The cooling sequence of NGC 6791. Upper panel: observed WD LF of NGC 6791 (corrected for completeness) compared with a theoretical LF calculated for an age of 8.5 Gyr using a [Fe/H] = 0.3 WD isochrone (with c07 opacities) from models calculated without including the effect of ²²Ne distillation (see the main text for details). Lower panel: CMD of the observed WD cooling sequence of NGC 6791 together with [Fe/H] = 0.3, 8.5 Gyr isochrones calculated without ²²Ne distillation and with either the c07 (solid) or b20 (dotted) opacities.