Properties and occurrence rates of $Kepler$ exoplanet candidates as a function of host star metallicity from the DR25 catalog

TL;DR

This study analyzes over 2800 Kepler exoplanet candidates to explore how host star metallicity correlates with planetary properties like radius, mass, and orbital period, revealing significant trends that inform planet formation theories.

Contribution

It provides a comprehensive analysis of the relationship between host star metallicity and exoplanet characteristics using the latest Kepler data and Gaia-based radius measurements, confirming and extending previous findings.

Findings

Host star metallicity increases with planetary radius.

Metallicity correlates positively with planet mass up to 4 Jupiter masses.

Higher host star metallicity is associated with shorter orbital periods (<10 days).

Abstract

Correlations between the occurrence rate of exoplanets and their host star properties provide important clues about the planet formation processes. We studied the dependence of the observed properties of exoplanets (radius, mass, and orbital period) as a function of their host star metallicity. We analyzed the planetary radii and orbital periods of over 2800 $Kepler$ candidates from the latest $Kepler$ data release DR25 (Q1-Q17) with revised planetary radii based on $Gaia$~DR2 as a function of host star metallicity (from the Q1-Q17 (DR25) stellar and planet catalog). With a much larger sample and improved radius measurements, we are able to reconfirm previous results in the literature. We show that the average metallicity of the host star increases as the radius of the planet increases. We demonstrate this by first calculating the average host star metallicity for different radius bins and then supplementing these results by calculating the occurrence rate as a function of planetary radius and host star metallicity. We find a similar trend between host star metallicity and planet mass: the average host star metallicity increases with increasing planet mass. This trend, however, reverses for masses $> 4.0\, M_\mathrm{J}$: host star metallicity drops with increasing planetary mass. We further examined the correlation between the host star metallicity and the orbital period of the planet. We find that for planets with orbital periods less than 10 days, the average metallicity of the host star is higher than that for planets with periods greater than 10 days.