The Herbig Ae/Be stars: what we have learnt with ESPaDOnS

The Herbig Ae/Be stars: what we have learnt with ESPaDOnS

E. Alecian, G.A. Wade, C. Catala, C. Folsom, J. Grunhut, J.-F. Donati, P. Petit, S. Bagnulo, S.C. Marsden,

J.D. Landstreet, T. Böhm, J.-C. Bouret, J. Silvester

Armagh Workshop21/02/2008

E. Alecian Armagh Workshop

21/02/2008

Problematic 1

• Origin of the magnetic fields in the Ap/Bp stars– Favoured hypothesis : the fossil field hypothesis

some of the intermediate mass PMS star should be magnetic

topology of B(PMS A/B) = topology B(Ap/Bp)intensity B(PMS A/B) compatible with intensity

B(Ap/Bp) (assuming the magnetic flux conservation)

– Other hypothesis : the core dynamo


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Problematic 2

• Origin of the slow rotation of the Ap/Bp stars– Hypothesis 1 : magnetic braking during the PMS

phase (Stepien & Lanstreet 2002)

magnetic PMS A/B stars should existPMS A/B stars should have a diskEvolution of the rotation during the PMS phase

– Hypothesis 2 : the magnetic field cannot survive in fast rotators (Lignières et al. 1996)

No magnetic fast rotators during the PMS phase


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Strategy (1)

• Observation of the field Herbig Ae/Be stars– Detection of magnetic field– Characterisation of their magnetic fields– Compare to the magnetic fields of Ap/Bp stars

Fossil field hypothesis test

– vsini determination– Compare to vsini of Ap/Bp star– vsini as a function of age

Origin of slow rotation hypothesis tests


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Strategy (2)

• Observations of the Herbig stars in young clusters and associations– stars of a single cluster: = age and = initial conditions– ≠ clusters ≠ ages and ≠initial conditions

Disentangle evolutionary effects from initial condition effects

Understand the evolution of the magnetic field during the PMS phase, and its impact on the evolution of the stars


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The Herbig Ae/Be stars

• A and B stars with emission lines• IR emission• Association with nebulae• Intermediate-mass PMS stars

Progenitors of the main sequence A/B stars

• Characteristics associated with magnetic activity :– resonance lines as N V and O VI, X-ray emission :

hot chromospheres or coronae (e.g. Bouret et al. 1997)

– magnetospheric accretion (e.g. Mannings & Sargent 1997)

– rotational modulation of resonance lines : wind structured by magnetic field (e.g. Catala et al. 1989, 1999)

} definition (Herbig 1960)


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Magnetic fields in Herbig Ae/Be stars ?

• AB Aur : Catala et al. (1993), Catala et al. (1999)no detection

• HD 100546 : Donati et al. (1997)no detection

• HD 104237 : Donati et al. (1997)1st detection (recently confirmed)

• HD 139614 : Hubrig et al. (2004)detection not confirmed with more accurate observations

• HD 101412 : Wade et al. (2007)detection (recently confirmed)

But now we have ESPaDOnS !


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ESPaDOnS (CFHT, Hawaii)

• High-resolution spectropolarimeter : R = 65000, broad spectral range (370 - 1080 nm)

• Reduction : Libre-Esprit package (Donati et al. 1997, 2007)

• Least Squares Deconvolution method (Donati et al., 1997)

More lines, better S/N ratio, larger magnitude V range of the star

Increase our chances to detect magnetic fields


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Field Herbig Ae/Be stars (HAeBe) study


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Our sample

• Catalogues : Vieira et al . (2003) and Thé et al. (1994)

• 55 Herbig Ae/Be stars

• 1.5 – 15 Msun

• PMS life = from birthline to ZAMS

birthlines Palla & Stahler (1993)

ZAMS


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Our sample

• Catalogues : Vieira et al . (2003) and Thé et al. (1994)

• 55 Herbig Ae/Be stars

• 1.5 – 15 Msun

• PMS life = from birthline to ZAMS

• Stars:– with convective envelope, or

– with convective core, or

– totally radiative

Convective envelope

disappearing

Convective core

apparition


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Observations and reduction

• For each star: – (one or many) Stokes I and V spectra

– Determination of Teff and log(g)

– LSD method: mask of Teff and log(g) of the star, not including Balmer lines and lines contaminated by emission

– Searching for a Zeeman signature in the LSD V profile


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Results

A0, vsini~8.6 km/s

Wonderful Zeeman signatures !!!

B3, vsini~26 km/s B9, vsini~41 km/s

A2, vsini~9.8 km/s

55 observed, 4 magnetic ~7% magnetic Herbig Ae/Be stars


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HD 200775

• Binary SB2 (P~3.9 y)

Alecian et al. (2008)


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HD 200775

• Binary SB2 (P~3.9 y)

• TB~TA=19000 K

• Primary magnetic, vsini~26 km/s

• Secondary non-magnetic, vsini~56 km/s

• Emission from the secondary

• Secondary largely redder than the primary Ls>Lp and Ms>Mp Alecian et al. (2008)


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HD 72106

• Binary SB2– asini = 0.8 "

– Porb>1600 d

• Primary: B9 Ap ZAMS, magnetic, vsini~41 km/s

• Secondary: A3 PMS, non-magnetic, vsini~54 km/s

Folsom et al., in prep.


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HD 72106

P

S



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HD 72106

• Binary SB2– asini = 0.8 "

– Porb>1600 d

• Primary: B9 Ap ZAMS, magnetic, vsini~41 km/s

• Secondary: A3 PMS, non-magnetic, vsini~54 km/s



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HD 190073

• Single, PMS

• Te = 9250K, vsini=0-8.3 km/s

• Numerous emission in the spectrum: fwhm = 65 km/s

Catala et al. (2007)


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HD 190073



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HD 190073

• Single, PMS

• Te = 9250, vsini=0-8.3 km/s

• Numerous emission in the spectrum: fwhm = 65 km/s

• Halpha: PcygnidM/dt = 1.4 10-8 M/y

v = 290 km/s

Tbase = 18000 K



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V380 Ori


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V380 Ori

Tp = 10500 K Ts = 6000 K


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V380 Ori


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V380 Ori

• Binary SB2• Primary: B9 magnetic• Secondary: G0.5 non-

magnetic• LSD profiles


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V380 Ori

Primary SecondaryLSD Profiles

vsiniP~10 km/s vsiniS~20 km/s


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Magnetic field characterisation : Method• Observations of the stars at different rotation phase• Compute I and V:

– I(,) : G(instr,v(,) )

– V(,) dI/d Bl (,)

(weak field approximation)

– Bl (,) : oblique rotator model

(Stift 1975)

– Integration over the surface : limb-darkening law

• Comparison of the synthetic to observed I, V and Bl

• Compute 2 for (P,0,,Bd,ddip)

2 minimisation

B

ObsD

ddip

i


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Magnetic field characterisation : HD 200775

P = 4.328 d. i = 13 ° = -102° Bd = 1000 G ddip = 0.10 R*

On the ZAMS: P = 1.2 d Bd = 3.6 kGAlecian et al. (2008)


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Magnetic field characterisation : HD72106

P = 0.63995 d. i = 23° = 60° Bd = 1300 G ddip = 0 R*


On the ZAMS: P = 0.63995 d Bd = 1.3 kG


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Magnetic field characterisation : HD 190073

• 3 different hypothesis :– Pole-on star = 0– Long Period

• In all cases:– Simple dipolar Zeeman signature– Signature stable over more than 2

years

strong probability for an organised magnetic field

• Bd = 100 - 1000 G

ZAMS: Bd = 400 - 4000 G


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Magnetic field characterisation : V380 Ori

P = 7.6 d.i = 34° = -95°

Bd = 1.4 kG

ddip = 0 R*

P = 9.8 d.i = 47° = -95°

Bd = 1.4 kG

ddip = 0 R*

2 dipole solutions

ZAMS

P=4.5 d

Bd=2.4kG

ZAMS

P=5.8 d

Bd=2.4kG


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Other detections

• SemelPol +UCLES (AAT) = antecedent of ESPaDOnS• Simple Zeeman signature consistent with an organised field

HD 104237 HD 101412

A4, vsini = 11.6 km/s Bl = -50 G

A0, vsini = 4.8 km/s Bl = -120 G

Thanks to S.C. Marsden


21/02/2008

First conclusions

• 7% magnetic HAeBe stars• Projection of magnetic Ap/Bp stars on the PMS

phase prediction of 5-10% magnetic HAeBe stars• Large scale organised magnetic field• Magnetic intensity of the HAeBe projected on the

ZAMS : same order of the intensity of B(Ap/Bp): (assuming the magnetic flux conservation)

HD 200775: on the ZAMS Bd = 3.6 kGV380 Ori: on the ZAMS Bd = 2.4 kGHD 72106: already on the ZAMS Bd = 1.3 kGHD 190073: on the ZAMS Bd = 400 - 4000 G

Strong arguments in favour of the fossil field theory

Statistical Study


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The undetected sample

• 41 stars

• Detection significance distribution

• Monte-Carlo simulation:– i: random distribution : bimodal distribution (0°

or 90°)

– random phase for each data

– dipole of fixed B

Wade et al., in prep.


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The undetected sample

• 41 stars• Detection significance

distribution• Monte-Carlo simulation:

– i: random distribution : bimodal distribution (0°

or 90°)– random phase for each data– dipole of fixed B

• Kolmogorov-Smirnov testHomogeneous population

of dipole with B<450 G

Wade et al., in prep.


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Distribution of vsini

• All field magnetic HAeBe are slow rotators• No magnetic HAeBe are fast rotators

• Magnetic HAeBe stars seem to have been braked more than the non-magnetic HAeBe stars

Magnetic HAeBe stars

Non magnetic HAeBe stars


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Period in function of time

• No clear evolution of the period• Majority of HAeBe: between 40 and 80% of their PMS track• To study period evolution we need younger stars than our sample


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Evolution of vsini to the ZAMS

• vsini HAeBe on the ZAMS close to normal A/B stars• Evolution from HAeBe age to MS consistent with

angular momentum conservation

Normal A/B starsNormal HAeBeNormal HAeBe on

the ZAMS Royer et al. (2007)


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Cluster study


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NGC 6611 sample

• Age = ~1 MyrYounger than HAeBe

• 3 - 20 MsunFill the hole in the HRD


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NGC 2244 Sample

• Age ~ 8 Myr

• 2 - 20 Msun


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NGC 2264 sample

• Age = 9Myr

• 1.5 - 9 Msun


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Cluster resultsNGC6611 W601 NGC 2264 83 NGC2244 201

17 observed stars

1 magnetic

17 observed stars

1 magnetic

29 observed stars

1 magnetic

B1.5, vsini~180 km/s B1, vsini~25 km/sB3, vsini~65 km/s

Alecian et al. (2008), accepted


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vsini of the cluster magnetic stars

• NGC6611 W601 180 km/s ~ 1 Myr B1.5

• NGC2244 201 25 km/s ~ 8 Myr B1

• Can we see a sign of the evolution of the rotation in the magnetic HAeBe stars?

vsini age Sp.T.

Alecian et al. (2008), accepted


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Conclusions (1) : Field HAeBe study

• Magnetism:– 7% magnetic HAeBe

– HAeBe magnetism in favour of the fossil field hypothesis

• Rotation:– vsini(magnetic HAeBe) < vsini(non magnetic HAeBe)

– Magnetic HAeBe: slow rotators and very youngA braking mechanism acts very early during the PMS phase

– Dvsini(HAeBe on ZAMS) = Dvsini(A/B Norm)Constant angular momentum evolution from the age of

HAeBe to the MS


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Conclusions (1): preliminary cluster study

• Magnetism– Detections in 2 cluster, none in one cluster

The initial conditions may play a role on the presence (or on the intensity) of magnetic fields

• Rotation– At 1Myr, one magnetic star with vsini~200

km/sPromising for the study of the angular momentum

evolution, as well as the impact of magnetic field on the rotation evolution of HAeBe stars


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Conclusion (2): Fossil Field against Convective Core hypothesis• 5 magnetic stars are in the totally

radiative phase• These stars have the same type of

magnetic field of the stars with a convective core

Core convection does not appear to be responsible for the presence of magnetic fields in HAeBe stars

The magnetic fields of the intermediate mass stars are very likely FOSSIL


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Open Issues

• Unanswered questions :– Only a fraction of stars is magnetic : why all the stars are not magnetic ?– Clusters: idem– Binaries : one magnetic + one non-magnetic– Decentered dipole (or dipole + quadrupole) : how the molecular cloud

contraction can form that field topology ?– The active stars are not magnetic

• After de main sequence phase: giant phase, white dwarfs, neutron stars ?

• Before the PMS phase: molecular cloud contraction, proto-stellar phase ?

• What constraints on the magnetic winds and magnetospheric accretion models can we put using our results ?

• Can we lower the detection limit of the undetected sample ?


21/02/2008

HD 35929

• Observed with Narval

• A5

• vsini~60 km/s

• Inside the instability strip of delta-Scuti pulsators

Need more observations

The Herbig Ae/Be stars: what we have learnt with ESPaDOnS

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