195 9MNRAS.119. .150E as 6700Athequalityremainsgood,andperfectlyadequateforlineidentification there areavailablefourdifferentdispersionsattheCassegrainspectrograph forbidden nebularlinesweretaken,asfar possible,fromIraS.Bowen(3), separate Hartmannformulaeoverlappingat4500 A.Thewave-lengthsofthe and thedeterminationoflinestrengths.\ has beensoclassifiedinthepast,and,forlast-named,velocityisnot them, NGC6302,doesnot,strictly,rankasaplanetarynebula,althoughit wave-lengths, e.g.ofunidentifiedlinesand of blends,fromA.B.Wyse(5). exclusively forCassegrainwork.Thiscameralenshastheenormousadvantage at theNewtonianfocus(2).Thec-dispersionofformerinstrument the bestmethodsofinvestigation.Thisispartlyduetofactthat and aconsiderableamountofexperimenthashadtobedevoteddiscovering (known asa,b,c,andd)(1),togetherwiththesmallspectrographforuse methods forobtainingdifferentkindsofdataare,toanextent,inconflictwith course ofamoregeneralprogrammeonplanetarynebulae.Thesecond motion andspectrumforthesefivenebulae,whichhavebeenobservedinthe of permittedandotherforbiddenlinesfrom Charlotte E.Moore(4),andother of producingaspectruminexcellentfocustobeyond5000A,whileasfar (49 A/mm)hasprovedbyfarthemostuseful,andisnowemployedalmost given. with thenormalforstellarradialvelocitywork, inordertogiveasatisfactory blends, linesofuncertainwave-length,andall linestotheredofA^.Aniron each other. number ofcomparisonlines.Theresultsfrom theCassegrainspectra(TableI), In derivingvelocities,thelinesusedwereselected soastoexcludefaintlines, arc comparisonspectrumwasused,withthe exposuretripledascompared clear thatanadequate coveragefordeterminationofvelocityand spectral show goodagreement with thoseofCampbellandMoore(6).It now seems © Royal Astronomical Society • Provided by theNASA Astrophysics Data System These notesaimatprovidingdetailsofstructure,radialvelocity,internal Planetary nebulaeshowaverygreatrangeinformandsurfacebrightness, For thereductionoftheseplatesnewtableswerecomputedusingtwo For thedeterminationofradialvelocitiesanddescriptionspectra, m0 motions andformoffivesouthernobjects,NGC3918,6302,6326,IC4776, are reported. and Anon16*1i3*5,—5152',madewiththeRadcliffe74-inchreflector, NOTES ONFIVESOUTHERNGASEOUSNEBULAE The resultsofobservationsthespectra,radialvelocities,internal (Communicated byH.M.AstronomerattheCape) (Received 1958November27) David S.Evans Summary 195 9MNRAS.119. .150E 11m characteristics, forthoseobjectsobservablewiththeCassegraininstrument, can besecuredwiththreeplatesofeach:onefairlyshortexposure(e.g. No. 2,1959Notesonfivesoutherngaseousnebulae NGC 3918 Anon 16i3*5 each pushedasfarispracticable,oneblue(i03aO),andpanchromatic is itworthwhiletoattemptsecurespectraonhigherdispersionforastudyof proved practicabletoextendanexposureovermorethanonenight,and,in (i03aF). Theselongexposuresarelimitedbythefactthat,sofar,ithasnot by Wyse(5).Onlyifanexaminationofthelinesinvioletrevealsstructure for thestudyofstructure.Atsamefocussmallspectrographgiving IC 4776 consequence, the“depth”reachedisusuallynotasgreatthatattained internal motion. 1-2 hours),onfastblue-sensitiveplates(Kodaki03aO),andtwolongexposures, information mightbegainedconcerningthesystematicandaccidentalerrors a dispersionof400A/mmhasbeenusedtoobtain“deep”spectrabright objects, ortoreachveryfaintones.Itmightbehopedthat,byduplicating very faintsouthernplanetaries.Unfortunately,furtherworkwillbenecessary from asinglespectrumcouldbetolerated.Forusefulresultsontheplanetaries, before thishopecanberealized.Forobjectswithlargevelocitydispersion, of Newtonianradialvelocitiestoopenupthewholefield observations ofthesameobjectatCassegrainandNewtonianfoci,sufficient probable errorofaNewtonianresultbyeight timesascomparedwiththe however, thisfiguremustbereducedbyafactor ofatleastfour.Otherthings whole dekker,thelinesmaybemeasuredat mid-dekker,andafairlywell- are curved:forallextragalacticsystemsyet observed,thespectrumfills being equal,thereduceddispersionalone may beexpectedtoputupthe such asextragalacticnebulaeorglobularclusters,aprobableerrorof20km/sec planetary nebula. and thisintroducesanotheruncertainty.Again, thebestlinesforextragalactics N, usuallythebestlines forplanetaries.Finally,thelowdispersion ofthe are HandK,wherethe prismaticdispersionistwiceasgreatnear and established curvaturecorrectionapplied.For theplanetaries,difficulties Cassegrain c-dispersion.Thelinesgiven by theNewtonianspectrograph of offsetguidingaresuchthatthespectrum isnotalwayscentrallyplaced, of thecomponents agivenblendusuallyvaryfromplanetary nebulato Newtonian spectrograph leadstoblendingoflines,andtherelative strengths 2 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Direct photographsattheNewtonianfocushaveusuallybeenavailable Nebula 0 6302 6326 -51 52' Maximum exposures(minutes)forvarious dispersions andemulsions(103aseries) a:0 ciOc:Bc:Fd:BN:0 90 135*...260 270 120 60 ...1S0 63 320240 * Hgsensitized. Table I 180 135 150 155 120 180 — 38-o±o*8 — i6*i±0*5 + 8*8±o*6 +19*1 ±0*7 Fc +mTotal -36 —16 *4 + 11 +18*8 plates 151 9 7 5 5 2 195 9MNRAS.119. .150E intensities havebeen“builton”,usingtheobservedin have beenfoundtobesurprisinglyconsistent),adjustedforplate-sensitivity in thevariousspectra,thesebeingassociatedwithnumbersempiricallyindicating corresponds toastrongerline.Thefiguresarebasedoneye-estimates(these represent tnieline-strengths:itisonlyhopedthat,ingeneral,alargernumber the relativeline-strengthswithineachspectrum.Noclaimismadethatthese Newtonian spectra. according tothemanufacturer’sspecifications.Forextremeviolet still muchlessthanintheCassegrainspectrograph,sothatafarbetteraccount well shown,and,althoughthereismuchabsorptionbelow3900A,this fast, andpermitsobservationsofobjectscompletelyoutreachthe of theobjectsdescribedinthesenotes.InTableIIarelistedlinesfound of thevioletandnearultra-violetspectrumisrendered. information canbederivedfromthesespectra.Theinstrumentisextremely Cassegrain spectrograph.Forthebrightersystemscontinuumisusually of planetarioscannotyetbeobtainedwiththeNewtonianspectrograph,much i $2DavidS.EvansVol.119 4387-93 4471-48 44I5-6 4287-40 4267-2 4363*19 4340 *47 4076*35 4244-00 4207-5 4199-9 4177-21 4120-8 4101-74 4097-31 4068*60 4026-1 3994 3970-07 3967-47 3888-8 3868-76 3835*39 3819*61 3797*90 3770-63 3759*87 375o*i5 3726-04 3728*80 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System After thesepreliminaryremarkswemaynowreturntoadetaileddiscussion However, eventhoughsatisfactoryvelocitydeterminationsofthevelocities Hi( +Nm) O n-[Fe11] He 11-Nin He i-He11 He i-Oii H i-Hei [Ne in] [Ne in] [O in] [Fen] [Fen] [Fen] N in [S11] [S ii] He i [On] [On] He i O in He i C ii Hi Hi Hi Hi Hi Hi Ion NGC 391816*13*1.563o26326 ft. 29 20 18 12 17 26 12 9 3 3 3*5 i*5 i*5 i*5 2*5 i*5 8 i Table II { {ft. {.5 -51° 52' Anon 4O IS ft. ft. ft. 2 1-5 P I I ft. ft. ft. ft. ft. ft. ft. ft. ft. 16 17 12 o-i 0-3 0-2 3 0-2 23 17 23 18 12 5 0-8 o*5 0-6 0*4 3*3 0-2 i*5 i-i IC 4776 14 21 10 16 ii 0-2 9 0-3 0- 7 0-7 6 0-9 9 3 1- o 195 9MNRAS.119. .150E No. 2,1959 in thepresentstudyshow doublingofthelinesonhighdispersion. Ordinary bright object,ofdiameter 13",withnodetectablecentralstar.Thespectra used photograph (Fig.9,Plate 9).Itwasthenfoundtobeasimple,round, very velocity of20*1km/sec. OnoneplatethewholelengthsofÀÀ3686 and3967 measures oftheseparation onthreea-dispersionplatesgaveamean expansion 4523*60 4552*65 4541*59 4628*8 4640*9 4634*16 4861*33 4649*1 4871*58 4711*9 4658*1 4921*93 4769*3 4733*7 4724*7 4701*0 4685 *68 4958*93 4740*20 5006*86 5207*2 5200*41 5197*94 5015*68 5754*57 6242*5 5875*6 5978*4 6363*82 6312*06 6300*31 6403*7 6253 6548*06 6562*82 6493 6461 6435*10 6583*37 6678*15 6730*78 6716*42 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System This objecthasbeendiscussedbyEvansand Thackeray(7),whogivea hmo m NGC 3918,ii47*8,—5654'(1950),1=262° 6j i=+4°*4. [Fe iii]-0ii [A iv]-Hei N111-O ii C 111-Oii [Fe in] [Fe in] [Fe in] Si in? [Om] [Om] [A iv] He ii [S in] He ii N in ? Sin [Nn] N in [Nn] [Nn] [Ni] [Ni] He i [Ä v] He i [S ii] [Su] [O i] [O i] He i On Ion He i Hi Hi Notes onfivesoutherngaseousnebulae153 1m NGC3918 16*i*5NGC6302NGC6326IC4776 3 1000 300 100 324 123 Table II—{continued) ft. ft. 51 10 16 13 ft. 30 55 13 ii 13 7 2 i*5 8 6 5 9 -51° 52' Anon 100 17 ft. ft. ft. 4 8 { 1000 2100 1200 v. ft. V. ft. 320 100 470 170 ft. ft. ft. 71 10 35 14 15 ii 30 o*9 3 4 5 6 8 1040 294 100 232 18 0*7 o*8 i*3 640 240 100 767 156 77 41 37 ft. ft. ft. 15 0*3 o*5 o*4 6 3*5 i i 5 195 9MNRAS.119. .150E into twoblobsofnebulosity, oneofthembeingpointed.Byan accident, than twoarcsofnebulosity tonorthandsouthofthecentralstar. Alonger of Horrors”planetarynebulae. the latterisbadlyblendedwithotherlinesofsamemultipletoccurring the linelistofTableII,thatthisobjecthasonlyjustdetectable, exposure suchasthat shown inEvansandThackeray(7)plumps theseout seem tobeattributableforbiddenFein,andthedegreeofexcitationis and ATj,lessthanone-tenthasstrongHj8.Mostofthelinesinspectrum of acentralstar.The“line-strengths”TableIIsuggestanobject not inthecaseofthiscandidateforwhathasbeencalled“TheChamber fairly highexcitation. which candefinitelybeidentifiedasanabsorptionlineoriginatinginthespectrum close enoughtoitformablendattheverylowdispersionwhichobtains. here. The[Fein]lineatÀ4658istwiceasstrongA^,anditmaybethat phenomenally low.Anexampleofthetroublegivenbyblendsmaybeinstanced For anyordinaryplanetary,itwouldbefantastictofeelsuchconcern,but to bemeasurable—andarapiddecrement,interpretedastheheadofBalmer a completelensshape.OntheNewtonianspectrumthereiscontinuum Plate 11),butisfartoofainttobewithinrangeoftheCassegrainspectrograph. series. Thenumerouslinesrecordedonthisspectrum,andtheverysmall to measuretheshapesindetail.Itwasfoundthatwereconsistent Recently, twoNewtonianspectrahavebeenobtained.Itwillbeseenfrom either ontheNewtonianplatesorintermsofline-lengthsCassegrain scale, makeitimpossibletobedogmatic,butthereisnothinginthecontinuum detectable downtoapproximately3550A;itshowsafinestructure—too spectra, and,indeed,thedoublelinesfadeawayattheirendsbeforeforming and, onanother,oftheformerlineweresowelldefinedthatitwaspossible with theuniformexpansionofashelldiameter18"-4velocity 154 DavidS.EvansVol.119 19*9 km/sec.Thediametersoinferredisrathergreaterthanthatobserved, © Royal Astronomical Society • Provided by theNASA Astrophysics Data System As seeninthetelescope thisgrislycreatureseemstoconsistofno more This systemisalsoincludedinEvansandThackeray'slist((7),Fig.15, m,0 Fig. i.—Anon,16bi35,—5152'.C/.EvansandThackeray ((7)2%.15,Plate11). hm0 Anon i6i3*5,—5152',/=299°-3,—2°*i. 195 9MNRAS.119. .150E Monthly NoticesofR.A.S. © Royal Astronomical Society •Provided bytheNASA Astrophysics DataSystem m 1956 August8,lO^aE-i-Wratten filter/205,45. Scale: 3"-9/mm. NGC 6302 David S.Evans,Notesonfivesouthern gaseousnebulae Vol. 119,PlateS 195 9MNRAS.119. .150E this systemhasbeenincludedattheedgeoftwodeeperplatestakenon1958 is nodekkerforthenebularspectrum(only for thecomparison),extreme August 16byDrThackerayand,particularlyontheredplateofpair prints is3to4minutesofarc.There no distortionofthelineson the intensitydropatcentre.OnNewtonian spectrum,wherethere are concerned,buthalfadozenstarscanbepickedoutbyinspectionwhich spectrum, wheretheoxygenpairatA3726-28 isblended.Onthisfilm, length ofthelinescorrespondstoaboutno". Theoveralldiameteronthe are brightontheredplatebutalmostinvisibleblue. in thesystem,suggestingthatitismuchlargerandmoredistantthananordinary luminous gas,shapedlikethewingsofabutterfly,separatedbyrelatively and onlyio°fromthegalacticcentre.Thesystemisillustratedin indicates aregionofdoubtfulnebulosity. indicate theformasshownonshortexposures.Thedottedareatonorth accompanying plates.Thesmallsizedreproductionshowsashortexposure complete theant-likeform(Fig.1).Thedottedlinessuperposedonblobs of filmsensitivity(i03aO). at most5km/sec.Thelinesinthevioletwere onlydetectedontheNewtonian which appear.Thetwoprintsarewell-matchedasfarthebrighterstars taken underconditionsofsuperbseeing.Referencetothelistline-strengths side. Anotherstrikingfeatureisthelargenumberofextremelyredstars shows that,althoughHaisverystrong,À6583strongerstill,andmustreally (lOßaE plusGG11filter),itcanbeseenthatthecreaturehaslegswhich predominantly transverse. Apossibleinterpretationisthatof a collision nebula, withthesliteastandwest.Thelines oftenresembleskittlesshowing exemplified bythestarimmediatelytosouthofcentresystem. from this.Theimpressionconveyedisthatofdynamicinteraction,as the wholeregioncontainsagooddealofgaswhich,inouterparts,islighted these frontsnearthepointwheretheyareclosesttoeachother.Behind planetary. Thetwootherplatesareoflonger,matchedexposures,andwere dark lane.Thereisnocentralstar,butthereareanumberofstarsinvolved blue plate,fromwhichitcanbeseenthatthesystemcomprisestwolobesof continuous emissionwas detected,extendingfromabout3900Ato thelimit be measured,anditisthoughtthatdeviations fromthemeancouldnotexceed near oneofthebrightstarsinfield,andthereisanotherfaintwispSf up inapatchyway.Forexample,twofilamentsformtheletters“ON” structure, stronglyreminiscentofthatseeninsolarprominences.Evidently of platesrepayscloserstudy.Thetwohalvesthesystemincorporateaseries velocity changealong thelines,itmaybeinferredthatmotions are On bothplatesthisshowsapatchofluminosity“bankedup”onitspreceding fronts lieaseriesofwispsgaswhich,intheredplate,showfinefilamentary of opposedshellsorfronts,andtheregionsgreatestluminosityliewithin be responsibleforthemajorpartofdensityonredplate.Thispair Cassegrain spectraduetodifferentialradial velocitywhichcouldprofitably No. 2,IÇ59Notesonfivesoutherngaseousnebulae155 © Royal Astronomical Society • Provided by theNASA Astrophysics Data System All thespectrahavebeentakenbyguidingonbrightestpartof This isaveryremarkablediffusenebula,practicallyinthegalacticplane, Since theformsuggests dynamicinteraction,butthereisnomarked radial 11m0 NGC 6302,17io*4,-3703',b= 12 195 9MNRAS.119. .150E for changeexcepttosplittheblendat4712Ainto4711*34,[Aiv]and revision ofthosegivenbyBowen(3).Teststhereductionourspectra probably bepreferabletousethenewwave-lengths infuturework. 4713*17, HeI,infactassigningthetabulatedlinestoformer.Itwill probable errorofthemean.Sofarasidentificationsgo,thereseemsnoneed using thesewave-lengthsshowamaximumchangeinthederivedvelocity of 0-6km/secandalmostinvariablyaslightreductionintheprobableerror of theresult.Thechangesareneversignificantincomparisonwith 62, 1955).Thenebularwave-lengthsadoptedthererepresentafurtherslight I. S.BowenandR.MinkowskionthespectrumofNGC7027{Ap,J,,122, performance oftheNewtonianspectrograph. has keptmeinformedofhisextremelycarefulandilluminatingstudiesthe irregularly ellipticalnebula”.Wrightidentifiedninelinesinitsspectrum. and toDrT.D.Kinman,who,bothinpersonaldiscussionbycorrespondence for drawingmyattentiontohisrecentphotographsoftheanonymoussystem, the continuumduetocentralstarcanbetracedthroughoutfilm Dr P.A.Waymaninthistask.MythanksarealsoduetoD.Thackeray sensitivity, (i03aO),butnodetailcanbemadeout. The spectrumisveryrich:theexcitationlow.OnNewtonian easy, andIammuchindebtedtotheskilledassistanceofMrJ.Churms as ifthereisarealpaucityorweaknessoflinesinthered.TheNewtonian Plate 11).Itmaybearingnebulawithbrightspotonthering,orsecond with theproductionofshockfronts.Itmaybeprofitabletosearchforradio plates havenotshownupanylinesintheredexceptHa,anditdoesseem star associated.Otherwiseitisnotparticularlyremarkable.Thepanchromatic spectrum showsacontinuumstartingwellbelowÀ3727. emission fromthissystem,which,sofarastheauthorisaware,hasnot previously beennotedasaradiosource. 156 NotesonfivesoutherngaseousnebulaeVol.119 (5) A.B.Wyse,Ap.J,,95, 356,1942. (4) CharlotteE.Moore,Princeton Univ,Cont.20,1945. (2) DavidS.Evans,M.N.,116,659,1956. (8) W.H,Wright,LickObs. Pub.,13,PartVI,1918. (6) W.Campbelland J. H.Moore,LickObs.Pub.,13,PartIV,1918. (3) IraS.Bowen,Ap.J.,121,306,1955. (1) M.W.Feast,A.D.ThackerayandWesselink, Mem,RA.S,,67,51,1954^ (7) DavidS.EvansandA. D.Thackeray,M.N.,no,429,1950. © Royal Astronomical Society • Provided by theNASA Astrophysics Data System Royal Observatory, 1958 November, Note,—A refereehasdrawnmyattentiontothepaperofL.H.Aller, Acknowledgments,—The collectionoftheobservationalmaterialhasnotbeen This objectwasdescribedbyW.H.Wright(8)as“asmallbright This objecthasbeendescribedbyEvansandThackeray((7),Fig.18, Cape ofGoodHope: 11m0 NGC 6326,17i6*8,-5142',/=305°*6,6=-9-. hm0 s IC 4776,i842-6,—33°24',/=329*4 References