NLTE Analysis of Y i and Y ii in the Atmospheres of FGK Stars

• Published in: The Astrophysical journal Vol. 957; no. 1; pp. 10 - 33
• Main Authors: Alexeeva, Sofya, Wang, Yu, Zhao, Gang, Wang, Feng, Wu, Yong, Wang, Jianguo, Yan, Hongliang, Shi, Jianrong
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.11.2023; IOP Publishing
• Subjects: Abundance; Astrophysics; Atmosphere; Chemical abundances; Chemical evolution; Galactic archaeology; Galactic evolution; Hydrogen atoms; Inelastic collisions; Ionization; Iron; Metallicity; Reference stars; S-process; Stars; Stellar atmospheres; Stellar nucleosynthesis; Strontium; Thermodynamic equilibrium; Yttrium; Zirconium
• DOI: 10.3847/1538-4357/acf5e1
• ISSN: 0004-637X

The nonlocal thermodynamical equilibrium (NLTE) line formation of Y i and Y ii is considered in 1D LTE model atmospheres of FGK-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 and Y ii ) can reach up to −0.31 dex. In the atmospheres of FGK-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 ≤ [Fe/H] ≤ +0.24 metallicity range, using high-resolution spectra. For stars with [Fe/H] ≤ −1.5, [Y/Fe] versus [Fe/H] diagram reveals a positive trend with an average value of [Y/Fe] ≃ 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 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.