Impact of $(\alpha,n)$ 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 to the r-process and to an additional process. Here we assume the additional process corresponds to the weak r-process or alpha-process taking place in neutrino-driven winds. Based on a trajectory obtained from hydrodynamical simulations we study the astrophysics and nuclear physics uncertainties with our main focus on the $(\alpha,n)$ reactions. These are critical to redistribute the matter and allow to further move it from light to heavy elements after nuclear statistical equilibrium freezes out. In this first sensitivity study, we vary all $(\alpha,n)$ 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 under the conditions found in the wind. Our results show that $(\alpha,n)$ reactions are indeed very important 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. This will uniquely allow to reduce the nuclear physics uncertainties and thus to use observations to constrain and understand the astrophysical conditions in the wind. 
Julia Bliss, Almudena Arcones, Fernando Montes, Jorge Pereira
astro-ph.SR astro-ph.HE nucl-ex nucl-th