Abstract

The effects of rotation in progenitor models for Type Ia supernovae are addressed. After discussing processes of angular momentum transport in carbon+oxygen white dwarfs, we investigate pre-explosion conditions of accreting white dwarfs. It is shown that differential rotation will persist throughout the mass accretion phase, with a shear strength near the threshold value for the dynamical shear instability. It is also found that rotational effects stabilise the helium shell source and reduce the carbon abundance in the accreted envelope.

Introduction

Unlike core collapse supernovae, Type Ia supernovae (SNe Ia) occur exclusively in binary systems (e.g. Livio 2000). Although it is still unclear which kinds of binary systems lead to SNe Ia, non-degenerate stars such as main sequence stars, red giants or helium stars are often assumed as the white dwarf companion (e.g. Hachisu et al. 1999, Langer et al. 2000, Han & Podsiadlowski 2003, Yoon & Langer 2003). This leads us to consider the spin-up of the white dwarf, since the transfered matter from those companions should form a Keplerian disk that carries a large amount of angular momentum. The observation that white dwarfs in cataclysmic variables rotate much faster than isolated ones (Sion 1999) provides evidence that accreting white dwarfs are indeed spun up. A rapidly rotating progenitor may also explain the asphericity implied by the polarizations observed in SNe Ia explosions (Wang, this volume). Here we discuss implications of the spin-up of accreting white dwarfs for the progenitors of SNe Ia.