Book contents
- Frontmatter
- Contents
- Preface
- 1 Historical overview
- 2 Observations of stellar winds
- 3 Basic concepts: isothermal winds
- 4 Basic concepts: non-isothermal winds
- 5 Coronal winds
- 6 Sound wave driven winds
- 7 Dust driven winds
- 8 Line driven winds
- 9 Magnetic rotator theory
- 10 Alfvén wave driven winds
- 11 Outflowing disks from rotating stars
- 12 Winds colliding with the interstellar medium
- 13 The effects of mass loss on stellar evolution
- 14 Problems
- APPENDIX 1 The chronology of stellar wind studies
- APPENDIX 2 Elements of thermodynamics
- APPENDIX 3 De l'Hopital's rule for equations with a singular point
- APPENDIX 4 Physical and astronomical constants
- Bibliography
- Object index
- Index
5 - Coronal winds
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- 1 Historical overview
- 2 Observations of stellar winds
- 3 Basic concepts: isothermal winds
- 4 Basic concepts: non-isothermal winds
- 5 Coronal winds
- 6 Sound wave driven winds
- 7 Dust driven winds
- 8 Line driven winds
- 9 Magnetic rotator theory
- 10 Alfvén wave driven winds
- 11 Outflowing disks from rotating stars
- 12 Winds colliding with the interstellar medium
- 13 The effects of mass loss on stellar evolution
- 14 Problems
- APPENDIX 1 The chronology of stellar wind studies
- APPENDIX 2 Elements of thermodynamics
- APPENDIX 3 De l'Hopital's rule for equations with a singular point
- APPENDIX 4 Physical and astronomical constants
- Bibliography
- Object index
- Index
Summary
Coronal winds are stellar winds driven by gas pressure due to a high temperature of the gas. In the case of the sun a coronal temperature of about 2 × 106 K is reached in the outer layers of the solar atmosphere. The solar photosphere, where the visual radiation from the sun is emitted, has a temperature of about 6000 K. Above the photosphere the temperature rises with height to a few times 106 K. The temperature rise beyond the photosphere is due to the dissipation of mechanical energy or the reconnection of magnetic fields that originate in the convection zone below the photosphere. Other forces, such as those produced by Alfvén waves, may play a role in the coronal holes which are regions of lower temperatures and higher mass flux. However in this chapter on coronal winds, we will only consider the effects of gas pressure and heat conduction in the production of a stellar wind.
All non-degenerate stars with effective temperatures less than about 6500 K are expected to have a convection zone below their surface, so in principle chromospheres and coronae could exist around all cool stars. However, very luminous cool stars can also have winds driven by other mechanisms such as wave pressure or radiation pressure on dust grains. If these stars have a high mass loss rate, then the heating cannot compete with the cooling of the outflowing gas.
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- Chapter
- Information
- Introduction to Stellar Winds , pp. 118 - 127Publisher: Cambridge University PressPrint publication year: 1999