Cold r-Process in Supernovae

The r-process in a low temperature environment is explored, in which the neutron emission by photodisintegration does not play a role. A semi-analytic neutrino-driven wind model is utilized for this purpose. The temperature in a supersonically expanding outflow can quickly drop to a few 108 K, where the (n,γ)-(γ,n) equilibrium is never achieved during the heavy r-nuclei synthesis. In addition, the neutron capture competes with the β-decay owing to the low matter density. Despite such non-standard physical conditions, a solar-like r-process abundance curve can be reproduced. The cold r-process predicts, however, the low lead production compared to that expected in the traditional r-process conditions, which can be a possible explanation for the low lead abundances found in a couple of r-process-rich Galactic halo stars