Astron. Astrophys. 347, 617-629 (1999)

Heating and cooling by iron in cool star winds

P. Woitke and E. Sedlmayr

Institut für Astronomie und Astrophysik, TU Berlin, Sekr. PN 8-1, Hardenbergstrasse 36, D-10623 Berlin, Germany (woitke@physik.tu-berlin.de)

Received 22 December 1998 / Accepted 9 March 1999

Abstract

The role of iron for the energy balance in the extended atmospheres and circumstellar envelopes of cool stars is explored. Based on large non-LTE model atoms for Fe I and Fe II, we study the influence of fine-structure, forbidden, permitted and bound-free transitions on the radiative heating and cooling of the gas under various temperature, density and radiation field conditions. The results are compared to those obtained in LTE and to those calculated when ignoring optical depth effects in the lines. The number of levels in the model atoms necessary to achieve convergence of the results is discussed.

Key words: atomic processes hydrodynamics radiation mechanisms: thermal shock waves stars: chromospheres stars: circumstellar matter

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Contents

• 1. Introduction
• 2. Basic equations
• 3. Atomic data
  • 3.1. Model atom for Fe I
  • 3.2. Model atom for Fe II
• 4. Calculation of the composition of the gas
• 5. Results
  • 5.1. Investigated range of parameters
  • 5.2. Results as function of n_(H), T, and T_rad
  • 5.3. Comparison with limiting cases
  • 5.4. Which lines are important?
  • 5.5. Influence of the velocity gradient
  • 5.6. Results as a function of the size of the model atoms
• 6. Discussion: why are the forbidden and fine-structure lines so important?
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: June 30, 1999
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