The vertical structure of T Tauri accretion disks II. Physical conditions in the disk

Abstract

We present a self-consistent analytical model for the computation of the physical conditions in a steady quasi-Keplerian accretion disk. The method, based on the thin disk approximation, considers the disk as concentric cylinders in which we treat the vertical transfer as in a plane-parallel medium. The formalism generalizes a work by Hubeny (1990), linking the disk temperature distribution to the local energy dissipation and leads to analytical formulae for the temperature distribution which help to understand the behaviour of the radiation propagated inside the disks. One of the main features of our new model is that it can take into account many heating sources. We apply the method first to two sources: viscous dissipation and stellar irradiation. We show that other heating sources like horizontal transfer or irradiation from the ambiant medium can also be taken into account. Using the analytical formulation in the case of a modified Shakura & Sunyaev radial distribution that allow the accretion rate to be partly self-similar in the inner region, and, for an alpha and beta prescription of the viscosity, we obtain two-dimensional maps of the temperature, pressure and density in the close environment of low mass young stars. We use these maps to derive the observational properties of the disks such as spectral energy distributions, high resolution spatial images or visibilities in order to underline their different behaviours under different input models.