Pre-solar grains from supernovae and novae

Pre-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.