Exoplanets in the Galactic context: Planet occurrence rates in the thin disk, thick disk and stellar halo of Kepler stars

TL;DR

This study analyzes how exoplanet occurrence rates vary across different Galactic stellar populations, revealing that thin disk stars are more likely to host planets than thick disk or halo stars, influenced by stellar age and kinematics.

Contribution

It introduces a Bayesian method to compare exoplanet occurrence rates among Galactic components using stellar abundances and kinematics, highlighting the impact of stellar dynamical history.

Findings

Thin disk stars host more close-in super Earths.

Older, metal-poor stars have lower planet occurrence.

Stellar age and kinematics influence planet distribution.

Abstract

In order to gain a better understanding of planet formation and evolution, it is important to examine the statistics of exoplanets in the Galactic context. By combining information on stellar elemental abundances and kinematics, we constructed separate samples of Kepler stars according to their affiliation to the Galactic components of thin disk, thick disk and stellar halo. Using a Bayesian analysis with conjugate priors, we then investigated how planet occurrence rates differ in different regions of planet properties. We find that young, slow and metal-rich stars, associated mainly with the thin disk, host on average more planets (especially close-in super Earths) compared to the old, fast and metal-poor thick disk stars. We further assess the dependence between stellar properties such as spectral type and metallicity, and planet occurrence rates. The trends we find agree with those found by other authors as well. We argue that in the Galactic context, these are probably not the main properties that affect planet occurrence rates, but rather the dynamical history of stars, and especially stellar age and kinematics, impact the current distribution of planets in the Galaxy.