NOAO >   Observing Info >   Approved Programs >   2005A-0511

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Proposal Information for 2005A-0511


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: Inese I. Ivans, California Institute of Technology
CoI: Andrew McWilliam, Carnegie Observatories (OCIW)

Title: Chemical Compositions of Newly Discovered Very Metal-Poor Red Giants

Abstract: We propose to continue a high-resolution spectroscopy program for very metal-poor (VMP) red giant stars with [Fe/H] \le -2.5 in the halo and thick disk of the Galaxy. Thanks to previous medium-resolution spectroscopy using NOAO observing facilities, the HK-II survey has been able to \it newly discover some 50 [Fe/H] \le -2.5 \it red giant stars with 11 \le B \le 15.5, over 7000 deg^2 (one-sixth of the entire sky). Comprehensive chemical abundance analyses for the old stars placed at various directions and distances will allow us to understand early history of the Galactic chemical evolution. During the course of this program, we have already discovered a new highly r- process enhanced VMP star, II 16033-02187, a red giant with [Fe/H]=- 2.48 and [Eu/Fe]=+1.6, based on a preliminary analysis for high- resolution spectra taken with KPNO 4-m/Echelle in May 2004. We expect to identify additional 1-2 r-process enriched VMP red giants, and if detected, age dating of such stars by the use of long-lived radioactive species (e.g., Th and U) may place a strong constraint on lower limits on the age of the Universe. Also, detailed abundance studies of carbon enhanced metal-poor stars will help understand the relation between neutron-capture processes (particularly s-process) and carbon enhancement at the early Galactic times. The results from this effort will enable us to have ``refined'' metallicity distribution function of [Fe/H] \le -2.5 populations and, combined with proper motions from astrometric surveys (e.g., UCAC2 and USNO B1), will provide full space motions of the extremely old stars to uncover the chemo-dynamical history of the early Galaxy.


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