{
  "id": "1609.00679",
  "version": "v1",
  "published": "2016-09-02T17:41:48.000Z",
  "updated": "2016-09-02T17:41:48.000Z",
  "title": "G64-12 and G64-37 are Carbon-Enhanced Metal-Poor Stars",
  "authors": [
    "Vinicius M. Placco",
    "Timothy C. Beers",
    "Henrique Reggiani",
    "Jorge Melendez"
  ],
  "comment": "6 pages, 3 figures; accepted for publication in ApJ Letters",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We present new high-resolution chemical-abundance analyses for the well-known high proper-motion subdwarfs G64-12 and G64-37, based on very high signal-to-noise spectra (S/N ~ 700/1) with resolving power R ~ 95,000. These high-quality data enable the first reliable determination of the carbon abundances for these two stars; we classify them as carbon-enhanced metal-poor (CEMP) stars based on their carbonicities, which both exceed [C/Fe] = +1.0. They are sub-classified as CEMP- no Group-II stars, based on their location in the Yoon-Beers diagram of absolute carbon abundance, A(C) vs. [Fe/H], as well as on the conventional diagnostic [Ba/Fe]. The relatively low absolute carbon abundances of CEMP-no stars, in combination with the high effective temperatures of these two stars (Teff ~ 6500 K) weakens their CH molecular features to the point that accurate carbon abundances can only be estimated from spectra with very high S/N. A comparison of the observed abundance patterns with the predicted yields from massive, metal-free supernova models reduces the inferred progenitor masses by factors of ~ 2-3, and explosion energies by factors of ~ 10-15, compared to those derived using previously claimed carbon abundance estimates. There are certainly many more warm CEMP-no stars near the halo main-sequence turnoff that have been overlooked in past studies, directly impacting the derived frequencies of CEMP-no stars as a function of metallicity, a probe that provides important constraints on Galactic chemical evolution models, the initial mass function in the early Universe, and first-star nucleosynthesis.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-09-02T17:41:48.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "carbon-enhanced metal-poor stars",
      "metal-free supernova models reduces",
      "relatively low absolute carbon abundances",
      "well-known high proper-motion subdwarfs",
      "accurate carbon abundances"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 6,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}