Coordinated Exosat and spectroscopic observations of flare stars and coronal heating

Abstract

The X-ray flux of dMe stars is thought to arise from two distinct mechanisms, one involving a continuous `quiescent' emission from a high-temperature plasma and the other involving the dramatic flare events which have long been known to occur on these stars. We present here some results of simultaneous monitoring of the two flare stars, UV Ceti and EQ Peg, with Exosat and ground-based optical spectroscopy. We observe short-timescale variability in the 0.1-2-keV emission from both these objects and, in the case of UV Ceti, find a strong correlation between the soft X-ray and Hγ fluctuations. The implication is that much of the low-level X-ray flux previously considered `quiescent' probably originates from small flare events.