Ledoux Convection in Protoneutron Stars—A Clue to Supernova Nucleosynthesis?

Abstract

Two-dimensional hydrodynamical simulations of the deleptonization of a newly formed neutron star (NS) were performed. Driven by negative lepton fraction and entropy gradients, convection starts near the neutrinosphere about 20-30 ms after core bounce but moves deeper into the protoneutron star (PNS), and after about 1 s the whole PNS is convective. The deleptonization of the star proceeds much faster than in the corresponding spherically symmetrical model because the lepton flux and the neutrino (ν) luminosities increase by up to a factor of 2. The convection below the neutrinosphere raises the neutrinospheric temperatures and mean energies of the emitted ν's by 10%-20%. This can have important implications for the supernova (SN) explosion mechanism, and it changes the detectable ν signal from the Kelvin-Helmholtz cooling of the PNS. In particular, the enhanced νe flux relative to the e flux during the early post-bounce evolution might solve the overproduction problem of certain elements in the neutrino-heated ejecta in models of Type II SN explosions.