Constraints on r-process nucleosynthesis from 129I and 247Cm in the early Solar system

Abstract

ABSTRACT GW170817 has confirmed binary neutron star mergers as one of the sites for rapid neutron capture (r) process. However, there are large theoretical and experimental uncertainties associated with the resulting nucleosynthesis calculations and additional sites may be needed to explain all the existing observations. In this regard, abundances of short-lived radioactive isotopes (SLRIs) in the early Solar system (ESS), which are synthesized exclusively by r-process, can provide independent clues regarding the nature of r-process events. In this work, we study the evolution of r-process SLRIs 129I and 247Cm as well as the corresponding reference isotopes 127I and 235U at the solar location. We consider up to three different sources that have distinct 129I/247Cm production ratios corresponding to the varied r-process conditions in different astrophysical scenarios. In contrast to results reported in a recent study, we find that 129I and 247Cm in the ESS do not come entirely from a single major event but get contributions from at least two more minor contributors. This has a dramatic effect on the evolution of the 129I/247Cm ratio, such that the measured ESS value in meteorites may not correspond to that of the ‘last’ major r-process event. Interestingly, however, we find that the 129I/247Cm ratio, in combination with the observed 129I/127I and 247Cm/235U ratio in the ESS, can still provide important constraints on the properties of proposed r-process sources operating in the Milky Way.