Hot White Dwarfs, OB Subdwarfs, and Dark Clouds

The authors describe a method of using UBV photographic photometry to survey obscured regions in the Galactic plane for hot white dwarfs and OB subdwarfs. From an initial survey of two regions, the first towards the Coalsack, and the second covering part of the Scorpius-Centaurus cloud, the authors have found at least six white dwarfs, one probable interacting binary, five B subdwarfs, and two O subdwarfs. The space densities computed from these, admittedly sparse, statistics are similar to those deduced from Green's analysis of the Palomar-Green survey and thus a factor of 3 higher than Fleming et al's recent reanalysis of those data. The authors find a space density of ≡2.0×10^-2stars pc^-3 for white dwarfs with M_V ≤ 13.0.