2010MNRAS.402.2060W

The exploration of chemical abundances in globular cluster giant branch stars has revealed element-abundance inhomogeneities between the stars. This study has investigated a sample of giant branch stars in the globular cluster 47 Tucanae, which were observed at a resolution of R ∼ 110000 using the Ultraviolet Échelle Spectrograph on the Very Large Telescope. The analysis of these stars showed non-local thermodynamic equilibrium (non-LTE) effects on the abundances derived from the sample of atomic lines under an LTE approximation. The stellar parameters for each star were redetermined using only high-excitation-potential Fei lines. The resulting chemical abundance analysis showed enhancements in both the light and heavy s-process element abundances with mean values of <[ls/Fe]> = 0.53±0.09 dex and <[hs/Fe]> = 0.40 ± 0.11 dex. However, no trend was found between the ratio of the heavy to light s-process element abundances ([hs/ls] = -0.13±0.14 dex) and metallicity ([Fe/H] = -0.89±0.09 dex) due to the small spread in both of these values. This indicates that the heavy-element-abundance enhancements are not due to third dredge-up of internal nucleosynthesis products in these evolved stars. The source of the heavy-element enhancements is therefore primordial or pollution event related in origin.