A latitude-dependent wind model for Mira's cometary

We present a 3D numerical simulation of the recently discovered cometary structure produced as Mira travels through the galactic ISM. In our simulation, we consider that Mira ejects a steady, latitude-dependent wind, which interacts with a homogeneous, str

8

002 yaM 5 ]hp-ortsa[ 1v9450.508:0viXraAcceptedforpublicationinApJL

PreprinttypesetusingLATEXstyleemulateapjv.05/04/06

ALATITUDE-DEPENDENTWINDMODELFORMIRA’SCOMETARYHEAD

A.C.Raga1,J.Cant´o2,F.DeColle3,A.Esquivel1,P.Kajdic4,A.Rodr´ guez-Gonz´a

lez1,P.F.Vela´zquez1AcceptedforpublicationinApJL

ABSTRACT

Wepresenta3DnumericalsimulationoftherecentlydiscoveredcometarystructureproducedasMiratravelsthroughthegalacticISM.Inoursimulation,weconsiderthatMiraejectsasteady,latitude-dependentwind,whichinteractswithahomogeneous,streamingenvironment.Theaxisym-metryoftheproblemisbrokenbythelackofalignmentbetweenthedirectionoftherelativemotionoftheenvironmentandthepolaraxisofthelatitude-dependentwind.Withthismodel,weareabletoproduceacometaryheadwitha“doublebowshock”whichagreeswellwiththestructureoftheheadofMira’scomet.Wethereforeconcludethatatime-dependenceintheejectedwindisnotrequiredforreproducingtheobserveddoublebowshock.

Subjectheadings:circumstellarmatter–hydrodynamics–stars:AGBandpost-AGB–stars:indi-vidual(Mira)–ISM:jetsandout ows

1.INTRODUCTION

“doublebowshock”structureoftheheadofMira’scomet

Martinetal.(2007)http://doc.guandang.netetarystructureextendingover2 inthesky,withitsInmodellingthestructuresofplanetarynebulae(PNe),headcenteredonMira.TheseobservationswerecarrieditisquitecommontoconsiderthatthewindfromAGBoutwiththeGALEXsatellite,witha lterwithacen-starshasastrong,equatorialdensityenhancement.Suchtralwavelengthλc=1516 AandaFWHM λ=256 A.alatitude-dependentwindcanbeusedforreproducingMartinetal.(2007)speculatethatpartoftheobservedthestructuresofmanyobservedPNeandProto-PNeemissioncouldbeassociatedwiththe uorescentUV(see,e.g.,Balick&Frank2002).

linesoftheH2molecule.Also,partoftheemission(par-InthecaseofMira,wecouldalsobeseeingtheinterac-ticularlyintheheadofthecometarystructure)couldtionofalatitude-dependentwindwithanenvironmentcorrespondtoemissionfromionizedspecies(e.g.,fromwhichsweepspastthesource.Wehave,however,fewCIV)withlineswhichfallinthebandwidthofthe l-constraintsofthecharacteristicsandorientationofthister.WepresentaschematicdiagramoftheUVimageoflatitude-dependentwind.TheonlyrealobservationalMira’scometofMartinetal.(2007)inFigure1.

constraintisthattheMirabinarysystemhasanorbitalMiraisabinarysystemwithanAGBstarandalessplanethatlieswithin～30 fromthelineofsight,andatluminouscompanionwhichisprobablyawhitedwarf.anangleof130→180 (measuredEfromN),withveryThebinarysystemmovesthroughtheplaneofthegalaxyhighuncertainties(seePrieuretal.2002).Ifweassumewithaspatialvelocityof≈130kms 1,atanorienta-thatthepolaraxisofthelatitude-dependentwindliestionof≈30 withrespecttotheplaneofthesky,asperpendiculartotheorbitalplane,wewouldthenhavecanbededucedfromthepropermotion(Turonetal.toplaceitclosetotheplaneofthesky,andatanangle1993),radialvelocity(Evans1967)andHipparcos-basedof40→90 (measuredEfromN).Thisdirectionforthedistance(107pc,Knappetal.2003).Thepropermotionpolaraxis,takentogetherwiththedirectionofMira’sisdirectedatanangleof187 (measuredEfromN,seepropermotion(seeabove)impliesthatthepolaraxisofWareingetal.2007).

theout owhastolieatanangleα～33→83 withWareingetal.(2007)computeda3Dsimulation,inrespecttothedirectionofrelativemotionoftheISMwhichtheymodelthisobjectastheinteractionbetweenwhichisstreamingpastMira’swind.

anisotropicwindfromtheasymptoticgiantbranchAfterexploringalimitedsetof～10parametercom-(AGB)primarystarandastreaming,homogeneousbinations,wehavechosenamodelinwhichtheanglemedium.Theirsimulationproducesstructureswhicharebetweenthepolaraxisofthelatitude-dependentwindsimilartotheobservedcometarystructure.However,itandthedirectionofthestreamingenvironmenthasaisclearthatthepredicted owdoesnotshowthede-valueof70 ,whichisconsistentwiththeobservationstailedstructureofcondensationsobservedintheheadofdescribedabove.In§2,wedescribethechoiceofparam-Mira’scomet(seeFigure3ofMartinetal.2007).

etersforourmodel,andtheresultsfromthenumericalInthepresentpaperweexplorewhetherornotthe

time-integration.In§3,wediscusstheresults.

Electronic1address:raga@nucleares.unam.mx2.THEMODEL

Aut´Instituto2onomadeM´deexico,CienciasAp.70-543,Nucleares,UniversidadNacionalWemodelthecometarytailofMiraastheinteractionM´eInstitutodeAstronom´ a,Universidad04510D.F.,NacionalM´exicoAut´onomaofalatitude-dependentwindwithahomogeneousenvi-3xico,ronmentinrelativemotionwithrespecttoMira.ForthePlace,DublinAp.Institute70-543,04510forAdvancedD.F.,M´exico

destellarwind,weconsideradensityoftheform:4M´exico,InstitutoDublin04510de2,IrelandStudies(DIAS),31FitzwilliamD.F.,Geof´M´ sica,exico

UniversidadNacionalAut´onomadeρ(r,θ)=

A

We present a 3D numerical simulation of the recently discovered cometary structure produced as Mira travels through the galactic ISM. In our simulation, we consider that Mira ejects a steady, latitude-dependent wind, which interacts with a homogeneous, str

2Ragaetal.

Fig.1.—SchematicdiagramoftheUVimageoftheheadofMira’scomet,showingthestructuresseeninFigure3ofMartinetal.(2007).ThepropermotionofMiraisdirectedatanangleof≈7 totheWofS(NisupandEisleft),approximatelyalignedwiththelargescalestructureofthecometarytail.Therefore,whencomparingthisdiagramwiththemodelpredictions(Figures2-4),onehastoallowforthissmalldeviationfromtheverticaldirectionofMira’smotion.InthisFigure,weintroducelabelsA-Finordertoidentifythedi erentstructureswhicharediscussedinthetext.

whereristhesphericalradiusandθisthepolaran-gle(measuredoutfromthesymmetryaxisofthewind).Inthisequation,Aisascalingconstant,ξ>1istheequator-t …… 此处隐藏：13959字，全部文档内容请下载后查看。喜欢就下载吧 ……