Detectibility of Mixed Unburnt C+O in Type Ia Supernova Spectra

Motivated by recent 3-D calculations of the explosion of Type Ia supernova via a pure deflagration we calculate the observed spectra at 15-25 days past maximum light of a parameterized model which has a considerable fraction of unburnt C+O in the central regions. Rather than attempting a self consistent 3-D calculation, which is beyond the scope of current computer codes, we modify the composition structure of the 1-D deflagration model W7. In our exploratory parameterized calculations, we find that a central concentration of C+O is not ruled out by observations for the epochs we study. We briefly examine whether nebular phase spectra could be incompatible with observations.