Left panel: temperature distribution with Rosseland optical depth from a representative snapshot of the  [Fe/H]  =  −3 turnoff-star surface convection simulation computed solving the radiative transfer equation self-consistently for a source function with a coherent scattering term (standard case). Darker shades indicate higher probability. Blue curve: mean stratification from the corresponding simulation computed assuming a Planckian source function and no contribution of scattering to total extinction in optically thin layers. Right panel: corresponding temperature distribution with Rosseland optical depth from the simulation assuming a Planckian source function and scattering as true absorption everywhere (mean temperature stratification shown in red). Dashed lines (both panels): mean temperature stratification from the standard-case simulation. All snapshots were taken 80 min after the start of the simulations.