Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012apj...745...38l&link_type=abstract
The Astrophysical Journal, Volume 745, Issue 1, article id. 38 (2012).
Astronomy and Astrophysics
Astronomy
1
Astrochemistry, Circumstellar Matter, Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Late-Type, Stars: Winds, Outflows, Supernovae: General
Scientific paper
We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains in the CR2 chondrite Northwest Africa (NWA) 852. Thirty-one O-anomalous grains were detected: 24 were identified as silicates (~78 ppm) the remaining 7 are Al-rich oxides (~38 ppm). NWA 852 is the first C2 chondrite containing O-anomalous presolar dust in concentrations comparable to other more primitive meteorites. Eight presolar SiC grains have been found, representing the highest abundance (~160 ppm) observed so far in primitive meteorites. 15N-enriched matter is also present, although very heterogeneously distributed. Twenty-six of the O-anomalous grains are enriched in 17O, originating from the outflows of low-mass asymptotic giant branch (AGB) stars. We calculate a silicate/oxide abundance ratio of ~2, which indicates a higher degree of aqueous alteration than observed for other presolar-grain-rich meteorites. NWA 852 thus stands between the presolar-grain-rich CR3 chondrites (MET 00426, QUE 99177) and CR2 chondrites with low presolar grain abundances (Renazzo, NWA 530). We calculate an initial presolar silicate abundance of ~800 ppm for NWA 852, if silicate destruction by aqueous alteration is taken into account. Transmission electron microscope (TEM) investigation of one presolar Al-rich grain of an AGB star origin revealed that the grain mainly consists of a single crystal of hibonite with slightly varying orientations. A distinct subgrain (d < 100 nm) with a Ca/Ti ratio of ~1 is located in the central region, most likely indicating a perovskite-like phase. Our data suggest this phase to be a primary condensate and not an alteration product.
Hoppe Peter
Leitner Jesse
Vollmer Christian
Zipfel Jutta
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