# Not Gone with the Wind: Planet Occurrence is Independent of Stellar Galactocentric Velocity

## TL;DR

This study shows that planet occurrence in the Solar neighborhood is independent of stellar galactocentric velocity, revealing that previous apparent correlations are due to selection biases rather than physical differences.

## Contribution

It demonstrates that the observed correlation between planet hosts and slower velocities is an artifact of Kepler's selection function, establishing velocity independence in planet occurrence.

## Key findings

- Planet hosts are slower than field stars by ~40 km/s, but this is a selection bias.
- Velocity distribution of non-host stars with similar properties matches that of planet hosts.
- Probability of hosting a planet is independent of stellar velocity, with v0 > 976 km/s at 99% confidence.

## Abstract

We demonstrate that planet occurrence does not depend on stellar galactocentric velocity in the Solar neighborhood. Using Gaia DR2 astrometry and radial velocity data, we calculate 3D galactocentric velocities for 197,090 Kepler field stars, 1647 of which are confirmed planet hosts. When we compare the galactocentric velocities of planet hosts to those of the entire field star sample, we observe a statistically significant (KS p-value = $10^{-70}$) distinction, with planet hosts being apparently slower than field stars by $\sim$40 km/s. We explore some potential explanations for this difference and conclude that it is not a consequence of the planet-metallicity relation or distinctions in the samples' thin/thick disk membership, but rather an artefact of Kepler's selection function. Non Kepler-host stars that have nearly identical distances, temperatures, surface gravities, and Kepler magnitudes to the confirmed planet hosts also have nearly identical velocity distributions. Using one of these identical non-host samples, we consider that the probability of a star with velocity $v_{\mathrm{tot}}$ hosting a planet can be described by an exponential function proportional to $e^{(-v_{\mathrm{tot}}/v_0)}$. Using a Markov Chain Monte Carlo sampler, we determine that $v_0 > $976 km/s to 99% confidence, which implies that planets in the Solar neighborhood are just as likely to form around fast stars as they are around slow stars. Our work highlights the subtle ways in which selection biases can create strong correlations without physical underpinnings.