Helium accreting CO white dwarfs with rotation: Helium novae instead of double detonation

Abstract

We present evolutionary models of helium-accreting carbon-oxygen white dwarfs in which we include the effects of the spin-up of the accreting star induced by angular momentum accretion, rotationally induced chemical mixing and rotational energy dissipation. Initial masses of 0.6 M⊙ and 0.8 M⊙ and constant accretion rates of a few times 10-8 M⊙/yr of helium-rich matter have been considered, which is typical for the sub-Chandrasekhar mass progenitor scenario for Type la supernovae. It is found that the helium envelope in an accreting white dwarf is heated efficiently by friction in the differentially rotating spun-up layers. As a result, helium ignites much earlier and under much less degenerate conditions compared to the corresponding non-rotating case. Consequently, a helium detonation may be avoided, which questions the sub-Chandrasekhar mass progenitor scenario for Type la supernovae. We discuss implications of our results for the evolution of helium star plus white dwarf binary systems as possible progenitors of recurrent helium novae.