T_eff and radius of stars in the SF18 sample with measured Gaia parallaxes. Results for different sets of model atmospheres are shown as red circles (logg = 8, He-pure models), blue squares (logg = 9, pure-He models), and black dots with error bars (logg = 8, log(N_H/N_He) = −6). Overlaid with long dashed lines are theoretical WD evolutionary tracks for 0.606 M_⊙ (CO-core) and 1.16 M_⊙ (ONe-core) WD models. Short dashed lines show curves of constant logg determined from evolutionary models.