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왜소은하 Segue 1 : 우주초기의 진화를 멈춘 화석은하 발견

Segue 1 : An Unevolved Fossil Galaxy from the Early Universe
  • 작성자 : KASI
  • 작성일 : 2014-04-15
  • 조회수 : 3424
  • 저자Anna Frebel, Joshua D. Simon, Evan N. Kirby
  • AbsractWe present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant
    stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star
    observed by Norris et al. (2010), high-resolution spectra have now been obtained
    for every red giant in Segue 1. Remarkably, three of these seven stars have
    metallicities below [Fe/H] = -3.5, suggesting that Segue 1 is the least
    chemically evolved galaxy known. We confirm previous medium-resolution analyses
    demonstrating that Segue 1 stars span a metallicity range of more than 2 dex,
    from [Fe/H] = -1.4 to [Fe/H] = -3.8. All of the Segue 1 stars are
    alpha-enhanced, with [alpha/Fe] ~ 0.5. High alpha-element abundances are typical
    for metal-poor stars, but in every previously studied galaxy [alpha/Fe] declines
    for more metal-rich stars, which is typically interpreted as iron enrichment
    from supernova Ia. The absence of this signature in Segue 1 indicates that it
    was enriched exclusively by massive stars. Other light element abundance ratios
    in Segue 1, including carbon-enhancement in the three most metal-poor stars,
    closely resemble those of metal-poor halo stars. Finally, we classify the most
    metal-rich star as a CH star given its large overabundances of carbon and
    s-process elements. The other six stars show remarkably low neutron-capture
    element abundances of [Sr/H] < -4.9 and [Ba/H] < -4.2, which are
    comparable to the lowest levels ever detected in halo stars. This suggests
    minimal neutron-capture enrichment, perhaps limited to a single r-process or
    weak s-process synthesizing event. Altogether, the chemical abundances of Segue
    1 indicate no substantial chemical evolution, supporting the idea that it may be
    a surviving first galaxy that experienced only one burst of star formation.

      



     


  • 게재정보ASTROPHYSICAL JOURNAL(2014.3.24)에 실린 연구논문을 게시함
  • 첨부파일
  • 원 문http://arxiv.org/abs/1403.6116
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