Explosions of Sub--Chandrasekhar Mass White Dwarfs in Two Dimensions

Abstract

The hydrodynamics of detonations of white dwarfs, having a carbon-oxygen core and a helium envelope, are examined in a two-dimensional geometry. Various combinations of the masses of the CO core and the overlying He layer are examined. Nuclear burning is directly computed with an alpha network from <SUP>12</SUP>C to <SUP>56</SUP>Ni as a part of the hydrodynamic calculation. The nucleosynthesis yield is similar to that needed for Type Ia supernovae to explain the variation in alpha elements relative to iron in Population II stars. Significant amounts of radioactive <SUP>44</SUP>Ti are produced. The yields are similar to those predicted from one-dimensional computations, despite the very nonspherical hydrodynamic behavior. Light curves are simulated and compared to observations of Type Ia supernovae. The observed variation in peak absolute luminosity and in post-maximum decline rate is reproduced in a natural way. A rough comparison of predicted velocities with observations of Ca II H and K, Mg II λ4481 and Si II λ6355 in SN 1989B (in NGC 3627) is promising; implications for the use of Type Ia supernovae as distance indicators are discussed, and the key importance of spectral synthesis is stressed.