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 \pm 0.005 \pm 0.034 ( \pm statistical \pm 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 can not 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 .