What do actinide-boost stars reveal about the r-process?
Marius Eichler
Darmstadt University of Technology, Germany

About half of the heavy elements in the universe are produced by the rapid neutron capture process (r-process). The decays of the radioactive r-process nuclei result in a characteristic light curve (termed kilonova or macronova), which has recently been observed for the first time in the aftermath of the neutron star merger GW170817. Apart from this direct observation, spectral abundance analyses of extremely metal-poor stars give us an insight into the properties of the r-process site(s), since they carry the fingerprint of only one r-process event.

Several extremely metal-poor stars are known to have an enhanced thorium abundance compared to most other stars. These actinide-boost stars have likely inherited material from an r-process that operated under different conditions than the most frequent r-process in the galaxy. I will discuss the sensitivity of actinide production in r-process calculations on the hydrodynamical conditions as well as nuclear physics. Furthermore, our calculations show that actinide-enhanced ejecta also should be distinguishable from the "regular" composition in other ways, for instance in the second r-process peak abundances. In kilonova light curves, a strong actinide enhancement could be observable by a strong heating contribution of α-decays roughly 60 days after the merger event.