The Frequency of Warm Carbon-Enhanced Metal-Poor Stars in SDSS-I DR-5

Details The Frequency of Warm Carbon-Enhanced Metal-Poor Stars in SDSS-I DR-5 The Frequency of Warm Carbon-Enhanced Metal-Poor Stars in SDSS-I DR-5

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20924202m&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #242.02; Bulletin of the American Astronomical Society,

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There exists current a debate concerning the frequency of stars with large enhancements of carbon ([C/Fe] > +1.0) among very metal-poor ([Fe/H] <-2.0) stars in the Galactic halo. Some authors, e.g., Marsteller et al. (2005) and Lucatello et al. (2006), have concluded that a rather high frequency, on the order of 20%-25% exists, while other authors (e.g., Cohen et al. 2005) have claimed lower frequencies. One of the difficulties in making a precise estimate is that many previous samples of stars are dominated by giants, which are subject to alteration of the surface carbon abundance due to evolutionary effects. Fortunately, there is now an attractive alternative. The publicly available stellar database from SDSS-I (DR-5) contains large numbers (more than 24,000) warm (Teff >= 5700 K), very metal-poor stars (many of which were selected as calibration objects during the course of SDSS-I) which are not expected to have evolved to the point where carbon can be diluted on their surfaces. An estimate of the frequency of carbon-enhanced stars from this sample should provide one of the best available estimates of the true value of this quantity. In order to obtain estimates of [Fe/H] and [C/Fe] for this large sample, I have developed an automated spectral synthesis technique, making use of Sneden's MOOG program. With reasonable first estimates of the atmospheric parameters for our sample (obtained by the SDSS/SEGUE spectroscopic pipeline discussed elsewhere in this meeting), this approach quickly converges to the best available combination of [Fe/H] and [C/Fe] required to fit the spectral regions around the CaII K and CH G-bands. I will discuss the resulting frequency of carbon-enhanced metal-poor stars among the very metal-poor stars in this sample.

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