Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains?

Fujiya, Wataru; Hoppe, Peter; Zinner, Ernst; Pignatari, Marco; Herwig, Falk

Abstract

We report C, Si, and S isotope measurements on 34 presolar silicon carbide grains of Type AB, characterized by 12 C/ 13 C < 10. Nitrogen, Mg-Al-, and Ca-Ti-isotopic compositions were measured on a subset of these grains. Three grains show large 32 S excesses, a signature that has been previously observed for grains from supernovae (SNe). Enrichments in 32 S may be due to contributions from the Si/S zone and the result of S molecule chemistry in still unmixed SN ejecta or due to incorporation of radioactive 32 Si from C-rich explosive He shell ejecta. However, a SN origin remains unlikely for the three AB grains considered here, because of missing evidence for 44 Ti, relatively low 26 Al/ 27 Al ratios (a few times 10 -3 ), and radiogenic 32 S along with low 12 C/ 13 C ratios. Instead, we show that born-again asymptotic giant branch (AGB) stars that have undergone a very-late thermal pulse (VLTP), known to have low 12 C/ 13 C ratios and enhanced abundances of the light s-process elements, can produce 32 Si, which makes such stars attractive sources for AB grains with 32 S excesses. This lends support to the proposal that at least some AB grains originate from born-again AGB stars, although uncertainties in the born-again AGB star models and possible variations of initial S-isotopic compositions in the parent stars of AB grains make it difficult to draw a definitive conclusion. © 2013. The American Astronomical Society. All rights reserved.

Citation

Fujiya, W., Hoppe, P., Zinner, E., Pignatari, M., & Herwig, F. (2013). Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains?. Astrophysical journal. Letters, 776(2), L29. https://doi.org/10.1088/2041-8205/776/2/l29

• Journal Article Type: Article
• Acceptance Date: Sep 20, 2013
• Online Publication Date: Oct 4, 2013
• Publication Date: Oct 20, 2013
• Deposit Date: Jun 29, 2018
• Publicly Available Date: Jul 25, 2018
• Journal: Astrophysical Journal Letters
• Print ISSN: 2041-8205
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 776
• Issue: 2
• Article Number: L29
• Pages: L29
• DOI: https://doi.org/10.1088/2041-8205/776/2/l29
• Keywords: Astrochemistry; Circumstellar matter; Nuclear reactions, nucleosynthesis, abundances; Supernovae: general
• Public URL: https://hull-repository.worktribe.com/output/561758
• Publisher URL: http://iopscience.iop.org/article/10.1088/2041-8205/776/2/L29/meta
• Contract Date: Jun 29, 2018