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Numerical simulations of star-disk interaction

Numerical simulations of star-disk interaction. Miljenko Cemeljic . TIARA (ASIAA & NTHU) JETSET (IASA & University of Athens, Greece). Outline. Young stars and outflows Magnetic fields in the outflows Resistive simulations of disk-jet transition Star-disk interaction

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Numerical simulations of star-disk interaction

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  1. Numerical simulations of star-disk interaction Miljenko Cemeljic  TIARA (ASIAA & NTHU) JETSET (IASA & University of Athens, Greece)

  2. Outline • Young stars and outflows • Magnetic fields in the outflows • Resistive simulations of disk-jet transition • Star-disk interaction • Summary

  3. Disk, Star & Jet • Protostellar jet – launched from the disk, collimated to few pc´s. • High velocity of the jet matter: 200-500 km/sec, knots <300 km/sec. Non-relativistic outflows. • Terminal velocity ~ escape velocity of the central object. • Magnetic field in the vicinity of young stars ~kG .

  4. Jets in different scale • The same scale in all figures, 1000 AU

  5. Observations vs. simulations

  6. Magnetic fields and jets • Outflows exceed Eddington limit - magnetically driven. • Magnetic field collimates and accelerates the jet. • Lorentz force in MHD: FL~q(E+uxB)→ FL~jxB • Open questions: • Origin of magnetic field • Jet launching mechanism • Timescale in jet launching (knots)

  7. Equations of resistive MHD • Magnetic diffusivity η • very small in astrophysics → anomalous diffusivity • Turbulent diffusivity η introduced

  8. Model of MHD jet formation Ferreira, 1997 • Disk as a boundary condition • Ideal MHD, Ouyed & Pudritz, 1997 • Time-dependent, resistive MHD simulations-ZEUS-3D • Open field threading the disk • Fendt & Cemeljic, 2002 • Disk evolution included • Casse & Keppens, 2002, 2004 • Cemeljic & Fendt, 2003 • Kuker et al. 2003, 2004

  9. Casse & Keppens, 2002

  10. Simulations with stellar dipole field • M. Kuker et al. 2003 – CTTS simulations, disk and disk corona included in the simulations, star as b.c. • Magnetic field: stellar dipole field • Tdisk=7000K, Thalo=5000K • Density in disk ~10 000 times larger than in halo

  11. After 22 and 26 rotations

  12. Magnetic star-disk coupling • X-winds model • Setup: dipole field • Resistive MHD • Viscous disk • Accretion rate in the disk prescribed • Stellar wind interaction with the disk corona

  13. Simulations of disk-jet transition • Disk evolution included • Disk corona initially notin hydrostatic equilibrium. • Vertically uniform magnetic field • Magnetic diffusivity: Gaussian • vanishing outside the disk • Setup: • Disk in the active grid • Small inflow area (accretion inflow) • „Sink” for R<Ri • ZxR=125x80=(60x40)Ri

  14. Jet launching • Persistent outflow forms • Jet launched from inner part of the disk (R<15Ri) • Disk remains in equilibrium • Quasistationarity after T~150 • Consistent with the Casse & Keppens (2002) results • Caveat: low resolution runs

  15. Star, disk & halo • Rotating star as a b.c. • Corona in hydrostatic equilibrium. • THIN resistive disk. • Stellar dipole field. • RADIAL inflow in the disk. • RxZ=(80x125)=(12x12)Ri

  16. ... after a few rotations

  17. Summary • ZEUS-3D mounted and tested on PC-cluster in TIARA. • Time-dependent simulations of the interaction between the stellar magnetic field and the disk matter. • Eventually to do ZEUS-MP setup for full 3D simulations of the disk-jet transition.

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