  In the context of Be stars, we restudied the viscous transonic decretion disk
model of these stars. This model is driven by a radiative force due to an
ensemble of optically-thin lines and viscosity considering the Shakura Sunyaev
prescription. The non-linear equation of motion presents a singularity (sonic
point) and an eigenvalue, which is also the initial condition at the stellar
surface. Then, to obtain this eigenvalue, we set it as a radial quantity and
perform a detailed topological analysis. Thereafter, we describe a numerical
method for solving either Nodal and Saddle transonic solutions. The value of
the viscosity,"alpha", barely determine the location of the sonic point, but it
determines the topology of the solution. We found two Nodal solutions, which
are almost indistinguishable between them. Saddle solutions are founded for
lower values of "alpha" than the required of the Nodal solutions. In addition,
rotational velocity do not play a determine role in the velocity (and density)
profile, because viscosity effects collapse all the solutions to almost a
unique one in a small region above the stellar surface. A suitable combination
of line force parameters and/or disk temperature, give location of the sonic
point lower than 50 stellar radii, describing a truncated disk. This could
explain the SED turndown observed in Be stars without needing a binary
companion.
