1997A&A...327..577D

The spatial distribution and the population nature of subdwarf B type stars in the galaxy is investigated based on the kinematics of these stars. With new and available proper motions, radial velocities, and distances, the orbits of 41 stars have been calculated using a galactic mass model. The orbits are well behaved and 10 stars reach to |z|≥2kpc. Many orbits are very eccentric, reaching in to just 2kpc from the galactic centre, or veering out to beyond 20kpc. None of the stars can be identified uniquely as classical Population II objects. The average eccentricity ecc of the orbits of our sample is 0.24, the average normalised z-extent nze of the orbits is 0.16, and the asymmetric drift of our sample is -36km/s. This suggests that our sample of sdB stars is part of a population of thick disk stars. A statistical analysis of the orbits shows that the subdwarf stars have a spatial distribution in z compatible with an exponential one with a scale height h_z of about 1.0kpc. However, since only few stars reach to large z the spatial distribution is only well defined to z ≃2kpc. The distribution in z shows a relative minimum near z=0pc and has maxima near z=300pc. This reflects the smaller probability to find the stars in the disk than away from the disk, as expected for any orbit reaching to larger z. Scale height studies based on limited samples of stars in specified directions can therefore easily be flawed when they do not reach to large enough distances to overcome this aspect of the z-distribution.