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

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!

Can We Turn the Problem Around?

OPACITY Sound Speed

measurements constrain the temperature gradient

dT/dr related to k k related to

abundance Bailey et al. 2008

Sounding the Solar Abundances Two scalar

quantities are sensitive to internal abundances:

Rcz, measures opacity @ CZ base

=> O Ysurf, measures

core opacity=> Fe

Interiors-Based Abundances

Delahaye & Pinsonneault 2006

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

COMPOSITION DEPENDENCE

~ 1-3% change in the normalized acoustic depth per 0.1 dex in [Z/X] !

Y = 0.271

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 6200-6350K

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

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

Open Cluster

Spindown

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

Interesting Core/Envelope

Coupling Timescale

Coupling timescales of order 100 Myr are needed to explain open cluster spindown

NOT expected from naïve theory

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

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

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

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)