The Century Survey Galactic Halo Project I: Stellar Spectral Analysis

The Century Survey Galactic Halo Project is a photometric and spectroscopic survey from which we select relatively blue stars (V −R < 0.30 mag) as probes of the Milky Way halo. The Survey strip spans the range of Galactic latitude 35 < b < 88, allowing us to study the nature of populations of stars and their systematic motions as a function of Galactic latitude. One of our primary goals is to use blue horizontal-branch stars to trace potential star streams in the halo, and to test the hierarchical model for the formation of the Galaxy. In this paper we discuss spectroscopy and multi-passband photometry for a sample of 764 blue stars in the Century Survey region. Our sample consists predominantly of Aand F-type stars. We describe our techniques for determination of radial velocities, effective temperatures, metallicities, and surface gravities. Based on these measurements, we derive distance estimates by comparison with a set of calibrated isochrones. We devote special attention to the classification of blue horizontal-branch stars, and compare the results obtained from the application of the techniques of Kinman et al., Wilhelm et al., and Clewley et al. We identify 55 blue horizontal-branch stars. Our large sample of stars also uncovers a number of unusual objects, including three carbon-enhanced stars, a late B-type star located 0.8 kpc above the Galactic plane, and a DZ white dwarf. Subject headings: Galaxy: halo — Galaxy: stellar content — stars: horizontal branch — stars: abundances