Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun

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A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l; b) = (65{sup o}; 48{sup o}). The horizontal branch at g{sub 0} = 18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is <V{sub r}> = -157 {+-} 4 km s{sup -1}, corresponding to V{sub gsr} = -10 km s{sup -1}; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] {approx} -2.4, which is significantly more metal poor than the stellar spheroid. We ... continued below

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15 pages

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Harrigan, Matthew J.; Newberg, Heidi Jo; Newberg, Lee A.; Poly., /Rensselaer; Yanny, Brian; /Fermilab et al. February 1, 2010.

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A new moving group comprising at least four Blue Horizontal Branch (BHB) stars is identified at (l; b) = (65{sup o}; 48{sup o}). The horizontal branch at g{sub 0} = 18.9 magnitude implies a distance of 50 kpc from the Sun. The heliocentric radial velocity is <V{sub r}> = -157 {+-} 4 km s{sup -1}, corresponding to V{sub gsr} = -10 km s{sup -1}; the dispersion in line-of-sight velocity is consistent with the instrumental errors for these stars. The mean metallicity of the moving group is [Fe/H] {approx} -2.4, which is significantly more metal poor than the stellar spheroid. We estimate that the BHB stars in the outer halo have a mean metallicity of [Fe/H]=-2.0, with a wide scatter and a distribution that does not change much as a function of distance from the Sun. We explore the systematics of SDSS DR7 surface gravity metallicity determinations for faint BHB stars, and present a technique for estimating the significance of clumps discovered in multidimensional data. This moving group cannot be distinguished in density, and highlights the need to collect many more spectra of Galactic stars to unravel the merger history of the Galaxy.

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15 pages

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  • Journal Name: Submitted to Mon.Not.Roy.Astron.Soc.

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  • Report No.: FERMILAB-PUB-10-066-A-CD
  • Grant Number: AC02-07CH11359
  • DOI: 10.1111/j.1365-2966.2010.16552.x | External Link
  • Office of Scientific & Technical Information Report Number: 975172
  • Archival Resource Key: ark:/67531/metadc932551

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  • February 1, 2010

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 9, 2016, 10:28 p.m.

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Harrigan, Matthew J.; Newberg, Heidi Jo; Newberg, Lee A.; Poly., /Rensselaer; Yanny, Brian; /Fermilab et al. Statistical Properties of Blue Horizontal Branch Stars in the Spheroid: Detection of a Moving Group approximately 50 kpc from the Sun, article, February 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc932551/: accessed September 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.