1977ApJ. . .217 . .693H The AstrophysicalJournal,217:693-715,1977November1 © 1977.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. remained nearmaximumlightwithlittlechange,and evolution (Herbig1966).However,becauseonlyone such eventhadbeenobserved,becauseFUOri recognized whenY1057Cygrosetomaximumlight; because nothingwasknownofthepreoutburststate outburst butratheraphenomenonofearlystellar however, asecondexampleofthephenomenonwas the natureandfrequencyofthisphenomenon. A greatdealofnewobservationalinformationisnow of thestar,furtherprogressseemedblocked.In1970, purpose ofthispapertodiscusstheopticalmaterial and in1974athirdcase,VI515Cyg,wasdiscovered. now onhandandtooffersometentativeideasupon been discussed(Herbig1966), andalthoughone available, onVI057Cyginparticular,anditisthe 1937 flare-upofFUOrirepresentednotanova December 8beforethe147thMeeting oftheSociety. Astronomical Society,givenin Chicago,Illinois,on1975 About adecadeagoitwasarguedthatthe1936- The historyandspectrumofFUOrihasalready t LickObservatoryBulletin,No. 763. * TheHenryNorrisRussell Lecture oftheAmerican © American Astronomical Society • Provided by theNASA Astrophysics Data System d 4 maximum in1970afterarisetimeofabout390,andhassincedeclinedby1.7mag(pg) tion lines,PCygnistructureatHa,displacedshellcomponents,andstrongLiiA6707.Much possibly morethan27)tobrightenthelast2mag.FUOriitselfhassince1960fadedveryslightly, by about0.2mag(inB).Allthespectraaremuchalike:ForGsupergiantshavingwideabsorp- 6 years.VI515Cyghasrisenverymuchmoreslowlyfrommag17,requiringatleast12years(or velocity shellswereapparentlyalsoejected.Someofthespectralpeculiaritiescanbeunderstood brightness andamoderateincreaseinradius.Thistookplaceratherslowly,butseveralhigh- detailed informationisnowavailableforV1057Cyg,whichdefinitelyknowntohavebeen velocity ofexpansionthatdisappearedinafewyearsaftertheoutburst.Inallthreecases,their a TTaustarbeforeitsoutburst.The5.5magbrighteningwasduetolargeriseinsurface reflection nebulaewhichbecamevisiblewhenthestarsbrightened.Theobservedfrequencyof projected. Similarly,allthreestarshavestronginfraredexcessesandareattachedtoarc-shaped radial velocitiesshowthatthestarssharemotionofmolecularcloudsuponwhichtheyare qualitatively iftheobservablepartofstellaratmosphereisverythick,withadepth-dependent three eruptionsinabout80years,togetherwiththeknownnumberofTTaustarsthatlumi- nosity inthenearerassociations,indicatesthatunlessthereissomefundamentalmisunderstanding frequent leveloccursinafewpeculiarTTaustars,asmightbeexpectedifthephenomenondecays roughly 10years.Thereisaspeculativepossibilitythatsimilaractivityonminorbutmore activity intrinsictothestarshowsthatshell-clearinghypothesesatleastareuntenable. as thestarages.Thecauseofoutburstsremainsunknown,butfactthattheyrepresentan of thesituation,FUOri-typeeruptionsarerepetitiveandrecurinaverageTTaustarafter Subject headings:nebulae:general—stars:evolutionpre-main-sequence Lick Observatory,BoardofStudiesinAstronomyandAstrophysics,UniversityCalifornia,SantaCruz The secondandthirdmembersoftheFUOriclasshavenowbeendiscovered:VI057Cygreached I. INTRODUCTION ERUPTIVE PHENOMENAINEARLYSTELLAREVOLUTION*! II. FUORIONIS stars :variables Received 1977February22;acceptedApril25 G. H.Herbig ABSTRACT 693 _1 1 _1 important characteristicofthestar—itsinfrared excess—was discoveredsubsequently,thataswell recent photometricbehaviorandnewevidenceonits connection withVI057Cyg(§111)orinthegeneral discussion (§V).Atthispoint,onlythestar’smore some otherofitspropertieswillbeconsideredlaterin association withinterstellarmatterwillbedescribed. the linesplitting(Ay=80kms)inbluehave fading about2yearsfollowinginitialrise,andaslow fading ofabout0.2mag(in5)in15years. available sources(identifiedinthelegend).Thesudden that this“composite”spectrumappearsapproxi- been obtainedatLicksince1963(Herbig1966); oscillation thathaddisappearedby1960,areapparent. FU Orifrom1936tothepresent,compiledall lower resolutions,thespectrumisaconfusedmixof Since thattime,therehasbeenaslowbutdefinite August showedthestrong Na iDabsorptionsata red, a34Âmm~Lickcoudé spectrogramof1975 longward emissionsinHand Kremainstrong.Inthe star andshelllines.A1976MaunaKeaplateshows mately asonthelastLick spectrogram. Thesharp, displacement of-98kms , whileonplatesof 12 No spectrogramsofadequatedispersiontoresolve Figure 1showsthephotographic/5lightcurveof 1977ApJ. . .217 . .693H © American Astronomical Society • Provided by theNASA Astrophysics Data System w »•^3 -s ^S; 22 e 'o-2'S O -; öb® ! 2 « * OnO h Sb« !iS ^ :|2 !S xVO ^ JO ^ ►2S; ON 0) X? -o o 2-0 a « cd i—] wT^i a? C/5 T—I O cd o® xT ^ c R V) 1977ApJ. . .217 . .693H -1 1 -1 emission, movedfrom—165to—llOkms.Itis apparent thatalthoughFUOriisnowphotometrically absorption atHa,fringedonoccasionbylongward three red-regionspectrograms,usinglinesuncon- quiescent, therearestillshort-termchangestaking taminated byshellcomponentsandwithempirical place initsshellstructure. wavelengths establishedbyF-Gsupergiantvelocity individual platevelocities,basedon9-12linesper 1975 Decemberand1976Augusttheywereat standards observedwiththesameequipment.The this resolution,perhapsbecauseoftheratherwide plate, showedsomewhatmorescatterthanexpectedat together withradialvelocitiesfromtheradiofrequency stellar lines.ThemeanvelocityisgiveninTable1, — 76kms“.Onthesamespectrograms,powerful western edgeofB35.Withintheuncertainties,FUOri CO linesinthedarkcloudB35whichcontains shares theradialvelocityofneighboringinter- S264 whichsurroundsB35,andfromHainthebright FU Ori,fromtheHaemissionlineinHnregion VI515 Cyghavesimilarlyclosekineticassociations stellar matter.ItwillbeshownlaterthatVI057and with cloudmaterial. discovered byWenzel(1963),andconfirmed Haro 1971).Lightvariationsweresubsequently many emission-Hastarsinthearea(Herbig1958; H iiregionNGC7000.Itwasfirstnotedasoneofthe to 16.4.Atthistimethestarwasratherred:Haro apparent; theextremerangereportedwasm=14.7 the shiftbetweenMandel’sphotographicandphoto- (1974), andMandel(1975a,6).Noperiodicitywas index ofabout+2mag.Theonlyinformationonthe visual lightcurvescorrespondstoanaveragecolor premaximum spectrumofVI057Cygcomesfroma (1972) estimatedthatR—I=+1.8in1965,while Robinson andHarwood(1971),Welin(19716),Filin single Lick430Âmm spectrogram obtainedin no absorptionlineswerevisible andnotypecouldbe slope ofthecontinuumwas likealate-typestar,but Fe i,nemissionlinestypical ofaTTaustar.The pg 1957 (Herbig1958),which showedBalmer,Caii, The radialvelocityofFUOriwasmeasuredonthese VI057 Cygliesinaverydensedustpocketthe © American Astronomical Society • Provided by theNASA Astrophysics Data System Star : Cloud : -1 -1 CO emission,B35+27.9±0.1 3 34Âmmspectrograms,1975-76+27± 3 16Âmmspectrograms,1962-63+30±2 Ha inbrightrim,B35+27.5+1.5 H« inAOriHnregion(S264)+23.8±8 CO emission,B35+28 a) EarlyHistory III. V1057CYGNI Radial VelocitiesofFUOrionisandtheAssociatedInterstellarMaterial Source ERUPTIVE PHENOMENAINSTELLAREVOLUTION TABLE 1 1 (km s") V ±cr Qv (Plate 5). assigned. ThisspectrogramisshowninFigure2 brighter thanthisvalue.Thephotographic/i?light reached maximumataboutm=10.5on1970.7.On curve, compiledfromallavailableobservations,is some magnitudesystems,thepeakwas0.2-0.3mag was achangeofslopeontherise,inthatstar brightened morerapidlybeforeitreachedm=12 shown inFigure3.Thereissomeindicationthatthere than afterward.Thetotalrisetimewasabout390days. The slowpostmaximumdeclinehasbeensmooth,with no signoftheabruptdropabout1magshownby fading ofVI057Cyghasbeenattheaveragerate by Welin(1971a),andtheannouncementcirculated FU Oritwoyearsafteritsinitialrise(Fig.1).The vs conjunction withtheSun,andspectroscopycouldnot maximum. AfewobservationsweremadeatLick about 4monthsafterthestarhadpassedthrough begin inearnestuntil1971April.Itisthereforeof almost immediatelybutthestarwasthennearlyin from theearlierspectrograms. some importancetoderivewhatinformationonecan pg Am =1.7in6years. unique objective-prismplate,whichisshownin after theeruptionwasunderwaythatbyWelinin Dr. Welinhasverykindlyfurnishedacopyofthis replaced byahotterspectrumshowingonlyBalmer continuum withTTau-typeemissionlineshadbeen minimum andmaximumwerequitedifferent:thecool spectrogram. ClearlythespectraofV1057Cygat Figure 2togetherwiththeLick1957preoutburst tively asB3,althoughearlyAwouldbeequally spectral typeonWelin’splate.Heclassifiedittenta- absorptions. Thereissomedisagreementaboutthe is weak.AtthebottomofFigure2anotherlow- acceptable becauseHeiisnotpresentandCanA3933 1970 September,verynearlyatmaximumlight. dispersion spectrogramobtained atLickabout4^ pg months followingWelin’s;this exposurewastakenby west (lowinthelightsof SantaClaraValley:note announcement, whenthestar wasalmostlostinthe Mr. E.A.Harlanjustfollowing thereceiptofWelin’s About 1969.6,VI057Cygbegantobrightenand The 1970brighteningofVI057Cygwasdiscovered The firstspectrogramknowntohavebeenobtained This paper Georgelin and1970 Herbig 1966 Lada 1976,privatecommunication Lo 1975,privatecommunication Hippelein 1976,privatecommunication b) SpectralClassification Reference 695 1977ApJ. . .217 . .693H © American Astronomical Society • Provided by theNASA Astrophysics Data System 1977ApJ. . .217 . .693H the verystrongHgilines).ThespectrumofVI057Cyg those 4^months.ThefirstLickcoudéspectrogram lines andmetallictooweaktobeseenattheresolu- turn looksverymuchthesame,andonthatplate appears essentiallythesameonthisasWelin’s classified intheconventionalway,usingBalmer type iscertainlynotB3.Iftheearliestcoudéplatesare was takenjust1^monthslater,in1971March.It exposure: thetypehasnotchangedsignificantlyin except thosecenteredat4000-4300 Âwereobtainedwith EC, 120inchcoudéspectrograph. Allthelatterspectrograms Crossley reflector,nebularspectrograph. LS,36inchrefractor. 40 mmimageintensifiers. LS-44522. EC-9290. EC-9740. CS-5771. 4) Theplateprefixeshavethe followingmeanings.CS, 2) PlatetakenbyL.V.Kuhi. 3) PlatetakenbyR.P.Kraft. 1) PlatetakenbyE.A.Harlan. 44529. 44525. © American Astronomical Society • Provided by theNASA Astrophysics Data System Plate 10043. 10294. 10256. 10295. 10713. 10668. 10454. 12628. 12627. 12022. 10957. 10714. 10700. 13674. 13663. 13662. 13661. 13195. 12629. 12392. 11659. 11632. 11505. 11406. 11379. 13451. 9410. 9405. 9380. 9414. 9411. 9472. 9471. 5772. 9499. 9864. 9707. 9702. 9591. 9504. Lick SpectrogramsofVI057Cygni -1 1971 Jan.23 1971 Jan.21 1971 Apr.8 1971 Mar.8 1971 May16 1971 May16 1971 May11 1971 Apr.15 1971 Apr.13 1971 Apr.13 1971 Feb.10 1971 June5 1971 May16 1971 May16 1971 May9 1971 Nov.8 1971 Sep.7 1971 July28 1971 July27 1971 June29 1971 June6 1972 Mar.4 1972 July23 1972 May24 1972 Mar.6 1972 Mar.6 1974 Aug.29 1974 June4 1973 Dec.9 1973 Aug.15 1973 Aug.13 1973 July14 1972 Sep.22 1972 July23 1972 July22 1972 June27 1973 Apr.22 1973 Mar.24 1975 Nov.14 1975 Oct.28 1975 Oct.28 1975 Oct.28 1975 Aug.16 1975 Apr.29 1974 Aug.29 1974 Aug.29 Date (UT)(Âmm) Notes toTable2A TABLE 2A ERUPTIVE PHENOMENAINSTELLAREVOLUTION Disp. Central 350 350 130 48 48 75 75 34 34 34 34 34 34 34 40 34 34 34 34 34 34 34 34 34 34 16 16 16 16 34 17 16 16 34 34 34 34 16 16 11 16 16 16 11 17 11 4300 4340 4340 4340 4300 4200 6500 6300 4000 4200 4000 4200 8200 6300 3950 3950 4200 8300 6400 4000 4000 4050 4000 4000 4200 6100 6350 6500 6350 6350 6350 8200 5900 6350 6350 6560 6300 8200 6350 6560 8200 6350 6560 5800 6300 6300 Note 1 _1 -1 1 - 1 1 -1 1 1 ignored. Infinerdetail,however,thespectrumdoes early F,IIorIIIoverthese2years,ifHandCanare progressive changeinspectraltypefromA3-5IIto faded, theincreasingcomplexityofmetallic-line expressed asanaxialrotation,theirwidthscorre- region onanumberofthesespectrogramsisshownin which thestarbecametoofaint.The3900-4000 tions ofFigure2,thenthetypeisearlyAandfairly structure willbediscussedlater),andcorrespondstoa spectrum inFigure4isapparent(theCanline tive, buttheyspanonlytheyears1971-1973,after the BalmerandCanlineshavecomplexvariable tion ofB3for1970Septemberisbestdisregarded. that thetypechangedsignificantlybetween1970 high luminosity.Inotherwords,thereisnoevidence inconsistencies areencounteredintheF-typespectrum temperature-sensitive lineratiosarediscrepant.Such sponded toaboutpsin/=70kms".Asthestar covering thephotographicregionaremostinstruc- velocities andotherdata.The16Âmmseries VI057 Cygobtainedtodate,togetherwithradial these eruptiveobjectsarepeculiarindetail. not matchthesecompromisetypes:anumberof Figure 4(Plate6).Themetalliclineswerenotsharp; structures. Table2listsalltheLickspectrogramsof the yellow-redin1971-1973concurwithblue The 120inch(3m)34Âmmcoudéplatescovering earlier thanthosedeterminedfrom6000-6600Âlines. V1057 Cyginthe3900-4300Âregionaresystematically at suchlowdispersionisoflimitedsignificancebecause September and1971March,sothetentativeclassifica- indicating acoolingofthestar,butfromaboutF5II temperature-sensitive toestablishwhetherthistrend which timenobluespectrogramsweretaken,thetype to GOlb.Subsequently,in1974and1975during of FUOrialso.Itisnotsurprisingthatthespectra in theredcontinuedtochangeslowly,G2-5and excluded. Intheblue,firstspectrogramsof1971 present intheradialvelocities.InFigure5areplotted continues tpstilllongerwavelengths,butthefactthat available inthe8000Âregionarenotsufficiently luminosity classlborII.Unfortunatelythefeatures relaxed to—20kms“,probablydeclinedfurther 6000 and6600Â.LinesofH,Can,Naihavebeen metallic linesinthe3800-4400Âregion,andbetween mated thetypeasaboutF5in1.0umregion from —18to—14kms in1972,andwasat March andAprilshowedalargenegativevelocity, against timethevelocitiesmeasuredfromunblended Shanin, Shevchenko,andShcherbakov(1975)esti- gram of1973.Duringthis entireepisodeandin an averageof—ISkms“ . Intheredduring1971 1974 suggeststhatitdoesnot. 1974-1975 theredregionshowed onlyascatteraround — 40to—50kms,whichthroughthe1971season — Bkms“onthesingle IfiÂmm" bluespectro- The coudéplatesshow,however,thatclassification One unexpectedfeatureisthatthespectraltypesof Another manifestationofthesameeffectseemstobe c) RadialVelocitiesandLineStructure 697 1977ApJ. . .217 . .693H _1 EC-9380 conflicts andinconsistencies. of theCanfeaturesat—368km s.Thesevelocitiesweremeasuredononlythisplate. -1 -1 t Absorptioncomponentswere present inHj3,Hy,HSat—366kms,whichcorrespondsto thedisplacement * Thesetypesarenotofhighaccuracy.Thespectrumisdifficult toclassify,andindetailthereareanumberof % AcomponentofHßwaspresent at—296kms. 10668 11406 10957 10454 11659..... 9499 9707 9702 9591..... 9504 9405 9864 Plate © American Astronomical Society • Provided by theNASA Astrophysics Data System EC-9290 F5II velocities fromthisspectrogram. agreement. parentheses whenthecenterofgravitywholelinewasmeasuredinstead, 10256.. .F7:II 10043t F5II 10714.. .F8-G0Ib,II 10700 F5-G0II 10294.. . 11632. 11379. § Thecomponentoflesserdisplacementisthestronger. 12629. 12022. Note.—v isthemeanvelocityfromnlines,andostandarddeviationofv,internal 13195. 12628. 12392. t Thecomparisonspectrumisoverexposed,whichmayaccountforthesomewhatdiscrepant t Thefeaturewaseitherofftheplateoroutsideregionofgooddefinition, 13663. 13661...... G2-5Ib,II 13451. * Thedisplacementgivenisofthepointpeakintensityinemissionline.velocity 13662 13674. v 9414 9472 9470 F5II 9410. F5:II Plate A7-F1 II A3-5 II A7-F1 II A5-F0 II A5 II A2: II A5 II A3-5 II An An A5 II FO-3 II,III Spectral Type* Blue GO lb GO lb GO lb GO-2 lb G2-5 Ib,Il G5 Ib G2-5 Ib,II Spectral Type Red Data fromSpectrogramsofthe5800-6700ÂRegion Data fromSpectrogramsofthe3800-4800ÂRegion Metallic Lines -13 -16: -13 -16 -18 -20 -29 -26 -26 -30 -26 -40: -52: -16 -17 3 -12 11 -13 13 -10 15 -16 12 Metallic -11 16 -15 13 -17 12 -10 10 -13 2 -18 10 -30 11 -18 13 -10 7 -26 10 -18 9 -9 11 -9 v no -6 132 Lines 26 23 20 32 13 12 19 17 12 12 2 6 6 TABLE 2B 13 TABLE 2C 2 (-54) -474 (-35) -277,-355 Em.* Abs. Radial Velocities -25 -457 -34 -558 -31 -281 -41 -370 -38 -369,-517 -20 -246 -31 -274,-357 -17 -285 _14 -244 -21 -266 -15 -229,-318 -17 -277 -17 -157,-350 (-7) -285 Balmer Cores -19 —211,—371§ -24 -213,-383§ -9 -227 1 Velocities -27: -26: -38 -41: -68: -54 -55 -26 -71 -68 -69 -67: -89: (km s“) Radial v -1 (kms) Ha t t t n 2 2t 2 2 2 3 3 5Î 5 5 5 5 3 -29 -20: -15: -18 -16 -15 -17 -18 -17 -23 -22 -10 -23 -26 -50 -28 -27 -38 -32: -11 -128,-185§ -16 -116 -17: p -13 -169 -11 -125: -9 -143: AA5889, 5895 Ca iiAbsorption -105 -107 -107 -105 -102 Underexposed Underexposed Underexposed Components -99 Unresolved Unresolved Nai -168 -154: t t t -156 -284 -173 -189 -199 — 200 -210 -206 -197 -208 -212 -209 -276: -288 -311 -311 -368 -304 P 1977ApJ. . .217 . .693H _1 _1 1 1 1 identified withthevelocityofHnregionand there wasnosignofthelargenegativevelocities velocity arelistedinTable3.AsforordinaryTTau first plateof1971Februarytoanasymptoteabout between VI057Cygandthesurroundinginterstellar A numberofindependentdeterminationsthat this wasonavelocityscaleentirelydifferentfromthat ponent ofHadiddeclinefrom—560kmsonthe component ofH«followingmaximum(notethevelocityscalediffersfromthatinupperpanel).Barsconnectvelocitiesmeasured tunately, theLickspectrograms donotpermitdeter- depend uponwavelengthand linestrength.Unfor- a deepenvelope,inwhich oneseestodepthsthat velocity andofspectraltype isduetostratificationin material isbeyondquestion. stars (Herbig1977),theclosekinematicrelationship molecular clouduponwhichVI057Cygisprojected. in theblue.Thevelocityof—13to—15kmsat ceased, thelargenegativeshiftofblue-regionlinesin1971hadcomeintoessentialagreementwithstellarvelocityabout which themetalliclinevelocitiesstabilizedmustbe measured intheblue.ThePCygniabsorptioncom- when thelinewasresolvableintotwocomponents. interstellar velocities(fromTable3)areindicatedontheright.Lowerpanel,decreaseofdisplacementPCygabsorption red (filledcircles)during1971-1975.Theerrorbarsindicate±1a,frominternalagreement.By1973,whenthelôÂmm“series -13 kms\Thered-regionvelocitiesshowednocleardeparturefromameanofabout-15"duringtheentireepisode. -220 kms"in1975(Fig.5andFig.6[PI.7]),but (km/sec) Presumably thiswavelength dependenceofradial Eïg, Upperpanel,radialvelocitiesfromthemetallic-linespectrumofV1057Cyginblue-ultraviolet(opencircles)and V 1 © American Astronomical Society • Provided by theNASA Astrophysics Data System -40- -20-- -60- -200 -600 -400-- JD 244100018002600 0 + '¡I- J Blue-ultravioletRegion Maximum Light Red Region ERUPTIVE PHENOMENAINSTELLAREVOLUTION * ! METALLIC LINESPECTRUM DISPLACED ABSORPTIONATHa ! ' •I 1 1 tion componentremainsatabout—210kms" the exposuresofFigure4,strongestCanabsorp- the stellarlinein1972,andnotatallthereafter.On in H,Kdisappearedduringtheseasonalgapbetween emission feature:seeFigure4.Thesewideemissions filled approximatelytothecontinuumlevelbyabroad limit, whichwouldprovideatestoftheroleplayed through 1971.Thenextstrongest isalsoofconstant gross Canshellstructurewasmeasurableagainst seen intheH,Klines.Thereasonthatthisabsorption by thecontinuousopacityinthisphenomenon. mination ofvelocityfromlinesbelowtheBalmer star isthatthroughthe1971seasonstellarlinewas structure isvisibleatallagainsttheCanlineofanA5 in 1972,andhadeffectdisappeared by1974,asnoted triplet through1971andearly 1972. Theywereweakerlater Shanin, Shevchenko,andShcherbakov (1975). 1971 Septemberand1972May.Consequentlyonlythe 1 The velocitystructureoftheejectedmaterialisbest Emissioncomponentswerepresent intheinfraredCan i - —'/OH 1720 COem HU region ^ em HgCO abs Ha em, 699 1977ApJ. . .217 . .693H _1 -1 1 1 1 _1 -12 1 1 1 -1 1 _1 -1 1 3 1 1 near —160kmscouldbemeasured.Thiswas spectrograms, althoughononeplate(thatof1971 measured near—310kmsonmostofthese velocity, —lOSkms“.Aweakercomponentwas ground ofthestarline,onlyasinglewidecomponent June 29)itwasbroaderandstrongershiftedto this areahavebeenmeasuredbyAdams(1949)near features werealsopresentat—16kms'.Thesemust be theinterstellarCanlines,whichinbrightstars components. OnallthelóÁmm“plates,narrow probably ablendofthe—105and—210kms probably correspondtominimaatabout—230and velocities ofabout—14kms. there werethreewell-definedexpandingshells:alow- component whichappearedearlyin1972andre- the Lickdata. 700 To summarize,duringthe2yearsfollowingmaximum mained near—150kms'through1973-1975;this the entriesinTable2busuallyrefertoblend.The detectable ononlythebetterhigh-dispersionplates; excitation onenear—105kms'seenonlyinNai could beablendoftheCancomponentsat—105and of thePCygniabsorptionatHawasconsistently Ha thatcorrespondedtotheCanlineat—105kms'. measurements byKolotilov(1975)ofthestructure HCO cloudabsorption—14.4Lo(Bechisand1975),MinnGreenberg1973 Transient 1720MHzOHmaseremission—14.6LoandBechis1974 Ha emission,NGC7000—16Hippelein1973 CO cloudemission—11.8BechisandLo1975 existed through1975.Iftheywereejectedatthe shell near—310kmsseenstronglyinH,weakly and Can;oneofmediumexcitationnear—210kms“ beginning oftherisetomaximumlight,thatmaterial Na istructure,thethreeshellsoflesservelocitystill the displacedalthoughusuallyunresolvedHaand at —517kmscanbeseenonthethirdspectrogram due tothefadingoutofoneormoreabsorption shortward shiftoftheHaabsorptionwasprobably shown byH,Nai,andCan;ahigherexcitation Ha onfivespectrogramsin1974seemcompatiblewith 11 Âmmspectrogramoflate1973.Thisduplicity — BóBkms“.In1972,againstthedepressedback- must bythenhaveexpandedtodistancesof100- systems atevenlargerdisplacement.Suchacomponent Ca ii,andnotatallinNai.Theearlydeclinethe of Figure6.Judgingfromthecontinuingpresence are observedinTTaustars(Herbig 1977),andindeedthere Fig. 2. as aweakKlineontheearlylow-dispersion spectrogramsin 330 AUfromthestar. — 320kms'thatweremeasuredintheHalineonan — 210kms“.Nocomponentwasevermeasuredin 2 1 2 3 1 The Caiicomponentsat—210and—SlOkms" The Nailinesshowedonlyasingledisplaced ItisthismassofunresolvedCa nstructurethatappears Displacedcomponentsatvelocities upto—300kms~ © American Astronomical Society • Provided by theNASA Astrophysics Data System 1 Source v(kms~)Reference Q Interstellar CloudVelocitiesnearVI057Cygni TABLE 3 HERBIG 1 1 -1 1 1 emissions inH,K1971weretoopoorlydefined Ha followedthepatternofwholeblueabsorption that theinfraredCaiiemissionlinesalsoshoweda significantly differentfromthatofthestar.Thebroad assumed ameanvelocitynear—20kms“,not spectrum: itwasnegativelyshiftedin1971andlater for velocitymeasurement,butthereissomeindication it movedslowlylongwardduringthetimewas emission atthattime;liketheCanandHaemission, positive driftthrough1971-1972,beforetheydis- appeared. TheOiA8446linewasalsopresentin measurable. those inHandK,butHawasastrongemissionline graphic region,theonlyemissionlinesobservedwere whose absorptioncomponentfluctuatedinstrength respect tothemetalliclinesinblue,byanamount in Figure6.Afewearlyplatesshowedshortward which decreasedfromabout—40kms“in1971to always showedapersistentshortwardshiftwith lines remainedinabsorption.Theircores,however, having thesamedisplacementasatHa,butmain as theemissionfaded:seestackofspectrograms they arenowquitestrong.Thesamefeatureshave absorption componentsatthehigherBalmerlines Welin (1976).Theymighthavebeendetectable longward ofthecentersH,Klines(Herbig strengthening ofrathernarrowemissioncomponents had beenobservedinFUOriwastheappearanceand features areseentobeasymmetric,theshortwardedges discovered independentlyataboutthesametimeby taken in1976,6yearspastmaximum,andwere fair strength,ona27ÂmmMaunaKeaplate earlier, butnoadequatespectrogramswereobtained now appearedinVI057Cyg.Theyweredetected, being obliteratedbyoverlyingCaiiabsorptionofthe suggest rathersomeconnection with theoutburst. excluded thatsomeoftheseshells predatethe1970eruption. has nowdevelopedasimilarshell,whichinFUOri at Lickin1973-1975.InFUOri16Âmm“the The changesofthePCygniabsorption atHa(Fig.6),however, of theemissioninVI057Cygmaymeanthatstar shortward-shifted shell.Thesimilarlongwardshift V1057 Cygatminimum(§VI). Thepossibilitycannotbe 1966). Firstdetected11yearspastmaximumlight, was indirectevidenceforsuchstructure intheBalmerlinesof —15 kms"in1973. The velocityofthePCygniemissioncomponentat On the1971spectrogramscoveringphoto- An interestingpostmaximumphenomenonthat Vol. 217 1977ApJ. . .217 . .693H No. 3,1977 region ofnormalcolorscorrespondingtothe1975-1976redspectraltypesthesestars.ThepeculiarpositionV1057Cyg in is composedoflow-levellinesneutralandionized The sinuouslineisthemainsequenceU—B,BVrelationship.straightaconventionalreddeningpathfrom the FU OriandVI057CygarefromthesourcescitedinFigs.13,whilethoseforVI515Stone’sobservations(Table 7). inferred denseshelltothemoredisplacedstructures inadequate resolutiontoshowsuchasecondsetof that wereseenearlierinCanisunknown.These metals. TheMaunaKeaplateofVI057Cygis red persistedasthestarcooled,inlateryearsbothcorrespondingcolorslaynearasinglereddeninglinesuchthatshown. newly appearedCanemissionlinesarestrongerand emissions thatfilledtheH,KlinesofVI057Cygfor absorption linesdirectly.Therelationshipofthis the firstyearfollowingmaximumlight. narrower, andarequitedistinctfromtheverybroad 1971 and1972isbelievedtobecausedbyitsabnormallybrightblue-ultraviolet.Eventhoughthecolordifferencebetweenblue is showninFigure7,togetherwiththelocationsof given inthecaption.Thereasonforthree-color behavior ofVI057Cygisclearer,however,ifthe slow movementofthestarinF)-plane February andhascontinuedtothepresenttime.The reddened referencestarwhosespectraltypeisan in Table4;theequipmentwassameasthatused here weremadebyMr.R.Stone.Thedetailsaregiven scanner spectrophotometryisfirstexamined.The FU OriandVI515Cyg;thesourcesofdataare the time.ForcomparisonwithGrasdalen’s1971 magnitude differencesbetweenVI057Cygandade- by Grasdalen(1973).InFigure8areplottedthe approximate matchfortheredtypeofVI057Cygat Crossley scannerobservationsof1975-1976discussed de-reddened forE(B—V)= 0.03bythestraight-line by MillerandMathews(1972). Forcomparisonwith approximations toWhitford’s extinctioncurvegiven scans, thereferencestarchosenis41Cyg,F5II, stars areßDra[G2II,E{B—V) ~0.09]andaAqr Stone’s 1975-1976spectrophotometry, thereference Fig. 7.—FUOriandVI515Cyginthetwo-colordiagram,migrationofVI057between19711976.Thedatafor Multicolor photometryofVI057Cygbeganin1971 © American Astronomical Society • Provided by theNASA Astrophysics Data System d) ColorsandSpectrophotometry ERUPTIVE PHENOMENAINSTELLAREVOLUTION 4800 Âatthe5000-8000slope,risessystematically VI057 Cyg,insteadofcontinuingshortwardabout (1976). Theseplotsshowthatthecontinuumof star dataweretakenfromthecompilationbyBreger fit anotherstraightlinethroughtheseA<5000 through theblue-violet.Itispossibleinprincipleto [G2 lb,E(B—V)=0.10].Inallcases,thereference 4036.. . . 4566.. .. 4464.. .. 4255.. .. 4167.. .. 4785.. .. 3862.. . . 3704.. . . 7100.. .. 7780.. .. 7550.. .. 6790.. .. 6436.. .. 6056.. .. shortward ofA5263,32Âlongward. are m(A)=—2.5logF+const. Thebandpasseswere49 5840.. .. 5556.. .. 5263.. .. m(5556). 8090.. .. 5000.. .. 8370.. .. v * TheobservationsarebyR.Stone. Thequantitiestabulated A (Â) Scanner SpectrophotometryofVI057Cygni* Nov. 18 -0.32 -1.38 -1.11 -0.94 -0.67 -0.46 -1.82 -1.78 -2.36 1975 10.43 2.94 2.62 0.92 0.00 0.40 0.73 1.97 1.53 1.70 1.95 1.30 TABLE 4 July 27 -0.46 -1.16 -1.00 -0.67 -0.29 -1.37 -1.77 -1.65 -1.56 1976 10.45 2.22 2.73 3.19 0.90 0.45 0.70 0.00 1.46 1.79 1.92 1.28 Aug. 25 -0.42 -0.25 -0.95 -0.65 -1.35 -1.14 -1.58 -1.51 -1.75 10.48 1976 0.98 2.02 2.22 2.80 3.31 0.78 0.00 0.45 701 1.87 1.52 1.36 1977ApJ. . .217 . .693H 702 type ofV1057CygatthattimewasaboutF5II,theslopegives variable in1971,asmeasuredbyGrasdalen(1973),and41Cyg (F5 II)aftercorrectionforreddening.Sincetheredspectral Cyg. Theupperplotismagnitudedifferencesbetweenthe its reddening;thestraightlinesegmentscorrespondto reddening accordingtoWhitford’sextinctioncurvewith E(B —V)1.08.TheabnormalbrightnessofV1057Cyg shortward ofabout4800Âcanbeseen.Filledcirclesrepresent to beapparentatthisscale,datafrom1971Apr.1areshown variable asmeasuredin1975-1976byStone(Table4)minus from 1971Sept.19ascrosses.Thelowerplotrepresentsthe mean pointsforthreenights;whentheseparationissufficient represent thedataof1975Nov.18,andcrossesmean as opencircles,from1971June23half-filledand de-reddened ßDra(G2II)andaAqr(G2lb).Opencirclesnow E(B -V)~1.02.Avalueof1.0hasbeenadoptedinthetext. The wavelengthsshownwerechosentoavoidstrongspectral points, tocorrectthatslopeforthereddeningderived features. Thezeropointsoftheordinatesarearbitrary. bright shortwardof4800Â.Thereddeninginferredisnow from thefitforA<5000Â,andtoreadatable 1976 July27andAug.25.V1057Cygisseenstilltobetoo the resultsinTable5mustbeconsideredasonly indicative. Theprogressivechangeduring1971in wavelength rangebelow5000Âavailableforthisfitis spectral typeofthecorrespondingstar.However, of (B—V)versusMKtype(FitzGerald1970)the particular isprobablybelowtherealresolutionof small, andthescatterofdataratherlargesothat 0 Fig. 8.—DifferentialscannerspectrophotometryofVI057 © American Astronomical Society • Provided by theNASA Astrophysics Data System 1971 Apr.1GrasdalenA 1975 Nov.18..Stone\ G2Ib,IIfl.00 1971 Sept.19Grasdalen) 1971 June23Grasdalen >F5II1.08 1976 Aug.*...Stone/ \105 * Meanofthescans1976July 27andAug.25. 2.8 2.42.01.6I/X^ Date ObserverA>5000ÂFit 5000Â4000-4800AClassII Spectral TypeInferredfromtheContinuumSlopeofVI057 Cygni,4000-4800 MK Type,FromFor if Assumed E(B—V)(B-Corresponding 0 HERBIG TABLE 5 spectral typescorrespondingtotheslopeofblue observations. Nevertheless,itisstrikingthatthese continuum arenotfarfromthetypesestimated is thusfurtherevidence,inadditiontothatfromthe directly fromthespectrogramsofthatregion.There violet oneseesadeeperandhotterregionofthe spectral typesandradialvelocities,thatintheblue- the jumpinVI057Cygwasmuchsmallerthan for twonightsin1971.Hecomparedthisregionwitha object thanintheyellow-red. expected. Thisdiscrepancyisnotsostrikingifthe Cyg belowtheBalmerlimitremainthoseofGrasdalen, variable isdifferencedagainstarealA5IIIstar.It Carbon-Gingerich modelatmosphere,andnotedthat not obvioushowlargeajumpwouldbeexpectedinthe stratified-envelope picturethatissuggestedbythe ing positionofV1057Cyginthe(U—B,B—K)-plane other evidence. (Fig. 7)mustreflectthis“composite”energydistri- is AandacrossapossiblyabnormalBalmerjump,the bution :theUbandfallsinregionwheretype B bandiscentralintheA-typeregion,whileVlies the starfadedaftermaximumlight,discrepancy largely intherangewherestarhasanFtype.As between thecontinuumslopesshortwardandlong- the effectofadiminishingBalmerjumpuponU ward ofabout4800Âwasmaintained(Table5)but should drivethestarinsenseitwasindeed observed tomoveinFigure7. a remarkablysmallregionofFigure7.In1975- lie nearthereddeninglinedrawninFigure7,soany intrinsic colorsareallthesame,theninterstellar perturbation ofUandBmustnowbesmall.Ifthe Cyg, G2-5lborII.Thecorrespondingnormalcolors reddening ofeachcanbeestimatedbyadoptingthe FU Ori,F5-G0pIb;V1515Cyg,G0-G2VI057 which therelativepositionsinFigure7yieldE{B—V)— 1976, theirred-regiontypeswerenotgreatlydifferent: 0.8 forFUOriand1.0VI515Cyg. scanner valueofE(B—V)=1.0forVI057Cyg,from the de-reddenedcolorsorenergydistributionlong- ward of5000Â,undertheassumptionsthat The onlyscannerdataonthecontinuumofVI057 To returntothebroad-bandphotometry,start- All threeFUOristarsarenowgroupedtogetherin The radiusofVI057Cygcanbecalculatedfrom e) DimensionsofV1057Cygni ( +0.07:A3 10.23: F0: 0.17 :A8-9 0.33: F3: 0.20: F0: Vol. 217 1977ApJ. . .217 . .693H No. 3,1977 K0 surfacebrightness4.45.83.54.6 /?—/=+1.8 atminimum11.911.89.59.3 extinction isnormalandnottime-dependent.The visual surfacebrightnessinmagnitudes,Sy,canbe and recentlyrecalibratedintermsofintrinsicR—I obtained fromrelationshipsgivenbyWesselink(1969) (1976). Thesurfacebrightnessisexpressedas and V—RcolorsbyBarnes,Evans,Parsons where CisthecolorandabaregivenbyBarnes et al.Or,theradiuscanbeobtaineddirectlyfrom is theVmagnitudecorrectedforextinction. where disthedistanceinsameunitsasR,andF the typeobservedformoreluminousTTauristars by assumingthatthesurfacebrightnessofV1057Cyg was thenapproximatelythatofadKOstar,whichis is notclassifiable.)ThevalueofVcanbetakeneither the E(B—V)=1.0of§IIW,sothatV^11.0;or phase, correctedforMandel’s(1975)colorindexand as Herbig’s(1958)m=16.0atsomeunknown only aconjecturebecausethe1957plateofVI057Cyg such asTTauandRY(Herbig1977).(Butthisis distance of600pc,essentiallythatGrasdalen Table 6.Theamountofextinctiondoesnotenter photovisual data,whenceasbeforeF^11.5.A an averagem^14.5canbereadfromMandel’s 0 crucially; asanillustration,asecondsetofradiiare (1973), isadopted,andtheresultingradiiaregivenin estimate thatR—/=+1.8. Correctedforreddening shown forthecaseofE(B—V)=1.2. 0 to amuchlowersurfacebrightness, ofabouttypeMl. to muchlargerradii(Table 6) becauseitcorresponds of amount—/)=0.82E(Z? —F),thiscolorleads 0 ps The resultisquitesensitive tothevalueassumedfor 0 v The preoutburstradiusprobablyisbestobtained log R=d—0.2F-2(0bC)0.174,(2) o A preoutburstradiusisalsocalculablefromHaro’s © American Astronomical Society • Provided by theNASA Astrophysics Data System Assumption andE(B—F)=1.0or1.2E{B SV =-10(tf-bC)+27.21,(1) 1971 Mar.1216.014.8 1971 May817.716.4 1971 June2815.814.6 1971 Sept.22-2416.915.6 1976 Aug.2514.313.2 1975 Nov.1813.612.6 1976 July2714.813.6 1975-76 datesarethoseofthescansbyStone(Table4). * Insolarunits. t The1971datesarethoseofthemulticolorobservationsbyRiekeetal.1972. ERUPTIVE PHENOMENAINSTELLAREVOLUTION Datet WithE(B-F)=1.0Butif1.2: Calculated RadiiofVI057Cygni* A. PreoutburstRadii B. PostmaximumRadii If Vo=11.011.5 TABLE 6 -1 1 -1 1 R —I.Haro’svalueisonlyanestimate;ifitwerein error bythenotunreasonableamountof0.3mag, reason, thepreviousvalueispreferred. resulting radiuschangeisbyafactorof1.7.Forthis for determiningtheradiusinthisway.)Once and scannerdataareavailablefor1971, peculiar energydistribution,UBVdataareunsuitable m(5556Â) minusm(7100Â)isdeterminedforinter- relationship betweenV—Randthescannercolors observations alonein1975-1976.(Becauseofthe follow asbefore:Table6. stellar reddening,thesurfacebrightnessesandradii rising fromminimumtomaximumlight,andthat photometric risetime,thentheaverageradialvelocity radial expansionbyabout13Rtookplaceoverthe subsequently ithasbecomeslightlysmaller.Ifthe early 1971spectrograms(40kmsfromthemetallic Clearly, thelargeexpansionvelocitiesmeasuredon of thephotospherewasonlyabout0.3kms“. cores, 500kmsfromthePCygnistructureofHa) spectrum intheblue,bOkms"fromBalmer refer nottothemotionofthissurface,butrather rapidly risingshellsthatareopticallythinintheir visual continua. Woolf 1971;Cohen19730;Rieke,Lee,andCoyne Q very brightinthe20/xregion. InFigure9isplottedthe maximum light,andrevealedthatthestarwasthen infrared excessobservedin 1971, displayedasmagni- tudes abovethecontinuum of anF5IIstarhavingthe It hasbeenshownbySimon etal.(1972)andby same F;conventionalreddening hasbeenremoved. 1972) beganin1971March,about6monthsafter Following maximumlight,bothVRphotometry These resultsshowthatthestarexpandedwhen Infrared photometryofVI057Cyg(Cohenand /) InfraredExcesses 703 1977ApJ. . .217 . .693H 704 512 1 a) section showstheinfraredexcessesofFsupergiants E(B —V)’sgivenin§III*/,hasbeenremoved.Thelower time. Normalreddening,ofamountcorrespondingtothe normal colorscorrespondingtotheredspectraltypeat by theVmagnitudeandextendedtolongerwavelengths Humphreys andNey(1974).TheV1057Cygphotometryis HD 101584and89Herinthesameformat;dataarefrom 1971), V1515CygandFUOri,referredtoabaselinedefined observations ofVI515CygarebyCohen(1974)andK.M. by Cohen(1973a,1975)andRiekeetal.(1972).The Lee andLowasquotedbyRiekeetal.,Cohen(19736, ture :acomponentnear200Kisrequiredforthe be fittedbythermaldustemissionatasingletempera- Merrill (1976,privatecommunication).ThoseofFUOriareby that thelatterisduetofree-freeemissionencounters Rieke, Lee,andCoyne(1972)thatthisexcesscannot 1975). the entireinfraredexcessisduetoasinglethick difficulties inthevisualregion.)Thepossibilitythat about 1800Kfor1-5/xm.(Analternativeproposal temperature ifthegrainsaretransparent(seeAndriesse region wherethe20/xmexcessoriginatescanbemade nongray particleemissivityhasnotbeenexplored. dust shellhavingamajortemperaturegradientand 10-20/xm region,andamuchhottercomponentat as follows.Theratiooffluxesat10and20/xm measured bySimon(1975)canbeconvertedtoa at thosewavelengthsisknown.Theconventional %R*(T*/T) =270AU.On theotherhand, dilute radiationfieldofan F5 IIstarhavingT= assumption isthateocÀ“(Greenberg1968),so units isLB*/L*€oumBs,where theB’sarerespec- effective emittingareaofthe shellat20/xminstellar Ts ^185K.Ifthistemperatureisproducedbythe 6500 K,thenthecorresponding shellradiusR< 1976 forajustification)andiftheratioofemissivities S eif A s2 s Fig. 9.—TheinfraredexcessesofVI057Cyg(meansfor A veryroughestimateofthedimensions © American Astronomical Society • Provided by theNASA Astrophysics Data System 0.55 1.02.24.810.20.^ HERBIG (2) i3) _1 -1 tive Planckfunctions,€isthegrainemissivity, circular emittingsurface,theradiusofthatsurfaceis 20 /xm.Iftheshellisrepresentedinprojectionbya and L/L*correspondstothe8magexcess,allat used isuncertain,butitmaybeoftheorder0.1 RW =60/€omAU.Thecorrectvalueofetobe the emittingregionisprovidedbyobservationof (Bussoletti andZambetta1976),whencejRæ the starandthatofOHmasersource(Lo upon thecoincidencebetweenopticalpositionof diameter wasnolargerthan1''5,fromwhichR^ 600 AU.Finally,ahighupperlimitontheradiusof 900 AU.Asimilarlimitresultsfromthetolerances Rieke, Lee,andCoyne(1972)thatat22/xmits will beusedforillustrativepurposes,butitisclearly 20um a mostuncertainnumber. Bechis 1974).AcompromisevalueofRx300AU s between 1971and1974,buttheirratiohasbeenvery nearly preserved,sothisdoesnotrepresentadecrease 2U20 um in theinfraredexcesstoarrivalofhigh-speed were launchedballisticallyabout1969.6whenthe gas oftheshellsseeninCan,Nai,andHa.Ifthese of T(Simon1975).Onemightexpectsomeresponse s eruption began,the310kmsshellshouldhave s reached thedistanceofR=300AUin1974,and the 210kmssystemin1977.Itisimaginablethat which wasfadingevenatthetimeofitsdiscoveryin passage ofonetheseshellswasresponsibleforthe s quenching ofihetransientOH1720MHzemission important thattheinfraredphotometryofVI057Cyg continue, notonlysothatsucheffectsmightbe Bechis 1974;Lo,privatecommunication1975).Itis detected butalsosothatthegeneralevolutionof s dust shellcanbefollowed. s nebula” suchasthosesuspectedtoexistaroundmany present nearthestarbeforeeruption,asa“solar T Taustars,andisnowradiatingrethermalizedstellar energy atacorrespondinglyhigherlevel.Aspointed 1973.5, andhaddisappearedby1974.8(Lo cloud ejectedfromthestarin1969isuntenable:it out bySimon,thealternativeofanexpandingdust then wemaybeviewingthatatVI057Cygapproxi- should bynowhavecooledperceptibly,contraryto observation. Therearereasonstosuspectthatthedust nebulae aroundyoungstarsarediskshaped;ifso, They are:theshapeofreflectionnebulositysur- to somedispute,butcollectivelycarryacertainweight. mately pole-on.Thereasonsareindividuallysubject interpret asaconicalnebulaseenapproximately rounding thestar,whichBechisandLo(1975) axially; thelackofasignificantamountcircum- as wouldbeexpectedifthediskofscattererswere stellar planepolarizationorofcircumstellarextinction, being viewedfromahighlatitude;theinterpretation and Simon(1975)intermsof adiskseenapproximately of thevariablecircularpolarizationbyWolstencroft ing ittoline-of-sightextinction ofthestaratshorter pole-on. Ifsuchisindeedthe geometry,thenspherical models whichaccountforthe infraredexcessbyequat- wavelengths areofcourseunnecessary. Iffuturework The 10and20/xmfluxesdecreasedbynearly1mag It seemsprobablethatthiscircumstellardustwas Vol. 217 1977ApJ. . .217 . .693H d characteristic ofpre-main-sequencestars,because tion, and5.7magforFUOriin1970-1972.Yetitis for VI515CygatthetimeofCohen’s(1974)observa- in 1971(whichhadfallento7.5magby1974),6.7 excesses ofthesametype(Humphreys,Strecker,and very youngstarsareknowntodisplayinfrared to benotedthatsuchexcessesarenotaunique through theirdiskswouldbeveryfaintoptically,and Ney 1971;Humphreysand1974a,b).Theexcesses no apparentconnectionwithinterstellarmatteror several brightF-andG-typesupergiantswhichhave members oftheclassisprobablysignificant:at bility, becausesucheventsseenfromlowlatitudes binaries, andHumphreys(1976)hassuggestedthatin might wellhavebeenmissed. questioning theinterpretationongroundsofimproba- a pole-ongeometry,thiswouldnotbegroundsfor No. 3,1977 by thecoolcomponent. shown inFigure9.Botharesingle-linespectroscopic should showthatFUOriandVI515Cygalsorequire not beenpresentatminimum.Thenebulosityappears nebulosity surroundingVI057Cyghadappeared HD 101584theexcessarisesincircumstellardustshed of twotheseobjects,HD101584and89Her,are variable justinsideitssouthwestedge;thebrightest broken, ellipticalringabout60"by90",withthe and thePalomarSkySurveyplateshowthatithad ellipse, about95"northeastofthestar.Thespectrum in thering,andalargesectionalongnorthsideis shortly followingmaximumlight;bothhismaterial filter photographsincludingandexcludingHa(Fig.10) section oftheringisthatnearestvariable,about on large-scalephotographs(Fig.10[PI.8])asa nebulosity wasnotejectedfromthestaratrecent was illuminatedasthestarbrightened,case absent. Fainternebulosityisvisiblealsooutsidethe 18 /¿mtheseamount(Fig.9)to8.0magforV1057Cyg velocity inthatareaisthesameassurrounding at FUOri.Inbothcases,onecanbecertainthatthe demonstrate thatitisreflection. of theringhasapparentlynotbeenobtained,but The firstknownphotographofthenebulosityisthat molecular cloud. more, atVI057Cyg,COobservationsoftheringwest motions attherequiredvelocityarepresent.Further- the impressionthatonit, sectionoftheringlying reproduced byWelin(1971a,Fig.2b),takenon 600 pc,crossthecloudatrateof1"in3.5days. outburst: thedirectphotographsshowthatnocross nebulosity nearerthestarthan onlaterphotographs. light. Thatexposureisnot strong, butonedoeshave of thestarbyBechisandLo(1975)showthatradial 60" northeastofthestaris fainter withrespecttothe 12" westandsouthwest.Thereisconsiderablestructure 1970 December22,approximately 100aftermaximum The presenceofinfraredexcessesinallthree Welin (1971a)discoveredthataneccentricringof This nebulositymustbeapreexistingstructurethat The waveofilluminationfromVI057Cygwould,at © American Astronomical Society • Provided by theNASA Astrophysics Data System g) TheReflectionNebulae ERUPTIVE PHENOMENAINSTELLAREVOLUTION d d immediately afterdiscoverywiththeCrossleyreflector the modelofnebulaproposedbyBechisandLo unreasonable thatarcactuallyliesfarenough telescope, filter,exposuretime,andemulsiontype, present time.Thesenegatives,alltakenwiththesame possibility. taken inmid-1970shouldbefound,however,the delayed significantlylonger.Onenotesthatinfact behind theplaneofskyforitsilluminationtobe ever, theprojectionfactorisunknown,anditnot differential wouldprobablybeimperceptible.How- The lighttraveltimetothatpointwouldbe210,but matter islikelytoremainasonlyaninteresting arc. Unlesssomeforgottenphotographoftheregion (1975) postulatesjustthatlocationforparticular 210 beforethatplatewasexposedthevariable in Figure11(Plate9).Presumablythisfadingis at LickbyMr.E.A.Harlan,andhascontinuedtothe only about0.2-0.3magfainter,andsuchasmall response tothepostmaximumdeclineinstar’s faded inbrightnesswithoutanyobviouschange structure. The1971-1975platesarereproduced show thatsince1971thewholenebulahasslowly will bedifficultbecausethefadingisslow.Aphoto- light-time effectsinthenebulaasvariabledeclines brightness, whichamountedtoabout1.0maginR bright arcextendingfromthestarisembeddedinan present atVI515Cyg(see§IV),andFUOria metric studyofthesenegativesisunderway. is thatitrepresentsthesurfaceofacavitytowhose arcs orincompleteringsareassociatedwithanumber amorphous massofreflectionnebulosity.Suchdust over theintervalrepresentedinFigure11.Detectionof ejected fromthestaratanearliereruption. tangentially tothesouthwestside.Anotherpossibility complete ringatVI057Cyg,LoandBechis(1975) of pre-main-sequencestars(seethephotographsin that acuriousarcofnebulosityprotrudedfromthe emission-Ha starsnearthereflectionnebulaNGC boundary theinterveningdusthasbeendrivenbygas have proposedthatitisaconicalsurfaceviewed Herbig 1960),sotheyarenotanexclusivepropertyof photographic image,nofollow-upobservationswere brighter ona1954Crossleyplatethanoneof1912, covered inthesameobscuredarea,8'southwestof FU Orionis-likeobjects.Inthecaseofnearly tail, butontheassumption thatitwasthecometary published abriefnoteonthestaranditsnebulous but despitethisunusuallylargerangeandthefact taken soonthereafterrevealed aspectrumverymuch Two 120inchcoudéspectrograms oftheredregion nebula Parsamyan22,which infactliesabout9'east. made atLickuntil1974.Atthattime,Cohen(1974) BD +41°3731.Thevariablewasnotedasabout3mag 6914 (Herbig1960),afaintvariablestarwasdis- like thatofFUOri:anearly G-typestarofhigh A seriesofdirectplatesVI057Cygwasbegun A nearlycompleteellipticalringofnebulosityis About 1954,inconnectionwiththesearchfor IV. VI515CYGNI 705 1977ApJ. . .217 . .693H a slowerbutcontinuousrisefromabout1956to very muchindebtedtotheseastronomersfortheir is showninthereproductionsofCrossleyplates than 1maginamplitude,superposedupontheslow Nantucket estimates;thelatter{filledcircles)indicate it becamevisiblenearm=15.5.Thestarcontinued to whichhavebeenaddedseveralobservationsofB curve ofV1515Cygsince1922isshowninFigure13, in advanceofpublication.Thephotographiclight cooperation, andforplacingthismaterialatmydisposal (1975, privatecommunication)atNantucket.Iam was shortlythereafterinvestigatedbyWenzeland significantly brighterthanithadbeenin1954;therise and astrongLiiA6707line.Furthermore,thestarwas powerful shortward-displacedabsorptionsatNaiD, luminosity withbroadlines,PCygnistructureatHa, Wenzel andGessnerhavebeen extendedtomag18by history ofVI515Cyg.The comparison-star m.’sof secular brightening.Theirrealityisconfirmedby it hasattainedmaximumlightorwillcontinueto the comparisonstars.Thedifficultycouldbeduetoa are compatibleinthisrangetoabout0.1mag.The however, adiscrepancybetweenthetwoseries.Its to brightenslowly.Between1957and1970thereis, the first(Nantucket)platesin1920until1948,when Gessner (1975)onSonnebergplates,andbyHoffleit tainties ofthetabularvalues,inunits0.01mag. 706 a singleexposureobtained withtheLick20inch and Hoffleithavenotedadditionalfluctuations,less upon oneortheotherseries. has establishedthatthetwocomparison-starsequences It doesnotlieinthemagnitudesystems:MissHoffleit sense isthattheSonnebergobservations(Fig.13, brighten isnotobvious.BothWenzelandGessner star in1975-1976hasbeennear5=13.7,butwhether compatible withthephotoelectricobservations.The once againcomeintoessentialagreementandare color effect,ortotheinfluenceofsmallnebulosity star isneartheedgeofmostNantucketplates,and open circles),whichshownearlyconstantlightfrom made atLickin1975-1976byMr.R.Stone(Table7). Stone’s Fobservationsin Table7. Miss Hoffleithasremarkedthattheimagecharacter of thevariableisfrequentlydifferentfromthose 1976 Aug.2812.13(1)1.59(2)1.06(7) 1975 Sept.25...... 12.30(2)1.52(3)1.09 1976 Sept.2311.93(2)1.62(3)1.10(5) 1975 Sept.2412.27(2)+1.57(3)+1.11(4) 1912, 1954,and1975inFigure12(Plate10). 1975. Thereasonforthisdifferenceisnotunderstood. 1960 to1975,are0.5-1.0magbrighterthanthe pg 12 pg At myrequest,thephotometrichistoryofstar The variablewasbelowthelimitofbothseriesfrom Only fragmentaryinformation existsontheearlier Whatever thereason,since1970twoserieshave * Thenumbersinparenthesesaretheestimateduncer- Date (UT)VB—VU-B © American Astronomical Society • Provided by theNASA Astrophysics Data System UBVObservations ofVI515CygnibyR.Stone* TABLE 7 HERBIG _ 1 1- tion ofVI515Cygwithitsmolecularcloudisthus Wilson aregiveninTable8.Thestarmaintainedan variety ofinstrumentsatLick,Heidelberg,andMount this extendedsequence,onearlyplatestakenwitha Astrograph andaAm=4.0magobjectivegrating. demonstrated; thesamesituationhasalreadybeen three 34Âmmcoudéspectrogramsoftheredregion extending tothesouthandwesthasinmeantime real. usually eitherneartheplatelimitoroutsidefield shown toholdforFUOriandY1057Cyg. around thenearby+41°3731.Thekinematicassocia- (1973) andbyKnappetal.(1977)fortheCOemission taken in1974-75.Themeanvelocityis—12± ring of16"by21". lies ontheeasternedgeofanearlycompleteelliptical indicated rangeofover0.6magatminimumlightis uncertainties inthesemagnitudesbecausethestarwas approximately levelbrightness,averagingaboutm= Estimates ofthevariable’sbrightnesswithrespectto of Y1057andVI515Cygare bothmanifestationsof also beenmeasuredbyLoren,VandenBout,andDavis appeared. Thereisnosignofthisnewnebulosity plates of1975showthisnorthwestarcasstillpresent west oftheimageVI515Cyg.Thisfeaturedoesnot plates between1948and1954showanarrowarcof field wastakenon1954October1,whenthestar 2 kms“.Aheliocentricvelocityof—12shas on anyoftheearlierexposures.Thusvariablenow but muchfainter,whileanewandbrighterarc heavily comaticimageofthestaronaMountWilson taken atminimumlight,butitmaybepresentinthe bright nebulosityextendingabout14"tothenorthand tion plate,thevariableshowsessentiallyacontinuous region CrossleyslitlessspectrogramoftheNGC6914 of gooddefinition.Thereforeitisnotcertainthatthe appear onanyoftheearlierLickorHeidelbergplates absorption atHa. spectrum ofVI515Cygatminimum.Thefirstred- spectrum, buttheredoesappeartobeabroadshallow already atm=14.5,onitsrise.Onthatlow-resolu- 1919 Oct.27Mt.Wilson100inch17.3 1912 Aug.13LickCrossley17.0 1894 June7LickWillard>15.8 1920 Aug.11.Mt.Wilson100inch17.4 1903 Sept.21KönigstuhlBruce>17.6 1901 July16,18....KönigstuhlBruce17.5: 17.4, between1901and1920.Thereareconsiderable 100 inchnegativeof1920.Crossleyand120 pg pg The radialvelocityofY1515Cygwasmeasuredon It hasherebeenimplicitlyassumed thattheeruptions The Lick,MountWilson,andPalomarAtlasdirect Unfortunately therearenoobservationsofthe Date ObservatoryTelescopem pg Early MagnitudesofY1515Cygni a) SpectralCharacteristics V. GENERALDISCUSSION TABLE 8 1977ApJ. . .217 . .693H © American Astronomical Society • Provided by theNASA Astrophysics Data System o o sj- o o to o o rO o rO CM o O O O O O OJ 00 O O O Q CM M- CM •g.2 .l-S 3? « Ö ß fe e o 1977ApJ. . .217 . .693H y y y 4 the FUOriphenomenon,despiterelativelyslow interesting resemblancetothesethreeobjects,yetit types ofluminosityclasslborII(inthered)with has beennearitspresentbrightnesssinceatleastthe tion, butinfuturecasesthatinformationmaynot three wereobservedtorisefromaminimummagnitude absolute magnitudesatminimum.Thefactthatall excesses, thepeculiarreflectionnebulae,similar common anddistinctivecharacteristics:lateForG photometric developmentofVI515Cyg.Anessential whether thesestarsallhavethesamespectraltype properties oftheFUOrivariablesremainunanswered. always beavailable.Forexample,SUAurhasan spectra arenotpreciselyidenticalbuthavecertain basis forthisbeliefisspectroscopic.Thepostmaximum secondary propertiesthatarenotunique:theinfrared earlier 2yearsbeforeisimpossibletosay,butone lines alone,wasgivenbyWellmannandHachenberg classification ofFUOriwasat+2;thisYerkes lithium abundance,andshortwardshellcomponents ables havingthesecharacteristicshaveaswellsome sion isinthePCygnistructureatHa.Thethreevari- at HaandD,whiletheonlyconspicuouslineemis- at astrengthapproximatingchondriticorTTauri-like somewhat diffuseabsorptionlines,LiiÀ6707present (1939). Whetherthetypehadbeensubstantially at maximumlight.ThedataisbestforVI057Cyg: For example,theevidenceisinadequatetoestablish of longdurationwascoursetheprimaryconsidera- differences inspectraltype,radialvelocity,energy tion intheblue,whileredtypeis1975-1976was VI515 Cygisoflittlehelp:thereasyetnoinforma- notes thatat+26thebluetypewasgivenasF2:pI-II, of A8ataboutthesametime,fromHandCan spectrogram of1939Februaryhasbeenclassified about 0.7years(0.7)aftermaximumitwasclassified 708 as A3-5IIintheblue,F5red.Thefirstblue intrinsic changesinthestar:spectraatmaximum energy distributionwasnormal. length. Norisitknownwhetherthesamephenomenon between blueandredareseparatedbyadiscontinuity films weretakenoriginallyby P. C.Keenan,andarethose however, thattheeruptionwasaccompaniedby near 4800Â,oriftheyvarycontinuouslywithwave- distribution, andcircularpolarizationofVI057Cyg maximum. G0-G2 lb.Butitisnotcertainthatthisstaryetat so nolargechangeissuggested.Theinformationon F0 labbyW.Morgan.Alesspreciseclassification 1850s. me toexaminealltheearly40inch negativesofFUOri.These tion ofthisspectrogramonthe MK system,andforallowing and atminimumwerecompletelydifferent;there mentioned byStruve(1939). scanner observationsbyStoneshowthatin1976the (Wellmann andHachenberg1939;Bartaya1962),but available forFUOriuptoabout1960isconflicting occurs intheotherstars;whatlittleevidencethatis 12 4 A numberofquestionsaboutthespectroscopic Another unresolvedissueiswhetherthecurious The observationsofVI057Cyghavedemonstrated, IamverygratefultoDr.Morgan forhisrecentclassifica- © American Astronomical Society • Provided by theNASA Astrophysics Data System HERBIG 5 variable starshavebeenlessextensive thanearlier. allow forthefactthat,inrecent decades,routinesurveysfor consequence oftheintroduction ofphotography.Itdoesnot particular M'limitcomesfromthefactthat’s in comparisonswiththeTTausurveystatistics.This the starhasfaded.Alltheseshowthatflare-up in theyearfollowingmaximum;therehasbeena discovery ofgalacticnovaerose sharply justbefore1900,asa stars inthesethreeassociationsiscompletetodifferent and +7.5(Table9B).TheLicksurveyforemission-Ha at minimumlightforallthreestarsliebetween+7.0 than aboutM=+4inthisvolumearecandidates years, and{tí)itisnotsomespecialminorityofTTau the Mpvaluesatminimum(takenanintermediate was nottheresultofsimpleremovalascreen. continuing changeinthespectraltypeandradiusas in thosethreeassociations;thephotographicabsolute T TaustarsbrighterthanM'=M+^+8.0 examples rangefrom+3to+4).Specifically,itis (because theM’satminimumofthreeknown but ratherthetotalpopulationofTTaustarsbrighter stars whichissusceptibletotheFUOriphenomenon, within 1kpcinthenorthernskyduringpast80 uncertain correctionsfordistanceandextinctionare tions indicatethatithappenedinresponsetothe That maywellhavehappened(§Vi/),buttheobserva- preexisting circumstellardustorgashasnotbeen caused whenalargecoolshellwasdissipatedtoreveal to maximumdemonstratesthattheflare-upwasnot magnitude uncorrectedforextinctionmustbeused assumed thatthesethreecasesaredrawnfromthe made that{a)noothersucheventshaveoccurred involved. Theseobjectsatminimumclearlyhave point inthepreoutburstranges)are+3to+4, variables arelistedinTable9A.Itisinterestingthat disturbed orredistributedasaresultoftheoutburst. thesis studyoftheNGC7000region,whichfortunately is, VI515Cygwasnotfoundinavariablestarsurvey although itmustberememberedthatsomewhat a smaller,hotterstarwithin.Thisdoesnotmeanthat Furthermore, theincreaseofradiusfromminimum major changesintheradialvelocityandlinestructure was underwayatjusttherighttime. undetected forsometimehaditnotbeenWelin’s luminous TTaustars. luminosities comparablewiththoseofthemore star’s outburst,nottheconverse. upon asamplesizeof3.Thisnumberissurelylower from theobservedfrequencyofFUOriphenom- at all,andtheflare-upofVI057Cygmighthavegone which twoofthethreeexampleswerediscovered.That been missed,judgingfromthecircumstancesunder limit onthenumberofsucheventsthatwereobserv- enon, withduereservationaboutconclusionsbased star studies.Almostcertainlysomeexampleshave able duringthepast80yearsofphotographicvariable pg pg g p&pg pf? 5 Thisnumbercomesfromtheempirical factthattherateof To proceed,thefundamentalassumptionsarenow Some usefulparametersforthethreeknownFUOri Consider whatgeneralizationsmightbemade b) StatisticsandaFrequencyEstimate Vol. 217 1977ApJ. . .217 . .693H 3 No. 3,1977 ing thattheN(M')versusM'relationship these othergroupsofTTaustarsaswell.Thedetails ATpg’s. Reductiontothe+8.0limitismadebyassum- holds intheTaurus-Aurigadarkcloudsappliesto number ofcandidatesisestimatedtobeabout120. given inHerbig(1962,p.75).Inthisway,thetotal of thesecorrectionsareshowninTable10.Anexample of suchacorrectionanditsstatisticaluncertaintyis On thisbasis,themeantimebetweensuccessiveFU have indeedbeenmissed,risshorter;iflessluminous Orionis-like outburstsinanindividualTTaustaris stars inthosethreeassociations.Whereareallthe T Taustarsarealsosusceptible,itislonger. vgpg r =80x120/3^310years.Ifsomeexamples FU Orionis-likeeventsthatonthisbasiswouldbe FU FU But thisassumesthattheonlycandidatesareTTau © American Astronomical Society • Provided by theNASA Astrophysics Data System V1515 Cyg../if1960>4000\1050t1.0<-0.6+3.3 V1057 Cyg..1970.73906001.0-2.4+3.1var* FUOri 1937.1but5000.8-2.1+4.1var Star Maximum(days)(pc)(mag.)max.min. NGC 7000/IC507030+6.25 3.2 98. NGC 69144+6.75: 2.6 10. A OribyTonantzintlaresults.The correctionfactorsincol.(4)areobtainedfromtheassumption thatthe A Ori40?+11.25 0.23 9.? shape oftheluminosityfunction forTTaustarsintheTau-Aurcloudsisgeneral. Total 120: Explanation.—The dataincols. (2)and(3)arefromtheLickHasurveys,supplementedin caseof Association orKnownEmission-LimitingM'g Extend toNumber P V1515 Cyg..>4,000>3.9+7.3 V1057 Cyg..7,500?5.5*+7.1et VYTau 150-7003.3mean+8.1M0e«V(Li) EXLup 200-18002.0+6:§M0:eV(Li) FUOri >14,6006.2+7.2 error. UZTauE.... 150?3.9+8.9Ml,3eV(Li) Cloud HaStarsofSurveyM' g =+8.0M'g=+8.0 P § Thereisnoreliabledeterminationofthedistance,soM'gmaybesubstantiallyin * Ameanmgof16.0atminimumisassumed, t TheseclassificationsarefromHerbig1977. t ThedistanceisthatofRacine1968. (1) (2)(3) (4) (5) \if 1975>10,000. P P Star (days)(mag.)MinimumatMinimum}: Year ofRiseTimeDistanceE(B—V)Mg P Comparison ofFuOrionisVariablesandEruptiveTTauriStars Estimated NumbersofTTauriStarsBrighterthanM'= +8.0 pg ERUPTIVE PHENOMENAINSTELLAREVOLUTION Total NumberofFactorto Estimated Some StatisticsoftheFUOrionisVariables Duration ofPg Maximum RangeatSpectralType d < 380 > 120 TABLE 9A TABLE 9B TABLE 10 3 4 expected inrichassociationsliketheOrionNebula these threeeventsaretrulyallthathavetakenplace perhaps forunknownreasonssomeassociationsare and NGC2264?Surelysomehavebeenmissed; within thepast80yearsinallnorthernassociations more activethanothers.Ifonetakestheviewthat within 1kpcforwhichTTausurveystatisticsare Note thatnoallowanceismadeforheavilyobscured by afactorofabout4.2,sor=13x10years. available, thenthenumberofeligiblestarsisincreased The roundvalueofrä10yearswillbeusedin T Taustarsthatdonotappearinthestatisticsatall. uncertain. uncertainties involved,thisnumberisextremely what follows,butitisclearthatbecauseofthehuge FU FU This suggestionthattheFUOriphenomenonis Correction 709 1977ApJ. . .217 . .693H 6 4 4 4 6 4 6 4-1 in agivenstar,isunexpected.Butconsidertheobvious recurrent, andwithaspacingofonlyabout10years requires thatallknowncandidateswillhavebeen 710 alternative, namely,toassumethatsuchaflare-up new TTaustarsmustbesuppliedonthesametime exhausted inseveraltimes10years,whichmeansthat occurs onlyonceinalifeofgivenTTaustar.This required tomaintainthenumberofintermediate-mass tional considerations.(1)Therateofstarformation tion wouldbeinconflictwiththefollowingobserva- phase isonlyabout10years. estimated. Ifthisiscomparedwiththenumberof scale, andthisimpliesthatthedurationofTTau T Taustarsinthesamevolume,thenappropriate main-sequence starsinthesolarvicinitycanbe contraction andmain-sequencelifetimesleadtoa it seemsunlikelythatcouldbeinerrorbyafactorof years (Herbig1970).Thisisonlyaroughestimate,but mean durationoftheTTauphaseabout5x10 duration oftheTTauphasewereonly10years,then as OrionorNGC2264is1to5x10years.Ifthe two possiblepresentstatesforsuchformerTTau single eruptionsometimeinthepast.Therewouldbe a cluster,100to500otherstarswhichhadtheir one wouldexpecttofind,foreveryTTaustarinsuch 500. (2)Arepresentativeageforayoungclustersuch there wouldbe100to500suchmembersofyoung clusters wouldcontainlargenumbersofpeculiar (b) Theymightremainbright,inwhichcaseyoung clusters foreveryTTaustar;thisisnotobserved. but withouttheTTaucharacteristics,inwhichcase stars :(a)Theymightbefaint,abovethemainsequence, represents arelativelysuperficialeventafterwhichthe tion fortheFUOriphenomenonisdismissed.The unsuccessful. where afairlythoroughsearchatLickwasquite served. Suchstarscouldreadilyberecognized,yetthey point ofviewtakenhereisthatsuchaneruption F-G supergiantslikeFUOri;again,thisisnotob- must beveryrare,forexample,intheOrionNebula this idea.Thereisobviouslynouniquevalueofthe departed fromthestatewhichGrasdalen(1973) relatively rapidfadingofVI057Cyg,whichhasclearly star returnstoessentiallyitsformerstate.The contributed byvariablesthathavenotcompletely rate ofreturntominimumlight.Itmightbethatsome studied, andtheslowdeclineofFUOribothsupport declined fromtheirmostrecenteruption. of thedispersioninluminositiesTTaustarsis support oforincontradiction tothismorecomplicated correspondingly higherfrequency than10“yrstarto tions. Thiswouldofcourserequire thatminoritytoeruptata a specialsubgroupofTTaustars thatundergoessucherup- on themainsequence,theninagivenobjectthey simpler hypothesis. counterproposal, soitseemspreferable toremainwiththe maintain theobservedrate.There isnoevidenceeitherin 6 A claimthattheTTauphaseisofsuchshortdura- For thesereasons,the“only-once-per-star”assump- If theeruptionsoccurinTTaustarsbutareabsent Analternativeassumptionwouldhavebeenthatitisonly © American Astronomical Society • Provided by theNASA Astrophysics Data System c) CanVestigesofthePhenomenon Be FoundinOtherStars? HERBIG probably weakeninintensity,duration,orfrequency T Taustarsorpost-Tobjects.Thequestion of ceasingabruptly.Ifso,minoractivityreminiscent as thestarevolvestowardmainsequence,instead degree; however,amongthehundredsknown,three whether suchactivityexistsisnoteasilyanswered because allTTaustarsareerraticallyvariabletosome variable onthebasisoffiveobservedflare-upsoccur- unusual starscanbecited. of theFUOriphenomenonmightbepresentinolder One Harvardobjective-prismplateobtainedwhenthe ring atspacingsof5to13years(McLaughlin1946). grams takenatanintermediatemagnitudedemon- in emission,andastrongLiiÀ6707absorption.The with thevariableatminimum,confirmsthis: Fe ii,whicharenotcharacteristicofnovae.Slitspectro- star wasbrightshowedemissionlinesofH,Can,and unfortunately, thespectrumwasnotobservedduring best-observed maximumwasin1955-1956,shown strated thattheobjectwasinfactaTTaustar(Herbig absorption spectrumisaboutMOVwithHaandHei this event. Figure 14.Thestarwasbrightforabout250days; clouds, andisattimesquiteactive,risingquicklyfrom intervals thestarcanremainquiescent.Atminimum, episodes, thesealmostUGeminorum-likemaxima minimum lightforintervalsof150to700daysbefore 1950). ArecentLickspectrogramoftheredregion, type isMOV.Thespectrumnearmaximumhasbeen the spectruminredisunmistakablythatofaTTau subsiding again(seeFig.15).Duringthemostactive occur withspacingsof1-2years.Thenforlong narrow low-excitationlines,notablyofFei. star, withHainemissionandLiiÀ6707strong;the took placein1894,1943,perhapsmorethanonce or ofanyotherTTaustar:itiscrowdedwithrather observed atLick,butitisquiteunlikethatofFUOri Tau appearsasadoubleTstarof3"separation between 1946and1950,in1974.Normally,UZ attained =11.0.Afragmentarylightcurveforthe because ofmajormaximaobservedin1921(Bohlin that in1921itwastheeasterncomponenterupted correspond toaboutV=12.9,i?—KH-1.3. Several othermaximaoflesseramplitudeprobably unresolved imageofUZTauonBohlin’splatesshow and smallAm.Thetwotogetheratminimumlight type hadappeared.About5 weekslater,thevariable was theeasternstarthatactive.Eventhough Measures ofthepositionphotocenter (Herbig, unpublished).Joy(1942,1943,1945),asthe (visually), arichemission-linespectrumoftheTTau unfortunately nospectroscopic observationswere was 1magstillbrighter(in integratedlight),but object hadthenbrightenedonlybyabout0.4mag the spectrumofUZTau at fullmaximumlightis 1923) andin1924(Esch1924),thefirstofwhich 1921-1922 maximumisshownaspartofFigure16. made atthattime.Theonly informationavailableon 1943 maximumwasjustbeginning,showedthatagainit Bohlin’s (1923)remark,from avisualobservationwith EXLupi wasatfirstthoughttobeanova-like VY TauriisattheedgeofTaurus-Aurigadark UZ Tauriwasformanyyearsregardedasanova Vol. 217 1977ApJ. . .217 . .693H No. 3,1977 eastern componentatminimumhasbeenclassified refractor, thatthespectrumappearedcontinuous.The an ocularspectroscopeontheStockholm16cm lines ofH,Hei,[Oi]arepresent,LiiÀ6707isstrong, in theredasMltoM3VbyHerbig(1977);emission in theblueasdM1.5ebyJoy(JoyandAbt1974) the FUOrioutbursts,butismuchmorefrequent. and thespectrumisthatofaconventionalTTaustar. variables isofsmallerrangeandshorterdurationthan as theFUOristars.TheeruptiveactivityofTTau shows sectionsoftheirlightcurvestothesamescale M' valuesforthesethreevariables,andFigure16 the othertworarelyeruptivestars.Butthismaynot the same:veryactiveVYTaustandsapartfrom The detailsofthebehaviorTTaustarsarenot identical atminimum,andthesimplesthypothesisis be afundamentalmatter.Thespectraareessentially surely theonlyonejustifiedatthistime,namely,that it canoperateatdifferentscalesinobjects. tively activesmall-rangevariablesaredrivenbythe the physicalmechanismsresponsibleforthesespas- process limitedtoaminorityofyoungstars,andthat modic eruptionsisthesameinallthree,thatita theoretical guidancecanbeprovided,aconvincing the FUOrivariables,cannotbetaken.Unlesssome discovery ofexampleshavingintermediateproperties. connection betweenthetwofamilieswillrequire same phenomenonthatoneseesonalargerscalein pg matter intheinnersolarnebulacanbehypothesized. Orionis-like eruptions,thensomeoftheeffectsupon Certainly, dustgrainsnearthestarwouldbemelted with analbedoAz0.5wouldhavetheirtemperatures raised toT=1500Katadistanceof TqU =6500KwhenR\1R©,thenlargegrains connection withtheinfrared excess(§III/)would or vaporized.If,asforVI057Cygnearmaximum, Very smallparticlessuch as thoseconsideredin possible thatthechondrules—primitive, roundish attain thesametemperature atabout1.5AU.Itis g Table 9Bcontainsdataonthelightvariationsand However, thelargerstep,toclaimthattheserela- If theyoungSununderwentoneormoreFU © American Astronomical Society • Provided by theNASA Astrophysics Data System 21 d) ApplicationstotheEarlySolarSystem Fig. 14.—The1955-1956maximumofEXLup.Theobservationsarevisualestimates(BatesonandJones1957). r =(T*/r)iR*(l-A)' = 0.5AU.(3) g ERUPTIVE PHENOMENAINSTELLAREVOLUTION 1955.0 1956.0 1,2 _1 -1 -2 16-2_ -3 4 14-2_3 9 15-2 2 _1 14 meteorites—may havefrozenfromdustmeltedon millimeter-sized objectsfoundembeddedinchondritic in thecaseofSuntherewasmorethanone in themeteoritescouldprovidesomeevidencewhether remelting episode. such anoccasion.Itwouldbeinterestingiftherecord VI057 Cygcouldexertasignificantdynamiceffecton circumstellar dust.Theparticlesizerangeinwhichit would beeffectivecanestimatedasfollows.The essentially filledthestarline.Itisdifficulttore- complex structureoftheCanlinesobservedin1971 construct thisbackground“continuum,”butan (Fig. 4)wasseenagainstabroademissionfeaturethat relate logtV/btot=Tref\Nlmcb, equivalent widthofthe—210kmscomponent attempt todosoleadsaroughvalueforthe where NistheCancolumndensityandb With anoscillatorstrength/=0.69,onefindsthat Doppler parameter,byastandardcurveofgrowth. (for example)ifb=¿>c/A8kms,thenA A3933 ofJF=685mÂ.FromÀ3933alone,onecan the backgroundthereismuchtooconfusedby cm. Unfortunately,althoughthesamefeatureat resolution ofthesespectrogramsistoolowfora presence ofHeforanestimateWtobemade,and 1 x10ionscm;if6=12kms,A=1.5 if thesolarsystemmassratioofallelementstoCaby direct determinationofb.Ifitisassumedthat6# a valueofbtobedetermined.Furthermore,the in thehigh-speedshellisp=NxymJzgem,where that theshellsmustbethinnerthantheirseparation thickness oftheshell.Forlatter,onecansayonly raç isthemassofaCaatomandzline-of-sight mass, x=1.410,holds,thentheaveragedensity A0K ejected atthestartofoutburst;therefore,zä 10 ionscm;if6=20kms,A2x x at thattime,whichwasabout5x10kmiftheywere a a \¡y isthefractionofCaatomsthatexistasn,and 10 kms“,thenNxionscmatthattime.If where r/rexpressesthe dependence ofpuponr, K v uponadustparticleofradius ais — 210kmsispresentintheCailA3968linealso, c a 10 cm. 0 It alsoseemsthatthehigh-velocitygasejectedfrom The forceexertedbythismaterial arrivingatvelocity 1957.0 2 F =7Tpvra/r, (4) 0 711 © American Astronomical Society • Provided by the NASA Astrophysics Data System 1977ApJ. . .217 . .693H 16 -3 in lightofthepresentresults.Thefirsttwothese phasized in§Va,suchexplanations(Poveda1965; categories representonce-onlyevents,whichfacethe under severalgeneralheadings,whichwillbecriticized than aboutcentimetricsizewillbedrivenoutwardfor is notknown;butcertainlyj»1.Thereforeunder that thebasicphenomenon is intrinsictothestar. continuing changesinT^fand RofVI057Cygshow seem ruledout:thespectroscopic activityandthe objections of§Nb. zjv, orseveralmonthsundertheseassumptions.The this setofcircumstances,circumstellarparticlesless the distancefromstar.Onotherhand, curves ofUZTau,EXLup,andVYTau.ThemagnitudesLuparevisual;allothersphotographic. in thepast,speculationhasalsoassignedtoso- leaving behindthelargerlumps.Thisisarolethat, finer dustandgasfurtheroutinthesolarnebula, 4 x10“Aycm.TheionizationcorrectionforCa,y, gravitational forceuponthatparticleis Larson 1972;CohenandWoolf 1972;Welin1973) of theoutbursts.Thesesuggestionsareclassifiable called “TTaurisolarWind.” large uncertaintiesinvolved,particularlyinthevalues as longthegasisimpinginguponthem:foratime and particlepressureexceedsgravity,F/F>1,for from theseeruptionswillhavetheeffectofdriving Nevertheless, itdoesappearthatthehigh-speedshells all particlessmallerthanacriticalradius= where s=3gcmisthedensityofsolid.Thus of Nandy,makethisestimateaveryapproximate. G c c There hasbeennolackofproposalsforthecause 2. Permanentstructuralreadjustment ofthestar.The Fig. 16.—ComparisonofsectionstheearlylightcurvesFUOrí,VI057Cyg,andVI515Cygwithfragments 1. Dissipationofacircumstellarscreen.Asem- © American Astronomical Society • Provided by theNASA Astrophysics Data System VI. COMMENTSONSUGGESTEDEXPLANATIONS 32 W 2 F =47rGæt*ûs/3r,(5) F 4zsGm*a’ g G F _3Nxymrv... OF THEPHENOMENON c&0 ERUPTIVE PHENOMENAINSTELLAREVOLUTION 3 45 proposal (Grasdalen1973)thatV1057Cygwasastar moved toitsproperradiative-equilibriumevolutionary infrared source,andbecausetheradiuschangeduring track nowseemsimprobableasthestarfadesandgrows of 89ttwhichfollowingtheoutbursthadfinally tained bytheenergyreleased insuchaneventfor the flare-up,ofVI057Cygatleast,wasinopposite the starappearedtobeejectingmaterial.Thesugges- that whichledtoGrasdalen’smassestimate,suspect. cooler. Thespectralpeculiaritieswouldinanycase is about10L,andthiscould inprinciplebemain- the forbiddenregiontoaHayashitrack(Herbig1966) tion thattheflare-uprepresentsrapidcollapseacross tion componentofHeA3970.Thereforeatthattime is reallyastarof8mostunconvincing,nor tions. UlrichandDrake(1975,unpublished)have tion oftheriseinFUOriandVI057Cyg(hundreds the emergenceofashockwaveatstellarsurface make aconventionalatmosphericanalysis,suchas If anobjectlikeJupiterfelltothesurfaceofa1 sense. known examplescameupfrominvisibilityasapure now alsoappearsuntenable,becausenoneofthe by thesuppressionofA3968shortwardabsorp- has beenobservedinotherTTaustars,andiscaused points intheoppositesense.ThespectrumofVI057 recently takenplace.Infact,whatevidenceexists there anyevidencethataccretiononscalehas response toarapidaccretionarybuildupfromabout (Appenzeller andTscharnuter1974,1975),thedura- several decades.However, the initialflare-upof about 5x10ergs.Thepresent luminosityofFUOri star, thekineticandnuclear energyreleasedwouldbe suggested thattherewasastructuralreadjustmentin slow thermalpulseismoreinaccordwiththeobserva- at leastanorderofmagnitudelonger.Theconcepta On thepossibilitythatinitialbrighteningrepresents strongly inemission,whileCanÀ3968isabsent.This Cyg atminimum(Fig.2)showstheCanA3933line of days)istoolong;therisetimeforVI515Cygwas 1 to89tt-Asindicated,theclaimthatV1057Cyg 0 o 0 3. Resultoftheinfallalargeobjectontostar. 713 1977ApJ. . .217 . .693H 4 3 reaches thepointwhereignitionbeginsatbottom; period oftimebysurfacereactionsasarebelievedto proposal isthatDmightbeproducedoveralong purely adhoc,andfacesseriousdifficulties.The durations actuallyobserved. star wouldbeverysuddenandnotoftheextended rapidly consumetheremainder.Althoughthisidea in aconvectionzonetooshallowtoreachthetempera- take placeinsomesolarflares(Anglin1975),stored recurrent outburstsandthesubsidenceofactivity ture requiredforDburninguntiltheconcentration tions. Butitisdoubtfulthatarealstarofthemass would berequiredoverthe10yearsbetweenerup- has attractivefeatures,suchastheabilitytoexplain would behaveinthisway.Shevchenko(1975)has and asthetemperaturethenrises,D(/?,y)Hereactions (about 32tt)appropriateforsuchashallowzone as thestarages,anenormousrateofDproduction Petrov (1976)haveproposedthatTTaustars enon. considered othernuclearexplanationsforthephenom- phenomenon, transfermostofthesubphotospheric energy intothehighatmosphereviamagnetohydro- motions and,muchasinonetheoryofthesunspot strong surfacefieldswhichinteractwithconvective rise tothefullradiativevalue,thuscausingFU field shouldforsomereasondropbelowacritical 714 would beunderstandable.Ontheotherhand,it repetitive flaring,andadecayoftheactivitywithage, value (afewthousandgauss)normalconvectionwould depressed bythecorrespondingfactor.Ifsurface dynamic waves,sothatthevisualsurfacebrightnesses finally subsides,thestarwillproceedtomain mum light;i.e.,thatwhenthemagneticactivity implication thatthenormalstateofstarismaxi- conflicts withthepointofviewthispaperinits Orionis-like flareup.Theideaisattractiveinthat abruptly resume,andthesurfacebrightnesswould sequence onatrackappropriatetolargemass. the originalstellarsurface.Butwhystarshould star, andthatanopticallythicklayerdidformabove to theextentthatmaterialwascertainlyejectedby increase areboththeconsequencesofsomeinternal mian’s (1971)suggestionissupportedbyobservation in apreexistingenvelopeoffastparticles.Ambartsu- 0 phenomenon isasyetavailable. perturbation. simpler toassumethattheejectionandluminosity suddenly begintoejectmatterisunexplained.It plausible explanationsisa forward step.Somefacts enon, althoughtheelimination ofsomeseemingly proportional increaseinunderstanding ofthephenom- of theFUOriclassfromone tothreehasnotleda are nowestablished:based onasinglefortunate 4. Subsurfacenuclearreactions.Thismechanismis 5. Strongsurfacemagneticfield.Gershbergand The enlargementofthenumberknownexamples In short,noconvincingexplanationoftheFUOri 6. Thermalizationbyejectedmaterialoftheenergy © American Astronomical Society • Provided by theNASA Astrophysics Data System VII. FINALREMARKS HERBIG 4-1 inference fortheothers,progenitorsareTTau preoutburst spectrogramofVI057Cygandreasonable nosity increaseofV1057Cygisnowseentobethe result ofalargeincreaseinsurfacebrightnessand stars; thereisnochance,forexample,thattheyare the outerlayersofstarhasbeenconstructed;there time oftheeruption.Itisclearalsothatrate rather slowly,incontrasttotheejectionofshells modest increaseineffectiveradius.Thesetakeplace accreting interloperssuchaswhitedwarfs.Thelumi- velocity canaccountforsome.Thesignificanceofthe high-velocity gas,althoughitisunprovedthatallthe three eventsinabout80yearsisastatisticalaccident— is probablyresponsibleforthelargeinfraredexcesses, shells observedatVI057Cygwerelaunchedthe while moredistantdustproducesthecuriously ubiquitous dustremainsconjectural:nearbymaterial differ greatlyfromonestartoanother.Nomodelof it isdifficultnottoconcludethattheeruptionsare a deepatmospherewithdepth-dependentexpansion are majorpeculiaritiestobeexplained,butpossibly of thebrighteningandsubsequentdeclinecan when morecasesarediscoveredandcarefulallowance repetitive, andwithasurprisinglyhighfrequency. and ifanythingthatnumbershouldbealowerlimit— ordered reflectionnebulae.Unlesstheobservedrateof is madeforincompleteness.Inafewdecades,some The valueof10“yearstarthatresultsfromthe perhaps somepasteventsthatwereoverlookedcan Welin, andW.Wenzelhavebeenexceedinglygenerous, encourage seriousconsiderationoftheproblem,as conditions thatobservationhasnowprovidedshould graphs. Onthetheoreticalside,tightenedboundary be detectedinTTauri-richregionsonoldphoto- T Taustar.Notonlyshouldnewexampleserupt,but have returnedtominimumlight,anditshouldbe simplest interpretationofthedatawillbesuperseded described inthisLecture.Spacelimitationprohibits have helpedmeinonewayoranotherduringthework distinct fromqualitativeoruntestableconjecture. questions willbeclarified:VI057Cygmaybythen photometry andphotoelectricscans,respectively. Drs. P.Bodenheimer,G.Grasdalen,H.Hippelein, specific acknowledgment,soIcanonlysaythat obvious whetheritresumestheappearanceofanormal I. AppenzelleroftheLandessternwarte,Heidelberg, I acknowledgealsothecourtesiesextendedby advice. Messrs.E.A.HarlanandR.P.S.Stoneat Simon, andS.C.Wolffhaveprovidedmuchgood and Iammostgrateful.Drs.A.M.Boesgaard,T. C. Lada,F.Lo,K.M.Merrill,W.Morgan,G. D. Hoffleit,G.R.Knapp,L.V.Kuhi,B.Kukarkin, Mount Hamiltonhavecontributedabsolutelyessential and P.-O.LindbladoftheStockholm Observatoryin Directors H.W.BabcockoftheHaleObservatories, spectrograms anddirectphotographs,UBV allowing metoexamineplates intheirfiles.Mr.D.R. cooperation fromthescientific, technical,and Soderblom hasprovidedinvaluable computingand observational assistance,and Ihavereceivedsuperb I amdeeplyindebtedtothemanycolleagueswho Vol. 217 1977ApJ. . .217 . .693H written attheInstituteforAstronomy,Universityof 1Q7SAvtrAn4ft^97 Ambartsumian, V.A.1971,Astrofizika,7,557. Adams, W.S.1949,Ap.109,354. administrative groupsatSantaCruzandMount Anglin, J.D.1975,Ap./.,198,733. Andriesse, C.D.1976,M.N.R.A.S.,175,13P. Hawaii, andIappreciateverymuchthehospitalityof Appenzeller, I.,andTscharnuter,W.1974,Astr.Ap.,30,423. Hamilton. 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LI 69. 715 1977ApJ. . .217 . .693H American Astronomical Society •Provided bythe NASA Astrophysics Data System o in r^ o 0m Ö to < o if) O 3 O r- O CL r^ cn LÜ Ö PLATE 5 3 00 w 318 -1 03 °< s "Ö >r^.S2^ H S r" :>+->s-hcc3 ^ >43£3O n 2: po.'ö^ irí ^(ü* ¿3 CÇDC.P Ü (DfSol^ C 73>vî * ,Pajö e-S gs-s— fe 7-“ P ^CD>+J c ° Oo^ G g G ö G c °O043$ ! 43bO^2?43 OiH43 ¡ ij.p^ ¡êig^ 5i3^ 2g i. 1^1“ 'i£g| ^jlso »Sc^o X> &PO l-H ^P43 & 4H ^ o>S" rv Q< ^ O43o g< 05J_lO c'Sq'- íál c P 1977ApJ. . .217 . .693H © American Astronomical Society •Provided bythe NASAAstrophysics Data System PLATE 6

Fig. 4.—The structure of the Ca n H and K lines in VI057 Cyg, 1971-1973. Thfe wing of the broad emission line that filled K during 1971 can be seen just longward of the complex shell absorptions. The anomalous strength and displacement of the —310 km s-1 feature in H and K on the single exposure of 1971 June 29 is obvious. In 1972 and 1973, the Ca n shell components may still have been present but were almost lost in the stellar H and K. The Ca n line at — 16 km s"1 is interstellar. The original dispersion was 16 Â mm-1, coudé spectrograph, 120 inch reflector. Herbig (see page 697) 1977ApJ. . .217 . .693H _1 structure anddisplacementoftheabsorptioncomponent,areconspicuous.Thegrowingcomplexityspectrum spectrograph, 120inchreflector. Herbig (seepage699) reflects theincreasinglylatertype.Thesespectrogramsweretakenwithseveralimageintensifiers,andplatescalescouldnotbewell matched, hencethestaggeredappearanceoflinesespeciallyonright.Theoriginaldispersionwas34Âmm,coudé Fig. 6.—TheHaregionofVI057Cygfrom1971to1975.ThefadingtheemissioncomponentHa,andchangesin © American Astronomical Society •Provided bythe NASAAstrophysics Data System JL Ha 6707 L¡ I 1 1971 FEB10 1973 MAR24 1972 MAR4 1974 JUNE4 1975 APR29 PLATE 7 AUG 29 AUG 13 APR 15 JULY 23 NOV 8 MAY 16 AUG 16 1977ApJ. . .217 . .693H is about166".Inthisandthefollowingdirectphotographs,northaboveeasttoleft. emission spectrum.ThescaleofthisandFig.11canbeobtainedfromthefactthatangulardistancebetweentwobrightstars Herbig (seepage705) Harlan. ThetwopassbandsincludeandexcludeHa;thecomparabledensityofnebulosityonbothshowsthatitcannothave an Fig. 10—DirectphotographsofthenebulosityatV1057Cyg,takenin1971AprilandMaywithCrossleyreflector,byE.A. © American Astronomical Society • PLATE 8 « ^• # 6000-6700A ‘’5200-6400A Provided bytheNASA Astrophysics Data System 1977ApJ. . .217 . .693H © American Astronomical Society •Provided bythe NASAAstrophysics Data System PLATE 9

1973 MAY 30 * ^ 1*974 MAY 30 ; ^ 1975 SEPT 30 Fig. 11.—Direct photographs of the nebulosity at VI057 Cyg between 1971 and 1975, showing the slow fading of both nebula and star. These plates were taken in red light (6000-6700 Â) with the Crossley reflector; the exposure time was 1 hour on Kodak 103a-E emulsion behind a Schott RG-1 filter. Herbig (see page 705) 1977ApJ. . .217 . .693H © American Astronomical Society •Provided bythe NASAAstrophysics Data System PLATE 10 o o K)

Fig. 12.—Direct photographs taken with the Crossley reflector, showing the brightening of V1515 Cyg between 1912 and 1975. The first two plates were centered on NGC 6914, which is out of the area shown here. The bright nebulous star in the upper left is BD +41°3731. Herbig (see page 706)