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Accepted to AJ Preprint typeset using L ATEX style emulateapj v. 6/22/04 THE CENTURY SURVEY GALACTIC HALO PROJECT III: A COMPLETE 4300 DEG 2 SURVEY OF BLUE HORIZONTAL BRANCH STARS IN THE METAL-WEAK THICK DISK AND INNER HALO

By Warren R. Brown, Timothy C. Beers, Ronald Wilhelm, Carlos Allende Prieto, Margaret J. Geller, Scott J. Kenyon and Michael J. Kurtz

Abstract

Accepted to AJ We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300 deg 2 of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane |Z | < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H] = −1.7, a rotation velocity gradient of dvrot/d|Z | = −28 ± 3.4 km s −1 in the region |Z | < 6 kpc, and a density scale height of hZ = 1.26 ± 0.1 kpc. The BHB stars located at 5 < |Z | < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [Fe/H] = −2.0 and a mean Galactic rotation of −4 ± 31 km s −1. We infer the density of halo and thick disk BHB stars is 104 ± 37 kpc −3 near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 ± 1 % near the Sun

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