bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the properties of very young massive infrared sources (Mitteilungen der Universitäts‐Sternwarte zu Jena Nr. 169)
Authors: Gürtler J. , Henning T. H. , Dorschner J. , Friedmann C. 
Published: July 2007

AbstractThe data compiled for 34 very young massive compact infrared source (Becklin‐Neugebauer objects) in a separately published catalogue serve as the basis for an investigation of their general properties.First, the correlations of the strength of the ice and silicate bands at 3.1 μm and 10 μm, resp., with each other and with other parameters of the sources are investigated. In accordance with theoretical expectations the strengths of both bands are not well correlated with each other. The ratio τ10/τ3 of their optical depths veries from 0.85 to 8 (and possibly up to 22). That implies for the number densities of the grains that (naked) silicate grains always are considerably more abundant than ice grains (grains with ice mantles). It follows from the discussion of the relationships between τ10, the temperature parameter of the sources, and their luminosity that relations between τ10 and temperature and possibly between τ10 and the luminosity exist.Stellar wind models for the ionized region around the embedded star are favoured after the analysis of the intensities of the hydrogen infrred emission lines and the radio continuum.The limited observational data do not yet allow a decision on a correlation between the silicate band depth and energy content and/or the velocity of the bipolar outflow detected in a number of sources.The BN objects are clearly more frequently associated with H2O masers than OH masers. The linear separations of the infrared peaks from the masers are compatible with models where the H2O masers are situated near the edges the gas‐dust shells of the BN objects.
Analytic solution to the problem of nuclear energy generation rate in a simple stellar model
Authors: Haubold H. J. , Mathai A. M. 
Published: July 2007

AbstractThis paper deals with complete analytic solution to the problem of evaluating the total net rate of nuclear energy generation and the basic integral of the luminosity of a purely gaseous star in hydrostatic equilibrium. It is assumed that the total energy production is proportional to certain powers of the density and temperature and that the density inside the star is a nonlinear function varying from the centre to the surface.
Polar motion estimates from linear combinations of independent series
Authors: Vicente R. O. , Wilson C. R. 
Published: July 2007

AbstractThis paper describes methods for combining independent observations of polar motion into a single time series, and applies these methods to satellite laser ranging, Doppler, and astrometric polar motion data taken over the period 1981‐‐1983. The polar motion data are treated as complex valued time series, yielding one estimate of the noise level for each series, rather than a separate estimate for X and Y components. Estimates of the noise level which take advantage of the existence of simultaneous observations are preferred. Linear combination of the data may be performed in both the time and the frequency domain, and examples of each are present. The results of analyzing three years of observations show little difference between the Allan and conventional variance. Present day Doppler determinations do not show marked improvement compared to classical astrometric results. Thus, the astrometric observations are still useful.
Cataclysmic variables and the amplitude‐cycle length relationship
Authors: Richter G. A. 
Published: July 2007

AbstractAfter a survey of the latest state of knowledge on cataclysmic variables in general (Chapter 1) and recurrent novae in particular (Chapter 2), the amplitude‐cycle length relationship (A‐C relation) is rederived (Chapter 3) after statistical correction for published incorrect values of C. While the A‐C relationship of dwarf novae is of the form A = ‐0.40 + 2.50 log C, it is, presumably for physical reasons less sharply defined for the few known recurrent novae.
Induced causality
Authors: Bleyer U. , Liebscher D.‐E. 
Published: July 2007

AbstractAlternatives to General Relativity with respect to its causal structure are deeply connected with Mach's hypothesis of the cosmic origin of inertial properties. We consider the main features of a theoretical scheme to construct such alternatives and show that observable effects may be estimated without full construction of a theory. From the point of these alternatives, the light cone of Special Relativity is highly degenerated, and any deviation from General Relativity in the direction considered will reduce this degeneracy. Therefore the effects possible in the alternatives considered provide tests already on the level of Special Relativity.
Gravitationally induced supercurrents in the Schwarzschild field
Authors: Zimdahl W. 
Published: July 2007

AbstractUsing the jellium model the behaviour of electronic properties in solids in external gravitational fields is investigated. The charge carriers are influenced by the gravitational field both directly and via the gravitationally induced lattice deformations. As an example we treat London superconductors on circular orbits in the Schwarzschild field of the earth. This motion induces alternating supercurrents with frequencies of the order 0,3 s−1. There exists a general relativistic difference of the oscillation frequencies in different directions. Its relative value is of the order 10−9.
Early star formation and galaxy formation triggered by the evolution of large‐scale density perturbations
Authors: Mücket J. P. 
Published: July 2007

AbstractThe evolution of small‐scale density perturbations on the background of increasing large‐scale perturbations of supercluster size will be considered. In the case that the characteristic length scales of both perturbation modes differ significantly, the interaction between both modes has to be taken into account already within lowest order of approximation. It will be shown that in this case an effective amplification for the smaller‐scale perturbations occurs. For these perturbations the characteristic times of evolution decreases in dependence on the considered mass‐scales more or less rapidly. Therefore, the growth of adiabatic density perturbations on mass‐scales up to galaxy masses seems to be triggered by the density evolution of superclusters which the smaller‐mass perturbations are embedded in. A model for the formation of observed condensed matter distribution will be proposed.
Green's functions of the induction equation on regions with boundary. II. Spherical regions
Authors: Bräuer H.‐J. , Rädler K.‐H. 
Published: July 2007

AbstractIn an earlier paper the evolution of a magnetic field was considered which permeates an electrically conducting fluid and its non‐conducting surroundings. It was shown how the tensorial Green's function of the initial value problem posed by the governing equations can be constructed. The present paper gives a more detailed analysis of the case where the fluid occupies the interior of a sphere. The construction is carried out for arbitrary motions of the fluid. More special results are derived for differential rotation with angular velocity depending only on the radius, and explicit expressions of Green's functions are given for rigid body rotation.
An astrometric model for Tautenburg Schmidt plates
Authors: Yatsenko A. I. , Kur'Yanova A. N. , Dick W. R. 
Published: July 2007

AbstractThe major principles of establishing a statistical model for plates of the Tautenburg Schmidt telescope (134/200/400) are described. The model is intended to be used for the Monte Carlo simulation of the determination of coordinates and proper motions. It has been tested with orthogonal polynomials by determining positions of stars. Under certain conditions linear equations are sufficient for the reduction of measured to standard coordinates when using the AGK3 as the reference system.
Measures of 104 faint common motion pairs of LUYTEN'S NLTT catalogue on prints of the Palomar Sky Survey
Authors: Gellera D. 
Published: July 2007

AbstractFor 104 faint common motion pairs of the New Luyten Catalogue of stars with proper motions larger than two tenth of an arcsec (NLTT) position angles and separations have been measured on prints of the Palomar Observatory Sky Survey. For each pair a finding chart is given.
A Programme to derive from terrestrial observations the rotation of the HIPPARCOS system with reference to the inertial system
Authors: Dick W. R. , Ruben G. , Schilbach E. , Scholz R.‐D. 
Published: July 2007

AbstractThe connection of the HIPPARCOS system with a quasi‐inertial system can be reached by transforming the HIPPARCOS proper motions to absolute proper motions. The Tautenburg Schmidt telescope provides such proper motions with respect to extragalactic objects with an accuracy of 0″.6/100a. The telescope as well as the measuring and reduction technique are described. The accuracy of the link of the HIPPARCOS system to extragalactic objects depends on the accuracy of the transformation matrix which represents the time‐depending part of the rotation matrix to be applied to the whole HIPPARCOS catalogue. To obtain a reliable estimate for the error of transformation we used the error propagation law. An accuracy of 0″.12/100a for the transformation can be achieved with six Tautenburg fields.
On the structure of the low surface brightness dwarf galaxies in the M81 group
Authors: Karachentseva V. E. , Karachentsev I. D. , Richter G. M. , von Berlepsch R. , Fritze K. 
Published: July 2007

AbstractA detailed photometry of spheroidal dwarf galaxies in the M81 group has been carried out. The integral characteristics and the structural parameters of the spheroidal dwarfs has been determined. Their luminosity profiles are well fitted to a King law. The investigated spheroidal dwarfs together with the prototypes of the Local Group form a common sequence according to their main parameters. The observational data presented show that dSphs are not linked evolutionary with normal E and dE galaxies, but probably form a separate branch together with irregular low surface brightness dwarfs.
Spacetimes admitting a universal redshift function
Authors: Dautcourt G. 
Published: July 2007

AbstractThe conditions are given for a velocity congruence in a Riemannian spacetime admitting a universal redshift function R. This function allows to calculate in a simple way (as a quotient ofR values taken at the emission and registration event) the redshift or blueshift connected with an emitter and observer both following the congruence. Spacetimes and congruences with an universal redshift function are shortly discussed.
Precession and the long‐time magnetic variables
Authors: Lehmann H. 
Published: July 2007

AbstractThe model of forced precession of a star gravitationally influenced by a companion is tested for a small group of stars having time‐scales of magnetic changes in the order of some years up to some decades. Results show that the observed secular periods cannot be reduced to a common time‐scale of regular precession. The main difficulty is the evident discrepancy between the oblateness of the stars required by the model and that attainable from rotational or magnetic flattening. Only the observed behaviour of the star 52 Her could be interpreted as a precessional motion.
The binary system 53 Cam
Authors: Scholz G. , Lehmann H. 
Published: July 2007

AbstractThe orbital elements of the spectroscopic binary 53 Cam were revised using 136 radial velocity measurements. The positions in the vicinity of the periastron predicted for the secondary under the assumption of the spectroscopic orbital elements do not agree with those found by speckle interferometric observations. Nevertheless, we try to estimate the mass of the secondary and the dimensions of the binary system.
Local effects in pure astronomical refraction
Authors: Kurzyńska Krystyna 
Published: July 2007

AbstractOn the grounds of a ten‐year material of aerological soundings for Pozna$ (φ = 52° 24′, $LD = 1h 07m.5, h0 = 85 m) a statistical analysis is made of both temporal and local effects in the pure astronomical refraction. No appreciable effects of temporal variations of higher layers of the local atmosphere have been recorded so that the instantaneous local pure refraction can be approximated accurately enough by the average local pure refraction calculated for an instantaneous value of the refractive index n0 at the ground level. A systematic difference is recorded, however, between the standard pure refraction calculated for a given value of n0 and the local one. This difference is proved to be rather sharply defined, so it is reasonable to introduce the notion of local correction to the standard pure refraction. For Poznan, this correction is negative and amounts 0″.01 atz0 = 60°, 0″.1 at z0 = 77°, 1″ at z0 = 85°, and 3″ at z0 = 87°. At z0 = 82° it overestimates the variance of stochastic refraction anomalies (image motion) integrated over time 60 s. The paper answers the long time discussed question whether we should apply the notion of local pure refraction and if yes, in what way.
Entropy production in a non‐conservative gravitational theory
Authors: Wolf C. 
Published: July 2007

AbstractThe production of entropy is calculated in a Friedman Universe governed by a non‐conservative gravitational theory permitting the creation of matter. The calculation has two motivations, the first is that it represents a mechanism to generate the large entropy per baryon observed, and secondly, it simulates the ten dimensional mechanism for entropy production by the out‐of‐equilibrium condition between massive string modes and massless modes with the added condition of energy non‐conservative gravitation.
A search for the age‐dependency of Ap star parameters
Authors: RÖdiger G. , Scholz G. 
Published: July 2007

AbstractSome observational data of the sample of the magnetic chemically peculiar stars (MCP stars) are investigated statistically. For the MCP stars of spectral types later than A2 both the frequency distribution and the R ⋅ sin i‐values suggest the existence of a linear relation between stellar diameter and rotation period. The MCP stars of spectral types earlier than B9 show an overpopulation of small R ⋅ sin i which may indicate the existence of a second group with smaller radius in this sample. The equatorially symmetric rotator is used as the magnetic model. With respect to its temporal behaviour the effective magnetic field is separated into dipolar and quadrupolar contribution. Both signs of the axisymmetric quadrupole moment appear with equal frequency. The dipole moment which produces the amplitude of the Beff(t) curve forms for longer periods two groups which are separated by a distinct gap. Both of the groups exhibit magnetic fields which are the stronger the greater the stellar radius is, contrary to what is expected for frozen‐in fields. The dominance of magnetic curves without polarity reversal for longer‐period stars is in accordance with predictions of the dynamo theory.
Charged black holes in compactified higher‐dimensional Einstein‐Maxwell theory
Authors: Heinrich O. 
Published: July 2007

AbstractA solution of the higher‐dimensional Einstein‐Maxwell‐dilation equations with a Ricci‐flat internal manifold and a 4‐geometry describing a non‐rotating charged black hole is presented. The black hole carries a scalar hair formed by a linear combination of the dilaton and the internal scale factor.
Simultaneous creation of electron‐positron pairs and photons due to their interaction in Robertson‐Walker universes
Authors: Lotze K.‐H. 
Published: July 2007

AbstractThe influence of the electromagnetic interaction upon particle creation in expanding Robertson‐Walker universes is investigated applying an S‐matrix scheme. We discuss all processes contributing to the number density of created particles up to second order in the coupling constant. One process is of particular importance being the only source of photons. It is considered in more detail and evaluated explicitly for a time‐symmetrically expanding radiation‐dominated Friedman universe as well as statically bounded expansions.
Galactic evolution with bimodal star formation. I. A simple model
Authors: Meusinger H. 
Published: July 2007

AbstractModels for the history of the star formation rate are presented which essentially follow three assumptions: (i) high‐mass star formation is mainly initiated by collisions of molecular clouds while low‐mass stars are formed in a spontaneous mode; (ii) the bimodal IMF is responsible for the structure in the present‐day mass function of nearby stars; (iii) the global molecular gas density can be described in terms of the total gas density and the metal abundance. Some properties of these models are confronted with observations in the Solar neighborhood (total density, gas fraction, OB star formation rate, star formation efficiency, present‐day mass function, age‐metallicity relation, white dwarf luminosity function). Special attention is given to the question of the nature of dark matter in the galactic disk within the frame of these models.Es werden Modelle für die zeitliche Entwicklung der Sternentstehungsrate vorgestellt, die im wesentlichen von drei Annahmen ausgehen: (i) Die Entstehung massereicher Sterne wird durch Kollisionen von Molekülwolken initiiert, während masseärmere Sterne spontan entstehen; (ii) Die bimodale IMF ist verantwortlich für die Strukturin der gegenwärtigen Massenverteilung der nahen Sterne; (iii) Die globale Dichte des molekularen Gases kann durch die gesamte Gasdichte und die Häufigkeit schwerer Elemente ausgedrückt werden. Einige Eigenschaften der Modelle werden mit Beobachtungsdaten der Sonnenumgebung konfrontiert (Gesamtdichte, Gasanteil, Entstehungsrate der OB Sterne, Sternstehungseffektivität, gegenwärtige Massenverteilung der Sterne, Alter‐Metallgehalt Relation, Leuchtkraftfunktion weißer Zwerge). Besondere Aufmerksamkeit wird der Frage nach der Natur der dunklen Materie in der galaktischen Scheibe im Rahmen dieser Modelle gewidmet.
Quasars in the field of 88 Leonis
Authors: Erculiani‐Abati L. , Afanasjev V. L. , Spiridonova O. , Lorenz H. 
Published: July 2007

AbstractSpektroskopisch bestätigte Quasare im 25 Quadratgrad großen A1‐Feld bis zu einer Grenzgroße von mB = 18.0 werden untersucht. Die abgeschätzte Quasar Flächendichte von 0.28 ± 0.11 Objekte pro Quadratgrad auf der Grundlage der “vollständigen” Quasar‐Stichprobe im A1 Feld liegt guter Übereinstimmung mit der beobachteten integralen Anzahl‐Helligkeitsbeziehung. Wir betrachten jedoch diese Flächendichte, bedingt durch Selektionseffekte bei der Farbauswahl der Objekte, insbesondere deren Helligkeitsabhängigkeit, nur als Untergrenze. Die Quasar Flächendichte im A1 Feld kann bis zu 30% unterschätzt sein und entspricht damit der kürzlich bestimmten Unvollständigkeit der BQS Durchmusterung.
Galactic evolution with bimodal star formation. II. Expectations and problems
Authors: Meusinger H. 
Published: July 2007

AbstractBimodal star formation is an interesting hypothesis from the point of view of galactic evolution. It is believed that bimodal star formation scenarios provide answers to several outstanding problems. In this paper the question is discussed whether by means of LARSON's (1986) bimodal IMF the chemical evolution (D, He, Fe), the nature of the dark matter, the luminosity function of white dwarfs, and the structure in the field star luminosity function in the solar neighborhood can be explained simultaneously.
Long‐term behaviour of the stellar brightness in eclipsing minima of SV Cam
Authors: Hempelmann A. , Rüdiger G. 
Published: July 2007

AbstractThe time dependence of the brightness at both central eclipses of the RS CVn binary SV Cam – observed between 1973 and 1980 by PATKOS – is analysed to check the activity model of this star, which was derived from light variations outside the eclipses by Busso et al. Their detection of a cycle of about 10 years is confirmed by the observations of the primary eclipses, whereas from observations of the secondary eclipses an unambiguous determination of a cycle length was not possible. Obviously, the cycle is superimposed with fluctuating short‐term variations which exist in time scales from days up to months. These fluctuations are observed not only at the primary eclipse but also at the secondary eclipse. Correlations between the fluctuations at these two orbital phases suggest the primary component of SV Cam to be the main contributor to the variations observed.
Photographic observations of the dwarf nova SS UMi
Authors: Richter G. A. 
Published: July 2007

AbstractBeobachtungen auf 4180 Platten der Sonneberger Himmelsüberwachung ergaben, daß es sich um einen SS‐Cygni‐Stern mit einer Zyklenlänge zwischen etwa 30 … 48 Tagen handelt. Es werden mögliche Bahnumlaufperioden diskutiert.
Binaries in the vicinity of the open cluster IC 4665.I. V 378 Oph
Authors: Kraicheva Z. , Popova M. , Antov A. 
Published: July 2007

AbstractThe first results of the programme for investigation of binary stars, which are possible members of open clusters, are presented. The distribution is given for spectroscopic and eclipsing binaries in the wide vicinity of the open cluster IC 4665.Results of photometric study of the variable V 378 Oph are also presented. There are controversial data for this object concerning its brightness changes. Our observations confirm that it is a ß Lyrae type binary and its period was determined. A mean light curve is drawn. Some peculiarities are mentioned which demand additional observations, possibly electrophotometric and spectroscopic ones, too. The probability is discussed for V 378 Oph to be a member of Mel 186 (Cr 359) or IC 4665 clusters.
Models of dusty envelopes around Vega‐like stars
Authors: Men'Shchikov A. B. 
Published: July 2007

AbstractSimple evolutionary models of dust envelopes around Vega, Sun, β Pictoris and Ross 128 are constructed. The infrared spectra of the envelopes are calculated under the assumption that the minimum radii of the particles are determined by the Poynting‐Robertson effect, while their growth to maximum sizes is due to effective coagulation. A comparison with observations of the dust envelopes by IRAS shows that the model can satisfactorily explain the main properties of the protoplanetary disk evolution.
Absolute proper motions of blue objects in the vicinity of M33
Authors: Richter G. A. , Scholz R.‐D. 
Published: July 2007

Abstract36 objects with mainly negative (U—B) indices were investigated for variability and proper motions. 10 objects with significant or suspected proper motions and 8 variable objects were detected. Using these criteria, it was possible to separate white dwarfs from quasi‐stellar objects to some extent.
Beobachtungen Kleiner Planeten. IX
Authors: Börngen F. 
Published: July 2007

AbstractEs wird eine Übersicht über die im Jahr 1988 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten gegeben. 386 Objekte wurden entdeckt und für diese 1218 Positionen gerechnet. Es handelt sich um 87 numerierte Objekte sowie um 299 Planetoiden mit provisorischer Bezeichnung. Unter letzteren sind 252 neue Bezeichnungen. Für 40 im Berichtszeitraum numerierte Planeten haben Tautenburger Beobachtungen einen Beitrag geleistet. Darunter sind acht in Tautenburg entdeckte Planetoiden.
Simple methods for orbit determination and identification of asteroids. I
Authors: Kristensen L. K. 
Published: July 2007

AbstractThe many discoveries of main belt asteroids with insufficient observations for reliable orbits cause special difficulties for identifications and data storage; mainly because of the mixing of objects due to their motion in α and δ. This problem may be reduced by substituting positions by slowly and smoothly varying quantities. A rational system of preliminary designations will be proposed, and surveys and compact ephemerides are discussed. All computations are very simple and performed on a small, programmable pocket computer.