Recent spectroscopic observations of stellar flares and possible stellar mass ejections

Flares are frequent energetic explosions in the stellar atmosphere, and are thought to occur by impulsive releases of magnetic energy stored around starspots. Large flares (so called “superflares”) generate strong high energy X+UV emissions and coronal mass ejections (CMEs), which can greatly affect the planetary environment and habitability. Recent Kepler/TESS photometric data have revealed the statistical properties of superflares on G, K, M-type stars. Young rapidly-rotating stars (e.g., “Young Suns”) and cooler stars (“M dwarfs”) tend to have frequent flares, which can be more “hazardous” for the habitable planets. However, we still do not know the emission mechanisms of superflares, and how large CMEs are associated with superflares on these active stars. Then recently, these active flare stars have been investigated in more detail through multi-wavelength campaign observations. In particular, we have worked on the observation campaigns of young G-dwarfs (young Sun analogs) and M-dwarfs, and have reported candidates of stellar filament/prominence eruptions, probably leading to CMEs, as a blue-shifted absorption/emission of chromospheric lines associated with stellar flares. Notably, the erupted masses for superflares are larger than those of the largest solar CMEs, indicating severe influence on various planets including exoplanets and young Earth/Mars.  In this presentation, I will overview our recent observation results of flares and stellar CME candidates described in the above, and discuss future prospects on further multi-wavelength observations, and the importance of more collaborations with solar-based observation/modeling studies.