  We present high-precision multi-band photometry for the globular cluster (GC)
M2. We combine the analysis of the photometric data obtained from the Hubble
Space Telescope UV Legacy Survey of Galactic GCs GO-13297, with chemical
abundances by Yong et al.(2014), and compare the photometry with models in
order to analyze the multiple stellar sequences we identified in the
color-magnitude diagram (CMD). We find three main stellar components, composed
of metal-poor, metal-intermediate, and metal-rich stars (hereafter referred to
as population A, B, and C, respectively). The components A and B include stars
with different $s$-process element abundances. They host six sub-populations
with different light-element abundances, and exhibit an internal variation in
helium up to Delta Y~0.07 dex. In contrast with M22, another cluster
characterized by the presence of populations with different metallicities, M2
contains a third stellar component, C, which shows neither evidence for
sub-populations nor an internal spread in light-elements. Population C does not
exhibit the typical photometric signatures that are associated with abundance
variations of light elements produced by hydrogen burning at hot temperatures.
We compare M2 with other GCs with intrinsic heavy-element variations and
conclude that M2 resembles M22, but it includes an additional stellar component
that makes it more similar to the central region of the Sagittarius galaxy,
which hosts a GC (M54) and the nucleus of the Sagittarius galaxy itself.
