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Recent studies suggest that the helium content of multiple stellarpopulations in globular clusters (GCs) is not uniform. The range of heliumvaries from cluster to cluster with more massive GCs having, preferentially,large helium spread. GCs with large helium variations also show extended-bluehorizontal branch (HB). I exploit Hubble Space Telescope photometry toinvestigate multiple stellar populations in NGC6266 and infer their relativehelium abundance. This cluster is an ideal target to investigate the possibleconnection between helium, cluster mass, and HB morphology, as it exhibits anextended HB and is among the ten more luminous GCs in the Milky Way. Theanalysis of color-magnitude diagrams from multi-wavelength photometry revealsthat 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 withprimordial helium while the blue MS is highly helium-enhanced by DeltaY=0.08+-0.01. Furthermore, the red MS exhibits an intrinsic broadening that cannot be attributed to photometric errors only and is consistent with a spread inhelium of ~0.025 dex. The comparison between NGC6266 and other GCs hostinghelium-enriched stellar populations supports the presence of a correlationamong helium variations, cluster mass, and HB extension.

Helium and Multiple Populations in the Massive Globular Cluster NGC6266 (M62)