Spectral analysis of the hybrid PG 1159-type central stars of the
  planetary nebulae Abell 43 and NGC 7094
  Stellar post asymptotic giant branch (post-AGB) evolution can be completely
altered by a final thermal pulse (FTP) which may occur when the star is still
leaving the AGB (AFTP), at the departure from the AGB at still constant
luminosity (late TP, LTP) or after the entry to the white-dwarf cooling
sequence (very late TP, VLTP). Then convection mixes the He-rich material with
the H-rich envelope. According to stellar evolution models the result is a star
with a surface composition of $\mathrm{H}\approx\,20\,$% by mass (AFTP),
$\approx 1\,$% (LTP), or (almost) no H (VLTP). Since FTP stars exhibit
intershell material at their surface, spectral analyses establish constraints
for AGB nucleosynthesis and stellar evolution. We performed a spectral analysis
of the so-called hybrid PG 1159-type central stars (CS) of the planetary
nebulae Abell 43 and NGC7094 by means of non-local thermodynamical equilibrium
models. 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 with
AFTP evolutionary tracks, we derive stellar masses of
$0.57^{+0.07}_{-0.04}\,M_\odot$ and determine the abundances of H, He, and
metals up to Xe. Both CS are likely AFTP stars with a surface H mass fraction
of $0.25 \pm 0.03$ and $0.15 \pm 0.03$, respectively, and a Fe deficiency
indicating subsolar initial metallicities. The light metals show typical PG
1159-type abundances and the elemental composition is in good agreement with
predictions from AFTP evolutionary models. However, the expansion ages do not
agree with evolution timescales expected from the AFTP scenario and
alternatives should be explored.
