Ubrzanje metoda za rešavanje problema prenosa polarizovanog zračenje u više dimenzija i njihova primena

Abstract

Multidimensional radiative transfer is an essential ingredient of modern approach to modeling of astrophysical objects. Realistic modeling calls for the assumption of non-local thermodynamic equilibrium (NLTE), which, in turn requires self-consistent solution of coupled equations of radiative transfer statistical equilibrium. This approach allows us to compute emergent spectrum from a given model of the object, which is, in principle, a necessary step in interpretation of observational results. Thanks to the high-resolution and high signal to noise observations, it is often possible to measure not only intensity of the light but also its state of polarization. For interpretation of such observations it is necessary to solve radiative transfer problem for polarized radiation. This thesis deals with non-LTE transfer of (generally polarized) radiation in twodimensional media. Thesis can be divided in two parts. In the first part, we present a numerical method for the formal solution of the radiative transfer equation in 2D Cartesian coordinate system. This method allows us to explicitly account for the contribution of non-local source functions to the local specific intensity, and, hence, to the local scattering integral. The knowledge of these contributions is necessary for an iterative solution of coupled equations of radiative transfer and statistical equilibrium. Based on this formal solution we introduce two novel schemes for multidimensional NLTE radiative transfer which have so far been used only in 1D geometry: symmetric Gauss-Seidel iteration and “Sweep-by-sweep” implicit lambda iteration, latter one being based on “Forth-and-back” implicit lambda iteration. Both methods utilize implicit use of the local source function and the source function corrections each sweep of the computational grid (four times per iteration). “Sweep-by-sweep” implicit lambda iteration also uses the idea of iteration factors and achieves acceleration of about factor of seven with respect to the referent ...