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An Iterative Phase-Space Explicit Discontinuous Galerkin Method for Stellar Radiative Transfer in Extended Atmospheres

by Valmor F De Almeida
Publication Type
Journal
Journal Name
Journal of quantitative spectroscopy and radiative transfer
Publication Date
Page Numbers
254 to 269
Volume
196

A phase-spacediscontinuousGalerkin(PSDG)methodispresentedforthesolutionofstellarradiative
transfer problems.Itallowsforgreateradaptivitythancompetingmethodswithoutsacrificing generality.
The methodisextensivelytestedonasphericallysymmetric,static,inverse-power-lawscatteringat-
mosphere. Resultsfordifferentsizesofatmospheresandintensitiesofscatteringagreedwithasymptotic
values.Theexponentiallydecayingbehavioroftheradiative field inthediffusive-transparenttransition
region, andtheforwardpeakingbehavioratthesurfaceofextendedatmosphereswereaccurately
captured.Theintegrodifferentialequationofradiationtransferissolvediterativelybyalternatingbe-
tween theradiativepressureequationandtheoriginalequationwiththeintegraltermtreatedasan
energy densitysourceterm.Ineachiteration,theequationsaresolvedviaanexplicit, flux-conserving,
discontinuous Galerkinmethod.Finiteelementsareorderedinwavefrontsperpendiculartothechar-
acteristic curvessothatelementallinearalgebraicsystemsaresolvedquicklybysweepingthephase
space elementbyelement.Twoimplementationsofadiffusiveboundaryconditionattheoriginare
demonstratedwhereinthe finite discontinuityintheradiationintensityisaccuratelycapturedbythe
proposed method.Thisallowsforaconsistentmechanismtopreservephotonluminosity.Themethod
wasprovedtoberobustandfast,andacaseismadefortheadequacyofparallelprocessing.Inaddition
to classicaltwo-dimensionalplots,resultsofnormalizedradiationintensityweremappedontoalog-
polar surfaceexhibitingalldistinguishingfeaturesoftheproblemstudied.