LEDOUX CONVECTION IN PROTONEUTRON STARS - A CLUE TO SUPERNOVA NUCLEOSYNTHESIS

Two-dimensional hydrodynamical simulations of the deleptonization of a newly formed neutron star (NS) were performed. Driven by negative lep ton fraction and entropy gradients, convection starts near the neutrin osphere about 20-30 ms after core bounce but moves deeper into the pro toneutron star (PNS), and after about 1 s the whole PNS is convective. The deleptonization of the star proceeds much faster than in the corr esponding spherically symmetrical model because the lepton flux and th e neutrino (nu) luminosities increase by up to a factor of 2. The conv ection below the neutrinosphere raises the neutrinospheric temperature s and mean energies of the emitted nu's by 10%-20%. This can have impo rtant implications for the supernova (SN) explosion mechanism, and it changes the detectable nu(e) signal from the Kelvin-Helmholtz cooling of the PNS. In particular, the enhanced v, flux relative to the <(nu)o ver bar>(e), flux during the early post-bounce evolution might solve t he overproduction problem of certain elements in the neutrino-heated e jecta in models of Type II SN explosions.