NOAO >   Observing Info >   Approved Programs >   2005A-0239

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Proposal Information for 2005A-0239


PI: Jaehyon Rhee, California Institute of Technology, rhee@srl.caltech.edu
Address: Space Astrophysics Laboratory, MC 405-47, 1200 E. California Blvd., Pasadena, CA 91125, U.S.A.

CoI: Timothy C. Beers, Michigan State University

Title: A New Search for Very Metal-Poor Giant Stars with [Fe/H] \le -2.0 in 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 chemical abundances and 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-deficient red giant stars are ideal probes into both inner and outer halo, since they are intrinsically luminous, and thus more distant. We propose to continue a \it new search for very metal-poor (VMP) red giants with [Fe/H] \le -2.0 from intermediate to high Galactic- latitudes. The HK-II survey was designed to discover a large sample of \it cooler, VMP stars 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. The HK-II VMP red giant candidates are chosen without proper-motion and temparature biases. Thus far, medium-resolution spectroscopic follow-up using KPNO 2.1-m and CTIO 1.5-m telescopes has newly confirmed some 120/140 VMP red giants/sub-giants with [Fe/H] \le - 2.0 in the first sample selected from about 100 plates. In particular, the detection efficiency of \it bona fide VMP red giant stars is greater than 50% at both higher and lower Galactic latitudes, which is quite encouraging. Some 1200 VMP star candiates have been newly chosen from the remaing 200 plates, and they will be the targets of this spectroscopy. This effort will provide a number of useful stars for high-dispersion abundance analysis, and thus will help unravel the early nucleosynthesis and stellar dynamics in the Galaxy.


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