Journal
NEW ASTRONOMY REVIEWS
Volume 50, Issue 7-8, Pages 574-577Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.newar.2006.06.045
Keywords
radioisotopes; interstellar dust; supernovae; AGB stars; nucleosynthesis
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Presolar grains in primitive meteorites are characterized by large isotopic anomalies in essentially all the analyzed elements. Among these anomalies are excesses in the daughter isotopes of short-lived radioisotopes. These excesses indicate the incorporation of short-lived now extinct isotopes into the grains at the time of their formation. So far laboratory studies of presolar grains have established evidence for the initial presence of the isotopes V-49, Na-22, Ti-44, Ca-41, Tc-99, and Al-26. Evidence for these isotopes have been found in presolar silicon carbide, graphite, and oxide grains from supernovae (V-49, Na-22, Ti-44, Ca-41, and Al-26) and AGB stars (Ca-41, Tc-99, and Al-26). We analyzed presolar hibonite (CaAl12O19) grains, whose oxygen isotopic ratios indicate an origin in AGB stars, for their Al-Mg and Ca-K isotopic systems, determined the initial Al-26/Al-27 and Ca-41/Ca-40 ratios, and compared them with theoretical models of the production of these isotopes in AGB stars. Whereas the abundance of Ca-41, which is produced by neutron capture, agrees with the models, the abundance of Al-26, which is produced by proton capture, greatly exceeds theoretical predictions. The production of this radioisotope requires a process in addition to H shell burning, cool bottom processing. (c) 2006 Elsevier B.V. All rights reserved.
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