Application of a global polytropic model to the Jupiter's system of satellites: a numerical treatment

We study the so-called inverse planetary problem (i.e., given the distances from the centre, masses, and radii of, say, three planets of a planetary system, find the optimum polytropic index, mass, and radius of their star, and also other quantities of interest, which depend either explicitly or implicitly on the foregoing ones, e.g., central and mean density, central and mean pressure, central and mean temperature, etc.) for the system of satellites of Jupiter. In particular, Jupiter is considered as star and its satellites as planets of a proper planetary system, which is then treated numerically on the basis of the so-called global polytropic model, developed recently by the first author.     

Connection between X-ray and optical variability in NGC 4151

We have used long light curves in the X-ray (ARIEL V, EXOSAT, Ginga and others), UV (IUE), and optical (data of intensive ground-based monitoring) ranges of NGC 4151 to investigate connections between variations in these spectral fields. Applying Fourier (CLEAN algorithm) and modern cross-correlation analysis, we revealed the different character of the variability and the cross-correlation between high and low states of the nucleus. In contrast to earlier results, we found that X-ray and optical fluxes correlate in the active state without any apparent delay.In the power spectrum of the optical and X-ray light curves in the high state we found the existence of the same period of about 65 days, which disappeared in the low state.We confirmed previous data that X-ray variations correlate more strongly with UV and optical continuum variability during the low state, but it is possible that the optical variations appear to lag behind those involving X-rays by several tens of days.Strong variations in H line profile and [Fe X]6374 line intensity variations correlate with the observed X-ray covering dip in 1990 (Yaqoobet al., 1993).We discuss briefly the implications of these results.     

Evolution, punctuational crises and the threat to civilization

The relationship between punctuated equilibrium and impact crises is critically examined in the light of our present knowledge of asteroids and comets. It turns out that the emphasis on relatively narrow epochs associated with occasional NEO impacts is probably misplaced. Rather priority should be given to the wider and more frequent epochs associated with multiple NEO debris impacts which result in so-called punctuational crises afflicting the planets. These comprise the global coolings, super-Tunguska events and generally enhanced fireball flux produced by the larger orbital debris whenever an active, dormant or dead comet fragments and produces a trail. Taken as a whole and in conjunction with the target, the response function is inevitably complex. Nevertheless we broadly expect that the strength of a punctuational crisis will vary as the progenitor comet mass, the inverse dispersion of its debris and the inverse delay since fragmentation. The encounter of P/SL-9 with Jupiter may be taken as representing an extreme punctuational crisis where the dispersion and delay were exceptionally small. The more familiar crises affecting the Earth with less extreme values of dispersion and delay, which have resulted in civilization being disturbed a good many times during recent millennia, are no less important however. Indeed, the next such threat to civilization ostensibly has a roughly 1 in 4 lifetime chance. Any support for the Spaceguard programme which detracts from consideration of these punctuational crises, whatever their strength, would seem now to be peculiarly wide of the mark.     

On the instability of “folded” equilibria of a flexible nonstretchable thread attached to the satellite in a circular orbit

The author considers a problem of Lyapunov's stability of relative equilibria of a flexible nonstretchable thread attached to the satellite moving in a circular Keplerian orbit in the first approximation. When it is in the position of relative equilibrium, the thread is known to be situated either along the radius vector of the orbit (the radial equilibrium) or along the circular orbit (the tangential equilibrium) and in each case the thread can be in a folded state. The author shows that folded radial equilibria of the thread are always unstable while tangential ones are unstable if the thread is sufficiently short in comparison with the radius of the orbit. The generalized Chetaev functional has been constructed to prove the instability.     

Comparative Analysis of “Exact” and “Approximate” Methods for Estimating the Absolute and Relative Elements of Detached Close Binary Systems

In this paper the star characteristics (luminosities, spectra, masses, absolute and relative radii of the components, mass ratio, major semiaxis, and orbital inclination) of close binary systems (CBS) with detached components are compared element-by-element. Svechnikov and Perevozkina's Catalog of the orbital elements, masses, and luminosities of pre-main sequence-type eclipsing variable stars with known photometric and spectroscopic elements and Svechnikov and Kuznetsova's Catalog of approximate photometric and absolute elements of eclipsing variable stars are used as initial data. The orbital elements contained in the first catalog are determined from solutions of the known photometric light curves and the known radial velocity curves, while the orbital elements for the second catalog were estimated using data from the General Catalog of Variable Stars (GCVS) IV employing approximate statistical relationships such as mass-radius, mass-luminosity, and mass-spectrum, along with the dependence of the orbital inclination on the depth of the principal minimum and others. Possible reasons for discrepancies among the compared quantities are discussed.     

Stability of a Riemann S Ellipsoid with a Spheroidal Halo

The stability of Riemann S ellipsoids inside an oblate halo with respect to the second form of oscillations is investigated. It is shown that some ellipsoids with reverse internal circulation of matter, which are stable inside a spherical halo or in its absence, become unstable with respect to second odd forms of oscillation inside an oblate halo. Here there is asymmetry between conjugate ellipsoids from the standpoint of their stability. Only those conjugate ellipsoids that correspond to higher frequencies of reverse circulation of matter than their corresponding angular rotation rates are unstable. The domains of instability of light and heavy conjugate embedded ellipsoids are obtained as a function of the oblateness measure and relative density of the halo.     

Solar EUV flux variations near activity maxima

Data on solar emission variations in the extreme ultraviolet range <1300 (EUV-range) performed on board the Prognoz satellites and the Phobos spacecraft by the thermoluminescent method are presented. Flux variations from the 11-years cycle are factors of 2–2.5, and that by the 27-days cycle do not exceed 30%.     

Spectroscopic Observations of New Galaxies with a UV Excess. III

The results of the spectroscopic observation of 23 galaxies with a UV excess from Kazarian's lists are presented. The spectra were obtained on the 2.6-m telescope of Byurakan Observatory with a Byu FOSC-2 camera. Two grisms, red and green, were used in the observations. Emission lines are observed in the spectra of 21 of the galaxies.     

The photogravitational restricted three-body problem

The photogravitational restricted three-body problem is reviewed and the case of the out-of-plane equilibrium points is analysed. It is found that, when the motion of an infinitesimal body is determined only by the gravitational forces and effects of the radiation pressure, there are no out-of-plane stable equilibrium points.     

The effect of toroidal magnetic field and differential rotation on self-gravitating polytropic models,II

In this paper we compute differentially rotating polytropic models distorted by toroidal magnetic field. In particular, we study rotating sequences, which do not terminate with a critical rotation. In the computations we use the so-called complex-plane strategy and multiple partition technique, which are numerical methods developed recently by the first author.