Kinematics in the z = 2.81 Galaxy and the Evidence for Rotation     

Milan M. Ćirković 《Astrophysics and Space Science》2003,283(2):273-277

The existence of rotation signatures in damped Lyαabsorption systems represents a crucial test of the hypothesis that these features arise in disks of normal spiral galaxies. We apply the method for evaluating such signatures to the metal absorption lines in QSO 0528-250. In particular, the systemic redshift of the absorber is inferred from the recent detection of emission in the absorber by Möller and Warren. The kinematics of this absorber are particularly interesting because molecular hydrogen, the densest ISM component of the assumed foreground absorbing galaxy, is detected. Contrary to a recent claim, the method yields a satisfactory value for the assumed rotation velocity of the absorber.  相似文献   

The carbohydrates in relation to mineralogic and granulometric composition of surface sediments in the karst estuary (River Krka estuary,Yugoslavia)     

Olga Hadz̆ija  Mladen Jurac̆ić  Marija Luić  Maja Tonković  Biserka Jeric̆ević 《Estuarine, Coastal and Shelf Science》1985,21(5):701-709

The investigation of mineral, granulometric and chemical composition of sediments of the River Krka estuary (Yugoslavia) were performed in order to elucidate the origin of the sediments and the pattern of sedimentation. Estuarine surface sediments were found to be fine-grained with a bimodal distribution. Environmental conditions in estuarine sediments favour conservation of the organic matter (anoxic conditions). The carbohydrates in the sediments were investigated to determine whether they are of terrigenous or authigenous origin. Glucose, galactose, mannose, xylose, rhamnose, glucosamine and glucuronic acid were detected in the sediments. Their mutual relationship indicates a preferentially terrigenous source of sedimented organic material in estuarine sediments.  相似文献   

Minor planet short periodic perturbations: The indirect part of the disturbing function     

Zoran Knežević 《Celestial Mechanics and Dynamical Astronomy》1993,55(4):387-404

Leverrier's development of the indirect part of the disturbing function has been extended to include terms up to degree 4 in eccentricity and inclination; the resulting series has been expressed with respect to a fixed plane, and in a computer readable form (a list of integers). Tests have been performed for the relative significance of the terms of degrees 2, 3 and 4, and estimates have been obtained for the accuracy of the short periodic perturbations of a minor planet, and of the corresponding mean orbital elements. It was found that: (i) even in extreme cases, the indirect part of the disturbing function gives rise to very small short periodic perturbations; (ii) bodies of very high eccentricity/inclination and those close to mean motion resonances are most significantly affected; (iii) indirect perturbations for minor planets can be computed up to the degree 2 terms only, without any significant loss of accuracy; and (iv) higher degree indirect perturbations appear to be important only for their contribution to the long periodic effects of higher order (with respect to the perturbing mass).  相似文献   

Application of the global modal approach to the spiral galaxies     

Natalia Orlova  Vladimir Korchagin  Nobuhiro Kikuchi  Shoken. M. Miyama  Aleksei Moiseev 《Astrophysics and Space Science》2003,284(2):739-742

We have tested the applicability of the global modal approach in the density wave theory of spiral structure for a sample of spiral galaxies with measured axisymmetric background properties. We report here the results of the simulations for four galaxies: NGC 488, NGC 628, NGC 1566, and NGC 3938. Using the observed radial distributions for the stellar velocity dispersions and the rotation velocities we have constructed the equilibrium models for the galactic disks in each galaxy and implemented two kinds of stability analyses - the linear global analysis and 2D-nonlinear simulations. In general, the global modal approach is able to reproduce the observed properties of the spiral arms in the galactic disks. The growth of spirals in the galactic disks can be physically understood in terms of amplification by over-reflection at the corotation resonance. Our results support the global modal approach as a theoretical explanation of spiral structure in galaxies. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Deuterated hydrogen molecule and search for early structure-formation signatures in the Universe     

Ramona Núñez-López  Anton Lipovka  Vladimir Avila-Reese 《Monthly notices of the Royal Astronomical Society》2006,369(4):2005-2012

Possible detection of signatures of structure formation at the end of the 'dark age' epoch  ( z ∼ 40–20)  is examined. We discuss the spectral–spatial fluctuations in the cosmic microwave background radiation (CMBR) temperature produced by elastic resonant scattering of CMBR photons on deuterated hydrogen (HD) molecules located in protostructures moving with peculiar velocity. Detailed chemical kinematic evolution of HD molecules in the expanding homogeneous medium is calculated. Then, the HD abundances are linked to protostructures at their maximum expansion, whose properties are estimated by using the top-hat spherical approach and the Λ cold dark matter (ΛCDM) cosmology. We find that the optical depths in the HD three lowest pure rotational lines for high-peak protohaloes at their maximum expansion are much higher than those in LiH molecule. The corresponding spectral–spatial fluctuation amplitudes, however, are probably too weak to be detected by current and forthcoming millimetre telescope facilities. We extend our estimates of spectral–spatial fluctuations to gas clouds inside collapsed CDM haloes by using results from a crude model of HD production in these clouds. The fluctuations for the highest peak CDM haloes at redshifts ∼20–30 could be detected in the future. Observations will be important to test model predictions of early structure formation in the Universe.  相似文献   

Declination variations for zenith stars     

R. Grujić  G. Teleki  B. Jovanović 《Astrophysics and Space Science》1991,177(1-2):373-376

The variations of the declinations of 36 Belgrade zenith stars from BZS1₇₀ Catalogue published in Astronomy and Astrophysics,177, 313–316 (1987) are examined by spectral analysis. The prospect is to evaluate multiples of the Chandler period of which the most prominent for all stars is the double one.  相似文献   

Exponential distance relations in planetary-like systems generated at random     

Vladimir Pletser 《Earth, Moon, and Planets》1988,42(1):1-18

It is often thought that the exponential distance relations that can be found amongst the distances of the planets and of the satellites of Jupiter, Saturn, and Uranus, of the form a _n = ⁿ , with a _n being the semi-major axis of the n ^th body, can be similarly represented by sequences of sorted random numbers generated with some constraints corresponding to certain physical processes. We give in this paper some indications showing that pure chance or random processes only cannot explain the planetary and satellite distance distributions, in particular the exponential spacings, by comparing the distance relations of the real systems to these of planetary-like systems generated at random.Exponential distance relations for the present planetary and satellites systems of Jupiter, Saturn and Uranus are described, considering the two cases without and with introduction of holes for the large spacings observed in the sequences of bodies.Random systems are created by generating distances at random following uniform, normal and exponential distributions, with no consideration for other orbital elements or masses as we are only interested in distance relations. Random systems without constraints are first compared to the real systems. In a following step, random systems with a corresponding number of bodies to that of the real systems and with the constraint of having a number of large spacings equivalent to that of the real systems are investigated. In a later step, we impose on the generation process the additional constraint of the closeness not too close condition, i.e. for the random systems to have distances between adjacent bodies greater than critical attraction distances calculated by considering the present masses of the real main planets and satellites.Comparisons of the regression coefficients means of the exponential distance relations of random systems to the characteristics of the real systems show that there are significant differences, in particular the coefficients of the random systems are on average smaller than for the corresponding real systems, except for some particular cases which are shown not to be significant.It is concluded that distance relations observed in the present real systems can not be compared to sequences of sorted random numbers. Furthermore, additional physical processes other than the closeness not too close, have to be considered to explain the observed distance relations and in particular the exponential spacings.  相似文献   

An estimate of the contribution of high nergy cosmic-ray protons to the absorbed dose inventory of a cometary nucleus     

M. P. Ryan Jr.  I. G. Draganić 《Astrophysics and Space Science》1986,125(1):49-67

We discuss the contribution of cosmic-ray protons at all energies above 1 MeV to the absorbed doses of the surface layers of a comet. Since there exists no calculation which takes into account proton energy losses by means of losses to electrons and nuclear collisions (in a cascade process), and losses due to the low energy end-products of the cascade, we have made a rough estimate of all of these contributions. An analytical formula is proposed that allows a rapid estimate of ranges and the dose absorbed at any depth. We give dose-depth curves for two extreme values of the energy at which nuclear collisions begin to dominate the slowing-down process, and for an intermediate value we display the dose-depth curve down to 20 m from the surface. The relevance of these findings to dosimetry in comets and some alterations of cometary material are considered. The need for improving the analytical expression proposed is stressed.  相似文献   

The magnetic and thermodynamical structure of a coronal hole     

Vladimir A. Osherovich  Erast B. Gliner  Israel Tzur  Michael L. Kuhn 《Solar physics》1985,97(2):251-266

A nonpolytropic model of a polar coronal hole at 2 R R 5 R is constructed. Our main assumptions are: (1) the magnetic structure of the Sun can be described by a combination of dipole-like and radial fields; (2) in the magnetically dominated region [(v ²/2) < (B ²/8)] the influence of the outflow on the magnetic structure is negligible. The magnetic and thermodynamic structures are obtained by solving the force balance equation for plasma with the observationally derived electron density. Profiles of velocities in the acceleration regime are presented and the influence of the outflow on the thermodynamic structure of the solar corona above the polar region is discussed.This paper is the first part of a joint project of the Space Environment Laboratory, the Joint Institute for Laboratory Astrophysics, and the High Altitude Observatory, NCAR. The second paper by Munro and Tzur is in preparation.Work done while at the Space Environment Laboratory, NOAA, ERL, Boulder, CO 80303, U.S.A.1982–83 Visiting Fellow at the Joint Institute for Laboratory Astrophysics, National Bureau of Standards and University of Colorado.The National Center for Atmospheric Research is sponsored by the National Science Foundation.Visitor at NCAR.  相似文献   

Multiple discriminant analysis of the Drava River alluvial plain sediments     

Zoran Peh  Robert Šajn  Josip Halamić  Lidija Galović 《Environmental Geology》2008,55(7):1519-1535

Three discriminant function models are raised and cross-compared in order to distinguish geochemical patterns characteristic for the Drava River floodplain sediments. Based on data representing total element concentrations in samples collected from alluvium (A), terrace (T), and unconsolidated bedrock (B) at the border of a floodplain, four element clusters emerged accounting for discrimination between the referred groups of sediments. The most prominent is contaminant/carbonate cluster characteristic for alluvium. The other two are: silicate cluster typical for unconsolidated geological substrate (Neogene sedimentary rocks); and naturally dispersed heavy metal cluster separating terrace from the former two groups. Models introducing depth intervals and single profiles as grouping criteria reveal identical sediment-heavy metal matrices. The second important issue of this paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments, based on established geochemical pattern. The mapped geological units can be reconsidered by the post hoc assignments to a different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically with absolute certainty.  相似文献