Sulphur abundances in Terzan 7

Free access article

Issue		A&A 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

Letter

Sulphur abundances in Terzan 7

E. Caffau¹, P. Bonifacio², R. Faraggiana³ and L. Sbordone^{4, 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)

Abstract
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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