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Precision Stellar astrophysics with song

Precision Stellar astrophysics with song. Marc Pinsonneault (OSU). Precision Stellar Astrophysics. New Era in Astronomy Seismology Large Surveys We can now measure things which have been assumed in stellar modeling Three specific examples: Helium Absolute metallicity Internal rotation.

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Precision Stellar astrophysics with song

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  1. Precision Stellar astrophysics with song Marc Pinsonneault (OSU)

  2. Precision Stellar Astrophysics • New Era in Astronomy • Seismology • Large Surveys • We can now measure things which have been assumed in stellar modeling • Three specific examples: • Helium • Absolute metallicity • Internal rotation

  3. Absolute Metallicity • Crucial for chemical evolution • Limiting factor in near-field cosmology, stellar ages from Gaia… • Atmospheres models have complex systematic errors; lack calibrators • Interiors models have simpler physics….independent composition tests!

  4. OPACITY Sound Speed measurements constrain the temperature gradient dT/dr related to k k related to abundance Can We Turn the Problem Around? Bailey et al. 2008

  5. Sounding the Solar Abundances • Two scalar quantities are sensitive to internal abundances: • Rcz, measures opacity @ CZ base => O • Ysurf, measures core opacity => Fe

  6. Interiors-Based Abundances Delahaye & Pinsonneault 2006

  7. Absolute Abundances in Stars • Basic method: Measure the acoustic glitch at the CZ base • First order: depth set by the effective temperature and surface gravity • Second order: metallicity

  8. COMPOSITION DEPENDENCE Van Saders & Pinsonneault 2011 deep CZ Y = 0.271 shallow CZ ~ 1-3% change in the normalized acoustic depth per 0.1 dex in [Z/X] !

  9. HOW WELL CAN WE MEASURE COMPOSITION? -Can measure absolute [Z/X] to within 0.2 – 0.3 dex -More sensitive to composition in mean density space

  10. Standard physics Li dip 6200-6350K Fully mixed (no diffusion) WHAT CAN WE LEARN ABOUT THE PHYSICS? If we believe the photospheric abundances and other observationally derived quantities . . . Example: Rotational mixing and the Li dip: Detectable at 3σ with ~10 pairs of stars with our assumed errors

  11. Internal Rotation • Rotation can have a major impact on stellar structure and evolution • Mixing • Structural effects • Internal angular momentum transport is a difficult, and currently unresolved, problem • Magnetic fields • Waves • Hydrodynamic mechanisms

  12. Open Cluster Spindown Rapid rotators, high mass: Solid Body spin down Slow rotators, high mass: Solid Body models FAIL IMPLICATION: Transient differential rotation with radius in stars with shallower surface convection zones Rapid AND slow rotators, Low Mass: Solid Body Spin Down Denissenkov et al. 2010

  13. Interesting Core/Envelope Coupling Timescale • Coupling timescales of order 100 Myr are needed to explain open cluster spindown • NOT expected from naïve theory

  14. Convection Zone Rotation: Testing the Dynamo • Surface latitudinal differential rotation (photometry or spectroscopy) + • Rotational splitting in dwarfs = • Test of the universality of the solar convection zone profile

  15. Core Rotation in Subgiants • Mixed models permit the detection of core rotation in evolved stars • Strong structural evolution in subgiants: • Core contraction, envelope expansion • Relatively shallow surface CZ => g modes sample the radiative core • Sensitive measure of the transport timescale in radiative interiors

  16. Core Rotation in Giants • Red giants have deep surface convection zones • Different rotation profiles in the convection zone predict radically different core rotation rates • Rapid rotation predicted from detected rates in core He-burning stars (Pinsonneault et al. 1992) • g-mode rotation rates can therefore test differential rotation in convection zones • Rotation dependence • Dynamo theory in a slowly rotating domain

  17. The Role of SONG • Modest sample sizes => strongest role will be designing experiments to attack specific problems • Search for science complementary to Kepler: • Sensitivity (lower MS) • Geography (different galactic lines of sight) • Additional constraints (clusters, binaries, interferometric radii)

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