197 5ApJ. . .195. .6313 4-3 16 The AstrophysicalJournal,195:631-642,1975February1 © 1975.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. identical physicalprocessesareprobablyinvolvedin emission nebulaeassociatedwithcertainTTauristars ionization mechanismsuggestedbyMagnanand by theseobjects.Thefast-particle(100keVprotons) their production.Amongtheionizationmechanisms and theHerbig-Haro(H-H)objectsindicatethat account convincinglyfortheuniquespectradisplayed that havebeenproposedforthenebulae,nonecan distance of100keVprotonsattheelectrondensities consequence ofthisscatteringisthatthethermalizing scattering efficiencyofproton-electronencounters.A Schatzman (1965)didnotconsidertheCoulomb factor of100toexplaintheobservedextentabout for theTTauemissionnebula(Burnham’sNebula), and Schwartz1973;1974)istoosmallbya of ~10cmderivedfortheseobjects(Böhm,Perry, was maintainedinastateofessentiallycomplete chromospheric-like circumstellarenvelopeofTTau the indirectradiativeionizationprocesssuggestedby H-H objects.Inthatstudy,itwasassumedthe waves originatingfromviolentconvectioninthestar. ionization bythedepositionofenergyfromshock Schwartz (1974)isofquestionablerelevanceforthe T TauristarsorTauri-likeareassociatedwith density gas.Althoughrecentevidencesuggeststhat cape theenvelopetoionizeextended,lower- like emission(i.e.,strongHandKlinesofCan Recombination Lyman-continuumphotonsthenes- other permittedmetalliclines)inH-Hobjects.Ifsuch some H-Hobjects(Strom,Strom,andGrasdalen 10 cmforthenebulae.Althoughseeminglyplausible tronomy, Inc.,undercontract withtheNationalScience which isoperatedbytheAssociation forResearchinAs- 1974è), thereisnoevidenceforstrongchromospheric- Foundation. The spectralandmorphologicalsimilaritiesofthe t VisitingastronomeratKittPeak NationalObservatory, * LickObservatoryBulletin,No. 673. © American Astronomical Society • Provided by theNASA Astrophysics Data System T TAURINEBULAEANDHERBIG-HARONEBULAE:EVIDENCEFOREXCITATION with TTausuggestthepresenceofextendedmassoutflowwhichissupersonicrespecttomediumin intracloud medium,producingemissionspectrasimilartothatpredictedbytheshock-wavemodelsofCox.An which thestarisembedded.Itsuggestedthatradiatingshocksmayformwhereflowinterfaceswith filling factor,andtheenergybalancerequirementsofsystemarealsocompatiblewithhypothesis.The Emission Nebulasupportstheshockwavehypothesis.Thecharacterofemission-linespectrum,small N Tanalysisbasedupontherelativeintensitiesofnear-infraredandbluelines[On]inBurnham’s higher rateofmassoutflowthanisindicatedforTTau. Herbig-Haro Nebulae,ifproducedbythesamemechanism,mustinvolvecentralobjectswithaconsiderably Subject headings:circumstellarshells—nebulaepre-main-sequencestarsstellarwinds eie Lick Observatory,BoardofStudiesinAstronomyandAstrophysics,UniversityCalifornia,SantaCruz Radial velocitiesoftheemissionnebulaeandNGC1555(Hind’sReflectionNebula)whichareassociated I. INTRODUCTION BY ASTRONGSTELLARWIND* Richard D.Schwartz*)* Received 1974July9 ABSTRACT 631 -1 1 emission doesoccur,butissoheavilyobscuredby understand howionizingradiationcouldpenetrate circumstellar dustthatitisnotvisible,difficultto hypothesis thatthenebulamaybeexcitedbyastrong losity surroundingTTauispresentedinsupportofa stellar windwhichformsshockwavesuponinter- such ashelltoproducethenebula. tached tothe2.1-metertelescopeatKittPeakNational of thishypothesisfortheH-Hobjectsarediscussed. action withtheintracloudmedium.Theimplications west orientedslitwithaprojectedwidthof2"and Observatory wasemployedtoobtainuntrailedspectra T TauandNGC1555kindlyfurnishedbyGeorge extends aboutlO"southwardfromthestar,andNGC which werecalibratedwithaspotsensitometer.Figure length ofy.lwasusedfortwoexposurescentered2" of theTTaurinebulaon1973December6.Aneast- 2 isareproductionofthespectrumtaken4"south to thestarandNGC1555isindicatedscale.The simultaneous detectionofBurnham’sNebula,which and 4",respectively,southofthestar.Thisallowed the star,coveringrange4800-7600Âatadisper- spectra wererecordedonnitrogen-bakedIIIa-Jplates Herbig. Thelocationofthespectrographslitrelative 35" to60"westofthestar.Figure1isaphotograph condensation lyingabout45" southwest ofTTau.(See tions fromthetimeofHind’s discoveryofthenebulain Barnard 1895,1899foranhistorical accountoftheobserva- sion of125Âmm.Figure3isanenlargementthe 1555 (Hind’sNebula),whichissituatedintheregion nebula. Curtis in1914-1915confirmBarnard’s descriptionofthe 1852.) Directplatestakenwith theCrossleyreflectorby 1 In thisstudy,newevidenceontheemissionnebu- The Carnegieimagetube(CIT)spectrographat- Intheearlyliterature,NGC1555isdescribedasaround II. OBSERVATIONS 197 5ApJ. . .195. .6313 region 6200-6800Âfromtheplatetaken2"southof position, achangewhichmayhavebeenassociatedwith years, andreportedadramaticincreaseinbrightness from scatteringofstellarcontinuaduringtheexposure. the star.Thestrongcontinuuminfigure3resulted 632 in 1935.Baade’s100-inch(2.5-m)photographtaken were undetectedintheearlierstudy(Schwartz1974). nebula since1940. little morphologicalchangehasoccurredinthe Lampland’s observation.Crossleyplatesand120-inch greatly extendedtothewestandnorthfromitsearlier Lampland (1936)observedthenebulaforover20 (3-m) platestakenintheperiod1950-1962revealthat blend of[On]A7319and[Cah]A7324.Inaddition, lines ofHeiA5876and[Nn]A5754havebeende- allowed detectionofthenear-infraredlinesHei First, thegreaterredsensitivityofCITsystem covered neartheinneredgeofNGC1555.Theshorter tected. Second,anewemissionnebulahasbeendis- detection offeaturesinthevicinityNGC1555. reflection ofthespectrumTTau,dominatedbya slit lengthusedintheearlierstudydidnotallow À7065, [Fen]A7155,[Cail]A7291,[OA7330,anda 1940 (seeJoy1945)showsthatNGC1555hadbecome graphs oftheregion(cf.fig.1),indicatingthat tinuum. Thespectrumcorrelateswellwithphoto- velocity structureoftheemissionlinesasonemoves from 20"to35"westofthestar,perhapsmerging reflection nebulaextendsfromabout35"to60"west Figures 2and3showthatthebulkofNGC1555isa strong Hafeaturesuperposeduponastellarcon- fig. 3). westward fromBurnham’sNebula,throughthenew examination revealssignificantchangesintheradial emission nebula,andintoNGC1555(seeespecially sing noapparentcontinuum,appearsintheregion strong inthelinesof[Sn],[NandHa,butposses- of thestar.Thediscreteemissionnebula,especially slightly withthereflectionnebula.Third,aclose a) N,TofBurnham'sNebulafromthe[On]Lines upon therelativelinestrengthsofdifferentatomicand means ofadiagnosticA,Tplotwhichreliedlargely ionic species.Asnotedinthatstudy,interpretation conditions inBurnham’sNebulawerestudiedby from thesamephysicalregion.Thepresentdataallow not knowiftheemissionfromdifferentspeciesarises ing [On]showsthat,whereastheA3726/A3729intensity equilibrium equationsforthefive-levelionrepresent- of suchadiagramishazardouswheninfactonedoes 25,000° K. ratio isprimarilytemperature-sensitive forT^ ratio isdensity-sensitive,theA7330/(A3726+A3729) an estimateofNandTVinthenebulabasedupon have beenobtainedina manner describedinthe [O u]lineintensitiesonly.Asolutiontothestatistical e e e e Several featuresemergefromthesespectrawhich In thepreviousstudy(Schwartz1974),physical The relativeintensitiesof the near-infraredlines © American Astronomical Society • Provided by theNASA Astrophysics Data System III. DATAANALYSIS SCHWARTZ 3- 4 -3 2-3 4340 4102 4071 4571 4861 3934 ...... 3889 3868 3729 ...... 3726 4959 3968 6300 5200 5159 5007 6563 6548 6363 ...... 5876 5754 6584 7319 +7324 7291 7155 7065 7330 6731 6717 sities, butarenotcalibratedrelativetoHß. Dufour spectrum. earlier studyusingtheLickautomatedGaertner lines onthepresentdeep-exposureplatesaretoo microphotometer. Inaddition,becausethebrighter dense toretrieveanyintensityinformation,theinfra- red lineshavebeennormalizedtotheHßintensity for E(B—V)=0.3iscontainedincolumn(3)of detected todateandtheirrelativeintensitiescorrected the earlierstudy.Acompletelistofemissionlines 20 percentofthephotoelectricintensityreportedin (= 100)byusingtheintensityofintermediateline implied bytheA3729/A3726ratio,A7330/(A3726+ table 1.ForthedensityofN=5x10cm based upontheintensityratio ofthered[Sii]lines. on thepresentplates.Therelativeintensityof This issubstantiallydifferent fromthedensity(10 cm) impliedbythesamelines inBurnham’sNebula. Hind’s Nebulaisfoundto have A=8x10cm of formationtheselines. A3729) ratioimpliesthatT>15,000°Kintheregion [Ca ii]A7291lineobtainedinthiswayagreestowithin [N ii]A6584forwhichanintensitycouldbeobtained e e e § Intensitiespoorlycalibrated. # WavelengthregionnotcoveredbyOsterbrockand t OsterbrockandDufour1973. * Schwartz1973.tBöhmetal. The newfaintemissionnebulawhichborders II LinesappearinH-H1withaboutsamerelativeinten- A(Â) Relative LineIntensitiesinNebulae H8 He i Ca ii,He,[Nem] H]8 Hy Ca ii [O ii] [O ii] He i Mg I] HS Ha [O i] [S ii] [Ne in] [N ii] [O I] [Nil] [Fe ii] [O in] [O hi] [O ii] [Ni] [Ca ii] [Fe ii] [S ii] [Nil] [O ii],[Caii] [S ii] Identification TABLE 1 Burnham’s Nebula* HHItN- 108 340 126 Í6Ó 171 134 106 (10)§ 41 63 22 45 22 67 38 24 30 10 55 15 16 13 15 (5)§ 6 9 7 8 221 408 A 100 198 114 23 24 56 73 29 36 69 70 30 51 16 87 18 9 4 7 8 (648) (172) I 296 100 124 (27) (45) (41) (16) 40 44 96 51 36 36 77 31 18 12 5 8 197 5ApJ. . .195. .6313 in thespectrographicmeasurementsdiscussedtextisindicatedapproximatelytoscale.Northattop;eastleft. star. Theshortlineappearinginthelowerpartofphotographis30"long(ED1687). The overexposedstellarimageobscuresmostofBurnham’sNebulawhichispresentasafaintprotuberancesouthwardfromthe Fig. 1.—Lick120-inchphotographofTTauandNGC1555takenbyG.H.Herbigon1962December30.Theslitpositionused © American Astronomical Society •Provided bythe NASAAstrophysics Data System 197 5ApJ. . .195. .6313 © American Astronomical Society Provided bythe NASA Astrophysics Data System 197 5ApJ. . .195. .6313 1 slit wasorientedasinfigure1,placed4"southofthestar.Thewavelength rangeoftheplateis4800Â

Fig 3.—Enlargement of the wavelength region 6200 Â < À < 6800 Â from a spectrum taken 2" south of T Tau with a 30-minute exposure. The strong continuum resulted from stellar light scattered into the spectrograph by variable seeing. The locations of Burnham’s Nebula, the faint emission nebula, and NGC 1555 are indicated in the figure. The object located about 95" east and T Tau is either a very faint Ha emission line star, or a compact reflection nebula. No object appears at this position on direct plates taken prior to 1962 (C.I.T. 2104c). 197 5ApJ. . .195. .6313 © American Astronomical Society Provided bythe NASA Astrophysics Data System 197 5ApJ. . .195. .6313 -1 1 -1 -1 -1 ///, following interpretationis offered inaneffortto provide aunifiedpictureof massflowinthesystem. it isevidentthatsignificantradialvelocitydifferences variation alongtheslit.Inspiteofsizableerrors, defined line-centerscausedbytheradialvelocity expanding awayfromthestar, theobservedvelocity nebular linesweresomewhatdiffuse,withpoorly reliably theaccuraciesofmeasurements,since The largererrorsquotedintable2indicatemore occur amongthethreenebularcomponents.The duction usingsixcomparisonlinesaverage6kms. compare favorablywithearlierstudies(Herbig1962). upon measurementsoftheLiiÀ6707lineonlyon Herbig’s platesisfoundtobe22kms“.Theseresults dispersion image-tubeplates,theagreementseems extend about10"eastandwestofthestar,fromwhich velocities. However,avestigeofthenebulaappearsto quite remarkable.Theradialvelocityofthestarbased kms. Consideringthedifficultiesencounteredin Nebula athighdispersion(10Âmm)furnishedby the nebulaisimplied.TwoLickplatesofBurnham’s exposed ontheCITplatestoobtainaccurateradial central portionofBurnham’sNebulaistooheavily obtaining reliableradialvelocitiesfrommoderate- G. Herbigyieldaheliocentricvelocityof12.8±2.0 an averageheliocentricvelocityof8±15kmsfor and theaveragevelocitiesfromHaonlyinline2.The where theaveragevelocitieswithrespecttoTTau obtained fromHa+[Sn][Naregiveninline1, tion alongtheslitinspectrogramsoffigures2and the linesof[Sn],[NandHaasafunctionopposi- nebula. tor hasbeenusedtomeasuretheradialvelocitiesof on theplate.Theresultsaredisplayedintable2, slit withacomparatorlengthcorrespondingto10" 3. Measurementsweremadeat5"intervalsalongthe measurements obtainedfromtwoplates.Valueswithoutquotederrorsrepresentsinglemeasurements.Forbiddenlineswerenot detected at20Eand40-60W(Hind’sNebula).ThecomparatorslitlengtheachpositionwaslO". Ha (166)§+28-18(-4)t+10-45-55-20+33(+37)|| [Nn] +[Sn]Ha...(--12)1-12(-15)t-18(-21)§-59-58-55(-44)t§ 1 ,,,F If theHalineinNGC1555 isreflectedfromdust The residualsobtainedintheradialvelocityre- The LickObservatoryGrantoscilloscopecompara- § Linesareveryweak;measurementsuncertain. t Forbiddenlinesonlyusedintheaverageradialvelocity. t AveragevelocityofBurnham’sNebulaobtainedfrommeasurements10"EandWthebrightestportion * AllradialvelocitiesareexpressedrelativetothatofTTauforwhichV=+22kms".Errorsstandarddeviations 1 AveragevalueofvelocitiesatfourpositionsinNGC1555.Haisextremelyfaint60"W. 0 Spectral Region20'E15"E10"E0KTW15"W20"W25"W30"W35"W40-60W © American Astronomical Society • Provided by theNASA Astrophysics Data System b) TheRadialVelocityField T TAURINEBULAEANDHERBIG-HARO639 ±8 ±14±5±12+17 ±8 ±11±18±10±14±22 Radial Velocities*inNebulaenearTTauri Burnham’sFaint < Nebula Emission¿NGC1555* TABLE 2 _1 -1 -1 real, itwouldbeconsistentwith anexpansionvelocity extreme weaknessoftheHalineatthatposition.If velocity computedabove. profiles (Kuhi1964)agreefavorablywiththeexpansion the farsideofTTauwith8 x222°. mass-loss velocitiesimpliedbytheviolet-displaced Burnham’s Nebulaexhibit forbidden-line widthsof of 95kmsahighlyobscured reflectionnebulaon Burnham’s Nebulaisveryuncertainowingtothe absorption featuresinthecircumstellaremissionline configuration ofthestarandnebulaemustremain in thecalculationcanbejustifiedapriori,implied yield asolutiontoequations(1)and(2)giving only suggestive.Itisinteresting,however,thatthe would lieonthenearsideofTTauwithrespectto values ofV=37kmsand—58 the starandNGC1555(i.e.,d=6),observed that theemissionnebulaislocateddirectlybetween where Vistheexpansionvelocityofgaswith velocity withrespecttothestargivenby observer. Sinceneitherofthetwoassumptionsused emission nebula.IfitisassumedthatV=,and respect tothestar,anddisanglebetweenline faint emissionnebulawouldexhibitanobservedradial of sighttothestarandalinejoiningwith line joiningthestarwithNGC1555.Likewise, the anglebetweenlineofsighttostaranda velocity ofthedustwithrespecttostar,anddis Nebula withrespecttothestar,Visexpansion where VistheobservedradialvelocityofHind’s is relatedtotheexpansionvelocitybyrelation 6 ^52°,V=z95kms.Thatis,thenebulae d he dg g dg g d d h dg The largepositiveradialvelocityfound20"eastof Finally, Herbig’shigh-dispersion platesof Position Vh =(1—COS0),(1) d V =—cos9,(2) eg 197 5ApJ. . .195. .6313 -1 1 -1 -1 -1 projected radialvelocitycomponent(about—10km lines superposedupontheTTaucontinuumwhich expect fromthermalbroadeningalone.Theforbidden velocities rangingfromabout—100to+100kms. when thespectrographslitisplaceddirectlyon the lineofsighttostar,yieldingonlyasmall formed frommatterejectedmostlyatrightanglesto however, appearingtorivalthewidthofcircumstellar about 20kms",considerablygreaterthanonewould Ha (200kms).Evidently,Burnham’sNebulais appear indirectstellarspectraaremuchbroader, a) TheExcitationMechanismoftheTTauriNebulae superposed uponthestellarcontinuumwhichappear s withrespecttothestar).Thefaintforbiddenlines star inalldirectionswithprojectedline-of-sight star apparentlyoriginateinmatterejectedfromthe 640 flow encounterstheambientintracloudmedium.The might expectshockwavestoforminregionswherethe medium inwhichTTauisembedded.Therefore,one certainly supersonicwithrespecttotheintracloud T TaunebulaandH-H1arecomparedwiththatof following pointslendsupporttothishypothesis: models ofCox(1972)canaccountforthecharacter the supernovaremnantN49inLargeMagellanic lines ofCan,seemtobeuniquethiskindmodel. the spectrum.Therelativelygreatstrengthoflines Osterbrock andDufourconcludethattheshockwave Cloud studiedbyOsterbrockandDufour(1973). This valueisconsistentwiththatimpliedbythe transition regionintheshockwithTx20,000°K. of [Oi]and[Sn],theappearanceHK densities whichareconsiderablylowerthanthose Nebula. ThisisconsistentwithCox’sshockwave implied bythe[Sn]A6717/A6731ratioinBurnham’s model, inwhichthe[Sn]radiationwouldbeexpected to ariseprimarilyfromthecooleranddenserre- nebula aroundTTau,andusingtheabsolutenebular combination regionbehindtheshock. 100 kms,the[On]radiationshouldemergefroma process, afeaturewhichwouldbeconsistentwith predicted fluxes.Thatis,onlyasmallvolumeofthe that afillingfactoroftheorder0.05isrequiredto temperature reportedbySchwartz(1974),onefinds [O n]lineratiosdiscussedin§111.Moreover,the flux of8mfuat3.7cmreported bySpencerand Hß fluxmeasurement,electrondensity,and [O n]À3726/À3729intensityratioimplieselectron radiating shocks.Itshouldbenotedthattheradio region observedisactuallyinvolvedintheemission account forthedifferencebetweenobservedand e circumstellar envelopesurrounding TTau.Apparently Schwartz (1974)refersto emission fromthedense no radioemissionisdetected fromBurnham’s Nebula, aresultwhichisnot surprisingsincethefilling The outflowvelocitiesindicatedin§IIIarealmost i) Intable1,theemission-lineintensitiesof ii) Cox’smodelpredictsthat,forashockwithV= iii) Crudelyestimatingthevolumeofemission © American Astronomical Society • Provided by theNASA Astrophysics Data System IV. DISCUSSION SCHWARTZ 32-1 4 2 3 -1 via theshocks. Nebula appearstobedetachedfromthestellarimage T TautakenbyG.Herbigintheperiod1959-1962 the starandnebula.Inaddition,significantnebular in thesensethatadipintensityoccursbetween energy oftheoutflowisconvertedtonebularradiation by Schwartz(1974),ifitisassumedthatthekinetic emission isseentoarisefromaregionsurroundingthe Lorre (Herbigand1975)revealthatBurnham’s and analyzedwithimage-processingtechniquesbyJ. duce thetotalradiativeoutputofnebulameasured is isotropic.Thissufficientbyafactorof2topro- in themassflowisabout2x10ergssif factor reducesthepredicted3.7cmnebularfluxtoless however, littlenebularemissionisencountereduntil defined bySchwartz1974).Tothewestofstar, (corresponding roughlytothe“innernebula”as than 1mfu. star totheeastandnorthadistanceof3"or4" rate fromTTau,onefindsthatthekineticenergyflux evidence foraveryfaintbridgeconnectingTTauwith period 1959-1962.Kuhi(1964)notesthattheveloci- uniform inspaceand/ortime.Intermittentflows velocities. Thisimpliesthatthemassflowisnot faint emissionnebulabetweenNGC1555andthe NGC 1555,afeaturewhichisprobablyrelatedtothe one approachestheregionofNGC1555.Lorrefinds displaced absorptionfeatureschangewithtime, ties ofthemassoutflowindicatedbyviolet- Nebula decreasedsignificantlyinintensitythe directions fromthestar.Apparentlyflowiscon- could leadtoradiatingshockswithtime-scalevaria- direction ofNGC1555. star discussedintheprecedingsection.Thedatalead tions typicalofthoseobservedinBurnham’sNebula. sometimes showingmultiplecomponentsatdifferent strained byhigherambientclouddensitiestothe one totheconclusionthatmatterisflowinginall density oftheambientintracloudgasintowhich south, east,andnorthofthestarascomparedwith the stellarwindisbeingdriven.AccordingtoCox, maximum pressurebehindtheshockarisesin a purehydrogengas, where nistheambientintracloudhydrogennumber velocity oftheshock,nandarehydrogen density, raisthemassofhydrogenatom,v electron numberdensitiesinthe[On]emittingregion, [O n]emittingregion.Thisleadstotheconditionfor 2 x10°KinCox’stheory.)Usingthenumbers derived in§III,andassuming thatthe[On]regionis and Tistheelectrontemperatureinregion.(r= implies that«=10cm~ fortheambientpre- completely ionized,ashock velocityoflOOkms expects indarkclouds. shocked gas,avaluewhichis consistentwithwhatone H e H0 e H v) Aremarkableseriesofdirectphotographs iv) UsingKuhi’s(1964)estimateforthemass-loss Herbig’s photographsalsoindicatethatBurnham’s Finally, usingCox’stheoryonecanestimatethe 2 nmVo =(n+)kT, Re Vol. 195 197 5ApJ. . .195. .6313 variations andthespectraldifferencesobservedin hypothesis cannotaccounteasilyforboththelight 2 showcharacteristicallydifferentspectra,indicating condensations ofH-H2.These featureswillbedis- in someH-Hobjects)withemission-lineratiosdis- prevail (seeSchwartz1974foracomparisonofcir- pothesis ofStrometal.(1974a,Z>).Inthiscase,one cussed ingreaterdetailaforthcoming paper(Böhm, that theyareprobablyproducedinsitu.TheStrom reflection. Similarly,individualcondensationsinH-H NGC 1555indicatesthatitcannotbetheresultof tinctly differentfromeitherBurnham’sNebulaor discovery ofafaintemissionnebulanearNGC1555 from thecircumstellarvicinityofTTau,thenitshould 2 whichexhibitextremelylargelinetocontinuum H-H nebulae.IncontrasttothehypothesisofStrom morphological similaritiesbetweentheTTauand (reminiscent ofsomethefaintercondensationsseen cumstellar andnebularlineratios).Moreover,the exhibit lineratiostypicalofthosefoundinthecircum- nothing morethanareflectionnebularedirectinglight characteristics distinctlydifferentfromthoseofthe Burnham’s Nebulaandthenewemissionnebulawest circumstellar gasenvelopewhosetotalnebularemis- ratios (Böhm,Schwartz,andSiegmund1974)isa possess “holes”intheappropriateplacestoallow would obscurethestaranditscircumstellargas from thereflectionofnebularemissionwhichorigi- tions areproducedinsituasaresultofmatterflow et al.1914b(seealsoStrom,Grasdalen,andStrom nebula, oneisimpressedwiththegreatspectraland which appearinthenebulae.Inaddition,onewould Schwartz, andSiegmund1975). emission nebulae.Also,ifBurnham’sNebulawere of thestar)providestrongevidenceagainsthy- this hypothesistoexplainobjectslikeH-H1and visible radiationtoescapeandproducetheobserved envelope fromdirectobservation,butwhichwould rangement ofcircumstellardustaroundastarwhich directly. Thishypothesisrequiresaveryspecialar- nates inacircumstellarenvelopethatisnotvisible like aconvincingtheoryformasslossinpre-main- to clarifyboththespatialandtemporaldynamics theoretical workonradiatingshockswillbenecessary stellar envelope,asituationwhichcertainlydoesnot sees clearlyareflectionnebula(NGC1555)whichhas sion dominatesthetotalvisiblefluxfromstar. condensations asreflectionnebulae.Alsorequiredin away fromastellarorprotostellarobject.Strometal. observed flows. sequence objectswhich\youldaccountforthe of theTTaunebulaiscorrect,itclearthatmore sis isarecentpolarizationstudy ofthecondensations No. 3,1975 1974a), Ibelievethatthenebularemissioncondensa- 1974a, bsuggestthatthecondensationsresultentirely The “H-Hobjects”surroundingTTau(i.e., Apart fromthepresenceofastarinTTau If thehypothesispresentedhereforproduction The strongestevidenceinfavor ofStrom’shypothe- © American Astronomical Society • Provided by theNASA Astrophysics Data System b) TheHerbig-HaroNebulae T TAURINEBULAEANDHERBIG-HARO by mixingwithnebularradiationintheselines.The polarized, althoughthepolarizationmightbelessened that theymaypossessthehighestrateofmassloss. bers oftheclass.Atsametime,indicationis presence ofmorecircumstellarmasswouldcertainly zations inthecondensationsofH-H1and2is fact thatStrometal.(1974c)reportverysmallpolari- T TauilluminatesNGC1555proximatetoanemis- visually fromthelineofsightcouldilluminatedustin (Hayashi 1966;Larson1969) whichpredictthat This isatvariancewithexisting evolutionarymodels gressive clearingofcircumstellarmatterisindicative be consistentwiththefactthatcentralobjectsin velocities) thanthemassoutflowfromTTau.The have moretotalmassintheflowand/orhigher must becorrespondinglymoreenergetic(i.e., would appeartobeintermediatebetweenthesetwo An obvioustestwouldbetomeasurethepolarizations as thoseofHa,andHKCan,wouldbe the vicinityofemissioncondensations(muchas polarization iscommontoboththeforbiddenlines tion. Itseemsevidentthat processes connectedwith H-H 1and2maybeamongtheyoungestmem- H-H 1and2aretotallyobscured.Ifthepro- Photoelectric measurementsindicatethatthetotal extremes, withacentralobjectdetectableoverthe range 0.3^