The Astrophysical Journal,2010, 709:1157-1173

Isotopic Analysis of Supernova SiC and Si3N4 Grains from the Qingzhen (EH3) Chondrite

Lin, Yangting; Gyngard, Frank; Zinner, Ernst

Abstract

We report Al-Mg, Ca, and Ti isotopic data in 16 silicon carbide grains and four silicon nitride grains from the Qingzhen enstatite chondrite. Previous C, N, and Si isotopic measurements had identified these grains as type X grains, believed to have an origin in Type II supernovae (SNe). The grains analyzed include both subtypes X1 and X2. Twelve SiC and three Si3N4 grains show evidence for initial 26Al, and eight SiC grains evidence for 44Ti; 11 SiC grains have 49Ti excesses, possibly indicating the initial presence of 49V. A correlation with subtype is shown for 44Ti: X2 grains that have the highest inferred 44Ti/48Ti ratios. A weaker correlation exists for N ratios: X2 grains with 12C/13C > 300 have higher 14N/15N ratios than X1 grains. We compare our data and data from previous reports with the SN models by Rauscher et al. The SN models can explain the C and N isotopic ratios fairly well if material from the 15N-rich spike in the He/N zone of the 25 M sun SN model is used. They also can explain the 44Ti/48Ti ratios of the X1 and X2 grains. For the latter, substantial contributions from the inner Ni core are required. They indicate that not for all grains the 49Ti excesses can be attributed to decay of 49V and material from the He/C zone, where 49Ti is produced by neutron capture, is needed. The SN models, however, fail in explaining the Si isotopic ratios of most of the grains in a satisfactory fashion and the distinction between X1 and X2 grains. They also fail in explaining the observed correlation between the 26Al/27Al ratios and 12C/13C (and 14N/15N) ratios.

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