Fig. 6. Elements of the second column of the matrix as function of for various values of (i.e. of the magnetic field strength B). Solid lines : =0.1, dotted lines : =0.3, short-dashed lines : =0.5, dot-dashed lines : =1, triple-dot-dashed lines : =3, and long-dashed lines : =10. The case of =1 is highlighted for clarity. This figure is useful to understand the and dependence of the polarized source vector components , shown in the Figs. 7 and 9