LITHIUM IN ROSAT-DISCOVERED CANDIDATE MEMBERS IN THE ALPHA-PERSEI CLUSTER

We present lithium observations of 23 X-ray selected candidate members of alpha Per, which are part of a larger sample of stars identified t hrough two ROSAT surveys of the cluster. Our observations on one hand allowed us to confirm membership for 18 of the candidates, thus sugges ting that a high percentage of the whole X-ray selected candidates are probably cluster members. On the other hand, we had the possibility t o significantly enlarge the Li database for this cluster. The distribu tion of Li abundances for stars in our sample (or 'new' members) is in good agreement with that for previously known (or 'old') members, alt hough 'new' members in the 5000-4700 T-eff interval stay on the upper envelope of the Li vs. T-eff diagram. The comparison of the merged 'ne w' + 'old' sample with the younger IC 2602 and IC 4665 clusters and wi th the older Pleiades confirms that stars more massive than the Sun do not undergo any PMS Li destruction, whereas some depletion occurs dur ing the early phases on the ZAMS. We readdressed the issue of the star -to-star scatter and Li-rotation connection for both a Per and the Ple iades; as several previous studies have pointed out, fast rotators, as a group, show higher lithium than slow rotators. At the same time, ho wever, fast rotators exhibit a much narrower dispersion than slow rota tors. We demonstrate that this dicothomy is unlikely due to projection effects and suggest that the reason for it could reside in the PMS ro tational history and, in particular, in the presence (absence) of a ci rcumstellar disk. As to very cool stars (T-eff < 4500 K), we find that a Per members do not seem to have higher lithium than the Pleiades. T his result, however, must be confirmed with a larger sample of a Per s tars before any conclusion can be drawn.