H₂ density, HCN abundance with respect to H₂, rotational temperature in the vibrational ground state, and gas expansion velocity projected onto the line of sight derived from the asymmetric envelope model. The abscissas are the depth across the envelope measured from the closer position to Earth backwards. The ordinates are the position in the plane of the sky along an undetermined direction since the 2D envelope model shows cylindrical symmetry around the line of sight. Each quantity is plotted twice, at large scale (left) and at small scale (right). In the maps to the left, the yellow dotted-dashed and dashed circles represent the HCN dissociation radii derived in this work for the spherically symmetric envelope model (R_ph = 168R_⋆) and for the asymmetric model that accounts for the self-absorption in the pure rotational lines (R_ph = 380R_⋆), respectively (see text). In the maps to the right, the filled orange circle is the central star.