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

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 $0.463_{-0.088}^{+0.082}{M}_{\mathrm{Jup}}$. We also find that the host star is metal rich ($[Fe/H]=0.27\pm 0.09$ dex) and has the lowest effective temperature ($T_{\mathrm{eff}}=3322\pm 49$ 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 $\sim 30M_{\oplus }$, 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.

10 pages, 5 figures. Accepted for publication in PASJ