Atmospheric Activity in the Outer Envelopes of Cool Dwarf Stars

Abstract

We review the observed properties of the radiation from flare star atmospheres and stellar flare regions. Data from satellite and ground-based instruments are used to investigate interrelations between the photospheres, chromospheres, transition regions and coronae of these stars. Both dMe and dM stars obey the same relationships for the outer layers of the atmosphere, but these connections fail to be valid at the photospheric level. This may be a manifestation of an age effect. Quiescent and flaring surface fluxes are high for bright active stars with radiative cores, and become progressively smaller for fully convective low mass stars. The change in interior structure may lead to a change of dynamo mode in these stars. The close connection between quiescent and flaring parameters suggests a common cause for all forms of observable radiation losses.The flare power of a star is directly proportional to its flare frequency. dMe stars are 100–1000 times more active than dM stars of similar luminosity. Bright stars are more than 100 times more active than faint flare stars. Recent multi-frequency observations of flares show that the X-ray, ultraviolet, and optical spectral regions contribute approximately equal amounts of radiation during flares. In some active dMe stars the flare radiation in these spectral windows accounts for 0.1–0.3% of their bolometric luminosity. This is comparable to the amount emitted from the quiescent atmosphere.KeywordsFlare ActivityBolometric LuminosityFlare StarFaint StarFlare EnergyThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.