Models for Type I supernova. I - Detonations in white dwarfs

In a series of papers, the properties of white dwarfs provoked into nuclear instability by accretion will be explored. The results bear many close similarities to the observed properties of Type I supernovae, especially their energetics, light curves, nucleosynthesis, and spectra. In this paper a class of "detonating white dwarfs" is explored. The final evolution of carbon-oxygen white dwarfs in binary systems undergoing mass exchange at rates in the range 10-9 to 10-8Mₛun;yr-1 is considered. Three models are constructed having initial carbon-oxygen core masses 0. 5, 0. 8, and 1. 2 Mₛun; and accreting helium at rates of 10-8, 2×10-9, and 10-9Mₛun;yr-1, respectively. In all cases continued evolution leads to the accumulation of a thick helium layer surrounding the core, degenerate helium ignition, detonation and mass ejection. Detailed isotopic nucleosynthesis has also been computed for these models and implications for Galactic chemical evolution and γ-line astronomy are discussed. At present, the class of detonating models does not agree well with spectroscopic constraints upon common Type I events.