New Subdwarfs. VI. Kinematics of 1125 High-Proper-Motion Stars and the Collapse of the Galaxy
Abstract
The UVW velocity components and the planar eccentricities and angular momenta are calculated for 878 stars from the radial-velocity catalog of Paper V using photometric distances from data in Paper IV. An additional 247 high-velocity stars from the literature bring the total sample to 1125 stars. The kinematic data are combined with ultraviolet-excess values δ(0.6) from the photometric catalog to study again the correlations of kinematics and metal abundance among stars of high proper motion. Two Lindblad kinematic components can be identified in the data. Nearly half the sample belongs to a low >V< velocity component. This component, which is identified as part of the Gilmore-Reid-Wyse thick disk, has an intermediate mean metallicity of >[Fe/H]< ≡ -0.5. The second component, comprising the other half of the sample, is composed of the extremely high-velocity halo stars whose kinematic distribution in W is a monotonic function of metallicity over the entire metallicity range of 0 ⪆ [Fe/H] ⪆ -4. The authors conclude that collapse of the Galaxy occurred in the past and that there is a metallicity gradient in the halo in situ to at least z ≡ 20 kpc. The galactic rotation of the halo decreases systematically from the local standard of rest value of 220 km s-1 (assumed) to zero as Fe/H changes from the solar value to ≡10-4, suggesting that spin-up occurred as the collapse proceeded. The escape velocity at the solar circle is estimated to be ≡450 km s-1. This value is expected to be a lower limit, giving a limit on the ratio of total mass of the Galaxy to the mass inside the solar circle to be MT/MR_sun; ⪆ 3.
- Publication:
-
The Astronomical Journal
- Pub Date:
- January 1987
- DOI:
- 10.1086/114291
- Bibcode:
- 1987AJ.....93...74S
- Keywords:
-
- Gravitational Collapse;
- Milky Way Galaxy;
- Stellar Composition;
- Stellar Motions;
- Subdwarf Stars;
- Ubv Spectra;
- Halos;
- Metallicity;
- Radial Velocity;
- Astrophysics;
- GALAXIES: THE GALAXY;
- STARS: PROPER-MOTION;
- STARS: STELLAR DYNAMICS