Bright Metal-poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields

Abstract

We present a sample of 1777 bright (9 < B < 14) metal-poor candidates selected from the Hamburg /ESO Survey (HES). Despite saturation effects present in the red portion of the HES objective-prism spectra, the data were recoverable and quantitative selection criteria could be applied to select the sample. Analyses of medium-resolution (∼2 Å) follow-up spectroscopy of the entire sample, obtained with several 2-4 m class telescopes, yielded 145 new metal-poor stars with metallicity [Fe/H] < -2.0, of which 79 have [Fe/H] < -2.5 and 17 have [Fe/H] < -3.0. We also obtained C/Fe estimates for all of these stars. From this, we find a frequency of C-enhanced ([C/Fe] > 1.0) metal-poor ([Fe/H] < -2.0) giants of 9% ±2%, which is lower than previously reported. However, the frequency rises to similar (>20%) and higher values with increasing distance from the Galactic plane. Although the numbers of stars at low metallicity are falling rapidly at the lowest metallicities, there is evidence that the fraction of carbon-enhanced metal-poor stars is increasing rapidly as a function of declining metallicity. For ∼60 objects, high-resolution data have already been obtained; one of these, HE 1327-2326, is the new record holder for the most iron-deficient star known.