magnetic fields of pre-main sequence low- and intermediate ... · magnetic fields of pre-main...
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Magneticfieldsofpre-mainsequencelow-andintermediate-massstars
E.AlecianIPAG,Grenoble-AlpesUniversity
STARRYFinalconference,June2019
MAGNETICFIELDMEASUREMENTS
Zeemaneffect• ifBl≠0
→ linesplitting→ linecircularpolarisation
• Intheweakfieldapprox.: Δλ=Cgλ2|B|
V=-Cgλ2(dI/dλ)Bl
J ~ 0
J > 0
I/Ic
I/Ic
Q P
V/Ic = Q - P V/Ic = 0 Longitudinal
magneticfield
Δλ
Modulusofmagneticfield
Zeemanbroadening
Johns-Krull2009
TiIlinesBsensitive
COlinesBsensitive
ZeemanbroadeningWhatdowemeasure?
I(λ)
Δλê f|B|
ê <|B|>
f:fillingfactor
ZeemanbroadeningWhatdowemeasure?
I(λ)
Δλê
Σfi|Bi|
ê <|B|>
f:fillingfactor
Disk-lockingprediction
Johns-Krull2009
|B|ImportantforunderstandingdynamosprocessesNOTformagnetosphericaccretionprocesses
Zeemaneffect• ifBl≠0
→ linesplitting→ linecircularpolarisation
• Intheweakfieldapprox.: Δλ=Cgλ2|B|
V=-Cgλ2(dI/dλ)Bl
J ~ 0
J > 0
I/Ic
I/Ic
Q P
V/Ic = Q - P V/Ic = 0 Longitudinal
magneticfield
Δλ
Modulusofmagneticfield
StokesVObservations*High-resolution spectropolarimeter:
ESPaDOnS @ CFHTNARVAL @ TBLHARPSpol @ ESO3.6mSPIRou @ CFHT => Require multi-line analysis
Multi-lineanalysismethods:- PCA(Semeletal.2006)- SVD(Carrolletal.2012)- LSD(Donatietal.1997)
noise noise
I(λ)
V(λ)
VI
LSDmeanprofiles
ZeemanVsignature
VèBl èLargescalefield
©O.Kochukhov
ZeemanDopplerImaging
ZDIofTWA8A 1. MonitoringoverfewProt2. Sphericalharmonicdecomposition3. PotentialfieldextrapolationHill+2019
Photospheric+CaIRTlinesLkCa15,Donati+2019
MagneticpropertiesinTTauristarsMAPPandMaTYSSEprojects(PI:J.-FDonati)ESPaDOnS,HARPSpol,Narval
Hilletal.(2019,2017),Donatietal.(2019…2011)
TheHerbigAe/Besurvey
Convective-Radiativelimit
Alecianetal.(2013)
ESPaDOnS,Narvalobservations
BasicMagneticpropertiesHerbigAe/Bestars
• 300G–3kG• Dipolar• Stable
• Fossilfield(noncontinuouslysustainedbydynamo)
TTauristars
• 1to5kG• Topologystrongly
dependentontheinternalstructure
• Highlyvariable
• Dynamofields
THEORIGINOFMAGNETICFIELDSINRADIATIVESTARS
0.5M¤
4M¤
Rad.Core+
Conv.Env.
FullyRadiative
Conv.Core+Rad.Env.
FullyConvective
PMSevolutionofthenakedstar
Alecian+2013,Villebrun+2019
PMSevolutionofthenakedstar
low-massprotostar
3M¤PMS
=>3M¤ZAMS
PMSevolutionofthenakedstar
low-massprotostar
3M¤PMS
=>3M¤ZAMS
Allstarsgothroughafullyconvectivephase
FieldrelaxationduringthePMSphase
Norotation§ Numericalandanalyticalwork:
⇒ Mixedstableconfigurations(Braithwaite&Nordlund2006;Duezetal.2010;Duez&Mathis2010)
Withrotation§ Lowestenergystate:dipolarfields§ Initialhelicityandangularmomentum
impactthefinalstate(Emeriau&Mathis2015)
Backin2014
Backin2014Herbigstars Low-massstars
Backin2013
?
Intermediate-massTTauristars(IMTTS)
IMTTSSurveyESPaDOnS+HARPSpolsnapshotobservations38targets(PIs:Alecian,Hussain)
IMTTSSurveyResultsVillebrunetal.(2019)
©Villebrunetal.2019
IMTTSSurveyResultsVillebrunetal.(2019)
©Villebrunetal.2019
Magnetic
NotMagnetic
2%M★
25%R★
IMTTSSurveyResultsVillebrunetal.(2019)
©Villebrunetal.2019
Magnetic
NotMagnetic
2%M★
25%R★
HOWNON-MAGNETICARENON-MAGNETICSTARS?
Blimitdetermination• Hypothesis:adipolarfieldmaybehiddenintheVsignal• MCsimulations
– i,β,φrotrandomtrials– Bdfixed– ComputenoisysyntheticVprofiles
– Computethe#ofdetection
Alecianetal.(2016),Alecianetal.inprep.
Blimitdetermination• Hypothesis:adipolarfieldmaybehiddenintheVsignal• MCsimulations
– i,β,φrotrandomtrials– Bdfixed– ComputenoisysyntheticVprofiles
– Computethe#ofdetection
Alecianetal.(2016),Alecianetal.inprep.
90%
300G
HD142666
Magnetismatintermediate-masses
AdaptedfromVillebrunetal.2019
Magnetismatintermediate-masses
AdaptedfromVillebrunetal.2019
Magnetismatintermediate-masses
Blim<500G
Alecian,Lebretonetal.inprep.
Accretionsignaturesinpoorly-magneticstars
Blim<500G
Alecian,Lebretonetal.inprep.
HD142666
HeID3
PAR1394HeID3
Accretionsignaturesinpoorly-magneticstars
Blim<500G
Alecian,Lebretonetal.inprep.
HD142666
HeID3
PAR1394HeID3
Accretionsignaturesinpoorly-magneticstars
Blim<500G
Alecian,Lebretonetal.inprep.
HD142666
HeID3
PAR1394HeID3
TakeHomeMessages• B-fieldofTTSbecomemorecomplexastheconvectiveenvelopebecomethiner
• WTTSandCTTSshowsimilarfieldproperties
• OnceMCE<2M★ magneticfielddisappears,withinfew0.1Myr(forM★<3M¤)
• SomeHAeshavelowB-fieldbutshowstrongaccretionsignatures
What’snext?
MonitoringIMTTS
©Villebrunetal.2019
HavebeenmonitoredwithESPaDOnSandHARPSpol
What’snext?
MonitoringIMTTS
©Villebrunetal.2019
HavebeenmonitoredwithESPaDOnSandHARPSpol
What’snext?
Workinprogress=>Bfieldpropertiesandevolutionbeforedisappearing
TheClassI/Flat-spectrumobjectswithSPIRou
Addressmagnetism,rotationandaccretionprocessesduringtheembeddedphase
What’snext?
THANKYOU!