STUDIES OF HOT B-SUBDWARFS .11. A REDETERMINATION OF THE DENSITY OF HOT, HYDROGEN-RICH SUBDWARFS IN THE GALACTIC PLANE

We have reanalyzed the statistical properties of the sample of hydroge n-rich hot subdwarfs identified in the Kitt Peak-Downes survey in orde r to derive an improved value of the density D-0 of these stars in the plane of the Galaxy. Our analysis is based on photoelectric Stromgren photometry for 22 of these stars, all brighter than V similar to 15.0 . The value of the average absolute magnitude of the KPD objects we re determine is at least 1 mag brighter than that derived in the initial investigation. Three methods are then considered to derive D-0, under the assumption of an exponential distribution of stars in the directio n perpendicular to the Galactic plane: fits to the number of stars as a function of apparent brightness and as a function of vertical distan ce above the plane, as well as the 1/V-m' method. We find that the dis tribution of hot, hydrogen-rich subdwarf stars can be satisfactorily r eproduced with a midplane space density D-0 = 3.8 +/- 1.7 x 10(-7) pc( -3), a factor of similar to 5 lower than initial estimates, but in agr eement with the recent determination of Villeneuve et al. based on the Palomar-Green sample at high galactic latitudes.