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Stellar post asymptotic giant branch (post-AGB) evolution can be completelyaltered by a final thermal pulse (FTP) which may occur when the star is stillleaving the AGB (AFTP), at the departure from the AGB at still constantluminosity (late TP, LTP) or after the entry to the white-dwarf coolingsequence (very late TP, VLTP). Then convection mixes the He-rich material withthe H-rich envelope. According to stellar evolution models the result is a starwith a surface composition of $\mathrm{H}\approx\,20\,$% by mass (AFTP),$\approx 1\,$% (LTP), or (almost) no H (VLTP). Since FTP stars exhibitintershell material at their surface, spectral analyses establish constraintsfor AGB nucleosynthesis and stellar evolution. We performed a spectral analysisof the so-called hybrid PG 1159-type central stars (CS) of the planetarynebulae Abell 43 and NGC7094 by means of non-local thermodynamical equilibriummodels. We confirm the previously determined effective temperatures of$T_\mathrm{eff} = 115\,000\pm 5\,000\,$K and determine surface gravities of$\log (g\,/\,\mathrm{cm/s^2}) = 5.6\pm 0.1$ for both. From a comparison withAFTP evolutionary tracks, we derive stellar masses of$0.57^{+0.07}_{-0.04}\,M_\odot$ and determine the abundances of H, He, andmetals up to Xe. Both CS are likely AFTP stars with a surface H mass fractionof $0.25 \pm 0.03$ and $0.15 \pm 0.03$, respectively, and a Fe deficiencyindicating subsolar initial metallicities. The light metals show typical PG1159-type abundances and the elemental composition is in good agreement withpredictions from AFTP evolutionary models. However, the expansion ages do notagree with evolution timescales expected from the AFTP scenario andalternatives should be explored.

Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC 7094