Convection Affects Magnetic Turbulence in White Dwarf Accretion Disks

Matt Coleman (IAS)

I examine the accretion disks which power outbursts in two types of white dwarf binary systems: dwarf novae (DNe) and AM CVns. Accretion disks in these systems are thermally unstable, causing some of the observed variations. The source of "normal outbursts" in these systems ultimately originates from ionization transitions (H for DNe and He for AM CVns). These ionization transitions cause significant temperature dependence in opacities and equation of states, culminating in the occurrence of convection within these accretion disks. Local stratified shearing-box simulations were used to show that this convection has a significant impact on the turbulence and dynamos generated by the magnetorotational instability (MRI). Most notably, convection enhances the stress to pressure ratio, often denoted by alpha. These results were then incorporated into the disk instability model to generate the first theoretical lightcurves for dwarf novae outbursts which incorporate MRI physics.

Thursday, September 14, 2017