  Structure and spectral energy distributions (SEDs) of externally irradiated
circumstellar disks are often computed on the basis of the two-temperature
model of Chiang & Goldreich. We refine these calculations by using a more
realistic temperature profile which is continuous at all optical depths and
thus goes beyond the two-temperature model. It is based on the approximate
solution of the radiation transfer in the disk obtained from the
frequency-integrated moment equations in the Eddington approximation. We come
up with a simple procedure (``constant g_z approximation'') for treating the
vertical structure of the disk in regions where its optical depth to stellar
radiation is high. This allows us to obtain expressions for the vertical
profiles of density and pressure at every point in the disk and to determine
the shape of its surface. Armed with these analytical results we calculate the
full radial structure of the disk and demonstrate that it favorably agrees with
the results of direct numerical calculations. We also describe a simple and
efficient way of the SED calculation based on our adopted temperature profile.
Resulting spectra provide very good match (especially at short wavelengths) to
the results of more detailed (but also more time-consuming) SED calculations
solving the full frequency- and angle-dependent radiation transfer within the
disk.
