bluuebunny/crossref_metadata_2025_split huggingface dataset:
UW Persei
Authors: Richter G. A. 
Published: July 2007

AbstractVon diesem Doppelobjekt konnte die Durchsicht von 314 photographischen Aufnahmen zusätzlich zu den 3 bekannten historischen Aufhellungen kein weiteres Maximum liefern. Es gelang nicht nachzuweisen, welche der beiden Komponenten die veränderliche ist. Das UV‐Defizit der helleren Komponente macht dessen Zugehörigkeit zur Gruppe der kataklysmischen Veränderlichen nicht sehr wahrscheinlich; für die schwächere Komponente läßt sich keine Aussage machen.
AM Cas — Spectral variations during the eruption cycles
Authors: G. A. Richter , P. Notni , H. Tiersch 
Published: July 2007

AbstractSpectroscopic investigations of this dwarf nova of Z Camelopardalis type were performed during quiescence and eruption. Although over the period of spectroscopic observations the cycle‐length was only 8d.2 at times, no systematic differences to results on objects of larger cycle‐lengths could be established.
Nonlinear dynamo effects for an inhomogeneously turbulent rotating fluid
Authors: Kichatinov L. L. 
Published: July 2007

AbstractThe mean electromotive force and the turbulent stress tensor are derived for an inhomogeneously turbulent conducting fluid under global rotation. The influence of the mean magnetic field on microscale turbulence is taken into account. As a result, the coefficients of magnetic field generation and sources of differential rotation are now functions of the magnetic field; i.e. nonlinear effects are involved. Only nonlinear corrections quadratic in the magnetic field are included (weak nonlinearity). These corrections reduce the $aL‐effect of the $aL$OM‐dynamo for both slow and rapid rotation. Some astrophysical implications are discussed. It is suggested that observed torsional oscillations of the Sun may be brought about by cyclic variations of the magnetic corrections to theA‐effect of differential rotation over the solar activity cycle.
On the accuracy of the Refraction Tables of Pulkovo Observatory, fifth edition
Authors: Kurzyńska K. 
Published: July 2007

AbstractA systematic deviation has been found of the refraction given in Pulkovo Tables, fifth edition, from the standard refraction calculated for the same ground level meteorological conditions by the procedure described in one of our previous papers. This deviation, negative for zenith distances smaller than 75° and positive for zenith distances larger than 80°, is considerably greater than the error proven to be admissible for the pure refraction determined in the latter way. The value of deviation is of the order of 0″.03 already at z0 = 45°. For zenith distances smaller than 75° the deviation originates almost exclusively from unsufficiently accurate corrections for the air humidity. For larger zenith distances the deviation originates mainly from the correction for the air temperature and contributions of the remaining corrections can partly compensate for it. In conclusion a proposition of a new unique standard of the pure refraction is stated.
Report on the physical characteristics of Vaidya‐Tikekar's exact relativistic model for a superdense star
Authors: Knutsen H. 
Published: July 2007

AbstractWe report here the results of our examination of the physical properties of Vaidya‐Tikekar's model for a relativistic star. Full details will be published elsewhere. The analysis yields a strong indication that the model is stable with respect to infinitesimal radial oscillations. We find that the adiabatic speed of sound is smaller than the speed of light everywhere inside the fluid sphere if the radius of the sphere is larger than 1.46 times its Schwarzschild radius. We also find that the fluid must necessarily be supraluminal somewhere if the speed of sound is decreasing outwards close to the center. We further find that the strong energy condition is fulfilled everywhere if it is fulfilled at the center. Since the ratio of the pressure p and the density ⋅ is decreasing outwards, this indicates that the temperature gradient is negative. We also find that the relativistic adiabatic index is larger than two. Demanding the fluid to be causal, and taking the pressure and the density to be somewhere given by 7.4 ⋅ 1033 dynes/cm3 and 5.1 ⋅ 1014 g/cm3, we calculate the maximum mass of the fluid sphere to be 3 solar masses.
On Ellis' programme within fourth order gravity
Authors: Schmidt H.‐J. 
Published: July 2007

AbstractFor the non‐tachyonic curvature squared action we show that the expanding Bianchi‐type I models tend to the dust‐filled Einstein‐de Sitter model for t tending to infinity if the metric is averaged over the typical oscillation period. Applying a conformal equivalence between curvature squared action and a minimally coupled scalar field (which holds for all dimensions > 2) the problem is solved by discussing a massive scalar field in an anisotropic cosmological model.
Analysis and results of cooperative magnetographic measurements III. Vertical gradients of the magnetic field in the sunspot photosphere
Authors: Hofmann A. , Rendtel J. 
Published: July 2007

AbstractWe compare vertical gradients of sunspot magnetic fields which were derived for the first time from nearly simultaneous vector magnetograms. The measurements were obtained in the photospheric lines Fe I 5250 and Fe I 5253 by the vector magnetographs of the Sayan‐Observatory (Irkutsk) and the Solar Observatory “Einsteinturm”. The gradients derived from the different measurements show a good correspondence with respect to the numerical values as well as to the morphological structure of the distributions in the magnetograph's field of view. In the umbral region of the spot the vertical gradients amount to about 0.32 Gkm‐1 indicating that the umbral field can extend with strong field strengths into chromosphere and corona. A circle‐like area with opposite sign to the umbral gradient was found on the boundary between penumbra and surrounding photosphere. The physical significance of this area should be the goal of further observations and interpretations.Wir vergleichen Vertikalgradienten des Magnetfeldes von Sonnenflecken, die erstmals aus fast simultan aufgenommenen Vektormagnetogrammen abgeleitet wurden. Die Messungen erfolgten unter Verwendung der photosphärischen Linien Fe I 5250 Å und Fe I 5253 Å mit den Vektormagnetografen des Sayan‐Observatoriums (Irkutsk) und des Sonnenobservatoriums “Einsteinturm”. Die aus den verschiedenen Messungen ermittelten Gradienten zeigen sowohl hinsichtlich der numerischen Werte als auch bezüglich der morphologischen Struktur ihrer Verteilung im Bildfeld der Magnetografen eine gute Übereinstimmung. Im Kern des Flecks erreicht der Vertikalgradient 0,32 g kin‐1. Das weist darauf hin, daß sich das umbrale Feld mit hoher Feldstärke bis in die Chromosphäre und Korona erstrecken kann. Ein kreisförmiges Gebiet mit entgegengesetztem Vorzeichen zum umbralen Gradienten ist an der Grenze zwischen Penumbra und umgebender Photosphäre zu finden. Die physikalische Bedeutung dieses Gebietes soll durch weitere Beobachtungen und Auswertungen geklärt werden.
On a simple model for self‐regulating star formation in the galactic disk
Authors: Meusinger H. 
Published: July 2007

AbstractStar formation in galaxies is a process with feedback to the interstellar medium (ISM) and possibly it is part of a self‐regulating cycle. DOPITA (1985) proposed a model in which star formation in spiral and irregular galaxies is self‐regulated by the pressure in the ISM. In the present paper it is shown that available data for radial distributions of gas, total mass and the flux of Lyman continuum photons in the disk of our Galaxy do not support such a simple model. Several possible causes are discussed.
Rotation and free precession of the comet Halley nucleus
Authors: Möhlmann D. 
Published: July 2007

AbstractRotational properties (rotation, precession) of the nucleus of comet Halley are investigated on the basis of image processing results of VEGA and GIOTTO and a compilation of recurrence periodicity of 71 events of activity of P/Halley in 1986. It is shown that the analysis of recurrence periodicity gives strong indications for the two periods of 2.2 days and 4.9 days. These periods are well compatible with the three known positions of the nucleus of comet Halley, as they were derived from image processing of the data of VEGA‐1 and ‐2 and GIOTTO. The resulting long‐axis mode of rotation and precession can be described by a 4.9 days rotation around the long axis which is precessing once around the total angular momentum vectorMwith a period of 2.2 days and with an angle θ1= 73° between the long axis and the spatially fixedM, while the angle ω1between the vector Ω of angular velocity and the long axis is given by ω1= 52°.
Instellar extinction curves originated in single clouds
Authors: Krelowski J. , Wegner W. 
Published: July 2007

AbstractThe paper presents great differences between extinction curves derived from spectra of bright nearby stars, likely to be obscured by only single clouds. The differences concern the shapes of the curves as well as the total‐to‐selective extinction ratios (R) which, in some cases, reach the value of about 15. The changes of extinction laws coincide with those of intensity ratios of two prominent diffuse bands at 578 nm and 579.7 nm. We have concluded that physical (optical) parameters of single interstellar clouds differ seriously; interstellar absorption features observed in the spectra of heavily reddened stars are usually ill‐defined averages over many different clouds. The lack of reasonable identification of structural details of interstellar grains follows this fact. The derived individual extinction curves are proposed to be compared with theoretical or laboratory results.
Two populations of open clusters
Authors: Strobel A. 
Published: July 2007

AbstractThe paper proposes a division of the local open clusters into two different disklike subpopulations on the base of the metallicity enhancement history, spatial distribution in the Galaxy and morphology of their C‐M diagrams. The thin disk population objects exhibit higher metallicities and are more closely concentrated to the center and the disk of the Galaxy than the thick disk clusters. The former contain also frequently blue stragglers while the later exhibit the presence of Clump giant members, typical for the thick disk globular clusters. Kinematical properties of the two considered open cluster subpopulations remain unknown due to the lack of observational data.
Relationship of solar coronal millimetre wave sources to bursts in the centimetre range
Authors: Urpo S. , Teräsranta H. , Krüger A. , Hildebrandt Potsdam J. , , Ruždjak V. 
Published: July 2007

AbstractA sample of 48 observations of coronal mm‐wave (off‐limb) sources (CMMSs) has been analysed in order to check relationships to cm‐wave bursts and to study the emission process. CMMSs appear to be related to gradual and/or stronger microwave bursts with post‐burst increase which start up to a few hours prior to the time of the mm‐wave observations. The lifetime of CMMSs is much larger than that of these bursts. The interpretation of the mm‐wave emission by optically thick bremsstrahlung at the temperature Tb,o ≈ 104 K (which also corresponds to observations in Hα) requires emission measures N2e Δs ≧ 2 · 1028 cm−5 at 37 GHz. On the other hand, optically thin bremsstrahlung at temperatures of Te ≈ 5 · 106–107 K (which are observed in X‐rays) can apply to cm‐waves. Application of this mechanism to mm‐waves, too, would require source sizes much smaller than the half‐power beam width (HPBW) of the radio telescopes (so that in this case the presently observed brightness temperatures Tb,o would be underestimated).
Turbulence influenced line formation in stellar atmospheres
Authors: Stahlberg J. 
Published: July 2007

AbstractThe influence of stochastic velocity fields with finite correlation lengths on the formation of spectral lines is taken into account without restrictions to specific velocity models. To construct a perturbation theory treating the influence of stochastic motion on the radiative transfer we start with the stochastic transfer equation for plane‐parallel atmospheres and expand it to an infinite hierarchical system. An appropriate cut‐off of the infinite system admits to achieve exactly the micro‐ and macroturbulent limit at every level of approach. The formalism is derived forn‐point correlations of the absorption coefficient and specialised for 2‐point correlations.
The line‐ratio method applied to vectormagnetographic measurements
Authors: Bachmann G. 
Published: July 2007

AbstractSince solar magnetic fields are inhomogeneous, the averaging of Stokes parameter I within the entrance slit of the magnetograph is different from averaging Stokes Q0 and V, because the former contains also light from non‐magnetic, while the latter only contain light from magnetic regions. If the magnetographic calibration functions are calculated for homogeneous magnetic fields, errors arise, when they are used to reduce measurements of inhomogeneous fields. Therefore, we propose to use the line‐ratio method to transform magnetographic measurements into the parameters of the magnetic vector field. The Q ratios and the V ratios of two carefully selected lines are free from errors of this kind. This is also the case for the Q ratios in line core and line wings in single‐line magnetographs. An iterative method is presented to calculate the magnetic field parameters using the corresponding new calibration functions. An important advantage is, that the influence of scattered light in sunspots is also eliminated in a good approximation and the filling factor in plages can be estimated.This method is now used to determine magnetic vector fields in plages and sunspots of active regions with a new double‐vector magnetograph.
The asymmetry of the Coma cluster of galaxies
Authors: Baier F. W. , Fritze K. , Tiersch H. 
Published: July 2007

AbstractA detailed reinvestigation of the Coma cluster basing on enlarged observational material of number density distributions and radial velocities of galaxies as well as radio and x‐ray data is performed and supports our previous conclusion that this cluster possesses a substructure. This substructure is in the south‐western region of the cluster and produces the impression of an elongated cluster structure in the direction of the bridge between Coma and A 1367. A 1656 seems to be a cD‐like cluster with NGC 4874 as the only dominating giant central galaxy.
Mixed metric perturbations in Kaluza‐Klein cosmologies
Authors: Bleyer U. , Polnarev A. G. , Liebscher D.‐E. 
Published: July 2007

AbstractWe consider metric perturbations of Kaluza‐Klein cosmological models filled with phenomenological matter. We find the exact solution for the development in time of the mixed perturbations, which have one index in the ordinary and one in the internal space. The initial values are assumed to be taken from the results of the quantum fluctuation analysis. The contraction of the internal scales produces effectively massive field modes in the ordinary space. The comparison of this particle creation with dark matter estimations informs us about the fundamental parameters of the model.
Populations of Rydberg states of atoms in nebulae
Authors: Gulyaev S.A. , Nefedov S.A. 
Published: July 2007

AbstractPopulations of highly‐excited states of hydrogen in gaseous nebulae are calculated including effects of lowering the atomic ionization potential. Factors bn and dln bn/dn were computed for a large range of temperature and densities. Collisions only between adjacent levels (Δn = ±1) were included in the set of the statistical balance equations. Results predict the existence of a negative branch of the dln bn/dn curve. They have to be taken into account in calculating the nebulae models.
The calculation of standard coordinates in Schmidt plate astrometry
Authors: Dick W.R. 
Published: July 2007

AbstractStarting from an exact definition of the tangential point on Schmidt plates the three azimuthal projections used in Schmidt plate astrometry are compared and plate‐tilt effects, which differ from those on astrographic plates, are discussed. It is shown that the azimuthal equidistant projection should be used preferably in Schmidt plate reduction. Practical recommendations are given to minimize the number of significant terms in the reduction model.
Results of magnetographic line‐ratio measurements
Authors: Bachmann G. 
Published: July 2007

AbstractWe adapt the line‐ratio method to magnetographic measurements. The method yields information on inhomogeneous magneitc fields without resolving their fine structure. Supplementing the magnetic field measurements, each day several polarization calibrations were made to eliminate the influence of the instrument. Modified theoretical calibration curves served for the transformation into inclination angles and magnetic field strength. The circular polarization along some scans across two sunspots practically shows the same distributions in both wings. The linear polarization in these selected scans attained only about half as large values as the circular polarization. The maxima were found in the steep parts of the V distributions. Comparing the two lines a similar behaviour was found, but also differences of about 0.5 percent, which may be significant.The inclination angles determined by means of calibration curves also seem to be more accurate than those calculated from transverse and longitudinal magnetic field components. As an evidence the results in sunspots and faculae are quoted. The values separately determined for the lines scattered only by 3 respectively 7 degrees from the mean values. In the darkest points of an umbra practically accordance of inclination and heliocentric angle was obtained, i.e., the magnetic vector was directed perpendicular to the surface. From the amount of the circular polarization in faculae comparing it with results of model calculations the filling factors were determined. Our results arranged between 3 and 11 percent nearly agree with the values by SOLANKI and STENFLO (1984).The line‐ratio method in the version adapted to our magnetograph yielded from the V ratios in sunspots an average of 1880 G, but from the Q0 ratios an average of 2240 G. In faculae both values are practically identical and run to 1980 G. These results show that the line‐ratio method is superior to the old reduction procedure of magnetographic measurements.
On an alternative method for approximate solution of linear stochastic differential equations
Authors: Stahlberg J. 
Published: July 2007

AbstractAn approximate method for solving formal linear stochastic differential equations of first order is proposed. On the basis of the Reynold averaging technique, the stochastic differential equation is transformed into an infinite hierarchical system. This infinite system is cut off in such a manner that uncorrelated (totally randomly) and totally correlated stochastic processes are exactly included. By this the applicability of the Reynold method is extended.
On the total kinetic energy of our galaxy
Authors: Ninković S. 
Published: July 2007

AbstractThe total kinetic energy of the Galaxy is estimated from the potential energy by applying the virial theorem. The limits of the potential energy depend strongly on the value of the local escape velocity. They are estimated to be between −7. 1016 MȮ km2s−2 and −1. 1016 MȮ km2s−2 (escape velocity approximately between 450 km s−1 and 600 km s−1). The specific kinetic energy of the Galaxy as a whole is most likely about 21 000 km2s−2, being equally distributed among the subsystems if the local escape velocity is near its lower limit; the higher the local escape velocity is, the higher is the specific kinetic energy of the Galaxy due to the influence of the dark corona. The specific kinetic energy of the dark corona tends to become equal to that of the Galaxy as a whole for very high values of the local escape velocity. For the purpose of estimating the totl potential energy of the Galaxy, inter alia, a new model of the Milky Way is developed, which yields both the potential and the density analytically so that it is suitale for calculating the galactocentric orbits.
Nearby galaxies. I. The catalogue
Authors: Schmidt K.‐H. , Boller T. 
Published: July 2007

AbstractThe data of 289 nearby galaxies have been compiled. The inclusion of a galaxy into the catalogue depends on its redshift as in the catalogue of Kraan‐Korteweg and Tammann (1979) (vLG = 500 kms−1) or on the fact that the objects are known to be certain or probable members of nearby groups. The galaxies in the sample form the Local Group with 51 certain und probable members and several additional groups. One third of the galaxies in the catalogue (96 objects) does not seem to belong to any group.The main emphasis is to get a distance‐limited sample of galaxies, especially of dwarf objects. It is intended to discuss the properties of the sample in a following part of the investigation.
Orbits in an anisotropic radiation field
Authors: Mioc V. , Radu E. 
Published: July 2007

AbstractThe elliptic‐type motion around a source whose luminosity is anisotropic is being perturbatively treated. Using a Fourier expansion for the perturbing force, exact expressions describing the evolution of each orbital element are determined from Newton‐Euler equations. For near‐unit frequency the resonant solutions are pointed out. An approximate expression for the variation of the nodal period is determined, too. The behaviour of the radius vector of the unstable orbit (resonance case) is pointed out, showing periodic variations of constantly increasing amplitude. The (both angular and physical) time scale for escape is estimated. Concrete astronomical situations modellable in this way are mentioned.
Minor planet observations 1984‐1990
Authors: Fogh Olsen H. J. 
Published: July 2007

AbstractAn overview of the minor planet search performed in the period 1984–1990 at Brorfelde Observatory is presented. All basic information about the observations is given but the positions are not presented because they are already published in Minor Planet Circulars. 1973 positions have been measured on 413 plates. 303 positions belong to unknown minor planets. At the end of 1992, 42 of these are numbered, having got enough observations to calculate a reliable orbit.
Variations of the solid Earth's center of mass due to oceanic tides
Authors: Brosche P. , Wünsch J. 
Published: July 2007

AbstractPeriodic variations in the location of the center of mass of the solid Earth due to ocean tides are derived from the ocean tide model of Seiler (1991). The sum of nine partial tides leads to changes in the coordinates X, Y, Z within a range of 1cm.
Rapid oscillations of five stars in the spectral range G and K. II
Authors: Hildebrandt G. 
Published: July 2007

AbstractThe five stars HD 11112, HD 170747, HD 186651, HD 205390 and HD 224834 are a second group of objects enclosed in a larger observational programme for the search of rapid oscillations. They have been observed with the 50 cm photoelectrical ESO telescope at La Silla (Chile). For the star HD 205390 a variation of 163.8 min was found. The two objects HD 11112 and HD 186651 are suspected to be variable with periods of 139 min and 142.2 min and its overtones, respectively. But a verification of these results is necessary. For the last two objects HD 170747 and HD 224834 no variations were detected.