Same as Fig. A.1, but for different envelope compositions. In model 1 (solid lines), y_L = 10⁹ g cm⁻² is assumed, in model 14 (dash-dotted lines) we assume a heavy element envelope with y_L = 10⁶ g cm⁻², and in model 15 (dotted lines) we assume an envelope with a large light element column depth (y_L = 10¹¹ g cm⁻²). For a thicker light element column depth, the thermal conductivity in the envelope is higher, increasing the effective temperature (T_eff(T_b)). At low temperatures ( K) the T_b − T_eff relation used here for models 1 and 14 converges.