Astron. Astrophys. 333, 219-230 (1998)

Non-LTE analysis of neutral magnesium in the solar atmosphere

G. Zhao ^{1, 2}, K. Butler ¹ and T. Gehren <sup>1

1</sup> Institut für Astronomie und Astrophysik der Universität München, Scheinerstrasse 1, D-81679 München, Germany
² Beijing Astronomical Observatory, Chinese Academy of Sciences, 100080 Beijing, P.R. China

Received 15 May 1997 / Accepted 16 December 1997

Abstract

We investigate the formation of neutral magnesium lines in the solar photosphere with an atomic model containing 83 levels plus the ground state of Mg II connected via radiative and collisional interactions. Synthetic line flux and intensity profiles are compared with the solar spectrum to study the relevant physical processes and their influence on the level populations and line profiles. For neutral magnesium with the photoionization edges of its three lowest states at 1620, 2514 and 3757 Å  the reduction of the ultraviolet radiation field due to metallic line absorption has been taken into account using Kurucz' (1992) ODF opacities. In the photosphere of a cool star excitation and ionization due to collisions with neutral hydrogen can outweigh electron collisions. Therefore the influence of different types of collisional interactions with electrons and neutral hydrogen atoms is examined.

General agreement with solar line profiles in the visible and infrared is found for an atomic model with both electron collisions and strongly reduced but significantly large neutral hydrogen collision rates. Our investigation thus extends previous results to lines of all different excitation energies. The atomic model found from the analysis of the solar spectrum will serve as a reference for the investigation of cool metal-poor stars in which both the reduced electron collision rates and the enhanced UV intensities lead us to expect more pronounced deviations from LTE.

Key words: atomic processes line: formation Sun: abundances Sun: photosphere

Send offprint requests to: T. Gehren

Contents

• 1. Introduction
• 2. Atomic model
  • 2.1. Radiative transition data
  • 2.2. Collisional transition data
    • 2.2.1. Electron collisions
    • 2.2.2. Collisions with hydrogen atoms
• 3. Model atmospheres
  • 3.1. Statistical equilibrium calculations
  • 3.2. Background opacities
• 4. Results
  • 4.1. Departure coefficients
  • 4.2. Line profiles
    • 4.2.1. Intercombination line
    • 4.2.2. Excited lines
    • 4.2.3. Emission lines near 12µm
• 5. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998
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