Radiative transport in finite homogenous cylinders by the Monte Carlo technique

Abstract

The transfer of resonance line radiation in homogeneous cylinders of various shapes and optical thicknesses is studied by means of the Monte Carlo method in order to investigate the effects of geometry on (non-LTE) source functions and emergent line intensity profiles. It is found that increasing the larger cylinder dimension (radius or length) produces no change in the source function except to extend it at a constant level. For cylinders with the same axial optical thickness as a slab, we find that the axial source function is effectively the same as that of a slab whenever the radius of the cylinder exceeds its length. Further, when the length exceeds the radius, the radial source function approximates the source function for a slab of optical thickness equal to that of the cylinder radius, provided this is less than a thermalization length. Emergent line shapes are calculated and are found to be strongly dependent upon the position and aspect. Scaling laws are given which permit estimation of the source function at an arbitrary point in a cylinder without a detailed solution of the transfer problem.