Model Accretion Disks

Tlusty was also designed to calculate the vertical structure of accretion disks.

The disk is assumed in steady state, geometrically thin and in Keplerian rotation. The vertical structure is solved for a set of axially symmetric concentric rings where a plane-parallel 1-D atmosphere calculation is performed. The atmosphere at each disk radius (specified in the disk midplane) is in hydrostatic equilibrium, with a depth-dependent gravity that arises from the vertical component of the central star's gravitational force on the disk material. The disk radiates all the mechanical energy dissipated by viscous shearing between the Keplerian orbits. The basic assumptions are:

The disk is divided into a set of concentric rings, each behaving as an independent plane parallel radiating slab; no assumptions about optical thickness are made. One run of Tlusty calculates the vertical structure of one ring;
Hydrostatic equilibrium in the vertical direction;
Energy balance is considered as a balance between the net radiation losses (calculated exactly, without invoking neither the optically thin, nor the optically thick [diffusion] approximations), and the dissipated mechanical energy;
The dissipated energy is proportional to viscosity, which is given through the Reynolds number;
The effect of illumination of the disk by the central star is taken into account.