Panel a) The Rosseland-mean opacities, κ_R    [cm²   g^-1] , as a function of lgT for ATLAS12/MHD-Q (dotted line) in comparison with OP (continuous line) and OPAL (dashed line) envelope models of T_eff = 25   000 K and lgg = 4.0. Panel c) The same as panel a), but OP/IRON bound-free absorptions of metals are included in the ATLAS12/MHD-Q model (dotted line). Panel e) The same as panelc), but OP opacities are used for hydrogen and helium. Panel g) The same as panel a), but the ATLAS12/OP model is plotted by means of an A/OP line. The right-hand side panels show the same as the left-hand side ones, but for the diagrams of κ_R vs. lgR.