Open AccessDistant 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
Author(s) -
Clewley L.,
Warren S. J.,
Hewett P. C.,
Norris John E.,
Evans N. W.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07921.x
Subject(s) - physics , astrophysics , stars , photometry (optics) , galaxy , velocity dispersion , astronomy , halo , radial velocity
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 16 < B < 21.3 field blue horizontal‐branch (BHB) stars. We present accurate BV CCD photometry and spectra for 142 candidate A‐type stars selected from ub j r 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 [Fe/H]=−1.8 with dispersion 0.5. Subsequent papers will describe a second survey of BHBs to heliocentric distances 70 < R < 125 kpc and present a new estimate of the mass of the Galaxy.