{
  "id": "1401.7109",
  "version": "v1",
  "published": "2014-01-28T08:21:05.000Z",
  "updated": "2014-01-28T08:21:05.000Z",
  "title": "The Na-O anticorrelation in horizontal branch stars. IV. M22",
  "authors": [
    "R. G. Gratton",
    "S. Lucatello",
    "A. Sollima",
    "E. Carretta",
    "A. Bragaglia",
    "Y. Momany",
    "V. D'Orazi",
    "S. Cassisi",
    "M. Salaris"
  ],
  "comment": "Accepted for publication on Astronomy and Astrophysics. 23 pages, 21 figures",
  "doi": "10.1051/0004-6361/201323101",
  "categories": [
    "astro-ph.SR"
  ],
  "abstract": "We obtained high-resolution spectra for 94 candidate stars belonging to the HB of M22 with FLAMES. The HB stars we observed span a restricted temperature range (7,800<Teff<11,000 K), where about 60% of the HB stars of M22 are. Within our sample, we can distinguish three groups of stars segregated (though contiguous) in colours: Group 1 (49 stars) is metal-poor, N-normal, Na-poor and O-rich with abundances that match those determined for the primordial group of RGB stars from previous studies. Group 2 (23 stars) is still metal-poor, but it is N- and Na-rich, though only very mildly depleted in O. We can identify this intermediate group as the progeny of the metal-poor RGB stars that occupy an intermediate location along the Na-O anti-correlation. The third group (20 stars) is metal-rich, Na-rich, and O-rich and likely corresponds to the most O-rich component of the previously found metal-rich RGB population. We did not observe any severely O-depleted stars and we think that the progeny of these stars falls on the hotter part of the HB. The metal-rich population is also over-abundant in Sr, in agreement with results for corresponding RGB and SGB stars. However, we do not find any significant variation in the ratio between the sum of N and O abundances to Fe. There is some evidence of an enhancement of He content for Groups 2 and 3 stars (Y=0.338\\pm 0.014\\pm 0.05). Our results agree with the proposition that chemical composition drives the location of stars along the HB of a GC. Furthermore, we found a number of fast rotators. They are concentrated in a restricted temperature range along the HB of M22.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2014-01-28T08:21:05.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "horizontal branch stars",
      "na-o anticorrelation",
      "restricted temperature range",
      "hb stars",
      "metal-poor rgb stars"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "journal": "Astronomy and Astrophysics",
      "year": 2014,
      "month": "Mar",
      "volume": 563
    },
    "note": {
      "typesetting": "TeX",
      "pages": 23,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2014A&A...563A..13G"
    }
  }
}