The Einstein Extended Medium-Sensitivity Survey Second Epoch: Results for the Stars

Abstract

We present X-ray data from the ROSA T all-sky survey for those sources cataloged in the Einstein Extended Medium Sensitivity Survey (EMSS) which have been identified with Galactic stars. This "second epoch" of X-ray data, taken 10 yr later, is used to study coronal flux variability for the most active examples of late-type stars. About 72% of the EMSS stars have been redetected by ROSA T. While the F stars appear to have remained constant, we find evidence for a general decrease in X-ray flux for the M and solar-type stars. This is probably due to the fact that an X-ray-selected sample will preferentially detect stars while flaring. In contradiction to this, the RS CVn binaries have been redetected at higher X-ray flux levels for the sample as a whole.