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

TL;DR

This study analyzes acid-cleaned presolar silicon carbide grains from Murchison to understand isotopic compositions, revealing insights into stellar nucleosynthesis and the existence of large, low-concentration $^{13}C$ pockets in AGB stars.

Contribution

It introduces a novel method of using correlated Sr and Ba isotopic ratios to distinguish effects of $^{13}C$ concentration and pocket size in stellar nucleosynthesis.

Findings

Acid washing effectively removes contamination from SiC grains.

Correlated isotopic ratios reveal large, low-$^{13}C$ concentration pockets.

Multiple mixing processes are implied in parent AGB stars.

Abstract

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 $^{88}Sr$/$^{86}Sr$ and $^{138}Ba$/$^{136}Ba$ ratios in mainstream SiC grains, we are able to resolve the effect of $^{13}C$ concentration from that of $^{13}C$-pocket mass on s-process nucleosynthesis, which points towards the existence of large $^{13}C$-pockets with low $^{13}C$ concentration in AGB stars. The presence of such large $^{13}$R-pockets with a variety of relatively low $^{13}C$ concentrations seems to require multiple mixing processes in parent AGB stars of mainstream SiC grains.