The Light Element Abundance Distribution in NGC 5128 from Planetary
  Nebulae
  The light element abundance pattern from many planetary nebulae (PNe)
covering the upper 4 mag. of the [O III] luminosity function was observed with
ESO VLT FORS1 multi-slit. Spectra of 51 PNe over the wavelength range 3500-7500
Angstrom were obtained in three fields at 4, 8 and 17 kpc, for a distance of
3.8 Mpc. Emission line ratios are entirely typical of PN such as in the Milky
Way. The temperature sensitive [O III]4363A line was weakly detected in 10 PNe,
both [O II] and [O III] lines were detected in 30 PNe, and only the bright [O
III]5007A line in 7 PN. Cloudy photoionization models were run to match the
spectra by a spherical, constant density nebula ionized by a black body central
star. He, N, O and Ne abundances with respect to H were determined and, for
brighter PNe, S and Ar; central star luminosities and temperatures are also
derived. For 40 PNe with Cloudy models, from the upper 2 mag. of the luminosity
function, the most reliably estimated element, oxygen, has a mean 12+log(O/H)
of 8.52. No obvious radial gradient is apparent in O/H over a range 2-20 kpc.
Comparison of the PN abundances with the stellar population, from the spectra
of the integrated starlight on the multi-slits and photometric studies,
suggests [Fe/H]=-0.4 and [O/Fe]=0.25. The masses of the PN central stars in NGC
5128 from model tracks imply an epoch of formation more recent than for the
minority young population from colour-magnitude studies. The PNe progenitors
may belong to the young tail of a recent, minor, star formation episode or
derive from other evolutionary channels.[Abridged]
