1. Magnetism in Herbig Ae/Be stars and the link to the Ap/Bp stars E. Alecian, C. Catala, G.A. Wade, C. Folsom, J. Grunhut, J.-F. Donati, P. Petit, S. Bagnulo, S.C. Marsden, J.D. Landstreet, T. Böhm, J.-C. Bouret, J. Silvester CNRS Summer school La Rochelle, 24 - 28 September 2007

2. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Plan 1.Introduction 2.Field Herbig Ae/Be stars study : magnetism 3.Field Herbig Ae/Be stars study : rotation 4.Cluster study 5.Conclusion and Open Issues

3. 1. Introduction

4. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The intermediate mass stars (1) Pre-main sequence (PMS): from birthline to ZAMS  Herbig Ae/Be stars (HAEBE) Main sequence (MS): around the ZAMS  A/B stars A/B stars HAEBE

5. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The intermediate mass stars (2) HAEBE stars: –radiative inside + convective envelope, or –convective core + radiative envelope, or –totally radiative A/B stars –convective core + radiative envelope Convective envelope disappearing Convective core apparition

6. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The chemically peculiar stars Ap/Bp : ~5% of A/B stars Abundances anomalies compared to normal A/B stars Slow rotators Ap/Bp: Magnetic stars : 300G to 30kG, large scale organised magnetic field : mostly dipole+quadrupole

7. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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) –The core dynamo hypothesis

8. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Problematic 2 Origin of the slow rotation of the Ap/Bp stars –Hypothesis 1 : magnetic braking during the PMS phase (Stepien 2000)  magnetic PMS A/B stars should exist  PMS A/B stars should have a disk  Evolution 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  We need to observe the PMS intermediate mass stars

9. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The Herbig Ae/Be stars A and B stars with emission lines IR emission Association with nebulae 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)  Many indirect signs of magnetic fields

10. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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

11. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Strategy (2) Observations of the HAEBE 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

12. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 What is our method ? The spectropolarimetry: polarisation study inside the spectral lines Recall: Zeeman effect in the stars  Stokes V parameter ≠ 0 In the weak field approximation (B<10kG): V  dI/d * B l  We observe the Stokes V spectra

13. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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 !

14. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 ESPaDOnS (CFHT, Hawaii) + LSD: the good formula High-resolution spectropolarimeter : R = 65000, broad spectral range (370 - 1080 nm) Reduction : Libre-Esprit package (Donati et al. 1997, 2007) Least Squares Deconvolution (LSD) 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 For more details see the talk of Coralie Neiner

15. 2. Field Herbig Ae/Be stars study : magnetism

16. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Our sample Catalogues : Vieira et al. (2003) and Thé et al. (1994) 55 Herbig Ae/Be stars 1.5 – 20 Msun 

17. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Observations and reduction For each star: –(one or many) Stokes I and V spectra –Determination of T eff and log(g) –LSD method: mask of T eff 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

18. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 LSD for I =*=* Spectrum Mask Stokes I profile Donati et al. (1997)

19. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 LSD for V B non détecté B0B0 Spectra Stokes V profile Mask =*=* Stokes V profile  Zeeman signature

20. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 A0, vsini~8.6 km/s Results Wonderful Zeeman signatures !!! 55 observed, 4 magnetic  ~7% magnetic Herbig Ae/Be stars B3, vsini~26 km/sB9, vsini~41 km/s A2, vsini~9.8 km/s

21. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 How characterise their magnetic fields ? 1.Model the time variations of B l 2.Model the time variations of the Stokes V profiles Observations of the stars at different time

22. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The oblique rotator model Compute I, V and B l : –I( ,  ) : G(  instr,v( ,  ) ) –V( ,  )  dI/d B l ( ,  ) (weak field approximation) –B l ( ,  ) : oblique rotator model (Stift 1975) –Integration over the surface : limb-darkening law 5 parameters: (P,  0, ,B d,d dip ) B  Obs D d dip  i

23. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 The Oblique rotator model : Example i = 50 °  = -60° B d = 1000 G

24. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 First method: the longitudinal field B l Mean over the lines Stokes V parameter Stokes I parameter (Donati et al. 1997)

25. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Longitudinal field variations of HD 200775 P = 4.328 j Alecian et al. 2007  2 = 1.25  Estimation of the period

26. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 2nd method: Fitting the Stokes V profiles Compute a grid of V by varying the 5 parameters: –  0 : the reference phase –P : the rotation period –  : the magnetic obliquity –B d : the dipole intensity –d dip : the dipole position  2 minimisation

27. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Magnetic field characterisation : HD 200775 P = 4.328 d. i = 13 °  = -102° B d = 1000 G d dip = 0.10 R * Alecian et al. (2007)

28. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Magnetic field characterisation : V380 Ori P = 7.6 d. i = 34°  = -95° B d = 1.4 kG d dip = 0 R * P = 9.8 d. i = 47°  = -95° B d = 1.4 kG d dip = 0 R * 2 dipole solutions

29. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Magnetic field characterisation : HD72106 P = 0.63995 d. i = 23°  = 60° B d = 1300 G d dip = 0 R * Folsom et al. (2007)

30. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Catala et al. (2007) 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 B d = 100 - 1000 G

31. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Other detections SemelPol +UCLES (AAT) = antecedent of ESPaDOnS Simple Zeeman signature consistent with an organised field HD 104237HD 101412 A4, vsini = 11.6 km/sB l = -50 G A0, vsini = 4.8 km/sB l = -120 G Thanks to S. Bagnulo and S.C. Marsden

32. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Fundamental parameters of the stars Position in the HR diagram compared to evolutionary tracks  M, R, age, PMS time  Proportion of PMS time performed: gives the evolutionary status (independent of the mass)  R on the ZAMS

33. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 First conclusions on the magnetic field 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 in HAEBE stars 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 B d = 3.6 kG  V380 Ori: on the ZAMS B d = 2.4 kG  HD 72106: already on the ZAMS B d = 1.3 kG  HD 190073: on the ZAMS B d = 400 - 4000 G  Strong arguments in favour of the fossil field theory

34. 3. Field Herbig Ae/Be stars study : rotation

35. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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

36. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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

37. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Evolution of vsini to the ZAMS vsini HAEBE on the ZAMS close to normal A/B stars No clear indications of braking from HAEBE age to MS Norm A/B starsNon magnetic HAEBE Non magnetic HAEBE on the ZAMS Royer et al. (2002)

38. 4. Cluster study

39. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 NGC 6611 sample Age = ~1 Myr  Younger than the field HAEBE 3 - 20 Msun  Fill the whole in the HRD 

40. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 NGC 2244 Sample Age ~ 8 Myr 2 - 20 Msun

41. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 NGC 2264 sample Age = 9Myr 1.5 - 9 Msun

42. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Cluster results NGC6611 W601NGC 2264NGC2244 201 12 observed stars 1 magnetic 12 observed stars 1 magnetic 18 observed stars 0 magnetic Does the initial conditions play a role ? ? B1.5, vsini~180 km/sB1, vsini~25 km/s

43. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 vsini of the cluster magnetic stars NGC6611 W601180 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? vsiniageSp.T.

44. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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 young  A 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

45. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Conclusions (1): preliminary cluster study Magnetism –Detections in 2 clusters, 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~180 km/s  Promising for the study of the angular momentum evolution, as well as the impact of magnetic field on the rotation evolution of HAEBE stars

46. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 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

47. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Open Issues Unanswered questions : –Only a fraction of stars is magnetic : why all the stars are not magnetic ? –Clusters –Binaries : one magnetic + one non-magnetic –Protostellar phase : is the field able to survive during that phase ? –Decentered dipole (or dipole + quadrupole) : how the molecular cloud contraction can form that field topology ?

48. E. Alecian CNRS Summer School La Rochelle, 24 - 28 Septembre 2007 Thank you for your attention