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circumstellar matter; dust; extinction; nuclear reactions; nucleosynthesis; abundances supernovae : general
Abstract:
We report Si, Ca, and Ti-V isotopic data for seven presolar silicon carbide grains of type X separated from the Murchison CM2 meteorite. The silicon carbide X grains most likely formed in the ejecta of Type II supernova explosions as indicated by large isotopic anomalies. The X grains of this study have Si- 29/Si-28 and Si-30/Si-28 ratios of 0.56-0.75 and 0.41-0.62 times the solar value, respectively. Slight enrichments in Ca- 44 are observed, possibly due to the decay of radioactive Ti-44 (t(1/2) = 60 yr). While Ti-46/Ti-48, Ti-47/Ti-48, and Ti-50/Ti- 48 ratios are close to solar, all X grains have enhanced Ti- 49/Ti-48 ratios of up to 1. 9 times the solar ratio. The Ti- 49/Ti-48 ratios are positively correlated with V-51/Ti-48 ratios, suggestive of the incorporation of live V-49 (t(1/2) = 330 days) during silicon carbide condensation. This implies that the grains formed on a timescale of several months after supernova explosion.
