A WFC3/HST view of the three stellar populations in the Globular Cluster
  NGC6752
  Multi-band Hubble Space Telescope photometry reveals that the main sequence,
sub-giant, and the red giant branch of the globular cluster NGC6752 splits into
three main components in close analogy with the three distinct segments along
its horizontal branch stars. These triple sequences are consistent with three
stellar groups: a stellar population with a chemical composition similar to
field halo stars (population a), a population (c) with enhanced sodium and
nitrogen, depleted carbon and oxygen and enhanced helium abundance (Delta Y
~0.03), and a population (b) with an intermediate (between population a and c)
chemical composition and slightly helium enhanced (Delta Y ~0.01). These
components contain ~25% (population a), ~45% (population b), and ~30%
(population c) of the stars. No radial gradient for the relative numbers of the
three populations has been identified out to about 2.5 half mass radii.
