Characterizing $r$-Process Sites through Actinide Production

Erika M. Holmbeck, Rebecca Surman, Anna Frebel, G. C. McLaughlin, Matthew R. Mumpower, Trevor M. Sprouse, Toshihiko Kawano, Nicole Vassh, Timothy C. Beers

Published 2020-01-23Version 1

Of the variations in the elemental abundance patterns of stars enhanced with $r$-process elements, the variation in the relative actinide-to-lanthanide ratio is among the most significant. We investigate the source of these actinide differences in order to determine whether these variations are due to natural differences in astrophysical sites, or due to the uncertain nuclear properties that are accessed in $r$-process sites. We find that variations between relative stellar actinide abundances is most likely astrophysical in nature, owing to how neutron-rich the ejecta from an $r$-process event may be. Furthermore, if an $r$-process site is capable of generating variations in the neutron-richness of its ejected material, then only one type of $r$-process site is needed to explain all levels of observed relative actinide enhancements.