2005/05/16 by Warren R. Brown, Margaret J. Geller, Scott J. Kenyon +4 · 25 citations
Medicine · Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Blue straggler #Galactic halo #Galaxy #Globular cluster #Halo #Horizontal branch #Luminosity #Luminosity function #Medicine #Metallicity #Physics #Population #Sky #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/431976
published in The Astronomical Journal 130(3), 1097-1110 (Institute of Physics) · 14 pages, including 16 figures, accepted for publication in AJ
arxiv created 2005/05/16 · openalex publication_date 2005/09/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We discuss a 175 deg 2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and we find that the 2MASS and SDSS color selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely runaway B7 star 6 kpc below the Galactic plane. The global properties of the BHB samples are consistent with membership in the halo population: the median metallicity is [Fe/H] = -1.7, the velocity dispersion is 108 km s -1 , and the mean Galactic rotation of the BHB stars 3 kpc < | z | < 15 kpc is -4 ± 30 km s -1 . We discuss the theoretical basis of the Preston, Shectman, and Beers M V -color relation for BHB stars and conclude that the intrinsic shape of the BHB M V -color relation results from the physics of stars on the horizontal branch. We calculate the luminosity function for the field BHB star samples using the maximum likelihood method of Efstathiou and coworkers, which is unbiased by density variations. The field BHB luminosity function exhibits a steep rise at bright luminosities, a peak between 0.8 < M V < 1.0, and a tail at faint luminosities. We compare the field BHB luminosity functions with the luminosity functions derived from 16 different globular cluster BHBs. Kolmogorov-Smirnov tests suggest that field BHB stars and BHB stars in globular clusters share a common distribution of luminosities, with the exception of globular clusters with extended BHBs.