ARE LATE B-TYPE STARS INTRINSIC X-RAY EMITTERS

In the ROSAT all-sky survey close to one hundred X-ray sources have be en identified with late B-type stars of spectral type B7 - B9. Previou s X-ray observations have suggested that stars in this spectral range are devoid of X-ray emission. In order to study whether late B-type st ars represent a new class of X-ray sources or whether the detected X-r ay emission originates from a companion star we have selected a sample of known visual binaries, with a late B-type star as the primary and detected in the ROSAT all-sky survey, for follow-up observations with the ROSAT High Resolution Imager (HRI). In the first 8 systems studied with the HRI we could identify 6 late B-type stars and an Ap star as the X-ray source. Our observations cast doubts on the usual argument t hat in the case of an X-ray emitting late B-type star with a late-type companion, the X-ray emission always comes from the companion star.