Spectroscopy of hot stars in the galactic halo. III. Analysis of a large sample of field horizontal-branch and other A-type stars

Ronald Wilhelm, Timothy C. Beers, Jesper Sommer-Larsen, Jeffrey R. Pier, Andrew C. Layden, Chris Flynn, Silvia Rossi, Per Rex Christensen

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46 Scopus citations


We present results from an analysis of medium-resolution spectroscopy and UBV photometry for a sample of 1121 A-type stars in the halo (and disk) of the Galaxy. A previously developed calibration technique is used to assign estimates of effective temperature, surface gravity, and stellar metal abundance, as parameterized by [Fe/H]. Radial velocities are reported with an accuracy of ∼10 km s-1. Distance estimates are obtained for the stars with well-determined luminosity classes. Note that although we refer to "A-type" stars, which dominate the present sample, the present data set includes roughly 100 stars of later spectral types, as a result of the temperature range we have chosen to explore in this paper (6000 K ≤ Teff ≤ 10,000 K). Included in the hot star sample are 444 stars we classify as field horizontal-branch stars, 416 we classify as main-sequence-gravity A-type (or slightly later) stars (including stars that are likely members of the blue metal-poor population, the so-called BMPs), 140 stars we classify as likely metallic-line (Am) or peculiar (Ap) stars, and 121 stars that cannot be unambiguously classified based on the present data. Examination of the distributions in metallicity and velocity indicates that the field horizontal-branch and main-sequence A-type samples are quite distinct; hence we expect only a modest amount of cross-contamination between the subsamples. We identify 58 RR Lyrae candidates among the hot star sample, based on incompatibilities in their photometric and spectroscopic data. There are 19 stars in the sample that have been previously classified as RR Lyrae variables, and one additional star that had been previously suggested as a variable, though not necessarily of the RR Lyrae class. There are 115 stars in the sample that were previously classified as BMPs by Preston, Beers, & Shectman, most of which fall into the main-sequence A-type category, but 10 of which are found among the Am/Ap classifications. Furthermore, 53 of stars previously considered to be BMPs are shown by our analysis to have metal abundances [Fe/H] > -1, which calls their identification with this population somewhat into question.

Original languageEnglish
Pages (from-to)2329-2380
Number of pages52
JournalAstronomical Journal
Issue number5
StatePublished - May 1999


  • Galaxy: halo
  • Stars: horizontal-branch
  • Stars: population II

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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