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Fundamental Parameters of Stars

Fundamental Parameters of Stars. SUSI workshop, 29.05.2008 at Univ. of Sydney Regner Trampedach, Mt. Stromlo. Which Fundamental Parameters?. Stellar structure and evolution: Mass Age Composition Stellar atmospheres: Effective temperature Surface gravity Composition.

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Fundamental Parameters of Stars

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

  2. SUSI Workshop, Univ. of Sydney Which Fundamental Parameters? Stellar structure and evolution: Mass Age Composition Stellar atmospheres: Effective temperature Surface gravity Composition

  3. SUSI Workshop, Univ. of Sydney Which ones can we measure? Mass in a few (binary) cases ...that's it! But why not? Composition and age are highly model dependent Surface gravity only weakly constrained by spectroscopy – and model dependent Teff can only be determined from R and Lbol

  4. SUSI Workshop, Univ. of Sydney Observational Fundamental Parameters • Fbol, which combined with • gives us Lbol • RUD which combined with limb-darkening gives R • M from binaries or... • 〈ϱ〉 from asteroseismology • Only age and composition are not directly observable.

  5. SUSI Workshop, Univ. of Sydney RUD + Limb Darkening = R Reduced to a scalar correction factor... Depends on model atmosphere 1D LDs might all be close – 3D is different! Procyon 1D → 3D: 1.081 → 1.064 ~1.6% ⇔Teff +50K (Prieto et al. 2002)‏ 3D 1D Procyon 3D 1D

  6. SUSI Workshop, Univ. of Sydney 3D Convection Simulations By Nordlund & Stein, also used by Asplund Rectangular box in surface => plane para. Resolution: 150x150x82 Opacity: bf- and ff-opacity from MARCS package (Gustafsson 1975). Lineopacity:Opacity distribution functions from ATLAS9 (Kurucz 1992)‏ Eq. of State:Mihalas, Hummer & Däppen (1988), MHD EOS, 15 elements

  7. SUSI Workshop, Univ. of Sydney 3D Convection Simulations By Nordlund & Stein, also used by Asplund Rectangular box in surface => plane para. Resolution: 150x150x82 Opacity: bf- and ff-opacity from MARCS package (Gustafsson 1975). Lineopacity:Opacity distribution functions from ATLAS9 (Kurucz 1992)‏ Eq. of State:Mihalas, Hummer & Däppen (1988), MHD EOS, 15 elements

  8. SUSI Workshop, Univ. of Sydney 3D vs. 1D Stratification Main effect: Expanded atmosphere by Turbulent pressure Convective fluct.s + non-linear opacity Generally smoother features in 3D Smaller range in ad in 3D Averages not connected via the EOS et al.

  9. SUSI Workshop, Univ. of Sydney What Theoreticians Need Common problem: We don't quite know what kind of star we are looking at ⇔ making it hard to discriminate btw. Models We need more stellar radii – MS stars! We need limb-darkening observations Especially around MS Teff differ btw various methods ⇔wrong stratification in our models d < 22pc, σ(R) < 3%, Hipparcos , B=200m, H band Kervella (2008)

  10. SUSI Workshop, Univ. of Sydney Thanks for giving us SUSI

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