C II 5145, C III 5696, and C IV 5801 line profiles for model D30 (black lines, see Table 2) and similar models with relatively small changes in effective temperature (T_eff) and gravity (log g). Upper panels: red lines correspond to a D30 model with T_eff increased by 1000 K, the green lines to a model with T_eff decreased by the same value, while the blue lines display the reaction to a decrease of Ṁ by a factor of three. Lower panels: red and green lines correspond to a D30 model with log g increased and decreased by 0.15 dex, respectively.