The Light Curve of Supernova 1987A: The Structure of the Presupernova and Radioactive Nickel Mixing

Abstract

We have studied the influence of the presupernova structure and the degree of Ni-56 mixing on the bolometric light curve of SN 1987A in terms of radiation hydrodynamics in the one-group approximation by abandoning LTE and by taking into account nonthermal ionization and the contribution of spectral lines to opacity. Our study shows that moderate Ni-56 mixing at velocities of < 2500 km/s can explain the observed light curve if the density of the outer layers of the presupernova exceeds the value obtained in the evolutionary model of a single nonrotating star severalfold. Abandoning LTE and allowing for nonthermal ionization when solving the equation of state and calculating the mean opacities and the thermal emission coefficient leads to a significant difference between the gas temperature and the radiation temperature in the optically thin layers of the supernova envelope. We demonstrate the fundamental role of the contribution of spectral lines to the opacity in an expanding envelope and of the accurate description of radiative transfer in reproducing the observed shape of the bolometric light curve. We have found that disregarding the contribution of spectral lines to the opacity introduces an error of 20% into the explosion energy, and that a similar error is possible when determining the mass of the ejected matter. The resonant scattering of radiation in numerous lines accelerates the outer layers to velocities of 36 000 km/s; this additional acceleration affects the outer layers with a mass of 10^{-6} Msun. Proper calculations of the supernova luminosity require that not only the delay effects, but also the limb-darkening effects be taken into account.