Comparison of Chromospheric and Coronal Activity in the Hyades and Pleiades
Abstract
We present results from our extensive survey of chromospheric and coronal activity in lower main-sequence members of the Hyades open cluster. We have obtained H alpha spectroscopy of ninety-one probable cluster members, twenty-three of which lie within three fields for which we have deep ROSAT X-ray observations. Twenty of the twenty-three stars are detected. Combining these observations with data from the literature, we find that the mean ratio log (L_alpha / Lbol) is roughly constant for Mbol > 8, with a substantial dispersion. The X-ray-to-bolometric luminosity ratio increases with decreasing Mbol, although the relation may flatten for Mbol > 9. Comparing this behaviour with stars in the Pleiades cluster, there are significant differences: first, the log (L_alpha / Lbol) relation in the Pleiades increases for Mbol < 10, but appears to turn over sharply at fainter magnitudes, with the lower luminosity stars having nearly an order of magnitude lower H alpha luminosity; second, we find no evidence for saturation in the log (L_X / Lbol) ratio. However, none of the lower luminosity Pleiades stars with low H alpha luminosity have X-ray observations.
- Publication:
-
American Astronomical Society Meeting Abstracts #184
- Pub Date:
- May 1994
- Bibcode:
- 1994AAS...184.4305H