Research Note

Aluminum abundances of multiple stellar generations in the globular cluster NGC 1851 ^⋆,⋆⋆

¹ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
e-mail: eugenio.carretta@oabo.inaf.it
² Dept. of Physics and Astronomy, Macquarie University, Sydney, NSW, 2109 Australia
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy

Received: 26 March 2012
Accepted: 30 May 2012

Abstract

We studied the distribution of aluminum abundances among red giants in the peculiar globular cluster NGC 1851. Aluminum abundances were derived from the strong doublet Al i 8772–8773 Å measured on intermediate-resolution FLAMES spectra of 50 cluster stars acquired under the Gaia-ESO public survey. We coupled these abundances with previously derived abundances of O, Na, and Mg to fully characterize the interplay of the NeNa and MgAl cycles of H-burning at high temperature in the early stellar generation in NGC 1851. The stars in our sample show well-defined correlations between Al, Na and Si; Al is anticorrelated with O and Mg. The average value of the [Al/Fe] ratio steadily increases from the first generation stars to the second generation populations with intermediate and extremely modified composition. We confirm on a larger database the results recently obtained by us: the pattern of abundances of proton-capture elements implies a moderate production of Al in NGC 1851. We find evidence of a statistically significant positive correlation between Al and Ba abundances in the more metal-rich component of red giants in NGC 1851.