(2) Centro de Astrofisica da Universidade do Porto,
Rua do Campo Alegre 823, 4150 Porto, Portugal
The use of the Baldwin et al. (1981) or Veilleux & Osterbrock (1987) diagnostic diagrams allows the unambiguous classification of the nuclear emission line regions of most galaxies into one of three categories: nuclear HII regions or starbursts, Seyfert 2 galaxies and Liners. However, a small fraction of them have a "transition" spectrum. We present spectral observations of 15 "transition" objects at high-dispersion (66 ┼/mm around the H, [NII] 6548,6584 and/or H, [OIII] 4959,5007 emission lines. We show that most of these spectra are composite, due to the simultaneous presence on the slit of a Seyfert nucleus and a HII region. Seyfert 2s and Liners seem to occupy relatively small and distinct volumes in the three-dimensional space 5007/ H, 6584/H, 6300/H.
keywords : Galaxies: nuclei -- Galaxies: active