Non-LTE abundances of zinc in different spectral type stars and the Galactic [Zn/Fe] trend based on quantum-mechanical data on inelastic processes in zinc-hydrogen collisions

Abstract

ABSTRACT We present a new model atom of Zn i-Zn ii based on the most up-to-date photoionization cross-sections, electron-impact excitation rates, and rate coefficients for the Zn i + H i and Zn ii + H− collisions. The latter were calculated using the multichannel quantum asymptotic treatment based on the Born–Oppenheimer approach. Non-LTE analysis was performed for the first time for lines of Zn i and Zn ii in the ultraviolet (UV) spectra of two very metal-poor reference stars: HD 84937 and HD 140283. We found consistent non-LTE abundance from the resonance Zn i 2138 Å line, the subordinate lines, and the lines of Zn ii. In both stars, non-LTE leads to 0.17 dex higher average abundance from Zn i, while, for Zn ii lines, non-LTE corrections are minor and do not exceed 0.06 dex. Using lines of Zn i in the high-resolution spectra, we determined the non-LTE abundances for a sample of 80 stars in the −2.5 ≤ [Fe/H] ≤ 0.2 metallicity range. The [Zn/Fe] versus [Fe/H] diagram reveals a dip, with [Zn/Fe] ≃ 0.3 in the most metal-poor stars, a close-to-solar value for [Fe/H] ∼−1.2, and increasing [Zn/Fe] up to 0.3 in the thick disc stars. The close-to-solar metallicity stars have subsolar [Zn/H] ≃ −0.1, on average. Non-LTE abundances of zinc were derived for the first time for seven reference F- to B-type stars. We provide a grid of the non-LTE abundance corrections.