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.

TypeIa SNe arestandardcandlesonceweapplythedeclineratecorrection(moreluminousSNe fademoreslowly).

Δm15 =magnitudechange15daysafterpeak,correlateswithpeakabsolutemagnitude

Note,though,thattheabsolutemagnitudesshownherearederivedfromHubbleLawdistances,andthusdepend ontheadoptedHubbleConstant.Theyarenotindependentlycalibrated.

CalibratingTypeIa SNe

Tocalibratethepeakluminosity,wewantCepheiddistancestogalaxiesthathavehostedobservedTypeIa supernovae.

Thesituationin1997:

hMB(max)i = �19.51± 0.06

scatter=0.17mag

Muchprogresssincethen!(fromRiess+16)

CepheidPeriod-Luminosityplotsforeachgalaxy

RethinkingtheCepheids:Howwelldoweknowthecalibratedperiod-luminosityrelation?

Remember,togetthecalibratedCepheidP-Lrelationships,wehadtohavedistancestoCepheids,whichhaveuncertaintiesoftheirown.

ParallaxDistances

DirectTrigonometricParallaxesforMilkyWayCepheids fromHubble

Riess+18

RethinkingtheCepheids:Howwelldoweknowthecalibratedperiod-luminosityrelation?

Remember,togetthecalibratedCepheidP-Lrelationships,wehadtohavedistancestoCepheids,whichhaveuncertaintiesoftheirown.

Givenadirectgeometricdistancefromparallax(orothermethods),youcancalibratetheCepheidP-Lrelationship.

(IfyourCepheidP-Lrelationiscalibratedwrong,geometricdistancesandCepheiddistanceswilldisagree.)

GivendistancesfromCepheids,youcancalibratetheTypeIa SNepeakmagnitudes.

(IfyourSNe mags arecalibratedwrong,CepheiddistancesandSNedistanceswilldisagree.)

GivendistancesfromSNe,youcansolvefortheHubbleconstantbymakingluminositydistancematchformoredistantSNe.

(IfyourHubbleconstantiswrong,SNe distancesandluminositydistanceswilldisagree.)

ThewholedistanceroutetoH0,intwosteps.

H0 =73.24± 1.74km/s/Mpc (Riess+16)H0 =73.52± 1.62km/s/Mpc (Riess+18)