A Milky Way with a massive, centrally concentrated thick disc: new
  Galactic mass models for orbit computations
  In this work, two new axisymmetric models for the Galactic mass distribution
are presented. Motivated by recent results, these two models include the
contribution of a stellar thin disc and of a thick disc, as massive as the thin
counterpart but with a shorter scale-length. Both models satisfy a number of
observational constraints: stellar densities at the solar vicinity, thin and
thick disc scale lengths and heights, rotation curve(s), and the absolute value
of the perpendicular force Kz as a function of distance to the Galactic centre.
We numerically integrate into these new models the motion of all Galactic
globular clusters for which distances, proper motions, and radial velocities
are available, and the orbits of about one thousand stars in the solar
vicinity. The retrieved orbital characteristics are compared to those obtained
by integrating the clusters and stellar orbits in pure thin disc models. We
find that, due to the possible presence of a thick disc, the computed orbital
parameters of disc stars can vary by as much as 30-40%. We also show that the
systematic uncertainties that affect the rotation curve still plague computed
orbital parameters of globular clusters by similar amounts.
