3D MHD Simulation of a Pulsationally-Driven MRI Decretion Disc
arXiv:2110.03693 · doi:10.1093/mnras/stab2880
Abstract
We explore the pulsationally driven orbital mass ejection mechanism for Be star disc formation using isothermal, 3D magnetohydrodynamic (MHD) and hydrodynamic simulations. Non-radial pulsations are added to a star rotating at 95\% of critical as an inner boundary condition that feeds gas into the domain. In MHD, the initial magnetic field within the star is weak. The hydrodynamics simulation has limited angular momentum transport, resulting in repeating cycles of mass accumulation into a rotationally-supported disc at small radii followed by fall-back onto the star. The MHD simulation, conversely, has efficient (Maxwell 0.04) angular momentum transport provided by both of turbulent and coherent magnetic fields; a slowly decreting midplane driven by the magnetorotational instability and a supersonic wind on the surface of the disc driven by global magnetic torques. The angle and time-averaged properties near the midplane agree reasonably well with a 1D viscous decretion disc model with a modified , in which the gas transitions from a subsonic thin disc to a supersonic spherical wind at the critical point. 1D models, however, cannot capture the multi-phase decretion/angular structure seen in our simulations. Our results demonstrate that, at least under certain conditions, non-radial pulsations on the surface of a rapidly rotating, weakly magnetized star can drive a Keplerian disc with the basic properties of the viscous decretion disc paradigm, albeit coupled to a laminar wind away from the midplane. Future modeling of Be star discs should consider the possible existence of such a surface wind.
arXiv commentAccepted by MNRAS. 16 pages, 10 figures
References in corpus (36)
- Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
- The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
- Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: I. Isothermal, Nonrotating, Radially Driven Flow
- Be-star rotation: how close to critical?
- Hydrodynamical Simulations of Corotating Interaction Regions and Discrete Absorption Components in Rotating O-Star Winds
- Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
- Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: III. Angular Momentum Loss and Rotational Spindown
- Super-Eddington Accretion Disks around Supermassive black Holes
- Viscous Effects on the Interaction between the Coplanar Decretion Disc and the Neutron Star in Be/X-Ray Binaries
- A Statistical Study of Threshold Rotation Rates for the Formation of Disks around Be Stars
- Viscous Transonic Decretion in Disks of Be Stars
- Giant Outbursts in Be/X-ray Binaries
- Dynamical Evolution of Viscous Disks around Be Stars. I: photometry
- Locality of MHD Turbulence in Isothermal Disks
- Mass and angular momentum loss via decretion disks
- Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
- Non-LTE Monte Carlo Radiative Transfer: II. Non-Isothermal Solutions for Viscous Keplerian Disks
- A Magnetically Torqued Disk Model for Be Stars
- On the evolutionary status of Be stars. I. Field Be stars near the Sun
- First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
- The signature of the magnetorotational instability in the Reynolds and Maxwell stress tensors in accretion discs
- Disk Loss and Disk Renewal Phases in Classical Be Stars I: Analysis of Long-Term Spectropolarimetric Data
- The pseudo-photosphere model for the continuum emission of gaseous discs
- A Pulsational Mechanism for Producing Keplerian Disks around Be Stars
- Accretion disc formation around the neutron star in Be/X-ray binaries
- Transport of angular momentum by stochastically excited waves as an explanation for the outburst of the rapidly rotating Be star HD49330
- The Effect of Density on the Thermal Structure of Gravitationally-Darkened Be Star Disks
- Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): II The Relative Importance of MRI and Spiral Shocks
- Variations of the amplitudes of oscillation of the Be star Achernar
- Modelling decretion discs in Be/X-ray binaries
- A New Diagnostic of the Radial Density Structure of Be Disks
- The Thermal Structure of Gravitationally-Darkened Classical Be Star Disks
- Long-term evolution of accretion discs in Be/X-ray binaries
- The Effect of Rotational Gravity Darkening on Magnetically Torqued Be Star Disks
- One-armed spiral structure of accretion discs induced by a phase-dependent mass transfer in Be/X-ray binaries
- Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks