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

Bertrand Plez (1) , J. G. Cohen (2)

1 Astrophysique Stellaire
2 Palomar Observatory

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 ± 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 ± 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.

Mots clés: stars: abundances; stars: carbon; stars: Population II; stars: individual: G77-61; stars; abundances -stars; carbon -stars; Population II -stars; individual; G77-61

Domaines: Astrophysique stellaire et solaire [astro-ph.SR]

Bertrand Plez, J. G. Cohen. Analysis of the carbon-rich very metal-poor dwarf G77-61. Astronomy and Astrophysics - A&A, 2005, 434, pp.1117-1124. ⟨10.1051/0004-6361:20042082⟩. ⟨hal-00364859⟩