Opacity as a function of temperature for fixed values of the opacity parameter R defined as , where T₆ is the temperature in units of 10⁶ Kelvin. The values of log R, which are held constant, are indicated along the curves. The data is taken from the OPAL tables with a composition of X = 0.7000, Y = 0.2960, Z = 0.004 (Iglesias & Rogers 1996). The black horizontal line shows the electron scattering opacity κ_e for a hydrogen mass fraction of X = 0.7. At a temperature of 200 000 K, log R = −5 implies a density of ρ = 8 × 10^-8 g cm^-3 and log R = −8 implies a density of ρ = 8 × 10^-11 g cm^-3.