Opacity at 5160 Å as a function of the Rosseland optical depth for DQZ white dwarfs with T_eff = 8000 K, log g = 8, log C/He = −5.5, and different Ca/He values (black lines correspond to log Ca/He = −11.5 and red lines to log Ca/He = −9.5). The dashed lines show the total opacity, while the solid lines show the opacity due to the Swan bands only. The wavelength chosen for this figure (5160 Å) corresponds to where the Swan bands are strongest. The grey region indicates where the Swan bands are formed.