First Results from ROSAT All-Sky Survey Observations of the Hyades Cluster
Abstract
We present preliminary ROSAT all-sky survey results for the Hyades cluster. We detected 108 Hyades cluster members as X-ray sources with L(y) greater than about 3 x 10 exp 28 ergs/s. A number of short-period, chromospherically active binary systems and the giants Theta1 Tau and Gamma Tau are among the most X-ray-luminous objects in the cluster. The second brightest X-ray source, HR 1394 = 71 Tau = VB 141, is a long-period lunar occultation binary. Seven cluster members were also seen in the Wide Field Camera EUV all-sky survey. Among the stars detected in both X-rays and EUV is the Hyades white dwarf EG 37 (= VR 16), confirming an earlier serendipitous EXOSAT detection. We also report the first X-ray detection of the Hyades K0 giant Epsilon Tau, at roughly the survey limit. This new result establishes all four Hyades giants as X-ray emitters, although with an about 50:1 range in L(x). A comparison of Einstein and ROSAT data for three of the giants suggests that long-term X-ray variability, perhaps due to activity cycles, may be partly responsible for the wide dispersion in L(x).
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1992
- DOI:
- 10.1086/186631
- Bibcode:
- 1992ApJ...399L.159S
- Keywords:
-
- Open Clusters;
- Rosat Mission;
- Sky Surveys (Astronomy);
- Spaceborne Astronomy;
- X Ray Stars;
- Astronomical Catalogs;
- Astronomical Maps;
- Binary Stars;
- Giant Stars;
- K Stars;
- Astronomy;
- GALAXY: OPEN CLUSTERS AND ASSOCIATIONS: GENERAL;
- STARS: CORONAE;
- X-RAYS: STARS