High-time-cadence Spectroscopy and Photometry of Stellar Flares on M-dwarf YZ Canis Minoris with Seimei Telescope and TESS. II. Statistical Properties of Blue/Red Asymmetries in the Hα Line

Abstract

M-dwarfs frequently produce flares, and their associated coronal mass ejections (CMEs) may threaten the habitability of close-in exoplanets. M-dwarf flares sometimes show prominence eruption signatures, observed as blue/red asymmetries in the H α line. In Paper I, we reported four candidates of prominence eruptions, which show large diversity in their durations and velocities. In this study, we statistically investigate how blue/red asymmetries are related to their flare and starspot properties, using the data set from 27 H α flares in Paper I and previously reported 8 H α flares on an M-dwarf, YZ Canis Minoris. We found that these asymmetry events tend to show larger H α flare energies compared to nonasymmetry events. In particular, five out of six blue asymmetry events are not associated with white-light flares, whereas all seven red asymmetry events are associated with white-light flares. Furthermore, their starspot distributions estimated from the Transiting Exoplanet Survey Satellite light curve show that all prominence eruption candidates occurred when starspots were located on the stellar disk center as well as on the stellar limb. These results suggest that flares with lower heating rates may have a higher association rate with prominence eruptions and/or the possibility that prominence eruptions are more detectable on the limb than on the disk center on M-dwarfs. These results provide significant insights into CMEs that can affect the habitable world around M-dwarfs.

Keywords

• Stellar flares
• Stellar coronal mass ejections
• Optical flares
• M dwarf stars
• Flare stars