Fundamental Parameters of Stars
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Transcript of Fundamental Parameters of Stars
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
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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.
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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.
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
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)
29.05.200829.05.2008 SUSI Workshop, Univ. of SydneySUSI Workshop, Univ. of Sydney Regner TrampedachRegner Trampedach
Thanks for giving us SUSIThanks for giving us SUSI