Low dispersion spectra have been obtained of five planetary nebulae in the elliptical galaxy NGC 5128 ( Centaurus-A ) from the catalogue of Hui et al .
( [ 1993b ] ) .
The planetary nebulae ( PN ) cover a range of galactocentric radius from 7.9 to 17.7 ^ { \prime } ( 8 to 18Kpc ) .
The spectra display typical emission lines of H I , He I , He II , [ O III ] , [ N II ] and [ S II ] and appear very similar to high excitation planetary nebulae in the Galaxy .
This implies that , from a stellar evolution viewpoint , there should be no peculiar effects introduced by considering the bright cut-off of the PN luminosity function for distance estimation .
In particular the brightest PN detected in NGC 5128 is not spectroscopically unusual .
One of the PN shows relatively strong He II and [ N II ] lines and the derived N/O ratio indicates that it may be a Type I nebula , considered to arise from a high mass progenitor star .
Determinations of the oxygen abundance of the five PN shows a mean value 0.5 dex below solar .
Given that NGC 5128 is an elliptical galaxy with a presumably metal rich stellar content , the low metallicities of the PN are unexpected , although a similar situation has been observed in the bulge of M 31 .