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

TL;DR

This study analyzes aluminum and related element abundances in red giants of the globular cluster NGC 1851, revealing multiple stellar generations with distinct chemical signatures and correlations among elements.

Contribution

It provides new measurements of aluminum abundances in NGC 1851 and links these to other element patterns, enhancing understanding of stellar nucleosynthesis in the cluster.

Findings

Al abundances increase from first to second generation stars

Correlations between Al, Na, and Si observed

Positive correlation between Al and Ba in metal-rich stars

Abstract

We study 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 A measured on intermediate resolution FLAMES spectra of 50 cluster stars acquired under the Gaia-ESO public survey. We coupled these abundances with previously derived abundance of O, Na, 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 going 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 (Carretta et al. 2011a): 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.