Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae

We present detailed non-LTE synthetic spectra of hydrodynamic supernovae (SNe) Ia models. We make no assumptions about the form of the spectrum at the inner boundary. We calculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar “helium detonators.” Gamma-ray deposition is handled in a simple, accurate manner. We have parameterized the storage of energy, which arises from the time-dependent deposition of radioactive decay energy, in a reasonable manner that spans the expected range. We find that the Chandrasekhar-mass deflagration model W7 of Nomoto, Thielemann, & Yokoi shows good agreement with the observed spectra of SN 1992A and SN 1994D, particularly in the UV, where our models are expected to be most accurate. The sub-Chandrasekhar models do not reproduce the UV deficit observed in normal SNe Ia. They do bear some resemblance to subluminous SNe Ia, but the shapes of the spectra (i.e., the colors) are opposite that of the observed ones, and the intermediate-mass element lines (such as Si II and Ca II) are extremely weak, which seems to be a generic difficulty of the models. Although the sub-Chandrasekhar models have a significant helium abundance (unlike Chandrasekhar-mass models), helium lines are not prominent in the spectra near maximum light and thus do not act as a spectral signature for the progenitor.