A corundum (Al 2 0 3 ) grain from the Orgueil meteorite is greatly enriched in 17 0 and 26 Mg*. The measured 16 0jl 7 0 is 1028 ± 11 compared to e 6 0/ 17 0)0 = 2610. This is the largest 17 0 excess so far observed in any meteoritic material. The 26 Mg excess e 6 Mg*) is most plausibly due to in situ decay of 26 AI. The inferred ~2 6 Al/~7Al) 0 ratio ~f 8.9 x 10-4 is "'18 times larger than the 5 x 10-s value commonly observed in refractory mclus10ns formed m the solar system. The large 17 0

more »

... ss and high 26 Mg* / 2 7 AI ratio unambiguously identify this corundum as a presolar oxide grain. Enrichments in 17 0 and 26 AI are characteristic of H-burning and point to red giant or AGB stars as likely sources.