Marc Pinsonneault (OSU)

 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

 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!

OPACITY  Sound Speed measurements constrain the temperature gradient  dT/dr related to    related to abundance Bailey et al. 2008

 Two scalar quantities are sensitive to internal abundances:  Rcz, measures CZ base => O  Ysurf, measures core opacity => Fe

Delahaye & Pinsonneault 2006

 Basic method: Measure the acoustic glitch at the CZ base  First order: depth set by the effective temperature and surface gravity  Second order: metallicity

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

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

Standard physics Fully mixed (no diffusion) Li dip K 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 3 σ with ~10 pairs of stars with our assumed errors

 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

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

 Coupling timescales of order 100 Myr are needed to explain open cluster spindown  NOT expected from naïve theory

 Surface latitudinal differential rotation (photometry or spectroscopy) +  Rotational splitting in dwarfs =  Test of the universality of the solar convection zone profile

 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

 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

 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)