Fossil magnetic field of accretion disks of young stars

Abstract

We elaborate the model of accretion disks of young stars with the fossil large-scale magnetic field in the frame of Shakura and Sunyaev approximation. Equations of the MHD model include Shakura and Sunyaev equations, induction equation and equations of ionization balance. Magnetic field is determined taking into account ohmic diffusion, magnetic ambipolar diffusion and buoyancy. Ionization fraction is calculated considering ionization by cosmic rays and X-rays, thermal ionization, radiative recombinations and recombinations on the dust grains. Analytical solution and numerical investigations show that the magnetic field is coupled to the gas in the case of radiative recombinations. Magnetic field is quasi-azimuthal close to accretion disk inner boundary and quasi-radial in the outer regions. Magnetic field is quasi-poloidal in the dusty "dead" zones with low ionization degree, where ohmic diffusion is efficient. Magnetic ambipolar diffusion reduces vertical magnetic field in 10 times comparing to the frozen-in field in this region. Magnetic field is quasi-azimuthal close to the outer boundary of accretion disks for standard ionization rates and dust grain size a_d=0.1 micrometers. In the case of large dust grains (a_d > 0.1 micrometers) or enhanced ionization rates, the magnetic field is quasi-radial in the outer regions. It is shown that the inner boundary of dusty "dead" zone is placed at r=(0.1-0.6) AU for accretion disks of stars with M=(0.5-2) M_{\odot}. Outer boundary of "dead" zone is placed at r=(3-21) AU and it is determined by magnetic ambipolar diffusion. Mass of solid material in the "dead" zone is more than 3 M_{\oplus} for stars with M \geq 1 M_{\odot}.

21 pages, 7 figures, 3 tables, Accepted for publication in Astrophysics and Space Science (2014); corrected typos, removed duplicated equations on page 4, removed uncited references

References in corpus (11)

• Theory of Star Formation
• Magnetic Fields in the Formation of Sun-Like Stars
• The Burst Mode of Protostellar Accretion
• Magnetic fields in protoplanetary disks
• Heat and Dust in Active Layers of Protostellar Disks
• Global MHD simulations of stratified and turbulent protoplanetary discs. I. Model properties
• Assembling the Building Blocks of Giant Planets around Intermediate Mass Stars
• Mean-Field Magnetohydrodynamics of Accretion Disks
• New composite models of partially ionized protoplanetary disks
• The Fractional Ionization of the Warm Neutral Interstellar Medium
• The Effects of Large-Scale Magnetic Fields on Disk Formation and Evolution

Cited by in corpus (7)

• Ionization and Dust Charging in Protoplanetary Disks
• Magnetic fields in circumstellar disks: The potential of Zeeman observations
• Theory of fossil magnetic field
• Large-scale magnetic field in the accretion discs of young stars: the influence of magnetic diffusion, buoyancy and Hall effect
• Mid-Infrared Polarization of Herbig Ae/Be Discs
• Magnetic field buoyancy in accretion disks of young stars
• Dynamics of magnetic flux tubes in accretion discs of T Tauri stars