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The Sun as a star – an overview of the solar internal structure and evolution

The Sun as a star – an overview of the solar internal structure and evolution. J ørgen Christensen-Dalsgaard Institut for Fysik og Astronomi, Aarhus Universitet Danish AsteroSeismology Centre High Altitude Observatory. A model of a stellar interior?. Birthplace of the Sun. Early life.

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The Sun as a star – an overview of the solar internal structure and evolution

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  1. The Sun as a star – an overview of the solar internal structure and evolution Jørgen Christensen-Dalsgaard Institut for Fysik og Astronomi, Aarhus Universitet Danish AsteroSeismology Centre High Altitude Observatory

  2. A model of a stellar interior?

  3. Birthplace of the Sun

  4. Early life

  5. Stellar timescales

  6. PHYSICS OF THE SOLAR INTERIOR (I)

  7. Another simple parenthesis

  8. PHYSICS OF THE SOLAR INTERIOR (II)

  9. Another parenthesis Note: numerical value is not great, but functional dependence is qualitatively right!

  10. Convective instability

  11. Convective instability

  12. TREATMENTS OF CONVECTION Convection is a turbulent phenomenon. Hence drastic approximations are required to treat it in stellar physics • Mixing-length ``theory'‘. Assume single dominant eddy scale at each position. Efficiency parametrized by mixing length ℓ = c Hp setting scale of eddies. • Local formulations. • Non-local formulations, averaging over eddy motion and over eddies at given. • Time-dependent formulation, if underlying physical model is assumed. • Canuto & Mazzitelli formulation. Takes some account of spectrum of turbulence. • Hydrodynamical simulations, including more or less detailed physics. Extremely time-consuming, restricted to small region of star. Requires approximate treatment of unresolved scales. • Two-dimensional or three-dimensional.

  13. Temperature gradients

  14. PHYSICS OF THE SOLAR INTERIOR (III)

  15. OVERVIEW OF PHYSICS OF THE SOLAR INTERIOR Basic equations: Composition characterized by abundances X, Y, Z of H, He and the rest

  16. CONSTITUTIVE PHYSICS OF THE SOLAR INTERIOR (I)

  17. CONSTITUTIVE PHYSICS OF THE SOLAR INTERIOR (II)

  18. Helium settling Nuclear burning Changes in composition • The evolution of stars is controlled by the changes in their interior composition: • Nuclear reactions • Convective mixing • Molecular diffusion and settling • Circulation and other mixing processes outside convection zones

  19. Stellar birthline Palla & Stahler (1999) General stellar evolution Pre-main-sequence evolution (Iben 1965)

  20. General stellar evolution Main sequence and beyond (Iben 1967)

  21. Solar evolution 11 Gyr 10.5 Gyr 10 Gyr End of central hydrogen burning 9 Gyr 6 Gyr Present sun 1 Gyr

  22. KNOWN `GLOBAL' PROPERTIES OF THE SUN • Total mass M¯ (assume no mass loss) • Present surface radius R¯ • Present surface luminosity L¯ (assuming isotropic radiation) • Present age (depending slightly on models of solar-system formation) • Present surface heavy-element composition, relative to hydrogen, (somewhat uncertain). • Composition not known for helium

  23. CALIBRATION OF SOLAR MODELS • Adjust initial helium abundance Y0 to obtain the observed present luminosity • Adjust initial heavy-element abundance Z0 to obtain observed present ratio Zs/Xs • Adjust parameter of convection treatment (e.g. mixing-length parameter c) to obtain observed present radius.

  24. Properties of Model S • OPAL96 equation of state • OPAL 92 opacities • Nuclear parameters from Bahcall & Pinsonneault (1994) • Diffusion and settling of helium and heavy elements from Michaud & Proffitt (1993) • Mixing-length theory of convection

  25. The solar internal sound speed Sun - Model S

  26. Neutrino generation

  27. Solar neutrino spectrum

  28. 8 B 8 B 8 B 8 B Neutrino results • Eksperiments: • 37Cl + ne!37Ar (Homestake): 8B, 7Be • 71Ga + ne!71Ge (GALLEX, SAGE): pp, etc • n + e-!n + e- (in water; Kamiokande, SK): 8B

  29. Neutrino oscillations

  30. Neutrino results 8 B 8 B 8 B 8 B 8 B

  31. Pijpers, Houdek et al. Z = 0.015 Model S Revision of solar surface abundances Asplund et al. (2004; A&A 417, 751. 2005; astro-ph/0410214 v2): • Improvements: • Non-LTE analysis • 3D atmosphere models • Consistent abundance determinations for a variety of indicators

  32. How do we correct the models? Basu & Antia (2004; ApJ 606 L85): an opacity increase to compensate for lower Z is required Seaton & Badnell (2004; MNRAS 354, 457): recent Opacity Project results do indicate some increase over the OPAL values, but hardly enough Antia & Basu (2005; ApJ 620, L129): could the neon abundance be wrong?

  33. The neon story Ne x 2.5 Bahcall et al. (2005; ApJ, in the press [astro-ph/0502563]) Drake & Testa (2005; Nature, in the press [astro-ph/0506182 v1]): X-ray observations of nearby stars indicate such a neon increase

  34. Sackmann & Boothroyd (2003; ApJ 583, 1024) Faint early Sun problem? Problems with the early climate of the Earth and Mars?? But what about helioseismology??

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