Convection Simulation of an A-star

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Convection Simulation of an A-star

• By
• Regner Trampedach
• Mt. Stromlo Observatory, Australian National
  University
• 8/19/04

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Hydro-dynamics

• Solve Euler equations
• Conservation of
• Mass d? /dt -u ? ? -? ? u
• Momentum ? du /dt -? u ? u ? (T - Pgas) ?
  g
• Energy dE /dt -? uE (T - Pgas)?
  u ? qrad
• Regular horizontal and optimized vertical grid

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Radiation Dynamics

• Simplified by only needing forward solution
• More expensive by factor NxNyNf Nt
• Binning the rad. transfer according to opacity gt
  speed-up by Nbin /N? , Nbin 4
• Binning is calibrated against 1D average sim.
• About to change to Sparse/Selective OS
• More stable accurate and converges

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Assumptions

• No rotation
• No magnetic fields
• (Scaled) Solar abundances
• Uniform gravitational field
• No diffusion
• No radiative levitation of individual species
• LTE EOS and radiation

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A few collaborators

• Convection-code Robert F. Stein, Michigan State
  University
• Åke
  Nordlund, Copenhagen Observatory
• Equation of State Werner Däppen, University of
  Southern California
• Radiative Transfer Martin Asplund, Mt. Stromlo
  Observatory
• Asteroseismology Jørgen Christensen-Dalsgaard,
  Aarhus Univ.
• Dali
  Georgobiani, Stanford
• and many more...

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The Dynamic Sun
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Vertical Temperature cut of? -Boo
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Solar Line Calculation

• Abundance analysis
• Agreement between FeI, FeII and meteoritic
• Lower C, N and O abundances at odds with
  helioseismology
• Synthetic spectra/line-profiles
• No free parameters, e.g., micro-/macro-turb.
• Agree both in shape (bisectors) and shifts

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The A-star simulation

• 7300 K, logg4.3, Fe/H 0.0
• 10010082 grid-points
• 11.4511.4513.10 Mm
• About 5 pressure scale-heights
• 5.6 and 6.4 decades of pressure and density
• 19 mins. with 50 s resolution
• p-modes with ? 12 mins., A1.5 km/s

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3D-1D(a 1)

• gt? -inversion
• gt T-gradient
• More structure in photosphere
• lt u and Pturb
• Seperate conv. Zones
• Diff. internal structure

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3D-1D(a 2)

• Larger? ,T
• gt T-gradient
• More structure in photosphere
• gt Pturb-peak
• No overshoot
• Very Different internal struct.

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T-inversion

• Up to 10 000 K
• Factor 10 density invers.
• Related to ionization?

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Summary

• Have changed lower boundary to accomodate
  radiative zone
• Have included optically thick radiative transfer
• Have started running a simulation on the border
  between A and F

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Prospects for the Future

• Calculate new and improved EOS-tables
• Use it as basis for new opacity calculation using
  the newest cross-section data
• Implement an improved radiative transfer scheme
  in the convection simulations
• Build a grid of convection models, using the new
  EOS, opacities and rad. Transfer
• Expanding coverage in (Teff, g, Z )