  Recent studies suggest that the helium content of multiple stellar
populations in globular clusters (GCs) is not uniform. The range of helium
varies from cluster to cluster with more massive GCs having, preferentially,
large helium spread. GCs with large helium variations also show extended-blue
horizontal branch (HB). I exploit Hubble Space Telescope photometry to
investigate multiple stellar populations in NGC6266 and infer their relative
helium abundance. This cluster is an ideal target to investigate the possible
connection between helium, cluster mass, and HB morphology, as it exhibits an
extended HB and is among the ten more luminous GCs in the Milky Way. The
analysis of color-magnitude diagrams from multi-wavelength photometry reveals
that also NGC6266, similarly to other massive GCs, hosts a double main sequence
(MS), with the red and the blue component made up of the 79+-1% and the 21+-1%
of stars, respectively. The red MS is consistent with a stellar population with
primordial helium while the blue MS is highly helium-enhanced by Delta
Y=0.08+-0.01. Furthermore, the red MS exhibits an intrinsic broadening that can
not be attributed to photometric errors only and is consistent with a spread in
helium of ~0.025 dex. The comparison between NGC6266 and other GCs hosting
helium-enriched stellar populations supports the presence of a correlation
among helium variations, cluster mass, and HB extension.
