Abstract: Primitive meteorites contain presolar grains that originated in stellar outflows and supernova ejecta. The isotopic compositions of some of these grains (low-density graphite grains, SiC grains of type X, and silicon nitride) indicate a supernova origin. In particular, the initial presence of 44Ti (now detected in the form of large 44Ca excesses) and 28Si excesses are proof that the carrier grains formed in supernova ejecta. The presence of these two isotopes, which are produced in the inner layers of the star, in carbonaceous grains is evidence for extensive mixing of different supernova layers in the explosion. Other isotopic signatures characteristic of supernova grains are 15N and 18O excesses, large inferred 26Al/27Al and 41Ca/40Ca ratios and excesses in 42Ca, 43Ca, and 49Ti. Mixing of supernova layers can explain most isotopic features but a few problems such as the association of 15N with 26Al in grains remain. The fact that all supernova grains identified so far are graphite, SiC and Si3N4 and no oxide grains with supernova signatures have been found remains a puzzle.
Publication Year: 1997
Publication Date: 1997-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 32
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