Correlated Strontium and Barium Isotopic Compositions of Acid-cleaned Single Mainstream Silicon Carbides from Murchison

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Nan Liu, Michael R. Savina, Roberto Gallino, Andrew M. Davis, Sara Bisterzo, Frank Gyngard, Franz Käppeler, Sergio cristallo, Nicolas Dauphas, Michael J. Pellin, and Iris Dillmann

The Astrophysical Journal
Volume 803, Number 1
ApJ 803 12. doi:10.1088/0004-637X/803/1/12

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We present strontium, barium, carbon, and silicon isotopic compositions of 61 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing both strontium and barium contamination. For the first time, by using correlated 88Sr/86Sr and 138Ba/136Ba ratios in mainstream SiC grains, we are able to resolve the effect of 13C concentration from that of 13C-pocket mass on s-process nucleosynthesis, which points toward the existence of large 13C pockets with low 13C concentrations in asymptotic giant branch stars. The presence of such large 13C pockets with a variety of relatively low 13C concentrations seems to require multiple mixing processes in parent asymptotic giant branch stars of mainstream SiC grains.

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