[P-AE17] Exoplanets

[PAE17-14] Starspot mapping with parallel tempering for M-dwarf flare stars

*Kai Ikuta¹, Kosuke Namekata², Yuta Notsu^3,4, Hiroyuki Maehara², Satoshi Honda⁵, Daisaku Nogami⁶, Kazunari Shibata^6,7, Mayuko Mori¹, Akihiko Fukui¹, Norio Narita¹ (1.The University of Tokyo, 2.National Astronomical Observatory of Japan, 3.Tokyo Institute of Technology, 4.University of Colorado Boulder, 5.University of Hyogo, 6.Kyoto University, 7.Doshisha University)

Keywords:Starspot, Stellar flare, M-dwarf, Bayesian inference, Parallel tempering, Exoplanet transit

Starspots are apparent manifestations of stellar magnetic activity on the stellar surface of M-, K-, G-dwarfs. Stellar flares are closely associated with spots and caused by releasing their magnetic energy. It is essential to understand the relation between spots and flares in the exoplanetary context because spots make transiting exoplanets difficult to detect and characterize, and flares affect the formation and habitability of exoplanets around the star. Spots fluctuate the light curves by rotating in and out of the line of sight, and the periodicity and amplitude of the light curves can provide information on the spot location and size, and the stellar differential rotation. However, it is difficult to estimate such a large number of parameters simultaneously since there are many spots on the surface. Therefore, we implemented a code to decipher the stellar surface from the light curves. The code enables to deduce many parameters by parallel tempering and to calculate the model evidence for comparing the number of spots. We applied the code to the light curves of bright M-dwarf flare stars, AU Microscopii (AU Mic; harboring debris disk and two planets), YZ Canis Minoris (YZ CMi), and EV Lacertae, observed by Transit Exoplanet Survey Satellite (TESS) in the prime and extended missions. These targets have been observed by spectroscopic monitoring of their flares, and these are suitable for investigating the relation between spots and flares. As results, the spot location and size are uniquely deduced and almost consistent with those in studies by Doppler imaging techniques. The spot location is suggested to be not correlated with flares in the light curve because the spot is always visible in all phases of the light curve. The structure variation of the light curve for AU Mic and YZ CMi in two years can be explained by the variation in the spot position and size due to the differential rotation or spot emergence/decay. These studies allow us to investigate effects of spots on the characterization of transiting exoplanets using MuSCAT facilities.