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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 Jørgen Christensen-Dalsgaard Institut for Fysik og Astronomi, Aarhus Universitet Danish AsteroSeismology Centre High Altitude Observatory
Another parenthesis Note: numerical value is not great, but functional dependence is qualitatively right!
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.
OVERVIEW OF PHYSICS OF THE SOLAR INTERIOR Basic equations: Composition characterized by abundances X, Y, Z of H, He and the rest
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
Stellar birthline Palla & Stahler (1999) General stellar evolution Pre-main-sequence evolution (Iben 1965)
General stellar evolution Main sequence and beyond (Iben 1967)
Solar evolution 11 Gyr 10.5 Gyr 10 Gyr End of central hydrogen burning 9 Gyr 6 Gyr Present sun 1 Gyr
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
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.
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
The solar internal sound speed Sun - Model S
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
Neutrino results 8 B 8 B 8 B 8 B 8 B
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
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?
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
Sackmann & Boothroyd (2003; ApJ 583, 1024) Faint early Sun problem? Problems with the early climate of the Earth and Mars?? But what about helioseismology??