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TOPoS: III. An ultra iron-poor CEMP multiple system

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  • E. Caffau
  • P. Bonifacio
  • M. Spite
  • F. Spite
  • L. Monaco
  • L. Sbordone
  • P. Francois
  • A. Gallagher
  • B. Plez
  • S. Zaggia
  • H.-G. Ludwig
  • R. Cayrel
  • Andreas Koch
  • M. Steffen
  • S. Salvadori
  • R.S. Klessen
  • S. Glover
  • N. Christlieb
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Article numberL6
<mark>Journal publication date</mark>11/2016
<mark>Journal</mark>Astronomy and Astrophysics
Volume595
Number of pages6
Publication statusPublished
Early online date12/10/16
Original languageEnglish

Abstract

Aims. One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum. Methods. We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2 m VLT telescope to measure radial velocities and determine the chemical composition of the system. Results. Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function (CCF) for eight spectra, and in one case there is evidence for the presence of a third peak. Chemical analysis of the spectrum obtained by averaging all the spectra for which the CCF showed a single peak found that the iron abundance is [Fe/H]=–4.97. The system is also carbon enhanced with [C/Fe]=+3.91 (A(C) = 7.44). From the permitted oxygen triplet we determined an upper limit for oxygen of [O/Fe]< +3.52 such that C/O > 1.3. We are also able to provide more stringent upper limits on the Sr and Ba abundances ([Sr/Fe] < +0.70, and [Ba/Fe] < +1.46, respectively).