Iranian Journal of Astronomy and Astrophysic
Volume:8 Issue: 2, Summer 2021

It is investigated how the plasma evaluates due to the propagation of the nonlinear Alfven wave. Magnetic null points that are detected in the solar corona have 3D structures which are prevalent in the solar atmosphere. In this study, we consider the real 3D structure with a 3D magnetic null point. The shock-capturing Godunovtype PLUTO code is used to solve the resistive magnetohydrodynamic (MHD) set of equations in the context of wave-plasma energy transfer to find out how the plasma evaluates. An initially symmetric Alfv´en pulse at a specific distance from a magnetic null-point is kicked towards the isothermal null-point. Alfven wave propagation around a 3D magnetic null point results in magnetoacoustic waves perturbations which propagate towards the null point and refracts around the null point.It is found that nonlinear Alfven wave propagation around a 3D magnetic null point results in plasma density perturbations due to the compressible magnetoacoustic waves perturbations.

We study Brueckner event Oscillations in Solar Transition Region (TR), with simultaneous observations from the Si IV 1402 Å spectra and slit-jaw images (SJI) 1400 Å based on the Interface Region Imaging Spectrograph (IRIS) on 2014 August 17, and January 27. Study of these events can significantly help us for understanding the mechanisms of the mass and energy transporting from chromosphere toward TR and corona. We obtained intensity profiles from spectrum perpendicular to the slit in three altitudes from the limb, and then by fitting Gaussian intensity profiles, the transverse fluctuations up to 3200 km altitude along the slit were computed. We observed that Si IV spectra shows blue and red wing enhancements in the line profiles indicating upward and downward twisted. Average of Doppler velocities in the first and second data for the three altitudes were obtained 35 and 80 km/s respectively. The results of wavelet analysis of fluctuations revealed dominant periods of 1.5, 3, 5 minutes. According to our results, it was suggested that the fluctuations in the Brueckner events with one wing enhancement and both wing enhancements, illustrated the swaying and rotational motions of spicules over their axes, respectively. The swaying and rotating motions are responsible for kink and twisted Alfvenic supper and hyper sonic waves propagations, respectively.

We consider Brans Dicke scalar vector tensor gravity to study an inflationary scenario of the accelerating expansion of theuniverse for which the anisotropy property occurs. We study both primordial inflation and late inflationary period of the universe.To do so we use Bianchi I line element where spatial part has cylindrical symmetry along $x$ direction in the local Cartesian coordinates. To seek stabilization of our obtained metric solution we apply dynamical system approach to obtain critical manifolds in phase space and determine which of them confirms the inflation with stable nature in presence of the anisotropy property of spacetime. We solve dynamical equations for different directions of the timelike dynamical vector field. We obtain several critical manifolds whose nature of stable (sink) or quasi stable (saddle) are dependent to direction of the used vector field. At last we should point that observational constraint on the Brans Dicke parameter ω>40000 which satisfied by the well known Brans Dicke scalar tensor gravity is not valid for our modified scalar vector Brans Dicke gravity because of presence of timelike dynamical vector field.

The process of dust grain charging with the help the orbit limited motion theory (OLM) and a kinetic model in the relativistic regime considers in the critical areas of the dust grain density when it is very low and vice versa. A relativistic kappa distribution for currents carried by ion and electron employs and the electrical potential of dust grain by the numerical analyses calculates by using the relativistic cross-section. In the critical area when the dust grain density is high, it shows that by increasing the electron-to-ion temperature ratio, the relativistic effects increase and the electrical potential of dust grain decreases. Also, it indicates that in the critical areas, the Colombian force between the dust grain and the plasma particles play an important role and has a great impact on the process of charging. Moreover, it indicates when the density of dust grain is high, as the relativistic effects increased, the dust charging process increases and at low dust grain density, as the relativistic effect increases, the charge of the dusts decreases. It indicates that the electrical potential of the dust grain is much greater affected by the degree of electron nonextensive relative to the nonextensive degree of ion. Finally, it indicates when the dust grain density is high; the relativistic effects due of increasing temperature play a more prominent role in the dust charging process, while at low dust grain density; the relativistic effects because of changing the energy of the rest mass play a more prominent role.

The effect of dust particle charge fluctuation on the electrical potential in the plasma sheath is determined by solvation of Poisson' equation with the help OLM theory and a Tsallis distribution for current carried by electrons, a cold ion fluid and negatively charged immobile dust grains. It is indicated that the nature of electrical potential in plasma sheath dependent to the Sagdeev potential and the properties of electrostatic sheath strongly affected by fluctuations of dust grain charge that modified the Bohm criterion condition. For the first time, by solving the Sagdeev potential, a function is obtained which shows that when this function becomes negative, the ions accelerate into the region of the sheath and form an electrostatic sheath. This nonlinear function is heavily dependent on nonextensive degree of electron, the ion density ratio to electron and kind of plasma gases. It is showed that the farther we go from the Maxwell equilibrium distribution function, the ions need a higher initial velocity to be able to separate from the main body of the plasma and move towards the plasma sheath and the wall. Finally, the results are indicated that considering the dust particle charge fluctuations and the electron nonextensivity degree play an important role on electrostatic sheath formation and modify Bohm criterion.

The structure of a thin geometrically, axisymmetric, a stationary disk around a central black hole threaded by a bipolar magnetic field has been Studied that drives jets by extracting angular momentum. In this work, it is assumed that the effect of viscosity turbulence is negligible. If the effect of viscosity turbulence is negligible and the lines of the initial magnetic field have the required curvature, the magnetic force can be the only factor that determines the material leaving the disk. A primary poloidal magnetic field is applied to the disk, which has two components r and z. The equations that describe the vertical structure of the disk in a cylindrical system have been solved. We assume that the angular velocity is not completely Keplerian and the deviation from the Keplerian rotation enters the equations. It was seen that for a smaller ejection rate (a smaller ), the deviation from the Keplerian rotation is greater. The vertical structure equations of the disk were written with the presence of the polytropic equation. The gas with polytropic state equation with different gammas is given in this paper. For all gases, the variation in the toroidal magnetic field in the vertical direction is similar and for a constant ejection rate, the monoatomic gas has a greater deviation from the Keplerian rotation. Our results show in the presence of the polytropic equation and the deviation from Keplerian rotation, the process of mass reduction in the vertical direction for diatomic gas occurs faster.