Panel a) The Rosseland-mean opacities, κ_R    [cm²   g^-1] , as a function of lgT for OPAL (thick line) and OP (thin line) models of T_eff = 25   000 K and lgg = 4.0. The chemical abundance parameters X = 0.708 and Z = 0.0172 are assumed. Panel b) The ratio of OP to OPAL Rosseland-mean opacities are displayed for input parameters of (lgT and lgρ) taken from the OPAL model shown in panel a). Panel c) The same as panel b), but for gas pressures.