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Barium isotopic composition of mainstream silicon carbides from Murchison : constraints for s-process nucleosynthesis in asymptotic giant branch stars

Pellin, Michael J.; Savina, Michael R.; Willingham, David G.; Pignatari, Marco; Bisterzo, Sara; Cristallo, Sergio; Dauphas, Nicolas; Davis, Andrew M.; Gallino, Roberto; Gyngard, Frank; Herwig, Falk; Liu, Nan; Pellin, Michael Joseph; Savina, Michael; Straniero, Oscar; Willingham, David

Authors

Michael J. Pellin

Michael R. Savina

David G. Willingham

Sara Bisterzo

Sergio Cristallo

Nicolas Dauphas

Andrew M. Davis

Roberto Gallino

Frank Gyngard

Falk Herwig

Nan Liu

Michael Joseph Pellin

Michael Savina

Oscar Straniero

David Willingham

Abstract

We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ(138Ba/136Ba) values are found, down to −400 permil, which can only be modeled with a flatter 13C profile within the 13C pocket than is normally used. The dependence of δ(138Ba/136Ba) predictions on the distribution of 13C within the pocket in AGB models allows us to probe the 13C profile within the 13C pocket and the pocket mass in asymptotic giant branch (AGB) stars. In addition, we provide constraints on the 22Ne(α,n)25Mg rate in the stellar temperature regime relevant to AGB stars, based on δ(134Ba/136Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ(134Ba/136Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i-process), which is activated by the Very Late Thermal Pulse (VLTP) during the post-AGB phase and characterized by a neutron density much higher than the s-process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, 130Ba and 132Ba, in single SiC grains. These isotopes are destroyed in the s-process in AGB stars. By comparing their abundances with respect to that of 135Ba, we conclude that there is no measurable decay of 135Cs (t1/2= 2.3 Ma) to 135Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before 135Cs decayed.

Journal Article Type Article
Publication Date May 1, 2014
Journal The astrophysical journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 786
Issue 1
Article Number ARTN 66
Pages 66
Institution Citation Savina, M. R., Pellin, M. J., Willingham, D. G., Pignatari, M., Bisterzo, S., Cristallo, S., …Willingham, D. (2014). Barium isotopic composition of mainstream silicon carbides from Murchison : constraints for s-process nucleosynthesis in asymptotic giant branch stars. The Astrophysical journal, 786(1), 66. https://doi.org/10.1088/0004-637x/786/1/66
DOI https://doi.org/10.1088/0004-637x/786/1/66
Keywords Dust, extinction, Nuclear reactions, nucleosynthesis, abundances, Stars : AGB and post-AGB, Stars : carbon
Publisher URL http://iopscience.iop.org/article/10.1088/0004-637X/786/1/66/meta;jsessionid=B78EFA96E3A04989125A2AD4C526CDA1.c3
Copyright Statement © 2014. The American Astronomical Society. All rights reserved
Additional Information This is a copy of an article published in The astrophysical journal, 2014, v.786 issue 1. Reproduced by permission of the AAS.

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Copyright Statement
© 2014. The American Astronomical Society. All rights reserved



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