Emission lines in the ring of UGC 4599 and nearby galaxies. Upper plot: BPT-diagram for the ring HII regions, both from our long-slit spectroscopy (with error bars) and from Salzer et al. (2020) (squares). The measurements for the common HII region are connected by a dashed blue line. The lines that divide excitation mechanisms are from Kewley et al. (2001) (the dashed green line) and from Kauffmann et al. (2003) (the red dotted line). Bottom plot: view of the red part of the continuum-subtracted long-slit spectrum at PA = 132°.