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 .