Structure and kinematics of the Taurus star-forming region from Gaia-DR2
  and VLBI astrometry
  Aims:We take advantage of the second data release of the Gaia space mission
and the state-of-the-art astrometry delivered from very long baseline
interferometry observations to revisit the structure and kinematics of the
nearby Taurus star-forming region. Methods: We apply a hierarchical clustering
algorithm for partitioning the stars in our sample into groups (i.e., clusters)
that are associated with the various molecular clouds of the complex, and
derive the distance and spatial velocity of individual stars and their
corresponding molecular clouds. Results: We show that the molecular clouds are
located at different distances and confirm the existence of important depth
effects in this region reported in previous studies. For example, we find that
the L 1495 molecular cloud is located at $d=129.9^{+0.4}_{-0.3}$ pc, while the
filamentary structure connected to it (in the plane of the sky) is at
$d=160.0^{+1.2}_{-1.2}$ pc. We report B 215 and L 1558 as the closest
($d=128.5^{+1.6}_{-1.6}$ pc) and most remote ($d=198.1^{+2.5}_{-2.5}$ pc)
substructures of the complex, respectively. The median inter-cloud distance is
25 pc and the relative motion of the subgroups is on the order of a few km/s.
We find no clear evidence for expansion (or contraction) of the Taurus complex,
but signs of the potential effects of a global rotation. Finally, we compare
the radial velocity of the stars with the velocity of the underlying $^{13}$CO
molecular gas and report a mean difference of $0.04\pm0.12$ km/s (with r.m.s.
of 0.63 km/s) confirming that the stars and the gas are tightly coupled.
