NLTE analysis for Y I and Y II in atmospheres of F-G-K stars

Sofya Alexeeva, Yu Wang, Gang Zhao, Feng Wang, Yong Wu, Jianguo Wang, Hongliang Yan, Jianrong Shi

Published 2023-09-04Version 1

The non-local thermodynamical equilibrium (NLTE) line formation of Y I and Y II is considered in 1D LTE model atmospheres of F-G-K-type stars. The model atom was constructed with the most up-to-date atomic data, including quantum cross sections and rate coefficients for transitions in inelastic collisions of Y I and Y II with hydrogen atoms. For seven reference stars, we obtained an agreement between NLTE abundances inferred from the two ionization stages, while the difference in LTE abundance (Y I - Y II) can reach up to -0.31 dex. In the atmospheres of F-G-K-type stars, for both Y I and Y II lines, the NLTE abundance corrections are positive. In solar metallicity stars, the NLTE abundance corrections for Y II lines do not exceed 0.12 dex, while in atmospheres of metal-poor stars they do not exceed 0.21 dex. For Y I lines, the NLTE abundance corrections can reach up to 0.5 dex. We determined the yttrium NLTE abundances for a sample of 65 F and G dwarfs and subgiants in the -2.62~$\leq$~[Fe/H]~$\leq$~+0.24 metallicity range, using high-resolution spectra. For stars with [Fe/H]~$\leq$~-1.5, [Y/Fe] versus [Fe/H] diagram reveals positive trend with an average value of [Y/Fe]~$\simeq$~0. For metal-poor stars, among Sr, Y, and Zr, the arrangement [Sr/Fe] < [Y/Fe] < [Zr/Fe] remains consistent. The current study is useful for the Galactic chemical evolution research. The model atom will be applied for NLTE yttrium abundance determination in very metal-poor stars studied with LAMOST and Subaru.