CLOUDY is a general purpose radiative transfer code designed to deal with a variety of astrophysical situations. Johns & Basri (1995) show that it can be very useful for the study of T Tauri stars. The procedure followed by those authors is used here to assist in the computation of Pa Beta and Br Gamma line profiles for a moving medium.
A particular model is set up by defining the properties of the central star: effective temperature and radius; and the various flow parameters: temperature, velocity and turbulent velocity dependence with radius and density at the base of the flow; and the size of the region to be modeled.
For CLOUDY to run such a model the Wind command must be used. This option assumes a radial spherically symmetric flow and uses the Sobolev approximation. The model hydrogen atom used by version C90.03a of CLOUDY, the one used here, is presented in Ferguson & Ferland (1997). For the calculations presented in this work a hydrogen atom with 15 levels (the default number) was used.
The Johns & Basri (1995b) procedure requires a modification to the original CLOUDY code in order to accommodate the input of temperature, velocity and turbulent velocity dependence with radius. The Johns & Basri changes were implemented in CLOUDY version 90.03a. This version was further modified in order to allow radial infall. This was done by simply allowing the code to work with negative velocities.
A run of CLOUDY results in the output of the population of each hydrogen level at each radius for the specified parameters.