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The Standard Solar Model and Its Evolution

The Standard Solar Model and Its Evolution. Marc Pinsonneault Ohio State University. Collaborators: Larry Capuder Scott Gaudi. Summary. The Sun is predicted to become brighter as it ages for fundamental stellar structure reasons

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The Standard Solar Model and Its Evolution

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  1. The Standard Solar Modeland Its Evolution Marc Pinsonneault Ohio State University Collaborators: Larry Capuder Scott Gaudi

  2. Summary • The Sun is predicted to become brighter as it ages for fundamental stellar structure reasons • This luminosity evolution is extremely insensitive to assumptions about the input physics, except mass loss… • …and the rotation of the Sun, and by extension mass loss, was very similar to the current values for the last 4 Gyr

  3. Standard Solar Model • Initial Conditions: Mass, Composition, Evolutionary State • Equations of Stellar Structure • Conservation Laws • The Solar Calibration • Reproduce current solar properties, adjust model uncertainties

  4. In the Beginning… • There are interesting problems around the formation of the Sun • Rotation: • Hydrodynamic assembly phase • Protostar-disk interaction • Mixing and Light Element Depletion • However, subsequent solar evolution is insensitive to the initial conditions (Vogt-Russell theorem)

  5. Standard Model Assumptions and Ingredients • Equation of State: OPAL; close to ideal gas • Energy Generation: Adelberger et al. 2010; primarily pp • Opacities: OP or OPAL; radiative core • Convection Theory: MLT; convective envelope • Gravitational settling included • Rotation, rotational mixing, mass loss not included

  6. Standard Luminosity Evolution • Early transient phase (~30 Myr) when the Sun contracts and heats up • Steady core H burning phase where the Sun steadily brightens

  7. Why does the Sun brighten as it ages? • Pressure gradient balances gravity • Sun remains hot through H fusion • 4 1H => 1 4He has a necessary implication: • 8 particles -> 3 particles • To balance gravity fewer particles must move faster and the density must rise • These factors drive higher energy generation rates and luminosities in stars

  8. Hotter More Luminous

  9. Structural and Luminosity Changes Bahcall, Pinsonneault & Basu 2001

  10. What Tools Do We Have to Test the Sun? • Current Solar Properties: M, L, age, composition, solar wind… • Neutrinos • Helioseismology • Sound speed profile • Core helium profile • Scalar constraints: convection zone depth, surface helium

  11. GoodAgreement! • Solar neutrinos • Helioseismology implies a high O abundance • Disagreement with some recent models claiming a lower solar O, but only at ~ 2 s • Sound speed agreement to 0.1 – 1% in any case

  12. How Reliable is Solar Evolution? • Vary input ingredients within error ranges • Vary sources of input physics (opacities, equation of state, heavy element mixture) to test systematic errors

  13. Net Result: Almost a Perfect Invariant! Solar L(t) is within 0.5% or better at all points during MS evolution

  14. What About Mass Loss? • Any change to solar evolution would require a drastic alteration… • The current solar mass loss rate ~1.3 x 1012 g/s is far too small to impact evolution • What properties of the ancient Sun could have been very different? • Look at rotation

  15. Young Stars Can Be Rapid Rotators Denissenkov, Pinsonneault & Terndrup 2010

  16. Link With Mass Loss • More rapid rotation is linked with higher coronal X-ray luminosities and mass loss rates (Wood et al. 2005) • dM/dt ~ Lx • Lx measures coronal heating, and is observed to up to 1000x larger than solar for young stars • Higher past mass loss is reasonable

  17. Lx is a strong function of mass and rotation rate Rossby number Rotation Period Pizzolato et al. 2003

  18. Angular Momentum Evolution • Protostellar initial state • Star-disk coupling • Core-envelope coupling Epstein & Pinsonneault 2012 Denissenkov, Pinsonneault & Terndrup 2010

  19. Simple Extension of the Standard Model with Mass Loss • Evolve assuming…. • dM/dt = (w/wsun)^a *(dM/dt)sun • w evolution from standard assumptions • Observed saturation in X-ray flux

  20. Solar Evolution With Mass Loss • Some Early Changes Possible • However…. • Rapid spin down • Solar wind rapidly converges • to present-day value

  21. What About More Severe Mass Loss? • Basic issue: • Enhanced solar mass loss is most naturally driven by more rapid rotation in the younger Sun • Solar analogs are observed to reach a few times solar rotation in a few hundred Myr • Implies mass loss rates of order 10x solar or less for 90% of the solar age Sackmann & Boothroyd 2003

  22. Tests and Future Directions • Important tests of rotational history from Kepler and CoRoT will be arriving soon • Crucial check on old field stars • Experimental tests of solar interiors physics • Improved Wind Models

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