A large-scale spectroscopic survey of early-type stars at high galactic latitudes

We present new model atmosphere analyses of optical spectroscopy of a large sample of B-type stellar candidates. Of a total of 298 objects, the largest sample of its kind to date, 205 were drawn from the Palomar Green Survey of high Galactic latitude ultraviolet-excess stellar objects and comprise a complete magnitude-limited sample. Effective temperatures, surface gravities, and helium abundances for the hot subdwarf (high-gravity) component of the sample are derived from a detailed line profile analysis of the hydrogen and helium absorption lines in intermediate-resolution (3-5 Angstrom FWHM) optical spectra. A separate analysis of the lower gravity component is made using a newly calculated grid of synthetic spectra. Additional estimates of the effective temperatures are made from wide-and intermediate-band photometry taken from the literature. We are currently undertaking two follow-up programs. (1) Detailed abundance analyses of high-resolution echelle spectra of the lower gravity component of the survey using modern model atmosphere and synthetic spectrum techniques will differentiate between massive Population I main-sequence B stars and low-mass, lower luminosity Population II blue horizontal branch stars and post-asymptotic giant branch stars. (2) The derived atmospheric parameters for the higher gravity component, the field extended horizontal branch stars, will be combined with radial velocity measurements to determine their spatial and kinematic distributions, which will distinguish between competing evolutionary scenarios for this hot, evolved stellar population.