Showing papers in "Astrophysics and Space Science in 1987"

The linear stability of libration points of the photogravitational restricted three-body problem when the smaller primary is an oblate spheroid

Abstract: This paper deals with the stationary solutions of the planar restricted three-body problem when the more massive primary is a source of radiation and the smaller primary is an oblate spheroid with its equatorial plane coincident with the plane of motion. The collinear equilibria have conditional retrograde elliptical periodic orbits around them in the linear sense, while the triangular points have long- or short-periodic retrograde elliptical orbits for the mass parameter 0 ≤ μ < μcrit, the critical mass parameter, which decreases with the increase in oblateness and radiation force. Through special choice of initial conditions, retrograde elliptical periodic orbits exist for the case μ = μcrit, whose eccentricity increases with oblateness and decreases with radiation force for non-zero oblateness.

Self-creation cosmological solutions

Abstract: The field equations for Barber's two self-creation theories of gravitation are solved for Friedmann-Robertson-Walker space times, using perfect fluid energy-momentum tensors. Barber's first theory is discussed for the radiation dominated case, whereas cosmologies according to Barber's second sefl-creation theory are constructed for vacuum-dominated, radiation-dominated, and dust-filled cases.

A role of cosmic rays in generation of radio and optical radiation by plasma mechanisms

Abstract: The radiation of ultrarelativistic particles is examined in a quasi-uniform magnetic field superimposed by a wide spectrum of magnetic, electric, and electron density inhomogeneities created in a turbulent plasma. The radiation spectrum from a particle of a given energy is shown to acquire a high-frequency power-law tail with the same spectral index as the index ν of small-scale turbulence. For a power-law spectrum of ultrarelativistic electrons, dN(ℰ)/dℰ ~ ℰ−ξ, with a cut-off at some energy ℰmax, the radiation spectrum consists of a few power-law ranges; the radiation intensity may suffer jumps at frequencies which separate these ranges. In the high-frequency range the spectral index ν is determined by small-scale magnetic and electric fields. At intermediate frequencies the main contribution comes from the synchrotron radiation in a large-scale field; the radiation spectrum has an index α=(ζ−1)/2. The same index may be produced by large-scale Langmuir waves. At lower frequencies the radiation spectrum increases owing to the transition radiation caused by electron density fluctuations; in this case the spectral index is equal to ζ+1−ν. The possibility of diagnostics of high-frequency cosmic plasma turbulence from radiation of high-energy particles is discussed. It is shown that the proposed theory may explain some features in the spectra of several cosmic objects.

Effect of shocks on interstellar turbulence and cosmic-ray dynamics

Abstract: A theoretical model for the interstellar turbulence is developed. In this model the fluctuation spectrum is formed due to reflection of shocks, produced by supernovae, on interstellar clouds. The spectra of turbulence and the diffusion coefficient of cosmic rays are derived. It is demonstrated that local enhancements of the ionization rate by cosmic rays accelerated by supernova shocks may be responsible for fast renewal of warm ionized envelopes around cores of standard ISM clouds.

Local interstellar medium

Abstract: This paper reviews and analyses various observational data about the local interstellar medium (LISM)-a volume with a radius of about 200 pc near the Sun. There are collected radio, IR, optical, UV, and X-ray observations of the ISM and data on the Sco-Cen association. All available information confirms Weaver's (1979) conclusions that the Sun is located near an edge of a giant cavern with a radius of about 180 pc and the cavern center coincides with the Sco-Cen associated center. The outer rim of the cavern is observed as numerous, very longHi flaments, filaments of the interstellar polarization, and soft X-rays radiated by coronal gas with a temperature of about 106K. Close environment (from 10−4 to 2–5 pc) of the Sun is filled by warm (about 104 K)Hi with the number density 0.1–0.2 cm−3, which is a corona of the local cloud of the ISM. The central part of the cloud is observed to the galactical center direction at a distance of 10–20 pc as Sancini and van Woerden's (1970)Hi filament. The cloud blown round by stellar winds has a horseshoe-like shape, bordering the Sun. Tinbergen's (1982) ‘patch of polarization’ is observational evidence of the shape.

Are lynds dark clouds fractals

Abstract: We have used the catalogue of dark nebulae compiled by Lynds (1962) to investigate the geometrical nature of the darkest, opacity class 5 to 6, clouds. There would appear to be some evidence that these objects are fractals of dimensionD=1.4.

Birkhoff-type theorem in the scale-covariant theory of gravitation

Abstract: It is shown that an analog of Birkhoff's theorem of general relativity exists in the scale-covariant theory of gravitation when the gauge function which occurs in the theory is independent of time.

Transformation of geocentric to geodetic coordinates without approximations

Abstract: An exact and relatively simple analytical transform of the rectangular coordinates to the geodetic coordinates is presented. It does not involve any approximation and the accuracy of practical calculations depends exclusively on the round-off errors. The algorithm is based on one solution to the quartic equation in tg(45°-ψ/2), where ψ is the parametric (or eccentric) latitude.

The ecology of rotators

Abstract: A generalized physical object, a gravimagnetic rotator (or simply, rotator), is considered. It is specified by the three characteristics: a mass, a magnetic field, and an angular momentum. A rotator interacts with its environment (plasma) via two kinds of the physical fields, the electromagnetic and the gravitational ones. This rotator is a useful theoretical consideration for quite different astrophysical objects: neutron stars, white dwarfs, magnetic stars, super-mass stars (spinars), etc. The ecology of rotators involves the classification of rotators concerning their interaction with the environment, determination of the evolutionary laws and their energetic interpretation, the analysis of stochastic fluctuations, and statistical description of evolution of rotator ensemble. These problems resemble those considered in synergetics. Possible implications for some particular astronomical objects are briefly described: X-ray and radiopulsars, single white dwarfs, X-ray bursters, cataclysmic variables, magnetic stars, active galactic nuclei, and quasars. A number of self-similar solutions are derived.

Techniques for the analysis of data from coded-mask X-ray telescopes

Abstract: Several techniques useful in the analysis of data from coded-mask telescopes are presented. Methods of handling changes in the instrument pointing direction are reviewed and ways of using FFT techniques to do the deconvolution considered. Emphasis is on techniques for optimally-coded systems, but it is shown that the range of systems included in this class can be extended through the new concept of ‘partial cycle averaging’.

Star complexes and associations in the Andromeda galaxy

Abstract: Large-scaleU andB plates obtained with the 2 m Ritchey-Chretien telescope of the Rozhen Observatory (Bulgaria) were searched for new resolved star groups and for independent delineation of the boundaries of the known ones in M31. We detected 210 groups as real O-associations the mean diameter of which is 80 pc. Many of Hodge's open clusters are also reclassified as O-associations. The majority of van den Bergh's OB-associations were recognized as star complexes and their mean diameter is 650 pc. Almost all O-associations are located inside the star complexes. A dozen of new star complexes (mainly around the dark lanes between OB78 and OB22) and numerous groups presumably not containing O-stars were found out. The nature of these groups has to be object of further investigations. Young star groups closer than 3 kpc to the center of M31 were not identified.

Very early cosmology in the maximal acceleration hypothesis

Abstract: It is stressed that the very early Universe provides an example of a physical system in which the phenomenological consequences of a natural limit for the accelerations cannot be neglected. It is shown that the existence of such limit leads necessarily to modify the standard model in a way which avoids the initial singularity and introduces an inflationary expansion of the power-law type. The possibility is also suggested to relate the maximal acceleration hypothesis to a decaying vacuum scenario, in which the cosmological constant is proportional to the radiation density, and is then a decreasing function of the cosmic time.

A unified presentation of the Voigt functions

Abstract: This paper aims at presenting a unified study of the Voigt functionsK(x,y) andL(x,y) which play a rather important role in several diverse fields of physics such as astrophysical spectroscopy and the theory of neutron reactions. Explicit expressions for these functions are given in terms of relatively more familiar special functions of one and two variables; indeed, each of these representations will naturally lead to various other needed properties of the Voigt functions.

A Survey of Nova Remnants

Abstract: Exnovae and nova shells are generally faint and difficult to observe. Only a few have been studied, and even less of them in sufficient detail. We give a progress report on our survey of exnovae and nova shells, especially on the results of a spectral survey of novae in the southern Milky Way. The three-dimensional structure in the light of Hα derived for the nebula of GK Per is displayed.

Time variation of the flare index during the 21st solar cycle

Abstract: In this study, the flare index during the solar activity cycle 21, is calculated for every day from 1 January, 1976 to 31 March, 1986. We determined that the chromospheric activity for the whole disc was significantly higher during the 21 st solar cycle, as compared to the preceding cycle. We also found out that the activity began and reached its maximum earlier on the northern hemisphere. Finally, we determined that the time variation of the flare indices for the eastern and western hemispheres are in good agreement.

One hundred and fifty-three diatomic molecules, molecular ions, and radicals of astrophysical interest

Abstract: A critical analysis of the 583 available references in literature has been made to select 153 diatomic molecules, molecular ions, and radicals of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the dissociation energy, spectral region, transition levels, astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, Galaxy, etc.); computed theoretical parameters (i.e., FCFs, transition probabilities, r-centroids, PE curves), and available laboratory data with respective references. In many problems involving the estimation of the physical condition (viz., temperature, pressure, density, and abundance) of the emitter, in various cosmic sources, it is desirous to have a knowledge of the theoretical parameters as well as the experimental details for the molecular spectra of interest. A few important areas of active research in laboratory astrophysics have also been identified in this article: laboratory astrophysics, molecular cloud chemistry, isotopic abundance, planetary and cometary atmospheres through satellites. Besides, some interesting plots of the dissociation energy vs molecular weight, dissociation energy vs total atomic number, dissociation energy vs atomic number differences, ionization potential vs total atomic number, ionization potential vs atomic number differences, and ionization potential vs molecular weight for respective molecules have also been enumerated. Thirty-one new diatomic molecules/molecular ions/radicals of astrophysical significance have also been listed.

Birkhoff-type theorem for electromagnetic fields in self-creation cosmology

Abstract: A result having formal similarity to Birkhoff's theorem in general relativity has been proved in the presence of electromagnetic fields in a self-creation theory of gravitation proposed by Barber, when the scalar field is independent of time.

Vacuum Friedmann Model in Self-Creation Cosmology

Abstract: The field equations of the self-creation theory of gravitation proposed by Barber are solved for a vacuum with the aid of a space-time metric of Friedmann. Some physical properties of the solution are discussed.

An exact similarity solution in radiation magneto-gas-dynamics for the flows behind a spherical shock wave

Abstract: An exact similarity solution for a spherical magnetogasdynamic shock is obtained in the case when radiation energy, radiation pressure and radiative heat flux are important. The total energy of the shock wave increase with time. We have shown that due to the magnetic field the flow variables are considerably changed. Also, due to increases in radiation pressure number the radiation flux is increased.

The Pomeau-Manneville Intermittent Transition to Chaos in Hydrodynamic Pulsation Models

Abstract: Hydrodynamic simulations of nonlinear pulsation for less-massive cool supergiants have been performed by several authors. Outburst of large amplitude oscillations at times is one of common features of these models. To find out routes of the transition from the limit cycles to the irregular pulsations. We performed hydrodynamic simulation for a series of models of luminosity log(L/L ⊙)=3.505, andT e =5300 K with the range of the mass 1.4M ⊙≤M≤1.5M ⊙. With decreasing the mass, we confirm a transition from limit cycles to irregular oscillations. The nature of the transition is finally specified by examining the dissipation of pulsational kinetic energies in limit cycle models, when pulsations start with larger amplitudes than their limiting pulsations. We find that the rates of dissipation are so small that they might be marginally stable. Furthermore, the oscillation starting with even larger amplitudes gets the kinetic energies until it reaches a limit where the oscillation induces strong shock waves and dissipates its kinetic energy. Thus, we conclude that the model which has the stable limit cycle near the transition has another unstable fixed point above the limit cycle. The transition, therefore, is induced by disappearance of these two fixed points, as the mass, the control parameter in our case, is varied, and is found exactly in aggreement with the intermittency proposed by Pomeau and Manneville as a route to chaos in dissipative systems.

Low-frequency plasma turbulence during solar wind-comet interaction

Abstract: The pick up cometary ion distributions are shown to excite Alfvenic mode instabilities, slow ion-acoustic mode instability and a lower hybrid instability during solar wind-comet interaction. The growth rates of all these instabilities become larger as the comet is approached. The lower hybrid instability is shown to account for the low-frequency 0–300 Hz electrostatic turbulence observed near comet Halley. The Alfven modes can grow to large amplitudes and become modulationally unstable, in the presence of low-frequency density fluctuations, going over to envelope Alfven solitons. A model consisting of a gas of Alfven solitons is suggested to explain the hydromagnetic turbulence observed near comet Halley and comet Giacobini-Zinner.

Elemental Abundances for Stellar S-Process Studies

Abstract: Nuclear reaction network calculations of heavy element enhancements are tabulated for different values of the mean neutron exposure τ0. These tables are useful for comparison with observeds-process abundance patterns which appear to span a wide range in τ0.

The gas scintillation proportional counter in the spacelab environment: in-flight performance and post-flight calibration

Abstract: We describe the in-orbit performance of the gas scintillation proportional counter which formed part of the Spacelab-1 payload. Discontinuities in the instrument gain are observed (similar to those of the xenon-filled GSPC's on the EXOSAT and TENMA satellites). A post-flight recalibration of the instrument was performed using synchrotron radiation, which found the discontinuities to be coincident with the xenonL edges.

Giant infrared bubble in Cepheus

Abstract: A ring-shaped infrared emission region is recognizable on the IRAS Sky Flux images of a Cepheus region which happens to include the association Cepheus OB 2. The ring is easily visible both at 60 and 100 microns. The approximate galactic coordinates of its centre arel=102°.8 andb=+6°.7, with an outer diameter of 7 deg. IC 1396 and several otherHii regions, such as S 129, S 133, S 134, and S 140 are apparently parts of the ring. If it is assumed that these Hii regions are physically connected to the ring its distance must be about 900 pc and its diameter 120 pc. The existence of several arc-shaped Hα filaments along the ring, the proper motion of the nearby runaway star λ Cephei, and the possible presence of the [Fex] λ6375 interstellar line in the spectra of two stars of Cep OB 2 combine to suggest that the infrared ring might well be a result of a supernova explosion which occurred in this region about 2–3 million years ago.

White dwarf models of supernovae and cataclysmic variables

Abstract: If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae and observations. We describe various types of evolution of accreting white dwarfs as a function of binary parameters (i.e, composition, mass, and age of the white dwarf, its companion star, and mass accretion rate), and discuss the conditions for the precursors of exploding or collapsing white dwarfs, and their relevance to cataclysmic variables. Particular attention is given to helium star cataclysmics which might be the precursors of some Type I supernovae or ultrashort period X-ray binaries. Finally we present new evolutionary calculations using the updated nuclear reaction rates for the formation of O+Ne+Mg white dwarfs, and discuss the composition structure and their relevance to the model for neon novae.

Quasi-normal modes of a black hole

Abstract: The quasi-normal modes of a black hole are calculated requiring that the ingoing amplitudes vanish at infinity. The amplitude is obtained by making the solutions valid close to and far away from the horizon. The normal-modes are obtained in the form of polynomial solutions.

The Interaction of Nova Shells with the Interstellar Medium

Abstract: Decelerations of the shells around the novae V603 Aql, V476 Cyg, DQ Her and GK Per were determined from photographs and recent CCD observations. The deceleration is larger for higher expansion velocities, the mean half-lifetime, after which the expansion velocity has dropped to half its initial value, is 75 years.

Physical Constants and Evolution of the Universe

Abstract: A cosmological model is discussed which is based on interpretation of the red shift by decrease of the light speed with time everywhere in the Universe beginning with a certain moment of time in the past. The model is described by a metric in which the light speed depends on time and the radius of the curvature of three-dimensional space remains constant (c-metric). It is shown that this metric leads to the same observed facts and formulas of different characteristics that the metric of standard cosmology does but with essentially different physical interpretation. Such a property is the consequence of conformity of spaces being defined by both metrics. The agreement with the fundamental physics laws is achieved by introducing the evolution of a number of other fundamental constants synchronously with the variation of the light speed. The model considered connected the evolution of the Universe with evolution of physical constants and permits explaining some unclear cosmological phenomena — for example, a high isotropy of the relict background and superluminal speed in quasars.

Kinetic Alfvén waves in extended radio sources

Abstract: We study a model of extended radio sources (ERS), in particular, extragalactic jets and radio lobes, which are inhomogeneous and where noncompressive Alfven and surface Alfven waves (and not shocks and magnetosonic waves) are primarily excited. We assume that a negligible thermal population exists (i.e., the ion density at the low-energy cut-off of the power law distribution is greater than the ion density of the thermal population, if present). Due to internal instabilities and/or the interaction of the ERS with the ambient medium, surface Alfven waves (SAW) are created. We show that even very small amplitude SAW are mode converted to kinetic Alfven waves (KAW) which produce large moving accelerating potentials π, parallel to the magnetic field. Neglecting nonlinear perturbations, and for typical physical parameters of ERS, we obtaineπ≳1 MeV. Wesuggest that these potentials are important in acceleration (e.g., injection energy) and reacceleration of electrons in ERS. We show that energy losses by synchrotron radiation can be compensated by reacceleration by KAW. The relation between KAW acceleration, and previously studied cyclotron-resonance acceleration by Alfven waves, is discussed.