Journal Article

Heavy-element abundances in low-gravity globular cluster stars: 47 Tuc*

C. C. Worley, P. L. Cottrell, I. McDonald and J. Th. van Loon

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 3, pages 2060-2074
Published in print March 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.16041.x
Heavy-element abundances in low-gravity globular cluster stars: 47 Tuc*

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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 Tucanæ, which were observed at a resolution of R∼ 110 000 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 Fe i 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.

Keywords: stars: abundances; stars: AGB and post-AGB; globular clusters: individual: 47 Tuc

Journal Article.  11400 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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