Early‐Type Stars in the Galactic Halo from the Palomar‐Green Survey. I. A Sample of Evolved, Low‐Mass Stars

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Abstract
We present high-resolution spectroscopic observations of early-type stars drawn from a complete sample based on low-resolution spectroscopy of targets from the Palomar-Green Survey by Green, Schmidt, & Liebert. Qualitatively, the metal-line spectra are sharp and are therefore indicative of extremely low projected rotational velocities. Hence the objects are characterized as members of an old, evolved population (for example, blue horizontal branch or post-asymptotic giant branch). By careful choice of Population I, Galactic disk B stars, we have computed differential abundances between the targets and their main-sequence analogs. The CNO abundances from model-atmosphere analyses suggest the presence of nucleosynthesis dredge-up products in the stellar photospheres. With one exception, the stars all have [Fe/H] abundances consistent with their progenitor objects being metal deficient. Some conclusions are drawn as to the previous evolution (red giant branch, horizontal branch, or asymptotic giant branch) of the stars.

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