Diagnostic diagrams for gas excitation determination. The classical BPT (Baldwin et al. 1981) diagram is shown in the left plot and an advanced version proposed by Cid Fernandes et al. (2010), including the Hα emission-line equivalent width, is shown in the right plot. The bordering lines between young star excitation, to the left of these lines, and the other mechanisms are those from Kewley et al. (2001; green dashed line) and from (Kauffmann et al. 2003; red dotted line). The black points represent the various parts of the UGC 5936 ring; the black star is the measurement of the south-eastern dwarf satellite.