The Evolution of the Kinematics of Nebular Shells in Planetary Nebulae
  in the Milky Way Bulge
  We study the line widths in the [\ion{O}{3}]$\lambda$5007 and H$\alpha$ lines
for two groups of planetary nebulae in the Milky Way bulge based upon
spectroscopy obtained at the Observatorio Astron\'omico Nacional in the Sierra
San Pedro M\'artir (OAN-SPM) using the Manchester Echelle Spectrograph. The
first sample includes objects early in their evolution, having high H$\beta$
luminosities, but [\ion{O}{3}]$\lambda 5007/\mathrm H\beta < 3$. The second
sample comprises objects late in their evolution, with \ion{He}{2} $\lambda
4686/\mathrm H\beta > 0.5$. These planetary nebulae represent evolutionary
phases preceeding and following those of the objects studied by Richer et al.
(2008). Our sample of planetary nebulae with weak [\ion{O}{3}]$\lambda$5007 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 Richer et al. (2008). The sample with
strong \ion{He}{2} $\lambda 4686$ has a line width distribution
indistinguishable from that of the more evolved objects from Richer et al.
(2008), but a distribution in angular size that is systematically larger and so
they are clearly more evolved. These data and those of Richer et al. (2008)
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.
