Models for Type I supernovae - Partially incinerated white dwarfs

Abstract

White dwarf models are calculated for the explosions and light curves of Type I supernovae using full hydrodynamics and radiative diffusion. Comparison is made to recent observations. The models are based on the instantaneous thermonuclear burning of part or all of a degenerate carbon/oxygen/helium core. The Rayleigh-Taylor instability at the points of density/composition discontinuity is explored. Discontinuous jumps in the density can be smoothed somewhat, but not eliminated on a dynamical time-scale. The effects of radioactive decay of 56 Ni and 56 Co are incorporated by means of an absorption treatment of y-rays which allows the calculation of a y-ray energy deposition function in an arbitrary density profile. Complete trapping of positrons is assumed over the epochs calculated. The B and V magnitude light curves are calculated by assuming that the continuum is truncated shortward of 4000 Â and is Planckian at longer wavelengths. Observational constraints are the peak luminosity and shape of the light curve in various bands, the Doppler velocity of the material, and the composition. A model at the Chandrasekhar mass limit in which 1 M 0 is incinerated and for which the opacity in the incinerated portions is markedly less than in the unburned matter successfully matches many of the direct observational constraints. Any such model in which in excess of 0.7 M q is incinerated (in order to achieve the desired ejecta velocities) is necessarily bright and difficult to reconcile with H 0 ~ 100 km s -1 Mpc -1 . Such a model also suggests an overproduction of Fe compared with the Galactic abundance. Despite the qualitative appeal of the picture in which binary mass accretion raises a carbon-oxygen white dwarf to the Chandrasekhar limit, the demand to produce supernovae of the observed characteristics is not easily reconciled quantitatively with current calculations of hydrogen accretion.