X-rays from M-type Giants-Signs of Late Stellar Activity?
Abstract
M-type giants -- either on the RGB or the AGB -- are generally not known to exhibit significant stellar activity. Yet in the course of the ROSAT All-Sky survey a few such stars have been detected as luminous X-ray sources. We report recent Chandra observations that have ruled out the possibility of spurious identifications. First results from our optical spectroscopic follow-up study indicate variability in H-alpha and Ca I 6572 A lines that may be related to chromospheric activity. CORAVEL and ELODIE observations reveal faster rotation than usual and small-amplitude radial-velocity variations indicating binary nature for some of these stars. Chromospheric and coronal emission seems to be variable on rather short timescales. There are no hints for the stars being symbiotic systems up to now.
- Publication:
-
Stars as Suns : Activity, Evolution and Planets
- Pub Date:
- January 2004
- Bibcode:
- 2004IAUS..219..223H