Sulphur abundances in metal-poor stars
Department of Astronomy and Space Physics, Box 515, 75 120 Uppsala, Sweden e-mail: [korn;ryde]@astro.uu.se
Accepted: 12 September 2005
We investigate the debated “sulphur discrepancy” found among metal-poor stars of the Galactic halo with [Fe/H] < -2. This discrepancy stems in part from the use of two different sets of sulphur lines, the very weak triplet at 8694-95 Å and the stronger triplet lines at 9212-9238 Å. For three representative cases of metal-poor dwarf, turnoff and subgiant stars, we argue that the abundances from the 8694-95 lines have been overestimated which has led to a continually rising trend of [S/Fe] as metallicity decreases. Given that the near-IR region is subject to CCD fringing, these weak lines become excessively difficult to measure accurately in the metallicity regime of [Fe/H] < -2. Based on homogeneously determined spectroscopic stellar parameters, we also present updated [S/Fe] ratios from the 9212-9238 lines which suggest a plateau-like behaviour similar to that seen for other alpha elements.
Key words: stars: abundances / stars: atmospheres / stars: Population II / Galaxy: abundances / Galaxy: evolution / Galaxy: halo
© ESO, 2005