Spiral-wave-driven accretion in quiescent dwarf novæ

Abstract

Context. In dwarf novæ (DNe) and low-mass X-ray binaries, the tidal potential excites spiral waves in the accretion disc. Spiral-wave-driven accretion may be important in quiescent discs, where the angular momentum transport mechanism has yet to be identified. Previous studies were limited to unrealistically high temperatures for numerical studies or to specific regimes for analytical studies. Aims. We perform the first numerical simulation of spiral-wave-driven accretion in the cold temperature regime appropriate to quiescent discs, which have Mach numbers ≳100. Methods. We used the new GPU-accelerated finite-volume code IDEFIX to produce global hydrodynamics 2D simulations of the accretion discs of DN systems with a sufficiently fine spatial resolution to capture the short scale-height of cold, quiescent discs with Mach numbers ranging from 80 to 370. Results. Running the simulations on timescales of tens of binary orbits shows transient angular momentum transport that decays as the disc relaxes from its initial conditions. We find the angular momentum parameter α drops to values of ≪10−2, too weak to drive accretion in quiescence.