Theory of fossil magnetic field

Dudorov, A. E.; Khaibrakhmanov, Sergey A.

doi:10.1016/j.asr.2014.05.034

Cited by 19 publications

(13 citation statements)

References 35 publications

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“…According to modern theory of star formation, young stars with the accretion discs form as a result of gravitational collapse of rotating molecular cloud cores with magnetic field (see reviews by Inutsuka 2012;Li et al 2014). Numerical simulations show that the magnetic flux of the molecular cloud cores is partially conserved during the collapse, so it is natural to assume that the magnetic field of the accretion discs of young stars is the fossil one (see reviews of the theory of the fossil magnetic field by Dudorov 1995;Dudorov & Khaibrakhmanov 2015). The magnetic field of accretion discs can also be a result of dynamo (see, for example, Brandenburg et al 1995;Gressel & Pessah 2015;Moss et al 2016, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of magnetic flux tubes in accretion discs of T Tauri stars

Dudorov

Khaibrakhmanov

Соболев

2019

Monthly Notices of the Royal Astronomical Society

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Dynamics of slender magnetic flux tubes (MFT) in the accretion discs of T Tauri stars is investigated. We perform simulations taking into account buoyant, aerodynamic and turbulent drag forces, radiative heat exchange between MFT and ambient gas, magnetic field of the disc. The equations of MFT dynamics are solved using Runge-Kutta method of the fourth order. The simulations show that there are two regimes of MFT motion in absence of external magnetic field. In the region r < 0.2 au, the MFT of radii 0.05 a 0 0.16 H (H is the scale height of the disc) with initial plasma beta of 1 experience thermal oscillations above the disc. The oscillations decay over some time, and MFT continue upward motion afterwards. Thinner or thicker MFT do not oscillate. MFT velocity increases with initial radius and magnetic field strength. MFT rise periodically with velocities up to 5-15 km s −1 and periods of 0.5 −10 yr determined by the toroidal magnetic field generation time. Approximately 20% of disc mass and magnetic flux can escape to disc atmosphere via the magnetic buoyancy over characteristic time of disc evolution. MFT dispersal forms expanding magnetized corona of the disc. External magnetic field causes MFT oscillations near the disc surface. These magnetic oscillations have periods from several days to 1-3 months at r < 0.6 au. The magnetic oscillations decay over few periods. We simulate MFT dynamics in accretion discs in the Chameleon I cluster. The simulations demonstrate that MFT oscillations can produce observed IR-variability of T Tauri stars.

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Section: Introductionmentioning

confidence: 99%

Dynamics of magnetic flux tubes in accretion discs of T Tauri stars

Dudorov

Khaibrakhmanov

Соболев

2019

Monthly Notices of the Royal Astronomical Society

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“…One explanation for the origin of these fields is the fossil field theory, according to which the fields are remnants of the primordial fields of the interstellar gas from which the stars are formed (e.g. Braithwaite 2014;Dudorov & Khaibrakhmanov 2015, and references therein). Townsend & Owocki (2005) proposed that strong, large-scale magnetic fields can confine and guide the stellar winds along the field lines towards the magnetic equator, where material starts to accumulate.…”

Section: Introductionmentioning

confidence: 99%

Do A-type stars flare?

Pedersen

Antoci

Korhonen

et al. 2016

Mon. Not. R. Astron. Soc.

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For flares to be generated, stars have to have a sufficiently deep outer convection zone (F5 and later), strong large-scale magnetic fields (Ap/Bp-type stars) or strong, radiatively driven winds (B5 and earlier). Normal A-type stars possess none of these and therefore should not flare. Nevertheless, flares have previously been detected in the Kepler lightcurves of 33 A-type stars and interpreted to be intrinsic to the stars. Here we present new and detailed analyses of these 33 stars, imposing very strict criteria for the flare detection. We confirm the presence of flare-like features in 27 of the 33 Atype stars. A study of the pixel data and the surrounding field-of-view (FOV) reveals that 14 of these 27 flaring objects have overlapping neighbouring stars and 5 stars show clear contamination in the pixel data. We have obtained high-resolution spectra for 2/3 of the entire sample and confirm that our targets are indeed A-type stars. Detailed analyses revealed that 11 out of 19 stars with multiple epochs of observations are spectroscopic binaries. Furthermore, and contrary to previous studies, we find that the flares can originate from a cooler, unresolved companion. We note the presence of Hα emission in eight stars. Whether this emission is circumstellar or magnetic in origin is unknown. In summary, we find possible alternative explanations for the observed flares for at least 19 of the 33 A-type stars, but find no truly convincing target to support the hypothesis of flaring A-type stars.

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“…According to theory of fossil magnetic field (see review of the theory in [11,12]), stellar magnetic field, after separation from the external field, can be directed oppositely to the magnetic field of the accretion disk. Therefore, current layer can form near the boundary of stellar magnetosphere.…”

Section: Current Layermentioning

confidence: 99%

Outflows and particle acceleration in the accretion disks of young stars

Khaibrakhmanov

Dudorov

2019

EPJ Web Conf.

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Magneto-gas-dynamic (MGD) outflows from the accretion disks of T Tauri stars with fossil large-scale magnetic field are investigated. We consider two mechanisms of the outflows: rise of the magnetic flux tubes (MFT) formed in the regions of efficient generation of the toroidal magnetic field in the disk due to Parker instability, and acceleration of particles in the current layer formed near the boundary between stellar magnetosphere and the accretion disk. Structure of the disk is calculated using our MGD model of the accretion disks. We simulate dynamics of the MFT in frame of slender flux tube approximation taking into account aerodynamic and turbulent drags, and radiative heat exchange with external gas. Particle acceleration in the current layer is investigated on the basis of Sweet-Parker model of magnetic reconnection. Our calculations show that the MFT can accelerate to velocities up to 50 km s −1 causing periodic outflows from the accretion disks. Estimations of the particle acceleration in the current layer are applied to interpret high-speed jets and X-rays observed in T Tauri stars with the accretion disks. *

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Theory of fossil magnetic field

Cited by 19 publications

References 35 publications

Dynamics of magnetic flux tubes in accretion discs of T Tauri stars

Dynamics of magnetic flux tubes in accretion discs of T Tauri stars

Do A-type stars flare?

Outflows and particle acceleration in the accretion disks of young stars

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