface brightness system known (at 31.9 mag arcsec-2), 100 times more diffuse than the so-called ultra diffuse galaxies. The satellite was identified using a combination of astrometry, photometry, and variability data from Gaia Data Release 2, and its nature confirmed with deep archival DECam imaging, which revealed a conspicuous BHB signal. We have also obtained follow-up spectroscopy using AAOmega on the AAT, identifying 159 member stars, and we used them to measure the dwarf’s systemic velocity, 290.9 0.5 km s-1, its velocity dispersion, 5.7 1.1 km s-1, and mean metallicity, [Fe/H] = -1.4. From these properties we conclude that Antlia 2 inhabits one of the least dense dark matter (DM) haloes probed to date. Dynamical modelling and tidal-disruption simulations suggest that a combination of a cored DM profile and strong tidal stripping may explain the observed properties of this satellite. The origin of this core may be consistent with aggressive feedback, or may even require alternatives to cold dark matter (such as ultra-light bosons).

    87. Gruen, D., Zhang, Y., Palmese, A., et al., 2019, MNRAS, 488, 4389, Dark Energy Survey Year 1 results: the effect of intracluster light on photometric redshifts for weak gravitational lensing

      We study the effect of diffuse intracluster light on the critical surface mass density estimated from photometric redshifts of lensing source galaxies, and the resulting bias in a weak lensing measurement of galaxy cluster mass. Under conservative assumptions, we find the bias to be negligible for imaging surveys like the Dark Energy Survey with a recommended scale cut of 200 kpc distance from cluster centres. For significantly deeper lensing source galaxy catalogues from present and future surveys like the Large Synoptic Survey Telescope program, more conservative scale and source magnitude cuts or a correction of the effect may be necessary to achieve percent level lensing measurement accuracy, especially at the massive end of the cluster population.

    88. Pandey, S., Baxter, E. J., Xu, Z., et al., 2019, PhRvD, 100, 063519, Constraints on the redshift evolution of astrophysical feedback with Sunyaev-Zel’dovich effect cross-correlations

      An understanding of astrophysical feedback is important for constraining models of galaxy formation and for extracting cosmological information from current and future weak lensing surveys. The thermal Sunyaev-Zel’dovich effect, quantified via the Compton-y parameter, is a powerful tool for studying feedback, because it directly probes the pressure of the hot, ionized gas residing in dark matter halos. Cross-correlations between galaxies and maps of Compton-y obtained from cosmic microwave background surveys are sensitive to the redshift evolution of the gas pressure, and its dependence on halo mass. In this work, we use galaxies identified in year one data from the Dark Energy Survey and Compton-y maps constructed from Planck observations. We find highly significant (roughly 12 ) detections of galaxy-y cross-correlation in multiple redshift bins. By jointly fitting these measurements as well as measurements of galaxy clustering, we constrain the halo bias-weighted, gas pressure of the Universe as a function of redshift between 0.15 z 0.75 . We compare these measurements to predictions from hydrodynamical simulations, allowing us to constrain the amount of thermal energy in the halo gas relative to that resulting from gravitational collapse.

    89. Thirouin, Audrey, Sheppard, Scott S., 2019, AJ, 158, 53, Colors of Trans-Neptunian Contact Binaries

      The gri colors of seven likely and potential contact binaries in the Kuiper Belt were acquired with the Magellan-Baade telescope and combined with colors from the literature to understand contact binary surfaces. The likely and potential contact binaries discovered in the dynamically cold classical population display very red/ultra-red colors. Such colors are common in this sub-population and imply that the cold classical contact binaries were formed in situ. The likely contact binaries found in several mean motion resonances with Neptune have colors from moderately to ultra-red, suggesting different formation regions. Among the nine contact binaries discovered in resonances, five have very red/ultra-red colors and four have moderately red surfaces. Based on the very red/ultra-red colors and low to moderate inclinations of the contact binaries in resonances, these contact binaries are possibly escaped dynamically cold classicals that are now trapped in resonances. Moderately red surfaces are common in diverse sub-populations of the Kuiper Belt, thus pinpointing their origin is difficult though they are most likely captured objects that formed in the giant planet area. Finally, for the contact binary population we report an anti-correlation between inclination and g-r, as noticed in the rest of this belt. We also find hints of trends between eccentricity, perihelion distance, rotational period, and g-r, but as we are still dealing with a limited sample, additional data are required to confirm them.

    90. Healy, Brian F., Han, Eunkyu, Muirhead, Philip S., et al., 2019, AJ, 158, 89, Magnetic Inflation and Stellar Mass. III. Revised Parameters for the Component Stars of NSVS 07394765

      We perform a new analysis of the M-dwarf-M-dwarf eclipsing binary system NSVS 07394765 in order to investigate the reported hyper-inflated radius of one of the component stars. Our analysis is based on archival photometry from the Wide Angle Search for Planets, new photometry from the 32 cm Command Module Observatory telescope in Arizona and the 70 cm telescope at Thacher Observatory in California, and new high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrograph on the Discovery Channel Telescope. The masses and radii we measure for each component star disagree with previously reported measurements. We show that both stars are early M-type main-sequence stars without evidence for youth or hyper-inflation ({M}1={0.661}-0.036+0.008 {M} , {M}2={0.608}-0.028+0.003 {M} , {R}1={0.599}-0.019+0.032 {R} , {R}2={0.625}-0.027+0.012 {R} ), and we update the orbital period and eclipse ephemerides for the system. We suggest that the likely cause of the initial hyper-inflated result is the use of moderate-resolution spectroscopy for precise radial velocity measurements.

    91. Wang, M. Y., de Boer, T., Pieres, A., et al., 2019, ApJ, 881, 118, The Morphology and Structure of Stellar Populations in the Fornax Dwarf Spheroidal Galaxy from Dark Energy Survey Data

      Using deep wide-field photometry 3 yr data (Y3) from the Dark Energy Survey (DES), we present a panoramic study of the Fornax dwarf spheroidal galaxy. The data presented herea small subset of the full surveyuniformly cover a region of 25 deg2 centered on the galaxy to a depth of g 23.5. We use these data to study the structural properties of Fornax, overall stellar population, and its member stars in different evolutionary phases. We also search for possible signs of tidal disturbance. Fornax is found to be significantly more spatially extended than what early studies suggested. No statistically significant distortions or signs of tidal disturbances were found down to a surface brightness limit of 32.1 mag arcsec-2. However, there are hints of shell-like features located 20-40 from the center of Fornax that may be stellar debris from past merger events. We also find that intermediate-age and young main-sequence populations show different orientation at the galaxy center and have many substructures. The deep DES Y3 data allow us to characterize the age of those young stellar substructures with great accuracy, both those previously known and those newly identified as possible overdensities in this work, on the basis of their color-magnitude diagram morphology. We find that the youngest overdensities are all found on the eastern side of Fornax, where the Fornax field population itself is slightly younger than in the west. In summary, the high-quality DES Y3 data reveal that Fornax has many rich structures and provide insights into its complex formation history.

    92. Sanchez, Juan A., Reddy, Vishnu, Thirouin, Audrey, et al., 2019, ApJL, 881, L6, Physical Characterization of Active Asteroid (6478) Gault

      Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter <6 km. Near-infrared spectroscopic data obtained with the Infrared Telescope Facility showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.

    93. Clark, Catherine, van Belle, Gerard, Horch, Elliott, et al., 2019, ESS, 51, 316.03, Understanding the Multiplicity of TESS Exoplanet Host Candidates

      While at first glance multi-star systems seem quite extreme, they are in fact the most common type of star system in our galaxy, throughout the stellar mass distribution. In particular, 40 to 50% of exoplanet host stars reside within multiple star systems. Given the degree to which initially undetected multiplicity has skewed Kepler results, high-resolution imaging of our nearby low-mass neighbors is necessary for both accurate characterization of transiting exoplanets, as well as a better understanding of stellar astrophysics. To address this frequent gap in our knowledge of exoplanet hosts, we will utilize speckle interferometry to directly image TESS exoplanet host candidates to complete our knowledge of individual star multiplicity. Our investigation will expand upon the speckle observations taken as a part of the POKEMON speckle survey of nearby M-dwarfs to better constrain the multiplicity of low-mass TESS exoplanet host candidates, and to constrain M-dwarf multiplicity by subtype across the entire M-dwarf sequence.

    94. Cauley, Paul Wilson, Shkolnik, Evgenya L., Llama, Joe, et al., 2019, ESS, 51, 319.09, Magnetic fields of hot Jupiters calculated from star-planet interactions

      Planetary magnetic fields have a critical impact on atmospheric physics, damping winds on hot, short-period planets and potentially creating the necessary conditions for habitability on temperate terrestrial worlds by deflecting stellar wind particles. Despite their importance, exoplanet magnetic field detections remain elusive. For the first time, we report the derivation of the magnetic fields of a sample of hot Jupiters using flux-calibrated signals of magnetic star-planet interactions (SPI). We find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, 10 – 50 times larger than the values predicted by pure dynamo theories for planets with rotation periods of 2 to 4 days. Such large field strengths should have severe consequences for velocity flows in the planets’ atmospheres and exhibit peak frequencies of electron-cyclotron emission in the range of facilities such as LOFAR.

    95. Llama, Joe, Johns-Krull, Christopher, Prato, Lisa, et al., 2019, ESS, 51, 322.02, Formation and atmospheric constraints of the youngest hot Jupiter.

      The last three years have ushered in the era of young exoplanets. Despite young stars exhibiting extreme levels of variability, a handful of newly formed exoplanets have been detected through transits and radial velocity. We will present the latest results from our young planet survey. For the first time, using high-resolution infrared spectra, we have a direct detection of CO in the atmosphere of the youngest exoplanet CI Tau b, confirming the planet, and providing evidence for a hot start mechanism. Our discovery shows that hot Jupiters either form incredibly close to their parent star, or, that migration occurs within the first 2 Myr.

    96. van Belle, Gerard, Clark, Catherine, Horch, Elliott, et al., 2019, ESS, 51, 330.17, Exoplanet Host Star Characterization with QWSSI

      QWSSI, the Quad-camera Wavefront-Sensing Speckle Imager, is a next-generation speckle imager that is being developed for Lowell Observatory’s 4.3-meter Discovery Channel Telescopes. The principle behind QWSSI is to extend the capabilities of the speckle camera currently resident at Lowell, the Differential Speckle Survey Instrument (DSSI), in two ways. First, while DSSI currently observes in two visible channels, QWSSI will simultaneously observe in six narrow-band channels: four in the visible (0.5-0.9um), and one each in J- and H-band (1.2 and 1.6um). Second, the visible light unused for speckle imaging is carefully preserved and feeds a wavefront sensor (WFS), which is also run simultaneously with the speckle imaging. Simulations by Lobb (2016) indicate WFS data will provide significant gains in exploring stellar multiplicity, with marked improvements in primary-secondary contrast ratios and inner working angle (Horch et al. 2018). QWSSI will also be mountable on one of the three 1-meter telescopes being installed on the NPOI Array for engineering tests and preliminary science observations. QWSSI will expand on the already considerable exoplanetary work of the speckle imagers DSSI, NESSI (@ WIYN), Alopeke (Gemini-N), and Zorro (Gemini-S), improving the discovery space for existing targets, as well opening up new regions of that discovery space with its NIR channels.

    97. Reed, S. L., Banerji, M., Becker, G. D., et al., 2019, MNRAS, 487, 1874, Three new VHS-DES quasars at 6.7 < z < 6.9 and emission line properties at z > 6.5

      We report the results from a search for z > 6.5 quasars using the Dark Energy Survey (DES) Year 3 data set combined with the VISTA Hemisphere Survey (VHS) and WISE All-Sky Survey. Our photometric selection method is shown to be highly efficient in identifying clean samples of high-redshift quasars, leading to spectroscopic confirmation of three new quasars – VDES J0244-5008 (z = 6.724), VDES J0020-3653 (z = 6.834), and VDES J0246-5219 (z = 6.90) – which were selected as the highest priority candidates in the survey data without any need for additional follow-up observations. We have obtained spectroscopic observations in the near-infrared for VDES J0244-5008 and VDES J0020-3653 as well as our previously identified quasar, VDES J0224-4711 at z = 6.50 from Reed et al. We use the near-infrared spectra to derive virial black hole masses from the full width at half-maximum of the Mg II line. These black hole masses are 1-2 109 M. Combined with the bolometric luminosities of these quasars of Lbol 1-3 1047, these imply that the Eddington ratios are high, 0.6-1.1. We consider the C IV emission line properties of the sample and demonstrate that our high-redshift quasars do not have unusual C IV line properties when compared to carefully matched low-redshift samples. Our new DES + VHS z > 6.5 quasars now add to the growing census of luminous, rapidly accreting supermassive black holes seen well into the epoch of reionization.

    98. Angus, C. R., Smith, M., Sullivan, M., et al., 2019, MNRAS, 487, 2215, Superluminous supernovae from the Dark Energy Survey

      We present a sample of 21 hydrogen-free superluminous supernovae (SLSNe-I) and one hydrogen-rich SLSN (SLSN-II) detected during the five-year Dark Energy Survey (DES). These SNe, located in the redshift range 0.220 < z < 1.998, represent the largest homogeneously selected sample of SLSN events at high redshift. We present the observed g, r, i, z light curves for these SNe, which we interpolate using Gaussian processes. The resulting light curves are analysed to determine the luminosity function of SLSNe-I, and their evolutionary time-scales. The DES SLSN-I sample significantly broadens the distribution of SLSN-I light-curve properties when combined with existing samples from the literature. We fit a magnetar model to our SLSNe, and find that this model alone is unable to replicate the behaviour of many of the bolometric light curves. We search the DES SLSN-I light curves for the presence of initial peaks prior to the main light-curve peak. Using a shock breakout model, our Monte Carlo search finds that 3 of our 14 events with pre-max data display such initial peaks. However, 10 events show no evidence for such peaks, in some cases down to an absolute magnitude of <-16, suggesting that such features are not ubiquitous to all SLSN-I events. We also identify a red pre-peak feature within the light curve of one SLSN, which is comparable to that observed within SN2018bsz.

    99. Zhang, Y., Jeltema, T., Hollowood, D. L., et al., 2019, MNRAS, 487, 2578, Dark Energy Surveyed Year 1 results: calibration of cluster mis-centring in the redMaPPer catalogues

      The centre determination of a galaxy cluster from an optical cluster finding algorithm can be offset from theoretical prescriptions or N-body definitions of its host halo centre. These offsets impact the recovered cluster statistics, affecting both richness measurements and the weak lensing shear profile around the clusters. This paper models the centring performance of the redMaPPer cluster finding algorithm using archival X-ray observations of redMaPPer-selected clusters. Assuming the X-ray emission peaks as the fiducial halo centres, and through analysing their offsets to the redMaPPer centres, we find that { } 75 8 {{ per cent}} of the redMaPPer clusters are well centred and the mis-centred offset follows a Gamma distribution in normalized, projected distance. These mis-centring offsets cause a systematic underestimation of cluster richness relative to the well-centred clusters, for which we propose a descriptive model. Our results enable the DES Y1 cluster cosmology analysis by characterizing the necessary corrections to both the weak lensing and richness abundance functions of the DES Y1 redMaPPer cluster catalogue.

    100. Pollina, G., Hamaus, N., Paech, K., et al., 2019, MNRAS, 487, 2836, On the relative bias of void tracers in the Dark Energy Survey

      Luminous tracers of large-scale structure are not entirely representative of the distribution of mass in our Universe. As they arise from the highest peaks in the matter density field, the spatial distribution of luminous objects is biased towards those peaks. On large scales, where density fluctuations are mild, this bias simply amounts to a constant offset in the clustering amplitude of the tracer, known as linear bias. In this work we focus on the relative bias between galaxies and galaxy clusters that are located inside and in the vicinity of cosmic voids, extended regions of relatively low density in the large-scale structure of the Universe. With the help of mock data we verify that the relation between galaxy and cluster overdensity around voids remains linear. Hence, the void-centric density profiles of different tracers can be linked by a single multiplicative constant. This amounts to the same value as the relative linear bias between tracers for the largest voids in the sample. For voids of small sizes, which typically arise in higher density regions, this constant has a higher value, possibly showing an environmental dependence similar to that observed for the linear bias itself. We confirm our findings by analysing data obtained during the first year of observations by the Dark Energy Survey. As a side product, we present the first catalogue of three-dimensional voids extracted from a photometric survey with a controlled photo-z uncertainty. Our results will be relevant in forthcoming analyses that attempt to use voids as cosmological probes.

    101. Shin, T., Adhikari, S., Baxter, E. J., et al., 2019, MNRAS, 487, 2900, Measurement of the splashback feature around SZ-selected Galaxy clusters with DES, SPT, and ACT

      We present a detection of the splashback feature around galaxy clusters selected using the Sunyaev-Zel’dovich (SZ) signal. Recent measurements of the splashback feature around optically selected galaxy clusters have found that the splashback radius, rsp, is smaller than predicted by N-body simulations. A possible explanation for this discrepancy is that rsp inferred from the observed radial distribution of galaxies is affected by selection effects related to the optical cluster-finding algorithms. We test this possibility by measuring the splashback feature in clusters selected via the SZ effect in data from the South Pole Telescope SZ survey and the Atacama Cosmology Telescope Polarimeter survey. The measurement is accomplished by correlating these cluster samples with galaxies detected in the Dark Energy Survey Year 3 data. The SZ observable used to select clusters in this analysis is expected to have a tighter correlation with halo mass and to be more immune to projection effects and aperture-induced biases, potentially ameliorating causes of systematic error for optically selected clusters. We find that the measured rsp for SZ-selected clusters is consistent with the expectations from simulations, although the small number of SZ-selected clusters makes a precise comparison difficult. In agreement with previous work, when using optically selected redMaPPer clusters with similar mass and redshift distributions, rsp is 2 smaller than in the simulations. These results motivate detailed investigations of selection biases in optically selected cluster catalogues and exploration of the splashback feature around larger samples of SZ-selected clusters. Additionally, we investigate trends in the galaxy profile and splashback feature as a function of galaxy colour, finding that blue galaxies have profiles close to a power law with no discernible splashback feature, which is consistent with them being on their first infall into the cluster.

    102. Hoormann, J. K., Martini, P., Davis, T. M., et al., 2019, MNRAS, 487, 3650, C IV black hole mass measurements with the Australian Dark Energy Survey (OzDES)

      Black hole mass measurements outside the local Universe are critically important to derive the growth of supermassive black holes over cosmic time, and to study the interplay between black hole growth and galaxy evolution. In this paper, we present two measurements of supermassive black hole masses from reverberation mapping (RM) of the broad C IV emission line. These measurements are based on multiyear photometry and spectroscopy from the Dark Energy Survey Supernova Program (DES-SN) and the Australian Dark Energy Survey (OzDES), which together constitute the OzDES RM Program. The observed reverberation lag between the DES continuum photometry and the OzDES emission line fluxes is measured to be 358^{+126}_{-123} and 343^{+58}_{-84} d for two quasars at redshifts of 1.905 and 2.593, respectively. The corresponding masses of the two supermassive black holes are 4.4 109 and 3.3 109 M, which are among the highest redshift and highest mass black holes measured to date with RM studies. We use these new measurements to better determine the C IV radius-luminosity relationship for high-luminosity quasars, which is fundamental to many quasar black hole mass estimates and demographic studies.

    103. Camacho, H., Kokron, N., Andrade-Oliveira, F., et al., 2019, MNRAS, 487, 3870, Dark Energy Survey Year 1 results: measurement of the galaxy angular power spectrum

      We use data from the first-year observations of the DES collaboration to measure the galaxy angular power spectrum (APS), and search for its BAO feature. We test our methodology in a sample of 1800 DES Y1-like mock catalogues. We use the pseudo-C method to estimate the APS and the mock catalogues to estimate its covariance matrix. We use templates to model the measured spectra and estimate template parameters firstly from the C’s of the mocks using two different methods, a maximum likelihood estimator and a Markov Chain Monte Carlo, finding consistent results with a good reduced 2. Robustness tests are performed to estimate the impact of different choices of settings used in our analysis. Finally, we apply our method to a galaxy sample constructed from DES Y1 data specifically for LSS studies. This catalogue comprises galaxies within an effective area of 1318 deg2 and 0.6 < z < 1.0. We find that the DES Y1 data favour a model with BAO at the 2.6 C.L. However, the goodness of fit is somewhat poor, with 2/(d.o.f.) = 1.49. We identify a possible cause showing that using a theoretical covariance matrix obtained from C’s that are better adjusted to data results in an improved value of 2/(dof) = 1.36 which is similar to the value obtained with the real-space analysis. Our results correspond to a distance measurement of DA(zeff = 0.81)/rd = 10.65 0.49, consistent with the main DES BAO findings. This is a companion paper to the main DES BAO article showing the details of the harmonic space analysis.

    104. Omori, Y., Giannantonio, T., Porredon, A., et al., 2019, PhRvD, 100, 043501, Dark Energy Survey Year 1 Results: Tomographic cross-correlations between Dark Energy Survey galaxies and CMB lensing from South Pole Telescope +Planck

      We measure the cross-correlation between REDMAGIC galaxies selected from the Dark Energy Survey (DES) year 1 data and gravitational lensing of the cosmic microwave background (CMB) reconstructed from South Pole Telescope (SPT) and Planck data over 1289 deg2 . When combining measurements across multiple galaxy redshift bins spanning the redshift range of 0.15 <z <0.90 , we reject the hypothesis of no correlation at 19.9 significance. When removing small-scale data points where thermal Sunyaev-Zel’dovich signal and nonlinear galaxy bias could potentially bias our results, the detection significance is reduced to 9.9 . We perform a joint analysis of galaxy-CMB lensing cross-correlations and galaxy clustering to constrain cosmology, finding m=0.27 6-0.030+0.029 and S8=8{m/0.3 }=0.80 0-0.094+0.090 . We also perform two alternate analyses aimed at constraining only the growth rate of cosmic structure as a function of redshift, finding consistency with predictions from the concordance CDM model. The measurements presented here are part of a joint cosmological analysis that combines galaxy clustering, galaxy lensing and CMB lensing using data from DES, SPT and Planck.

    105. Omori, Y., Baxter, E. J., Chang, C., et al., 2019, PhRvD, 100, 043517, Dark Energy Survey Year 1 Results: Cross-correlation between Dark Energy Survey Y1 galaxy weak lensing and South Pole Telescope+P l a n c k CMB weak lensing

      We cross-correlate galaxy weak lensing measurements from the Dark Energy Survey (DES) year-one data with a cosmic microwave background (CMB) weak lensing map derived from South Pole Telescope (SPT) and Planck data, with an effective overlapping area of 1289 deg2 . With the combined measurements from four source galaxy redshift bins, we obtain a detection significance of 5.8 . We fit the amplitude of the correlation functions while fixing the cosmological parameters to a fiducial CDM model, finding A =0.99 0.17 . We additionally use the correlation function measurements to constrain shear calibration bias, obtaining constraints that are consistent with previous DES analyses. Finally, when performing a cosmological analysis under the CDM model, we obtain the marginalized constraints of m=0.26 1-0.051+0.070 and S88{m/0.3 }=0.66 0-0.100+0.085. These measurements are used in a companion work that presents cosmological constraints from the joint analysis of two-point functions among galaxies, galaxy shears, and CMB lensing using DES, SPT, and Planck data.

    106. Stringer, K. M., Long, J. P., Macri, L. M., et al., 2019, AJ, 158, 16, Identification of RR Lyrae Stars in Multiband, Sparsely Sampled Data from the Dark Energy Survey Using Template Fitting and Random Forest Classification

      Many studies have shown that RR Lyrae variable stars (RRL) are powerful stellar tracers of Galactic halo structure and satellite galaxies. The Dark Energy Survey (DES), with its deep and wide coverage (g 23.5 mag in a single exposure; over 5000 deg2) provides a rich opportunity to search for substructures out to the edge of the Milky Way halo. However, the sparse and unevenly sampled multiband light curves from the DES wide-field survey (a median of four observations in each of grizY over the first three years) pose a challenge for traditional techniques used to detect RRL. We present an empirically motivated and computationally efficient template-fitting method to identify these variable stars using three years of DES data. When tested on DES light curves of previously classified objects in SDSS stripe 82, our algorithm recovers 89% of RRL periods to within 1% of their true value with 85% purity and 76% completeness. Using this method, we identify 5783 RRL candidates, 28% of which are previously undiscovered. This method will be useful for identifying RRL in other sparse multiband data sets.

    107. Tegler, S. C., Stufflebeam, T. D., Grundy, W. M., et al., 2019, AJ, 158, 17, A New Two-molecule Combination Band as a Diagnostic of Carbon Monoxide Diluted in Nitrogen Ice on Triton

      A combination band due to a mechanism whereby a photon excites two or more vibrational modes (e.g., a bend and a stretch) of an individual molecule is commonly seen in laboratory and astronomical spectroscopy. Here, we present evidence of a much less commonly seen combination bandone where a photon simultaneously excites two adjacent molecules in an ice. In particular, we present near-infrared spectra of laboratory CO/N2 ice samples where we identify a band at 4467.5 cm-1 (2.239 m) that results from single photons exciting adjacent pairs of CO and N2 molecules. We also present a near-infrared spectrum of Neptunes largest satellite Triton taken with the Gemini-South 8.1 m telescope and the Immersion Grating Infrared Spectrograph that shows this 4467.5 cm-1 (2.239 m) CO-N2 combination band. The existence of the band in a spectrum of Triton indicates that CO and N2 molecules are intimately mixed in the ice rather than existing as separate regions of pure CO and pure N2 deposits. Our finding is important because CO and N2 are the most volatile species on Triton and so dominate seasonal volatile transport across its surface. Our result will place constraints on the interaction between the surface and atmosphere of Triton.

    108. Hunter, Deidre A., Laufman, Lauren, Oh, Se-Heon, et al., 2019, AJ, 158, 23, Gas Engaged in Noncircular Motions in LITTLE THINGS Dwarf Irregular Galaxies

      We have examined gas engaged in noncircular motions in 22 of the nearby LITTLE THINGS dwarf irregular galaxies. The H I data cubes have been deconvolved into kinematic componentsbulk rotation and noncircular motionsto produce maps of integrated gas, velocity field, and velocity dispersion in the different components. We found significant regions of gas engaged in noncircular motions in half of the galaxies, involving 1%-20% of the total H I mass of the galaxy. In one galaxy we found a pattern in the velocity field that is characteristic of streaming motions around the stellar bar potential and star formation at the end of bar. Two galaxies have large-scale filamentary structures found in their outer disks, and these filaments could be transient instabilities in the gas. We found no spatial correlation between noncircular motion gas and enhanced star formation. We found noncircular motion gas in only one galaxy associated with higher H I velocity dispersion.

    109. Kostov, Veselin B., Schlieder, Joshua E., Barclay, Thomas, et al., 2019, AJ, 158, 32, The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf

      We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R to 1.6 R . All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system.

    110. Garofali, Kristen, Levesque, Emily M., Massey, Philip, et al., 2019, ApJ, 880, 8, The First Candidate Colliding-wind Binary in M33

      We present the detection of the first candidate colliding-wind binary (CWB) in M33, located in the giant H II region NGC 604. The source was first identified in archival Chandra imaging as a relatively soft X-ray point source, with the likely primary star determined from precise astrometric alignment between archival Hubble Space Telescope and Chandra imaging. The candidate primary star in the CWB is classified for the first time in this work as a carbon-rich Wolf-Rayet star with a likely O-star companion based on spectroscopy obtained from Gemini-North. We model the X-ray spectrum using Chandra and XMM-Newton observations, and find the CWB to be well fit as a 1 keV thermal plasma with a median unabsorbed luminosity in the 0.5-2.0 keV band of L X 3 1035 erg s-1, making this source among the brightest of CWBs observed to date. We present a long-term light curve for the candidate CWB from archival Chandra and XMM-Newton observations, and discuss the constraints placed on the binary by this light curve, as well as the X-ray luminosity at maximum. Finally, we compare this candidate CWB in M33 to other well-studied, bright CWBs in the Galaxy and Magellanic Clouds, such as Car.

    111. Schwamb, Megan E., Fraser, Wesley C., Bannister, Michele T., et al., 2019, ApJS, 243, 12, Col-OSSOS: The Colors of the Outer Solar System Origins Survey

      The Colours of the Outer Solar System Origins Survey is acquiring near-simultaneous g, r, and J photometry of unprecedented precision with the Gemini North Telescope, targeting nearly 100 trans-Neptunian objects (TNOs) brighter than m r = 23.6 mag discovered in the Outer Solar System Origins Survey. Combining the optical and near-infrared photometry with the well-characterized detection efficiency of the Colours of the Outer Solar System Origins Survey target sample will provide the first flux-limited compositional dynamical map of the outer solar system. In this paper, we describe our observing strategy and detail the data reduction processes we employ, including techniques to mitigate the impact of rotational variability. We present optical and near-infrared colors for 35 TNOs. We find two taxonomic groups for the dynamically excited TNOs, the neutral and red classes, which divide at g – r 0.75. Based on simple albedo and orbital distribution assumptions, we find that the neutral class outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1. Including in our analysis constraints from the cold classical objects, which are known to exhibit unique albedos and r – z colors, we find that within our measurement uncertainty our observations are consistent with the primordial solar system protoplanetesimal disk being neutral class dominated, with two major compositional divisions in grJ color space.

    112. Cruikshank, D. P., Materese, C. K., Pendleton, Y. J., et al., 2019, AsBio, 19, 831, Prebiotic Chemistry of Pluto

      We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto’s surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., ). The red material associated with the H2O ice may contain nucleobases resulting from energetic processing on Pluto’s surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.

    113. Reddy, Vishnu, Kelley, Michael S., Farnocchia, Davide, et al., 2019, Icar, 326, 133, Near-Earth asteroid 2012 TC4 observing campaign: Results from a global planetary defense exercise

      Impacts due to near-Earth objects (NEOs) are responsible for causing some of the great mass extinctions on Earth. While nearly all NEOs of diameter > 1 km, capable of causing a global climatic disaster, have been discovered and have negligible chance of impacting in the near future, we are far from completion in our effort to detect and characterize smaller objects. In an effort to test our preparedness to respond to a potential NEO impact threat, we conducted a community-led global planetary defense exercise with support from the NASA Planetary Defense Coordination Office. The target of our exercise was 2012 TC4, the 10 m diameter asteroid that made a close pass by the Earth on 2017 October 12 at a distance of about 50,000 km. The goal of the TC4 observing campaign was to recover, track, and characterize 2012 TC4 as a hypothetical impactor in order to exercise the global planetary defense system involving observations, modeling, prediction, and communication. We made three attempts with the Very Large Telescope (VLT) on 2017 July 27, 31 and on 2017 August 5 and recovered 2012 TC4 within its ephemeris uncertainty at 2.2 arcmin from the nominal prediction. At visual magnitude V = 27, the recovery of 2012 TC4 is the faintest NEA detection thus far. If an impact during the 2017 close approach had been possible based on the 2012 astrometric data, these recovery observations would have been sufficient to confirm or rule out the impact. The first automatic detection by a survey (Pan-STARRS1) was on September 25, which is the earliest that 2012 TC4 would have been discovered in survey mode, if it had not been discovered in 2012. We characterized 2012 TC4 using photometry, spectroscopy and radar techniques. Based on photometric observations, we determined a rotation period of 12.2 min with an amplitude of 0.9 magnitudes. An additional lower amplitude period was detected, indicating that 2012 TC4 was in a state of non-principal axis rotation. The combined visible and near-infrared spectrum puts it in the taxonomic X-class. Radar images at 1.875 m resolution placed only a few range pixels on the asteroid, reveal an angular, asymmetric, and elongated shape, and establish that 2012 TC4 is less than 20 m on its long axis. We estimate a circular polarization ratio of 0.57 + -0.08 that is relatively high among NEAs observed to date by radar. We also performed a probabilistic impact risk assessment exercise for hypothetical impactors based on the 2012 TC4 observing campaign. This exercise was performed as part of ongoing efforts to advance effective impact risk models and assessment processes for planetary defense. The 2012 TC4 close approach provided a valuable opportunity to test the application of these methods using realistically evolving observational data to define the modeling inputs. To this end, risk assessments were calculated at several epochs before and during the close approach, incorporating new information about 2012 TC4 as it became available. Two size ranges were assessed-one smaller size range (H = 26.7) similar to the actual 2012 TC4, and one larger size range (H = 21.9) to produce a greater-damage scenario for risk assessment. Across the epochs, we found that only irons caused significant damage for smaller size. For the larger size case, however, hydrous stones caused the greatest damage, anhydrous stones caused the least damage, and irons caused moderate damage. We note that the extent of damage depends on composition in different size regimes and, after astrometry, size is the most important physical property to determine for an incoming object.

    114. Prat, J., Baxter, E., Shin, T., et al., 2019, MNRAS, 487, 1363, Cosmological lensing ratios with DES Y1, SPT, and Planck

      Correlations between tracers of the matter density field and gravitational lensing are sensitive to the evolution of the matter power spectrum and the expansion rate across cosmic time. Appropriately defined ratios of such correlation functions, on the other hand, depend only on the angular diameter distances to the tracer objects and to the gravitational lensing source planes. Because of their simple cosmological dependence, such ratios can exploit available signal-to-noise ratio down to small angular scales, even where directly modelling the correlation functions is difficult. We present a measurement of lensing ratios using galaxy position and lensing data from the Dark Energy Survey, and CMB lensing data from the South Pole Telescope and Planck, obtaining the highest precision lensing ratio measurements to date. Relative to the concordance CDM model, we find a best-fitting lensing ratio amplitude of A = 1.1 0.1. We use the ratio measurements to generate cosmological constraints, focusing on the curvature parameter. We demonstrate that photometrically selected galaxies can be used to measure lensing ratios, and argue that future lensing ratio measurements with data from a combination of LSST and Stage-4 CMB experiments can be used to place interesting cosmological constraints, even after considering the systematic uncertainties associated with photometric redshift and galaxy shear estimation.

    115. Cauley, P. Wilson, Shkolnik, Evgenya L., Llama, Joe, et al., 2019, NatAs, 3, 1128, Magnetic field strengths of hot Jupiters from signals of star-planet interactions

      Evidence of star-planet interactions in the form of planet-modulated chromospheric emission has been noted for a number of hot Jupiters. Magnetic star-planet interactions involve the release of energy stored in the stellar and planetary magnetic fields. These signals thus offer indirect detections of exoplanetary magnetic fields. Here, we report the derivation of the magnetic field strengths of four hot Jupiter systems, using the power observed in calcium uc(ii) K emission modulated by magnetic star-planet interactions. By approximating the fractional energy released in the calcium uc(ii) K line, we find that the surface magnetic field values for the hot Jupiters in our sample range from 20 G to 120 G, around 10-100 times larger than the values predicted by dynamo scaling laws for planets with rotation periods of around 2-4 days. However, these values are in agreement with scaling laws relating the magnetic field strength to the internal heat flux in giant planets. Large planetary magnetic field strengths may produce observable electron cyclotron maser radio emission by preventing the maser from being quenched by the planet’s ionosphere. Intensive radio monitoring of hot Jupiter systems will help to confirm these field values and inform the generation mechanism of magnetic fields in this important class of exoplanets.

    116. Abbott, T. M. C., Abdalla, F. B., Alarcon, A., et al., 2019, PhRvD, 100, 023541, Dark Energy Survey year 1 results: Joint analysis of galaxy clustering, galaxy lensing, and CMB lensing two-point functions

      We perform a joint analysis of the auto and cross-correlations between three cosmic fields: the galaxy density field, the galaxy weak lensing shear field, and the cosmic microwave background (CMB) weak lensing convergence field. These three fields are measured using roughly 1300 sq. deg. of overlapping optical imaging data from first year observations of the Dark Energy Survey (DES) and millimeter-wave observations of the CMB from both the South Pole Telescope Sunyaev-Zel’dovich survey and Planck. We present cosmological constraints from the joint analysis of the two-point correlation functions between galaxy density and galaxy shear with CMB lensing. We test for consistency between these measurements and the DES-only two-point function measurements, finding no evidence for inconsistency in the context of flat CDM cosmological models. Performing a joint analysis of five of the possible correlation functions between these fields (excluding only the CMB lensing autospectrum) yields S88{m/0.3 }=0.78 2-0.025+0.019 and m=0.26 0-0.019+0.029 . We test for consistency between these five correlation function measurements and the Planck-only measurement of the CMB lensing autospectrum, again finding no evidence for inconsistency in the context of flat CDM models. Combining constraints from all six two-point functions yields S8=0.77 6-0.021+0.014 and m=0.27 1-0.016+0.022 . These results provide a powerful test and confirmation of the results from the first year DES joint-probes analysis.

    117. Johns-Krull, Christopher M., Flagg, Laura, Nofi, Larissa, et al., 2019, AAS, 234, s, Direct Detection of CO in CI Tau b: Support for Hot Start Formation

      We analyze high resolution IR spectra of CI Tau, the host star of one of the few young planet candidates amenable to such observations. We confirm the planet’s existence with a direct detection of CO in the planet’s atmosphere. We determine a mass of 11.6 Mjup based on the amplitude of the planet’s radial velocity variations. We estimate the planet’s flux contrast with its host star to obtain an absolute magnitude estimate for the planet of 8.17 in the K band. This magnitude implies the planet formed via a “hot start” formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent, dynamical mass.

    118. Carvalho, Adolfo, Johns-Krull, Christopher M., Prato, Lisa A., 2019, AAS, 234, 201.06, Radial Velocity Monitoring of the Young Star Hubble 4

      We have been spectroscopically monitoring the young star Hubble 4 for approximately 10 years using the 2.7 m Harlan J. Smith telescope at McDonald Observatory. Our goal is to monitor this star’s radial velocity (RV) variations, and we have collected over 65 observations of this 2-3 Myr old T Tauri star. In addition, we analyze archival imaging of Hubble 4 obtained with the ACS instrument aboard the Hubble Space Telescope to measure the flux ratio between the members of this binary system. The RV measurements of Hubble 4 clearly reveal the long period ( 9 yr) variations due to the orbit of this binary (semi-major axis of 5.6 AU) as well as much shorter period ( 1.5 d) variations due to stellar rotation. By fitting and removing the variations due to orbital motion, we also find lower bound of 5 yr on the lifetime of star spots on the surface of the star. We discuss the implications of these findings for RV searches aimed at detecting planets around young stars.

    119. Hahne, Frederick, Horch, Elliott, Ciardi, David R., et al., 2019, AAS, 234, 303.01, Fundamental Stellar Parameters and Multiplicity Rates of M-Dwarfs through Optical Speckle and NIR AO Imaging

      We present preliminary fundamental stellar parameters and multiplicity rates of M dwarf stars using a combination of speckle imaging and adaptive optics. Our survey mainly uses the Differential Speckle Survey Instrument (DSSI) at Lowell Observatory’s Discovery Channel Telescope (DCT). DSSI observes speckle patterns simultaneously at two separate wavelengths and the data for this project are composed of observations which span from 2016 to 2018. More recently, the speckle data for some of the target stars that have been found to be binary have been supplemented with observations using Adaptive Optics (AO) at Palomar Observatory. The combination of speckle data in the visible and AO data in the near-infrared allows us to make robust determinations of the luminosities and effective temperatures of the components in each case. Using the known Mass-Luminosity Relation, we also estimate the component masses. A discussion of interesting systems will be given.

    120. Massey, Philip, Neugent, Kathryn F., Levesque, Emily M., 2019, AJ, 157, 227, The Discovery of Quasi-stellar Objects behind M31 and M33

      We report the discovery of 11 newly found quasars behind the stellar disks of the spiral galaxies M31 and M33 in the fields covered by the Local Group Galaxy Survey. Their redshifts range from 0.37 to 2.15. Most are X-ray, ultraviolet, and infrared sources. We also report the discovery of five normal background galaxies. Most of these objects were observed owing to their anomalous colors, as part of a program (reported elsewhere) to confirm spectroscopically candidate red supergiant plus B-star binaries; others were discovered as part of our identification of early-type massive stars based upon their optical colors. There are 15 previously known quasars in the same fields, for a grand total of 26, 15 behind M31 and 11 behind M33. Of these, only eight were discovered as part of surveys for quasars; the rest were found accidentally. The quasars are well distributed in the M31 and M33 fields, except for the inner regions, and have the potential for being good probes of the interstellar medium in these stellar disks, as well as serving as zero-point calibrators for Gaia parallaxes.

    121. Thirouin, Audrey, Sheppard, Scott S., 2019, AJ, 157, 228, Light Curves and Rotational Properties of the Pristine Cold Classical Kuiper Belt Objects

      We present a survey of the rotational and physical properties of the dynamically low inclination Cold Classical (CC) trans-Neptunian objects (TNOs). The CCs are primordial planetesimals and contain information about our solar system and planet formation over the first 100 million years after the Suns formation. We obtained partial/complete light curves for 42 CCs. We use statistical tests to derive general properties about the shape and rotational frequency distributions of the CCs and infer that they have slower rotations and are more elongated/deformed than the other TNOs. On the basis of the full light curves, the mean rotational period of the CCs is 9.48 1.53 hr compared to 8.45 0.58 hr for the rest of the TNOs. About 65% of the TNOs have a light-curve amplitude below 0.2 mag compared to the 36% of CCs with small amplitude. We present the full light curve of one likely contact binary, 2004 VC131, with a potential density of 1 g cm-3 for a mass ratio of 0.4. We have hints that 2004 MU8 and 2004 VU75 are perhaps potential contact binaries, on the basis of their sparse light curves, but more data are needed to confirm this finding. Assuming equal-sized binaries, we find that 10%-25% of the CCs could be contact binaries, suggesting a deficit of contact binaries in this population compared to previous estimates and to the (40%-50%) possible contact binaries in the Plutino population. These estimates are lower limits and may increase if nonequal-sized contact binaries are considered. Finally, we put in context the results of the New Horizons flyby of 2014 MU69.

    122. Hunter, Deidre A., Elmegreen, Bruce G., Berger, Clara L., 2019, AJ, 157, 241, H I Clouds in LITTLE THINGS Dwarf Irregular Galaxies

      We identify 814 discrete H I clouds in 40 dwarf irregular galaxies from the LITTLE THINGS survey using an automated cloud-finding algorithm. The cloud masses range from 103 to 107 M , have a surface density averaged over all of the clouds of 9.65 M pc-2, and constitute 2%-53% of the total H I mass of the host galaxy. For individual clouds, the mass including He varies with cloud radius as {log} {M}gas}=(2.11+/- 0.04) {log} {R}cl} +(0.78+/- 0.08) and the internal velocity dispersion varies as {log} {V}disp}=0.5 {log} {R}cl}-0.57+/- 0.21. The H I clouds tend to be in the outer regions of the galaxies, with 72% of the galaxies having more than 70% of their clouds outside one disk scale length and 32% of the galaxies having more than 50% of their clouds outside the radius encircling the H II emission. Thirty-six percent of the clouds are essentially non-self-gravitating from H I alone, with a virial parameter that exceeds vir 10, and 5% have vir 2. We estimate the missing molecular mass, based on the total star formation rate and a typical molecular consumption time of 2 Gyr, as observed in CO-rich galaxies. The resulting molecular fraction has a value averaged over the galaxies of 0.23 and correlates with both the surface density of star formation and the fraction of H I clouds in the outer regions. We conclude that a significant fraction of the inner parts of these dwarf galaxy disks is in the form of dark molecular gas, and that this fraction could be high enough to make the inner disks mildly gravitationally unstable as a precursor to star formation.

    123. Flagg, Laura, Johns-Krull, Christopher M., Nofi, Larissa, et al., 2019, ApJL, 878, L37, CO Detected in CI Tau b: Hot Start Implied by Planet Mass and M K

      We acquired high-resolution infrared spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planets existence with a direct detection of CO in the planets atmosphere. We also calculate a mass of 11.6 M J based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the K-band. This magnitude implies the planet formed via a hot start formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent dynamical mass.

    124. Levine, S., Henden, A., Terrell, D., et al., 2019, JAVSO, 47, 132, Solar System Objects and the AAVSO Photometric All-Sky Survey (APASS) (Abstract)

      (Abstract only) The AAVSO Photometric All-Sky Survey, data release 10 (APASS DR10) can be used for photometric calibration of observations of moving objects. Because APASS provides calibrated photometry over the whole sky, it makes it much simpler to tie together observations of objects, like asteroids and comets, that move appreciable distances over the time they are observed. Because the photometric standards are in each image, it will also be possible to recover photometry at the few percent level from non-photometric nights. In addition to providing calibration for new observations, the original APASS data comprise over 500,000 images, each 7.8 square degrees in size, taken over the course of more than nine years. We have searched those images for known Solar System bodies, and present the initial results of this search. For many of the objects found, we have simultaneous five color (B,V, g’, r’, and i’) photometry. APASS provides photometric standards in at least five colors over the magnitude range 7 to 17, which makes it a good match for calibration for telescopes ranging from a few inches in size up to several meters.

    125. Kavanagh, R. D., Vidotto, A. A., O. Fionnagain, D., et al., 2019, MNRAS, 485, 4529, MOVES – II. Tuning in to the radio environment of HD189733b

      We present stellar wind modelling of the hot Jupiter host HD189733, and predict radio emission from the stellar wind and the planet, the latter arising from the interaction of the stellar wind with the planetary magnetosphere. Our stellar wind models incorporate surface stellar magnetic field maps at the epochs 2013 June/July, 2014 September, and 2015 July as boundary conditions. We find that the mass-loss rate, angular momentum loss rate, and open magnetic flux of HD189733 vary by 9 per cent, 40 per cent, and 19 per cent over these three epochs. Solving the equations of radiative transfer, we find that from 10 MHz-100 GHz the stellar wind emits fluxes in the range of 10-3-5 Jy, and becomes optically thin above 10 GHz. Our planetary radio emission model uses the radiometric Bode’s law, and neglects the presence of a planetary atmosphere. For assumed planetary magnetic fields of 1-10 G, we estimate that the planet emits at frequencies of 2-25 MHz, with peak flux densities of 102 mJy. We find that the planet orbits through regions of the stellar wind that are optically thick to the emitted frequency from the planet. As a result, unattenuated planetary radio emission can only propagate out of the system and reach the observer for 67 per cent of the orbit for a 10 G planetary field, corresponding to when the planet is approaching and leaving primary transit. We also find that the plasma frequency of the stellar wind is too high to allow propagation of the planetary radio emission below 21 MHz. This means a planetary field of at least 8 G is required to produce detectable radio emission.

    126. Lasker, J., Kessler, R., Scolnic, D., et al., 2019, MNRAS, 485, 5329, First cosmology results using Type IA supernovae from the dark energy survey: effects of chromatic corrections to supernova photometry on measurements of cosmological parameters

      Calibration uncertainties have been the leading systematic uncertainty in recent analyses using Type Ia supernovae (SNe Ia) to measure cosmological parameters. To improve the calibration, we present the application of spectral energy distribution-dependent `chromatic corrections’ to the SN light-curve photometry from the Dark Energy Survey (DES). These corrections depend on the combined atmospheric and instrumental transmission function for each exposure, and they affect photometry at the 0.01 mag (1 per cent) level, comparable to systematic uncertainties in calibration and photometry. Fitting our combined DES and low-z SN Ia sample with baryon acoustic oscillation (BAO) and cosmic microwave background (CMB) priors for the cosmological parameters m (the fraction of the critical density of the universe comprised of matter) and w (the dark energy equation of state parameter), we compare those parameters before and after applying the corrections. We find the change in w and m due to not including chromatic corrections is -0.002 and 0.000, respectively, for the DES-SN3YR sample with BAO and CMB priors, consistent with a larger DES-SN3YR-like simulation, which has a w-change of 0.0005 with an uncertainty of 0.008 and an m change of 0.000 with an uncertainty of 0.002. However, when considering samples on individual CCDs we find large redshift-dependent biases (0.02 in distance modulus) for SN distances.

    127. Macaulay, E., Nichol, R. C., Bacon, D., et al., 2019, MNRAS, 486, 2184, First cosmological results using Type Ia supernovae from the Dark Energy Survey: measurement of the Hubble constant

      We present an improved measurement of the Hubble constant (H0) using the `inverse distance ladder’ method, which adds the information from 207 Type Ia supernovae (SNe Ia) from the Dark Energy Survey (DES) at redshift 0.018 < z < 0.85 to existing distance measurements of 122 low-redshift (z < 0.07) SNe Ia (Low-z) and measurements of Baryon Acoustic Oscillations (BAOs). Whereas traditional measurements of H0 with SNe Ia use a distance ladder of parallax and Cepheid variable stars, the inverse distance ladder relies on absolute distance measurements from the BAOs to calibrate the intrinsic magnitude of the SNe Ia. We find H0 = 67.8 1.3 km s-1 Mpc-1 (statistical and systematic uncertainties, 68 per cent confidence). Our measurement makes minimal assumptions about the underlying cosmological model, and our analysis was blinded to reduce confirmation bias. We examine possible systematic uncertainties and all are below the statistical uncertainties. Our H0 value is consistent with estimates derived from the Cosmic Microwave Background assuming a CDM universe.

    128. Abbott, T. M. C., Abdalla, F. B., Avila, S., et al., 2019, PhRvD, 99, 123505, Dark Energy Survey year 1 results: Constraints on extended cosmological models from galaxy clustering and weak lensing

      We present constraints on extensions of the minimal cosmological models dominated by dark matter and dark energy, CDM and w CDM , by using a combined analysis of galaxy clustering and weak gravitational lensing from the first-year data of the Dark Energy Survey (DES Y1) in combination with external data. We consider four extensions of the minimal dark energy-dominated scenarios: (1) nonzero curvature k, (2) number of relativistic species Neff different from the standard value of 3.046, (3) time-varying equation-of-state of dark energy described by the parameters w0 and wa (alternatively quoted by the values at the pivot redshift, wp, and wa), and (4) modified gravity described by the parameters 0 and 0 that modify the metric potentials. We also consider external information from Planck cosmic microwave background measurements; baryon acoustic oscillation measurements from SDSS, 6dF, and BOSS; redshift-space distortion measurements from BOSS; and type Ia supernova information from the Pantheon compilation of datasets. Constraints on curvature and the number of relativistic species are dominated by the external data; when these are combined with DES Y1, we find k=0.002 0-0.0032+0.0037 at the 68% confidence level, and the upper limit Neff<3.28 (3.55 ) at 68% (95%) confidence, assuming a hard prior Neff>3.0 . For the time-varying equation-of-state, we find the pivot value (wp,wa)=(-0.9 1-0.23+0.19,-0.5 7-1.11+0.93) at pivot redshift zp=0.27 from DES alone, and (wp,wa)=(-1.0 1-0.04+0.04,-0.2 8-0.48+0.37) at zp=0.20 from DES Y1 combined with external data; in either case we find no evidence for the temporal variation of the equation of state. For modified gravity, we find the present-day value of the relevant parameters to be 0=0.4 3-0.29+0.28 from DES Y1 alone, and (0,0)=(0.0 6-0.07+0.08,-0.1 1-0.46+0.42) from DES Y1 combined with external data. These modified-gravity constraints are consistent with predictions from general relativity.

    129. Loyd, R. O. Parke, France, Kevin, Jin, Meng, et al., 2019, hst, 15803, Constraining CME Masses on the Active K Star and Planet Host Epsilon Eridani

      If the frequent, energetic flares of active stars are each accompanied by a coronal mass ejection (CME), the effect on stellar and planetary evolution could be strong. Every CME event carries mass and angular momentum away from the star, and each has the potential to impact and strip atmospheric gas from orbiting planets. Developing observational constraints on stellar CMEs is essential to assessing their true impact on stellar and planetary evolution. Such constraints are possible via the unique FUV capabilities of HST. In the FUV, photometry of the coronal Fe XXI 1354 A emission line can constrain the mass of CMEs that accompany flares through an effect known as coronal dimming. Coronal dimming is a direct result of the ejection of emitting coronal material, which leaves behind a dark void reliably detected in Sun-as-a-star observations as a drop in the disk-integrated emission of coronal lines. We propose a coronal dimming analysis of 10 h of high S/N archival COS G130M data of the K dwarf planet host Epsilon Eridani (Eps Eri), containing several flares to constrain the masses of associated CMEs. We will accompany this analysis with detailed MHD modeling of Eps Eri’s corona to simulate the dimming in Fe XXI 1354 A emission following CMEs. This analysis will lay fundamental groundwork for future dedicated HST CME observations, develop theoretical tools for interpreting dimming signals through MHD analysis, and test whether CMEs could be a dominant contributor to Eps Eri’s high observed mass loss rate.

    130. Meza, E., Sicardy, B., Assafin, M., et al., 2019, A&A, 625, A42, Lower atmosphere and pressure evolution on Pluto from ground-based stellar occultations, 1988-2016

      Context. The tenuous nitrogen (N2) atmosphere on Pluto undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has recently (July 2015) been observed by the New Horizons spacecraft.
      Aims: The main goals of this study are (i) to construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) to constrain the structure of the lower atmosphere using a central flash observed in 2015.
      Methods: Eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between altitude levels of ~5 and ~380 km (i.e. pressures from ~ 10 bar to 10 nbar).
      Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived. (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia; and/or (b) hazes with tangential optical depth of ~0.3 are present at 4-7 km altitude levels; and/or (c) the nominal REX density values are overestimated by an implausibly large factor of ~20%; and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.

    131. Hromakina, T. A., Belskaya, I. N., Krugly, Yu. N., et al., 2019, A&A, 625, A46, Long-term photometric monitoring of the dwarf planet (136472) Makemake

      Aims: We studied the rotational properties of the dwarf planet Makemake.
      Methods: The photometric observations were carried out at different telescopes between 2006 and 2017. Most of the measurements were acquired in BVRI broad-band filters of a standard Johnson-Cousins photometric system.
      Results: We found that Makemake rotates more slowly than was previously reported. A possible lightcurve asymmetry suggests a double-peaked period of P = 22.8266 0.0001 h. A small peak-to-peak lightcurve amplitude in R-filter A = 0.032 0.005 mag implies an almost spherical shape or near pole-on orientation. We also measured BVRI colours and the R-filter phase-angle slope and revised the absolute magnitudes. The absolute magnitude of Makemake has remained unchanged since its discovery in 2005. No direct evidence of a newly discovered satellite was found in our photometric data; however, we discuss the possible existence of another larger satellite.


      Table A.1 is only available at the CDS via anonymous ftp to ( or via

    132. Marciniak, A., Ali-Lagoa, V., Muller, T. G., et al., 2019, A&A, 625, A139, Thermal properties of slowly rotating asteroids: results from a targeted survey

      Context. Earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the subsurface. However, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (TPM).
      Aims: Our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with TPM, and to verify whether thermal inertia increases with the rotation period.
      Methods: To decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 h, from multiple stations worldwide, adding in some cases data from WISE and Kepler space telescopes. For spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from IRAS, AKARI, and WISE.
      Results: We present new models of 11 slow rotators that provide a good fit to the thermal data. In two cases, the TPM analysis showed a clear preference for one of the two possible mirror solutions. We derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3-3+33 and 45-30+60 J m-2 s-1/2 K-1.
      Conclusions: Together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. The current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias.


      Full Table A.1 and photometric data from all individual nights are only available at the CDS via anonymous ftp to ( or via

    133. Navarro-Meza, S., Mommert, M., Trilling, D. E., et al., 2019, AJ, 157, 190, First Results from the Rapid-response Spectrophotometric Characterization of Near-Earth Objects Using RATIR

      As part of our multi-observatory, multifilter campaign, we present r-i color observations of 82 near-Earth objects (NEOs) obtained with the reionization and transients infrared camera (RATIR) instrument on the 1.5 m robotic telescope at the San Pedro Martirs National Observatory in Mexico. Our project is particularly focused on rapid-response observations of small (850 m) NEOs. The rapid response and the use of spectrophotometry allows us to constrain the taxonomic classification of NEOs with high efficiency. Here we present the methodology of our observations and our result, suggesting that the ratio of C-type to S-type asteroids in a size range of 30-850 m is 1.1, which is in accordance with our previous results. We also find that 10% of all NEOs in our sample are neither C- nor S-type asteroids

    134. Hinton, S. R., Davis, T. M., Kim, A. G., et al., 2019, ApJ, 876, 15, Steve: A Hierarchical Bayesian Model for Supernova Cosmology

      We present a new Bayesian hierarchical model (BHM) named Steve for performing Type Ia supernova (SN Ia) cosmology fits. This advances previous works by including an improved treatment of Malmquist bias, accounting for additional sources of systematic uncertainty, and increasing numerical efficiency. Given light-curve fit parameters, redshifts, and host-galaxy masses, we fit Steve simultaneously for parameters describing cosmology, SN Ia populations, and systematic uncertainties. Selection effects are characterized using Monte Carlo simulations. We demonstrate its implementation by fitting realizations of SN Ia data sets where the SN Ia model closely follows that used in Steve. Next, we validate on more realistic SNANA simulations of SN Ia samples from the Dark Energy Survey and low-redshift surveys (DES Collaboration et al. 2018). These simulated data sets contain more than 60,000 SNe Ia, which we use to evaluate biases in the recovery of cosmological parameters, specifically the equation of state of dark energy, w. This is the most rigorous test of a BHM method applied to SN Ia cosmology fitting and reveals small w biases that depend on the simulated SN Ia properties, in particular the intrinsic SN Ia scatter model. This w bias is less than 0.03 on average, less than half the statistical uncertainty on w. These simulation test results are a concern for BHM cosmology fitting applications on large upcoming surveys; therefore, future development will focus on minimizing the sensitivity of Steve to the SN Ia intrinsic scatter model.

    135. Soares-Santos, M., Palmese, A., Hartley, W., et al., 2019, ApJL, 876, L7, First Measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary-Black-hole Merger GW170814

      We present a multi-messenger measurement of the Hubble constant H 0 using the binary-black-hole merger GW170814 as a standard siren, combined with a photometric redshift catalog from the Dark Energy Survey (DES). The luminosity distance is obtained from the gravitational wave signal detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration (LVC) on 2017 August 14, and the redshift information is provided by the DES Year 3 data. Black hole mergers such as GW170814 are expected to lack bright electromagnetic emission to uniquely identify their host galaxies and build an object-by-object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and redshift completion is available. Here we present the first Hubble parameter measurement using a black hole merger. Our analysis results in {H}0={75}-32+40 {km} {{{s}}}-1 {Mpc}}-1, which is consistent with both SN Ia and cosmic microwave background measurements of the Hubble constant. The quoted 68% credible region comprises 60% of the uniform prior range [20, 140] km s-1 Mpc-1, and it depends on the assumed prior range. If we take a broader prior of [10, 220] km s-1 Mpc-1, we find {H}0={78}-24+96 {km} {{{s}}}-1 {Mpc}}-1 (57% of the prior range). Although a weak constraint on the Hubble constant from a single event is expected using the dark siren method, a multifold increase in the LVC event rate is anticipated in the coming years and combinations of many sirens will lead to improved constraints on H 0.

    136. Carpenter, Kenneth, van Belle, Gerard, Brown, Alexander, et al., 2019, BAAS, 51, 56, Stars at High Spatial Resolution

      We summarize compelling new scientific opportunities for understanding stars and stellar systems that can be enabled by sub-milliarcsec angular resolution, UV/Optical spectral imaging observations. These can reveal details of many dynamic processes that affect stellar formation, structure, and evolution.

    137. Holler, Bryan, Milam, Stefanie, Bauer, James, et al., 2019, BAAS, 51, 68, “It’s full of asteroids!”: Solar system science with a large field of view

      Next-generation space telescopes will have larger apertures, larger fields of view, and more sensitive instrumentation than their predecessors. The prospects for solar system science with these facilities are substantial, particularly in the area of space-based surveys for the detection of new minor bodies and irregular satellites.

    138. Isella, Andrea, Ricci, Luca, Andrews, Sean, et al., 2019, BAAS, 51, 174, Observing Planetary Systems in the Making

      We discuss science cases to support the development of sub-au imaging capabilities to image forming planets in the terrestrial region of nearby proto-planetary disks.

    139. Burgasser, Adam, Baraffe, Isabelle, Browning, Matthew, et al., 2019, BAAS, 51, 214, Fundamental Physics with Brown Dwarfs: The Mass-Radius Relation

      The lowest-mass stars, brown dwarfs and giant exoplanets span a minimum in the mass-radius relationship that probes the fundamental physics of extreme states of matter, magnetism, and fusion. This White Paper outlines scientific opportunities and the necessary resources for modeling and measuring the mass- radius relationship in this regime.

    140. Rau, Gioia, Montez, Rodolfo, Jr., Carpenter, Kenneth, et al., 2019, BAAS, 51, 241, Cool, evolved stars: results, challenges, and promises for the next decade

      This White Paper identifies compelling scientific opportunities in the field of Cool, Evolved Stars, describing the observational and theoretical challenges to our understanding, and the key advancements made. We portray the pathway towards understanding, and identify, through recommendations, which advancements are necessary in 2020-2030 & beyond.

    141. Rackham, Benjamin, Pinhas, Arazi, Apai, Daniel, et al., 2019, BAAS, 51, 328, Constraining Stellar Photospheres as an Essential Step for Transmission Spectroscopy of Small Exoplanets

      Transmission spectra probe the atmospheres of transiting exoplanets, but these observations are also subject to signals introduced by magnetic active regions on host stars. We outline scientific opportunities in the next decade for providing useful constraints on stellar photospheres for the purposes of exoplanet transmission spectroscopy.

    142. Ridgway, Stephen, Akeson, Rachel, Baines, Ellyn, et al., 2019, BAAS, 51, 332, Precision Analysis of Evolved Stars

      The broad recommendation of this paper is three-fold: recognize the essential role of stellar physics in all of astronomy and cosmology; note that a revolution in stellar measurement capabilities, datasets, and modeling is underway and gaining momentum; and support the scientists, their essential technologies and observatories.

    143. Bendek, Eduardo, Belikov, Ruslan, Guyon, Olivier, et al., 2019, BAAS, 51, 354, The value of astrometry for exoplanet science

      We describe the scientific importance of measuring exoplanet masses and how high-precision astrometry can be utilized for this purpose. We describe current technology development efforts and astrometry missions concepts being proposed by the community to detect and characterize exoplanets.

    144. van Belle, Gerard, Baines, Ellyn, Boyajian, Tabetha, et al., 2019, BAAS, 51, 381, High Angular Resolution Astrophysics: Fundamental Stellar Parameters

      A discussion of direct determination of fundamental stellar parameters, which has many profound and wide-ranging impacts throughout astrophysics.

    145. Schaefer, Gail, Duchene, Gaspard, Farrington, Christopher D., et al., 2019, BAAS, 51, 483, Binary and Multiple Star Systems at High Angular Resolution

      Binary and multiple star systems provide laboratories for measuring stellar masses and studying star formation, stellar evolution, and dynamical evolution over time. This paper outlines several areas in the context of binary stars that can be advanced over the next decade.

    146. Huber, Daniel, Basu, Sarbani, Beck, Paul, et al., 2019, BAAS, 51, 488, Stellar Physics and Galactic Archaeology using Asteroseismology in the 2020’s

      Asteroseismology is the only observational tool in astronomy that can probe the interiors of stars, and is a benchmark method for deriving fundamental properties of stars and exoplanets. In this white paper, we describe key science questions and necessary facilities to continue the asteroseismology revolution into the 2020’s.

    147. Monnier, John, Rau, Gioia, Bermudez, Joel Sanchez, et al., 2019, BAAS, 51, 498, Imaging the Key Stages of Planet Formation

      In this white paper, we explore how higher angular resolution beyond ALMA and 8m-class telescopes can extend our understanding of the key stages of planet formation, to resolve accreting circumplanetary disks themselves, and to watch planets forming in situ for the nearest star-forming regions.

    148. Monnier, John, Rau, Gioia, Baines, Ellyn K., et al., 2019, BAAS, 51, 514, The Future of Exoplanet Direct Detection

      Diffraction fundamentally limits our ability to image and characterize exoplanets. Interferometry offers some advantages in exoplanet detection and characterization and we explore in this white paper some of the potential scientific breakthroughs possible.

    149. Thilker, David, Lee, Janice, Capak, Peter, et al., 2019, BAAS, 51, 525, The Nature of Low-Density Star Formation

      How do stars manage to form within low-density, HI-dominated gas? Here we outline fundamental questions about the nature of star formation at low- density. We describe the wide-field, high-resolution imaging of stars, star clusters, and gas clouds in nearby galaxies needed to provide definitive answers and build a complete theory of star formation.

    150. Beyer, Ross A., Spencer, John R., McKinnon, William B., et al., 2019, Icar, 323, 16, The nature and origin of Charon’s smooth plains

      Charon displays extensive plains that cover the equatorial area and south to the terminator on the sub-Pluto hemisphere observed by New Horizons. We hypothesize that these plains are a result of Charon’s global extension and early subsurface ocean yielding a large cryoflow that completely resurfaced this area leaving the plains and other features that we observe today. The cryoflow consisted of ammonia-rich material, and could have resurfaced this area either by cryovolcanic effusion similar to lunar maria emplacement or a mechanism similar to magmatic stoping where lithospheric blocks foundered. Geological observations, modeling of possible flow rheology, and an analysis of rille orientations support these hypotheses.

    151. Binzel, R. P., DeMeo, F. E., Turtelboom, E. V., et al., 2019, Icar, 324, 41, Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS)

      Advancing technology in near-infrared instrumentation and dedicated planetary telescope facilities have enabled nearly two decades of reconnoitering the spectral properties for near-Earth objects (NEOs). We report measured spectral properties for more than 1000 NEOs, representing >5% of the currently discovered population. Thermal flux detected below 2.5 m allows us to make albedo estimates for nearly 50 objects, including two comets. Additional spectral data are reported for more than 350 Mars-crossing asteroids. Most of these measurements were achieved through a collaboration between researchers at the Massachusetts Institute of Technology and the University of Hawaii, with full cooperation of the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. We call this project the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS; myth-neos). While MITHNEOS has continuously released all spectral data for immediate use by the scientific community, our objectives for this paper are to: (1) detail the methods and limits of the survey data, (2) formally present a compilation of results including their taxonomic classification within a single internally consistent framework, (3) perform a preliminary analysis on the overall population characteristics with a concentration toward deducing key physical processes and identifying their source region for escaping the main belt. Augmenting our newly published measurements are the previously published results from the broad NEO community, including many results graciously shared by colleagues prior to formal publication. With this collective data set, we find the near-Earth population matches the diversity of the main-belt, with all main-belt taxonomic classes represented in our sample. Potentially hazardous asteroids (PHAs) as well as the subset of mission accessible asteroids (V 7 km/s) both appear to be a representative mix of the overall NEO population, consistent with strong dynamical mixing for the population that interacts most closely with Earth. Mars crossers, however, are less diverse and appear to more closely match the inner belt population from where they have more recently diffused. The fractional distributions of major taxonomic classes (60% S, 20% C, 20% other) appear remarkably constant over two orders of magnitude in size (10 km to 100 m), which is eight orders of magnitude in mass, though we note unaccounted bias effects enter into our statistics below about 500 m. Given the range of surface ages, including possible refreshment by planetary encounters, we are able to identify a very specific space weathering vector tracing the transition from Q- to Sq- to S-types that follows the natural dispersion for asteroid spectra mapped into principal component space. We also are able to interpret a shock darkening vector that may account for some objects having featureless spectra. Space weathering effects for C-types are complex; these results are described separately by Lantz, Binzel, DeMeo. (2018, Icarus 302, 10-17). Independent correlation of dynamical models with taxonomic classes map the escape zones for NEOs to main-belt regions consistent with well established heliocentric compositional gradients. We push beyond taxonomy to interpret our visible plus near-infrared spectra in terms of the olivine and pyroxene mineralogy consistent with the H, L, and LL classes of ordinary chondrites meteorites. Correlating meteorite interpretations with dynamical escape region models shows a preference for LL chondrites to arrive from the 6 resonance and H chondrites to have a preferential signature from the mid-belt region (3:1 resonance). L chondrites show some preference toward the outer belt, but not at a significant level. We define a Space Weathering Parameter as a continuous variable and find evidence for step-wise changes in space weathering properties across different planet crossing zones in the inner solar system. Overall we hypothesize the relative roles of planetary encounters, YORP spin-up, and thermal cycling across the inner solar system.

    152. Stern, C., Dietrich, J. P., Bocquet, S., et al., 2019, MNRAS, 485, 69, Weak-lensing analysis of SPT-selected galaxy clusters using Dark Energy Survey Science Verification data

      We present weak-lensing (WL) mass constraints for a sample of massive galaxy clusters detected by the South Pole Telescope (SPT) via the Sunyaev-Zel’dovich effect (SZE). We use griz imaging data obtained from the Science Verification (SV) phase of the Dark Energy Survey (DES) to fit the WL shear signal of 33 clusters in the redshift range 0.25 z 0.8 with NFW profiles and to constrain a four-parameter SPT mass-observable relation. To account for biases in WL masses, we introduce a WL mass to true mass scaling relation described by a mean bias and an intrinsic, lognormal scatter. We allow for correlated scatter within the WL and SZE mass-observable relations and use simulations to constrain priors on nuisance parameters related to bias and scatter from WL. We constrain the normalization of the -M500 relation, A_SZ=12.0_{-6.7}^{+2.6} when using a prior on the mass slope BSZ from the latest SPT cluster cosmology analysis. Without this prior, we recover A_SZ=10.8_{-5.2}^{+2.3} and B_SZ=1.30_{-0.44}^{+0.22}. Results in both cases imply lower cluster masses than measured in previous work with and without WL, although the uncertainties are large. The WL derived value of BSZ is { } 20{{ per cent}} lower than the value preferred by the most recent SPT cluster cosmology analysis. The method demonstrated in this work is designed to constrain cluster masses and cosmological parameters simultaneously and will form the basis for subsequent studies that employ the full SPT cluster sample together with the DES data.

    153. Kessler, R., Brout, D., D’Andrea, C. B., et al., 2019, MNRAS, 485, 1171, First cosmology results using Type Ia supernova from the Dark Energy Survey: simulations to correct supernova distance biases

      We describe catalogue-level simulations of Type Ia supernova (SN Ia) light curves in the Dark Energy Survey Supernova Program (DES-SN) and in low-redshift samples from the Center for Astrophysics (CfA) and the Carnegie Supernova Project (CSP). These simulations are used to model biases from selection effects and light-curve analysis and to determine bias corrections for SN Ia distance moduli that are used to measure cosmological parameters. To generate realistic light curves, the simulation uses a detailed SN Ia model, incorporates information from observations (point spread function, sky noise, zero-point), and uses summary information (e.g. detection efficiency versus signal-to-noise ratio) based on 10 000 fake SN light curves whose fluxes were overlaid on images and processed with our analysis pipelines. The quality of the simulation is illustrated by predicting distributions observed in the data. Averaging within redshift bins, we find distance modulus biases up to 0.05 mag over the redshift ranges of the low-z and DES-SN samples. For individual events, particularly those with extreme red or blue colour, distance biases can reach 0.4 mag. Therefore, accurately determining bias corrections is critical for precision measurements of cosmological parameters. Files used to make these corrections are available at

    154. Abbott, T. M. C., Alarcon, A., Allam, S., et al., 2019, PhRvL, 122, 171301, Cosmological Constraints from Multiple Probes in the Dark Energy Survey

      The combination of multiple observational probes has long been advocated as a powerful technique to constrain cosmological parameters, in particular dark energy. The Dark Energy Survey has measured 207 spectroscopically confirmed type Ia supernova light curves, the baryon acoustic oscillation feature, weak gravitational lensing, and galaxy clustering. Here we present combined results from these probes, deriving constraints on the equation of state, w , of dark energy and its energy density in the Universe. Independently of other experiments, such as those that measure the cosmic microwave background, the probes from this single photometric survey rule out a Universe with no dark energy, finding w =-0.8 0-0.11+0.09. The geometry is shown to be consistent with a spatially flat Universe, and we obtain a constraint on the baryon density of b=0.06 9-0.012+0.009 that is independent of early Universe measurements. These results demonstrate the potential power of large multiprobe photometric surveys and pave the way for order of magnitude advances in our constraints on properties of dark energy and cosmology over the next decade.

    155. Stern, S. A., Weaver, H. A., Spencer, J. R., et al., 2019, Sci, 364, aaw9771, Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object

      The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69s origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.

    156. Moreno, F., Jehin, E., Licandro, J., et al., 2019, A&A, 624, L14, Dust properties of double-tailed active asteroid (6478) Gault

      Context. Asteroid (6478) Gault was discovered to exhibit a comet-like tail in observations from December 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt.
      Aims: We seek to investigate the grain properties of the dust ejected from asteroid (6478) Gault and to give insight into the activity mechanism(s).
      Methods: We use a Monte Carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. The code takes into account the brightness contribution of the asteroid itself. The model is applied to a large data set of images spanning the period from 2019 January 11 to 2019 March 13. In addition, we carried out both short- and long-term photometric measurements of the asteroid.
      Results: It is shown that, to date, asteroid (6478) Gault has experienced two episodes of impulsive dust ejection, which took place around 2018 November 5 and 2019 January 2. These two episodes released at least 1.4 107 kg and 1.6 106 kg of dust, respectively, at escape speeds. The size distribution, consisting of particles in the 1 m-1 cm radius range, follows a broken power law with bending points near 15 m and 870 m. On the other hand, the photometric series indicate a nearly constant magnitude over several 5-7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust.
      Conclusions: The dust particles forming Gault’s tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes.

    157. Brout, D., Scolnic, D., Kessler, R., et al., 2019, ApJ, 874, 150, First Cosmology Results Using SNe Ia from the Dark Energy Survey: Analysis, Systematic Uncertainties, and Validation

      We present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.017 < z < 0.849. We combine the DES-SN sample with an external sample of 122 low-redshift (z < 0.1) SNe Ia, resulting in a DES-SN3YR sample of 329 SNe Ia. Our cosmological analyses are blinded: after combining our DES-SN3YR distances with constraints from the Cosmic Microwave Background, our uncertainties in the measurement of the dark energy equation-of-state parameter, w, are 0.042 (stat) and 0.059 (stat+syst) at 68% confidence. We provide a detailed systematic uncertainty budget, which has nearly equal contributions from photometric calibration, astrophysical bias corrections, and instrumental bias corrections. We also include several new sources of systematic uncertainty. While our sample is less than one-third the size of the Pantheon sample, our constraints on w are only larger by 1.4, showing the impact of the DES-SN Ia light-curve quality. We find that the traditional stretch and color standardization parameters of the DES-SNe Ia are in agreement with earlier SN Ia samples such as Pan-STARRS1 and the Supernova Legacy Survey. However, we find smaller intrinsic scatter about the Hubble diagram (0.077 mag). Interestingly, we find no evidence for a Hubble residual step (0.007 0.018 mag) as a function of host-galaxy mass for the DES subset, in 2.4 tension with previous measurements. We also present novel validation methods of our sample using simulated SNe Ia inserted in DECam images and using large catalog-level simulations to test for biases in our analysis pipelines.

    158. Zhang, Y., Yanny, B., Palmese, A., et al., 2019, ApJ, 874, 165, Dark Energy Survey Year 1 Results: Detection of Intracluster Light at Redshift 0.25

      Using data collected by the Dark Energy Survey (DES), we report the detection of intracluster light (ICL) with 300 galaxy clusters in the redshift range of 0.2-0.3. We design methods to mask detected galaxies and stars in the images and stack the cluster light profiles, while accounting for several systematic effects (sky subtraction, instrumental point-spread function, cluster selection effects, and residual light in the ICL raw detection from background and cluster galaxies). The methods allow us to acquire high signal-to-noise measurements of the ICL and central galaxies (CGs), which we separate with radial cuts. The ICL appears as faint and diffuse light extending to at least 1 Mpc from the cluster center, reaching a surface brightness level of 30 mag arcsec-2. The ICL and the cluster CG contribute 44% 17% of the total cluster stellar luminosity within 1 Mpc. The ICL color is overall consistent with that of the cluster red sequence galaxies, but displays the trend of becoming bluer with increasing radius. The ICL demonstrates an interesting self-similarity featurefor clusters in different richness ranges, their ICL radial profiles are similar after scaling with cluster R 200m , and the ICL brightness appears to be a good tracer of the cluster radial mass distribution. These analyses are based on the DES redMaPPer cluster sample identified in the first year of observations.

    159. Neugent, Kathryn F., Levesque, Emily M., Massey, Philip, et al., 2019, ApJ, 875, 124, Binary Red Supergiants. II. Discovering and Characterizing B-type Companions

      The percentage of massive main-sequence OB stars in binary systems is thought to be as high as 100%. However, very few Galactic binary red supergiants (RSGs) have been identified, despite the fact that these stars are the evolved descendants of OB stars. As shown in our recent paper, binary RSGs will likely have B-type companions, as dictated by stellar evolution considerations. Such a system will have a very unique photometric signature due to the shape of the spectral energy distribution. Using photometric cutoffs, it should therefore be possible to detect candidate RSG+B star binary systems. Here we present our spectroscopic follow-up observations of such candidates. Out of our initial list of 280 candidates in M31 and M33, we observed 149 and confirmed 63 as newly discovered RSG+B star binary systems. Additional spectra of four candidate systems in the Small Magellanic Cloud confirmed all of them as new RSG+B star binaries including the first known RSG+Be star system. By fitting BSTAR06 and MARCS model atmospheres to the newly obtained spectra, we place estimates on the temperatures and subtypes of both the B stars and RSGs. Overall, we have found 87 new RSG+B star binary systems in M31, M33 and the Small and Large Magellanic Clouds. Our future studies are aimed at determining the binary fraction of RSGs.

    160. Wang, M. Y., Koposov, S., Drlica-Wagner, A., et al., 2019, ApJL, 875, L13, Rediscovery of the Sixth Star Cluster in the Fornax Dwarf Spheroidal Galaxy

      Since first noticed by Shapley in 1939, a faint object coincident with the Fornax dwarf spheroidal has long been discussed as a possible sixth globular cluster (GC) system. However, debate has continued over whether this overdensity is a statistical artifact or a blended galaxy group. In this Letter we demonstrate, using deep DECam imaging data, that this object is well resolved into stars and is a bona fide star cluster. The stellar overdensity of this cluster is statistically significant at the level of 6-6.7 in several different photometric catalogs including Gaia. Therefore, it is highly unlikely to be caused by random fluctuation. We show that Fornax 6 is a star cluster with a peculiarly low surface brightness and irregular shape, which may indicate a strong tidal influence from its host galaxy. The Hess diagram of Fornax 6 is largely consistent with that of Fornax field stars, but it appears to be slightly bluer. However, it is still likely more metal-rich than most of the GCs in the system. Faint clusters like Fornax 6 that orbit and potentially get disrupted in the centers of dwarf galaxies can prove crucial for constraining the dark matter distribution in Milky Way satellites.

    161. DeMeo, Francesca E., Polishook, David, Carry, Benoit, et al., 2019, Icar, 322, 13, Olivine-dominated A-type asteroids in the main belt: Distribution, abundance and relation to families

      Differentiated asteroids are rare in the main asteroid belt despite evidence for 100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope.


      We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of 600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

    162. Bird, M. K., Linscott, I. R., Tyler, G. L., et al., 2019, Icar, 322, 192, Radio thermal emission from Pluto and Charon during the New Horizons encounter

      One component of the REX instrument on NASA’s New Horizons spacecraft was an investigation of the radio continuum radiation from Pluto and Charon during the flyby on 14 July 2015. The planetary thermal emission was recorded at a wavelength of 4.17 cm (7.18 GHz) during approach, departure, and specifically on the non-illuminated hemispheres of Pluto and Charon during the respective intervals between occultation ingress and egress. We derive the brightness temperatures for these disk-resolved and unresolved observations. The mean values and 1 deviations of brightness temperature for the unresolved sunlit disk are 33.2 1.4 K and 47.2 5.3 K for Pluto and Charon, respectively, consistent with the global albedos of the two bodies as well as with previous ground-based estimates at smaller wavelengths. A slightly colder temperature of 29.0 2.5 K was determined for the disk-integrated nightside of Pluto and a larger drop in temperature was observed for Charon (40.9 0.9 K), implying a smaller thermal inertia for Charon than Pluto. The measured brightness temperature of Pluto across the nightside diametric scan reached a maximum of 29.0 1.5 K in the center of the disk. The profile shape is attributed to an emissivity effect, which favors thermal emission toward higher elevation angles. As a first approximation, the effective emissivity for thermal emission is calculated for the case when Pluto and Charon are uniformly smooth homogenous spheres. Under this assumption, the effective emissivity for these observations is close to unity for all probable surface constituents, implying that the effective temperature of the Pluto subsurface is only a few percent higher than the observed brightness temperature. A considerably lower subsurface emissivity is implied, however, if the higher atmospheric temperatures near the surface determined from the REX occultation measurements are also valid for the subsurface.

    163. Cook, D. O., Lee, J. C., Adamo, A., et al., 2019, MNRAS, 484, 4897, Star cluster catalogues for the LEGUS dwarf galaxies

      We present the star cluster catalogues for 17 dwarf and irregular galaxies in the HST Treasury Program `Legacy ExtraGalactic UV Survey’ (LEGUS). Cluster identification and photometry in this sub-sample are similar to that of the entire LEGUS sample, but special methods were developed to provide robust catalogues with accurate fluxes due to low cluster statistics. The colours and ages are largely consistent for two widely used aperture corrections, but a significant fraction of the clusters are more compact than the average training cluster. However, the ensemble luminosity, mass, and age distributions are consistent suggesting that the systematics between the two methods are less than the random errors. When compared with the clusters from previous dwarf galaxy samples, we find that the LEGUS catalogues are more complete and provide more accurate total fluxes. Combining all clusters into a composite dwarf galaxy, we find that the luminosity and mass functions can be described by a power law with the canonical index of -2 independent of age and global SFR binning. The age distribution declines as a power law, with an index of – 0.80 0.15, independent of cluster mass and global SFR binning. This decline of clusters is dominated by cluster disruption since the combined star formation histories and integrated-light SFRs are both approximately constant over the last few hundred Myr. Finally, we find little evidence for an upper-mass cut-off (<2) in the composite cluster mass function, and can rule out a truncation mass below 104.5M but cannot rule out the existence of a truncation at higher masses.

    164. Kovacs, A., Sanchez, C., Garcia-Bellido, J., et al., 2019, MNRAS, 484, 5267, More out of less: an excess integrated Sachs-Wolfe signal from supervoids mapped out by the Dark Energy Survey

      The largest structures in the cosmic web probe the dynamical nature of dark energy through their integrated Sachs-Wolfe imprints. In the strength of the signal, typical cosmic voids have shown good consistency with expectation AISW = Tdata/Ttheory = 1, given the substantial cosmic variance. Discordantly, large-scale hills in the gravitational potential, or supervoids, have shown excess signals. In this study, we mapped out 87 new supervoids in the total 5000 deg2 footprint of the Dark Energy Survey at 0.2 < z < 0.9 to probe these anomalous claims. We found an excess imprinted profile with AISW 4.1 2.0 amplitude. The combination with independent BOSS data reveals an ISW imprint of supervoids at the 3.3 significance level with an enhanced AISW 5.2 1.6 amplitude. The tension with CDM predictions is equivalent to 2.6 and remains unexplained.

    165. Jacobs, C., Collett, T., Glazebrook, K., et al., 2019, MNRAS, 484, 5330, Finding high-redshift strong lenses in DES using convolutional neural networks

      We search Dark Energy Survey (DES) Year 3 imaging data for galaxy-galaxy strong gravitational lenses using convolutional neural networks. We generate 250 000 simulated lenses at redshifts > 0.8 from which we create a data set for training the neural networks with realistic seeing, sky and shot noise. Using the simulations as a guide, we build a catalogue of 1.1 million DES sources with 1.8 < g – i < 5, 0.6 < g – r < 3, r_mag > 19, g_mag > 20, and i_mag > 18.2. We train two ensembles of neural networks on training sets consisting of simulated lenses, simulated non-lenses, and real sources. We use the neural networks to score images of each of the sources in our catalogue with a value from 0 to 1, and select those with scores greater than a chosen threshold for visual inspection, resulting in a candidate set of 7301 galaxies. During visual inspection, we rate 84 as `probably’ or `definitely’ lenses. Four of these are previously known lenses or lens candidates. We inspect a further 9428 candidates with a different score threshold, and identify four new candidates. We present 84 new strong lens candidates, selected after a few hours of visual inspection by astronomers. This catalogue contains a comparable number of high-redshift lenses to that predicted by simulations. Based on simulations, we estimate our sample to contain most discoverable lenses in this imaging and at this redshift range.

    166. van Belle, Gerard T., 2019, NatAs, 3, 480, An improved stellar yardstick in the shadows

      Measurement of the diffraction pattern of starlight during an asteroid occultation opens up new territory in stellar angular size determinations.

    167. Oszkiewicz, Dagmara, Kryszczynska, Agnieszka, Kankiewicz, Pawe, et al., 2019, A&A, 623, A170, Physical and dynamical properties of the unusual V-type asteroid (2579) Spartacus

      Context. Asteroid (2579) Spartacus is a small V-type object located in the inner main belt. This object shows spectral characteristics unusual for typical Vestoids, which may indicate an origin deeper than average within Vesta or an origin from an altogether different parent body.
      Aims: Our main goal is to study the origin of Spartacus. We derive the spin of Spartacus and a convex shape model of Spartacus in order to increase the knowledge of the body’s physical properties. The rotational parameters are then used to investigate dynamical evolution of the object as well as to distinguish regions sampled by spectral observations to determine whether its surface displays heterogeneity.
      Methods: We collected lightcurves available from the literature (oppositions of 2009, 2012) and obtained additional photometric observations at various telescopes in 2016, 2017, and 2018. We used the lightcurve inversion method to derive a spin and convex shape model. We have collected spectral observations over two rotational periods of Spartacus and determined its spectral parameters using the modified Gaussian model (MGM). We then dynamically integrated the orbital elements of Spartacus, taking into account existing information, including its thermal properties, size and the derived spin axis orientation.
      Results: We find two models for (2579) Spartacus: (a) = 312 5, = -57 5 and (b) = 113 5, = -60 5 both retrograde. We find that the drift direction for Spartacus is consistent with separation from Vesta, and after a backward integration of 1 Gyr the asteroid reaches the boundary of the family. We did not observe spectral variations with rotation, thus the body most likely has a homogeneous surface. Additionally, new spectral analysis indicates that the 1.0 and 2.0 m band centers are within ranges that are typical for Vestoids while the area ratio of these bands is about half that of typical Vestoids.
      Conclusions: The asteroid (2579) Spartacus is in retrograde rotation and has a drift direction consistent with an origin from Vesta. The revised spectral band centers are within ranges typical for Vestoids, while band area ratio (BAR) is unusually low compared to that of other V-types. The dynamical model shows that the asteroid could have migrated to its current location from the edges of the Vesta family within 1 Gyr, but an origin from an earlier impact on Vesta could also be plausible.

    168. Schleicher, David G., Knight, Matthew M., Eisner, Nora L., et al., 2019, AJ, 157, 108, Gas Jet Morphology and the Very Rapidly Increasing Rotation Period of Comet 41P/Tuttle-Giacobini-Kresak

      We present results from our 47 night imaging campaign of Comet 41P/Tuttle-Giacobini-Kresak conducted from Lowell Observatory between 2017 February 16 and July 2. Coma morphology revealed gas jets, whose appearance and motion as a function of time yielded the rotation period and other properties. All narrowband CN images exhibited either one or two jets; one jet appeared as a partial face-on spiral with clockwise rotation, while the second jet evolved from a side-on corkscrew, through face-on, to corkscrew again, with only a slow evolution throughout the apparition due to progressive viewing geometry changes. A total of 78 period determinations were made over a 7 week interval, yielding a smooth and accelerating rotation period starting at 24 hr (March 21 and 22) and passing 48 hr on April 28. While this is by far the fastest rate of change ever measured for a comet nucleus, the torque required is readily within what can exist given likely properties of the nucleus. If the torque remained constant, we estimate that the nucleus could have stopped rotating and/or begun to tumble as soon as only 2 months following perihelion and will certainly reach this stage by early in the next apparition. Working backward in time, Tuttle-Giacobini-Kresak would have been rotating near its rotational breakup velocity three to four orbits earlier, suggesting that its extreme 7 mag outburst observed in 2001 might have been caused by a partial fragmentation at that time, as might the pair of 1973 8 mag outbursts if there had been an earlier spin-down and spin-up cycle.

    169. Banda-Huarca, M. V., Camargo, J. I. B., Desmars, J., et al., 2019, AJ, 157, 120, Astrometry and Occultation Predictions to Trans-Neptunian and Centaur Objects Observed within the Dark Energy Survey

      Trans-Neptunian objects (TNOs) are a source of invaluable information to access the history and evolution of the outer solar system. However, observing these faint objects is a difficult task. As a consequence, important properties such as size and albedo are known for only a small fraction of them. Now, with the results from deep sky surveys and the Gaia space mission, a new exciting era is within reach as accurate predictions of stellar occultations by numerous distant small solar system bodies become available. From them, diameters with kilometer accuracies can be determined. Albedos, in turn, can be obtained from diameters and absolute magnitudes. We use observations from the Dark Energy Survey (DES) from 2012 November until 2016 February, amounting to 4,292,847 charge-coupled device (CCD) frames. We searched them for all known small solar system bodies and recovered a total of 202 TNOs and Centaurs, 63 of which have been discovered by the DES collaboration as of the date of submission. Their positions were determined using the Gaia Data Release 2 as reference and their orbits were refined. Stellar occultations were then predicted using these refined orbits plus stellar positions from Gaia. These predictions are maintained, and updated, in a dedicated web service. The techniques developed here are also part of an ambitious preparation to use the data from the Large Synoptic Survey Telescope (LSST), that expects to obtain accurate positions and multifilter photometry for tens of thousands of TNOs.

    170. Doctor, Z., Kessler, R., Herner, K., et al., 2019, ApJL, 873, L24, A Search for Optical Emission from Binary Black Hole Merger GW170814 with the Dark Energy Camera

      Binary black hole (BBH) mergers found by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors are of immense scientific interest to the astrophysics community, but are considered unlikely to be sources of electromagnetic emission. To test whether they have rapidly fading optical counterparts, we used the Dark Energy Camera to perform an i-band search for the BBH merger GW170814, the first gravitational wave (GW) detected by three interferometers. The 87 deg2 localization region (at 90% confidence) centered in the Dark Energy Survey (DES) footprint enabled us to image 86% of the probable sky area to a depth of i 23 mag and provide the most comprehensive data set to search for electromagnetic (EM) emission from BBH mergers. To identify candidates, we perform difference imaging with our search images and with templates from pre-existing Dark Energy Survey (DES) images. The analysis strategy and selection requirements were designed to remove supernovae and to identify transients that decline in the first two epochs. We find two candidates, each of which is spatially coincident with a star or a high-redshift galaxy in the DES catalogs, and they are thus unlikely to be associated with GW170814. Our search finds no candidates associated with GW170814, disfavoring rapidly declining optical emission from BBH mergers brighter than i 23 mag (L optical 5 1041 erg s-1) 1-2 days after coalescence. In terms of GW sky map coverage, this is the most complete search for optical counterparts to BBH mergers to date.

    171. Brout, D., Sako, M., Scolnic, D., et al., 2019, ApJ, 874, 106, First Cosmology Results Using Type Ia Supernovae from the Dark Energy Survey: Photometric Pipeline and Light-curve Data Release

      We present griz light curves of 251 SNe Ia from the first 3 years of the Dark Energy Survey Supernova Programs (DES-SN) spectroscopically classified sample. The photometric pipeline described in this paper produces the calibrated fluxes and associated uncertainties used in the cosmological parameter analysis by employing a scene modeling approach that simultaneously models a variable transient flux and temporally constant host galaxy. We inject artificial point sources onto DECam images to test the accuracy of our photometric method. Upon comparison of input and measured artificial supernova fluxes, we find that flux biases peak at 3 mmag. We require corrections to our photometric uncertainties as a function of host galaxy surface brightness at the transient location, similar to that seen by the DES Difference Imaging Pipeline used to discover transients. The public release of the light curves can be found at

    172. Buratti, B. J., Hicks, M. D., Hillier, J. H., et al., 2019, ApJL, 874, L3, New Horizons Photometry of Pluto’s Moon Charon

      The New Horizons spacecraft extended the range in solar phase angle coverage for Plutos moon Charon from 1.8the maximum observable from Earthto 170. This extraordinary expansion in range has enabled photometric modeling and a robust determination of Charons phase integral and Bond albedo at visible wavelengths. Photometric modeling shows that Charon is similar in its photometric properties to other icy moons, except that its single particle phase function is more isotropic, suggesting the Kuiper Belt may represent a new regime for surface alteration processes. Charons phase integral is 0.70 0.04 and its Bond albedo is 0.29 0.05.

    173. Lin, Hsing Wen, Gerdes, David W., Hamilton, Stephanie J., et al., 2019, Icar, 321, 426, Evidence for color dichotomy in the primordial Neptunian Trojan population

      In the current model of early Solar System evolution, the stable members of the Jovian and Neptunian Trojan populations were captured into resonance from the leftover reservoir of planetesimals during the outward migration of the giant planets. As a result, both Jovian and Neptunian Trojans share a common origin with the primordial disk population, whose other surviving members constitute today’s trans-Neptunian object (TNO) populations. The cold (low inclination and small eccentricity) classical TNOs are ultra-red, while the dynamically excited “hot” (high inclination and larger eccentricity) population of TNOs contains a mixture of ultra-red and blue objects. In contrast, Jovian and Neptunian Trojans are observed to be blue. While the absence of ultra-red Jovian Trojans can be readily explained by the sublimation of volatile material from their surfaces due to the high flux of solar radiation at 5 AU, the lack of ultra-red Neptunian Trojans presents both a puzzle and a challenge to formation models. In this work we report the discovery by the Dark Energy Survey (DES) of two new dynamically stable L4 Neptunian Trojans, 2013 VX30 and 2014 UU240, both with inclinations i > 30, making them the highest-inclination known stable Neptunian Trojans. We have measured the colors of these and three other dynamically stable Neptunian Trojans previously observed by DES, and find that 2013 VX30 is ultra-red, the first such Neptunian Trojan in its class. As such, 2013 VX30 may be a “missing link” between the Trojan and TNO populations. Using a simulation of the DES TNO detection efficiency, we find that there are 162 73 Trojans with Hr < 10 at the L4 Lagrange point of Neptune. Moreover, the blue-to-red Neptunian Trojan population ratio should be higher than 17:1. Based on this result, we discuss the possible origin of the ultra-red Neptunian Trojan population and its implications for the formation history of Neptunian Trojans.

    174. Guarnieri, Pierandrea, Maraston, Claudia, Thomas, Daniel, et al., 2019, MNRAS, 483, 3060, Candidate massive galaxies at z 4 in the Dark Energy Survey

      Using stellar population models, we predicted that the Dark Energy Survey (DES) – due to its special combination of area (5000 deg2) and depth (i = 24.3) – would be in the position to detect massive (1011 M) galaxies at z 4. We confront those theoretical calculations with the first 150 deg2 of DES data reaching nominal depth. From a catalogue containing 5 million sources, 26 000 were found to have observed-frame g – r versus r – i colours within the locus predicted for z 4 massive galaxies. We further removed contamination by stars and artefacts, obtaining 606 galaxies lining up by the model selection box. We obtained their photometric redshifts and physical properties by fitting model templates spanning a wide range of star formation histories, reddening and redshift. Key to constrain the models is the addition, to the optical DES bands g, r, i, z, and Y, of near-IR J, H, Ks data from the Vista Hemisphere Survey. We further applied several quality cuts to the fitting results, including goodness of fit and a unimodal redshift probability distribution. We finally select 233 candidates whose photometric redshift probability distribution function peaks around z 4, have high stellar masses [log (M*/M) 11.7 for a Salpeter IMF] and ages around 0.1 Gyr, i.e. formation redshift around 5. These properties match those of the progenitors of the most massive galaxies in the local Universe. This is an ideal sample for spectroscopic follow-up to select the fraction of galaxies which are truly at high redshift. These initial results and those at the survey completion, which we shall push to higher redshifts, will set unprecedented constraints on galaxy formation, evolution, and the re-ionization epoch.

    175. Abbott, T. M. C., Abdalla, F. B., Alarcon, A., et al., 2019, MNRAS, 483, 4866, Dark Energy Survey Year 1 Results: Measurement of the Baryon Acoustic Oscillation scale in the distribution of galaxies to redshift 1

      We present angular diameter distance measurements obtained by locating the BAO scale in the distribution of galaxies selected from the first year of Dark Energy Survey data. We consider a sample of over 1.3 million galaxies distributed over a footprint of 1336 deg2 with 0.6 < zphoto < 1 and a typical redshift uncertainty of 0.03(1 + z). This sample was selected, as fully described in a companion paper, using a color/magnitude selection that optimizes trade-offs between number density and redshift uncertainty. We investigate the BAO signal in the projected clustering using three conventions, the angular separation, the co-moving transverse separation, and spherical harmonics. Further, we compare results obtained from template based and machine learning photometric redshift determinations. We use 1800 simulations that approximate our sample in order to produce covariance matrices and allow us to validate our distance scale measurement methodology. We measure the angular diameter distance, DA, at the effective redshift of our sample divided by the true physical scale of the BAO feature, rd. We obtain close to a 4 per cent distance measurement of DA(zeff = 0.81)/rd = 10.75 0.43. These results are consistent with the flat CDM concordance cosmological model supported by numerous other recent experimental results.

    176. Shajib, A. J., Birrer, S., Treu, T., et al., 2019, MNRAS, 483, 5649, Is every strong lens model unhappy in its own way? Uniform modelling of a sample of 13 quadruply+ imaged quasars

      Strong-gravitational lens systems with quadruply imaged quasars (quads) are unique probes to address several fundamental problems in cosmology and astrophysics. Although they are intrinsically very rare, ongoing and planned wide-field deep-sky surveys are set to discover thousands of such systems in the next decade. It is thus paramount to devise a general framework to model strong-lens systems to cope with this large influx without being limited by expert investigator time. We propose such a general modelling framework (implemented with the publicly available software LENSTRONOMY) and apply it to uniformly model three-band Hubble Space Telescope Wide Field Camera 3 images of 13 quads. This is the largest uniformly modelled sample of quads to date and paves the way for a variety of studies. To illustrate the scientific content of the sample, we investigate the alignment between the mass and light distribution in the deflectors. The position angles of these distributions are well-aligned, except when there is strong external shear. However, we find no correlation between the ellipticity of the light and mass distributions. We also show that the observed flux-ratios between the images depart significantly from the predictions of simple smooth models. The departures are strongest in the bluest band, consistent with microlensing being the dominant cause in addition to millilensing. Future papers will exploit this rich data set in combination with ground-based spectroscopy and time delays to determine quantities such as the Hubble constant, the free streaming length of dark matter, and the normalization of the initial stellar mass function.

    177. Dominguez Sanchez, H., Huertas-Company, M., Bernardi, M., et al., 2019, MNRAS, 484, 93, Transfer learning for galaxy morphology from one survey to another

      Deep learning (DL) algorithms for morphological classification of galaxies have proven very successful, mimicking (or even improving) visual classifications. However, these algorithms rely on large training samples of labelled galaxies (typically thousands of them). A key question for using DL classifications in future Big Data surveys is how much of the knowledge acquired from an existing survey can be exported to a new data set, i.e. if the features learned by the machines are meaningful for different data. We test the performance of DL models, trained with Sloan Digital Sky Survey (SDSS) data, on Dark Energy Survey (DES) using images for a sample of 5000 galaxies with a similar redshift distribution to SDSS. Applying the models directly to DES data provides a reasonable global accuracy (90 per cent), but small completeness and purity values. A fast domain adaptation step, consisting of a further training with a small DES sample of galaxies (500-300), is enough for obtaining an accuracy >95 per cent and a significant improvement in the completeness and purity values. This demonstrates that, once trained with a particular data set, machines can quickly adapt to new instrument characteristics (e.g. PSF, seeing, depth), reducing by almost one order of magnitude the necessary training sample for morphological classification. Redshift evolution effects or significant depth differences are not taken into account in this study.

    178. West, Michael J., De Propris, Roberto, Bremer, Malcolm N., et al., 2019, NatAs, 3, 362, Publisher Correction: Ten billion years of brightest cluster galaxy alignments

      When this Letter was originally published, Supplementary Table 1 was mistakenly omitted; it is now available at 10.1038/s41550-019-0728-9.

    179. Singer, K. N., McKinnon, W. B., Gladman, B., et al., 2019, Sci, 363, 955, Impact craters on Pluto and Charon indicate a deficit of small Kuiper belt objects

      The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely 4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.

    180. Horch, Elliott P., Tokovinin, Andrei, Weiss, Samuel A., et al., 2019, AJ, 157, 56, Observations of Binary Stars with the Differential Speckle Survey Instrument. VIII. Measures of Metal-poor and Triple Stars from 2015 to 2018

      We present 248 speckle observations of 43 binary and 19 trinary star systems chosen to make progress in two main areas of investigation: the fundamental properties of metal-poor stars and star formation mechanisms. The observations were taken at the Gemini North and South telescopes during the period 2015 July to 2018 April, mainly with the Differential Speckle Survey Instrument but also with a few early results from the new Alopeke speckle camera at Gemini North. We find that the astrometry and photometry of these observations as a whole are consistent with previous work at Gemini. We present five new visual orbits for systems important in understanding metal-poor stars, three of which have orbital periods of less than 4 yr, and we indicate the degree to which these and future observations can impact our knowledge of stellar properties and star formation. In particular, we find a decrease in mass at fixed spectral type for metal-poor stars versus their solar-metallicity analogs that is consistent with predictions that are made from current stellar models.

    181. Raghunathan, S., Patil, S., Baxter, E., et al., 2019, ApJ, 872, 170, Mass Calibration of Optically Selected DES Clusters Using a Measurement of CMB-cluster Lensing with SPTpol Data

      We use cosmic microwave background (CMB) temperature maps from the 500 deg2 SPTpol survey to measure the stacked lensing convergence of galaxy clusters from the Dark Energy Survey (DES) Year-3 redMaPPer (RM) cluster catalog. The lensing signal is extracted through a modified quadratic estimator designed to be unbiased by the thermal Sunyaev-Zeldovich (tSZ) effect. The modified estimator uses a tSZ-free map, constructed from the SPTpol 95 and 150 GHz data sets, to estimate the background CMB gradient. For lensing reconstruction, we employ two versions of the RM catalog: a flux-limited sample containing 4003 clusters and a volume-limited sample with 1741 clusters. We detect lensing at a significance of 8.7(6.7) with the flux (volume)-limited sample. By modeling the reconstructed convergence using the Navarro-Frenk-White profile, we find the average lensing masses to be {M}200{{m}}=({1.62}-0.25+0.32 [{stat}.]+/- 0.04 [{sys}.]) and ({1.28}-0.18+0.14 [{stat}.]+/- 0.03 [{sys}.]) {10}14 {M} for the volume- and flux-limited samples, respectively. The systematic error budget is much smaller than the statistical uncertainty and is dominated by the uncertainties in the RM cluster centroids. We use the volume-limited sample to calibrate the normalization of the mass-richness scaling relation, and find a result consistent with the galaxy weak-lensing measurements from DES.

    182. Chuss, David T., Andersson, B. -G., Bally, John, et al., 2019, ApJ, 872, 187, HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1

      We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 m at angular resolutions of 5, 8, 14, and 19 for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the hourglass configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin-Neugebauer/Kleinman-Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.

    183. Abbott, T. M. C., Allam, S., Andersen, P., et al., 2019, ApJL, 872, L30, First Cosmology Results using Type Ia Supernovae from the Dark Energy Survey: Constraints on Cosmological Parameters

      We present the first cosmological parameter constraints using measurements of type Ia supernovae (SNe Ia) from the Dark Energy Survey Supernova Program (DES-SN). The analysis uses a subsample of 207 spectroscopically confirmed SNe Ia from the first three years of DES-SN, combined with a low-redshift sample of 122 SNe from the literature. Our DES-SN3YR result from these 329 SNe Ia is based on a series of companion analyses and improvements covering SN Ia discovery, spectroscopic selection, photometry, calibration, distance bias corrections, and evaluation of systematic uncertainties. For a flat CDM model we find a matter density {{{ }}}{{m}}=0.331+/- 0.038. For a flat wCDM model, and combining our SN Ia constraints with those from the cosmic microwave background (CMB), we find a dark energy equation of state w=-0.978+/- 0.059, and {{{ }}}{{m}}=0.321+/- 0.018. For a flat w 0 w a CDM model, and combining probes from SN Ia, CMB and baryon acoustic oscillations, we find {w}0=-0.885+/- 0.114 and {w}a=-0.387 +/- 0.430. These results are in agreement with a cosmological constant and with previous constraints using SNe Ia (Pantheon, JLA).

    184. Sickafoose, A. A., Bosh, A. S., Levine, S. E., et al., 2019, Icar, 319, 657, A stellar occultation by Vanth, a satellite of (90482) Orcus

      A stellar occultation by the large trans-Neptunian object (90482) Orcus was predicted to occur on 2017 March 07. Observations were made at five sites in North and South America: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories, California; Las Cumbres Observatory’s 1-m telescope at McDonald Observatory, Fort Davis, Texas (ELP); NASA’s 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawai’i; the 0.6-m Southeastern Association for Research in Astronomy (SARA-CT) telescope at Cerro Tololo, Chile; and the 4.1-m Southern Astrophysical Research (SOAR) telescope on Cerro Pachon, Chile. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at the IRTF. Solid-body occultations were observed from two sites. Post-event reconstruction suggested an occultation of two different stars observed from two different sites. Follow-up, speckle imaging revealed a second star, which verified that the occulting body in both cases was Orcus’ satellite, Vanth. The two single-chord detections, with an anomalously large timing delay in one chord, have lengths of 291 125 km and 434.4 2.4 km. The observations, combined with a non-detection at a nearby site, allow a tight constraint of 443 10 km to be placed on Vanth’s size (assuming it is spherical). A 3- upper limit of 1-4 bar (depending on constituent) is found for a global Vanth atmosphere. The immersion and emersion profiles are slightly different, with atmospheric constraints 40% higher on immersion than on emersion. No rings or other material were detected within ten thousand kms of Vanth, and beyond 8010 km from Orcus, to the tightest optical depth limit of 0.1 at 5 km scale. The occultation probed as close as 5040 km from Orcus, placing an optical depth limit of 0.3 at 5 km scale on any encircling material at that distance.

    185. Schindler, Kevin, Buckingham, William, 2019, AAS, 233, 135.06, Apollo Astronaut Training at Arizona’s Observatories

      As part of their training to explore the Moon, Apollo astronauts visited several astronomical observatories in Arizona, including Lowell, Kitt Peak, the Naval Observatory Flagstaff Station (NOFS) and the campus observatory at Arizona State College (now Northern Arizona University – NAU). This involved comparing live observations of the Moon through telescopes with photographs of the lunar surface, as well as studying charts to familiarize themselves with the depiction of topographic features. The first of this training occurred in January 1963, when the Next 9 group of astronauts traveled to Flagstaff. They visited Meteor Craterto study an impact crater like they would see on the Moonand Sunset Crater to explore volcanic structures. They then headed to Lowell Observatory to learn about the lunar mapping being carried out there by the Aeronautical Chart and Information Center (ACIC), a branch of the United States Air Force. Later, the astronauts split into three groups for viewing the Moon through telescopes, with one group staying at Lowell, another going to the campus observatory, and the third heading to NOFS. The following year, several smaller groups of astronauts, representing the first three classes, went to Kitt Peak during trips that also saw them study geology elsewhere in the state. At Kitt Peak they enjoyed the unusual opportunity of viewing the Moon through the McMath-Pierce Solar Telescope.

    186. Nofi, Larissa, Prato, Lisa, Johns-Krull, Christopher, et al., 2019, AAS, 233, 140.25, Preliminary Results from a Young Exoplanet RV Survey

      Observing and characterizing newly-formed planets around young stars is important for developing planet formation and evolution theory. However, given challenges in detecting young planetary systems, current models are primarily based on systems that are billions of years old. It is therefore unclear which exoplanetary properties are indicators of formation conditions, or of later evolution. We are conducting an infrared radial velocity survey to detect and confirm young exoplanets around T Tauri stars using the Immersion Grating Infrared Spectrograph (IGRINS) on the 4.3-m Lowell Observatory Discovery Channel Telescope (DCT). IGRINS simultaneously observes H- and K-bands at a resolution of ~45,000. Infrared spectroscopy is less susceptible to apparent RV variability caused by starspots on active young stars than optical observations. Our sample consists of ~100 T Tauri stars of age 1 to a few Myr in the relatively nearby Taurus star forming region. We present early results on our search for RV variability of T Tauri stars, indicative of the presence of hot Jupiters with the IGRINS + DCT system.

    187. Graham, Sean, Prato, Lisa, Schaefer, Gail, et al., 2019, AAS, 233, 155.05, H Band Observations of the Candidate Young Spectroscopic Binary UY Auriga B and its Disk

      Binaries dominate the stellar census; understanding disk evolution in these complex environments is crucial in order to form a complete and accurate model for planet formation. UY Auriga is a ~2 Myr old classical T Tauri binary with a separation of ~0.9″. The system contains a number of complex gas-dust interactions between the circumbinary and circumstellar disks. Multiple epochs of high-resolution H-band spectroscopy show that UY Aur B exhibits extreme spectral variability over a period of 13 years or more; it is also known to be highly photometrically variable. We explore whether UY Aur B might itself be a close, short-period binary and provide estimates of accretion properties and possible orbital solutions and component mass ratios.

    188. van Belle, Gerard, Patane, Simon, Riley, Daniel, et al., 2019, AAS, 233, 158.25, Optimast Structurally Connected Interferometry Enabled by In-Space Robotic Manufacturing and Assembly

      Future goals for astrophysics at the frontiers of high spatial resolution drive the need for large effective apertures beyond what the current generation of space observatories provides. Space-based interferometry delivers on this promise and enables cost-effective observation of faint objects at unprecedented levels of angular resolution. Using the Made In Space (MIS) Optimast capability, a simple, two aperture Structurally Connected Interferometer (SCI) is produced via in-space Additive Manufacturing (AM) technology. This capability allows the two modest apertures to be packaged efficiently for launch and then placed at a large separation, coherently, in order to achieve a greater effective angular resolution . Optimast enables the manufacturing and deployment of large primary trusses unconstrained by launch loads or volume restrictions that meet science requirements for the high angular resolutions (in the milliarcsecond regime) necessary for applications such as characterization of planets near bright stars, and measurement individual objects in dense star clusters. Space-based deployment of an interferometer unfettered by the turbulent atmosphere will markedly increase the sensitivity reach of such an instrument relative to its ground-based counterparts. Adapting the MIS Optimast technology to produce long baseline structures with low thermal expansion materials enables simultaneous structural fabrication and positioning of the optical subsystems to the required static, thermal deflection, and oscillation tolerances. An Optimast-SCI baseline structure eliminates parasitic mass and provides superior absolute position control over traditional deployable structures at much lower cost, mass, and integration complexity.

    189. Powell, Erick, Horanzy, Rochelle, Schutte, Maria, et al., 2019, AAS, 233, 163.10, Characterizing Changes in the Be Star Population of NGC 663

      Characterizing the amplitude and wavelength dependence of variations in the intrinsic polarization of classical Be stars can help inform how these circumstellar disks change over time. Since the observed polarization is a superposition of a component arising from the interstellar medium (ISP) and a component intrinsic to the Be star itself, robustly determining the ISP component is critical to isolating the intrinsic component. We present our analysis of multi-epoch, multi-wavelength photometric and polarimetric imaging of NGC 663. NGC 663 is an open cluster that is known to host a large population of Be stars. We use GAIA Data Release 2 to refine the distance and membership of NGC 663, and use these results to construct a refined field star polarization map towards the cluster, thereby enabling us to better quantify the ISP along the line of sight. This program is supported by NSF-AST 1411563, 1412110, and 1412135, along with the NSF REU program at the University of Oklahoma.

    190. Llama, Joe, Cabrera, Tomas, Luna, Jessica, et al., 2019, AAS, 233, 247.32, Detection of water in the atmosphere of the hot Jupiter HD 102195b

      The composition and structure of hot Jupiter atmospheres provide a fossil record of their primordial origins, potentially holding the key to distinguishing between the various proposed formation mechanisms. High-resolution spectroscopic observations of exoplanet atmospheres enable us to resolve molecular bands into many individual spectral lines in a pattern that is unique to each molecule. By then exploiting the Doppler shift of the planet over multiple nights we can separate the planet spectrum from that of the host star and Earths atmosphere. Here, we use the high-resolution infrared spectrograph IGRINS (R=45,000, =1.4-2.5 microns) on the 4.3m Discovery Channel Telescope to observe the spectrum of the hot Jupiter HD 102195b. Our analysis reveals a 4 detection of water in the atmosphere of this heavily irradiated hot Jupiter.

    191. Prato, Lisa, Nofi, Larissa, 2019, AAS, 233, 254.03, The Lowell Observatory Predoctoral Scholar Program

      Lowell Observatory is pleased to solicit applications for our Predoctoral Scholar Fellowship Program. Now beginning its eleventh year, this program is designed to provide unique research opportunities to graduate students in good standing, currently enrolled at Ph.D. granting institutions. Lowell staff research spans a wide range of topics, from astronomical instrumentation, to icy bodies in our solar system, exoplanet science, stellar populations, star formation, and dwarf galaxies. Active collaborations, the new Ph.D. program at Northern Arizona University, and strong, cooperative links across the greater Flagstaff astronomical community create an exciting, multi-institutional locus in northern Arizona. Lowell Observatory’s new 4.3 meter Discovery Channel Telescope is operating at full science capacity and boasts some of the most cutting-edge and unique instrumentation available in optical/infrared astronomy. Student research is expected to lead to a thesis dissertation appropriate for graduation at the doctoral level at the student’s home institution. For more information, see and links therein. Applications for Fall 2019 are due by May 1, 2019; alternate application dates will be considered on an individual basis.

    192. Lewis, Briley L., Stansberry, John, Holler, Bryan, et al., 2019, AAS, 233, 255.12, Distribution and Energy Balance of Pluto’s Nitrogen Ice, as seen by New Horizons in 2015

      Pluto’s surface is geologically complex, to a significant extent because of volatile ice frosts that are mobile on seasonal and longer time scales. Here, we analyze New Horizons LEISA spectral data to globally map the nitrogen ice, including nitrogen with methane diluted in it, in order to learn about the seasonal processes influencing ice redistribution, and to calculate the globally averaged energy balance. We take advantage of the shifted bands of methane in solid solution with nitrogen, which are much stronger than the 2.15-micron nitrogen band, to more completely map the distribution of the nitrogen ice. We present the resulting maps of the encounter-hemisphere distribution of nitrogen, as well as characterization of its average latitudinal dependence and an examination of how the distribution at the global scale depends on topography. We also use the encounter-hemisphere distribution of nitrogen ice to infer the latitudinal distribution of nitrogen over the rest of Pluto, allowing us to calculate the global energy balance. Under the assumption that Pluto’s nitrogen-dominated 11.5 microbar atmosphere is in vapor-pressure equilibrium with the nitrogen ice, the ice temperature is 37.180.10 K. Combined with our global energy balance calculation, this implies that the average bolometric emissivity of Pluto’s nitrogen ice is probably in the range 0.5 – 0.9, and that there is a significant reservoir of N2 ice in the un-illuminated areas south of -38 latitude. The global pattern of volatile transport at the time of the encounter was from north to south, with condensation of volatile ices likely occurring southward from approximately Pluto’s equator (including in the un-illuminated regions south of -38 latitude). The transition between condensation and sublimation within Sputnik Planitia is correlated with changes in the grain size and CH4 concentration derived from the spectral maps. The low emissivity of Pluto’s N2 ice suggests that Pluto’s atmosphere may undergo an extended period of constant pressure even as Pluto recedes from the Sun in its orbit.

    193. Clark, Catherine, van Belle, Gerard, Horch, Elliott, et al., 2019, AAS, 233, 259.03, The POKEMON Speckle Survey of Nearby M-dwarfs

      The POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey of nearby M-dwarfs intends to inspect, at diffraction-limited resolution, every low-mass star out to 15pc, along with selected additional objects to 25pc. The primary emphasis of the survey is the detection of low-mass companions to these M-dwarfs for refinement of the low-mass star multiplicity rate. Given the priority these targets will have for upcoming exoplanet studies using TESS and JWST – and the degree to which initially undetected multiplicity has affected Kepler results – a comprehensive survey of our nearby low-mass neighbors will produce a homogenous, complete catalog of fundamental utility. Prior knowledge of those secondary objects – or robust non-detections, as will be captured by this survey – will help immediately clarify the nature of exoplanet transit detections from these current and upcoming missions. POKEMON is using Lowell Observatory’s 4.3-m Discovery Channel Telescope (DCT) with the Differential Speckle Survey Instrument (DSSI) speckle camera, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) speckle imager on 3.5-m WIYN; the survey takes advantage of the extremely rapid observing cadence rates possible with WIYN and (especially) DCT. The current status and results are from the first 20+ nights of observing.

    194. Laufman, Lauren, Hunter, Deidre, Oh, Se-Heon, 2019, AAS, 233, 351.18, Mechanisms for Inducing Star Formation in the Dwarf Irregular Galaxy DDO 133

      Dwarf irregular galaxies are important to study for several reasons. First, they are the most abundant galaxy in the universe; in the Local Group we have more than fifty dwarfs and just three spirals. In addition to being the most common, they are the closest analogue to the building blocks of the early universe and their lack of heavy elements imitates early universe star formation conditions. However, the models say that dwarf irregulars shouldn’t be able to continuously form stars; they aren’t dense enough to reach the critical density for gravitational instabilities to form and collapse the gas clouds. We present a study of peculiar gas motions and their connection with star formation in the dwarf irregular galaxy DDO 133. Using primarily HI data cubes from the VLA, we build moment maps to identify the motion and location of the gas, and use previously written code to deconvolve these moment maps into bulk and peculiar motions. We identify a stellar bar in DDO 133 with characteristic streaming motions of HI around said bar, likely causing the significant amounts of HI and star formation observed at the ends of the bar. This research was funded by NSF grant 1461200 to Northern Arizona University to support the 2018 Research Experiences for Undergraduates program.

    195. Massey, Philip, Neugent, Kathryn, Morrell, Nidia, et al., 2019, AAS, 233, 353.01, A Modern Search for Wolf-Rayet (WR) Stars in the Magellanic Clouds: A Final Census

      Wolf-Rayet (WR) stars evolved from massive OB stars, where the outer hydrogen-rich layers have been stripped away by some mechanism: stellar winds, close binary companions, episodic mass-loss during a Luminous Blue Variable phase, or all of the above. We have recently carried out a new survey of the Small and Large Magellanic Clouds (SMC, LMC) discovering 15 new WR in the LMC, bringing the total known to 154. We also found 12 Of-type stars, incluing rare Onfp and Of?p stars, and a variety of other interesting emission-lined stars. Most exciting, however, has been our discovery of new class of WRs, which we are calling WN3/O3s. These have the typical emission lines of a high-excitation nitrogen-rich (WN) Wolf-Rayet, but the absorption lines of a hot O-type star. However, they are many magnitudes too faint to be WN3+O3 binaries. Rather, the emission and absorption originate from the same object. Detailed analysis of our Magellan spectra have shown that the physical properties of these stars are similar to normal WNs, but with the presence of more hydrogen and much lower mass-loss rates. About 8% of the LMC’s WN-type population is made up of these newly found objects, and so these are not a consequence of some rare and special process. The question then is how did these WN3/O3s evolve? Are they simply a short-lived phase in the normal evolution of WRs, a “missing link” between O-type stars and WRs that occurs only in certain metallicity regimes? Or have they evolved by binary evolution? Drop by our poster and hear what we have to say on the issue! This work was supported by the National Science Foundation through AST-1612874.

    196. Aadland, Erin, Massey, Philip, Neugent, Kathryn, et al., 2019, AAS, 233, 353.05, Shedding Light on the Isolation of Luminous Blue Variables

      In the traditional view of massive star evolution, luminous blue variables (LBVs) are a transitionary phase between massive O-type stars and Wolf-Rayet stars (WRs). A debate has sprouted over whether this single star evolution is flawed and perhaps a binary evolutionary track describes the LBV phase better. The root of this debate has been the question of isolation (projected angular separation) of LBVs from their nearest neighboring O-type star. LBVs, traditionally, have relatively short lifetimes, and as a result they should not disperse far from their birthplace or be isolated. A recent study found that LBVs have an isolation more similar to that of red supergiants (RSGs) than traditionally thought possible given single star evolution. A similar study, however, found the opposite result. Both of these studies used spectroscopically identified O-type stars, which for the Large Magellanic Cloud is extremely incomplete, and does not necessarily represent the high mass stars we expect to be LBV progenitors in any event. Therefore, we re-examined the question of isolation using photometric criteria to select the highest mass unevolved stars (“bright blue stars” or BBSs) to use as our comparison sample. We find that LBVs are no more isolated than BBSs or WRs, and were able to statistically rule out the possibility of LBVs coming from the same distribution as the RSGs. We also note the number of LBVs in or near OB associations is comparable to the number of BBSs or WRs, and not to that of RSGs. Therefore, we conclude that the isolation of LBVs is consistent with the traditional picture of massive single star evolution. This work was supported by the National Science Foundation through AST-1612874.

    197. Prato, Lisa, Sullivan, Kendall, Lindstrom, Kyle, et al., 2019, AAS, 233, 366.13, Identifying and Characterizing New Spectroscopic Binaries in Orion

      Double-lined, young spectroscopic binaries provide the opportunity for precise measurements of pre-main sequence stellar mass ratios. In conjunction with additional information, such as orbital inclinations based on astrometric photocenter orbits, available in the future from GAIA, very precise stellar component masses may be determined. Mass ratio distributions yield clues to the formation of the closest binaries, a poorly understood problem. Absolute young star masses are important to test and refine the pre-main sequence evolutionary models that are central to the determination of properties such as the initial mass function, secondary star mass function, and star formation history of young clusters. We report on the results of our optical and infrared observations to identify and characterize new spectroscopic binaries in the Orion star forming region. Support for this research was provided in part by NSF award AST-1518081.

    198. Lindstrom, Kyle, Prato, Lisa, Graham, Sean, et al., 2019, AAS, 233, 367.04, Binary Stars and their Planet-Forming Disks

      The majority of stars in our Galaxy reside in binary or higher order multiple systems. This can have profound effects on the evolution of the stars and in particular their circumstellar disks and the planet formation therein. In this poster we address several fundamental questions: how do circumstellar disks in binaries evolve, are these disks stable, and are their properties favorable for planet formation? To address these topics, our team is completing a spectroscopic survey of over 100 binary systems in young, nearby star forming regions, including Taurus Auriga, using the Keck II and Discovery Channel Telescopes. Our goal is to analyze these spectra to infer the properties of the stars themselves, as well as their constituent disks. To accomplish this, we generate synthetic spectra with a wide range of effective temperatures, surface gravities, rotational velocities, radial velocities, veiling, and magnetic field strengths for comparison with our target spectra. We present some preliminary results and a discussion of their consequences with respect to the evolution of these systems. This research was supported in part by NSF awards AST-1313399 and AST-1518081 and by NASA Keck KPDA funds.

    199. Hartman, Zachary, van Belle, Gerard, Lepine, Sebastien, et al., 2019, AAS, 233, 418.03, The SUPERWIDE Catalog of Wide Binaries and an Initial Look at the Higher Order Multiplicity of K and M dwarf Wide Binaries

      We present the SUPERWIDE catalog of wide binaries that were identified through a Bayesian analysis of high proper motions stars (m>40 mas/yr) from the Gaia DR2 catalog. Initially identified through an earlier search of the SUPERBLINK high proper motion catalog, these binaries were found by their proximity on the sky, common proper motion and similar distances. Taking those pairs with a probability of being a “true” binary (i.e. gravitationally bound system) greater than 99%, we identify ~22,000 wide binaries with projected physical separations between ~100 AU to ~1 pc. We present initial results of an ongoing speckle survey of these wide binaries devoted to the identification of higher order multiples. Using data collected through the POKEMON M-dwarf multiplicity survey, we have examined ~15 wide binaries to see if they are in fact triple or quadruple systems. With this information and more to come, we intend to determine the higher order multiplicity fraction for K and M dwarf wide binaries as a function of their physical separation in order to provide constraints for the possible formation mechanisms of these wide systems.

    200. Thilker, David, Lee, Janice, Rafelski, Marc, et al., 2019, AAS, 233, 443.10, Enabling Efficient HST UV Exploration of the Low Surface Brightness Universe

      We present a pilot program with HST to broadly enable high-resolution UV exploration of star formation at low densities in nearby galaxies using a strategy to increase observing efficiency by up to a factor of two. The increased efficiency achieved with WFC3’s eXtra-wide filter set makes more tractable programs which require several tens to hundreds of orbits to aggregate sufficient numbers of resolved massive stars, young star clusters, and clumps to build statistical samples. We aim to enable basic characterization of the ensemble properties of star formation in the low density regime in its primary units. We will discuss first results based on a Local Volume dwarf galaxy (Holmberg I) and a more distant low surface brightness spiral (UGC 9024).

    201. Heilman, Micha, van Belle, Gerard, Clark, Jim, et al., 2019, AAS, 233, 462.07, Developing Low-Cost Adaptive Optics Telescopes for Long Baseline Optical Interferometry

      Our research examines the use of adaptive optics (AO) in tandem with low-quality optics to determine if diffraction limited results can be achieved using active corrective optics. The 1m scale of wavefront corrections provided by AO systems are substantially greater than the ~50nm construction specifications of typical telescopes. Thus, this pairing of optics and software could increase image quality while decreasing cost by significantly (~20x) relaxing mechanical requirements. As a baseline, we measured a 6in lab-quality flat with a Zygo interferometer, an instrument built for surface inspection of diffraction-limited optics. To contrast this result, we similarly inspected a low-quality mirror. We found roughly 2 full waves, about 1m, of smoothly varying static wavefront distortion across the ~5in Zygo inspection aperture. Our lab setup consisted of a Thorlabs AO Kit (model 7) with light source, deformable mirror (DM), and Shack-Hartman wavefront sensor (WFS). A 2.5cm beam expanded from a 0.34mW laser diode hit the low-quality mirror, which retroreflected into the AO system and was re-collimated to 5mm to match the sensor diameter of the WFS. Fifteen data sets were collected to find the Peak-to-Valley (PV) and root-mean-square (rms) of the wavefront measured from the low-quality mirror and the reconstructed wavefront corrected by the DM. This second data set was used to calculate the difference between the measured and reconstructed wavefronts. The process was repeated by replacing the low-quality mirror with a lab-quality mirror rated to /20. The PV measurement for the low-quality mirror was 55m with a rms of 12.7m, compared to the lab-quality mirror whose PV was 53m with a rms of 10.8m. The difference between the low-quality mirror’s wavefront and the DM reconstructed wavefront was a PV of 0.21m with a rms of 0.04m. The resultant wavefront corrected 80% past it’s predicted outcome of 1m. Our results indicate it would be advantageous to use a telescope design that assumes integral AO from the outset; further benefits come from tailoring the telescopes to the narrow set of specifications that emphasize use in a narrow-angle long-baseline optical interferometry system.

    202. Jones, Terry Jay, Dowell, C. Darren, Lopez Rodriguez, Enrique, et al., 2019, ApJL, 870, L9, SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic Wind

      We present far-infrared polarimetry observations of M82 at 53 and 154 m and NGC 253 at 89 m, which were taken with High-resolution Airborne Wideband Camera-plus (HAWC+) in polarimetry mode on the Stratospheric Observatory for Infrared Astronomy. The polarization of M82 at 53 m clearly shows a magnetic field geometry perpendicular to the disk in the hot dust emission. For M82 the polarization at 154 m shows a combination of field geometry perpendicular to the disk in the nuclear region, but closer to parallel to the disk away from the nucleus. The fractional polarization at 53 m (154 m) ranges from 7% (3%) off nucleus to 0.5% (0.3%) near the nucleus. A simple interpretation of the observations of M82 invokes a massive polar outflow, dragging the field along, from a region 700 pc in diameter that has entrained some of the gas and dust, creating a vertical field geometry seen mostly in the hotter (53 m) dust emission. This outflow sits within a larger disk with a more typical planar geometry that more strongly contributes to the cooler (154 m) dust emission. For NGC 253, the polarization at 89 m is dominated by a planar geometry in the tilted disk, with weak indication of a vertical geometry above and below the plane from the nucleus. The polarization observations of NGC 253 at 53 m were of a insufficient signal-to-noise ratio for a detailed analysis.

    203. Robbins, Stuart J., Beyer, Ross A., Spencer, John R., et al., 2019, JGRE, 124, 155, Geologic Landforms and Chronostratigraphic History of Charon as Revealed by a Hemispheric Geologic Map

      Geologic mapping has been used for over 200 years as a technique to synthesize a complicated surface into a more simplified product, identifying similar types of surface features, and placing them into a relative stratigraphy. Geomorphologic mapping has applied those principles to other terrestrial bodies throughout the solar system and has formed an important product set to understand these surfaces, plan future exploration, and conduct different scientific endeavors. We created a geomorphologic map of the New Horizons encounter hemisphere of Pluto’s binary companion, Charon. Ten primary geomorphologic unit categories were identified, covering approximately 35% of Charon’s surface, and we used lower resolution data to speculate about other regions of Charon. Over 1,000 linear features were mapped, nearly 90% of them are tectonic in nature, and we use these to provide evidence of Charon being active in its past. Additionally, we placed the mapped features into a chronostratigraphic sequence, and we present a possible surface history for the body. The northern terrain typified by large crustal blocks is the oldest, having fractured early in Charon’s history, and potentially similar blocks were submerged in a cryoflow of which the now solid surface of Vulcan Planitia is the remnant today.

    204. McClintock, T., Varga, T. N., Gruen, D., et al., 2019, MNRAS, 482, 1352, Dark Energy Survey Year 1 results: weak lensing mass calibration of redMaPPer galaxy clusters

      We constrain the mass-richness scaling relation of redMaPPer galaxy clusters identified in the Dark Energy Survey Year 1 data using weak gravitational lensing. We split clusters into 4 3 bins of richness and redshift z for 20 and 0.2 z 0.65 and measure the mean masses of these bins using their stacked weak lensing signal. By modelling the scaling relation as <M200m|, z> = M0(/40)F((1 + z)/1.35)G, we constrain the normalization of the scaling relation at the 5.0 per cent level, finding M0 = [3.081 0.075(stat) 0.133(sys)] . 1014 M at = 40 and z = 0.35. The recovered richness scaling index is F = 1.356 0.051 (stat) 0.008 (sys) and the redshift scaling index G = -0.30 0.30 (stat) 0.06 (sys). These are the tightest measurements of the normalization and richness scaling index made to date from a weak lensing experiment. We use a semi-analytic covariance matrix to characterize the statistical errors in the recovered weak lensing profiles. Our analysis accounts for the following sources of systematic error: shear and photometric redshift errors, cluster miscentring, cluster member dilution of the source sample, systematic uncertainties in the modelling of the halo-mass correlation function, halo triaxiality, and projection effects. We discuss prospects for reducing our systematic error budget, which dominates the uncertainty on M0. Our result is in excellent agreement with, but has significantly smaller uncertainties than, previous measurements in the literature, and augurs well for the power of the DES cluster survey as a tool for precision cosmology and upcoming galaxy surveys such as LSST, Euclid, and WFIRST.

    205. Crocce, M., Ross, A. J., Sevilla-Noarbe, I., et al., 2019, MNRAS, 482, 2807, Dark Energy Survey year 1 results: galaxy sample for BAO measurement

      We define and characterize a sample of 1.3 million galaxies extracted from the first year of Dark Energy Survey data, optimized to measure baryon acoustic oscillations (BAO) in the presence of significant redshift uncertainties. The sample is dominated by luminous red galaxies located at redshifts z 0.6. We define the exact selection using colour and magnitude cuts that balance the need of high number densities and small photometric redshift uncertainties, using the corresponding forecasted BAO distance error as a figure-of-merit in the process. The typical photo z uncertainty varies from 2.3{{ per cent}} to 3.6{{ per cent}} (in units of 1+z) from z = 0.6 to 1, with number densities from 200 to 130 galaxies per deg2 in tomographic bins of width z = 0.1. Next, we summarize the validation of the photometric redshift estimation. We characterize and mitigate observational systematics including stellar contamination and show that the clustering on large scales is robust in front of those contaminants. We show that the clustering signal in the autocorrelations and cross-correlations is generally consistent with theoretical models, which serve as an additional test of the redshift distributions.

    206. Mozurkewich, David, Jorgensen, Anders, van Belle, Gerard T., 2019, JAI, 8, 1950005, Coherent Integration in Astronomical Interferometry: Theory and Practice

      Ground-based long-baseline astronomical interferometry operates in a regime where short integration exposures are demanded by working in the presence of a turbulent atmosphere. To reduce piston noise to less than one radian per aperture, these exposure times are on order 10 milliseconds or less in the visible. It has long been recognized that, in the low signal-to-noise ratio (SNR) regime, the visibility SNR is improved by co-adding frames, each rotated by an estimate of its phase. However, implementation of this technique is challenging. Where it is most needed, on low SNR baselines and when combining multiple phases to estimate the phase for a lower SNR baseline, phase errors reduce the amplitude by a large amount and in a way that has proven difficult to calibrate. In this paper, an improved coherent integration algorithm is presented. A parameterized model for the phase as a function of time and wavelength is fit to the entire data set. This framework is used to build a performance model which can be used in two ways. First, it can be used to test the algorithm; by comparing its performance to theory, one can test how well the parameter fitting has worked. Also, when designing future systems, this model provides a simple way to predict performance and compare it to alternative techniques such as hierarchical fringe tracking. This technique has been applied to both simulated and stellar data.

    207. Armstrong, J. T., Jorgensen, A. M., Mozurkewich, D., et al., 2019, JAI, 8, 1950012-246, Interferometric Fringe Visibility Null as a Function of Spatial Frequency: A Probe of Stellar Atmospheres

      We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening.


      Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency u0 at which the real part of the fringe visibility Re(V) vanishes. That spatial frequency is determined by u0=B/0, where B is the projected baseline length, and 0 is the wavelength at which the null is observed. Since B changes with the Earths rotation, 0 also changes. If u0 is constant with wavelength, 0 varies in direct proportion to B. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both.

      In this paper, we introduce the use of variations of u0 with as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter UD, 0(0), given by UD, 0=1.22/u0(0), as a convenient and intuitive parameterization of u0(0), we demonstrate this concept by using model atmospheres to calculate the brightness distribution for Ophiuchi and to predict UD, 0(0), and then comparing the predictions to coherently averaged data from observations taken with the NPOI.


    1. Shkolnik, E. L., Ardila, D. R., Barman, T., et al., 2018, AGUFM, 2018, P24C-05, A Dedicated Ultraviolet CubeSat for Astrophysics, SPARCS (Star Planet Activity Research CubeSat)

      Knowing the ultraviolet (UV) environments of planets orbiting low-mass stars (0.1-0.6 Msun; a.k.a. M dwarfs) will be crucial to understanding the composition of planetary atmospheres and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. For each target, SPARCS will observe continuously over at least one complete stellar rotation (5 – 45 days). SPARCS will also advance UV detector technology by flying high quantum efficiency, UV-optimized detectors developed at JPL. These 2D-doped detectors have a long history of deployment demonstrating greater than five times the quantum efficiency of the detectors used by GALEX. SPARCS will pave the way for their application in missions like LUVOIR or HabEx, including interim UV-capable missions.


      Funding for SPARCS is provided by NASA’s Astrophysics Research and Analysis program, NNH16ZDA001N.

    2. Thomas, C., Rivkin, A., Pravec, P., et al., 2018, AGUFM, 2018, P51A-02, Observations of Didymos: Past Results and Future Plans

      The binary near-Earth asteroid (65803) Didymos is the target for the two components of the Asteroid Impact and Deflection Assessment (AIDA) mission. The NASA DART (Double Asteroid Redirection Test) mission is scheduled to impact the Didymos secondary during its apparition in 2022. ESA’s proposed Hera mission will arrive years later to obtain in situ observations of the system following the DART impact. One key scientific goal of AIDA is to measure and characterize the deflection caused by the impact. A combination of spacecraft and ground and space based optical and radar observations in 2022 will provide the required data for AIDA to meet its top-level mission goals.


      Photometric observations of Didymos were taken in 2003, 2015, and 2017. These observations have been used to determine the orbital period and constrain the orbital pole of the system. We used these observations to determine the number and precision of observations needed prior to the DART impact in 2022. We will observe the Didymos system during the 2019 and 2020-2021 apparitions to further characterize the system by obtaining additional lightcurve observations and spectra. These planned observations will provide us with the opportunity to establish the state of the system before impact to a high level of precision. We will place additional constraints on the inclination of the satellite orbit, the long-term effects of Binary YORP (BYORP), and whether the satellite is in synchronous rotation with the primary. The Didymos apparitions in 2019 and 2020-2021 will be much fainter than that in 2022. We anticipate observations at a range of large ground-based and space-based facilities. We will discuss what is currently known about the Didymos system, our observing plans prior to the DART impact, and our observing plans during the impact apparition.

    3. Cauley, P. Wilson, Shkolnik, Evgenya L., Llama, Joe, et al., 2018, AJ, 156, 262, Evidence of Magnetic Star-Planet Interactions in the HD 189733 System from Orbitally Phased Ca II K Variations

      Magnetic star-planet interactions (SPI) provide a detection method and insight into exoplanet magnetic fields and, in turn, exoplanet interiors and atmospheric environments. These signatures can be sporadic and difficult to confirm for single-epoch observations of a system due to inhomogeneous stellar magnetospheres and periodic variability in stellar magnetism. Thus, an ideal SPI search consists of multiple epochs containing observations on consecutive nights spanning at least one complete planetary orbit. Such data sets are rare but do exist for some of the most intensely studied hot Jupiter systems. One such system is HD 189733 for which six suitable SPI data sets exist, the result of spectroscopic monitoring to perform some of the first SPI searches and also to study the stars magnetic field. Here we perform a uniform analysis of six archival Ca II K data sets for HD 189733, spanning 2006 June through 2015 July, in order to search for magnetic SPI signatures in the chromospheric line variations. We find significant evidence for modulations of Ca II K with a 2.29 0.04 day period in the 2013 August data, which is consistent with the planets orbital period. The peak in the orbital variations occurs at orb 0.9, which corresponds to the SPI emission leading the planet with a phase difference of 40 from the sub-planetary point. This is consistent with the phase-lead predictions of nonlinear force-free magnetic field SPI models. The stellar magnetic field strength at the planets orbit was greatest in 2013 August, which, due to the energy released in magnetic SPI scaling with B *, lends strength to the SPI interpretation.

    4. Massey, Philip, Levine, Stephen E., Neugent, Kathryn F., et al., 2018, AJ, 156, 265, A Runaway Giant in the Galactic Halo

      New evidence provided by the Gaia satellite places the location of the runaway star J01020100-7122208 in the halo of the Milky Way (MW) rather than in the Small Magellanic Cloud (SMC) as previously thought. We conduct a reanalysis of the stars physical and kinematic properties, which indicates that the star may be an even more extraordinary find than previously reported. The star is a 180 Myr old 3-4 M G5-8 bright giant, with an effective temperature of 4800 100 K, a metallicity of Fe/H = -0.5, and a luminosity of {log}L/{L} =2.70+/- 0.20. A comparison with evolutionary tracks identifies the star as being in a giant or early asymptotic giant branch stage. The proper motion, combined with the previously known radial velocity, yields a total Galactocentric space velocity of 296 km s-1. The star is currently located 6.4 kpc below the plane of the MW, but our analysis of its orbit shows it passed through the disk 25 Myr ago. The stars metallicity and age argue against it being native to the halo, and we suggest that the star was likely ejected from the disk. We discuss several ejection mechanisms, and conclude that the most likely scenario is ejection by the MWs central black hole based upon our analysis of the stars orbit. The identification of the large radial velocity of J01020100-7122208 came about as a happenstance of it being seen in projection with the SMC, and we suggest that many similar objects may be revealed in Gaia data.


      This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

    5. Khain, T., Becker, J. C., Adams, F. C., et al., 2018, AJ, 156, 273, Dynamical Analysis of Three Distant Trans-Neptunian Objects with Similar Orbits

      This paper reports the discovery and orbital characterization of two extreme trans-Neptunian objects (ETNOs), 2016 QV89 and 2016 QU89, which have orbits that appear similar to that of a previously known object, 2013 UH15. All three ETNOs have semimajor axes a 172 au and eccentricities e 0.77. The angular elements (i, , ) vary by 6, 15, and 49, respectively, between the three objects. The two new objects add to the small number of TNOs currently known to have semimajor axes between 150 and 250 au, and they serve as an interesting dynamical laboratory to study the outer realm of our solar system. Using a large ensemble of numerical integrations, we find that the orbits are expected to reside in close proximity in the (a, e) phase plane for roughly 100 Myr before diffusing to more separated values. We find that an explanation for the orbital configuration of the bodies as a collision product is disfavored. We then explore other scenarios that could influence their orbits. With aphelion distances over 300 au, the orbits of these ETNOs extend far beyond the classical Kuiper Belt and an order of magnitude beyond Neptune. As a result, their orbital dynamics can be affected by the proposed new solar system member, referred to as Planet Nine in this work. With perihelion distances of 35-40 au, these orbits are also influenced by resonant interactions with Neptune. A full assessment of any possible new solar system planets must thus take into account this emerging class of TNOs.

    6. Aadland, Erin, Massey, Philip, Neugent, Kathryn F., et al., 2018, AJ, 156, 294, Shedding Light on the Isolation of Luminous Blue Variables

      In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance to the nearest spectroscopically identified O-type star to define the degree of isolation. However, our knowledge of the spectroscopic content of the LMC is quite spotty. Here we re-examine the issue using carefully defined photometric criteria to select the highest-mass unevolved stars (bright blue stars, or BBSs), using spatially complete photometric catalogs of the LMC, M31, and M33. Our study finds that the LBVs are no more isolated than BBSs or WRs. This result holds no matter which sample of LBVs we employ. A statistical test shows that we can rule out the LBVs having the same distribution as the RSGs, which are about 2 more isolated. We demonstrate the robustness of our results using the second-closest neighbor. Furthermore, the majority of LBVs in the LMC are found in or near OB associations as are the BBS and WRs; the RSGs are not. We conclude that the spatial distribution of LBVs therefore is consistent with the standard picture of massive star evolution.

    7. Abbott, T. M. C., Abdalla, F. B., Allam, S., et al., 2018, ApJS, 239, 18, The Dark Energy Survey: Data Release 1

      We describe the first public data release of the Dark Energy Survey, DES DR1, consisting of reduced single-epoch images, co-added images, co-added source catalogs, and associated products and services assembled over the first 3 yr of DES science operations. DES DR1 is based on optical/near-infrared imaging from 345 distinct nights (2013 August to 2016 February) by the Dark Energy Camera mounted on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. We release data from the DES wide-area survey covering 5000 deg2 of the southern Galactic cap in five broad photometric bands, grizY. DES DR1 has a median delivered point-spread function of g=1.12, r = 0.96, i = 0.88, z = 0.84, and Y = 0.90 FWHM, a photometric precision of <1% in all bands, and an astrometric precision of 151 {mas}. The median co-added catalog depth for a 1.95 diameter aperture at signal-to-noise ratio (S/N) = 10 is g = 24.33, r = 24.08, i = 23.44, z = 22.69, and Y = 21.44 {mag} . DES DR1 includes nearly 400 million distinct astronomical objects detected in 10,000 co-add tiles of size 0.534 deg2 produced from 39,000 individual exposures. Benchmark galaxy and stellar samples contain 310 million and 80 million objects, respectively, following a basic object quality selection. These data are accessible through a range of interfaces, including query web clients, image cutout servers, jupyter notebooks, and an interactive co-add image visualization tool. DES DR1 constitutes the largest photometric data set to date at the achieved depth and photometric precision.

    8. Leggett, S. K., Bergeron, P., Subasavage, John P., et al., 2018, ApJS, 239, 26, Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample

      This paper presents new trigonometric parallaxes and proper motions for 214 stars. The measurements were made at the US Naval Observatory Flagstaff Station between 1989 and 2017, and the average uncertainty in the parallax values is 0.6 mas. We find good agreement with Gaia Data Release 2 measurements for the stars in common, although there may be a small systematic offset similar to what has been found by other investigators. The sample is matched to catalogs and the literature to create a photometric data set that spans the ultraviolet to the mid-infrared. New mid-infrared photometry is obtained for 19 stars from archived Spitzer mosaics. New optical spectroscopy is presented for seven systems and additional spectra were obtained from the literature. We identify a subsample of 179 white dwarfs (WDs) at distances of 25-200 pc. Their spectral energy distributions (SEDs) are analyzed using model atmospheres. The models reproduce the entire flux-calibrated SED very well and provide the atmospheric chemical composition, temperature, surface gravity, mass, and cooling age of each WD. Twenty-six WDs are newly classified, and 12 systems are presented as candidate unresolved binaries. We confirm one WD+red dwarf system and identify two WDs as candidate dust disk systems. Twelve old and high-velocity systems are identified as candidate thick disk or halo objects. The WDs in the sample generally have Galactic disk-like ages of <8 Gyr and masses close to the canonical 0.6 M .

    9. Monnier, John D., Kraus, Stefan, Ireland, Michael J., et al., 2018, ExA, 46, 517, The planet formation imager

      The Planet Formation Imager (PFI, is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.

    10. Jenniskens, Peter, Albers, Jim, Tillier, Clemens E., et al., 2018, M&PS, 53, 2445, Detection of meteoroid impacts by the Geostationary Lightning Mapper on the GOES-16 satellite

      Bolides are detected by the Geostationary Lightning Mapper onboard the GOES-16 weather satellite, which takes images of Earth at a rate of 500 Hz in a 1.1 nm wide pass band centered on 777.4 nm wavelength. Ten case studies are discussed. These initial results were obtained using the Level 0 data received during the nonoperational in-orbit postlaunch test period. GLM positions and timings are sufficiently accurate to assist in trajectory and orbit reconstruction. GLM samples the light curve nearly completely, unaffected by onboard and downlink processes tailored to lightning data. Sufficient data on the instantaneous background scene are provided to reconstruct the baseline drift in the brightest pixels. The agreement to within a factor of 2-3 between measured total radiated energy from GLM and that derived from other space-borne observations implies that during the bolide’s peak brightness the GLM pass band is dominated by continuum emission, rather than O I line emission. The reported flux is corrected for angle-from-nadir shifts in the central wavelength of the pass band, which overestimates continuum flux by only up to 20% for most of the GLM field of view, but more so if the bolide is observed far from nadir. Assuming a 6000 K blackbody spectrum, GLM is able to detect bolides with peak visual magnitude (at a normalized 100 km distance) brighter than about -14 in nighttime, and slightly brighter in daytime.

    11. Tarsitano, F., Hartley, W. G., Amara, A., et al., 2018, MNRAS, 481, 2018, A catalogue of structural and morphological measurements for DES Y1

      We present a structural and morphological catalogue for 45 million objects selected from the first year data of the Dark Energy Survey (DES). Single Sersic fits and non-parametric measurements are produced for g, r, and i filters. The parameters from the best-fitting Sersic model (total magnitude, half-light radius, Sersic index, axis ratio, and position angle) are measured with GALFIT; the non-parametric coefficients (concentration, asymmetry, clumpiness, Gini, M20) are provided using the Zurich Estimator of Structural Types (ZEST+). To study the statistical uncertainties, we consider a sample of state-of-the-art image simulations with a realistic distribution in the input parameter space and then process and analyse them as we do with real data: this enables us to quantify the observational biases due to PSF blurring and magnitude effects and correct the measurements as a function of magnitude, galaxy size, Sersic index (concentration for the analysis of the non-parametric measurements) and ellipticity. We present the largest structural catalogue to date: we find that accurate and complete measurements for all the structural parameters are typically obtained for galaxies with SEXTRACTOR {MAG_AUTO_I} 21. Indeed, the parameters in the filters i and r can be overall well recovered up to {MAG_AUTO} 21.5, corresponding to a fitting completeness of { } 90{{ per cent}} below this threshold, for a total of 25 million galaxies. The combination of parametric and non-parametric structural measurements makes this catalogue an important instrument to explore and understand how galaxies form and evolve. The catalogue described in this paper will be publicly released alongside the DES collaboration Y1 cosmology data products at the following URL:

    12. Cawthon, R., Davis, C., Gatti, M., et al., 2018, MNRAS, 481, 2427, Dark Energy Survey Year 1 Results: calibration of redMaGiC redshift distributions in DES and SDSS from cross-correlations

      We present calibrations of the redshift distributions of redMaGiC galaxies in the Dark Energy Survey Year 1 (DES Y1) and Sloan Digital Sky Survey (SDSS) DR8 data. These results determine the priors of the redshift distribution of redMaGiC galaxies, which were used for galaxy clustering measurements and as lenses for galaxy-galaxy lensing measurements in DES Y1 cosmological analyses. We empirically determine the bias in redMaGiC photometric redshift estimates using angular cross-correlations with Baryon Oscillation Spectroscopic Survey (BOSS) galaxies. For DES, we calibrate a single-parameter redshift bias in three photometric redshift bins: z [0.15, 0.3], [0.3,0.45], and [0.45,0.6]. Our best-fit results in each bin give photometric redshift biases of |z| < 0.01. To further test the redMaGiC algorithm, we apply our calibration procedure to SDSS redMaGiC galaxies, where the statistical precision of the cross-correlation measurement is much higher due to a greater overlap with BOSS galaxies. For SDSS, we also find best-fit results of |z| < 0.01. We compare our results to other analyses of redMaGiC photometric redshifts.

    13. Erkal, D., Li, T. S., Koposov, S. E., et al., 2018, MNRAS, 481, 3148, Modelling the Tucana III stream – a close passage with the LMC

      We present results of the first dynamical stream fits to the recently discovered Tucana III stream. These fits assume a fixed Milky Way potential and give proper motion predictions, which can be tested with the upcoming Gaia Data Release 2 (DR2). These fits reveal that Tucana III is on an eccentric orbit around the Milky Way and, more interestingly, that Tucana III passed within 15 kpc of the Large Magellanic Cloud (LMC) approximately 75 Myr ago. Given this close passage, we fit the Tucana III stream in the combined presence of the Milky Way and the LMC. We find that the predicted proper motions depend on the assumed mass of the LMC and that the LMC can induce a substantial proper motion perpendicular to the stream track. A detection of this misalignment will directly probe the extent of the LMC’s influence on our Galaxy, and has implications for nearly all methods which attempt to constraint the Milky Way potential. Such a measurement will be possible with the upcoming Gaia DR2, allowing for a measurement of the LMC’s mass.

    14. Sevilla-Noarbe, I., Hoyle, B., Marcha, M. J., et al., 2018, MNRAS, 481, 5451, Star-galaxy classification in the Dark Energy Survey Y1 data set

      We perform a comparison of different approaches to star-galaxy classification using the broad-band photometric data from Year 1 of the Dark Energy Survey. This is done by performing a wide range of tests with and without external `truth’ information, which can be ported to other similar data sets. We make a broad evaluation of the performance of the classifiers in two science cases with DES data that are most affected by this systematic effect: large-scale structure and Milky Way studies. In general, even though the default morphological classifiers used for DES Y1 cosmology studies are sufficient to maintain a low level of systematic contamination from stellar misclassification, contamination can be reduced to the O(1 per cent) level by using multi-epoch and infrared information from external data sets. For Milky Way studies, the stellar sample can be augmented by { }20{{ per cent}} for a given flux limit. Reference catalogues used in this work are available at

    15. Ahrens, Caitlin J., Grundy, William M., Mandt, Kathleen E., et al., 2018, SSRv, 214, 130, Recent Advancements and Motivations of Simulated Pluto Experiments

      This review of Pluto laboratory research presents some of the recent advancements and motivations in our understanding enabled by experimental simulations, the need for experiments to facilitate models, and predictions for future laboratory work. The spacecraft New Horizons at Pluto has given a large amount of scientific data already rising to preliminary results, spanning from the geology to the atmosphere. Different ice mixtures have now been detected, with the main components being nitrogen, methane, and carbon monoxide. Varying geology and atmospheric hazes, however, gives us several questions that need to be addressed to further our understanding. Our review summarizes the complexity of Pluto, the motivations and importance of laboratory simulations critical to understanding the low temperature and pressure environments of icy bodies such as Pluto, and the variability of instrumentation, challenges for research, and how simulations and modeling are complimentary.

    16. Cauley, P. Wilson, Kuckein, Christoph, Redfield, Seth, et al., 2018, AJ, 156, 189, The Effects of Stellar Activity on Optical High-resolution Exoplanet Transmission Spectra

      Chromospherically sensitive atomic lines display different spectra in stellar active regions, spots, and the photosphere, raising the possibility that exoplanet transmission spectra are contaminated by the contrast between various portions of the stellar disk. To explore this effect, we performed transit simulations of G-type and K-type stars for the spectral lines Ca II K at 3933 A, Na I 5890 A, H I 6563 A (H), and He I 10830 A. We find that strong facular emission and large coverage fractions can contribute a non-negligible amount to transmission spectra, especially for H, Ca II K, and Na I D, while spots and filaments are comparatively unimportant. The amount of contamination depends strongly on the location of the active regions and the intrinsic emission strength. In particular, active regions must be concentrated along the transit chord in order to produce a consistent in-transit signal. Mean absorption signatures in Na I and H, for example, can reach 0.2% and 0.3%, respectively, for transits of active latitudes with line emission similar in strength to moderate solar flares. Transmission spectra of planets transiting active stars, such as HD 189733, are likely contaminated by the contrast effect, although the tight constraints on active region geometry and emission strength make it unlikely that consistent in-transit signatures are due entirely to the contrast effect. He I 10830 A is not strongly affected and absorption signatures are likely diluted, rather than enhanced, by stellar activity. He I 10830 A should thus be considered a priority for probing extended atmospheres, even in the case of active stars.

    17. Hsieh, Henry H., Ishiguro, Masateru, Kim, Yoonyoung, et al., 2018, AJ, 156, 223, The 2016 Reactivations of the Main-belt Comets 238P/Read and 288P/(300163) 2006 VW139

      We report observations of the reactivations of the main-belt comets (MBCs) 238P/Read and 288P/(300163) 2006 VW139 that also track the evolution of each objects activity over several months in 2016 and 2017. We additionally identify and analyze archival SDSS data showing 288P to have been active in 2000, meaning that both 238P and 288P have now each been confirmed to be active near perihelion on three separate occasions. From data obtained of 288P from 2012-2015 when it appeared inactive, we find best-fit R-band H, G phase function parameters of H R = 16.80 0.12 mag and G R = 0.18 0.11, corresponding to effective component radii of r c = 0.80 0.04 km, assuming a binary system with equally sized components. Fitting linear functions to ejected dust masses inferred for 238P and 288P soon after their observed reactivations in 2016, we find an initial average net dust production rate of {\dot{M}}d=0.7+/- 0.3 kg s-1 and a best-fit start date of 2016 March 11 (when the object was at a true anomaly of = -63) for 238P, and an initial average net dust production rate of {\dot{M}}d=5.6+/- 0.7 kg s-1 and a best-fit start date of 2016 August 5 (when the object was at = -27) for 288P. Applying similar analyses to archival data, we find similar start points for previous active episodes for both objects, suggesting that minimal mantle growth or ice recession occurred between the active episodes in question. Some changes in dust production rates between active episodes are detected, however. More detailed dust modeling is suggested to further clarify the process of activity evolution in MBCs.


      Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) (programs 12BH43, 15AT05, and 16BT05), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de lUnivers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii, and at the Gemini Observatory (programs GN-2011B-Q-17, GN-2012A-Q-68, GN-2012B-Q-106, GN-2016B-LP-11, and GS-2016B-LP-11), which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation (NSF) on behalf of the Gemini partnership: the NSF (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina), and Ministerio da Ciencia, Tecnologia e Inovacao (Brazil).

    18. Neugent, Kathryn F., Levesque, Emily M., Massey, Philip, 2018, AJ, 156, 225, Binary Red Supergiants: A New Method for Detecting B-type Companions

      With the exception of a few well-known and studied systems, the binary population of red supergiants (RSGs) remains relatively uncharacterized. Famous systems such as VV Cep, 31 Cyg, and Aur contain RSG + B star binaries, and here we explore whether B stars are the main type of companion we expect from an evolutionary point of view. Using the Geneva evolutionary models, we find that this is indeed the case. However, few such systems are known, and we use model spectra to determine how easy such binaries would be to detect observationally. We find that it should be quite difficult to hide a B-type companion given a reasonable signal-to-noise in the optical/blue portion of the spectrum. We next examine spectra of Magellanic Cloud RSGs and newly acquired spectra of Galactic RSGs looking for new systems and refining our conclusions about what types of stars could be hidden in the spectra. Finally, we develop a set of photometric criteria that can help select likely binaries in the future without the overhead of large periodic or spectroscopic surveys.

    19. Thirouin, Audrey, Moskovitz, Nicholas A., Binzel, Richard P., et al., 2018, ApJS, 239, 4, The Mission Accessible Near-Earth Objects Survey: Four Years of Photometry

      Over 4.5 years, the Mission Accessible Near-Earth Object Survey assembled 228 near-Earth object (NEO) light curves. We report rotational light curves for 82 NEOs, constraints on amplitudes and periods for 21 NEOs, light curves with no detected variability within the image signal-to-noise and length of our observing block for 30 NEOs, and 10 tumblers. We uncovered two ultra-rapid rotators with periods below 20 s,2016 MA with a potential rotational periodicity of 18.4 s, and 2017 QG18 rotating in 11.9 sand estimated the fraction of fast/ultra-rapid rotators undetected in our project plus the percentage of NEOs with a moderate/long periodicity undetectable during our typical observing blocks. We summarize the findings of a simple model of synthetic NEOs to infer the objects morphology distribution using the measured distribution of light curve amplitudes. This model suggests that a uniform distribution of axis ratio can reproduce the observed sample. This suggests that the quantity of spherical NEOs (e.g., Bennu) is almost equivalent to the quantity of highly elongated objects (e.g., Itokawa), a result that can be directly tested thanks to shape models from Doppler delay radar imaging analysis. Finally, we fully characterized two NEOs2013 YS2 and 2014 FA7as appropriate targets for a potential robotic/human mission due to their moderate spin periods and low v.

    20. Earle, Alissa M., Grundy, W., Howett, C. J. A., et al., 2018, Icar, 314, 195, Methane distribution on Pluto as mapped by the New Horizons Ralph/MVIC instrument

      The data returned from NASA’s New Horizons spacecraft have given us an unprecedented, detailed look at the Pluto system. New Horizons’ Ralph/MVIC (Multispectral Visible Imaging Camera) is composed of 7 independent CCD arrays on a single substrate. Among these are a red channel (540-700 nm), near-infrared channel (780-975 nm), and narrow band methane channel (860-910 nm). By comparing the relative reflectance of these channels we are able to produce high-resolution methane “equivalent width” (based on the 890 nm absorption band) and spectral slope maps of Pluto’s surface. From these maps we can then quantitatively study the relationships between methane distribution, redness, and other parameters like latitude and elevation. We find Pluto’s surface to show a great diversity of terrains, particularly in the equatorial region between 30N and 30S latitude. Methane “equivalent width” also shows some dependence on elevation (while spectral slope shows very little).

    21. Grundy, W. M., Bertrand, T., Binzel, R. P., et al., 2018, Icar, 314, 232, Pluto’s haze as a surface material

      Pluto’s atmospheric haze settles out rapidly compared with geological timescales. It needs to be accounted for as a surface material, distinct from Pluto’s icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales. This paper explores how a steady supply of atmospheric haze might affect three distinct provinces on Pluto. We pose the question of why they each look so different from one another if the same haze material is settling out onto all of them. Cthulhu is a more ancient region with comparatively little present-day geological activity, where the haze appears to simply accumulate over time. Sputnik Planitia is a very active region where glacial convection, as well as sublimation and condensation rapidly refresh the surface, hiding recently deposited haze from view. Lowell Regio is a region of intermediate age featuring very distinct coloration from the rest of Pluto. Using a simple model haze particle as a colorant, we are not able to match the colors in both Lowell Regio and Cthulhu. To account for their distinct colors, we propose that after arrival at Pluto’s surface, haze particles may be less inert than might be supposed from the low surface temperatures. They must either interact with local materials and environments to produce distinct products in different regions, or else the supply of haze must be non-uniform in time and/or location, such that different products are delivered to different places.

    22. Schenk, Paul Michael, Beyer, Ross A., McKinnon, William B., et al., 2018, Icar, 314, 400, Basins, fractures and volcanoes: Global cartography and topography of Pluto from New Horizons

      The 2015 New Horizons flyby has produced the first high-resolution maps of morphology and topography of Pluto and Charon, the most distant objects so mapped. Global integrated mosaics of Pluto were produced using both LORRI framing camera and MVIC line scan camera data, showing the best resolution data obtained for all areas of the illuminated surface, 78% of the body. A unique feature of the Pluto imaging data set is the observation of terrains illuminated only by light scattered from atmospheric haze, allowing us to map terrains in the southern hemisphere that would otherwise have been in darkness. MVIC 4-color data were combined with the panchromatic map to produce full color global maps. Digital elevation models (DEMs) over 42% of Pluto were produced using combinations of MVIC hemispheric scans and LORRI mosaics, from which slopes at scales of 1 km can be determined. Pluto can be divided into regions each with distinct topographic signatures, corresponding with major physiographic terrain types. Large areas of Pluto are comprised of low-relief moderately cratered plains units. Deeply pitted and glaciated plains east of Sputnik Planitia are elevated 0.7 km. The most dominant topographic feature on Pluto is the 1200-by-2000-km wide depression enclosing the bright Sputnik Planitia ice sheet, the surface of which is 2.5-to-3.5 km deep (relative to the rim) and 2 km deep relative to the mean radius. The partial ring of steep-sided massifs, several of which are more than 5 km high, along the western margins of Sputnik Planitia produce some of the locally highest and steepest relief on Pluto, with slopes of 40-50. The second major topographic feature is a complex, eroded, ridge-trough system 300-400 km wide and at least 3200 km long extending north-to-south along the 155 meridian. This enormous structure has several kilometers of relief. It may predate the large impact event forming the basin, though some post-Sputnik Planitia deformation is evident. The large depressed, partially walled plain, Hyecho Palus, lies due southwest of Sputnik Planitia. Near the center of Hyecho Palus lie the circular constructional edifices Wright and Piccard Montes. Wright Mons rises 4.5 km above these plains, with a central depression 4.5 km deep, whereas Piccard Mons, best observed in haze-light, rises 5.5 km above the plains but has a bowl-shaped central depression 5.5 km below the plains for a total relief of up to 11 km, the greatest observed on Pluto. Both of these features are interpreted as constructional (volcanic?) in nature. Additional prominent topographic features include a 2-3 km high and 600 km wide dome centered on the illuminated IAU pole and the amoeboidal plateaus of “bladed” terrains in the equatorial region, which rise 2-5 km above local terrains and are the highest standing geologic units on the encounter hemisphere. The mean elevations in the integrated DEM for the two radio occultation areas are consistent with the 5-6 km difference in elevation as determined independently by the radio experiment, and a limb profile near the egress point confirms the presence of elevated bladed terrains in that area. Local relief of 3-5 km at massifs, troughs and pits supports conclusions that the icy shell of Pluto is relatively rigid. Numerous examples of topographic control of ice or frost deposition occur across Pluto, including the distinct coloration of the polar dome, the elevated terrains of eastern Tombaugh Regio, and along the ridge-trough system, where ridge tops and fossae rims are covered in different ices than at lower elevations. The topographic hypsogram of Pluto’s encounter hemisphere is strongly bimodal due to the large Sputnik Planitia depression. Otherwise the topographic signature of Pluto is controlled by deviations from the otherwise dominant low plains, including elevated bladed terrain plateaus and the depressed volcanic province including Wright and Piccard Montes.

    23. Cook, Jason C., Ore, Cristina M. Dalle, Protopapa, Silvia, et al., 2018, Icar, 315, 30, Composition of Pluto’s small satellites: Analysis of New Horizons spectral images

      On July 14, 2015, NASA’s New Horizons spacecraft encountered the Pluto-system. Using the near-infrared spectral imager, New Horizons obtained the first spectra of Nix, Hydra, and Kerberos and detected the 1.5 and 2.0 m bands of H2O-ice on all three satellites. On Nix and Hydra, New Horizons also detected bands at 1.65 and 2.21 m that indicate crystalline H2O-ice and an ammoniated species, respectively. A similar band linked to NH3-hydrate has been detected on Charon previously. However, we do not detect the 1.99 m band of NH3-hydrate. We consider NH4Cl (ammonium chloride), NH4NO3 (ammonium nitrate) and (NH4)2CO3 (ammonium carbonate) as potential candidates, but lack sufficient laboratory measurements of these and other ammoniated species to make a definitive conclusion. We use the observations of Nix and Hydra to estimate the surface temperature and crystalline H2O-ice fraction. We find surface temperatures < 20 K ( <70 K with 1- error) and 23 K ( < 150 K with 1- error) for Nix and Hydra, respectively. We find crystalline H2O-ice fractions of 78-22+12 % and > 30% for Nix an Hydra, respectively. New Horizons observed Nix and Hydra twice, about 2-3 hours apart, or 5 and 25% of their respective rotation periods. We find no evidence for rotational differences in the disk-averaged spectra between the two observations of Nix or Hydra. We perform a pixel-by-pixel analysis of Nix’s disk-resolved spectra and find that the surface is consistent with a uniform crystalline H2O-ice fraction, and a 50% variation in the normalized band area of the 2.21 m band with a minimum associated with the red blotch seen in color images of Nix. Finally, we find evidence for bands on Nix and Hydra at 2.42 and possibly 2.45 m, which we cannot identify, and, if real, do not appear to be associated with the ammoniated species. We do not detect other ices, such as CO2, CH3OH and HCN.

    24. Schenk, Paul Michael, Beyer, Ross A., McKinnon, William B., et al., 2018, Icar, 315, 124, Breaking up is hard to do: Global cartography and topography of Pluto’s mid-sized icy Moon Charon from New Horizons

      The 2015 New Horizons flyby through the Pluto system produced the first high-resolution topographic maps of Pluto and Charon, the most distant objects so mapped. Global integrated mosaics of the illuminated surface of Pluto’s large icy moon Charon have been produced using both framing camera and line scan camera data (including four-color images at up to 1.47 km pixel scales), showing the best resolution data at all areas of the surface. Digital elevation models (DEMs) with vertical precisions of up to 0.1 km were constructed for 40% of Charon using stereo imagery. Local radii estimates for the surface were also determined from the cartographic control network solution for the LORRI framing camera data, which validate the stereo solutions. Charon is moderately cratered, the largest of which is 250-km across and 6 km deep. Charon has a topographic range over the observed hemisphere from lowest to highest of 19 km, the largest topographic amplitude of any mid-sized icy body (including Ceres) other than Iapetus. Unlike Saturn’s icy moons whose topographic signature is dominated by global relaxation of topography and subsequent impact cratering, large-scale tectonics and regional resurfacing dominate Charon’s topography. Most of Charon’s encounter hemisphere north of the equator (Oz Terra) is broken into large polygonal blocks by a network of wide troughs with typically 3-6 km relief; the deepest of these occur near the illuminated pole and are up to 13 km deep with respect to the global mean radius, the deepest known surfaces on Charon. The edge of this terrain is defined by large tilted blocks sloping 5 or so, the crests of which rise to 5 or 6 km above Charon mean, the highest known points on Charon. The southern resurfaced plains, Vulcan Planitia, consist of rolling plains, locally fractured and pitted, that are depressed 1 km below the mean elevation of the disrupted northern terrains of Oz Terra that comprise much of the northern hemisphere (but 2-2.5 km below the surfaces of the blocks themselves). These plains roll downward gently to the south with a topographic range of 5 km. The outer margins of Vulcan Planitia along the boundary with Oz Terra form a 2-3-km-deep trough, suggesting viscous flow along the outer margins. Isolated massifs 2-4 km high, also flanked by annular moats, lie within the planitia itself. The plains may be formed from volcanic resurfacing of cryogenic fluids, but the tilted blocks along the outer margins and the isolated and tilted massifs within Vulcan Planitia also suggest that much of Charon has been broken into large blocks, some of which have been rotated and some of which have foundered into Charon’s upper “mantle”, now exposed as Vulcan Planitia, a history that may be most similar to the disrupted terrains of Ariel.

    25. Chan, K. C., Crocce, M., Ross, A. J., et al., 2018, MNRAS, 480, 3031, BAO from angular clustering: optimization and mitigation of theoretical systematics

      We study the methodology and potential theoretical systematics of measuring baryon acoustic oscillations (BAO) using the angular correlation functions in tomographic bins. We calibrate and optimize the pipeline for the Dark Energy Survey Year 1 data set using 1800 mocks. We compare the BAO fitting results obtained with three estimators: the Maximum Likelihood Estimator (MLE), Profile Likelihood, and Markov Chain Monte Carlo. The fit results from the MLE are the least biased and their derived 1 error bar are closest to the Gaussian distribution value after removing the extreme mocks with non-detected BAO signal. We show that incorrect assumptions in constructing the template, such as mismatches from the cosmology of the mocks or the underlying photo-z errors, can lead to BAO angular shifts. We find that MLE is the method that best traces this systematic biases, allowing to recover the true angular distance values. In a real survey analysis, it may happen that the final data sample properties are slightly different from those of the mock catalogue. We show that the effect on the mock covariance due to the sample differences can be corrected with the help of the Gaussian covariance matrix or more effectively using the eigenmode expansion of the mock covariance. In the eigenmode expansion, the eigenmodes are provided by some proxy covariance matrix. The eigenmode expansion is significantly less susceptible to statistical fluctuations relative to the direct measurements of the covariance matrix because of the number of free parameters is substantially reduced.

    26. Abbott, T. M. C., Abdalla, F. B., Annis, J., et al., 2018, MNRAS, 480, 3879, Dark Energy Survey Year 1 Results: A Precise H0 Estimate from DES Y1, BAO, and D/H Data

      We combine Dark Energy Survey Year 1 clustering and weak lensing data with baryon acoustic oscillations and Big Bang nucleosynthesis experiments to constrain the Hubble constant. Assuming a flat CDM model with minimal neutrino mass (m = 0.06 eV), we find H_0=67.4^{+1.1}_{-1.2} {km s^{-1} Mpc^{-1}} (68 per cent CL). This result is completely independent of Hubble constant measurements based on the distance ladder, cosmic microwave background anisotropies (both temperature and polarization), and strong lensing constraints. There are now five data sets that: (a) have no shared observational systematics; and (b) each constrains the Hubble constant with fractional uncertainty at the few-per cent level. We compare these five independent estimates, and find that, as a set, the differences between them are significant at the 2.5 level (2/dof = 24/11, probability to exceed = 1.1 per cent). Having set the threshold for consistency at 3, we combine all five data sets to arrive at H_0=69.3^{+0.4}_{-0.6} {km s^{-1} Mpc^{-1}}.

    27. MacCrann, N., DeRose, J., Wechsler, R. H., et al., 2018, MNRAS, 480, 4614, DES Y1 Results: validating cosmological parameter estimation using simulated Dark Energy Surveys

      We use mock galaxy survey simulations designed to resemble the Dark Energy Survey Year 1 (DES Y1) data to validate and inform cosmological parameter estimation. When similar analysis tools are applied to both simulations and real survey data, they provide powerful validation tests of the DES Y1 cosmological analyses presented in companion papers. We use two suites of galaxy simulations produced using different methods, which therefore provide independent tests of our cosmological parameter inference. The cosmological analysis we aim to validate is presented in DES Collaboration et al. (2017) and uses angular two-point correlation functions of galaxy number counts and weak lensing shear, as well as their cross-correlation, in multiple redshift bins. While our constraints depend on the specific set of simulated realisations available, for both suites of simulations we find that the input cosmology is consistent with the combined constraints from multiple simulated DES Y1 realizations in the m8 plane. For one of the suites, we are able to show with high confidence that any biases in the inferred S8 = 8(m/0.3)0.5 and m are smaller than the DES Y1 1 – uncertainties. For the other suite, for which we have fewer realizations, we are unable to be this conclusive; we infer a roughly 60 per cent (70 per cent) probability that systematic bias in the recovered m (S8) is sub-dominant to the DES Y1 uncertainty. As cosmological analyses of this kind become increasingly more precise, validation of parameter inference using survey simulations will be essential to demonstrate robustness.

    28. Anguita, T., Schechter, P. L., Kuropatkin, N., et al., 2018, MNRAS, 480, 5017, The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2016 follow-up campaign – II. New quasar lenses from double component fitting

      We report upon the follow-up of 34 candidate lensed quasars found in the Dark Energy Survey using NTT EFOSC, Magellan-IMACS, KECK-ESI, and SOAR-SAMI. These candidates were selected by a combination of double component fitting, morphological assessment, and colour analysis. Most systems followed up are indeed composed of at least one quasar image and 13 with two or more quasar images: two lenses, four projected binaries, and seven nearly identical quasar pairs (NIQs). The two systems confirmed as genuine gravitationally lensed quasars are one quadruple at zs = 1.713 and one double at zs = 1.515. Lens modelling of these two systems reveals that both systems require very little contribution from the environment to reproduce the image configuration. Nevertheless, small flux anomalies can be observed in one of the images of the quad. Further observations of nine inconclusive systems (including seven NIQs) will allow to confirm (or not) their gravitational lens nature.

    29. Pursiainen, M., Childress, M., Smith, M., et al., 2018, MNRAS, 481, 894, Rapidly evolving transients in the Dark Energy Survey

      We present the results of a search for rapidly evolving transients in the Dark Energy Survey Supernova Programme. These events are characterized by fast light-curve evolution (rise to peak in 10 d and exponential decline in 30 d after peak). We discovered 72 events, including 37 transients with a spectroscopic redshift from host galaxy spectral features. The 37 events increase the total number of rapid optical transients by more than a factor of two. They are found at a wide range of redshifts (0.05 < z < 1.56) and peak brightnesses (-15.75 > Mg > -22.25). The multiband photometry is well fit by a blackbody up to few weeks after peak. The events appear to be hot (T 10 000-30 000 K) and large (R 1014 – 2 1015 cm) at peak, and generally expand and cool in time, though some events show evidence for a receding photosphere with roughly constant temperature. Spectra taken around peak are dominated by a blue featureless continuum consistent with hot, optically thick ejecta. We compare our events with a previously suggested physical scenario involving shock breakout in an optically thick wind surrounding a core-collapse supernova, we conclude that current models for such a scenario might need an additional power source to describe the exponential decline. We find that these transients tend to favour star-forming host galaxies, which could be consistent with a core-collapse origin. However, more detailed modelling of the light curves is necessary to determine their physical origin.

    30. Treu, T., Agnello, A., Baumer, M. A., et al., 2018, MNRAS, 481, 1041, The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2016 follow-up campaign – I. Overview and classification of candidates selected by two techniques

      The primary goals of the STRong lensing Insights into the Dark Energy Survey (STRIDES) collaboration are to measure the dark energy equation of state parameter and the free streaming length of dark matter. To this aim, STRIDES is discovering strongly lensed quasars in the imaging data of the Dark Energy Survey and following them up to measure time delays, high resolution imaging, and spectroscopy sufficient to construct accurate lens models. In this paper, we first present forecasts for STRIDES. Then, we describe the STRIDES classification scheme, and give an overview of the Fall 2016 follow-up campaign. We continue by detailing the results of two selection methods, the outlier selection technique and a morphological algorithm, and presenting lens models of a system that could possibly be a lensed quasar in an unusual configuration. We conclude with the summary statistics of the Fall 2016 campaign. Including searches presented in companion papers (Anguita et al.; Ostrovski et al.), STRIDES followed up 117 targets identifying 7 new strongly lensed systems, and 7 nearly identical quasars, which could be confirmed as lenses by the detection of the lens galaxy. 76 candidates were rejected and 27 remain otherwise inconclusive, for a success rate in the range of 6-35 per cent. This rate is comparable to that of previous searches like SDSS Quasar Lens Search even though the parent data set of STRIDES is purely photometric and our selection of candidates cannot rely on spectroscopic information.

    31. Zuntz, J., Sheldon, E., Samuroff, S., et al., 2018, MNRAS, 481, 1149, Dark Energy Survey Year 1 results: weak lensing shape catalogues

      We present two galaxy shape catalogues from the Dark Energy Survey Year 1 data set, covering 1500 deg2 with a median redshift of 0.59. The catalogues cover two main fields: Stripe 82, and an area overlapping the South Pole Telescope survey region. We describe our data analysis process and in particular our shape measurement using two independent shear measurement pipelines, METACALIBRATION and IM3SHAPE. The METACALIBRATION catalogue uses a Gaussian model with an innovative internal calibration scheme, and was applied to riz bands, yielding 34.8M objects. The IM3SHAPE catalogue uses a maximum-likelihood bulge/disc model calibrated using simulations, and was applied to r-band data, yielding 21.9M objects. Both catalogues pass a suite of null tests that demonstrate their fitness for use in weak lensing science. We estimate the 1 uncertainties in multiplicative shear calibration to be 0.013 and 0.025 for the METACALIBRATION and IM3SHAPE catalogues, respectively.

    32. Vilenius, E., Stansberry, J., Muller, T., et al., 2018, A&A, 618, A136, “TNOs are Cool”: A survey of the trans-Neptunian region. XIV. Size/albedo characterization of the Haumea family observed with Herschel and Spitzer

      Context. A group of trans-Neptunian objects (TNOs) are dynamically related to the dwarf planet 136108 Haumea. Ten of them show strong indications of water ice on their surfaces, are assumed to have resulted from a collision, and are accepted as the only known TNO collisional family. Nineteen other dynamically similar objects lack water ice absorptions and are hypothesized to be dynamical interlopers.
      Aims: We have made observations to determine sizes and geometric albedos of six of the accepted Haumea family members and one dynamical interloper. Ten other dynamical interlopers have been measured by previous works. We compare the individual and statistical properties of the family members and interlopers, examining the size and albedo distributions of both groups. We also examine implications for the total mass of the family and their ejection velocities.
      Methods: We use far-infrared space-based telescopes to observe the target TNOs near their thermal peak and combine these data with optical magnitudes to derive sizes and albedos using radiometric techniques. Using measured and inferred sizes together with ejection velocities, we determine the power-law slope of ejection velocity as a function of effective diameter.
      Results: The detected Haumea family members have a diversity of geometric albedos 0.3-0.8, which are higher than geometric albedos of dynamically similar objects without water ice. The median geometric albedo for accepted family members is pV = 0.48-0.18+0.28, compared to 0.08-0.05+0.07 for the dynamical interlopers. In the size range D = 175-300 km, the slope of the cumulative size distribution is q = 3.2-0.4+0.7 for accepted family members, steeper than the q = 2.0 0.6 slope for the dynamical interlopers with D < 500 km. The total mass of Haumea’s moons and family members is 2.4% of Haumea’s mass. The ejection velocities required to emplace them on their current orbits show a dependence on diameter, with a power-law slope of 0.21-0.50.


      Herschel is an ESA space observatory with science instruments provided by a European-led Principal Investigator consortia and with important participation from NASA.

    33. Gschwend, J., Rossel, A. C., Ogando, R. L. C., et al., 2018, A&C, 25, 58, DES science portal: Computing photometric redshifts

      A significant challenge facing photometric surveys for cosmological purposes is the need to produce reliable redshift estimates. The estimation of photometric redshifts (photo- zs) has been consolidated as the standard strategy to bypass the high production costs and incompleteness of spectroscopic redshift samples. Training-based photo- z methods require the preparation of a high-quality list of spectroscopic redshifts, which needs to be constantly updated. The photo- z training, validation, and estimation must be performed in a consistent and reproducible way in order to accomplish the scientific requirements. To meet this purpose, we developed an integrated web-based data interface that not only provides the framework to carry out the above steps in a systematic way, enabling the ease testing and comparison of different algorithms, but also addresses the processing requirements by parallelizing the calculation in a transparent way for the user. This framework called the Science Portal (hereafter Portal) was developed in the context the Dark Energy Survey (DES) to facilitate scientific analysis. In this paper, we show how the Portal can provide a reliable environment to access vast datasets, provide validation algorithms and metrics, even in the case of multiple photo- zs methods. It is possible to maintain the provenance between the steps of a chain of workflows while ensuring reproducibility of the results. We illustrate how the Portal can be used to provide photo- z estimates using the DES first year (Y1A1) data. While the DES collaboration is still developing techniques to obtain more precise photo- zs, having a structured framework like the one presented here is critical for the systematic vetting of DES algorithmic improvements and the consistent production of photo- zs in future DES releases.

    34. Bair, Allison N., Schleicher, David G., Knight, Matthew M., 2018, AJ, 156, 159, Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)

      We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double-corkscrew morphology with two near-polar jets oriented approximately east-west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of R.A./decl. = 81/+29 with an obliquity of 97 and a sidereal rotation period of 41.45 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long -80/125 and an 10 radius and a western source area at lat/long +77/245 and an 20 radius, 4 larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology based on OH was quite different from that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO2. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H2O+ and OH+, respectively. We measured water production both before and after perihelion and extrapolated peak water production at perihelion to be about 1.0 1029 molecules s-1. We estimated an active fraction of only 4%-5% and a nucleus radius of up to 8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.

    35. Li, T. S., Simon, J. D., Kuehn, K., et al., 2018, ApJ, 866, 22, The First Tidally Disrupted Ultra-faint Dwarf Galaxy?: A Spectroscopic Analysis of the Tucana III Stream

      We present a spectroscopic study of the tidal tails and core of the Milky Way satellite Tucana III, collectively referred to as the Tucana III stream, using the 2dF+AAOmega spectrograph on the Anglo-Australian Telescope and the IMACS spectrograph on the Magellan Baade Telescope. In addition to recovering the brightest nine previously known member stars in the Tucana III core, we identify 22 members in the tidal tails. We observe strong evidence for a velocity gradient of 8.0+/- 0.4 {km} {{{s}}}-1 {\deg }-1 over at least 3 on the sky. Based on the continuity in velocity, we confirm that the Tucana III tails are real tidal extensions of Tucana III. The large velocity gradient of the stream implies that Tucana III is likely on a radial orbit. We successfully obtain metallicities for four members in the core and 12 members in the tails. We find that members close to the ends of the stream tend to be more metal-poor than members in the core, indicating a possible metallicity gradient between the center of the progenitor halo and its edge. The spread in metallicity suggests that the progenitor of the Tucana III stream is likely a dwarf galaxy rather than a star cluster. Furthermore, we find that with the precise photometry of the Dark Energy Survey data, there is a discernible color offset between metal-rich disk stars and metal-poor stream members. This metallicity-dependent color offers a more efficient method to recognize metal-poor targets and will increase the selection efficiency of stream members for future spectroscopic follow-up programs on stellar streams.

    36. Clarke, C. J., Tazzari, M., Juhasz, A., et al., 2018, ApJL, 866, L6, High-resolution Millimeter Imaging of the CI Tau Protoplanetary Disk: A Massive Ensemble of Protoplanets from 0.1 to 100 au

      We present high-resolution millimeter continuum imaging of the disk surrounding the young star CI Tau, a system hosting the first hot Jupiter candidate in a protoplanetary disk system. The system has extended mm emission on which are superposed three prominent annular gaps at radii 13, 39, and 100 au. We argue that these gaps are most likely to be generated by massive planets so that, including the hot Jupiter, the system contains four gas giant planets at an age of only 2 Myr. Two of the new planets are similarly located to those inferred in the famous HL Tau protoplanetary disk; in CI Tau, additional observational data enables a more complete analysis of the system properties than was possible for HL Tau. Our dust and gas dynamical modeling satisfies every available observational constraint and points to the most massive ensemble of exoplanets ever detected at this age, with its four planets spanning a factor 1000 in orbital radius. Our results show that the association between hot Jupiters and gas giants on wider orbits, observed in older stars, is apparently in place at an early evolutionary stage.

    37. Safrit, Taylor, Steckloff, Jordan K., Bosh, Amanda S., et al., 2018, DPS, 50, 106.03, The Formation of Bilobate Comet Shapes through Sublimative Torques

      Approximately 70 percent of observed cometary nuclei are bilobate (made of two primary masses connected by a narrow neck) (Hirabayashi et al. 2016). Subcatastrophic collisions between cometary bodies can result in these shapes, but require impact speeds an order of magnitude smaller than typical impact velocities in the scattered disk (Gomes et al. 2008), the reservoir from which most Jupiter-family comets (JFCs) originate. Additionally, only 10-20 percent of similarly-sized asteroids are bilobate (Benner et al. 2015), suggesting that the mechanism producing bilobate shapes must be unique to comets. We investigate a novel mechanism for bilobate comet nucleus formation in JFCs, in which sublimative torques acting on comet nuclei during their dynamical migration through the Centaur region spin them up to disruption. Simulations of rotationally disrupted, comet-like rubble-piles (with strengths of 1-10 Pa and internal friction angles of 35) (Steckloff and Samarasinha 2018) find that rotationally disrupted nuclei reform as bilobate objects (Sanchez and Scheeres 2016; Sanchez and Scheeres 2018). Although centaurs are too distant for H2O ice to sublimate vigorously, they are near enough to the Sun for CO2 and CO ices to do so. We therefore focus on whether CO2– and CO-driven sublimative torques are sufficient to rotationally disrupt centaurs. We combine simulations of the dynamical evolution of centaurs with our SYORP sublimative torque model to compute the torques created by the sublimation of CO2 and CO ices. We find that JFCs smaller than 100 kilometers in radius typically experience sufficient sublimative torques during their migration through the Centaur region to be restructured into bilobate shapes. This suggests that the observed bilobate distribution of comet shapes is likely the result of cometary sublimative evolution, rather than a primordial property of objects in cometary reservoirs. Thus, we expect to observe more bilobate shapes as comets migrate inward. This population-scale shape evolution could be detected with occultation studies.

    38. Farnham, Tony, Knight, Matthew M., Bodewits, Dennis, et al., 2018, DPS, 50, 106.05, HST Observations of the Nucleus of Comet 41P/Tuttle-Giacobini-Kresak

      In early 2017, we discovered that comet 41P/Tuttle-Giacobini-Kresak (TGK), was spinning down at an incredibly rapid rate, with a rotation period that changed from 20 hours in early March (Farnham et al. CBET 4375, 2017) to 27 hours in late March (Knight et al. CBET 4377 2017) and >42 hours in early May (Bodewits et al. Nature 553, 186, 2017). These results indicate that the comet’s rotation period decreased by 0.5 hr/day during this time periodthe fastest changes ever observed in any comet. Thus, TGK is ideal for testing models of cometary dynamics, allowing us to investigate how the torques respond to changing production rates and illumination conditions. Furthermore, if the spin-down of TGK continues at this pace over the next apparition or two, it may be possible to document a comet’s behavior as it transitions through a slow-rotation end state (e.g., will it enter a stage of complex rotation? Spin up in the opposite direction? Or will it exhibit some other response?). To follow up on this work, we were awarded 10 orbits of HST WFC3/UVIS time in December 2017 to observe the lightcurve of TGK. Our goal is to characterize the rotation state of the nucleus after its activity had subsided. Results from this work will not only provide a measurement of the “final” spin state achieved during the 2017 apparition, but will also define the initial state for future monitoring of any continuing changes over the next apparition. We can also take advantage of the high resolution of the HST images to separate the nucleus signal from that of any coma that is present. This allows us to constrain properties of the nucleus, including its general size and shape, that will be used in models of the comet’s dynamical evolution. Although we requested our 10 orbits to be spaced over a 7-day baseline to cover any expected rotation period, scheduling constraints forced us to restrict our observational window to 3.5 days. This affects our ability to fully define the lightcurve, but otherwise our analyses will continue as planned. We will present results from this work, and will discuss how they might relate to the rapid evolution of the comet’s dynamics.

    39. Pinilla-Alonso, Noemi, Popescu, Marcel, Fernandez-Valenzuela, Estela, et al., 2018, DPS, 50, 200.02, The hypnotic dance of Patroclus and Menoetius: Ground-based observations of their 2017-2018 mutual event season.

      Trojans are a significant portion of the small bodies population located within two clouds in the L4 and L5 Lagrangian points of Jupiter’s orbit. The study of primitive small bodies is relevant to the origin and nature of volatile and organic material in the early Solar System. Dedicated studies of the nature of these bodies can significantly improve our understanding of their nature, origin and evolutionary mechanisms. Lucy, a mission of the NASA’s Discovery Program, is planned to launch in October 2021 for a 12-year journey. Lucy will explore seven different primitive small bodies, six of which will be Trojans. The mission will use a suite of remote sensing instruments to map the geology, surface color, composition, thermal and other physical properties of the targets at close range. Our international team performed observations during 2017 and 2018 to record the light-curve of the mutual events of the binary system formed by Patroclus and Menoetius, providing a unique opportunity to refine their orbit characteristics as well as other properties of the system (sizes, shape, and mass of both objects). Patroclus is the first binary trojan to be discovered. Previous studies by Marchis, et al. (2016, Nature, 439) determined the mutual orbit of the system to have a period of 4.283 0.004 days and a semimajor axis of 680 20 km, leading to a system mass of (1.36 0.11) x 1018kg and an average bulk density of 0.8 0.2 g cm-3. When the plane of their mutual orbit is aligned with the direction to the Sun or to an observer, Patroclus and Menoetius take turns eclipsing or occulting one another. Such an alignment occurs during mutual event seasons, twice during the 12 year orbit around the Sun. We show, for the first time, a collection of light-curves that are the result of about 20 detections. Our analysis puts a special focus on the differences between the observations and the models of the orbit (Grundy et al. 2018, Icarus 305) providing unique and crucial information that includes the possible topographic variation on Menoetius’ south pole, a refinement to the orbit model, and improved predictions for shadowing and occultation events.

    40. Hanley, Jennifer, Groven, Jessica J., Grundy, William, et al., 2018, DPS, 50, 203.10, Characterization of Possible Two Liquid Layers in Titan Seas

      The lakes and seas of Titan are composed primarily of methane and ethane, with the concentration of dissolved nitrogen from the atmosphere dependant on the ratio of methane to ethane, the temperature, and pressure. Previous models have predicted the existence of two liquid layers in equilibrium with the vapor phase under certain temperature and pressure conditions (e.g. Cordier et al., 2017, Nature Astronomy). Our previous experiments have confirmed the presence of the two liquid phase at colder temperatures and higher pressures than what exists on the surface of Titan. In the Astrophysical Ices Lab at Northern Arizona University, we have performed a new series of experiments to understand the conditions under which the two liquid layers will form. We have incorporated Raman spectroscopy to allow us to measure the composition of the samples. In all experiments performed so far, the lower layer is enriched in nitrogen and methane, while the upper layer is enriched in methane and ethane, although both layers have all three species present. The initial ratio of methane to ethane will control the relative volumes of the two liquids, though it does not appear to affect their compositions. Comparing to Cordier et al. (2017), we find the two liquid phase does not form at 85 K until a pressure of greater than 1.83 bar is reached, compared to the 1.7 bar predicted. Our results show that at Titan surface pressure (1.44 bar), a mixture of methane, ethane and nitrogen will remain in one liquid down to 82 K, where it will then split into two liquids. We will present these experimental results detailing the conditions under which the two liquid phases form, as well as the composition of the liquids. These results can inform whether they might occur on Titan, and how that might impact understanding of previous mission results from Cassini, as well as future missions, and guide current theoretical models.

    41. Bair, Allison N., Schleicher, David G., Farnham, Tony, 2018, DPS, 50, 210.06, The Extremely Active Comet C/Hale-Bopp (1995 O1): Production Rates from Nearly Five Years of Narrowband Photometry

      Comet C/Hale-Bopp (1995 O1) was an intrinsically bright object that exhibited the highest continuous gas and dust production rates ever measured for a comet. We will report on our extensive narrowband photometry observations of H-B, including 332 individual sets of photometry obtained on a total of 98 nights at Lowell and Perth Observatories. Our observations span nearly 5 years, beginning with inbound measurements on 1995 July 25 (heliocentric distance, r, of 7.14 AU), continuing through perihelion (1997 April 1; perihelion distance of 0.91 AU), then extending outbound until 2000 March 3 (r of 10.58 AU). A thorough analysis of this dataset has been delayed for numerous reasons, including the long timeline of post-perihelion observations and the calibrating of our then-new HB comet filter set (Farnham et al. 2000, Icarus 147, 180). We additionally discovered that, due to its extremely high production rates, the size of the collision zone for H-B was much larger than normal, especially near perihelion, requiring an adjustment to our standard scalelengths and an empirical adjustment to the derived water production rates. From our first observations, it was clear that H-B was unique. The dust production, even at 7.14 AU, had an Af of 50,000 cm – much higher than that measured for any comet in our database at any heliocentric distance. H-B’s highest production rates were measured near perihelion, where Af peaked at 1.2106 cm and the water production rate, also by far our highest value measured for any comet, reached 3.591031 molecules s-1. The effective active area required to produce the measured water production is 2100 km2, implying a minimum nucleus diameter of 26 km; however the existence of isolated jets strongly indicates that the entire surface of the nucleus is not active, which means the actual size is likely to be at least 2 as large. These and other results from this unique comet will be presented. This research has been supported by NASA’s Planetary Astronomy Program.

    42. Schleicher, David, Knight, Matthew, 2018, DPS, 50, 210.12, Narrowband Observations of Comet 21P/Giacobini-Zinner During Its Excellent 2018 Apparition

      During its last excellent apparition in 1985, Comet 21P/Giacobini-Zinner was discovered to have a highly unusual composition, with C2 and C3 each depleted by about a factor of six compared to either OH or CN (Schleicher et al. 1987), making G-Z the prototype of what would become the carbon-chain depleted compositional class (A’Hearn et al. 1995). The comet also exhibited an odd pre-/post-perihelion asymmetry, with all production rates dropping by a factor of several in the six weeks surrounding perihelion. The current apparition, with very similar circumstances to that of 1985, presents an exceptional opportunity to further study this interesting object. The goals of our multi-instrument observing campaign from Lowell Observatory include greatly extending the heliocentric distance range over which we measure production rates, obtaining narrowband images to study expected jet morphology, and obtaining high resolution spectroscopy to measure isotopic ratios when the comet is brightest in September (though spectroscopic results are not expected to be available in time for presentation). Thus far we have obtained a total of 21 sets of photometry over five nights beginning May 17 (1.82 AU), and imaging on 11 nights beginning June 13 (1.57 AU). Based on the strong asymmetry in production rates about perihelion that we measured in 1985, along with successful studies of seasonal effects in several other comets in recent years, we predicted that G-Z was likely to have a single dominant jet whose source was in summer inbound and rapidly changed to winter near perihelion. Indeed, our new imaging exhibits a broad feature towards the northeast having about 120 width that shows little rotational variation. This is consistent with a mid-to-high latitude source region perpetually in sunlight producing a filled corkscrew of material. How this feature evolves during this apparition, a preliminary model of G-Z’s jet morphology, along with associated photometric results, will be presented. This research is supported by NASA Planetary Astronomy Program grant NNX14AG81G and Solar System Observations Program grant 80NSSC18K0856.

    43. Noll, Keith, Grundy, William, Buie, Marc, et al., 2018, DPS, 50, 217.04, Deep Search for Satellites of Lucy Trojans with HST

      We report on the first deep satellite search of the Trojan asteroids that are targets of NASA’s Lucy mission. This search was carried out using the Hubble Space Telescope in a 10 orbit program in cycle 25. The observations were obtained from February – September 2018. The primary goal of the observations is to search for faint companions to the Trojans that will be visited by the Lucy spacecraft. Deep imaging was accomplished using WFC3 UVIS in standard imaging mode with the F555W filter which delivers good PSF quality and high sensitivity. The observations were designed to reach S/N=5 for a limiting magnitude of V25.5 at separations 0.2 arcsec from the primary object which approximates the Lucy spacecraft encounter distance. The search can detect satellites at least five magnitudes fainter than the faintest target, Polymele. At closer separations PSF fitting is required to search for close-in any satellites. The UVIS2-C1K1C subarray was used for all observations and covers the entire stable region of the Hill spheres of our targets. The Lucy mission was selected by NASA in January 2017 and is planned for launch in October 2021. Early discovery of any satellites will enable early planning for observations and significantly enhance the scientific return of the mission. Orbiting material is also a potential spacecraft hazard and a deep search for any evidence of bound material is a necessary precaution for the mission. At the time of the abstract deadline two of the five targets have been observed with HST – all are scheduled to be observed by the end of September. We will report on the latest results.

    44. Dustrud, Shyanne, Lindberg, Gerrick E., Grundy, Will, et al., 2018, DPS, 50, 221.09, Modeling the Phase Diagram and Properties of Titan’s Lakes via Molecular Dynamics

      Nitrogen, methane, and ethane are abundant on Titan. The ternary system of these three compounds is present as liquids in lakes and seas. Knowledge of their phase behavior and thermodynamic properties is crucial for understanding the behaviors of Titan’s fluid bodies and their interaction with the surface and atmosphere. The development of a full phase diagram is of fundamental importance in the understanding of how the bodies of liquid behave on the surface of Titan; additionally, the material properties such as, densities, heat capacities, or viscosity are vital to better the understanding of the stability of the liquids and their bulk behavior. Utilizing a thermodynamic approach that assumes ideality of the system, phase behavior can be predicted. Molecular dynamics simulations (MD) offer a unique insight to the harsh conditions of the outer solar system, enabling the real effects of non-ideal interactions to be quantified. Material properties can then be calculated from the results of MD simulations for a variety of compositions and conditions. MD offers not only common observables, but it also provides an understanding at the atomistic level of what occurs in a mixture. Combining a theoretical approach with experimental, the exact boundaries of the predicted phase transitions can be elucidated and the theoretical approach validated. The Astrophysics Ice Lab at Northern Arizona University is home to a laboratory apparatus capable of cooling samples to 30K, and designed with windows to allow for spectroscopy of a bulk sample. Raman spectroscopy in particular is a powerful tool in evaluating the interactions between molecules within a mixture and allows for a more in-depth study of the systems in question. We will present on our findings and material properties calculated from MD simulations of the ternary mixture under conditions relevant to Titan.

    45. Fraser, Wesley C., Bannister, Michele T., Marsset, Michael, et al., 2018, DPS, 50, 302.04, Col-OSSOS: The Compositional Structure of the Protoplanetesimal Disk

      The surfaces of trans-Neptunian objects (TNOs) are poorly understood. Small TNOs fall into at least three classes of object based on their surface colours and albedo. Despite nearly two decades of gathering TNO surface information, a taxonomy has still not been agreed upon. The development of a robust taxonomy is one of the goals of the Colours of the Outer Solar System Origins Survey (Col-OSSOS). After a quick overview of the program, we present taxonomic results from Col-OSSOS. From u, g, r, z and J photometry of a sample of 79 TNOs, we find evidence for only three separate taxons based on their colours. One of the taxons consists entirely of a single dynamical population, the so-called cold classical TNOs, which stand out in colour space, possessing unique (r-z) compared to similarly optically red dynamically excited TNOs. The other two taxons are the known neutral and red classes of dynamically excited TNOs, which are approximately divided by optical colour at (g-r)=0.75. These classes exhibit a broad continuum in colour, rather than occupying similar mean colours for all class members. From albedo considerations, we demonstrate that in the dynamically excited populations, the neutral class outnumbers the red class by at least a factor of 4, but could be as numerous as 11:1. The minimal number of detected taxons argues for a moderately homogenous protoplanetary disk, with only a pair of substantive compositional divisions spanning roughly 20-45 AU, and a disk which is heavily dominated by the neutral class of object.

    46. Thirouin, Audrey, Sheppard, Scott S., 2018, DPS, 50, 302.05, Lightcurves of the Dynamically Cold Classical Trans-Neptunian Objects

      The dynamically Cold Classical trans-Neptunian objects (TNOs) have low inclination, low eccentricity, and are not in Neptune resonances. Because they have likely remained far from the Sun, and formed near where they exist today, these TNOs are thought to be primordial and thus important to understand our Solar System’s formation and evolution. Even though more than 600 Cold Classicals (CCs) are known, only 19 have been studied for rotational lightcurves. In addition to this low number, most of the studied CCs are the larger objects and known wide binary systems and thus our understanding of this population is highly biased. Therefore, in order to improve our knowledge of the CCs and give context to the next flyby of the NASA’s New Horizons mission, we started a survey of the CCs with the Discovery Channel and the Magellan telescopes for lightcurves and colors. Our survey is the first entirely dedicated to the study of the rotational and physical properties of this population. Over the past three years, we observed some 40 non-binary CCs with absolute magnitudes from 5 to 7.2 mag. Sparse and complete lightcurves obtained through our survey are used to constrain the contact binary fraction, the shape and rotational frequency distributions of the CCs. By comparing the properties of the Cold Classicals to the other dynamical groups, we aim to extract the primordial characteristics of the trans-Neptunian population. We also report the discovery of the first two likely contact binaries detected through lightcurves in this dynamical group. Using our results and the literature, we estimate that only about 10% of the CCs could be contact binaries, which is significantly lower than our estimate of contact binaries in the Plutino population of some 40-50%. This low population of CC contact binaries is also surprising given that the CC have a larger fraction of equal-sized wide-binary systems while the Plutinos have very few known wide binaries. This suggests the different scattering histories of the TNO populations affected the formation of contact binaries. Finally, a new equal-sized wide binary, 2014 LQ28, was identified from our observations. This work is supported by the National Science Foundation, grant #1734484.

    47. DeMeo, Francesca, Polishook, David, Carry, Benoit, et al., 2018, DPS, 50, 310.07, Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to Families

      Differentiated asteroids are rare in the main asteroid belt despite evidence for 100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope. The success rate for confirming A-types from SDSS candidates is 33% – 20 of the 60 objects observed. We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of 600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

    48. Bosh, Amanda S., Sickafoose, Amanda A., Levine, Stephen E., et al., 2018, DPS, 50, 311.01, The 2017 occultation by Vanth: a revised analysis

      In March 2017, we observed an occultation by members of the Orcus system. Two chords were obtained, along with three negative detections (Sickafoose et al. 2017; Sickafoose et al. 2018, submitted). Initial geometric analysis of these data was consistent with an occultation by Orcus and Vanth, of a single star (Bosh et al. 2017). Subsequent speckle imaging of the occultation star using DSSI on Gemini-South (Horch et al. 2009) revealed a double star with a separation of 252 mas and a magnitude difference of 0.93 at 692 nm. Reanalysis of the geometry of this event with this new stellar information shows that the two positive detections are consistent with occultations by Orcus’ satellite Vanth at both the 3-m IRTF (chord length 434.39 2.36 km) and the 1-m Las Cumbres ELP telescope at McDonald Observatory (chord length 291.1 124.9 km; larger uncertainty due to deadtime uncertainty). These observations suggest that the IRTF chord was close to being central on Vanth; in fact, it must be near central because a non-detection at Sierra Remote Observatories (0.6-m ATUS) constrains the geometry. We are not able to determine if there is any deviation from sphericity due to the uncertainty in the chord length of our second chord, from ELP, however it is consistent with a spherical shape for Vanth. Initial estimates of the size of Vanth from thermal measurements (Brown et al. 2010; Fornasier et al. 2013) are approximately 280 km, with an albedo of approximately 0.25. Later observations of Orcus/Vanth made with ALMA give a diameter for Vanth of 475 75 km, with an albedo of 0.08 0.02 (Brown & Butler 2018). Our occultation measurement agrees with this new measurement for Vanth’s size, and further constrains the size. Vanth is therefore darker than Orcus, implying either a difference in origin or in subsequent evolution. As reported in Sickafoose et al. (2018, submitted), neither atmosphere nor rings were detected in the occultation data.

    49. Weaver, Harold, Porter, Simon B., Spencer, John, et al., 2018, DPS, 50, 311.03, Searches for KBO Binaries using New Horizons LORRI

      The New Horizons (NH) spacecraft is currently traversing the densest portion of the Kuiper belt (r 43 AU), enabling observations of known Kuiper belt objects (KBOs) at unique geometries, including at large phase angles not possible from the inner solar system and at ranges that provide higher spatial resolution than available from Earth, or Earth-orbiting, facilities. New Horizons carries a large aperture (20.8 cm) visible light imaging system, the LOng Range Reconnaissance Imager (LORRI), whose resolution (IFOV=1,4 arcsec for 1×1 and 4×4 modes, respectively) permits searches for binaries at finer spatial scales than available from the Hubble Space Telescope (HST). We have already scheduled observations of 13 KBOs (1 Plutino, 1 Hot Classical, 1 Scattered Disk, and 10 Cold Classicals) that pass within 1 AU of the NH spacecraft, and we are actively searching for additional candidates using ground-based telescopes. Five of the KBOs pass within 0.2 AU of the NH spacecraft, including two with ranges of 0.1 AU (73 km/pix for 1×1 mode). LORRI’s photometric sensitivity for these satellite searches (V 16.3 in 1×1 mode after co-adding 125 0.5s exposures; V 21 in 4×4 mode after co-adding 50 30s exposures) is comparable to, or exceeds, that available from HST. Five of the six highest resolution (1×1 mode) NH KBO satellite searches are being conducted during the latter half of 2018, although most of the data will not be downlinked to Earth until 2019. Here we report on the binary search limits achieved for the five NH distant KBO observations already obtained and our plans for the upcoming searches.

    50. Tegler, Stephen C., Stufflebeam, Terrence, Grundy, William, et al., 2018, DPS, 50, 311.05, A New, Unusual, and Diagnostic Band in Near-Infrared Spectra of Laboratory Ice Samples and Triton

      We present near-infrared spectra of carbon monoxide (CO) and nitrogen (N2) ice mixtures obtained in the Northern Arizona University Astrophysical Ice Laboratory. We confirm the existence of an unidentified band at 4466 cm-1 (2.239 m) in these mixtures that was first reported by Quirico and Schmitt (1997, Icarus, 128, 181-188). A systematic laboratory study of the band has led us to some surprising results. Specifically, the band is strongest for a sample with near equal amounts of CO and N2; however, the band is not present in a pure CO ice sample nor a pure N2 ice sample. Nor is the band present in a CO and argon (Ar) mixture. Furthermore, the 2.239 m band shifts for 13CO in an N2 ice sample and for C18O in an N2 ice sample, but not for 12C16O in a 14N2 enriched (15N14N depleted) ice sample. We looked into the solid state phase behavior of the mixtures, and found CO and N2 are fully miscible in one another. We mapped the temperature and composition dependence of the alpha – beta N2 phase transition and found the band in both N2 phases. Our experiments suggest the band arises from some sort of interaction between individual CO and N2 molecules in the solid state. In addition to laboratory spectra, we present a recently obtained near-infrared spectrum of Triton taken with the 8-meter Gemini Telescope in Chile and the IGRINS spectrograph. The 2.239 m band weakly appears in the spectrum. Besides laboratory and telescope spectra, we present the results of our theoretical efforts to better understand the interaction between the CO and N2 molecules giving rise to this band. Our work shows the 2.239 m band has important applications for remote sensing of icy outer system objects. In particular, its detection on icy bodies like Triton, and perhaps future detections on Pluto, Eris, and Makemake, demonstrates the CO and N2 molecules are intimately mixed together. Perhaps spectrographs on future spacecraft could exploit this band to better understand the chemical makeup of the ice on this class of bodies.

    51. Magnuson, Mitchell, Moskovitz, Nicholas, Devogele, Maxime, et al., 2018, DPS, 50, 312.07, The Mission Accessible Near Earth Object Survey (MANOS): Spectrophotometric Characterization of Small NEOs

      The Mission Accessible Near Earth Object Survey (MANOS) Spectrophotometric Characterization of Small NEOs The Mission Accessible Near Earth Object Survey (MANOS) was designed to characterize sub-km, low delta-v, newly discovered near-Earth objects (NEOs). A subset of MANOS includes collecting color photometry in the Sloan Digital Sky Survey (SDSS) filter set, which can be used to produce rough taxonomic assignments for our targets. Such information is critical for (1) understanding how the Solar System formed as NEOs are remnants from the epoch of planet formation, (2) the interpretation of meteorites as NEOs are their primary producers, and (3), resource extraction missions in space; which are soon to become reality with future manned missions expected to extend beyond low earth orbit. MANOS utilizes 4-m (Lowell Observatory’s Discovery Channel Telescope, SOAR) and 8-m (Gemini North and South) telescopes which enables traditional spectroscopy down to an apparent visual magnitude of 19.5 and 20.5 respectively. The NEOs observed by MANOS have an average absolute magnitude of H > 21, corresponding to objects with a mean diameter in the 100m range. These relatively small targets are most often discovered near peak brightness around V 20-21 mag, with follow up observations during subsequent apparitions being infeasible as targets return on average 100 times fainter (Galache et al. 2015). By performing coarse spectrophotometry, we are offered a unique opportunity to characterize particularly small NEOs, a currently under sampled portion of the NEO population. Our comprehensive data set contains spectrophotometric results for over 100 targets. These data will be compared to the Sloan Digital Sky Survey Moving Object Catalog, which contains a similar size sample of km-scale NEOs. It is understood that while more than 80% of meteorites have origins traced to S-type asteroids (Harvey & Cassidy 1989), only 60% of the large NEOs are designated as such (Binzel et al. 2018). Our sample bridges the gap between meteorites and large NEOs, and thus can provide insight into this discrepancy. This work is supported by the NASA NEOO program, grant number NNX17AH06G.

    52. Levine, Stephen, Henden, Arne, Terrell, Dirk, et al., 2018, DPS, 50, 315.03, Applications of the AAVSO Photometric All-Sky Survey (APASS) to observations of objects in our Solar System

      The AAVSO Photometric All-Sky Survey (APASS) is designed to provide photometric standards over the entire sky in the magnitude range 6.5 < V < 17.5mag in B, V, u, g, r, i, z and Y filter passbands. For the magnitude range, APASS is well matched to optical telescopes from 8-cm up to 2- to 3-meters in diameter. The survey was originally conceived to facilitate variable star observations. However, having photometric standards in every image taken can be of great utility to the Solar System community as well. Not only does this make it easier to combine extended time series photometry of observations of objects like asteroid and comets that move appreciably, it also makes it possible to recover photometry at the few percent level for data taken under non-photometric conditions (e.g. as demonstrated with SDSS data by Ivezic et al 2007, AJ, 134, 973). APASS data have been taken between 2010 and 2018 with twin ASA 20-cm astrographs installed at northern and southern hemisphere sites. Over the course of the survey, we have accummulated over 500,000 images, each 2.8 x 2.8 degrees in size. We present initial results of our work to compile a catalogue of all the serendipitous observations of asteroids and comets in those images. For the bulk of the survey data, we have contemporaneous five color (B,V,g,r,i) imaging.

    53. Hsieh, Henry, Ishiguro, Masateru, Knight, Matthew M., et al., 2018, DPS, 50, 408.06, The Reactivation and Nucleus Characterization of Main-Belt Comet 358P/PANSTARRS (P/2012 T1)

      We present observations of main-belt comet 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to 2017 December (Gemini program IDs GS-2017A-LP-11 and GS-2017B-LP-11), as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H_R=19.5+/-0.2 mag and G_R=-0.22+/-0.13 for the nucleus, corresponding to an effective radius of r_N=0.32+/-0.03 km (assuming an albedo of p_R=0.05). The object appears significantly brighter (by >1 mag) than expected starting in 2017 November, while a faint dust tail oriented approximately in the antisolar direction is also observed on 2017 December 18. We conclude that 358P has become active again for the first time since its previously observed active period in 2012-2013. These observations make 358P the seventh main-belt comet candidate confirmed to exhibit recurrent activity near perihelion with intervening inactivity away from perihelion, strongly indicating that its activity is sublimation-driven. Fitting a linear function to the ejected dust masses inferred for 358P in 2017 when it is apparently active, we find an average net dust production rate of 2.0+/-0.6 kg/s (assuming a mean effective particle radius of a_d=1 mm) and an estimated activity start date of 2017 November 8+/-4 when the object was at a true anomaly of 316+/-1 degrees and a heliocentric distance of R=2.54 AU. This work has been published in Hsieh et al. (2018, AJ, 156, 39). We will also present new observations of the object obtained after the submission of this abstract from 2018 August through 2018 October (Gemini program ID GS-2018B-LP-11), during which its previously-observed activity is expected to continue, and report whether we find any evidence of changes in activity strength between the object’s 2012-2013 and 2017 active periods. The authors acknowledge support from NASA Solar System Observations grant NNX16AD68G and the State of Arizona Technology and Research Initiative Program.

    54. Moskovitz, Nicholas, Schottland, Robert, Burt, Brian, et al., 2018, DPS, 50, 408.08, astorb at Lowell Observatory: A comprehensive system to enable asteroid science

      astorb is a database of orbital elements for all known asteroids in the Solar System (780,489 objects as of 12 July 2018), has been hosted at Lowell Observatory for over 20 years, and is actively curated to be automatically updated as new objects are discovered. Front-end access to the database and associated tools are available at Modernization and upgrades to the astorb system are ongoing with expected completion by mid-2019. Upgrades currently implemented include the addition of physical properties, such as albedo and rotation period, and redesigned observational planning tools, such as ephemeris and finder chart generators. Data on physical properties are pulled from multiple sources including NASA’s Planetary Data System (PDS), the asteroid Lightcurve Database (LCDB), and a number of project-specific online compilations. Future upgrades will include additional physical properties, enhanced query capabilities, and a system for credentialed user input to the database as a way to facilitate rapid dissemination of observational results. User feedback on desired additional functionality is invited. The combination of physical properties and tools for observational prediction provides a powerful system for planning and conducting new science investigations. Through queries that execute in just a few seconds we can answer complex questions such as: which members of the Vesta dynamical family have measured albedos and are observable tonight? what is the lowest numbered asteroid without a measured albedo and when is it next observable? which Main Belt asteroids with known spectral types are passing through opposition this week? These examples highlight the type of queries for which astorb is optimized. We will present the current state of the astorb system and highlight some of the novel tools available to the community. This work is supported by the NASA PDART program, grant number NNX16AG52G.

    55. Person, Michael J., Schindler, Karsten, Bosh, Amanda S., et al., 2018, DPS, 50, 416.10, Airborne and Ground Observations of the Stellar Occultation by Triton on 5 October 2017

      On 5 October 2017, Triton occulted the 13th magnitude star UCAC4 410-143659 as seen from the Eastern US, North Atlantic, and Europe. Our collaboration observed this event from the Stratospheric Observatory for Infrared Astronomy (SOFIA) aircraft, as well as numerous (over two dozen) ground stations throughout the US and Europe. Here, we present the preliminary results of analyzing this dataset and highlight a number of features of Triton’s atmosphere. Initial reduction of the data indicates that the atmospheric pressure increases seen throughout the 90’s have stabilized or perhaps begun to reverse, as the current pressures are more comparable to those measured during the earlier occultations of the 1990’s than the later ones, although still greater than the pressure observed by Voyager 2 in 1989. Careful calibration of the multi-wavelength observations made from SOFIA indicates a clear atmosphere at the levels to which we are sensitive (>35 km), with no signs of the various particulate dust plumes or cloud-like structures seen by Voyager 2 below 8 km altitude. Data reduction is progressing and a final report is in preparation.

    56. Sickafoose, Amanda A., Levine, Stephen E., Bosh, Amanda S., et al., 2018, DPS, 50, 502.02, Pluto’s atmosphere after New Horizons: results from stellar occultations in 2017 and 2018

      Stellar occultations have been employed for the last thirty years to characterize Pluto’s atmosphere. The atmospheric pressure has increased between 1988 and 2015 (e.g. Bosh et al. 2013; Sicardy et al. 2015). Evolution in the shape of the occultation light curves over time has revealed waves in the upper atmosphere (e.g. Hubbard et al. 2009; Person et al. 2008) and suggests a thermal gradient, possibly combined with extinction-generating events, in the lower atmosphere (e.g. Elliot et al. 2007; Olkin et al. 2014). Occultation data have been combined with volatile transport models (Hansen & Paige 1996; Young 2013) to predict Pluto’s atmospheric properties during and beyond the 2015 flyby of NASA’s New Horizons spacecraft. Some models indicate that Pluto’s atmosphere should collapse over a relatively short timescale; however, recent results are consistent with models that have no atmospheric collapse, stemming from high thermal inertia and a permanent, northern cap (e.g. Olkin et al. 2015). Here, we report results from two stellar occultations by Pluto, in 2017 and 2018. A single chord was observed at each epoch. The first occultation was on 2017 August 07, with a shadow path over the Pacific Ocean. The star had visible magnitude of 14.5, with relative velocity of 20.8 km s-1. Observations were taken from NASA’s 3-m Infrared Telescope Facility in Hawaii. The dataset includes 2.5-second, visible-wavelength images from MORIS (MIT Optical Rapid Imaging System), and low-resolution, near-infrared spectra from SpeX with 3-second integration time. The second occultation was on 2018 April 09, with a shadow path over the western United States. The star had visible magnitude of 17.9, with relative velocity of 6.4 km s-1. Visible-wavelength images, at 10 Hz, were taken from the 4.3-m Discovery Channel Telescope in Arizona with a POETS (Portable Occultation Eclipse and Transit System). The 2018 observation was central, with half-light to half-light chord length of 2280 km. The 2017 observation had half-light to half-light chord length of 1650 km. The shape of both light curves is indicative of a body with an atmosphere. We present results for atmospheric model fits to these light curves and place them in context.

    57. Mommert, Michael, Trilling, David, Knight, Matthew M., et al., 2018, DPS, 50, 505.05, Systematic Characterization and Monitoring of Potentially Active Asteroids: The Case of Don Quixote

      Over the previous decades, activity has been observed in about 20 Solar System small bodies that were until then known as asteroids. Activation mechanisms have been proposed for these objects, including the sublimation of volatiles, rotational instability, and recent impacts; all these mechanisms provide strong constraints on the physical properties and evolution of these objects. The identification of more active asteroids will improve our understanding of the processes triggering activity as well the nature of asteroids in general. We present first results from our “Systematic Characterization and Monitoring of Potentially Active Asteroids” program, which obtains BVRI colors and performs V-band photometric monitoring of a sample of 103 dormant comet candidates and 10 near-Sun asteroids. The goal of this program is to find activity in and provide a spectrophotometric taxonomic classification for our targets in order to place limits on the volatile contents of these potentially active populations and improve our understanding of their evolution. We present the case of near-Earth asteroid (3552) Don Quixote in which we discovered activity in multiple wavelength regimes. In October 2017 we observed activity using Spitzer Space Telescope observations that agrees with findings by Mommert et al. (2014, ApJ 781), suggesting continuous activity from the sublimation of CO or CO2. While close in time optical observations did not reveal any dust activity, observations in March 2018 revealed for the first time episodic dust activity in this object (Mommert et al., 2018, CBET 4502). Follow-up observations in June 2018 with the 30m IRAM sub-millimeter telescope show a lack of emission from the CO(2-1) line and hence suggest that activity in this object is most likely triggered by the sublimation of CO2. Our observations suggest that Don Quixote is most likely a weakly active CO2-rich comet. The finding of faint activity in Don Quixote underscores the necessity of a systematic monitoring campaign to find activity. This program is based upon work supported by NASA under Grant No. NNX17AG88G.

    58. Protopapa, Silvia, Cruikshank, Dale, Dalle Ore, Cristina, et al., 2018, DPS, 50, 506.01, Are multiple coloring agents present across the surface of Pluto and its large satellite Charon?

      The New Horizons flyby of Pluto has revealed a complex world rich in a variety of landforms, colors, and compositions (Stern et al., 2015). The color imaging of Pluto’s encounter hemisphere obtained by the Multi-spectral Visible Imaging Camera (MVIC) component of the Ralph instrument (Reuter et al., 2008) displays a latitude-dependent distribution of colors ranging from dark red to yellow (Olkin et al., 2017). Laboratory experiments suggest that Pluto’s coloration may be due to the presence on the surface of tholin-like materials, which are organic compounds produced through photolysis and radiolysis of native material found on the surface and atmosphere of the dwarf planet. Tholins produced in the laboratory exhibit a wide range of colors (Materese et al., 2015; Cruikshank et al., 2016). Pluto’s largest moon Charon displays distinctly reddish tholin coloration around its north pole (Grundy et al. 2016a). Grundy et al. 2016b put forth the idea that this might be the result of gas from Pluto transiently cold-trapped and processed at Charon’s winter pole. The true contribution of the coloring agents cannot be assessed without consideration of the visible spectral domain as in Protopapa et al. (2017). This is due to the fact that the diagnostic spectral signature of tholins is a strong red slope in the visible part of the spectrum. We present a characterization of the tholin material across the surface of Pluto and its moon Charon through radiative transfer modeling of the New Horizons Ralph/LEISA (Linear Etalon Imaging Spectral Array, infrared spectrometer) and MVIC data. We compare our findings with optical constants of Pluto tholin we compute from laboratory reflectance measurements by Materese et al. (2015). The ultimate goal is understanding the variety of tholins on the surface of Pluto and Charon, and the processes responsible for their formation and distribution.

    59. Schmitt, Bernard, Gabasova, Leila, Philippe, Sylvain, et al., 2018, DPS, 50, 506.02, Evidence of local CH4 stratification on Pluto from New Horisons LEISA data and a complete N2 ice map.

      The diurnal, seasonal and astronomical cycles on Pluto trigger sublimation-transport-condensation cycles of the volatile ices (N2, CH4, CO) with different amplitudes and time constants at the surface. The qualitative distribution of the two major volatile ice phases identified on the surface of Pluto, N2-rich:CH4:CO ice and CH4-rich ice, has been mapped by Schmitt et al. (2017) and the spatial transitions between the predominant zone of these phases have been highlighted. The first quantitative composition map has been derived by Protopapa et al. (2017). A surprising observation, but not discussed in Schmitt et al. paper, was that the CH4 qualitative abundance maps obtained from different CH4 bands display relatively different spatial distributions, but with regular evolutions at a given location from the weakest to the strongest CH4 bands. In this talk we demonstrate that these band depth changes reflect a stratification of CH4, either in the CH4 concentration in N2-rich ice and/or in the relative abundance between the N2-rich:CH4:CO and CH4-rich ices, depending on the area. For this we use in addition our ‘CH4 state index’ based on the spectral position of the CH4 bands and a new N2 ice distribution map including the area where the N2 ice band is too weak to be observed directly. The stratification of CH4 is shown to result from the differential sublimation between N2 and CH4 which tends to concentrate CH4 in N2 ice grains and, according to the phase diagram, produces a CH4-rich phase that accumulates on the surface. We will show that several different configurations appear to exist at the surface of Pluto according to the latitude and the altitude, and that they may be the witness of different stages in the sublimation-condensation cycles or of different timescales. The occurence, the CH4 concentration and the depth of these stratified terrains can be correlated with the nitrogen sublimation fluxes obtained by volatile transport models (Bertrand et al. 2018).

    60. Singer, Kelsi N., Schenk, Paul M., McKinnon, William B., et al., 2018, DPS, 50, 506.04, Cryovolcanic Constructs on Pluto

      Pluto’s surface has experienced considerable endogenic and exogenic resurfacing [1]. The terrains on Pluto represent a variety of ages, from seemingly ancient to surprisingly young. Some of the very young terrains are the result of the volatile ices on Pluto’s surface (e.g., the convecting nitrogen-ice-rich plains of Sputnik Planitia). But Pluto also has several examples of more recent activity (terrains with few-to-no superimposed craters), that appear to be primarily made out of non-volatile water ice. The most prominent examples of potential cryovolcanism are two enormous topographic constructs with wide, deep central depressions [2]. The informally named Wright Mons stands 4 km high and the main mound spans 150 km. The informally named Piccard Mons is 7 km high and 225 km wide. The central depressions are dissimilar from a typical terrestrial shield volcano in that they are much wider (e.g., the Wright Mons central depression is 40-45 km wide, taking up 1/3rd of the total feature width) and deeper (the floors extend down to or below the level of the surrounding terrain). The central depression of Wright does not exhibit wall terraces that are typical indicators of collapse in terrestrial volcanoes. Instead, the central depression walls and floor have a large-scale hummocky texture similar to that the exterior of Wright, with individual hummocks on average 8-10 km across. A few terrains around Wright may be older, more fractured or cratered, examples of the terrain on the flanks. Thus there is some evidence for multiple episodes of terrain emplacement, but distinct flow fronts are not obvious. Each potential example of cryovolcanism found in the outer solar system is unique, and Pluto’s features expand the information we have to understand this enigmatic process. We will present image, topographic, and composition data for Wright and Piccard along with geologic mapping results. We will discuss potential formation mechanisms in light of available empirical and model constraints. [1] Moore, J.M. et al. (2016) Science 351, 1284-1293. doi:10.1126/science.aad7055 [2] Singer, K.N. et al. (2016) Planetary Mappers Meeting 1920, #7017,

    61. Cruikshank, Dale, Umurhan, Orkan M., Moore, Jeffrey M., et al., 2018, DPS, 50, 506.05, Recent cryovolcanism on Pluto

      The Virgil Fossae region on Pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. Situated in the fossae channels and in the surrounding terrain are exposures of H2O ice in which there is entrained opaque red-colored matter of unknown composition. The H2O ice is also seen to carry spectral signatures at 1.65 and 2.2 m of NH3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. High-resolution images from the New Horizons spacecraft provide a base map upon which a map of H2O ice obtained at lower spatial resolution with the New Horizons LEISA mapping spectrometer is superimposed. Analysis of the LEISA map demonstrates that in areas where there is a minimal amount of CH4 ice, the exposed H2O ice exhibits the maximum NH3 signature, localized in one end of the main channel of the fossae complex. The NH3-H2O is distributed in patterns suggesting flow of cryolava along the fossa floor and ejection of cryoclastics in ballistic trajectories well beyond the fossa channels. Muted topography (craters and fossae) may represent mantling by cryoclastic deposits that also bear the NH3 signature in H2O ice and the red color. We present a model of the flow of a cryogenic magma emerging from sources in Virgil Fossa indicating that the extent of the flow can be several km. The appearance of the frozen magma over the full length (>200 km) of the main channel in the Virgil Fossae complex and extending through the north rim of Elliot crater and varying in elevation over a range of 2km, suggests that it emerged from multiple sources, probably along the length of the strike direction of the normal fault(s) defining the graben. The source or sources of the ammoniated H2O are one or more subsurface reservoirs that may or may not connect to the putative global ocean postulated for Pluto’s interior. In a separate study in which we take the red-colored matter to be a complex organic tholin, we show that the chemistry in such a mixture is likely to produce amino acids and many nucleobases, including the five used in terrestrial biological systems (Cruikshank et al., submitted).

    62. Pendleton, Yvonne, Cruikshank, Dale P., Materese, Christopher K., et al., 2018, DPS, 50, 506.06, Prebiotic Chemistry of Pluto

      The variety of surface colors on Pluto results from the synthesis of complex organics in the atmosphere and on the surface. There is new evidence that tholins and other organics from a subsurface aquifer were carried to the surface by ammoniated liquid water to form deposits of unique color and chemical properties. Pluto’s Virgil Fossae exhibits an exposure of H2O-NH3 ice and a uniquely red color that may contain tholins produced in such a subsurface environment. Geological evidence in images from the NASA New Horizons spacecraft supports the view that ammoniated water carrying a uniquely colored red tholin-like material emanated from one or more sources from a part of Virgil Fossae. Emission from these sources appears to have progressed along parts of the fossae before freezing upon contact with the vacuum and cold solid surface. In addition, material may have traveled on ballistic trajectories for >100 km. Pluto’s organic tholins and ices, when viewed in the context of laboratory syntheses of complex molecules of prebiological importance, lead to a deeper understanding of the plausible chemistry that may be occurring on icy bodies in the outer Solar System. Compounds such as nucleobases, including those of biological significance, may have formed on the surface from UV irradiation of nitrogen-rich tholins ejected with warm subsurface water in cryovolcanic events. Alternatively, these complex molecules may have formed in subsurface fluid that emerged in and around Virgil Fossae. Laboratory irradiation of ice mixtures reflecting Pluto’s composition have produced strongly colored complex organics including possible aromatic molecules. Recent experiments with pyrimidine and purines frozen in H2O-NH3 ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al. 2017 Astrobiology 17, 761). It is also possible that some of the oldest organics on Pluto derive from the material inherited prior to the formation of the planet. Thus, geological processes recently revealing buried tholins on Pluto may be unveiling organics of either early Solar System legacy or interior processes within Pluto.

    63. Beyer, Ross A., Spencer, John, McKinnon, William B., et al., 2018, DPS, 50, 506.08, The Nature and Origin of Charon’s Smooth Plains

      Charon displays extensive plains that cover the equatorial area and south to the terminator on the sub-Pluto hemisphere observed by New Horizons. We hypothesize that these plains are a result of Charon’s global extension and early subsurface ocean yielding a large cryoflow composed of mantle material that completely resurfaced this area leaving the plains and other features we that we observe today. The resurfacing of the plains is not the result of a singular eruptive or effusive center from which cryoflows spread out across the more than 400,000 square kilometers of Vulcan Planitia. We hypothesize that the resurfacing was the result of ammonia-rich cryo-material from the last stages of ocean freezing either buoyantly rising and flowing out on to the pre-Vulcan lowlands, or as a result of more severe disruption that resulted in crustal blocks foundering, and the buoyant, viscous cryo-material under those blocks rising up and spreading out. Under these hypotheses, there would be no singular effusive center, but the sources of the plains material would be in many places across the region, and as the material flowed across the pre-Vulcan lowlands or enveloped the foundering blocks, it would create an extensive plains unit. Geological observations, modeling of possible flow rheology, and an analysis of rille orientations support the conclusion that the extensive plains on Charon are a vast cryoflow emplaced unit, similar to those seen on Ariel and Miranda and possibly other icy worlds in the solar system. Charon fits into the panoply of icy satellites which display evidence for the movement of cryoflows and resurfacing.

    64. Devogele, Maxime, Moskovitz, Nicholas, Thomas, Cristina, et al., 2018, DPS, 50, 508.01, The Mission Accessible Near-Earth Objects Survey (MANOS): First Results from the Visible Spectroscopic Survey

      The Mission Accessible Near-Earth Objects Survey (MANOS) started in August 2013 and is a multi-year survey supported by the National Optical Astronomy Observatory (NOAO) and Lowell Observatory, and funded by the NASA NEOO (Near-Earth Object Observations) program. It aims at characterizing sub-km, low delta-v (typically <7 km/s), Near-Earth Objects (NEOs) by collecting astrometry, lightcurve photometry, and reflectance spectra. The physical properties of NEOs are known to be size dependent. However, some open questions remain such as whether these objects are rubble piles or monolithic bodies, or whether they are covered by regolith. A compositional discrepancy between large NEOs (>1km) and meteorite collection is also observed (Stuart et al., 2004; Vernazza et al., 2008). Laboratory measurements have also shown that grain size can cause variation in spectral slope or absorption band depth (Cooper et al., 1999;Cloutis et al., 2013). The smallest NEOs can have rotation periods under 1 minute (Thirouin et al., 2016), while asteroids larger than 150m do not rotate faster than 2.2 hours. This supports the hypothesis of small asteroids being monolithic and structurally different than larger ones. We report here the first results from MANOS on the visible spectroscopic properties. We have analysed roughly 300 asteroids with a mean size around 80 meters (H 25), and with some targets as small as few meters (H=30). This represents one of the largest comprehensive spectroscopic datasets for NEOs < 100 meters. We will discuss the compositional properties of this sample relative to other NEOs (km and sub-km) (Perna et al., 2018; Thomas et al., 2011, and DeMeo et al., 2008), and to Main Belt asteroids (Bus et al., 2002 and DeMeo et al., 2009) and compare them with the meteorite population. All spectroscopic data have been reduced using a new python based pipeline for asteroid spectroscopic reduction developed to be easily portable to any visible spectrograph. The use of the same pipeline for all data obtained by this survey allows us to obtain a consistent data set of spectral properties of small NEOs. This work is supported by the NASA NEOO program, grant number NNX17AH06G.

    65. Gustafsson, Annika, Moskovitz, Nicholas, Knight, Matthew M., et al., 2018, DPS, 50, 508.10, Asteroid 3200 (Phaethon): Simultaneous Visible and Near-Infrared Observations

      The Near-Infrared High Throughput Spectrograph (NIHTS) is a low resolution spectrograph that operates from 0.86-2.4 microns on Lowell Observatory’s 4.3-m Discovery Channel Telescope (DCT) in Happy Jack, AZ. Using a dichroic mirror which transmits visible wavelengths and reflects the near-infrared, we have the opportunity to operate the Large Monolithic Imager, an independent visible wavelength CCD, simultaneously with NIHTS. In combination with the premier non-sidereal tracking capabilities of the DCT, NIHTS is an extremely efficient instrument and is expected to make significant contributions to several areas of astronomy. We present an overview of the first NIHTS spectroscopic results which also employed simultaneous optical LMI imaging of asteroid 3200 (Phaethon). The unique active asteroid Phaethon, dynamically related to the parent body of the Geminid meteor shower (Whipple 1983), made a close approach to Earth in December 2017. The target passed within 0.07 AU and provided a rare opportunity to search for rotationally resolved compositional differences across the surface of the 5 km body. Phaethon is a B-type NEO (Bus and Binzel 2002), dynamically linked to Main-belt asteroid Pallas (2) (deLeon et al. 2010). Phaethon’s dayside temperatures are 1000 K from solar radiation heating near perihelion at 0.14 AU (Jewitt 2010). As a result, the activity on the surface is unlikely a result of near-surface ice sublimation, but instead, a combination of thermal fracture, dehydration cracking, radiation pressure sweeping, and electrostatic effects (Jewitt 2010). Due to the mass loss that the object has undergone, it is hypothesized that the surface would show evidence of the effects of solar radiation through spectral reddening. We observed Phaethon before and after closest approach between December 14, 2017 and December 18, 2017 obtaining both near-infrared spectra with NIHTS and visible lightcurves with LMI in SDSS r’ and a narrow-band Blue Continuum comet filter (4420-4500 A) centered at 4453 A. We report our time-resolved spectroscopic findings of this unique object. This work is supported in part by the NASA NEOO program, grant number NNX17AH06G.

    66. Holler, Bryan J., Grundy, William, Buie, Marc W., et al., 2018, DPS, 50, 509.03, Breaking the degeneracy of Eris’ pole orientation

      The most massive trans-Neptunian object, (136199) Eris, has one known satellite, Dysnomia. By observing changes in Dysnomia’s orbit projected on the sky over multiple different epochs, we were able to break the mirror degeneracy and determine the pole orientation of Eris. Images of the Eris/Dysnomia system were obtained with WFC3/HST in January and February 2018 (program 15171). These images were taken through the F606W filter and visits were scheduled to capture Dysnomia at different orbital phases. We also folded in data from ACS/HRC/HST and NIRC2/Keck programs from 2005/2006 (Brown and Schaller, 2007) and WFC3/HST program 13668 from 2015. The 2005/2006 data were considered “Epoch 1” and the 2015 and 2018 data were combined into “Epoch 2.” PSF-fitting produced relative astrometry of Dysnomia with respect to Eris and was used to fit Keplerian orbits to each epoch. Comparison of the orbit fits from these different epochs enabled the determination of Eris’ rotation pole orientation, assuming Dysnomia orbits in Eris’ equatorial plane. We report that Eris’ obliquity is 78, the sub-solar latitude in early 2018 was 42, and the next period of mutual events will occur in 2239, all in agreement with Orbit 1 from Brown and Schaller (2007). With this viewing geometry, approximately 30% of the visible hemisphere of Eris is in constant sunlight. Assuming a peak-to-valley amplitude of 0.10 mag (Roe et al., 2008) due entirely to albedo variations, the hemispheres representing the maximum and minimum in the light curve have a 10% difference in albedo. Eris’ high visible geometric albedo (0.96; Sicardy et al., 2011) and this small albedo difference together imply that Eris’ surface lacks large-scale, low-albedo features like Cthulhu Macula on Pluto.

    67. Agnello, A., Lin, H., Kuropatkin, N., et al., 2018, MNRAS, 479, 4345, DES meets Gaia: discovery of strongly lensed quasars from a multiplet search

      We report the discovery, spectroscopic confirmation, and first lens models of the first, strongly lensed quasars from a combined search in WISE and Gaia-DR1 over the DES footprint. Their Einstein radii span a range between 2.0 arcsec and 0.4 arcsec. Two of these (WGD2038-4008, RA = 20:38:02.65, Dec. = -40:08:14.64; WGD2021-4115, RA = 20:21:39.45, Dec. = -41:15:57.11) also have confirmed deflector redshifts. The four-image lens WGD2038-4008, with source and deflector redshifts s = 0.777 0.001 and zl = 0.230 0.002, respectively, has a deflector with radius Reff 3.4 arcsec, stellar mass log (M_{}/M_{})=11.64^{+0.20}_{-0.43}, and extended isophotal shape variation. Simple lens models yield Einstein radii RE = (1.30 0.04) arcsec, axis ratio q = 0.75 0.1 (compatible with that of the starlight) and considerable shear-ellipticity degeneracies. The two-image lens WGD2021-4115 has zs = 1.390 0.001 and zl = 0.335 0.002, and Einstein radius RE = (1.1 0.1) arcsec, but higher-resolution imaging is needed to accurately separate the deflector and faint quasar image. Analogous lens model degeneracies hold for the other six lenses (J0146-1133, J0150-4041, J0235-2433, J0245-0556, J0259-2338, and J0508-2748) shown in this paper.

    68. Troxel, M. A., Krause, E., Chang, C., et al., 2018, MNRAS, 479, 4998, Survey geometry and the internal consistency of recent cosmic shear measurements

      We explore the impact of an update to the typical approximation for the shape noise term in the analytic covariance matrix for cosmic shear experiments that assumes the absence of survey boundary and mask effects. We present an exact expression for the number of galaxy pairs in this term based on the survey mask, which leads to more than a factor of three increase in the shape noise on the largest measured scales for the Kilo-Degree Survey (KiDS-450) real-space cosmic shear data. We compare the result of this analytic expression to several alternative methods for measuring the shape noise from the data and find excellent agreement. This update to the covariance resolves any internal model tension evidenced by the previously large cosmological best-fitting 2 for the KiDS-450 cosmic shear data. The best-fitting 2 is reduced from 161 to 121 for 118 degrees of freedom. We also apply a correction to how the multiplicative shear calibration uncertainty is included in the covariance. This change shifts the inferred amplitude of the correlation function to higher values. We find that this improves agreement of the KiDS-450 cosmic shear results with Dark Energy Survey Year 1 and Planck results.

    69. Mommert, Michael, McNeill, Andrew, Trilling, David E., et al., 2018, AJ, 156, 139, The Main Belt Asteroid Shape Distribution from Gaia Data Release 2

      Gaia Data Release 2 includes observational data for 14099 pre-selected asteroids. From the sparsely sampled G-band photometry, we derive lower-limit light curve amplitudes for 11665 main belt asteroids (MBA) in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a > b and b = c, we find an average b/a = 0.80 0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semimajor axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that MBAs greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of MBAs as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.

    70. Stern, S. Alan, Grundy, William M., McKinnon, William B., et al., 2018, ARA&A, 56, 357, The Pluto System After New Horizons

      The New Horizons (NH) flyby of the Pluto-Charon binary planet and its system of four small surrounding satellites in mid-2015 revolutionized our knowledge of this distant planet and its moons. Beyond providing rich geo-logical, compositional, and atmospheric data sets, NH demonstrated that Pluto has been surprisingly geologically and climatologically active throughout the past 4+ Gyr and that the planet exhibits a remarkably complex range of atmospheric phenomenology and geological expressions that rival Mars in their richness. In contrast, Pluto’s large, planet-sized satellite Charon, though also geologically complex, has no detected active surface volatiles, has no detectable atmosphere, has much more muted colors, has lower albedo, and exhibits only ancient terrains. Pluto’s system of four small satellites orbiting outside of Charon is itself dynamically complex and geologically interesting. Here, we review both what was known about the Pluto system before NH and what it has taught us about the Pluto system specifically and, by inference, other small planets in the Kuiper Belt. We go on to examine the natural next steps in Kuiper Belt exploration.

    71. Chang, C., Baxter, E., Jain, B., et al., 2018, ApJ, 864, 83, The Splashback Feature around DES Galaxy Clusters: Galaxy Density and Weak Lensing Profiles

      Splashback refers to the process of matter that is accreting onto a dark matter halo reaching its first orbital apocenter and turning around in its orbit. The clustercentric radius at which this process occurs, r sp, defines a halo boundary that is connected to the dynamics of the cluster. A rapid decline in the halo profile is expected near r sp. We measure the galaxy number density and weak lensing mass profiles around REDMAPPER galaxy clusters in the first-year Dark Energy Survey (DES) data. For a cluster sample with mean M 200m mass 2.5 1014 M , we find strong evidence of a splashback-like steepening of the galaxy density profile and measure r sp = 1.13 0.07 h -1 Mpc, consistent with the earlier Sloan Digital Sky Survey measurements of More et al. and Baxter et al. Moreover, our weak lensing measurement demonstrates for the first time the existence of a splashback-like steepening of the matter profile of galaxy clusters. We measure r sp = 1.34 0.21 h -1 Mpc from the weak lensing data, in good agreement with our galaxy density measurements. For different cluster and galaxy samples, we find that, consistent with CDM simulations, r sp scales with R 200m and does not evolve with redshift over the redshift range of 0.3-0.6. We also find that potential systematic effects associated with the REDMAPPER algorithm may impact the location of r sp. We discuss the progress needed to understand the systematic uncertainties and fully exploit forthcoming data from DES and future surveys, emphasizing the importance of more realistic mock catalogs and independent cluster samples.

    72. Devogele, Maxime, Moskovitz, Nicholas, Thomas, Cristina, et al., 2018, EPSC, EPSC2018-572, The Mission Accessible Near-Earth Objects Survey (MANOS): first results from the visible spectroscopic survey

      The Mission Accessible Near-Earth Objects Survey (MANOS) aims at characterizing sub-km, low delta- v, newly discovered Near-Earth Objects (NEOs). This survey, started in August 2013, is collecting astrometry, lightcurve photometry, and reflectance spectra of this under-studied portion of the NEO population. The MANOS program is using 1 to 8 meter tele- scopes located around the world. Here we present the first results of the visible reflectance spectroscopy survey obtained with the 8.1-meter Gemini North and South telescopes, the 4.3-meter Discovery Channel Telescope and the 4.1-meter SOAR telescope.

    73. Hromakina, Tetiana, Belskaya, Irina, Krugly, Yurii, et al., 2018, EPSC, EPSC2018-692, An extensive photometric study of the dwarf planet Makemake

      We will present a photometric study of the dwarf planet Makemake based on new observational data obtained between 2006 and 2017 using 0.7 to 3.6-m telescopes around the world. Based on this extensive dataset we derive a high precision rotational period estimate. The resulting lightcurve has a small peak-to-peak amplitude variability, that implies an almost spherical shape or an elongated object in a pole-on orientation. Multi-colour observations allowed us to measure surface colours of Makemake. The magnitude phase dependence slope is quite low and is similar to other bodies with methane ice-rich surfaces. Combining our and literature data we tested Makemake for the existence of long-term brightness variations, and searched for the signs of a satellite.

    74. Oszkiewicz, Dagmara, Kryszczynska, Agnieszka, Kankiewicz, Pawe, et al., 2018, EPSC, EPSC2018-846, The unusual V-type asteroid (2579) Spartacus

      Asteroid (2579) Spartacus is a small V-type object located in the inner main belt (the main delivery region for meteorites). It shows spectral characteristics different from typical values for Vestoids, which may indicate origin deeper within Vesta then other V-types or a different parent body. We determine physical and dynamical properties of (2579) Spartacus and discuss its possible origin scenarios.

    75. Figura, Joe, Haughwout, Christian, Cahoy, Kerri, et al., 2018, JSSat, 7, 719, Initial Demonstration of an Uplink LED Beacon to a Low Earth Orbiting CubeSat
    76. Avila, S., Crocce, M., Ross, A. J., et al., 2018, MNRAS, 479, 94, Dark Energy Survey Year-1 results: galaxy mock catalogues for BAO

      Mock catalogues are a crucial tool in the analysis of galaxy surveys data, both for the accurate computation of covariance matrices, and for the optimization of analysis methodology and validation of data sets. In this paper, we present a set of 1800 galaxy mock catalogues designed to match the Dark Energy Survey Year-1 BAO sample (Crocce et al. 2017) in abundance, observational volume, redshift distribution and uncertainty, and redshift-dependent clustering. The simulated samples were built upon HALOGEN (Avila et al. 2015) halo catalogues, based on a 2LPT density field with an empirical halo bias. For each of them, a light-cone is constructed by the superposition of snapshots in the redshift range 0.45 < z < 1.4. Uncertainties introduced by so-called photometric redshifts estimators were modelled with a double-skewed-Gaussian curve fitted to the data. We populate haloes with galaxies by introducing a hybrid halo occupation distribution-halo abundance matching model with two free parameters. These are adjusted to achieve a galaxy bias evolution b(zph) that matches the data at the 1 level in the range 0.6 < zph < 1.0. We further analyse the galaxy mock catalogues and compare their clustering to the data using the angular correlation function w(), the comoving transverse separation clustering < 0.8(s) and the angular power spectrum C, finding them in agreement. This is the first large set of three-dimensional {RA,Dec.,z} galaxy mock catalogues able to simultaneously accurately reproduce the photometric redshift uncertainties and the galaxy clustering.

    77. Jeffrey, N., Abdalla, F. B., Lahav, O., et al., 2018, MNRAS, 479, 2871, Improving weak lensing mass map reconstructions using Gaussian and sparsity priors: application to DES SV

      Mapping the underlying density field, including non-visible dark matter, using weak gravitational lensing measurements is now a standard tool in cosmology. Due to its importance to the science results of current and upcoming surveys, the quality of the convergence reconstruction methods should be well understood. We compare three methods: Kaiser-Squires (KS), Wiener filter, and GLIMPSE. Kaiser-Squires is a direct inversion, not accounting for survey masks or noise. The Wiener filter is well-motivated for Gaussian density fields in a Bayesian framework. GLIMPSE uses sparsity, aiming to reconstruct non-linearities in the density field. We compare these methods with several tests using public Dark Energy Survey (DES) Science Verification (SV) data and realistic DES simulations. The Wiener filter and GLIMPSE offer substantial improvements over smoothed Kaiser-Squires with a range of metrics. Both the Wiener filter and GLIMPSE convergence reconstructions show a 12 per cent improvement in Pearson correlation with the underlying truth from simulations. To compare the mapping methods’ abilities to find mass peaks, we measure the difference between peak counts from simulated CDM shear catalogues and catalogues with no mass fluctuations (a standard data vector when inferring cosmology from peak statistics); the maximum signal-to-noise of these peak statistics is increased by a factor of 3.5 for the Wiener filter and 9 for GLIMPSE. With simulations, we measure the reconstruction of the harmonic phases; the phase residuals’ concentration is improved 17 per cent by GLIMPSE and 18 per cent by the Wiener filter. The correlationbetween reconstructions from data and foreground redMaPPer clusters is increased 18 per cent by the Wiener filter and 32 per cent by GLIMPSE.

    78. Kammer, Joshua A., Becker, Tracy M., Retherford, Kurt D., et al., 2018, AJ, 156, 72, Probing the Hill Sphere of (486958) 2014 MU69: HST FGS Observations during the 2017 July 17 Stellar Occultation

      We observed the 2017 July 17 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU69, the close flyby target of the extended New Horizons mission. Rather than capture a solid body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU69 at distances ranging from 20000 km to 75000 km from the main body.

    79. Becker, J. C., Khain, T., Hamilton, S. J., et al., 2018, AJ, 156, 81, Discovery and Dynamical Analysis of an Extreme Trans-Neptunian Object with a High Orbital Inclination

      We report the discovery and dynamical analysis of 2015 BP519, an extreme trans-Neptunian object (TNO) detected by the Dark Energy Survey at a heliocentric distance of 55 au, perihelion of 36 au, and absolute magnitude H r = 4.3. The current orbit, determined from a 1110 day observational arc, has a semimajor axis a 450 au, eccentricity e 0.92, and inclination i 54. With these orbital elements, 2015 BP519 is the most extreme TNO discovered to date, as quantified by the reduced Kozai action, { }0={(1-{e}2)}1/2\cos i, which is a conserved quantity at fixed semimajor axis a for axisymmetric perturbations. We discuss the orbital stability and evolution of this object and find that, under the influence of the four known giant planets, 2015 BP519 displays rich dynamical behavior, including rapid diffusion in semimajor axis and more constrained variations in eccentricity and inclination. We also consider the long-term orbital stability and evolutionary behavior within the context of the Planet Nine hypothesis and find that 2015 BP519 adds to the circumstantial evidence for the existence of this proposed new member of the solar system, as it would represent the first member of the population of high-i, -shepherded TNOs.

    80. Shipp, N., Drlica-Wagner, A., Balbinot, E., et al., 2018, ApJ, 862, 114, Stellar Streams Discovered in the Dark Energy Survey

      We perform a search for stellar streams around the Milky Way using the first 3 yr of multiband optical imaging data from the Dark Energy Survey (DES). We use DES data covering 5000 deg2 to a depth of g > 23.5 with a relative photometric calibration uncertainty of <1%. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of 50 kpc. We search for stellar streams using a matched filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of 11 new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extratidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, and the large- and small-scale distribution of dark matter around the Milky Way.

    81. Mudd, D., Martini, P., Zu, Y., et al., 2018, ApJ, 862, 123, Quasar Accretion Disk Sizes from Continuum Reverberation Mapping from the Dark Energy Survey

      We present accretion disk size measurements for 15 luminous quasars at 0.7 z 1.9 derived from griz light curves from the Dark Energy Survey. We measure the disk sizes with continuum reverberation mapping using two methods, both of which are derived from the expectation that accretion disks have a radial temperature gradient and the continuum emission at a given radius is well described by a single blackbody. In the first method we measure the relative lags between the multiband light curves, which provides the relative time lag between shorter and longer wavelength variations. From this, we are only able to constrain upper limits on disk sizes, as many are consistent with no lag the 2 level. The second method fits the model parameters for the canonical thin disk directly rather than solving for the individual time lags between the light curves. Our measurements demonstrate good agreement with the sizes predicted by this model for accretion rates between 0.3 and 1 times the Eddington rate. Given our large uncertainties, our measurements are also consistent with disk size measurements from gravitational microlensing studies of strongly lensed quasars, as well as other photometric reverberation mapping results, that find disk sizes that are a factor of a few (3) larger than predictions.

    82. Neugent, Kathryn F., Massey, Philip, Morrell, Nidia, 2018, ApJ, 863, 181, A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds. IV. A Final Census

      We summarize the results of our 4 yr survey searching for Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud. Over the course of this survey we have discovered 15 new WR stars and 12 Of-type stars. In this last year we discovered two rare Of-type stars: an O6.5f?p and an O6nfp, in addition to the two new Of?p stars discovered in our first year and the three Onfp stars discovered in our second and third years. However, even more exciting was our discovery of a new type of WR star, ones we are calling WN3/O3s owing to their spectroscopic signatures. We describe the completeness limits of our survey and demonstrate that we are sensitive to weak-lined WRs several magnitudes fainter than any we have discovered, arguing that there is not a population of fainter WRs waiting to be discovered. We discuss the nature of the WN3/O3s, summarizing the results of our extensive spectroscopy and modeling. We also examine the important claim made by others that the WN3/O3s are isolated compared to other massive stars. We find that if we use a more complete sample of reference massive stars, the WN3/O3s show the same spatial distribution as other early WNs, consistent with a common origin. Finally, we use this opportunity to present the Fifth Catalog of LMC Wolf-Rayet Stars, which includes revised coordinates and updated spectral types for all 154 known LMC WRs.


      This paper includes data gathered with the 1 m Swope and 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile.

    83. Moore, Jeffrey M., McKinnon, William B., Cruikshank, Dale P., et al., 2018, GeoRL, 45, 8111, Great Expectations: Plans and Predictions for New Horizons Encounter With Kuiper Belt Object 2014 MU69 (“Ultima Thule”)

      The New Horizons encounter with the cold classical Kuiper Belt object 2014 MU69 (informally named “Ultima Thule,” hereafter Ultima) on 1 January 2019 will be the first time a spacecraft has ever closely observed one of the free-orbiting small denizens of the Kuiper Belt. Related to but not thought to have formed in the same region of the solar system as the comets that been explored so far, it will also be the most distant, and most primitive body yet visited by spacecraft. In this letter we begin with a brief overview of cold classical Kuiper Belt objects, of which Ultima is a prime example. We give a short preview of our encounter plans. We note what is currently known about Ultima from Earth-based observations. We then review our expectations and capabilities to evaluate Ultima’s composition, surface geology, structure, near space environment, small moons, rings, and the search for activity.

    84. Luque, E., Santiago, B., Pieres, A., et al., 2018, MNRAS, 478, 2006, Deep SOAR follow-up photometry of two Milky Way outer-halo companions discovered with Dark Energy Survey

      We report the discovery of a new star cluster, DES 3, in the constellation of Indus, and deeper observations of the previously identified satellite DES J0222.7-5217 (Eridanus III). DES 3 was detected as a stellar overdensity in first-year Dark Energy Survey data, and confirmed with deeper photometry from the 4.1-m Southern Astrophysical Research (SOAR) telescope. The new system was detected with a relatively high significance and appears in the DES images as a compact concentration of faint blue point sources. We determine that DES 3 is located at a heliocentric distance of 76.2 kpc and it is dominated by an old (9.8 Gyr) and metal-poor ([Fe/H] -1.84) population. While the age and metallicity values of DES 3 are comparable to typical globular clusters (objects with a high stellar density, stellar mass of 105 M and luminosity MV -7.3), its half-light radius (rh 6.87 pc) and luminosity (MV -1.7) are more indicative of faint star cluster. Based on the angular size, DES 3, with a value of rh 0{^’.}31, is among the smallest faint star clusters known to date. Furthermore, using deeper imaging of DES J0222.7-5217 taken with the SOAR telescope, we update structural parameters and perform the first isochrone modelling. Our analysis yields the first age (12.6 Gyr) and metallicity ([Fe/H] -2.01) estimates for this object. The half-light radius (rh 11.24 pc) and luminosity (MV -2.4) of DES J0222.7-5217 suggest that it is likely a faint star cluster. The discovery of DES 3 indicates that the census of stellar systems in the Milky Way is still far from complete, and demonstrates the power of modern wide-field imaging surveys to improve our knowledge of the Galaxy’s satellite population.

    85. Chiu, I., Mohr, J. J., McDonald, M., et al., 2018, MNRAS, 478, 3072, Baryon content in a sample of 91 galaxy clusters selected by the South Pole Telescope at 0.2 <z < 1.25

      We estimate total mass (M500), intracluster medium (ICM) mass (MICM), and stellar mass (M) in a Sunyaev-Zel’dovich effect (SZE) selected sample of 91 galaxy clusters with masses M500 2.5 1014 M and redshift 0.2 < z < 1.25 from the 2500 ^2 South Pole Telescope SPT-SZ survey. The total masses M500 are estimatedfrom the SZE observable, the ICM masses MICM are obtained from the analysis of Chandra X-ray observations, and the stellar masses M are derived by fitting spectral energy distribution templates to Dark Energy Survey griz optical photometry and WISE or Spitzer near-infrared photometry. We study trends in the stellar mass, the ICM mass, the total baryonic mass, and the cold baryonic fraction with cluster halo mass and redshift. We find significant departures from self-similarity in the mass scaling for all quantities, while the redshift trends are all statistically consistent with zero, indicating that the baryon content of clusters at fixed mass has changed remarkably little over the past 9 Gyr. We compare our results to the mean baryon fraction (and the stellar mass fraction) in the field, finding that these values lie above (below) those in cluster virial regions in all but the most massive clusters at low redshift. Using a simple model of the matter assembly of clusters from infalling groups with lower masses and from infalling material from the low-density environment or field surrounding the parent haloes, we show that the measured mass trends without strong redshift trends in the stellar mass scaling relation could be explained by a mass and redshift dependent fractional contribution from field material. Similar analyses of the ICM and baryon mass scaling relations provide evidence for the so-called `missing baryons’ outside cluster virial regions.

    86. Abbott, T. M. C., Abdalla, F. B., Alarcon, A., et al., 2018, PhRvD, 98, 043526, Dark Energy Survey year 1 results: Cosmological constraints from galaxy clustering and weak lensing

      We present cosmological results from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). We combine three two-point functions: (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. To demonstrate the robustness of these results, we use independent pairs of galaxy shape, photometric-redshift estimation and validation, and likelihood analysis pipelines. To prevent confirmation bias, the bulk of the analysis was carried out while “blind” to the true results; we describe an extensive suite of systematics checks performed and passed during this blinded phase. The data are modeled in flat CDM and w CDM cosmologies, marginalizing over 20 nuisance parameters, varying 6 (for CDM ) or 7 (for w CDM ) cosmological parameters including the neutrino mass density and including the 457 457 element analytic covariance matrix. We find consistent cosmological results from these three two-point functions and from their combination obtain S88(m/0.3 )0.5=0.77 3-0.020+0.026 and m=0.26 7-0.017+0.030 for CDM ; for w CDM , we find S8=0.78 2-0.024+0.036, m=0.28 4-0.030+0.033, and w =-0.8 2-0.20+0.21 at 68% C.L. The precision of these DES Y1 constraints rivals that from the Planck cosmic microwave background measurements, allowing a comparison of structure in the very early and late Universe on equal terms. Although the DES Y1 best-fit values for S8 and m are lower than the central values from Planck for both CDM and w CDM , the Bayes factor indicates that the DES Y1 and Planck data sets are consistent with each other in the context of CDM . Combining DES Y1 with Planck, baryonic acoustic oscillation measurements from SDSS, 6dF, and BOSS and type Ia supernovae from the Joint Lightcurve Analysis data set, we derive very tight constraints on cosmological parameters: S8=0.802 0.012 and m=0.298 0.007 in CDM and w =-1.0 0-0.04+0.05 in w CDM . Upcoming Dark Energy Survey analyses will provide more stringent tests of the CDM model and extensions such as a time-varying equation of state of dark energy or modified gravity.

    87. Sheppard, Scott S., Williams, Gareth V., Tholen, David J., et al., 2018, RNAAS, 2, 155, New Jupiter Satellites and Moon-Moon Collisions

      We report the discovery of 12 new satellites of Jupiter, giving Jupiter 79 known satellites. The new finds are between 23rd-24th mag in the r-band and 1-3 km in diameter assuming dark albedos. Nine of the discoveries are in the distant retrograde satellite groupings. Two of the new satellites are in the closer Himalia prograde group near 28 degrees in inclination. S/2016 J2, nicknamed Valetudo, has an orbit unlike any other known outer satellite and is the most distant prograde satellite around any planet at 0.36 Hill radii. Numerical simulations show S/2016 J2 is very stable, with average and range of i=34.2+-3 deg, e=0.216+-0.125, and a=18.9+-0.7 million km over 100 Myrs. Our stability simulations show a S/2016 J2 like orbit would be stable out to a=21.8 million km or 0.41 Hill radii, but no further, unlike more distant and eccentric retrograde satellites. S/2016 J2’s large semi-major axis means it significantly overlaps the orbits of the distant retrogrades. A prograde-retrograde moon-moon collision between outer satellites of Jupiter has likely happened over the age of the solar system.

    88. Fausti Neto, A., da Costa, L. N., Carnero, A., et al., 2018, A&C, 24, 52, DES science portal: Creating science-ready catalogs

      We present a novel approach for creating science-ready catalogs through a software infrastructure developed for the Dark Energy Survey (DES). We integrate the data products released by the DES Data Management and additional products created by the DES collaboration in an environment known as DES Science Portal. Each step involved in the creation of a science-ready catalog is recorded in a relational database and can be recovered at any time. We describe how the DES Science Portal automates the creation and characterization of lightweight catalogs for DES Year 1 Annual Release, and show its flexibility in creating multiple catalogs with different inputs and configurations. Finally, we discuss the advantages of this infrastructure for large surveys such as DES and the Large Synoptic Survey Telescope. The capability of creating science-ready catalogs efficiently and with full control of the inputs and configurations used is an important asset for supporting science analysis using data from large astronomical surveys.

    89. Hunter, Deidre A., Adamo, Angela, Elmegreen, Bruce G., et al., 2018, AJ, 156, 21, A Comparison of Young Star Properties with Local Galactic Environment for LEGUS/LITTLE THINGS Dwarf Irregular Galaxies

      We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and blue compact dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates; OB associations by mass and mass surface density; O stars by their numbers and near-ultraviolet absolute magnitudes; and H II regions by H surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, H I surface density, and star formation rate (SFR) surface density. We find no trend of cluster characteristics with environmental properties, implying that larger-scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases any memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and H I surface density, and there is a trend of higher H II region H surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas is found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of SFR density. However, there is an increase in the ratio of the number of clusters to the number of O stars with increasing pressure, perhaps reflecting an increase in clustering properties with SFR.

    90. Hsieh, Henry H., Ishiguro, Masateru, Knight, Matthew M., et al., 2018, AJ, 156, 39, The Reactivation and Nucleus Characterization of Main-belt Comet 358P/PANSTARRS (P/2012 T1)

      We present observations of main-belt comet (MBC) 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to December, as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H R = 19.5 0.2 mag and G R = -0.22 0.13 for the nucleus, corresponding to an effective radius of r N = 0.32 0.03 km (assuming an albedo of p R = 0.05). The object appears significantly brighter (by 1 mag) than expected starting in 2017 November, while a faint dust tail oriented approximately in the antisolar direction is also observed on 2017 December 18. We conclude that 358P has become active again for the first time since its previously observed active period in 2012-2013. These observations make 358P the seventh MBC candidate confirmed to exhibit recurrent activity near perihelion with intervening inactivity away from perihelion, strongly indicating that its activity is sublimation-driven. Fitting a linear function to the ejected dust masses inferred for 358P in 2017 when it is apparently active, we find an average net dust production rate of \dot{M}=2.0+/- 0.6 kg s-1 (assuming a mean effective particle radius of {\bar{a}}d=1 mm) and an estimated activity start date of 2017 November 8 4 when the object was at a true anomaly of = 316 1 and a heliocentric distance of R = 2.54 au. Insufficient data is currently available to ascertain whether activity strength has changed between the objects 2012-2013 and 2017 active periods. Further observations are therefore highly encouraged during the objects upcoming observing window (2018 August through 2019 May).

    91. Bertrand, T., Forget, F., Umurhan, O. M., et al., 2018, Icar, 309, 277, The nitrogen cycles on Pluto over seasonal and astronomical timescales

      Pluto’s landscape is shaped by the endless condensation and sublimation cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia ice sheet, which is thought to be the main reservoir of nitrogen ice, displays a large diversity of terrains, with bright and dark plains, small pits and troughs, topographic depressions and evidences of recent and past glacial flows. Outside Sputnik Planitia, New Horizons also revealed numerous nitrogen ice deposits, in the eastern side of Tombaugh Regio and at mid-northern latitudes.


      These observations suggest a complex history involving volatile and glacial processes occurring on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model designed to simulate the nitrogen cycle over millions of years, taking into account the changes of obliquity, solar longitude of perihelion and eccentricity as experienced by Pluto. Using this model, we first explore how the volatile and glacial activity of nitrogen within Sputnik Planitia has been impacted by the diurnal, seasonal and astronomical cycles of Pluto. Results show that the obliquity dominates the N2 cycle and that over one obliquity cycle, the latitudes of Sputnik Planitia between 25S-30N are dominated by N2 condensation, while the northern regions between 30N and -50N are dominated by N2 sublimation. We find that a net amount of 1 km of ice has sublimed at the northern edge of Sputnik Planitia during the last 2 millions of years. It must have been compensated by a viscous flow of the thick ice sheet. By comparing these results with the observed geology of Sputnik Planitia, we can relate the formation of the small pits and the brightness of the ice at the center of Sputnik Planitia to the sublimation and condensation of ice occurring at the annual timescale, while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are instead related to the astronomical timescale. We also perform simulations including a glacial flow scheme which shows that the Sputnik Planitia ice sheet is currently at its minimum extent at the northern and southern edges. We also explore the stability of N2 ice deposits outside the latitudes and longitudes of the Sputnik Planitia basin. Results show that N2 ice is not stable at the poles but rather in the equatorial regions, in particular in depressions, where thick deposits may persist over tens of millions of years, before being trapped in Sputnik Planitia. Finally, another key result is that the minimum and maximum surface pressures obtained over the simulated millions of years remain in the range of milli-Pascals and Pascals, respectively. This suggests that Pluto never encountered conditions allowing liquid nitrogen to flow directly on its surface. Instead, we suggest that the numerous geomorphological evidences of past liquid flow observed on Pluto’s surface are the result of liquid nitrogen that flowed at the base of thick ancient nitrogen glaciers, which have since disappeared.

    92. Hoyle, B., Gruen, D., Bernstein, G. M., et al., 2018, MNRAS, 478, 592, Dark Energy Survey Year 1 Results: redshift distributions of the weak-lensing source galaxies

      We describe the derivation and validation of redshift distribution estimates and their uncertainties for the populations of galaxies used as weak-lensing sources in the Dark Energy Survey (DES) Year 1 cosmological analyses. The Bayesian Photometric Redshift (BPZ) code is used to assign galaxies to four redshift bins between z 0.2 and 1.3, and to produce initial estimates of the lensing-weighted redshift distributions n^i_PZ(z) dn^i/dz for members of bin i. Accurate determination of cosmological parameters depends critically on knowledge of ni, but is insensitive to bin assignments or redshift errors for individual galaxies. The cosmological analyses allow for shifts n^i(z)=n^i_PZ(z- z^i) to correct the mean redshift of ni(z) for biases in n^i_PZ. The zi are constrained by comparison of independently estimated 30-band photometric redshifts of galaxies in the Cosmic Evolution Survey (COSMOS) field to BPZ estimates made from the DES griz fluxes, for a sample matched in fluxes, pre-seeing size, and lensing weight to the DES weak-lensing sources. In companion papers, the zi of the three lowest redshift bins are further constrained by the angular clustering of the source galaxies around red galaxies with secure photometric redshifts at 0.15 < z < 0.9. This paper details the BPZ and COSMOS procedures, and demonstrates that the cosmological inference is insensitive to details of the ni(z) beyond the choice of zi. The clustering and COSMOS validation methods produce consistent estimates of zi in the bins where both can be applied, with combined uncertainties of _{ z^i}=0.015, 0.013, 0.011, and 0.022 in the four bins. Repeating the photo-z procedure instead using the Directional Neighbourhood Fitting algorithm, or using the ni(z) estimated from the matched sample in COSMOS, yields no discernible difference in cosmological inferences.

    93. Gruen, D., Friedrich, O., Krause, E., et al., 2018, PhRvD, 98, 023507, Density split statistics: Cosmological constraints from counts and lensing in cells in DES Y1 and SDSS data

      We derive cosmological constraints from the probability distribution function (PDF) of evolved large-scale matter density fluctuations. We do this by splitting lines of sight by density based on their count of tracer galaxies, and by measuring both gravitational shear around and counts-in-cells in overdense and underdense lines of sight, in Dark Energy Survey (DES) First Year and Sloan Digital Sky Survey (SDSS) data. Our analysis uses a perturbation theory model [O. Friedrich et al., Phys. Rev. D 98, 023508 (2018), 10.1103/PhysRevD.98.023508] and is validated using N -body simulation realizations and log-normal mocks. It allows us to constrain cosmology, bias and stochasticity of galaxies with respect to matter density and, in addition, the skewness of the matter density field. From a Bayesian model comparison, we find that the data weakly prefer a connection of galaxies and matter that is stochastic beyond Poisson fluctuations on 20 arcmin angular smoothing scale. The two stochasticity models we fit yield DES constraints on the matter density m=0.2 6-0.03+0.04 and m=0.2 8-0.04+0.05 that are consistent with each other. These values also agree with the DES analysis of galaxy and shear two-point functions (3x2pt, DES Collaboration et al.) that only uses second moments of the PDF. Constraints on 8 are model dependent (8=0.9 7-0.06+0.07 and 0.8 0-0.07+0.06 for the two stochasticity models), but consistent with each other and with the 3 x 2pt results if stochasticity is at the low end of the posterior range. As an additional test of gravity, counts and lensing in cells allow to compare the skewness S3 of the matter density PDF to its CDM prediction. We find no evidence of excess skewness in any model or data set, with better than 25 per cent relative precision in the skewness estimate from DES alone.

    94. Friedrich, O., Gruen, D., DeRose, J., et al., 2018, PhRvD, 98, 023508, Density split statistics: Joint model of counts and lensing in cells

      We present density split statistics, a framework that studies lensing and counts-in-cells as a function of foreground galaxy density, thereby providing a large-scale measurement of both 2-point and 3-point statistics. Our method extends our earlier work on trough lensing and is summarized as follows: given a foreground (low redshift) population of galaxies, we divide the sky into subareas of equal size but distinct galaxy density. We then measure lensing around uniformly spaced points separately in each of these subareas, as well as counts-in-cells statistics (CiC). The lensing signals trace the matter density contrast around regions of fixed galaxy density. Through the CiC measurements this can be related to the density profile around regions of fixed matter density. Together, these measurements constitute a powerful probe of cosmology, the skewness of the density field and the connection of galaxies and matter. In this paper we show how to model both the density split lensing signal and CiC from basic ingredients: a non-linear power spectrum, clustering hierarchy coefficients from perturbation theory and a parametric model for galaxy bias and shot-noise. Using N-body simulations, we demonstrate that this model is sufficiently accurate for a cosmological analysis on year 1 data from the Dark Energy Survey.

    95. Scowen, Paul A., Shkolnik, Evgenya L., Ardila, David, et al., 2018, SPIE, 10699, 106990F, Monitoring the high-energy radiation environment of exoplanets around low-mass stars with SPARCS (Star-Planet Activity Research CubeSat)

      Roughly 40 billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1-0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of low-mass star high-energy radiation.

    96. Levine, Stephen E., DeGroff, William T., Bida, Thomas A., et al., 2018, SPIE, 10700, 107004P, Status and performance of Lowell Observatory’s Discovery Channel telescope and its growing suite of instruments

      Lowell Observatory’s Discovery Channel Telescope (DCT) is a 4.3-m telescope designed and constructed for optical and near infrared astronomical observation. The DCT is equipped with a cube at the RC focus capable of interfacing to five instruments along with the wave front sensing and guider systems at the f/6.1 RC focus. Over the period 2016 through mid-2018 the instrument cube ports were fully populated as several instruments new to the DCT were brought on-line (NIHTS, IGRINS, EXPRES). The primary and secondary mirrors of the telescope were re-aluminized, and the coating process modified. The facility operational modes have been refined to allow for greater flexibility and faster response to unexpected science opportunities. This report addresses operational methods, instrumentation integration, and the performance of the facility as determined from delivered science data, lessons learned, and plans for future work and additional instruments.

    97. van Belle, G. T., Armstrong, J. T., Benson, J. A., et al., 2018, SPIE, 10701, 1070105, Many interesting things are afoot at the Navy Precision Optical Interferometer

      The Navy Precision Optical Interferometer (NPOI) is currently undergoing a fundamental renaissance in its functionality and capabilities. Operationally, its fast delay line (FDL) infrastructure is completing its upgrade from a VME/VxWorks foundation to a modern PC/RTLinux core. The Classic beam combiner is being upgraded with the New Classic FPGA-based backend, and the VISION beam combiner has been upgraded over this past summer with low-noise EMCCD cameras, resulting in substantial gains in sensitivity. Building on those infrastructure improvements, substantial upgrades are also in progress. Three 1-meter PlaneWave CDK1000 telescopes are being delivered to the site, along with their relocatable enclosure-transporters, and stations are being commissioned for those telescopes with baselines ranging from 8 meters to 432 meters. Baseline-wavelength bootstrapping will be implemented on the facility back-end with a near-infrared beam combiner under development. Collectively, these improvements mark substantial progress in taking the facility towards realizing its full intrinsic potential.

    98. Armstrong, J. Thomas, Schmitt, Henrique R., Restaino, Sergio R., et al., 2018, SPIE, 10701, 107010B, An infrared beam combiner for wavelength bootstrapping at the NPOI

      Since 1994, the Navy Precision Optical Interferometer (NPOI) has operated at visual wavelengths (450 to 850 nm). Its primary Classic backend is a pupil-plane combiner that disperses the light at a resolution R 50, uses avalanche photo-diodes as photon-counting detectors, and scans interference fringes by modulating the delay at 1 kHz. The newer NPOI image-plane combiner, VISION (Tennessee State University), which is similar to CHARA’s MIRC and is currently being upgraded, dispenses with delay modulation. We are now developing a third backend to expand into the near infrared. Its primary purpose will be to stabilize the NPOI for high-resolution observations by bootstrapping from the infrared to visual wavelengths.

    99. Monnier, John D., Ireland, Michael, Kraus, Stefan, et al., 2018, SPIE, 10701, 1070118, Planet formation imager: project update

      The Planet Formation Imager (PFI) is a near- and mid-infrared interferometer project with the driving science goal of imaging directly the key stages of planet formation, including the young proto-planets themselves. Here, we will present an update on the work of the Science Working Group (SWG), including new simulations of dust structures during the assembly phase of planet formation and quantitative detection efficiencies for accreting and non-accreting young exoplanets as a function of mass and age. We use these results to motivate two reference PFI designs consisting of a) twelve 3m telescopes with a maximum baseline of 1.2km focused on young exoplanet imaging and b) twelve 8m telescopes optimized for a wider range of young exoplanets and protoplanetary disk imaging out to the 150K H2O ice line. Armed with 4 x 8m telescopes, the ESO/VLTI can already detect young exoplanets in principle and projects such as MATISSE, Hi-5 and Heimdallr are important PFI pathfinders to make this possible. We also discuss the state of technology development needed to make PFI more affordable, including progress towards new designs for inexpensive, small field-of-view, large aperture telescopes and prospects for Cubesat-based space interferometry.

    100. Hahne, Frederick W., Horch, Elliott P., van Belle, Gerard T., et al., 2018, SPIE, 10701, 107012A, Two-color speckle imaging of M-dwarfs with the Discovery Channel telescope

      Lowell Observatory and Southern Connecticut State University are currently involved in a joint project to determine the stellar multiplicity rates and the fundamental stellar parameters of M dwarf stars using the Differential Speckle Survey Instrument (DSSI) at Lowell’s Discovery Channel Telescope (DCT). DSSI observes speckle patterns simultaneously at two separate wavelengths, allowing color measurements of the components of a binary system to be made in a single observation. This paper will describe the initial data gathering process, which began in 2016. Since then, over 1000 stars have been observed. We summarize the analysis on these objects so far, and discuss the relevance of these observations for existing and future space missions such as TESS, JWST, and Gaia.

    101. Mace, Gregory, Sokal, Kimberly, Lee, Jae-Joon, et al., 2018, SPIE, 10702, 107020Q, IGRINS at the Discovery Channel Telescope and Gemini South

      The Immersion GRating INfrared Spectrometer (IGRINS) was designed for high-throughput with the expectation of being a visitor instrument at progressively larger observing facilities. IGRINS achieves R45000 and > 20,000 resolution elements spanning the H and K bands (1.45-2.5m) by employing a silicon immersion grating as the primary disperser and volume-phase holographic gratings as cross-dispersers. After commissioning on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory, the instrument had more than 350 scheduled nights in the first two years. With a fixed format echellogram and no cryogenic mechanisms, spectra produced by IGRINS at different facilities have nearly identical formats. The first host facility for IGRINS was Lowell Observatory’s 4.3-meter Discovery Channel Telescope (DCT). For the DCT a three-element fore-optic assembly was designed to be mounted in front of the cryostat window and convert the f/6.1 telescope beam to the f/8.8 beam required by the default IGRINS input optics. The larger collecting area and more reliable pointing and tracking of the DCT improved the faint limit of IGRINS, relative to the McDonald 2.7-meter, by 1 magnitude. The Gemini South 8.1-meter telescope was the second facility for IGRINS to visit. The focal ratio for Gemini is f/16, which required a swap of the four-element input optics assembly inside the IGRINS cryostat. At Gemini, observers have access to many southern-sky targets and an additional gain of 1.5 magnitudes compared to IGRINS at the DCT. Additional adjustments to IGRINS include instrument mounts for each facility, a glycol cooled electronics rack, and software modifications. Here we present instrument modifications, report on the success and challenges of being a visitor instrument, and highlight the science output of the instrument after four years and 699 nights on sky. The successful design and adaptation of IGRINS for various facilities make it a reliable forerunner for GMTNIRS, which we now anticipate commissioning on one of the 6.5 meter Magellan telescopes prior to the completion of the Giant Magellan Telescope.

    102. Dunham, Edward W., Bida, Thomas A., Chylek, Tomas, et al., 2018, SPIE, 10702, 107023E, NIHTS: the near-infrared high throughput spectrograph for the Discovery Channel Telescope

      NIHTS is a first-generation instrument now in use on Lowell Observatory’s Discovery Channel Telescope. It is a nearinfrared prism spectrograph of the BASS design featuring high throughput and low dispersion that is intended for observations of faint solar system and astrophysical objects over the YJHK spectral range. An unusual feature is its ability to observe simultaneously with the Large Monolithic Imager, an optical CCD camera, by means of a dichroic fold mirror. This is particularly valuable for time-variable targets such as Kuiper Belt Objects, asteroids, exoplanet transits, and brown dwarfs. We describe its design details and performance both in the lab and on the telescope.

    103. Lawrence, Jon, Ben-Ami, Sagi, Brown, David M., et al., 2018, SPIE, 10702, 10702A6, Wide-field multi-object spectroscopy with MANIFEST

      MANIFEST is a multi-object fibre facility for the Giant Magellan Telescope that uses `Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeinglimited instruments, offers access to larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via integral-field-units; image-slicers; and in some cases higher spatial and spectral resolution. The TAIPAN instrument on the UK Schmidt Telescope is now close to science verification which will demonstrate the feasibility of the Starbug concept. We are now moving into the conceptual development phase for MANIFEST, with a focus on developing interfaces for the telescope and for the instruments.

    104. Bacigalupo, Carlos, Goodwin, Michael, Brown, Rebecca, et al., 2018, SPIE, 10706, 107065V, Acquisition and guiding for TAIPAN using Starbugs

      The AAO Starbugs is a multi-functional positioning device used in the TAIPAN instrument currently being commissioned on the UK Schmidt Telescope at Siding Spring Observatory in Australia. TAIPAN is part of a design study for MANIFEST which is a fibre positioning instrument proposed for the Giant Magellan Telescope. The acquisition and guiding system for TAIPAN uses nine standard Starbugs, referred to as Guide Bugs. Each one uses a 7000 core coherent polymer fibre bundle on individual guide stars. This provides an astrometric reference frame for science fibre positioning, telescope guiding, instrument alignment and focus, all of which are invariant to telescope and atmospheric geometric anomalies. Guide Bugs are a technology that will enable improved science results for the TAIPAN instrument. In this paper we outline the design features and provide an update on software development.

    105. Flagg, Laura, Johns-Krull, Christopher, Prato, Lisa, et al., 2018, csss, 41, A Search for the Direct Detection of the 2 Myr Old Hot Jupiter Orbiting CI Tau

      Characterizing young exoplanets is critical for putting limits on planet formation scenarios. However, as of yet, only a few young exoplanet candidates have even been discovered, and no young planet with a model-independent mass has had its spectrum or brightness measured. A good candidate for such a detection is CI Tau b, an msini = 8.1 Mjup planet in a 9 day orbit around a 2 Myr old classical T Tauri star. We use high spectral resolution K band echelle spectroscopy to look for direct signatures of the planet itself, taking advantage of the large expected radial velocity variations of the planet as it orbits CI Tau. We report on our efforts to directly detect the spectrum of CI Tau b and present a tentative measurement of CO absorption in this young exoplanet. The properties of the planet determined from this CO detection are consistent with those described in the discovery paper and favor “hot start” formation models.

    106. Malko, Bradley Ann, Hunter, Deidre Ann, 2018, AAS, 232, 218.01, Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

      Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

    107. Henden, Arne A., Levine, Stephen, Terrell, Dirk, et al., 2018, AAS, 232, 223.06, APASS Data Release 10

      The AAVSO Photometric All-Sky Survey (APASS) has been underway since 2010. This survey covers the entire sky from 7.5 < V < 16.5 magnitude, and in the BVugrizY bandpasses. A northern and a southern site are used, each with twin ASA 20cm astrographs and Apogee Aspen CG16m cameras, covering 2.9×2.9 square degrees with 2.6arcsec pixels. Landolt and SDSS standards are used for all-sky solutions, with typical 0.02mag calibration errors on the bright end. DR9 is currently available through VizieR. DR10 is a complete reprocessing of all 500K images taken with the system, including hundreds of nights not part of DR9. Sextractor is used for star finding and centroiding; DAOPHOT is used for aperture photometry; the plate-solving library is used for basic astrometry, supplanted with more precise WCS that utilizes knowledge of the optical train distortions. With these changes, DR10 includes many more stars than prior releases. We describe the survey, its remaining limitations, and prospects for the future, including a very-bright-star extension.

    108. Thirouin, Audrey, Sheppard, Scott S., 2018, AJ, 155, 248, The Plutino Population: An Abundance of Contact Binaries

      We observed 12 Plutinos over two separated years with the 4.3 m Lowells Discovery Channel Telescope. Here, we present the first light-curve data for those objects. Three of them (2014 JL80, 2014 JO80, and 2014 JQ80) display a large light-curve amplitude explainable by a single elongated object, but they are most likely caused by a contact binary system due to their light-curve morphology. These potential contact binaries have rotational periods from 6.3 to 34.9 hr and peak-to-peak light-curve variability between 0.6 and 0.8 mag. We present partial light curves, allowing us to constrain the light-curve amplitude and the rotational period of another nine Plutinos. By merging our data with the literature, we estimate that up to 40% of the Plutinos could be contact binaries. Interestingly, we found that all of the suspected contact binaries in the 3:2 resonance are small with absolute magnitude H > 6 mag. Based on our sample and the literature, up to 50% of the small Plutinos are potential contact binaries.

    109. Harris, Hugh C., Dahn, Conard C., Subasavage, John P., et al., 2018, AJ, 155, 252, Distances of Dwarf Carbon Stars

      Parallaxes are presented for a sample of 20 nearby dwarf carbon stars. The inferred luminosities cover almost two orders of magnitude. Their absolute magnitudes and tangential velocities confirm prior expectations that some originate in the Galactic disk, although more than half of this sample are halo stars. Three stars are found to be astrometric binaries, and orbital elements are determined; their semimajor axes are 1-3 au, consistent with the size of an AGB mass-transfer donor star.

    110. Gatti, M., Vielzeuf, P., Davis, C., et al., 2018, MNRAS, 477, 1664, Dark Energy Survey Year 1 results: cross-correlation redshifts – methods and systematics characterization

      We use numerical simulations to characterize the performance of a clustering-based method to calibrate photometric redshift biases. In particular, we cross-correlate the weak lensing source galaxies from the Dark Energy Survey Year 1 sample with redMaGiC galaxies (luminous red galaxies with secure photometric redshifts) to estimate the redshift distribution of the former sample. The recovered redshift distributions are used to calibrate the photometric redshift bias of standard photo-z methods applied to the same source galaxy sample. We apply the method to two photo-z codes run in our simulated data: Bayesian Photometric Redshift and Directional Neighbourhood Fitting. We characterize the systematic uncertainties of our calibration procedure, and find that these systematic uncertainties dominate our error budget. The dominant systematics are due to our assumption of unevolving bias and clustering across each redshift bin, and to differences between the shapes of the redshift distributions derived by clustering versus photo-zs. The systematic uncertainty in the mean redshift bias of the source galaxy sample is z 0.02, though the precise value depends on the redshift bin under consideration. We discuss possible ways to mitigate the impact of our dominant systematics in future analyses.

    111. Davis, C., Rozo, E., Roodman, A., et al., 2018, MNRAS, 477, 2196, Cross-correlation redshift calibration without spectroscopic calibration samples in DES Science Verification Data

      Galaxy cross-correlations with high-fidelity redshift samples hold the potential to precisely calibrate systematic photometric redshift uncertainties arising from the unavailability of complete and representative training and validation samples of galaxies. However, application of this technique in the Dark Energy Survey (DES) is hampered by the relatively low number density, small area, and modest redshift overlap between photometric and spectroscopic samples. We propose instead using photometric catalogues with reliable photometric redshifts for photo-z calibration via cross-correlations. We verify the viability of our proposal using redMaPPer clusters from the Sloan Digital Sky Survey (SDSS) to successfully recover the redshift distribution of SDSS spectroscopic galaxies. We demonstrate how to combine photo-z with cross-correlation data to calibrate photometric redshift biases while marginalizing over possible clustering bias evolution in either the calibration or unknown photometric samples. We apply our method to DES Science Verification (DES SV) data in order to constrain the photometric redshift distribution of a galaxy sample selected for weak lensing studies, constraining the mean of the tomographic redshift distributions to a statistical uncertainty of z 0.01. We forecast that our proposal can, in principle, control photometric redshift uncertainties in DES weak lensing experiments at a level near the intrinsic statistical noise of the experiment over the range of redshifts where redMaPPer clusters are available. Our results provide strong motivation to launch a programme to fully characterize the systematic errors from bias evolution and photo-z shapes in our calibration procedure.

    112. Cushing, Michael C., Moskovitz, Nicholas, Gustafsson, Annika, 2018, RNAAS, 2, 50, Spectroscopic Confirmation That 2MASS J07414279-0506464 Is a Mid-type L Dwarf

      We present a low-resolution near-infrared spectrum of 2MASS J07414279-0506464, a mid-type L dwarf candidate recently identified by Scholz & Bell. The spectrum was obtained using the Near-Infrared High Throughput Spectrograph (NIHTS) on Lowell Observatory’s 4.3 m Discovery Channel Telescope and indicates that 2MASS J07414279-0506464 has a spectral type of L5.

    113. Lucey, John R., Smith, Russell J., Schechter, Paul L., et al., 2018, RNAAS, 2, 62, A New Quadruple-image Gravitational Lens in an Edge-on Disk Galaxy at z = 0.0956

      We report the serendipitous discovery of a quadruply-lensed source behind the z=0.095 edge-on disk galaxy 2MASXJ13170000-1405187, based on public imaging survey data from Pan-STARRS PS1 and the VISTA Hemisphere Survey. Follow-up imaging from Magellan/LDSS3 shows that the background source is spatially extended (i.e. not a QSO), and that two of the lensed images are observed through a prominent dust ring in the disk of the lens galaxy. We summarise results of preliminary modelling, which indicates an Einstein radius of 1.44 arcsec, and a K-band mass-to-light ratio of 0.5, relative to the solar value.

    114. Neugent, Kathryn F., Massey, Philip, Morrell, Nidia I., et al., 2018, AJ, 155, 207, A Runaway Yellow Supergiant Star in the Small Magellanic Cloud

      We recently discovered a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity of 300 km s-1, which is much larger than expected for a star at its location in the SMC. This is the first runaway YSG ever discovered and only the second evolved runaway star discovered in a galaxy other than the Milky Way. We classify the star as G5-8 I and use de-reddened broad-band colors with model atmospheres to determine an effective temperature of 4700 250 K, consistent with what is expected from its spectral type. The stars luminosity is then log L/L 4.2 0.1, consistent with it being a 30 Myr 9 M star according to the Geneva evolution models. The star is currently located in the outer portion of the SMCs body, but if the stars transverse peculiar velocity is similar to its peculiar radial velocity, in 10 Myr the star would have moved 1.6 across the disk of the SMC and could easily have been born in one of the SMCs star-forming regions. Based on its large radial velocity, we suggest it originated in a binary system where the primary exploded as a supernovae, thus flinging the runaway star out into space. Such stars may provide an important mechanism for the dispersal of heavier elements in galaxies given the large percentage of massive stars that are runaways. In the future, we hope to look into additional evolved runaway stars that were discovered as part of our other past surveys.


      This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

    115. Bannister, Michele T., Gladman, Brett J., Kavelaars, J. J., et al., 2018, ApJS, 236, 18, OSSOS. VII. 800+ Trans-Neptunian ObjectsThe Complete Data Release

      The Outer Solar System Origins Survey (OSSOS), a wide-field imaging program in 2013-2017 with the Canada-France-Hawaii Telescope, surveyed 155 deg2 of sky to depths of m r = 24.1-25.2. We present 838 outer solar system discoveries that are entirely free of ephemeris bias. This increases the inventory of trans-Neptunian objects (TNOs) with accurately known orbits by nearly 50%. Each minor planet has 20-60 Gaia/Pan-STARRS-calibrated astrometric measurements made over 2-5 oppositions, which allows accurate classification of their orbits within the trans-Neptunian dynamical populations. The populations orbiting in mean-motion resonance with Neptune are key to understanding Neptunes early migration. Our 313 resonant TNOs, including 132 plutinos, triple the available characterized sample and include new occupancy of distant resonances out to semimajor axis a 130 au. OSSOS doubles the known population of the nonresonant Kuiper Belt, providing 436 TNOs in this region, all with exceptionally high-quality orbits of a uncertainty a 0.1% they show that the belt exists from a 37 au, with a lower perihelion bound of 35 au. We confirm the presence of a concentrated low-inclination a 44 au kernel population and a dynamically cold population extending beyond the 2:1 resonance. We finely quantify the surveys observational biases. Our survey simulator provides a straightforward way to impose these biases on models of the trans-Neptunian orbit distributions, allowing statistical comparison to the discoveries. The OSSOS TNOs, unprecedented in their orbital precision for the size of the sample, are ideal for testing concepts of the history of giant planet migration in the solar system.

    116. Grundy, W. M., Noll, K. S., Buie, M. W., et al., 2018, Icar, 305, 198, The upcoming mutual event season for the Patroclus-Menoetius Trojan binary

      We present new Hubble Space Telescope and ground-based Keck observations and new Keplerian orbit solutions for the mutual orbit of binary Jupiter Trojan asteroid (617) Patroclus and Menoetius, targets of NASA’s Lucy mission. We predict event times for the upcoming mutual event season, which is anticipated to run from late 2017 through mid 2019.

    117. Garcia-Fernandez, M., Sanchez, E., Sevilla-Noarbe, I., et al., 2018, MNRAS, 476, 1071, Weak lensing magnification in the Dark Energy Survey Science Verification data

      In this paper, the effect of weak lensing magnification on galaxy number counts is studied by cross-correlating the positions of two galaxy samples, separated by redshift, using the Dark Energy Survey Science Verification data set. This analysis is carried out for galaxies that are selected only by its photometric redshift. An extensive analysis of the systematic effects, using new methods based on simulations is performed, including a Monte Carlo sampling of the selection function of the survey.

    118. Baxter, E. J., Raghunathan, S., Crawford, T. M., et al., 2018, MNRAS, 476, 2674, A measurement of CMB cluster lensing with SPT and DES year 1 data

      Clusters of galaxies gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint in the CMB on arcminute scales. Measurement of this effect offers a promising way to constrain the masses of galaxy clusters, particularly those at high redshift. We use CMB maps from the South Pole Telescope Sunyaev-Zel’dovich (SZ) survey to measure the CMB lensing signal around galaxy clusters identified in optical imaging from first year observations of the Dark Energy Survey. The cluster catalogue used in this analysis contains 3697 members with mean redshift of \bar{z} = 0.45. We detect lensing of the CMB by the galaxy clusters at 8.1 significance. Using the measured lensing signal, we constrain the amplitude of the relation between cluster mass and optical richness to roughly 17 {per cent} precision, finding good agreement with recent constraints obtained with galaxy lensing. The error budget is dominated by statistical noise but includes significant contributions from systematic biases due to the thermal SZ effect and cluster miscentring.

    119. Jenniskens, Peter, Baggaley, Jack, Crumpton, Ian, et al., 2018, P&SS, 154, 21, A survey of southern hemisphere meteor showers

      Results are presented from a video-based meteoroid orbit survey conducted in New Zealand between Sept. 2014 and Dec. 2016, which netted 24,906 orbits from +5 to -5 magnitude meteors. 44 new southern hemisphere meteor showers are identified after combining this data with that of other video-based networks. Results are compared to showers reported from recent radar-based surveys. We find that video cameras and radar often see different showers and sometimes measure different semi-major axis distributions for the same meteoroid stream. For identifying showers in sparse daily orbit data, a shower look-up table of radiant position and speed as a function of time was created. This can replace the commonly used method of identifying showers from a set of mean orbital elements by using a discriminant criterion, which does not fully describe the distribution of meteor shower radiants over time.

    120. Cauley, P. Wilson, Shkolnik, Evgenya L., Llama, Joe, 2018, RNAAS, 2, 23, Transit Time Derivation for Hot Planet Bow-shocks

      We present an analytical estimate of hot planet bow-shock transit times that will be useful for planning observations of such signatures.

    121. Sacchi, E., Cignoni, M., Aloisi, A., et al., 2018, ApJ, 857, 63, Star Formation Histories of the LEGUS Dwarf Galaxies. II. Spatially Resolved Star Formation History of the Magellanic Irregular NGC 4449

      We present a detailed study of the Magellanic irregular galaxy NGC 4449 based on both archival and new photometric data from the Legacy Extragalactic UV Survey, obtained with the Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3. Thanks to its proximity (D = 3.82 0.27 Mpc), we reach stars 3 mag fainter than the tip of the red giant branch in the F814W filter. The recovered star formation history (SFH) spans the whole Hubble time, but due to the age-metallicity degeneracy of the red giant branch stars, it is robust only over the lookback time reached by our photometry, i.e., 3 Gyr. The most recent peak of star formation (SF) is around 10 Myr ago. The average surface density SF rate over the whole galaxy lifetime is 0.01 M yr-1 kpc-2. From our study, it emerges that NGC 4449 has experienced a fairly continuous SF regime in the last 1 Gyr, with peaks and dips whose SF rates differ only by a factor of a few. The very complex and disturbed morphology of NGC 4449 makes it an interesting galaxy for studies of the relationship between interactions and starbursts, and our detailed and spatially resolved analysis of its SFH does indeed provide some hints on the connection between these two phenomena in this peculiar dwarf galaxy.


      Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555.

    122. Li, T. S., Simon, J. D., Pace, A. B., et al., 2018, ApJ, 857, 145, Ships Passing in the Night: Spectroscopic Analysis of Two Ultra-faint Satellites in the Constellation Carina

      We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the Carina II (Car II) and Carina III (Car III) dwarf galaxy candidates, recently discovered in the Magellanic Satellites Survey (MagLiteS). We identify 18 member stars in Car II, including two binaries with variable radial velocities and two RR Lyrae stars. The other 14 members have a mean heliocentric velocity {v}hel}=477.2+/- 1.2 {km} {{{s}}}-1 and a velocity dispersion of { }v={3.4}-0.8+1.2 {km} {{{s}}}-1. Assuming Car II is in dynamical equilibrium, we derive a total mass within the half-light radius of {1.0}-0.4+0.8 {10}6 {M} , indicating a mass-to-light ratio of {369}-161+309 {M} /{L} . From equivalent width measurements of the calcium triplet lines of nine red giant branch (RGB) stars, we derive a mean metallicity of {{[Fe/H]}}=-2.44+/- 0.09 with dispersion { }{{[Fe/H]}}={0.22}-0.07+0.10. Considering both the kinematic and chemical properties, we conclude that Car II is a dark-matter-dominated dwarf galaxy. For Car III, we identify four member stars, from which we calculate a systemic velocity of {v}hel}={284.6}-3.1+3.4 {km} {{{s}}}-1. The brightest RGB member of Car III has a metallicity of {{[Fe/H]}} =-1.97+/- 0.12. Due to the small size of the Car III spectroscopic sample, we cannot conclusively determine its nature. Although these two systems have the smallest known physical separation ({{ }}d 10 {kpc}) among Local Group satellites, the large difference in their systemic velocities, 200 {km} {{{s}}}-1, indicates that they are unlikely to be a bound pair. One or both systems are likely associated with the Large Magellanic Cloud (LMC), and may remain LMC satellites today. No statistically significant excess of -ray emission is found at the locations of Car II and Car III in eight years of Fermi-LAT data.

    123. Drlica-Wagner, A., Sevilla-Noarbe, I., Rykoff, E. S., et al., 2018, ApJS, 235, 33, Dark Energy Survey Year 1 Results: The Photometric Data Set for Cosmology

      We describe the creation, content, and validation of the Dark Energy Survey (DES) internal year-one cosmology data set, Y1A1 GOLD, in support of upcoming cosmological analyses. The Y1A1 GOLD data set is assembled from multiple epochs of DES imaging and consists of calibrated photometric zero-points, object catalogs, and ancillary data productse.g., maps of survey depth and observing conditions, star-galaxy classification, and photometric redshift estimatesthat are necessary for accurate cosmological analyses. The Y1A1 GOLD wide-area object catalog consists of 137 million objects detected in co-added images covering 1800 {\deg }2 in the DES grizY filters. The 10 limiting magnitude for galaxies is g=23.4, r=23.2, i=22.5, z=21.8, and Y=20.1. Photometric calibration of Y1A1 GOLD was performed by combining nightly zero-point solutions with stellar locus regression, and the absolute calibration accuracy is better than 2% over the survey area. DES Y1A1 GOLD is the largest photometric data set at the achieved depth to date, enabling precise measurements of cosmic acceleration at z 1.

    124. Singer, Kelsi N., Schenk, Paul M., Beyer, Ross A., et al., 2018, EGUGA, 5761,