## 2. The vertical structureWe assume that -
The disc is geometrically thin and all gradients in the vertical direction are much greater than the corresponding ones in the radial direction. -
The radiative transfer can be treated in the grey approximation and only the vertical directions are considered. (`two stream approximation') -
LTE prevails throughout the entire disc. Deviations from LTE will be discussed in a subsequent paper. We believe that LTE has an effect on the details but not on the general picture discussed here.
The equation for hydrostatic equilibrium in the vertical direction is where The condition of thermal equilibrium is: where is the viscous energy dissipation per unit volume. We assume here that the entire energy dissipated by the viscous forces is carried away by radiation i.e. we ignore at this moment convection and any other non radiative energy transport mechanisms. The radiative transfer equation is: where where in the notation of SW and we use the model approximation for the viscous energy dissipation. The boundary conditions are: The above equations, together with the boundary conditions form a closed set, and can be solved for the disc structure for given and . © European Southern Observatory (ESO) 1999 Online publication: March 18, 1999 |