1996AJ 111. 12 41H THE ASTRONOMICALJOURNALVOLUME111,NUMBER3MARCH1996 brightest ofallthePleiadesNebulae,hasneverbeenphoto- commented: “itcanbereadilyunderstoodwhythis,the middle, andverycometaryinappearance.”Hemeasuredthe in diameter,ofthe13(magnitude),graduallybrighter close southandfollowingMerope(23Tau)...Itisabout30" ered anewandcomparativelybrightroundcometarynebula with theLick36in.refractor,Barnard(1891a)“...discov- would coalescewiththatofthenebula.” graphed. Asufficientlylongexposuretosecureanimpres- center, againvisually,as970east,3577southof23Tau,and himself hadalreadynoted“thisapparentlyinsignificant sion ofthenebula,wouldsooverexposeMeropethatitslight missed itasnomorethanthebrightestportionofwide- affront tothepowerofphotography.Pritchardsaidthathe wasindeedphotographable,andinfactappearedon fleck” onanOxfordAstrographplateof1889,andhaddis- (1891), seeminglyincensedatwhatheregardedasBarnard’s ever, hestressedthatitoughtnottoberegardedas“an Astronomical SocietyinPenticton,B.C. inMay1995. tinctly brighteranddifferentinformfromthestripes insignificant fleck”:itwasreallyaremarkableobject,dis- spread Pleiadesreflectionnebulosity. wisps characteristicoftheordinary Pleiadesnebulosity.As some 36in.refractorplatesalreadyintheLickfiles.How- 'An expandedversionofthePetriePrize Lecture,givenbeforetheCanadian 1241 Astron.J.Ill (3),March1996 In 1890,whileexaminingthebrighterstarsinPleiades © American Astronomical Society • Provided by the NASA Astrophysics Data System Shortly thereafter,BarnardwastakentotaskbyPritchard Barnard (1891b)respondedatlength.Headmittedthatthe -1 fan-shaped withtheaxispointingverynearlytoward23Tau.Itsbluecolorandfactthatitsspectrum by Barnardin1890,itisadifficultobjectbecauseonlyabout30"from23Tau,ofV=4.2.It IC 349isthebrightestareainPleiadesreflectionnebulosity,byafactorofabout15.Discoveredvisually being dissipatedintheradiationfieldof23Tauasitapproachesthatstar.Therelativevelocityvectoris is theresultofachanceencounterbetweenclusterandmolecularcloudatrelativecrossmotion appears identicaltothatofthestarshowsitalsoisareflectionnebula.ThegeneralPleiadesnebulosity The shapeofthefanIC349iscompatiblewithamodelinwhichsmalldustparticlesejectedfrom Tau-Aur clouds;thepropermotionofIC349isinferredfrommotionscloudTTauristars. obtained fromthepropermotionandradialvelocityofcluster,COnearby about 12kms.ItisproposedthatthesemistellarobjectatheadofIC349partcloudand nucleus arebeingsweptbackwardbythecombinedeffectsofradiationpressurefrom23Tauanddrag Society. exerted byinterclustergas.Itisunknownwhetherthenucleusadust-shroudedpre-main-sequencestaror a denseconcentrationofgasanddustseveralhundredA.U.indiameter.©1996AmericanAstronomical Institute forAstronomy,UniversityofHawaii,2680WoodlawnDrive,Honolulu,Hawaii96822 1. HISTORY 1 IC 349:BARNARD’SMEROPENEBULA Received 1995October18;revisedDecember6 Electronic mail:[email protected] 0004-6256/96/111 (3)/1241/ll/$6.00 G. H.Herbig ABSTRACT brightest areasofthefamiliarPleiadesnebulosity. refractor, byBurnham(1892),withsimilarresults.Without will appearlater,thisisquitecorrect:thesurfacebrightness has yettobeanswered:“whetherthenewnebulaisdrifting nard withthestatementthat“judgingfromitssituationand of IC349inVisabout15timeshigherthanthatthe made in1895(Barnard1895). in spacewithMeropeandtheotherstarsofthisfamous the heavens.”Heanticipatedaquestionthat,centurylater, mentioning Pritchard,BurnhamsupportedhiscolleagueBar- group.” Barnardhimselfreportednewvisualmeasurements appearance, (IC349)isoneofthemostsingularobjectsin 349, wasmeasuredthefollowingyear,againwith36in. There wasnosuggestionofanucleusorstellarcondensa- the “round,brightnebula”at36"from23TauinP.A.166°. tion beingpresent.Burnhaminfactcommenteduponthe thereafter byanoteKeeler(1898),describingIC349asit absence ofanysuchstructure. ,” andboundedbytwo wisps ofnebulosity. in 1914-1915,probablybyS.B.Nicholson.Allconfirm files takenbetween1898and1900,twoothersobtained appeared onaseriesofexposuresobtainedwiththeCrossley refractor, oneofwhichisreproduced inhisnote.Hede- Keeler’s descriptionofthenebulaasroughlypentagonalin 36 in.reflectoratLick.TherearesixsuchplatesintheLick shape, “withthemostsalientanglepointingdirectlyto (1922) ofIC349onplatestaken withtheAllegheny30in. Barnard’s Meropenebula,subsequentlycataloguedasIC All thesevisualmeasuresagreedinlocatingthecenterof So endedthevisualhistoryofIC349,followedshortly More instructive,however,isa descriptionbyTrumpler © 1996Am.Astron. Soc.1241 1996AJ 111. 12 41H which haveno suchinstrumentalstructure, and withtheLick with theAllegheny (Trumpler1922)and Lickrefractors, fact), noristhereanysignificant structurestillnearer23Tau. This isdemonstratedbyconventional photographstaken much fainterstreakoftheordinaryMeropenebulosity ex- den bythebrightverticalbar inFigs.1and2(aCCDarti- tending throughthestartoward aboutPA.157°;itcanbe longer exposuresshowthatIC349issuperimposedupon a pler, asfartheywent.Thenebulaispentagonalinoutline, one wispextendingbeyondtheapextoward23Tau.The the pentagonalfan.Thereisamarginalsuggestionofatleast called the“nucleus.”Thereisconsiderablestructurewithin with itsaxisofsymmetrypointingnearlybutnotexactly seen dimlyinFig.2. toward 23Tau.Attheapexisasemistellarknot,hereafter this imageryconfirmedthedescriptionsbyKeelerandTrum- hind amaskinthefocalplane.EvenbetterCCDimages were obtainedwiththe88in.reflectoronMaunaKeain easily seen,particularlywhenthebrightstarwashiddenbe- reflector. Whilesettingupfortheseobservations,theob- of IC349weretakenattheprimefocusLick120in. em imagesofIC349[seeFigs.1(Plate38)and2]. this structuredescribedbyTrumplerisrecognizableonmod- well markedbyaratherstronglinerunningnorth-south.”All 120 in. reflector, whose diffractionspikes areoriented at45° FWHM oLQ.8 arcsecthroughout. _^ ^ server hadtobestruckbythebrightnessofIC349:itis also formingarightangle.Thewesternedgeofthenebulais lel totheseandsituated7"farthersoutharetwosimilarlines nebula) fromwhichtwoarms,about10"long,goouttothe Fig. 2.IC349:a20sexposurebehindBfilteratthe//10Cassegrainfocus of the88in.telescope.Theareashownisabout26"square. southeast andsouthwestformingnearlyarightangle.Paral- sation (thiswasthefirstmentionofanysuchfeaturein scribed thenebulaasstartingfrom“amarkedroundconden- 1993. ExamplesoftheseareshowninFigs.1,2,and3.All 0 1242 G.H.HERBIG:IC349 There appearstobenoimportant structureofIC349hid- More recently,in1980-1981,severaldirectphotographs © American Astronomical Society •Provided bythe NASAAstrophysics Data System 2 -1 eters of2.1, 3.8, and5.0arcsec;theseeing diskhada with theAPPHOT packageofIRAF,andwith aperturediam- rated beforeanequallysatisfactory solutionfortheextinc- to beusedinstead.Consequently thepresentphotometricre- tion coefficientswaspossible, socoefficientsdeterminedon equately fromthoseobservations, butskyconditionsdeterio- region fromLandolt(1991).Thetransformations the a goodnightearlierintheyear withthesameequipmenthad instrumental totheLandoltBVRIsystemweredefined ad- IC 349fieldwerematchedwithsimilarseriesonastandard sults areofonlyfairquality. The reductionswerecarriedout about 7'onaside.Exposuresrangingfrom5to60s the a Tektronix2048CCDbehindBVRIfilters;thefieldwas 23, underonlyfairphotometricconditions.Thedetectorwas at thef/10focusof88in.telescopeon1993November with aperiodof11.8h(McNamara1987). Balmer lines,andvaryinintensityonatimescaleofyears and shallow,aconsequenceofthelargevsini=280kms argued thatIC349hasaquitedifferentexplanation. telescope byMr.PaulKalas. to themeridian.Thisresultwasconfirmedmorerecentlyby Fig. 3.ImagesofIC349behindaBfilter(upperleft),Vright),R (Slettebak 1982).Thestarisalsoslightlyvariableinlight, (Slettebak etal.1992).Emissioncoresarepresentinthe striking, butasidefromitclearlybeingunipolar,willbe a CCDimagetakenwithcoronagraphicdeviceatthe88in. indication thatthereislittlecontributionbyHaemission. ment oftheÆ-bandbrightnessIC349withrespecttoVand/isacrude (lower left),andIright).Thefactthatthereisnosignificantenhance- “cometary” nebulaeatRMon,HKOri,andLkHa-208is A seriesofCCDframescenteredon23Tauwereobtained 23 TauitselfistypeB6IVe.Itsabsorptionlinesarebroad The resemblanceofIC349tothewell-known 2. PHOTOMETRYANDSPECTROSCOPY 1242 1996AJ 111. 12 41H -2 nearly superimposeduponthenarrowfilamentthatdefines 1243 G.H.HERBIG:IC349 the easternedgeoffan,andsoappearstobeelongatedin the imagesofstarsonallCCDframes(exceptinI) profile, wasr.'32±0'.T0.Therenoobviousdependence weighted meanFWHMofallthestarsonframeswas quadratically fromthatofthecorenucleus.The order todefinetheinstrumentalprofile,andthensubtracted about P.A.318°.One-dimensionalGaussianswerefittedto 0'.'82, andthatofthecore,followingremovalstellar points withintheIC349nebulosity.Themeasuredare nucleus, asmeasuredthroughthethreeapertures,andfor7 upon color. just described.Asacheck,theywerechosentocoincidewith respect to23Tau.ThesurfacebrightnessSVinmagarcsec identified inTable1bytheirrectangularcoordinates(inarc- uncertainty inthecorrectionforbackgroundofscattered is simplytheVmagnitudecorrectedforaperturearea. used inthereductionswasthenfluxreadoffsmooth from thestaroneithersideofIC349.Thebackgroundlevel light from23TauuponwhichIC349lies.Thefalloffwith the raysandstreakswhichissueirregularlyfromstar curves drawnthroughthosepoints.Thisignores,ofcourse, CCD framethefluxatmanypointsalongradiiextending distance fromthestarwasmappedbymeasuringonevery sec, abeingpositivetotheeast,ynorth)with image; somecanbeseeninFigs.1and3. cant colordifferencebetweenIC349andthegeneralreflec- nebulosity wasquitebright,bytheproceduresandapertures was measuredattwopointsinthefieldwheregeneral tion nebulosityilluminatedby23Tau.Thesurfacebrightness two oftheareasinMeropenebulositythathadbeen the factthatthereisnoareainthesesmallCCDframes measured byO’Dell(1965).Someuncertaintyarisesfrom Three pointsofminimumbrightnesswerefoundbyinspec- is completelyfreeofsometracethegeneralnebulosity. provided bytheiragreementwith measuresofskybrightness reductions. Someconfidencein thesebackgroundlevelswas tion ofPOSSprintswherethesurfacebrightnesswaslow, and thebackgroundlevelatthese lowpointswasusedinthe taken thesamenight. on framesofnebula-freefieldselsewhere intheskythatwere The nucleusofIC349issymmetricbutnonstellar.It © American Astronomical Society • Provided by the NASA Astrophysics Data System The VandB—resultsaregiveninTable1forthe The largestsourceoferrorinthedataTable1is It isimportanttodeterminewhetherthereanysignifi- The twodatasets arenotcloselycomparable, however: Region Ax nucleus nucleus nucleus A G C D B E F Table 1.MagnitudesandsurfacebrightnessesinIC349. (arcsec) +6.5 +12. +7.5 +5.5 +9.5 +7. +3. +2. -29. -32. -30. -35. -32. -35. -26. Ay ApertureVB—Sv -24. 2.1 5.0 3.8 2.1 3.8 3.8 3.8 3.8 3.8 3.8 16.42 15.02 15.36 16.14 15.66 15.91 15.90 15.74 16.38 16.39 -0.19 -0.19 -0.21 -0.20 -0.16 -0.28: -0.26 -0.38: -0.31 -0.50: 18.52 18.36 17.77 18.27 17.99 17.49 19.01 18.28 18.53 19.00 -2 either sideoftheeffectivewavelengthJohnsonBfilter the threemuchsmallerapertures.Furthermore,twoof while thepresentonesaremeansoffluxesthrough O’Dell’s measuresweremadethrougha63"diaphragm, Another ofO’Dell’spassbandsfellat5620Â,notfarfrom mean ofthe4110and4630ÂfluxesisnotfarfromB. near 4400À.Itwasassumedforthepresentpurposethat O’Dell’s filterbandpasseswereat4110and4630Á,on that the5620ÁpassbandisalmostequivalenttoV.Since teristics werepublished),soagainitcouldonlybeassumed the Vpassbandnear5500Â(nodetailsoffiltercharac- B —Vresultsfromthepresentobservationsaregivenin O’Dell’s measuresweredifferentialwithrespectto23Tau, they canthenbeconvertedtomagnitudesarcsecandcol- ors (SrandB'-V'),areshowninTable2.TheS, last twocolumns.Thethreeentriesrefertobrightareas been publishedbyJohnson(1960),whomeasuredUBVfor mag brighterthanO’Dell’s,althoughthatmaybeonlya in filamentsoftheordinaryPleiadesnebulosity. consequence ofthesystematicdifferencesbetweentwo his Table2(b),andforthisareahemeasuredS=20.9,B~V made througha150"diaphragmandthusaverageovercon- three regionsabout3'from23Tau.Hisobservationswere in Table2. area 3'southofthestarincludesO’Dell’sIIandregion1 sets ofdatamentionedabove. R andIimagesarenotreproducedherebecauseofthedif- cardinal directionsfrom23Tau,whereCCDbleedingalong siderable structureinthefilamentarynebulosity.Johnson’s columns anddiffractionspikesissignificantontheseframes. (1977) becausehissurfacebrightnessesweremeasuredinthe brightnesses ofthebrighterareas inIC349areabout3mag the presentphotometrydoesnotdiffersignificantly,asasys- ficulty ofallowingadequatelyfortheparticularlycomplex are thesamewithintheiruncertainties.(Theresultsfrom 349 andofthegeneralMeropenebulosity,asmeasuredhere, brightest pointsintheentirePleiades. near 23Tau,whichaccordingto O’Dell,arethemselvesthe brighter thanthebrightestregions ofthegeneralnebulosity tem, fromthoseofO’DellandJohnson. scattered lightbackgroundonthoseframes.)Furthermore, = —0.13.Theseareinreasonableagreementwiththevalues v tered lightbackground from23Tau.Aphotographic-region v The presentVsurfacebrightnessesseemtobeabout0.4 No effortwasmadetoreproducethephotometryofWitt Surface photometryofthePleiadesnebulosityhasalso The conclusionis,however,thattheB—VcolorsofIC Comparison ofTables1and2showsthatthesurface Spectroscopy ofIC349isdifficult becauseofthescat- Table 2.SurfacebrightnessesandcolorsofPleiadesnebulosity. O’Dell II O’Dell I Region AxAy 3 2 1 (arcsec) +144. +148. -47. -91. -91. +161. -113. -172. -189. -88. > 21.11 21.39 Sy B—VSB-V v O’Dell Thispaper -0.31 -0.39 20.98 21.83 21.18 20.76 20.70 -0.10 -0.45 -0.27 -0.22 -0.5: 1243 1996AJ 111. 12 41H 2 2 -2 region, obtainedin1986withaCCDandhencemorereadily corrected forbackground,showsonlyaweakcontinuumand Lick coudespectrogram(/?=6700)ofIC349inthered like thatof23Tauitself,althoughitisnotclearwhatpre- be expectedifshockedgaswerepresent. Ha structureisverysimilartothatobservedin23Tau centrally reversedHacoreofthestellarspectrum.Theentire tained atthesametime,revealsthatlatterisinfact a broadHaabsorptionlinewithsomenoisycentralemission caution wastakentoexcludescatteredlightfromthestar.A spectrogram obtainedbyAmy(1977)appearstobemuch structure. Aproperlyexposedspectrumof23Tauitself,ob- 349 spectrumofnarrowHor[SIi]emissionlinesasmight not differdetectablyfromthegeneralPleiadesnebulosity. fan, arepurereflectionnebulaethatincolorandspectrumdo nucleus, wasstrongerinthesameproportion. it hadbeenin1986.TheHaemissionthenucleusofIC mentally scatteredlightfrom23Tau,wasmuchstrongerthan Ha emissioninthefieldaroundIC349,muchofitinstm- on the88in.telescopeatMaunaKea.Theseshowedthat in 1995withthe//31CassegrainFaintObjectSpectrograph Furthermore, the1986and1995spectroscopyprovesthatIC 1244 G.H.HERBIG:IC349 in thespectrumofthatstar. 349, andinthefanwhereslitcrossedit7'.'5southof having inprojectionacircularoutlineofdiameterD.Al- 349 isindeedilluminatedby23Tau,andrespondstochanges 1982 byHanuschiketal.(1988).ThereisnosignintheIC that thestar-nucleuslineisactuallyinclinedatanangleato lie eitherinfrontoforbehindtheplanesky;assume though inprojectionitappearsonlydfromthestar,can the remarkablebrightnessofnucleusIC349?Consider light from23Tau,whatalbedowouldberequiredtoexplain the skyplane,abeingpositiveifobjectisbehind.If a perfectlywhiteLambertiandiskilluminatedby23Tau,and is thestellarfluxatunitdistance,totalamountoflight 2- a)/2.Theactualareaofthediskis7tD/4cos£,soifF* normal bisectstheanglebetweenstarandSun,so/=6=(tt/ leaves atangle6,thenforsimplicityassumethatthedisk illumination arrivesatanangleitothedisknormal,and utes FJAirrattheSun,soobservedmagnitudediffer- scattered fromthediskandreceivedcmatSunis ence betweennucleusandstar is where risthedistancefromSun.Thestaritselfcontrib- 0 (1) © American Astronomical Society Low-resolution {R=760)spectraofIC349wereobtained These observationsindicatethatIC349,bothnucleusand The questionthenarises:ifitisseenentirelyinscattered ^ 4-?- 2 cosa De1 -V* =-2.5logl 3. THEBRIGHTNESSOFNUCLEUS 2 / cosacos[(7r/2—a)/2] Provided bythe NASA Astrophysics Data System (2) Table 3.CalculatedVmagnitudesandBondAlbedoforaLambertianDisk illuminated by23Tauri. to beassignedthenucleusaccountforfactthatitis The lastcolumncontainstheBondalbedoAthatwouldhave Lambertian scatterer”magnitudesVofTable3follow. tures; extrapolatedtoanapertureof1"54,thenV=16.63, its Vmagnitudeasmeasuredthroughseverallargeraper- the Vframes,beforeallowanceforseeing.Table2contains and since^=4.17D210A.U.,theideal“white apertures inTable3. 349 resemblesadark,dustysurface.Theresultismuchthe same ifthecalculationiscarriedoutforV’sandlarger nebulosity couldbecausedbythemovementofcluster lying fragmentoftheextensiveTau-Aurdarknebulaewhich ity inthePleiadesisresultofachanceencounterbetween V— Vmagnitudesfainterthanthiscalculationpredicts. by White&Bally(1993). more specificbyJones&Herbig(1979),GordonAmy gested thatsomeofthefilamentarystructurePleiades apparently thefirsttopointthisoutinprint,whenhesug- lie totheeastandsouthofPleiades.Amy(1977)was the starclusterandamolecularcloud,veryprobablyanout- stars withrespecttothenebulosity.Thesameviewwasmade on therelativemotionofthatnebulawithrespectto century old,whichlieinobservatoryarchivesandcontain ber oftheclusterhaving+10,(c)noristhereany stars.Asaconsequence,thereisnoproofthatIC images ofIC349,thereisasyetnoastrometricinformation M-type dwarf(aswouldbeexpected atthatluminosity). (1984), WhiteBreger(1987),andingreatestdetail toward 23Tau by therelativemotionofcluster andcloud, that thenucleusofIC349isa dust condensationoradusty the Pleiadesreflectionnebulae, wepursuetheassumption indication intheopticalspectrumofpresenceaK-or not stellar,(b)itscoloristhatexpectedofastellarmem- improbable, however,because(a)thenucleusofIC349is 349 isnotadynamicalmemberofthatcluster.Thatseems nuc star belongingtotheTau-Aurclouds, thatitisbeingcarried nuc , The nucleushasaFWHMofl'.54orabout210A.U.on Clearly, atthisresolutionthenon-stellarnucleusofIC It isnowgenerallyrecognizedthatthereflectionnebulos- Despite allthephotographicplates,someofthemovera Since itscolorisinfactcomparable tothebluishcolorsof 4. THEMOTIONOFIC349 -30 12.790.03 -60 14.690.17 a (°) ^nucA 60 13.260.04 30 12.190.02 0 12.100.015 1244 1996AJ 111. 12 41H -1 , -1 -1 -1 -1 -1 -1 -1 -1 because thepropermotionofcloudscanbeinferredfrom radiation fieldofthatstar. the relativemotionofIC349and23Taucanbeestimated clouds, whosemainstructureslieabout5°totheeast,then and thatitisnowintheprocessofbeingdissipated that oftheTTauristarsimbeddedwithinthem.Thenearest this subcloudasdeterminedbyJones&Herbig(1979)is: concentration ofTTSliesbetween/=168°and170°,b= referred totheLSR,is+7.5±1kms.Themeanradial tion ofunitweight.ReducedtothepositionPleiades, the secondfiguresarestandarddeviationsofanobserva- these become+0.'91±0'.'91,—2.'64±0'.'71. /¿=+0'.'61±0'.'91 cent,/z¿=-2'.77±0'.'71where precisely onthesamesystem:thatofPleiadesisnear tion ofthePleiadesiswelldetermined;Olano&Poppel velocity ofthePleiadesis-3.0±0.2kms(Morseetal 1245 G.H.HERBIG:IC349 cent. & Mizuno(1991),theCOradialvelocityofthissubcloud, to anetworkofAGK-3stars(Jones&Herbig1979).The FK4 (Jones1973),whiletheTTaurimotionswerereferred tive crossmotionofthecloudswithrespecttoclusteris clarified whenHipparcosresultsbecomeavailable. difference isnotbelievedtobelarge,butthematterwill moving atOcenttowardPA.325^32°withrespecttothe locities.) ties anddispersionsinallthepropermotionsradialve- cluster mean.(Theuncertaintiesonthepositionangleare (1987) giveitas/¿=2'.'0±0'.7cent,¡jl=—A"2±0”\ - 15°and-17°.Themeanpropermotionforthe17TTSin results arenotsignificantlydifferent.Therelativevelocity mean propermotionsofall75TTSintheentireTau-Aur outer dimensionsoftheerrorboxdefinedbyuncertain- vector isthen273centtowardPA.334^26°*whichnow cloud complex,andwiththeoverallaverageCOvelocity, the generaldirectionofstar;seeFig.4. which meansthatineithercase,projectionitismoving in 1991; LiuetalRosvick1992).Thepropermo- particles woulddefineastronglycurvedbanner,convex in moving acrossthatdirection,radiation-pressuredrivendust the directionof23Tau.Thatis,ifnucleuswasinstead fact thatthedustfanofIC349issymmetricwithrespect to IRAS images. White &Ballyinterpretthis featureasthe the directionofmotion,contrarytowhatisobservedat IC a with thatdeducedbyWhite & Bally(1993)fromthecavity tion ofrelativemotioninferred inthiswayconflictsseverely extending eastandsouthofthe Pleiadesthatcanbeseenin 12 kms,andatthePleiades,cloudsIC349are lar medium.If sOjthenitindicatesthatthe mediumismov- wake ofthecluster asitmovesthroughthe ambient interstel- 349. 15 kms. a0 # If thenucleusofIC349ismovingwithTau-Aur According toUngerechts&Thaddeus(1987)andFukui It mustbenoted,however,thatthesetwomotionsarenot If thesepropermotionsaretakenliterally,thentherela- If thesecalculationsarecarriedthroughinsteadwiththe The nucleusiscurrently25"from23TauinPA.164°, As willbeshownlater,thisresultisconsistentwiththe On theotherhand,ithastobe pointedoutthatthedirec- American Astronomical Society •Provided bythe NASA Astrophysics Data System Fig. 4.ThevelocityvectorofthenucleusIC349,projectedonplane Pleiades thatarederivedinthetext. of thesky(solidline).Thedashedlinesindicateuncertaintyindirection involved combinetomaximumeffect.Themotioninthenext1000years of thevectorthatresultswhenerrorsanddispersionsallquantities no obviousexplanationofthisdisagreementifthelayer not thedirectioninferredfromTTS,P.A.325°.Thereis ing withrespecttotheclustertowardsaboutP.A.95°.Thisis assumes thevaluesofpropermotionIC349withrespectto borhood ofastarisreminiscentthesituationcomet clouds whichcontaintheTTS.Thisissuewillbeconsidered interstellar materialseenbyIRASbelongstotheTau-Aur point thatfrozenvolatilesevaporate,andinescapingcarry near theSun,wherecomet’snucleusiswarmedto the again inSec.6,below. perature thatthedustwillassume intheradiationfieldof23 because oftheirlowangular resolution.However,thetem- remains instructive. IC 349isnotapparentonthe coaddedIRASimages,possibly dust withthem.Thisanalogywillbepursuedhereasfar it Tau canbeestimated. Thatwouldestablish whetherthedust evaporate. is atleastwarm enoughforfrozenmaterials suchasCOto 2000- 3000 - 4000 - 1000 - The ejectionofdustfromanonstellarobjectintheneigh- The temperatureofthenucleus ofIC349isnotknown. Q.U. 5. THETEMPERATUREOFNEBULARDUST — 30" — 10 — 20 M 0 1245 1996AJ 111. 12 41H 8-21 8 be obtainedfromtheexpressionwhichequatesheating by absorptionwiththecoolingthermalemission: 1246 G.H.HERBIG:IC349 cate” particlescanbecalculatedfromtheopticalconstants by theparticlefrom23Tauwasassembledthatmea- tabulated byDraine(1985).Anestimateofthefluxreceived where F*{\)representsthefluxreceivedbyparticle. measured byO’Connell(1973),andthefluxdensitiesat2.3, 0.33 and1.08/umascompiledbyBreger(1976) sured between0.12and0.32/jmfortheunreddenedB6V the IUEdata.Below0.12/im,surfacefluxesfor star HD90994byIUE(Wuetai1983).Thefluxesbetween and reducedtoastandarddistanceof1A.U.Thetotalflux magnitude between23Tau(B6IV)andHD90994(B6V), these fluxeswerecorrectedforthedifferenceinabsolute ibility withtheIUEfluxesinregionofoverlap.Finally, Andersen (1991),thedistanceofHD90994,andforcompat- were adjustedfortheradiusofanormalB6Vaccordingto 3.6, and4.9/jumgivenbyGehrzetal.(1974)werejoinedto inferred fromSchmidt-Kaler’smeanMySforB6Vand 6.1 X10ergscmsthusobtainediscomparablewiththat B6IV andAndersen’sLILqforB6V(7.0X10). T= 14500Kandlogg4.0astabulatedbyKurucz(1979) tance from23Tauisspecified.AtthedistanceofPleiades Jo larger valuesoftheseparation,itbeingunlikelythat calculated T’sforthetwoparticlesizesthatandseveral of 25"correspondstoabout3400A.U.Table4givesthe of Eq.(3).Thiscanbeseenifßissettounityin(3); tures aresignificantlyhigherthantheblackbodyequivalent nebula liespreciselyintheplaneofsky.Thesetempera- of heatwithinthenucleus,as, for example,fromacentral the resultingTat3400A.U.is30K,independentofparticle (135 pc),theprojecteddistanceofnucleusfrom23Tau fraction oftheCO inaCO:watericemixture would evapo- star orastheresultofviscousheating. size. e abs The temperatureofaparticleilluminatedby23Taucan © American Astronomical Society • Provided by the NASA Astrophysics Data System The MieefficiencyfactorsQfor“astronomicalsili- The expression(3)canbesolvedforTwhend,thedis- 2 According tothereviewbyRickman (1992),asubstantial Of courseallthisassumesthat there isnointernalsource abs = ÍÖabs(ö,X)4'n-airß(X,r)dX,(3) Jo Separation T(K) 6-5 4000. 9278 3400. 9882 7000. 7765 5500. 8370 3700. 9580 (an) a=10~cm10 Table 4.Predicteddustgraintemperatures. 1 -6 -1 nucleus ofIC349,andentirelysowhatliesinside,thisis ever, sinceweareignorantofconditionsatthesurface rate at50-100K.PresumablyCOfrostonthesurfaceof no morethanaplausibleplacetostart. it couldbe,giventhetemperaturesinTable4,thatout- flow ofdustinIC349isdrivenbyevaporatingCO.How- silicate grainswouldevaporateatstilllowertemperatures,so pressure from23Tau,bythegravitationofbothnucleus the nucleusofIC349willbecontrolledbyradiation FWHM) is1.4kms”.However,aparticlepropelledupward has beentakentobe0.1M.Inthatcase,thevelocityof Pleiades nebulosity.Itispossibletocomputethemotionof and 23Tau,bydragfromthematerialofambient pressure of23Tau.WhateverM,underthiscircumstance, with avelocityofonly0.7uwillascendtopeakaltitude escape atther=90A.U.level(halfofmeasured ejection velocitiesofabout0.7uandgreaterwillbesuffi- will havebeencaughtupandsweptawaybytheradiation of r,butitwillusuallynotfallbackbecausebythattime such aparticleundersimplifyingassumptions. ded inthefollowingcalculationsofparticletrajectoriesare: the nucleus. cient toremovetheparticlefromgravitationaldomainof particle sizesispresent. through thespectrum,andthatgrainisnearlyenough lisions withtheambientgas,particlepropertiesdonot with adragcoefficientofunity. change duringflight:theyexperiencenomassdueto spherical thatconventionalMieß’saremeaningful. of thenucleus,isthereafternotinfluencedbyanygasre- sputtering oraccretion,andtheyinteractwiththemedium forced byawindfrom23Tauhasbeenignored. leased atthesametime. noted, itwastakenas0.1M©forthesecalculations. plane oftheskythatprojectedseparationsaremeaningful. “astronomical silicate,”thatthoseopticalpropertieshold 0 nuc tude oftheradiationpressure/drag force,thelatterdecreasing lar fan.Thisangledependson the ratioofvtomagni- number reproducestheobserved openingangleofthenebu- calculations forsilicatesofradius a=10cm,becausethat distance ofr=90A.U.hasbeen usedintheseillustrative esc 0 esc 0 as particlesize increases. Thusanyopening angle canbe significant radialvelocityuj.Avalueofj=9.0kmsata C] 0 e The motionofverysmallsilicateparticleslaunchedfrom For thecalculationsofparticletrajectoriestofollow,M The mostseriousconceptualassumptionsthatareimbed- (a) ItisassumedthattheparticlecomposedofDraine’s Numerical assumptionsare: (c) Itisassumedthatexceptfordecelerationduetocol- (b) Noaccountistakenofthelikelihoodthatarangein (d) Itisassumedthattheparticle’smotion,onceitfree nuc (e) Thepossibilitythatradiationpressurecouldberein- (g) Thatthemotionofnucleusisnearlyenoughin (f) Thatthemassofnucleusitselfisnotlarge;as (h) Thatthedustparticlesemergefromnucleuswitha 6. MODELINGTHENEBULA 1246 1996AJ 111. 12 41H 1 -3 -6 -3 preserved bysimultaneouslyadjustingujandainopposite directions. to 23Tau,butpointsintheoppositedirection.Thestaris coincides withthevelocityvectorofnucleusrespect its velocityvectorand23Taulieinthexyplane.Thexaxis located atsomepositivey,definedbytheassumptionasto system travelingwiththenucleus,andinwhich the directionofmotionnucleus. 1247 G.H.HERBIG:IC349 e where negative inthesecondquadrant),pisparticledensity(as tween thepositiveyaxisanddirectionto23Tau(0is distance fromthenucleus,6isangleatnucleusbe- nucleus withrespectto23Tauandtheambientmedium.It is assumedtobe12kms“,followingSec.4.Theparticle above, takentobe3.0gcm),andu*isthevelocityof tance rfromthecenterofnucleus,movesradiallyaway in n. density inthemediumthroughwhichnucleusismoving numerically stepbystep,andthesubsequentmotionof particles ofradiusa=10cmwasreleasedateachincre- at velocityuj,thenEqs.(4),(5),and(6)canbeintegrated grain followed.Inthepresentcalculations,anewgroupof face ofthenucleus,andwerefollowedindividuallythereaf- ment ofthemotionnucleusalongxaxis.They = + resulting fandidnotdependupondetailsnearr,forex- ter. Experimentshowedthatinmostcasestheshapeof were launchedfrom32pointsspreaduniformlyoverthesur- motion component.Nordidtheopeningangledependon lope, orwhethertheparticlevelocitycontainedanorbital ample, whetherthenucleuswasadiskorsphericalenve- mass assumedforthenucleus, forexampleifMwere taken tobe1.0insteadof0.1M . density oftheambientmedium: A:ifthegasdensityislow, combined effect ofujandthevelocityatwhich thegrainis of thedustleavingnucleus iscontrolledlargelybythe say n^5cm,thendragisa minoreffectandthemotion 0 H e 0 mc Q e H y —û~ 2+Vz © American Astronomical Society • Provided by the NASA Astrophysics Data System The trajectoryoftheparticlewasfollowedinacoordinate x =+■ The equationsofmotionarethen ^ drcdApad~' /= Q{\)F^\)d\.(7) Here, disthedistanceofparticlefrom23Tau,rits Given thestartingcoordinatesofaparticlewhich,atdis- .. CM* vr Two extremecasescanbevisualized dependinguponthe _ GM*zGMI33nm nucH 2 z{v) J 0.05/am ~ 4pa f 10/am ^r*-’ 3nm GM, H sin 0— cos fl— GM n GM y mc cd Apa Z— sin0 (4) (5) (6) -3 Eqs. (2)-(4)predominates.AttheotherextremeisB:n driven byradiationpressure.Inthiscase,thethirdtermin the ambientmedium;4thtermpredominates. is thedragresultingfrommotionofnucleusthrough large, >100cm,inwhichcasethemajorforceondust B itwouldliealongthevelocityvectorofnucleus.The precise propermotioninformationislacking,onecannot proximately thesamedirection(Fig.4).Sincesufficiently Tau, butaccordingtoSec.4,thenucleusismovinginap- direct imagesshowthatthefanaxispointsverynearlyat23 now choosebetweenthetwopossibilities. tion isonthexyplane,whichplaneofsky,and this procedure,Fig.4beingtakenintoaccount.Theprojec- upper leftshowsthepathofnucleus,movingleftwards viewed fromthedirectionofpositivez.Thediagramin panels showthepredictedshapeofIC349fanat toward 23Tauattheoriginistakenas5°.Thethreeother Tau. Theanglebetweenthevelocityvectoranddirection along thexaxistowardorigin,wherenucleusisas- present timeifdustejectionbegan3000yearsago(C),2000 H sumed tobelocatedatthepresenttime,3400A.U.from23 years (B),or1000beforethepresent.(Theslightcur- vature ofthemotionnucleuswithrespecttoxaxis is notshowninthediagram.) Tau, andsmallestatthestartofejection.Theyhavenoother for thoseparticlesreleasedwhenthenucleuswasnearest23 quantitative significance. have consideredthepossibilitythatitismovingnotin tion ofIC349withrespectto23Tau(Fig.4),onemight proaching theclusternottowardP.A.325°but As anillustrationoftheconsequence,asimilarcalculation was carriedoutforthespecificexampleofnucleusap- general directionofthatstar,butevenatalargeangletoit. Fig. 6.TheotherpanelsshowthepredictedstructureofIC years ago,asshowninthesketchupperleftpanelof of minimumangularseparationfrom23Tauseveralhundred 95°, whichisthedirectionenvisagedbyWhite&Bally before thepresent.Inallcases,fanwouldhavebeen (1993). Inthatcase,thenucleusmusthavepassedpoint upon thedust.Ifdragbyinterclustergasweredominant, dust tailsofcometspassingneartheSun.Ofcourse,this curved, convextothedirectionofmotion,asisseenin 349 ifejectionofdusthadbegun1000,2000,or3000years no curvatureintheplaneofskyisobserved,direction fan wouldnotbecurvedbutthentheaxisliealong assumes thatradiationpressureisthedominantforceacting the velocityvector,nottoward23Tauasisobserved.Since of motiontoward325°(Figs.4and5)mustbenearerthe truth thanthatitmovestoward95°(Fig.6). velocity vectorissonearlydirected toward23Tau,thecur- the three-dimensionalfansofFig. 5,butbecausetherethe vature isinthelineofsightand soisnotseeninprojection, tension ofthefan. although itdoeshavetheeffect oflimitingtheapparentex- In caseAthefanaxiswouldbedirectedtoward23Tau,in Figure 5showstheevolutionofIC349asmodelledby The sizeoftheindividualpointsintheseplotsisgreatest If therehadbeennoinformationonthedirectionofmo- Of course,thatsamecurvature presumablyispresentin 1247 1996AJ 111. 12 41H 6 procedure ofSec.6.Thediagramontheupperleftshowsthreestartingpositions:1000,2000,and3000yearsbeforepresent.significance Fig. 5.ThreesnapshotsofthedevelopmentdustfanIC349asitmovesalongvector4towarditspresentposition,calculatedby 1248 G.H.HERBIG:IC349 dot sizesisexplainedinthetext. nonisotropic ejection,ortimevariationofvj.Butthe that couldbeaddedtothemodelmightaccountforsuch not explainedatall,althoughonecanimaginecomplications thing tobedesired.Thearcandfilamentswithinthefanare IC 349fan,atleastneartheapex,butmatchleavessome- motion, expansionvelocity—becomesavailable. for elaboratingthissimplemodelwillcomewhenbetterin- formation ontheinputparameters—radialvelocity,proper structures, suchasrotationofthenucleus,orintermittent follows. mass-loss rateoverthelastt years.Theprocedureisas fan. Therebyoneobtainsavalue of(M),theaveragedust quantity canbeestimatedfrom the surfacebrightnessof years, soallsuchmaterialnowinthenebulahasbeenejected the timetrequiredforasilicategrainofradiustobe 2200 A.U.fromthenucleus.ThemodelingofSec.6gives of dustinvolved,butundersimplifyingassumptionsthat during thattime.Themodelssaynothingabouttheamount swept outtothatdistance.Fora=10“cm,tisabout900 single-scattered radiation of23Tau.Theangle 0andthe e a a a a © American Astronomical Society • Provided by the NASA Astrophysics Data System Such calculationsdoreproducethegeneraloutlineof The outeredgeofIC349onthepresentimagesisabout All theF-bandluminosityof the fanisassumedtobe 23 Tau

NOW Î + 7. MASSLOSS -1000 yr-3000 < ¿<—¿—í—¿— ABC -2000 yr 2 -2 2 projected separationofaparticlefrom23Tauweredefined by theparticleindirectionatowardSunis,perunit if F*istheV-bandfluxemittedby23Tau,scattered in Sec.6.Thescatteringangleattheparticleisa=O+ir/l,so where f(a,a)containsthedirectionaldependenceof used: solid angle, becomes ticle radiusandopticalconstants.LetNbethetotalnumber where g=(cosa)andfollowsfromMietheory,givenpar- scattering. Inthiscase,theHenyey-Greensteinfunctionwas If thecolumnisnotopticallythin, however,thisexpression of scatterersinagivencmcolumnthenebula,sothatif arcsec attheSunbutinmagnitudes cm”atthesource, i> isthesurfacebrightnessofnebulanotinmagnitudes neb f(a,a) = N= F 2 ira sinaQf sce 2 s\n(XTTaQf{a,a), (8) sci O 2000400060008000a.u. 2 23/2 1-g 1 4i7 (1+g—2gcosa)’ v 2.512*~ 4000 -6000 -4000 -2000 2000 O 1248 (10) (9) 1996AJ 111. 12 41H 21 3 -65 132 1249 G.H.HERBIG:IC349 to beinthedirectionofP.A.95°,insteadtoward325°.Sinceradiationpressureisalwaysdirectedawayfromstar,axisfanturnsasnucleus Fig. 6.ThreesnapshotsofthedevelopmentdustfanIC349,asin5,butnowmotionnucleustowarditspresentpositionisassumed moves alongitstrajectory.SuchcurvatureisnotobservedforIC349. bedo beingy. IC 349fanwasmeasuredforabout300smallareas,each where c=yfsinaid,andtheparticleal- the fanexceptforimmediateareaofnucleus.Con- ventional V,B-Vvalueswereextractedforeachofthe 3X3 pixelssquare,or0'.'63onaside,coveringessentiallyall elements ofthisarraybythephotometricproceduresSec. The thirdcolumngivesM=N4irap/3,thedustmassif in Table5fora=3.0X10and3.0X10“cm,0=0°. ticle columndensitiesforeach3X3pixelareaarethen 3, andconvertedtodustcolumndensitiesasabove.Thepar- that singlesize.Thefourthcolumncontainstinyears,from all thelightofnebulaisscatteredbysilicategrains (0.63 X135X1.496X10)V. fraction oftheejecteddusttohavebeendrivenoutabout the modelingofSec.6,timerequiredforasubstantial mass-loss rateM,incolumn5. portions, but that alltheSiwasbound upinthe terial containedalltheelements intheirnormalcosmicpro- known. Ifonewerepreparedto assumethattheejectedma- 2200 A.U.inthefan.Fromthese followtheaveragesilicate 23 a a a -5000 4000 - © American Astronomical Society • Provided by the NASA Astrophysics Data System V=- —logjl-—,(h) The surfacebrightnessacrosstheVandBimagesof The results,summedovertheentirefan,areshownasN The amountofgaswhichaccompanies thisdustisun- a 0 - c J Il_ 3 \2/ NOW N 23 Tau B 0 1000 yr A 5000 —e— 2000 yr B _l IL © 3000 yr C 10000 4- -5 -3 to grainsizeandcompositionthatweremademakethe Table 5givestheM’smultipliedbythatfactor. total mass:silicategrainsisabout2400:1.Thelastcolumnof Mgi iFeSiO4grains(Draine&Lee1984),thentheratio the surfacebrightnessoffan.Nordoesoneknowif Grains ofothersizesandcompositionssurelycontributeto calculations, butitcannotbejustifiedonphysicalgrounds. cosmic proportions. surface layersofthenucleuscontainallelementsintheir g areabout0.7,sothatif<2=1.0andthegrainslargely the visual,andthattheyallhaveaveragea=2.0X10 grains responsibleforconventionalinterstellarextinctionin cm. Theopticsofreflectionnebulaesuggestthatbothyand heavy elementsinthegas,thenmassratioofgas:grains Table 5follow.Ifthesegrainscontainallthecondensible ice, withp=1.0gcm,thenthenumbersinlastrowof surface brightnessofthenucleusisproducedbykind would beabout60:1.ThelastcolumnofTable5showsM nucleus during its passagenear23Tau,andhence towhat they arecomparablewithmass-loss ratesfoundforpre-main- sequence stars.Butitwouldbe prudent nottotakethemtoo scaled upbythatfactor. fl 09 seriously. Mass-lossrates,and thetotalmasslostby sca a I Formally, thisratioisconsistentwiththeassumptionsas At theotherextremewouldbesuppositionthat All theseguessesforMaresurprisingly high,although 0 a.u.500010000 5000 “i 1r

10000 a.u. _L 5000 1249 1996AJ 111. 12 41H 5 6 2 if a=3.0X1(Tcm.Clearlythesearelowerlimitsonr.the can betestedasfollows.Ifallthesilicateparticlesejected gaseous componentofIC349. degree itwillsurvivethatpassage,awaitspectroscopyofthe present themselves: the conceptofanopaquenucleusatopticalwavelengthsis a =3.0X1(Tcm,t=0.52.Theresultisessentiallythesame through adiameterisT=2rnQ7ra.Forthecaseof form throughouttheinterior,thenopticalthickness is dueentirelytosuchparticles,andparticledensityuni- interval t,thentheaverageparticledensityjustabove 5), andifallhavebeenejectedatvelocityujoveratime surface exists;i.e.,thatitisopticallythick.Thisassumption phenomenon wouldbeshortiftheilluminatingstarwereat what weseeistheperipheryofitscircumstellarenvelope(or consistent withtheotherparametersobtainedhere. contribute totheopacity.Butcalculationdoesshowthat density surelyincreasesinward,andparticlesofothersizes are ofradiusa,andthetotalnumberinfanisN(Table rest withrespecttothesurroundingnebulosity.Thatisusu- disk) beingdissipated. is notself-luminous:itseenonlyinscatteredlightfrom23 on thetruenatureofnucleusIC349.Inoptical,it cloud. Thiswouldbetheconventionalsituation,andespe- Tau-Aur clouds,anditisthesurfacelayersthatarebeing Tau. Infraredimagingmayrevealwhetherornotthereisa 1250 G.H.HERBIG:IC349 with themolecularcloud.The situation attheOrionNebula ders ifobjectslikeIC349can be foundelsewhere.Thereis ena ofrelativelyshortduration might beobservable. one, andsooneoughtnottobesurprisedifunusualphenom- lifetimes. ThesituationatthePleiadesisquitedifferent, cially soforstarsofhighermasshavingshortmain-sequence objects likeIC349bythefactthatdurationofsucha star inside.Untilthatcanbeestablished,twopossibilities a heavybiasfavoringthePleiades becauseofitsnearness, ally thecasewherestarwasformednearby,inthatsame swept away. and becauseofthespecialcircumstance ofitsassociation since theretheassociationofclusterandcloudisatransient “surface” isn=N^.Iftheopacityofnucleus 0aext a e a a 2.0(—5) 40.9481.495(-6)1000.1.495(-9)608.97(-5) 3.0(—5) 39.9911.671(—6)1200.1.392(-9)24003.34(-6) 3.0(—6) 44.2573.083(-5)1000.3.083(-8)24007.40(-5) (cm) (M)(yr)/yi) © American Astronomical Society • Provided by the NASA Astrophysics Data System In alltheforegoing,nucleushasbeenregardedasifa With theinformationnowonhand,onecanonlyspeculate Whether (a)or(b)isnearerthe truth,onenaturallywon- If (b)werethecase,onecouldaccountforrarityof (b) Or,itisahigh-densitycondensationbelongingtothe (a) Thereisapre-main-sequencestardeepinside,and 0Q a logNMatagas/dustMtot a Table 5.ThemassofdustintheIC349fan. 8. DISCUSSIONANDCONCLUSIONS -1 1- 6 12 5 -6 -1 -1 -1 jects havebeendetectedneartheTrapeziumbydirectimag- near-infrared passbandschosentoavoidthestrongeremis- many years.Theyaredetectableondirectimagesobtainedin is quitedifferent,becausethatregiondominatedbythe Hayward etal1994;McCullough1995).Sincepoint ing withtheHST(Prosseretal1994;Stauffer about 17.5,andaFWHMof0'.'4.Anumbersuch ionizing radiationfieldandwindsfromtheTrapeziumOB place atIC349isanalogoustothatobservedincometsnear imaging fromtheground(McCaughrean&Stauffer1994; stars. Atthatdistance,thenucleusofIC349wouldhaveV near thethermalvelocityofescapinggas,whichforH0 account forthesurvival,orregeneration,ofsuchobjectson The mostmassivecomponentoftheTrapeziumhasamain envelopes aroundlow-luminositystarsthatareionizedand the generalopinionseemstobethattheyarecircumstellar O’Dell etal1993;&Wen1994),andbyinfrared sion linesoftheHuregion.Morerecently,manysuchob- from theSun(Combi1989;Bockelée-Morvanetal1990; have givenvaluesof1-2kmsforcometsatr^lA.U. tions fromtheshapesofinfraredandradio-frequencylines the ,wherenucleusiswarmedsufficientlythatfrozen dust shroudofmuchgreateropticalthickness. sources aredetectableinmostofthese“compactobjects,” Larson etal1991);i.e.,somewhathigherthanexpected.The and COat7=300Kisabout0.6kms.Actualdetermina- with them.Thecometaryvaluesofujareexpectedtobe volatiles suchasCOevaporate,andinescapingcarrydust 349 with23Tauisofmuchshorterduration,andinvolvesa such atimescale.Clearly,theencounterofnucleusIC sequence lifetimeofabout5X10yr,soonewouldhaveto shaped bytheradiationandwindsfromTrapeziumstars. by JohnBally,shownosignof IC349.Suchanobservation because COmapsofthearea, verykindlymadeavailable result ofsomeinternalactivity,notbecausetheheating increasing theparticlesize.Forexample,ifa=10~instead obviously, thecometaryanalogybreaksdownhere. than thethermalvelocityofvolatilesatabout100K duce theobservedopeningangleoffanIC349neces- calculations whichgeneratedFigs.5and6repro- contrived particlepopulation.Nevertheless,itseemsun- ever, thisisaveryartificialsolution,requiringcarefully of 10cm,theshapefanwouldbeaboutsameif opening angleoftheresultingfancouldbepreservedby sarily assumethatuj=9kms.Thisisverymuchlarger would notonlyprovidefrom thelineprofile,butwould detectable fromIC349.Thiswill beanontrivialobservation, of ujdirectly,aswouldbepossibleifCOemissionwere for possibilitya,above. the surfaceby23Tau.Onemayseeinthisfactsomesupport (0.3-0.4 kms),thetemperaturecalculatedinSec.5.Very “fuzzy stars”havebeenknownintheOrionNebulafor give theradialvelocityofIC349 aswell. avoidable thatdustisbeingejectedfromthenucleusas uj werethentakenas6kmsinsteadof9.How- 2 e e e e As notedabove,thephenomenonpostulatedtobetaking If amuchsmalleri;werepreferred,itistruethatthe It isimportantthataneffortbemadetomeasurethevalue Submillimeter observations arealsorecommended. Zuck- ej 1250 1996AJ 111. 12 41H Tau at800/xm,butwithabeamsizeFWHPofonlyabout erman &Becklin(1993)havereportedameasurementof23 contribution fromIC349. nucleus alsobecameavailable—toreplacetheindirectesti- mate fromTTauristarsthatwasusedhere—thenthisentire exercise couldberepeatedonafirmerbasis. 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