图象的模型及其统计特性

本文对图象的统计特性及其适用模型作了分析。讨论了以前常用的平稳图象模型的缺陷,对实际图象的统计特性作了分析,认为它是非平稳的,不满足各态历经性,同时在空间上是高度相关的;讨论了相应的随机参数统计模型和描述性统计模型。指出作用于整幅图象的“全局”图象复原算法比每次只独立计算单个象元的“点”图象复原算法更为优越。     

Star-forming processes in Cepheus OB2

The properties of IRAS point sources in the region of the “Cepheus bubble” were studied. This bubble is a possible very old supernova remnant which includes the association Cepheus OB2. A large number of sources which are probably low- and medium-mass embedded stars are situated around the bubble. It is concluded that whereas high-mass stars which have formed in the bubble are already on the main sequence, lower-mass stars are still embedded in their parent clouds.     

Rotating anisotropic two-fluid magnetocharged cosmological models in general relativity

Presenting some interesting new solutions, rotating models of anisotropic two-fluid universes coupled with a magnetic field are investigated and studied, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. Here special discussion is made of the physically interesting class of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background and the second a non-comoving perfect fluid which will model the observed material content of the universe. Besides studying their physical and dynamical properties the effects of rotation on these models are studied and the reactions of the magnetic and gravitational fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are also made, in the course of which the amount of anisotropy induced in pressure distribution by a small deviation from the Friedmann metric is also investigated. The models obtained here are found to be theoretically satisfactory and thereby substantiates the possibilities of existence of such astrophysical objects in this Universe and may be taken as good examples of real astrophysical situations.     

Radiating anisotropic two-fluid model universes involving rotation in general relativity

Radiating anisotropic two-fluid model universes coupled with a scalar field when a slow rotation is introduced in them are studied here, where the anisotropic pressure is generated by the presence of two non-interacting perfect fluids which are in relative motion with respect to each other. Special discussion is made of the physically interesting class of models in which one fluid is a comoving radiative perfect fluid which is taken to model the cosmic microwave background and the second a non-comoving perfect fluid which will model the observed material content of the Universe. Here we take up four analytic solutions. The effects of rotation on these models are studied and the reactions of the scalar and the radiation fields with respect to the rotational motion are discussed. Analysis on the rotational perturbations are also made, in the course of which the amount of anisotropy induced in the pressure distribution by a small deviation from the Friedmann metric is also investigated. It is shown that such anisotropies could grow faster than the expansion of the Universe. The rotating models we obtain here are found to be theoretically satisfactory and they may be taken as physically acceptable models.     

ON NAMING METEORITES

To improve the labelling value of meteoritic names, new meteorites should be assigned geographical names which are not used for other meteorites, which are simple, and, if possible, of mnemonic value. A Committee on Meteoritic Nomenclature should be established to supervise the assignment of new meteorite names, and to assist in the work necessary to confirm that new meteorite finds are not paired with meteorites which were previously cataloged.     

The jet in M87

The jet is assumed to be ejected from the nucleus supersonically into a gas which is at rest; the knots that result are related to those which are observed and an estimate of the jet temperature follows. The magnetic field and particle density inside the jet are discussed and observations are suggested.     

Cosmological Models with Variable G and Λ

Einstein's equations with variable gravitational and cosmological constants are considered in the presence of a perfect fluid for the anizotropic Bianchi I universe in a way which conserving the energy-momentum tensor. Two solutions are found, one of which the cosmological term varies inversely with power law of time. The other of which cosmological term is constant.     

Peculiarities in the Formation of Molecular Clouds in the Central Regions of Spiral Galaxies

The limitations imposed by the shear instability on the formation of gigantic molecular clouds in the central regions of spiral galaxies are examined. The criteria obtained here are illustrated using the example of six galaxies for which the detailed rotation curves are known. The different mechanisms for formation of molecular clouds which apply in the central and edge regions of disk galaxies are evaluated.     

Deflection of jets induced by jet–cloud and jet–galaxy interactions

The model first introduced by Raga & Cantó in which astrophysical jets are deflected on passing through an isothermal high‐density region is generalized by taking into account gravitational effects on the motion of the jet as it crosses the high‐density cloud. The problem is also generalized for relativistic jets in which gravitational effects induced by the cloud are neglected. Two further cases, classical and relativistic, are discussed for the cases in which the jet is deflected on passing through the interstellar gas of a galaxy in which a dark matter halo dominates the gravitational potential. The criteria for the stability of jets due to the formation of internal shocks are also discussed.     

Search for HH-Objects and Emission-Line Stars in Star Forming Regions. I. The Lynds 1340 Dark Cloud

Spectroscopic and photometric observations of objects embedded in the L1340 dark cloud are reported. An entire series of HH-objects in the RN07 region was discovered, including new ones that form two or three flows. It is suspected that several cases of HH emission are included. In addition, 14 emission stars, of which 11 are new, were found in this region. Most of these stars are localized inside the RN07 nebula which, therefore, encompasses a compact cluster of very young stars. Other nebulous objects inside the L1340 cloud, many of which are associated with IR sources, are described. As a whole, this cloud represents an extremely active star forming region.     

A comparison of numerical integration methods in the equatorial magnetic-binary problem

In this paper we compare several Runge-Kutta type methods of fourth-order when they are applied in the Equatorial Magnetic-Binary Problem (EMBP) for which the analytical solutions are not known. The results of the comparison are presented with tables and diagrams, and the most efficient method is proposed according to the used criteria which are described.Section of Mechanics.Section of Mathematics.     

Asteroid rotation: IV. 1979 observations

Results of photoelectric lightcurve observations made during 1979 are reported. Of a total of 53 asteroids observed, reliable rotation periods are reported for 22 asteroids for which no previous values are known, 7 periods are reported which are revisions of previously reported values, and for 12 other asteroids periods are suggested which are admittedly of low reliability and those objects should be reobserved. In addition, phase relations are presented for many of the asteroids, fitted to the theoretical phase function of Lumme and Bowell (Astron. J., 86, 1705, 1981). Adopting their formalism, mean absolute magnitudes at zero phase angle, $\text{V}\text{(0°)}$, for 52 asteroids, and values of the multiple scattering parameter, Q, for 22 asteroids are reported. For comparison purposes, the absolute magnitude, V(1,0) and the linear phase coefficient, βv, in the traditional system are computed. In the appendixes (1) the methods of observation and data reduction are discussed, which are recommended to other lightcurve observers in the hope of standardizing reporting practices as much as possible; and (2) a cumulative index of all asteroid rotation data of which the authors are aware is presented.     

Variable stars in the globular cluster NGC 6362

We report the results of a CCD search for short-period variables in the field of a southern globular cluster NGC 6362. We identified 19 new candidate variables, five of which are cluster RR Lyraes, four are probable SX Phe-type stars and eight are eclipsing binaries. Of the discovered binaries, three are EA-type systems, two of which are located on the cluster CMD in the turn-off region and the third 1 mag above the turn-off point, in the yellow straggler region. Five other systems are of W UMa type, three of which are foreground objects and two are likely cluster members. The remaining two candidates exhibit a modulation of the brightness level with an amplitude of 0.1–0.2 mag; further observations are needed to reveal the nature of their variability. Phased VI light curves for 20 variables (18 RR Lyrae stars and two blue stragglers) located in the central region of the cluster are presented.     

Thermal condensations in coronal magnetic fields

Conditions under which cool condensations can form in the solar corona are investigated using the powerful phase plane method to analyse the energy and hydrostatic balance equations. The importance of the phase plane approach is that the conclusions deduced are not sensitive to the actual choice of boundary conditions adopted which only determine the actual contour. The importance of heating variations and area divergence are studied as well as the influence of gravity for their effect on the formation of cool condensations. The cool temperature at which optically thin radiation and heating balance is important and the links with other cool solutions are mentioned.     

Effects of sherically-symmetric gravitational lenses produced by galaxies and clusters

Images are considered which are produced by a spherically symmetric gravitational lens from a source of small angular size. Simple analytic expressions are derived to describe the position, amplification, shape distortion and time delay for these images provided the mass distribution of the lens corresponds to the King model. Possible types of images are analysed (single and triple images, as well as degenerate double ones at caustics) which may be formed at different positions of the observer relative to the light source and lens. The focal length of galaxies of different types is evaluated on the basis of the obtained results and the conditions are determined at which these galaxies may considerably affect the images of distant sources.     

Magnetohydrostatic structures in the solar atmosphere

Separable two-dimensional solutions to the isothermal magnetohydrostatic equations are presented which include the effect of gravity. Examples of three types of linear solution are given in which photospheric magnetic fields are prescribed and the field topologies are discussed. In addition, a new nonlinear solution is discussed. The functional form of the pressure distribution is restricted by the separable assumption. An analysis suggests that these are the only separable analytical solutions.     

Periodic orbits near infinity in the restrictedN-body problem

This paper shows that there exist two families of periodic solutions of the restrictedN-body problem which are close to large circular orbits of the Kepler problem. These solutions are shown to be of general elliptic type and hence are stable. If the restricted problem admits a symmetry, then there are symmetric periodic solutions which are close to large elliptic orbits of the Kepler problem.     

Recovery of the mean Jovian temperature structure from inversion of spectrally resolved thermal radiance data

The mean thermal structure of the Jovian atmosphere near the temperature minimum (0.1 bar) is recovered by inversion of thermal radiance data. Improvements over previous studies of this type are made in two respects. (1) Care is taken to select data sources which are on a consistent calibration scale and from a frequency region which minimizes the variance in the recovered temperature. (2) The accuracy in the temperature recovery vs the vertical resolution capability is studied quantitatively. The contributions of various sources of systematic error, which generate significant uncertainty in the recovered thermal structure, are assessed. Sources of systematic error include assumptions about the stratospheric NLTE source function, the extent of cloud cover, the methane mixing ratio, and the calibration scale. Future investigations are outlined which would reduce such uncertainties and provide consistency with a wider range of data on the Jovian upper atmosphere.