Dynamical and kinematical near homoaxial rotations suitable for representation of nonuniformly rotating stars with extended atmospheres

In this paper, a nontrivial velocity tensor is suitably defined to represent in the common frame the so-called classes of dynamical and kinematical near homoaxial rotations of a deformable finite material continuum. These classes have simple and interesting physical interpretation, especially for treating of nonuniform rotation and its applications to astrophysics. Some important subclasses and derived classes (in the sense of related superclasses) are also discussed.Two coordinate systems are further introduced, one of which rotates uniformly while the other rotates nonuniformly, the latter defined by means of a generalized orthogonal coordinate transformation. Suitable conditions are then given, asserting that the above systems are preferred in the sense of preserving the motion of the continuum in its inertial class.Finally, the required concepts of homotropy and distributivity are defined and the method, by which the established mathematical framework will be subsequently used in applications, is discussed.     

Drift Kelvin-Helmholtz instabilities in space plasmas

We implement a complex-plane strategy and a multiple partition technique to the computation of polytropic models distorted by very strong and very rapid differential rotation. We also verify with our numerical results a heuristic relation between stability and virial theorem.     

On quasi-integrable problems. The example of the artificial satellites perturbed by the Earth's zonal harmonics

With the Hamiltonian parameters developed for the two-fixed-centers problem a simple and very accurate expression of the quasi-integral can be given for the motion of artificial satellites perturbed by the Earth's zonal harmonics. This motion can be considered as integrable.A theoretical analysis shows that Hénon's semi-ergodic regions or chaotic regions are extremely small in this problem, and almost all orbits are of the regular or quasi-periodic type. Furthermore, the relative difference between the true motion and the corresponding integrable motion remains forever less than 10^–14 for all regular orbits even in the vicinity of critical inclinations.For chaotic orbits this very small difference remains verified at least for centuries, nevertheless there are some exceptional orbits that finally diverge from the integrable model.     

Some studies on Hα-flares and microwave bursts in relation to sunspot magnetic configurations

Sunspot associated H-flares and microwave bursts occurring during the period 1972 to 1974 have been examined in relation to the magnetic strength and configurations of the sunspots and sunspot groups (abbreviated as spots). Important results obtained are: (i) percentage occurrences of flares exceeds those of microwave bursts up to a magnetic field strength of 2000 G while the reverse is true for higher field strength of spots, (ii) flare productivity (average number of flares per spot) and also burst productivity are comparatively higher in the case of and types of spots than in the case of other types of spots, (iii) the above productivities are predominantly high when magnetic configuration of spots changes during their life time, and (iv) impulsive type of microwave bursts are more associated with spots having changing type of magnetic configuration.     

A ‘magnetospheric’ scenario of the solar flare in a quadrupole magnetic configuration

An attempt is made to impart a constructive character to the concept of the solar flaremagnetospheric substorm analogy. An idealized scheme for a two-ribbon solar flare in the originally closed magnetosphere of the active region is discussed. The basis is formed by a terrestrial substorm scenario with two active phases (Mishin et al., 1992). While a quadrupole magnetic configuration turns out to be a solar analog of the Earth's magnetosphere. A physical mechanism that sustains the preflare storage phase, is provided by an instability like a stretching instability of the closed geomagnetotail. The storage process is attributed to the emergence into the corona of closed magnetic flux lines in adjacent (to the location of the would-be flare) regions. The flare flash-phase is determined by the change-over of the stretching instability to a disruption instability of a nonstationary (not neutral) current sheet inside the storage zone. The final recovery phase corresponds to the wellknown Pneuman-Kopp model.     

Containment of an adiabatic plasma on magnetic lines of force by a self-generated electrostatic field

One component of a three-fluid adiabatic plasma is under certain conditions contained in a restricted region of space by a large-scale electrostatic field generated within the plasma. The containment is discussed here for plasma consisting of ions and two populations of electrons characterized by different pitch angle distribution functions.The bouncing motion of electrons along open fieldlines between a magnetic mirror and an electrostatic mirror produces a velocity distribution function similar to that generated by bouncing particles on closed fieldlines.     

The velocity field in the atmosphere of δ Cephei

Observations related to the photospheric velocity field of Cephei can be interpreted as follows: during the whole cycle of pulsations the only motion form in the atmosphere is a wave motion with a nearly constant full amplitude of approximately 15 km s^–1, and a wavelength of about 10⁶ km (which are quantities, about equal to the amplitudes of pulsational velocity and radius of the star). There are no significant small-scale turbulent velocity components. The microturbulent and macroturbulent velocities, as derived from spectral line observations, are fully compatible with this picture.     

On the influence of massless scalar and vector electromagnetic fields on the singularity character in anisotropic cosmology

It is shown that, for the scalar-tensor cosmology (STC) by Jordan-Brans-Dicke (JBD), in general anisotropic solution the oscillatory mixmaster regime near the singularity will be destroyed by the scalar source-free field and replaced by monotonousV ₃-collapse into the point or into the line and plane (only in caseG0) even in the presence of the primordial source-free electromagnetic (EM) field.     

The ‘naked’ singularity in the scalar-tensor gravitation theory

The complete analysis of possible types of non-relativistic and ultra-relativistic motions in the field of the naked singularity of the STGT is given. The problem of the infall of a monochromatic radiation emitter on the naked singularity is studied. In spite of the absence of a freezing effect in the STGT, the naked singularity is not observable, for the brightness of the falling emitter decreases much faster than in the GTR. Atrr _g , the trajectory of particles and light are quite similar to that of the GTR, and due to this fact the naked singularity is observationally indistinguishable from a black hole.     

Magnetic reconnection in high-temperature plasma of solar flares

Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets.     

A quantitative bifurcation analysis of Hénon-like 2D maps

We numerically study the bifurcations of two nonlinear maps, with the same linear part, which depend on a parameter namely the Hénon quadratic map and the so called beam-beam map. Many families of periodic orbits which bifurcate from the central family, are studied. Each family undergoes a sequence of period doubling bifurcations in the quadratic map, But the behavior of the beam-beam map is completely different. Inverse bifurcations occur in both maps. But some families of the same type which bifurcate inversely in the quadratic map do not bifurcate inversely in the beam-beam map, even though both maps have common linear part.     

Hydrodynamic models of Planetary Nebulae

This article tries to give a short review of the hydrodynamic modelling of Planetary Nebulae to date. I start by discussing the types of observations the modelling aims to reproduce and then discuss the results of different types of models. First the simplified models in which evolutionary changes in the stellar properties are neglected, then the evolutionary models in which these effects are taken into account. The simplified models can reproduce single shell nebulae with the right kinematic properties. The evolutionary models can reproduce multiple shells and some of the kinematic and morphological differences between various ions. I also briefly discuss some of the difficulties which have not been addressed and/or solved by the numerical modelling, such as the point-symmetric nebulae, some of the collimated phenomena, and clumpiness.Abbreviations AGB Asymptotic Giant Branch - PN Planetary Nebulae - YSO Young Stellar Object     

An apparent ‘even-odd’ cycle distribution in Mt. Wilson ‘numbers of spots’ data

Mt. Wilson numbers of spots data (as defined in Howard et al., 1984) appear to be distributed according to even-odd cycle numbering. Linear fits of annual numbers of spots versus annual sunspot number for even- and odd-numbered cycles have slopes which are statistically different at the 5% level of significance. The existence of an even-odd split in Mt. Wilson numbers of spots data may be due either to a real difference in even- and odd-numbered cycles on the Sun or to a difference in weather at Mt. Wilson (perhaps, related to the 22-yr rhythm of drought in the western United States) during even- and odd-numbered cycles, or both. For cycle 22, an even-numbered cycle, the peak numbers of spots is estimated to be near 2600.     

The development and production of new,non-standard methods of observations with the radio telescope RATAN-600

The recent modernization of the RATAN-600 radio telescope at the Special Astrophysical Observatory has provided an opportunity to develop new procedures, called relay and zoned relay, for utilizing the new cone-surface secondary reflector. The geometric area, the horizontal beamwidth spatial resolution, and the permissible radiometer bandwidth are discussed. We are also able to estimate the changes in the sensitivities of the radio telescope-radiometer systems. The new procedures, called relay and zoned relay, allow us to obtain two-dimensional images of radio objects and to track the development of rapidly varying sources in any azimuth.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.     

The abelian higgs sunspot endowed with a local conformal symmetry

We show that the requirement of alocal conformal symmetry of the Abelian Higgs sunspot leads, at least formally, to a complex-valued electromagnetic potential, whose imaginary part is a conformal compensating potential. It is shown that there exists a fundamental difference between conformal and ordinary electromagnetic fields; whereas the ordinary total magnetic flux of a spot is quantized its conformal analogue has to vanish if the Higgs field is to be single-valued. We further stress that such a complex-valued Abelian Higgs field configuration mimics quite well, under certain conditions (all the salient features of) the classical Abelian Higgs sunspot.     

Galaxy-formation in pancake-models

Three concepts, statistically fair samples, high spatial resolution of pancakes and dynamical thresholding of density are used to define a procedure of extracting the large-scale distribution of luminous matter from pancake-models.Paper presented at the 11 th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Is water-ice the carrier of the 3μm-absorption in infrared objects?

It is shown that Mie theory predictions of extinction for pure water-ice with the optical constant measured at 100 K do not fit in detail the observed ice absorption feature in infrared objects, although we attempt to explain the observations by considering size distribution and shape of the grains.In addition, based on a similarity between the ice band and the absorption band found in carbon stars, we feel it is questionable whether or not the ice band can really be attributed to the interstellar water-ice.     

The binning analysis: Towards a better significance test

We demonstrate that the problems encountered with the binning analysis essentially lie in the significance test which is used. We review and analyse most of the existing significance tests and show that the use of those based on randomization processes considerably improves the situation. For the one-dimensional binning analysis, we apply the 2 within 4 randomization test, whereas for the two- and the three-dimensional binning analyses we introduce two innovations: the 4 within 16 randomization test and the 8 within 64 randomization test, respectively.     

Predictions of exceptionally strong ‘4430’ in the backscattered light from reflection nebulae

The strength of the 4430 interstellar spectrum feature in the backscattered light from certain reflection nebulae is shown to be a sensitive indicator of the feature's origin.Backscattering 4430 profiles have been computed for several, models of silicate, graphite, dirtyice-coated graphite, and silicon carbide grains with impurities. The effect on these profiles of both non-sphericity of the grains and finite optical thickness of the reflection nebula have been considered. For silicate grains, the 4430 central depth is predicted to be up to ten times its value in the corresponding extinction profile, whereas for graphite only a rather weak feature is expected. Some comments are made concerning the future comparison of observations with these theretical results.     

An iterative technique for computing rotating visco-polytropic models

In this paper we develop and implement a complex-plane iterative technique for computing rotating visco-polytropic models. The viscosity of the models is determined in view of the relaxation condition that differential rotation depends only on the distance from the rotation axis. To this purpose we develop and implement a viscosity-evaluated-upwards technique which fits viscosity, within a few percent, with the required condition. We compute various models, and we study in detail some of them that satisfy, within a few percent, the condition above, and also the boundary condition of a vanishing surface stress vector.