Precision Stellar astrophysics with song

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)