Sulphur in the Globular Clusters 47 Tucanae and NGC 6752

TL;DR

This study measures sulphur abundances in two globular clusters, revealing no star-to-star variation and potential correlations with other elements, thus providing new insights into chemical compositions of such clusters.

Contribution

First measurement of sulphur in globular clusters, using high-resolution spectra and advanced modeling techniques, filling a significant gap in chemical abundance studies.

Findings

Sulphur abundance in NGC 6752 shows no star-to-star variation.

Mean <[S/Fe]> in NGC 6752 is +0.49, consistent with field stars.

Possible correlation between sulphur and sodium abundances.

Abstract

The light elements Li, O, Na, Al, and Mg are known to show star to star variations in the globular clusters 47 Tuc and NGC 6752. Such variations are interpreted as due to processing in a previous generation of stars. In this paper we investigate the abundances of the alpha-element sulphur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph. We use high resolution spectra of the S I Mult. 1, acquired with the UVES spectrograph at the 8.2m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra are analyzed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO5BOLD hydrodynamic models and apply corrections due to NLTE effects taken from the literature. In the cluster NGC 6752 sulphur has been measured only in four subgiant stars. We find no significant star to star scatter and a mean <[S/Fe]> = +0.49 +- 0.15, consistent with what observed in field stars of the same metallicity. In the cluster 47 Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean <[S/Fe]> = +0.18 +- 0.14. While this result is compatible with no star to star scatter we notice a statistically significant correlation of the sulphur abundance with the sodium abundance and a tentative correlation with the silicon abundance.