The Origin of the Far-Ultraviolet Continuum in Solar and Stellar Flares

Abstract

A continuum in the far-ultraviolet region observed in IUE spectra of dMe stars in a flaring state is discussed and compared with that observed in solar flares. Similar continuous emission observed in solar flare far-ultraviolet spectra has been identified with neutral silicon recombination radiation excited by intense lines. This also appears to be the case for stellar flares, as is deduced here from the proportionality of far-ultraviolet line and continuum power for several flares on dMe stars, two flares on an RS CVn star (II Peg), and the spotted active binary BY Dra. The only solar flare observation available, from Skylab, obeys this same linear relation. Other emission mechanisms are considered, but they are unlikely to give the observed continuum flux.