Seed abundances for r-processing in the helium shells of supernovae

The production of r-process nuclei as a consequence of shock heating of the helium shells in supernovae is examined. The assumption of an initial (seed) distribution which is enriched in heavy s-process elements relative to solar system matter is found to allow production of r-process abundance features compatible with observations. Such an enrichment is consistent, for example, with the high Ba/Sr ratios characteristic of barium stars. This may result from the mixing of hydrogen-rich matter into the helium shells during earlier phases of stellar evolution. With such enrichments, the production of r-process nuclei in solar proportions in the helium shells of supernovae (the 'helium' driven r-process) becomes possible.