The Problem ofHipparcosDistances To Open Clusters. II. Constraints From Nearby Field Stars

This paper examines the discrepancy between distances to nearby open clustersas determined by parallaxes from Hipparcos compared to traditional mainsequence fitting. The biggest difference is seen for the Pleiades, and ourhypothesis is that if the Hipparcos distance to the Pleiades is correct, thensimilar subluminous ZAMS stars should exist elsewhere, including the immediatesolar neighborhood. We examine a color-magnitude diagram of very young andnearby solar-type stars and show that none of them lie below the traditionalZAMS, despite the fact that the Hipparcos Pleiades parallax would place itsmembers 0.3 magnitude below that ZAMS. We also present analyses andobservations of solar-type stars that do lie below the ZAMS and show that theyare subluminous because of low metallicity and that they have the kinematics ofold stars.Comment: 22 pages (including 4 tables) plus 6 figure