Extreme ^(26)Mg and ^(17)O enrichments in an Orgueil corundum: Identification of a presolar oxide grain

A corundum (Al_2O_3) grain from the Orgueil meteorite is greatly enriched in ^(17)O and ^(26)Mg^*. The measured ^(16)O/^(17)O is 1028 ± 11 compared to ^(16)O/^(17)O)_☉ = 2610. This is the largest ^(17)O excess so far observed in any meteoritic material. The ^(26)Mg excess (^(26)Mg^*) is most plausibly due to in situ decay of ^(26)Al. The inferred ^(26)Al/^(27)Al)_0 ratio of 8.9 x 10^(-4) is ~ 18 times larger than the 5 x 10^(-5) value commonly observed in refractory inclusions formed m the solar system. The large ^(17)O excess and high ^(26)Mg^*/^(27)Al ratio unambiguously identify this corundum as a presolar oxide grain. Enrichments in ^(17)O and ^(26)Al are characteristic of H-burning and point to red giant or AGB stars as likely sources