Showing papers in "Astrophysics and Space Science in 1983"

A new method for the analysis of apsidal motions in eclipsing binaries

Abstract: In this paper, a new method for the determination of apsidal motion parameters in eccentric eclipsing binaries is presented. A sequential procedure has been followed throughout allowing an automatized on-line computation of the elements and their accuracies as well as a more realistic fit to the observed times of minima. A determination of individual mean errors for the parameters of fit give us the possibility to compare the results with available theoretical models of stellar structure. In the procedure, we have introduced a determination of preliminary elements by means of Fourier transform and extended the practical equations to terms up to the fifth power of the eccentricity. An application to the well-known case of the eclipsing binary GL Car has been made. Our analysis shows an apsidal motion period of 25.3 years with a value of 0.152 for the orbital eccentricity.

Self-modulational formation of pulsar microstructures

Abstract: A nonlinear plasma theory for self modulation of pulsar radio pulses is discussed. A nonlinear Schroedinger equation is derived for strong electromagnetic waves propagating in an electron positron plasma. The nonlinearities arising from wave intensity induced particle mass variation may excite the modulational instability of circularly and linearly polarized pulsar radiation. The resulting wave envelopes can take the form of periodic wave trains or solitons. These nonlinear stationary waveforms may account for the formation of pulsar microstructures.

Hydrodynamical models of type II supernovae

Abstract: A series of hydrodynamical models of type-II supernova outbursts (SNII) has been calculated. Approximate relations connecting the total outburst energy e, the mass of envelope ejectedM, the presupernova radiusR, and the amount of ionizing quanta radiated by the supernovaeN H with such values as the duration of the light curve plateau Δt, and absolute magnitude in the wavelength bandV and photospheric velocityU PH observed near the middle of the plateau have been established. Advantage has been taken of the relations to obtain a preliminary evaluation for the characteristics of the average SN II: e=7×1050 erg,M=6M ⊙,R=500R ⊙,N H=2×1058. The SNIIs with plateau-like light curves seem to be accounted for by thermonuclear explosions of degenerate cores of red giant stars and result in a total disruption of the star without any stellar remnant. To the contrary, SNIIs with linear light curves have substantially different properties (in particular, they throw considerably less massive envelopes off). These SNII must signify the birth of collapsed objects—neutron stars (pulsars) or black holes.

Characteristics of activity energetics of the UV cet-type flare stars

Abstract: A quantitative comparison of energetics of different manifestations of the activity of the UV Cet-type flare stars — sporadic flares, quiet chromospheres and coronae and stellar spots — have been carried out. On the basis of a statistical analysis of about 1800 flares registered for 23 flare stars, the energy spectra of flares have been constructed and time-averaged powers of optical radiation of flares —L flares — have been estimated. By use of spectroscopic observations of 26 flare stars between flares, the total radiation in Balmer lines of quiet chromospheres —L Bal — have been found. On the basis of these data and the soft X-ray observations of 29 flare stars, the mean of the ratiosL flares/L bol,L Bal/L bol andL X /L bol have been found to be equal to (1–2)×10−4. By use of photometric observations for 9 stars, the total starspot radiation deficits —L spots — have been estimated as (4×10−3−6×10−2)×L bol. Discussions of probable underestimates in the valuesL flares,L Bal,L X , andL spots leads to the conclusion that the total power of non-equilibrium processes that take place in flare star atmospheres is close to the total starspot radiation deficit in these stars.

Theory of NP 0532 pulsar radiation and the nature of the activity of the Crab Nebula

Abstract: Plasma processes in the magnetospheres of pulsars are considered. A self-consistent radiation model of the pulsar NP 0532 and the Crab Nebula is presented. It is based on the consideration of cyclotron instability in a relativistic electron-positron plasma in a strong magnetic field. This instability onsets near the light cylinder of pulsar NP 0532. The pitch-angle and energy distribution of particles, caused by cyclotron instability development is found. It is shown that X- and γ-ray radiation of the pulsar is explained by the synchrotron radiation of beam particles. The scattering of excited oscillations on plasma particles is responsible for nonzero pitch-angles of the latter. As a result, synchrotron radiation originates which is within optical frequencies. The synchrotron luminosity evaluated coincides with that observed for NP 0532 in that spectral region. Cyclotron waves are pumped to lower frequencies due to nonlinear scattering by plasma particles and leave the pulsar magnetosphere as observable radio waves.

Phenomenological Study of Massive Accretion Stars

Abstract: The effects of accretion during core-hydrogen burning and during shell hydrogen burning at constant rates of 3e−3M0yr−1 and 3e−4M0yr−1 on twelve massive stars of 10M0 and 30M0, with and without stellar wind mass loss are examined. For each case relaxation series are computed after 14M0 and after 29M0 have been accreted. The accretion series with the slower rate are well able to adjust their structure almost instantaneously to the increasing mass. The series with the rapid accretion rate show severe overluminosity, having envelopes strongly deviating from thermal equilibrium. After relaxation they return to the normal positions of their corresponding slow accretion models. The process of semi-convection enables the Main-Sequence models to increase their convective core and their core-hydrogen content. The hydrogen shell-burning models increase their intermediate fully convective zone both in size and in hydrogen content.

Period changes of Cepheid variables

Abstract: Secular period changes of one hundred northern Cepheids are investigated with the help of O−C diagrams. With the classical Cepheids the rate of observed period changes is in good agreement with that determined from stellar evolution theory. The period noise cannot mask the evolutionary period changes especially in longer period Cepheids for which the occurrence of parabolic O−C graphs is unusually frequent.

Dynamical friction in a mean field approximation

Abstract: An exact formula is derived for the average frictional force acting upon a ‘test’ star which moves along a prescribed trajectory amongst a collection of ‘field’ stars which are characterized by a Maxwellian distribution of velocities. In the limit that the actual stellar trajectories may be approximated by their average forms, as determined by the mean gravitational field, one obtains a relatively simple expression which establishes an important connection with the fluctuation-dissipation theorem. For the case of an infinite, homogeneous system, one recovers Chandrasekhar's classical result. Alternatively, by allowing for the possibility of nearly periodic motion, one is led to new and intriguing phenomena.

Mass transfer effects on the flow past an accelerated vertical plate with constant heat flux

Abstract: In the present paper, mass transfer effect on the free-convection flow of an incompressible viscous fluid past a uniformly accelerated infinite vertical plate is discussed when there is a constant heat flux between fluid and plate. The expressions for the velocity field and the skin-friction have been obtained by the Laplace-transform technique. The influence of the various parameters entering into the problem is extensively discussed with the help of graphs and table.

Fragmentation of the universe

Abstract: We have tested the hypothesis that the universe underwent a single fragmentation event, separating into protogalactic volumes at a relatively early stage after the Big Bang. Assuming that the present total luminosity of each galaxy is proportional to its mass, we plotted the number and mass distribution of a thousand nearby galaxies just as we would in an analysis of fragments from a laboratory high-explosive experiment. The results are consistent with the single-fragmentation hypothesis.

Theory of Superdense Matter and Degenerate Stellar Configurations

Abstract: During the last two decades the theory of degenerate stellar configurations has been developed in works by Ambartsumian and Sahakian, as well as in some other papers. This article is further progress in this direction.

Effects of Free Convection Currents and Mass Transfer on Flow Past a Vertical Oscillating Plate

Abstract: An exact analysis of the flow caused by an oscillating vertical plate in the presence of free-convection currents and foreign mass has been presented. Solutions have been derived by Laplace-transform technique. Velocity profiles and leading edge effects have been shown for different gases present in air. During the course of discussion, the effects of Gr (Grashof number), Gm (modified Grashof number), Sc (Schmidt number), on the flow have been discussed. It has been observed that at all small values of Sc, transition from conduction to convection exists but at large values of Sc, such a transition is not present.

The heterogeneous condensation of interstellar ice grains

Abstract: Processes of heterogeneous condensation are investigated. We consider the situation that vapor and solid grains of which material is other than that of the vapor coexist and the saturation of the vapor increases with time. If the contact angle of the condensate to the solid is small (≳90°), the condensate will be formed as mantles coating the solid grains but only a fraction of the solid grains will be coated by mantles. The ratio of core-mantle grains to bare solid grains in number will be smaller as the density of the vapor and the time scale of saturation increase are large. Actual calculations are made by adopting H2O ice as the mantle material and magnesium silicate as the core material.

The waiting point approximation in R-process calculations

Abstract: The steady flow approximation to the r-process has been used to evaluate the validity of the waiting point assumption (that, for a given charge number Z, neutron captures become balanced by neutron photodisintegrations) under a variety of conditions The criterion for the accuracy of the approximation for any set of nuclei with the same value of Z is that the ratio of the total rate of neutron photodisintegration in those nuclei to the total rate of neutron captures should be close to unity No set of conditions involving neutron production by helium thermonuclear reactions (at temperatures up to 10 to the 9th K) could be found for which the waiting point approximation is useful for all values of Z, and it is recommended that all such r-process calculations not use this approximation At higher temperatures, such as those characteristic of explosive carbon burning (2 x 10 to the 9th K), the waiting point approximation is much better

Cosmic-ray antimatter: A primary origin hypothesis

Abstract: The present investigation is concerned with the possibility that the observed cosmic-ray protons are of primary extragalactic origin, taking into account the significance of the current antiproton data. Attention is given to questions regarding primary antiprotons, antihelium fluxes, and the propagation of extragalactic cosmic rays. It is concluded that the primary origin hypothesis should be considered as a serious alternative explanation for the cosmic-ray antiproton fluxes. Such extragalactic primary origin can be considered in the context of a baryon symmetric domain cosmology. The fluxes and propagation characteristics suggested are found to be in rough agreement with the present antiproton data.

Apsidal motion in the eclipsing binary AS Cam

Abstract: Multi-colourWBVR photoelectric observations of the eclipsing binary AS Cam have been carried out and the photometric elements, absolute dimensions, and the angular velocity of a periastron motion ( $$\mathop \omega \limits^ \cdot _{obs}$$ ) are determined. The obtained value of $$\mathop \omega \limits^ \cdot _{obs}$$ is almost three times smaller than that theoretically predicted.

LRS Bianchi type-V universes filled with matter and radiation

Abstract: In this paper we have investigated some LRS Bianchi type-V cosmologicla models representing a viscous fluid distribution with a null electromagnetic field and streaming neutrinos. Various physical and kinematical features of these models have also been explored.

DDO integrated photometry of globular clusters and initial chemical evolution of the galaxy

Abstract: Integrated photometry of 91 galactic globular clusters was carried out with theUBV and DDO systems. A method to determine reddening is presented. Metal abundances were obtained by means of a calibration ofC(42–45)0 vs [Fe/H]. Thirteen other clusters whose metallicity values were made compatible with those observed here, were added to the sample totalizing a homogenous set of [Fe/H] estimates for 104 globular clusters. This sample is used to analyze the spatial distribution of metallicities. An estimate of the intrinsic metal abundance frequency distribution of the globular cluster system is provided. The chemical properties of the globular cluster system are compared with one-zone-chemical-enrichment models which take into account gas loss from star formation regions. It is concluded that these models cannot describe the complete chemical enrichment of the globular cluster system.

On Hierarchical Cosmology

Abstract: Progress in laboratory studies of plasmas and in the methods of transferring the results to cosmic conditions, together within situ measurements in the magnetospheres, are now causing a ‘paradigm transition’ in cosmic plasma physics. This involves an introduction ofinhomogeneous models with double layers, filaments, ‘cell walls’, etc.

Effect of rotation and tidal distortions on the structure of polytropic stars

Abstract: The averaging technique of Kippenhahn and Thomas has been used in conjunction with Kopal's method of evaluating various parameters on the Roche equipotentials, to determine the effects of rotation and tidal distortions on the shapes and structures of the polytropic models of the stars.

Structurally stable approximations to Friedmann—Lemaître world models

Abstract: Friedmann—Lemaitre cosmology is briefly reviewed in terms of dynamical systems It is demonstrated that in certain cases bulk viscosity dissipation structurally stabilizes Friedmann—Lemaitre solutions It turns out that, for A=0, there are structurally stable solutions if ξ~e1/2, where ξ is the bulk viscosity coefficient For A≠0 structurally stable solutions are essentially those with ξ=const The role of structural stability in physics and cosmology is shortly discussed

The evolution of supernova remnants. I. Analysis of observational data

Abstract: The observational data analysis is based on the selection of 14 shell-type SNR, whose distances are quite reliable. Parameters of those SNR characterizing the values of the mean electron densityn e, the change ofk 2/7 H and velocity of expansionV are taken. The other parameters of SNR, such as energy of explosion, energy in magnetic field, and relativistic particles, and its increase during the expansion of SNR, are taken and analysed.

The empirical mass-luminosity relation

Abstract: On the basis of the most recent data for visual and spectrophotometric binaries, the empirical mass-luminosity relation has been investigated. It is shown that, for the sample collected, the relation may be divided into three parts, for which numerical relations are given. A table summarizing the observational results on the fractional mass of the secondary component in visual systems is given.

An imaging spectrometric observatory for spacelab

Abstract: The large payload capacity of the Space Shuttle Orbiter offers the first opportunity to launch into space an instrument able to simultaneously measure the entire spectrum of atmospheric emission, from the extreme UV to the near-IR, with high spectral resolution and high sensitivity while obtaining global and altitude coverage. This capability would provide a database for atmospheric process studies. The Spacelab Imaging Spectrometric Observatory (ISO) comprises an array of five spectrometers designed to make full use of the Space Shuttle as an observing platform for atmosphere remote sensing, and covers the 300-12,000-A wavelength range with a 2-7 A resolution. Area array detectors can scan the entire wavelength range in less than 20 sec and, being two-dimensional, permit spectral imaging in one direction and spatial imaging on the other.

General vacuum-universe solutions in Brans-Dicke cosmology

Abstract: By a rescalation of the scalar field ϕ of the Jordan-Brans and Dicke cosmology, the general solutions of the Friedmannian ‘vacuum’ Universe are obtained. Only the flat space solution was previously known. Each solution is caracterized by the sign of the second time derivative of the rescaled field ψ≡ϕR3 (R being the scale factor of the Robertson-Walker line-element):\(\ddot \psi\) = 0 (flat space),\(\ddot \psi\) 0 (open space), so that the solutions are mutually exclusive. Of these, the open space one is damped-oscillatory andR attains its absolute minimum, equal to zero, in only one of the two ‘extreme’ cycles. Otherwise,R min remains positive. If the ϕ-field is dominant near the singularity, these solutions may have physical significance.

Spectra of radiation from a strongly magnetized plasma

Abstract: Radiation from an optically thick, tenuous, isothermal and magnetized plasma is considered under conditions typical for X-ray pulsars, in the approximation of coupled diffusion of normal modes. The spectra are calculated of the fluxes and specific intensities of outgoing radiation, their dependences on the plasma densityN, temperatureT and magnetic fieldB are analysed with due regard to the vacuum polarization by a strong magnetic field. Simple analytical expressions are obtained in the limiting cases for the fluxes and intensities. It is shown that atEB »Ea (EB=11.6B12 keV,Ea≃0.1N221/2T1−3/4 keV,B12=B/1012 G,N22=N/1022 cm−3,T1=T/10 keV) the magnetic field strongly intensifies the flux and changes its spectrum in the regionEa ≲E ≲EB. AtE ≲T the spectrum of the energy flux is almost flat in the region\(\sqrt {E_a E_B } \lesssim E \lesssim E_B \). For homogeneous plasma without Comptonization the cyclotron line atE≃=EB appears in emission, though in many other cases it may appear in absorption. The vacuum polarization may produce the ‘vacuum feature’ atE≃EW≃13N221/2B12−1 keV, which, as a rule, appears in absorption. The intensity spectra vary noticeably with the direction of radiation, in particular, at some directions nearB, the spectra become harder than in other directions. Quantization of the magnetic field (EB>T) strongly increases the plasma luminosity (∝EB/T for homogeneous plasma). The results obtained explain a number of basic features in the observed X-ray pulsar spectra.

Comment on the general vacuum solutions in Brans-Dicke cosmology

Abstract: We would like to point out that the non-flat FRW-solutions of the Brans-Dicke theory, recently obtained by Chauvet, can be presented in a much simpler form.

Stability of the equilibrium distributions of interstellar gas, cosmic rays, and magnetic field in an external gravitational field

Abstract: An interstellar medium consisting of regular and turbulent magnetic fields, thermal gas and cosmic rays is tested for stability in a stellar gravitational field. Cosmic rays are described by the diffusion-convection equation and the stability region of the system is determined. It is shown that the presence of cosmic rays is a stabilizing factor if the cosmic-ray diffusion coefficient is sufficiently small. The dependence of the maximum growth rate of instability on the cosmic-ray diffusion coefficient is qualitatively determined.

Solar system history as recorded in the Saturnian ring structure

Abstract: Holberg's analysis of the Voyager Saturn photographs in reflected and transparent light, and occultation data of stars seen through the rings are discussed. A hyperfine structure, with 10,000 ringlets can be explained by the Baxter-Thompson negative diffusion. This gives the ringlets a stability which makes it possible to interpret them as fossils, which originated at cosmogonic times. It is shown that the bulk structure can be explained by the combined cosmogonic shadows of the satellites Mimas, Janus and the Shepherd satellites. This structure originated at the transition from the plasma phase to the planetesimal phase. The shadows are not simple void regions but exhibit a characteristic signature. Parts of the fine structure, explained by Holberg as resonances with satellites, are interpreted as cosmogonic shadow effects. However, there are a number of ringlets which can neither be explained by cosmogonic nor by resonance effects. Analysis of ring data can reconstruct the plasma-planetesimal transition with an accuracy of a few percent.

On the evolution of interacting, magnetized, galactic plasmas

Abstract: The advent of three-dimensional, electromagnetic, and fully relativistic particle simulations allows a detailed study of a magnetized, rotating plasma, galaxy model. When two such models are simulated, an interaction yielding results resembling observational data from double radio sources, including the emission of synchrotron radiation, are obtained. Simulation derived morphologies, radiation intensities, frequency spectra, and isophote patterns are directly compared to observations. The constituent plasma parameters associated with the source Cygnus A are found to ben e =1.8×10−3 cm−3,T=2.8 keV,B=20–30 gamma, with a small population of electrons accelerated to GeV energies by a rotation induced electric field. The results of these simulations, involving a computational resource of five CDC 7600 and five Cray-1 computers, strongly supports an inhomogeneous version of the Klein world model.