Fig. 2
Kniazev et al. (2008) diagrams used for distinguishing between PNe and H ii regions. The SySt are marked with blue symbols and PNe with gray symbols. The SySt that fall into the PNe region in the [O iii] diagnostic diagram are marked with red symbols. The S-type SySt are marked with open circles, the D′-type SySt with full circles, and D-type SySt with triangles.
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