Evolution of helium-accreting carbon-oxygen white dwarfs towards helium-detonations

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It is believed that thermonuclear explosions in accreting white dwarfs are responsible for many luminous transients in the Universe, including Type Ia supernovae that are important objects for the precision cosmology and for the chemical evolution of the universe. Recently, detonations of the highly degenerate helium shell in a CO white dwarf that slowly accretes helium-rich matter has been proposed as a possible mechanism for Type Ia supernovae as well as for some peculiar Type Ib supernovae. The observable outcomes of a helium detonation sensitively depends on the thermodynamic conditions of the helium shell when it ignites. This project will systematically explore the evolution of helium-accreting CO white dwarfs in close binary systems, to predict which types of explosion would occur via helium detonation in the universe. Following-up our previous studies on the effects of rotation on the evolution of accreting white dwarfs, we will first investigate the effects of magnetic torques due to the so-called Spruit-Tayler dynamo on the evolution of helium-accreting white dwarfs and its implications for supernova explosions induced by helium detonations. Particular attention will be given to the consequences of frictional heating in differentially rotating layers in white dwarfs that are spun-up by mass and angular momentum accretion, and to rotationally induced chemical mixing. Following this, we will calculate self-consistent binary star evolution models to investigate whether time-dependent mass transfer in a close binary system would lead to a merger or significant change of the binary orbit, so as to affect the final fate of the system. With these studies, we will be able to produce realistic progenitor models for helium detonations, and to address the questions whether the majority of ordinary SNe Ia can be produced via helium detonations, which other transients (helium novae, peculiar SNe Ia, or peculiar SNe Ib) would be expected otherwise, and what would be the consequences for nucleosynthesis.