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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?