Issue |
A&A
Volume 580, August 2015
|
|
---|---|---|
Article Number | A129 | |
Number of page(s) | 17 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201525956 | |
Published online | 19 August 2015 |
Sulphur in the Sculptor dwarf spheroidal galaxy⋆,⋆⋆
Including NLTE corrections
1
Kapteyn Astronomical Institute, University of Groningen,
PO Box 800,
9700AV
Groningen,
The Netherlands
e-mail:
asa@astro.rug.nl
2
Department of Astronomy and Astronomical Observatory, Odessa
National University, Ukraine, and Isaac Newton Institute of Chile,
Odessa branch, Shevchenko Park,
65014
Odessa,
Ukraine
3
GEPI, Observatoire de Paris-Meudon, CNRS, Université Paris
Diderot, 92125
Meudon Cedex,
France
4
Laboratoire Lagrange, Université de Nice Sophia Antipolis, CNRS,
Observatoire de la Côte d’Azur, CS34229, 06304
Nice Cedex 4,
France
5
Institute of Astronomy, Madingley Road,
Cambridge CB3 0HA,
England
Received: 24 February 2015
Accepted: 4 May 2015
In Galactic halo stars, sulphur has been shown to behave like other α-elements, but until now, no comprehensive studies have been done on this element in stars of other galaxies. Here, we use high-resolution ESO VLT/FLAMES/GIRAFFE spectra to determine sulphur abundances for 85 stars in the Sculptor dwarf spheroidal galaxy, covering the metallicity range −2.5 ≤ [ Fe / H ] ≤ −0.8. The abundances are derived from the S I triplet at 9213, 9228, and 9238 Å. These lines have been shown to be sensitive to departure from local thermodynamic equilibrium, i.e. NLTE effects. Therefore, we present new NLTE corrections for a grid of stellar parameters covering those of the target stars. The NLTE-corrected sulphur abundances in Sculptor show the same behaviour as other α-elements in that galaxy (such as Mg, Si, and Ca). At lower metallicities ([ Fe / H ] ≲ −2) the abundances are consistent with a plateau at [ S / Fe ] ≈ + 0.16, similar to what is observed in the Galactic halo, [ S / Fe ] ≈ + 0.2. With increasing [Fe/H], the [S/Fe] ratio declines, reaching negative values at [ Fe / H ] ≳ −1.5. The sample also shows an increase in [S/Mg] with [Fe/H], most probably because of enrichment from Type Ia supernovae.
Key words: stars: abundances / galaxies: abundances / galaxies: evolution / galaxies: individual: Sculptor dwarf spheroidal / galaxies: dwarf
Based on observations made with ESO/VLT/FLAMES at the La Silla Paranal observatory under program ID 089.B-0304(B).
Appendix is available in electronic form at http://www.aanda.org
© ESO, 2015
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