The neutrino driven wind during a core collapse supernova is an attractive site for r-process nucleosynthesis. The initial electron fraction $Y_e$ in the wind depends on observable neutrino energies and luminosities. The mean antineutrino energy is limited by supernova SN 1987A data while lepton number conservation constrains the ratio of antineutrino to neutrino luminosities. If $Y_e,$ in the wind, is to be suitable for rapid neutron capture nucleosynthesis, then the mean electron neutrino energy could be significantly lower than that predicted in present supernova simulations. Alternatively, there could be a rapid increase of the mean antineutrino energy at late times. However, this is not seen in the SN 1987A data. Finally, there could be new neutrino physics such as oscillations to sterile neutrinos.

• Received 30 October 2001

DOI:https://doi.org/10.1103/PhysRevD.65.083005