1996A&A...309L..51H

Based on new pointed ROSAT data, we revise the X-ray dividing line for late-type giants in the HR diagram. We compare the new data with well calibrated evolutionary tracks and suggest that the resulting picture can entirely be understood as a consequence of the different evolutionary history of stellar activity in different mass-ranges. In particular, hot coronae disappear slowly in the course of stellar evolution, since the evolutionary tracks are parallel to the revised X-ray dividing line and do not cross it. Furthermore, hybrid stars turn out to be quite common: they are just more massive, more active and maintain some coronal plasma beyond the onset of cool winds. Hence, the latter may be mostly independent of the decrease of stellar activity.