Effect of Coriolis force on the equilibrium structures of rotating stars and stars in binary systems

Kopal (Adv. Astron. Astrophys. 9:1–65, 1972) introduced the concept of Roche equipotentials to incorporate the effects of rotation and tidal distortions on the equilibrium structure and periods of small oscillations of rotating stars and stars in binary systems. However his expression for the Roche equipotential accounts for only the effects of centrifugal and gravitational forces and does not take into account the effect of Coriolis force. In this paper we have suitably modified Kopal’s expression for Roche equipotentials to incorporate into it the effect of Coriolis force as well. The modified expression for the Roche equipotential has then been used to compute the equilibrium structures and shapes of polytropic models of rotating stars and stars in binary systems.     

The role of the Coriolis force on the stability of rotating magnetic stars and the origin of convective motions

Based on the method of the energy principle, the effect of the Coriolis force in the stability of rotating magnetic stars is examined and the conditions for instability is derived. It is shown that, in these stars, the effect of this force is to inhibit the onset of convective motion. Discussion is given on the possibility of hydromagnetic dynamo processes in respect to the convective motion inside these stars.     

Electron beam propagation in plasmas

Electron beam propagation in a fully ionized plasma has been studied using a one-dimensional particle simulation model. The electrostatic results show the essential features of beam-plasma interactions. It is found that the return currents are enhanced by the beam-plasma instability which accelerates ambient plasmas. The results also show the heating of ambient plasmas and the trapping of plasmas due to the locally generated electric field. The electromagnetic simulations show much the same results as the electrostatic simulations do. We discuss the results in context of the heating of coronal plasma during solar flares.     

Instability of rotating isotropic and anisotropic plasmas

The instability in a horizontal layer of stratified compressible isotropic and anisotropic plasmas has been studied to include simultaneously the effects of Coriolis forces and the finiteness of the ion Larmor radius. Using an integral approach, the dispersion relation has been derived in both cases for plasmas having density stratified exponentially along the vertical. The dispersion, relation has been solved numerically and it is found that both the FLR and Coriolis forces have stabilizing influence on the instability in the isotropic plasmas. The same result is obtained for the case of anisotropic plasmas where also the dispersion relation has been evaluated numerically.     

Thin electron beam propagation in plasmas

The propagation of dense electron beams and the interaction with the ambient plasmas are studied by using two-dimensional electrostatic simulations. When the width of the beam is of the order of electron gyro-radius, the beam electrons move across the magnetic field lines and the beam-plasma interaction becomes prominent with the reduced beam density. When the width of the beam is of the order of ion gyro-radius, the propagation of beam electrons is possible only with the formation of the ion channel. However, since the time scale of the ionic motion is much longer than that of the electronic motion, most of the beam electrons return back to the original beam injection region     

Wave processes in nonlinear beams during propagation of waves in pulsar plasmas with different magnetic field orientations

The propagation of nonlinear three-dimensional waves in the form of gaussian beams in pulsars is examined. The defining equations for the wave motion of a plasma with high particle velocities, high electrical conductivity, high wave frequency, and high magnetic fields are the standard equations of magnetogas dynamics. Nonlinear, time-dependent equations are derived for relatively small perturbations of the medium and the orders of magnitude of the parameters of motion such that all the terms in the time-dependent equation are of the same order are written down. Various directions of the unperturbed magnetic field and of the wave propagation which may arise during plasma motion in quasars are considered. In a number of cases a closed analytic solution can be constructed for the propagation of axially symmetric gaussian beams. __________ Translated from Astrofizika, Vol. 49, No. 3, pp. 409–417 (August 2006).     

Coupling of micropulsation wave modes by the Coriolis force

It is suggested that near to the Earth in the equatorial plane the Coriolis force is as important as the Hall effect in the coupling of micropulsation wave modes.     

Wave propagation in the photosphere

Using a 32 minutes sequence of observation, brightness and velocity fluctuations in the wings of the Mgi line at 5172.7 Å and Fe ii line at 5197.578 Å are analysed. The analysis of phase shifts and amplitude ratios leads to the following conclusions:

Simulations of the supersonic radiative jet propagation in plasmas

Supersonic plasma jets are ubiquitous in astrophysics. Our study focus on the jets emanated from Herbig-Haro (HH) objects. They have velocities of a few hundred km/s and are extending over the distances more than a parsec. Interaction of the jets with surrounding matter produces two specific structures in the jet head: the bow shock and the Mach disk. The radiative cooling of these shocks affects strongly the jet dynamics. A tool to understand the physics of these jets is the laboratory experiment. A supersonic jet interaction with surrounding plasma was studied on the PALS laser facility. A collimated high-Z plasma jet with a velocity exceeding 400 km/s was generated and propagated over a few millimeters length. Here we report on study the effect of radiative cooling on the head jet structure with a 2D radiative hydrodynamic code. The simulation results demonstrated the scalability of the experimental observations to the HH jets.     

Wave propagation in the magnetosphere of Jupiter

The magnetosphere of Jupiter has been the subject of extensive research in recent years due to its detectable radio emissions. Observations in the decimetric radio band have been particular helpful in ascertaining the general shape of the Jovian magnetic field, which is currently believed to be a dipole with minor perturbations. Although there is no direct evidence for thermal plasma in the magnetosphere of Jupiter, theoretical considerations about the physical processes that must occur in the ionosphere and magnetosphere surrounding Jupiter have lead to estimates of the thermal plasma distribution. These models of the Jovian magnetic field and thermal plasma distribution, specify the characteristic plasma and cyclotron frequencies in the magnetosplasma and thereby provide a basis for estimating thelocal electromagnetic and hydromagnetic noise around Jupiter. Spatial analogs of the well-known Clemmow-Mullaly-Allis (CMA) diagrams have been constructed to identify the loci of electron and ion resonances and cutoffs for the different field and plasma models. Regions of reflection, mode coupling, and probable amplification are readily identified. The corresponding radio noise properties may be estimated qualitatively on the basis of these various electromagnetic and hydromagnetic wave mode regions. Frequency bands and regions of intense natural noise may be estimated. On the basis of the models considered, the radio noise properties around Jupiter are quite different from those encountered in the magnetosphere around the Earth. Wave particle interactions are largely confined to the immediate vicinity of the zenographic equatorial plane and guided propagation from one hemisphere to the other apparently does not occur, except for hydromagnetic modes of propagation. The characteristics of these local signals are indicative of the physical processes occurring in the Jovian magnetosphere. Thus, as a remote sensing tool, their observation will be a vital asset in the exploration of Jupiter.     

Effect of the Coriolis force and slowly varying flow on the Kelvin-Helmholtz instability

The effect of the Coriolis force on the Kelvin-Helmholtz instability has been investigated, in which basic velocities of fluid are varying slowly with lateral coordinatey. The problem is solved by J.W.K.B. approximation method. Parabolic and other types of profiles for wide long channel flow have also been studied in detail.     

Nonlinear propagation of electromagnetic waves in magnetized electron-positron plasmas

The nonlinear interaction of the external magnetic field-aligned circularly polarized electro-magnetic radiation with a cold electron-positron plasma is considered. A set of nonlinear equations is derived describing the coupling of the radiation with cold electrostatic oscillations. Modulational instabilities and wave localization are discussed.     

Wave propagation in the quiet solar chromosphere

In order to precise previous results about wave propagation in the quiet chromosphere (N. Mein and P. Mein, 1976), we study the behaviour of Doppler shifts and intensity fluctuations in 3 lines of Ca ii. We use the same observation as in our previous work, that is to say a sequence of spectra lasting 27 mn, taken at Sacramento Peak Observatory solar tower. Results can be summarized as follows:

1. Phase-lag between intensity fluctuations and dopplershifts is always near 90° in the Ca ii lines, even for frequencies as high as 15 mHz, and whatever is the location in the chromospheric network.
2. Magneto-acoustic waves propagating vertically in a vertical or horizontal magnetic field could account for the observations only if they were, on one hand reflected in the upper atmosphere, on the other hand propagating with a very high sound or Alfvén speed. The lower limit for the speed (70 km s^-1) does not seem to be realistic. Oblique waves could be investigated for better agreement.

     

Electrostatic solitons in rotating dusty plasmas with anisotropic ion pressure

The Zakharov-Kuznetsov (ZK) equation is derived for electrostatic wave in a rotating magnetoplasma with anisotropic ion pressure and in the presence of stationary charged dust particles. The anisotropic ion pressure is defined using double adiabatic Chew-Golberger-Low (CGL) theory. The reductive perturbation method is employed to study the dynamics of obliquely propagating low frequency ion acoustic wave with adiabatic ions. It is found that the ion pressure anisotropy, polarity, density of the dust particles and rotational frequency have significant effects on the formation nonlinear structures in rotating magnetized dusty plasmas. The numerical results are also presented for illustration.     

Dispersion and stability of waves in plasmas in the presence of a coriolis force

The dispersion law for the propagation of waves in cold magnetized plasmas is derived for arbitrary directions of the rotation axis with respect to the static magnetic field. The waves are shown to be stable, not only in the case of a cold plasma, but in any plasma case which yields hermitian mobility tensors. An interesting special case is when the rotation and magnetization axes are parallel, because then for suitable values of rotation and external magnetic field the two effects can cancel each other, though only for one plasma species at the time. The rotation thus decisively affects and shifts the number and width of the existing pass- and stop-bands in a magnetized plasma. The inclusion of thermal effects through a scalar barotropic pressure is not nearly as significant.     

Nonlinear propagation of Alfvén waves in cometary plasmas

Large-amplitude Alfvén waves propagating along the guide magnetic field in a three-component plasma are shown to be spatially localized due to their nonlinear interaction with nonresonant electrostatic density fluctuations. A new class of subsonic Alfvén soliton solutions are found to exist in the three-component plasma. The Alfvén solitons can be relevant in explaining the properties of hydromagnetic turbulence near the comets.     

Wave propagation in a magnetic cylinder

The nature of oscillations in a magnetic cylinder embedded in a magnetic environment is investigated. It is shown that the standard slender flux tube analysis of a kink mode in a cylinder excludes the possibility of a second mode, which arises under photospheric conditions. Under coronal conditions, two widely separated classes of oscillation can be freely sustained, one on an acoustic time-scale and the other on an Alfvénic time-scale. The acoustic-type oscillations are always present, but the much shorter period, Alfvénic-type, oscillations arise only in high density (strictly, low Alfvén velocity) loops. An application to waves in fibrils is also given, and suggests (following Wentzel, 1979) that they are fast kink waves propagating in a density enhancement.     

Wave propagation in intense flux tubes

The nature of non-adiabatic wave propagation in a slender magnetic flux tube is explored. The results of the theory are compared with the observations of Giovanelli et al. (1978), and found to be in general agreement. Those observations, of tubes in the photosphere-chromosphere, show outwardly propagating waves, with periods of 300 s, which take some 19 s to propagate from one level of line formation to another level higher in the atmosphere. In sharp contrast to this, is the time of 7 s for a similar disturbance outside the tube to propagate between the same two levels of line formation, estimated to be some 600 km apart in the field-free atmosphere. It is argued that the sharply contrasting propagation times for the tube and its environment is principally due to the elasticity of the tube and its subsequent propensity for propagation. A non-adiabatic disturbance may be essentially propagating within the tube but essentially non-propagating outside, with considerably slower phase speeds thus arising inside the tube. The theory suggests that the observed disturbances are non-adiabatic, acoustic-gravity waves channelled along a magnetic flux tube and modulated by external pressure variations.     

Wave propagation in two-fluids self-gravitating plasma

Wave propagation is considered in self-gravitating collisionless magnetized plasma, when the Larmor frequency exceeds the plasma frequency. The external magnetic field is assumed to be strong and a modified two-fluids theory is used to describe the plasma. We find that there are three modes of wave propagation parallel to the magnetic field. The condition of hose instability is affected. The change in the dispersion relation due to the two-fluids theory is also discussed.