Non-spherical core collapse supernovae and nucleosynthesis

Motivated by observations of supernova SN 1987A, various authors have simulated Rayleigh-Taylor (RT) instabilities in the envelopes of core collapse supernovae (for a review, see Mueller 1998). The non-radial motion found in these simulations qualitatively agreed with observations in SN 1987A, but failed to explain the extent of mixing of newly synthesized 56Ni quantitatively. Here we present results of a 2D hydrodynamic simulation which re-addresses this failure and covers the entire evolution of the first 5 hours after core bounce.Comment: 4 pages, 1 figure, LaTeX, requires espcrc1.sty. To appear in Nucl. Phys. A., the proceedings of the conference "Nuclei in the Cosmos 2000", held in Aarhus, Denmark, June 27-July 1, 200

Nucleosynthesis and Clump Formation in a Core Collapse Supernova

High-resolution two-dimensional simulations were performed for the first five minutes of the evolution of a core collapse supernova explosion in a 15 solar mass blue supergiant progenitor. The computations start shortly after bounce and include neutrino-matter interactions by using a light-bulb approximation for the neutrinos, and a treatment of the nucleosynthesis due to explosive silicon and oxygen burning. We find that newly formed iron-group elements are distributed throughout the inner half of the helium core by Rayleigh-Taylor instabilities at the Ni+Si/O and C+O/He interfaces, seeded by convective overturn during the early stages of the explosion. Fast moving nickel mushrooms with velocities up to about 4000 km/s are observed. This offers a natural explanation for the mixing required in light curve and spectral synthesis studies of Type Ib explosions. A continuation of the calculations to later times, however, indicates that the iron velocities observed in SN 1987 A cannot be reproduced because of a strong deceleration of the clumps in the dense shell left behind by the shock at the He/H interface.Comment: 8 pages, LaTeX, 2 postscript figures, 2 gif figures, shortened and slightly revised text and references, accepted by ApJ Letter

On the hydrodynamics of the matter reinserted within superstellar clusters

We present semi-analytical and numerical models, accounting for the impact of radiative cooling on the hydrodynamics of the matter reinserted as strong stellar winds and supernovae within the volume occupied by young, massive and compact superstellar clusters. First of all we corroborate the location of the threshold line in the mechanical energy input rate vs the cluster size plane, found by Silich et al. (2004). Such a line separates clusters able to drive a quasi-adiabatic or a strongly radiative wind from clusters in which catastrophic cooling occurs within the star cluster volume. Then we show that the latter, clusters above the threshold line, undergo a bimodal behavior in which the central densest zones cool rapidly and accumulate the injected matter to eventually feed further generations of star formation, while the outer zones are still able to drive a stationary wind. The results are presented into a series of universal dimensionless diagrams from which one can infer: the size of the two zones, the fraction of the deposited mass that goes into each of them and the luminosity of the resultant winds, for clusters of all sizes and energy input rates, regardless the assumed adiabatic terminal speed V_A.Comment: 18 pages, 6 figures, accepted for publication in Ap

Core Collapse and Then? The Route to Massive Star Explosions

The rapidly growing base of observational data for supernova explosions of massive stars demands theoretical explanations. Central of these is a self-consistent model for the physical mechanism that provides the energy to start and drive the disruption of the star. We give arguments why the delayed neutrino-heating mechanism should still be regarded as the standard paradigm to explain most explosions of massive stars and show how large-scale and even global asymmetries can result as a natural consequence of convective overturn in the neutrino-heating region behind the supernova shock. Since the explosion is a threshold phenomenon and depends sensitively on the efficiency of the energy transfer by neutrinos, even relatively minor differences in numerical simulations can matter on the secular timescale of the delayed mechanism. To enhance this point, we present some results of recent one- and two-dimensional computations, which we have performed with a Boltzmann solver for the neutrino transport and a state-of-the-art description of neutrino-matter interactions. Although our most complete models fail to explode, the simulations demonstrate that one is encouragingly close to the critical threshold because a modest variation of the neutrino transport in combination with postshock convection leads to a weak neutrino-driven explosion with properties that fulfill important requirements from observations.Comment: 14 pages; 3 figures. Invited Review, in: ``From Twilight to Highlight: The Physics of Supernovae'', Eds. W. Hillebrandt and B. Leibundgut, Springer Series ``ESO Astrophysics Symposia'', Berli

Global Anisotropies in Supernova Explosions and Pulsar Recoil

We show by two-dimensional and first three-dimensional simulations of neutrino-driven supernova explosions that low (l=1,2) modes can dominate the flow pattern in the convective postshock region on timescales of hundreds of milliseconds after core bounce. This can lead to large global anisotropy of the supernova explosion and pulsar kicks in excess of 500 km/s.Comment: 3 pages, 2 figures, contribution to Procs. 12th Workshop on Nuclear Astrophysics, Ringberg Castle, March 22-27, 200