Constraints on the Progenitors of SNeIa & Implicat

arXiv:astro-ph/0104257v116Apr2001ConstraintsontheProgenitorsofTypeIaSupernovaeandImplicationsfortheCosmologicalEquationofStateInmaDom´ınguezDept.deF´ısicaTe´oricaydelCosmos,UniversidaddeGranada,18071Granada,[e-mail]¨oflichDepartmentofAstronomy,TheUniversityofTexasatAustin,TX78712Austin,[e-mail]rvatorioAstronomicodiCollurania,64100Teramo,[e-mail]revolutioncalculationshavebeenperformedtoquantifytheinfluenceofthemainsequencemassMMSandthemetallicityZoftheprogenitoronthestructureoftheexplodingWDwhicharethoughttobetheprogenitorsofSNeIa.Inparticular,westudytheeffectsofprogenitorsonthebrightnessdeclinerelationM(ΔM15)whichisacornerstonefortheuseofSNeIaascosmologicalyard-stick.BoththetypicalMMSandZcanbeexpectedtochangeaswegobackintime.Weconsidertheentirerangeofpotentialprogenitorswith1.5to7M⊙andmetallicitiesbetweenZ=0.02to1×10−10.Ourstudyisbasedonthedelayeddetonationscenariowithspecificparameterswhichgiveagoodaccountoftypicallightcurvesandspectra.BasedonthestructuresfortheWD,detailedmodelcalculationshavebeenperformedforthehydrodynamicalexplosion,nucleosynthesisandlightcurves.Themainsequencemasshasbeenidentifiedasthedecisivefactortochangetheenergeticsoftheexplosionand,consequently,dominatesthevariationsintherise-timetodeclinerelationoflightcurves.MMShaslittleeffectonthecolorindexB-V.ForsimilardeclineratesΔM15,thefluxatmaximumbrightnessrelativetothefluxontheradioactivetaildecreasessystematicallywithMMSbyabout0.2m.Thischangegoesalongwithareductionofthephotosphericexpansionvelocityvphbyabout2000km/sec.AchangeinthecentraldensityoftheexplodingWDhassimilareffectsbutproducestheoppositedependencybetweenthebrightnesstotailratioandvphand,therefore,canbeseparated.Themetallicityalterstheisotopiccompositionoftheouterlayersoftheejecta.SelectivelineblanketingatshortwavelengthsdecreaseswithZandchangessystematicallytheintrinsiccolorindexB-Vbyupto−0.06m,anditaltersthefluxesintheUbandandtheUV.ThechangeinB-Viscriticalifextinctioncorrectionsareapplied.TheoffsetinthecalibrationofM(ΔM15)isnotmonotonicinZand,ingeneral,remains≤0.07m.Weuseourresultsandrecentobservationstoconstraintheprogenitors,andtodiscussevolutionaryeffectsofSNeIawithredshift.Thenarrowspreadinthefiducialrise-timetodeclinerelationinlocalSNeIarestrictstherangeofmainsequencemassestoafactorof2.The–2–upperlimitof1dayforthedifferencebetweenthelocalanddistancesamplesupporttheneedforapositivecosmologicalconstant.Thesizeofevolutionaryeffectsaresmall(ΔM≈0.2m)butareabsolutelycriticalforthereconstructionofthecosmologicalequationofstate.Subjectheadings:supernovae-cosmologicalparameters-distancescale1.IntroductionThelastdecadehaswitnessedanexplosivegrowthofhigh-qualitydataforsupernovaebothfromthespaceandgroundobservatorieswithspectacularresults,andnewperspectivesfortheuseofSNeIaascosmologicalyardsticksandforconstrainingthephysicsofsupernovae.Oneofthemostimportantnewdevelopmentsinobservationalsupernovaresearchwastoestablishthelong-suspectedcorrelationbetweenthepeakbrightnessofSNeIaandtheirrateofdecline,M(ΔM15),bymeansofmodernCCDphotometry(Phillips1993).SNeIahaveprovidednewestimatesforthevalueoftheHubbleconstant(H0)basedonapurelyempiricalprocedure(Hamuyetal.1996ab,Riess,Press&Kirshner,1996),andonacomparisonofdetailedtheoreticalmodelswithobservations(H¨oflich&Khokhlov1996,hereafterHK96;Nugentetal.1997).Thevaluesobtainedareingoodagreementwithoneanother.Morerecently,theroutinesuccessfuldetectionofsupernovaeatlargeredshifts,z(e.g.Perlmutteretal.1995,1997;Riessetal.1998;Garnavichetal.1998),hasprovidedanexcitingnewtooltoprobecosmology.ThisworkhasprovidedresultsthatareconsistentwithalowmatterdensityintheUniverseand,mostintriguingofall,yieldedhintsforapositivecosmologicalconstantΩΛof≈0.7.ItisworthnotingthatthedifferencesinthemaximummagnitudebetweenΩΛ=0and0.7is≈0.25mforredshiftsbetween0.5to0.8.Theseresultspromptedthequestforthenatureofthethe’dark’energy,i.e.cosmologicalequationofstate.Currentcandidatesincludeanetworkoftopologicaldefectssuchasstrings,evolvingscalarfields(i.e.quintessence),ortheclassicalcosmologicalconstant.Forarecentreview,seeOstriker&Steinhardt(2001),andPerlmutter,Turner&White(1999b).ToseparatebetweenthecandidatesbySNeIa,therequiredaccuracyhastobebetterthan0.05to0.1m(Albrecht&Weller2000).TheresultsonΩΛandfutureprojectstomeasurethecosmologicalequationofstatedependontheempiricalM(ΔM15)whichiscalibratedlocally.Thisleavessystematiceffectsasthemainsourceofconcern.Indeed,thereisalreadysomeevidencethatSNeIaundergoevolution.Ithasbeenargued,thatthelocalSNIasamplecoversallthepossiblevariationsthatmaycomefromdifferentprogenitors,differentexplosionmechanismsandenvironments,etc..ForlocalSNeIa,theobservationalandstatisticalcharacteristicsdependontheirenvironment.Theyoccurlessofteninellipticalsthaninspirals,andthemeanpeakbrightnessisdimmerinellipticals(Branchetal.1996;Wang,H¨oflich&Wheeler1997;Hamuyetal.2000).Intheouterpartofspiralsthebrightnessissimilartoellipticalswhile,inmorecentralregions,bothintrinsicallybrighterandd