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E.J. Lentz, E. Baron, D. Branch (University of Oklahoma), P.H. Hauschildt (University of Georgia), P.E. Nugent (LBNL)
We have calculated a grid of photospheric phase atmospheres of Type~Ia supernovae (SNe~Ia) with metallicities from ten times to one thirtieth the normal metallicity in the C+O layer of the deflagration model, W7 (Nomoto et al. 1984, Thielemann et al. 1986). We have modeled the spectra using the multi-purpose NLTE model-atmosphere and spectrum-synthesis code, PHOENIX. We show models for the epochs 7, 10, 15, 20, and 35 days after explosion. When compared to approximately corresponding spectra observed at epochs -12, -9, -4, 0, and 15 days after peak B magnitude, these synthetic spectra fit reasonably well. The spectra show a consistent variation in the overall level of the UV `contiunuum' with higher fluxes for models with lower metallicity in the unburned C+O layer. The models show higher temperatures in the outer layers of C+O with lower metallicity and less surface cooling from the metals. The UV features also move consistently to the blue with higher metallicity demonstrating that they are forming at shallower and faster layers in the atmosphere. The last, and potentially most useful, effect is the blueward movement of the Si~II feature at 6150~Å\ with increasing C+O layer metallicity. We also demonstrate the more complex effects of modifying the 54Fe content of the incomplete burning zone in W7 at maximum light. We discuss effects of the results on the use of SNe~Ia for cosmology. We briefly address some shortcomings of the W7 model when compared to observations.
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