Abstract
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 $\alpha$-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.
Highlights
The observational features in active galactic nuclei (AGN) and X-ray binaries can be successfully explained by the standard geometrically thin, optically thick accretion disc model (Shakura & Sunyaev 1973)
Since the observational evidences and magnetohydrodynamics (MHD) simulations have expressed the toroidal magnetic field and the magnetic diffusivity are important in accretion flows, Faghei (2011a) examined the selfsimilar solutions of viscous and resistive advection-dominated accretion flows (ADAFs) in the presence of a toroidal magnetic field
Sharma et al (2008) studied the effects of thermal conduction on magnetized spherical accretion flows using global axisymmetric MHD simulations. In their model, when the magnetic energy density becomes comparable to the gravitational potential energy density, the plasma due to resistivity is heated to roughly the virial temperature, the mean inflow becomes highly subsonic, and most of the energy released by accretion is transported to large radii by thermal conduction and the accretion rate became much smaller than Bondi accretion rate
Summary
The observational features in active galactic nuclei (AGN) and X-ray binaries can be successfully explained by the standard geometrically thin, optically thick accretion disc model (Shakura & Sunyaev 1973). Since the observational evidences and magnetohydrodynamics (MHD) simulations have expressed the toroidal magnetic field and the magnetic diffusivity are important in accretion flows (see Faghei 2011a and references therein), Faghei (2011a) examined the selfsimilar solutions of viscous and resistive ADAFs in the presence of a toroidal magnetic field He did not consider the effects of thermal conduction in his model. Sharma et al (2008) studied the effects of thermal conduction on magnetized spherical accretion flows using global axisymmetric MHD simulations In their model, when the magnetic energy density becomes comparable to the gravitational potential energy density, the plasma due to resistivity is heated to roughly the virial temperature, the mean inflow becomes highly subsonic, and most of the energy released by accretion is transported to large radii by thermal conduction and the accretion rate became much smaller than Bondi accretion rate.
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