Hot sublimous stars at high galactic latitudes. IV. Physical parameters and distances of 18 hot subdwarf stars and their spatial distribution.

We present uvby photometry and optical spectra in the wavelength range of 4000 to 5000 Å of 18 hot subdwarf stars; 13 of them are classified as sdB, 4 as sdOB and one as sdO star.

Effective temperatures and surface gravities are determined using reddening free colour indices of the 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±O.O2M_sun and calculate their distances. The helium abundances, determined from the equivalent widths of the λ4471 Å absorption line, do not show any correlation with the physical parameters.

A subsample of 11 sdB- and sdOB-stars is statistically complete in a field defined by 35° < 95° and 28° < b <40° down to a limiting magnitude of y = 14.2. The z-distribution of the stars is exponentially decreasing with a scale height of 180⁺¹⁹⁰_-60 pc. We therefore conclude that 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.