Showing papers in "Astrophysics and Space Science in 1989"
TL;DR: In this paper, empirical correlations between line widths of photospheric absorption lines were investigated as a measure of the stellar projected rotational velocityv sini- and of circumstellar emission lines in Be stars.
Abstract: I re-investigate empirical correlations between line widths of photospheric absorption lines — as a measure of the stellar projected rotational velocityv sini- and of circumstellar emission lines in Be stars. The degree of this correlation is a measure for the kinematic, i.e., rotational, contribution to the total emission line broadening.
53 citations
TL;DR: In this paper, the authors identified members of the Galaxy components according to stellar ages, metallicities and galactic orbits, and found that the local thin disk has a maximum age of 11 billion years and a small abundance scatter partially controlled by the radial gradient of abundances.
Abstract: Members of the Galaxy components are identified according to stellar ages, metallicities and galactic orbits. The local thin disk is found to have a maximum age of 11 billion years and a small abundance scatter partially controlled by the radial gradient of abundances. Metal-rich and old metal-poor stars belong to inner galactic populations and SMRs represent the ultimate star generation in the bulge. The thick disk forms a smooth transition between the halo and thin disk.
42 citations
TL;DR: In this article, the history of star formation in dwarf irregular galaxies was studied using deep CCD observations of irregulars in the Local Group and a new method of numerical simulations based on stellar evolutionary tracks.
Abstract: In order to study the history of star formation in dwarf irregular galaxies we have started a project of deep CCD observations of irregulars in the Local Group. For the theoretical interpretation of the colour-magnitude diagrams resulting from these observations we present a new method of numerical simulations based on stellar evolutionary tracks. The preliminary results concerning the galaxies WLM and Sextans B are summarized.
37 citations
TL;DR: In this paper, it is shown that there do not exist spatiallyhomogeneous and anisotropic Bianchi type-I cosmological models in Rosen's (1973) bi-metric theory of gravitation when the source of the gravitational field is a perfect fluid distribution.
Abstract: It is shown that there do not exist spatially-homogeneous and anisotropic Bianchi type-I cosmological models in Rosen's (1973) bi-metric theory of gravitation when the source of the gravitational field is a perfect fluid distribution. A vacuum cosmological model, in this theory, is presented and studied.
36 citations
TL;DR: In this paper, a spatially homogeneous and anisotropic Bianchi type-VI0 cosmological model was obtained for the second self-creation theory of gravitation in the presence of perfect fluid with pressure equal to energy density.
Abstract: Spatially-homogenous and anisotropic Bianchi type-VI0 cosmological models are obtained, in Barber's second self-creation theory of gravitation, both in vacuum and in the presence of perfect fluid with pressure equal to energy density. Some properties of the model are discussed.
36 citations
TL;DR: In this paper, a detailed investigation of the evolution of low-mass binaries is performed for the case when the secondary fills its Roche lobe at the stage of core hydrogen exhaustion, and the obtained results are compared with observational data for ultra-short periodic X-ray systems MXB 1820-30 and MXB 1916-05.
Abstract: A detailed investigation of the evolution of low-mass binaries is performed for the case when the secondary fills its Roche lobe at the stage of core hydrogen exhaustion. The obtained results are compared with observational data for ultra-short periodic X-ray systems MXB 1820-30 and MXB 1916-05. In the frame of the proposed evolutionary scenario it is possible to obtain for MXB 1820-30 its periodP=11.4 min twice (see Figure 2). In the first case the parameters of the system are:M2 ≈ 0.13−0.15M⨀,X≈0.05–0.13, |P/P| ≈ (3.6−6.2) } 10−7 yr−1, M2 ≈ (4.1−9.6) } 10−9M⨀ yr−1, for the second:M2 ≈ 0.08−0.09M⨀,X= 0, |P/P| ≈ (1.3−1.5) } 10−7 yr−1, M2 ≈ (1.4−1.8) } 10−8M⨀ yr−1. It is suggested that MXB 1916-05 is the progenitor of the system MXB 1820-30 (M2 = 0.1M⨀,X ≃ 0.221,M2 ≃ 1.8 × 10−10M⨀ yr−1).
35 citations
TL;DR: In this paper, the authors compared the luminosity functions of galaxies of various Hubble types in the core of the Formax cluster to luminosity function of the Virgo cluster from Sandageet et al.
Abstract: In these first results from a photographic survey of nearby clusters and groups of galaxies, we compare the luminosity functions of galaxies of various Hubble types in the core of the Formax cluster to luminosity functions in the core of the Virgo cluster from Sandageet al. (1985). The galaxy classifications for the two clusters are based on identical plate material, and are hence directly comparable. The properties (galaxy density, velocity dispersion, X-ray luminosity) of the two clusters are quite different, yet we find few significant differences in the luminosity functions, or in the morphological mix of galaxies between the two clusters. In particular, while there is some indication that the ratios of giants to dwarfs and early to late-type galaxies in the two clusters differ, we cannot exclude the possibility that the ratios are identical. We discuss the selection limits of our survey and the completeness corrections that must be applied to the faint end of the luminosity function. The effective surface brightness of early-type galaxies in our sample decreases with decreasing luminosity. We show that this correlation is not an artifact of our selection criteria for dwarf spheroidal galaxies and use it to determine the relative distances to the Fornax and Virgo clusters. We also present evidence for a radial variation in the luminosity function of dwarf ellipticals within the two clusters in the sense that the faint end of the luminosity distribution is enhanced at the centre of each cluster.
28 citations
TL;DR: In this paper, the field equations of the generalized field theory constructed by Mikhail and Wanas have been applied to a well-established geometrical structure given earlier by H. P. Robertson in connection with the cosmological problem.
Abstract: The field equations of the generalized field theory constructed by Mikhail and Wanas have been applied to a well-established geometrical structure given earlier by H. P. Robertson in connection with the cosmological problem. A unique solution, representing a specified expanding Universe (withq
0=0, Ω0=0.75,k=−1) has been obtained. The model obtained has been compared with cosmological observations and with FRW-models of relativistic cosmology. It has been shown that the suggested model is free of particle horizons. The existence of singularities has been discussed. The two cases, when the associated Riemannian-space has a definite or indefinite metric are considered. The case of indefinite metric with signature (+ − − −) is found to be characterized byk=−1, while the case of +ve definite metric is characterized byk=+1. Apart from that difference, the two cases give rise to the same cosmological parameters. It has been shown that energy conditions are satisfied by the material contents in both cases.
27 citations
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TL;DR: The Galileo project as mentioned in this paper is a 3.5 m Italian telescope that consists of a duplication of the ESO New Technology Telescope (NTT) with modifications introduced in order to allow, beyond the Nasmyth foci, a prime focusf/2.2 station, a trappedf/6 focus, and a small Cassegrainf/20 facility.
Abstract: The Galileo project comprises the design, building, and operation of a 3.5 m Italian telescope the main elements (diameter, mechanical structure, active optics, etc.) of which consist of a duplication of the ESO New Technology Telescope (NTT). Modifications have been introduced in order to allow, beyond thef/11 Nasmyth foci, a prime focusf/2.2 station, a trappedf/6 focus, and a small Cassegrainf/20 facility. Other changes with respect to the NTT have been made to the control and data acquisition system, and to the service building. The telescope could be operational at the end of 1992.
27 citations
TL;DR: In this paper, the authors presented the results of the calculations of anomalous extinction laws characterized by different values of the ratio of the total to selective extinctionR=Av/E(B-V).
Abstract: In this paper we present the results of the calculations of anomalous extinction laws characterized by different values of the ratio of the total to selective extinctionR=Av/E(B-V). As far as we are aware, no such theoretical extinction laws have been published before. The calculation is based on the Mie theory of light scattering by small particles assuming a two-grain dust model of Mathiset al. (1977) and by adopting theri particle size (a) distribution, given byn(a)=a−3.5, in which the minimum and maximum size is taken to be 0.005 and 0.22 μm, respectively. Furthermore, we use the dielectric functions for the two types of grains, graphite and ‘astronomical silicate’, as derived by Draine and Lee (1984), published in tabular form by Draine (1985). Following Mathis and Wallenhorst (1981), we then obtained the anomalous extinction laws by changing the upper size cutoff of the particles.
26 citations
TL;DR: In this paper, the Ernst-Wild solution with conical singularities removed is discussed and the physical quantities characterizing the modified solution including electromagnetic fourpotential, electric, and magnetic field fluxes through the upper hemisphere of the horizon, equatorial and meridional circumferences on the horizon are calculated.
Abstract: The Ernst-Wild solution with conical singularities removed is discussed. The physical quantities characterizing the modified solution including electromagnetic four-potential, electric, and magnetic field fluxes through the upper hemisphere of the horizon, equatorial and meridional circumferences on the horizon are calculated.
TL;DR: In this paper, a scalar field theory of gravitation is presented, which is derived from the space-time torsion which is shown to be the generator of gravity and inertia as well as spin.
Abstract: The present paper presents, within the Einstein conceptual framework, a scalar field theory of gravitation. The Ω-field, however, is not superimposed on the space-time manifold from outside the given geometry but is derived from the space-time torsion which is shown to be the generator of gravitation and inertia as well as spin. The theory predicts the three crucial tests of gravitation to the same degree of accuracy as does Einstein's theory. But it also predicts gravitational radiation emitted by a pulsating sphere and a singularity free cosmology in contradiction to Einstein's results. Above all, the scalar gravitational field can be easily quantized in the present context.
TL;DR: In this paper, surface photometry is carried out for the photometric standard galaxy NGC 3379 on the basis of two plates in the blue band taken with the Bejing Schmidt telescope.
Abstract: Surface photometry is carried out for the photometric standard galaxy NGC 3379 on the basis of two plates in the blue band taken with the Bejing Schmidt telescope. The results, including luminosity profiles, photometric parameters, integrated luminosity distribution, ellipticity and position angle variation, are presented in various forms of figures and tables. Especially our geometric profiles, i.e., ellipticity and position angle variations reach up to ≈5′, much fainter region than that any previous study did. The accuracy of the present data is checked by comparing them with the surface photometry in the literature. We find the zero-point ≈0.12 mag brighter than the calibration of de Vaucouleurs and Capaccioli (1979), which agrees with the values 0.10–0.15 mag difference claimed by recent observations. The systematic differences is found to be less than ≈0.1 mag.
TL;DR: In this paper, the filamentation instability of finite amplitude left-hand circularly polarized Alfven waves was investigated taking into account the second-order density and magnetic field perturbations that are created by the Alfven wave pressure.
Abstract: The filamentation instability of finite amplitude left-hand circularly polarized Alfven waves has been investigated taking into account the second-order density and magnetic field perturbations that are created by the Alfven wave pressure. The minimum scale length and time over which the filamentation occurs, are found. Our results are applied to Alfven waves that should scatter cosmic rays in the interstellar medium (ISM).
TL;DR: In this article, the characteristics of the loop prominence of the April 27, 1981 solar flare event were examined using the results of H-alpha observations by the Astrophysical Observatory in Catania (Italy), the Purple Mountain Observatory in Nanking (China), together with hard-X-ray and gamma-ray burst data from the SMM Gamma-Ray Spectrometer.
Abstract: This paper examines the characteristics of the loop prominence of the April 27, 1981 solar flare event, which occurred on the limb (about 90 deg), using the results of H-alpha observations by the Astrophysical Observatory in Catania (Italy), the Purple Mountain Observatory in Nanking (China), together with hard-X-ray and gamma-ray burst data from the SMM Gamma-Ray Spectrometer. The analysis shows that there existed a second abrupt energy release for this event, almost 20 min after the end of the impulsive phase of the flare, which appears to be associated with the rapidity in upward motion or activation of the loop prominence. It is suggested that a possible mechanism for a second energy release may be the reconnection of new emerging magnetic field with the existing magnetic field lines.
TL;DR: In this paper, an exact solution of Einstein's equations for a static isentropic perfect fluid sphere is examined in detail, and the analysis yields a strong indication that the model isstable with respect to infinitesimal radial pulsations.
Abstract: An exact solution of Einstein's equations for a static isentropic perfect fluid sphere is examined in detail. The analysis yields a strong indication that the model isstable with respect to infinitesimal radial pulsations. This means that the temperature is decreasing outwards. We prove that the adiabatic speed of sound is everywhere less than the speed of light if and only if the radius of the sphere is larger than 1.61 times its Schwarzschild radius. We further show that the strong energy condition is fulfilled everywhere if and only if the radius is larger than 1.76 times the Schwarzschild radius. The necessary and sufficient condition for the speed of sound to be decreasing outwards is given, and we find that this criterion is fulfilled if the fluid is causal. Taking the values of the pressure ρ and the density ρ to be somewhere given by the maximum values from Baymet al.'s equation of state, i.e., ρ0=5.1×1014 g cm−3 andp0=7.4×1033 dyne cm−2, we find the maximum mass of the fluid sphere to be 2.5 solar masses.
TL;DR: In this paper, the first and second-order extinction coefficients in the UAVRI and DDO systems are derived for the first time at CASLEO, which defines an extinction curve which is discussed in the framework of atmospheric absorption theory.
Abstract: The first-and second-order extinction coefficients in theUBVRI and DDO systems are derived for the first time at CASLEO. They define an extinction curve which is discussed in the framework of atmospheric absorption theory. From this curve the first-order extinction coefficients for the Washington and Stromgren systems are inferred. From a photometric point of view, CASLEO occupies a preferred place among the observatories of the world. A comparison of theUBV extinction coefficients obtained at Bosque Alegre with previous determinations supports the conclusion that the sky transparency at this station has deteriorated in the ultraviolet in the last years.
TL;DR: In this article, it was shown that torsion-coupling constant (which depends on energy asE−2) can pass through the values of the coupling constants of the other interactions during the evolution of the universe.
Abstract: We present arguments to show that torsion-coupling constant (which depends on energy asE−2) can pass through the values of the coupling constants of the other interactions during the evolution of the Universe. An energy-dependent torsion-coupling constant helps in a natural way to understand the ratios of the coupling strengths of the different fundamental interactions.
TL;DR: In this article, a family of symmetric-periodic orbits in the three-dimensional elliptic problem with a variation of the mass ratio μ and the eccentricitye was calculated.
Abstract: With an orbit of the three-dimensional circular problem as a starting point, we have calculated families of symmetric-periodic orbits in the three-dimensional elliptic problem with a variation of the mass ratio μ and the eccentricitye. Afterwards, we have studied their evolution and stability.
TL;DR: In this article, the authors formulated the problem of the collapse of a spherically-symmetric, radiating body in general relativity and derived an analytic solution to Einstein's field equations describing the core of a collapsing star.
Abstract: In this paper we formulate the problem of the collapse of a spherically-symmetric, radiating body in general relativity. The requirement that the metric and its normal derivative be continuous across the boundary imposes conditions upon the evolution of the star and allows identification of physical phenomena measured by a distant observer. A solution to Einstein's field equations for the exterior of a spherically-symmetric radiating body is that derived originally by Vaidya in 1951. By requiring the continuity described above we identify the mass, luminosity, velocity, and time increment measured by a distant observer in terms of the metric parameters evaluated in a frame comoving with the outer boundary. We also assume that the interior metric is a sum of products of functions of the radius and time. The continuity requirements allow the evolution of two of the three functions of time to be determined. The evolution of the third function, describing the motion of the core, is determined by the imposition of an equation of state at the center. The adiabatic index derived from the Baym-Bethe-Pethick equation of state was used to provide this last equation. A major result is obtaining an analytic solution to Einstein's field equations describing the core of a collapsing star. As a consequence of this solution we found that for the relatively small values of the adiabatic index (Γmax∼1.6), the star smoothly made the transition to a final collapsed state. Neither bounce nor shock wave was obtained. Also, there is a readily understood connection between the adiabatic index, and such parameters of the edge of the core as the velocity and acceleration. Finally, the analytic solutions provide the time-scales for the collapse which are significantly different from that of free-fall. The retarding effects of pressure upon the collapse are apparent. It is hoped that such analytic solutions will provide insight into more complicated dynamic systems in general relativity.
TL;DR: Theoretical model of cylindrical MHD shock waves are presented under the action of monochromatic radiation into non-uniform stellar atmosphere with a constant intensity on unit area as mentioned in this paper.
Abstract: Theoretical model of cylindrical MHD shock waves are presented under the action of monochromatic radiation into non-uniform stellar atmosphere with a constant intensity on unit area. Gas is assumed to be grey and opaque and shock to be transparent.
TL;DR: In this paper, the authors considered the possibility of transition of the current universe expansion to contraction, based on the fact that a homogeneous universe is structured into non-homogeneous units, the latter expanding as a whole.
Abstract: The author considers the possibility of transition of the current universe expansion to contraction. The considerations are based on the fact that a homogeneous Universe is structured into non-homogeneous units, the latter expanding as a whole. An analysis of the effects of these wholes on further development shows that in the future contractions may occur only locally; however, the current spatial expansion of the Universe cannot be replaced by a global contraction.
TL;DR: In this paper, the model of the pulsar magnetosphere filled with massless charged particles (rest massm = 0) is considered. And the problem of the magnetosphere is stated mathematically in the case of oblique magnetic moment and ejection of only electrons.
Abstract: The model of the pulsar magnetosphere filled with massless charged particles (rest massm=0) is considered. The gas of charged massless particles can be found in two different phases: (1) dynamical phase (DP), when the particles move with nonvanishing energy e along some base line, determined by the electromagnetic field only, (2) statical phase (SP), when the particles have vanishing energy e=0. The pulsar magnetosphere occurs to be divided into regions of different types: (a) the accelerating regions (DP-regions) containing only DP, (b) the capture regions, containing only SP, (3) leaky capture regions, where DP moves through SP. The leaky capture regions are the active regions, which are responsible for the pulsar radioemission. In the case of oblique magnetic moment the equation for the capture surface has been obtained. The capture region is formed around this surface. Expressions for jumps of the electromagnetic field, the current density and the charge density on the capture region boundary have been obtained. The problem of the pulsar magnetosphere is stated mathematically in the case of oblique magnetic moment and ejection of only electrons.
TL;DR: In this paper, it was shown that the universe is expanding during the evolutionary phase with the limit velocity of the signal propagation, and the discovery of this fact throws a new light on a number of cosmological questions.
Abstract: From the special theory of relativity it follows that the Universe is expanding during the expansive evolutionary phase with the limit velocity of the signal propagationc. The discovery of this fact throws a new light on a number of cosmological questions.
TL;DR: For the region after the recombination era of the Universe the hydrodynamical density waves are analyzed including shear viscosity and heat conduction for ρ =ρc and ρ <ρc (ρc is the critical density of the universe) as discussed by the authors.
Abstract: For the region after the recombination era of the Universe the hydrodynamical density waves are analyzed including shear viscosity and heat conduction for ρ=ρc as well as for ρ<ρc(ρc is the critical density of the Universe). Very near to the end of the recombination era (z=1200) we find the well-known Jeans instability. It is shown that the influence of the shear viscosity on the instabilities in negligible, however, a visible influence of the bulk viscosity is present.
TL;DR: In this paper, it is shown that the latin-square algorithm is a useful estimate for the least-squares inference of the optical properties of turbid media bounded by an inhomogeneous reflecting surface.
Abstract: In a series of papers (cf. Bellmanet al., 1965a, b; Kagiwadaet al., 1975), an estimation of optical properties of turbid media has been made, in the least-squared sense, with the aid of quasi-linearization and invariant imbedding. Recently, an extension of the above procedure to the three-dimensional case with horizontally inhomogeneous albedo of the underlying surface has been attempted (Ueno, 1982). From computational aspects the numerical evaluation is not so easy, even by means of high-speed electronic computers. In the present paper it is shown that the latin-square algorithm is a useful estimate for the least-squares inference of the optical properties of turbid media bounded by an inhomogeneous reflecting surface.
TL;DR: In this paper, the authors studied the three-dimensional equilibrium points of a magnetic-binary system and developed the procedure for finding these equilibria, and then they studied their stability by using the method of the characteristic exponents.
Abstract: The author's aim has been to study the three-dimensional equilibrium points of a magnetic-binary system. First he develops the procedure for finding these equilibria, and then he studies their stability by using the method of the characteristic exponents. Finally an example in a concrete system is given to verify the described procedure.
TL;DR: In this article, photoelectric observations of the eclipsing variable TZ Bootis, obtained in 1983 and 1986, in the two coloursB andV are compared with the previous light curves of the system.
Abstract: Photoelectric observations of the eclipsing variable TZ Bootis, obtained in 1983 and 1986, in the two coloursB andV are presented: They are compared with the previous light curves of the system. The light curve changes show that the system TZ Bootis has a solar-like activity cycle with a period of 1500 days. The primary shows a transit, whereas the secondary shows an occultation minima. The maxima exhibit a large difference suggesting a large complication in the system. The (O-C) trend indicates that the period did not remain constant; a satisfactory representation of all the observed time of minimum light was obtaiend assuming a linear trend in the (O-C)s. The star may be classified to A-type W UMa systems.
TL;DR: In this article, multi-colour WBVR photoelectric observations of the eclipsing binaries IT Cas, CO Cep, and AI Hya were carried out and the photometric elements and absolute parameters of the orbits and components were obtained.
Abstract: Multi-colourWBVR photoelectric observations of the eclipsing binaries IT Cas, CO Cep, and AI Hya were carried out. The photometric elements and the absolute parameters of the orbits and components were obtained. The valuation of the angular rate of the apsidal motion of AI Hya based on the comparison of our observations with the previous photoelectric light curve of this system was derived.
TL;DR: In this article, it was shown that the planetary nebulae can be divided into three types according to the values of the mass of shell and a central star, and criteria are given using which one can determine the mass type of the nebula.
Abstract: It is shown that the planetary nebulae can be divided into three types according to the values of the mass of shell and a central star. The criteria are given using which one can determine the mass type of the nebula. The distance scale of each mass-type planetary nebulae is given. The distribution of planetary nebulae in the Galaxy, their formation rate, scale-height and other physical and kinematic characteristics are investigated. A catalogue of planetary nebulae emitting in the radio range is given.