Extra Mixing and Isotope Ratios in AGB stars

Physics Under the Bonnet of a STELLAR Evolution CodeRichard J. StancliffeArgelander Institut fr Astronomie, Universitt Bonn

M, X, Z

Macrophysics:Stellar structureChemical mixingConvectionMass lossMicrophysics:Reaction ratesOpacitiesEquation of stateMachinery:Solution methodResolutionStellar Structure equations

Chemical evolution equations

Xi+ mixingMachinery IDivide star into mesh points

Differential equations become difference equationsSee Meynet, Maeder, Mowlavi (2004)Information not always available where you want it!

Choices have to be made not always obvious whats correctrk, mk, Lkrk+1, mk+1, Lk+1rk-1, mk-1, Lk-1Xk, Tk, kXk+1, Tk+1, k+1Xk-1, Tk-1, k-1MACHINERY IISolve all equations together (simultaneous) or do some then others (non-simultaneous)?Stancliffe (2006)

Have to get time and space resolution correct!

And then it all has to converge

Lattanzio et al. (2015)CONVECTIONImportant for two things:Energy transportMixing of material

Nearly always mixing length theoryNeeds calibration!

Where do convective boundaries go Schwarzchild vs. Ledoux?

Magic et al. (2015)CONVECTIVE OVERSHOOTINGMost common form of extra mixing

Parameterisation of our ignorance of convective boundaries

Excellent review of physics by Viallet et al. (2015)

Needs calibration and it might not be the same for all phases!

Stancliffe et al. (2015)Overshooting not overshooting just a way of making cores bigger9

STARSMESAStancliffe et al. (2015)Seismic calibration?KIC 10526294

Slowly pulsating B star (Papics et al. 2014)

g-modes probe stellar interior

Moravveji et al. (2015) determine f = 0.017Based on MESA + GYRE calculations

Moravveji et al. (2015)Core helium burningOvershooting may not be the same at all evolutionary phases

Core He burning has long been a problematic phase for stellar evolution

Seismology suggests that cores may be larger than models currently predict

Constantino et al. (2015)OTHER PHYSICSGravitational settling

Rotation

Magnetic fields

(Binaries)Input physicsEquation of state

Reaction ratesNACREREACLIB

Opacities (Warrick Ball Fri.)OPALType I or Type IIOPSounds simple, right?

Stancliffe et al., submitted

CalibrationStellar models still calibrated on one thing: the SUN

But which Sun?

And what parameters are included in the calibration?

And what physics do you include?

Asplund 09Grevesse & Sauval 98

WARNINGS!Are your tracks properly calibrated?

Are you using the correct metallicity?With an appropriate opacity table?

Dont forget the uncertainty compare different codes where possible!

Beyond the main sequenceMore problems occur beyond the main sequence

Effective temperature of giant branch depends on boundary conditions

May be uncertain to 100K

See also: VandenBerg et al. (2008), Salaris & Cassisi (2015)

Dotter et al. (2007)ConclusionsDont treat stellar codes like black boxes!

Perform resolution tests

How calibrations are done is importantWhere are they valid?

Seismology to help with free parameters?