Abstract
AbstractPre-solar grains from supernova ejecta – silicon carbide of type X, Si3N4 and low-density graphite – are characterized by Si isotopic anomalies (mainly 28Si excesses), low 14N/15N, high 26Al/27 Al ratios, and occasionally by excesses in 44Ca (from 44Ti decay). Overall isotopic features of these SiC and graphite grains can be explained by mixing of inner Si-rich zones and the outer C-and He-rich zones, but supernova models require fine tuning to account for 14N/15N and 29Si/28Si ratios of the grains. Isotopic ratios of Zr, Mo and Ba in SiC X grains may be explained by a neutron burst model. Some of the pre-solar nanodiamonds require a supernova origin to explain measured xenon isotopic ratios. Only a few nova grain candidates, with low 12C/13C, 14N/15N, and high 26Al/27 Al ratios, have been identified.
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