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
6 - Sound wave driven 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
In stars with a convection zone just below the photosphere, the convective motions might create acoustic waves which propagate outwards through the photosphere. These sound-waves produce an extra pressure, i.e. ‘wave pressure’ in the atmosphere. This pressure will depend on the density and on the amplitudes of the waves. The gradient of the wave pressure results in a force that can drive a stellar wind. If a stellar wind is driven by acoustic wave pressure it is called a ‘sound wave driven wind’.
In this chapter we will first explain the concept of wave pressure by studying the motion of a particle in the presence of an oscillating force. This simple case, first developed by Landau and Lifshitz (1959) shows that oscillations may result in a net force in the direction of the oscillations. In § 6.1 we discuss the motions of particles in an oscillatory field, such as in a sound wave, and we show that this produces a ‘wave pressure’. In § 6.2 we introduce the concepts of the ‘wave action density’ and the ‘acoustic wave luminosity’. These are useful concepts for describing sound wave driven winds. The pressure due to acoustic waves is described in § 6.3. Section (6.4) descibes sound wave driven wind assuming no dissipation of acoustic energy. This results in estimates of the both the mass loss rate and the wind velocity. In § 6.5 we discuss sound wave driven winds with dissipation of the acoustic energy.
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- Introduction to Stellar Winds , pp. 128 - 144Publisher: Cambridge University PressPrint publication year: 1999