The problem of Hipparcos distances to open clusters. II. Constraints from nearby field stars

This paper examines the discrepancy between distances to nearby open cluste rs as determined by parallaxes from Hipparcos compared to traditional main- sequence fitting. The biggest difference is seen for the Pleiades, and our hypothesis is that if the Hipparcos distance to the Pleiades is correct, th en similar subluminous zero-age main-sequence (ZAMS) stars should exist els ewhere, including in the immediate solar neighborhood. We examine a color-m agnitude diagram of very young and nearby solar-type stars and show that no ne of them lie below the traditional ZAMS, despite the fact that the Hippar cos Pleiades parallax would place its members 0.3 mag below that ZAMS. We a lso present analyses and observations of solar-type stars that do lie below the ZAMS, and are show that they are subluminous because of low metallicit y and that they have the kinematics of old stars.