Sailing on the Sagittarius Stream with Gaia DR2. I. The globular cluster
  NGC5634
  We use Gaia DR2 data to show that the globular cluster NGC5634 is physically
associated with an arm of the Sagittarius Stream, the huge system of tidal
tails created by the ongoing disruption of the Sagittarius dwarf spheroidal
galaxy (Sgr dSph). Two additional arms of the Stream are also detected along
the same line of sight, at different distances. We show that the Sgr Stream
stars surrounding NGC5634 are more metal-poor, on average, than those found in
the more distant Stream arm lying behind the cluster and in the main body of
Sgr~dSph, confirming that a significant metallicity (and, presumably, age)
gradient is present along the Stream. This analysis demonstrates the potential
of the Gaia DR2 catalogue to directly verify if a cluster is physically
associated to the Stream or not, without the need to rely on models of the
tidal disruption of this system. [Withdrawn: see comments]
