distant standard candles: type iasupernovaeburro.case.edu/academics/astr328/notes/sneh0.pdf ·...
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DistantStandardCandles:TypeIa Supernovae
Review:
• Whitedwarfheldupbyelectrondegeneracypressure.Indegeneracy,pressuredependsonlyondensity,nottemperature.
• Inabinarysystem,masstransferfromcompanionslowlyaddsmasstotheWD,increasingcentraldensityandtemperature.
• Whenmassreaches1.3Msun,tempsgethighenoughthatC/Ocanbeginfusing.Thisreleasesenergyandraisescoretemp,whichinturndrivesfasterC/Ofusion.
• Runawayeffect.WhenhalftheC/OconvertstoFe,enoughenergyisreleasedthatthestarblowsup.
Buttheyarerare.Typicallynotfeasiblefordistancestoaparticular galaxy,butgoodforstatistical/cosmologicalstudiesofexpansionrate.
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TypeIa SNe arestandardcandlesonceweapplythedeclineratecorrection(moreluminousSNe fademoreslowly).
Δm15 =magnitudechange15daysafterpeak,correlateswithpeakabsolutemagnitude
Note,though,thattheabsolutemagnitudesshownherearederivedfromHubbleLawdistances,andthusdepend ontheadoptedHubbleConstant.Theyarenotindependentlycalibrated.
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CalibratingTypeIa SNe
Tocalibratethepeakluminosity,wewantCepheiddistancestogalaxiesthathavehostedobservedTypeIa supernovae.
Thesituationin1997:
hMB(max)i = �19.51± 0.06
scatter=0.17mag
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Muchprogresssincethen!(fromRiess+16)
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CepheidPeriod-Luminosityplotsforeachgalaxy
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RethinkingtheCepheids:Howwelldoweknowthecalibratedperiod-luminosityrelation?
Remember,togetthecalibratedCepheidP-Lrelationships,wehadtohavedistancestoCepheids,whichhaveuncertaintiesoftheirown.
ParallaxDistances
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DirectTrigonometricParallaxesforMilkyWayCepheids fromHubble
Riess+18
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RethinkingtheCepheids:Howwelldoweknowthecalibratedperiod-luminosityrelation?
Remember,togetthecalibratedCepheidP-Lrelationships,wehadtohavedistancestoCepheids,whichhaveuncertaintiesoftheirown.
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Givenadirectgeometricdistancefromparallax(orothermethods),youcancalibratetheCepheidP-Lrelationship.
(IfyourCepheidP-Lrelationiscalibratedwrong,geometricdistancesandCepheiddistanceswilldisagree.)
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GivendistancesfromCepheids,youcancalibratetheTypeIa SNepeakmagnitudes.
(IfyourSNe mags arecalibratedwrong,CepheiddistancesandSNedistanceswilldisagree.)
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GivendistancesfromSNe,youcansolvefortheHubbleconstantbymakingluminositydistancematchformoredistantSNe.
(IfyourHubbleconstantiswrong,SNe distancesandluminositydistanceswilldisagree.)
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ThewholedistanceroutetoH0,intwosteps.
H0 =73.24± 1.74km/s/Mpc (Riess+16)H0 =73.52± 1.62km/s/Mpc (Riess+18)
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