Globular clusters: absolute proper motions and Galactic orbits
  We cross-match objects from several different astronomical catalogs to
determine the absolute proper proper motions of stars within the 30-arcmin
radius fields of 115 Milky-Way globular clusters with the accuracy of
1--2~mas/yr. The proper motions are based on positional data recovered from the
USNO-B1, 2MASS, URAT1, ALLWISE, UCAC5, and GAIA DR1 surveys with up to 10
positions spanning an epoch difference of up to $\sim$~65~years, and reduced to
GAIA DR1 TGAS frame using UCAC5 as the reference catalog. Cluster members are
photometrically identified by selecting horizontal- and red-giant branch stars
on color-magnitude diagrams, and the mean absolute proper motions of the
clusters with a typical formal error of $\sim$~0.4~mas/yr are computed by
averaging the proper motions of selected members. The inferred absolute proper
motions of clusters are combined with available radial-velocity data and
heliocentric distance estimates to compute the cluster orbits in terms of the
Galactic potential models based on Miyamoto and Nagai disk, Hernquist spheroid,
and modified isothermal dark-matter halo (axisymmetric model without a bar) and
the same model + rotating Ferre's bar (non-axisymmetric). Five distant clusters
have higher-than-escape velocities, most likely due to large errors of computed
transversal velocities, whereas the computed orbits of all other clusters
remain bound to the Galaxy. Unlike previously published results, we find the
bar to affect substantially the orbits of most of the clusters, even those at
large Galactocentric distances, bringing appreciable chaotization, especially
in the portions of the orbits close to the Galactic center, and stretching out
the orbits of some of the thick-disk clusters.
