  In a previous paper (Veron et al. 1997) we presented medium resolution (3.4 A
FWHM) spectroscopic observations of 15 "transition objects", selected for
having an ambiguous location in the Veilleux & Osterbrock (1987) diagnostic
diagrams, and showed that most of them were in fact "composite", this being due
to the simultaneous presence on the slit of both a Seyfert or Liner nucleus and
a HII region. Here, we report new spectroscopic observations of 53
emission-line galaxies with a "transition" spectrum, bringing up to 61 the
total number of observed objects in an unbiased sample of 88 "transition
objects". Almost all of the observed galaxies have a "composite" nature,
confirming the finding that true "transition" spectra may not exist at all. By
eliminating "composite objects" from the diagnostic diagrams, a clear
separation between the different classes of nuclear emission-line regions
(Seyfert 2s, Liners and HII regions) becomes apparent; by restricting the
volume occupied by the different line-emitting regions in the 3-dimensional
diagnostic diagrams, we are also restricting the range of possible physical
parameters in these regions. There seems to be no continuity between Seyfert 2s
and Liners, the two classes occupying distinct volumes in the 3-dimensional
space defined by [OIII]5007/Hbeta, [NII]6583/Halpha, and [OI]6300/Halpha.

Astrophysics