PI: Thomas Lebzelter, University of Vienna, email@example.com
Address: Department of Astronomy, Tuerkenschanzstrasse 17, Vienna A1180, Austria
CoI: Kenneth Hinkle, NOAO
CoI: Michael Lederer, University of Vienna
CoI: Verne Smith, NOAO
Title: Nucleosynthesis in the final stages of stellar evolution
Abstract: One of the important characteristics of AGB evolution is the 3rd dredge-up where freshly produced ^12C and s-process elements are brought up into the stellar atmosphere. Heavy mass loss occurring during and following the AGB phase enriches the interstellar material with the elements produced in stellar interiors. Stellar evolution models provide quite detailed predictions for the 3rd dredge-up enrichment but quantitative checks so far are restricted to field stars or to indirect methods. Using improved model atmospheres and high resolution Phoenix/Gemini spectra we propose the determination of carbon and oxygen abundances and isotopic ratios for stars along the AGB in selected globular clusters. After having been granted time in 2005B to do these measurements for NGC 1846, we apply for an extension to two further globular clusters of different age and metallicity, namely NGC 1978 and Ruprecht 106. Only with data from different environments we will be able to set good constraints to the mixing models. The sensitivity provided by Phoenix on an 8 m class telescope allows high spectral resolution observations of both giants and AGB stars in these two clusters.
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