Radiative transfer in dust clouds. I. Hot-centered clouds associated with regions of massive star formation

We have developed a program which accurately integrates the equation of radiative transfer in a spherically symmetric dust cloud illuminated by a central star. The intensity of the radiation field is calculated as a function of frequency and direction at a grid of radial points. The distribution of angular directions is chosen carefully so that the moments of the intensity can be accurately calculated. For the integration along a ray in any chosen direction, the step-length is automatically adjusted to obtain the desired accuracy. The iteration to obtain the temperature distribution continues until the conditions of flux conservation and radiative balance are both satisfied