11

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

Boundary

Marina RomanovaMarina Romanova

Cornell UniversityCornell University

May 18, 2010May 18, 2010

Min Long (University of Illinois)

Richard Lovelace (Cornell University)

Akshay Kulkarni (Harvard University)

J.-F. Donati (CNRS, Toulouse France

COLLABORATORS:

22

Disk-magnetosphere Interaction

I. Accretion to stars with complex fields (3D MHD)II. Outflows from disk-magnetosphere boundary (2D)

Uchida & Shibata 1985Camenzind 1990Konigl 1991; Lovelace et al. 1995

Matt & Pudritz 2005

I. Accretion to Stars with Complex Fields

B=Bdip+Bquad+Boct + …

3D simulations

Cubed sphere grid

N=40,50,60Koldoba, et al. 2002

44

3D simulations of accretion to Tilted Dipoles

Romanova, Ustyugova, Koldoba & Lovelace 2003,2004

Different tilts

2 funnel streams

High-latitude spots

Ang. Momentum – inner disk

55

The dipole may off-center

Long , Romanova, Lovelace 2008

Both poles are misplaced to the right

66

Aligned Quadrupole and Dipole Fields

Dipodrupole

Long , Romanova, Lovelace 2007

77

Misaligned dipole and quadrupole

Long, Romanova, Lovelace 2008

88

Octupole Field

Hot spots – 2 rings

Long, Romanova, Lamb, Kulkarni, Donati 2009

99

V2129 oph BP Tau

Magnetic field of V2129 Oph & BP Tau

Dipole: 0.35 kG Octupole: 1.2 kG

Dipole: 1.2 kG Octupole: 1.6 kG

Potential (vacuum) extrapolations Donati, Jardine, Gregory et al., 2007, 2008

1010

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)

1111

Accretion to V2129 Oph

Romanova, Long et al. 2009

1212

Comparison with a pure dipole field case

• Dipole field determines the funnel flow and disk-star interaction • Octupole field shapes spots

Observed chromosphericspot in CaII line

Romanova, Long et al. 2009

1313

Light curves

V2129 Oph BP TauV2129 Oph BP Tau

Romanova et al. 2009 Long et al. 2010

1414

Magnetic field of V2129 Oph

Romanova et al. 2009

Magnetic field distribution near the star (top) and at larger distances

1515

Matter flux problem

Dipole field with 350G polar field can not stop the disk at 7 R unless accretion rate is very small

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

Romanova et al. 2009

1616

Matter flux problem

Disk comes closer – octupolar belt spots dominate

Probably, the dipole component is 2-3 times larger

Romanova et al. 2009

1717

Modeling accretion to BP Tau

Dipole: 1.2 kG Octupole: 1.6 kG

Long et al 2010

1818

II. Outflows: Different Possibilities

Shu et al. 1994Blandford & Payne 1982Konigl & Pudritz 2000

Matt & Pudritz 2005,…

Ferreira, Dougados, Cabrit 2006

Configuration favorable for outflowsConfiguration favorable for outflows

Bunching, v > d

1919

Disk-Magnetosphere Interaction

c

star

c

disk

V = VKeplerian

X-type winds (Shu et al. 1994) but:• Star may rotate slowly – no fine-tuning• Matter flows into cones

Magnetic force

Conical Winds

Romanova et al. 2009

2121

Background – matter flux, arrows – velocity. Young stars: T=2 years

Stars of any spin: Conical Winds

2222

Rapidly-rotating stars: Propeller regime

Slow

Con

ical

Win

d

Poynting Jet

Slow Conical W

ind 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

2323

Outflows at the Propeller Stage: Conical Winds + Axial Jet

A star spins-down due to axial magnetic jet

2424

Winds from Stars with Complex Fields Different initial configurations of the fieldDifferent initial configurations of the field

Different quadrupole momentsDifferent quadrupole moments

Lovelace et al. 2010

2525

Wind is Asymmetric:

2626

2727

Flip-Flop Outflows in Pure Dipole case

Lovelace et al. 2010

2828

HST HST Observations:Observations:

Cycle of inflation Cycle of inflation

Simulations:Simulations: 7 years

Major outbursts: 2 months

HH30HH30

Propeller CasePropeller Case

Ustyugova et al. 2010

2929

MRI-driven Accretion (large-scale turbulence)

Long simulations: T=2,500 days = 7 years

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

BB

Another study of episodic outbursts: Caroline D’Angelo & Spruit, H.

BBBB

Romanova et al. 2010

3030

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

Summary

3131

References:Camenzind, M. 1990, Reviews in Modern Astronomy, v. 3, (1990), p. 234 D’Angelo, C. & Spruit, H. 2010, MNRAS, eprint arXiv:1001.1742Ferreira, J., Dougados, C., Cabrit, S. 2006, A&A, 453, 785Koldoba, A.V., Romanova, M.M., Ustyugova, G.V., Lovelace, R.V.E. 2002, ApJL, 576, L53Konigl, A. 1991, ApJ, 370, L39Konigl, A. & Pudritz, R. 2000, Protostars and Planets IV, p.759Long, M., Romanova, M.M., & Lovelace, R.V.E. 2007, MNRAS, 374, 436“—”—” 2008, MNRAS, 386, 1274Long, M., Romanova, M.M., Lamb, F.K., Kulkarni, A.K., Donati, J.-F. 2009, MNRAS, in press, eprint arXiv:0911.5455Lovelace,R.V.E., Romanova, M.M., & Bisnovatyi-Kogan, G.S. 1995, MNRAS, 274, 244Lovelace, R.V.E., Romanova, M.M., Ustyugova, G.V., Koldoba, A.V. 2010, MNRAS, in pressMatt, S. & Pudritz, R. 2005, ApJ, 632, L135Romanova, M.M., Ustyugova, G.V., Koldoba, A.V., Lovelace, R.V.E. 2003, ApJ, 595, 1009“—”—” 2004, ApJ, 610, 920“—”—” 2009, MNRAS, 399, 1802Romanova, M.M.,Long, M., Lamb, F.K., Kulkarni, A.K., Donati, J.-f. 2009, in press, eprint arXiv:0912.1681Shu, F.H. et al. 1994, ApJ, 429, 797Uchida, Y. & Shibata, K. 1985, PASJ, 37, 515Ustyugova, G.V., Koldoba, A.V., Romanova, M.M., Lovelace, R.V.E. 2006, ApJ., 646,304