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

We present results from an analysis of medium-resolution spectroscopy and U BV photometry for a sample of 1121 A-type stars in the halo land disk) of t he Galaxy. A previously developed calibration technique is used to assign e stimates of effective temperature, surface gravity, and stellar metal abund ance, as parameterized by [Fe/H]. Radial velocities are reported with an ac curacy of similar to 10 km s(-1). Distance estimates are obtained for the s tars with well-determined luminosity classes. Note that although we refer t o "A-type" stars, which dominate the present sample, the present data set i ncludes roughly 100 stars of later spectral types, as a result of the tempe rature range we have chosen to explore in this paper (6000 K less than or e qual to T-eff less than or equal to 10,000 K). Included in the hot star sample are 444 stars we classify as held horizonta l-branch stars, 416 we classify as main-sequence-gravity A-type (or slightl y later) stars (including stars that are likely members of the blue metal-p oor population, the so-called BMPs), 140 stars we classify as likely metall ic-line (Am) or peculiar (Ap) stars, and 121 stars that cannot be unambiguo usly 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 mo dest amount of cross-contamination between the subsamples. We identify 58 RR Lyrae candidates among the hot star sample, based on inco mpatibilities in their photometric and spectroscopic data. There are 19 sta rs 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 s ample that were previously classified as BMPs by Preston, Beers, & Shectman , most of which fall into the main-sequence A-type category, but 10 of whic h are found among the Am/Ap classifications. Furthermore, 53 of stars previ ously considered to be BMPs are shown by our analysis to have metal abundan ces [Fe/H] > -1, which calls their identification with this population some what into question.