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NLTE Ionization Equilibrium of Nd II and Nd III in Cool A and Ap Stars

This talk outlines the NLTE calculations for the ionization equilibrium of Nd II and Nd III in cool A and Ap stars. The models of Nd II/Nd III atoms and the method of NLTE calculations are discussed, along with the NLTE corrections and their application to Ap stars. The uncertainty of the NLTE calculations is also addressed.

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NLTE Ionization Equilibrium of Nd II and Nd III in Cool A and Ap Stars

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  1. NLTE ionization equilibrium of Nd II and Nd III in cool A and Ap stars. L. I. Mashonkina, T.A. Ryabchikova Institute of Astronomy RAS A. N. Ryabtsev Institute of Spectroscopy RAS

  2. Outline of the talk 1. Short Introduction 2. Models of Nd II/Nd III atoms and method of NLTE calculations 3. NLTE corrections 4. Application to Ap stars 5. Uncertainty of NLTE calculations

  3. Term structure Nd II (1651 levels) Nd III (607 levels)

  4. Accelerated Lambda Iteration method , realized in the code DETAIL (Munich University) was used. The final model atom includes : 247 Nd II levels + 68 Nd III levels + Nd IV ground state. Energy levels : NIST, Blaise et al. (1984), our calc. Oscillator strengths: VALD + our calculations. Photoionization cross-sections: hydrogenic Collisional cross-sections: van Regemorter (1962) (allowed trans.), Ω = 1. (forbid. Trans.) NLTE line formation

  5. NLTE effects on Nd II and Nd III populations

  6. NLTE corrections for Nd II and Nd III lines

  7. b-factors Nd distribution NLTE Nd calculations in the atmosphere of roAp star γ Equ

  8. roAp star γ Equ Comparison between the observed and computed line profiles. Nd II 5319 --- top Nd III 5294 --- bottom Observations -- black line, LTE calculations in stratified atmosphere -- blue dashed line NLTE calculations in stratified atmosphere -- red line

  9. Uncertainty of NLTE calculations NLTE abundance correction variations : photoionization cross-sections (stratified Nd) σ(ph-ion) : ΔNLTE= 1.07 - 1.31 (Nd II) and ΔNLTE= (-0.42) – (-0.48) (Nd III) σ(ph-ion) / 100 → NLTE effects decrease : ΔNLTE= 0.56 - 0.80 (Nd II) and ΔNLTE = (-0.26) – (-0.34) (Nd III) σ(ph-ion) x 100 → NLTE effects increase : ΔNLTE= 1.16 - 1.56 (Nd II) and ΔNLTE = (-0.41) – (-0.50) (Nd III) collisional cross-sections (homogeneous Nd) σ(coll) : ΔNLTE= 0.07 – (-0.04) (Nd II) and ΔNLTE= (-0.27) – (-0.31) (Nd III) σ(coll) x 10 → NLTE effects decrease : ΔNLTE= 0.05 – (-0.02) (Nd II) and ΔNLTE= (-0.17) – (-0.20) (Nd III)

  10. Acknowledgements We are very grateful to : Prof. Thomas Gehren for providing the codesDETAILandMAFAGS Presidium RAS Programme''Nonstationary phenomena in astronomy'', RFBR grant number04-02-16788, the Russian Federal Programme''Astronomy'' for partial financial support. All NLTE calculations were performed using eridani computer of the Institute of Astronomy and Astrophysics of Munich University.

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