We study the line widths in the [O III]λ5007 and Hα lines for two groups of planetary nebulae in the Milky Way bulge based upon spectroscopy obtained at the Observatorio Astronómico Nacional in the Sierra San Pedro Mártir (OAN-SPM) using the Manchester Echelle Spectrograph. The first sample includes objects early in their evolution, having high Hβ luminosities, but [O III]λ5007/Hβ < 3. The second sample comprises objects late in their evolution, with He II λ4686/Hβ > 0.5. These planetary nebulae represent evolutionary phases preceeding and following those of the objects studied by . Our sample of planetary nebulae with weak [O III]λ5007 has a line width distribution similar to that of the expansion velocities of the envelopes of AGB stars, and shifted to systematically lower values as compared to the less evolved objects studied by . The sample with strong He II λ4686 has a line width distribution indistinguishable from that of the more evolved objects from , but a distribution in angular size that is systematically larger and so they are clearly more evolved. These data and those of form a homogeneous sample from a single Galactic population of planetary nebulae, from the earliest evolutionary stages until the cessation of nuclear burning in the central star. They confirm the long-standing predictions of hydrodynamical models of planetary nebulae, where the kinematics of the nebular shell are driven by the evolution of the central star.

Aims. We aim to study the viscous interaction of the solar wind with the ionosphere of Venus in the magnetic polar regions by means of hydrodynamical computer simulations. Methods. We use a finite difference code developed for the solution of the Navier-Stokes, continuity and energy equations. Results. We have calculated the flow properties, the shape and location of the boundary layer and the shock formed as a consequence of the viscous interaction over the magnetic poles of the planet and advected downstream. By comparing our results to the flow properties measured by the Venera 10 and Mariner 5 spacecraft in the Venus ionosheath, we determine that a Reynolds number for the flow near the value Re = 20 is necessary to reproduce the position of the intermediate transition as well as the shock front. Also, on the basis of our results we predict the existence of a stagnation region for the solar wind flow extending considerably upstream from the viscous interaction region.