Showing papers in "Astrophysics and Space Science in 1997"
175 citations
TL;DR: A brief survey of the experimental observations on many Tokamaks is presented in this article, where a qualitative description of the relevant theoretical ideas and how they have evolved from early magnetic reconnection models in response to increasingly detailed experimental data, is also presented.
Abstract: The Sawtooth instability is a familiar feature in Tokamak plasmas. It appears as a regularly recurring reorganisation of the core plasma. A brief survey of the experimental observations on many Tokamaks is presented. A qualitative description of the relevant theoretical ideas and of how they have evolved from early magnetic reconnection models in response to increasingly detailed experimental data, is also presented.
166 citations
TL;DR: In this article, it appears that NGC 1068 is a relatively normal spiral galaxy in which large-scale gravitational disturbances are funneling matter into the nucleus, and at the center of it all, a 10-20 million solar mass black hole is accreting at close to its Edding limit.
Abstract: At the end of three days' spirited discussion of the type 2 Seyfert galaxy NGC 1068, what do we think we understand about this object? New observations -- particularly in the infrared and radio -- are helping to resolve old problems, while drawing attention to new ones. It appears that NGC 1068 is a relatively normal spiral galaxy in which large-scale gravitational disturbances are funneling matter into the nucleus. A collimated outflow disturbs the interstellar medium out to kiloparsec scales, but the nucleus itself is hidden behind an opaque screen. Radio observations have now pierced the screen, and suggest that at the center of it all, a 10-20 million solar mass black hole is accreting at close to its Eddington limit.
131 citations
TL;DR: In this paper, exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the cases of non-resonant, modified non-onant and resonant cases are given in terms of H -functions, G-functions and in computable series forms.
Abstract: Nuclear reactions govern major aspects of the chemical evolution of galaxies and stars. Analytic study of the reaction rates and reaction probability integrals is attempted here. Exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the cases of nonresonant, modified nonresonant, screened nonresonant and resonant cases are given. These are expressed in terms of H-functions, G-functions and in computable series forms. Computational aspects are also discussed.
67 citations
TL;DR: In this article, numerical simulation of the spectra of the Pleiades brown dwarfs Calar 3 and Teide 1 is discussed, showing that the structure of absorption bands observed in the spectrum depends mainly on Teff, whereas the dependence on gravity is much weaker.
Abstract: Results of the numerical simulation of spectra of the Pleiades brown dwarfs Calar 3 and Teide 1 are discussed. Synthetical spectra were computed for several model atmospheres from a grid of Allard and Hauschildt (1995). From the comparison of computed and observed spectra we have found that: – the spectrum of Teide 1 may be reasonably well fitted by JOLA in the visible region, including the spectral regions around the Li I lines at λλ 670.8 and 812.6 nm. – The structure of absorption bands observed in the spectrum of Teide 1 and Calar 3 depends mainly on Teff. The dependence on gravity is much weaker. – A comparison of observed and computed spectra shows that effective temperatures of these Pleiades brown dwarfs is Teff ≈ 2900 K.
66 citations
TL;DR: In this paper, a Cherenkov water detector with volume 9× 9 × 26 cubic meters is described, where the spatial lattice of the detector is formed by quasispherical measuring modules, which allow to detect Cherekov light from any direction with practically equal efficiency, and the possibility of neutrino induced muon detection under conditions of high background on the Earth's surface is discussed.
Abstract: A Cherenkov water detector with volume 9× 9 × 26 cubic meters is described.The spatial lattice of the detector is formed by quasispherical measuring modules which allow to detect Cherenkov light from any direction with practically equal efficiency. Each of the modules consists of six PMTs directed along rectangular coordinate axes. The possibility of neutrino-induced muon detection under conditions of high background on the Earth's surface is discussed. Experimental data obtained during Spring 1996 are analysed.
66 citations
TL;DR: In this article, the modulational interactions of the electromagnetic waves and the electron-sound waves are studied and the possibility of soliton formation is investigated in hot electron-positron unmagnetized plasma with small fraction of cold electron-ion plasma.
Abstract: The hot electron-positron unmagnetized plasma with small fraction of cold electron-ion plasma is investigated. The modulational interactions of the electromagnetic waves and the electron-sound waves are studied. The possibility of soliton formation is investigated.
55 citations
TL;DR: In this paper, the dispersion law for a low-frequency generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field, is derived.
Abstract: In electron-positron plasmas some of the plasma modes are decoupled due to the equal charge-to-mass ratio of both species. We derive the dispersion law for a low-frequency, generalized X-mode, which exists at all angles of propagation with respect to the static magnetic field. Its nonlinear evolution is governed by a Korteweg-de Vries equation, valid at all angles of propagation except strictly parallel propagation, for which a different approach leads to a vector form of the modified Korteweg-de Vries equation. The nonlinearity is strongest at perpendicular propagation. Ultrarelativistic effects are discussed.
55 citations
TL;DR: In this paper, the detailed structure and kinematics of the neutral hydrogen (HI) are studied in order to determine the relationship between AGN and their host galaxy, which is an important tracer of galactic dynamics.
Abstract: Neutral hydrogen is an important tracer of galactic dynamics. Hence, observations of the detailed structure and kinematics of HI are vital in order to determine the relationship between AGN and their host galaxy.
50 citations
TL;DR: The results on shock waves in plasmas containing variable-charge dust grains are reviewed in this article, where the problems where the shock wave in dust can be important are formulated.
Abstract: The results on shock waves in plasmas containing variable-charge dust grains are reviewed. The problems where the shock waves in dusty plasmas can be important are formulated. The dusty plasma is presented as an open, highly dissipative system where there is a tendency to self-organization. An anomalous dissipation originating from the charging processes results in a possibility of existence of a new kind of shock waves. The shock waves related to this dissipation can be important for description of star formation, shocks in supernova explosions, particle acceleration in shocks, formation of dusty crystals, etc.
49 citations
TL;DR: In this article, a 1.5-scale IRAM interferometer map of CO 2↛1 emission in the central few arcseconds of NGC 1068 is presented.
Abstract: We present preliminary results from 1.5″ resolution IRAM interferometer maps of CO 2↛1 emission in the central few arcseconds of NGC 1068. This study is unlike other studies of the CO content of this galaxy since it resolves for the first time the central dense gas concentration seen previously in HCN observations. The HCN ‘disk’ is resolved into two prominent peaks symmetrically located ~1″ from the S1 radio peak. These peaks are likely tracing gas located on x2 orbits at the Inner Lindblad Resonance (ILR). The kinematic structure is also very complex with three distinct velocity components visible in the central ~2″.
TL;DR: In this paper, a new path equation in AP geometry is derived, which can be considered as a geodesic equation modified by a torsion term, whose numerical coefficient jumps by steps of one half.
Abstract: A new path equation in absolute parallelism (AP) geometry is derived. The equation is a generalization of three path equations derived in a previous work. It can be considered as a geodesic equation modified by a torsion term, whose numerical coefficient jumps by steps of one half. The torsion term is parametrized using the fine structure constant. It is suggested that the new equation may describe the trajectories of spinning particles under the influence of a gravitational field, and the torsion term represents a type of interaction between the quantum spin of the moving particle and the background field. Weak field limits of the new path equation show that the gravitational potential felt by a spinning particle is different from that felt by a spinless particle (or a macroscopic body). As a byproduct, and in order to derive the new path equation, the AP-space is reconstructed using a new affine connexion preserving metricity. The new AP-structure has non-vanishing curvature. In certain limits, the new AP-structure can be reduced either to the ordinary Riemannian space, or to the conventional AP-space.
TL;DR: In this article, the Schwarzschild problem is investigated in an astrophysical framework, exemplified by two likely scenarios: motion of a particle in the photogravitational field of an oblate, rotating star, or in that of a star which generates a Schwarzschild field using McGehee-type transformations.
Abstract: The Schwarzschild problem (the two-body problem associated to apotential of the form A/r + B/r3 has been qualitativelyinvestigated in an astrophysical framework, exemplified by two likelysituations: motion of a particle in the photogravitational field ofan oblate, rotating star, or in that of a star which generates aSchwarzschild field Using McGehee-type transformations, regularizedequations of motion are obtained, and the collision singularity isblown up and replaced by the collision manifold λ (a torus)pasted on the phase space The flow on λ is fullycharacterized Then, reducing the 4D phase space to dimension 2, theglobal flow in the phase plane is depicted for all possible values ofthe energy and for all combinations of nonzero A and B Eachphase trajectory is interpreted in terms of physical motion,obtaining in this way a telling geometric and physical picture of themodel
TL;DR: In this paper, it is shown that, in each case, when the soure of the gravitation field is a perfect fluid distribution, Bianchi type cosmological models do not exist.
Abstract: Spatially-homogeneous and anisotropic Bianchi type-III, V, VI0 cosmological models in Rosen's (1973) bimetric theory of gravitation are considered. It is shown that, in each case, when the soure of the gravitation field is a perfect fluid distribution Bianchi type cosmological models do not exist. Hence vacuum models are presented and studied.
TL;DR: In this article, the authors used a composite galaxy model consisting of a disk-halo, bulge, nucleus and dark halo components in order to investigate the motion of stars in the ther-z plane.
Abstract: We use a composite galaxy model consisting of a disk-halo, bulge, nucleus and dark-halo components in order to investigate the motion of stars in ther-z plane It is observed that high angular momentum stars move in regular orbits The majority of orbits are box orbits There are also banana-like orbits For a given value of energy, only a fraction of the low angular momentum stars — those going near the nucleus — show chaotic motion while the rest move in regular orbits Again one observes the above two kinds of orbits In addition to the above one can also see orbits with the characteristics of the 2/3 and 3/4 resonance It is also shown that, in the absence of the bulge component, the area of chaotic motion in the surface of section increases, significantly This suggests that a larger number of low angular momentum stars are in chaotic orbits in galaxies with massive nuclei and no bulge components
TL;DR: In this article, the structure of the SS 433 supercritical accretion disk derived from spectral and photometric data is described, and a correct value of the mass function has been found, which shows that the optical star is massive.
Abstract: The structure of the SS 433 supercritical accretion disk derived from spectral and photometric data is described. In the disk plane, gas outflows at a velocity of about 100-150 km/s, while above the disk plane, the velocity increases sharply and reaches ≈ 1500 km/s at polar angle ≉ 60°. The outer parts of the accretion disk are involved in the precessional motion, which means that the slaved disk precession model is correct. There is complex periodic variability in the radial velocities of SS 433. Apart from the well-known precessional and orbital variability, the strongest cycle is 1/7 of the precession period, P7 = 23.228 ± 0.005 days. This is interpreted as evidence for a spiral shock in the accretion disk. The He II λ4686 line consists of two components: a stream-formed narrow Gaussian profile and a broad double-peaked one. The latter is completely eclipsed at phase 0.0. Its blue and red peaks are probably emitted in gaseous cocoons around the bases of the relativistic jets. A correct value of the mass function has been found, which shows that the optical star is massive. The relativistic star's mass is estimated to be Mx ≳ 6M⊙.
TL;DR: In this article, the long time behavior of one-dimensional self-gravitating system is numerically investigated, and itinerant behavior among quasiequilibria is discovered, and its origin is clarified.
Abstract: Long time behavior of one-dimensional self-gravitating system is numerically investigated. Itinerant behavior among quasiequilibria is discovered, and its origin is clarified. The macroscopic distributions of the quasiquilibria are different from the isothermal distribution, but the transient states, which appears between two successive quasiequilibria, resemble the isothermal distribution. Averaging over the is itinerancy gives approximately the thermal equilibrium.
TL;DR: In this article, an overview of the optical effects caused by a supernova explosion in a dense circumstellar wind is presented, including thermal conductivity between the shocked wind and fragmented shocked ejecta, interaction of the wind with a relativistic precursor, and emission from accelerated fragments of shocked wind clouds.
Abstract: An overview of the optical effects caused by a supernova explosion in a dense circumstellar wind is presented. Some unclear points and difficulties of the conventional models are pointed out and additional processes suggested, namely, thermal conductivity between the shocked wind and fragmented shocked ejecta, interaction of the wind with a relativistic precursor, and emission from accelerated fragments of shocked wind clouds. A simple model is proposed for cloud formation in the pre-supernova wind.
TL;DR: In this paper, the effects of the gravitational coupling of a multicomponent plasma to a neutral dust are discussed, where wave dispersion properties and susceptibility to gravitational collapse are investigated.
Abstract: Perpendicularly propagating electromagnetic waves in magnetized, multispecies, self-gravitating dusty plasmas are investigated in terms of their wave dispersion properties as well as with respect to their susceptibility to gravitational collapse. In particular, waves on the ordinary as well as extraordinary mode branches are considered. Within the one-dimensional propagation model employed, all modes except the ordinary mode produce density perturbations that can be unstable to gravitational collapse. The wavelengths that are unstable are comparable to the well-known Jeans length for a neutral gas/dust, but there are interesting modifications due to the presence of a magnetic field and charged particles. Furthermore, the effects of the gravitational coupling of a multicomponent plasma to a neutral dust are discussed.
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TL;DR: The discovery of high-T solids within expanding supernova interiors was first discussed in this paper, where the authors proposed SUNOCON as a specific scientific name for such objects.
Abstract: Only a very small fraction of interstellar dust mass originates within the cooling expansions of supernova interiors; but those solids are exciting and important for other reasons. Thermally condensed (high-T) solids that do originate in this way may provide the refractory cores of a significant fraction of interstellar medium (ISM) grains. Hoyle & Wickramasinghe (1970) had predicted this source of grains. Clayton (1975a, 1975b) introduced the possibility of finding such grains in meteorites through their isotopic peculiarities, which were inherited during condenstaion within young supernova ejecta. Such thermally condensed cores within expanding supernova interiors were designated by the acronym SUNOCON by Clayton (1978) as a specific scientific name for such objects. The discovery of these grains, preserved within the meteorites from the beginnings of the solar system and now studied in high detail in laboratories, is the topic of this paper.
TL;DR: In this paper, the effect of the polarity reversals of the polar magnetic field of the Sun on the heliosphere was investigated using both open and closed models of the system and showed that even and odd solar activity cycles can be explained in terms of different contributions of convection, diffusion and drift mechanisms.
Abstract: Monthly cosmic-ray data from Inuvik (0.16 GV) and Climax (2.96 GV) Neutron Monitor stations has been studied with the aid of solar activity parameters for the time period 1947–1995. Systematic differences in the overall shape of successive 11-year modulation cycles and similarities in the alternate 11-year cycles seem to be related to the polarity reversals of the polar magnetic field of the Sun. This suggests a possible effectiveness of the Hale cycle during even and odd solar activity cycles. Our results can be understood in terms of open and closed models of the heliosphere. Positive north pole of the Sun leads to open heliosphere where particles reach the Earth more easily when their access route is by the heliospheric oolar regions (even cycles) than when they gain access along the current sheet (odd cycles). In this case as the route of access becomes longer due to the waviness of the neutral sheet, the hysteresis effect of cosmic-rays is also longer. This interpretation is explained in terms of different contributions of convection, diffusion and drift mechanisms to the whole modulation process influencing cosmic-ray transport in the heliosphere.
TL;DR: In this paper, a study at HST-like spatial resolution of the gas kinematics in the innermost part of NGC 1068 is presented, based on observations with the integral field spectrograph TIGER mounted on the CFH Telescope.
Abstract: We present a study at HST-like spatial resolution of the gas kinematics in the innermost part of NGC 1068. This work is based on observations with the integral field spectrograph TIGER mounted on the CFH Telescope. We first derived the final spatial PSF of our data and checked its photometric integrity by comparison with two independent [OIII] HST images (FOC and WFPC2). We then performed a spatial deconvolution of the data-cube constraining the sum of the deconvolved velocity-slices to be as close as possible to the HST image. The resulting deconvolved data-cube has then a resolution similar to the HST image. It shows that the velocity distribution of the inner clouds detected with the HST differs strongly from a simple NE-SW ejection flow. We thus show that the previous interpretations of the double-peaked lines NE of the nucleus must be revisited.
TL;DR: In this article, the effect of time dependent bulk viscosity on the evolution of Friedmann models with zero curvature in Brans-Dicke theory is studied and the physical properties of cosmological solutions are also discussed.
Abstract: The effect of time dependent bulk viscosity on the evolution of Friedmann models with zero curvature in Brans-Dicke theory is studied. The solutions of the field equations with ‘gamma-law’ equation of state p = (γ-1) ρ, where γ varies continuously as the Universe expands, are obtained by using the power-law relation φ = bRn, which lead to models with constant deceleration parameter. We obtain solutions for the inflationary period and radiation dominated era of the universe. The physical properties of cosmological solutions are also discussed.
TL;DR: In this article, the authors studied the second self-creation theory of gravitation in the presence of perfect fluid by using the gamma-law equation of state p =(γ-1)ρ.
Abstract: Spatially homogeneous and isotropic Robertson-Walker model of the universe is studied in Barber's second self-creation theory of gravitation in the presence of perfect fluid by using ‘gamma-law’ equation of state p =(γ-1)ρ. The parameter gamma varies continuously with cosmological time. Exact solutions of the field equations are obtained for inflationary period and radiation-dominated era by using the power law relation φ Rn-3 = B. Some physical properties of the models are also discussed.
TL;DR: In this article, the authors proposed a method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field, which can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determined fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular noncircular motion in the spiral density wave.
Abstract: General ideas, as well as experimental and theoretical efforts concerning the prediction and discovery of new structures in the disks of spiral galaxies – giant anticyclones - are reviewed. A crucial point is the development of a new method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field. This method can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determination of fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular non-circular motion in the spiral density wave, which makes it possible to build more accurate models of the mass distribution in the galaxy; 4) refinement of parameters of the rotating gaseous disk: inclination angle, center of rotation and position angle of the major dynamical axis, systematic velocity. The method is demonstrated using the restoration of the velocity field of the galaxy NGC 157 as an example. Results for this and some other spiral galaxies suggest that giant anticyclones are a universal property of galaxies with grand design structure.
TL;DR: In this article, totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation both in vacuum and in the presence of stiff-matter.
Abstract: Totally anisotropic Bianchi type-II cosmological solutions are presented in Barber's second self-creation theory of gravitation both in vacuum and in the presence of stiff-matter. The corresponding cosmological models have no finite singularity. The stiff-matter model gives essentially an empty universe for large time. Some physical and kinematical properties of the models are discussed.
TL;DR: The radio jet axis of NGC 1068 is characterised by energetic activity from x-ray to radio wavelengths as discussed by the authors, and the nuclear spectrum is quasar-like (power law + blue excess) with a luminosity 2-5 times higher than inferred by Pier et al.
Abstract: The radio jet axis of NGC 1068 is characterised by energetic activity from x-ray to radio wavelengths Detailed kinematic and polarization studies have shown that this activity is confined to bipolar cones centered on the AGN which intersect the plane of the disk Thus, molecular clouds at 1 kpc distance along this axis are an important probe of the nuclear ionizing luminosity and spectrum Extended 108µm emission coincident with the clouds is reasonably understood by dust heated to high temperatures by the nuclear radiation field This model predicts that the nuclear spectrum is quasar-like (power law + blue excess) with a luminosity 2-5 times higher than inferred by Pier et al (1994) Consequently, there is little or no polyaromatic hydrocarbon (PAH) emission associated with the radio-axis molecular clouds We review this model in the light of new observations A multi-waveband collage is included to illustrate the possible orientations of the double cones to our line of sight and the galaxian plane
TL;DR: In this paper, it was shown that the equilibrium statistical distribution that these particles must obey, is that of the Tsallis non-extensive statistics, the distribution differing very slightly from the usual Maxwellian distribution.
Abstract: In this paper we will show that, assuming the existence of a long-range microscopic memory of the random force, acting in the solar core, mainly on the electrons and the protons rather than on the light and heavy ions (or, equally, assuming the existence of an anomalous diffusion of solar core constituents of light mass and of normal diffusion of heavy ions), the equilibrium statistical distribution that these particles must obey, is that of the Tsallis non-extensive statistics, the distribution differing very slightly from the usual Maxwellian distribution. Due to the high-energy depleted tail of the distribution, the nuclear rates are reduced and, using earlier results on the standard solar model neutrino fluxes, calculated by Clayton and collaborators, we can evaluate fluxes in good agreement with the experimental data. While the proton distribution is only very slightly different from the Maxwell one there is a slightly larger difference with the electron distribution.
TL;DR: The available observational date and cosmological models indicate the possible existence of supercivilizations with ages of technological development 6-8 gigahers larger than on the Earth as discussed by the authors, and the probability of their detection is probably conne with observations at wavelengths from 3 mcm to 3 mm, and also with the solution of the hidden mass problem and searches for multiconnection of the Universe
Abstract: The available observational date and cosmological models indicate the possible existence of supercivilizations with ages of technological development 6-8 gigayears larger than on the Earth The probability of their detection is probably conne with observations at wavelengths from 3 mcm to 3 mm, and also with the solution of the hidden mass problem and searches for multiconnection of the Universe
TL;DR: In this paper, the authors describe the observational aspects of these irregularities, namely glitches and timing noise, and review and assesses the theoretical models that have been proposed to explain the irregularities.
Abstract: Whilst considerable data have been gathered on the rotational behaviour of pulsars since their discovery, the mechanisms behind the rotational irregularities observed in these objects are still not well understood. This paper describes the observational aspects of these irregularities, namely glitches and timing noise. In addition, it reviews and assesses the theoretical models that have been proposed to explain the irregularities.