On the Origin of High-Altitude Open Clusters in the Milky Way
  We present a dynamical study of the effect of the bar and spiral arms on the
simulated orbits of open clusters in the Galaxy. Specifically, this work is
devoted to the puzzling presence of high-altitude open clusters in the Galaxy.
For this purpose we employ a very detailed observationally motivated potential
model for the Milky Way and a careful set of initial conditions representing
the newly born open clusters in the thin disk. We find that the spiral arms are
able to raise an important percentage of open clusters (about one-sixth of the
total employed in our simulations, depending on the structural parameters of
the arms) above the Galactic plane to heights beyond 200 pc, producing a
bulge-shaped structure toward the center of the Galaxy. Contrary to what was
expected, the spiral arms produce a much greater vertical effect on the
clusters than the bar, both in quantity and height; this is due to the sharper
concentration of the mass on the spiral arms, when compared to the bar. When a
bar and spiral arms are included, spiral arms are still capable of raising an
important percentage of the simulated open clusters through chaotic diffusion
(as tested from classification analysis of the resultant high-z orbits), but
the bar seems to restrain them, diminishing the elevation above the plane by a
factor of about two.
