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T.C. Beers (Michigan State), N. Christlieb (Hamburger Sternwarte, Germany), M.S. Bessell (MSSSO, Australia), V. Hill (Observatoire de Paris-Meudon, France), P.S. Barklem, A. Korn (Uppsala Observatory, Sweden), S.G. Ryan (Open Univ., UK), S. S. Rossi (IAG, Brazil), J. Rhee (Yonsei Univ., S. Korea, and Caltech)
In recent years, a handful of extremely metal-deficient stars have been identified that exhibit moderate to large enhancements of their abundance ratios (relative to Fe) of elements associated with the astrophysical r-process, enabling detections of radioactive species such as U and Th. Our understanding could be greatly improved by increasing the numbers of known r-process-enhanced, metal-poor stars, as well from building the sample to the point where meaningful measures of the frequency of the phenomenon, especially as a function of metallicity, could be ascertained.
We describe the present status of HERES -- The Hamburg/ESO R-process Enhanced Star survey. This survey is based upon "snapshot" high-resolution VLT/UVES spectra of large numbers of giants with [Fe/H] < -2.5. Spectra of sufficient quality to detect the presence of the EuII line (4019 Å), a distinctive neutron-capture feature, have now been obtained for over 300 very metal-deficient giants chosen from the Hamburg/ESO survey, along with a small number of targets from the HK survey of Beers and colleagues. We discuss the number of moderate- and highly- r-process enhanced stars discovered, update our estimate of the frequency of their detection, and present a discussion of the distribution of ~ 20 other easily-measured elements in each of these stars (e.g., C, Ca, Mg, Si, Co, Ni, Sr, Ba, etc.).
This work has received partial support from NSF grants AST 00-98508 and AST 00-98549. Support has also been received from the Deutsche Forschungsgemeinschaft (Re 353/44-1), the Swedish Research Council, PPARK (UK: PPA/O/S/1998/00658), FAPESP and CNPq (Brazil).
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.