{
  "id": "1507.04662",
  "version": "v1",
  "published": "2015-07-16T17:34:36.000Z",
  "updated": "2015-07-16T17:34:36.000Z",
  "title": "Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-$s$ stars",
  "authors": [
    "C. Abate",
    "O. R. Pols",
    "R. G. Izzard",
    "A. I. Karakas"
  ],
  "comment": "23 pages, 8 figures, accepted for publication on Astronomy & Astrophysics",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "Many observed CEMP stars are found in binary systems and show enhanced abundances of $s$-elements. The origin of the chemical abundances of these CEMP-$s$ stars is believed to be accretion in the past of enriched material from a primary star in the AGB phase. We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-$s$ stars were formed. For this purpose we compare a sample of $67$ CEMP-$s$ stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-$s$ stars in three groups based on the observed abundance of europium. In CEMP$-s/r$ stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP$-s/nr$ stars. No measurement of europium is currently available for CEMP-$s/ur$ stars. On average our models reproduce well the abundances observed in CEMP-$s/nr$ stars, whereas in CEMP-$s/r$ stars and CEMP-$s/ur$ stars the abundances of the light-$s$ elements are systematically overpredicted by our models and in CEMP-$s/r$ stars the abundances of the heavy-$s$ elements are underestimated. In all stars our modelled abundances of sodium overestimate the observations. This discrepancy is reduced only in models that underestimate the abundances of most of the $s$-elements. Furthermore, the abundance of lead is underpredicted in most of our model stars. These results point to the limitations of our AGB nucleosynthesis model, particularly in the predictions of the element-to-element ratios. Finally, in our models CEMP-$s$ stars are typically formed in wide systems with periods above 10000 days, while most of the observed CEMP-$s$ stars are found in relatively close orbits with periods below 5000 days.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-07-16T17:34:36.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "carbon-enhanced metal-poor stars",
      "binary evolution",
      "statistical analysis",
      "binary systems",
      "low-metallicity agb stars"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 23,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}