!!! CANCELLED !!! On radiative transfer in stellar atmospheres
by Dr. Olgica Kuzmanovska (Ss. Cyril and Methodius University, Department of Physics, Faculty of Natural Sciences and Mathematics)
at SMI - Boltzmanngasse 3, 1090 Wien ( 3-2-08 - Seminarraum )
!!! CANCELLED !!!
The observed spectra of stars are consisted of continuum and absorption spectral lines, They are the only source of information of the dynamical and structural properties of the stellar interiors. The spectral lines formed in the outer layers, i.e. the atmospheres, are result of complex mutual interaction of the radiation field and the state of matter. Thus, one of the central problems of the astrophysical spectroscopic diagnostics is the radiative transfer (RT) in the spectral lines. Its solution is performed by numerical calculations. Due to the important role of scattering processes that relate distant points of the atmosphere via the radiation field, the RT problem is non-local. Additionally, for the case of multi-level atoms, the problem is non-linear; the coupling of the atomic level populations (state of matter) and the radiation field intensities in the corresponding line transitions has to be performed by simultaneous solution of the two main sets of equations: RT and statistical equilibrium. The non-linearity of the problem requires a use of some kind of iterative procedure. In the past few decades various numerical methods have been developed, using different approaches and numerical techniques. Some will be presented here, with emphasis on two of them: the Iteration Factors Method (IFM) and Forth-and-Back Implicit Lambda Iteration (FBILI).