10–1
1 1 . B in a ry s ta r e v o lu ti o n a n d S N Ia
10–2 Closebinarystarevolution1C lo s e b in a ri e s : T h e R o c h e p o te n ti a l
R.HynesInaclosebinarysystem:Gravitationalpo- tentialdescribedbytheRochepotential: ΦR(r)=−GM1 |r−r1|−GM2 |r−r2|−1 2(ω×r)2 andwhere ω= GM a31/2 ˆe Stellarsurfacesareisosurfacesofthispo- tential =⇒starsarenon-spherical =⇒Stellarmagnitudechangeswithorbit.
10–3 TypIasupernovae1
S N Ia
Aftercorrectionofsystematiceffectsand timedilatation(expansionoftheuniverse, seelater): SNIalightcurvesalllookthesame =⇒
standardcandle 10–4 TypIasupernovae2T h e S u p e rn o v a C o s m o lo g y P ro je c ts •
SupernovaIasurveys: TheSupernovaCosmology Project http://www-supernova.lbl.gov•
TheHigh-zSNsearch http: //cfa-www.harvard.edu/supernova•
Measuringdistancestoz∼
1.510–5 TypIasupernovae3
T h e S u p e rn o v a C o s m o lo g y P ro je c ts
Calan/Tololo (Hamuy et al, A.J. 1996)Supernova Cosmology Project
effective m
B (0.5,0.5) (0, 0) ( 1, 0 ) (1, 0) (1.5,–0.5) (2, 0) (ΩΜ,ΩΛ) = ( 0, 1 )
Flat Λ = 0
redshift z
14
16
18
20
22
24
26 0.020.05 0.10.20.5 1.00.020.05 0.10.20.5 1.0
Perlmutter, et al. (1998)
FAINTER (Farther) (Further back in time)
MORE REDSHIFT (More total expansion of universe since the supernova explosion) In flat universe: ΩM = 0.28 [± 0.085 statistical] [± 0.05 systematic] Prob. of fit to Λ = 0 universe: 1%
•
Hubblerelationnolonger linear, dependentonΩmandΩΛ 10–6 TypIasupernovae4T h e S u p e rn o v a C o s m o lo g y P ro je c ts
Cosmologicalconstantisnon-zero TheexpansionoftheUniverseis accelerating10–7 TypIasupernovae5
T h e S u p e rn o v a C o s m o lo g y P ro je c ts
10–8 TypIasupernovae6S tr u c tu re o f a w h it e d w a rf
C/Ocorestabilisedbypressureofdegenerateelectrongas10–9 TypIasupernovae7
S tr u c tu re o f a w h it e d w a rf
SNIa=ThermonuclearexplosionofCOwhitedwarfwhenpushedtothe Chandrasekharlimit(1.4M⊙)(viaaccretion?). =⇒
Alwayssimilarprocess =⇒
Verycharacteristiclightcurve:fastrise,rapidfall,exponentialdecay (“FRED”)withhalf-timeof77d. 77dtimescalefromradioactivedecayNi56→Co56→Fe56 (“selfcalibration”oflightcurveifsameamountofNi56producedeverywhere) Calibration:SNeIainnearbygalaxieswhereCepheiddistancesknown. Atmaximumlight: MB=−
19.3±
0.11mag⇐ ⇒
L∼
109...10 L⊙ Observableoutto&1Gpc=⇒
coversalmostthewholeuniverse... 10–10 TypIasupernovae8S N Ia : O p e n q u e s ti o n s ? O p e n Q u e s ti o n : lig h t c u rv e s •
Howwellisthemaximumbrightnesscalibrated?•
DoesthemaximumSNIa-brightnesschangeastheuniverseages?⇒ O p e n Q u e s ti o n s : A s tr o p h y s ic s •
WhataretheprogenitorsofSNIa?•
HowdoesaSNIa-explosionproceed?10–11 TypIasupernovae9
E x p lo s io n -s c e n a ri o s fo r S N Ia
1.whitedwarfmassreachesChandrasekharmasslimit(1.4M⊙)→
explosive C-burningisignited 2.ThermonuclearexplosionformassesslightlybelowtheChandrasekharmass limit•
WDaccretesHe-richmaterial,explosiveHe-burningatthebottomofthe He-envelopewhentheHe-massexceeds0.15M⊙•
triggersC-burningfrontprogressinginwards He-burningfrontproceedsoutwards•
Problem:predictedchemicalcompositionisindisagreementwith observations (a)Double-WDscenario(DD=DoubleDegenerate): MergingoftwowhitedwarfswithatotalmassofMCh. (b)WD+mainsequencestar/redgiant(SD=singledegenerate)accretion fromthecompanionstaruntilMChisreached 10–12 TypIasupernovae10E x p lo s io n -s c e n a ri o s fo r S N Ia •
ElectrondegenerateC/Ocoreisnearly isothermal.Cmaybeignitedatdifferent pointsinthecoresimultaneously.•
burntmostlyintoFe,incompleteburningleads tolotsofSiaswell.•
explosionissubsonic(”deflagration”),(cf.for- estfire)verythinflame.•
evolveintoasupersonicexplosion(”detona- tion”)•
turbulenceisofgreatimportance•
verydifficulttomodel(differentscales) ExplosionofC/Ocoreleavesnoremnantbehind. Mainsourceofironintheuniverse.10–13 TypIasupernovae11
S N Ia : s in g le d e g e n e ra te s c e n a ri o W D + m a in s e q u e n c e s ta r/ re d g ia n t (S D )
Differenttypesofcompanionstars cataclysmicvariable:WD+MV-star:•
relativelysmallmasstransferratesM≈
10−9 M⊙/yr•
H-richmaterialaccumulatesatthesurfaceoftheWD•
H-burningigniteswhenMH=10−4 M⊙isreached.Electrongasis degenerate→
thermonuclearrun-awayprocess(similartoheliumflash,but atthesurfaceofthestar• ⇒
Nova-outburst,envelopeisejected•
massoftheWDstaysthesame! 10–14 TypIasupernovae12S N Ia : s in g le d e g e n e ra te s c e n a ri o
WD+A/FV-stars/redgiant:•
highmasstransferratesM≈
10−6 M⊙/yr•
steadyH-burningonthesurfaceofthewhitedwarf.Electrongasis non-degenerate(noflash!)•
WDslowlyincreasesitsmassuntil1.4M⊙isreached•
candidates:symbioticstars,supersoftX-raysources(extremelyrare) OpenQuestions: 1.Howtopreventcommonenvelopeejection? 2.HowtoavoidHe-DetonationbeforetheChandrasekharmassisreached? 3.Aretheresufficientlymanyprogenitorsystems?10–15 TypIasupernovae13
S N Ia : s in g le -d e g e n e ra te s c e n a ri o
1.after1.CE:whitedwarf+MS 2.after2.CE:whitedwarf+Helium star companionsurvives 10–16 TypIasupernovae14D o u b le d e g e n e ra te s c e n a ri o (D D ) M e rg in g o f tw o w h it e d w a rf s in a b in a ry •
Everybinaryloosesenergybygravitationalwaveradiation.• →
decreaseoforbitalseparationandperiod.•
AccordingtoEinstein’sART:Perioddecrease: ˙Porb=−96 5G3 M2 µ c54π2 GM
4/3 P−5/3 orb withM=M1+M2andµ=M1M2 M1+M2
•
Timeuntilmerging: τ=1.0·107M1/3 M1M2P8/3 yr•
Example:M1=M2=0.8M⊙,P=10h⇒
τ=8.5·
109 yr.10–17 TypIasupernovae15
D o u b le d e g e n e ra te s c e n a ri o •
Evolutionofabinarythroughtwo commonenvelopephasesleadsto aclosepairofwhitedwarfs.•
WDsmergeviagravitationalwave radiation 10–18 TypIasupernovae16D o u b le d e g e n e ra te s c e n a ri o
MergingoftwoWD(1.2M⊙+0.4M⊙) (SPHSimulation)10–19 TypIasupernovae17
S im u la ti o n o f th e G a la c ti c W D p o p u la ti o n
Ingredientsforbinarypopulationsynthesis: 1.Initialdistributions: starformationrate(SFR), initialmassfunction(IMF), binaryfrequency,distributionofmassratios distributionofseparations 2.evolution:masstransfer,commonenvelopeejection(efficiencyparameter αCEunknown!) Predictions:•
massdistributionofdoubledegenerates•
perioddistribution•
1/9ofallknownWDshouldbeinclosebinarysystems• ≈
1/40binary-WDshouldbeSNIaprogenitors 10–20 TypIasupernovae18S u rv e y s fo r ra d ia l- v e lo c it y v a ri a b le w h it e d w a rf s
Highresolutionspectrumofawhite dwarf10–21 TypIasupernovae19
S u rv e y s fo r ra d ia l- v e lo c it y v a ri a b le w h it e d w a rf s
Earlyattemptsinthe1990s(Bragalgliaetal.1990,Safferetal.1998,Maxted& Marsh1999) Total: Observed:150 DoubleDegenerates:15 WD0957-666:shortperiodP=88min,willmergein2·108 yrs,buttotalmass ofthesystemis0.7M⊙only. Radial-velocitycurveofthevisiblecomponentintheWD0957−666system 10–22 TypIasupernovae20T h e S P Y s u rv e y
SPYkeyprojectattheESOVLT(ledbyErlangen/Bamberg)•
Spectraof≈
1000WDwithUVES-Spectrographat8m-UT2ofVLT•
takingtwospectraatrandomepoch,afewnightslater UVES-spectrograph•
Echelle-Spectrograph•
blue+redchannel•
UVES-Set-upused: –Spectralrange3300...6650Å –2′′ -slit⇒spectralresolutionatHα≤0.3Å10–23 TypIasupernovae21
T h e S P Y s u rv e y •
Requirements: –TotalmassnearChan- drasekharmass. –Timescaleformergingvia GWRlessthantheageofthe universe.→
Orbitalperiod lessthanhalfaday•
SPYresults: doubledegenerateprogenitor candidatesforSNIadoexist 10–24 TypIasupernovae22C E e v o lu ti o n a n d s te lla r m e rg e rs : H o t s u b lu m in o u s s ta rs
Hotsubluminousstars:•
twovarieties:sdB(H-rich)andsdO (He-rich)•
coreheliumburningobjects•
lienearorbeyondthehotendofthe horizontalbranch•
highestfractionofclosebinariesfor anyknownclassofstar10–25 TypIasupernovae23
