Projection of the nova shell in cylindrical coordinates. The system is presented so the equatorial plane is located at Z = 0. Left: average view on the ρ–Z plane. Right: average view on the ϕ-Z plane. In both panels, Hα emission is presented in red-black colour scale, while [OIII] is presented in blue. The contour levels indicate the flux corresponding to 1, 2, and 3 times the standard deviation value on each plane. The lines in the ρ–Z plane indicate an ellipse with an equatorial radius of 8090 au and an axial ratio of 1.35 (grey dashed line), and an equatorial radius of 10 990 au and an axial ratio of 0.91 (brown dotted line).