Annu. Rev. Astron. Astrophys. 1998. 36: 17-55 Copyright © 1998 by Annual Reviews. All rights reserved

4. PHYSICAL PROPERTIES

The immediate progenitors of SNe Ia are believed to be carbon-oxygen (C-O) white dwarfs in close binary systems, and no other kind of progenitor has been under serious consideration for some time. During the 1980s, general consensus was also that the first nuclear ignition was of carbon, deep inside the white dwarf. This event would be followed by the outwards propagation of a subsonic nuclear flame (a "deflagration"), the velocity of which had to be (and still has to be) parameterized. One particular nuclear-hydrodynamical deflagration model called W7 (Nomoto et al 1984) was parameterized in such a way that its radial composition structure with (Branch et al 1985) or without (Harkness 1991a) ad hoc compositional mixing of its outer layers was able to give a good account of the spectral features of normal SNe Ia. Thus W7 became the standard SN Ia model, and this is where matters stood when the physics of SNe was reviewed in this series by Woosley & Weaver (1986) and still at the time of Branch & Tammann (1992). Since then, many people have put much effort into seeking the nature of the progenitor binary systems, constructing hydrodynamical explosion models, and calculating light curves and spectra of models.