The CAI Database: 26Al–26Mg Isotope SystematicsOPEN ACCESS
Emilie T. Dunham, Ming-Chang Liu, Aman Burman, Fatima Jorge-Chavez, Danielle Leuer, Ashley K. Herbst, François L. H. Tissot, and Kevin D. McKeegan
The Astrophysical Journal Supplement Series, Volume 282, Number 1, published 22 December 2025
“We present a publicly available calcium–aluminum-rich inclusion (CAI) database that focuses on the initial 26Al/27Al0 ratio in CAIs, designed in a way that researchers in cosmochemistry and astrophysics may find useful. To date, the database contains 497 CAIs from 75 peer-reviewed papers. The CAIs are from all chondrite groups and cover different CAI types, textures, and sizes. The database includes the paper; the host meteorite; the CAI name and type; the 26Al/27Al0, Mg26 0 , and δ25Mg values and their uncertainties; the number of regression points; the maximum 27Al/24Mg; the mean-squared weighted deviation; the CAI size; and CAI descriptions. We grouped the CAIs in different ways to discuss 26Al/27Al0 ratio distributions with implications for the CAI formation timeline. Overall, we agree with previous authors that CAIs have a bimodal 26Al distribution: CAIs with robust isochrons (n = 151) have a median 26Al/27Al0 = 4.8 × 10−5 (with a 1σ standard error of 0.1), while those with isotopic anomalies (n = 87) have a median 26Al/27Al0 = 0.3 × 10−5 (with a 1σ standard error of 0.2). However, the large standard deviation of both groups (1.3 and 2.3, respectively) indicates that the 26Al/27Al0 values scatter ignificantly within each population. CAI types and groups can have distinct 26Al/27Al0 and Mg26 0, but the unmelted inclusions (n = 33) have the highest median 26Al/27Al0 = 5.1 × 10−5 and a low median Mg26 0 = −0.05‰. We find slightly different 26Al/27Al0 distributions between CAI chondrite types, but no differences between petrographic types or sizes. These observations can help us to understand CAI formation in the context of astrophysical models.
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