{
  "id": "1211.3157",
  "version": "v1",
  "published": "2012-11-13T23:14:12.000Z",
  "updated": "2012-11-13T23:14:12.000Z",
  "title": "The Most Metal-Poor Stars. IV. The Two Populations With [Fe/H] < -3.0",
  "authors": [
    "John E. Norris",
    "David Yong",
    "M. S. Bessell",
    "N. Christlieb",
    "M. Asplund",
    "Gerard Gilmore",
    "Rosemary F. G. Wyse",
    "Timothy C. Beers",
    "P. S. Barklem",
    "Anna Frebel",
    "S. G. Ryan"
  ],
  "comment": "Accepted for publication in ApJ",
  "categories": [
    "astro-ph.GA",
    "astro-ph.SR"
  ],
  "abstract": "We discuss the carbon-normal and carbon-rich populations of Galactic halo stars having [Fe/H] < -3.0, utilizing chemical abundances from high-resolution, high-S/N model-atmosphere analyses. The C-rich population represents ~28% of stars below [Fe/H] = -3.1, with the present C-rich sample comprising 16 CEMP-no stars, and two others with [Fe/H] ~ -5.5 and uncertain classification. The population is O-rich ([O/Fe] > +1.5); the light elements Na, Mg, and Al are enhanced relative to Fe in half the sample; and for Z > 20 (Ca) there is little evidence for enhancements relative to solar values. These results are best explained in terms of the admixing and processing of material from H-burning and He-burning regions as achieved by nucleosynthesis in zero-heavy-element models in the literature of \"mixing and fallback\" supernovae (SNe); of rotating, massive and intermediate mass stars; and of Type II SNe with relativistic jets. The available (limited) radial velocities offer little support for the C-rich stars with [Fe/H] < -3.1 being binary. More data are required before one could conclude that binarity is key to an understanding of this population. We suggest that the C-rich and C-normal populations result from two different gas cooling channels in the very early Universe, of material that formed the progenitors of the two populations. The first was cooling by fine-structure line transitions of CII and OI (to form the C-rich population); the second, while not well-defined (perhaps dust-induced cooling?), led to the C-normal group. In this scenario, the C-rich population contains the oldest stars currently observed.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2012-11-13T23:14:12.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "metal-poor stars",
      "radial velocities offer little support",
      "c-normal populations result",
      "fine-structure line transitions",
      "light elements na"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-637X/762/1/28",
      "journal": "The Astrophysical Journal",
      "year": 2013,
      "month": "Jan",
      "volume": 762,
      "number": 1,
      "pages": 28
    },
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1202623,
      "adsabs": "2013ApJ...762...28N"
    }
  }
}