X-ray emission from hybrid-chromosphere stars

The observations of hybrid stars made by the Exosat X-ray satellite are considered, and emphasis is placed on the hybrid star alpha TrA. Attention is focused on the determination of the column density of IS hydrogen toward the stars in order to interpret X-ray observations of stellar coronal emission. The coronal properties of alpha TrA are discussed as well as implications of the general coronal properties of hybrid stars. An analysis of the X-ray data, in conjunction with transition region properties of the star, shows that the X-ray emitting plasma is likely to have a temperature of at least 10 to the 6th K. The X-ray luminosity of the star is calculated to be about 5 x 10 to the 29th ergs/s over the 1-300 A spectral region and 7 x 10 to the 28th ergs/s in the 0.2-4 keV energy range for N(H) = 5 x 10 to the 19th /sq cm and a temperature of 10 to the 6th K.