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Sulfur isotopic compositions of submicrometer SiC grains from the Murchison meteorite

Xu, Yuchen; Zinner, Ernst; Gallino, Roberto; Heger, Alexander; Pignatari, Marco; Lin, Yangting


Yuchen Xu

Ernst Zinner

Roberto Gallino

Alexander Heger

Yangting Lin


We report C, Si, N, S, Mg-Al, and Ca-Ti isotopic compositions of presolar silicon carbide (SiC) grains from the SiC-rich KJE size fraction (0.5-0.8 μm) of the Murchison meteorite. One thousand one hundred thirteen SiC grains were identified based on their C and Si isotopic ratios. Mainstream, AB, C, X, Y, and Z subtypes of SiC, and X-type silicon nitride (Si₃N₄) account for 81.4%, 5.7%, 0.1%, 1.5%, 5.8%, 4.9%, and 0.4%, respectively. Twenty-five grains with unusual Si isotopic ratios, including one C grain, 16 X grains, 1 Y grain, 5 Z grains, and 2 X-type Si₃N₄ grains were selected for N, S, Mg-Al, and Ca-Ti isotopic analysis. The C grain is highly enriched in ²⁹Si and ³⁰Si (δ²⁹Si = 1345‰ ± 19‰, δ³⁰Si = 1272‰ ± 19‰). It has a huge ³²S excess, larger than any seen before, and larger than that predicted for the Si/S supernova (SN) zone, providing evidence against the elemental fractionation model by Hoppe et al. Two SN models investigated here present a more satisfying explanation in terms of a radiogenic origin of ³²S from the decay of short-lived ³²Si (τ1/2 = 153 yr). Silicon-32 as well as ²⁹Si and ³⁰Si can be produced in SNe by short neutron bursts; evidence for initial 44Ti (τ1/2 = 60 yr) in the C grain is additional evidence for an SN origin. The X grains have marginal ³²S excesses, much smaller than expected from their large ²⁸Si excesses. Similarly, the Y and Z grains do not show the S-isotopic anomalies expected from their large Si isotopic anomalies. Low intrinsic S contents and contamination with isotopically normal S are the most likely explanations.


Xu, Y., Zinner, E., Gallino, R., Heger, A., Pignatari, M., & Lin, Y. (2015). Sulfur isotopic compositions of submicrometer SiC grains from the Murchison meteorite. The Astrophysical journal, 799(2), 156.

Journal Article Type Article
Acceptance Date Nov 19, 2014
Online Publication Date Jan 27, 2015
Publication Date Feb 1, 2015
Deposit Date Jan 4, 2016
Publicly Available Date Nov 23, 2017
Journal Astrophysical journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 799
Issue 2
Pages 156
Keywords Astrochemistry, Circumstellar matter, Nuclear reactions, nucleosynthesis, abundances, Supernovae: general, Stars: AGB and post-AGB
Public URL
Publisher URL;
Additional Information Copy of article published in: Astrophysical journal, 2015, v.799, issue 2


Article.pdf (3.7 Mb)

Copyright Statement
© 2015. The American Astronomical Society. All rights reserved.

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