Five groups of red giants with distinct chemical composition in the
  globular cluster NGC 2808
  The chemical composition of multiple populations in the massive globular
cluster (GC) NGC~2808 is addressed with the homogeneous abundance re-analysis
of 140 red giant branch (RGB) stars. UVES spectra for 31 stars and GIRAFFE
spectra for the other giants were analysed with the same procedures used for
about 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, and
in the Fe-group do not show intrinsic scatter. On our UVES scale the
metallicity of NGC~2808 is [Fe/H]=-1.129+/-0.005+/-0.034$ (+/-statistical
+/-systematic error) with sigma=0.030 (31 stars). Main features related to
proton-capture elements are retrieved, but the improved statistics and the
smaller associated internal errors allow to uncover five distinct groups of
stars along the Na-O anticorrelation. We observe large depletions in Mg,
anticorrelated with enhancements of Na and also Si, suggestive of unusually
high temperatures for proton-captures. About 14% of our sample is formed by
giants with solar or subsolar [Mg/Fe] ratios. Using the [Na/Mg] ratios we
confirm the presence of five populations with different chemical composition,
that we called P1, P2, I1, I2, and E in order of decreasing Mg and increasing
Na abundances. Statistical tests show that the mean ratios in any pair of
groups cannot be extracted from the same parent distribution. The overlap with
the five populations recently detected from UV photometry is good but not
perfect, confirming that more distinct components probably exist in this
complex GC.
