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Magnetism in Herbig Ae/Be stars and the link to the Ap/Bp stars

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. Plan.

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Magnetism in Herbig Ae/Be stars and the link to the Ap/Bp stars

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  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. Plan • Introduction • Field Herbig Ae/Be stars study : magnetism • Field Herbig Ae/Be stars study : rotation • Cluster study • Conclusion and Open Issues CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  3. 1. Introduction

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

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

  6. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  7. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  8. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  9. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

  11. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  12. 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 * Bl  We observe the Stokes V spectra CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

  14. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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

  17. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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

  20. Wonderful Zeeman signatures !!! Results B3, vsini~26 km/s B9, vsini~41 km/s 55 observed, 4 magnetic  ~7% magnetic Herbig Ae/Be stars A0, vsini~8.6 km/s A2, vsini~9.8 km/s CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  21. How characterise their magnetic fields ? Observations of the stars at different time • Model the time variations of Bl • Model the time variations of the Stokes V profiles CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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

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

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

  26. 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 • Bd : the dipole intensity • ddip: the dipole position • 2 minimisation CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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

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

  30. Magnetic field characterisation : HD 190073 Catala et al. (2007) • 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

  32. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  33. 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 Bd = 3.6 kG • V380 Ori: on the ZAMS Bd = 2.4 kG • HD 72106: already on the ZAMS Bd = 1.3 kG • HD 190073: on the ZAMS Bd = 400 - 4000 G Strong arguments in favour of the fossil field theory CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

  35. Distribution of vsini Magnetic HAEBE stars Non magnetic HAEBE stars • 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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

  38. 4. Cluster study

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

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

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

  42. Cluster results NGC6611 W601 NGC 2264 NGC2244 201 B1.5, vsini~180 km/s B1, vsini~25 km/s ? 12 observed stars 1 magnetic 12 observed stars 1 magnetic 18 observed stars 0 magnetic Does the initial conditions play a role ? CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  43. vsini of the cluster magnetic stars vsini age Sp.T. • 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? CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  44. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

  45. 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 CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

  47. 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 ? CNRS Summer School La Rochelle, 24 - 28 Septembre 2007

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

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