Sketch of the ionization structure of nova V339 Del as seen on a cut perpendicular to the orbital plane that contains the burning WD (the black circle). The neutral H i zone is optically thick to the distance of the WD pseudophotosphere (heavy solid line). The ionized H ii zone has the opening angle ΔΩ, and i is the orbital inclination (its value is unknown). The top panel shows the structure around the beginning of the fireball stage, the middle one at its end, and the bottom panel shows the situation when the dust emission is present in the ejecta simultaneously with the H i atoms, hard radiation from the burning WD, and the large amount of the nebular emission (see Fig. 2, Sect. 4.2).