Supernova Mixtures Indicating Isotopic Ratios of Presolar Grains

Astronomy and Astrophysics – Astrophysics

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Introduction: Most of SiC X and low density graphite grains show excesses of ^28Si and some of them have an evidence for the original presence of ^44Ti, so that they are believed to originate from supernovae. The isotopic and elemental signatures are considered to reflect large-scale heterogeneous mixing in supernova ejecta. We investigate supernova mixtures indicating isotopic ratios of individual single SiC X and low density graphite grains as many as possible. Supernova mixing model: We use the abundance distribution of the supernova ejecta of He star models of 3.3, 4, 6, and 8 solar masses in Yoshida, Umeda, & Nomoto (2005; ApJ 631, 1039), which correspond to zero-age main sequence stars of 13, 15, 20, and 25 solar masses. We divide the supernova ejecta into seven layers, i.e., the Ni, Si/S, O/Si, O/Ne, C/O or O/C, He/C, and He/N layers. Then, for individual single SiC X and low density graphite grains, we seek the mixtures indicating the smallest difference in several isotopic ratios from the corresponding grains. Results: In the case of SiC X grains, the mixtures reproducing five isotopic ratios in ^ 12C/^13C, ^14N/^15N, ^16O/^17O, ^16O/^18O, ^26Al/^27Al, ^29Si/^28Si, ^30Si/^ 28Si, and ^44Ti/^48Ti are obtained. For nineteen low density graphite grains, the mixtures reproducing six isotopic ratios in ^12C/^13C, ^14N/^15N, ^16O/^ 17O, ^16O/^18O, ^26Al/^27Al, ^29Si/^28Si, and ^30Si/^28Si. The isotopic ratio different from the corresponding grains is one of ^12C/^13C, ^14N/^15N, and ^ 26Al/^27Al in most cases. The mixing ratios of the mixtures strongly depend on reproduced isotopic ratios. The main component of the mixtures is one of the Ni, He/C, and He/N layers for most mixtures. Most of the obtained mixtures indicate the C/O ratio larger than unity.

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