判断双星自转同步性的一种新方法

本文提出了判断双星自转同步性的一种新方法．把假定双星为同步自转时的拱线进动周期的理论计算值与该双星的观测值之比作为同步自转参量,以判断双星同步自转情况．利用此方法对ＹＣｙｇ和ＣＷＣｅｐ两对双星系统中子星同步自转情况做了判断．结果表明,其中ＣＷＣｅｐ为同步自转双星,ＹＣｙｇ为接近同步自转双星．最后将所得结果与其他作者用直接测量自转速度方法所得的结果进行比较,结果符合得很好     

Chaotic behaviour of solar radio flux

The presence of a chaotic attractor is investigated in time series of 10.7 cm solar flux. The correlation dimension and the Kolomogorov entropy have been calculated for the time period 1964–1984. The values found for the Kolmogorov entropy show that chaos is indeed present. The correlation dimension found for high solar activity is 3.3 and for low solar activity is 4.5, indicating that a low-dimensionsion chaotic attractor is present in the time series analysed.     

Critical properties of spherically symmetric accretion in a fractal medium

Spherically symmetric transonic accretion of a fractal medium has been studied in both the stationary and the dynamic regimes. The stationary transonic solution is greatly sensitive to infinitesimal deviations in the outer boundary condition, but the flow becomes transonic and stable when its evolution is followed through time. The evolution towards transonicity is more pronounced for a fractal medium than it is for a continuum, and in the former case the static sonic condition is met on relatively larger length scales. The dynamic approach also shows that there is a remarkable closeness between an equation  of motion for a perturbation in the flow, and the metric of an analogue acoustic black hole. The stationary inflow solutions of a fractal medium are as much stable under the influence of linearized perturbations as they are for the fluid continuum.     

Finite Larmor radius effects on the Rayleigh-Taylor instability of a rotating plasma of variable density

The Rayleigh-Taylor instability in a rotating plasma of variable density has been investigated to include simultaneously the effects of viscosity and the finiteness of the ion Larmor radius. It is shown that, for a plasma in which the density is stratified along the vertical, the solution is characterized by a variational principle. Making use of this, proper solutions have been otained for a semiinfinite plasma in which the density varies exponentially. The dispersion relation has been solved numerically and it is found that the influence of the effects of both FLR and viscosity is stabilizing. The Coriolis forces are found to have a dual role, stabilizing for small wave numbers and destabilizing for large wave numbers. The range of the small wave numbers, over which the Coriolis forces have a stabilizing influence, is found to increase with Coriolis forces.     

Magnetohydrodynamic equilibrium and stability of pre-flare loops

The equilibrium and stability of a loop in which energy storage occurs prior to a solar flare is discussed. Working on the hypothesis, that the onset of the flare begins only after sufficient magnetic energy has been stored in the loop typical values of parameters which describe the equilibrium are found for a magnetic field with a constant twist. The stability of this configuration is examined next and it is shown that for the force-free case, the structure is always unstable to kinking for any degree of twist. However, a slight deviation from the force-free configuration, through the presence of a small positive transverse pressure gradient, can stabilize the loops for moderate degrees of twist. The range of wave-numbers for which instability occurs and the maximum growth rates are also presented. Lastly, it is shown that the pressure gradients required to stabilize a pre-flare loop do not lead to conflict with observations.     

A Stochastic Prediction Model for the Sunspot Cycles

A stochastic prediction model for the sunspot cycle is proposed. The prediction model is based on a modified binary mixture of Laplace distribution functions and a moving-average model over the estimated model parameters. A six-parameter modified binary mixture of Laplace distribution functions is used for the modeling of the shape of a generic sunspot cycle. The model parameters are estimated for 23 sunspot cycles independently, and the primary prediction-model parameters are derived from these estimated model parameters using a moving-average stochastic model. A correction factor (hump factor) is introduced to make an initial prediction. The hump factor is computed for a given sunspot cycle as the ratio of the model estimated after the completion of a sunspot cycle (post-facto model) and the prediction of the moving-average model. The hump factors can be applied one at a time over the moving-average prediction model to get a final prediction of a sunspot cycle. The present model is used to predict the characteristics of Sunspot Cycle 24. The methodology is validated using the previous Sunspot Cycles 21, 22, and 23, which shows the adequacy and the applicability of the prediction model. The statistics of the variations of sunspot numbers at high solar activity are used to provide the lower and upper bound for the predictions using the present model.     

Ground-based optical CCD experiments for GRB and optical transient detection

We present details of one operational ground-based experiment for optical detection of GRBs and two which are under consideration/development. The wide-field CCD camera is already in manual burst alert operation with promising results. The Optical Transient Monitor is a CCD-based double monitor suitable for network use for reliable detection of short-lived phenomena in the sky. The system is well suited for correlated efforts with GRB projects. The third experiment is a robotic telescope with automatic response to GRB burst alert messages received via the Internet link. It is expected to get CCD frames with a FOV of 20 deg (needed for BACODINE triggers) of positions of newly detected GRBs within 1 minute.     

Effective potential energy for relativistic particles in the field of inclined rotating magnetized sphere

The dynamics of a charged relativistic particle in electromagnetic field of a rotating magnetized celestial body with the magnetic axis inclined to the axis of rotation is studied. The covariant Lagrangian function in the rotating reference frame is found. Effective potential energy is defined on the base of the first integral of motion. The structure of the equipotential surfaces for a relativistic charged particle is studied and depicted for different values of the dipole moment. It is shown that there are trapping regions for the particles of definite energies.     

“Spektr-UF” project

The “Spektr-UF” project is intended for the design and development of a large space observatory operating in the ultraviolet (UV) band of the spectrum inaccessible for survey from the surface of the Earth. The main observatory instrument is a space telescope T-170M with a primary mirror 1.7 m in diameter; it will be equipped with high and low resolution spectrographs and cameras for high-quality UV imaging. In respect of capabilities, the project is similar to the American Hubble Space Telescope (HST), and exceeds the latter in some parameters. The project is included in the Russian Federal Space Program for the period 2006–2015. The launch is planned for 2016. The project is under development by the Lavochkin Association in cooperation with the Institute of Astronomy, Russian Academy of Sciences.     

The center of lateral iso-density contours for inclined cosmic air showers

The horizontal lateral density of a cosmic air shower with a non-zero zenith angle is asymmetric. The asymmetry consist of a stretching of the iso-density contours to ellipses and to a shift of the center of the elliptic contours with respect to the core of the shower. The shift is caused by atmospheric attenuation. The modeling of the attenuation results in an equation for the shift as a function of zenith angle and the size of the iso-density contours. A more accurate equation is obtained by investigating the shift in lateral densities of simulated showers. It is shown how the shift can be incorporated in an elliptic lateral density function. A linear approximation for the shift allows for an analytical solution for the shifted elliptic density. Its predictions for the polar variations of the density are compared with data of simulated showers.     

The relation between extended radio and line emission for radio-loud quasars

We explore the relationship between the extended radio and line emission for a radio-loud quasar sample including both core-dominated and lobe-dominated quasars. A strong correlation is present between the extended radio and broad-line emission. The core emission is also correlated with the broad-line emission for core-dominated quasars in the sample. The statistical behaviour of the core emission of lobe-dominated quasars is rather different from that of core-dominated quasars. The extended radio luminosity is a good tracer for jet power, while the core luminosity can only be a jet power tracer for core-dominated quasars.     

Magnetodynamic stability of a fluid cylinder under the lundquist force-free magnetic field

The magnetodynamic (in)stability of a conducting fluid cylinder subject to the capillarity and electromagnetic forces has been developed. The cylinder is pervaded by a uniform magnetic field but embedded in the Lundquist force-free varying field that allows for flowing a current surrounding the fluid. A general eigenvalue relation is derived based on a study of the equilibrium and perturbed states. The stability criterion is discussed analytically in general terms. The surface tension is destabilizing for small axisymmetric mode and stable for all others. The principle of the exchange of stability is allowed for the present problem due to the non-uniform behaviour of the force-free field. Each of the axial and transverse force-free fields separately exerts a stabilizing influence in the most dangerous mode but the combined contribution of them is strongly destabilizing. Whether the model is acted upon the electromagnetic force (with the Lundquist field) the stability restrictions or/and the capillarity force are identified.Several reported works can be recovered as limiting cases with appropriate simplifications.     

Acceleration of particles by electron plasma waves in a moderate magnetic field

A general scheme is established to examine any magnetohydrodynamic (MHD) configuration for its acceleration potential including the effects of various types of plasma waves. The analysis is restricted to plasma waves in a magnetic field with electron cyclotron frequency less than, but comparable to, the electron plasma frequency (moderate field). The general role of electron plasma waves is examined in this paper independent of a specific MHD configuration or generating mechanism in the weak turbulence limit. The evolution of arbitrary wave spectra in a non-relativistic plasma is examined, and it is shown that the nonlinear, process of induced scattering on the polarization clouds of ions leads to the collapse of the waves to an almost one-dimensional spectrum directed along the magnetic field. The subsequent acceleration of non-relativistic and relativistic particles is considered. It is shown for non-relativistic particles that when the wave distribution has a negative slope the acceleration is retarded for lower velocities and enhanced for higher velocities compared to acceleration by an isotropic distribution of electron plasma waves in a magnetic field. This change in behavior is expected to affect the development of wave spectra and the subsequent acceleration spectrum.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Statistical tests for changes in the amplitude, frequency or phase of a sinusoidal variation

The problem considered is that of testing for small changes over time in the properties of a sinusoidal signal contaminated by noise. Two test statistics are proposed. The first is a frequency domain statistic based on the spectrum of the data, while the second is a time domain statistic due to Nyblom. Power studies are used to show that the Nyblom statistic is generally the better. The form of the Nyblom statistic appropriate for phase-change tests also performs well in testing for frequency changes.     

Long nonlinear waves in a compressible magnetically structured atmosphere

The Benjamin-Ono equation is derived for long slow sausage waves propagating in a vertical magnetic slab embedded into a stratified atmosphere, provided that the slab thickness is much smaller than the scale height of the atmosphere. The soliton propagation in a nonstratified atmosphere is discussed. The approximate formulas describing the slow evolution of the amplitude and the length of a soliton propagating in a very weakly stratified atmosphere are obtained. The exact soliton-like solution for an atmosphere with a linearly growing temperature is found.     

Planetary magnetism

The origin and maintenance of planetary magnetic fields are discussed. The discussion is not limited to dynamo theories although these are almost universally favored. Thermoelectric currents are found to be a possible alternative for Jupiter. Two energy sources for dynamos are considered: convection and precessionally induced fluid flow. The earth is the most favorabl planet for a precessionally driven dynamo, although Neptune is a possibility. Jupiter is likely to have a convectionally driven dynamo, as may Saturn, but the relevant properties of Saturn are not yet well known. Conclusions for each planet are given.     

Suppression of the kink instability for magnetic flux ropes in the chromosphere

Energy storage in chromospheric flux ropes is discussed, in the context of solar flares. The structure is represented by a cylindrically symmetric magnetic field of finite length. The field is assumed to be approximately force-free. The stability of the field to a kink perturbation is investigated. Flux ropes are rooted in dense photospheric material. So the ends of the field lines are taken to be fixed on rigid boundaries for all perturbations. An energy perturbation method is used and the boundary conditions give a stabilizing effect. It is shown that for a moderate degree of twisting the fields are stable to a kink perturbation. Thus energy can be stored in cylindrical fields prior to release in a solar flare.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Free convection effects on the hydromagnetic oscillatory flow in the stokes problem past an infinite porous vertical limiting surface with constant suction-I

In this work an analysis of Stokes' problem for a two-dimensional unsteady hydromagnetic free convection flow, of an incompressible viscous electrically conducting fluid, past an infinite vertical porous limiting surface is presented, when the free stream velocity oscillates in time about a constant mean value. The flow is subjected to a constant suction, through the porous wall, and the difference between the wall temperature and the free stream is moderately large causing the free convection currents. The mathematical analysis is presented for the hydromagnetic boundary layer flow without taking into account the induced magnetic field. This is a valid assumption for small magnetic Reynolds number. Analytical expressions for the velocity field, the temperature field and for their related quantities are obtained. The influence of the various parameters entering into the problem is extensively discussed. A comparative study with hydrodynamic case is also made wherever necessary.     

A study of the fragmentation of molecular clouds and the form of initial mass-function for low-mass protostellar fragments

Opacity limited fragmentation is considered for a spherically-collapsing isothermal molecular cloud in a low temperature range where molecular hydrogen and grains are the only cooling and opacity sources. The minimum Jeans mass of a fragment is calculated for different values of the parameters. The form of the initial mass function (IMF) is derived for low-mass protostellar fragments for different values of the parameters. They are discussed and compared with observations. A rough estimate of the cloud mass contained in the brown-dwarf regime is given.     

Solutions of the Fokker-Planck equation for the early time when the diffusive modes are not yet valid

The transport of energetic charged particles in fluctuating magnetic fields is analysed by means of the Fokker-Planck equation for the early time, when the diffusive modes are not yet valid. Exact solutions are found for the particle fluxes integrated over space; after these have reached a time-independent final steady state, the usually considered diffusive modes of the velocity-integrated density become valid. The time for that is finite. The analysis is done both for a constant and a divergent mean magnetic field.