bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accretion disks in bimetric theory of gravitation. A strong field test of general relativity?
Authors: Paul H. G. 
Published: July 2007

AbstractThe sensitivity of accretion disk models with respect to its inner boundary conditions, being located in the strong gravity region of a highly compact central body, is used to discuss a possibility of strong field tests of gravitation via compact source observations. Within the bimetric theory of gravitation the optically thin bremsstrahlung model is calculated as an example for this possibility. Using this model to describe the innermost region of the “bimetric disk”, significant differences with respect to the corresponding results in Einstein's theory were found. The more massiv and compact “bimetric disk” radiates softer with higher luminosity.
S‐matrix approach to interacting quantum field theory in curved space‐time1)
Authors: Audretsch J. 
Published: July 2007

AbstractWe give an analysis of mutually interacting quantum fields in given unquantized Robertson‐Walker universes using an S‐matrix approach. Transition probabilities and particle number mean values are discussed in detail with the intention to read off the underlying physics and to apply them to scattering and decay processes.
Einstein‐Gleichungen mit Zusatztermen 4. Ordnung und Raum‐Zeit‐Modelle vom Bianchi‐Typ I
Authors: John R. W. 
Published: July 2007

AbstractDie Einsteinschen Gleichungen, verallgemeinert durch additive Terme, die Ableitungen der Metrik bis zur 4. Ordnung enthalten, werden im Vakuum‐Fall auf kosmologische Raum‐Zeit‐Modelle vom Bianchi‐Typ I angewandt.
Definitive orbit of minor planet (29) Amphitrite from 91 oppositions 1825‐‐1985 and a new determination of the mass of Jupiter
Authors: Schmadel L. D. 
Published: July 2007

AbstractMinor planet (29) Amphitrite will serve as a target for the first asteroid flyby with NASA spacecraft Galileo on December 6, 1986. It also represents a first priority object for solar system observations with the ESA astrometry satellite Hipparcos which is scheduled to be launched in 1988. In order to meet the high astrometric accuracy requirements, a definitive orbit based on 1,577 observations from 91 apparitions covering the time span 1825 to 1985 is evaluated. (29) Amphitrite moves near to the 3:1 resonance to Jupiter and seems particularly suited for a new determination of the mass of the Jupiter system. A most probable mass value of 1/(1047.369±0.029) solar masses is obtained and the relaibility of this result is discussed.
Distribution of luminous blue stars in M33
Authors: Ivanov G. R. , Kunchev P. Z. 
Published: July 2007

AbstractM33 luminous stars with MV ≲ ‐7 and U‐‐B < o are selected in this paper. The spatial distribution of the stars shows a good agrement with the associations and HII regions. However HII regions are absent in the three youngest associations in M33 (t ≈ 5 ÷ 7 × 10yr). It is supposed that the true distance modulus of M33 derived from the brightest blue stars is 24.2. An age gradient across the arms is absent. The spiral arms outlined by the luminous stars differ form those in M31. They are diffuse and wide. The multiarm features of M33 support the stochastic self‐propagating model.
Die Hadamard‐Konstruktion Greenscher Funktionen auf gekrümmter Raum‐Zeit: Physikalische Zusammenhänge und explizite strenge Resultate
Authors: John R. W. 
Published: July 2007

AbstractZunächst wird die mathematisch‐physikalische Bedeutung kovarianter Greenscher Funktionen im relativistischen Gravitationsfeld‐gemäß EINSTEIN: auf gekrümmter Raum‐Zeit‐in Verbindung mit ihrer Konstruktion nach HADAMARD erörtert. Sodann werden für den Fall einer allgemeinen statischkugelsymmetrischen Raum‐Zeit die Konstruktionsgleichungen für eine skalare Greensche Funktion in symmetrieangepaßte Form gebracht, was einen günstigen Ausgangspunkt zur expliziten Berechnung der Hadamard‐Bauelemente gibt. Bei Anwendung der so gewonnenen Grundgleichungen auf eine spezielle einparametrige Schar von Modell‐Metriken gelingt es, bis zur expliziten strengen Berechnung von Schweifterm‐Koeffizienten einer masselosen Greenschen Funktion vorzudringen; sie sind zugleich Koeffizienten in der Schwinger‐DeWitt‐Entwicklung des Feynman‐Propagators zur entsprechenden Ruhmasse enthaltenden Klein‐Gordon‐Gleichung auf gekrümmter Raum‐Zeit.
The interstellar 217 nm band: a third catalogue of equivalent widths
Authors: Friedemann C. , Röder U.‐K. 
Published: July 2007

AbstractUsing the data obtained with the ultraviolet photometer in the Astronomical Netherlands Satellite the equivalent widths of the interstellar 217 nm band as well as other parameters characterizing the behaviour of the continuous interstellar extinction in the wavelength region of the band have been derived for 790 O, B stars with colour excesses E(B ‐ V) ≥ 0·4 mag.
The cycle length of the U Geminorum star HT Cassiopeiae
Authors: Wenzel W. 
Published: July 2007

AbstractThe mean cycle length of the catalysmic binary HT Cas, which is remarkable because of the shortness of its orbital period, has been determined as 400d±50d. The hitherto assuixed value of 30d proved unfounded. Some aspects arising when classifying long‐cycle objects and SU Ursae Majoris variables are pointed out, a s well as the relation between large cycle length and small accretion rate.
Determination of gravitational potential for axisymmetric mass‐distribution. IV. Some hydrodynamical test results
Authors: Tschaepe R. 
Published: July 2007

AbstractEconomy of computing the gravitational potential for quasihydrostatic and hydrodynamical models, respectively, (axisymmetric mass distribution in spherical coordinates) suggests the application of the successive overrelaxation method in spherical coordinates, because a good approximation of potential from a previous cycle leads to the wanted solution by means of only few iterations.
Monopole abundance from first‐order GUT phase transition of the early Universe
Authors: Bagoly Zs. , Lukács B. , Paál G. 
Published: July 2007

AbstractMonopole annihilation and pair creation are investigated in a first order GUT symmetry breaking phase transition without inflation. It is found that even with complete initial monopole suppression, some monopoles are inevitably produced during the transition. According to this, some constraints are obtained for initial and equilibrium monopole densities in order to be compatible with the present observational limits even without inflation.
Comparing selfinteracting scalar fields and R + R3 cosmological models
Authors: Schmidt H.‐J. 
Published: July 2007

AbstractWe generalize the well‐known analogies between m2φ2 and R + R2 theories to include the selfinteraction λφ4‐term for the scalar field. It turns out to be the R + R3 Lagrangian which gives an appropiate model for it. Considering a spatially flat Friedman cosmological model, common and different properties of these models are discussed, e. g., by linearizing around a ground state the masses of the resp. spin 0‐parts concide. Finally, we prove a general conformal equivalence theorem between a Lagrangian L = L(R), L′L″ ≠ 0, and a minimally coupled scalar field in a general potential.
On the mechanism of the “Noisar” phenomenon in magnetic close binary systems
Authors: Andronov I. L. 
Published: July 2007

AbstractThe mechanisms of “Noisar” phenomenon in AM Herculis‐type stars are discussed. In an accretion column above the surface of the magnetized degenerate star the instability of some types may be excited, such as axi‐symmetrical quasi‐periodical penetration of the low‐density “bulks” from the column axis to the outer parts; “boiling” with “bulks” moving inside or outside the column; “tornado” with low‐density region rapidly rotating around the column axis; “switchings” of the accretion from one half of the “polar cap” to another and vice versa. The oscillations of different plasma clots (“spaghetti”) may interfer causing flux changes as well. Such “Noisar” oscillations appear in different regions of the accretion column (at the upper shock and near the column base, respectively), so hard and soft X‐ray fluxes might not have correlation in their variability. The observations are in qualitative agreement with the models.
V 361 Lyrae: An exotic binary system with a “Hot Spot” between the components?
Authors: Andronov I. L. , Richter G. A. 
Published: July 2007

AbstractA phenomenological model for V 361 Lyr is proposed. Probably it is a binary system which consists of a mass accreting primary star with mass of about M1 ≈ 0·81 M⊙ and radius R1 ≈ (6.1 ± 0·4) · 1010 cm and a mass losing secondary with about M2 ≈ 0·77 M⊙ and R2 ≈ 5.8 · 1010 cm. The secondary fills its Roche lobe, but the primary is something smaller than this lobe, contrary to the models of W UMa‐type systems. So the hot spot appears in the atmosphere of the primary, but not in a disk, like in cataclysmic variables. The luminosity of the hot spot, L = (6‐15) · 1032 erg/s, is large enough to be the main emission source of the system in visible light. So phenomenologically the object may be somewhat between W UMa‐type stars and cataclysmic variables.
The interpretation of oscillations in sunspot umbrae
Authors: Žugžda Y. D. , Locāns V. , Staude J. 
Published: July 2007

AbstractWe review possibilities for an interpretation of oscillations observed in several period bands (3 min., 5 min., 20 min.) and at different heights in sunspot umbrae. At subphotospheric depths two independent resonators are acting: A resonator for slow, quasi‐transverse waves can explain the lifetimes of bright umbral dots (≥20 sec.), while a resonator for fast (acoustic), quasi‐longitudinal waves could result in the 5‐min. oscillations. The acoustic resonator strongly couples with the slow‐mode longitudinal resonator at photospheric and chromospheric heights, the latter produces the resonance peaks in the 3‐min. period band. The whole scheme of resonance levels generalizes and corroborates a chromospheric resonator model earlier proposed by the present authors. Comparisons with alternative models and recent measurements show that the present model most naturally explains the majority of observed data.
The LMC supernova (SN 1987 A) as a probe for the outcome of stellar collapse
Authors: Haubold H.‐J. , Gottlöber S. , Mücket J. P. , Müller V. , Kämpfer B. 
Published: July 2007

AbstractImplications from the available information on the supernova SN 1987 A are discussed for the supernova models. We derive an upper bound of 10–25 eV for the neutrino rest mass.
Phenomenological models of cosmic phase transitions
Authors: KÄmpfer B. 
Published: July 2007

AbstractPhenomenological models of cosmic phase transitions are presented. We consider phase transitions (i) with fixed initial and final states or (ii) in the relaxation time approximation. The Friedmann equations are solved and the entropy production due to the non‐equilibnum transition is calculated for a bag model equation of state. Numerical examples are given for the confinement transition, but the formulae presented apply directly to the GUT transition, too.
On spinor field equations of BUCHDAHL and WÜNSGH
Authors: Illge R. 
Published: July 2007

AbstractThe field equations of BUCHDAHL and WÜNSCH for the description of fields of particles with nonzero rest mass and arbitrary spin in curved space‐times are considered. The Lagrangian, the field equations and the energy‐momentum tensor for fields of integer spin are formulated by means of real tensor fields.
The formation of primordial stars triggered by the evolution of large‐scale density perturbations
Authors: M$Uucket J. P. , Haubold H. J. 
Published: July 2007

AbstractThis paper summarizes the basic idea of coupling of density perturbation modes in Newtonian cosmology and the formation of primordial stars. The way of deriving the second‐order differential equation governing the growth of two coupled adiabatic density perturbation modes in the matter era is briefly discussed. A Jeans criterion for the growth of short wavelength perturbations is given. A mechanism is proposed for the cosmological origin of Population III stars.
Semiregular variable RX Bootis: Double‐period optical variation of a cosmical maser?
Authors: Andronov I. L. , Kudashkina L. S. 
Published: July 2007

AbstractPeriodogram analysis of 349 photovisual observations showed the peaks corresponding to periods 352 ± 5d, 179.1 ± 0.3d and 162.4 ± 0.8d. The first value is very close to 1 year, so it might not be justified by the present observations. The other two values obtained by ‘two‐parameter’ search seem to be independent periods, but not the effect of ‘observational windows’. No other significant peaks were detected in the interval from 65d to 100d.
Analysis and results of cooperative magnetographic measurements. I. Correction, comparison and discussion of measurements
Authors: Hofmann A. , Grigorjev V. M. , Selivanov V. L. , Klvana M. 
Published: July 2007

AbstractOn June 24, 1983 cooperative magnetographic measurements were made with the vectormagnetographs of the Sayan Observatory (Irkutsk) and the Potsdam Solar Observatory “Einsteinturm” and with the longitudinal magnetograph of the Ondrejov Observatory. Additionally, the maximum field strengths in the sunspot were measured with the photographic method. Using the photographically measured field strengths as reference values we provide a method to eliminate the influences of stray light in a time series of vectormagnetograms. A comparison of nearly simultaneous magnetograms shows a good correspondence in general. The deviations of the zero points as well as the scales are comparable with the results of other authors. Regarding the magnetic field distribution the magnetograms reflect a substantial nonsymmetric structure in the spot under study. The magnetic field lines tend to concentrate into several flux tube clusters. In one region of the penumbra we find a magnetic field with nearly longitudinal character in close neighbourhood of a strong, nearly horizontal flux tube bundle. This indicates a strong nonradial horizontal field gradient in the penumbra.
Particle content and degrees of freedom of a gravitational field in 4th order theories of gravity
Authors: M$Oubius K. 
Published: July 2007

AbstractIn gravitational theories of 4‐th order, the influence of certain properties of the field equations (tracelessness, conformal invariance, scale in variance respectively their breaking) for the “particle content” (number of degrees of freedom, mass, spin) is investigated. Using the plane‐wave ansatz valid in linearized theory it is possible to determine the mass content of the theory, but one cannot get assertions about the number of degrees of freedom and the spin states corresponding to the field quanta. In the linearized theory, this can be done with a spin projection formalism.Using the Cauchy initial value problem and a counting method first developed by EINSTEIN one can get, however, a useful definition of the concept of the degrees of freedom for the full nonlinear theory. This is due to the fact that this method allows to incorporate the concrete structure of the field equations (and thus their nonlinearities). Analysing different general‐relativistic field theories via these approaches the influence of the various structures of nonlinearities is discussed. It is, in particular, shown that those results obtained by the spin projection formalism can be reproduced by “nonlinear methods”.
Analysis and results of cooperative magnetographic measurements. II. Comparison and interpretation of the current densities
Authors: Hofmann A. , Grigorjev V. M. , Selivanov V. L. 
Published: July 2007

AbstractWe compare and interpret distributions of vertical electric current densities derived from nearly simultaneous vector measurements by the magnetographs of the Sayan Observatory (Irkutsk) and the Potsdam Solar Observatory. The derived distributions of current densities of the different observations are in good agreement referring to the scaling factors and the morphological structure. The zero points differ within the noise level amounting to 0.8 * 10‐3 Am‐2 for the Sayan observation and to 1.3 * 10‐3 Am‐2 for the Potsdam observation. In the spot under study we found several current filaments indicating that the spot is clustered by several flux bundles. An azimuthal current between (5.9 ± 1.4) * 1011 A and (6.8 ± ± 1.5) * 1011 A flowing around a (relatively isolated) flux bundle can be derived from the observations.
Catalogue of Abell clusters of galaxies with published photometric data
Authors: Baier Potsdam‐Babelsberg F. W. , Ziener Tautenburg R. , 
Published: July 2007

AbstractThis catalogue is a compilation of references of publications with photometric data in and around Abell clusters of galaxies.Die Arbeit enthält eine Zusammenstellung der Publikationen mit photometrischen Daten für Abell‐Haufen und ihre Umgebung.
Numerical simulation of colour equations for the uvby system
Authors: Reimann H. G. , Böhm M. , Pfau W. 
Published: July 2007

AbstractThe results of numerical simulation of colour equations of uvby photometry for filter‐defined bandpasses are presented. It is shown that linear transformation equations to the standard system are valid for instrumental systems deviating by no more than 2.5 nm in peak transmission wavelengths. The comparison with the results of observations is satisfying.Im Ergebnis einer numerischen Farbgleichungssimulation im uvby‐System wird nachgewiesen, daß für Instrumentensysteme mit Abweichungen der Wellenlängen maximaler Transmission bis zu 2.5 nm gegenüber den Standardwerten eine lineare Transformation möglich ist. Der Vergleich mit Beobachtungsresultaten zeigt eine gute Übereinstimmung.
Beobachtungen Kleiner Planeten. VIII
Authors: Börngen F. 
Published: July 2007

AbstractEs wird eine Übersicht gegeben über die im Jahr 1987 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten. Es wurden 290 Objekte entdeckt und für diese 845 Positionen gerechnet. Es handelt sich um 75 numerierte Objekte, von denen drei auf der kritischen Liste von EMP 1988 stehen, sowie um 215 Planetoiden mit provisorischen Bezeichnungen. Von letzteren erhielten 191 neue Bezeichnungen. Für 17 im Berichtszeitraum numerierte Planeten haben Tautenburger Beobachtungen einen Beitrag geleistet. Darunter sind zwei in Tautenburg entdeckte Planetoiden: 1967 GF1 erhielt die Nummer (3539) und den Namen Weimar, der Trojaner 1973 UF5 die Nummer (3540) und den Namen Protesilaos.A summary is given about the Minor Planet survey performed in 1987 on Tautenburg Schmidt plates. There were discovered 290 asteroids and calculated 845 positions for them. These are 75 numbered objects and 215 asteroids with provisional designations, 191 of them have new designations. Tautenburg observations could give a tribute to 17 planets numbered in the period of this report, including two asteroids discovered in Tautenburg: 1967 GF1 received the number (3539) and the name Weimar, the Trojans 1973 UF5 the number (3540) and the name Protesilaos.
Cosmic strings and strings in gravitational waves
Authors: Schmidt H.‐J. , Semmelmann U. 
Published: July 2007

AbstractWe consider strings with the Nambu action as extremal surfaces in a given space‐time, thus, we ignore their back reaction. Especially, we look for strings sharing one symmetry with the underlying space‐time. If this is a non‐null symmetry the problem of determining ihc motion of the string can be dimensionally reduced. We get exact solutions for the following cases: straight and circle‐like strings in a Friedmann background, straight strings in an anisotropic Kasner background, different types of strings in the metric of a gravitational wave. The solutions will be discussed.Wir betrachten Strings mit der Nambu‐Wirkung als Extremalflächen in einer gegebenen Raum‐Zeit, d. h., wir ignorieren ihre Rückwirkung. Wir interessieren uns dabei besonders für solche Strings, die eine Isometrie mit der unterliegenden Raum‐Zeit gemeinsam haben. Handelt es sich dabei um eine nicht‐lichtartige Symmetrie, so läß Bt sich das Problem der Bestimmung der Stringbewegung dimensionsreduzieren. Wir erhalten exakte Lösungen für die folgenden Fälle: gerade und kreisrunde Strings im Friedmann‐Hintergrund, gerade Strings im anisotropen Kasner‐Hintergrund sowie verschiedene Stringtypen in der Metrik einer Gravitationswelle. Die Lösungen werden diskutiert.
On the discovery of the Apollo object 1987SB
Authors: Elst E. W. , Ivanova V. , Shkodrov V. 
Published: July 2007

AbstractOn september 22nd, 1987, a fast moving object of 17th magnitude was discovered at the Bulgarian National Observatory by ELST, IVANOVA, and SHKODROV (1987). Due to international collaboration the Apollo‐type asteroid 1987SB could be followed up to the 15th January 1988.
K 23 — a spatially isolated low surface brightness dwarf galaxy?
Authors: Bronkalla W. , Richter G. M. , Karachentsev I. D. , Karachentseva V. E. 
Published: July 2007

AbstractThe attention is called to a relatively rare case of an apparently “isolated” dwarf spheroidal galaxy K 23 (α = 02h40m.5, δ = +16·31'). The large‐scale plates obtained with the 6 m telescope have been scanned, and the photometric data and King model parameters determined. According to these data K 23 is similar to the well‐known prototypes in the Local Group and M 81 group.An analysis of the spatial galaxy distribution shows, that K 23 is probably placed in the bridge connecting the Local Supercluster and Perseus‐Pisces Supercluster and is not truely spatially isolated.
Equilibrium flavor dynamics during the cosmic confinement transition
Authors: Kämpfer B. 
Published: July 2007

AbstractThe dynamics of the flavor composition of strongly interacting matter during the cosmic confinement transition is followed in a simplified thermodynamical model. Relying on thermal, mechanical, and chemical equilibrium we analyse the strangeness fraction of strongly interacting matter. Due to equilibrium with respect to ΔS = 0 and ΔS = 1 weak interactions the relations between different flavors depend strongly on the poorly known lepton excess. In a universe where the lepton (antilepton) excess is in the same order of magnitude as the baryon excess, the strange quark abundances are suppressed (enhanced). In the hadron phase the strange baryons carry up to a half of the baryon excess.
Influence of rotational darkening on ultraviolet interstellar extinction
Authors: Friedemann C. 
Published: July 2007

AbstractThe influence of rotational darkening on ultraviolet stellar fluxes of fast rotating stars has been rediscussed. For this aim ANS filter‐photometric magnitudes of weakly reddened B stars (E(B ‐ V) 0.1 mag) were corrected for interstellar extinction. The distribution of the stars in the rotationa velocity — colour index diagrams displays a scatter exceeding the photometric errors. The distributions of the stars agree qualitatively with the theoretically calculated colour indices.The effect of rotational darkening should be taken into account as a possible source for individual deviations of the interstellar extinction from the average law.