STScI Preprint #1217

The Problem of Hipparcos Distances to Open Clusters. II. Constraints from Nearby Field Stars

Based on data from the ESA Hipparcos astrometry satellite

This paper examines the discrepancy between distances to nearby open clusters 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, then similar subluminous ZAMS stars should exist elsewhere, including the immediate solar neighborhood. We examine a color-magnitude diagram of very young and nearby solar-type stars and show that none of them lie below the traditional ZAMS, despite the fact that the Hipparcos Pleiades parallax would place its members 0.3 magnitude below that ZAMS. We also present analyses and observations of solar-type stars that do lie below the ZAMS and show that they are subluminous because of low metallicity and that they have the kinematics of old stars.

Status:

Appeared in: The Astrophysical Journal, 504:192-199, 1998

Affiliations:

¹) Space Telescope Science Institute 3700 San Martin Drive Baltimore, MD 21218 USA

²) University of California Observatories/Lick Observatory Board of Studies in Astronomy and Astrophysics University of California, Santa Cruz CA 95064

³) Dept. of Physics and Astronomy San Francisco State University, San Francisco CA 94132

⁴) Harvard-Smithsonian Center for Astrophysics 60 Garden Street, Cambridge MA 02138

⁵) Astronomy Department, Ohio State University 174 West 18th Avenue, Columbus OH 43210