Impact of ( α , n ) reactions on weak r-process in neutrino-driven winds

After a successful core-collapse supernova, a neutrino-driven wind develops where it is possible to synthesize lighter heavy elements (30 < Z < 45). In the early galaxy, the origin of these elements is associated with the r-process and to an additional process. Here we assume that the additional process corresponds to the weak r-process (sometimes referred to as alpha-process) taking place in neutrino-driven winds. Based on a trajectory obtained from hydrodynamical simulations we study the astrophysics and nuclear physics uncertainties of a weak r-process with our main focus on the ( α , n ) reactions. These reactions are critical to redistribute the matter and allow it to move from light to heavy elements after nuclear statistical equilibrium freezes out. In this first sensitivity study, we vary all ( α , n ) reactions by given constant factors which are justified based on the uncertainties of the statistical model and its nuclear physics input, mainly alpha optical potentials for weak r-process conditions. Our results show that ( α , n ) rate uncertainties are indeed crucial to predict abundances. Therefore, further studies will follow to identify individual critical reactions. Since the nucleosynthesis path is close to stability, these reactions can be measured in the near future. Since much of the other nuclear data for the weak r-process are known, the reduction in nuclear physics uncertainties provided by these experiments will allow astronomical observations to directly constrain the astronomical conditions in the wind.