Stellar atmosphere and spectrum modelling

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Stellar atmosphere and spectrum modelling

• Ian Short
• Department of Astronomy and Physics
• and
• Institute for Computational Astrophysics (ICA)
• Saint Marys University

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Stellar atmosphere
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What we can learn

• Stellar parameters
• Effective temperature,Teff
• Surface gravity, g
• ? Luminosity (Lbol), Mass (M), Radius (R)
• Type of star
• Place in Hertzsprung-Russell Diagram

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Hertzsprung-Russell diagram
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What we can learn

• Chemical composition
• Atmospheric structure
• Classically 1D T(z), P(z),
• Frontier 2D, 3D T(x,y,z), P(x,y,z),

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What we can learn

• Exotic physical processes
• Gas motions
• Winds, large-scale currents, turbulence
• Magnetic fields
• Chemical peculiarities, magneto-hydrodynamic
  (MHD) phenomena

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Solar flux spectrumNeckel Labs (1981), Labs et
al. (1987)
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Periodic table of chemical elements
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Computational Modeling
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Computational atmospheric model
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Solar flux spectrumNeckel Labs (1981), Labs et
al. (1987)
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Chemical composition
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Chemical compositionGalaxy formation,
evolutionEg. extremely metal poor (XMP) stars
(Fe/H lt -4)
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Exotic physicsEg. Chromospheric emission and
heating in cool stars
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Horizontal inhomogeneityAsplund, M., et al.,
2005, AA, 431, 693, etc.
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Horizontally homogeneous model
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(No Transcript)
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Non-local thermodynamic equilibrium (Non-LTE)
Statistical equilibrium (SE)
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The Iron curtainFe I 494 levels, 6903 lines
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The Iron curtainFe II 617 levels, 13675 lines
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Pluto _at_ SMUFunding CRC, CFI, NSRIT, SMU
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Stars of interestBrown dwarfs (BDs), Extremely
metal poor (XMP) stars, Sun,