Expansion properties as derived from the line peak separation of spatially resolved line profiles for the same six α = 3 sequences shown in Figs. 12 and 13 vs. the post-AGB age, for Hβ (left) and [O iii] 5007 Å (right). The line profiles are simulated using a central numerical aperture of 1  ×  10¹⁶ cm (or 0″̣67 at a distance of 1 kpc). At low ages, the profiles are still singly peaked, and thus V_peak = 0. The [O iii] profiles are only plotted up to model ages of about 10 000 yr because beyond this age the profiles develop a complex structure due to recombination. The five black dots along the abscissas correspond again to the snapshots depicted in Figs. 5−9.