Fundamental Parameters of Stars SUSI workshop, 29.05.2008 at Univ. of Sydney Regner Trampedach, Mt. Stromlo

Fundamental Parameters of Fundamental Parameters of StarsStars

SUSI workshop, 29.05.2008 at Univ. of SydneySUSI workshop, 29.05.2008 at Univ. of Sydney

Regner Trampedach, Mt. StromloRegner Trampedach, Mt. Stromlo

29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach

Which Fundamental Which Fundamental Parameters?Parameters?

Stellar structure and evolution:Stellar structure and evolution: MassMass AgeAge CompositionComposition

Stellar atmospheres:Stellar atmospheres: Effective temperatureEffective temperature Surface gravitySurface gravity CompositionComposition


Which ones can we measure?Which ones can we measure?

Mass in a few (binary) casesMass in a few (binary) cases ...that's it!...that's it!

But why not?But why not? Composition and age are highly model Composition and age are highly model

dependentdependent Surface gravity only weakly constrained by Surface gravity only weakly constrained by

spectroscopy – and model dependentspectroscopy – and model dependent TTeffeff can only be determined from can only be determined from RR and and LLbolbol


Observational Fundamental Observational Fundamental ParametersParameters

FFbolbol, which combined with, which combined with

gives us gives us LLbolbol

RRUDUD which combined with limb-darkening which combined with limb-darkening gives gives RR

MM from binaries or... from binaries or... ⟨⟨ϱ⟩ϱ⟩ from asteroseismology from asteroseismology

Only age and composition are not directly Only age and composition are not directly observable.observable.


RRUDUD + Limb Darkening = + Limb Darkening = RR Reduced to a scalar Reduced to a scalar

correction factor...correction factor... Depends on model Depends on model

atmosphereatmosphere 1D LDs might all be 1D LDs might all be

close – 3D is different!close – 3D is different! Procyon 1D Procyon 1D →→ 3D: 3D:

1.081 1.081 →→ 1.064 ~1.6% 1.064 ~1.6% ⇔⇔ TTeffeff +50 +50 K K (Prieto et al. 2002)(Prieto et al. 2002)

3D

1D

Procyon

3D

1D


3D Convection Simulations3D Convection Simulations

By Nordlund & Stein, also used by AsplundBy Nordlund & Stein, also used by Asplund

Rectangular box in surface => plane para.Rectangular box in surface => plane para.

Resolution: 150x150x82Resolution: 150x150x82

Opacity: bf- and ff-opacity from MARCS Opacity: bf- and ff-opacity from MARCS package (Gustafsson 1975). package (Gustafsson 1975).

Lineopacity:Opacity distribution functions Lineopacity:Opacity distribution functions from ATLAS9 (Kurucz 1992) from ATLAS9 (Kurucz 1992)

Eq. of State:Mihalas, Hummer & DEq. of State:Mihalas, Hummer & Dääppen ppen (1988), MHD EOS, 15 elements (1988), MHD EOS, 15 elements


3D Convection Simulations3D Convection Simulations

By Nordlund & Stein, also used by AsplundBy Nordlund & Stein, also used by Asplund

Rectangular box in surface => plane para.Rectangular box in surface => plane para.

Resolution: 150x150x82Resolution: 150x150x82

Opacity: bf- and ff-opacity from MARCS Opacity: bf- and ff-opacity from MARCS package (Gustafsson 1975). package (Gustafsson 1975).

Lineopacity:Opacity distribution functions Lineopacity:Opacity distribution functions from ATLAS9 (Kurucz 1992) from ATLAS9 (Kurucz 1992)

Eq. of State:Mihalas, Hummer & DEq. of State:Mihalas, Hummer & Dääppen ppen (1988), MHD EOS, 15 elements (1988), MHD EOS, 15 elements


3D vs. 1D Stratification3D vs. 1D Stratification

Main effect: Expanded atmosphere byMain effect: Expanded atmosphere by

Turbulent pressureTurbulent pressure

Convective fluct.s + non-linear opacityConvective fluct.s + non-linear opacity Generally smoother features in 3DGenerally smoother features in 3D Smaller range in ad in 3DSmaller range in ad in 3D Averages not connected via the EOS Averages not connected via the EOS et al.et al.


What Theoreticians NeedWhat Theoreticians Need

Common problem: We don't quite know Common problem: We don't quite know

what kind of star we are looking at what kind of star we are looking at ⇔⇔ making it hard to discriminate btw. Modelsmaking it hard to discriminate btw. Models

We need more stellar radii – MS stars!We need more stellar radii – MS stars! We need limb-darkening observationsWe need limb-darkening observations

Especially around MSEspecially around MS

Teff differ btw various methods Teff differ btw various methods ⇔⇔ wrong stratification in our modelswrong stratification in our modelsd < 22 pc, σ(R) < 3%, Hipparcos , B=200 m, H band

Kervella (2008)


Thanks for giving us SUSIThanks for giving us SUSI

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Fundamental Parameters of Stars SUSI workshop, 29.05.2008 at Univ. of Sydney Regner Trampedach, Mt. Stromlo