2007ApJ...666.1048Y

Most of supernova-originating presolar grains, such as silicon carbide type X (SiC X) and low-density graphite, show excesses of ²⁸Si. Some of them also indicate evidence for the original presence of short-lived nuclei ⁴⁴Ti. In order to reproduce isotopic and elemental signatures of these grains, large-scale heterogeneous mixing in supernova ejecta is required. I investigate supernova mixtures that reproduce as many isotopic ratios as possible of 18 individual SiC X and 26 individual low-density graphite grains. The supernova ejecta are divided 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, mixtures indicating isotopic ratios with small differences from those of individual single grains are sought. Mixtures reproducing five isotopic ratios in ^ 12^C/13^C, 14^N/15^N, 26^Al/ 27^Al, 29^Si/28^Si, 30^Si/ 28^Si, and ⁴⁴Ti/⁴⁸Ti are obtained for three SiC grains. For 10 SiC X grains for which five, four, or three isotopic ratios have been measured, the mixtures reproducing all measured isotopic ratios are also found. For 20 low-density graphite grains, the mixtures reproducing six isotopic ratios in ¹²C/¹³C, ¹⁴N/^ 15^N, 16^O/17^O, 16^O/18^O, 26^Al/27^Al, 29^Si/28^Si, 30^Si/28^Si, and ⁴⁴Ti/⁴⁸Ti are obtained. The mixing ratios of each mixture strongly depend on reproduced isotopic ratios. The main component of most mixtures is one of the Ni, He/C, and He/N layers. The carbon-to-oxygen ratio of the mixtures is larger than unity for most cases. The ratios of Fe/C and Fe/Si in the mixtures have large varieties. Most of the mixtures for low-density graphite indicate Fe/Si larger than unity. The elemental signatures of the mixtures will constrain grain formation in supernovae.