Exoplanets & Exomoons

Revising Properties of Planet-Host Binary Systems. IV. The Radius Distribution of Small Planets in Binary Star Systems is Dependent on Stellar Separation

By Keith Cowing
Status Report
June 26, 2024
Filed under , , , , , , , , , , ,
Revising Properties of Planet-Host Binary Systems. IV. The Radius Distribution of Small Planets in Binary Star Systems is Dependent on Stellar Separation
Radius versus Teff for all observed systems, showing both initial Kepler values from DR25 (magenta points; Berger et al. 2018) and the revised primary star values from this work (navy points), with the initial and revised values for each system connected by a black line. The underlying curves are MIST isochrones at various ages. The lower panel indicates the percent residual between the 1 Gyr evolutionary model and the final primary star radius for accepted systems. — astro-ph.EP

Small planets (Rp≤4R) are divided into rocky super-Earths and gaseous sub-Neptunes separated by a radius gap, but the mechanisms that produce these distinct planet populations remain unclear.

Binary stars are the only main-sequence systems with an observable record of the protoplanetary disk lifetime and mass reservoir, and the demographics of planets in binaries may provide insights into planet formation and evolution.

To investigate the radius distribution of planets in binary star systems, we observed 207 binary systems hosting 283 confirmed and candidate transiting planets detected by the Kepler mission, then recharacterized the planets while accounting for the observational biases introduced by the secondary star.

We found that the population of planets in close binaries (ρ≤100 au) is significantly different from the planet population in wider binaries (ρ>300 au) or single stars. In contrast to planets around single stars, planets in close binaries appear to have a unimodal radius distribution with a peak near the expected super-Earth peak of Rp∼1.3R and a suppressed population of sub-Neptunes.

We conclude that we are observing the direct impact of a reduced disk lifetime, smaller mass reservoir, and possible altered distribution of solids reducing the sub-Neptune formation efficiency. Our results demonstrate the power of binary stars as a laboratory for exploring planet formation and as a controlled experiment of the impact of varied initial conditions on mature planet populations.

Kendall Sullivan, Adam L. Kraus, Travis A. Berger, Trent J. Dupuy, Elise Evans, Eric Gaidos, Daniel Huber, Michael J. Ireland, Andrew W. Mann, Erik A. Petigura, Pa Chia Thao, Mackenna L. Wood, Jingwen Zhang

Comments: 19 pages, 9 figures, 6 tables. Accepted to AJ. Full tables available upon request to the first author prior to publication
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2406.17648 [astro-ph.EP] (or arXiv:2406.17648v1 [astro-ph.EP] for this version)
Submission history
From: Kendall Sullivan
[v1] Tue, 25 Jun 2024 15:41:13 UTC (997 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻