Program: GS-2006B-C-6

Title:Nucleosynthesis in the final stages of stellar evolution
PI:Thomas Lebzelter
Co-I(s): Kenneth Hinkle, Michael Lederer

Abstract

One of the important characteristics of AGB evolution is the 3rd dredge-up where freshly produced $^{12}$C 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. In December 2005 we successfully obtained first measurements for NGC 1846 clearly showing the expected dredge up behavior. This semester 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.

Publications using this program's data