A Uniform Determination of the Bulk Metallicities and Alpha Enrichments of Confirmed Exoplanet Systems with TRES

TL;DR

This study provides a uniform spectroscopic catalog of 625 exoplanet host stars, analyzing their metallicities and alpha-element enrichments to explore their influence on planet formation and system characteristics.

Contribution

It introduces a comprehensive, uniform measurement of stellar parameters, including [$ ext{Fe/H}$] and [$ ext{alpha}$/Fe], for a large sample of exoplanet hosts using the neural network spectral code uberMS.

Findings

Subsolar metallicity giant-planet hosts are significantly alpha-enhanced.

Alpha enrichment may help form giant planets in low-metallicity environments.

Modest evidence suggests alpha-enhanced stars may host more multi-planet systems.

Abstract

We present a uniform spectroscopic characterization of 625 F, G, and K stars hosting 859 confirmed exoplanets using high-resolution archival optical spectra from the Tillinghast Reflector Echelle Spectrograph (TRES). We use the neural network spectral code uberMS, which combines spectra with broadband photometry to estimate precise and accurate stellar parameters. We determine stellar effective temperatures, surface gravities, radii, luminosities, projected rotational velocities, [Fe/H] abundances, and [$\alpha$/Fe] enrichments for most confirmed planet hosts observed by TRES. This uniform catalog can be used for a broad range of astrophysical studies, particularly to explore links between stellar [$\alpha$/Fe] and a suite of observed exoplanet properties. Combining our metallicity measurements with galactic kinematics, we identify 58 planet hosts that are likely members of the thick disk. We investigate the chemical environments of giant-planet formation by comparing the [$\alpha$/Fe] distributions of giant-planet host stars across different metallicity regimes. We find that subsolar metallicity giant-planet hosts are significantly enhanced in [$\alpha$/Fe] relative to Fe-rich giant-planet hosts and to the average Fe-poor field star, at high statistical significance. This suggests that enhanced $\alpha$-element abundances may partially compensate for low-Fe content and thus enable the formation of giant planets in metal-poor environments. We additionally compare the [$\alpha$/Fe] distributions of single- and multi-planet hosts and find modest evidence that $\alpha$-enhanced stars may preferentially host multi-planet systems. Finally, we recover previously observed trends between stellar metallicity and planetary eccentricity.