  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.
