Large-scale magnetic field of the accretion disks of T Tauri stars

2018 ◽  
Vol 14 (S345) ◽  
pp. 297-298
Author(s):  
Alexander E. Dudorov ◽  
Sergey A. Khaibrakhmanov ◽  
Sergey Yu. Parfenov ◽  
Andrey M. Sobolev
Keyword(s):  
Magnetic Field ◽  
Accretion Disks ◽  
Large Scale ◽  
Young Stars ◽  
T Tauri ◽  
Ionization Structure ◽  
Large Scale Magnetic Field ◽  
Field Geometry ◽  
Simulation Results

AbstractThe large-scale magnetic field in the accretion disks of young stars is investigated. Main features of our magnetohydrodynamical (MHD) model of the accretion disks and typical simulation results are presented. We discuss the role of MHD effects, ionization structure, magnetic field geometry and strength of the accretion disks.

scholarly journals Magnetic geometries of Sun-like stars: exploring the mass-rotation plane

2008 ◽  
Vol 4 (S259) ◽  
pp. 441-442
Author(s):  
Pascal Petit ◽  
B. Dintrans ◽  
M. Aurière ◽  
C. Catala ◽  
J.-F. Donati ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Solar Rotation ◽  
Physical Parameters ◽  
Solar Mass ◽  
Rotation Rates ◽  
Large Scale Magnetic Field ◽  
First Results ◽  
Field Geometry ◽  
Rotation Plane

AbstractSun-like stars are able to continuously generate a large-scale magnetic field through the action of a dynamo. Various physical parameters of the star are able to affect the dynamo output, in particular the rotation and mass. Using the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France), it is now possible to measure the large-scale magnetic field of solar analogues (i.e. stars very close to the Sun in the mass-rotation plane, including strict solar twins). From spectropolarimetric time-series, tomographic inversion enables one to reconstruct the field geometry and its progressive distortion under the effect of surface differential rotation. We show the first results obtained on a sample of main-sequence dwarfs, probing masses between 0.7 and 1.4 solar mass and rotation rates between 1 and 3 solar rotation rate.

scholarly journals Magnetic Flux Transport in Protostellar Accretion Disks

1997 ◽  
Vol 163 ◽  
pp. 692-692
Author(s):  
John Contopoulos ◽  
Arieh Königl
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Accretion Disks ◽  
Large Scale ◽  
Turbulent Viscosity ◽  
Flux Transport ◽  
Disk Structure ◽  
Large Scale Magnetic Field ◽  
Field Lines ◽  
Open Magnetic Field

AbstractCentrifugally driven winds from the surfaces of magnetized accretion disks are a leading candidate for the origin of bipolar outflows and have also been recognized as an attractive mechanism for removing the angular momentum of the accreted matter. The origin of the open magnetic field lines that thread the disk in this scenario is, however, still uncertain. One possibility is that the field lines are transported through the disk, but previous studies have shown that this process is inefficient in disks with turbulent viscosity and diffusivity. Here we examine whether the efficiency can be increased if angular momentum is transported from the disk surfaces by large-scale magnetic fields instead of radially by viscous stresses. In this picture, the removal of angular momentum is associated with the establishment of a global poloidal electric current driven by the radial EMF in the disc, and it does not necessarily need to involve super-Alfvénic outflows. We address this problem in the context of protostellar systems and present representative solutions of the time evolution of a resistive disk that is initially threaded by a uniform vertical field anchored at a large distance from its surfaces. We assume that the angular momentum transport in the disk is controlled by the large-scale magnetic field and take into account the influence of the field on the disk structure.

scholarly journals ACCRETION DISKS WITH A LARGE SCALE MAGNETIC FIELD AROUND BLACK HOLES

2013 ◽  
Vol 53 (A) ◽  
pp. 677-682
Author(s):  
Gennady Bisnovatyi-Kogan ◽  
Alexandr S. Klepnev ◽  
Richard V.E. Lovelace
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Accretion Disk ◽  
Accretion Disks ◽  
Large Scale ◽  
Outward Diffusion ◽  
Large Scale Magnetic Field ◽  
Jet Collimation ◽  
The Magnetic Field ◽  
Inner Parts

We consider accretion disks around black holes at high luminosity, and the problem of the formation of a large-scale magnetic field in such disks, taking into account the non-uniform vertical structure of the disk. The structure of advective accretion disks is investigated, and conditions for the formation of optically thin regions in central parts of the accretion disk are found. The high electrical conductivity of the outer layers of the disk prevents outward diffusion of the magnetic field. This implies a stationary state with a strong magnetic field in the inner parts of the accretion disk close to the black hole, and zero radial velocity at the surface of the disk. The problem of jet collimation by magneto-torsion oscillations is investigated.

scholarly journals OBLIQUE MAGNETIC FIELDS AND THE ROLE OF FRAME DRAGGING NEAR ROTATING BLACK HOLE

2014 ◽  
Vol 54 (6) ◽  
pp. 398-413 ◽  
Author(s):  
Vladimír Karas ◽  
Ondřej Kopáček ◽  
Devaky Kunneriath
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Large Scale ◽  
Frame Dragging ◽  
Rotating Black Hole ◽  
Large Scale Magnetic Field ◽  
Set Up ◽  
Magnetic Null ◽  
Future Work

<p>Magnetic null points can <span style="font-size: 10px;">develop near the ergosphere boundary of a rotating black hole by the combined effects of strong gravitational field and the frame-dragging mechanism. The induced electric component does not vanish in the magnetic null and an efficient process of particle acceleration can occur in its immediate vicinity. Furthermore, the effect of imposed (weak) magnetic field can trigger an onset of chaos in the motion of electrically charged particles. The model set-up appears to be relevant for low-accretion-rate nuclei of some galaxies which exhibit episodic accretion events (such as the Milky Way's supermassive black hole) embedded in a large-scale magnetic field of external origin with respect to the central black hole. In this contribution we summarise recent results and we give an outlook for future work with the focus on the role of gravito-magnetic effects caused by rotation of the black hole.</span></p>

scholarly journals The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya

2011 ◽  
Vol 417 (1) ◽  
pp. 472-487 ◽  
Author(s):  
J.-F. Donati ◽  
S. G. Gregory ◽  
S. H. P. Alencar ◽  
J. Bouvier ◽  
G. Hussain ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Tauri Star ◽  
T Tauri ◽  
Large Scale Magnetic Field

scholarly journals T Tauri stars: magnetic fields and planets

2021 ◽  
Vol 2 (1) ◽  
pp. 9-20
Author(s):  
Konstantin Grankin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Magnetic Coupling ◽  
Short Review ◽  
T Tauri Stars ◽  
Young Stars ◽  
Doppler Imaging ◽  
Hot Jupiters ◽  
T Tauri

In this short review we present the results of a study of the large-scale magnetic topologies of T Tauri stars (TTS). A small spectropolarimetric survey of 8 young stars was carried out within two international projects MaPP (Magnetic Protostars and Planets) and MaTYSSE (Magnetic Topologies of Young Stars and the Survival of massive close-in Exoplanets) between 2009 and 2016. For each of our targets we reconstructed the brightness map and the magnetic field topology using Zeeman–Doppler imaging (ZDI). This review contains a brief description of spectropolarimetricdata, the ZDI method, one example of the reconstruction of brightness and magnetic maps, and the properties of magnetic fields of 8 TTS. Our results suggest that AA Tau and LkCa 15 interact with their disks in the propeller mode when their rotation is actively slowed by the star/disk magnetic coupling. We find that magnetic fields of some TTS are variable on a time scale of a few years and are thus intrinsically nonstationary. We report on the detection of a giant exoplanet around V830 Tau and TAP 26. These two new detections suggest that the type II disk migration is efficient at generating newborn hot Jupiters (hJs) around young TTS. The result of our survey is compared to the global picture of magnetic field properties of twenty TTS in the Hertzsprung–Russell diagram. The comparison shows that WTTS exhibit a wider range of field topologies as compared to CTTS, and that magnetic fields of all TTS (CTTS and WTTS as a whole) are mostly poloidal and axisymmetric when they are mostly convective and cooler than 4300 K. This needs to be confirmed with a larger sample of stars.

scholarly journals Magnetic fields in astrophysical objects

2008 ◽  
Vol 366 (1884) ◽  
pp. 4453-4464 ◽  
Author(s):  
L.J Silvers
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Accretion Discs ◽  
Weak Magnetic Fields ◽  
Large Scale Magnetic Field ◽  
Astrophysical Objects ◽  
Recent Developments ◽  
The Magnetic Field

Magnetic fields are known to reside in many astrophysical objects and are now believed to be crucially important for the creation of phenomena on a wide variety of scales. However, the role of the magnetic field in the bodies that we observe has not always been clear. In certain situations, the importance of a magnetic field has been overlooked on the grounds that the large-scale magnetic field was believed to be too weak to play an important role in the dynamics. In this article I discuss some of the recent developments concerning magnetic fields in stars, planets and accretion discs. I choose to emphasize some of the situations where it has been suggested that weak magnetic fields may play a more significant role than previously thought. At the end of the article, I list some of the questions to be answered in the future.

scholarly journals The role of magnetic field geometry in the evolution of neutron star merger accretion discs

2019 ◽  
Vol 490 (4) ◽  
pp. 4811-4825 ◽  
Author(s):  
I M Christie ◽  
A Lalakos ◽  
A Tchekhovskoy ◽  
R Fernández ◽  
F Foucart ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Large Scale ◽  
Gamma Ray ◽  
Long Duration ◽  
Field Geometry ◽  
General Relativistic ◽  
R Process ◽  
Magnetohydrodynamic Simulations

ABSTRACT Neutron star mergers are unique laboratories of accretion, ejection, and r-process nucleosynthesis. We used 3D general relativistic magnetohydrodynamic simulations to study the role of the post-merger magnetic geometry in the evolution of merger remnant discs around stationary Kerr black holes. Our simulations fully capture mass accretion, ejection, and jet production, owing to their exceptionally long duration exceeding 4 s. Poloidal post-merger magnetic field configurations produce jets with energies Ejet ∼ (4–30) × 1050 erg, isotropic equivalent energies Eiso ∼ (4–20) × 1052 erg, opening angles θjet ∼ 6–13°, and durations tj ≲ 1 s. Accompanying the production of jets is the ejection of $f_\mathrm{ej}\sim 30\!-\!40{{\ \rm per\ cent}}$ of the post-merger disc mass, continuing out to times &gt;1 s. We discover that a more natural, purely toroidal post-merger magnetic field geometry generates large-scale poloidal magnetic flux of alternating polarity and striped jets. The first stripe, of $E_\mathrm{jet}\simeq 2\times 10^{48}\, \mathrm{erg}$, Eiso ∼ 1051 erg, θjet ∼ 3.5–5°, and tj ∼ 0.1 s, is followed by ≳4 s of striped jet activity with $f_\mathrm{ej}\simeq 27{{\ \rm per\ cent}}$. The dissipation of such stripes could power the short-duration gamma-ray burst (sGRB) prompt emission. Our simulated jet energies and durations span the range of sGRBs. We find that although the blue kilonova component is initially hidden from view by the red component, it expands faster, outruns the red component, and becomes visible to off-axis observers. In comparison to GW 170817/GRB 170817A, our simulations underpredict the mass of the blue relative to red component by a factor of few. Including the dynamical ejecta and neutrino absorption may reduce this tension.

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