Smail Mostefaoui and Peter Hoppe 2004 ApJ 613 L149 doi:10.1086/424842
Smail Mostefaoui1 and Peter Hoppe1
Show affiliationsWe report the discovery of 12 in situ presolar silicate and spinel grains, 140-590 nm in size, in the Acfer 094 meteorite. These grains represent a matrix-normalized abundance of presolar O-rich dust of 170 parts per million. Among the 10 silicate grains are three olivines, four pyroxenes, and three grains with glasslike composition. Eleven grains have large excesses in 17O with 17O/16O ratios of up to 2.9 times the solar ratio and slightly lower than or close-to-solar 18O/16O ratios. These grains most likely formed in 1.5-1.65 M
red giant branch (RGB) or asymptotic giant branch (AGB) stars with close-to-solar metallicity. One pyroxene grain has close-to-solar 17O/16O and 18O/16O of 3.8 times solar. Silicon- and Fe-isotopic ratios of this grain are suggestive of the formation in an RGB or AGB star, probably with higher-than-solar metallicity. 29Si/28Si and 30Si/28Si ratios of the silicate grains vary by ~16%, are positively correlated with one another, and fall to the 30Si-poor side of the Si mainstream line characteristic for presolar SiC from AGB stars. This gives independent confirmation for the view that the Si mainstream line reflects the Galactic chemical evolution of the Si isotopes, except for a small shift due to dredge-up of matter from the He shell in AGB stars.
circumstellar matter; dust, extinction; Galaxy: evolution; nuclear reactions, nucleosynthesis, abundances
Issue 2 (2004 October 1)
Received 2004 May 18, accepted for publication 2004 July 28
Published 2004 August 31
Smail Mostefaoui and Peter Hoppe 2004 ApJ 613 L149
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