Evidence for radiogenic sulfur-32 in type Ab presolar silicon carbide grains?
Fujiya, Wataru; Hoppe, Peter; Zinner, Ernst; Pignatari, Marco; Herwig, Falk
Dr Marco Pignatari M.Pignatari@hull.ac.uk
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.
|Journal Article Type||Article|
|Publication Date||Oct 20, 2013|
|Journal||Astrophysical Journal Letters|
|Publisher||American Astronomical Society|
|Peer Reviewed||Peer Reviewed|
|APA6 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|
|Keywords||Astrochemistry; Circumstellar matter; Nuclear reactions, nucleosynthesis, abundances; Supernovae: general|
|Copyright Statement||©2013 IOP|
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