Hot sublumous stars at high galactic latitudes. II. Physical parameters and distances of 37 sdB stars.

Abstract

Spectra and photometry of 37 subdwarf B stars mainly selected from Green et al. (1986), are analyzed to derive effective temperatures, surface gravities and helium abundances. Effective temperatures lie between 23,500 K and 32,000 K with values for log g between 4.5 and 5.6. The helium abundances vary between 0.03 and about 6 percent (number fractions) without showing any correlation with surface gravities or effective temperatures. From the (log g, Teff) diagram it is concluded that the sdB stars belong to the extended horizontal branch. Using the effective temperatures and the surface gravities, the distances of the stars are determined. They lie between 360 pc and 2.5 kpc. A statistically complete subsample allows the derivation of a z-distribution with scale height of 250 pc and a disk space density of 1.0 x 10 to the -6th/pc cu. The scale height is in line with the evolutionary state of these subdwarf B stars as members of the old disk population and as immediate progenitors of low-mass white dwarfs.