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 $\alpha$-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

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 $\gamma=5/3$. In this scenario, it was assumed that the angular momentum transport is due to viscous turbulence and used $\alpha$-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 $\beta[=p_{mag}/p_{gas}]$, where $p_{mag}$ and $p_{gas}$ 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

Thermal instability in ionized plasma

We study magnetothermal instability in the ionized plasmas including the effects of Ohmic, ambipolar and Hall diffusion. Magnetic field in the single fluid approximation does not allow transverse thermal condensations, however, non-ideal effects highly diminish the stabilizing role of the magnetic field in thermally unstable plasmas. Therefore, enhanced growth rate of thermal condensation modes in the presence of the diffusion mechanisms speed up the rate of structure formation.Comment: Accepted for publication in Astrophysics & Space Scienc