On the origin and evolution of s-process elements

The evolution of s-process abundances in the solar neighborhood is studied, using alternative stellar production sites and galactic models. Production in either low-mass or medium-mass stars, as suggested in Ulrich's alternative models for FG Sge for example, can account for the solar-system abundances. Either case is consistent with independent limits on subsequent neutron exposure of nuclei produced in explosive oxygen and silicon burning and of r-process material. The cases could be distinguished by observations of the ratios of s-process to primary metal abundances in stars of different ages. The predictions are not strongly dependent on the model used for galactic evolution.