Host Star Dependence of Small Planet Mass-Radius Distributions

TL;DR

This study investigates whether the mass-radius relationship of small exoplanets depends on the host star type, finding current data consistent with no dependence but indicating higher heavy-element content around M dwarfs.

Contribution

It introduces a hierarchical Bayesian model to analyze host star dependence in small planet mass-radius distributions using Kepler data.

Findings

Current data shows no significant host star dependence.

M dwarfs tend to have higher heavy-element mass in close-orbiting planets.

Framework facilitates comparison between different planet surveys.

Abstract

The planet formation environment around M dwarf stars is different than around G dwarf stars. The longer hot protostellar phase, activity levels and lower protoplanetary disk mass of M dwarfs all may leave imprints on the composition distribution of planets. We use hierarchical Bayesian modeling conditioned on the sample of transiting planets with radial velocity mass measurements to explore small planet mass-radius distributions that depend on host star mass. We find that the current mass-radius dataset is consistent with no host star mass dependence. These models are then applied to the \textit{Kepler} planet radius distribution to calculate the mass distribution of close-orbiting planets and how it varies with host star mass. We find that the average heavy-element mass per star at short orbits is higher for M dwarfs compared to FGK dwarfs, in agreement with previous studies. This work will facilitate comparisons between microlensing planet surveys and \textit{Kepler}, and will provide an analysis framework that can readily be updated as more M dwarf planets are discovered by ongoing and future surveys such as \textit{K2} and \textit{TESS}.