Selections from 2019: A Giant Planet Around an Evolved Binary


Editor’s note: In these last two weeks of 2019, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

Orbital Period Variation of KIC 10544976: Applegate Mechanism versus Light Travel Time Effect

Published March 2019

Main takeaway:

In a study led by Leonardo Almeida (Federal University of Rio Grande do Norte and University of São Paulo, Brazil), scientists announce evidence for a 13-Jupiter-mass planet around an evolved binary system, KIC 10544976, that consists of a white dwarf and a red dwarf star orbiting each other once every 0.35 days.

Why it’s interesting:

This is the first planet found orbiting an evolved binary like this one, and it raises questions as to how it formed. Was the planet born at the same time as the stars, and somehow survived the end of life of the binary member that evolved into a white dwarf? Or was the planet instead born later, out of the gas ejected by this star as it died? By studying the KIC 10544976 planet with next generation telescopes, we should be able to answer this question.

How the planet was discovered:

Observations of the eclipsing binary stars show timing variations in the eclipses. This change in orbit could be caused by one of two things: either the gravitational tug of an additional unseen, massive body, or period fluctuations in the magnetic field of the red dwarf. By studying the magnetic activity cycle for the red dwarf using years of flare and starspot data, Almeida and collaborators were able to rule out the hypothesis that magnetic activity caused the eclipse timing variations. This made the presence of a giant planet the most likely explanation.


L. A. Almeida et al 2019 AJ 157 150. doi:10.3847/1538-3881/ab0963