The planetary nebula surrounding the final thermal pulse object V4334 Sagittarii

Optical imaging and long-slit spectroscopy of the planetary nebula (PN) sur rounding the last thermal pulse object V4334 Sagittarii an presented. Using any reasonable distance consistent with the observed nebula reddening of E (B - V) = 0.71 +/- 0.09, the physical dimensions, kinematics, abundances an d ionized mass are typical of evolved planetary nebulae (PNe). With the mos t firmly established observational quantities, nebular photoionization mode ls are constructed, which show that it is likely that some recombination ha s already occurred (if n(e) similar to 200 cm(-3)). The models give good co nstraints on the surface temperature of the precursor [log(T-s/K) = 5.1 +/- 0.2], but not on its luminosity [log (L-s/L-.) similar to 3.3 +/- 1.3]. Th ese results are only consistent with white dwarf cooling tracks if 0.546 < M <0.836 M-. and give good agreement with the initial position for the test model of last thermal pulse evolution recently presented by Iben & MacDona ld.