Spiral-wave-driven accretion in quiescent dwarf nov{\ae}

TL;DR

This study uses advanced GPU-accelerated simulations to investigate spiral wave-driven accretion in cold, quiescent dwarf novae discs, finding that angular momentum transport is too weak to sustain accretion during quiescence.

Contribution

First numerical simulation of spiral wave-driven accretion in cold dwarf novae discs with realistic Mach numbers using GPU acceleration.

Findings

Angular momentum transport decays over time in simulations.

The effective alpha parameter drops below 0.01 in quiescent discs.

Spiral wave-driven accretion is insufficient to explain quiescent accretion rates.

Abstract

In dwarf nov{\ae} 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. 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. We use the new GPU-accelerated finite volume code Idefix to produce global hydrodynamics 2D simulations of the accretion discs of dwarf nov{\ae} systems with a fine-enough spatial resolution to capture the short scale-height of cold, quiescent discs with Mach numbers ranging from 80 to 370. 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 {\alpha} drops to values << 0.01 , too weak to drive accretion in quiescence.