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GETTING READY for PICARD HELIOSEISMOLOGY PROGRAM December 3-4 2008

GETTING READY for PICARD HELIOSEISMOLOGY PROGRAM December 3-4 2008. Light Perturbations from stellar non-radial oscillations - an application to solar limb observations - Thierry Toutain /Janine Provost School of Phys. and Astron. Birmingham / UNS CNRS OCA Cassiopée.

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GETTING READY for PICARD HELIOSEISMOLOGY PROGRAM December 3-4 2008

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  1. GETTING READY for PICARD HELIOSEISMOLOGY PROGRAM December 3-4 2008 Light Perturbationsfrom stellar non-radial oscillations-an application to solar limb observations -Thierry Toutain /Janine ProvostSchool of Phys. and Astron. Birmingham / UNS CNRS OCA Cassiopée

  2. Purpose: estimate, on the solar disk, the relative perturbation of the intensity emitted by the photosphere in the visible continuum due to non-radial oscillations.Pioneering work by Dziembowski(1977).Buta and Smith (1979) +adiabatic oscillation and black-body approximation.Berthomieu and Provost (1990) + thickness of the photosphere and grey photosphere approximation.Toutain and Gouttebroze (1993), Staude (1994) + some radiative transfer.Toutain, Berthomieu and Provost (1999) + sphericity of the photosphere (to allow for calculations of intensity perturbation at the limb). 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  3. Model of intensity on the solar disk 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  4. 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  5. EmergingIntensity across the solar disk(μ0 = cos θ0) center limb Sphericity of the emitting layers cannot be neglected for the outer ~3% (~30”) of the disk because the total optical depth along the line of sight drops quickly below 1. 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  6. Perturbation of the intensitywhich perturbation formalism to use:Eulerian or Lagrangian? Eulerian: integrate perturbation along the line of sight (Toutain and Gouttebroze,1993; ) Lagrangian: follow fluid elements (Berthomieu and Provost,1990), distorted line of sight?

  7. Schematic shape of a star perturbed by a l=2 oscillation As shown by Toutain, Berthomieu and Provost (1999) the 2 formalisms, lagrangian and eulerian, lead to a same intensity perturbation, except at the limb (blue region) where fluid elements moving out the line of sight are not always replaced with similar fluid elements. So Eulerian formalism is requested to study intensity perturbation at the solar limb. 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  8. Intensity perturbation across the solar diskfor a radial p-mode limb center 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  9. Intensity perturbation across the solar diskfor a l=1 p-mode m = 0 m = 1 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  10. Intensity perturbation across the solar diskfor a l=1 g-mode m = 0 m =1 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  11. Results • Taking into account sphericity of the photosphere reveals a possible significant increase of the relative intensity perturbation at the solar limb for some modes of oscillation: - both for p and g-modes - and only for l+m even modes • The effect on the full-disk perturbation is expected to be small 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  12. Explanation:Near the limb the photosphere is transparent and the intensity perturbations are driven by the global upward/downward motions of the photosphere which change the opacity of the layer crossing the line of sight. The perturbation is then roughly proportional to the derivative of the intensity: DI/ I(0) ~ 1/ I(0).dI(0)/dm .Plm(m) 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  13. Limitations • Adiabatic eigenfunctions • Simplified radiative transfer (only ion H-) • No interaction between convection and oscillations • Amplitude estimate assuming energy equipartition or surface velocity (excitation mechanism?) 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  14. Observational evidences?(1) 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  15. Observational evidences?(2) 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  16. Theory / MDI observations (Toner et al 1999) 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

  17. Conclusion • Because of the sharp fall-off of the visible continuum intensity near the solar limb we expect solar oscillations (both p and g-modes) to produce larger relative intensity perturbations. • Study of limb intensity p-mode signals both with LOI and MDI seems to suggest a significant increase of the signal at the limb ( factor 2-3). • Need more evidences for p modes and check for a possible g-mode signature with new instruments (PICARD...). 3/12/2008 Th. Toutain, J. Provost Getting ready for Picard helioseismology program

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