Stabilization of helium shell burning by rotation in accreting white dwarfs

Abstract

The currently favored scenario for the progenitor evolution of Type Ia supernovae (SNe Ia) presumes that white dwarfs in close binary systems grow to the Chandrasekhar limit via mass accretion from their non-degenerate companions. However, the accreted hydrogen and/or helium usually participate thermally unstable or even violent nuclear reactions in a geometrically confined region, due to the compactness of the white dwarf. Since shell flashes induced by the thermal instability might induce significant loss of mass, efficient mass increase of white dwarfs by hydrogen and/or helium accretion has been seriously questioned. A good understanding of the stability of thermonuclear shell sources is therefore crucial in order to investigate the evolution of accreting white dwarfs as SNe Ia progenitors. Here, we present a quantitative criterion for the thermal stability of thermonuclear shell sources, and discuss the effects of rotation on the stability of helium shell burning in helium accreting CO white dwarfs with Mdot \approx 10^{-7} ... 10^{-6} Msun/yr. In particular, we show that, if the effects of rotation are properly considered, helium shell sources are significantly stabilized, which might increase the likelihood for accreting white dwarfs to grow to the Chandrasekhar limit.