An Estimation of the Galactic Escape Velocity from High-Velocity Metal-Poor Stars

Abstract

A large number of high-velocity stars was included in the Hipparcos Input Catalogue for the purpose of determining the galactic escape velocity in the solar vicinity. However, the ‘fastest’ stars known, listed by Carney et al. (1994, CLLA) were not included because they are too faint. In the intersection between the CLLA list and the Hipparcos Catalogue (770 common stars), the metaldeficient stars with the most reliable parallaxes (${\left( {\frac{{{\sigma _{\pi }}}}{\pi }} \right)_{{HIP}}} \leqslant 0.15$) are used for recalibrating CLLA absolute magnitudes and photometric parallaxes, using metallicities and VandenBerg et al. (1998) isochrones. In this way, about twenty non-Hipparcos stars get improved parallaxes and are added to our primary sample of Hipparcos high-velocity stars, for a better determination of the escape velocity from the Galaxy.