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

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

Abstract

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.