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Sökning: WFRF:(Jacobson Heather R.)

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1.
  • Bessell, Michael S., et al. (författare)
  • Nucleosynthesis in a Primordial Supernova : Carbon and Oxygen Abundances in SMSS J031300.36-670839.3
  • 2015
  • Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 806:1
  • Tidskriftsartikel (refereegranskat)abstract
    • SMSS J031300.36-670839.3 (hereafter SM0313-6708) is a sub-giant halo star, with no detectable Fe lines and large overabundances of C and Mg relative to Ca. We obtained Very Large Telescope-Ultraviolet and Visual Echelle Spectrograph (UVES) spectra extending to 3060 angstrom showing strong OH A-X band lines enabling an oxygen abundance to be derived. The OH A-X band lines in SM0313-6708 are much stronger than the CH C-X band lines. Spectrum synthesis fits indicate an [O/C] ratio of 0.02 +/- 0.175. Our high signal-to-noise ratio UVES data also enabled us to lower the Fe abundance limit to [Fe/H](< 3D >,NLTE) < -7.52 (3 sigma). These data support our previous suggestion that the star formed from the iron-poor ejecta of a single massive star Population III supernova.
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2.
  • Jacobson, Heather R., et al. (författare)
  • High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the Skymapper Survey
  • 2015
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 807:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The SkyMapper Southern Sky Survey is carrying out a search for the most metal-poor stars in the Galaxy. It identifies candidates by way of its unique filter set which allows for estimation of stellar atmospheric parameters. The set includes a narrow filter centered on the Ca II K 3933 angstrom line, enabling a robust estimate of stellar metallicity. Promising candidates are then confirmed with spectroscopy. We present the analysis of Magellan Inamori Kyocera Echelle high-resolution spectroscopy of 122 metal-poor stars found by SkyMapper in the first two years of commissioning observations. Forty-one stars have [Fe/H] <= -3.0. Nine have [Fe/H] <= -3.5, with three at [Fe/H] similar to -4. A 1D LTE abundance analysis of the elements Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, Ba, and Eu shows these stars have [X/Fe] ratios typical of other halo stars. One star with low [X/Fe] values appears to be "Fe-enhanced," while another star has an extremely large [Sr/Ba] ratio: >2. Only one other star is known to have a comparable value. Seven stars are "CEMP-no" stars ([C/Fe] > 0.7, [Ba/Fe] < 0). 21 stars exhibit mild r-process element enhancements (0.3 <= [Eu/Fe] < 1.0), while four stars have [Eu/Fe] >= 1.0. These results demonstrate the ability to identify extremely metal-poor stars from SkyMapper photometry, pointing to increased sample sizes and a better characterization of the metal-poor tail of the halo metallicity distribution function in the future.
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