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

Results of numerical calculations of Type II supernova light curves are presented. The model progenitor stars have 6 M_☉ cores and various envelopes, originating from a numerically evolved 20 M_☉ star. Five parameters that affect the light curves are examined: the ejected mass, the progenitor radius, the explosion energy, the ⁵⁶Ni mass, and the extent of ⁵⁶Ni mixing. The following effects have been found: (1) the larger the progenitor radius, the brighter the early-time light curve, with little effect 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 ⁵⁶Ni mass, the brighter the overall light curve after 20-50 days, with no effect on the early light curve; and (5) the more extensive the ⁵⁶Ni 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, ⁵⁶Ni mass, and ⁵⁶Ni 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 ⁵⁶Ni mixing and mixing between the hydrogen and helium layers, occurs. The model photospheric temperatures and velocities are presented, for comparison to observation.