3 research outputs found
Resistive and magnetized accretion flows with convection
We considered the effects of convection on the radiatively inefficient
accretion flows (RIAF) in the presence of resistivity and toroidal magnetic
field. We discussed the effects of convection on transports of angular momentum
and energy. We established two cases for the resistive and magnetized RIAFs
with convection: assuming the convection parameter as a free parameter and
using mixing-length theory to calculate convection parameter. A self-similar
method was used to solve the integrated equations that govern the behavior of
the presented model. The solutions showed that the accretion and rotational
velocities decrease by adding the convection parameter, while the sound speed
increases. Moreover, by using mixing-length theory to calculate convection
parameter, we found that the convection can be important in RIAFs with magnetic
field and resistivity.Comment: 7 pages, 3 figures, accepted by Ap&S
Self-similar solutions of viscous and resistive ADAFs with thermal conduction
We have studied the effects of thermal conduction on the structure of viscous
and resistive advection-dominated accretion flows (ADAFs). The importance of
thermal conduction on hot accretion flow is confirmed by observations of hot
gas that surrounds Sgr A and a few other nearby galactic nuclei. In this
research, thermal conduction is studied by a saturated form of it, as is
appropriated for weakly-collisional systems. It is assumed the viscosity and
the magnetic diffusivity are due to turbulence and dissipation in the flow. The
viscosity also is due to angular momentum transport. Here, the magnetic
diffusivity and the kinematic viscosity are not constant and vary by position
and -prescription is used for them. The govern equations on system have
been solved by the steady self-similar method. The solutions show the radial
velocity is highly subsonic and the rotational velocity behaves sub-Keplerian.
The rotational velocity for a specific value of the thermal conduction
coefficient becomes zero. This amount of conductivity strongly depends on
magnetic pressure fraction, magnetic Prandtl number, and viscosity parameter.
Comparison of energy transport by thermal conduction with the other energy
mechanisms implies that thermal conduction can be a significant energy
mechanism in resistive and magnetized ADAFs. This property is confirmed by
non-ideal magnetohydrodynamics (MHD) simulations.Comment: 8 pages, 5 figures, accepted by Ap&S
Self-Similar Solutions for Viscous and Resistive ADAF
In this paper, the self-similar solution of resistive advection dominated
accretion flows (ADAF) in the presence of a pure azimuthal magnetic field is
investigated. The mechanism of energy dissipation is assumed to be the
viscosity and the magnetic diffusivity due to turbulence in the accretion flow.
It is assumed that the magnetic diffusivity and the kinematic viscosity are not
constant and vary by position and -prescription is used for them. In
order to solve the integrated equations that govern the behavior of the
accretion flow, a self-similar method is used. The solutions show that the
structure of accretion flow depends on the magnetic field and the magnetic
diffusivity. As, the radial infall velocity and the temperature of the flow
increase, and the rotational velocity decreases. Also, the rotational velocity
for all selected values of magnetic diffusivity and magnetic field is
sub-Keplerian. The solutions show that there is a certain amount of magnetic
field that the rotational velocity of the flow becomes zero. This amount of the
magnetic field depends on the gas properties of the disc, such as adiabatic
index and viscosity, magnetic diffusivity, and advection parameters. The
solutions show the mass accretion rate increases by adding the magnetic
diffusivity and in high magnetic pressure case, the ratio of the mass accretion
rate to the Bondi accretion rate decreases as magnetic field increases. Also,
the study of Lundquist and magnetic Reynolds numbers based on resistivity
indicates that the linear growth of magnetorotational instability (MRI) of the
flow decreases by resistivity. This property is qualitatively consistent with
resistive magnetohydrodynamics (MHD) simulations.Comment: 18 pages, 3 figures, accepted by JA&