Effects of rotation on the helium burning shell source in accreting white dwarfs

¹ Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands e-mail: S.C.Yoon@astro.uu.nl
² Institut für Physik, Universität Potsdam, 14415 Potsdam, Germany
³ : ZARM, University of Bremen Am Fallturm, 28359 Bremen, Germany

Received: 25 February 2004
Accepted: 3 June 2004

Abstract

We investigate the effects of rotation on the behavior of the helium-burning shell source in accreting carbon-oxygen white dwarfs, in the context of the single degenerate Chandrasekhar mass progenitor scenario for type Ia supernovae (SNe Ia). We model the evolution of helium-accreting white dwarfs of initially 1 , assuming four different constant accretion rates (2, 3, 5 and  ). In a one-dimensional approximation, we compute the mass accretion and subsequent nuclear fusion of helium into carbon and oxygen, as well as angular momentum accretion, angular momentum transport inside the white dwarf, and rotationally induced chemical mixing. Our models show two major effects of rotation: a) The helium-burning nuclear shell source in the rotating models is much more stable than in corresponding non-rotating models – which increases the likelihood that accreting white dwarfs reach the stage of central carbon ignition. This effect is mainly due to rotationally induced mixing at the CO/He interface which widens the shell source, and due to the centrifugal force lowering the density and degeneracy at the shell source location. b) The C/O-ratio in the layers which experience helium shell burning – which may affect the energy of an SN Ia explosion – is strongly decreased by the rotationally induced mixing of α-particles into the carbon-rich layers. We discuss implications of our results for the evolution of SNe Ia progenitors.