M13 multiple stellar populations seen with the eyes of Str\"omgren
  photometry
  We present a photometric study of M13 multiple stellar populations over a
wide field of view, covering approximately 6.5 half-light radii, using archival
Isaac Newton Telescope observations to build an accurate multi-band Str\"omgren
catalogue. The use of the Str\"omgren index $c_{y}$ permits us to separate the
multiple populations of M13 on the basis of their position on the red giant
branch. The comparison with medium and high resolution spectroscopic analysis
confirms the robustness of our selection criterion. To determine the radial
distribution of stars in M13, we complemented our dataset with Hubble Space
Telescope observations of the cluster core, to compensate for the effect of
incompleteness affecting the most crowded regions. From the analysis of the
radial distributions we do not find any significant evidence of spatial
segregation. Some residuals may be present in the external regions where we
observe only a small number of stars. This finding is compatible with the short
dynamical timescale of M13 and represents, to date, one of the few examples of
fully spatially mixed multiple populations in a massive globular cluster.
