NOAO >   Observing Info >   Approved Programs >   2002B-0325

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Proposal Information for 2002B-0325


PI: Jaehyon Rhee, University of Virginia, rhee@virginia.edu
Address: PO 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 the stars (mostly dwarfs and sub-giants near the main-sequence turnoff), but the spatial scales have mostly been limited to include only a few kpc from the Sun. Horizontal-branch stars and metal-poor giants are ideal probes of the kinamatics of the inner and outer halo, since they are intrinsically luminous, and thus more distant. We propose 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 cooler metal-poor stars, without proper-motion bias, from new quantitative selection methodology which makes use of Artificial Neural Network techniques of \it digital scans of the original HK photographic plates in combination with 2MASS JHK photometry. Recent spectroscopic tests have revealed that roughly 50% of the HK-II candidates near the North Galactic Pole are \it bona fide metal-poor stars with [Fe/H] \le -2.0. In addition, the HK-II selection technique has turned out to be very efficient to discover horizontal- branch stars. 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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