EDP Sciences
Free access
Volume 436, Number 2, June III 2005
Page(s) L9 - L12
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500110

A&A 436, L9-L12 (2005)
DOI: 10.1051/0004-6361:200500110


Sulphur abundances in Terzan 7

E. Caffau1, P. Bonifacio2, R. Faraggiana3 and L. Sbordone4, 5

1  Liceo L. e S.P.P. S. Pietro al Natisone, Annesso al Convitto Nazionale "Paolo Diacono", Piazzale Chiarottini 8, Cividale del Friuli (Udine), Italy
    e-mail: elcaffau@libero.it
2  Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
    e-mail: bonifaci@ts.astro.it
3  Dipartimento di Astronomia, Università degli Studi di Trieste, Italy
    e-mail: faraggiana@ts.astro.it
4  ESO European Southern Observatory - Alonso de Cordova 3107 Vitacura, Santiago, Chile
5  Universitá di Roma 2 "Tor Vergata" - via della Ricerca Scientifica, Rome, Italy
    e-mail: sbordone@mporzio.astro.it

(Received 1 March 2005 / Accepted 19 April 2005)

We present here the first measurements of sulphur abundances in extragalactic stars. We make use of high resolution spectra, obtained with UVES at the ESO 8.2 m Kueyen telescope, of three giants of the Globular Cluster Terzan 7, which belongs to the Sagittarius dwarf galaxy. We measure the sulphur abundances using the lines of $\ion{S}{i}$ multiplet 1. The S/Fe ratios for all three stars are nearly solar, thus considerably lower than what is found in Galactic stars of comparable iron content $({\rm [Fe/H]} \sim -0.50$). This finding is in keeping with the abundances of other $\alpha$-chain elements in this cluster and in Sagittarius and other dSphs in general. These low $\alpha$-chain elements to iron ratios suggest that Sagittarius and its Globular Clusters have experienced a low or bursting star-formation rate. Our sulphur abundances imply $\langle \log ({\rm S/O})\rangle = -1.61$ which is comparable to what is found in many $\ion{H}{ii}$ regions of similar oxygen content, and is slightly lower than the solar value ( $\log ({\rm S/O})_{\odot} = -1.51$). These are also the first measurements of sulphur abundances in a Globular Cluster, thus a direct comparison of Terzan 7 and Galactic Globular Clusters is not possible yet. However our analysis suggests that the lines of $\ion{S}{i}$ multiplet 1 should be measurable for other Globular Clusters at least down to a metallicity ~-1.5.

Key words: nucleosynthesis -- stars: abundances -- globular clusters: individual: Terzan 7 -- galaxies: abundances -- galaxies: dwarf -- galaxies: individual Sgr dSph

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© ESO 2005