The non-local thermodynaic equilibrium ( non-LTE ) line formation for the two ions of zirconium is considered through a range of spectral types when the Zr abundance varies from the solar value down to [ Zr/H ] = -3 .
The model atom was built using 148 energy levels of Zr I , 772 levels of Zr II , and the ground state of Zr III .
It was shown that the main non-LTE mechnism for the minority species Zr I is ultraviolet overionization .
Non-LTE leads to systematically depleted total absorption in the Zr I lines and positive abundance corrections , reaching to 0.33 dex for the solar metallicity models .
The excited levels of Zr II are overpopulated relative to their thermodynamic equilibrium ( TE ) populations in the line formation layers due to radiative pumping from the low-excitation levels .
As a result , the line source function exceeds the Planck function leading to weakening the Zr II lines and positive non-LTE abundance corrections .
Such corrections grow towards lower metallicity and lower surface gravity and reach to 0.34 dex for log \leavevmode \nobreak g = 2.0 and [ M/H ] = -2 at T _ { eff } = 5500 K. As a test and first application of the Zr I-Zr II model atom , Zr abundance was determined for the Sun on the basis of 1D LTE model atmosphere .
Lines of Zr I and Zr II give consistent within the error bars non-LTE abundances , while the difference in LTE abundances amounts to 0.28 dex .
The solar abundance of zirconium obtained with the MAFAGS solar model atmosphere is \log \varepsilon _ { Zr, \odot } = 2.63 \pm 0.07 .