{
  "id": "1310.3276",
  "version": "v1",
  "published": "2013-10-11T20:01:04.000Z",
  "updated": "2013-10-11T20:01:04.000Z",
  "title": "Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars",
  "authors": [
    "Young Sun Lee",
    "Timothy C. Beers",
    "Thomas Masseron",
    "Bertrand Plez",
    "Constance M. Rockosi",
    "Jennifer Sobeck",
    "Brian Yanny",
    "Sara Lucatello",
    "Thirupathi Sivarani",
    "Vinicius M. Placco",
    "Daniela Carollo"
  ],
  "comment": "19 pages, 10 figures, 6 tables, accepted for publication in AJ on August 20, 2013",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the SDSS and SEGUE. By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N > 15 to a precision better than 0.35 dex. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] > +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] < -2.5, 31% for [Fe/H] < -3.0, and 33% for [Fe/H] < -3.5. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] < -2.5. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = -2.5, jumping from 15% for [Fe/H] < -2.5 to about 75% for [Fe/H] < -3.0. When we impose a restriction with respect to distance from the Galactic mid-plane (|Z| < 5 kpc), the frequency of the CEMP giants does not increase at low metallicity ([Fe/H] < -2.5), but rather, decreases, due to the dilution of C-rich material in stars that have undergone mixing with CNO-processed material from their interiors. The frequency of CEMP stars near the main-sequence turnoff, which are not expected to have experienced mixing, increases for [Fe/H] < -3.0. [abridged]",
  "revisions": [
    {
      "version": "v1",
      "updated": "2013-10-11T20:01:04.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "cemp stars",
      "carbon abundance estimation",
      "carbon-enhanced metal-poor stars",
      "cumulative cemp frequency",
      "sdss/segue spectra"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "doi": "10.1088/0004-6256/146/5/132",
      "journal": "The Astronomical Journal",
      "year": 2013,
      "month": "Nov",
      "volume": 146,
      "number": 5,
      "pages": 132
    },
    "note": {
      "typesetting": "TeX",
      "pages": 19,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 1305745,
      "adsabs": "2013AJ....146..132L"
    }
  }
}