Measurements on silicon carbide from Murchison meteorite: Data for C, N, and SI

Details Measurements on silicon carbide from Murchison meteorite: Data for C, N, and SI Measurements on silicon carbide from Murchison meteorite: Data for C, N, and SI

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.550w&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 550-551

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Chemical Composition, Interstellar Matter, Meteoritic Composition, Murchison Meteorite, Silicon Carbides, Anomalies, Asymptotic Giant Branch Stars, Carbon Isotopes, Ion Probes, Nitrogen Isotopes, Silicon Isotopes

Scientific paper

Interstellar grains are supposed to condense in the mass-losing atmospheres of low-mass red giant stars during their asymptotic giant branch (AGB) phase. With respect to the solar system these AGB stars are expected to produce highly anomalous isotopic compositions of the CNO elements and also of many other light elements. We have analyzed about 30 single SiC grains from the Murchison meteorite separate MS1, using a modified CAMECA IMS 3f ion microprobe, employing an O primary beam. We have measured the isotopic signatures of C, N as negative secondary ions C(-) and CN(-), and Si as positive secondary ions. According to high-resolution plots, mass 27, which corresponds to CN(-), was free from B contamination. The main argument for an interstellar origin of meteoritic grains is their anomalous isotopic composition. Most of our SiC grains contained isotopically normal C, but we found three grains with higly anomalous C-12/C-13 ratios: Grain 1 has a C-12/C-13 ratio of 295, grain 2 one of 520. In these two grains only the C isotopes were analyzed. The C-12/C-13 ratio of grain 3 is 310, which, together with an N-14/N-15 ratio of 300, indicates that this grain might be a 'Y' grain. The data for the silicon isotopes of most grains fall close to the slope 1.3 line; only two grains are distinct. The small size of these grains only allowed us to measure the Si isotopes. In the case of grain 5 the isotopic composition, which is almost pure Si-28, suggests an origin in a supernova, or, that the Si might be produced by Mg burning in the He-burning shell of an AGB star.

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