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B. Marsteller, T.C. Beers (Michigan State), S. Rossi (IAG, Brazil), C. Sneden (Univ. of Texas), N. Christlieb (Hamburger Sternwarte, Germany), M. Bessell, J.E. Norris (MSSSO, Australia), J. Rhee (Yonsei Univ., S. Korea, and Caltech), S.G. Ryan (Open Univ., UK)
Very metal-deficient stars that exhibit enhancements of their carbon abundances are of crucial importance for understanding a number of issues: The nature of stellar evolution among the first generations of stars, the shape of the Initial Mass Function, and the relationship between carbon enhancement and neutron-capture processes, in particular the astrophysical s-process. One fundamental result from recent objective-prism surveys dedicated to the discovery of metal-deficient stars is that the frequency, and perhaps, the level, of carbon enhancement increases greatly with declining metallicity.
Most previous discoveries of these important stars have been serendipitous, as the stars were initially targeted because of their apparently low overall metallicity, and it was only discovered later that carbon was strongly enhanced. To more completely explore this phenemonon, we have undertaken spectroscopic follow-up of a published list of metal-deficient candidates from the Hamburg/ESO prism survey (Christlieb et al. 2001, A & A, 375, 366) that show clearly strong carbon features directly on the survey plates. We have obtained spectra for some 350 of the 413 stars in the sample, and will report on their observed properties, including estimates of their [Fe/H] and [C/Fe], their radial velocities, and their spatial distribution. Of particular importance, we find that the upper envelope of carbon enhancement observed for these stars is nearly constant, at [C/H] = -1.0, over the metallicity range -4.0 < [Fe/H] < -2.0 ; this same level of [C/H] applies to the most iron-deficent star yet discovered, HE 0107-5240. Implications of these results will be discussed.
This work has received partial support from NSF grants AST 00-98508 and AST 00-98549. Support has also been received from FAPESP and CNPq (Brazil), the Deutsche Forschungsgemeinschaft (Re 353/44-1), the Australian Research Council (DP0342613), and PPARK (UK: PPA/O/S/1998/00658).
The author(s) of this abstract have provided an email address for comments about the abstract: beers@pa.msu.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.