Models for type Ia supernovae with composition inversions

Hydrodynamic models of type Ia supernovae are calculated which may correspond to certain possible outcomes of the evolution of binary systems which contain two degenerate white dwarfs. It is found that, unless the outer mantle is highly depleted in C, the detonation of a helium core within a C/O mantle results in a virtually complete incineration of the star, with no intermediate mass elements, at velocities of about 10,000 km/s. A mantle of O/Ne/Mg on a He core burns only to the Si peak but leaves insufficient carbon-burning product to be consistent with type Ia supernovae. For deflagrating models with a C/O core and mantle of O/Ne/Mg, it is found that if the C/O core mass is less than some limit between 0.5 and 0.9 solar mass, insufficient thermonuclear energy is released, resulting in velocities too small to correspond to observed type Ia supernovae. 42 references.