# Small Planets in the Galactic Context: Host Star Kinematics, Iron, and $\alpha$ Element Enhancement

## TL;DR

This study investigates how the occurrence of small close-in planets around stars relates to stellar iron abundance and kinematics, revealing distinct patterns linked to alpha element enhancement and stellar velocity.

## Contribution

It introduces a combined analysis of iron and alpha element abundances with stellar kinematics to explain small planet occurrence patterns, highlighting the importance of both factors.

## Key findings

- Higher small planet occurrence in iron-poor, high-velocity stars.
- Increased planet occurrence with iron abundance in slower stars.
- Identification of two stellar regions favoring small planet formation.

## Abstract

We explored the occurrence rate of small close-in planets among $\textit{Kepler}$ target stars as a function of the iron abundance and the stellar total velocity $V_\mathrm{tot}$. We estimated the occurrence rate of those planets by combining information from LAMOST and the California-$\textit{Kepler}$ Survey (CKS) and found that iron-poor stars exhibit an increase in the occurrence with $V_\mathrm{tot}$ from $f < 0.2$ planets per star at $ V_\mathrm{tot} < 30\ \mathrm{km~s}^{-1}$ to $f \sim 1.2$ at $V_\mathrm{tot} > 90\ \mathrm{km~s}^{-1}$. We suggest this planetary profusion may be a result of a higher abundance of $\alpha$ elements associated with iron-poor, high-velocity stars. Furthermore, we have identified an increase in small planet occurrence with iron abundance, particularly for the slower stars ($V_\mathrm{tot} < 30\ \mathrm{km~s}^{-1}$), where the occurrence increased to $f \sim 1.1$ planets per star in the iron-rich domain. Our results suggest there are two regions in the $([\mathrm{Fe}/\mathrm{H}],[\alpha/\mathrm{Fe}])$ plane in which stars tend to form and maintain small planets. We argue that analysis of the effect of overall metal content on planet occurrence is incomplete without including information on both iron and $\alpha$ element enhancement.