Stellar Sapphires: The Properties and Origins of Presolar Al₂O₃in Meteorites

Thirty-seven isotopically highly anomalous presolar grains and one presolar grain Al 2 O 3 MgAl 2 O 4 from a separate of the Tieschitz H3.6 ordinary chondrite were identied out of 17,000 isotopically normal refractory oxide grains by an automatic 16O/18O low mass resolution ion-imaging mapping technique in the ion microprobe. Eight additional presolar grains were found by high mass resolution Al 2 O 3 ion probe measurements of all three stable O isotopes in individual grains, including several that would have been missed by the ion-imaging search. Forty-ve of the grains were analyzed for their 16O/17O and 16O/18O ratios. Twenty-four grains were also analyzed for Al-Mg and 17 of them have large excesses of 26Mg, attributable to the radioactive decay of 26Al. The highly anomalous isotopic composition of the grains is evidence for their presolar, stellar origin.