SN 1984A and delayed-detonation models of Type Ia supernovae

SN 1984A shows unusually large expansion velocities in lines from freshly synthesized material, relative to typical Type Ia supernovae (SNe Ia). SN 1984A is an example of a group of SNe Ia which have very large blueshifts of the P Cygni features but otherwise normal spectra. We have modeled several early spectra of SN 1984A with the multipurpose non-LTE (NLTE) model atmosphere and spectrum synthesis code PHOENIX. We have used as input two delayed-detonation models: CS15DD3 (Iwamoto et al.) and DD21c Wheeler, & Thielemann). These models show line-expansion velocities which (Hoflich, are larger than that for a typical deflagration model like W7, which we have previously shown to Dt the spectra of normal SNe Ia quite well. We find these delayed-detonation models to be reasonable approximations to large absorption feature blueshift SNe Ia, like SN 1984A. Higher densities of newly synthesized intermediate-mass elements at higher velocities, v > 15,000 km s(-1), are found in delayed-detonation models than in deflagration models. We find that this increase in density at high velocities is responsible for the larger blueshifts in the synthetic spectra. We show that the variations in line width in observed SNe Ia are likely due to density variations in the outer, high-velocity layers of their atmospheres.