PI: Jaehyon Rhee, University of Virginia, firstname.lastname@example.org
Address: Department of Astronomy, P.O. Box 3818, Charlottesville, VA 22903-0818, U.S.A.
CoI: Timothy C. Beers, Michigan State University
Title: New Metal-Poor Giants and Horizontal-Branch Stars from the HK-II Survey
Abstract: The early chemo-dynamical history of the Milky Way can be strongly contrained by exploration of the observed properties of old stars in the halo and thick-disk of the Galaxy. There have been a few successful anaylses of dynamical motions of such stars, but the spatial scales have mostly been limited to include only a few kpc from the Sun since most of them are dwarfs and sub-giants near the main-sequence turnoff. Metal- poor giants and horizontal-branch stars are ideal probes of the kinamatics of the inner and outer halo, since they are intrinsically luminous, and thus more distant. We propose to continue a \it new search for field horizontal- branch stars and extremely metal-deficient giants with [Fe/H] \le -2.0 in the thick disk and halo of the Galaxy. The HK-II survey was originated to identify \it cooler metal-poor stars, without proper- motion bias, from new quantitative selection methodology which makes use of Artificial Neural Network techniques to \it digital scans of the original HK photographic plates in combination with 2MASS JHK photometry. Recent spectroscopic observations have revealed that roughly 30% of the HK-II candidates are \it bona fide metal-poor stars with [Fe/H] \le -2.0 (particulary, 50% of detection efficiency for HK-II stars near the North Galactic Pole). In addition, the HK-II selection technique has turned out to be very efficient to discover horizontal-branch stars too. Metallicities and radial velocities obtained from this medium-resolution spectroscopic follow-up, combined with proper motions and parallaxes from ongoing and future astrometric surveys, will provide full space motions for numerous extremely old stars. These efforts will help unravel the early nucleosynthesis and stellar dynamics in the Galaxy.
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