The Hubble Space Telescope UV Legacy Survey of Galactic Globular
  Clusters. X. The radial distribution of stellar populations in NGC 2808
  Due to their extreme helium abundance, the multiple stellar populations of
the globular cluster NGC 2808 have been widely investigated from a photometric,
spectroscopic, and kinematic perspective. The most striking feature of the
color-magnitude diagram of NGC 2808 is the triple main sequence (MS), with the
red MS corresponding to a stellar population with primordial helium, and the
middle and the blue MS being enhanced in helium up to Y$\sim$0.32 and
$\sim$0.38, respectively. A recent study has revealed that this massive cluster
hosts at least five distinct stellar populations (A, B, C, D, and E). Among
them populations A, B, and C correspond to the red MS, while populations C and
D are connected to the middle and the blue MS. In this paper we exploit
Hubble-Space-Telescope photometry to investigate the radial distribution of the
red, the middle and the blue MS from the cluster center out to about 8.5
arcmin. Our analysis shows that the radial distribution of each of the three
MSs is different. In particular, as predicted from multiple-population
formation models, both the blue MS and the middle MS appears to be more
concentrated than the red MS with a significance level for this result wich is
above 3{\sigma}.
