NOAO >   Observing Info >   Approved Programs >   2005A-0166

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Proposal Information for 2005A-0166


PI: Soo-Chang Rey, California Institute of Technology, screy@srl.caltech.edu
Address: Space Astrophysics Laboratory, 1200 E. California Blvd., MC 405-47, Pasadena, CA 91125

CoI: Jaehyon Rhee, California Institute of Technology
CoI: Young-Wook Lee, Yonsei University, S. Korea
CoI: Alistair Walker, Cerro Tololo Inter-American Observatory

Title: Star Formation History of \omega Centauri

Abstract: We propose to perform medium-resolution spectroscopic observations for a large sample of stars located in the red giant-branch (RGB) and blue horizontal-branch of \omega Cen. Direct metal abundance analysis for the spectra will allow us to check whether there exist the most metal-rich ([Fe/H] ~ -0.5), red horizontal-branch (RHB) clump stars positionally overlapping with RGB stars of more metal-poor ([Fe/H] < - 1.0) populations in the color-magnitude diagram (CMD) of \omega Cen. In case of successful detection of the most metal-rich RHB clump stars, comparing observed location of the stars in the CMD with that predicted from our horizontal-branch (HB) population models will enable us to measure accurate age range encompassed by the most metal-rich and the most metal-poor populations. On the other hand, absence of such stars would support the recently suggested idea of distinctive high enhancement and large variation of helium abundance for stars in \omega Cen. Furthermore, this scenario can be confirmed from spectroscopic abundance analysis for stars around hot HB blue tail. This endeavor will clarify accurate age-metallicity relation as well as complex formation and enrichment history of \omega Cen.


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