SILICON ABUNDANCES IN NEARBY STARS FROM THE Si I INFRARED LINES

We have used high-resolution, high signal-to-noise ratio infrared spectra from the Subaru Telescope atop Mauna Kea. Line formation calculations of Si I infrared lines in the atmospheres of nearby stars are presented. All abundance results of [Si/Fe] are derived from local thermodynamic equilibrium (LTE) and NLTE statistical equilibrium calculations and spectrum synthesis methods. We found that NLTE effects for Si I infrared lines are important even for metal-rich stars (>0.1 dex), and the NLTE effects may depend on the surface gravities. A good agreement of silicon abundances between the optical and infrared lines is obtained when the NLTE effects are included, while a large difference is found for the LTE results. The derived silicon abundances are overabundant for metal-poor stars.