Radiative Transfer Diagnostics: Understanding Multi-Level Transfer Calculations

Abstract

Efficient methods are now available for solving multi - level, multi-transition non-LTE transfer problems in stellar atmospheres in the approximation of complete redistribution. Once such a solution is obtained, however, it is frequently desirable to know more about the solution than simply the emergent intensity or the flux. We present a means by which one may easily understand how all the line and continuum transitions are formed. We cast each transition into an equivalent two-level form, consisting of a scattering and a source term. The behavior of these terms with height immediately reveals how the line excitation is driven. Numerical perturbations of the atomic rates, both collisional and radiative, about this solution reveal the sensitivity of the scattering and source terms to various atomic rate and helps one to identify the other interlocking radiative and collisional transitions important to the formation of a spectral line. We demonstrate this method through application to the formation of the solar hydrogen lines and the Lyman continuum.

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.