ROSAT HRI survey of the open cluster Stock 2
S. Sciortino 1,
G. Micela 1,
F. Favata 2,
A. Spagna 3 and
M.G. Lattanzi 3
Received 14 October 1999 / Accepted 2 February 2000
We have obtained two deep HRI observations toward the open cluster Stock 2 in order to assess the X-ray luminosity level of the 112 high-probability cluster members falling in the area we have surveyed. Members have been selected on the basis of the result of a recent proper motion study based on the same photographic material and the same reduction scheme as the GSC-II project. We have reached a limiting sensitivity of 3 1029 erg/sec for Stock 2 members and have detected 19 X-ray sources. The attained limiting sensitivity has prevented a complete sampling of the coronal emission level of Stock 2, and we have detected only three solar-type and one B9V members. We have derived the X-ray luminosity function for the Stock 2 stars in the 0.43 0.8 color range and have compared it with the X-ray luminosity functions of the dG members of Praesepe, Hyades and Pleiades open clusters. While the limiting sensitivity of our observations and the present uncertainties in Stock 2 and other cluster distances do not allow to derive firm conclusion, yet, our data indicate that the coronal emission level of Stock 2 solar-type stars is more similar to that of the Hyades (or the Praesepe) than to the Pleiades one.
This in turn suggests that either Stock 2 is older than previously reported or that the current age-rotation-activity paradigm need to be revised. In this latter case Stock 2 would likely belong to the small group of open clusters (Praesepe, NGC6333 and IC 4675) for which recent X-ray surveys indicate a more complex age-rotation-activity relation than currently thought.
Key words: Galaxy: open clusters and associations: individual: Stock 2 stars: activity stars: late-type X-rays: stars
Send offprint requests to: S. Sciortino, (email@example.com)
© European Southern Observatory (ESO) 2000
Online publication: June 5, 2000