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Title: Metal-poor stars observed with the Magellan telescope. II. Discovery of four stars with [Fe/H] ≤ –3.5

We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor (EMP, [Fe/H] ≤ –3.0), with four having [Fe/H] ≤ –3.5. Chemical abundances or upper limits are derived for these stars based on high-resolution (R ∼ 35,000) Magellan/MIKE spectroscopy, and are in general agreement with those of other very and extremely metal-poor stars reported in the literature. Accurate metallicities and abundance patterns for stars in this metallicity range are of particular importance for studies of the shape of the metallicity distribution function of the Milky Way's halo system, in particular for probing the nature of its low-metallicity tail. In addition, taking into account suggested evolutionary mixing effects, we find that six of the program stars (with [Fe/H] ≤ –3.35) possess atmospheres that were likely originally enriched in carbon, relative to iron, during their main-sequence phases. These stars do not exhibit overabundances of their s-process elements, and hence may be, within the error bars, additional examples of the so-called CEMP-no class of objects.
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ;  [6]
  1. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
  2. Massachussetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
  3. Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, D-69117 Heidelberg (Germany)
  4. Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)
  5. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia)
  6. Departamento de Astronomia-Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, SP 05508-900 (Brazil)
Publication Date:
OSTI Identifier:
22348163
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 781; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ATMOSPHERES; CARBON; DISTRIBUTION FUNCTIONS; ELECTROMAGNETIC PULSES; IRON; METALLICITY; MILKY WAY; RESOLUTION; S PROCESS; SPECTROSCOPY; STARS; TELESCOPES