Magnetism and Rotation in Herbig Ae/Be stars E. Alecian Laboratoire d’Astrophysique de l’Observatoire de Grenoble In collaboration with G.A. Wade, C. Catala, C. Folsom, J. Grunhut, et al.

We are starting a session on massive stars and related objects

Magnetism and rotation in the low-mass stars Convective dynamo  surface magnetic fields … M < 1.5 M 

Magnetism and rotation in the low-mass stars Convective dynamo  surface magnetic fields … … of complex configuration, … … interacting with the environment … M < 1.5 M 

Magnetism and rotation in the low-mass stars Convective dynamo  surface magnetic fields … … of complex configuration, … … interacting with the environment … M < 1.5 M  … leading to an evolution of their angular momentum. Bouvier et al. 1997, A&A 318, 495

The Ap/Bp stars 1.5 M  < M < 15 M   Chemically peculiar stars  ~5% of the MS A/B stars  No convective envelope, but … Magnetic fields are observed !!!  Very different from the low-mass stars: -Large-scale magnetic fields: mainly dipolar -Fields strengths: from 300 G to 30 kG -Do not correlate with stellar properties -Stable over many years  Slow rotators compared to the normal A/B star  The origin must be different from the low-mass stars

… concentrated in the protostar... Origin of the Ap/Pb stars magnetic fields The fossil field theory … producing a strong, slowly decaying stellar magnetic field... Galactic magnetic flux is swept up during star formation... …which may survive well beyond the MS phase. PMS ?

Origin of the Ap/Pb stars magnetic fields The fossil field theory, implications During the pre-main sequence (PMS) phase : –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)

Origin of the slow rotation of the Ap/Bp stars Hypothesis 1 : magnetic braking during the PMS phase (Stepien 2000) –Star-disk magnetic coupling, or –Magnetised winds Hypothesis 2 : the magnetic field cannot survive in fast rotators (Aurière et al. 2007) –Rotational instabilities in young PMS stars would diffuse the magnetic fields

The Herbig Ae/Be stars Definition (Herbig 1960): –A and B stars with emission lines –Lies in an obscured region –Association with nebulae –IR excess Characteristics associated with magnetic activity: –Highly ionised species (N V, O VI), X-ray emission:  hot chromospheres or coronae (e.g. Bouret et al. 1997) –rotational modulation of non- photospheric lines:  wind structured by magnetic field (e.g. Catala et al. 1989, 1999) –magnetospheric accretion (Muzerolle et al. 2004) X- rays Obs. O VI, NV AB Aur H  variations Catala et al The CIR theory Bouret et al. 1997

Magnetic fields in Herbig Ae/Be stars ? AB Aur : Catala et al. (1993), Catala et al. (1999) no detection HD : Donati et al. (1997) no detection HD : Donati et al. (1997) 1st detection (recently confirmed) HD : Hubrig et al. (2004) detection not confirmed with more accurate observations HD : Wade et al. (2007) detection (recently confirmed) We were missing: - high-efficiency polarimeter - large-aperture telescope - high spectral resolution - broad spectral range

ESPaDOnS at the 3.6m Canada-France- Hawaii Telescope High-resolution spectropolarimeter : R = 65000, broad spectral range ( nm) Reduction : Libre-Esprit package (Donati et al. 1997)

Our HAeBe survey Our sample: –Field HAeBes: Catalogues : Vieira et al. (2003) and Thé et al. (1994) Ages: 1Myr - 30 Myr –Young clusters: NGC 2264: age ~ 2.6 Myr Park & Sung (2000) NGC 2244: age ~ 2.3 Myr Park & Sung (2002) NGC 6611: age < 1 Myr de Winter et al. (1997) –128 HAeBe stars –Mass range: 1.5 – 20 M  Observations and reductions: –(one or many) Stokes I and V spectra –Libre Esprit reduction package –LSD method Alecian et al., in prep.

NGC B1, vsini~25 km/s Discovery of magnetic fields A0, vsini~8.6 km/s B3, vsini~26 km/sB9, vsini~41 km/s NGC B3, vsini~65 km/s A2, vsini~5 km/s 128 observed, 7 magnetic  ~5% magnetic Herbig Ae/Be stars NGC B1.5, vsini~180 km/s Catala et al. 2007, Alecian et al. 2008a, Alecian et al. 2008b, Folsom et al. 2008, Alecian et al. 2009

Other detections SemelPol +UCLES (AAT) = antecedent of ESPaDOnS Observations in April 2007 and March 2010 Simple Zeeman signatures consistent with an organised field HD HD A4, vsini = 11.6 km/s B l = -50 G A0, vsini = 4.8 km/s B l = -120 G

Compute I and V: –B l ( ,  ) : oblique rotator model (Stift 1975) –I( ,  ) : G(  instr,v( ,  ) ) –V( ,  )  dI/d B l ( ,  ) (weak field approximation) –Integration over the surface : limb-darkening law Comparison of the synthetic to observed I and V Compute  2 for (P,t 0,i, ,B d,d dip )  2 minimisation Magnetic field characterisation : Method B  Obs D d dip  i

Magnetic field characterisation : V380 Ori P = d. i = 32 °  = 66° B d = 2.12 kG d dip = 0 R * On the ZAMS: B d = 4.5 kG Alecian et al. 2009

HAeBe Magnetism- Conclusions For the 4 stars studied so far (HD , HD , HD 72106, V380 Ori) : Magnetic fields mainly dipolar with B d from 300 G to 2.1 kG Projection on the ZAMS: 1.2 < B d < 4.5 kG Catala, Alecian et al. 2007, Alecian et al. 2008a, Folsom et al. 2008, Alecian et al % of magnetic HAeBe stars Expected characteristics in the progenitors of the Ap/Bp stars  Very strong proofs in favor of the fossil field hypothesis

Distribution of vsini All field magnetic HAeBe are slow rotators No magnetic HAeBe are fast rotators Similar dichotomy on the MS  Magnetic stars have already been braked, OR  Fast rotators have already dissipated their fields Magnetic HAeBe stars Normal HAeBe stars Alecian et al., in prep. Abt et al. 1995

Conclusions Magnetism –~ 5% of HAeBe stars are magnetic –with mainly dipolar magnetic fields –with strengths from 300 G to 2 kG, projected on the ZAMS: from 1.2 to 4.5 kG  We find a fossil link between the magnetic fields of PMS and MS stars Rotation –Magnetic stars are more braked than the normal stars –Whatever the mechanism responsible of this dichotomy is, it must happen during the very early stages of PMS evolution, or even before

Open Issues Non-homogeneity: –Why only 5% of the intermediate mass stars are magnetic ? –Why in a same cluster, only a few percent is magnetic ? –Why in a close binary system, one is magnetic and the other one is not ? What is happening during the intermediate mass T Tauri phase: the partially convective phase ? Why do we have already slow rotators in the PMS phase, and what is happening in the core of the proto-stellar phase ?

What is inside the protostar ???  Structure  Magnetic fields  Internal Dynamic + Impact on magnetic fields  Protostar-environment interaction

References Alecian et al. 2008a, MNRAS 385, 391 Abt et al. 1995, ApJS 99, 135 Alecian et al. 2008b, A&A 481, L99 Alecian et al. 2009a, MNRAS Aurière et al. 2007, A&A 475, 1053 Bouret et al. 1997, A&A 328, 606 Bouvier et al. 1997, A&A 318, 495 Catala et al. 1989, A&A 221, 273 Catala et al. 1993, A&A 278, 187 Catala et al. 1999, A&A 345, 884 Catala et al. 2007, A&A 462, 293 Donati et al. 1997, MNRAS 291, 658 Folsom et al. 2008, MNRAS 391, 901 Herbig 1960, ApJS 4, 337 Hubrig et al. 2004, A&A 428, L1 Muzerolle et al. 2004, ApJ 617, 406 Stepien 2000, 353, 227 Wade et al. 2007, MNRAS 376, 1145