Testing the Planet-Metallicity Correlation in M-dwarfs with Gemini GNIRS Spectra

TL;DR

This study uses near-infrared spectra from Gemini GNIRS to investigate the planet-metallicity correlation in M-dwarfs, finding that planet-hosting M-dwarfs tend to be more metal-rich, supporting core accretion theory.

Contribution

First application of GNIRS spectra to determine metallicities of M-dwarfs, confirming the planet-metallicity correlation and its dependence on planet type.

Findings

Planet-hosting M-dwarfs are more metal-rich than non-hosts.

M-dwarfs with giant planets are more metal-rich than those with smaller planets.

Results support the core accretion model of planet formation.

Abstract

While the planet-metallicity correlation for FGK main-sequence stars hosting giant planets is well established, the results are not so clear for M-dwarf stars, for which precise metallicity measurements are not straightforward. However, new techniques using near infrared spectra show promising results. Using these, we determine stellar parameters and metallicities for a sample of 16 M-dwarf stars, 11 of which host planets, with near-infrared spectra from the Gemini Near-Infrared Spectrograph (GNIRS). We find that M-dwarfs with planets are preferentially metal-rich compared to those without planets. This result, based on GNIRS spectra, is supported by the analysis of a relatively larger sample of M stars with planets (18 in total) and a control sample of 213 M stars without known planets, obtained from the catalogue of Terrien et al. (2015). This, on the one hand, coincides with the trend (not only for M- but also for solar-type stars) reported in the literature and, on the other hand, demonstrates the utility of GNIRS spectra to obtain reliable stellar parameters of M stars. We also find that M dwarfs that harbor giant planets are preferentially more metallic than those associated with low-mass planets (Neptune or super-Earth type). This trend also agrees with that previously reported for solar-type stars. These results would favor the core accretion model for planetary formation.