Accretion onto Stars with Complex Fields and Outflows from the Disk-Magnetosphere Boundary

1. Accretion onto Stars with Complex Fields and Outflows from the Disk-Magnetosphere Boundary Marina Romanova Cornell University May 18, 2010 COLLABORATORS: Min Long (University of Illinois) Richard Lovelace (Cornell University) Akshay Kulkarni (Harvard University) J.-F. Donati (CNRS, Toulouse France

2. Disk-magnetosphere Interaction Uchida & Shibata 1985 Camenzind 1990 Konigl 1991; Lovelace et al. 1995 Matt & Pudritz 2005 I. Accretion to stars with complex fields (3D MHD) II. Outflows from disk-magnetosphere boundary (2D)

3. I. Accretion to Stars with Complex Fields B=Bdip+Bquad+Boct + … • 3D simulations • Cubed sphere grid • N=40,50,60 Koldoba, et al. 2002

4. 3D simulations of accretion to Tilted Dipoles • Different tilts • 2 funnel streams • High-latitude spots • Ang. Momentum – inner disk Romanova, Ustyugova, Koldoba & Lovelace 2003,2004

5. The dipole may off-center Both poles are misplaced to the right Long , Romanova, Lovelace 2008

6. Aligned Quadrupole and Dipole Fields Dipodrupole Long , Romanova, Lovelace 2007

7. Misaligned dipole and quadrupole Long, Romanova, Lovelace 2008

8. Octupole Field Hot spots – 2 rings Long, Romanova, Lamb, Kulkarni, Donati 2009

9. Magnetic field of V2129 Oph & BP Tau V2129 oph BP Tau Dipole: 1.2 kG Octupole: 1.6 kG Dipole: 0.35 kG Octupole: 1.2 kG Potential (vacuum) extrapolations Donati, Jardine, Gregory et al., 2007, 2008

10. Model, Initial field, V2129 Oph M=1.35 M_Sun R=2.4 R_Sun P=6.35 days Rcor=6.8 R_star M_dot=6.3 10^10 Donati et al., 2007)

11. Accretion to V2129 Oph Romanova, Long et al. 2009

12. Comparison with a pure dipole field case Observed chromospheric spot in CaII line • Dipole field determines the funnel flow and disk-star interaction • Octupole field shapes spots Romanova, Long et al. 2009

13. Light curves V2129 OphBP Tau Romanova et al. 2009 Long et al. 2010

14. Magnetic field of V2129 Oph Magnetic field distribution near the star (top) and at larger distances Romanova et al. 2009

15. Matter flux problem Mdot =3x10^-8 (Eisner 05) Mdot=4x10^-9 (Mohanty Mdot=10^-8 (Donati 07) Mdot=6x10^-10 (Donati 09) Simulations: 3x10^-11 Theory: 4x10^-11 Dipole field with 350G polar field can not stop the disk at 7 R unless accretion rate is very small Romanova et al. 2009

16. Matter flux problem Disk comes closer – octupolar belt spots dominate Probably, the dipole component is 2-3 times larger Romanova et al. 2009

17. Modeling accretion to BP Tau Dipole: 1.2 kG Octupole: 1.6 kG Long et al 2010

18. II. Outflows: Different Possibilities Ferreira, Dougados, Cabrit 2006 Shu et al. 1994 Matt & Pudritz 2005,… Blandford & Payne 1982 Konigl & Pudritz 2000 Configuration favorable for outflows Bunching, av > ad

19. Disk-Magnetosphere Interaction c c Wstar Wdisk

20. Conical Winds V = VKeplerian Magnetic force • X-type winds (Shu et al. 1994) but: • Star may rotate slowly – no fine-tuning • Matter flows into cones Romanova et al. 2009

21. Stars of any spin: Conical Winds Background – matter flux, arrows – velocity. Young stars: T=2 years

22. Rapidly-rotating stars: Propeller regime Poynting Jet Slow Conical Wind Slow Conical Wind • Two-component outflow forms • Conical winds carry most of matter outwards • Poynting jet carries energy and ang. momentum Romanova et al. 2005; Ustyugova et al. 2006; Romanova et al. 2009

23. Outflows at the Propeller Stage: Conical Winds + Axial Jet A star spins-down due to axial magnetic jet

24. Winds from Stars with Complex Fields Different initial configurations of the field Different quadrupole moments Lovelace et al. 2010

25. Wind is Asymmetric:

27. Flip-Flop Outflows in Pure Dipole case Lovelace et al. 2010

28. Propeller Case Simulations: 7 years Major outbursts: 2 months HST Observations: Cycle of inflation HH30 Ustyugova et al. 2010

29. MRI-driven Accretion (large-scale turbulence) B B B • A star is in the propeller regime • turbulent cells and centrifugal force prevent funnel accretion • Spikes of accretion are observed (few months – one year) • Accumulation and penetration of matter Romanova et al. 2010 Long simulations: T=2,500 days = 7 years Another study of episodic outbursts: Caroline D’Angelo & Spruit, H.

30. Summary • If a star with very complex field has a notable dipole component then it determines the disk-star interaction • Complex field determines the shape of spots • Conical outflows may form if magnetic flux is bunched • Propeller-driven outflows carry angular momentum out of the star • Outflows may be episodic • Outflows from star with complex fields are asymmetric

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