Presolar grains from supernovae and novae

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Presolar grains from supernovae are the second most abundant type of presolar grains in meteorites after those from red giants and asymptotic giant branch (AGB) stars. Supernova grains that have been extensively studied by ion probe include silicon carbide (SiC) of type X, which comprises about 1% of the total SiC in meteorites, low-density graphite (1.65-1.72 g/cm^3), and silicon nitride (Si[3] N[4]). They are characterized by lower ^14N/^15N ratios than the solar ratio, high ^26Al/^27Al (up to 0.6), and ^28Si excesses (up to 8 times solar). A few grains show the presence of ^44Ti. Travaglio et al. (1999) mixed different zones of supernova models by Woosley and Weaver (1995) and concluded that the isotopic feature of low-density graphite grains can be explained if a small amount of material from the inner Si-rich zone is ejected and mixed into the outer He-rich zones. However, ^15N and ^29Si yields predicted in the models are short of reproducing the isotopic ratios of the supernova grains. It remains to be seen that models that incorporate rotation in the stellar structure as well as a better determination of the ^26Mg(α,n)^29Si reaction rate at T=1-4×10^9 K will be able to increase these yields. Only a few SiC and graphite grains of a possible nova origin have been identified. Low ^12C/^13C (4-9) and ^14N/^15N (5-20) and high ^30Si/^28Si ratios (up to 2.1 times solar) of the grains are consistent with predicted ratios from ONe nova models if nova ejecta were mixed with isotopically close-to-solar material (Amari et al, 2001). Recently, Nittler and Hoppe (2005) pointed out that low ^12C/^13C and ^14N/^15N ratios may not necessarily imply that the grains formed in novae and that supernovae can be another source of these grains. References: Amari S. et al. (2001) ApJ, 551, 1065-1072. Travaglio C. et al. (1999) ApJ, 510, 325-354. Nittler L. R. and Hoppe P. (2005) ApJ, 631, L89-L92. Woosley S. E. and Weaver T. A. (1995) ApJ Suppl. Ser. 101, 181-235.

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