The Eccentricity Distribution of Short-Period Planet Candidates Detected by Kepler in Occultation

TL;DR

This study analyzes the eccentricity distribution of about 50 short-period planet candidates from Kepler data, revealing a predominantly low-eccentricity population with a small subset exhibiting higher eccentricities, and explores correlations with stellar and planetary properties.

Contribution

It introduces a two-component Gaussian mixture model for eccentricity distribution, improving upon simpler models, and provides insights into the relationship between eccentricity and host star/planet characteristics.

Findings

Majority (~90%) of planets have low eccentricity (~0.01).

Approximately 10% of planets have higher eccentricity (~0.22).

Eccentricity distribution varies with host star metallicity and planet size.

Abstract

We characterize the eccentricity distribution of a sample of ~50 short-period planet candidates using transit and occultation measurements from NASA's Kepler Mission. First, we evaluate the sensitivity of our hierarchical Bayesian modeling and test its robustness to model misspecification using simulated data. When analyzing actual data assuming a Rayleigh distribution for eccentricity, we find that the posterior mode for the dispersion parameter is $\sigma=0.081 \pm^{0.014}_{0.003}$. We find that a two-component Gaussian mixture model for $e \cos \omega$ and $e \sin \omega$ provides a better model than either a Rayleigh or Beta distribution. Based on our favored model, we find that $\sim90\%$ of planet candidates in our sample come from a population with an eccentricity distribution characterized by a small dispersion ($\sim0.01$), and $\sim10\%$ come from a population with a larger dispersion ($\sim0.22$). Finally, we investigate how the eccentricity distribution correlates with selected planet and host star parameters. We find evidence that suggests systems around higher metallicity stars and planet candidates with smaller radii come from a more complex eccentricity distribution.