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

SN 1984A shows unusually large expansion velocities in lines from freshly s ynthesized material, relative to typical Type Ia supernovae (SNe Ia). SN 19 84A 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 atmosp here and spectrum synthesis code PHOENIX. We have used as input two delayed -detonation models: CS15DD3 (Iwamoto et al.) and DD21c Wheeler, & Thieleman n). These models show line-expansion velocities which (Hoflich, are larger than that for a typical deflagration model like W7, which we have previousl y shown to Dt the spectra of normal SNe Ia quite well. We find these delaye d-detonation models to be reasonable approximations to large absorption fea ture 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 tha t this increase in density at high velocities is responsible for the larger blueshifts in the synthetic spectra. We show that the variations in line w idth in observed SNe Ia are likely due to density variations in the outer, high-velocity layers of their atmospheres.