Analysis of the carbon-rich very metal-poor dwarf G77–61
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 C_2 bands of both ^(13)C and ^(12)C 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 ^(12)C/^(13)C = 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.
Additional Information© 2005 ESO. Article published by EDP Sciences. Received 28 September 2004; Accepted 5 January 2005; Published online 18 April 2005. Based in part on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. We thank N. Christlieb for suggesting a re-investigation of this star. B. Freytag is thanked for suggesting the microturbulence estimate, and R. Cayrel and E. josselin for useful comments. The entire Keck/HIRES user communities owes a huge debt to Jerry Nelson, Gerry Smith, Steve Vogt, and many other people who have worked to make the Keck Telescope and HIRES a reality and to operate and maintain the Keck Observatory. We are grateful to the W. M. Keck Foundation for the vision to fund the construction of the W. M. Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality, none of the observations presented herein would have been possible. J.G.C. is grateful to the National Science Foundation for partial support under grant AST-0205951. This publication makes use of data from the Two Micron All-Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Published - aa2082.pdf
Accepted Version - 0501535.pdf