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1978AJ. : THEASTRONOMICALJOURNALVOLUME83,NUMBER1JANUARY1978 13 Astron.J.83(1), Jan.1978 axies andofClustersGalaxies (ZwickyandHerzog Since theactualareacovered bytheclusterextends available tousbyC.Kowal, wasusedasthereference beyond thecontourlinegiven intheCatalogueofGal- for SNeappearingintheregion oftheComacluster. of ,hasbeenextensivelysearchedforsupernovae derived bycollectingdatafromrandomlychosengal- of themembergalaxies,itshouldalsoprovideabetter cluster shouldexhibitahighrateofSNproductionand, galactic poleitsuffersaminimumoflocalobscuration properties oftheclusteranditsmembersalsoascon- of thestructureclusteranddistribution These studieshavecontributedtoagoodunderstanding axies ofdifferenttypesandorigin. sample forstudyingtheSNphenomenonthanthose as aresultoftheuniformitymorphologicaltypes and, asZwicky(1961)pointedout,itcanbeobserved tributors ofSNe. light ofthisknowledge,itappearsinteresttostudythe its membersaccordingtotypeandluminosity.Inthe Gregory 1975andreferencestherein)whohaveassem- investigated bymanyauthors(seeRoodetal.1972; northern observatories.Duetoitslargepopulation,the in themorefavorableconditionsbysomeofmajor (SNe) since1958.Becauseofitspositionnearthenorth phological typesforalargenumberofclustermembers. bled acompletesampleofradialvelocitiesandmor- 1963), hereafter CGCG,acircularregion 5° inradius 1974), completethroughAugust 1976andkindlymade II. SUPERNOVAEANDTHEIRPARENTGALAXIES An updatedcopyoftheSNcatalog(Sargentetal. The Comacluster,oneofthenearestregularclusters © American Astronomical Society • Provided by the NASA Astrophysics Data System In recentyearstheComaclusterhasbeenexhaustively 1O average galaxyper600yrhasbeenfound.Therateunitluminosity(1OL)appears members hasbeenisolatedandanobservedrateofsupernovaproductiononeSNper if comparedwiththedistributionofclustermembers.Areliablesample with theaveragelightcurveprovidedameanmagnitudeatmaximumm=15.5±0.2, curves reanalyzed.UnpublishedobservationsarereportedforSN1963c,1963m,and All thesupernovaesofardiscoveredinComaclusterhavebeenidentifiedandtheirlight significantly lowerthanthatpreviouslyderivedforEandSOgalaxies. cluster isused.Thelocationoftheparentgalaxieswithinmayappearpeculiar corresponding toanabsolutemagnitudeM=—18.7ifadistancemodulusof34.2forthe 1962i, whichisfoundtobelongabackgroundgalaxy.FortypeIsupernovae,comparison 0 0 p I. INTRODUCTION SUPERNOVAE INTHECOMACLUSTEROFGALAXIES Asiago AstrophysicalObservatoryandUniversityofTrieste,Italy 0004-6256/78/8301-0013Í00.90 Received 7September1977 Roberto Barbon ABSTRACT hm cluster center,itsmembershipmaybequestioned,since owing tothelargedistance(7.°5)ofNGC4375from of thevelocitydistributionclustermembersbut, value oftheapparentmagnitude attainedatmaximum data onthelight curvesofSNe1962i, 1963c, and distance indicators.Tothisend, besidespresentingnew given byBarbonetal.(1973a) canbemade.Areliable of 9165km/s(Zwicky1965).Thisvaluefitstothetail discovered inthevicinityofinspectedareaexcept The recessionvelocitiesincolumn9aremainlyfrom available photometricdataand theaveragelightcurves maining unclassifiedSNe,acomparisonbetweenthe discussion ofthephotometricmaterialasgiveninSec. Gregory (1975).Othersourcesaregivenasfootnotesto important intheproblemof thecalibrationofSNeas by SNeIintheComacluster maybeinferred,whichis Coma galaxiesareoftypeI.Forthese,andforthere- the center(Roodetal.1972;Gregory1975). large velocitydispersionsarelikelytobefoundonlynear perhaps SN1960jinNGC4375,whichhasavelocity belong tothecluster. 6946 km/swithadispersionof896(Gregory the basisofComahavingameanrecessionvelocity the table.Thelastcolumnidentifiesclustermemberson is consideredbytherespectiveauthorstobeEandSa. thors: NGC4874isclassifiedEbyGregory(1975)and membership ofitsparentgalaxyisprovedonlybythe their parentgalaxiesasreportedintheSNcatalog. give relevantdataontypeandmagnitudeoftheSNe this regionarelistedinTableI.Thesuccessivecolumns spected. AlltheSNeoccurringingalaxiesbelongingto and centeredatcoordinate1257,+28°15'wasin- Different morphologicaltypesaregivenbyotherau- III. Bythesametoken,SN1962ihasbeenfoundnotto Maza andvandenBergh(1976),whereasNGC4944 1975). ForSN1963m,novelocityisavailableandthe Table IalsoshowsthatmostoftheSNefoundin No otherSNeoccurringinComagalaxieshavebeen © 1978Am.Astron. Soc.13 00 00 oo 1978AJ. PQ verted tom'=F+(^pg“E)o>whichdifferfromm 14 RBARBON:SUPERNOVAE color isknownonlyfromt= —5,someofthepremaxi- date ofavisualobservation,(m—F)omayberead observations canbeconverted; sincethebehaviorof shortcoming ofthismethod is thatnotallofthevisual dure alsohastheadvantageof testingtheconsistencyof available, usingthe(m—F)o,trelation.Thisproce- the inferredvalueofepoch ofmaximumíq.A be determinedbycomparingdirectlytheoriginalblue curve” builtupfromdataavailableintheliteraturefor mum observations,ifnotall, cannotbeused. magnitudes withtheconvertedm'or,ifcolorsare magnitudes onlyifreddeningispresent.Thislattercan from Rust’sdiagram.TheVobservationsarethuscon- the followingsixwell-observedtypeISNe:196Id, directly thevisualmagnitudeswithan“averageVlight ual SNeisgivenintheSec.III. able alongiterativeprocedure,basedonfirstguessof case ofaKmgtransformation,ananalogous(m conversion methodsfortypeISNebasedprimarilyon observed magnitudeswiththeaveragelightcurvesof more straightforwardmethodthatgives/qbycomparing magnitudes tothemsystem.Inthesecasesweuseda maximum isknown.Whenthisquantitynotavail- bona fideComaclusterSNe.Beforecomparingthe in theFband.Rust(1974)discussedextensivelyseveral ¿o, mustbeappliedtothedatainorderconvertV Pskowski’s (B—V)q,trelation(Pskowski1971).Inthe has tobemade,sincemostoftheobservationsweremade — F)o,trelationhastobeusedoncetheepochof Barbon etal.(1973a),aconversiontothemgsystem pg 1963m, arediscussionofthephotometryindivid- pg pg 1962a, 1970j,1971g,1971i,and1972h.Then,ateach Anon 1255.9+27;andZwickyBarbon(1967)for1304.3+28. Ppg pg P HE THELIGHTCURVESOFCOMACLUSTER Sources ofthevelocitiesotherthanGregory(1975)areRoodetal.(1972)forNGC4725andAnon1308.7+29;Zwicky(1969) v meansavisualmagnitude. © American Astronomical Society • Provided by the NASA Astrophysics Data System Table IIlistsallthephotometricdataavailablefor It hasbeenshown byBertola(1964)thatthe Fmax- 1959b 1968h 1963m 1963c 1961d 1969h 1940b 1950a 1968b 1976a 1962a 19621 1973f SN N 4725 N 4921 N 4725 N 4944 N 4874 Anon Anon Anon Anon Anon Anon Anon 1 4051 SUPERNOVAE h \248™0 12 58.5 12 57.2 12 55.9 12 55.3 12 48.3 13 01.5 12 59.0 12 55.5 12 48.0 13 08.7 13 04.3 13 00.5 R.A. Table I.SupernovaeinthefieldofComacluster. / +25°46 +28 06 +28 20 +28 09 +25 46 +28 28 +28 08 +28 17 +28 14 +27 24 +28 08 +27 47 +29 50 Dec. Notes toTableI 10.2 13.3 13.7 14.8 13.7 16.3 15.3 14.8 10.2 15.3 16.0 19.0 16.6 me. cline whichispresentinthelatter,theyaremoreuseful of ananonymousellipticalgalaxy.Observationswere when onlyfragmentarylightcurvesareavailable. the maximaofotherSNefoundincluster. as alsonotedbyKowal(1968),islowifcomparedwith of thenucleusananonymousE0galaxy,inaregion significance and,duetotheratherconstantrateofde- draw thefinalresults.Theyhaveahigherstatistical curves, andnottheaveragevisual,havetobeused difference hasnegligibleeffectonthefittingtoav- made withthePalomar48-in.Schmidttelescopeon sumed (Sandage1973).ThevalueofmoforSN1961d, shown schematicallyinFig.1.Forthisobject,asforthe can bereachedyieldingapparentmagnitudeatmaxi- a goodfittotheaveragebluecurvefor“fast”subtype in whichthegalaxycontributionisnolongerdetected. erage bluelightcurves.Itisimportanttostressthatthese the adoptedconversionprocedure,wefoundthatthis imum occurs2or3dayslaterthantheblueone.With the degreeofaccuracypossible,fittingprocedureis mum mo=16.2andzeroreddening.Asanexampleof following ones,zerogalacticobscurationhasbeenas- Zwicky’s photovisualobservationsasoutlinedpreviously, It wascaughtbeforemaximumandthelightcurve (Zwicky 1961)sets¿oon16January.Afterprocessing 1950a I2 1962a I128 1973f I:1 1968b 3 1963c I72 1961d I112 1959b pec116 1976a 1 1963m 31 SN SN 1963c.Thisoccurredontheboundaryregion SN 1961d.Thisobjectappearedexceedinglyfarout Table v\6.5 v\6.2 v 15.9: WSN 12.8 15.7 18.5 17.7 17.4 16.6 15.0: 16.5 15.6 17.2 Type ram vp Number ofphotometricobservationsforcluster Typec SBb SBb Sa SO Sb SOp SO S El EO E E/SO members. TypesN pec This paper This paper Humason (1950) IAUC No.2521 Zwicky etal.(1969) Zwicky andBarbon(1967) Zwicky (1961) Barbon (1967) IAUC No.2921 I: I: I 12 050 4945 6044 7473 Source 6137 7009 7181 5472 7190 1109 1109 Vo member Cluster 14 15 R. BARBON: SUPERNOVAE 15

Table Photovisual and photographic observations of SN 19621, SN 1963c, and Sn 1963m. SN 1962ia SN 1963cb SN 1963mc Date mv Date Date 29 May 1962 18.00 24 Jan 1963 16.10 20 Jun 1963 15.95 30 May 17.60 25 Jan 15.70 18 Jul 17.55 29 Jun 18.95 16 Feb 17.45 19 Jul 17.95 18.60 30 Jun 19.80 18 Feb 17.05 1 Jul 19.05 20 Mar 18.50 30 Jul 20.2: 23 Mar 18.45 2 Aug 20.05 25 Mar 18.50 23 Apr 19.40 25 Apr 19.20 a SN 1962i, last plate before outburst: 5 May 1962. b SN 1963c, last plate before outburst: 3 Dec 1962. c SN 1963m, last plate before outburst: 14 May 1963.

seven 103a-D and two 103a-O plates, which were re- of a nonmember galaxy and a SN of unknown type duced by the author using as calibrating sequence the matching the apparent maxima of the type I in Coma, Selected Area 57 included on the same field of the seems very unlikely. cluster. Table III gives the measured magnitudes, with SN 1968b and SN 1950a. Information on these standard deviations never exceeding 0.1 mag, and Fig. objects consists only of a few mpg observations of low 2 shows the of this SN. The last plate before accuracy. SN 1968b flared up in NGC 4874, one of the outburst was taken on 3 December and the color, on brightest members of the cluster, and was first observed 24-25 January, was mpg — V = —0.4. Combining this during the rise in brightness (Zwicky et al. 1969). The information with the available observations, the epoch type of the SN is not known, but if type I is assumed, the of maximum to was very likely 21-22 January. The fit fit of the scanty data available gives mo in the range to the average blue light curve “fast” subtype gives an 17.1-16.7, much fainter than the mean for this type at maximum mo = 15.5 with 0.05 (unless large reddening is present, which seems unlikely reddening. Applying a correction of Apg = 3.55E (Rust owing to the early type of the parent galaxy). 1974), the corrected magnitude is mo = 15.3. SN 1950a was found by Humason in the elliptical SN 1963m. This object appeared on the outskirts of galaxy IC 4051. The type was inferred from the color an SO peculiar galaxy. As for the previous SN, no pho- tometric observations, besides discovery, were available to date. Four 48-in. plates have been reduced by the author, as in the case of SN 1963c. The magnitudes and the light curve are reported in Table III and shown in Fig. 2. The accuracy of the measurements has been es- timated as 0.1 mag. The velocity of the parent galaxy and the type of the SN are not known and the above proce- dure, valid only for type I SNe, cannot be applied. However, we can make the ad hoc assumption that the object was of type I and check its consistency on the basis of the derived results. The last plate before discovery is dated 14 May. This, combined with the average visual curve and the three V observations, yields 13-21 June as probable interval for the maximum. On 19 July, the SN had a color mpg — V = +0.65. This value is consis- tent with a maximum occurring on 21-22 June. If we allow for some reddening, the maximum would occur later, thus causing a discrepancy between the two de- terminations. Choosing 21 June as the epoch of the maximum and applying the usual conversion procedure, a good fit to the “fast” average light curve is obtained, confirming that no reddening is present and yielding mo Fig. 1. Example of the fitting procedure as applied to the case of = 15.5. Since this value agrees very well with those of SN 196Id. Dots represent photovisual magnitudes, which are con- other SNe, we can conclude that SN verted to the photographic system (crosses) as explained in the text. 1963m was probably of type I and its parent galaxy is a Open circles are original mPg observations. The solid line is the mean probable member of the cluster. The other possibility, light curve for fast type I supernovae.

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1978AJ. : 16R.BARBON:SUPERNOVAE available data for theComaclusterSNehave beendis- is themagnitudereportedat discovery,m=16.5. SNe, theapparentbluemagnitude atmaximumismo Coma clustertypeISNe. zero reddening,aswasfoundformostoftheprevious to theSNcatalog,itreachedavisualmagnitudeV= was caughtduringtheriseinbrightnessand,according galaxies havevelocitiesinagreementwiththecluster membership. SN1973f,whichwasprobablyoftypeI, the announcementofdiscoveriesbyKohoutekand Lovas, respectively.AsshowninTableI,theparent in theComaclusterregion,verylittleisknownbesides = 15.75-15.8.Thisvalueisin therangeshownbyother verted tothemgsystem,“fast”averagelightcurve gives abetterfittoallofthedatacombined,yieldingmo subtype thisSNbelongs.IftheVobservationsarecon- uary butdonotdetermineunequivocallytowhich observations settheepochofmaximumon22Jan- light curvesincethefirstriseinbrightness.Them suburban formationoflowsurfacebrightness.”The SN appearsneartheprincipalaxisofEorSOgalaxy cluster. AccordingtoZwickyandBarbon(1967),“the servations cannotbetreatedaccordingtotheusual about 17.8inthevisual. procedure. Barbon(1967)optedforapossibletypeIII 16.2. UsingRust’s(mg—K),trelationandassuming photovisual andphotographicmagnitudesdefinethe and outsidethediskwithinsomewhatirregular = 15.1andnegligiblereddening. available informationrulesoutatypeI,sothattheob- cluster, anditshowedunusualphotometricbehavior.The (long-standing maximum)withapeakmagnitudeof center ofthespiralgalaxyNGC4921,amember tions, althoughverymeager,givemo=15.0. given inBarbon(1967).Itappearedquitefarfromthe and therateofdecline(Humason1950).Theobserva- P vg P Before concludingthissection, inwhichallofthe For SN1976a,ofunknowntype, theonlyobservation SN 1973fandSn1976a.OfthelatesttwoSNefound © American Astronomical Society • Provided by the NASA Astrophysics Data System SN 1962a.Itisoneofthebest-studiedSNein SN 1959b.Athoroughdiscussiononthisobjectis Fig. 2.LightcurvesofsupernovaeinthefieldComacluster.Dotsandopencirclesrepresentphotovisualphotographic magnitudes, respectively.Thesymbolvstandsforthelastplatebeforeoutburst. used, thesame methodhasbeenappliedto thephoto- real orhasbeeninducedby theconversionprocedure late-type galaxies.Tocheck whether thisdiscrepancyis stated byBarbonetal.(1973a) that“fast”SNeIprefer of earlymorphologicalclasses (E,SO),whereasitwas “fast” subtype.Thecorresponding parentgalaxiesare have meanbluelightcurvesthat canbefittedwelltothe shown thatfouroutofsixtypeISNeintheComacluster faint forthisSNtobelongthecluster. magnitudes become16.5and16.8.Thesevaluesaretoo absorption correctionofA=3.55jE’,thecorrected mo =17.2and17.5,respectively.Applyingan subclasses andyieldsapparentmagnitudesatmaximum observations, maybeequallydonewiththetwotypeI version procedureofthephotovisualmagnitudes,as the combineddata,iflowweightisgiventofaintest described atthebeginningofthissection,givessame This latterepochisalsoconfirmedbythecolormea- results, confirmingacolorexcessof0.2.Thefittingto surements ifweallowforareddeningof0.2.Thecon- or, givinglowerweighttothefaintestpoint,=AJune. the mobservationsgivetwopossibilities:/o=22May occurred inafaintanonymousgalaxyalsobelongingto maximum on6June.Theaveragebluelightcurveand into accountthatthelastplatebeforeoutburstdates5 must becheckedthroughthephotometricdata.Taking parent galaxyisnotavailable,sothatclustermembership larger than0.1mag.Thevelocityofrecessionthe which, accordingtotheSNcatalog,wasprobablyoftype the regioninvestigatedinthispaper. cussed, wereportonsomeobservationsobtainedwiththe May, thephotovisualobservationssetepochof puted standarddeviationsofthemeasurementswerenot 48-in. PalomarSchmidttelescopeofSN1962i,which I, aregiveninTableIIIandshownFig.2.Thecom- vg pg The photometricanalysiscarriedoutinSec.Illhas The magnitudesandthelightcurveofthisobject, IV. THEINTRINSICDISPERSIONOFTYPEISN MAXIMA 00 00 oo 1978AJ. PQ 17 R.BARBON:SUPERNOVAE visual observationsofthe“slow”typeISN1970j clude thattheconversionproceduredoesnotalter together withtheoriginalphotographicobservations, original “shape”oftheSNlightcurve.Thisdisap- again fitwelltothe“slow”averagelightcurve,wecon- derived forthesixtypeISNeinComaallowustocom- lation withthemorphologicalclassesofparentgal- clusions fromsmallsamples.MoredataontheSNI circles areforegroundandbackgroundobjects.Thesolidlineisthe to theclusterposition.Dotsaregalaxiesbelongingcluster,open axies canbestated. subtypes arethereforeneededbeforeadefinitecorre- should onceagainwarnusnottodrawstatisticalcon- pointing evidence,whichcontradictsanearlierresult, equal-population contourfortheComaclusterasdrawnin objects reachinthecluster.Assuming0.1magas pute themeanbrightness,anditsdispersion,thatthese (Barbon etal.1973b).Sincetheconvertedmagnitudes, tometry, themeanapparentmagnitudeatmaximumis weight toSNe1950aand1973fwhichhavepoorpho- accuracy ofthesinglemeasurementsandgivinghalf- viation is¿/=0.34.Thislatter valueismorerelatedto CGCG. to whichwearereferring,the correspondingmeande- et al.(1973a),themeandeviation atmaximumofthe mo =15.5±0.21withadispersion0.43.InBarbon of thespreadin the“shape”oftypeIlight curves. the intrinsicscatteroftype Imaximathanthefor- average bluelightcurvewas d=0.15.ForthesixSNe mer, whichshouldmoreproperly representameasure Fig. 3.LocationsoftheparentgalaxiesTableIascompared © American Astronomical Society • Provided by the NASA Astrophysics Data System The correctedapparentmagnitudesatmaximumjust The meanabsolutebrightnessreachedbytypeISNein the meanrecessionvelocityKq=6946km/s(Gregory distribution oftheclustermembers.Moreover,thereis occurred inbackgroundorforegroundgalaxies.(Notice tained fromSNeIbelongingtodifferentclusters. ment withthevaluereportedbyKowal(1968)andob- this clusteristhenM=—18.69mag,quiteinagree- density andasymmetricaldecreasetowardsthe galaxy distributionofthecluster;i.e.,acentralmaximum uniform ingalaxytypesandregularstructure,we that twoSNeflaredupinNGC4725.)Accordingtoour to clustermemberswhereastheremainingfour(circles) computing thelinearcorrelationcoefficient),itwillbe cording tothesurfacedensityofclustermembersand tribution isnotsignificant(byweightingthepointsac- one canmanagewithstatisticstoprovethatsuchadis- the distributionofSNeparentgalaxies.Although subgrouping intheComaclusterwhichmightexplain direction atP.A.=64°.Itisnotpossibletoexplainthe boundaries (Roodetal.1972).Althoughthepresent should expectaSNdistributionwhichsimulatesthe to beSNproducers.SincetheComaclusterisfairly from whichtheyoriginate.Accordingly,withinacluster, simulate, withinagalaxy,thedistributionofstars knowledge oftheSNphenomenon,theseobjectsshould previous discussion,nineobjects(dots)canbeassigned tified inTableIareplottedFig.3.Accordingtothe of SNeintheComaclusteris given.SNfrequencywas of interesttocheckwhetherthispeculiartrendiscon- SN 1950awasfoundbyHumasonon200-in.plates one platebythePalomarSchmidttelescopesandonly effect, sincetheComafieldiswhollysurveyedwithjust cluster, showaslighttendencytoconcentratealong sample issmall,atfirstglanceitseemsthatthelocation the membersofgalacticpopulationwhicharelikely the parentgalaxiesshouldhavesamedistributionas found sofarintheregionofComaclusterandiden- peculiar distributionofFig.3bymeansasampling than 15.7magwhich,intheregionoutlinedby of theparentgalaxiesshowninFig.3doesnotcorrelate first derivedby Zwicky(1938,1942)who gavevalues firmed whennewSNearefoundinthecluster. no correlationwiththedistributionofgalaxiesbrighter (Humason 1950). (except fortheobviousclusteringatcenter)with 1975), thedistanceofComaclusterisJ=69Mpc. vg VI. THESUPERNOVAFREQUENCY INTHECOMA The locationsoftheSNe(andtheirparentgalaxies) With theHubbleconstantH=100km/sMpcand To theauthor’sknowledge,thereisnoparticular In thissection,anestimateof therateofproduction V. DISTRIBUTIONOFTHEPARENTGALAXIES WITHIN THECOMACLUSTER CLUSTER 17 00 00 oo 1978AJ. PQ 0 A correctcomputationofthefrequencymusttherefore SN 1950ashouldalsobedisregardedsinceitflaredup galaxies fainterthan15.7mag,andSN1976a,which time coveragefortheperiod1950-1958ispoorlyknown. before thebeginningofsystematicsearchand appeared inagalaxylocatedoutsideofGregory’sarea. frequency: SN1962aand1963mwhichoccurredin magnitude anddistancefromtheclustercenter, following SNecannotbeusedinthecomputationof proper “controltime”foreachphotograph(Barbon and thetimecoveragecanbereadilycomputedoncea for providingthisinformationtheperiod1967-1976) two newonesincluded).Thedatesthisfieldhasbeen Gregory’s area(onlythreeobjectsareexcludedandonly different choice ofthemeanlightcurve, to allowfor derive thevalueofcontrol time,wemakeuseofthe quency per“unitluminosity” willthenbeattempted.To which hasameaningpeculiar totheparticularsample photographed since1958areknown(wethankC.Kowal 48-in. SNsearch(4.°5X4.5)matchesalmostexactly galaxies showingthefollowingdistributioninapparent in Comawereofthistype.It willlaterbeshownthata average lightcurvefortypeI SNe, sincemostoftheSNe we areusing,willbegivenfirst. Anestimateofthefre- rest ononlyfiveobjects. magnitude: Gregory’s sampleofclustermembersismadeup207 location neartheclustercenterarelikelytobemembers, the fivegalaxieswithnoredshift,whichowingtotheir ognized asbackgroundorforegroundobjects.Including served forredshiftandonly9outof211havebeenrec- galaxies brighterthan15.7maganduptoadistanceof cluster, becauseoftheuniformityclusterpopu- sample galaxies.ThefrequencyofSNeintheComa strongly dependentontypesandluminositiesofthe values ofthefrequencyhigherthanpreviouslyfoundand five ofthegalaxieslistedinCGCGhavebeenob- tablished ahighlyreliableandhomogeneoussampleof in clustermembers.Moreover,Gregory(1975)hases- the actualtimecoverageofsearch. of clustermembersactuallysearchedforSNe,and(c) of aboutoneSNper360yr“averagenebula.”Later has criticizedtheconceptof“averagenebula,”giving firmed thisresult.MorerecentlyTammann(1970,1974) 18 R.BARBON:SUPERNOVAE 2.°79 fromtheclustercenter.Withinthisarea,allbut has ledtotheidentificationofnineSNewhichoccurred SNe whichdidoccurinclustermembers,(b)thenumber lation, shouldbeofinterestprovidedapropersamplecan be assembled.Thismustconsistof(a)thenumber Barbon (1968),onthebasisofalargersample,con- 1968) isassumed.Sincethegalaxysamplelimitedin © American Astronomical Society • Provided by the NASA Astrophysics Data System Most fortunately,theComafieldofPalomar The photometricanalysisgivenintheprevioussections In thefollowingafrequencyper“averagenebula,” 14.1