KINEMATICS OF DISK STARS IN THE SOLAR NEIGHBOURHOOD A.E. G'omez

Abstract

Using Hipparcos parallaxes and proper motions together with radial velocity complementary data (Coravel for late type stars and new ground-based data for early type stars) for several thousand B-F type stars, the velocity ellipsoid has been determined as a function of age. The variations with age of the ratio of the velocity dispersions, of the vertex deviation and the age-velocity dispersion relation (AVR) have been estimated. Our results confirm that mixing is not complete at about 0:8 \Gamma 1 Gyr. The shape of the velocity ellipsoid changes with time, getting rounder from oe U /oe V /oe W = 1=0:63=0:42 \Sigma 0:04 at about 1 Gyr to 1=0:7=0:62 \Sigma 0:04 at 4 \Gamma 5 Gyr. The AVR rises to a maximum, thereafter remaining roughly constant; there is no dynamically significant evolution of the disk after about 4 \Gamma 5 Gyr. The velocity dispersion in the direction perpendicular to the galactic plane saturates at about 15 \Gamma 17 km s \Gamma1 for thin disk stars. The vertex devi..