SIMBAD references

We use the radiative transfer code PHOENIX to study the line formation of the wavelength region 5000-7000 Å. This is the region where the SN Ia-defining Si II feature occurs. This region is important, since the ratio of the two nearby silicon lines has been shown to correlate with the absolute blue magnitude. We use a grid of LTE synthetic spectral models to investigate the formation of line features in the spectra of SNe Ia. By isolating the main contributors to the spectral formation, we show that the ions that drive the spectral ratio are Fe III, Fe II, Si II, and S II. While the former two strongly dominate the flux transfer, the latter two form in the same physical region inside the supernova. We also show that the naive blackbody that one would derive from a fit to the observed spectrum is very different than the true underlying continuum.