The unexpected kinematics of multiple populations in NGC6362: do
  binaries play a role?
  We present a detailed analysis of the kinematic properties of the multiple
populations (MPs) in the low-mass Galactic globular cluster NGC6362 based on a
sample of about 500 member stars for which radial velocities (RVs), Fe and Na
abundances have been homogeneously derived. At distances from the cluster
center larger than about 0.5 $r_h$, we find that first (FG - Na-poor) and
second generation (SG - Na-rich) stars show hints of different line-of-sight
velocity dispersion profiles, with FG stars being dynamically hotter. This is
the first time that differences in the velocity dispersion of MPs are detected
by using only RVs. While kinematic differences between MPs in globular clusters
are usually described in terms of anisotropy differences driven by the
different radial distributions, this explanation seems hardly viable for
NGC6362, where SG and FG stars are spatially mixed. We demonstrate that the
observed difference in the velocity dispersion profiles can be accounted for by
the effect of binary stars. In fact, thanks to our multi-epoch RV measurements
we find that the binary fraction is significantly larger in the FG sample
(f~14%) than in SG population (f<1%), and we show that such a difference can
inflate the velocity dispersion of FG with respect to SG by the observed amount
in the relevant radial range. Our results nicely match the predictions of
state-of-the art $N$-body simulations of the co-evolution of MPs in globular
clusters that include the effect of binaries.
