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 10⁻⁸M_sun;yr⁻¹ is considered. Three models are constructed having initial carbon-oxygen core masses 0.5, 0.8, and 1.2 M_sun; and accreting helium at rates of 10⁻⁸, 2×10⁻⁹, and 10⁻⁹M_sun;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.