Distant field blue horizontal branch stars and the mass of the Galaxy – II. Photometry and spectroscopy of UKST candidates 16 < B < 19.5, 11 < R < 52 kpc.

This is the second in a series of papers presenting a new calculation of the mass of the Galaxy based on radial velocities and distances for a sample of faint field blue horizontal-branch (BHB) stars. We present accurate BV CCD photometry and spectra for 142 candidate A-type stars selected from photometry of UK Schmidt telescope plates in six high-Galactic-latitude fields. Classification of these candidates produces a sample of 60 BHB stars at distances of 11–52 kpc from the Sun (mean 28 kpc), with heliocentric line-of-sight velocities accurate to 15 km s⁻¹, and distance errors <10 per cent. We provide a summary table listing coordinates and velocities of these stars. The measured dispersion of the radial component of the Galactocentric velocity for this sample is 108 ± 10 km s⁻¹, in agreement with a recent study of the distant halo by Sirko and coworkers. Measurements of the Ca ii K line indicate that nearly all the stars are metal-poor with a mean with dispersion 0.5. Subsequent papers will describe a second survey of BHBs to heliocentric distances and present a new estimate of the mass of the Galaxy. [ABSTRACT FROM AUTHOR]