Astron. Astrophys. 327, 252-264 (1997)

Thermal condensations in large stellar coronal loops

J.M. Ferreira ¹ and C.A. Mendoza-Brice no <sup>2

1</sup> Department of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS, Scotland
² Centro de Astrofísica Teórica, Facultad de Ciencias, Universidad de los Andes, Mérida, Venezuela

Received 29 November 1996 / Accepted 5 May 1997

Abstract

The equations ruling the thermal equilibrium along coronal loops on rapidly rotating solar-type stars are solved. The particular case of loops with lengths comparable or greater than a stellar radius is studied.

Depending on the base pressure, it is found that hot loops can exist either with very high coronal temperature (T ) or with a more solar like temperature (T ). Another type of solution consist of loops with a local temperature minimum at the summit which can be thought as representing a stellar slingshot prominence. A detailed study is presented and it is shown that these solutions are available in very general circumstances and without any special requirements such as those concerning the heating distribution along the loop or variations of the cross-sectional area.

The equilibrium structure of asymmetric loops is analysed. The maximum temperature of hot loops moves towards the loop leg with more heating, but surprisingly, depending on the parameters of the problem, the prominence solution can appear in either loop leg.

Key words: stars: magnetic fields stars: coronae plasmas

Send offprint requests to: J.M. Ferreira

Contents

• 1. Introduction
• 2. Physical considerations
  • 2.1. The heating function
  • 2.2. The cooling function
  • 2.3. The loop shape
• 3. The equations and their boundary conditions
• 4. Qualitative effects
  • 4.1. Spatially dependent heating function
  • 4.2. The effect of gravity and area variation
• 5. A typical solution
• 6. Dependence on the parameters
  • 6.1. Variation with heating deposition length-scale
  • 6.2. Variation with area expansion rate
  • 6.3. Variation with base pressure and heating
  • 6.4. The effect of the heating function
• 7. The effect of asymmetries on the solutions
  • 7.1. Hot loops
  • 7.2. Hot-cool loops
• 8. Discussion
• 9. Conclusions
• Acknowledgements
• Appendix A
  • Appendix A: prominence solutions in the presence of small-scale steady flows
• References

© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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