Position of RX J0122.9–7521 on the log g-T_eff diagram, along with the other known PG 1159 stars. VLTP evolutionary tracks from Althaus et al. (2009) are depicted in grey and represent masses of 0.515, 0.530, 0.584, 0.741, and 0.870 M_⊙. The red track represents the potential evolutionary path of a merger product of a 0.45 M_⊙ helium-core white dwarf and a 0.35 M_⊙ carbon-oxygen-core white dwarf and was calculated by Miller Bertolami et al. (2022). The blue line represents the merger of two He white dwarfs with a total mass of 0.8 M_⊙ (Zhang & Jeffery 2012). The solid black line shows the wind limit, and the dashed black line shows the wind limit when the mass-loss rate is reduced by a factor of 10 (Unglaub & Bues 2000). The blue edges of instability are indicated by the two dotted black lines, corresponding to the unstable g-modes l=1 and l=2, respectively (Córsico et al. 2006).