Carbon Abundances of Three Carbon-Enhanced Metal-Poor Stars from High-Resolution Gemini-S/bHROS Spectra of the 8727A [C I] Line

Abstract

We present the results from an analysis of the 8727ang forbidden [C I] line in high-resolution Gemini-S/bHROS spectra of three CEMP stars. We find the [C/Fe] ratios based on the [C I] abundances of the two most Fe-rich stars in our sample (HIP 0507-1653: [Fe/H] = -1.42 and HIP 0054-2542: [Fe/H] = -2.66) to be in good agreement with previously determined CH and C_2 line-based values. For the most Fe-deficient star in our sample (HIP 1005-1439: [Fe/H] = -3.08), however, the [C/Fe] ratio is found to be 0.34 dex lower than the published molecular-based value. We have carried out 3D local thermodynamic equilibrium (LTE) calculations for [C I], and the resulting corrections are found to be modest for all three stars, suggesting that the discrepancy between the [C I] and molecular-based C abundances of HIP 1005-1439 is due to more severe 3D effects on the molecular lines. Carbon abundances are also derived from C I high-excitation lines and are found to be 0.45-0.64 dex higher than the [C I]-based abundances. Previously published non-LTE C I abundance corrections bring the [C I] and C I abundances into better agreement; however, targeted NLTE calculations for CEMP stars are clearly needed. We have also derived the abundances of N, K, and Fe for each star. The Fe abundances agree well with previously derived values, and the K abundances are similar to those of C-normal metal-poor stars. Nitrogen abundances have been derived from resolved lines of the CN red system. The abundances are found to be approximately 0.44 dex larger than literature values, which have been derived from CN blue bands near 3880 and 4215 ang. We discuss evidence that suggests that analyses of the CN blue system bands underestimate the N abundances of metal-poor giants.

Accepted for publication in AJ; 42 pages, 6 figures, 7 tables

References in corpus (13)

• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• First stars VI - Abundances of C, N, O, Li, and mixing in extremely metal-poor giants. Galactic evolution of the light elements
• HE 0557-4840 - Ultra-Metal-Poor and Carbon-Rich
• The Frequency of Carbon-Enhanced Metal-Poor Stars in the Galaxy from the HERES sample
• 3D Hydrodynamical Simulations of Surface Convection in Red Giant Stars. Impact on spectral line formation and abundance analysis
• Bright Metal-Poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields
• Carbon Stars in the Hamburg/ESO Survey: Abundances
• First stars X. The nature of three unevolved Carbon-Enhanced Metal-Poor stars
• The chemical compositions of the extreme halo stars HE0107-5240 and HE1327-2326 inferred from 3D hydrodynamical model atmospheres
• Chemical Abundance Analysis of the Extremely Metal-Poor Star HE 1300+0157
• Broadband UBVRI Photometry of Horizontal-Branch and Metal-Poor Candidates from the HK and Hamburg/ESO Surveys. I
• First Stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876--032
• The non-LTE line formation of neutral carbon in late-type stars

Cited by in corpus (4)

• Hubble Space Telescope Near-Ultraviolet Spectroscopy of the Bright CEMP-no Star BD+44 493
• CNO behaviour in planet-harbouring stars. II. Carbon abundances in stars with and without planets using the CH band
• The peculiar abundances of HE 1005-1439. A carbon-enhanced extremely metal-poor star contaminated with products of both s-and i-process nucleosynthesis
• Spectroscopic study of Ba and CEMP-s stars: Mass distribution of AGB progenitors