Multidimensional Radiative Transfer

A multidimensional radiative transfer code is presented, using the short characteristics scheme and the ALI method. The code uses the 2-level atom formulation, appropriate for strong resonance lines, and can operate with Cartesian, cylindrical and spherical coordinate systems, the last two assuming rotational symmetry about the z-axis. The emphasis of the code is on accurately treating large, three-dimensional velocity fields on a large number of spatial points and with high angular resolution, in order to deal with complete objects. To keep the code fast and reduce memory requirements, the code was parallelized for use on a cluster of networked PCs by using a spatial parallelization method, where the computational domain is divided spatially in independent subdomains. It is shown that such a method is both efficient and reliable. The accuracy of the code was tested at length and was found to be ~ 5% in most cases of interest. A spectrum synthesis code is then presented, using the long characteristics method and an Adaptive Mesh Refinement technique. The code can accurately calculate the emergent line profile for a specified inclination angle on a two-dimensional structure with a specified source function assuming rotational symmetry, in cylindrical and spherical coordinate systems. The accuracy of the code was determined to be of the order of 1%, given the structure and line source function. Both codes were then applied to the problem of rotation in expanding stellar winds. The spectroscopic effects of rotation were found to be significant for large inclination angles only, with the largest differences with respect to non-rotating of ~ 20%. The direction of the radiation volume force was found to change at most by a similar amount. Finally, the codes were applied to calculate line profiles for the disks in cataclysmic variables. The differences due to rotation were found to be significant, with the cores of strong resonance lines brightened by about 50% for small inclination angles. The radiation force was not found to be strongly affected