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We exploit multi-band Hubble Space Telescope photometry to investigatemultiple populations (MPs) along the red horizontal branches (HBs) and redclumps of fourteen metal-rich Globular Clusters (GCs), including twelve MilkyWay GCs and the Magellanic Cloud GCs NGC 1978 and NGC 416. Based on appropriatetwo-color diagrams we find that the fraction of 1G stars in Galactic GCscorrelates with cluster mass, confirming previous results based on red-giantbranch (RGB) stars. Magellanic-Cloud GCs show higher fractions of 1G stars thanGalactic GCs with similar masses, thus suggesting that the environment affectsthe MP phenomenon. We compared and combined our population fractions based onHB with previous estimates from MS and RGB, and we used ground-based UBVIphotometry (available for NGC 104, NGC 5927, NGC 6366, NGC 6838) to extend theinvestigation over a wide field of view. All studied GCs are consistent withflat distributions of 1G and 2G stars within ~1 arcmin from the cluster centerexcept NGC 416, where the 2G is more centrally concentrated. 2G stars of NGC104 and NGC 5927 are more centrally-concentrated than the 1G, whereas thedistribution is flat for NGC 6366 and NGC 6838. We discover that most of theanalyzed GCs exhibit extended sequences of 1G stars along the red HB, notconsistent with a simple population. The comparison between appropriatesynthetic and observed CMDs reveals that these extended distributions areconsistent with either star-to-star variation in helium or with an internalmetallicity spread, recalling the inhomogeneity of 1G stars along the ChMs.

Multiple stellar populations along the red Horizontal Branch and Red Clump of Globular Clusters