[P-AE17] Exoplanets

[PAE17-18] Mass determination of TOI-519b: a short-period transiting giant planet around a metal-rich mid-M dwarf

*Taiki Kagetani¹, Norio Narita¹, Akihiko Fukui¹, Masahiro Ikoma², Takanori Kodama¹, Tadahiro Kimura¹, Teruyuki Hirano³, Hiroyuki Tako Ishikawa³, Yasunori Hori³, Motohide Tamura^1,3, Takayuki Kotani³, IRD Intensive Team, IRD Instrument Team, IRTF Team (1.The University of Tokyo, 2.National Astronomical Observatory of Japan, 3.Astrobiology Center)

Keywords:Hot Jupiter, Transit, Low-mass star, Radial velocity

Since the start of the TESS survey, many exoplanet candidates around M dwarfs have been discovered. They have been followed up by ground-based telescopes by means of e.g., radial velocity (RV) measurements and transit photometry, and the radii, masses and orbital periods of many exoplanets have been confirmed. Observations to date show that short period (P < 10 day) and Jupiter-sized (R_p > 8 R_E) exoplanets, or hot Jupiters, are rare, especially around M dwarfs. In fact, the number of detected giant planets around M dwarfs is only about twenty, which reduces to seven when only short-period planets are considered (Kepler-45b, HATS-6b, NGTS-1b, HATS-71b, TOI-530b, HATS-74Ab, HATS-75b). This is consistent with the prediction by the core accretion theory of planet formation. However, it has been unclear if the discovered giant planets around M dwarfs were formed in the core-accretion scheme or not, and how rare such planets formed in this scheme are. In order to test the formation mechanisms of short-period giant planets around low-mass stars, it is important to determine not only planetary characteristics such as radius and mass but also host star's one such as effective temperature and metallicity.

TOI-519b is a giant substellar object around an M dwarf. This object was validated with multi-color photometric observations and phase curve analysis using light curves of TESS and MuSCATs (Parviainen et al. 2021). They show that TOI-519b has a Jupiter-like radius (R_p ~ 1.06 R_Jup) and has short orbital period (P ~ 1.26 day). However, they did not reject TOI-519b to be brown dwarf because they could not put strong upper limit on the planetary mass (M_p < 14 M_Jup), so in order to determine whether TOI-519b is giant planet or brown dwarf, we need to constrain its mass more strongly by RV surveys.

We carried out the RV surveys using Infrared Doppler (IRD) installed on Subaru Telescope under the Subaru-IRD TESS intensive follow-up program, and we found that the mass of TOI-519b is ~ 0.5 M_Jup, which shows that this object is definitely a giant planet, not brown dwarf. We also derived the stellar parameters, such as effective temperature (T_eff ~ 3250 K) and metallicity ([Fe/H] ~ 0.3) using spectra of both IRD and IRTF/SpeX . This primary star is metal rich and has the lowest effective temperature among the M dwarfs hosting short-period transit giant planets discovered so far.

In this talk, we will show the results of the analysis on mass determination and discuss the scenario of the planet formation taking into account the characteristics of the primary star.