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Astronomy&Astrophysicsmanuscriptno.paper (cid:13)cESO2017 January3,2017 ⋆ Brightness variations of the FUor-type eruptive star V346 Nor Á.Kóspál1,P.Ábrahám1,Ch.Westhues2,andM.Haas2 1 Konkoly Observatory, Research Centre for Astronomy and EarthSciences, Hungarian Academy of Sciences, PO Box 67, 1525 Budapest,Hungarye-mail:[email protected] 2 AstronomischesInstitut,Ruhr-UniversitätBochum,Universitätsstraße150,D-44801Bochum,Germany Receiveddate;accepteddate 7 ABSTRACT 1 0 Decades after the beginning of its FU Orionis-type outburst, V346 Nor unexpectedly underwent a fading event of ∆K = 4.6mag 2 around 2010. Weobtained near-infraredobservations and re-analysed data fromthe VISTA/VVVsurvey tooutline thebrightness evolution.InourVLT/NaCOimages,wediscoveredahaloofscatteredlightaroundV346Norwithasizeofabout0′.′04(30au).The n VISTAdataoutlinedawell-definedminimuminthelightcurveatlate2010/early2011,andtentativelyrevealedasmall-amplitude a periodicmodulationof58days.Ourlatestdatapointsfrom2016demonstratethatthesourceisstillbrighteningbuthasnotreached J the2008levelyet.Weusedasimpleaccretiondiskmodelwithvaryingaccretionrateandline-of-sightextinctiontoreproducethe 1 observednear-infraredmagnitudesandcolors.Wefoundthatbefore2008,thefluxchangesofV346Norwerecausedbyacorrelated changeofextinctionandaccretionrate,whiletheminimumaround2010wasmostlyduetodecreasingaccretion.Thesourcereached ] amaximalaccretionrateof≈10−4M yr−1 in1992. Acombinationofaccretionandextinctionchangeswasalreadyinvokedinthe R ⊙ literaturetointerpretthefluxvariationsofcertainembeddedyoungeruptivestars. S . Keywords. stars:formation–stars:circumstellarmatter–infrared:stars–stars:individual:V346Nor h p - o1. Introduction r tFUOrionis-typestars(FUors)arelow-masspre-mainsequence 400 s aobjectscharacterizedby 4-6magnitudeopticaloutburstsdueto [temporarily enhanced accretion from the circumstellar disk to the star (Hartmann&Kenyon1996). Following the outburstof 1 thefirstsuchobject,FUOriin1937,nowmorethantwodozen v 300 0FUors and FUor candidates are known (Audardetal. 2014). 5V346 Nor was discovered by Elias (1980) as a source within 2a few arcseconds of the HH 57 nebulosity, the latter being a 0faint,compactHαemittingknot(Schwartz1977),locatedinthe DEC offset 0Sa 187 molecular cloud within the Norma 1 association, at a 200 1.distanceof700pc(Reipurth1981,seealsoFig.1).Afewyears 0laterGraham(1983)reportedtheappearanceofastar-likesource 7at the northeastern tip of HH 57, probably coinciding with the 1source in Elias (1980). They mentioned that the star was not 100 :visible in 1976 (Schwartz 1977), but a diffuse patch is clearly v discernible in the blue plates of the ESO/SERC Sky Survey, i Xobtained in April–June 1975 (Holmbergetal. 1974; Reipurth r1981). Therefore, V346 Nor transformed from a faint diffuse anebula to a bright point-source some time between 1976 and 00 100 200 RA offset 300 400 Fig.1. V346 Nor (black plus sign inthe center) and itssurroundings 1980. Based on this and on the spectroscopic propertiesof the ina JHK colorcompositimage.Theobservations weretakenwithin S star, Reipurth&Krautter (1983) suggested that V346 Nor was the VISTAVariables in The ViaLactea (VVV) Survey on March 15, undergoingaFUor-typeoutburst.Frogel&Graham(1983)pre- 2010.Northisupandeastistotheleft.Thedisplayedareais2.′5×2.′5in sentedphotometryfrom2.2to20µmandremarkedthatthecol- size.ThedarklaneacrosstheimageisduetoextinctionbytheSa187 orsoftheobjectaresimilartothoseofFUOriandV1057Cyg. molecularcloud. Subsequent near-infrared (near-IR) photometry indicated that V346 Nor was gradually brightening in the K band, reaching a broad maximum between about 1990 and V346Nor,whileWeintraubetal.(1991)publishedsubmillime- 2000 (Frogel&Graham 1983; Reipurth&Wamsteker 1983; terandmillimeterphotometryforit.Bothgroupsconcludedthat Reipurth1985;Kenyon&Hartmann1991;Molinarietal.1993; theobjectissurroundedbyasignificantamountofcircumstellar Prustietal. 1993; Reipurthetal. 1997; Ábrahámetal. 2004, material,intheformofanactivelyaccretingdiskandaflattened see also Fig. 3). Kenyon&Hartmann (1991) presented the envelope. Recently, Krausetal. (2016) reported a dramatic broad-band optical-IR spectral energy distribution (SED) of brightnessdecreaseofV346Norandasubsequentbrightening. Articlenumber,page1of7 A&Aproofs:manuscriptno.paper 400 400 400 Cerro Armazones. IRIS is a 80cm telescope equipped with a ec) 2 J H KS 1k×1k infrared camera. The system provides a resolution of arcs 1300 300 300 0.74′′/pixelandafield-of-viewof13′×13′.Dataweretakenbe- C offset ( -10200 200 200 t2w2eaenndJu2n5e,2260,1260,1i0nathnedJJu,lyH1a,n2d01K0S,absawnedlsl.aIsnbdeivtwideueanlAfruagmuesst E 100 100 100 were combinedto eliminate the sky signal and correctfor flat- D -2 fielddifferences.V346NorwasnotvisibleintheJband,butwas 00 2 1001 0200 -1300 -2 40000 2 1001 0200 -1300 -2 40000 2 1001 0200 -1300 -2 400 detectedinallH andK frames.AllJ-bandimagesobtainedon S RA offset (arcsec) thesamenightwerecombinedintomosaics,and3σupperlim- 1.0 nsity 0.8 J H KS ipthsowtoemreedtreyteursminingetdh.eFsoarmtheeaoptehreturrfielatenrds,swkyeapnenrfuolrumsesidzeaspearstuforer e nt 0.6 theNaCoimages.Forthephotometriccalibration,weusedaset ed i ofabout502MASSstarswith qualityflag‘A’todeterminethe aliz 0.4 offsetbetweentheinstrumentalandthe2MASSmagnitudes.We m or 0.2 foundthatnocolortermwasneededforthistransformation.The N 0.0 uncertainty of the final photometryis the quadratic sum of the 0.0 0.1 0.2 0.3 0.4 0.0 0.1 0.2 0.3 0.4 0.0 0.1 0.2 0.3 0.4 Radius (arcsec) formaluncertaintyoftheaperturephotometryandthephotomet- riccalibration.TheresultingJupperlimitsandHK magnitudes Fig.2.Top:VLT/NaCo J,H,andK imagesofV346Norfrom2008. S S arepresentedinTab.B.1. The color scale is logarithmic. Bottom: Radial intensity profiles of V346Nor(solidcurves)andofanother,fainterstarvisibleinthefield We observed V346 Nor with the SMARTS 1.3m telescope of view(dashed curves) measured inour NaCo J, H, and K images. at Cerro Tololo on June 7 and August 9, 2016. The telescope S Theuncertaintyofthebrightnessprofileofthefainterstarisindicated isequippedwiththeANDICAMinstrument,whichprovidessi- byerrorbars, whiletheuncertaintyof V346Nor’sprofileislessthan multaneousopticalandIRimages.TheCCDfortheANDICAM thecurvethickness. is a Fairchild 447 2k×2k chip, which we used with 2×2 binning, resulting in a binned pixel scale of 0.371′′/pixel, and a field of view of about6′×6′. The IR Array for the ANDICAM They interpret these results as a 2-3 orders of magnitude drop is a Rockwell 1k×1k HgCdTe “Hawaii” Array, also used with in the accretion rate, followed by the onset of a new outburst. 2×2 binning, with 0.276′′/pixel binned scale and 2′.4×2′.4 field In order to better understand this spectacular event, and to of view. We used the Johnson-Kron-Cousins VRI optical and follow up the evolution of the system, we present new near-IR CIT/CTIO JHK IRfilters. A 5-pointditheringwasdoneto en- observations of V346 Nor, and re-evaluate the data taken by able bad pixel removal and sky subtraction in the IR images. the VISTA telescope. We analyze the brightness and color Bias and flat correction for the optical images were done by variations observed in V346 Nor and compare the results with the Yale SMARTS team. Although HH 57 is faintly visible in similar fading events of highly accreting young stellar objects our V and R images, V346 Nor itself is not detected in the fromtheliterature. optical. We used magnitude values from the UCAC4 catalog (Zachariasetal. 2013) to calibrate the images and determined 3σupperlimitsofV>20.8mag,R>19.6mag,andI>18.8mag 2. Observations,datareduction,andphotometry forV346Nor.Inthenear-IRregime,V346Norwasdetectedin We observed V346 Nor with the NaCo adaptive optics instru- allthreebands,andweperformedphotometrythesamewayas ment on the UT4 of European Southern Observatory’s Very described for the IRIS images. The resulting JHK magnitudes LargeTelescope(VLT)atCerroParanal,Chile,onApril10/11, forV346NorarepresentedinTab.B.1. 2008,aspartofproject381.C-0241(PI:Á.Kóspál).Theweather V346 Nor was covered as part of the VISTA Variables in conditionsweregoodandthetypicalopticalseeingwasaround the Via Lactea Survey,an ESO publicsurveyusing the VISTA 1′′. We obtained J, H, and K -band images with the N20C80 4.1mtelescopeandtheVIRCAMnear-IRcamera(Minnitietal. S dichroic and the 13maspixel−1 scale camera. We observed 2010). We downloaded all VIRCAM images from this survey 2MASSJ16323308−4457314asaphotometricstandardwiththe covering V346 Nor. To obtain photometry that can be com- same instrumentalsetup as the science target. This star is only paredwithourNaCO, IRIS,andSMARTSdata,we performed 2′ away from V346 Nor and has similar 2MASS magnitudes our own flux extraction with the same aperture as described (J=10.288mag, H=8.395mag, K =7.242mag). Our NaCo im- above.At some epochs, our values differ from those published S ages are displayed in Fig. 2. We obtained aperture photometry byKrausetal.(2016)forthesamemeasurements.Thereasonis forbothV346Norandthephotometricstandardusinganaper- probablyadifferenttreatmentoftheknownnon-linearityofthe ture radius of 2′′ and sky annulus between 2′.′6 and 3′.′9. This VIRCAM detectors for bright sources (e.g., Saitoetal. 2012). large aperture was chosen to include all the flux of V346 Nor, ThecorrectionweappliedisdescribedindetailsinAppendixA. which appears slightly extended in our NaCo images (see be- TheJandHphotometry,aswellastheKs-bandresultsafterthe low), therefore,our photometrycan be comparedto earlier un- non-linearitycorrectionarealsogiveninTab.B.1. resolved photometry from the literature. The obtained instru- mentalmagnitudeswereconvertedtostandardmagnitudesusing 3. Results the2MASSvaluesforthephotometricstandard.Wealsodown- loadedarchivalJandK -bandNaCoobservationsfromJune12, The top part of Figure 2 shows our NaCo JHK images from S S 2003,andreducedandextractedphotometryfromtheminasim- 2008 of V346 Nor, while the bottom panel displays the nor- ilar way. The obtainedbrightnessesof V346Nor are presented malized,azimuthallyaveragedradialbrightnessdistributionsof inTab.B.1. V346 Nor, and another, fainter star visible in the field of view Our group observed the area around V346 Nor with the at a distance of 5′.′7, position angle of 13◦ east of north. As- InfraRed Imaging System (IRIS) at Bochum Observatory near sumingthatthisnearbyfaintstarisapointsource,thecompari- Articlenumber,page2of7 Kóspáletal.:BrightnessvariationsofV346Nor 1980 1990 2000 2010 4 8 6 L 1983-88/2003 10 1989-1999 8 K 1979 12 ude 10 H AV = 10 mag 2008 agnit 12 J J 14 M 2016 14 16 16 18 2010 18 2 3 4 5 6 5000 10000 15000 J - Ks JD - 2 440 000 2010 2011 2012 2013 2014 2015 2016 Fig.4.Near-IRcolor-magnitudediagramforV346Nor.Thereddening 6 path ismarked withdashed line (Cardellietal. 1989). The solid gray curves indicate our reddened accretion disk model fits (see details in 8 L text). 10 e d u lowing3years,indicatingaslowerbrighteningrate.Asof2016 agnit 12 K August,V346Norhasnotyetreachedthebrightnesslevelitdis- M played in 1980–2000. This is well visible in the near-IR light 14 curves,butouropticalupperlimitsalsosupportsthis,asthestar H wouldhavebeenvisibleinourVRIimageshaditbeenasbright 16 asbetween1980–2000.The deepminimumwas also visible in 18 J theWISE3.4µmphotometry,althoughwithsmalleramplitude. 15000 15500 16000 16500 17000 17500 The lower panel of Fig. 3 shows that the minimum in the JD - 2 440 000 K-band has a parabola-like light curve shape. By fitting and Fig. 3. Near-IR light curves of V346 Nor. Data points are from subtractingasecond-orderpolinomialfromthe photometrybe- Elias (1980); Frogel&Graham (1983); Graham&Frogel (1985); tween 2010 and 2014, the obtained residuals are on the order Reipurth&Krautter (1983); Reipurth&Wamsteker (1983); Reipurth of 0.2mag, and suggest a possible periodic modulation. We (1985);Kenyon&Hartmann(1991);Molinarietal.(1993);Prustietal. calculated a Lomb-Scargle periodogram for the residuals, and (1993); Reipurthetal. (1997); Quanzetal. (2007); Connelleyetal. foundatentative58±2dayperiodinthedatawithafalsealarm (2008), the 2MASS, DENIS, AllWISE and NEOWISE catalogs probabilityof3×10−3 (seealso Fig.B.1 inAppendixB).Simi- (Cutrietal.2003;Cutri2013;Cutrietal.2015),andthiswork.Down- lar periodicitiesin the light curves were already found in, e.g., wardarrowsindicateupperlimits. V1647 Ori, where it was explained by an orbiting dust cloud (Acosta-Pulidoetal.2007),andinV960Mon,whereiswasex- plainedbyaputativeclosecompanion(Hacksteinetal.2015). sonofthebrightnessprofilesshowthatV346Norisextendedin the J and H bands,whileitis consistentwitha pointsourcein the K band. Deconvolvedsizes using Gaussian deconvolution S 4. DiscussionandConclusions are 0′.′041±0′.′016 (29±11au) in J, 0′.′037±0′.′010 (25±7au) in H, and we can give an upper limit of 0′.′02 (13au) for the KS- Thecolor-magnitudediagraminFig.4showsthatalldatapoints bandsize.Thesizeofthenear-IRemittingregionincircumstel- until 2008 form an approximately linear strip, while the later lardisksistypicallyonlyafewau,therefore,theemissionseen measurementsdeviatefromthistrend,suggestingdifferentphys- in the NaCo imageshasto be scatteredlight. The J and H im- ical mechanisms for the brightness and color changes before agesareslightlyasymmetricwiththenorthernpartslightlymore and after 2008.In order to reproducethe observations,in each extendedthanthe southernpart.No suchasymmetryis evident epoch we fitted the JHK data points by a steady, optically S intheKSimage. thick, geometrically thin, viscous accretion disk, with radially Figure 3 shows the near-IR light curves of V346 Nor. The constant mass accretion rate. Such disk models were success- first few data points indicate a brightening between 1979 and fully proposed and used to reproduce the SEDs of FUors by 1983,followedbyarelativelyconstantperioduntilabout1988. Hartmann&Kenyon(1996),Zhuetal.(2007),andKóspáletal. Afterwards,the K and L-banddata show a gradualbrightening (2016).Wecalculatedthedisk’sSEDbyintegratingthefluxesof until1992,alreadyreportedinÁbrahámetal.(2004).TheJand concentricannulibetweenthestellar radiusandR , assuming out H light curves were rather flat, with small, <1mag brightness blackbody emission. We reddened the model fluxes by differ- variations.After2003-2004thesourcesignificantlyfaded,espe- ent A values, using the extinction law from Savage&Mathis V ciallyatshortwavelengthsandin2008displayedsimilarbright- (1979) with R =3.1. Fixing the outer radius of the accretion V nessalthoughslightlyreddercolorthanthefirst JHK photome- disk (R = 2au, the exact value has a negligibleeffect on the out tryin1979. near-IRfluxes), we have only two free parameters,the product Sometimearound2008,V346Norstartedadramaticfading, of the stellar mass and the accretion rate MM˙, and the extinc- and reached a minimum around late 2010-early 2011 (Fig. 3, tionA .Wefixedthestellarmassandradiustotypicallow-mass V bottom). Afterwards, the source quickly brightened by ∆K = YSOvaluesof1M and3.0R (theresultingaccretionrateisin- ⊙ ⊙ 2.4maginabout3years,andanother∆K =0.6maginthefol- verselyproportionaltotheadoptedstellarmass).Theinclination Articlenumber,page3of7 A&Aproofs:manuscriptno.paper ofthe V346Nordiskis notknown,thusweadopted2/π≈40◦, The minimum of V346 Nor in 2010 was immediately fol- the mean expected value if the disk is randomly oriented. The lowedbythere-brighteningofthesource.Asof2016,thesource fittingprocedurewasperformedwithχ2minimization.Moreex- is on its way backto its 2008state in the color-magnitudedia- tremeextinctionlaws(uptoR =5.3,Cardellietal.1989)would gram(Fig.4).Thissuggeststhatthebrighteningisgovernedby V change the fitted A and M˙ values by less than 15%, which is the same process that was responsible for the fading, namely V withintheformaluncertaintyofourfittingprocedure. changing accretion at a constant high extinction. Indeed, our simple accretion disk model can reproduce the JHK fluxes The bluest points in Fig. 4 correspond to measurements S measuredin2016byassumingM˙ =3.3×10−6M yr−1,andA = obtained in 1983-88 and 2003, when the system exhibited ⊙ V 19.8mag.Thebrighteningofthesourceisstillongoing,andour approximately the same brightness and color. We found that these points can be well fitted by our disk model with M˙ = latestobservationssuggestthatafterarelativelyconstantperiod 1.0×10−5M yr−1 and line-of-sight reddening of A =6.7mag. after2013,V346Normighthaveenteredagainafastbrightening ⊙ V phase. Weobtainedsimilarlygoodfitsforthe1979and2008SEDswith M˙ =2.1×10−5M yr−1andM˙ =4.5×10−5M yr−1,respectively. In the classical FUor outburst models, the eruption ends ⊙ ⊙ whentheinnerdiskcompletelydepletes,andaneweruptioncan The reddening, however, was significantly higher, 16.7mag in startonlywhenthediskmaterialisreplenished,typicallyinsev- 1979 and 21.5mag in 2008. We simulated the time evolution eral thousand or ten thousand years (Bell&Lin 1994). There- of the system by computing a sequence of models of gradually changing A from 21.5 to 6.7 mag and M˙ from 4.5×10−5 fore, the relatively short minimum of V346 Nor is unlikely to V to1.0×10−5M yr−1.TheresultinglineisplottedinFig.4.For signaltheendofthelargeFUoroutburstintheclassicalsense.It ⊙ wasmorelikelyatemporaryhaltoftheaccretionontothestar.A mostepochs,ourdiskmodelfitstheSEDshapewellwithtypical formaluncertaintiesof 1-2mag in A and 10-30%in M˙. After similarphenomenonwasobservedinV899MonbyNinanetal. V (2015), and in V1647 Ori, where the 2004–2006 outburst fin- theminimumin2010,theshapeoftheSEDscanbereproduced ishedand thenrestarteda few yearslater. Thephysicalmecha- less wellwith theaccretiondiskmodel,resultingin formalun- certaintiesof6-8maginA ,anduptoafactorof6inM˙. nismofthistemporarystopisnotknownyet.Ninanetal.(2015) V speculated about several possible explanations, with the con- Thedatapointsobtainedbetween1989and1999aresituated straint that these processes should be able to return the system above the model line. These SEDs can also be fitted with our to the pre-fading state within a few years. The detailed under- disk model, but with higher M˙ values than at any time before. standingoftheevolutionoftheV346Noroutburstwillbringus A wasbetween12.1and19.2maginthisperiod.Inparticular, V closertotheunderstandingoftheseenigmaticsuddenfadingsof wefoundthattheaccretionrateshowedamaximumin1992Jan- eruptivestars. uary,withM˙=9.8×10−5andA =16.8mag.Here,weagaincom- V puted a sequence of models with gradually changing A from Acknowledgements. Theauthorsthanktherefereeforhis/herusefulcomments. V 19.2 to 12.1 mag and M˙ from 9.8×10−5 to 3.5×10−5M yr−1, ThisworkwassupportedbytheMomentumgrantoftheMTACSFKLendület ⊙ DiskResearchGroup,andbytheNKFIHresearchfundOTKA101393. alsoplottedinFig.4. Krausetal.(2016)suggestedthattheminimumaround2010 isrelatedtoalargedropintheaccretionrate.Usingouraccretion References disk model, we foundthat by keepinga constant A =21.5mag V between2008and2010,andaddinganaccretiondiskmodelof Ábrahám,P.,Kóspál,Á.,Csizmadia,S.,etal.2004,A&A,428,89 gradually increasing M˙ to the SED measured in 2010 we can Acosta-Pulido,J.A.,Kun,M.,Ábrahám,P.,etal.2007,AJ,133,2020 reachthe2008datapoint(Fig.4).Intheminimum,themeasured Audard,M.,Ábrahám,P.,Dunham,M.M.,etal.2014,ProtostarsandPlanets fluxesconstrainthemodelaccretionratebelow4×10−7M yr−1, VI,387 ⊙ Bell,K.R.&Lin,D.N.C.1994,ApJ,427,987 thusthe changein accretionratewas atleast afactorof100or Cardelli,J.A.,Clayton,G.C.,&Mathis,J.S.1989,ApJ,345,245 more, in agreementwith the findings of Krausetal. (2016). In Connelley,M.S.,Reipurth,B.,&Tokunaga,A.T.2008,AJ,135,2496 our modeling, the scattered light component, indicated by our Cutri,R.M.2013,VizieROnlineDataCatalog,2328 Cutri,R.M.,Mainzer,A.,Conrow,T.,etal.2015,ExplanatorySupplementto NaCo observationsin 2008, was not included,since its consis- theNEOWISEDataReleaseProducts,Tech.rep. tenttreatmentwouldbebeyondthescopeofthisLetter. Cutri, R. M., Skrutskie, M. F., van Dyk, S., et al. 2003, VizieR Online Data Catalog,2246 Ourresultsdemonstratedthatwhiletherapidfadingin2010 Elias,J.H.1980,ApJ,241,728 was an accretion event, the flux evolution beforehand was due Frogel,J.A.&Graham,J.A.1983,IAUCirc.,3792 to a correlatedchangeinextinctionandaccretionrate together. Graham,J.A.1983,IAUCirc.,3785 That is, increasing accretion rate is accompanied by growing Graham,J.A.&Frogel,J.A.1985,ApJ,289,331 Hackstein,M.,Haas,M.,Kóspál,Á.,etal.2015,A&A,582,L12 extinction towards the source. V346 Nor is similar to a group Hartmann,L.&Kenyon,S.J.1996,ARA&A,34,207 ofhighlyvariableyoungstellarobjectswhosefluxchangesare Hillenbrand,L.A.,Miller,A.A.,Covey,K.R.,etal.2013,AJ,145,59 duetoacombinedeffectofchangingaccretionrateandvariable Holmberg,E.B.,Lauberts,A.,Schuster,H.-E.,&West,R.M.1974,A&AS,18, circumstellarextinction.Suchobjectsare, e.g.,Hα11,PV Cep, 463 Kenyon,S.J.&Hartmann,L.W.1991,ApJ,383,664 V1647 Ori, and V899 Mon (Kunetal. 2011a,b; Mosonietal. Kóspál,Á.,Ábrahám,P.,Acosta-Pulido,J.A.,etal.2013,A&A,551,A62 2013; Ninanetal. 2015). V346 Nor also resembles the young Kóspál,Á.,Ábrahám,P.,Acosta-Pulido,J.A.,etal.2011,A&A,527,A133 eruptivestarV2492Cyginseveralaspects:thepre-outburstpo- Kóspál,Á.,Ábrahám,P.,Acosta-Pulido,J.A.,etal.2016,ArXive-prints sitionofV2492Cyginthenear-IRcolor-colordiagramisclose Kraus,S.,CarattioGaratti,A.,Garcia-Lopez,R.,etal.2016,MNRAS,462,L61 Kun,M.,Szegedi-Elek,E.,Moór,A.,etal.2011a,ApJ,733,L8 tothepointofthe2010minimumofV346Nor,italsounderwent Kun,M.,Szegedi-Elek,E.,Moór,A.,etal.2011b,MNRAS,413,2689 alargeaccretionchangeatthebeginningofitsoutburst,andin Minniti,D.,Lucas,P.W.,Emerson,J.P.,etal.2010,NewA,15,433 the highstate, theline-of-sightextinctionis continuouslyvary- Molinari,S.,Liseau,R.,Lorenzetti,D.,&Graham,J.1993,IAUCirc.,5727 ing (Kóspáletal. 2011, 2013; Hillenbrandetal. 2013). There- Mosoni,L.,Sipos,N.,Ábrahám,P.,etal.2013,A&A,552,A62 Ninan,J.P.,Ojha,D.K.,Baug,T.,etal.2015,ApJ,815,4 fore,theobservedvariabilityinbothV346NorandV2492Cyg Prusti,T.,Bontekoe, T.R.,Chiar,J.E.,Kester,D.J.M.,&Whittet, D.C.B. aregovernedbyacombinationofchangingaccretionandextinc- 1993,A&A,279,163 tion. Quanz,S.P.,Henning,T.,Bouwman,J.,etal.2007,ApJ,668,359 Articlenumber,page4of7 Kóspáletal.:BrightnessvariationsofV346Nor Reipurth,B.1981,A&AS,44,379 Reipurth,B.1985,A&A,143,435 Reipurth,B.&Krautter,J.1983,IAUCirc.,3823 Reipurth,B.,Olberg,M.,Gredel,R.,&Booth,R.S.1997,A&A,327,1164 Reipurth,B.&Wamsteker,W.1983,A&A,119,14 Saito,R.K.,Hempel,M.,Minniti,D.,etal.2012,A&A,537,A107 Savage,B.D.&Mathis,J.S.1979,ARA&A,17,73 Schwartz,R.D.1977,ApJS,35,161 Weintraub,D.A.,Sandell,G.,&Duncan,W.D.1991,ApJ,382,270 Zacharias,N.,Finch,C.T.,Girard,T.M.,etal.2013,AJ,145,44 Zhu,Z.,Hartmann,L.,Calvet,N.,etal.2007,ApJ,669,483 Articlenumber,page5of7 A&Aproofs:manuscriptno.paper 14 10-3 1.4 12 er 10-2 w o 10 1.2 V346 Nor e P K-KVISTA2MASS01..80 Lomb-Scargl 468 2 0.6 0 10 100 1000 Period (d) 0.4 11.0 11.5 12.0 12.5 0.4 K VISTA 0.2 Fig.A.1.Demonstrationofthenon-linearitycorrectionappliedforthe g photometryofV346Nor. ma 0.0 K ∆ -0.2 10.0 10.5 -0.4 0.0 0.5 1.0 1.5 2.0 Phase 11.0 e d nitu 11.5 Fig. B.1. Top: Lomb-Scargle periodogram of the light curve of ag V346Nor after removing aparabolictrend, asillustratedinFig.A.2. m 12.0 Ks 12.5 Tshhoewhitghheepsotwpeearskccoorrrreessppoonnddisngtotoafpaelsrieoadlaorfm58prdoabyasb.ilTithieesdoafsh1e0d−3lianneds 10−2. Bottom: Phase-folded light curve showing the data points after 13.0 removingtheparabolictrendandfoldedwithaperiodof58days. 13.5 15200 15500 15800 16100 16400 16700 JD-2,440,000 Fig. A.2. VISTA/VIRCAM photometry of V346 Nor without (green plussigns)andwith(redcircles)correctionfornon-linearity.Asterisks indicate our IRISphotometry. Theblack solidcurve isaparabola fit- tedtothedatapointstoremovethelong-termtrendbeforetheperiod analysis(seeSec.B). AppendixA: Near-IRphotometryofV346Nor The comparison of our aperture photometry with the 2MASS catalogrevealedtheknowndetectorissuethatstarsbrighterthan about11maginthe K bandenterthenon-linearregimeofthe S VIRCAM detector (Saitoetal. 2012). While close to its minimum V346 Nor was below this limit, after aboutMay 2013 it becamebrighterthan11mag.Inordertocorrectfortheunderes- timationofthesignal,weplottedtheoffsetsbetweentheinstru- mentalandthe2MASSmagnitudesforallstarswithqualityflag ‘A’ in the image as a function of the instrumental magnitude. We fitted the distribution of points with a first or second order polynomial,anddeterminedtheoffsetvalidforV346Norfrom thisfit(foranexample,seeFig.A.1).Thenecessarycorrection duetothenon-linearitywastypicallyinthe0.1–0.2magrange, withafewhighervaluesupto0.4–0.6mag.Fig.A.2showsthe K -band light curve without and with the non-linearitycorrec- S tion,demonstratingthatourcorrectionsignificantlyreducedthe scatterofthedatapointsobtainedcloseintime. AppendixB: Periodanalysis Articlenumber,page6of7 Kóspáletal.:BrightnessvariationsofV346Nor TableB.1.Near-IRphotometryofV346Nor. Date JD−2400000 J H K Telescope S 2003-06-12 52802.86 9.81±0.20 ... 7.48±0.20 VLT 2008-04-10 54567.78 12.63±0.16 10.11±0.09 8.16±0.14 VLT 2010-05-15 55271.34 17.65±0.04 15.09±0.09 12.27±0.07 VISTA 2010-06-26 55373.52 ... ... 12.69±0.09 IRIS 2010-06-27 55374.51 >17.37 ... ... IRIS 2010-06-28 55375.51 ... ... 12.73±0.09 IRIS 2010-07-01 55378.51 >16.98 15.86±0.22 12.66±0.09 IRIS 2010-08-14 55423.01 ... ... 12.57±0.04 VISTA 2011-05-12 55694.34 ... ... 12.38±0.03 VISTA 2011-05-13 55695.40 ... ... 12.41±0.03 VISTA 2011-05-15 55697.28 ... ... 12.41±0.04 VISTA 2011-05-16 55698.34 ... ... 12.45±0.04 VISTA 2011-05-29 55711.30 ... ... 12.65±0.04 VISTA 2011-06-08 55721.26 ... ... 12.68±0.04 VISTA 2011-08-17 55791.04 ... ... 12.40±0.04 VISTA 2011-08-22 55796.06 ... ... 12.40±0.04 VISTA 2011-08-31 55805.02 ... ... 12.43±0.03 VISTA 2011-09-01 55806.03 ... ... 12.45±0.04 VISTA 2011-09-19 55824.06 ... ... 12.58±0.04 VISTA 2011-10-02 55837.00 ... ... 12.58±0.03 VISTA 2012-06-04 56083.04 ... ... 11.86±0.04 VISTA 2012-06-04 56083.16 ... ... 11.86±0.04 VISTA 2012-06-20 56098.98 ... ... 11.75±0.04 VISTA 2012-06-20 56099.01 ... ... 11.75±0.04 VISTA 2012-06-20 56099.06 ... ... 11.76±0.04 VISTA 2012-06-26 56105.02 ... ... 11.69±0.05 VISTA 2012-06-26 56105.09 ... ... 11.68±0.04 VISTA 2012-06-29 56108.18 ... ... 11.74±0.04 VISTA 2013-05-26 56439.37 ... ... 10.61±0.04 VISTA 2013-06-26 56470.26 ... ... 10.65±0.04 VISTA 2013-06-27 56471.16 ... ... 10.67±0.04 VISTA 2013-06-29 56473.17 ... ... 10.67±0.03 VISTA 2013-06-30 56474.13 ... ... 10.73±0.04 VISTA 2013-07-01 56475.17 ... ... 10.72±0.04 VISTA 2013-07-13 56487.16 ... ... 10.56±0.04 VISTA 2013-07-17 56490.97 ... ... 10.51±0.04 VISTA 2013-07-20 56494.01 ... ... 10.49±0.03 VISTA 2013-07-20 56494.07 ... ... 10.48±0.04 VISTA 2013-07-20 56494.12 ... ... 10.47±0.03 VISTA 2013-07-20 56494.16 ... ... 10.48±0.03 VISTA 2013-07-20 56494.21 ... ... 10.48±0.04 VISTA 2013-07-21 56495.01 ... ... 10.44±0.03 VISTA 2013-07-21 56495.08 ... ... 10.47±0.03 VISTA 2013-07-21 56495.14 ... ... 10.46±0.04 VISTA 2013-07-21 56495.20 ... ... 10.45±0.04 VISTA 2013-07-24 56498.14 ... ... 10.44±0.04 VISTA 2013-07-27 56501.09 ... ... 10.46±0.03 VISTA 2013-07-30 56504.00 ... ... 10.51±0.04 VISTA 2016-06-07 57546.56 15.07±0.03 12.67±0.02 10.22±0.03 SMARTS1.3m 2016-08-10 57610.52 14.44±0.03 12.17±0.02 9.75±0.04 SMARTS1.3m 2016-08-22 57622.51 ... ... 9.90±0.02 IRIS 2016-08-25 57625.51 14.52±0.02 12.26±0.02 9.92±0.02 IRIS Articlenumber,page7of7