uvby - β photometry of high-velocity and metal-poor stars

Abstract

New uvby-\beta data are provided for 442 high-velocity and metal-poor stars; 90 of these stars have been observed previously by us, and 352 are new. When combined with our previous two photometric catalogues, the data base is now made up of 1533 high-velocity and metal-poor stars, all with uvby-\beta photometry and complete kinematic data, such as proper motions and radial velocities taken from the literature. Hipparcos, plus a new photometric calibration for M_v also based on the Hipparcos parallaxes, provide distances for nearly all of these stars; our previous photometric calibrations give values for E(b-y) and [Fe/H]. The [Fe/H],V(rot) diagram allows us to separate these stars into different Galactic stellar population groups, such as old-thin-disk, thick-disk, and halo. The X histogram, where X is our stellar-population discriminator combining V(rot) and [Fe/H], and contour plots for the [Fe/H],V(rot) diagram both indicate two probable components to the thick disk. These population groups and Galactic components are studied in the (b-y)_o,M_v diagram, compared to the isochrones of Bergbusch & VandenBerg (2001), to derive stellar ages. The two thick-disk groups have the mean characteristics: ([Fe/H], V(rot), Age, \sigma_W') ~ (-0.7 dex, 120 km/s, 12.5 Gyr, 62.0 km/s), and ~(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups, -2.31