Model calculations for scattering dominated atmospheres and the use of supernovae as distance indicators

Abstract

We present results of calculations of scattering dominated atmospheres in order to interpret the spectra of type II supernovae. We assume spherical geometry and a density profile which is either a power law or given by the expansion of a stellar structure. For hydrogen up to 8 energy levels are allowed to deviate from LTE. Effects of sphericity are most important for the continuum forming regions and are responsible for much higher colour temperatures in the optical wavelength range than the corresponding effective temperature would imply. Whereas non-LTE effects are small for the continuum flux in the optical range, they become most important for the hydrogen lines. The strong influence of line blanketing on the observed spectra is demonstrated. This effect can lead to significant errors in the interpretation of the spectra and in the Baade Wesselink method for using supernovae as distance indicators. The application of our model on the SN1987a imply a distance of 46∓ 4 kpc for the LMC.