Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National...

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Convection Convection Simulation of an Simulation of an A-star A-star By By Regner Trampedach Regner Trampedach Mt. Stromlo Observatory, Australian Mt. Stromlo Observatory, Australian National University National University 8/19/04 8/19/04
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Transcript of Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National...

Page 1: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Convection Convection Simulation of an A-Simulation of an A-

starstar

ByBy

Regner TrampedachRegner TrampedachMt. Stromlo Observatory, Australian National Mt. Stromlo Observatory, Australian National

UniversityUniversity

8/19/048/19/04

Page 2: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Hydro-dynamicsHydro-dynamics

• Solve Euler equationsSolve Euler equations• Conservation of:Conservation of:

– Mass: Mass: ddρ ρ //ddtt = -= -uu ∙∙∇∇ ρρ --ρρ ∇∇ ∙∙uu– Momentum: Momentum: ρρ dduu //ddtt = -= -ρρ uu ∙∙∇∇ uu ++∇∇ ((TT -- PPgasgas))

++ρρ gg– Energy: Energy: ddEE //ddtt = - = -∇∇ ∙∙uuEE + + ((TT -- PPgasgas))∇∇ ∙∙uu

++ρ ρ qqradrad

• Regular horizontal and optimized vertical Regular horizontal and optimized vertical gridgrid

Page 3: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Radiation DynamicsRadiation Dynamics

• Simplified by only needing forward solutionSimplified by only needing forward solution

• More expensive by factor More expensive by factor NNxx××NNyy××NNφ φ ××NNtt

• Binning the rad. transfer according to Binning the rad. transfer according to opacity => speed-up by opacity => speed-up by NNbin bin /N/Nλ λ , N, Nbinbin = 4= 4

• Binning is calibrated against 1D average Binning is calibrated against 1D average sim.sim.

• About to change to Sparse/Selective OSAbout to change to Sparse/Selective OS

• More stable + accurate and convergesMore stable + accurate and converges

Page 4: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

AssumptionsAssumptions

No rotationNo rotation

No magnetic fieldsNo magnetic fields

(Scaled) Solar abundances(Scaled) Solar abundances

Uniform gravitational fieldUniform gravitational field

No diffusionNo diffusion

No radiative levitation of individual No radiative levitation of individual speciesspecies

LTE EOS and radiationLTE EOS and radiation

Page 5: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

A few collaboratorsA few collaborators

Convection-code: Convection-code: Robert F. Stein, Michigan State Robert F. Stein, Michigan State UniversityUniversity

ÅÅke Nordlund, Copenhagen Observatoryke Nordlund, Copenhagen Observatory

Equation of State:Equation of State: Werner D Werner Dääppen, University of Southern ppen, University of Southern CaliforniaCalifornia

Radiative Transfer: Radiative Transfer: Martin Asplund, Mt. Stromlo Martin Asplund, Mt. Stromlo ObservatoryObservatory

Asteroseismology:Asteroseismology: J Jøørgen Christensen-Dalsgaard, Aarhus rgen Christensen-Dalsgaard, Aarhus Univ.Univ.

Dali Georgobiani, StanfordDali Georgobiani, Stanford

and many more...and many more...

Page 6: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

The Dynamic SunThe Dynamic Sun

Page 7: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Vertical Temperature cut ofVertical Temperature cut ofηη --BooBoo

Page 8: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Solar Line CalculationSolar Line Calculation

• Abundance analysisAbundance analysis– Agreement between FeI, FeII and Agreement between FeI, FeII and

meteoriticmeteoritic– Lower C, N and O abundances – at odds Lower C, N and O abundances – at odds

with helioseismologywith helioseismology

• Synthetic spectra/line-profilesSynthetic spectra/line-profiles– No free parameters, e.g., micro-/macro-No free parameters, e.g., micro-/macro-

turb.turb.– Agree both in shape (bisectors) and shiftsAgree both in shape (bisectors) and shifts

Page 9: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

The A-star simulationThe A-star simulation

• 73007300 K, logK, loggg=4.3, [Fe/H] = 0.0=4.3, [Fe/H] = 0.0

• 100100××100100××82 grid-points82 grid-points

• 11.4511.45×11.45×13.10×11.45×13.10 MmMm

• About 5 pressure scale-heightsAbout 5 pressure scale-heights

• 5.6 and 6.4 decades of pressure and 5.6 and 6.4 decades of pressure and densitydensity

• 19 mins. with 5019 mins. with 50 s resolutions resolution

• p-modes with p-modes with Π Π ==1212 mins., A=1.5mins., A=1.5 km/skm/s

Page 10: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

3D-1D(3D-1D(αα =1)=1)• >>ρρ -inversion-inversion

• > > TT-gradient-gradient

• More structure More structure in photospherein photosphere

• < < uu and and PPturbturb

• Seperate conv. Seperate conv. ZonesZones

• Diff. internal Diff. internal structurestructure

Page 11: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

3D-1D(3D-1D(αα =2)=2)• LargerρLargerρ , ,TT• > > TT-gradient-gradient

• More structure More structure in photospherein photosphere

• > > PPturbturb-peak-peak

• No overshootNo overshoot

• Very Different Very Different internal struct.internal struct.

Page 12: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

A vertical cut in the A-star A vertical cut in the A-star simulationsimulation

T: 1700 – 72500T: 1700 – 72500 K logK logρρ : -6.2 - 0.4 : -6.2 - 0.4

Convective

Page 13: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

A Local Temperature InversionA Local Temperature Inversion

T: 1700 – 72500T: 1700 – 72500 K logK logρρ : -6.2 - 0.4 : -6.2 - 0.4

Convective

Page 14: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

TT-inversion-inversion

• Up to 10Up to 10 000000

KK

• Factor 10 Factor 10 density density invers.invers.

• Related to Related to ionization?ionization?

Page 15: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

SummarySummary

• Have changed lower boundary to Have changed lower boundary to accomodate radiative zoneaccomodate radiative zone

• Have included optically thick Have included optically thick radiative transferradiative transfer

• Have started running aHave started running a simulation on simulation on the border between A and Fthe border between A and F

Page 16: Convection Simulation of an A-star By Regner Trampedach Mt. Stromlo Observatory, Australian National University 8/19/04.

Prospects for the FutureProspects for the Future• Calculate new and improved EOS-tablesCalculate new and improved EOS-tables

• Use it as basis for new opacity calculation Use it as basis for new opacity calculation using the newest cross-section datausing the newest cross-section data

• Implement an improved radiative transfer Implement an improved radiative transfer scheme in the convection simulationsscheme in the convection simulations

• Build a Build a gridgrid of convection models, using of convection models, using the new EOS, opacities and rad. Transferthe new EOS, opacities and rad. Transfer

• Expanding coverage in (Expanding coverage in (TTeffeff, , gg, , ZZ ))