SN 1984A and Delayed‐Detonation Models of Type Ia Supernovae

SN 1984A shows unusually large expansion velocities in lines from freshlysynthesized material, relative to typical Type Ia Supernovae (SNe Ia). SN 1984Ais an example of a group of SNe Ia which have very large blue-shifts of theP-Cygni features, but otherwise normal spectra. We have modeled several earlyspectra of SN 1984A with the multi-purpose NLTE model atmosphere and spectrumsynthesis code, PHOENIX. We have used as input two delayed detonation models:CS15DD3 (Iwamoto et al. 1999) and DD21c (Hoeflich, Wheeler & Thielemann 1998).These models show line expansion velocities which are larger than that for atypical deflagration model like W7, which we have previously shown to fit thespectra of normal SNe Ia quite well. We find these delayed detonation models tobe reasonable approximations to large absorption feature blue-shift SNe Ia,like SN 1984A. Higher densities of newly synthesized intermediate mass elementsat higher velocities, v > 15,000 km/s, are found in delayed detonation modelsthan in deflagration models. We find that this increase in density at highvelocities is responsible for the larger blue-shifts in the synthetic spectra.We show that the variations in line width in observed SNe Ia are likely due todensity variations in the outer, high-velocity layers of their atmospheres.Comment: 14 pages, 4 figures, ApJ, 2001, 547 in press(uses AASTEX v5 macros