A Parameter Study of Type II Supernova Light Curves Using 6 M_odot He Cores

Abstract

Results of numerical calculations of Type II supernova light curves are presented. The model progenitor stars have 6 $M{_\odot}$ cores and various envelopes, originating from a numerically evolved 20 $M{_\odot}$ star. Five parameters that affect the light curves are examined: the ejected mass, the progenitor radius, the explosion energy, the $^{56}$Ni mass, and the extent of $^{56}$Ni mixing. The following affects have been found: 1) the larger the progenitor radius the brighter the early--time light curve, with little affect on the late--time light curve, 2) the larger the envelope mass the fainter the early light curve and the flatter the slope of the late light curve, 3) the larger the explosion energy the brighter the early light curve and the steeper the slope of the late light curve, 4) the larger the $^{56}$Ni mass the brighter the overall light curve after 20 to 50 days, with no affect on the early light curve, 5) the more extensive the $^{56}$Ni mixing the brighter the early light curve and the steeper the late light curve. The primary parameters affecting the light curve shape are the progenitor radius and the ejected mass. The secondary parameters are the explosion energy, $^{56}$Ni mass and $^{56}$Ni mixing. I find that while in principle the general shape and absolute magnitude of a light curve indicate a unique set of parameters, in practice it is difficult to avoid some ambiguity in the parameters. I find that the nickel--powered diffusion wave and the recombination of helium produce a prominent secondary peak in all our calculations. The feature is less prominent when compositional mixing, both $^{56}$Ni mixing and mixing between the hydrogen and helium layers, occurs. The model photospheric temperatures and velocities are presented, for comparison to observation.