X-Ray Observations of Stellar Coronae and Winds

Abstract

Since the discovery in 1974 by Heise et al. (1975) with the ANS satellite of X-ray flares from YZ CMi and UV Cet, only a few attempts to observe X-rays from flare stars have succeeded. On the other hand, the discovery of X-ray emission from Capella by Catura, Acton and Johnson (1975) in a rocket flight has been followed by so many detections of RS CVn binaries by the low energy detectors (0.15 - 3 keV) of the HEAO A2 experiment that, while Catura et al. estimated that many variable soft X-ray sources probably exist, Walter, Charles and Bowyer (1978) could identify the RS CVn systems as a class of quiescent sources. They have higher temperatures than at first predicted, so they are ideal for detection in the energy range ¼ keV to a few keV, and the high space density provides many close candidates. Further information on these sources is now available from the GSFC Solid State Spectrometer Experiment on the Einstein Observatory, which with energy resolution of 140 eV can resolve the major complexes of line emission from Si, S, Fe and less abundant elements that are an important part of the emission of 10 million degree plasmas. The imaging experiments on the Einstein Observatory have detected X-ray emission from subsets of all types of stars, and results on the luminosities, variability and temperatures are just beginning to come out.