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 m) 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 (d29Si = 1345% 19%, d30Si = 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 (t 1/2 = 153 yr). Silicon-32 as well as 29Si and 30Si can be produced in SNe by short neutron bursts; evidence for initial 44Ti (t 1/2 = 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. Publication name | ASTROPHYSICAL JOURNAL, 799 (2):10.1088/0004-637X/799/2/156 FEB 1 2015 | Author(s) | Xu, Yuchen; Zinner, Ernst; Gallino, Roberto; Heger, Alexander; Pignatari, Marco; Lin, Yangting | Corresponding author | XU Yuchen xuyuchen@mail.iggcas.ac.cn 1. Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China 2. Laboratory for Space Sciences and Physics Department, Washington University, St. Louis, MO 63130, USA 3. Institute of Geology and Geophysics, Chinese Academy of Sciences, No. 19, Bei Tucheng Xilu, Chaoyang District, Beijing 100029, China. | View here for the details
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