SPECTRAL: A new evolutionary synthesis code. Application to the irregular Galaxy NGC 1560

A generalized iteration method is presented to solve the polarized line transfer equation for a two-level-atom in an arbitrarily oriented, weak magnetic field. The polarized redistribution matrix employed accounts self-consistently for collisions as well as the presence of a weak magnetic field responsible for the Hanle effect. The proposed numerical method of solution is based on a Polarized Approximate Lambda Iteration (PALI) method. A Fourier decomposition of the radiation field and of the phase matrix with respect to the azimuthal angle reduces the complexity of the problem. A generalized core-wing technique is proposed, which permits an efficient implementation of the frequency domain structure inherent in the polarized redistribution matrix. The numerical method is tested for its accuracy and efficiency by comparing with the existing methods.