H-R diagram for the sample of white dwarfs with PAN-STARRS nad BVK photometry (filled black dots; Dufour et al. 2017), pure hydrogen atmosphere cooling sequence of log g = 8 with (red dots and solid line) and without (green dots and solid line) H⁺₃ species considered in the chemical equilibrium. Dots represent the effective temperature sequence from 8000 K to 3000 K, from top to bottom, with an interval of 500 K.