1993AJ 106.1101F 2 3 THE ASTRONOMICALJOURNAL photographic andphotoelectricphotometryarenotwell supernovae isnotatrivialtask.Theclassicaltechniquesof tional ScienceFoundation. versities forResearchinAstronomy, Inc. undercontractwiththeNa- Astronomy Observatories,whichareoperated bytheAssociationofUni- galactic background.Supemovaearegenerallyfaint,occur suited tothejobofextractingastellarbrightnessfrom versity, Princeton,NJ08544. Present address:DepartmentofAstrophysical Sciences,PrincetonUni- Presidential YoungInvestigator. A1so atDepartmentofPhysics,Curry College. Visiting Astronomer,KittPeakNational Observatory,NationalOptical 1101 Astron.J. 106 (3),September1993 0004-6256/93/106(3)/! 101/12/$0.90 ©1993Am.Astron. Soc.1101 Obtaining highquality,wellsampledlightcurvesfor © American Astronomical Society • Provided by theNASA Astrophysics Data System 234 -1 -1 _1- Whitin Observatory(WO).Similarequipment,observingandreductionprocedureshavebeenadopted Michael W.Richmond,L.Baker,AlexeiV.Filippenko,RichardR.Treffers, light curveinVmatchesLeibundgut’s[Ph.D.thesis,UniversityofBasel(1988)]templatereasonably at allthreesitesandthereisgenerallygoodagreementamongthedatasets.TwootherTypela attached tosmalltelescopesatLeuschnerObservatory(LO),VanVleck(WO),and Cousins systemVRIphotometryhasbeenobtainedfortheTypelasupernova1992GwithCCDs well. SinceverylittleRand/photometryofsupernovaehasbeendonepreviously,ourdataprovidethe Supernovae, includingthespectroscopicallypeculiarSN199IT,arequitesimilar,andcombined Supernovae, 1991Mand199IT,wereobservedonlyatWO.Theshapesofthelightcurvesallthree existence ofsubstantialstructureintheRand/lightcurvesnormalTypelasupernovae(andits shows asecondarymaximum23±1daysaftertheprimarypeak,similartowhatisseeninnormalType first realdefinitionofSNlatemplatesinthosebands.TheItemplateisparticularinterestsinceit 0.05 mag,ifthereddeningofSN1991TisE(B—V)=0.13.IfTypelasupemovaeareassumedtobe of theseTypelasupernovaeatFareV—R=0.0andR—I=—0.3,withanuncertaintyaround an observationalchallengetomodelsoftheevent.TheobservedcolorsSN1991Mand199ITas absence inthepeculiarTypelaSN199Ibg)enhancestheirutilityascosmologicalprobesandprovides velocity ofNGC4527islessthanthis,thenSN199ITmustbeanoverluminousla.Tully&Shaya a functionoftimearequitesimilar,indicatingthattheysufferaboutthesameamountreddening.SN la supernovaeatJ,H,andKwavelengths.ThebehaviorinRisintermediatebetweenV/. km s.OurdataaloneyieldaHubbleconstantof75±15MpcifMatmaximumlightis of 1200±150kmsrelativetotheHubbleflowanddirectedawayfromGalaxy.Ifpeculiar good standardcandles,thenNGC4527,theparentgalaxyofSN199IT,musthaveapeculiarvelocity 1992G isclearlymoreheavilyreddenedthanthesetwo,byabout0.1maginR—I.Theintrinsiccolors (1984) regardNGC4527asanear-sidememberoftheVirgoclusterfallinginatapproximately1000 max —18.7 mag,and50±10kmsMpcifitis—19.6mag. v CCD PHOTOMETRYOFTHREETYPElaSUPERNOVAE:V,R,AND/LIGHTCURVES Department ofAstronomy,andCenterforParticleAstrophysics,UniversityCalifornia,Berkeley,California94720 1. INTRODUCTION Van VleckObservatory,WesleyanUniversity,Middletown,Connecticut06459 Department ofAstronomy,WellesleyCollege,Wellesley,Massachusetts02181 1 Charles H.FordandWilliamHerbst Electronic mail:[email protected] Received 1993March12;revisedApril13 VOLUME 106,NUMBER3 Priscilla J.Benson and YoungPaik ABSTRACT poral coverage.Therequiredtransformationsarecompli- to combinedatafrommorethanonesitegetgoodtem- ing itvirtuallyimpossibletoschedulesufficienttelescope Wesleyan University,andat LeuschnerObservatory groups atVanVleckObservatory (WO)onthecampusof launched independentlyonopposite coastsoftheU.S.by than 0.1mag(e.g.,Hamuyet al1990). achieve consistencyinthephotometry atthelevelofbetter closely matchedinstrumentalsystemsitcanbedifficultto nonstellar spectrumatalltimes.Unlessonehasvery cally duringitsinitialevolutionandhasadeterminedly cated bythefactthatasupernovachangescolordramati- time forthisworkatasharedfacility.Onegenerallyneeds without warningandfadeonatimescaleofmonths,mak- Several yearsagosupernovamonitoring programswere SEPTEMBER 1993 1993AJ 106.1101F 5 5 by theexpansionofUniverse(e.g.,Branch&Tam- program, includingWellesleyCollege,withitscampusfa- its onthedecelerationparameter,andaddressingfun- luminous objectscouldbeusedasstandardcandlesfor for SNela.Ithaslongbeenarguedthattheseextremely to anyparticulartype,inthispaperwediscussonlyresults interesting. Whileourobservingprogramisnotrestricted ity, wellsampledlightcurvesofalltypessupemovaeare the dataobtainedateachsite. reduction procedurehasbeenadopted,asdescribedinSec. are nearlyidentical,andaratheruniformobserving instrumental systemsatKNACschoolsandBerkeley and partlyasaresultofcommunicationplanning,the cility, WhitinObservatory(WO).Partlybygoodfortune several KNACinstitutionsparticipateintheeastcoast University ofCalifornia.Wesleyanisamemberthe mann 1990;Miller&BranchBoisseauWheeler is whetherornotSNelareallyarestandardcandles(e.g., mann 1992;Branch&Miller1993).Thecentralquestion damental issueofwhethertheredshiftisindeedproduced determining thedistancescaleinUniverse,settinglim- 2. Itishopedthatthisapproachwillenhancetheutilityof Keck NortheastAstronomyConsortium(KNAC)and be usedasstandardcandles.However,itappearslikely there arebothspectroscopicallyandphotometricallypecu- Pskovskii 1977;Leibundgut1988;&Tam- easily beidentifiedbytheirobservedproperties.Whatis penko etal1992b;Leibundgut1993)whichcannot liar SNela,suchasSN1986G(Phillipsetal1987;Frogel perhaps moreworrisomeareSNelahavinglessobvious that theseabnormalobjectsareratheruncommonandcan been doneintheUBVsystemanditsphotographiccoun- troscopy ofbrightnearbysupernovaeisneededtoascertain penko etal1992a;Phillips1992;Ruiz-Lapuente and lesspersistentpeculiaritiessuchasSN199IT(Filip- et al1987;Christianieia/.1992)andSN1991bg(Filip- by infraredobservers(Eliasetal1985;Frogel toelectric detectors,almostallsupernovaphotometryhas tudes) maybe. tometric properties(particularytheirabsolutemagni- how commontheseobjectsareandunusualtheirpho- et al1992).Agooddealofcarefulphotometryandspec- terpart (m,m);forexample,seeLeibundgutetal uncertain inthebluecomparedtoinfrared.Modem 1102 FORDETAL.:PHOTOMETRYOF3SNs (LO), whichisassociatedwiththeBerkeleycampusof programs. Memberinstitutionsare: Colgate, Haverford,Middlebury, funding fromtheW.M.KeckFoundation tosupporttheirastronomy data willstillberequiredforthe constructionofbolometric and near-infraredregions,wheretheeffectsofinterstellar CCD detectorshaveexcellentquantumefficiencyinthered Swarthmore, Vassar,Wellesley,Wesleyan, andWilliams. KNAC isagroupofeightcollegesand universitieswhichhavereceived 1991; vandenBergh&Pazder1992).Itisnowclearthat 1987), isthatextinctioncorrectionsarerelativelylargeand (1991). Aproblemwiththis,whichhasbeenemphasized (and atmospheric)extinctionaresmaller.WhileUBV pgy There are,ofcourse,avarietyreasonswhyhighqual- Owing tothebluesensitivityofphotographicandpho- © American Astronomical Society • Provided by theNASA Astrophysics Data System broad bandpasseswhichallowustoreachrelativelyfaint tails totheredanditispossiblethatsmallvariationsin photometric standardsavailable(Landolt1983,1992). the majorityofsupernovaefromthesetelescopeswillbe count ofthesmalltelescopesizesandrelativelypoorblue equipment andcommonstandardsareemployed).Onac- photometry obtainedatdifferentsites(evenwhensimilar spectra ofsupernovaetoproducesystematicdifferencesin in theredcouldcouplewithcomplexandevolving One disadvantageisthattheRand/filtershaveverylong objects withsmalltelescopesandthatthereisalargesetof institutions. Theadvantagesofthissystemarethatithas The Johnson/CousinsUBVRIsystemdescribedbyBessell curves inUBVandJHKcanbeformedtowhichvirtually of Typelasupernovaeandarguedthat“template”light in Baswell. restricted toVRI,withonlythebrighterobjectsobserved and ultravioletsensitivityoftheCCDchipsused,dataon CCD quantumefficienciesandatmospherictransparencies will concentratemoreonlongerwavelengthobservations. light curves,itisbothdesirableandlikelythatfuturework i£-band photometryontheCousinssystemforSN198IB. Type laSN1972E.Buta&Turner(1983)obtained pernovae ator/wavelengths.Leeetal(1972)obtained all SNelaadhere.Verylittleworkhasbeendoneonsu- been lacking,however,isenoughphotometryofnormal substantially fromtheCousinssystematRandI)for Type lasupernovaetoestablishtheformoftemplate tometry ofthesubluminousTypelaSN1991bg.Whathas which areincludedinthispaper.Filippenkoetal with significantgapsintheirtemporalcoverage.Balonek pemovae aregiveninSec.3.Thesedataused4 tributions ofthispaper.InSec.2ourobservingandreduc- light curvesinRandI.Thatisoneoftheprincipalcon- programs atBerkeleyandWesleyan,presentedVRIpho- et al(1991)presenteddataonSN1991TinVRI,someof Hamuy etal(1991)observedSN1980NinRand/but to discusstheissueofwhetherTypelasupernovaein tion techniquesaredescribed(seealsoFilippenkoetal discuss someimplicationsofourwork. our samplearegoodstandardcandlesand,inSec.5,we possible. Accordingtothemanufacturers, theMetachrome making iteffectively//7.5.For thereasonssetoutinSec. ler andChivensreflectorisused withafocalreducinglens information onWhitinObservatory,wherethe0.6mBoi- Berkeley andWesleyanwasgivenbyFilippenkoetal Inc. asthePM512andinuse atWOandWO,the II coatedFordAerospacechip marketedbyPhotometries, ( 1990)hasbeenadoptedatbothBerkeleyandtheKNAC UBVRI photometryontheJohnsonsystem(whichdiffers (1992b), inthefirstpublishedreportofphotometry 1992b) .VRIdataandlightcurvesforthreeTypelasu- 1, wehaveattemptedtokeep these systemsassimilar (1992b). Hereweprovideafewmoredetailsandinclude Leibundgut (1988)hasreviewedtheextantphotometry A briefaccountoftheobservingschemesemployedat 2. OBSERVATIONSANDREDUCTIONS 1102 1993AJ 106.1101F obtained atLOisshownasFig.1ofFilippenkoetal time offivetoeightminutes.Anexampleanimage erally obtainedandaveragedyieldinganeffectiveexposure quently, atWO,threetofiveexposuresperfilteraregen- ited toabout100sbytheabsenceofautoguiders.Conse- to 2000s.IndividualexposuresatWOandarelim- Berkeley dataareobtainedwithanautomatedtelescope used tomatchtheJohnson/CousinsUBVRIsystem.The identical filtersets,asgiveninBessell’s(1990)Table6are nearly identicalquantumefficiencycurves.Furthermore, frame asthesupernovaisattempted.Ingeneralitbestto tometry relativetocomparisonstarsonthesameCCD coast sites,arerarelyphotometric,onlydifferentialpho- fielding isaccomplishedusingobservationsofthetwilight supemovae currentlybrightenoughtobedetected.Flat- run byobservers,oftenundergraduatestudents.Onevery robotic whereastheWellesleyandWesleyantelescopesare principal differencebeingthattheBerkeleytelescopeis of SN1992GobtainedatWO. supemovae discussedhereobtainedatWO,andanimage tion equationsfordifferential photometric measurements, vide somedetailsoftheadopted transformationprocedure. work onmanynightsduringwhichchangingatmospheric completely neglectfirst-orderextinctioncoefficients,andto in Fig.1. order toincludethebestnearbycomparisonstarson tion thesupernovaawayfromcenteroffieldin pernova. Infact,atWO,itisgenerallynecessarytoposi- sufficiently brightstarsinthesameCCDfieldassu- parison stars.Often,however,thereareonlyoneortwo liar colors,andguardagainstpossiblevariabilityofcom- signal-to-noise ratio,lessensystematiceffectsduetopecu- use asmanycomparisonstarspossibletoimprovethe sky. Sinceatmosphericconditions,especiallyattheeast clear night,imagesinVRIorBVRIareobtainedofall similarly coatedThomsonTh7895chipusedatLO,have cally underprivilegedsitesare not yetwidespread,wepro- and sincephotometricprograms usingCCDsatclimati- programs willproduceafairly substantialamountofdata, tem iftheyaretobecombined.Sincewehopethatthese data muststill,however,betransformedtoastandardsys- conditions wouldmakeall-skyphotometryimpossible.The supemovae arelistedinTable1andmarkedontheimages same CCDframe.Thecomparisonstarsusedforthese 1103 FORDETAL.:PHOTOMETRYOF3SNs (1992b). Figure1ofthispapershowsimagesthethree (Richmond etal1993)andexposuretimesvaryfrom400 The observingproceduresatallsitesaresimilar,the The useoflocalcomparisonstarsmakesitpossibleto Following Hardie(1962)wemay writethetransforma- © American Astronomical Society • Provided by theNASA Astrophysics Data System Table 1.VRIphotometryofcomparisonstars. **Primary comparisonstarusedatLOandWO. * PrimarycomparisonstarusedatWO. T99ÏM 1992G 1991T Field Star 4** 1* 1* 1^ 3 2 2 16.80 17.11 16.84 15.78 15.29 13.70 14.01 15.80 16.48 16.29 15.41 14.30 12.97 13.55 14.63 15.92 15.87 15.08 13.26 12.34 13.19 T R—I, ratherthanB—V,asthefundamentalcolorsince follows: more traditionalV,asthefundamentalmagnitudeand magnitude ofacomparisonstar.WeuseR,insteadthe where Adenotesthemagnitudeofsupernovaminus and with secondorderextinctioncoefficientssettozero,as brators forfutureobservations. Thedifferencebetween to theflatnessofatmosphericextinctioncurveatthose unavailable. Thesymbolshavetheirusualmeanings:v,r, our Rand/dataareofhigherprecisionB—Visoften transformation slopesobtained fromLandoltstandards have, therefore,adoptedthose fieldsasourprimarycali- from Landolt(1992)donotshow suchanonlinearity.We from standardfielddatawhenthesecond-ordercoefficients mized andessentiallyeliminatedbythesimplepracticeof their alreadysmalleffectonthedatacanbefurthermini- fore, difficulttodeterminereliablevaluesforthem.Second, wavelengths (cf.Table1ofLandolt1992)anditis,there- to bequiteclosezerointheredandnear-infraredowing to zerofortworeasons.First,thecoefficientsareexpected our practicetosetthesecond-orderextinctioncoefficients and /aretheinstrumentalmagnitudes,R,(V—R), scribed below.Subsequenttests withnewcalibrationfields tunately italsoyieldsaslightlynonlineartransformationin this wastheonlysuchcalibrationfieldavailablethathasa these observationswasthe“dipperasterism”fieldinM67 0.5%. TheprimarycalibrationfieldatWOandfor made bydoingall-skyphotometryonphotometricnights, night, asisexpected. the samenights.Itonlyrequiresthatsecond-order the observationsofprogramandstandardfieldsbeon glecting theminthereductionprocessforsupernova. are neglectedthencompensatesfortheerrormadeinne- gram fields.ThesmallerrormadeindeterminingTvalues fields observedatroughlythesameairmassesaspro- determining transformationcoefficientsfromstandard sufficient numberofstarsappropriatebrightness.Unfor- gram areused;theydeterminedtoanaccuracyofabout slopes obtainedonmanynightsduringtheobservingpro- expected orfoundtochangemuchwithtime,soaverage was doneatWOandWO.Transformationslopesarenot a numberofstandardstarswithgoodrangeincolor,as as wasdoneatLOusingstandardsfromLandolt’s coefficients bereasonablysmallandstablefromnightto extinction coefficientsbemeasuredorappliedeventhat Note thatthisproceduredoesnotrequirefirst-order T andarethetransformationcoefficientslopes.Itis {R—I) arethestandardmagnitudeandcolorsT, (Schild 1983).Atthetimeofmosttheseobservations, (1983,1992) lists,orbyobservingasinglefieldcontaining V—R forCCDsystemsatWO andatKPNO,asde- vr1ri r L{R-I) =TMr-i) ar=A/*+t;a(r-/), A(V-R) =TA(v-r), Determination ofthetransformationslopesmaybe r9 vr 1103 1993AJ 106.1101F tained atCTIO,andbytheagreement betweendatasetson data onSN199ITobtained atWOwithsimilardataob- nal checksonourcalibrations comefromcomparingthe stars inthefieldofSN199IT toreducethosedata.Exter- have usedonlytheblueroftwopossiblecomparison parison starandthesupernovaisminimized.Therefore, we reduced datawhenthecolordifferencebetweencom- Any errorinthetransformationslopesisminimized determined fromtheM67fieldandignorenonlinearity. successful. Both checksshow thatourtransformation procedureis SN 1992Gobtainedatthe threedifferentobservatories. KPNO wassmall,soourproceduretoadopttheslopes and Schildstandards(i.e.,ignoringthenonlinearity) at 1104 FORDETAL.:PHOTOMETRYOF3SNs Wellesley imageisabout7arcminonaside. only thesmallerportionthatwascommontoeveryexposureobtained.Thesupernovaeandcomparisonstarsaremarked. Wesleyan framesofSNe1991Mand1992Gareabout4arcminonaside.TheframeSN199IThasthesamescaleasthesebutshows in thelowerrighthandcomer,animageofSN1992GobtainedatWellesley.Inallcases,northistopandeasttoleft.The Fig. 1.Imagesofthethreesupernovaediscussedinthispaperobtainedthroughan/filterwith0.6mtelescopeatWesleyanand, © American Astronomical Society •Provided bythe NASAAstrophysics Data System tometry, ingeneral, istoproperlycorrect forthelightof stars aregiveninTable1 to anestimatedaccuracyof mation coefficients.Photometric resultsforthecomparison same timeandusedtodetermine extinctionandtransfor- used. Landolt(1983,1992)standards wereobservedatthe three nightsin1992February,withthe0.9mtelescope at parison starsonthestandardsystemweobservedthem on for thelocalcomparisonstarorstars.Toplacecom- the supernovaoneachnighttostandardVRIvalues standard differentialmagnitudesandcolorsobtained for KPNO. TheT2KCCDandstandardKPNOfiltersetwere ±0.02 mag. Perhaps themost challengingaspectofsupernova pho- The laststepinthereductionprocessistoadd 1104 1993AJ 106.1101F 6 6 been thecase.Fordatadiscussedinthispaper,itturns 4. AtWO,internalerrors(±1er)calculatedfromPoisson correct morerigorouslyforthegalacticbackground.How- to obtainreferenceimagesofthegalaxiesinvolvedand these supernovaehavefadedsufficientlyitwillbepossible ination isnotaseriousproblemforourphotometry.When which hasthebrightestgalacticsurroundingsofourthree case ofSN1991Mand199IT.TheLOdatawerere- mined fromanannulusofinnerradius10"andwidth2.5" WO andWO.Anapertureof6"diameterhasbeenused standard routinesinIRAFhasbeenemployedatboth report observations.Simpleaperturephotometryusingthe to theirgalacticsurroundingsatalltimesforwhichwe cause allthreesupernovaewererelativelybrightcompared out thatbackgroundsubtractionisnotamajorissue,be- do thiswithmuchlessuncertaintythanhaspreviously advantages ofusingaCCDisthatitshouldbepossibleto have beendeletedfromtheplots andanalysissincethey systematically brighterthanexpected. Theseobservations except, perhaps,forthethreefaintest pointsinIwhichare ror estimates.ThisisalsotrueofthedataobtainedatWO comparison stars.Thereisnoevidenceofanysubstantial they werealsoreducedbydifferentmethodsusing only werethesedataobtainedatdifferentobservatories, parison ofresultsfromLOandWOforSN1992G.Not mate oftheexternalaccuracydatacomesfromcom- given inparenthesesnexttoeachmeasurement.Anesti- mag orlessforF,R,7<15butrisetoabout0.1at statistics andtheknownpropertiesofCCDare0.03 if anyatall,onthedatapresentedhere. ever, weanticipatethatthiswillhaveonlyaminoreffect, supemovae, givesusconfidencethatbackgroundcontam- agreement betweenthereduceddatasetsforSN1992G, duced usingtheDAOPHOTpackageinIRAF.Theexcellent in thecaseofSN1992Gandfromanoffsetaperture owing totherelativelypoorseeing.Skyvaluesweredeter- the galaxyinwhichsupernovaisembedded.Oneof National OpticalAstronomyObservatories systematic error.Thedataagreetowithintheinternaler- vary considerably,individualerrorsarecalculatedand IRAF (ImageReductionandAnalysis Facility)isdistributedbythe 1105 FORDETAL.:PHOTOMETRYOF3SNs 16.5 and0.3magat17.5.AtLO,whereexposuretimes Results forthesupernovaearegiveninTables2,3,and © American Astronomical Society • Provided by theNASA Astrophysics Data System 1 Table 2.PhotometryofSN199IMatWesleyan. bate (ÜT)J¿> 03-04-91 07-06-91 21- 05-91 20- 05-91 05-05-91 26-04-91 21-03-91 21-06-91 28-04-91 24-04-91 17-05-91 13-04-91 3. LIGHTCURVES 8428.722 8397.823 8396.725 8393.769 8381.778 8414.726 8374.863 8372.799 8370.726 8359.759 8349.737 8336.765 15.70 15.09 14.55 17.45 17.10 16.87 16.72 16.64 16.38 18.32 17.64 17.38 17.95 15.39 14.45 17.46 17.13 17.13 17.11 16.66 16.24 16.21 16.18 15.17 17.88 17.33 17.00 17.03 16.95 16.50 15.92 15.89 15.76 15.20 15.31 14.72 "T bundgut (1991)onMarch13.35 UTwasdescribedby They reportBVRIphotometry withanestimateduncer- was asinglemeasurementby Hook &McMahon(1991). visual. Theonlysubsequentphotometry weareawareof light. Theyestimateditsmagnitude tobearound15inthe them asshowingaTypelasupernova closetomaximum novae. peak in/anda“shoulder”R.AsimilarfeatureRwas later declineratethatwemeasureis,however,slightlyless was discoveredon1992Feb.9,atabout14thmagnitudeby Berkeley AutomatedSupernovaSearch(Pennypacker importance ofnear-infraredphotometryTypelasuper- in theirinstrumentalphotometryofSN199IT.Aswedis- though wenotethatBaloneketal(1991)sawthefeature published reportofasecondarypeakinCousins/,al- ary peaksatinfraredwavelengthshavebeenobservedby seen inSN1981BbyButa&Turner(1983),andsecond- curves showremarkablestructure,involvingasecondary there isgoodagreementonceagain.TheRand/light steep thanthetemplate,sothatby60daysaftermaximum the templateandourlightcurveafterabout40days.The day) andleadstoadiscrepancyofabout0.2magbetween ginally greaterthanthetemplatevalue(0.057magper rate ofdeclineis0.060±0.002magperday,whichmar- data andLeibundgut’s(1988)F-bandtemplate.Theinitial fairly close,althoughnotexact,agreementbetweenour maximum lightbylijimaetal(1992)onthebasisofa Sasaki (1992)anddescribedasaTypelasupernovanear and theonlyoneobservedatallthreesitesisSN1992G.It sites isgood. problem. Ingeneral,theagreementachievedamong with an//7.5systematasitewherelightpollutionis probably reflectthedifficultiesofworkingtofaintlimits et al1991).AspectrogramobtainedbySchmidt&Lei- cuss below,theexistenceofthesefeaturesenhances Lee etal.(1972)inSN1972EandbyEliasal Its F,R,andIlightcurvesareshowninFig.2.Thereis CCD magnitudeshavebeenreportedintheIAUCirculars. spectrogram obtainedon1992Feb.21.Nophotoelectricor (1981,1985) inelevenTypelasupernovae.Thisisthefirst The supernovaforwhichwehavethebesttimecoverage SN 1991Mwasdiscoveredon1991March12,bythe Table 3.PhotometryofSN199ITatWesleyan. Date (UT)JD 02-07-91 22- 06-91 07- 06-91 21- 05-91 06- 05-91 05- 05-91 29-04-91 24-04-91 20- 04-91 17-07-91 14-06-91 17-05-91 8454.584 8439.625 8421.625 8429.625 8414.631 8397.647 8393.674 8382.625 8381.646 8375.716 8370.617 8366.664 3.2SN1991M 3.1SN1992G 14.26 13.93 13.62 13.43 13.11 12.34 12.05 11.49 11.49 11.44 11.65 11.94 V 14.28 13.76 13.43 13.11 12.79 12.08 12.02 11.54 11.44 11.39 11.54 12.08 R 14.45 13.78 13.24 12.86 12.48 11.99 12.05 11.86 11.79 11.62 11.66 12.18 I 1105 1993AJ 106.1101F 1106 FORDETAL.:PHOTOMETRYOF3SNs for SN1991MareshowninFig.3.Whilethedata days beforeFaccordingtoourestimate.Theyfind tainty of±0.1magonJD2448330.8,whichisabout4 when ostensiblytransformedto thesamestandardsystem ing tocombinesupernovadata, especiallyCCDdatainthe tration ofthefactthattherecan bedifficultiesinattempt- our data,especiallyinRand 7. Thisisprobablyanillus- to reconcilethemeasurementofHookandMcMahonwith perfectly, withLeibundgut’s(1988)template.Itisdifficult and theVlightcurveagreeswell,althoughperhapsnot the lightcurvesareobviouslyquitesimilartoSN1992G sparser, havingbeenobtainedonlyatWO,theshapesof red, obtainedwithdifferent instrumental systemseven F= 14.27,R=14.17,and7=14.26mag.Ourlightcurves (e.g., Hamuye/a/.1990). max © American Astronomical Society • Provided by theNASA Astrophysics Data System * Observatories:Leuschner^L),Whitin(W),VanVleck(VV) Date(UT) lb 22- 02-92 20- 02-92 04- 03-92 03- 03-92 01- 03-92 28- 02-92 27- 02-92 21- 02-92 05- 03-92 04- 03-92 20- 04-92 21- 03-92 12- 03-92 10- 03-92 30- 03-92 26- 03-92 25- 03-92 24- 03-92 22- 03-92 13-03-92 13- 03-92 04- 04-92 29- 03-92 29- 03-92 27- 03-92 15- 03-92 05- 04-92 17-03-92 30-04-92 28- 04-92 22- 04-92 02-05-92 02- 05-92 23- 04-92 13-04-92 13- 04-92 12- 04-92 07-05-92 04- 05-92 19- 04-92 16- 04-92 13- 04-92 09-05-92 30-05-92 01- 06-92 27-05-92 25-05-92 22-05-92 02- 06-92 11- 05-92 05- 06-92 16-05-92 12- 05-92 12-06-92 16-06-92 16-06-92 14- 06-92 Table 4.PhotometryofSN1992GatBerkeley,Wellesley,andWesleyan. 8705.642 8673.74 8682.83 8680.86 8679.56 8674.77 8696.69 8694.92 8694.68 8693.76 8691.71 8687.68 8686.71 8707.72 8706.70 8703.68 8702.76 8698.65 8708.87 8711.57 8710.93 8725.69 8725.66 8717.67 8716.78 8734.78 8732.73 8731.69 8742.62 8740.72 8728.68 8744.92 8744.75 8753.73 8751.73 8746.58 8754.61 8775.73 8772.76 8769.72 8767.77 8764.73 8758.78 8789.72 8789.70 8785.70 8778.71 8787.72 8673 8685 8686 8725 8711 8726 8736 8750 8776 13.75 (0.01) 13.72 (0.01) 14.58 (0.05) 15.47 (0.03) 15.78 (0.03) 15.53 (0.02) 16.43 (0.03) 16.38 (0.06) 16.07 (0.04) 16.59 (0.03) 16.97 (0.05) 16.58 (0.06) 17.10 (0.07) 17.25 (0.17) 17.50 (0.06) 17.68 (0.08) 17.52 (0.16) 17.34 (0.15) 17.18 (0.08) 15.907 14.08 13.38 14.00 14.14 13.56 13.78 14.52 15.21 14.75 15.21 15.11 15.58 15.53 15.90 16.09 16.08 16.25 16.61 16.45 16.56 16.83 V E 13.82 (0.01) 15.05 (0.01) 16.26 (0.04) 16.26 (0.14) 16.28 (0.02) 16.55 (0.03) 16.51 (0.03) 16.65 (0.09) 16.76 (0.03) 16.70 (0.16) 16.81 (0.05) amateur astronomersinearlyApril1991(Knightetal heterogeneous observations,including eyeestimatesbyam- theme” ofSNela.Whether its absolutemagnitudewas peculiar SNla,butprobably justa“variationonthe clusion ofthesestudiesisthatSN199ITwasa“mildly” et al(1992)andJeffery(1992).Theprincipalcon- also beenthesubjectofmodelingeffortsbyRuiz-Lapuente ippenko etal(1992a)andPhillips(1992).Ithas tral andphotometricdevelopmenthavebeengivenbyFil- in thispaper.Filippenkoetal ( 1992a)obtainedavalueof unusual hasbeendebatedinthe literatureandisaddressed 1991 ).Extensivediscussionsofitssomewhatpeculiarspec- V= 11.3magforSN1991T basedonalargenumberof max 14.06 13.47 13.65 13.50 14.19 14.22 14.13 13.85 14.24 14.55 14.34 14.27 15.08 14.77 14.81 14.65 14.40 15.54 15.15 15.08 15.68 15.58 15.32 15.76 16.19 15.63 16.45 16.24 16.14 16.85 SN 199ITwasdiscoveredindependentlybyanumberof 13.! 14. 15 15 16 16. 16.55 (0.10) .59 (0.01) .71 (O.f' 99 (0.01) .36 (0.16) 45 (0.03) 16 (0.02) 65 (0.02) 45 < 38 ( 14 (0.03) 14.04 14.18 13.68 13.63 13.58 14.28 14.05 14.19 14.20 14.18 14.05 14.45 14.37 14.17 14.02 14.08 14.59 15.25 14.98 14.69 15.16 15.32 16.05 15.52 15.47 15.87 16.17 16.41 16.35 T i (0.04) \ (0.04) 01) 3.3SN1991T "ÜEsT" VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV VV w w W" W W W W W L L W L L L L L L L L L L L L L L L L L L L L L L L L L L 1106 1993AJ 106.1101F 1107 FORDETAL:PHOTOMETRYOF3SNs Wesleyan. TheVtemplateofLeibundgut (1988)isalsoshown. Fig. 3.VRIlightcurvesforSN1991M fromdataobtainedat Berkeley, Wesleyan,andWellesley.TheVtemplateofLeibundgut Fig. 2.VRIlightcurvesforSN1992Gfromdataobtainedat (1988) isalsoshown. © American Astronomical Society • Provided by theNASA Astrophysics Data System both magnitudeandtimetoget thebestdegreeofoverlap ner. First,theindividuallight curvesin/wereshifted R and/lightcurvesareindistinguishablefromthoseofSN shown inFig.6.Theywereformed inthefollowingman- is uncertainwhetherthespectralpeculiaritiesand template forthefirstfortydays,andthenalittlefaster.It slightly unusualslopesinVarerelated.Theshapesofthe template, asnotedbyPhillipsetal(1992),maybeseenin deviation oftheVlightcurvefromLeibundgut’s(1988) ment withthatgivenbyPhillipsetal(1992).Asmall with thatofPhillipsetal(1992)whichwaskindlypro- Figs. 4and5.Thedeclinerateisslightlyslowerthanthe of 11.45±0.05.Ourtimemaximumisingoodagree- a marginally,butnotsignificantly,brightervalueforF cally brighterbyabout0.05magandwe,therefore,derive sets isreasonablygood.OurVmagnitudesaresystemati- vided tousintabularformbyPhillips&Leibundgut to thoseofSN1992G,1991M,andLeibundgut’s They appearquitesimilar,althoughperhapsnotidentical, CTIO. OurlightcurvesforSN1991TareshowninFig.4. ateur astronomers.Phillipsetal(1992)found 1991M andSN1992G. (1993). Ascanbeseen,theagreementbetweendata (1988) Vtemplate.InFig.5wehavecombinedourFdata ^max— 11.50±0.04magfromtheirCCDphotometryat max Composite lightcurvesforthe threesupernovaeare Wesleyan. TheVtemplateofLeibundgut(1988)isalsoshown. Fig. 4.VRIlightcurvesforSN199ITfromdataobtainedat 5.4 TimesofMaximaandComposite LightCurves JD -2440000 1107 1993AJ 106.1101F it hasthemostsubstantialstructure—i.e.,secondary peak. CompositelightcurvesinVandRwereformedby mum inV)andFgivenTable5foreachsupernova. This procedureyieldsthevaluesfort(thetimeofmaxi- shifts togetthebestdegreeofoverlap,againjudgedbyeye. adopting thesetimeshiftsandapplyingonlymagnitude 1108 FORDETAL.:PHOTOMETRYOF3SNs The agreementbetweenthecompositeandtemplateis also giveninthattable.OurVcompositelightcurveis Values ofRand/ati,basedonthecompositecurves,are as judgedbyeye.WechoseIthereferencefilterbecause by Leibundgut(1988).ThecompositeRandIlightcurves of atemplateisvalidenterpriseinsomeaveragesense.It reasonably good.ThissupportsthenotionthatmostType shown inFig.6alongwithLeibundgut’s(1988)template. brighter thantheVtemplateatsomeepochs,othertwo also providessupportfortheparticularVtemplatederived la supernovaearesufficientlyhomogeneousthatformation more. Figure6demonstratesthat,whileSN199ITis pernovae maywelldifferfromthetemplateby0.1magor should proveusefulastemplatesforcomparisonwithother the reddeningisessentiallyzero inthedirectionofallthree time shiftsderivedfromthe/ lightcurves;noreddening SNe la.Itshouldbenoted,however,thatindividualsu- host galaxiesaccordingtoBurstein &Heiles(1982).Phill- corrections havebeenapplied. The Galacticcomponentof shown inFig.7.Theywereformed byapplyingonlythe supernovae areoftenfainterthanthetemplate. max Q 0 > shown. Fig. 5.AcomparisonbetweentheFlightcurvesobtainedforSN Leibundgut 19XX).TheVtemplateof(1988)isalso 199IT atWesleyanandCTIO(Phillipsetal1992;Phillips& Composite colorcurvesforthe threesupernovaeare © American Astronomical Society • Provided by theNASA Astrophysics Data System 11.5 12.5 13.5 14.5 11 — 12 13 14 15 PT - O - O 8360 83808400842084408460 I i O IAUCire. o CTIOSpectrophotmetry a Wesleyan □ CTIOCCD • Leibundgut _L JD -2440000 H 11—I|—Ip SN 1991T i ■.l Taylor (1986)yieldsvaluesofE(F—R)=0.07magand and thereddeningslopesinCousinssystemgivenby and theassumptionthatintrinsiccolorofaTypelaSN mag forSN199ITfromitsB—Vcoloratmaximumlight ips etal(1992)deriveareddeningofE(2?—F)=0.13 ists betweentheobservedcolorsofallthreesupernovaeas at Bmaximumis2?—F=0.0mag.Adoptingtheirresult for thereddeningofSN199ITiscorrect. that allthreeSNehavethesameintrinsiccolorsasafunc- a functionoftimesuggeststhatthereddeningsSNe E(7£—/)=0.09 mag.Therathergoodagreementthatex- a TypelasupernovaarearoundF—22=0.0magandR—I find thatatthetimeofFmaximum,intrinsiccolors reddening correctedcolorcurvesareshowninFig.8.We estimated uncertaintyofabout0.05magineachcase.The apply. ThisyieldsvaluesofE(j?—F)=0.18magforSN tion oftime,andthatthenormalreddeninglawslopes opinions expressedonbothsides (cf.vandenBergh& received agooddealofattention recentlywithvarying Pazder 1992;Branch&Tammann 1992;Branch&Miller 199IT. Wemayestimatethosereddeningsbyassuming 1991M and1992GarenotverydifferentfromthatofSN 1991M andE(Æ-F)=0.25magforSN1992G,withan = —0.3mag,assumingthatthePhillipsetal(1992)value Fig. 6.CompositeVRIlightcurvesforSNe1991M,199IT,and 4. ARETHESUPERNOVAEINOURSAMPLE“STANDARD Leibundgut’s (1988)Vmagnitudetemplateisalsoshown. 1992G. TimeandmagnitudeshiftsadoptedaregiveninTable5. The issueofwhetherSNela are standardcandleshas CANDLES?” Days 1108 1993AJ 106.1101F been usedinmostpreviousanalyses.Inparticular,redden- now producedfourgoodlightcurvesforTypela supemovae—the threediscussedinthispaperandSN small sample,ithastheadvantageofbeinghomogeneous the Typelasupemovaeinoursampleappeartobestan- take abrief,preliminarylookatthequestionofwhether den Bergh&Pazder1992),canbeapplied.We,therefore, ing corrections,whicharepotentiallyofgreatimportance and ofgoodphotometricprecisioncomparedtowhathas exist whichhaveabnormallightcurvesatallcolorsandare dard candles. ippenko etal1992b;Leibundgut1993).Itslight state unequivocallythatnotallSNelaarestandardcan- substantially subluminous.Theirexistenceallowsusto ingly clear.Mostimpressiveisthecompleteabsenceofa curves arecomparedinFig.9withthethreenormalType dles. ThebeststudiedexampleisSN199IbginM84(Fil- 1109 FORDETAL.:PHOTOMETRYOF3SNs much redderandfainterthannormalTypelasupemovae. Filippenko etal(1992b)demonstrate,SN199Ibgisalso secondary peakinthe/filterorshoulderRfilter.As la SNediscussedinthispaperandthedifferencesarestrik- 199 Ibg(Filippenkoetal1992b).Whilethisisstilla 1993). Theobservationalprogramsdescribedherehave It reachedanapparentbrightnessatmaximumofonly (e.g., Barbonetal1990;DellaValle&Panagia1992;van y First, itisnotedthatsomeTypelasupernovaeclearly Fig. 7.Observedcolorsasafunction of timesinceFforSNe © American Astronomical Society • Provided by theNASA Astrophysics Data System 199 IM,1991T,and1992G. max 0 20406080 100 1991M 1992G 1991T SET" AGE vr(Vn>.:) JgTC^r 30-04-91 8376.7±1.011.45±0.0511.38±0.0511.64±0.05 22-02-92 8674.7±1.013,63±0.0513.6013.66 19-03-91 8334.8±2.014.55±0.114.820.1 Table 5.TimeofmaximaandmagnitudesatVmaximum. VR and R—7=0.0mag,considerablyredderthanthesuper- cluster SNla.AtVmaximumitscolorswereV—R=0.2 novae describedhere.Thiscannotbeattributedtointer- supernova islocatedinanellipticalgalaxy,andtheshapes ture isnotseenwiththeproperstrength.Also, stellar extinctionsincetheexpectedNaIinterstellarfea- cally faintandredTypelasupernova.Filippenkoetal of thelightcurvesareunusual.Clearlythisisanintrinsi- light curvesdidnotshowthesecondarypeakscharacter- mal Typela.AlthoughnotobservedinRor/,itsJHK threat totheuseofSNelaascosmologicalprobes,since with strikinglyunusuallightcurvesdoesnotposeamajor istic ofnormalSNelaatthosewavelengths(Eliasetal harder todetect.Moreworrisomearesupernovaesuchas they aresoreadilyidentifiableand,beingsubluminous, than usualdeclineinF,butwasessentiallyindistinguish- only initspremaximumspectrumandhadaslightlyslower SN 199IT,whichexhibitedobviousspectralpeculiarities able initslightcurvefromnormalSNelamostrespects. If itsluminositywasabnormallyhigh,asFilippenkoetal F=14, about1.6magfainterthanexpectedforaVirgo ( 1992b)suggestthatSN1986Gmaybeasimilarlyabnor- 1985; Frogeletal1987). The existenceofasmallnumberTypelasupernovae Fig. 8.Intrinsiccolorsasafunctionof timesinceFforSNe are basedonanadoptedvalueofE(5— F)=0.13magforSN > c* & 7 0 199IT, andtheassumptionofanormal reddeninglaw. 199 IM,1991T,and1992G.Reddenings aregiveninthetextand max -.5 -.5 .5 .5 0 1 1=1 - □O(£ - ASN1991M n iJf—i—i—^—i—i—^—i—r +-I-H 1I'I11 OSN 1992G □ SN1991T _L O ÄO 0 20406080 100 'b a o a □ A43 T o J ^ijIL AGE o O A Intrinsic Colors o □ o 1109 1993AJ 106.1101F -1 1110 ings relativetoSN199IT,however,thereisanotherap- to useTypelasupernovaeasstandardcandles.Phillips will benecessarytouseextremecautionwhenattempting Tully-Fisher distancefortheparentgalaxyandaver- value ofFforSN199ITisingoodagreementwith age apparentbrightnessofVirgoclusterSNela.Sinceour et al(1992)concludedthattheabsolutemagnitudeofSN distance tothegalaxywouldyieldsameresultastheirs. Phillips etal(1992),ananalysisusingtheTully-Fisher proach thatwecantaketothisissue,asisnowdiscussed. Having twootherSNelawithknowndifferentialredden- the HubbleconstantinkmsMpcatpresentepoch pernova atmaximum,correctedforinterstellarextinction, Hubble’s lawyields and visthevelocityofHubbleflowatlocation and Mtobttheabsolutemagnitudeatmaximum.His Here wetakeFtobetheapparentbrightnessofsu- (1992a) andRuiz-Lapuenteetal.(1992)haveargued,it 199IT wassimilartothatofotherSNela,basedona max H v0 0 peculiar TypelaSN1991bg(Filippenkoetal.1992b). Fig. 9.AcomparisonbetweentheV,R,and/lightcurvesof relatively normalTypelaSNe1991M,199IT,and1992G,the Combining theequationfordistancemoduluswith F—5 \og{v)=Mlog(jEf+2 0HV © American Astronomical Society • Provided by theNASA Astrophysics Data System FORD ETAL.:PHOTOMETRYOF3SNs 1991M IÓ11512275 2463 0.514.1-2.7-2.9 1992G NGC32941561 1807 0.712.9-3.0-3.3 1991T NGC45271617 1912 0.411.1-4.9-5.3 1 1 SÑ Galaxyv(kms“) ««.(km a”)AvVÖV—51og(t/)51og(t/ 0e Days Table 6.Velocitiesandextinctioncorrected magnitudes. 1 note thatthesearebasedontheassumptionB—V three supernovaeinoursample.Itisquitestraightforward in thequantityonleft-handsideofequationfor Type laSNearestandardcandlesbylookingatthescatter ishingly small.Wecan,therefore,testthehypothesisthat to evaluateFgiventhereddeningsderivedinSec.3.We thors (e.g.,Tammann&Leibundgut1990)maybevan- scatter thanthereisinMwhichaccordingtosomeau- the parentgalaxy.Theright-handsideofthisequationisa found amongthesupernovaeinoursample.Adoptedval- will changebythesameamountsincetheyareallbased extinction correctedmagnitudesofallthreesupernovae dening ofSN199ITislessthan0.13mag,and(2)the important pointsarethat(1)itisunlikelythered- the workofBarbonetal(1973).Forthisdiscussion, that avalueof—0.15magismostappropriate,basedon siderably bluervalues;Branch&Tammann(1992)suggest constant, ifAfisaconstant;i.e.,thereshouldbenomore tial scatterinthequantityF—51og(u#)whichmaybe uncertainties inreddeningcannotaccountforanysubstan- ultimately ontheadoptedreddeningofSN199IT.Hence, ues ofAandFatmaximumforthesethreesupernovae to therestframeofLocalGroup,arealsogivenin are giveninTable6. Table 6.Theyarebasedon21cmdataobtainedbyGiov- and asyetunpublishedsurvey.Theyagreewellwithother anelli andHaynes(Salzer1993)aspartofanextensive nous (bymorethan2mag!)orthatitsparentgalaxy, conclude eitherthatSN199ITissubstantiallyoverlumi- adopted. Ifonesimplyusesvasanestimateofthe measures intheliteratureassummarizedbyPalumboetal The situationdoesnotimprovewhenonetakesintoac- NGC 4527,hasaverylargepeculiarvelocityrelativetothe ingly, itisSN199ITwhichthediscordantvalue;SNe large (seeTable6),exceedingtwomagnitudes.Interest- resulting variationinthequantityF—51og(y)isquite Virgo Cluster.Assumingaradialinfallat300kms(e.g., count thelikelymotionofLocalGrouptowards Hubble flow(orthatbotheffectsarepresentinthedata). Local GroupvelocitygivenbyPalumboetal(1983)were (e.g., vandenBergh&Pazder1992)haveproposedcon- Tully 1988),onecancorrectthespeedsofothergal- =0.0 magatF(Hamuyetal1991).Someauthors from 2.1to2.2mag. to increasethedeviationofSN199ITinF—51og(u) corrected velocities(v)aregiveninTable6.Theeffectis axies forthepeculiarvelocityofLocalGroupandthese 0 Vi lute magnitudeofSN199IT,wecancalculatewhatthe candles, andthatthereisnothingunusualabouttheabso- F 0 v0 1991M and1992Gagreewellwitheachother.Onemust (1983). Thecorrectionsfromheliocentricvelocitytothe Hi 0 max 0 c Radial velocities(u)fortheparentgalaxies,corrected If weassumethatSNelaare,infact,goodstandard 1110 1993AJ 106.1101F _1 -1 -1 -1 -1 cluster, wefindthatNGC4527wouldrequireapeculiar the dataonSNe1991Mand1992Gsuggest,using must be.AdoptingV—5\og(v)=3.1±0.4magwhich peculiar velocityofNGC4527relativetotheHubbleflow it hasa“normal”absolutemagnitude.Theerrorbars velocity of1220±150kmsrelativetotheHubbleflowif velocities correctedforLocalGroupinfallintotheVirgo that NGC4527ispartofthe“southernextension”or“X peculiar velocityseemsexceedinglylarge,itmustbenoted Tammann &Leibundgut(1990).Whileatfirstglancethis intrinsic spreadinMofabout0.25magasproposedby ential reddeningcorrections,Virgoclusterinfallrate,and quoted herereflectuncertaintiesinthephotometry,differ- cloud” oftheVirgocluster(e.g.,deVaucouleurs1973; infall velocityof986kmsintheirmodel.Weareleft ner 1991).Forexample,Tully&Shaya(1984)assignitan at substantialspeed(Tully&Shaya1984;PeletierWin- near-side memberwhichisundergoinginfalltothecluster the unfortunatepositionthatunusualsupernovainour Kenney &Young1988)andhaslongbeenproposedasa unusual. Clearlytheonlyrecourseistoincreasesample sample happenstoliewithinagalaxywhosekinematicsare parent galaxiesofTypelasupernovae,includingNGC attempted tomeasurepeculiarvelocitiesforanumberof pothesis thatSN199ITwasanoverluminousla. size! Atpresentwecanneitherconfirmnorrefutethehy- though sufficientdetailsoftheirmodelarenotgiventobe pears tobelessthanoursbyaboutafactoroftwo(al- 4527, byassumingtheyaregoodstandardcandles.They 1111 FORDETAL.:PHOTOMETRYOF3SNs certain). OnedifferenceisthattheyhaveconsideredSN agree withourresultthatthisisanear-sidemembergalaxy of theVirgocluster,buttheirderivedinfallvelocityap- of ameanvalueMatmaximum.The“conventional” leads toanestimatefortheHubbleconstantuponadoption mag quotedaboveforthequantityM—5\og(H)+2 proper directiontobringitintoagreementwithourresult. substantially influencetheirderivedinfallvelocityinthe extinction inBmustbeatleast0.5mag,andthiswould observed B—Vcolorofthesupernovaatmaximum, Burstein &Heiles(1982)extinctionvalue.Basedonthe 0H found. ArecentrecalibrationbyPierceetal.(1992) ment withwhatTammann&Leibundgut(1990)have which leadsto^f=50±10kmsMpc,ingoodagree- value isM=—19.6(e.g.,Branch&Tammann1992), km sMpcusingourdata.DellaValle&Panagia be discoveredatthecurrentrate andifourprogramscon- based onotherdatasets.IfType lasupernovaecontinueto of —19.24±0.18mag. Our conclusionisthatthe km sMpc,whichmaybe comparedwiththeirresult would predictM=—18.9±0.4 magforHq—75 solute magnitudeatmaximum(foragivenHubblecon- yielded A/y=—18.7mag,whichleadstof/=75±1 v stant). AssumingB—V=0.0magatL,ourresults data andanalysispresentedhere areconsistentwithresults 199IT tobeessentiallyunreddened,applyingonlythe B, derivingextinctioncorrectionsandcalibratingtheab- v v0 ( 1992)haveanalyzeddataon23TypelaSNeobservedat 0 v B 0 max We notethatMiller&Branch(1992)haverecently Finally, wenotethatthemeasurementof—3.1±0.4 © American Astronomical Society • Provided by theNASA Astrophysics Data System possible tostudythepeculiarvelocitydistributionofgal- upper limittothatscatter)inMmaybe.Itshouldalsobe more precisely,todeterminewhattheirtruescatter(or hypothesis thatTypelaSNearegoodstandardcandlesor, that theSNelaare,infact,reliablestandardcandles. axies bythismethod(cf.Miller&Branch1992),assuming within afewyearstotestinmorerigorousmannerthe tinue toobtaindataofthisquality,itshouldbepossible template lightcurve.Thisisnotunexpected,giventhesim- ported hereistheexistenceofasecondarypeakin/ be awealthofdataonTypelaSNeintheCousins/band. Johnson I.However,withthenowwidespreadavailability ilar shapesthathavebeenfoundintheinfraredand of redsensitiveCCDchips,itislikelythattherewillsoon and obtainedonlyafterprimarymaximum,toahighly therefore, thatuseoftheItemplatewillleadtoimproved structured templatesuchas/,thantoBorV.Itispossible, It ismucheasiertofitdata,evenwhensparselysampled 77, andKreportedbyEliasetal.(1985).Thissuggests values oftandFfornearbyTypelasupernovaeas- within theerrors)totimeofsecondarypeakin7, peak in7,23±1daysaftermaximumF,isidentical(to timescale oftwotothreeweeks.Thetimethesecondary infrared ataboutthetimeofmaximumanddissipatesona known originwhichdepressesthecontinuuminnear- et al.(1981,1985)attributeittoanopacitysourceofun- generally acceptedexplanationofthephenomenon.Elias infrared lightcurvesofTypelaSNe.Atpresentthereisno understand thereasonforsecondarypeakinnear- logical model(e.g.,Leibundgut1991). to testthetimedilationpredictionofstandardcosmo- possible toobtainexcellentmeasuresofFand,perhaps, ture intheirobserved/lightcurves,butitshouldstillbe For distantTypelaSNe,redshiftswillmodifythestruc- suming, ofcourse,thatmostdoadheretothetemplate. that thesamephysicalprocessisresponsibleforboth,and vae havebeenobtainedbyLynchetal.(1990,1992);these from around0.7/zmorlessto2.2more.Graham must actoverawiderangeofnear-infraredwavelengths, that theadditionalopacitysource(ifiscause) illuminate, butdonotsolve,theproblem. data inthe0.9to1.35/zmrangeforfiveTypelasuperno- et al.1990)arguethatthisisunlikely.Newspectroscopic quent studies(Harkness&Wheeler1990;Filippenko, v curve shapes,supportingLeibundgut’s (1988)result.We Type lasupernovae(includingsomespectroscopicallype- of SN199IT;itmayor nothavebeensomewhat cannot reachaclearconclusion ontheabsolutemagnitude culiar oneslikeSN199IT)havenearlyidenticallight good dealmoredataarerequired beforeafirmconclusion mogeneity formostTypelasupernovae whilenotingthata overluminous. Onthewholewe supportthenotionofho- {)max (1986) hasproposedthatsiliconisresponsible,butsubse- max One ofthemoreinterestingaspectsresultsre- These observationsshouldalsohelpspurattemptsto The photometryreportedheresuggeststhatnormal 5. DISCUSSION 1111 1993AJ 106.1101F logical probes. in significantlyimprovedlimitsonthescatterabsolute modeling ofpeculiarvelocitiesgalaxiescouldsoonresult of Typelasupernovae,whichshouldleadtolessuncertain their generoussupportofastronomyattheKNACinsti- more definitiveassessmentoftheirpotentialuseascosmo- magnitude oftheTypelasupernovae.Thiswillleadtoa reddening corrections,andimprovedmeasurements can bereached.Thecombinationofimprovedphotometry the PerkinFundfortheirsupportofastronomyatWes- tutions. 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