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

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