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We present a photometric and spectroscopic study of multiple populationsalong the asymptotic-giant branch (AGB) of the intermediate-metallicityglobular clusters (GCs) NGC2808 and NGC6121 (M4). Chemical abundances of O, Na,Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Y, and Ce in AGB stars fromhigh-resolution FLAMES+UVES@VLT spectra are reported for both clusters. Ourspectroscopic results have been combined with multi-wavelength photometry fromthe HST UV survey of Galactic GCs and ground-based photometry, plus propermotions derived by combining stellar positions from ground-based images andGaia DR1. Our analysis reveals that the AGBs of both clusters host multiplepopulations with different chemical composition.  In M4 we have identified two main populations of stars with different Na/Ocontent, lying on distinct AGBs in the mF438W vs. C_F275W,F336W,F438W and the Vvs.C_U,B,I pseudo-CMDs. In the more massive and complex GC NGC2808 three groupsof stars with different chemical abundances occupy different locations on theso-called "chromosome map" photometric diagram. The spectroscopic+photometriccomparison of stellar populations along the AGB and the red giants of this GCsuggests that the AGB hosts stellar populations with a range in heliumabundances spanning from primordial up to high contents of Y~0.32. On the otherhand, from our dataset, there is no evidence for stars with extreme heliumabundance (Y~0.38) on the AGB, suggesting that the most He-rich stars ofNGC2808 do not reach this phase.

Photometry and spectroscopy of multiple populations along the AGB of NGC2808 and NGC6121 (M4)