  EGB6 is an extended, faint old planetary nebula (PN) with an enigmatic
nucleus. The central star (PG0950+139) is a hot DAOZ-type white dwarf (WD). An
unresolved, compact emission knot was discovered to be located 0.166" away from
the WD and it was shown to be centered around a dust-enshrouded low-luminosity
star. It was argued that the dust disk and evaporated gas (photoionized by the
hot WD) around the companion are remnants of a disk formed by wind material
captured from the WD progenitor when it was an asymptotic giant branch (AGB)
star. In this paper, we assess the hot WD to determine its atmospheric and
stellar parameters. We performed a model-atmosphere analysis of ultraviolet
(UV) and optical spectra. We found Teff = 105,000 +/- 5000 K, log g = 7.4 +/-
0.4, and a solar helium abundance (He = 0.25 +/- 0.1, mass fraction). We
measured the abundances of ten more species (C, N, O, F, Si, P, S, Ar, Fe, Ni)
and found essentially solar abundance values, indicating that radiation-driven
wind mass-loss, with a theoretical rate of log(dot-M/M_sun/yr) = -11.0
(+1.1)(-0.8) prevents the gravitational separation of elements in the
photosphere. The WD has a mass of M/M_sun = 0.58 (+0.12)(-0.04) and its
post-AGB age (log(t_evol/yr) = 3.60 (+1.26)(-0.09)) is compatible with the PN
kinematical age of log(t_PN}/yr) = 4.2. In addition, we examined the UV
spectrum of the hot nucleus of a similar object with a compact emission region,
TOL26 (PN G298.0+34.8), and found that it is a slightly cooler DAOZ WD (Teff
about 85,000 K), but this WD shows signatures of gravitational settling of
heavy elements.
