Actinide-rich and Actinide-poor r-process-enhanced Metal-poor Stars Do Not Require Separate r-process Progenitors

• Main Authors: Holmbeck, Erika M. (Author), Frebel, Anna L. (Author), McLaughlin, G. C. (Author), Mumpower, Matthew R. (Author), Sprouse, Trevor M. (Author), Surman, Rebecca (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: American Astronomical Society, 2021-03-05T19:05:17Z.
• Subjects: Article
• Online Access: Get fulltext

The astrophysical production site of the heaviest elements in the universe remains a mystery. Incorporating heavy-element signatures of metal-poor, r-process-enhanced stars into theoretical studies of r-process production can offer crucial constraints on the origin of heavy elements. In this study, we introduce and apply the "actinide-dilution with matching" model to a variety of stellar groups, ranging from actinide-deficient to actinide-enhanced, to empirically characterize r-process ejecta mass as a function of electron fraction. We find that actinide-boost stars do not indicate the need for a unique and separate r-process progenitor. Rather, small variations of neutron richness within the same type of r-process event can account for all observed levels of actinide enhancements. The very low-Y[subscript e], fission-cycling ejecta of an r-process event need only constitute 10%-30% of the total ejecta mass to accommodate most actinide abundances of metal-poor stars. We find that our empirical Y e distributions of ejecta are similar to those inferred from studies of GW170817 mass ejecta ratios, which is consistent with neutron-star mergers being a source of the heavy elements in metal-poor, r-process-enhanced stars.
National Science Foundation (Grant AST-1716251)