Isotopic analysis of presolar graphite grains from Orgueil
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چکیده
We report the successful isolation and isotopic analysis of presolar graphite grains from the Orgueil CI chondrite. Isotopic measurements were made on seven density fractions, with grain sizes >1 lm: ORG1b (1.59–1.67 g cm ), 1c (1.67–1.75 g cm ), 1d (1.75– 1.92 g cm ), 1f (2.02–2.04 g cm ), 1g (2.04–2.12 g cm ), 1h (2.12–2.16 g cm ) and 1i (2.16–2.30 g cm ). We measured C, N, O, and Si isotopes with the NanoSIMS. All the fractions, except ORG1b and ORG1h, contain presolar graphite as demonstrated by the large range of C/C ratios (4–1746) measured in individual grains. The abundance of grains with isotopically light carbon increases with increasing density. Some of the low-density grains are enriched in O, N and Si. As the density increases, the grains mostly exhibit solar oxygen and nitrogen isotopic ratios. However, the high-density grains are enriched in Si and Si. The O and Si excesses indicate that the low-density grains originated from supernovae, while the high-density grains (with Si and C excesses) probably originated from AGB stars with low metallicities. 2006 Elsevier B.V. All rights reserved. PACS: 98.38.Cp; 98.80.Ft; 81.05.Uw; 97.60.Bw; 97.20.Jg; 97.10.Cv
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تاریخ انتشار 2006