KINEMATIC MODELING OF THE GALAXY .2. 2 SAMPLES OF HIGH PROPER MOTION STARS

We analyze two independent surveys, due to Fouts and Sandage and to Carney and Latham, of high proper motion stars with photoelectric photometry and line-of-sight velocity information. A purely kinematic study of both samples indicates that a two-component classical (disk + spheroid) model of the Galaxy is inadequate to represent the kinematics of stars in the solar neighborhood. A component with intermediate kinematic properties (old disk) is required. We determine an asymmetric drift of 50 ± 15 km s-1 and principal velocity dispersions of (66, 37, 38) ± 10 km s-1, in good agreement with the results of the metallicity-based analysis of Sandage and Fouts and of Carney and collaborators. The density of this component is poorly constrained, and is ∼10% ± 5% of the local disk density for the same color range; the scale height is less than 1 kpc. A "thick disk" model for the intermediate component, with much larger asymmetric drift, velocity dispersions, and scale height, is incompatible with these samples.