7 research outputs found
Viscous and resistive accretion flows with radially self-similar and outflows
The existence of outflow in accretion flows is confirmed by observations and
magnetohydrodynamics (MHD) simulations. In this paper, we study outflows of
accretion flows in the presence of resistivity and toroidal magnetic field. The
mechanism of energy dissipation in the flow is assumed to be the viscosity and
the magnetic diffusivity due to turbulence in the accretion flow. It is also
assumed that the magnetic diffusivity and the kinematic viscosity are not
constant and vary by position and -prescription is used for them. The
influence of outflow emanating from accretion disc is considered as a sink for
mass, angular momentum and energy. The self-similar method is used to solve the
integrated equations that govern the behavior of the accretion flow in the
presence of outflow. The solutions represent the disc which rotates faster and
becomes cooler for stronger outflows. Moreover, by adding the magnetic
diffusivity, the surface density and rotational velocity decrease, while the
radial velocity and temperature increase. The study of present model with the
magnitude of magnetic field implies that the disc rotates and accretes faster
and becomes hotter, while the surface density decreases. The disc thickness
increases by adding the magnetic field or resistivity, while it becomes thinner
for more losses of mass and energy due to the outflows.Comment: 7 pages, 7 figures, accepted by MNRA
Time Dependence of Advection Dominated Accretion Flow with a Toroidal Magnetic Field
The present study examines self-similarity evolution of advection dominated
accretion flow (ADAF) in the presence of a toroidal magnetic field. In this
research, it was assumed that the angular momentum transport is due to viscous
turbulence and -prescription was used for kinematics coefficient of
viscosity. In order to solve the integrated equations which govern the
dynamical behavior of the accretion flow, self-similar solution was used. The
solutions show that the behavior of physical quantities in a dynamical ADAF are
different from steady accretion flow and a disk with polytropic approach. The
solution indicates a transonic point in the accretion flow for all selected
amounts of advection parameter. Also, by adding strength of the magnetic field
and the degree of advection, the radial-thickness of the disk decreased and the
disk compressed. The model implies that the flow has differential rotation and
is sub-Keplerian at small radii and is super-Keplerian in large radii.Comment: 7 pages, 4 figures, accepted by MNRA
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
Time-Dependent of Accretion Flow with Toroidal Magnetic Field
In the present study time evolution of quasi-spherical polytropic accretion
flow with toroidal magnetic field is investigated. The study especially focused
the astrophysically important case in which the adiabatic exponent
. In this scenario, it was assumed that the angular momentum
transport is due to viscous turbulence and used -prescription for
kinematic coefficient of viscosity. The equations of accretion flow are solved
in a simplified one-dimensional model that neglects the latitudinal dependence
of the flow. In order to solve the integrated equations which govern the
dynamical behavior of the accretion flow, self-similar solution was used. The
solution provides some insight into the dynamics of quasi-spherical accretion
flow and avoids many of the strictures of the steady self-similar solution. The
effect of the toroidal magnetic field is considered with additional variable
, where and are the magnetic and
gas pressure, respectively. The solution indicates a transonic point in the
accretion flow, that this point approaches to central object by adding strength
of the magnetic field. Also, by adding strength of the magnetic field, the
radial-thickness of the disk decreases and the disk compresses. It was
analytically indicated that the radial velocity is only a function of Alfv'en
velocity. The model implies that the flow has differential rotation and is
sub-Keplerian at all radii.Comment: 6 pages, 2 figures, accepted by MNRA
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&