Simultaneous X-ray and ultraviolet observations of Epsilon Orionis and Kappa Orionis

Simultaneous observations were made with the Einstein Observatory, the International Ultraviolet Explorer, and the Copernicus satellite of the supergiant stars η Ori (B0 Ia) and κ Ori (B0.5 Ia). The X-ray observations spanned periods of 7 hours and 10 hours, and the ultraviolet observations spanned 15 and 18 hours for ηOri and κ Ori, respectively. For either star, no variations were detected in the X-ray flux or spectrum or in the ultraviolet line profiles of Auger enhanced ionization states. For ηOri, the X-ray count rate was the same as it was during an observation 11 months earlier, while for κ Ori, the X-ray count rate was 46% larger than it was 11 months earlier. This change could be explained by an increase in the source temperature from 106.3 K to 106.4 K, or by an increase in the source emission measure of 46 %, or by a decrease in the column density of the intervening matter of several times 1020 cm⁻². The ultraviolet line profiles are found to be insensitive to changes of X-ray flux which are less than 50 %. Various constraints imposed on current models for the X-ray production in early-type stars are discussed.