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

Date
2008-02
Authors
Brown, Warren R.
Beers, Timothy C.
Wilhelm, Ronald
Prieto, Carlos Allende
Geller, Margaret J.
Kenyon, Scott J.
Kurtz, Michael J.
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract

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 dv(rot)/d|Z|=-28 +/- 3.4 km s(-1) in the region |Z| < 6 kpc, and a density scale height of h(Z) = 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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Citation
Brown, Warren R., Timothy C. Beers, Ronald Wilhelm, Carlos Allende Prieto, Margaret J. Geller, Scott J. Kenyon, and Michael J. Kurtz. >The century survey Galactic halo project III: a complete 4300 DEG2 survey of blue horizontal branch stars in the metal-weak thick disk and Inner Halo.> The Astronomical Journal, Vol. 135, No. 2 (Feb., 2008): 564.