Computer Science
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........8n&link_type=abstract
Ph.D. Thesis Washington Univ., Seattle.
Computer Science
15
Gas Analysis, Graphite, Ion Probes, Meteoritic Composition, Neon Isotopes, Silicon Carbides, Asymptotic Giant Branch Stars, Gas Spectroscopy, Helium Isotopes, Murchison Meteorite, Sodium 22, Wolf-Rayet Stars
Scientific paper
Anomalous noble gas components, such as Ne-E, measured in bulk SiC and graphite fractions separated from meteorites have previously supported the presolar origin of these mineral grains. These prior measurements, however, were performed on samples containing many thousands of grains; any result derived from such bulk measurements is only an average of the many, perhaps dissimilar, constituents. This work reports the first measurements of 22Ne-E and 4He in a suite of single micron-sized presolar SiC and graphite grains separated from the Murchison (CM) meteorite. The analyses were performed using a laser gas extraction technique and a high-sensitivity noble gas mass spectrometer. C- and N-isotopic compositions were determined via ion microprobe analyses on a subset of the suite of grains to further constrain their origin. This work confirms that SiC and graphite are the carriers of Ne-E(H) and Ne-E(L), respectively. Only 4 percent of the SiC grains and 30 percent of the graphite grains carry the anomalous gas above the spectrometer detection limits, implying that several inferences based on bulk noble gas measurements about the lifetimes of presolar grains and the abundances of these grains in meteorites should be reconsidered. That He-4 is found only in the Ne-E(H)-rich SiC grains provides strong evidence against a Na-22 origin of Ne-E(H). The He-4 and Ne-22 in the gas-rich SiC grains were probably produced either in the He-burning shell of low mass asymptotic giant branch (AGB) stars or in Wolf-Rayet stars during the WN-WC transition. Although the C-isotopic compositions of the gas-rich SiC grains argue against grain formation from pure He-shell material, AGB stars still appear to be the most plausible site for the formation of Ne-E(H). The graphite grains, which carry only 22Ne-E(L) without any He-4, probably formed from Wolf-Rayet stars near the WN-WC transition, with the Ne-E(L) being produced directly by the implantation of Ne. One gas-rich graphite grain, however, does not conform to a Wolf-Rayet origin. Although this grain could plausibly have formed from a nova with the Ne-E(L) being produced from the in situ decay of Na-22, the C-isotopic composition of this grain is inconsistent with such a scenario. The results of this work argue strongly against the popular belief that Ne-E(H) and Ne-E(L) are derived solely from the in situ decay of novae-produced Na-22.
No associations
LandOfFree
The origin of neon-E: Neon-E in single interstellar silicon carbide and graphite grains does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The origin of neon-E: Neon-E in single interstellar silicon carbide and graphite grains, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The origin of neon-E: Neon-E in single interstellar silicon carbide and graphite grains will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1140946