Accretion onto Magnetized Stars Marina Romanova, Cornell University Collaborators: R. Lovelace, A. Koldoba, G. Ustyugova , A. Kulkarni, M. Long, R. Kurosawa, M. Bachetti, J.-F. Donati 14 Jul. 2010 Accreting Magnetized Stars: Young stars: B=103 G, R=1011 cm White dwarfs: cataclysmic variables –Intermediate polars B=106-108 G, R=5x108 cm Neutron stars: accreting millisecond pulsars, B=108-109 G, R=106 cm X-ray pulsars: B=1012 G -larger magnetospheres Black holes: variable magnetospheres Different problems and outline 1.Magnetospheric flow 2. Weak B-field, MBL 3. Outflows and jets Different codes, 2D, 3D Grids: spherical, cylindrical, Cubed sphere I. a- disks (40 years). avis and adif Matt & Pudritz 2005 - Wind-driven accretion - Spiral waves: a.m. transport - Partially ionized disks - Models describe MHD flow - Different instabilities - Variability, X-ray II. MRI disks 3D simulations of accretion onto tilted dipoles Two funnel streams Two hot spots Ordered light-curve Hot spots – slice across the funnel stream 4 Romanova, Ustyugova, Koldoba & Lovelace 2003,2004 Spectral analysis: 3D radiative transfer, TORUS φ=0 φ=0.25 φ=0.5 φ=0.75 Paβ emission map (upper) and profiles (lower) Kurosawa, Romanova & Harries, MNRAS, 2008 Comparisons with accreting tilted BHs Matter flow around tilted rotating magnetized star Romanova et al. 2003 Matter flow around tilted rotating BH Fragile, Blaes, Anninos, Salmonson 2007 In both cases matter chooses energetically favorable path Matter has tendency to flow in magnetic/BH equator (disk is warped) 3D simulations, larger scale, waves, QPOs Stable or unstable regimes: Chaotic light-curve, QPO oscillations Next talk Predicted: Arons & Lea 1976; Lamb 1976 Global simulations: Kulkarni & Romanova 2008; Romanova, Kulkarni, Lovelace 2008 Case of very small tilt: Q=2-5o QPO oscillations at different frequencies Spots rotate faster/slower than the star RXTE, future IXO Bachetti, Romanova, Kulkarni, Burderi & Di Salvo 2009 3D simulations of MRI-driven accretion, Q=30o B=0 B=0 Large-scale turbulence is observed like in case of nonmagnetic star (e.g., Hawley 2000) Low-m spiral modes Romanova et al. (in prep) 3D view of MRI-driven Accretion Matter accretes in funnel streams Funnels form episodically Variability is higher than in case of the laminar flow Romanova et al. (in prep) 2D simulations of MRI-driven Accretion Rcor=6 T=15 rotations at r=30 B B Different configurations of the seed poloidal field in the disk: - Parallel field -Parallel with cut - Different orientation - Loops animation MRI-driven accretion: Balbus & Hawley 1991, 1998; Hawley & Balbus 1999; Stone, Howley, Gammie, Balbus 1995; Hawley & Krolik 2001, and more Romanova et al. (in prep.) Episodic accretion in case of parallel fields Observations of accreting millisecond pulsar SAX J1808.4-3658 Simulations of the case Bdisk Bdip Simulations of the case Bdisk Bdip Romanova et al. (in prep) Variability in CTTS TW Hya DF Tau Rucinski et al. 2008 MOST: Microvariability & Oscillations of Stars (dT=100 min) Variability is not very high, factor of x1.5 Usually CTTS vary 0.1m-0.5m on the dynamical time-scale Reconnection – heating, particles acceleration e, g e-e+ e-i Spectrum: power law (R&L 1992) Large Flare (CTTS): 3.3x1031 erg/s Particles are accelerated in the current layer (Alfven 1968; Romanova & Lovelace 1992) 2. Magnetic boundary layer Tiny magnetosphere forms Ordered spots, frequency n=nstar Romanova & Kulkarni 2009 Unstable regime Spots rotate in the equatorial plane QPO, frequency of the inner disk (millisecond pulsars, Dwarf Novae) 3. Winds and Jets I. avis = adif avis >> adif II. outflows Matter inflows with the same rate as the Matter inflows faster than the field magnetic field diffuses out diffuses out Accretion, no outflows Accretion and outflows Field lines inflate c c Wstar Wdisk animation 19 Conical Winds formation avis=0.3 adif=0.1 Matter flux, velocity, field lines Compression of the magnetosphere (Shu et al. 1994) Magnetic force drives outflows Formation of Conical Winds Applications: EXORs, millisecond pulsars, CVs, BHs, more Propeller regime Poynting Jet 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 22 3D rendering Lower speed Higher speed B-lines GR simulations of outflows from BHs a/M=0.5 a/M=0.998 Poynting flux jet increases with a/M Krolik, Hawley, Hirose 2004 Poloidal current increases with a/M Hirose, Krolik, De Villiers, Hawley 2004 Propeller Case Simulations: 7 years Major outbursts: 2 months HST Observations: 25 Cycle of inflation Ustyugova et al. 2006 HH30 Flaring matter flux in the propeller regime: MRI Simulations (avis)max= 0.1 adif = 0.01 (numerical) a-disk simulations Lmatter avis=0.3 adif=0.1 field Accretion onto Stars with Complex fields Dipole+quadrupole 27 Realistic Magnetic Fields MIN LONG, Poster # 13 The magnetic field of the young star V2129 Oph is measured on the Surface of the star with the Doppler-Zeeman technique and extrapolated to the larger distances in force-free approximation Donati et al. 2007 3D field of V2129 modeled with 1.2 kG octupole and 0.35 kG dipole fields Long et al. 2010 Romanova et al. 2010 Pure octupole field Winds from Stars with Complex Fields Different quadrupole moments Lovelace, Romanova, Ustyugova, Koldoba , MNRAS 2010 29 Wind is Asymmetric: Lovelace, Romanova, Ustyugova, Koldoba , MNRAS 2010 30 Matter accretes from the disk onto the star either in funnel streams or trough instabilities. In MRI regime matter accretes in funnel streams but the higher level of variability is expected The weak magnetic field modifies the boundary layer: in stable regime - periodic signal, in the unstable regime – drifting QPOs. Outflows can be connected with periods of enhanced accretion and the bunching of the field lines. Persistent conical winds form. In the propeller regime accretion is episodic (in both MRI and laminar disks). Outflows have two components: slow heavy conical winds and fast Poynting jet Magnetic field of stars may be complex. May lead to formation of one-sided jets. See poster by Min Long on complex fields.