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NGC5824 is a massive Galactic globular cluster suspected to have an intrinsicspread in its iron content, according to the strength of the calcium tripletlines. We present chemical abundances of 117 cluster giant stars usinghigh-resolution spectra acquired with the multi-object spectrograph FLAMES. Themetallicity distribution of 87 red giant branch stars is peaked at[Fe/H]=-2.11+-0.01 dex, while that derived from 30 asymptotic giant branchstars is peaked at [Fe/H]=-2.20+-0.01 dex. Both the distributions arecompatible with a null spread, pointing out that this cluster did not retainthe ejecta of supernovae. The small iron abundance offset between the twogroups of stars is similar to those already observed among red and asymptoticgiant branch stars in other clusters. The lack of intrinsic iron spread rulesout the possibility that NGC5824 is the remnant of a disrupted dwarf galaxy, aspreviously suggested. We also find evidence of the chemical anomalies usuallyobserved in globular clusters, namely the Na-O and the Mg-Al anticorrelations.In particular, NGC5824 exhibits a huge range of [Mg/Fe] abundance, observedonly in a few metal-poor and/or massive clusters. We conclude that NGC5824 is anormal globular cluster, without spread in [Fe/H] but with an unusually largespread in [Mg/Fe], possibly due to an efficient self-enrichment driven bymassive asymptotic giant branch stars.

The chemical composition of NGC5824, a globular cluster without iron spread but with an extreme Mg-Al anticorrelation