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The chemical composition of multiple populations in the massive globularcluster (GC) NGC~2808 is addressed with the homogeneous abundance re-analysisof 140 red giant branch (RGB) stars. UVES spectra for 31 stars and GIRAFFEspectra for the other giants were analysed with the same procedures used forabout 2500 giants in 23 GCs in our FLAMES survey, deriving abundances of Fe, O,Na, Mg, Si, Ca, Ti, Sc, Cr, Mn, and Ni. Iron, elements from alpha-capture, andin the Fe-group do not show intrinsic scatter. On our UVES scale themetallicity of NGC~2808 is [Fe/H]=-1.129+/-0.005+/-0.034$ (+/-statistical+/-systematic error) with sigma=0.030 (31 stars). Main features related toproton-capture elements are retrieved, but the improved statistics and thesmaller associated internal errors allow to uncover five distinct groups ofstars along the Na-O anticorrelation. We observe large depletions in Mg,anticorrelated with enhancements of Na and also Si, suggestive of unusuallyhigh temperatures for proton-captures. About 14% of our sample is formed bygiants with solar or subsolar [Mg/Fe] ratios. Using the [Na/Mg] ratios weconfirm the presence of five populations with different chemical composition,that we called P1, P2, I1, I2, and E in order of decreasing Mg and increasingNa abundances. Statistical tests show that the mean ratios in any pair ofgroups cannot be extracted from the same parent distribution. The overlap withthe five populations recently detected from UV photometry is good but notperfect, confirming that more distinct components probably exist in thiscomplex GC.

Five groups of red giants with distinct chemical composition in the globular cluster NGC 2808