[P-EM11] Exoplanet

[PEM11-P12] Characterization of transiting sub-Neptune and outer giant planet candidate around mid-M dwarf TOI-654

*Kai Ikuta¹, Norio Narita^1,2, Takuya Takarada^2,3, Teruyuki Hirano^2,3, Akihiko Fukui¹, Takanori Kodama¹, Tadahiro Kimura¹, Yasunori Hori^2,3, Masahiro Ikoma^1,3, Takayuki Kotani^2,3, Motohide Tamura^1,2, IRD Intensive team, IRD Instrument team, MuSCAT team (1.The University of Tokyo, 2.Astrobiology Center, 3.National Astronomical Observatory of Japan)

Keywords:Extrasolar planet, Sub-Neptune, M-dwarf, Radial velocity, Subaru/IRD, Parallel tempering

Transiting exoplanet candidates have been detected by the Transit Exoplanet Survey Satellite (TESS) over five years of its observations. We have characterized the candidates by the follow-up observations with the MuSCAT (Multicolor Simultaneous Camera) series mounted on three telescopes at different longitudes in the northern hemisphere and the IRD (InfraRed Doppler) instrument mounted on the Subaru telescope. Some of the radial velocity (RV) data obtained with Subaru/IRD suggest that there are multiplanetary system candidates with an outer planet for which no transit has been detected during the TESS observation period. Therefore, to deduce parameters for such multiple planets and compare models with the different numbers of planets, it is essential to perform efficient parameter estimation and compute each of the model evidence. Then, we introduced a parallel tempering algorithm for the analysis of the RV data. We analyzed the RV data of a mid-M dwarf TOI-654 (radius = 0.43R_sun, effective temperature = 3400 K, distance = 57.8 pc) with a transit planet candidate TOI-654.01 (radius =2.37 R_earth, orbital period =1.53 day). As a result, the parameters of TOI-654.01 and the outer planet candidate are estimated to be the orbital period P = 1.53, 42.4 days and mass M_p sin i ~ 8 M_earth, 48 M_earth (~ 0.15 M_jup), respectively. From the analysis of activity indicators, there are no spurious signals for the period of the outer planet candidate. In our talk, we give discussions about its formation process and suggestions for the analysis of other multiplanetary system candidates obtained with IRD intensive observations and for future observations.