1996A&A...306..278C

Three serendipitous X-ray sources detected by the Einstein satellite were photometrically and spectroscopically observed during the course of a systematic study of known or suspected chromospherically active stars carried out at the European Southern Observatory (La Silla, Chile). Clear optical variability of the source 1E0315.7-1955 and 1E0505.0-0527 was discovered and their photometric periods computed. The data obtained for a third serendipitous source, 1E1127.9-1502, are also discussed. Spectral types, distances and X-ray fluxes have been estimated for all of the sources.