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!