Abstract
From ESO VLT ``on-band off-band'' imaging of the dwarf irregular - late type spiral NGC 3109, we have detected 20 planetary nebula (PN) candidates and many compact HII regions all over the galaxy. PN candidates have been selected as stellar objects with no detectable (or very faint) stellar continuum. Further spectroscopy (with VLT FORS multi-object) in the 3700-6800Å range has confirmed the PN nature of several candidates. Most of the PNe appear as low excitation nebulae. Spectra were also acquired for several HII regions. For many objects the [O III] 4363 line, sensitive to electron temperature, was detected, allowing a trustworthy determination of chemical abundances. Therefore a comparative analysis of chemical composition in both type of objects can be performed. We find that the HII regions present very similar O/H abundances (in average 12 + log O/H = 7.79+/-0.10), while O/H in PNe spreads in a larger range. Most of the PNe seem to be O-enriched.
