Origin of Low-26Al/27Al Corundum/Hibonite Inclusions in Meteorites

Most meteoritic calcium-rich, aluminum-rich inclusions formed from a reservoir with 26 Al/ 27 Al ≈ 5 × 10 −5 , but some record lower ( 26 Al / 27 Al ) 0 , demanding they sampled a reservoir without live 26 Al. This has been interpreted as evidence for “late injection” of supernova material into our protoplanetary disk. We instead interpret the heterogeneity as chemical, demonstrating that these inclusions are strongly associated with the refractory phases corundum or hibonite. We name them “low- 26 Al/ 27 Al corundum/hibonite inclusions” (LAACHIs). We present a detailed astrophysical model for LAACHI formation in which they derive their Al from presolar corundum, spinel, or hibonite grains 0.5–2 μ m in size with no live 26 Al; live 26 Al is carried on smaller (