High-Resolution Spectroscopy of Cool Carbon-Rich and Metal-Poor Star HD 209621

Abstract

Element abundances for HD 209621 obtained earlier display significant discrepancies, especially in the case of CNO and neutron-capture elements. Therefore we performed a detailed analysis of chemical composition of this star using a new high-resolution spectrum. Atmospheric parameters and abundance pattern are updated, and the mechanism of nucleosynthesis is examined. Abundances for 11 elements are calculated for the first time. The method of atmospheric models and spectral synthesis was used. The following values of atmospheric parameters are derived: Teff = 4400 K, log g = 1.0 (cgs) and ξt = 1.9 kms−1. The iron abundance of the star was found to be low, at [Fe/H] = -1.91±0.10. The carbon to oxygen ratio is high, C/O ≃ +2.0. Low carbon to nitrogen ratio, [C/N] ≃ -0.8, and low carbon isotopic ratio, 12C/13C = 17 ±5, are in agreement with the theory of nucleosynthesis of intermediate-mass AGB stars. The barium to europium ratio is high, [Ba/Eu] = +0.28, and is typical for carbon-enhanced metal-poor CEMP-r/s stars. The observed abundance pattern of neutron capture elements is reproduced well by the scaled solar system abundances.

Keywords

• stars
• abundances
• atmospheres
• spectroscopic binaries
• carbon
• individual
• hd 209621