Mul$bandPhotometryintheEarlyDetec$onofTypeIaSNeforWFIRST
MollyGrabillAstronomyandPhysics
[email protected],DiscoveryandtheUniverse
AbstractandResearchQues$on
TheWideFieldInfraredSurveyTelescope(WFIRST)isanastrophysicsmissionpresentlyconducGngpre-phaseAstudies.OneoftheprimaryscienGficmissiongoalsforWFIRSTistostudytheeffectofdarkenergyontheevoluGonoftheuniverse.TheWFIRST’sTypeIaSupernovae(SNe)SurveywillanswerthatquesGonbyusingtheWide-FieldInstrumenttomeasurethedistanceandredshiQoftheSNetoobservehowtheexpansionoftheuniverseisacceleraGng.OnlyIaSNeareusefulforthispurpose.Poznanskietal.(2002)developedanewclassificaGonmethod,findingthatSNeofdifferenttypesoccupieddifferentlocaGonsincolor-colordiagrams.TheirstudyuGlizedtheJohnson-CousinsUBVRIfilters(e.g.aplotofB-Vcolorsvs.R-Icolors)toobservehowthecolorsignatureofaSNvariesdependingontype.Inthisproject,thespectraltemplatesfromdifferenttypesofSNewereusedtogeneratecolor-colordiagramsusingthenear-IRfiltersthatwillbeintheWFIRSTobservatory,tofindtheuniquesignaturesofeachtypeofSNe.WereportresultsfromastudyoffiltercombinaGons,andhowtheseallowforthedevelopmentofcriteriathatdiscriminateagainstthemajorityofnon-IaSNeearlyintheirevoluGon.ThistechniqueenablesearlyselecGonofafairlypureSN-Iasamplesothatfollow-upobservaGonsofIaspectracanbeobtainedefficiently.ByusingthefiltercomparisonsJ-Hvs.H-F,Y-Jvs.J-H,andZ-Yvs.Y-Jinthecolor-colorplots,itwasdiscoveredthatTypeIaSNefollowauniquepathwheretheywouldbrighteninthebluer,near-infraredwavelengthsbeforepeak.ThiscanbeseenbytheleQwardmovementfromDay-19toDay0onthegraphs.ThistypeofmovementischaracterisGcfortheIaSNe,andisnotexhibitedinthepre-peakevoluGonoftheothertypesofSNe.ThisuniquesignaturewillallowforearlyidenGficaGonofTypeIaSNefortheWFIRST.
Background:IaSNeAmongallthedifferenttypesofsupernovaestudiedinthisexperiment,TypeIaarethemostunique.Theycontainnohydrogen,butasinglyionizedsiliconlinenearpeaklight.TheyalsoaretheonlytypeofSNethatcomefromthermalrunaway,aprocessthatoccurswhenawhitedwarfandanotherstararelockedinabinaryorbitcloseenoughthatmassbeginstoaccretefromonestarontothewhitedwarf.OncethewhitedwarfreachesitscriGcalmassattheChandrasekharlimit,itexplodes,formingtheTypeIaSNe.ThistypeofformaGoncausestheiruniquepropertyas“standardcandles”:theyconsistentlyexplodeatasimilarabsolutemagnitude(-19.3<M<-18.3).ThisvariaGoninintrinsicbrightnessiscorrelatedwiththeshapeofthelightcurve,someasurementsoftheevoluGonofeachSNcanbeusedtomeasureitsdistancewithanuncertaintyofonlyafewpercent.ThedistancemeasurementswillbeusedtofulfilloneoftheWFIRSTsciencegoals:understandingthenatureofdarkenergy.
MethodologyTocompletethetasksrequiredoftheexperiment,IdevelopedmulGplepiecesofsoQwareinPythonthatfollowedthesubsequentsteps:• ReadinaSNtemplate• NormalizethetemplatespectratoagivenB
magnitude(B=–19.3wasusedinthisexperiment)
• ApplyredshiQtonormalizedspectrainput(z=1wasused)
• ComputemagnitudesthroughlistofdesiredWFIRSTfiltersataspecificGme
• CreateanarrayoffiltercomparisonvaluesbaseduponidenGfiedfilters
• Plotfinalcolor-colordiagram
DiscussionofGraphsThegoalofthisprojectwastouGlizecolor-colorfiltergraphstodevelopamethodofeasilyandquicklyidenGfyingIaSNe,basedupontheiruniquesignature.Threegraphswerecreatedthatcoverthespectrumofnearandshort-wavelengthinfraredfilters,andoverallofthegraphs,theIaSNeexhibitedtwosignificantcharacterisGcs.First,earlypointsintheevoluGon(Day–19->0)wereallinthe‘bluest’regionoftheplots.ThisdisGnguishedIafromallbutII-PSNe(andII-LintheJ-Hvs.H-Fplot).WhatmadetheTypeIauniquewasthedirecGonthatitmoved.TheII-P&II-LSNmovedalongthe+Xaxis,whetheritwasY-J,J-H,orH-F,indicaGngthatitwasgraduallygeongredderoverGme.TheTypeIamovedintheoppositedirecGonunGlafewdaysaQerthepeakemission,aQerwhichtheirevoluGonwouldfollowthesametrendofreddeningastheothertypesofSNe.TheimplicaGonsofthisarepowerfulandcouldbeuGlizedbyWFIRSTaQerlaunch.ItappearsthattheposiGonandmoGonincolor-colorspacecanbeusedtodeterminethespectraltypeofSNeearlyintheirevoluGon.ThiswouldenableWFIRSTtoselectafairlypureSN-Iasampleusingonlyimagingdata,sothatfollow-upobservaGonsofIaspectracouldbeconductedwithease.OnlytypeIaSNecanbeusedforcosmologyanddarkenergyexperiments,soitiscrucialthatWFIRSTisabletodifferenGatehighly-redshiQedSNesothepropermeasurementsaretaken.
References/Acknowledgements
Kessler,R.,etal.2009,PASP121,1028Poznanski,D.,etal.2002,PASP114,833IwouldliketothankDr.JeffreyKrukforhisguidanceandpaGencewithmyconstantastronomyquesGons.IwouldalsoliketothankWFIRSTprojectmanagersKevinGradyandCathyPeddiefortheirsupportandenthusiasmthroughoutmyinternship.IwouldfinallyliketothankDr.AlanPeelforhismentorshipthroughthisprocess.
ConclusionThisprojectexaminedtheuseofcolor-colordiagramstodeterminethetypeofasupernovaatearlyGmes,andfoundthatitappearspromisingfordisGnguishingIaSNeofinterestforcosmologyfromtheother,morenumerous,typesofSNe.ThistechniquerequiresonlyimagingdataforSNdetecGonandtyping,whichsimplifiesWFIRSTdesignandoperaGons.FuturestudieswilladdresstheimpactofuncertainGesinquanGGessuchas:dustexGncGon(inboththehostgalaxyandintheMilkyWay),fluxmeasurements,andintheSNredshiQ.ThesestudieswillhelpdeterminethedetailsofthenecessaryobservaGonstobemadebyWFIRST,andwhatancillarydatamayberequired.
Figure3:SN1994DseeninthelowerleQcornerofgalaxyNGC4526.Anexampleofthehigh
luminosityofaTypeIaSNatpeak.
Source:Hubblesite
Figure2:TheTarantulaNebula:asupernova
remnantwithstar-formingregions
Source:Hubblesite
Figure4:ThespectraldataforaType1aSNeatvariousdaysbeforeandaQerpeak.TheearlyevoluGonischaracterizedbybotharapidbrighteningandaslightshiQofthepeakfluxto
shorterwavelengths,withsubsequentevoluGondemonstraGngagradualdimmingandshiQofthepeakfluxtolongerwavelengths.
Figure5:Thepeakspectraforthe5differenttypesofSNeusedinthisexperiment:Ia,Ib,Ic,II-L,andII-P,withtheWFIRSTfilters
atcorrespondingwavelengths.
Figure6:Color-ColorDiagramcomparingthebluestfilters,Z-Yvs.Y-Jatz=1.TheGmeevoluGonoftheSNeisillustratedbya
connectedplotofthecolorsforeachdatepresentinthespectraltemplate.ThelocusofIapointsarewell-separatedfromallbuttheII-Ppoints,anddifferfromthelauerinbehavior:theIapointsarenearlystaGonarypre-peak,whileIIPpointsmove
significantly.
Figure7:Color-ColorDiagramforY-Jvs.J-Hatz=1.TheIapointsarewell-separatedfromallbuttheII-PpointsatearlyGmes,andthelauercanbedisGnguishedduetodifferencesinevoluGon:Ia
pointsshiQtomorenegaGvevaluesofJ-HandY-JasGmeincreases,whileII-PpointsmoveintheoppositedirecGon.
Figure8:Color-ColorDiagramcomparingthereddestfilters,J-Hvs.H-Fatz=1.ThisfiltercombinaGonappearssomewhatlesspromisingthantheothers,asthelocusofII-Lpointsalso
overlapswiththeIapoints.TheonlyconGnuoustrendbetweenallthreegraphs(figures7-9)isthereversemoGonoftheTypeIa
linebeforepeak,whichwillbefurtherexplainedinthediscussionsecGon.Figure1:A3Dmodelofthe
interioroftheWide-FieldInstrument(WFI)onWFIRST.Thisinstrumentcontainsthefocalplaneassemblyandtheelementwheel,whichholdsthefiltersusedinthisexperiment.ThisinstrumentwillbeusedtosurveythousandsofIaSNe.Source:JonathanRuffa
Comple$ngtheResearchIwillbeconGnuingmyworkonthisresearchprojectatGoddardSpaceFlightCenterthroughthespringof2016.There,IwillconGnuecoding,butthisGmetakingintoaccountanyofthemanytypesoferrorthatwillbeintherealdatasetscapturedbyWFIRST.TherewillbeproblemswithdustexGncGon,bothinthesolarsystemandtheintergalacGcmedium.ThisdustexGncGonwillcauseaoverallreddeningofthecolormagnitudes,andmustbetakenintoaccountwhenanalyzingthechangesincolormagnitudes.Overallinthisproject,otherthantheobviousoflearningofhowtocodeinPythonandmoreabouttypeIaSNe,IprimarilylearnedhowtoconductmyselfinaprofessionalscienGficenvironment,anexperienceIwouldnotofhadattheUniversityofMaryland.
