{
  "id": "1503.02691",
  "version": "v1",
  "published": "2015-03-09T21:00:07.000Z",
  "updated": "2015-03-09T21:00:07.000Z",
  "title": "The Galactic evolution of sulphur as traced by globular clusters",
  "authors": [
    "Nikolay Kacharov",
    "Andreas Koch",
    "Elisabetta Caffau",
    "Luca Sbordone"
  ],
  "comment": "9 pages, 7 figures, accepted for publication in A&A",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "Sulphur is an important, volatile alpha element but its role in the Galactic chemical evolution is still uncertain. We derive the S abundances in RGB stars in three Galactic globular clusters (GC) that cover a wide metallicity range (-2.3<[Fe/H]<-1.2), namely M4, M22, and M30. The halo field stars show a large scatter in the [S/Fe] ratio in this metallicity span, which is inconsistent with canonical chemical evolution models. To date, very few measurements of [S/Fe] exist for stars in GCs, which are good tracers of the chemical enrichment of their environment. However, some light and alpha elements show star-to-star variations within individual GCs and it is yet unclear whether sulphur also varies between GC stars. We used the the infrared spectrograph CRIRES to obtain high-resolution (R~50000), high signal-to-noise (SNR~200 per px) spectra in the region of the S I multiplet 3 at 1045 nm for 15 GC stars selected from the literature (6 stars in M4, 6 stars in M22 and 3 stars in M30). Multiplet 3 is better suited for S abundance derivation than the more commonly used lines of multiplet 1 at 920 nm, since its lines are not blended by telluric absorption or other stellar features at low metallicity. We used spectral synthesis to derive the [S/Fe] ratio of the stars assuming local thermodynamic equilibrium (LTE). We find mean [S/Fe] = 0.58 +/- 0.01 +/- 0.20 dex (statistical and systematic error) for M4, [S/Fe] = 0.57+/-0.01+/-0.19 dex for M22, and [S/Fe] = 0.55+/-0.02+/-0.16 dex for M30. The negative NLTE corrections are estimated to be in the order of the systematic uncertainties. With the tentative exception of two stars with measured high S abundances, we conclude that sulphur behaves like a typical alpha element in the studied Galactic GCs, showing enhanced abundances with respect to the solar value at metallicities below [Fe/H] = -1.0 dex without a considerable spread.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-03-09T21:00:07.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "globular clusters",
      "galactic evolution",
      "alpha element",
      "gc stars",
      "stars assuming local thermodynamic equilibrium"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}