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Research at Lowell: Astronomers Identify Binary Central Stars of Planetary Nebula

Kepler Mission

Kepler Mission. Image credit: NASA.

The Kepler Mission allowed scientists to discover more than 2,000 exoplanets (planets outside of the solar system). Now, a team of astronomers led by former Lowell Observatory astronomer George Jacoby has used data from the Kepler/K2 extended mission to identify binary central stars in planetary nebulae. This will help to better understand the physical nature of planetary nebulae, which are useful for measuring extragalactic distances, chemical abundances, and other astronomical phenomena.

A planetary nebula is a shell of ionized gas around a dying star, created when the star expels its outer layers after it has run out of fuel to burn. In recent years, scientists have determined that some of these central stars are binary–two stars closely orbiting around a common center of mass. Scientists know that these binary systems create complex, non-spherical shapes for the nebula, and they also know that the majority (80-85%) of planetary nebulae are complex and non-spherical. But they haven’t yet observed enough such planetary nebulae binaries to see if their frequency matches that of the complex and non-spherical planetary nebulae. Jacoby and his team are helping to improve this.

George Jacoby.

Examining Light Curves

The team identified likely binary central stars by looking at the light curves of hundreds of stars. Light curves indicate the brightness of an object over time. Sometimes, the light curve of a star shows it to darken at a regular cadence. One explanation is that the target is actually two stars close together–a binary star system. This is the premise the team used in the study. The Kepler Mission, featuring a space-based telescope, was well suited for gathering the base data because it could detect tiny variations in brightness–10-100 times smaller than the levels of ground-based telescopes.

The team ultimately identified 34 likely binary central stars, 29 of which are new discoveries. While more research is needed to establish the actual percentage of the binary central stars, the study shows that the Kepler/K2 data is very useful in identifying the stars and sets the stage for further analysis.

The entire paper, which appears in Monthly Notices of the Royal Astronomical Society, is available to read here.

Jacoby, the former Deputy Director for Technology at Lowell Observatory, is the lead author. Two co-authors also have Lowell connections–Jonathan Hurowitz participated in an MIT field camp here and Alison Crocker was a visiting professor from Reed College for a year. The Kepler Mission itself also has strong Lowell ties: Longtime Lowell astronomer Ted Dunham served as a co-investigator and lead of the science team.