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We present aluminium abundances for a sample of about 100 red giant stars ineach of the Galactic globular clusters 47 Tuc (NGC 104) and M 4 (NGC 6121). Wehave derived homogeneous abundances from intermediate-resolution FLAMES/GIRAFFEspectra. Aluminium abundances are from the strong doublet Al I at 8772-8773 Aas in previous works done for giants in NGC 6752 and NGC 1851, and nitrogenabundances are extracted from a large number of features of the CN molecules,by assuming a suitable carbon abundance. We added previous homogeneousabundances of O and Na and newly derived abundances of Mg and Si for oursamples of 83 stars in M 4 and 116 stars in 47 Tuc to obtain the full set ofelements from proton-capture reactions produced by different stellargenerations in these clusters. By simultaneously studying the Ne-Na and Mg-Alcycles of H-burning at high temperature our main aims are to understand thenature of the polluters at work in the first generation and to ascertainwhether the second generation of cluster stars was formed in one or, rather,several episodes of star formation. Our data confirm that in M 4 only twostellar populations are visible. On the other hand, for 47 Tuc a clusteranalysis performed on our full dataset suggests that at least three distinctgroups of stars are present on the giant branch. The abundances of O, Na, Mgand Al in the intermediate group can be produced within a pollution scenario;results for N are ambiguous, depending on the C abundance we adopt for thethree groups.

An aluminium tool for multiple stellar generations in the globular clusters 47 Tuc and M 4