Accretion onto Stars with Complex Fields and Outflows from the Disk-Magnetosphere Boundary
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Transcript of Accretion onto Stars with Complex Fields and Outflows from the Disk-Magnetosphere Boundary
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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:
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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
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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
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The dipole may off-center
Long , Romanova, Lovelace 2008
Both poles are misplaced to the right
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Aligned Quadrupole and Dipole Fields
Dipodrupole
Long , Romanova, Lovelace 2007
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Misaligned dipole and quadrupole
Long, Romanova, Lovelace 2008
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Octupole Field
Hot spots – 2 rings
Long, Romanova, Lamb, Kulkarni, Donati 2009
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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
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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)
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Accretion to V2129 Oph
Romanova, Long et al. 2009
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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
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Light curves
V2129 Oph BP TauV2129 Oph BP Tau
Romanova et al. 2009 Long et al. 2010
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Magnetic field of V2129 Oph
Romanova et al. 2009
Magnetic field distribution near the star (top) and at larger distances
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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
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Matter flux problem
Disk comes closer – octupolar belt spots dominate
Probably, the dipole component is 2-3 times larger
Romanova et al. 2009
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Modeling accretion to BP Tau
Dipole: 1.2 kG Octupole: 1.6 kG
Long et al 2010
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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
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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
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Background – matter flux, arrows – velocity. Young stars: T=2 years
Stars of any spin: Conical Winds
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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
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Outflows at the Propeller Stage: Conical Winds + Axial Jet
A star spins-down due to axial magnetic jet
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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
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Wind is Asymmetric:
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Flip-Flop Outflows in Pure Dipole case
Lovelace et al. 2010
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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
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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
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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
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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