The galactic evolution ofs-process elements via asymptotic giant branch stars

We attempt to study the ability of asymptotic giant branch stars to produce s-process elements as a function of initial mass and metallicity. The normal methods of extracting information from spectroscopic observations of the surfaces of these stars are reviewed and it is shown how misleading some of the past claims are and which methods of analysis might eliminate the current confusion. Results from stellar evolution models are brought together in order to establish trends of certain parameters as functions of one or two other parameters. Using these parameterizations, we have determined the s-process abundances created by these stars for different scenarios, and we have related them to surface features that are observable. It is found that the two commonly advocated sources for s-process neutrons cannot produce observational features of MS and S stars as the scenarios are put forth in the literature. It is found, however, that perturbations of these models within the physical limitations of the more popular scenarios can result in observational features of MS and S stars. We also look at the limitations put upon various s-process scenarios by galactic chemical evolution, where we find that AGB stars as an s-process source are consistent with the trends in the heavy elements as a function of the metallicity history of the galaxy. It is also realized that the nucleosynthetic yield of any s-process source must be relatively insensitive to the initial composition of the progenitor star.U of I OnlyETDs are only available to UIUC Users without author permissio