Ratio of the excitation temperature (T_ex) and the kinetic temperature (T_kin) for various low- and high-J SiO transitions (top), and their corresponding line-emitting regions (bottom), as functions of radius across the CSE, from the best-fit model for IRAS 15194–5115. The solid lines are from a model that takes into account IR pumping, while the dashed lines are from a model that does not, but is otherwise identical. The line-emitting regions are normalised to the peak of the emitting region of the highest J transition shown.