HOT SUBLUMINOUS STARS AT HIGH GALACTIC LATITUDES .4. PHYSICAL PARAMETERS AND DISTANCES OF 18 HOT SUBDWARF STARS AND THEIR SPATIAL-DISTRIBUTION

We present Stromgren uvby photometry and optical spectra in the wavele ngth range of 4000 to 5000 angstrom of 18 hot subdwarf stars; 13 of th em are classified as sdB, 4 as sdOB and one as sdO star. Effective tem peratures and surface gravities are determined using reddening free co lour indices of the Stromgren and the Greenstein system and by fitting theoretical line profiles to the observed Balmer lines. Interpreting the hot subdwarfs as Extended Horizontal-Branch stars, we assume their masses to lie in the small range M = 0.50 +/- 0.02 M. and calculate t heir distances. The helium abundances, determined from the equivalent widths of the lambda4471 angstrom absorption line, do not show any cor relation with the physical parameters. A subsample of 11 sdB- and sdOB -stars is statistically complete in a field defined by 35-degrees < 1 < 95-degrees and 28-degrees < b < 40-degrees down to a limiting magnit ude of y = 14.2. The z-distribution of the stars is exponentially decr easing with a scale height of 180(-60)+190 pc. We therefore conclude t hat the field sdB- and sdOB-stars belong to the old disk population. 8 subdwarf stars show evidence for a cool companion. Their atmospheric parameters and distances are estimated by deconvolving the photometric data.