Unusual 29,30Si-rich SiCs of Massive Star Origin Found Within Graphites from the Murchison Meteorite

Details Unusual 29,30Si-rich SiCs of Massive Star Origin Found Within Graphites from the Murchison Meteorite Unusual 29,30Si-rich SiCs of Massive Star Origin Found Within Graphites from the Murchison Meteorite

Jun 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aj....139.2159c&link_type=abstract

The Astronomical Journal, Volume 139, Issue 6, pp. 2159-2169 (2010).

Astronomy and Astrophysics

Astronomy

5

Dust, Extinction, Nuclear Reactions, Nucleosynthesis, Abundances, Stars: Wolf-Rayet, Supernovae: General

Scientific paper

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.

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