Molecular line formation in the extremely metal-poor star BD+44 493

Abstract

Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The abundances of oxygen and carbon determined from individual lines based on an 1D-LTE analysis exhibit significant dependence on excitation potentials of the lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental abundances from individual spectral lines and their excitation potentials, respectively. The dependence is not explained by the uncertainties of stellar parameters, but suggests that the atmosphere of this object possesses a cool layer that is not reproduced by the 1D model atmosphere. This result agrees with the predictions by 3D model calculations. Although absorption lines of neutral iron exhibit similar trend, it is much weaker than found in molecular lines and that predicted by 3D LTE models.

7 figures, 2 tables, to appear in ApJ

References in corpus (3)

• CH in stellar atmospheres: an extensive linelist
• 3D Hydrodynamical Simulations of Surface Convection in Red Giant Stars. Impact on spectral line formation and abundance analysis
• HE 1327-2326, an unevolved star with [Fe/H]<-5.0. II. New 3D-1D corrected abundances from a VLT/UVES spectrum

Cited by in corpus (4)

• The Pristine Survey IV: Approaching the Galactic metallicity floor with the discovery of an ultra metal-poor star
• TOPoS: IV. Chemical abundances from high-resolution observations of seven EMP stars
• Detection of Phosphorus, Sulphur, and Zinc in the Carbon-Enhanced Metal-Poor Star BD+44 493
• Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. V. Oxygen abundance in the metal-poor giant HD 122563 from OH UV lines