Radial run of ion density (thick) and gas velocity (thin) for an initial nebular configuration with α = 3 density profile at age zero. The outer boundary is at r = 2.8  ×  10¹⁸ cm (outside the graph). The stellar parameters are given at the panel’s top and refer to the 0.595 M_⊙ post-AGB track shown in Fig. 3. Density and velocity at r = 1.0  ×  10¹⁶ cm correspond to an AGB mass-loss rate of 1.3  ×  10^-4 M_⊙ yr^-1. At r ≃0.1  ×  10¹⁶ cm, i.e. at the inner boundary of the envelope, density and velocity are set to the actual stellar wind properties for age zero, Ṁ = 2.5  ×  10^-7 M_⊙ yr^-1 and v = 60 km s^-1 (for Z = Z_GD, see text).