Astron. Astrophys. 344, 188-198 (1999)

Light perturbation from stellar nonradial oscillations: an application to solar oscillations

T. Toutain, G. Berthomieu and J. Provost

Observatoire de Nice, B.P. 4229, F-06304 Nice Cedex 4, France

Received 17 July 1998 / Accepted 23 December 1998

Abstract

We derive analytical expressions for the emerging intensity and flux perturbations due to stellar nonradial oscillations taking into account the sphericity of the emitting layers. These expressions are derived using both the Eulerian and Lagrangian formulations. We show, analytically and numerically, that these formulations are equivalent and that they lead, in the limit of a plane-parallel atmosphere, to analytical expressions derived in previous works. As an example, we compute for a grey atmosphere intensity perturbations for low-degree solar oscillations and show that some p and g modes can produce large variations of intensity on the very limb of the solar disk. We also compute the corresponding flux perturbations showing that differences between spherical and plane-parallel computations for modes below 4 mHz do not exceed 15 percents, the better agreement being for low frequencies.

Key words: Sun: oscillations stars: oscillations stars: atmospheres

Send offprint requests to: T. Toutain

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Contents

• 1. Introduction
• 2. From Euler to Lagrange formulation
  • 2.1. Derivation of the intensity perturbation using the Eulerian formulation
  • 2.2. Derivation of the intensity perturbation using the Lagrangian formulation
  • 2.3. The plane-parallel approximation
• 3. Total flux perturbation
  • 3.1. Spherical case
  • 3.2. The plane-parallel approximation
• 4. Numerical comparison of the different approaches
  • 4.1. Intensity at equilibrium
  • 4.2. Intensity perturbation
  • 4.3. Flux perturbation
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: March 10, 1999
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