Top: RVs of [O III] λ5007 line from medium-resolution spectra. They are shifted by −9 km s⁻¹ (grey dashed line) from the RG motion (orange line). Middle: RVs of blue and red components of the profile from high-resolution spectra. Both components follow the RG orbital motion, being shifted by −15 and +3.0 km s⁻¹ (grey dashed lines). Bottom: sketch of [O III] line zones in the vicinity of the RG at/around its polar regions as seen on the cut perpendicular to the orbital plane containing the binary axis (see Sect. 4.2.1). The H⁰/H⁺ boundary is estimated according to the wind compression disk model (see Fig. 2 of Skopal & Cariková 2015).