The ratio of fluxes from the warm WDP, ﹩{F}_{{\rm{WD}}}^{{\rm{warm}}}﹩, and the nebula, F_N, at selected wavelengths, 3600 Å, 4040 Å, 4700 Å, and 7300 Å, given by SED models. The rapid decrease of this ratio indicates a rapid opening of bipolar ionized regions (see Sections 4.3). The vertical line denotes a sudden change of this ratio between days 3.395 and 3.759, reflecting a change in the physical parameters of the warm WDP (see Section 4.6.2).