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 emissions and coronal mass ejections (CMEs), which can greatly affect the planetary environments. For haracterizing stellar CMEs, understanding of their sources (e.g., flares and erupting prominences) is important. Recent Kepler/TESS photometric data have revealed the statistical properties of superflares on G, K, M-type stars. Superflare stars are well characterized by the existence of large starspots on the surface, and their magnetic fluxes can explain well superflare energies. Flare frequency/energy depends on stellar rotation period and stellar temperature. Young rapidly-rotating stars and cooler stars tend to have frequent flares. Recent spectroscopic observation campaigns have detected some possible candidates of stellar prominence eruptions from G-M stars using blueshifts of chromospheric lines (e.g., H-alpha). They could be the start point for quantitatively discussing physical properties and time evolution of stellar CMEs, and their effects on the environment and habitability of various planets. In the early part of the talk, I briefly overview the recent statistical results of superflares from Kepler/TESS data. Then in the latter part, I discuss the recent reports of stellar prominence eruptions and how these results can help our understanding of stellar CMEs.

Invited talk at the Splinter Session "Solar and stellar coronal mass ejections"