EDP Sciences
Free access
Volume 434, Number 3, May II 2005
Page(s) 1117 - 1124
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20042082

A&A 434, 1117-1124 (2005)
DOI: 10.1051/0004-6361:20042082

Analysis of the carbon-rich very metal-poor dwarf G77-61

B. Plez1 and J. G. Cohen2

1  GRAAL, CNRS UMR 5024, Université Montpellier II, 34095 Montpellier Cedex 5, France
    e-mail: plez@graal.univ-montp2.fr
2  Palomar Observatory, Mail Stop 105-24, California Institute of Technology, Pasadena, Ca 91125, USA

(Received 28 September 2004 / Accepted 5 January 2005)

We present an analysis of the carbon dwarf G77-61, a known binary, based on high resolution Keck spectra. G77-61 has a very-low metallicity, although not as extreme as what was previously conjectured. This star is very carbon-enhanced, the spectra showing very strong CH, CN, and C2 bands of both 13C and 12C isotopes. Atomic lines are sparse, and often blended, but we were able to derive abundances for Na, Mg, Ca, Cr, Mn, and Fe. Its [Fe/H] of -4.03 $\pm$ 0.1 places it among the lowest metallicity stars known, and its very high [C/Fe] = +2.6 , and [N/Fe] = +2.6 among the most C and N-rich metal-poor stars. The carbon isotopic ratio is 12C/13C = 5 $\pm$ 1. No overabundance of s- or r-process elements is detectable, but the upper limits that can be set on these overabundances are not very constraining.

Key words: stars: abundances -- stars: carbon -- stars: Population II -- stars: individual: G77-61

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