{
  "id": "1504.05963",
  "version": "v1",
  "published": "2015-04-22T20:00:44.000Z",
  "updated": "2015-04-22T20:00:44.000Z",
  "title": "TOPoS: II. On the bimodality of carbon abundance in CEMP stars. Implications on the early chemical evolution of galaxies",
  "authors": [
    "P. Bonifacio",
    "E. Caffau",
    "M. Spite",
    "M. Limongi",
    "A. Chieffi",
    "R. S. Klessen",
    "P. François",
    "P. Molaro",
    "H. G. Ludwig",
    "S. Zaggia",
    "F. Spite",
    "B. Plez",
    "R. Cayrel",
    "N. Christlieb",
    "P. C. Clark",
    "S. C. O. Glover",
    "F. Hammer",
    "A. Koch",
    "L. Monaco",
    "L. Sbordone",
    "M. Steffen"
  ],
  "comment": "to be published on A&A",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. We here present our analysis of six CEMP stars. Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0<=[Ca/H]< -2.1 and 7.12<=A(C)<=8.65. For star SDSS J1742+2531 we were able to detect three FeI lines from which we deduced [Fe/H]=-4.80, from four CaII lines we derived [Ca/H]=-4.56, and from synthesis of the G-band we derived A(C)=7.26. For SDSS J1035+0641 we were not able to detect any iron lines, yet we could place a robust (3sigma) upper limit of [Fe/H]< -5.0 and measure the Ca abundance, with [Ca/H]=-5.0, and carbon, A(C)=6.90. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li)<1.8 for both stars. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. (Abridged)",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-04-22T20:00:44.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cemp stars",
      "early chemical evolution",
      "bimodality",
      "low-carbon band",
      "high-carbon band"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}