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1、OntheSpectrumandNatureofthePeculiarTypeIaSupernova1991TADAMFISHER,DAVIDBRANCH,KAZUHITOHATANO,andE.BARONDepartmentofPhysicsandAstronomy,UniversityofOklahoma,Norman,OK73019–0225,USAReceived;acceptedarXiv:astro-ph/9807032v12Jul1998–2–ABSTRACTAparameterizedsuperno
2、vasynthetic–spectrumcodeisusedtostudylineidentificationsinthephotospheric–phasespectraofthepeculiarTypeIaSN1991T,andtoextractsomeconstraintsonthecompositionstructureoftheejectedmatter.TheinferredcompositionstructureisnotlikethatofanyhydrodynamicalmodelforTypeIa
3、supernovae.EvidencethatSN1991TwasoverluminousforanSNIaispresented,anditissuggestedthatthispeculiareventprobablywasasubstantiallysuper–Chandrasekharexplosionthatresultedfromthemergeroftwowhitedwarfs.Subjectheadings:radiativetransfer—supernovae:individual(SN1991
4、T)—supernovae:general–3–1.IntroductionSN1991TwasawellobservedandspectroscopicallypeculiarTypeIasupernova(Filippenkoetal.1992;Ruiz–Lapuenteetal.1992;Phillipsetal.1992;Branch,Fisher,&Nugent1993).Beforeandaroundthetimeofmaximumlightitsopticalspectrumshowedstrongl
5、inesofFeIIIratherthantheusualSNIalinesofsinglyionizedelementsofintermediatemass,andalthoughthedeepredSiIIabsorptionthatischaracteristicofSNeIafinallydiddevelopaftermaximumlight,itneverreacheditsusualstrength.Inthispaperwereporttheresultsofastudyofphotospheric–p
6、hasespectraofSN1991Tusingtheparameterizedsupernovaspectrum–synthesiscodeSYNOW(Fisheretal.1997;Fisher1998).InSection2,previousstudiesoftheopticalspectraofSN1991Tarebrieflysummarized.Ourmethodof“direct”spectralanalysisisdescribedinSection3,andresultsarepresentedi
7、nSection4.InSection5wediscussevidencethatSN1991TwastooluminoustobeaChandrasekhar–massexplosion,andsuggestthatitprobablywasasubstantiallysuper–Chandraskharexplosionresultingfromthemergeroftwowhitedwarfs.AgeneraldiscussionappearsinSection6.2.PreviousStudiesofSN1
8、991TSpectraFilippenkoetal(1992)presentedopticalspectraobtainedfrom−12to+47days.(Thoughoutthispaper,epochsareindayswithrespecttothedateofmaximumlight,1991April28;Liraetal.1998).They
