Formation of Zr I and II lines under non-LTE conditions of stellar atmospheres |
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| Authors: | A B Velichko L I Mashonkina H Nilsson |
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| Institution: | 1.Institute of Astronomy,Russian Academy of Sciences,Moscow,Russia;2.Department of Atomic Astrophysics,Lund Observatory,Lund,Sweden |
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| Abstract: | The formation of Zr I and Zr II lines in stellar atmospheres under non-LTE conditions has been considered for the first time.
A model zirconium atom has been composed using 148 Zr I levels, 772 Zr II levels, and the ground Zr III state. Non-LTE calculations
have been performed for model atmospheres with T
eff = 5500 and 6000 K, log g = 2.0 and 4.0, M/H] = −3, −2, −1, 0. In the entire investigated range of parameters, the Zr I levels are shown to be underpopulated
relative to their LTE populations in the line formation region. In contrast, the excited Zr II levels are overpopulated, while
the ground state and lower excited levels of Zr II retain their LTE populations. Since the non-LTE effects cause the Zr I
and Zr II spectral lines being investigated to weaken, the non-LTE corrections to the abundance derived from Zr I and Zr II
lines are positive. For Zr II lines, they increase with decreasing metallicity and surface gravity up to 0.34 dex for the
model with T
eff = 5500, log g = 2.0, and M/H] = −2. The non-LTE effects depend weakly on temperature. The non-LTE corrections for Zr I lines reach 0.33
dex for solar-metallicity models. Zr I and Zr II lines in the solar spectrum have been analyzed. The non-LTE zirconium abundances
derived from lines in the two ionization stages are shown to agree between themselves within the error limits, while the LTE
abundance difference is 0.28 dex. The zirconium abundance in the solar atmosphere (averaged over Zr I and Zr II lines) is
log ɛZr,⊙ = 2.63 ± 0.07. |
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