Host star metallicity of directly imaged wide-orbit planets: implications for planet formation

TL;DR

This study analyzes the metallicity of stars hosting wide-orbit directly imaged planets, finding near-solar metallicities with significant scatter, suggesting diverse formation environments and similar planet-metallicity relations across different orbital distances.

Contribution

It provides uniform stellar parameter and metallicity measurements for a sample of directly imaged planet hosts, including first-time metallicity estimates for eight stars, and compares these to known planet-metallicity trends.

Findings

Host star metallicities are near solar with large scatter.

Metallicity may not be crucial for forming massive wide-orbit planets.

Planet mass-metallicity relation is similar to that of close-in super-Jupiters.

Abstract

Directly imaged planets are self-luminous companions of pre-main sequence and young main sequence stars. They reside in wider orbits ($\sim10\mathrm{s}-1000\mathrm{s}$~AU) and generally are more massive compared to the close-in ($\lesssim 10$~AU) planets. Determining the host star properties of these outstretched planetary systems is important to understand and discern various planet formation and evolution scenarios. We present the stellar parameters and metallicity ([Fe/H]) for a subsample of 18 stars known to host planets discovered by the direct imaging technique. We retrieved the high-resolution spectra for these stars from public archives and used the synthetic spectral fitting technique and Bayesian analysis to determine the stellar properties in a uniform and consistent way. For eight sources, the metallicities are reported for the first time, while the results are consistent with the previous estimates for the other sources. Our analysis shows that metallicities of stars hosting directly imaged planets are close to solar with a mean [Fe/H] = $-0.04\pm0.27$~dex. The large scatter in metallicity suggests that a metal-rich environment may not be necessary to form massive planets at large orbital distances. We also find that the planet mass-host star metallicity relation for the directly imaged massive planets in wide-orbits is very similar to that found for the well studied population of short period ($\lesssim 1$~yr) super-Jupiters and brown-dwarfs around main-sequence stars.