Modelling the circumstellar medium in RS Ophiuchi and its link to Type Ia supernovae

1.2 MB·

by  Richard A. Booth

Mon.Not.R.Astron.Soc.000,1–15(2015) Printed13January2016 (MNLATEXstylefilev2.2)
Modelling the circumstellar medium in RS Ophiuchi and its link to
Type Ia supernovae
R. A. Booth,1,2∗ S. Mohamed3 and Ph. Podsiadlowski2
1InstituteofAstronomy,UniversityofCambridge,MadingleyRoadCambridge,CB30HA,UK
2DepartmentofAstrophysics,UniversityofOxford,KebleRoad,OxfordOX13RH,UK
3SouthAfricanAstronomicalObservatory,POBox9,Observatory7935,CapeTown,WesternCape,SouthAfrica
6
1
0 13January2016
2

n
a ABSTRACT
J Recent interpretations of narrow, variable absorption lines detected in some Type Ia super-

1 novaesuggestthattheirprogenitorsaresurroundedbydense,circumstellarmaterial.Similar
1 variations detected in the symbiotic recurrent nova system RS Oph, which undergoesther-
monuclear outbursts every 20 years, making it an ideal candidate to investigate the origin

] of these lines. To this end, we present simulations of multiple mass transfer-novacycles in
E
RS Oph.We findthatthe quiescentmasstransfer producesa dense, equatorialoutflow,i.e.,
H
concentratedtowardsthe binaryorbitalplane,andanaccretiondisc formsaroundthe white
. dwarf.Theinteractionofasphericalnovaoutburstwiththeseasphericalcircumstellarstruc-
h
p turesproducesabipolaroutflow,similartothatseeninHSTimagingofthe2006outburst.In
- ordertoproduceanionizationstructurethatisconsistentwithobservations,amass-lossrate
o of 5×10−7M⊙yr−1 from the red giant is required.The simulations also producea polar
r
accretionflow,whichmayexplainthebroadwingsofthequiescentH lineandhardX-rays.
t
s Bycomparingsimulatedabsorptionlineprofilestoobservationsofthe2006outburst,weare
a
abletodeterminewhichcomponentsariseinthewindandwhichareduetothenovae.Weex-
[
plorethepossiblebehaviourofabsorptionlineprofilesastheymayappearshouldasupernova

1 occurinasystemlikeRSOph.OurmodelsshowsimilaritiestosupernovaelikeSN2006X,
v butrequireahighmass-lossrate,M˙ ∼ 10−6 to10−5M yr−1,toexplainthevariabilityin
5 ⊙
SN2006X.
3
6 Keywords: binaries:symbiotic–circumstellarmatter–stars:individual(RSOph)–stars:
2 winds,outflows–stars:novae,cataclysmicvariables–supernovae.
0
.
1
0
6
1 INTRODUCTION is close to the Chandrasekhar mass (Yaronetal. 2005). Com-
1
bined with the fact that the white dwarf mass may be increasing
: RSOphiuchi (RSOph) isasymbioticrecurrent nova; thesystem
v (Hachisu,Kato&Luna 2007; Hernanz&Jose´ 2008), this makes
Xi consists of a red giant and a white-dwarf companion that under- RSOphanidealcandidateTypeIasupernovaprogenitor.
goes nova outbursts approximately every 20 years. The most re-
r centoutburstwasin2006, inwhichasustainedmulti-wavelength A further possible connection between RS Oph and Type Ia
a
campaign resulted in improved estimates of the explosion pa- supernovae (SNeIa) isthedetection of narrow, time-variable ab-
rameters and geometry. Resolved VLBI and HST images con- sorptionlines,whichmayberelatedtothepresenceof acircum-
firmedtheasphericalnatureofthenovashell(O’Brienetal.2006; stellarmediumaroundthesupernovaprogenitor.Time-variableab-
Bodeetal. 2007; Rupen,Mioduszewski&Sokoloski 2008), and sorption lines were first detected in the Type Ia supernova SN
early X-ray emission from the outburst showed evidence of in- 2006X (Patatetal. 2007), in which the NaI D lines were first
teraction between the nova and a dense circumstellar medium observed to strengthen around maximum light, and then weaken
(CSM) (Sokoloskietal. 2006; Vaytetetal. 2011). The outburst by 60 days after the explosion. This behaviour was suggested to
was characterised by low ejecta mass, Mej ∼ 10−7 to originate in surrounding nova shells, which first recombine and
10−6 M⊙ (Sokoloskietal.2006),andhighejectavelocity,vej ∼ subsequently are swept up by the supernova. The RS Oph – su-
4000kms−1(Das,Banerjee&Ashok2006;Anupama2008).The pernova connection is further supported by the 2006 outburst of
ejecta mass and velocity estimates, together with the fast decline RS Oph, in which similar behaviours were seen in the NaI D
of the nova (Hounselletal. 2010), indicate that the white dwarf and CaII H & K lines (Patatetal. 2011). Time-variable absorp-
tionhassincebeendetectedinseveralother SNeIa(Simonetal.
2009; Blondinetal. 2009; Stritzingeretal. 2010) and statistical
∗ E-mail:[email protected] studies suggest that 20 to 25 per cent of SNe Ia may have pre-
(cid:13)c 2015RAS
2 Booth,Mohamed& Podsiadlowski
supernova outflows (Sternbergetal. 2011; Maguireetal. 2013). ing (Mohamed 2010; Mohamed,Mackey&Langer 2012). For
Theoriginof theselineshasbeen thesubject of arange of theo- temperatures above 104K, the NEI [Fe/H] = −0.5 cooling
reticalstudies,fromredgiant windsandrecurrentnovae (Chugai curves from Sutherland&Dopita (1993) were used. Following
2008; Moore&Bildsten 2012) totidal tailsejected from double- Mohamed,Mackey&Langer(2012),fine-structureandmolecular
degeneratesystems(Raskin&Kasen2013)orevennovaeinHe+ coolingprocessesincludingH ,COandH Owereusedattemper-
2 2
COsystems(Shen,Guillochon&Foley2013). aturesbelow104K.
Spectroscopic measurements of the velocities of both stars For the binary parameters, we assumed the values derived
has enabled an accurate determination of the orbital period, from the spectroscopic orbit for RS Oph (Brandietal. 2009) in
453.6 days, mass ratio, q = 0.6 and an eccentricity, e = 0 whichthebinaryorbitalperiodwas453.6days.Theinternalstruc-
(Dobrzycka&Kenyon 1994; Shoreetal. 1996; Fekeletal. 2000; tures of the white dwarf and red giant were not modelled in de-
Brandietal. 2009). Combined with the estimate for the white- tail,insteadtheirgravitywastreatedassumingpointpotentialswith
dwarfmass,thisallowsanaccuratedeterminationofthered-giant massesof1.38M⊙and0.8M⊙,respectively.Themasslossfrom
(RG)mass,MRG ≈0.8M⊙,inclination,i≈50◦andseparation, thered giant was modelled by injecting the particles closeto the
a ≈ 1.48AU. Measurements of the rotation period of the giant surfacetogiveamass-lossrateofapproximately10−7M⊙yr−1.
suggest that the giant is close to fillingitsRoche lobe unless the Theparticles were injected with alow velocity, v = 20kms−1,
redgiantissuper-synchronous,i.e.therotationperiodofthegiant much less than the escape speed of the RG, vesc ≈ 55kms−1.
is less than that of the binary (Zamanovetal. 2007; Brandietal. While this is sufficient to lift the material beyond the red giant’s
2009).SuchtightconstraintsonthephysicalparametersmakeRS Rochelobe,thematerialremainsboundtothebinary.Theescape
OphanidealcandidatefortestingtherecurrentnovamodelofSNe velocityisfinallyachievedviacontinuedtidalaccelerationofcir-
Ia. cumbinarymaterialbythebinary.
Observations provide a number of constraints on the CSM Since our simulations are aimed at studying the large scale
in RS Oph. Direct estimates of the quiescent mass-loss rates are structureofthecircumstellarenvironmentofrecurrentnovae,itis
somewhatuncertain,varyingfrombetweenM˙ ≈10−8 M⊙yr−1, notfeasibletoalsosimulateindetailtheflowstructureclosetothe
as estimated by dust emission (Evansetal. 2007), to M˙ ≈ whitedwarfduetotheverydifferenttime-scalesinvolved(tensto
10−6 M⊙yr−1 from NaI D absorption lines during the 2006 hundredsofyearsforthenovaeandhourstodaysfortheflowac-
outburst (Iijima 2008). The NaI D lines provide a measure of cretingontothewhitedwarf).Forthisreasonweuseasimplepre-
the wind velocity, from which Iijima (2008) obtained a velocity scriptiontotreataccretionontothewhitedwarf,anddonotinclude
of 33kms−1. High-resolution spectroscopy shows a range blue- any explicit mass-lossfromthe whitedwarf or itsaccretion disc,
shifted(out-flowing)componentsfrom10to37kms−1.Whilethe andtreat thewhitedwarf asasink. FollowingTheuns&Jorissen
slower components were weaker after the nova, the fastest com- (1993)andMohamed&Podsiadlowski (2012),themassofparti-
ponentsstrengthened(Patatetal.2011).Thecomplexstructureof cleswithinh˜ofthewhitedwarfisdecreasedbyafactor(r/h˜)2in
thewindisfurther demonstrated by thepresence at allepochs of eachtime-step,whereh˜istheaveragesmoothinglengthofparticles
ared-shifted(in-flowing)absorptioncomponentwithavelocityof within0.1auofthewhitedwarf.Particlesareremovedoncetheir
v.20kms−1. massdropsbelowonepercentoftheirinitialmass.Thiseffectively
Understanding how and where the absorption lines form in ensuresnopressurebuildupinthesinkregion.
theCSMiskeytounderstanding whether recurrent novae arere- Whilethisundoubtedlyaffectsthestructureoftheflowclose
sponsible for the origin of the lines in SN Ia. Simulations have tothewhitedwarf,wehavefound thatitmakesverylittlediffer-
already shown strong asymmetry in the mass loss from binary encetothelargescalestructureofthewind(exceptingthecooling
systems (Theuns&Jorissen 1993; Mastrodemos&Morris 1998; andtemperatureofthewind,discussedbelow).Despitetheuncer-
Mohamed&Podsiadlowski 2007; Walder,Folini&Shore 2008), taintiesassociatedwithourtreatment,theflowclosetothebinary
whichneedstobetakenintoaccountinrecurrentnovamodelsand hassomeinterestingfeaturesthatmaybeabletoexplainanumber
theirrelationtoSNeIa. of interesting observational properties of RS Oph. Therefore, we
In section 2 we present simulations of mass transfer in RS taketheapproachofdescribingthesefeatures,alongwiththeap-
Oph. We include multiple novae and build a model of the CSM propriatecaveatsandfurtherpossibleevidenceforthesefeatures.
around RS Oph. Using photoionization calculations we constrain The circumstellar wind structure formed after 13 orbits is
thequiescentmass-lossrateinRSOph.Insection4.1wecalculate shown in Fig. 1. The structure formed by the interaction of a
theoreticallineprofilesbeforeandafterthenovae. Bycomparing slow wind with a binary companion has been discussed in de-
themtoobservations,wedeterminetheoriginofthesecomponents tailbyTheuns&Jorissen(1993).Wethereforeonlyrepeatthede-
in RS Oph. In section 3 we investigate a polar inflow on to the tailsneededinthepresentwork.Thebinarypotentialconfinesthe
whitedwarfasapossibleexplanationforthebroadwingsobserved windtobinaryorbitalplane,formingatwo-armedspiralstructure.
inhydrogenlinesduringquiescence.Finally,wediscusstheresults One spiral forms in the flow passing the white dwarf and escap-
intermsoftheprospectsforSNeIainsection5. ingthroughoneoftheouterLagrangepoints(seeFig.1,label3).
ThesecondformsduetotheinteractionoftheRochelobeoverflow
streamthatpassesthroughtheinnerLagrangepoint,withthepart
ofthewindpassingthewhitedwarf(flowslabelled1and2,Fig.1)
2 CIRCUMSTELLARMODEL .Theseflowscanbeseeninthetopleftpanel ofFig.1,withthe
Rochelobeoverflowstreamflowingfromlefttoright,andthewind
2.1 QuiescentMass-lossPhase
arrivingfromthetop.
The RS Oph binary system, quiescent mass loss and nova out- The two spirals run into each other, forming a shock. The
bursts were modelled using the Smoothed Particle Hydrodynam- streamsmergeafterapproximately1.25orbits.Behindtheshock,
ics(SPH)codeGADGET-2(Springel2005),whichhasbeenmod- thespiralbecomesclumpy, drivenbycooling,whichisthermally
ified to include binary motion, stellar winds, accretion and cool- unstable around 103K. The clumps form at the resolution scale.
(cid:13)c 2015RAS,MNRAS000,1–15
CSM in RSOph 3
v [50 km/s] v [50 km/s]
1011 1011
2 2
1012
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1 1 1013
AU] 0 2 3 1013-3cm] AU] 0 1014-3cm]
y[ 1 1014 [g y[ 1015 [g
r r
-1 -1 1016
1015
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1016 1018
-2 -1 0 1 2 -2 -1 0 1 2
x [AU] x [AU]
v [50 km/s] 102 102
101 101
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] ]
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AU] 0 101-cm AU] 0 101-cm
[ g [ g
y [ z [
S S
102 102
-5 -5
103 103
-5 0 5 104 -5 0 5 104
x [AU] x [AU]
Figure1.SpiralstructureformedduringtheRSOphquiescentmass-lossphase.Theredgiantistotheleftofthewhitedwarfandaccretiondisc.UpperPanel:
Densitycross-sectionsthroughtheflowstructureandthevelocityrelativetothecentreofmass.Partofthewindfallsbackontothewhitedwarffromabove
andbelowtheplaneofthebinary.ThenumbersshowtheRochelobeoverflowstream(1),whichinteractswiththewindsweptupduringtheorbit(2)toform
aspiralwind,andthewindescapingthroughtheL1Lagrangepoint(3),whichformsanotherspiral.ThesolidwhitelinesshowthesizesoftheRochelobefor
theredgiantandwhitedwarf.LowerPanel:Large-scalestructure,showingthemergerofthetwospiralstreamsandthestratificationofthewind.Thecolour
barshowscolumndensityintegratedoverz/y.Atdistancesgreaterthanafeworbitalradii,thewindbecomesballisticandthevelocityisapproximatelyradial
andperpendiculartothespirals.
(whiletheresolution scaleistypicallylessthanthesizeofstruc- lutionsinceitiscontrolledbythemassflowintothewhitedwarf’s
tures in the flow, the physical size of the clumps is likely much Rochelobe,whichsuggestsanexplanationforthevaryingaccre-
smaller). tiondiscmass.Sincetheartificialviscosityislowerinhigherreso-
An accretion disc forms which extends to the edge of the lutionsimulationsahigherdiscmassisneededtomaintainasimilar
white dwarf’s Roche lobe, approximately 1013cm. The forma- accretionrateandthereforethediscmassadjustsitselftogivethe
tion of the accretion disc is enabled by the cooling; similarly to same accretion rate in steady state (1–2×10−8M⊙yr−1). Due
Theuns&Jorissen (1993), we found no accretion disc forms in totheuncertaintyintheaccretiondiscpropertiesfromthesimula-
simulationswherecoolingisneglected.Theouterpartsoftheac- tions,thediscussionwillbeguidedbyobservationswherepossible.
cretiondiscareonanellipticalorbitthatremainsalignedalongthe The passage of the whitedwarf through the windof the red
linebetween theredgiantand whitedwarf. Theaccretiondiscis giant as the binary rotates gives rise to a component of the wind
onlyresolvedverticallybyafewsmoothinglengthsinthesimula- thatfallsontothewhitedwarfandaccretiondisc,aswasoriginally
tionsandsincewehaveneglectedsourcesofheatingthethickness seeninthesimulationsofTheuns&Jorissen(1993).Whilethede-
of the accretion disc is likely an underestimate. We also find the tails of this flow are dependent on the structure of the accretion
massintheaccretiondiscisresolutiondependent(higherinhigher disc, the presence of some material falling onto the white dwarf
resolutionsimulations).Theaccretionrateisnotsensitivetoreso- andaccretiondiscreflectsthefactthatthepressurescaleheightin
(cid:13)c 2015RAS,MNRAS000,1–15
4 Booth,Mohamed& Podsiadlowski
102 Sincethegasremainingfromthepreviousnovaeismuchlessdense
thanthemateriallostduringquiescence,anyerrormadeinthelarge
20
101 scalewindstructureshouldbesmall.
Withinthe first day the nova ejecta interacts withthe accre-
10 tiondisc. Sincethe gasinthe accretiondiscismuch denser than
100
the nova ejecta, it immediately distorts the nova shell, restricting
AU] 0 101-2cm] tbheecoflmowebiinpothlaer.bTinhaeryreosrubltiitnalgpsltaruncetuarnedsfaorrecsinhgowthneinnoFviag.sh3e.lTlhtoe
[ g large wind mass close to the orbital plane causes the nova shells
z [
S todeceleratetovelocitiesof100to200kms−1astheentirewind
102
-10 duringthepreviousquiescentphaseissweptupoverthecourseof
afewyears.Thisresultsintheformationofanequatorialring-like
103 structure(componentsN1andN2,Fig.3)thatisconsiderablymore
-20 densethantherestofthenovashell.Whilethebipolar lobespri-
marilyconsistofnovaejecta,theequatorialringconsistsmainlyof
104
-20 -10 0 10 20 sweptupwindmaterialandwillthereforehaveasimilarcomposi-
x[AU] tiontotheredgiant.Inthepolardirections,thenovashellrapidly
escapestheCSMandremainsclosetoitsinitialvelocity.Asthefor-
Figure2.Columndensityinamodelwithnocooling, whichproducesa
wardshocktravelsdownthedensitygradientinthepolardirection,
lessstronglyconfinedwindstructure.Forcomparison,thecolourbarshows
it accelerates, and the swept-up circumstellar gas reaches veloci-
thesamecolumndensityrangeasFig.1,butthespatialscaleis2.5times
tiesof4000kms−1to4500kms−1.Thehighvelocityofejectain
largertodemonstratethelargerverticalextentoftheflow.
thepolardirectionsmeansthattheejectacatchupanddriveshocks
throughtheequatorialringsofthepreviousnovae.Thisinteraction
theaccretiondiscissmallerthanthescaleheightinthepartofthe leadstoclumpformationastheshellcoolsandfurtherenhancesthe
windthatisclosethebinary.Thereforethewindthatpassesabove clumpingintheoldshells.Whiletherepeatedshockingandcool-
thewhitedwarfisunabletosupportitselfandfallsontothewhite ingoftheoldernovashellscausestheshellstopartiallybreakup,
dwarfandaccretiondisc.Thepolarstreamthatarisesinoursimu- multipleequatorialringsmaybevisible.
lationscontributesanaccretionrateontothewhitedwarfoforder Wefindthattheaccretiondiscsurvivesthepassageofthenova
M˙ ∼5×10−9M⊙yr−1.Insections3and4.1wediscusstheev- sinceitisconsiderably moredense thanthenova ejecta. Thisre-
idenceforapolaraccretioncomponent. sultissomewhatsensitivetoourassumptions,sinceinsomeofthe
Althoughthewindbecomesballisticbeyondafewbinarysep- lowerresolutionsimulationstheaccretiondiscdidnotsurvive,due
arations,thetemperatureofthewindclosetothebinaryisimpor- to the lower mass in the accretion disc at lower resolutions. The
tantforcontrollingtheverticalscaleheightinthewindanddepends survivaloftheaccretiondiscwillalsodependonthedetailsofits
ontheheatingandcoolingmodelsused.Whilecoolinghasbeenin- structure,suchasitsscaleheight.However,our simulationsmost
cludedinthemodelspresented,nocontributiontoheatingfromthe likelyunderestimatethemassintheaccretiondiscandobservations
whitedwarf,accretiondiscorredgianthasbeenincluded.Thisre- duringthe2006outburstofRSOphsuggestthatthediscsurvives
sultsinlowtemperaturesinthewindclosetothebinaryandawind (Hachisuetal. 2006). The interaction of the nova ejecta with the
thatishighlyconfinedtothebinaryplane.Inmodelsinwhichthe accretion disc immediately strips the weakly bound gas from the
coolinghasbeensuppressedthewindislessstronglyconfinedto surface of the disc, which gets entrained in thenova shell. Addi-
binaryplane,resultinginlowerdensitiesneartheplanebuthigher tionally,oncethenovaejectahaspassedtheaccretiondisc(within
densities at higher latitudes, although clear asymmetries are still hoursinoursimulations),weseeevidenceforanadditionalphase
present. This is demonstrated in Fig. 2, which shows a model in ofmassloss.Thismasslossoccursbecauseinadditiontostripping
which the flow is adiabatic. Even in this extreme case, the wind thegas,thenovadrivesshocksthroughtheaccretiondisc,heatingit
remainsasymmetric.ThewindinRSOphislikelytoliebetween up.Thehighpressureintheshockedgasthendrivesanadditional
thesetwoextremes–theeffectthishasonrelationshiptoobserva- ‘evaporative wind’ from the surface of the accretion disc, which
tionsofRSOphisdiscussedfurtherinsection4.1. lastsforseveraldaysandappearsasanadditionalshell-likefeature
(componentA,Fig.3).Asimilareffectprovidesanimportantcon-
tributiontothe total mass lost when a supernova interacts witha
2.2 NovaeOutbursts
binarycompanion(Wheeler,Lecar&McKee1975).
Afterthequiescentmasstransferhasevolvedfor18years,anova Thehighestdensityinthenovashellsisintheequatorialring,
shellwasinjectedintothesimulation.Subsequentlytheinteraction which is nH ∼ 106cm−3 2000 days after the nova. This den-
betweenmultiplenovaeandthecircumstellarmediumweresimu- sityislower thanthe107cm−3 predicted by 1D analytical mod-
lated.Thenovaeweremodelledusingauniformshellfortheejecta, els(Moore&Bildsten2012)scaledtoacomparablemass-lossrate
insertedwithinthesinkregionaround thewhitedwarf. Thenova totheeffectivemass-lossrateinthebinaryplane.Thediscrepancy
masswastakentobeMej ≈ 2×10−7M⊙,andthevelocitywas maybeduetoavarietyofreasons.Onepossibilityisthatthe3D
settoproduceaterminalvelocity,vej ≈ 3500kms−1.Theinter- geometry allowsthe shell tospread out in thevertical directions,
nalenergyoftheejectawasinitiallysetto25percentofthekinetic whichisimpossiblein1D.Another possibilityisthatthesimula-
energy,ensuringthedynamicsaredominatedbytherampressure. tionsmaynotsufficientlyresolvethedenseshell.Thisintroduces
Threenovae,eachseparatedby18years,havebeenmodelled, anuncertaintyintotherecombinationtime-scale,whichdependson
eachusingthecircumstellarstructureformedbythepreviousno- thedensitythrought = (n α)−1,whereαistherecombination
r e
vae.Ratherthanre-computethequiescentmassloss,weassumed coefficientandn istheelectrondensity.Althoughthevelocityof
e
the presence of the previous novae had no effect on this phase. theabsorption lines formed in thenova shells should bereliable,
(cid:13)c 2015RAS,MNRAS000,1–15
CSM in RSOph 5
400 1018 400 1018
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AU] 0 105-2cm] AU] 0 105-2cm]
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-2000 107 -2000 107
108 108
-4000 -4000
109 109
-4000 -2000 0 2000 4000 -4000 -2000 0 2000 4000
x[AU] x[AU]
Figure3.Density structure 2000days after thesecond nova outburst. Upper Panel: Zoom-inoftheequatorial ring. Thelabels show thelocation ofthe
equatorialringsfromthefirst(N1)andsecondnovae(N2),alongwiththe‘evaporative’windfromtheaccretiondisc(A).Thefirstnovashell(N1)ismore
clumpy,reflectingtheadditionalcoolingphasethatitunderwentafterbeingshockedbytheejectafromthesecondnova.LowerPanel:Largescalestructure
ofthenovae,showingthebipolarstructureshapedbytheinteractionwiththeaccretiondiscandthewind.Thevelocityofthebipolarlobesismuchhigher
(4000kms−1)thantheslowmovingequatorialring(200kms−1).
since it iscontrolled by momentum conservation, theuncertainty Dobrzyckaetal. (1996) used UV observations to derive a hot
intherecombination time-scalemeansthestrengthofthesecom- component luminosity of 100 − 300L⊙, and a temperature
ponentsremainsonlyqualitative(seeSec.2.3). T ≈ 105K. Although this is the luminosity after the emis-
sionhas been reprocessed by theregion close tothe whitedwarf
(Anupama&Mikołajewska 1999), it is the appropriate luminos-
2.3 Mass-lossrateestimatefromtheionizationstateofthe ityforcalculatingtheionizationstateofmaterialinthewind.Soft
circumstellarmedium X-rays emitted as a result of the novae outbursts also contribute
to the ionizing flux. During quiescence an X-ray luminosity of
Theionizationconditionsofstellarwindscanbeaneffectivetracer 2×1032ergs−1wasmeasuredbyRXTEin1997,roughly12years
ofthemass-lossrate,since,neglectingopticaldepth,thephotoion-
afterthe1985outburst(Mukai2008).
ization rate from a point source scales as r−2, and the recombi-
nation ratescales asr−4 ina one-dimensional wind. This means Thequiescenthydrogenionizationstatewasmodelledusinga
thatunlesstheopticaldepthissufficienttoabsorbtheionizingflux Stro¨mgrensphereapproximationforlinesofsightfromeachpar-
theentirewindwillbeionized.InRSOph,hydrogenisonlyion- ticle to the white dwarf, with each line of sight treated indepen-
izedrelativelyclosetothewhitedwarf(Anupama&Mikołajewska dently and the ionization of each particlefound by balancing the
1999), an idea supported by our NaI D line profile modelling, UV photoionization with Case B recombination, taking into ac-
therefore we can use this to estimate the mass-loss rate from the count the optical depth along the line of sight. Case B recombi-
redgiant. nation assumes that any photons emitted with E > 13.6eV are
During quiescence the dominant ionizing flux in RS Oph reabsorbedlocallybyanotherhydrogenatomandcanbeneglected
comes from the hot component, although whether this flux is from the overall recombination rate. The effective photoioniza-
dominated by the white dwarf or accretion disc is unknown. tioncross-section iscalculated byaveraging thecross-section for
(cid:13)c 2015RAS,MNRAS000,1–15
6 Booth,Mohamed& Podsiadlowski
❍ recombination rate, which depends on the local electron density.
❳
✥ Wealso include collisional ionization which can dominate in the
✌✌
✠ ✵✡☞ ❳❍ novae; where thegasbehind theforward shock can reach 106K.
Thephotoionization, recombination andcollisionalionizationco-
efficients from Verner&Ferland (1996), Verneretal. (1996) and
✵✡☛
✞ Arnaud&Rothenflug(1985)wereused.
✝
☎✆ ✵
③ Since sodium is fully ionized in regions where hydrogen is
✵✡✟
ionized we focused on the ionization state of sodium in the neu-
tral hydrogen regions. Since in this region the optical depth to
✲✠ ✵✡✠
UV photons is large, we modelled the ionization of sodium ne-
glecting the contribution from the UV continuum short-ward of
✵ 13.6eV.Includingthesephotonserroneouslyionizeshydrogen,but
✲✟ ✲✠ ✵ ✠ ✟
①(cid:0)✁✂✄ makesonlyaminordifferencetotheionizationrateofsodium.For
Figure4.Structureofthehydrogenionizationfractionduringquiescence, photons with energies less than 13.6eV, we assumed the optical
foracross-sectionthroughtheredgiantandwhitedwarf.Thewindcloseto depth issmall. Theionization fraction of hydrogen isalso calcu-
theredgiantandtheaccretiondiscprovidesufficientopticaldepthtoshield latedintheneutral region, since, atapart fromthehighest densi-
thegasbehindthem,elsewherethegasisionized. Thethree-dimensional ties, hydrogen provides the dominant contribution to the electron
ionization structureisthereforeconical, centredonthewhitedwarf,with density.Sincetheionizationfractioncanbeverylowinthedens-
theadditionalneutralregionbehindtheredgiant.Contoursshowtheden-
est parts of the wind we applied a floor to the electron fraction,
sciotym.pNaoreteththeemspdairteiacltlsyc,atlheeisdeanpspirtyoxcimonattoeulyrstwshiocweacslewairdlyetahseinedFgieg.o1f.tThoe Xe =ne/nH =10−5,torepresentthecontributionfrommetals.
densewindregionneartheRG. Away from the white dwarf, the dominant contribution
to the hydrogen ionization rate comes from X-ray ionization,
whichwasalsoincludedintheionizationcalculationforsodium.
The X-ray ionizing rate was computed using the fits given by
photoionizationfromthegroundstateoverablack-bodyspectrum
at 105K. The Case B recombination coefficient at 104K from Kozma&Fransson(1992),whichshowthatapproximately40per
cent of the X-ray energy deposited goes into ionizing the gas.
Ferguson&Ferland(1997)isusedandthephotoionizationcross-
The rate of X-ray energy deposited can be estimated as F σ ,
sectionisfromVerneretal.(1996). X X
whereσ istheeffectiveX-rayabsorptioncross-sectionandF
TheresultsoftheStro¨mgrencalculationareshowninFig.4. X X
istheX-rayflux.Thiswasestimatedusingthecross-sectionfrom
Only the accretion disc and wind closest to the red giant pro-
Morrison&McCammon(1983),averagedoverablack-bodywith
vide sufficient optical depth that the gas becomes neutral, result-
temperature2×106K.Theobservedluminosityistranslatedintoa
ing in a conical ionization structure, with a larger neutral re-
fluxtakingaccountofthefactthattheX-rayemissioncomesfrom
gion in the gas shielded by the red giant. The low UV optical
theshockednovashells,whichareexternaltotheredgiantwind.
depth is in disagreement with Shore&Aufdenberg (1993) and
Inthiscase,treatingtheemissionasapointsourcewouldoveres-
Anupama&Mikołajewska (1999), who suggest a large optical
timate the flux near the binary. Instead the flux is approximated
depth isrequired to explain thelineratios, and that thehot com-
viaF = L /4πmax(r,r )2,whichgivesthecorrectlimitsfor
ponentisembeddedinaneutralwind.Thestrongabsorptionseen X X s
r≪r ,wherer istheradiusofthenovashell.Duringquiescence
intheBalmerseries(Bulla2013)andthepresenceofmetalabsorp- s s
weusedr = 1015cm.Duringoutburstr evolvessincethenova
tionlinessuchastheNaIDlinesthatforminthewind(Patatetal. s s
shells expand – we used the mean radius of X-ray emitting gas,
2011)alsosupportalargeopticaldepth.
whichistakentobethegaswithT >106K.
Thelargerdensityclosetothewhitedwarfmustmeanahigher
mass-loss rate, since the simulations over-estimate the density in During quiescence we calculated the ionization state in a
thewindbecausetheyneglectedphotoionizationheating.Recalcu- steady-stateapproximation,usingthesameluminositiesasforthe
latingtheionizationstructureformodelsinwhichthedensityhas Stro¨mgrenspherecalculations.Forthelineprofileevolutionafter
been scaled to mimic an increased mass-loss rate, we find that a thenovathequiescentUVfluxwasused,sinceweconsideredthe
mass-lossrateM˙ =5×10−7M⊙yr−1issufficienttoproducean evolutionofthelinesaftertheendofthesuper-softsourcephase.
ionized bubble around thewhitedwarf withaneutral region out- By this time accretion had resumed in RS Oph (Wortersetal.
sideit.Therelativelymodestincreaseinmass-lossrateissufficient 2007),sothequiescentUVfluxisappropriate.ForthesoftX-rays,
sincetheoptical depthissensitivetodensity; inahighlyionized we used the observed luminosity from Bodeetal. (2008). At the
region, theneutral fractionY ≈ nα/Fσ, whereF isthefluxof end of the super-soft phase, 100 days after the explosion, the lu-
ionizingphotons,nisthenumberdensityofhydrogenandσisthe minosity was 5× 1035ergs−1, decaying to the quiescent value
ionizationcross-section.Thisresultsintheopticaldepth,τ,obey- by 1200 days after theexplosion. During thistimetheionization
ing τ ∝ M˙2. The optical depths for the simulated NaID lines statewascalculatedtime-dependently,assumingthatbothsodium
discussedinsection4.1alsosupportahighermass-lossrateinRS andhydrogenwerefullyionizedattheendofthesuper-softsource
Oph. phase andthetemperatures weretaken fromtheSPHsimulation.
In order to calculate the NaID line profiles, the ionization We found the ionization fraction of sodium in the regions where
state of sodium must also be modelled, because its low ioniza- hydrogen is neutral was in the range 10−3 to 10−4 during qui-
tionenergy(5.1eV)meanssodiumcanremainphotoionizedinre- escence. Forthenovae, initiallythe hightemperature inthenova
gions where hydrogen is neutral. A detailed, time-dependent and shellpreventssodiumfromrecombining.Astheshellsexpandand
multi-species photoionization model in 3D is beyond the scope cool,sodiumintheequatorialringisabletorecombine.However,
of this work, instead we use a model that captures the impor- atlowerinclinationsthenovaejectaremainsionized.Theeffectsof
tant quantities for sodium, i.e., the photoionization rate and the ionizationcanbeseeninthelineprofilespresentedinsection4.1.
(cid:13)c 2015RAS,MNRAS000,1–15
CSM in RSOph 7
3 POLARINFLOW riving at a location r in the disc from a volume element d3r′ is
Thesimulationsshowthepresenceofapolarinflowinthesystem,
with gas falling back onto the binary from 1014cm. The accre- η(r′,ν′)d3r′
F = . (2)
tionrateinthiscomponent isapproximately 5×10−9M⊙yr−1 4π|r−r′|2
(Sec.2.1).Polaraccretionflowsareaubiquitousfeatureofbinary
Theprobabilitythatthefluxisscatteredthroughanangleθ tothe
s
windmodels,arisingduetothepassageofthewhitedwarfthrough theobserveris(1−exp(−τ))I(θ ),whereI(θ )∝1+cos2(θ )
s s s
the red giant wind (this can be seen in the upper right panel of
istheangularpartoftheThomsonscatteringcross-sectionandthe
Fig.1).
factor(1−exp(−τ))takesintoaccounttheopticaldepththrough
The occurrence of such a flow is supported, at least at dis-
thedisc.Thetotalluminositycanbewrittenas
tances of 1014cm, by thedetection of red-shifted components in
absorption lines of Na, Ca and K in RS Oph (Patatetal. 2011).
However, thestructureof theinflow within1012cm of thewhite L (ν)=(1−exp(−τ)) η(r′,ν′) I(θ (r′,r))d3r′d2r,
dwarfisaffectedbytheuseofasinkinthesimulationandisthere- s 4π|r−r′|2 s
Z
forenot well known. It isalsopossible that thestructure may be (3)
furthercomplicatedbytheoccurrenceofwindsfromtheaccretion
wheretheintegraloverd3r′isoverthevolumeoftheemittingre-
disc(notincludedinourmodels),since,althoughRSOphisbelow
the Eddington luminosity, L/L ∼ 10−2, line opacity maybe gionandtheintegrald2risoverthesurfaceofthedisc.Forcoher-
Edd
ent scattering the relationship between the emitted and observed
sufficientforRSOphtodriveadiscwind(Drew&Proga2000).
frequencies, ν′ = ν′(ν,r′,r),wascalculatedby considering the
X-ray observations of RSOph during quiescence tentatively
Doppler shift between the frame of the emitting gas and the rest
supportthepresenceofapolaraccretionflow.Nelsonetal.(2011)
frameofthediscatr′,followedbytheshiftbetweentheframeof
foundthatthehardX-rayemissioncanbeexplainedbyemission
thediscandtheobserver.
from shocked gas as it settles onto the white dwarf, and mea-
sured an accretion rate 2×10−9M⊙yr−1. They found a maxi- The resulting line profiles for a range of cone opening an-
gles and optical depths are shown in Fig. 5. In the conical mod-
mumtemperatureof6keV,whichcorrespondstoashockvelocity
v≈1.7×103kms−1.ThisvelocityisclosetothewidthoftheHα els, the density in the flow has been adjusted so that each model
has the same accretion rate and the observer is at an inclination
emissionlinewingsinRSOph(Zamanovetal.2005),suggesting
of45◦.Modelswithnegligibleopticaldepthintheaccretiondisc,
theHαemissioncouldariseinaninflow.
τ =0,producesymmetriclineprofilesmakingitimpossibletotell
WeestimatedtheHαemissionfromtheinflowusingasim-
whethertheemissionisduetoanoutfloworinflow.Thepresence
plified model in which the emission comes from gas in free-fall
ofscatteringbreaksthesymmetry,producingprofileswithstronger
ontothewhitedwarf.Weneglecttheeffectsofangularmomentum
red-shiftedemission.
ontheflow,exceptthatwedonotincludeemissionfromtheparts
offlowwithv > 1700kms−1,sinceithasbeenshockedtohigh Models with low conical opening angles produce double-
peakedprofilesandintermediatemodelscanproducetriplepeaked
temperaturesandformstheX-rayemittingcoolingflow.Theinflow
emission,althoughscatteringbytheaccretiondiscresultsinasin-
istakentobesphericallysymmetric;however,wealsoconsidered
glepeakedprofile.Wenotethatwhilethemodelwithanopening
anaxis-symmetricconicalstructure,sincetheaccretiondiscmust
angleθ = 30◦ andτ = 1mimicsaP-Cygniprofile,theHαpro-
blockpartoftheinflow.
fileinRSOphcannotbeproducedbythismechanismalone.The
Theluminosityisassumedtobeduetorecombination,
reason for thisisthat in thecentre of higher Balmer serieslines,
L(ν)=hνfα(T) n(r)2φ(ν′)d3r. (1) such as Hβ and Hγ, show P-Cygni profiles in which the flux is
ZV belowthelevelofthecontinuum,andabsorptionmustthereforebe
The line profile, φ(ν), was taken to be the Doppler profile, the present(Bulla2013).
density set viamass conservation, n = n0r02v0/(r2v(r)), where TheP-CygniabsorptioninRSOphcannotbeassociatedwith
v2(r) = −2GM(r−1−r−1)+v2.Thefrequencyν′ istherest- apolarinflow;sinceitisblue-shifted,itmustariseinanoutflow.
0 0
frame frequency and φ(ν′) is the Doppler emission profile. The Themostlikelyexplanationisthattheabsorptionarisesfurtherout
subscriptzerodenotesquantitiesmeasuredfromthesimulationsat inthewindwherethetemperatureislower.Thisiscompatiblewith
r0 = 2.5×1012cm,whichgivesn0 = 5×10−16gcm−3 and observationsofthe2006novainRSOph,whichshowthenarrow
v0 = 80kms−1. For the temperature, we use T = 30000K, P-Cygniprofilewasstillpresent2daysafterthenova(Patatetal.
which only affect the total luminosity. The emissivity from re- 2011).Fortheabsorbingmaterialtobeoutsidetheshockfrontat
combination has been approximated via hνfα(T)n(r)2, where this time the distance to the absorbing material must be at least
α is the recombination coefficient and f average number of Hα 5×1013cm.
photons per recombination. The recombination coefficient used Furthermore, unliketheHαlinewings, thevelocityabsorp-
is that for Case B, in which recombination photons emitted with tion component does not correlate with the motion of either the
hv > 13.6eVareassumedtobeimmediatelyreabsorbed. Inthis whitedwarfortheredgiant(Brandietal.2009).Incontrasttothis,
case,f ≈0.5(Storey&Hummer1995). thecentralvelocity,asmeasuredbytheHαlinewings,doescorre-
Self-absorption in the inflow has been neglected, however, latewiththemotionofthewhitedwarf.Thiscorrelationwouldbe
electron scattering froma razor thin accretion disc wasincluded. expectedforapolarinflowmodelsincethelinewingsdependonly
Emissionfrommaterialonthefarsideofthediscisreducedbya ontheaccretionrateandwhite-dwarfmass,notthedensityandve-
factorexp(−τ),whereτ istheopticaldepththroughthediscand locityawayfromthewhitedwarf.Therefore,wesuggestthepolar
scatteringwastreatedinthesinglescatteringapproximation. The inflow as an explanation for the line wings. However, the central
scatteredluminosity,L (ν),isderivedbyconsideringthescatter- componentmaybedominatedbyanoutflow.
s
ingofphotonsemittedatapointr′bytheaccretiondiscatapoint Whiletheassociationof Hαlinewingswithan inflow may
r. For an emissivity, η(r′,ν′) = hνfαn2(r′)φ(ν′), the flux ar- be compelling, we note that accretion disc wind models may be
(cid:13)c 2015RAS,MNRAS000,1–15
8 Booth,Mohamed& Podsiadlowski
1e28 1e28 1e27
4.5 1.0 5
4.0 0
3.5 0.1 0.8 4
1] 3.0 1 1] 1]
- - -
z 10 z 0.6 z 3
H 2.5 H H
1 1 1
- 2.0 - -
s s 0.4 s 2
g g g
r 1.5 r r
e e e
[ [ [
L L L
1.0
0.2 1
0.5
0.0 0.0 0
-700-350 0 350 700 -700-350 0 350 700 -700-350 0 350 700
v[km s-1] v[km s-1] v[km s-1]
Figure5.Hαemissionfromthepolarinflowmodel.Thekeydenotesthescatteringopticaldepthintheaccretiondiscandtheobserverisataninclinationof
45◦.Ineachmodeltheaccretionrateisthesame,buttheopeningangleofthepolarinflowincreaseslefttorightacrossthepanelswithθ=30◦,60◦and90◦
respectively.Notethedifferentluminosityscalesforthedifferentopeningangles.
abletoproduce similarlineprofiles.Calculationsoflinesformed higherthanthewidthoftheabsorptionlines,andislikelyassoci-
in disc-winds from white dwarf stars have been limited to res- atedwithemissionfromtheionizedregion.Thelineprofileswere
onance lines tend to produce absorption profiles for inclinations derived by calculating the optical depth tothe photosphere along
i & 70◦ (Progaetal. 2002). However, disc wind models for T linesof sight through theCSM.Thephotosphere wassubdivided
Tauri stars can produce similar Hα line profiles to those seen into lines of sight to ensure that the sub-structure along the line
in RS Oph (Kurosawa,Harries&Symington 2006). Polarization of sight is resolved. Finally, the flux from each line of sight was
measurementsmaybeabletodistinguishbetweeninflowandout- combinedandweightedbyarea.
flow models since, intheinflow models, the fractionof scattered Fig.6showstheresultingsyntheticlineprofiles.Forinclina-
lightcontributingtothebluewingislarger. tions i & 70◦, the line profile shows both red- and blue-shifted
components. Thered-shiftedcomponents ariseinthewindthatis
fallingbackontothewhitedwarfandaccretiondisc,andisthere-
forestrongestwhenthewhitedwarfisclosesttotheobserverand
4 SODIUMABSORPTIONLINES thelineofsightintersectsthemostmaterial.Theblue-shiftedcom-
ponentsarisefurtheroutintheCSM,beyond1014cm,whichhas
4.1 NaIDlinesinRSOph aterminalvelocityof10to20kms−1.Athigherinclinationsthis
Sodiumabsorptionlineshavebeensuggestedasausefuldiagnostic component isrelativelystablewithphasebecausethedistantma-
ofthecircumstellarenvironmentinbothsupernovaeandtheirpro- terialdominatesthelineprofileandcontributestoalllinesofsight
genitorsystems(Patatetal.2007;Chugai2008;Patatetal.2011). independent of phase. At low inclinations the contribution from
TheNaIDlines,togetherwithotherstrongmetallinessuchasthe materialatlargedistancesissmaller,duetothelowerdensityfar
CaII H &K lines,probe thedensityand ionizationconditions in above the mid-plane. Therefore, the high inclination line profiles
the circumstellar environment. We modelled the line profiles ex- aremoresensitivetothematerialclosetothebinary,whichvaries
pectedfromthesimulations,withtheaimofunderstandingwhere withphase.
theobservedfeaturesinRSOphformintheCSMandwhetherthe The inclination at which the behaviour of the blue-shifted
same circumstellar components can be responsible for metal line component changes from stable to phase-dependent depends on
variationsobservedinsomeSNIa. howconcentratedtheoutflowis.Forourcoolingmodel(Fig.6)this
We have modelled NaI D absorption line profiles directly occursati ∼ 70◦,butformodelswithoutcoolingthelineprofile
fromthe simulations, using the resultsfromthe ionization calcu- isstableforalargerrangeofinclinations,withthetransitionat30◦
lation described above. All neutral sodium atoms are assumed to to45◦.InRSOphtheblue-shiftedlinesarerelativelystable,which
be in the ground state and contribute to the absorption lines. We suggeststhattheoutflowinRSOpharelessstronglyconcentrated
presentlineprofilesfromcalculationsinwhichthemass-lossrate thaninourcoolingmodel,sincetheinclinationisi≈50◦.
hasbeenscaledto5×10−7M⊙yr−1,sincethisgivesbetteragree- Theabsorption linesformed inthenova shells areshown in
mentwithobservationsbothfortheionizationstructureandtheline Fig. 7. These lineswere modelled fromthe end of the super-soft
profiles.WedidnotincludeadetailedtreatmentfortheHIIregion source phase and assume that the central system had reached a
intheNaI Dlineionizationcalculation;insteadweneglectedthe quiescent steady-state once more. The evolution of the line pro-
contributionfromallmaterialwithin3×1013cm.Theresultsare filesisgovernedbythecompetingeffectsofrecombination,which
notparticularlysensitivetothischoiceofradius. strengthen the lines, and expansion which weakens them. Since
WeassumethatthecontinuumfluxaroundtheNaIDlinesis the nova shell expands rapidly in the polar directions this com-
dominated bytheredgiant. Thepresence ofanemissioncompo- ponent is not dense enough to form strong sodium lines (at 3 to
nent inRSOphlimitstheextenttowhichthisistrue(Patatetal. 4×103kms−1).Instead,theabsorptionlineprofilesati.60are
2011). The emission component has a width v ∼ 100kms−1, dominatedbythe‘evaporativewind’,whichhasv .100kms−1.
(cid:13)c 2015RAS,MNRAS000,1–15
CSM in RSOph 9
1.0
x
u 0.8
l
F

d 0.6
e
z
i
a
l 0.4
a
m
or 0.2 11.85 12.10 12.35 12.60
N i=60(cid:0)
12.10 12.35 12.60 12.85
1.0
x
u 0.8
l
F

d 0.6
e
z
i
a
l 0.4
a
m
r
o 0.2
N i=75(cid:0)
1.0
x
u 0.8
l
F

d 0.6
e
z
i
a
l 0.4
a
m
r
o 0.2
N i=90(cid:0)
0.0
-30-20-10 0 10 20 30-20-10 0 10 20 30-20-10 0 10 20 30-20-10 0 10 20 30
V [km/s] V [km/s] V [km/s] V [km/s]
Figure6.ModelNaIDabsorptionlinesproducedduringthequiescentmass-lossphase,atinclinationsof60◦(top),75◦(middle)and90◦(bottom).Thekey
denotesthenumberoforbitssincemasstransferbeganwheretheredgiantisnearesttotheobserveratphase0.Sincetheblue-shiftedcomponentsarisein
thecircumstellaroutflow,theydisappearatlowerinclinationsduetothelowercolumndepth.Thered-shiftedcomponentvarieslessstronglywithinclination
angle.
Thelargewidthofthelinefori=30◦isaresultoftheevaporative isconsiderablylowerthanthefastestobservedcomponent, which
windlyingalongthelineofsighttotheobserver,whileathigher hasavelocityv=−37kms−1.Whileadditionalsourcesofaccel-
inclinationslinesofsightcutacrosstheevaporativewind. erationcouldbeinvokedtoexplainthedifference,themostnatural
Forinclinationsofi & 60◦,theinteractionofthenovashell explanationcomesfromthenovae,whichshowtheevaporationof
with the wind is strong enough to produce an additional compo- gasfromtheaccretiondiscafterthenovahaspassedatvelocities
nenttothelineprofile,athighervelocitythanthematerialfromthe ofv∼−50kms−1.
accretiondisc.Initiallythecontinuedinteractionofthenovashell Observations before and after the 2006 outburst support
withthewindkeeps theshellhot,withcollisionalionizationpre- the suggestion of differing origin for the 10 to 20kms−1 and
ventingrecombinationinthesodium.Astheshelleventuallycools 37kms−1components.Sinceaftertheoutburstthelowervelocity
andrecombinesstrongabsorptionlinesappear.Whilethecompo- componentwasweaker,whilethehighervelocitycomponent was
nentsfromtheevaporativewindweakenovertime,theycanstillbe stronger(Patatetal.2011).Thestrengtheningofthehigh-velocity
seen2000daysafterthenova. componentisexpectedifitisassociatedwiththeevaporativewind,
The different absorption components in our models can be asitexpands and thelines weaken continually asthe nova shells
usedtodeterminetheoriginoftheabsorptioncomponentsobserved evolve. Similarly, lines arising in the wind should be weaker af-
inRSOph.Thegasthatfallsbackontothebinaryfromaboveand ter the nova as the nova shells sweep up the wind, which slowly
below the plane naturally explain the otherwise unexplained red- replenishesonceaccretionresumes.ObservationsofHαandHβ
shifted absorption components seen in RS Oph. Additionally we absorptionspriortothe2006novasupportthis,sincetheyhadthe
findtheterminalvelocityintheoutflowis10to20kms−1,which samevelocityastheslowNaIDcomponent,v∼−10kms−1,and
(cid:13)c 2015RAS,MNRAS000,1–15
10 Booth,Mohamed& Podsiadlowski
1.0
x
u 0.8
l i=30(cid:0)
F

d 0.6
e
z
i
a
l 0.4
a
m
or 0.2 150 310 530 860
N
310 530 860 2090
1.0
x
u 0.8
l i=45(cid:0)
F

d 0.6
e
z
i
a
l 0.4
a
m
r
o 0.2
N
1.0
x
u 0.8
l i=60(cid:0)
F

d 0.6
e
z
i
a
l 0.4
a
m
r
o 0.2
N
0.0
-225 -150 -75 0 -225 -150 -75 0 -225 -150 -75 0 -225 -150 -75 0
V [km/s] V [km/s] V [km/s] V [km/s]
Figure7.ContributionofthenovaejectatotheNaIDlinesforinclinationsof30◦(top),45◦(middle)and60◦(bottom).Thekeydenotestimeindayssince
thestartofthenovaoutburst.Thegreylinemarksthewindvelocityv ≈ −12kms−1,columndensitiesatvelocitiesgreaterthanthiswillbeaffectedby
interactionswiththeRGwind.Forinclinationsi.45◦,thehighvelocitycomponentsweakenasthenovashellevolves.Athigherinclinations,forlinesof
sightintersectingtheequatorialring,acomponentat150kms−1appearsoncetheringhascooledbelow103K.Thecomponentsat100kms−1fori=60◦
ariseinthegasevaporatedfromtheaccretiondisc.Theevaporativecomponentweakenscontinuallyafterthenova,andmayexplaintheadditionalmaterial
seenafterthe2006outburstofRSOph.
wereobserved tocontinuously strengthen during theperiod prior weuseasimpleapproximationduetoChevalier(1981)isused
tothe2006outburst(Brandietal.2009).Therefore,wesuggesta
2.61×1014t2/3cm t <40.7,
cexopmlabninaetidonqufoierstcheentlinmeassos-blsoesrsveadndinnRovSaOmpohd.el providesanatural Rp =(8.86×1013 d1− 1t0d8 2 tdcm tdd >40.7, (4)
wheret isthetimeinhdays.(cid:0)This(cid:1)exipressionoverestimatesthepho-
d
4.2 RSOphandTypeIasupernovae tosphericvelocityvp = Rp/tbyapproximately25percentwhen
compared with photospheric velocities from abundance tomogra-
InordertocompareoursimulationsofRSOphwithobservations phy (Stehleetal. 2005; Mazzalietal. 2008). Thesupernova pho-
ofTypeIasupernovae,wecalculatedthelineprofilesaswouldbe tospherebeginstorecedeafterapproximately60days,andthesu-
seenagainstasupernovaphotosphere.Fortheionizationconditions pernovastartstobecomeopticallythintocontinuumradiationand
inthesupernova,wefollowthehypothesissuggestedbyPatatetal. a model for the emissivity should be used instead of an approxi-
(2007) for explaining theobservations of SN2006X –thesuper- matephotosphere.Howeverthisdoesnotoccuruntilaftertheline
novainitiallyionizesthecircumstellarmedium,whichthenbegins profileshavefinishedevolving.
torecombine20daysaftertheexplosion.Thesupernovaistakento Weassumetheexplosionoccursaftertheendofthesimula-
beanexpandingspherewithavelocityof20,000kms−1,which tions,oncethreerecurrencetimesoccur,whichcorrespondstothe
sweepsupthecircumstellarmedium,andtheforthephotosphere lowest densityof, andlargest thedistancetotheinner-most nova
(cid:13)c 2015RAS,MNRAS000,1–15