Sub-Chandrasekhar models for Type Ia supernovae and astrophysical transients

Sub-Chandrasekhar models aim to explain Type Ia supernovae from the explosion of white dwarf stars with masses below the Chandrasekhar limit. An advantage of this scenario is the wide range of possible progenitor masses, which may lead to a wide range of explosion brightnesses. We study sub-Chandrasekhar models by means of hydrodynamic simulations, nucleosynthetic post-processing and multidimensional radiative transfer calculations. We find that an assumed detonation in an accreted He layer likely triggers a secondary detonation in the carbon-oxygen-white dwarf core, which leads to a complete explosion of the white dwarf star. In models with normal brightnesses (M _core ≥ 0.8 M_ȯ), the He detonation nucleosynthesis is, however, problematic for the observable predictions. We discuss potential changes to the model that may lead to an improvement in this respect. As a second scenario, we study explosions in systems with low-mass carbon-oxygen cores as candidates for faint astrophysical transients. For this scenario, the He detonation nucleosynthesis may be compatible with the observations. The occurrence of a secondary core detonation is shown to potentially leave an observable imprint in the light curves. Finally, we also discuss our models in the context of Galactic chemical evolution.