Table Of ContentAstronomy&Astrophysicsmanuscriptno.8520 (cid:13)c ESO2008
February4,2008
The physical structure of the point-symmetric and
quadrupolar planetary nebula NGC 6309
R.Va´zquez1,L.F.Miranda2,L.Olgu´ın1,3,S.Ayala3,4,
J.M.Torrelles5,M.E.Contreras1,andP.F.Guille´n1
8 1 InstitutodeAstronom´ıa,UniversidadNacionalAuto´nomadeMe´xico,Apdo.Postal877,22800Ensenada,B.C.,Mexico
0 e-mail:vazquez, mcontreras, [email protected]
0 2 InstitutodeAstrof´ısicadeAndaluc´ıa,CSIC,P.O.Box3004,E-18080Granada,Spain
2 e-mail:[email protected]
3 InstitutodeAstronom´ıa,UniversidadNacionalAuto´nomadeMe´xico,Apdo.Postal70-264,04510Me´xico,D.F.,Mexico
n
e-mail:[email protected]
a
J 4 Centro de Radioastronom´ıa y Astrof´ısica, Universidad Nacional Auto´noma de Me´xico, Apdo. Postal 3-72 (Xangari), Morelia,
Mich.,Mexico
0
e-mail:[email protected]
3
5 InstitutodeCienciasdelEspacio(CSIC)-IEEC,FacultatdeF´ısica,UniversitatdeBarcelona,Av.Diagonal647,08028Barcelona,
Spain
]
h e-mail:[email protected]
p
Received—/Accepted—
-
o
r ABSTRACT
t
s
a Aims.Weanalysethepoint-symmetricplanetarynebulaNGC6309intermsofitsthree-dimensionalstructureandofinternalvaria-
[ tionsofthephysicalconditionstodeducethephysicalprocessesinvolvedinitsformation.
Methods.WeusedVLA-Dλ3.6-cmcontinuum,ground-based,andHST-archiveimagingaswellaslongslithigh-andlow-dispersion
1
spectroscopy.
v
Results.Thelow-dispersionspectraindicateahighexcitationnebula,withlowtomediumvariationsofitsinternalphysicalconditions
1 (10,600K . T [O]. 10,900K;10,100K . T [N]. 11,800K;1440cm−3 . N [S]. 4000cm−3;1700cm−3 . N [Cl].
0 2600cm−3;100e0cm−3 . N [Ar]. 1700cm−3).Teheradiocontinuumemissionindicaetesameanelectrondensityof≃ 19e00cm−3,
6 emissionmeasureof5.1×1e05pccm−6,andanionisedmassM(H)≃0.07M .Intheopticalimages,thepoint-symmetricknotsshow
⊙
4 alackof[N] emissionascompared withsimilarfeaturespreviouslyknown inother PNe.Arichinternalstructureof thecentral
.
1 region isseen inthe HSTimages, resembling adeformed torus. Long slit high-dispersion spectra reveal a complex kinematics in
0 thecentralregion,withinternalexpansionvelocitiesrangingfrom≃ 20to30kms−1.Inaddition,thespectrallineprofilesfromthe
8 externalregionsofNGC6309indicateexpandinglobes(≃ 40kms−1)asthosegenerallyfoundinbipolarnebulae.Finally,wehave
0 foundevidenceforthepresenceofafainthalo,possiblyrelatedtotheenvelopeoftheAGB-starprogenitor.
: Conclusions.OurdataindicatethatNGC6309isaquadrupolarnebulawithtwopairsofbipolarlobeswhoseaxesareorientedPA=40◦
v andPA=76◦.Equatorialandpolarvelocitiesforthesetwopairsoflobesare29and86kms−1 forthebipolarsystematPA=40◦ and
i 25and75kms−1 forthebipolarsystematPA=76◦.Thereisalsoacentraltorusthatisexpandingat25kms−1.Kinematicalagefor
X
allthesestructuresisaround3700to4000yr.WeconcludethatNGC6309wasformedbyasetofwell-collimatedbipolaroutflows
r (jets),whichwereejectedintheinitialstagesofitsformationasaplanetarynebula.Thesejetscarvedthebipolarlobesintheprevious
a
AGBwindandtheirremnantsarenowobservedasthepoint-symmetricknotstracingtheedgesofthelobes.
Keywords.planetarynebulae:individual:NGC6309–ISM:kinematics–ISM:abundances
1. Introduction objectstocollimatedoutflowsfroma precessingcentralsource
known as bipolar rotating episodic jets (BRETs, see Lo´pez,
Inspite of alltheworkthatupto nowhasbeendonetounder- Va´zquez&Rodr´ıguez1995).However,insomecases,thereare
stand the origin of planetary nebulae (PNe) morphologies and notdefiniteproofsaboutthejetnatureofthesefeaturesasthey
theirevolution(e.g.,Kwok,Purton&FitzGerald1978;Kahn& are not confirmedby spectroscopicstudies(e.g. Va´zquez et al.
West 1985; Balick 1987; Icke 1988; Mellema 1995; Perinotto 1999a, Va´zquezetal.2002).Althoughsometheoreticalmodels
et al. 2004; Rijkhorst, Mellema & Icke 2005; Scho¨nberner et have intended to explain point-symmetric PNe (e.g., Cliffe et
al. 2005; Scho¨nberner et al. 2007), some morphologicalstruc- al. 1995; Livio & Pringle 1996, 1997; Garc´ıa-Segura& Lo´pez
tures still remain as unsolved problems. In particular, the so- 2000;Rijkhorst,Icke&Mellema2004),theoriginandshaping
calledpoint-symmetry(Stanghellini,Corradi&Schwarz,1993; ofthiskindofobjectsremainsapuzzle.
Gonc¸alves et al. 2003) appears enigmatic. Some observational
NGC 6309 is a PN whose morphologystrongly suggests a
studiesaboutpoint-symmetricPNe (e.g.Miranda&Solf1992; BRETscenarioforitsorigin,ascanbeseenintheHα+[N]and
Lo´pez, Meaburn & Palmer 1993) relate the formation of these [O]imagesbySchwarz,Corradi&Melnick(1992).Ithastwo
prominent,point-symmetric‘arms’formedbypairsofconden-
Sendoffprintrequeststo:R.Va´zquez sationsinadditiontoabrightinternalellipticalstructure.Some
2 Va´zquezetal.:ThephysicalstructureofNGC6309
Fig.1.ImagesofNGC6309inthelightofHα(topleft),[N](topright)and[O](bottomleft),includinganunsharpmaskingof
the[O] image(bottomright).Northisupandeastisleftinallthepanels.Smallframesareincludedinsidetheupperpanelsto
showthestructureofthecentralregion.
previous studies on NGC6309 have determined an expansion done.Inthispaper,wehavecarriedoutaradio-opticalstudyof
velocityV [O]=34kms−1(Sabbadin1984),aswellasmean NGC6309, including radio continuum mapping, optical imag-
exp
physical parameters and total abundances (Go´rny et al. 2004), ing, and long-slit optical spectroscopy,in both, high- and low-
namely, electron density and temperature N [S]=2600cm−3, dispersion.Wediscussourresultsonthemorphology,kinemat-
e
T [N]=12,097K, T [O]=11,845K; and abundance ratios ics,physicalconditions,ionicabundances,andnatureofthegas
e e
He/H=0.1, N/H=8.20, O/H=8.64, Ne/H=7.82, and S/H=6.49 emissiontoexplorethepossiblemechanismsinvolvedinthefor-
(logH=12,exceptforHe/Hratio).Armour&Kingsburgh(2001) mationofNGC6309.
foundsimilarvalues.NGC6309hasalsobeenincludedinthelist
ofPNewithlowionisationstructures(LIS)byGonc¸alvesetal.
(2003).Finally,thecentralstarofNGC6309hasbeenclassified 2. Observationsandresults
asa“weakemissionlinestar”byGo´rnyetal.(2004).
2.1.CCDground-basedimaging
Inspiteofthissuggestivemorphology,aninternalkinematic
study of NGC6309, as well as a full analysis of the physical We obtained narrow-band direct images with the Calar Alto
conditions in the different nebular regions, has not yet been Faint Object Spectrograph (CAFOS) in the 2.2m telescope at
Va´zquezetal.:ThephysicalstructureofNGC6309 3
Calar AltoObservatory(CAHA1) in1998July8.We usedtwo
filters centered in Hα (∆λ = 15Å) and [N]6583 (∆λ = 20Å) N NGC 6309
aswellasaCCD Loralwith2048×2048pixels.Theexposure
timeforbothimageswas1800s.Thescalewas0′.′33pixel−1and
the seeing was about1′.′7. We obtained an additionalimage on E
2004August 3 with the 1.5m telescope at the Observatoriode
SierraNevada2. The detectorwasa RoperScientificVersArray
CCDwith2048×2048pixels,eachof0′.′232pixel−1.Weusedan
[O]5007(∆λ=50Å)filterwithanexposuretimeof900s.The
imageswere reducedfollowingstandard procedureswithin the
MIDASpackage.Inthiscase,seeingwas1′.′3.
Figure 1 shows the images of NGC6309 in Hα, [N] and
[O]. Anadditionalunsharpmasking[O] imageisalsopre-
sented in Fig. 1 to show the link between internaland external
nebularstructures.Intheseimages,thehighcontrastbetweenthe
brightnessofthecentralregionandthatofthe‘arms’isevident.
Inparticular,thelackofemissionof[N]fromthe‘arms’isun-
expectedlyremarkablegiventhat,ingeneral,thiskindofpoint-
symmetric microstructures is related to LIS (Gonc¸alves et al.
2003).However,therearealsosomecasesinwhichtheemission
of [N] is marginal(e.g. IC5217;Miranda et al. 2006). In the
case of NGC6309, the lack of [N] from the point-symmetric 10" HST−WFPC2−F555W
knotsindicatesthatthesecannotbeconsideredasLIS.
The structureofthe ‘arms’consistsof atleast fourpairsof Fig.3. HST broad-bandCCD image of NGC6309 in the filter
point-symmetricknots, some of them clearly extendedperpen- F555W.
diculartotheircorrespondingradialvectorfromthecentralstar.
The central region of the NGC6309 is a bright ellipse (major
axis ≃ 20′′, PA−14◦) embedded in the main body of the neb- showsthe140secimageusingthefilterF555W(nearlyJohnson
ula. The arms appearto leave from the vertexesof this ellipse. V).Thisimagecanbecomparedwiththeopticalground-based
Theunsharpmasking[O]imagealsoshowsaconelikestruc- imagesin Fig. 1. The brightellipse is formedbymany clumps
turewithitsbaselocatedonthecentralellipseandthevertexon aswellasdiffusegas.Theellipse isopeninits SWandSEre-
theNEarm.In[O],faintemissionconnectsthearmswiththe gions,whereasanapparentlydoublestructureisobservedinthe
brightellipseandseemstotraceasymmetricallobes.Infact,the SandNregions.Inaddition,asystemoffaintbubblesisdetected
appearanceofNGC6309in[O]resemblesthatofaquadrupo- towardstheNE,whichisprobablyrelatedtothecone-likestruc-
lar PN in which one of the outflows (at PA40◦) protrude into tureseenin[O](seeabove).Giventheshortexposuretimeof
the lobesof the other (at PA76◦). Part of the SW lobe appears theHSTimage,evidenceofthe“arms”isverymarginal.
to be open.Finally, a circular fainthalo(probablyspherical)is
detectedin[O]image(Figs.1and2).Itscentercoincideswith
thecentralstarofthenebulaanditssizeis≃56′′. 2.3.λ3.6-cmVLA-D
In Fig. 2, we show the unsharp masking [O] image and We obtained radio continuum observations at λ3.6-cm, toward
label some morphologicalfeatures that will be discussed later. NGC6309 with the Very Large Array (VLA) of the National
Knots in the NE arm are named E1, E2, E3, and E4, whereas Radio Astronomy Observatory (NRAO)4 in the D configura-
thoseintheSWarmarenamedW1,W2,W3,andW4.Regions tionduring1996August8.ThestandardVLAcontinuummode
intheellipsearecalledR1andR2forthetipsofitsmajoraxis, with a 100 MHz bandwidthand two circular polarizationswas
andR3andR4forthosealongtheminoraxis. employed. The flux and phase calibrators were 1331 + 305
(adoptedfluxdensity5.2Jy)and1733−130(observedfluxden-
sity 10.7Jy), respectively. We set phase center at α(2000) =
2.2.HST-WFPC2imaging
17h14m03s.6, δ(2000) = −12◦54′37′′. The on-target integration
An Hubble Space Telescope (HST) broadbandimage from the time was 28 min. We calibrated the data and processed it us-
MASTArchive3wasusedinordertoimprovethegeneralview ing standardproceduresof the AstronomicalImage Processing
of the internal morphology of NGC6309 (proposal ID: 6119; System (AIPS) package of the NRAO. We obtained a cleaned
PI:H.E.Bond;Dateofobservation:1995August26).Figure3 map of NGC6309 using the task IMAGR of AIPS (parame-
terROBUST= −3;Briggs1995).Self-calibrationwasalsoper-
1 TheCentroAstrono´micoHispano-Alema´n(CAHA)atCalarAlto, formedresultinginafinalsynthesizedbeamof13′.′9indiameter
isoperatedjointlybytheMax-PlanckInstitutfu¨rAstronomieandthe andrmsnoiseofthemapofσ=33µJybeam−1.
InstitutodeAstrof´ısicadeAndaluc´ıa(CSIC).
The detected radio continuum emission is related to the
2 The Observatorio de Sierra Nevada is operated by the Consejo
central region and appears partially resolved. Based on a 2-D
Superior de Investigaciones Cient´ıficas through the Instituto de
Astrof´ısicadeAndaluc´ıa(Granada,Spain) Gaussianfit(taskIMFITinAIPS),weestimateasizeof≃19′′×
3 Some of the data presented in this paper were obtained from 16′′atPA=−27◦(seeFig.4).Thepositionoftheintensitypeak
the Multimission Archive at the Space Telescope Science Institute wasfoundatα(2000) = 17h14m04s.28,δ(2000) = −12◦54′37′′.
(MAST). STScI is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS5-26555. 4 The National Radio Astronomy Observatory is a facility of the
SupportforMASTfornon-HSTdataisprovidedbytheNASAOfficeof NationalScienceFoundationoperatedundercooperativeagreementby
SpaceScienceviagrantNAG5-7584andbyothergrantsandcontracts. AssociatedUniversities,Inc.
4 Va´zquezetal.:ThephysicalstructureofNGC6309
LOBE NE
HALO
RING
E1 R3
E2
R1
E3
R4
E4
W4
W3
CONE
R2 W2
W1
LOBE SW
20"
Fig.2.Unsharp-maskingimageofNGC6309inthelightof[O].Northisupandeastisleft.Mainmorphologicalfeaturesaswell
assomeregionsofparticularinterestarepointedoutandlabeled.
Thetotalflux densityfromthe radiomapis ≃ 115-mJy,which 2.4.Longslitlow-dispersionspectroscopy
issimilartothosemeasuredbyMilne&Aller(1982);Ratag&
Pottasch (1991); and Condon & Kaplan (1998); at 2cm (146- Low-dispersion optical spectra were obtained with the Boller
mJy); 6cm (102-mJy);and 21cm (132-mJy);respectively. We & Chivens spectrometer in the 2.1m UNAM telescope at the
didnotdetectemissionfromthe‘arms’. SanPedroMa´rtirObservatory(OAN-UNAM)in1999July19-
20 (grating of 300lines/mm) and 2002 August 7-8 (grating of
400lines/mm). In all of these cases, a CCD Tek 1024× 1024
We also derived the mean physical conditions, based on was used as detector. We set the slit width to 220µm (1.6′′).
the formalism of Mezger & Henderson (1967). Optically-thin Thespatialscale is 1′.′05pixel−1 whereasthespectralscale is 3
emission and T = 10,000K were assumed, obtaining the
e and4Åpixel−1forthegratingsof400and300lines/mm,respec-
following results: N = 1900cm−3; M(H)=0.07M ; EM =
e ⊙ tively.Wesettheslitatseveralpositionangles,whicharelabeled
5.1 × 105pccm−6. We assumed distance to the nebula to be
asC,J,K,L(gratingof300lines/mm),andA,C,andE(grating
2kpc as the average value from the different estimates, which
of400lines/mm),inFig.5.
range between 1.1 and 2.5kpc (e.g., Daub 1982, Phillips &
Pottasch 1984, Amnuel, et al. 1984, Maciel 1984, Cahn, Kaler Table1showsthedereddenedspectra(consideringcaseBof
&Stanghellini,1992). recombination)andphysicalconditionsobtainedwiththeFive-
Va´zquezetal.:ThephysicalstructureofNGC6309 5
to be quite uniform (T [O]=10750K, N [Cl]=2350cm−3,
-12 54 00 e e
N [Ar]=1430cm−3), withvariationswithinthe estimatedun-
e
certainties. However, those physical parameters obtained from
low-excitationemissionionsappearasseparatedintwodifferent
15 regimes (T [N]=10200K, and 11800K; N [S]=1620cm−3
e e
and3800cm−3).
0) The dereddened absolute Hβ flux values from regions R1,
0
0
2 R2, R3, and R4 are similar (see Table 1). However, the cor-
N (J 30 responding logarithmic extinction coefficients c spread from
O Hβ
TI 0.70to0.97(meanvalueincludingallregionsis0.87),probably
A
LIN due to differences in the internal dust distribution, as has been
EC 45 found in other PNe (e.g. Va´zquez et al. 1999b, Lee & Kwok
D
2005).
Inaddition,wepresentthemorecommonratiosforplasma
diagnosticsatthebottomofTable1, whichshowthatthesere-
55 00
gions are emitting by photoionisation-recombinationprocesses
with minimal or nonexistent shock-cooling contributions. This
could be expected in the surroundings of a hot luminous star,
15 howeverthereareseveralcasesofPNeinwhichshock-cooling
17 14 07 06 05 04 03 02 processesmakeanimportantcontributiontothemicrostructures
RIGHT ASCENSION (J2000)
emission (see Gonc¸alves2003 for a compilation).For compar-
Fig.4. Contour plot λ3.6-cm continuum map of NGC6309,
ison, previousspectroscopic studies of NGC6309 by Go´rny et
overimposedonaHαimage.Contourlevelsare10,20,30,40, al. (2004) give values of c(Hβ) ≃ 0.88, T ([O])≃11845K,
50,60,70,80,and90%ofthepeakflux(6.3×10−3Jy).Thehalf- T ([N])≃12097K,andN ([S])≃2600cme−3.
powerbeamwidth(13′.′9indiameter)isshowninthebottom-left e e
Wehavealsoestimatedionicandelementalabundancesfor
corner.
some regions using IRAF and the ICF (Ionisation Correction
Factors)method(Kingsburgh&Barlow1994),althoughweare
N aware that recently, Gonc¸alves et al. (2006) have noticed that
E
elementalabundancesderivedbyusingthismethodareoveres-
J K
timatediftheyareobtainedfromnarrow,long-slitspectra.The
G resultsareshowninTables2and3.
H L RegionsR1andR2aresimilarinphysicalconditionsaswell
as in ionic abundances. In both regions, the abundances of the
I threespeciesofoxygenaswellasHe+,Ar+2,N+,S+,andCl+2
areenhancedwithrespecttotheotherregions.Theoppositeoc-
A
cursforAr+3andHe+2.
B
Withreferencetoelementalabundances,theseareconsistent
C with the mean values for PNe and Type I PNe, within uncer-
tainties (see Table 3). The exception is N, which show a defi-
D
ciency, more in agreement with less-evolved objects, but con-
E
sistent with previous estimates (Armour & Kingsburgh 2001).
F Given the values of these abundances, NGC6309 would be a
Type II PN (intermediate population), according to the classi-
fication of Peimbert (1978). This is reinforcedby the low N/O
ratio,whichis in agreementwith theexpectedvaluefora low-
masscentralstar(0.6M⊙,accordingtoKwok2000).Ifthisin-
terpretationoftheabundancesisright,NGC6309wouldrepre-
sentanothercaseofanon-TypeIPNwithbipolaroutflows(see
Va´zquezetal.1999a).Thisstrengthenstheideapointedoutby
Fig.5.Slitsusedinspectroscopyoverimposedon[O]unsharp Va´zquezetal.thatsomelow-masscentralstarsmayalsodevelop
maskingimage. bipolarmorphologies,incontrasttothefactthatbipolarPNeare
usuallyassociatedwithrelativelymassivecentralstars(Corradi
&Schwarz1995).
LevelAtomDiagnosticsPackage(nebular)fromIRAF5 (apply-
ingtheextinctionlawbyHowarth1983fordereddening)forthe
regionsR1,R2,R3,R4,E2,W1,andW1. 2.5.Longslithigh-dispersionspectroscopy
Physical conditions can only be determined for the re-
Weobtainedhigh-dispersionopticalspectrawiththeManchester
gions of the central ellipse. Electron temperature and densi-
EchelleSpectrometer(MES)inthe2.1mtelescope(f/7.5)atthe
ties obtained from the high-excitation emission lines appears
SanPedroMa´rtirobservatory(OAN-UNAM)duringtheperiod
of 2001 May 22-23. We used a CCD SITe with 1024× 1024
5 TheImageReductionandAnalysisFacility(IRAF)isdistributedby
pixels was used as detector, and set the slit width to 150-µm
theNationalOpticalAstronomyObservatories,whichareoperatedby
theAssociationofUniversitiesforResearchinAstronomy,Inc.,under (1.6′′). A 2 × 2 binning was used, resulting in a spatial scale
cooperativeagreementwiththeNationalScienceFoundation. of0′.′6pixel−1andaspectralscaleof0.1Åpixel−1.Wecentered
6 Va´zquezetal.:ThephysicalstructureofNGC6309
the spectral range at the Hα emission line. The spectra were Table4.Basickinematicaldataforthemainmorphologicalfea-
wavelengthcalibratedwitha Th-Ararc lampto anaccuracyof turesinNGC6309.Angulardistanceandpositionangle(PA)are
±2kms−1.Theachievedspectralresolution,asindicatedbythe measuredfromthecentralstar.Radialvelocityismeasuredwith
FWHMofthecomparisonlines,was12kms−1.Severalspectra respecttothesystemicvelocity(–32kms−1)fromtheemission
wereobtainedwiththeslitorientedE-W(slitsAtoFonFig.5). lineindicatedinthelastcolumn.Uncertaintiesforthe firstrow
Weobtainedon2004July29-30,asecondseriesofspectra, applytotherest.
usingthesametelescopeandinstrument.Inthiscase,thespectra
were centered on the [O]λ5007 emission line (slits G, H, I,
andKonFig.5),andthespectralscalewas0.08Åpixel−1.
Feature PA Angular Radial Emission
Position-velocity(PV)mapsfortheHαand[O]λ5007are (◦) distance velocity line
shown in Fig. 6. We note that the Heλ6560 line is also ob- (′′) (kms−1)
servedinthePVmapsattheslitsB,C, andD.InthePVmaps
R1 –15±4◦ 9 ±3′′ 0±2kms−1 [O]
(Fig.6)relativepositionismeasuredwithrespecttothecentral
R2 +165 10 0 [O]
starwhereasradialvelocityismeasuredrelativetothesystemic R3 +75 4 +23 [O]
velocity,forwhichwededuceVLSR =−32±2kms−1,basedon R4 –105 4 –23 [O]
the expansionvelocityat the positionof the centralstar ([O] E1 +50 30 +35 [O]
spectrafromslitsHandK).Thisvalueisclosetothatreported E2 +60 26 +36 Hα,[O]
bySchneideretal.(1983)ofV ≃−33.4±2.8kms−1. E3 +70 27 +35 Hα
LSR
In a firststepto analysethe high-resolutionspectra,we ex- E4 +90 25 +24 Hα
tract from the PV maps the spatial position and radial velocity W1 –130 27 –34 Hα
W2 –120 25 –36 Hα,[O]
oftheindividualregionslabeledinFig.2.Theresultsarelisted
W3 –110 24 –34 Hα,[O]
in Table 4. The knots in the arms present a noticeable point-
W4 –90 21 –20 Hα
symmetry,bothintheir positionwith respecttothe centralstar
andintheirradialvelocity.Inthecaseoftheregionsinthebright
ellipse,R1andR2aremovingatthesystemicvelocitywhileR3
andR4,locatedalongtheminoraxis,presentthemaximumra- On the other hand, the PV map of slit I shows the radial
dialvelocityinthisstructure. velocity of feature E4 (the brightest feature) as ≃ +24kms−1,
in addition to the expansion velocity of lobe SW close to ≃
Inasecondstep,weanalysetheemission-linefeaturesinthe
40kms−1. Finally, the PV map of slit C covers the region at
PVmapsasawhole.SlitsHandKaretracingtheminorandma-
lobe NE corresponding to the cone-like structure. This region
joraxesoftheinternalellipse,respectively.InthePVmapofslit
expands to ≃ 25kms−1, and is located from 5′′ to 15′′ toward
H (Fig. 6), the regionsE2 and W2 can be noted as brightcon-
the East from the center. The kinematics of the cone is practi-
densationslocatedattheextremesoftheemission-linefeatures.
callyindistinguishablefromthatoflobeNE.
Maximum expansion velocity at the lobes can be measured as
2v ≃ 80kms−1 (SW lobe expansion is best viewed in panel
exp
I). The lobe NE shows a bulk radial velocity of ≃ +20kms−1 3. Discussion
(asmeasuredat20′′fromthecenter,panelH),whereasthelobe
SWpresents≃−20kms−1 (asmeasuredat20′′fromthecenter, 3.1.ThephysicalstructureofNGC6309
panelI).Thecentralregionalsoseemstobeexpanding,showing
Themostreasonableexplanationforthemorphologyandkine-
amaximumvelocitysplittingof2v ≃ 69±2kms−1,making
exp maticsofthecentralellipseisthatsuchstructurecorrespondsto
itdifficulttodeterminetheradialvelocityofthemicrostructures
a tilted expandingtorus.Althoughotherpossible structuresare
R3andR4accurately.However,thePVmapfromslitH([O])
possible,thisinterpretationappearstobeabetterfittoourdata.
shows evidence of two additional components separated ≃ 8′′
Assuming that the torus is circular and its diameter is ≃ 20′′,
and≃ 46kms−1 thatcouldbethesefeatures(locationsareindi-
wededuceaninclinationangleofthetorusaxiswithrespectto
catedonFig.6byapairofarrows).
thelineofsightof66◦.Theexpansionvelocityofthetorus,cor-
SlitKcrossesthemajoraxisoftheellipse.Inthecorrespond- rected by the inclination angle is V ≃ 25kms−1. Therefore,
exp
ingPVmap,avelocityellipseisobserved.FeaturesR1andR2 the size of this structure and its kinematic age are ≃ 0.2pc
movewiththesystemicvelocity.However,smallregionsbeyond
and3800yrrespectively,assumingadistanceof2kpc.Inaddi-
theellipsearealsofoundwithradialvelocitiesof≃±30kms−1.
tion,thenortheasternhalfofthetorusisblueshiftedwhereasthe
Maximumexpansionvelocityisobservedatthecenteroftheel-
southwesternhalfis redshifted.We notethat these calculations
lipse (2v ≃ 66±2kms−1), which is nearly compatible with
exp havebeenobtainedfromtheearth-basedobservations.Sincethe
previousspectroscopicstudies(Sabbadin1984,≃68±3kms−1; HST imageshowsa morecomplexstructurein the torus,these
Armour&Kingsburgh2001,≃64±5kms−1). resultsshouldbeconsideredasanapproximationonly.
From these slits (H and K), the presence of two expanding With regard to the bipolar lobes, it is clear that a model
asymmetricallobesandavelocityellipseinthecenterisevident. of a single bipolar system with a main axis cannot reproduce
Theexpansionofthesebipolarlobesisconfirmedwithdatafrom theobservedmorphology,giventheapparenttwodirectionsob-
the other slits, and the kinematics of their borders is traced by servedinthenebula.Therefore,wehaveconsideredaquadrupo-
thatofthepoint-symmetricknots. lar modelconsisting oftwo pairsof bipolarlobes, one ofthem
In the PV map from slit A, we detect an intense emission orientedatPA+76◦,coincidentwiththetorusaxis,andtheother
centeredat2′′ towardthewestandrelativevelocitycenteredat atPA+40◦,coincidingwiththeapparentprotrusionsinthelobes
V ≃ +20kms−1. This feature correspondsto the upper border along this axis. Each of these bipolar systems is described fol-
r
of the ellipse (≃ 5′′ above R1). Faint emission from the halo lowingtheformulationbySolf&Ulrich(1985),
is detected to the west of this feature (up to ≃ 10′′ − 25′′) in
agreementwiththeobservedsizeofthisstructure. V(φ)=Ve+(cid:16)Vp−Ve(cid:17)×sinα(|φ|), (1)
Va´zquezetal.:ThephysicalstructureofNGC6309 7
East West NE SW
A
G
B
)
s
/
m
k
(
y
t
i
c C H
o
l
e
v
e
v
i
t
a
l
e
R
D
I
SE NW
E
F K
Offset (arcsec)
Fig.6.Position-velocitygray/contourmapscorrespondingtotheslitsAtoFinthelightofHα(leftpanels),andslitsG,H,I,and
K in [O]λ5007(rightpanels).Slitorientationis indicated,beingthe same forall theleftpanels.Inthe rightpanelsorientation
is indicated on panels for slits G (valid also for H and I) and K. Velocity scale is different in left and right panels. The vertical
dashedlinesrepresenttheprojectedpositionofthecentralstarperpendiculartothecorrespondingslitposition.Oneachpanel,the
horizontaldashedlinecorrespondstothesystemicradialvelocity(V = −32±2kms−1).ArrowsinpanelHindicatelocationof
LSR
twofeaturesexplainedinthetext.
8 Va´zquezetal.:ThephysicalstructureofNGC6309
whereφisthelatitudeangleabovetheequator;V andV arethe
e p
equatorialandpolarexpansionvelocityrespectively;andαisan
exponentthatfitsthespecifichour-glassshape.Withthemainas-
sumptionthattheaxisofthetorusandthatofthebipolarejection
atPA+76◦arethesame,thekinematicsandmorphologyofthis
outflowcanbereasonablyreproducedwithV = 25kms−1 (ex-
e
pansionvelocityofthetorus),V =75kms−1,andα=6.There
p
isnoclueabouttheinclinationangleoftheoutflowatPA+40◦.
Ifweassumethesameinclinationangle,wefindreasonablefits
for this bipolar system with V = 29kms−1, V = 86kms−1,
e p
and α = 6. In Fig. 7, we show the hour-glass shapes deduced
from these fits overimposed on the unsharp-masking image of
NGC6309. The observed shape, as well as the kinematics of
the knots, are reasonably reproduced by the models. With the
model data and the assumption of a distance of 2kpc, we find
a kinematical age of 4000yr for the bipolar lobes at PA+40◦
and of 3700yr for the bipolar system at PA+76◦. These ages
arenotverydifferentfromeachotherandarealsosimilartothe
age deduced for the torus. This suggests that the formation of
thedifferentstructuresinNGC6309hasoccurredinarelatively
smalltimespan.Inaddition,asthesekindofoutflowshavebeen
observedinproto-planetarynebulae(PPN,e.g.Sahai1998),our
resultsimposeaminimalvalueoftime(≃ 4000yr)forthePPN
to PN stage in this nebula. Other structuressuch as the “cone” Fig.7. NGC6309 and the two bipolar outflows model. The fit
and the halo, are present in this nebula, but we must conduct oftwohour-glassmodelsisoverimposedonthe[O]unsharp-
furtherstudiestounderstandtheirphysicalproperties. maskingimagepresentedbefore.Thecentraltorusisalsodrawn.
3.2.TheformationofNGC6309
The appearance of NGC6309, as well as the position of the
point-symmetric knots perpendicular to a radial position vec-
torfromthecentralstar,stronglyresemblethepoint-symmetric
structures observed in Fleming1 (Lo´pez et al. 1993). Cliffe et
al. (1995) studied the interaction of a precessing jet with the
interstellar medium. They find that point-symmetric structures
can be formed by this interaction, and with the time, the indi-
vidualbow-shockscanmergeintoasingleshockstructure.The
ulterior evolution of such structures will lead to the formation
ofbipolarlobeswithnon-uniformbrightnessdistributionbeing
point-symmetric respect to the central star. On the other hand,
Garc´ıa-Segura&Lo´pez(2000)mademodelsofbipolarPNwith
point-symmetric structures using a steady misalignment of the
magneticcollimationaxiswithrespecttothe symmetryaxisof
the bipolar outflow. In their models, such morphology is also
producedbytheactionofjets.
A possible scenario for the formation of NGC6309 is that 20||
the knots are the remnants of high-velocity bipolar collimated
outflows that were ejected in the proto-planetarynebula (PPN)
stage. There is evidence that precessing jets in young proto-
PN carve bipolar or multipolar cavities in the initial stage of Fig.8. [O]/Hα ratio image. White represents high values of
PNe evolution (e.g. Sahai & Trauger 1998, Sahai et al. 2005, theratio.
Sa´nchez-Contrerasetal.2006).Insuchascenario,theprecess-
ingjetisejectedduringtheproto-PNphaseandafterthat,subse-
quently,itisstoppedandcooledbyitssurroundings.Theknots
follow the thermalexpansionof the bipolarlobes. In this case,
thebrightnessoftheknotscomesmainlyfromthephotoionisa- [O] emission is seen in the edge of the lobes, clearly related
tionprocess,astheshocked-cooledemissionhasturnedofforit to the point-symmetricknots. It is noticeable that the emission
ishiddenby theeffectofa high-excitationphotonsource.This vanishedattheendoftheSWlobe,possiblycorrespondingtoa
couldexplainthelackof[N]emissioninthepoint-symmetric breakingoftheshellduetotheactionoftheoutflow.According
knots. toMedinaetal.(2007),the[O] enhancementwouldbecom-
In addition, we constructed a [O]/Hα ratio image from patiblewithstructuresshapedbycollimatedoutflows,asinthe
images in Fig. 1. Such ratio image can be used as a diagnos- caseofIC4634.Finally,thecircularhaloprobablycorresponds
tic tool, as has been shown by Medina et al. (2007). Figure 8 totheremnantofthe envelopeejectedasaslowwindfromthe
showsthe[O]/Hαratioimageinwhichanenhancementofthe centralstarwhenitwasatitsAGBphase.
Va´zquezetal.:ThephysicalstructureofNGC6309 9
4. Conclusions Go´rny,S.K.,Stasinska,G.,Escudero,A.V.,Costa,R.D.D.2004,A&A,427,
231
We have carried out an analysis of the planetary nebulae Grevesse,N.,Asplund,M.,Sauval,A.J.2007,SpaceSci.Rev.,130,105
NGC6309, based on ground-based and space-based imaging, Howarth,I.D.1983,MNRAS,203,301
high-andlow-dispersionspectroscopy,aswellasVLA-Dradio Icke,V.1988,A&A,202,177
Kahn,F.D.&West,K.A.1985,MNRAS,2012,837
continuum.Wesummarizethemainconclusionsofthisworkas
Kingsburgh,R.L.&Barlow,M.J.1994,MNRAS,295,75
follows. Kwok,S.,Purton,C.R.,Fitzgerald,P.M.1978,ApJ,219,L125
NGC6309canbedescribedasaquadrupolarPNformedbya Kwok,S.2000,Theoriginandevolutionofplanetarynebulae.Cambridge;New
brightcentraltorus,twosystemsofbipolarlobesorientedatdif- York:CambridgeUniversityPress,2000.(Cambridgeastrophysics series;
33)
ferentdirections,andpoint-symmetricknotsthattracetheedges
Lee,T.-H.,Kwok,S.2005,ApJ,632,340
of the lobes. The torus expands at 25kms−1, whereas the po-
Livio,M.,Pringle,J.E.1996,ApJ,465,L55
larexpansionvelocityofthelobesis75kms−1forafirstbipolar Livio,M.,Pringle,J.E.1997,ApJ,486,835
systematPA76◦,and86kms−1foranotherbipolarsystematPA Lo´pez,J.A.,Meaburn,J.,Palmer,J.W.1993,ApJ,415,L135
40◦.Assumingadistanceof2kpcforthenebula,thekinematic Lo´pez,J.A.,Va´zquez,R.,Rodr´ıguez,L.F.1995,ApJ,455,L63
Maciel,W.J.1984,A&AS,55,253
ages of the structures ranges from 3700 to 4000yr, suggesting
Mellema,G.1995,MNRAS,277,173
thattheyhavebeenformedinashorttimespan.Theknotsatthe Medina, J. J., Guerrero, M. A., Luridiana, V., Miranda, L. F., Riera, A.,
edges of the lobes suggest that the lobes have been formed by Vela´zquez, P. F. 2007, in “Asymmetrical Planetary Nebulae IV”, eds. R.
rapidlyprecessingbipolarjets thatcarvedcavitiesin the previ- L.M.Corradi,A.Manchado,&N.Soker,Proceedingsinelectronicbook
(referencewillbepublishedinADS).
ousredgiantenvelope.Inadditiontothesestructures,wedetect
Mezger,P.G.,Henderson,A.P.1967,A&A,147,471
a circular halo surrounding the torus and bipolar lobes, which
Milne,D.K.,Aller,L.H.1982,A&AS,50,209
probablycorrespondstotheenvelopeejectedintheAGBphase Miranda,L.F.,Solf,J.1992A&A,260,397
bythecentralstar.Thereisalso aconelikestructureembedded Miranda,L.F.,Ayala,S.,Va´zquez,R.,Guille´n,P.F.2006A&A,456,591
inoneofthelobesandwithitsbaseonthetorus. Peimbert, M. 1978, in Planetary Nebulae, IAU Symp. 76, ed. Y. Terzian,
(Dordrecht:Reidel),215
We also study internalvariationsofthe physicalconditions
Perinotto,M.Scho¨nberner,D.,Steffen,M.,Calonaci,C.2004,A&A,414,993
and chemical abundances in NGC6309. The low-dispersion Phillips,J.P.,Pottasch,S.R.1984,A&A,130,91
spectra indicate a high-excitation nebula, with low to medium Ratag,M.A.,Pottasch,S.R.1991,A&AS,91,481
variations of its internal physical conditions (10,600K . Rijkhorst,E.-J.,Icke,V.,Mellema,G.2004,in“AsymmetricalPlanetaryNebulae
T [O] . 10,900K; 10,100K . T [N] . 11,800K; III” editors M. Meixner, J. Kastner, N. Soker, & B. Balick, ASP Conf.
e e Series,313,p.472
1440cm−3 . Ne[S] . 4000cm−3; 1700cm−3 . Ne[Cl]. Rijkhorst,E.-J.Mellema,G.&Icke,V.2005,A&AS,444,849
2600cm−3; 1000cm−3 . N [Ar] . 1700cm−3). The ra- Sabbadin,F.1984,A&AS,58,273
e
dio continuum emission indicates a mean electron density of Sahai,R.,Trauger,J.T.1998,AJ,116,1357
≃ 1900cm−3; emission measure of 5.1 × 105pccm−6; and an Sahai,R.,LeMignant,D.,Sa´nchez-Contreras, C.,Campbell,R.D.,Chafee,F.
H.2005,ApJ,622,L53
ionisedmass M(H)≃ 0.07M .Thelogarithmicextinctionco-
⊙ Sa´nchez-Contreras, C.,LeMignant, D.,Sahai, R.,Chaffee, F.H.,Morris, M.
efficientcHβ rangefrom 0.70to 0.97(mean value 0.87),which 2006inIAUSymp234,PlanetaryNebulaeinourGalaxyandBeyond,eds.
probablyisproducedbydifferencesintheinternaldustdistribu- M.J.Barlow&R.H.Mendez,CambridgeUniversityPress,pp.71
tion. Schneider,S.E.,Terzian,Y.,Purgathofer,A.,Perinotto,M.1983,ApJS,52,399
Schwarz,H.E.,Corradi,R.L.M.,Melnick,J.1992,A&AS,96,23
Shaver,P.A.,McGee,R.X.,Newton,L.M.,Danks,A.C.,Pottasch,S.R.1983,
Acknowledgements. RV, SA, LO, MEC, and PFG were supported by grants MNRAS,204,53
32214-E and 45848 (CONACYT), and by grants IN114199 and IN111903-3 Scho¨nberner,D.,Jacob,R,Steffen,M.,Perinotto,M.,Corradi,R.L.M.,Acker,
(PAPIIT-DGAPA-UNAM).LFM and SA were supported by grant AYA2005- A..2005,A&A,431,963
01495oftheSpanishMEC(cofunded byFEDERfunds).JMTacknowledges Scho¨nberner,D.,Jacob,R.,Steffen,M.,Sandin,C.2007,A&A,473,467,
partialfinancialsupportfromtheSpanishgrantAYA2005-08523-C03. Weare Solf,J.,Ulrich,H.1985,A&A,148,274
gratefultothestaffofalltheastronomicalfacilitiesusedinthisresearch,namely: Stanghellini,L.,Corradi,R.L.M.,Schwartz,H.E.1993,A&A,276,463
(a) Centro Astrono´mico Hispano-Alema´n, (b) Very Large Array of National Va´zquez,R.,Lo´pez,J.A.,Miranda,L.F.,Torrelles,J.M.,Meaburn,J.1999a,
Radio Astronomy Observatory, (c) Hubble Space Telescope Data Archive, MNRAS,308,939
(d) Observatorio Astrono´mico Nacional, operated by Universidad Nacional Va´zquez,R.,Torrelles,J.M.,Rodr´ıguez,L.F.,Go´mez,Y.,Lo´pez,J.A.,Miranda,
Auto´nomadeMe´xico,and(e)ObservatoriodeSierraNevada(IAA-CSIC).We L.F.1999b,ApJ,515,633
thanktheanonymousrefereeforcriticallyreadingthemanuscriptandforuse- Va´zquez,R.,Miranda,L.F.,Torrelles,J.M.,Olgu´ın,L.,Ben´ıtez,G.,Rodr´ıguez,
fulsuggestions.WealsothankfruitfuldiscussionswithDr.Mart´ınA.Guerrero L.F.,Lo´pez,J.A.2002,ApJ,576,860
(IAA-CSIC)andProf.MauricioTapia(IA-UNAM).Thisresearchhasmadeuse
oftheSIMBADdatabase,operatedatCDS,Strasbourg,France.
ListofObjects
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10 Va´zquezetal.:ThephysicalstructureofNGC6309
Table1.DereddenedspectraandphysicalconditionsfromdifferentregionsinNGC6309.IntensityvaluesarerelativetoI =100.
Hβ
Extinctionlaw(f )isfromHowarth(1983).Thesizeoftheintegrationregion(inarcsec)alongtheslitis7′.′4forR1,R2,R3,and
λ
R4,and5′.′3fortherest.Slitwidthwassetat1′.′6inallthecases.
Ion λ (Å) f R1 R2 R3 R4 E2 W1 W2
0 λ
[O] 3727 0.256 108 102 — — — — —
[Ne] 3869 0.230 163 165 — — — — —
[Ne] 3968 0.210 68 67 — — — — —
[S] 4071 0.189 6.5 — — — — — —
Hδ+He 4101 0.182 33 34 — — — — —
Hγ 4340 0.127 55 53 26 27 52 — —
[O] 4363 0.121 12 12 7.9 8.5 — — —
He 4471 0.095 8.2 7.1 3.4 3.2 — — —
He 4540 0.078 — — 2.8 3.3 — — —
N 4640 0.054 4.3 5.0 5.2 6.1 — — —
He 4686 0.043 29 31 81 79 86 106 —
[Ar] 4711 0.037 6.0 5.8 12 12 — — —
[Ar] 4740 0.030 4.6 4.6 9.4 9.3 — — —
Hβ 4861 0.000 100 100 100 100 100 100 100
[O] 4959 -0.024 487 464 335 365 341 364 451
[O] 5007 -0.036 1504 1466 993 1081 1046 1097 1238
N 5199 -0.082 0.9 — — — — — —
He 5411 -0.133 2.5 2.3 6.2 6.0 8.5 — —
[Cl] 5517 -0.154 1.1 1.0 0.7 0.7 — — —
[Cl] 5537 -0.157 1.0 1.0 0.7 0.6 — — —
[N] 5755 -0.195 1.0 1.0 0.6 — — — —
He 5876 -0.215 13 12 7.1 8.1 — — —
[O] 6300 -0.282 6.8a 7.2a 2.5 1.2 — — —
[S] 6312 -0.283 — — 1.8 1.7 — — —
[O] 6364 -0.291 1.9 1.8 0.8 0.4 — — —
[Ar] 6435 -0.302 — — 1.4 1.4 — — —
[N] 6548 -0.318 24 31 9.3 4.7 — — —
Hα 6563 -0.320 285 285 283 284 284 284 284
[N] 6583 -0.323 60 60 27 12 8.8 — —
He 6678 -0.336 3.4 3.6 2.4 2.6 — — —
[S] 6717 -0.342 8.0 9.1 2.9 1.3 — — —
[S] 6731 -0.344 11 12 4.8 2.1 — — —
[Ar] 7006 -0.380 — — 3.1 2.7 — — —
He 7065 -0.387 3.1 3.1 1.9 2.0 — — —
[Ar] 7136 -0.396 17 19 14 13 19 21 21
[Ar]+[Fe] 7170 -0.401 1 — 0.9 0.3 — — —
He 7178 -0.401 — — 0.9 0.7 — — —
[O] 7320 -0.419 5.6b 5.7b 2.3 1.4 — — —
[O] 7330 -0.420 — — 2.0 1.3 — — —
c 0.96 0.97 0.70 0.80 0.86 0.85 0.97
Hβ
log I -13.4 -13.5 -13.2 -13.4 -15.2 -15.3 -15.9
Hβ
T [O] (K) 10800 10900 10700 10600 — — —
e
T [N] (K) 10300 10100 11800 — — — —
e
N [S] (cm−3) 1800 1440 4000 3600 — — —
e
N [Cl] (cm−3) 2100 2350 2600 1700 — — —
e
N [Ar] (cm−3) >1000 >1500 >1700 >1500 — — —
e
logHα/[N] 0.533 0.499 0.889 1.244 — — —
logHα/[S] 1.182 1.142 1.565 1.913 — — —
log[Oiii]5007/Hα 0.723 0.711 0.545 0.580 — — —
logλ6717/λ6731 0.748 0.792 0.603 0.623 — — —
a Thisemissionlineisblendedwith[S]6312Å.
b Thisemissionlineisblendedwith[O]7330Å.
Meanuncertaintiesare∆c =±0.02,∆T =±500K,∆N =±400cm−3.
Hβ e e
