Small Planets in the Galactic Context: Host Star Kinematics, Iron, and $alpha$ Element Enhancement. (arXiv:1906.01982v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bashi_D/0/1/0/all/0/1">Dolev Bashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zucker_S/0/1/0/all/0/1">Shay Zucker</a>

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.

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.

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