Hello Listers, Here is an abstract and related articles I found tonight about Murchison meteorite and SiC, which are grains with highly unusual isotopic compositions, and these presolar grains are rare grains which are naturally of great interest because they permit to get insights into specific aspects of stellar nucleosynthesis and evolution.
Title: Unusual 29,30Si-rich SiCs of Massive Star Origin Found Within Graphites from the Murchison Meteorite Authors: Croat, T. K.; Stadermann, F. J.; Bernatowicz, T. J. Affiliation: AA(Department of Physics and Laboratory for Space Science, Washington University, Campus Box 1105, One Brookings Drive, St. Louis, MO 63130-4899, USA), AB(Department of Physics and Laboratory for Space Science, Washington University, Campus Box 1105, One Brookings Drive, St. Louis, MO 63130-4899, USA), AC(Department of Physics and Laboratory for Space Science, Washington University, Campus Box 1105, One Brookings Drive, St. Louis, MO 63130-4899, USA) Publication: The Astronomical Journal, Volume 139, Issue 6, pp. 2159-2169 (2010). (AJ Homepage) Publication Date: 06/2010 Origin: IOP AJ Keywords: dust, extinction, nuclear reactions, nucleosynthesis, abundances, stars: Wolf-Rayet, supernovae: general DOI: 10.1088/0004-6256/139/6/2159 Bibliographic Code: 2010AJ....139.2159C Abstract Correlated transmission electron microscopy and NanoSIMS isotopic studies have revealed two unusual SiCs with large 29,30Si enrichments within micron-sized graphites from the Murchison meteorite. Such anomalies are rare among the overall SiC population (in Lt0.01% of SiCs yet measured), whereas two of the three SiCs found within graphite show 29,30Si enrichments, in one case as large as 29Si/28Si = (2.28 ± 0.03) × solar and 30Si/28Si = (2.03 ± 0.03)× solar. C-burning and Ne-burning in massive stars (>8 M sun initial mass) during their post-main-sequence development are the only processes capable of producing sufficiently large 29,30Si enrichments. This material with heavy Si isotopic enrichments from the O/Ne and O/Si layers is later incorporated into carbonaceous stardust, either in ejecta from Type II supernovae or perhaps in the colliding winds of Wolf-Rayet binaries. Although often too small for Si isotopic measurements, four other SiC-containing graphites show other signatures of a massive star origin. Abundance estimates suggest that such unusual SiCs are present within ~1% of high-density graphites. This abundance can be reconciled with the much lower abundance in the overall SiC population if these unusual SiCs are naturally smaller (~200 nm or less) than SiCs from other isotopic subgroups and if differential destruction of small unusual SiCs occurs in massive star outflows unless these SiCs are encapsulated in graphite. Other related articles linking Murchison and SiCs http://www.lpi.usra.edu/meetings/LPSC98/pdf/1765.pdf http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1082.pdf Here are types and characteristics of presolar grains found in meteorites. Type Size Concentration in Meteorites Sources Diamond (C) 1-5 nanometers 1000 parts per million Supernovae Silicon carbide (SiC) 0.1-10 micrometers 10 parts per million Carbon-rich giant stars, or supernovae Graphite (C) 1-10 micrometers 2 parts per million Supernovae and carbon-rich giant stars Aluminum oxide (Al2O3) 1-5 micrometers 0.1 parts per million oxygen-rich giant stars Spinel (MgAl2O4) 1 micrometer 2 parts per billion oxygen-rich giant stars Silicon nitride (Si3N4) 1 micrometer 2 parts per billion Supernovae Table adapted from a 1993 Meteoritics review by Edward Anders and Ernst Zinner, and Conel Alexander's Carnegie Institution Yearbook 95, report "Stardust in the Laboratory." http://www.psrd.hawaii.edu/July97/Stardust.html Shawn Alan eBayshop http://shop.ebay.com/photophlow/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p4340 ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
