THE INTERPLAY BETWEEN PROTO-NEUTRON STAR CONVECTION AND NEUTRINO TRANSPORT IN CORE-COLLAPSE SUPERNOVAE

We couple two-dimensional hydrodynamics to realistic one-dimensional m ultigroup flux-limited diffusion neutrino transport to investigate pro to-neutron star convection in core-collapse supernovae, and more speci fically, the interplay between its development and neutrino transport. Our initial conditions, time-dependent boundary conditions, and neutr ino distributions for computing neutrino heating, cooling, and delepto nization rates are obtained from one-dimensional simulations that impl ement multigroup flux-limited diffusion and one-dimensional hydrodynam ics. The development and evolution of proto-neutron star convection ar e investigated for both 15 and 25 M-. models, representative of the tw o classes of stars with compact and extended iron cores, respectively. For both models, in the absence of neutrino transport, the angle-aver aged radial and angular convection velocities in the initial Ledoux un stable region below the shock after bounce achieve their peak values i n similar to 20 ms, after which they decrease as the convection in thi s region dissipates. The dissipation occurs as the gradients are smoot hed out by convection. This initial proto-neutron star convection epis ode seeds additional convectively unstable regions farther out beneath the shock. The additional proto-neutron star convection is driven by successive negative entropy gradients that develop as the shock, in pr opagating out after core bounce, is successively strengthened and weak ened by the oscillating inner core. The convection beneath the shock d istorts its sphericity, but on the average the shock radius is not boo sted significantly relative to its radius in our corresponding one-dim ensional models. In the presence of neutrino transport, proto-neutron star convection velocities are too small relative to bulk inflow veloc ities to result in any significant convective transport of entropy and leptons. This is evident in our two-dimensional entropy snapshots, wh ich in this case appear spherically symmetric. The peak angle-averaged radial and angular convection velocities are orders of magnitude smal ler than they are in the corresponding ''hydrodynamics-only'' models. A simple analytical model supports our numerical results, indicating t hat the inclusion of neutrino transport reduces the entropy-driven (le pton-driven) convection growth rates and asymptotic velocities by a fa ctor similar to 3 (50) at the neutrinosphere and a factor similar to 2 50 (1000) at rho = 10(12) g cm(-3), for both our 15 and 25 M-. models. Moreover, when transport is included, the initial postbounce entropy gradient is smoothed out by neutrino diffusion, whereas the initial le pton gradient is maintained by electron capture and neutrino escape ne ar the neutrinosphere. Despite the maintenance of the lepton gradient, proto-neutron star convection does not develop over the 100 ms durati on typical of all our simulations, except in the instance where ''low- test'' intial conditions are used, which are generated by core-collaps e and bounce simulations that neglect neutrino-electron scattering and ion-ion screening corrections to neutrino-nucleus elastic scattering. Models favoring the development of proto-neutron star convection eith er by starting with more favorable, albeit artificial (low-test), init ial conditions or by including transport corrections that were ignored in our ''fiducial'' models were considered. Our conclusions nonethele ss remained the same. Evidence of proto-neutron star convection in our two-dimensional entropy snapshots was minimal, and, as in our fiducia l models, the angle-averaged convective velocities when neutrino trans port was included remained orders of magnitude smaller than their coun terparts in the corresponding hydrodynamics-only models.