POSTEXPLOSION HYDRODYNAMICS OF SN-1987A

We present a comprehensive study of the postexplosion hydrodynamics of the ejecta of SN 1987A, encompassing the Rayleigh-Taylor instabilities at the shell interfaces and the dynamical effects of the energy input due to the radioactive decay of N-56 and Co-56. In an attempt to explain the observed high-velocity wings of the iron line of SN 1987A, we investigate the dependence of the hydrodynamical behavior on progenitor structure, initial perturbations, explosion energy, and dimensionality of the numerical simulation. We show that none of these factors leads to the required high-velocity tail of iron, although we are able to reproduce the line core adequately. This failure points toward early instabilities which would premix the nickel outward during, or shortly after, the explosion itself, and therefore enable the nickel to participate in the subsequent round of Rayleigh-Taylor instabilities. By artificially premixing nickel in our initial model, we find that this early mixing has to affect the inner 1.5 M . of the ejecta to reproduce the high-velocity wings at a time of 90 days. We speculate that the high-entropy bubble associated with the delayed mechanism is responsible for this premixing by driving convective motions early in the explosion.