Equilibrium temperature degeneracy in an optically thin gas. The attenuation factor is set at 6.3 × 10^-2, which corresponds to r ≈ 127 R_∗. Each panel refers to a different density. Left panel: 10^-10g cm^-3, right panel: 10^-12g cm^-3. Each curve corresponds to a different opacity data source: the thickest line – this work, using κ_P(T_gas,T_rad); the intermediate-thick line – this work, using κ(T_rad) instead of κ_P(T_gas,T_rad); the thinnest line – Helling et al. (2000), using κ(T_rad). The dashed parts of the lines mark unstable solutions (see text).