Galactic chemical evolution of exoplanet host stars: Are high-mass planetary systems young?

TL;DR

This study investigates how stellar chemical abundances relate to exoplanet mass, revealing that stars with giant planets tend to be younger and more metal-rich, consistent with Galactic chemical evolution and planet formation theories.

Contribution

It provides a large-scale analysis of chemical abundances in over 900 exoplanet host stars, linking stellar age, metallicity, and planet mass to Galactic chemical evolution.

Findings

Stars with giant planets are relatively younger.

Negative correlation between alpha-element abundance and planet mass.

Protoplanetary disk metallicity influences giant planet formation.

Abstract

The imprints of stellar nucleosynthesis and chemical evolution of the galaxy can be seen in different stellar populations, with older generation stars showing higher $\alpha$-element abundances while the later generations becoming enriched with iron-peak elements. The evolutionary connections and chemical characteristics of circumstellar disks, stars, and their planetary companions can be inferred by studying the interdependence of planetary and host star properties. Numerous studies in the past have confirmed that high-mass giant planets are commonly found around metal-rich stars, while the stellar hosts of low-mass planets have a wide range of metallicity. In this work, we analyzed the detailed chemical abundances for a sample of $>900$ exoplanet hosting stars drawn from different radial velocity and transit surveys. We correlate the stellar abundance trends for $\alpha$ and iron-peak elements with the planets' mass. We find the planet mass-abundance correlation to be primarily negative for $\alpha$-elements and marginally positive or zero for the iron-peak elements, indicating that stars hosting giant planets are relatively younger. This is further validated by the age of the host stars obtained from isochrone fitting. The later enrichment of protoplanetary material with iron and iron-peak elements is also consistent with the formation of the giant planets via the core accretion process. A higher metal fraction in the protoplanetary disk is conducive to rapid core growth, thus providing a plausible route for the formation of giant planets. This study, therefore, indicates the observed trends in stellar abundances and planet mass are most likely a natural consequence of Galactic chemical evolution.