Intensity (left panel) and Stokes Q/I (right panel) profiles as a function of wavelength in the spectral range centered on the K I D₂ line. The RT calculations were carried out in the absence of a magnetic field for a two-term atomic model with HFS, taking PRD effects into account. In the calculations illustrated in this figure and all those shown below, only the ³⁹K isotope was considered. The colored curves (see legend) represent the results of calculations considering the various atmospheric models presented in Fontenla et al. (1993) and Avrett (1995).