Changes of Δτ per 10 km for different models. Details are given in the title of panels and the arrangement of panels, parameters, and their units are the same as in Fig. 3. Thick black contour shows level τ = 1 for thermal Doppler width, a thin black line for 0.1 Å Doppler width and a grey line for 0.5 Å. Labels on the left side of the color scale correspond to thermal width and on the right side to 0.1 Å.