Early r-process enrichment in globular clusters
Prof. Evan Kirby
Department of Physics & Astronomy
University of Notre Dame
Stars in nearly all globular clusters show complex relations among the abundances of light elements (up to Na). Many also show anti-correlations of Mg and Al. Until now, only one cluster (M15) conclusively showed any star-to-star variation in neutron-capture elements, like Eu. Using a trick of stellar evolution, I show that these variations are primordial, not caused by external pollution. Then, I show that M92 also has variations in barium and lanthanide abundances (but not first-peak r-process) among the first generation of stars but not the second. The evidence points to a rare source of the "main" r-process that happened right at the start of the formation of the cluster.