Keck/HIRES Spectroscopic Analysis of Barium Abundances

Based on the high-resolution, high signal-to-noise-ratio spectra from the Keck/HIRES, we have analyzed the barium abundances of 602 stars. The parameter space of our sample are in the range of 4700 < $T_{eff}$ < 6100 K, −0.1 < [Fe/H] < 0.6 dex, and 2 < log g < 5 dex. It is found that the nonlocal thermodynamic equilibrium (NLTE) effects are large for barium, and the barium abundances can be underestimated by up to 0.2 dex compared to the the local thermodynamic equilibrium analysis for lines at 5853 and 6141 Å. In addition, the average barium abundances of the high- and low-α stars are −0.10 and 0.00 dex, respectively, and higher [Ba/Fe] corresponds to a lower [Mg/Fe] ratio. We note that there are 18 Ba-rich stars (with [Ba/Fe] > 0.3 in NLTE), which contains six dwarfs and 12 giants. The Ba-rich objects make up around 3% in our sample.