AAS 207th Meeting, 8-12 January 2006
Session 131 Galactic Astronomy in the SDSS
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[131.03] Estimation of Metallicity and Carbon Abundance for Carbon-Enhanced Metal-Poor Stars Based on SDSS Spectroscopy

B.E. Marsteller, T.C. Beers, T. Sivarani (Michigan State University & JINA), S. Rossi (Univ. of Sao Paulo, Brazil), J. Knapp (Princeton), B. Plez (U. Montpellier, France), J. Johnson (Ohio State)

The publicly available stellar database from SDSS contains many hundreds of metal-poor stars with large enhancements of carbon. The Galactic extension of SDSS, SEGUE, will identify several thousand more. Many of these Carbon-Enhanced Metal-Poor (CEMP) stars are likely to be enhanced in s-process elements created by AGB companions and dumped to the surviving member of a binary pair through either Roche-Lobe mass transfer or the operation of a stellar wind (CEMP-s stars). Based on previous high-resolution investigation of CEMP stars, an interesting subset of this sample is expected to show little or no s-process enhancement (CEMP-no stars).

Our present methodology for the estimation of [Fe/H] and [C/Fe] for CEMP stars is based on a calibration of line indices (e.g., for the CaII K line and the CH G band) discussed by Rossi et al. (2005). In some extreme cases, the presence of rather strong molecular carbon bands renders such approaches less than optimal. We are exploring spectral synthesis methods, based on a new library of carbon-enhanced MARCS model atmospheres, and synthetic ugriz colors generated from these models, in order to better constrain the determination of metallicity and carbon abundance for the CEMP stars discovered in SDSS. Based on this approach, we derive a new estimate of the frequency of CEMP stars as a function of metallicity. We also report on the feasibility of using the detection or non-detection of Sr and Ba as a means for roughly separating CEMP stars into the CEMP-s and CEMP-no classes.

B.M., T.C.B., and T.S. acknowledge partial support from grant AST 04-06784, as well as from grant PHY 02-16783, Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation.

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