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

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

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

Regner Trampedach SUSI Workshop, Univ. of Sydney Observational Fundamental Parameters F bol, which combined with F bol, which combined with  gives us L bol  gives us L bol R UD which combined with limb-darkening gives R R UD which combined with limb-darkening gives R M from binaries or... M from binaries or... 〈ϱ〉 from asteroseismology 〈ϱ〉 from asteroseismology Only age and composition are not directly observable.

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

Regner Trampedach 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

Regner Trampedach 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

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

Regner Trampedach 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 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 more stellar radii – MS stars! We need limb-darkening observations We need limb-darkening observations  Especially around MS  Teff differ btw various methods ⇔ wrong stratification in our models d < 22 pc, σ(R) < 3%, Hipparcos, B=200 m, H band Kervella (2008)

Regner Trampedach SUSI Workshop, Univ. of Sydney Thanks for giving us SUSI