Radiative transfer in cylindrical threads with incident radiation

Methods for the solution of non-LTE radiative transfer equations in a cylinder, with external incident radiation, have been developed in the framework of accelerated Λ-iteration methods. This paper is restricted to the so-called one-dimension problem. The first method under investigation treats a two-level atom in the Eddington approximation: the comparison of results with a semi-analytical method (restricted to homogeneous cylinders) is used to study the effects of radius discretization. The second method removes the Eddington approximation and uses detailed (multiray) angular integration of intensities. Finally, the method is extended to a multilevel atom with a treatment of radiative transfer in both lines and continua. It is applied to a model hydrogen atom with 20 levels and one continuum, with correction of the electron density. Convergence properties and results are discussed.