Relating jet structure to photometric variability: the Herbig Ae star HD 163296

3.6 MB·

by  L. E. Ellerbroek

Astronomy&Astrophysicsmanuscriptno.HD163296˙140115˙arxiv (cid:13)c ESO2014
January17,2014
Relating jet structure to photometric variability:
the Herbig Ae star HD 163296(cid:63)
L.E.Ellerbroek1,L.Podio2,3,C.Dougados4,2,S.Cabrit5,2,M.L.Sitko6,7,24,H.Sana8,L.Kaper1,A.deKoter1,9,
P.D.Klaassen10,G.D.Mulders11,I.Mendigut´ıa12,C.A.Grady13,14,K.Grankin15,H.vanWinckel9,F.Bacciotti3,
R.W.Russell16,24,D.K.Lynch16,17,24,H.B.Hammel7,18,24,L.C.Beerman6,19,24,A.N.Day6,20,24,
D.M.Huelsman6,21,24,C.Werren6,24,A.Henden22,andJ.Grindlay23
1 AstronomicalInstitute“AntonPannekoek”,UniversityofAmsterdam,SciencePark904,1098XHAmsterdam,TheNetherlands
e-mail:[email protected]
2 InstitutdePlane´tologieetd’AstrophysiquedeGrenoble,414,RuedelaPiscine,38400St-Martind’He`res,France
4 3 INAF-OsservatorioAstrofisicodiArcetri,LargoEnricoFermi5,50125,Florence,Italy
1 4 CNRS/UniversidaddeChile,LaboratoireFranco-Chiliend’Astronomie(LFCA),UMI3386,Santiago,Chile
0 5 LERMA,ObservatoiredeParis,UMR8112duCNRS,61Av.del’Observatoire,75014,Paris,France
2 6 DepartmentofPhysics,UniversityofCincinnati,CincinnatiOH45221,USA
7 SpaceScienceInstitute,4750WalnutStreet,Boulder,CO80303,USA
n
8 SpaceTelescopeScienceInstitute,3700SanMartinDrive,Baltimore,MD21218,USA
a
9 InstituutvoorSterrenkunde,KULeuven,Celestijnenlaan200B,3001Leuven,Belgium
J
10 LeidenObservatory,LeidenUniversity,POBox9513,2300RALeiden,TheNetherlands
5 11 LunarandPlanetaryLaboratory,TheUniversityofArizona,Tucson,AZ85721,USA
1 12 DepartmentofPhysicsandAstronomy,ClemsonUniversity,Clemson,SC29634-0978,USA
13 EurekaScientific,Inc.,Oakland,CA94602,USA
] 14 ExoplanetsandStellarAstrophysicsLaboratory,Code667,GoddardSpaceFlightCenter,Greenbelt,MD20771,USA
R
15 CrimeanAstrophysicalObservatory,ScientificResearchinstitute,98409,Crimea,Nauchny,Ukraine
S 16 TheAerospaceCorporation,LosAngeles,CA90009,USA
. 17 ThuleScientific,Topanga,CA90290,USA
h
18 AssociatedUniversitiesforResearchinAstronomy,Inc.,1212NewYorkAve.NW,Washington,DC20005,USA
p
19 DepartmentofAstronomy,UniversityofWashington,Seattle,WA98105,USA
-
o 20 DepartmentofPhysics,MiamiUniversity,Oxford,OH45056,USA
r 21 DepartmentofManagementScienceandEngineering,StanfordUniversity,Stanford,CA94305,USA
st 22 AmericanAssociationofVariableStarObservers,49BayStateRoad,Cambridge,MA02138,USA
a 23 Harvard-SmithsonianCenterforAstrophysics,60GardenStreet,Cambridge,MA02138,USA
[ 24 VisitingAstronomer,InfraredTelescopeFacility,operatedbytheUniversityofHawaiiunderCooperativeAgreementno.NNX-

08AE38AwiththeNationalAeronauticsandSpaceAdministration,ScienceMissionDirectorate,PlanetaryAstronomyProgram.
1
v Received;accepted
4
4 Abstract
7
3 Herbig Ae/Be stars are intermediate-mass pre-main sequence stars surrounded by circumstellar dust disks. Some are observed to
. produce jets, whose appearance as a sequence of shock fronts (knots) suggests a past episodic outflow variability. This “jet fossil
1
record”canbeusedtoreconstructtheoutflowhistory.Wepresentthefirstopticaltonear-infrared(NIR)spectraofthejetfromthe
0
HerbigAestarHD163296,obtainedwithVLT/X-shooter.Weaccuratelydeterminephysicalconditionsintheknots,aswellastheir
4
kinematic“launchepochs”.Knotsareformedsimultaneouslyoneithersideofthedisk,witharegularintervalof∼16yr.Thevelocity
1
dispersionrelativetothejetvelocity,aswellastheenergyinput,iscomparableinbothlobes.However,themasslossrate,velocity,
:
v andshockconditionsareasymmetric.Wefind M˙ /M˙ ∼ 0.01−0.1,whichisconsistentwithmagneto-centrifugaljetlaunching
jet acc
i models.Noevidencefordustisfoundinthehigh-velocityjet,suggestingalaunchregionwithinthesublimationradius(<0.5au).The
X
jetinclinationmeasuredfrompropermotionsandradialvelocitiesconfirmsitisperpendiculartothedisk.Atentativerelationisfound
r betweenthestructureofthejetandthephotometricvariabilityofthecentralsource.EpisodesofNIRbrighteningwerepreviously
a
detectedandattributedtoadustydiskwind.Wereportforthefirsttimesignificantopticalfadingslastingfromafewdaysuptoayear,
coincidingwiththeNIRbrighteningepochs.Thesearelikelycausedbydustliftedhighabovethediskplane;thissupportsthedisk
windscenario.Thediskwindislaunchedatalargerradiusthanthehigh-velocityatomicjet,althoughtheiroutflowvariabilitymay
haveacommonorigin.Nosignificantrelationbetweenoutflowandaccretionvariabilitycouldbeestablished.Ourfindingsconfirm
thatthissourceundergoesperiodicejectionevents,whichmaybecoupledwithdustejectionsabovethediskplane.
Keywords.Stars:formation–Stars:circumstellarmatter–Stars:variables:TTauri,HerbigAe/Be–ISM:jetsandoutflows–ISM:
Herbig-Haroobjects–Stars:individualobjects:HD163296
(cid:63) BasedonobservationsperformedwithX-shooter(program089.C-
0874) mounted on the ESO Very Large Telescope on Cerro Paranal,
Chile
1
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
1. Introduction continuum emission is observed up to ∼ 240 au; the outer gas
disk is detected in CO lines with a Keplerian rotation profile
HerbigAe/Bestars(HAeBe)areintermediate-mass(2−10M )
(cid:12) (Rosenfeldetal.,2013;deGregorio-Monsalvoetal.,2013).
pre-main sequence stars. Like their low-mass equivalent, the
Thenear-infrared(NIR)excesshasacomponentthatpeaks
classicalTTauristars(CTTS),HAeBestarsareassociatedwith
at 3 µm and is well fitted by a blackbody of 1500 K. This
accretion disks and, in a few cases, jets (e.g. Corcoran & Ray,
suggests emission by dust at the evaporation temperature.
1998;Gradyetal.,2000,2004).Keyquestionsarehowexactly
Interferometricobservations(Tannirkulametal.,2008a;Benisty
these jets are launched and how this process relates to disk ac-
et al., 2010a) show that a major fraction of this emission orig-
cretion(Ferreiraetal.,2006;Bai&Stone,2013).InHerbigsys-
inates from within the theoretical value of the dust sublima-
tems,thejet-diskcouplingmaybedifferentthaninCTTS.The
tion radius (R ∼ 0.5 au for HD 163296, eq. 1 in Dullemond
sub
relativelyhighstellarluminositycausesgrainparticlestorapidly
& Monnier 2010). Also, the emission profile is smooth, i.e.
evaporate at distances within ∼ 1 au, creating a dust-free zone
does not originate from a sharply contrasted inner disk rim.
(Kamaetal.,2009).AccretionisobservedinHAeBestars(e.g.
HD 163296 also shows significant variations in its NIR bright-
Muzerolleetal.,2004;Mendigut´ıaetal.,2011),soaninnergas
nessontimescalesofyears(Sitkoetal.,2008).
disk likely exists. Since jets are expected to originate (at least
A number of scenarios have been put forward to explain
in part) from this region (Blandford & Payne, 1982), they may
theseobservations.Hydrostaticdiskmodelsarenotpreferred,as
help to improve our understanding of the coupling of accretion
theNIRemissionismuchstrongerthanpredictedbyhydrostatic
andoutflowintheinnerdisk.
equilibrium;also,thesescenariosdonotexplainthephotometric
We may constrain the launching process by observing jet
variability. Alternative scenarios include a dust halo (Vinkovic´
structureandmotion.Jetsfromyoungstarsareusuallyobserved
et al., 2006) and a dusty disk wind (Bans & Ko¨nigl, 2012). In
as a sequence of shock fronts or “knots”. These are likely the
both cases, dust would not exist within R , but at larger dis-
sub
result of a variable outflow velocity (Rees, 1978; Raga et al.,
tances and above the disk plane, making its observation within
1990). A significant asymmetry in velocity and shock condi- R a projection effect. Vinkovic´ & Jurkic´ (2007) suggest that
sub
tions is often observed between the two lobes of jets (Hirth
dustejections,possiblyrelatedtojetlaunching,areresponsible
et al., 1994; Ray et al., 2007). By tracing the trajectories of
forNIRexcessandvariability.
the knots through space, we are able to reconstruct the epochs
The “fossil record” contained in the jet as described above
whentheywereformedandtheir(quasi-)periodicoccurence,if
mayhelpconstrainthephysicalpropertiesandvariabilityofthe
any (e.g., Ellerbroek et al., 2013). On-source photometric and
innerregionsofthedisk.InthispaperwepresentopticaltoNIR
spectroscopicobservationsthatweremadeduringthese“launch
spectra of the jet and central source. These were obtained with
epochs” (when available) may shed light on what happens in
X-shooterontheESOVeryLargeTelescope(VLT).Wecombine
the disk whenever a knot is created. These observations may
the spectra and archival images to reveal the outflow history of
also clarify the origin of the asymmetry between lobes, which
thesystem.Wethencomparethiswiththephotometricvariabil-
isobservedinmanyjetsystems.Inthispaperwecombinetime-
ity of the central object. In Sect. 2 we describe the newly ob-
resolved jet and disk observations and diagnostics to constrain
tainedandarchivalobservationaldata.InSect.3wepresentour
the properties of the launch mechanism, the structure of the
analysisofthejetkinematicsandphysicalconditions.InSect.4,
launchregion,theoriginofjetasymmetry,andtherelationwith
we present a multi-band lightcurve of the central object com-
diskaccretion.
piledfromarchivalandpreviouslyunpublisheddata.Weanalyze
The Herbig Ae star HD 163296 is a promising test case thevariabilityandcolorsofthesource,andestimateitshistoric
for this observing strategy. Its disk is well-studied and associ- accretionrate.InSect.5wediscusstheconstraintsputonthejet
ated with a jet, and a copious amount of time-resolved imag- launching by our observations. We also propose a possible ex-
ing and spectroscopic data are available. Located at a distance planationforthesourcevariabilityandcommentonitsrelation
of 119±11 pc (van Leeuwen, 2007), the system does not ap- withjetstructure.WepresentourconclusionsinSect.6.
pear to be associated with a star-forming cluster or dark cloud
(Finkenzeller & Mundt, 1984). Meeus et al. (2012) do find ex-
tended[Cii]emissionthatmayoriginatefromabackgroundor
2. Observations,datareductionandarchivaldata
surroundingmolecularcloud.
The bipolar jet HH 409 was discovered on coronagraphic Inthissectionwegiveanoverviewofthespectroscopicandpho-
images (and later confirmed with long slit data) of the Space tometricdatapresentedinthispaper.Animageofthejetin[Sii]
Telescope Imaging Spectrograph (STIS) on the Hubble Space and the definition of the knots can be found in Wassell et al.
Telescope (HST Grady et al., 2000; Devine et al., 2000). One (2006,W06;theirFig.1).
of the knots (A) has also been associated with X-ray emission
(Swartz et al., 2005). The high-velocity gas in the jet has ra-
2.1. VLT/X-shooterspectroscopy
dial velocities of 200 − 300 km s−1. A blue-shifted molecular
outflow (up to 13(cid:48)(cid:48) from the source) was found in CO 2–1 and Spectra of HD 163296 and its jet were obtained with VLT/X-
3–2emissionwiththeAtacamaLargeMillimiterArray(ALMA) shooter (Vernet et al., 2011), which covers the optical to NIR
byKlaassenetal.(2013)andalsorecoveredonSubMillimeter spectralregioninthreeseparatearms:UVB(290–590nm),VIS
ArrayCO2–1images(C.Qi,privatecommunication).Thema- (550–1010nm),andNIR(1000-2480nm).Table1liststheset-
terialinthemolecularoutflowpropagatesanorderofmagnitude tingsandcharacteristicsoftheobservations.Toobservethejet,
slower than the fast-moving jet, peaking at −18 km s−1 in the multiple overlapping pointings of the 11(cid:48)(cid:48) slit were performed.
systemicrestframe. On6July2012,oneshorton-sourceexposurewasfollowedby
TheradiusofthedustdiskaroundHD163296isestimated severaloffsets,coveringbothlobesoftheHH409jetupto25(cid:48)(cid:48).
ataround500au,basedonthenon-detectionofthered-shifted A narrow-slit deeper exposure covering the red lobe up to 40(cid:48)(cid:48)
jetuptothisdistance(Gradyetal.,2000)andtheextentofthe was taken on 7 July 2012. Sky frames were obtained before or
scattered light emission (Wisniewski et al., 2008). The 850 µm aftereveryexposuretocorrectfortelluricemissionlines.Since
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L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Table1.JournaloftheX-shooterobservations.
Target HD163296 HH409
Date 6Jul2012 6Jul2012 7Jul2012 2Jul2013 14Jul2013
UT(startobs.) 02:36 02:42 01:34 06:18 01:33
HJD-2400000(startobs.) 56114.608 56114.613 56115.565 56475.763 56487.565
Slitpositionangle(NthroughE) 42.5◦ 42.5◦ 42.5◦ 42.5◦ 42.5◦
Sectioncovered((cid:48)(cid:48)) 0 5−25 10−40 2−13 2−13
(measuredfromsource) (NEandSW) (NE) (NEandSW) (NEandSW)
Exposuretime(s) 2 240(5−15(cid:48)(cid:48)), 300 330 330
440(15−25(cid:48)(cid:48))
Slitwidth,UVB/VIS/NIR((cid:48)(cid:48)) 0.5/0.4/0.4 1.0/0.9/0.6 0.8/0.7/0.4 1.0/0.9/0.6 1.0/0.9/0.6
Resolution,∆(cid:51)(kms−1) 33/17/27 59/34/37 48/27/27 59/34/37 59/34/37
V-bandseeing((cid:48)(cid:48)) 0.8−0.9 0.8−0.9 0.6−0.8 0.6−0.8 0.6−0.8
thesourceisverybright,wehaveacquiredthejetspectrabyoff- 2.2. Archivaldata
setting the slit with respect to the source. As a result, the inner
jet region (< 5(cid:48)(cid:48)) is not covered in the 2012 observations. On Measurements of the positions of knots A, B, and C were
made on archived HST/STIS imaging and spectroscopy,
2and14July2013,follow-upobservationswerecarriedoutin
two offsets up to 2(cid:48)(cid:48) from the source, in order to constrain the HST/Advanced Camera for Surveys (ACS) imaging, and
GoddardFabry-Pe´rot(GFP)imaging(Devineetal.2000;Grady
positionsoftheinnerknots.
etal.2000;W06;Gu¨ntheretal.2013,G13).Thepositionofthe
TheframeswerereducedusingtheX-shooterpipeline(ver- knotswasmeasuredonthe[Sii]673nmlineintheSTISG750L
sion1.5.0,Modiglianietal.,2010),employingthestandardsteps spectra,andontheLyαlineintheSTISG140Mspectra.
ofdatareduction,i.e.biassubtraction,orderextraction,flatfield- Multi-wavelength photometric data of HD 163296 were
ing,wavelengthcalibration,andskysubtraction,toproducetwo- taken from various papers and data catalogs, as well as previ-
dimensional spectra. The wavelength calibration was verified ouslyunpublisheddata.Foranoverviewoftheseresources,see
by fitting selected OH lines in the sky spectrum, resulting in TableA.1.Overtheperiod1979–2012thesourcehas beenob-
a calibration accuracy of a few km s−1. Flux-calibration was served with a regularity that varies per band and epoch. The
performedusingspectraofthespectrophotometricstandardstar source is best covered in the optical bands. We retrieved data
GD153(aDAwhitedwarf).Thewidthoftheknotsperpendic- frommonitoringcampaignsconductedatMadainakObservatory
ulartothejetaxiswasassumedtobenarrowerthantheseeing, (see also Grankin et al., 2007) and at La Silla with the
sothattheslitlosseswereestimatedfrommeasuringtheseeing Swiss Telescope in the period 1983–2000. Observations from
FWHMfromthespatialprofileofapointsourceonthe2Dframe Las Campanas observatory cover the V-band from 2001–2009
(on the first night, HD163296, on the second night, a telluric (Pojmanski&Maciejewski,2004).
standard star). These estimates were refined by comparing the Most of the NIR observations were taken at the Infrared
obtainedSEDtotheaveragedphotometry(seeSect.4.1).They Telescope Facilty (IRTF) and at Mount Lemmon Observing
were subsequently corrected for the slit widths used in the jet Facility(MLOF)intheperiod1996–2009.Partofthesedataare
observations. This procedure results in an uncertainty of about alsopresentedinSitkoetal.(2008).SomeoftheLand M band
10%ontheabsolutefluxcalibration;therelativefluxcalibration data were extracted from spectra obtained with The Aerospace
isaccuratetowithin3%. Corporations Broad-band Array Spectrograph System (BASS),
The wavelengths and velocities used throughout this paper which covers the 3–13 µm wavelength region. BASS is de-
are expressed in the systemic rest frame, for which we adopt scribed more fully in Sitko et al. (2008). Additional JHKLM
(cid:51) = 5.8±0.2 km s−1 with respect to the Local Standard of photometric data were obtained using the SpeX spectrograph
sys
Rest,determinedbyQietal.(2011)basedonsub-mmemission (Rayner et al., 2003). 0.8–5 µm spectra were obtained using
lines from the outer disk. This value agrees with the observed a slit width of 0.8(cid:48)(cid:48) and the echelle diffraction gratings. Zero-
radialvelocityofphotosphericabsorptionlinesintheX-shooter point corrections were applied by also observing the star with
spectrumofHD163296,whichgive7.2±2.0kms−1. theprism(0.7-2.4µm)andaslitwidthof3.0(cid:48)(cid:48).Thismethodhas
beenshowntoprovideresultscomparabletophotometricimag-
Afterreduction,theframesweremerged,averagingtheover-
ing(within5%)whentheseeingis1.0arcsecorbetterandthe
lappingregionsbetweenobservations.Intheobservationsclos-
airmassdoesnotexceed2.0(seeSitkoetal.,2012).
est to the source, a reflection (“ghost spectrum”) of the central
The magnitudes are defined in the Johnson (UBVRI),
source was present at the edges of the slit. We subtracted this
2MASS (JHK ), and ESO (LM) filter systems. The measure-
s
contributioninthefollowingway.Inaregionaroundeveryemis-
mentshaveatypicaluncertaintyof0.01magintheopticaland
sionlineofinterest,ateveryspatialrowinthe2Dframes,wedi-
0.05magintheNIR.
videdthespectralprofilebytheon-sourcespectrum.Wethenfit-
tedazero-orderpolynomialtotheresidual.Finally,theoriginal
spectral profile was divided by the source spectrum multiplied
3. Results:thejet
by this fitted value. This results in a position–velocity diagram
freeofsourcecontamination(Fig.1).Faint,residualcontinuum W06presentanoverviewofHSTdataofthejet.Ithasaposition
emission is seen at +6−7(cid:48)(cid:48), which likely results from a back- angleof42.5±3.5◦ (norththrougheast)andextendsupto30(cid:48)(cid:48)
groundcontinuumsource(alsovisibleatthislocationintheim- in both the south-west (blue-shifted, or “blue lobe”) and north-
agesofGradyetal.2000). east (“red lobe”) direction. This section contains an analysis of
3
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Figure1. Position-velocity diagram of Hα, [S ii] λ673 nm, and [Fe ii] λ1643 nm in July 2012, and [S ii] λ673 nm in July 2013.
The y-axis denotes the position along the slit; y > 0 corresponds to the NE lobe, while y < 0 corresponds to the SW lobe. Due
to the brightness of the source, the central region was not observed. Black contours correspond to logF /[erg s−1 cm−2 Å−1]
λ
= (−17.5,−17,−16.5,−16,−15.5). The blue contours indicate the 3σ detection level of the knots. The black crosses denote the
derivedpositionsandvelocitiesoftheknots,andtheir1σuncertainties.NotethebowshockfeaturesinknotAandCinHα.
theX-shooterspectraofthejet.Itisdividedintotwoparts:the strained,aresimilartotheotherknots.Assumingconstantmo-
kinematicsandthephysicalconditions. tion for all knots allows us to make an estimate of their launch
epochs(t ).Theseepochsshouldthenbeviewedastheinter-
launch
valsduringwhichthebrightknotshaveformedinthejet,close
3.1. Kinematics:propermotionsvs.radialvelocities tothedrivingsource.
Since the knots are regularly spaced, a better constraint on
ThebipolarHH409jetconsistsofasequenceoflocalemission
their trajectories is obtained by making a global fit to the data
line maxima, or “knots” (Fig. 1). These knots are detected in
presented in Fig. 2a. We assumed that each knot was created
40 emission lines of various allowed and forbidden transitions:
H i, [C i], [N ii], [O i], [O ii], [S ii], Ca ii, [Ca ii], [Fe ii], and simultaneously with its counterpart, that knot creation is peri-
[Ni ii]. No H emission is observed along the jet. Fig. 1 dis- odic, and that knots propagate uniformly on either side of the
plays the X-s2hooter spectrum of the Hα, [S ii] λ673 nm, and system.WeomittedknotA2fromthefittingprocedure,asithas
[Fe ii] λ1643 nm emission lines. Knots A, A2, B, C, D, E, F, no counterpart. The best-fit model (χ2red = 0.82) has a period
G, and the onset of H, defined by W06, are indicated in this 16.0±0.7yrandpropermotionsvt,red = 0.28±0.01(cid:48)(cid:48) yr−1 and
2Dspectrum.Theknotpositionsareidentifiedbyco-addingthe vt,blue =0.49±0.01(cid:48)(cid:48)yr−1.TheglobalfitisdisplayedinFig.A.1.
position-velocity diagrams of a selection of the strongest emis- An independent estimate of the launch epoch estimates is
sionlines.Twomorerecentlyejectedknots:A3(identifiedinthis achievedbyusingX-shooterradialvelocities((cid:51))andassuming
r
work)andB2(alsoreportedbyG13)areonlypartlycoveredby thatthejetisperpendiculartothediskequatorialplane.Existing
the X-shooter slit in July 2012. The movements of these knots estimates of the disk inclination are based on interferometry of
aredeterminedfromtheJuly2013observationsandtheobserva- the outer disk (i = 46 ± 4◦, Isella et al. 2007; i = 44◦,
disk disk
tionsoftheLyαcounterpartofknotB2(G13)andthemolecular Rosenfeld et al. 2013) and the inner disk (i = 48 ± 2◦,
disk
counterpartofA3(Klaassenetal.,2013).Thejetlobesareasym- Tannirkulametal.2008a).Inthispaperweadoptthelattervalue.
metric,thebluelobebeingfaster(220−300kms−1)thanthered From the co-added position-velocity diagrams (Fig. 1) of the
lobe(130−200kms−1).Bow-shockfeaturesinknotAandC, brightest lines, a spectral profile is extracted at every pixel of
whicharespatiallyresolvedintheHSTimages(W06),showup width= 0(cid:48).(cid:48)2alongtheslit.AGaussianfunctionisfittedtothis
as sharp velocity drops in the X-shooter Hα position-velocity profile; its centroid velocity is converted to a launch epochs as
diagram. t = x/((cid:51) tani ). The fluxes and launch epochs of these
launch t r disk
Fig. 2a shows the measured positions (x) and lengths (es- individualcomponentsaredisplayedinFig.2b.The16-yearpe-
t
riodicityinthejetstructure,aswellastheconcurrenceofknots
timated as the FWHM of the spatial profiles along the jet axis)
inbothlobesareevidentfromthisfigure.
oftheknotsobservedoverthe1998–2013epoch.Thetrajecto-
riesofknotsA,A2,B,andCarewellfittedbyuniformmotion. Fig.2a(arrows)and2cillustratetheagreementinthelaunch
ThetrajectoriesofknotsA3,B2,andD–G,thoughpoorlycon- epoch estimates between the proper motion and radial veloc-
4
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Figure2.(a)PositionsoftheknotsofHH409overtime;verticalbarscorrespondtotheFWHMofthespatialprofile.Theshaded
bandsanddashedlinesarelinearfitstotheirtrajectories.Thearrowsrepresentthevelocitiesontheskycalculatedfromtheradial
velocitiesanddiskinclination.References:(1)Devineetal.(2000);(2)Gradyetal.(2000);(3)Wasselletal.(2006);(4)Gu¨nther
etal.(2013);(5)Klaassenetal.(2013).(b)LaunchepochsfromradialvelocitiesintheX-shooterspectra.Everysymbolrepresents
theflux(onalogarithmicscale)andt ofonerowofthetwo-dimensionalspectrum,obtainedthroughtheproceduredescribed
launch
inthetext.Onlypeaksabovethe3σbackgroundlevelaredisplayed.Thedatashowaperiodicityof16yr,whichwasalsoobtained
fromtheglobalfittothejetpropermotions(dottedlines).Thelaunchepochsalsoagreewellbetweentheblueandredlobes.(c)
Launch epochs of knots in the blue (open squares) and red (closed squares) lobes, derived from proper motions and from radial
velocities.Thedottedhorizontallinesareplottedona16-yearinterval;notethelogarithmicscale.
5
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
ity methods. The latter figure also demonstrates the periodic-
ity and simultaneity (in both lobes) of the launch events. The
jetinclinationanglecalculatedfromtheaveragejetvelocitiesis
i =tan−1(cid:104)v(cid:105)/(cid:104)v(cid:105)=47±2◦.Thered-shiftedknotsB2,B,andC
jet t r
arelaunchedsimultaneouslywiththeblue-shiftedknotsA3,A,
andH,respectively.ForknotH,t isestimatedfromitsposi-
launch
tionin2004andtheaverage(cid:51) inthebluelobe.Duetotheirhigh
r
velocities,thecounterpartsofthered-shiftedknotsD,E,F,and
GarelikelylocatedtensofarcsecondsbeyondknotHintheblue
lobe and are not covered by our observations. The most recent
launchepochtracedbyourobservationspeakedin2001–2004,
markingtheformationofknotsA3andB2.Intheremainderof
this paper, we adopt the t estimates from radial velocities,
launch
asthesehavethesmallestmeasurementerror.
3.2. Physicalconditions
The line emission along the jet is a result of collisional excita-
tioninshockfronts.Conditionsmayvarysignificantlybetween
the regions up- and downstream of the shock front (“pre”- and
“post”-shock, respectively; Hartigan et al. 1994). The physical
conditions of the shocked gas in the knots (post-shock elec-
tron and total density, n , n ; temperature, T ; and ion-
e,post H,post e
ization, X )canbeestimatedbycomparingobservedlineratios
e
withthosepredictedbycollisionalexcitationmodels(Bacciotti
& Eislo¨ffel 1999; for an application to X-shooter spectra see
e.g. Ellerbroek et al. 2013). Similarly, the pre-shock parame-
ters (shock velocity, (cid:51) ; pre-shock density n ; and mag-
shock H,pre
neticfield,B)canbeobtainedbycomparinglineratiostoshock
models(e.g.,Hartiganetal.,1994).
The results presented in this section are summarized in
Table2.Weconsidertheemission> 3σabovethebackground
noise.ThisisthecaseforknotsA,A2,andA3inthebluelobe
and B, C, and D in the red lobe. The line flux per knot is ob-
tained by integrating over the blue contours seen in Fig. 1. We
consideronlythehigh-velocityemission.Wedidnotcorrectfor
thespatialextentoftheknotsbeyondtheslitaperture,whichwe
assume to be low-velocity emission. The line fluxes predicted
by models and used in diagnostics in this section are corrected
to match the solar abundances of Asplund et al. (2005), which
resultsinascalingoftypically0.1dex.
3.2.1. Extinction
Extinctionbydustaffectstheobservedlineratiosandhencethe
estimated physical and shock parameters. The value of A can
V
beestimatedbyconsideringforbiddenlinesfromthesameupper
levelwhicharefarapartinthespectrum.[Feii]infraredlinesare
well suited for this purpose, although large uncertainties in the
Einsteincoefficientsaffecttheoutcome(seeNisinietal.,2005,
for a discussion). Alternatively H i lines can be used, but their
ratiosdependalsoonothermodelparameters,liketheshockve-
locity(Hartiganetal.,1994).
Figure3. Emission line ratios for six knots in the blue (open
Wefindthatwithintheerrorsthe[Feii]1643/1321nmand
symbols) and red (filled symbols) lobes. Contours indicate the
1643/1256 nm line ratios are consistent with theoretical ones
predictedratiosbythemodelsofHartiganetal.(1994)foragrid
computed for A = 0. Similarly, the Hα/Hβ line ratios follow
V of pre-shock densities, magnetic field strengths, and shock ve-
thepredictionsfromtheHartiganetal.(1994)shockmodelsfor locities.Thecoloredsymbolscorrespondtomodelswith(cid:51) =
the observed range in (cid:51) (see Sect. 3.2.3). Thus, we adopt shock
shock (15,20,25,30,35,40,50,60,70,80,90,100)kms−1.
A = 0 in the knots along the jet. This is consistent (assuming
V
a normal dust-to-gas ratio in the ISM) with the absence of in-
terstellar(gas)featuresinthespectrumofthecentralsourceand wellasthelowon-sourceextinctionmeasuredfromphotometry
the jet (Finkenzeller & Mundt, 1984; Devine et al., 2000), as (seeSect.4.1).
6
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Table2.PhysicalparametersandmasslossrateofHH409.
Knot x fromsource (cid:51) n X (cid:104)n (cid:105) T M˙ ,cr.sect. M˙ ,L M˙ ,L
t r e,post e H e jet jet [SII] jet [OI]
(July2012,(cid:48)(cid:48)) (102kms−1) (102cm−3) (102cm−3) (104K) (10−10M yr−1)
(cid:12)
Bluelobe
A 14.1±0.6 2.4±0.2 4.6±1.0 0.71±0.02 1.8±1.0 1.3±0.3 2.5±1.9 4.2±1.2 5.1±1.6
A2 11.8±0.8 2.6±0.3 5.9±0.8 0.75±0.01 2.2±1.2 1.5±0.3 2.1±1.7 4.2±0.9 5.1±1.2
A3 <7.6 2.7±0.2 6.5±0.8 0.80±0.01 2.3±1.3 1.5±0.3 1.0±1.1 4.1±0.9 5.0±1.2
Redlobe
B 9.2±0.7 1.7±0.2 6.7±0.3 0.32±0.01 5.8±3.2 1.0±0.1 2.5±2.3 11±1 13±2
C 13.7±1.0 1.7±0.2 3.4±0.2 0.43±0.03 2.2±1.2 1.1±0.1 1.9±1.4 8.6±1.6 10±1
D 17.9±0.9 1.5±0.1 2.4±0.3 0.21±0.01 3.2±1.8 0.9±0.1 4.4±3.0 6.6±1.3 8.0±1.6
3.2.2. Electrondensity,ionizationfraction,electron totalnumberdensityinthejetisoforder100cm−3.The[Sii]/Hα
temperature ratiointheredlobeisunderpredictedbyallmodelsexceptthose
with n = 1000cm−3 and B = 1000 µG.This may indicatethat
Theelectrondensity,hydrogenionizationfraction,andelectron
a strong magnetic field inhibits compression and enhances the
temperatureoftheshockedgasintheknotsarecalculatedfrom
emissionfromlowerionizationspecies.
theBEmethod(Bacciotti&Eislo¨ffel,1999).Wefindanelectron
densityof∼ 500cm−3 thatdecreasesalongthejet.Theioniza-
tionfractionishigherinthebluelobe(0.7−0.8)thaninthered 3.2.4. Masslossrate
lobe(0.2−0.4).Theelectrontemperaturedecreasesawayfrom
Themasslossrate M˙ isanimportantparameterinjetphysics.
thesourceandishigherinthebluelobe(T ∼ 1−1.5×104 K) jet
e It determines the amount of energy and momentum injected
thanintheredlobe(T ∼104K).Excitationconditionsarethus
e in the ISM, and its ratio with the accretion rate reflects the
higherinthebluelobethanintheredlobe.
(in)efficiency of the accretion process. Various methods have
These trends are similar to those found by W06 and G13,
been developed to calculate M˙ from the physical parameters
althoughthevaluesfor n foundbytheseauthorsare anor- jet
e,post (for a review, see Dougados et al., 2010). We apply two of
der of magnitude higher than our calculations. This can be due
these to our dataset: (1) we calculate the mass loss rate from
to the fact that the slit used in these studies (with a width of
thejetcrosssection(πR2),totaldensity(cid:104)n (cid:105),andvelocity((cid:51) =
0(cid:48).(cid:48)2)onlysamplesthecentralregionofthejet,whichislikelyto J H J
|(cid:51) |/cosi);and(2)fromthe[Sii]and[Oi]lineluminosities.
haveahigherdensity(seee.g.,Bacciottietal.,2000;Hartigan& r
Morse,2007).Thedifferencesintheseandotherparametersare
consistent within the large uncertainties in the line fluxes mea- Cross section: This method (“BE” method, Bacciotti &
suredbytheseauthors.Thetotaldensityinthepost-shockregion Eislo¨ffel, 1999) calculates the mass loss rate from the average
isestimatedasnH,post =ne,post/Xe,undertheassumptionthathy- density,velocity,andcrosssectionofthejet:
drogenatomsarethemaindonoroffreeelectrons.
M˙ =µm (cid:104)n (cid:105)πR2(cid:51) , (1)
jet H H J J
3.2.3. Shockvelocity,magneticfieldstrength,compression where we adopt µ = 1.24 for the mean molecular weight. We
take the jet radius R to be equal to half of the jet FWHM at
Fig. 3 displays the values of a selection of line ratios against J
the selected knot position as measured from resolved HST ob-
thosepredictedbyHartiganetal.(1994)foragridofshockmod-
els with n = (102,103,104) cm−3, B = (10,102,103) µG, servationsinthe[Sii]lines(W06).Fortheknotsconsidered,RJ
H,pre increasesfrom40auupto100auawayfromthesource.
and (cid:51) = 10 − 100 km s−1. The observed ratios are best
shock
represented by the models with pre-shock electron densities
n =100cm−3,whilethemagneticfieldstrengthBcanadopt Lineluminosities: Ifthephysicalconditionsareuniformwithin
H,pre
values of 10 − 100 µG. Finally, the observed line ratios indi- each knot, the mass loss rate is proportional to the number
cate that in the blue lobe the shock velocity is higher ((cid:51) ∼ of emitting atoms in the observed volume (Podio et al., 2006,
shock
80−100kms−1)thanintheredlobe((cid:51) ∼35−60kms−1). 2009):
shock
This is consistent with the higher excitation conditions in the
bluelobe(seealsoW06andG13). (cid:32) Xi X(cid:33)−1 (cid:51) sini
Thepre-shockdensityisoforder100cm−3,asindicatedby M˙jet =µmHLline hνAi fi X H J l , (2)
t
thecomparisonwithshockmodels.Fortheestimatedshockve-
locities and a typical magnetic field strength of 30 µG, the whereL isthelineluminosity;ν,A,and f arethefrequency,
line i i
compression factor,C = n /n varies between 6 and 20 radiative rate, and upper level population fraction for the con-
H,post H,pre
(Fig. 17 of Hartigan et al., 1994). We adopt C = 13 ± 7 in sideredtransition,respectively. Xi/X isthefractionofatomsof
all the knots. The average density is estimated as the geomet- the considered species in the Xi ionization state and X/H the
ricmeanofpre-andpost-shockdensities.Thiscanbeexpressed species’ relative abundance with respect to hydrogen. The up-
intermsofthepost-shockconditionsandthecompressionfactor per level population, f, is calculated from the statistical equi-
i
as(cid:104)n (cid:105)=n X−1C−1/2.(Hartiganetal.,1994).Theresulting librium equations using the values of n and T calculated
H e,post e e,post e
7
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
dustgrains(Savage&Sembach,1996).Whendustgrainsevap-
orate in the launching region or are sputtered in shocks along
thejet,thesespeciesarereleasedintothegas-phase(Jonesetal.,
1994;Jones,2000;Mayetal.,2000;Draine,2004;Guilletetal.,
2009, 2011). Gas phase depletion of refractory elements has
been observed by Nisini et al. (2005) and Podio et al. (2006,
2009, 2011) in HH jets from Class I sources at large distances
fromtheirdrivingsource.Ithasalsobeenobservedintheinner
100auofaCTTSjet(Agra-Amboageetal.,2011).
In order to check for the presence of dust grains in the jet
launch zone, we estimate the Ca and Fe gas-phase abundance
following the procedure illustrated in e.g., Nisini et al. (2005)
andPodioetal.(2006).Wecompareobservedlineratiosofre-
fractory(Ca,Fe)andnon-refractory(S)specieswithratioscom-
putedthroughtheestimatedparameters(n ,X ,andT ).We
e,post e e
use the flux ratios of [Ca ii] λ729 nm, [Fe ii] λ1256 nm, and
[Feii]λ1643nmto[Sii]λ673nm(Fig.4).
WeassumethatFeandSaresinglyionizedandusethe16-
levels model presented in Nisini et al. (2002, 2005) with colli-
sional coefficients by Nussbaumer & Storey (1988) for Fe and
by Keenan et al. (1996) for S. For the [Ca ii]/[S ii] ratio, it is
assumed that no neutral calcium is present, since its ionisation
potentialisverylow,6.1eV.Fortheionizationbalancewecon-
siderthreelimitingcases:
(1) AllcalciumisinCa+.Thisislikelyanoverestimate,assome
Camaybedoublyionized.
(2) The Ca++/Ca+ fraction is equal to the hydrogen ionisation
fraction,X .AsexplainedinPodioetal.(2009),thisisjusti-
e
fiedbecausetheionizationpotentialofCa+ issimilartothat
of hydrogen (11.9 eV and 13.6 eV, respectively). This also
Figure4. Top two panels: Predicted versus observed [Fe ii] / goesfortherecombinationandcollisionalionizationcoeffi-
[Sii]ratios,basedonthephysicalconditionsderivedinSect.3.2. cientsfortemperatureslowerthan3×104K.
Bottompanel:Sameasabove,for[Caii]/[Sii].Predictionsare (3) The Ca++/Ca+ fraction is calculated by assuming coronal
made for the three limiting cases discussed in the text. No evi- equilibrium at the estimated knot temperature T. Upward
denceisfoundfordepletionofrefractoryelementsinthejet. transitions are assumed to be due to electron collisions and
downward transitions occur by spontaneous emission. This
underestimatestheCa+ fraction,astherecanbenoequilib-
from the line diagnostics. The knot length lt is measured along riuminthejetwhilethegasismoving.
theslit.Thismethodisappliedtotwolines:[Sii]λ673nmand
[O i] λ630 nm. We assume that all sulphur is singly ionized. Fig.4showstheobservedandpredictedlineratios.Nosig-
Tocomputetheionizationfractionofoxygen,weconsidercol- nificantdepletionofrefractoryspeciesisfoundinthejetknots.
lisional ionization, simple and dielectronic recombination, and Somecareshouldbetakenwheninterpretingthisresult.Thecol-
chargeexchangewithH. lisionalcoefficientsandatomicparametersfor[Feii]transitions
The mass loss rates calculated from the line luminosities are affected by large uncertainties (Giannini et al., 2008). The
(Table2)agreewitheachotherwithintheuncertainties.Theval- [Fe ii] / [S ii] ratio may be overpredicted if foreground dust is
uesfromthecrosssectionmethodaresignificantlyandsystem- present, which we do not consider likely. The [Fe ii] and [S ii]
atically lower than these. This discrepancy may be caused by linesmayhavedifferentfillingfactors;theFelinescouldorigi-
an underestimated magnetic field strength and hence, an over- natefromadenserorlargerregion(seeNisinietal.,2005;Podio
estimated compression factor. Additionally, upon comparison etal.,2006).Whenthisistakenintoaccount,oneshouldtakethe
with the Hartigan et al. (1994) models (Fig. ??), the observed estimatedFegasabundanceasanupperlimit.Despitetheseun-
[Nii]λ683nm/[Oi]λ630nmratiossuggestalowerXethande- certainties,ouranalysisgivesnoindicationofdustgrainsinthe
rivedfromtheBEmethod,resultinginahigher M˙jet.Themass launchregionofthehigh-velocityjet.
lossrateisconstantacrosseachlobe;thosefoundfortheredlobe
areafactor2higherthaninthebluelobe.Theaveragemassloss
rateis(cid:104)M˙ (cid:105)=5±2×10−10M yr−1.
jet (cid:12) 4. Results:variabilityofthecentralsource
Inthissectionwedescribethehistoriclightcurveofthesource,
3.2.5. Dustcontent
aswellasthephotometricandspectroscopicaccretiondiagnos-
The line ratios observed in the jet may also be used to test for tics.WeadoptthestellarparametersdeterminedbyMontesinos
depletion of refractory species, such as Ca and Fe. This indi- et al. (2009), which we find to be consistent with the 2012 X-
catesthepresenceofdustinthejetlaunchregion.Thegas-phase shooter spectrum. These parameters are the effective tempera-
abundanceofthesespeciesisstronglydepletedintheISMwith tureTeff = 9250±200K,stellarradiusR∗ = 2.3±0.2R(cid:12),and
respecttosolarabundancesbecausetheiratomsarelockedonto massM =2.2±0.1M .
∗ (cid:12)
8
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Figure5.Top:LightcurveofHD163296inV(0.55µm)andL(3.76µm).Thedottedlineandthegrayshadedareascorrespondtothe
meanvalueand1σspread.ThetimeintervalsdenotedabovetheV-bandlightcurveareexpandedinthebottompanel.Horizontal
bars indicate the jet launch epochs estimated from radial velocities (Sect. 3.1). Bottom: V-band lightcurve for selected intervals,
exhibitingtheshape,duration,andfrequencyofthefadingevents.Thecalendardatecorrespondingtotheminimumvalueonthe
x-axisisdisplayedinthebottomleftcornerofeachgraph.Referencesforplotsymbols:(1)deWinteretal.(2001);(2)Manfroid
etal.(1991);(3)Mt.Maidanak(Grankinetal.,inprep.);(4)Swiss(thiswork);(5)Perrymanetal.(1997);(6)Hillenbrandetal.
(1992);(7)Eiroaetal.(2001)(8)Pojmanski&Maciejewski(2004);(9)AAVSO(thiswork);(10)Tannirkulametal.(2008b);(11)
Mendigut´ıa et al. (2013); (12) Sitko et al. (2008); (13) de Winter et al. (2001); (14) Berrilli et al. (1992); (15) BASS; (16) SpeX
(Sitkoetal.,2008,thiswork).SeeTableA.1formoredetails.
9
L.E.Ellerbroeketal.:Relatingjetstructurewithphotometricvariability:HD163296
Figure6. Average SED of HD 163296 (open symbols), fitted
witha9250KKuruczmodelreddenedwith A = 0.5;theNIR Figure7. (B−V,V) color-magnitude diagram for HD 163296.
V
Datapointsspantheperiod1983–2012;seeFig.5forthecover-
excessisfittedwithablackbodyat1500K(thecombinedmodel
ageofthisepoch.Onlypointswitherrors<0.1magareplotted.
spectrum is shown as a solid gray line). Filled symbols indi-
Fadingeventsin1988,1991,1993,and2000(letterscorrespond
cate measurements during NIR brightening and optical fading
to Fig. 5) are highlighted with colored symbols. During these
epochs; the number of observations are displayed in brackets.
events, the colors change along the extinction vector (Cardelli
Dash-dotted,dashed,anddottedgraylinesrepresentmodelsred-
denedwithA =0.7,0.9,and1.3,respectively. et al., 1989), which is plotted for RV = 3.1 and RV = 5.0. The
V
originofthisvector,indicatedwitharedcross,representsthein-
trinsiccolorsandmagnitudeofanA1Vstarat119pc(Kenyon
4.1. Photometricvariability &Hartmann,1995).
A lightcurve of HD 163296 is constructed from the collected
data described in Sect. 2.2 and summarized in Table A.1. The
toppanelofFig.5displaystheV-andL-banddataforthe1978– The 2002 event marked a 30% increase in flux in the L-band.
2013epoch.Fig.A.2displaysallthephotometricdata. Note,however,thatboththemeasurementerrorandtheintrinsic
The optical brightness of the source over the period 1980– scatter of the NIR brightness are large. A denser coverage of
2012fluctuatesaroundasteadylevel((cid:104)V(cid:105) = 6.93±0.14mag). thelightcurvewouldbeneededtoevaluatethesignificanceand
Overthisperiod,severalfadingeventsareseen,duringwhichthe uniquenessofsuchevents.
opticalbrightnessdecreasessignificantly.Themostprominentof Thephotometryduringfadingeventsisfurtherillustratedin
thesestartedinMarch2001andlastedforatleast6months(up Fig.6.TheaverageSEDwascomputedbytakingthemeanofthe
toatmost1.1years).Withinonemonth,Vincreasedupto0.71± photometry, omitting measurements that deviate more than 2σ
0.15 mag above its average value. The bottom panel of Fig. 5 fromthemeanvalue.Itisfittedwitha9250KKuruczmodeland
displaysa“zoomin”onthelightcurveoverthisandseveralother ablackbodyat1500K.Intheliterature,estimatesfortheextinc-
fading events. Fadings of order 0.1 mag occur predominantly tiondeviatefrom E(B−V) = 0.015(fromtheabsenceofinter-
in the 2001–2006 epoch with durations from hours to several stellargasabsorption; Devineetal.,2000)uptoE(B−V)=0.15
weeks. (fromSEDfitting; Tillingetal.,2012).Theaveragereddening
Optical photometric observations dating back as far as the in our photometric data is E(B−V) = 0.065±0.016 (Fig. 7).
1890s were obtained from the DASCH catalog (see Grindlay FortheplotinFig.6weadopt E(B−V) = 0.15andRV = 3.1,
et al., 2012). Since the target was either saturated or in the hence AV = 0.5(Cardellietal.,1989),whichbestfitstheSED
non-lineardomainonmostofthephotographicplates,wewere intheUBVRI-bands.Thedisagreementbetweentheextinction
only able to retrieve lower limits on the photometric measure- estimatesmaybeexplainedbyacircumstellarextinctioncarrier
ments. However, prolonged fadings of more than 3σ are ob- withalowergas-to-dustratiothanintheISM,variabilityofits
servedthroughoutthelightcurve,indicatingthatthesearerecur- column density, or both. The optical colors during the fading
ringevents. events in 1988, 1991, 1993, and 2000 are well fitted by an en-
In the NIR, the time coverage is much sparser. The mean hanceddustextinctionof∆AV ∼0.2−0.4magandRV =3.1−5.0
brightness in the L-band over the 1978–2012 period is (cid:104)L(cid:105) = (Fig.7).Themajorfadingeventin2001,forwhichcolorsarenot
3.36±0.10mag.ThemeanbrightnesslevelintheH,K,L,and available,impliesanenhancementofAV by0.7–0.8mag.
M bands is exceeded by 10% in three epochs: in 1986 (N = The2002NIRbrighteningmayhaveacommonoriginwith
obs
2, see Fig. A.2), 2001–2 (N = 3), and 2011–12 (N = 4). the optical fading in 2001. This is further reinforced by the si-
obs obs
The first two epochs were also reported by Sitko et al. (2008). multaneousmeasurementofopticalfadingandNIRbrightening
10