Evolutionary tracks in the (T_eff,log g)-diagram for the same models as in Fig. 17. The circles, stars, and squares indicate cooling ages of 1, 4, and 8 Gyr, respectively. For the 0.18 M_⊙ WD, the 1 Gyr symbols for the two models almost coincide. Moreover, we note that the models from this work are only calculated to an age of 14 Gyr, which prevents cooling ages exceeding 3 Gyr for the 0.18 M_⊙ model and 6 Gyr for the 0.27 M_⊙ model.