SIMBAD references

The use of the Baldwin et al. (1981PASP...93....5B) or Veilleux & Osterbrock (1987ApJS...63..295V) 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 (66Å/mm) around the Hα, [NII]λλ6548,6584 and/or Hβ, [OIII]λλ4959,5007 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 λ5007/Hβ, λ6584/Hα, λ6300/Hα.