The mass determination of TOI-519 b: a close-in giant planet transiting a metal-rich mid-M dwarf

TL;DR

This study precisely measures the mass of the transiting giant planet TOI-519 b around a metal-rich mid-M dwarf, revealing insights into its composition, host star properties, and potential formation mechanisms.

Contribution

First mass measurement of TOI-519 b using Subaru IRD, and analysis of its host star's metallicity and temperature, providing clues about planet formation around M dwarfs.

Findings

TOI-519 b has a mass of approximately 0.46 Jupiter masses.

Host star is notably metal-rich and has the lowest temperature among similar known systems.

The planet's core mass estimate supports formation via core accretion or disk instability.

Abstract

We report the mass determination of TOI-519 b, a transiting substellar object around a mid-M dwarf. We carried out radial velocity measurements using Subaru / InfraRed Doppler (IRD), revealing that TOI-519 b is a planet with a mass of $0.463^{+0.082}_{-0.088}~M_{\rm Jup}$. We also find that the host star is metal rich ($\rm [Fe/H] = 0.27 \pm 0.09$ dex) and has the lowest effective temperature ($T_{\rm eff}=3322 \pm 49$ K) among all stars hosting known close-in giant planets based on the IRD spectra and mid-resolution infrared spectra obtained with NASA Infrared Telescope Facility / SpeX. The core mass of TOI-519 b inferred from a thermal evolution model ranges from $0$ to $\sim30~M_\oplus$, which can be explained by both the core accretion and disk instability models as the formation origins of this planet. However, TOI-519 is in line with the emerging trend that M dwarfs with close-in giant planets tend to have high metallicity, which may indicate that they formed in the core accretion model. The system is also consistent with the potential trend that close-in giant planets around M dwarfs tend to be less massive than those around FGK dwarfs.