The X-ray emission of late-type evolved stars

We report on the main results of an extensive x-ray survey carried out on a magnitude-limited sample of late-type giant and supergiant stars. We have selected all the optical candidates in the Bright Star Catalogue, with luminosity classes from III to I and spectral types in the range F to M. The observed sample comprises 380 stars which fell into one of the Einstein Observatory Imaging Proportional Counter (IPC) fields of view, either as targets or serendipitously. This sample is about ten times larger than any previously x-ray studied sample of evolved stars. The whole optical population is limited to apparent visual magnitude mv < 7.1, but it is complete only to mv ∼ 6.3. We have indication that the subsample of stars with reliable trigonometric parallaxes, π > 0.01, is complete only up to mv < 5. On the basis of accurate statistical tests on the distributions of B-V colors, distances, and absolute visual magnitudes, we have also established that our observed sample is indistinguishable from the optical parent population. For this survey we have employed the final REV-1 x-ray data processing. (author)