PG 1159 (VLTP) evolutionary tracks of Miller Bertolami & Althaus (2006; from right to left: M_⋆ = 0.515, 0.530, 0.542, 0.565, 0.589, 0.609, 0.664, 0.741 M_⊙) in the log T_eff − log g diagram (thin dotted curves). The location of all known PG 1159 stars (variable, non-variable, and objects with no variability data) is shown, including SDSS J0349−0059 and VV 47 with their uncertainties. The uncertainty values for SDSS J0349−0059 are very low in the adopted scale and are not visible in the plot. The hot blue edges (blue curves) and the low-gravity red edges (upper red curves) of the theoretical GW Vir instability strip for ℓ = 1 (dashed) and ℓ = 2 (dotted) modes according to Córsico et al. (2006) are also depicted. The high-gravity red edge that is due to the competition of residual stellar winds against the gravitational settling of C and O (Quirion et al. 2012) is also included (lower red solid curve).