Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443...89h&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 1, p. 89-108
Astronomy and Astrophysics
Astrophysics
112
Deflagration, Detonation, Emission Spectra, Light Curve, Stellar Models, Supernovae, Local Thermodynamic Equilibrium, Nickel, Spectrum Analysis, Stellar Mass Ejection
Scientific paper
We present an analysis of the observed light curves and spectra of the Type Ia supernova SN 1994D in the galaxy NGC 4526. The sensitivity of theoretical light curves and spectra to the underlying hydrodynamical model is discussed. The calculations are consistent with respect to the explosion mechanism, the optical and infrared light curves, and the spectral evolution, leaving the description of the nuclear-burning front and the structure of the white dwarf as the only free parameters. The explosions are calculated using a one-dimensional Lagrangian code including a nuclear network (Khokhlov 1991). Subsequently, the light curves are constructed. Spectra are computed for several instants of time using the density, chemical, and luminosity structure resulting from the light-curve code. Our non-LTE (NLTE) code solves the relativistic radiation transport equations in a commoving frame consistently with the statistical equations and ionization due to gamma-radiation for the most important elements. About 300,000 additional lines are included, assuming LTE-level populations and an equivalent-two-level approach for the source functions. We find that the classical two-level approach underestimates thermalization processes by several orders of magnitude. Besides models already discussed in previous papers, a new series of delayed detonations has been included with a Ni-56 production ranging from approximately 0.2 up to 0.7 solar masses depending on the density at which the transition from a deflagration to a detonation occurs. The visual magnitude at maximum light MV ranges from approximately -18.4 to approximately -19.5 mag. Only one model with MV = 19.39 mag shows good agreement with the observations of SN 1994D both for B, V, R, and I colors and the spectral evolution. The deflagration velocity is close to the laminar deflagration (v = 0.03 cs), and the transition from the deflagration to the detonation occurs at rhotr = 2 x 107 g/cc. The initial central density of the white dwarf is 2.7 x 109 g/cc, i.e., about 20% lower than in our delayed detonation models previously considered. The lower density may be understood in terms of a high accretion rate on the progenitor. During the explosion, 0.6 solar masses of Ni-56 are produced. The need to reduce Ti in the outer layers becomes evident from the spectral fits. This may be explained by small-scale density fluctuations during the explosion or by different primordial metallicity in the exploding white dwarf.
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