Accretion disc backflow in resistive MHD simulations

Abstract

We investigate accretion onto a central star, with the size, rotation rate, and magnetic dipole of a young stellar object, to study the flow pattern (velocity and density) of the fluid within and outside of the disc. We perform resistive MHD simulations of thin $\alpha$-discs, varying the parameters such as the stellar rotation rate and magnetic field, and (anomalous) coefficients of viscosity and resistivity in the disc. To provide a benchmark for the results and to compare with known analytic results, we also perform purely hydrodynamic simulations (HD) for the same problem. Although obtained for a different situation with differing inner boundary condition, the disc structure in the HD simulations closely follows the analytic solution of Kluźniak and Kita (2000) -- in particular a region of "midplane" backflow exists in the right range of radii, depending on the viscosity parameter. In the MHD solutions, whenever the magnetic Prandtl number does not exceed a certain critical value, the midplane backflow exists throughout the accretion disc, extending all the way down to the inner transition zone where the disc transitions to a magnetic funnel flow. For values of the magnetic Prandtl number close to the critical value the backflow and the inner disc undergo a quasiperiodic radial oscillation, otherwise the backflow is steady, as is the disc solution. From our results, supplemented by our reading of the literature, we conclude that midplane backflow is a real feature of at least some accretion discs, whether HD $\alpha$-discs or MHD discs, including ones driven by MRI turbulence.

11 pages, 11 figures, 1 table Submitted to Monthly Notices of the Royal Astronomical Society (MNRAS)

References in corpus (8)

• PLUTO: a Numerical Code for Computational Astrophysics
• Two-Dimensional Transport of Solids in Viscous Protoplanetary Disks
• Convection Causes Enhanced Magnetic Turbulence in Accretion Disks in Outburst
• Magnetic torques on T Tauri stars: accreting vs. non-accreting systems
• Accretion discs with non-zero central torque
• Radial Transport and Meridional Circulation in Accretion Disks
• Inner dusty regions of protoplanetary discs -- II. Dust dynamics driven by radiation pressure and disc winds
• Backflow in simulated MHD accretion disks

Cited by in corpus (5)

• Magnetically threaded accretion disks in resistive magnetohydrodynamic simulations and asymptotic expansion
• Trends in torques acting on the star during a star-disk magnetospheric interaction
• 2.5-MHD models of circumstellar discs around FS~CMa post-mergers : II. Stationary accretion stage
• Inner dusty regions of protoplanetary discs -- III. The role of non-radial radiation pressure in dust dynamics
• Multipolar magnetic configuration: a trace of post-mergers events in circumstellar disks around FS CMa Stars