The location of the known DBV stars on the T_eff − log g plane. Also included are our DB white dwarf evolutionary tracks displayed with different colors according to the stellar mass. The location of KIC 8626021 according to spectroscopy is emphasized with a red star symbol, while the location of our asteroseismological models for this star is marked with orange circles connected with a dotted line. The largest circle corresponds to our best-fit model (model  2; see Sect. 4). For comparison, we include the location of the best-fit asteroseismological model of BKØ11 with a blue star symbol. The theoretical blue edge of the DBV instability strip corresponding to the version MLT2 (α = 1.25) of the MLT theory of convection, as derived by Córsico et al. (2009), is depicted with a blue dashed line. Note: the DBV star EC 05221 (Kilkenny et al. 2009) is not included because at present there is no any estimation of T_eff and log g available.