bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Model for the Binary Pulsar Radio Eclipse
Authors: Khechinashvili D. , Melikidze G. , Gil J. 
Published: July 2016

AbstractWe suggest that companions of two binary eclipsing pulsars, B1957+20 and J2051-0827, are degenerate magnetic dwarfs. The magnetospheres of the white dwarfs are infused with relativistic particles supplied by the pulsar wind. We demonstrate that the radio waves emitted by the pulsars are strongly damped due to cyclotron resonance with the plasma particles, in the magnetospheres of companions. Large stable continuos and frequency-dependent radio eclipses should occur as a result of this process. This agrees well with observations.
Neutron Star Atmospheres
Authors: Pavlov George G. , Zavlin V. E. 
Published: July 2016

AbstractProperties of the thermal radiation emitted by neutron stars (NSs) are determined by thin plasma layers (atmospheres) at their surfaces. The NS atmospheres are very different from those of usual stars due to the immense gravity and huge magnetic fields. Current models of hydrogen NS atmospheres show that the spectra deviate substantially from blackbody spectra of the same temperatures. Comparison of the model spectra with recent observations of soft X-ray and UV-optical radiation of NSs yields the surface temperatures considerably lower than those obtained from the blackbody fits. This conclusion have important implications for theories of NS cooling and for understanding fundamental properties of the superdense matter in the NS interiors.
Rapidly rotating strange stars
Authors: Gondek-Rosińska D. , Haensel P. , Zdunik J. L. , Gourgoulhon E. 
Published: July 2016

AbstractWe study effects of the strange quark mass,ms, and of the QCD interactions, calculated to lowest order inαc, on the rapid rotation of strange stars (SS). The influence of rotation on global parameters of SS is greater than in the case of the neutron stars (NS). We show that independently ofmsandαcthe ratio of the rotational kinetic energy to the absolute value of the gravitational potential energyT/Wfor a rotating SS is significantly higher than for an ordinary NS. This might indicate that rapidly rotating SS could be important sources of gravitational waves.
Theories of Polar Motion from Tisserand to Poincaré (1890 – 1910)
Authors: Melchior P. 
Published: July 2016

AbstractThe discovery by Seth C. Chandler (1891) that the motion of the pole (the reality of which had been established by K.F. Küstner and by the simultaneous latitude observations at Honolulu and Berlin by German astronomers) resulted from two componentsi.e.a free circular motion with a period of 427 days and a forced elliptical motion with a period of 365.25 days, raised considerable interest in the scientific community of astronomers and geophysicists.The celebratedMécanique Célesteof Tisserand (1890) had been published just one year before at a time when doubts still persisted and arguments could be presented in favor of the fixed pole. Starting with Tisserand’s arguments, we describe in this paper the impact of the successive contributions by A. Greenhill, S. Newcomb, Th. Sloudsky, S. Hough, G. Herglotz, A. Love, J. Larmor and H. Poincaré to the solution of the problems raised by the Chandler period.The lines of reasoning taken by these eminent scientists were rigorously correct so that, after about one hundred years, contemporary researchers, who benefit from a far better knowledge of the inner structure of the Earth and are able to take advantage of modern computing power, do not contradict any of their conclusions and instead refine them with an accuracy which was not imaginable one century ago.
Early Observational Evidence of Polar Motion
Authors: Verdun Andreas , Beutler Gerhard 
Published: July 2016

AbstractBessel was not able to detect significant latitude variations in his observation series made between May 1820 and June 1821 at Königsberg Observatory. He left the topic until July 22, 1843, when he suspected that the latitude might have changed since 1820. Between March 1842 and April 1843 Peters, one of Bessel’s students, performed an observation series of the pole’s zenith distance at the Pulkovo Observatory using new observation techniques and reduction methods first developed by Bessel. From this series he deduced a significant value of 0″.079 ± 0″.017 for the amplitude of polar motion, but he was not able to separate the expected 10 month Eulerian period from an annual signal possibly caused (as he supposed) by seasonal temperature variations. Peters’ successors at Pulkovo, Gyldén and Nyrén, continued to observe latitude. Using these observation series Nyrén derived in 1873 significant values for the amplitude of polar motion, but he was not able to determine the phase angles because he assumed the period of polar motion being known. We conclude that Peters probably was the first one to have observed a variation of the latitude, but that he and Nyrén were misled by the Eulerian period when modeling polar motion.
Coseismic Excitation of the Earth’s Polar Motion
Authors: Chao B.F. , Gross R.S. 
Published: July 2016

AbstractApart from the “shaking” near the epicenter that is the earthquake, a seismic event creates a permanent field of dislocation in the entire Earth. This redistribution of mass changes (slightly) the Earth’s inertia tensor; and the Earth’s rotation will change in accordance with the conservation of angular momentum. Similar to this seismic excitation of Earth rotation variations, the same mass redistribution causes (slight) changes in the Earth’s gravitational field expressible in terms of changes in the Stokes coefficients of its harmonic expansion. In this paper, we give a historical background of the subject and discuss the related physics. We then compute the geodynamic effects caused by earthquakes using Chao and Gross’ (1987) formulas based on Gilbert’s (1970) normal-mode summation scheme. The effects are computed using the centroid moment tensor (CMT) solutions for 15,814 major earthquakes from Jan., 1977, through Feb., 1999, as provided in the Harvard CMT catalog. The computational results update those of Chao and Gross (1987) and Chao et al. (1996), further strengthening their findings and conclusions: (i) the strong tendency for earthquakes to make the Earth rounder and more compact (however slightly) continues; (ii) so does the trend in the seismic “nudging” of the rotation pole toward the general direction of ~ 140°E, roughly opposite to that of the observed polar drift, but two orders of magnitude smaller in drift speed.
Secular Variation of Carloforte Latitude
Authors: Poma A. , Uras S. 
Published: July 2016

AbstractThe long series (1899.9–1979.0) of latitude observations made at Carloforte in the framework of the International Latitude Service is analyzed to determine a secular trend. The value of the linear rate obtained from the classical astrometric results agrees fairly well with the value derived from recent SLR and GPS observations carried out at the Cagliari Observatory.
On High Frequency Polar Motion and Length of Day Variations
Authors: Arfa-Kaboodvand K. , Groten E. 
Published: July 2016

AbstractThe 0.042-day Earth rotation data (diurnal and semidiurnal) computed by the International GPS Service were used to analyze the daily/sub-daily variations of polar motion (PM) and length of day (LOD). Systematic and advanced spectral analytical investigations of the degree of periodic variability have been carried out. They show that the prominent periodical components can be found at the tidal frequencies of zonal, tesseral and sectorial waves. These investigations should give better insight into the physical processes, which influence Earth orientation (i.e. due to the atmospheric and oceanic motions, tidal forces etc.). It should be the basis for the detailed modeling of excitation functions in the sub-diurnal range of the high-frequency spectrum.
Determination of the Long Period Nutation Terms from Optical Astrometry and VLBI Data
Authors: Yaya P. , Bizouard C. , Ron C. 
Published: July 2016

AbstractA 100-year long optical astrometric series of the Earth Orientation Parameters produced by a Czech team (Vondrák et al., 1998) has been analysed in order to determine components of nutation. Our interest is mostly focused on the long periodic terms: 18.6-year term, 9.3-year term and linear trend, still correlated in VLBI series which cover only the last 20 years. A comparison has been made with the corresponding values determined from the VLBI series.
Multiple Periodic RR Lyrae Stars Observational Review
Authors: Szeidl B. 
Published: July 2016

In this review paper I concentrate exclusively on the multiple periodic RR Lyrae stars and I do not wish to discuss the general problems of cluster variables. There are some excellent review papers on them (e.g. Preston, 1964).The majority of the RR Lyrae stars repeat their light curves from cycle to cycle with astonishing regularity. It was, however, discovered already in the early days of variable star research that some of them showed conspicuous changes in the height of maxima of their light curve and simultaneously the time of maxima could not be fitted in by a linear formula.
New Results on the Commensurability Cases of the Problem Sun-Jupiter-Asteroid
Authors: Schubart Joachim 
Published: July 2016

AbstractThe short-period terms are removed by averaging from special equations of motion for commensurability cases of the three-dimensional, elliptic, restricted three-body problem. Some examples of retrograde motion corresponding to the -1/1 commensurability, and an application to Hilda-type motion demonstrate the possibilities given by the method.
Triple Collision as an Unstable Equilibrium
Authors: Waldvogel Jörg 
Published: July 2016

AbstractThe family of trajectories near a triple collision solution in the planar problem of three bodies is investigated by means of linearization in the neighborhood of the parabolic free fall. The local topological structure of this family is found to be that of a saddle point in the R8. The corresponding stable manifold is the set of all triple collision solutions, whereas the instable manifold is formed by the parabolic solutions.In important cases of nonzero total energy the family of close encounters is quantitatively described in terms of hypergeometric functions. By means of homothetic transformations the close triple encounters are then related to three-body motion with zero energy and zero angular momentum. In this way almost all close encounters near a homothetic solution can be treated by using a small number of particular solutions of the three-body problem that may be calculated once for all.In practical examples the first order theory presented here predicts the escape velocity after a close triple encounter with a relative accuracy comparable to the closeness of the encounter.
Heavy Element Abundances In FG Satittae
Authors: Kipper T. , Kipper M. 
Published: July 2016

AbstractThe spectrogram of FG Sge obtained by the 6-m telescope in 1986 is analyzed. The iron peak elements are underabundant relative to the sun, and the heavy elements (Z>39) have abundances up to 3 dex (1, 000 times) higher than in the Sun.
Improving the Reference Frame by Radio–and Optical Astrometry of Radio Stars
Authors: de Vegt Chr. , Zacharias N. , Johnston K.J. , Hindsley R. 
Published: July 2016

AbstractA longterm program of precise radio – and optical astrometry of selected radio stars has been conducted in the last decade by our observatories using the VLA and astrographs on both hemispheres. Positions of 54 stars north of −26 deg. declination including 6 MASER stars have been obtained. The program status and some results from the southern hemisphere are reported.
Lateral Image PZT. Description and Operating Method
Authors: Garcia A.Lopez , Machi R.Lopez , Navarro J.L.Valdes , Orti J.A.Lopez 
Published: July 2016

AbstractWe faced the problem of designing and building a Photographic Zenith Tube with mercury basin and lateral plate-holder system providing enough accuracy to allow the determination of astronomical coordinates. This instrumentis intended to work as a prototype of a bigger and more accurate one to be designed and developed in the future (Lopez, A. et al.: 1983).
A Source of Systematic Error, Δδα, in Absolute Catalogs Compiled from Meridian Circle Observations
Authors: Miyamoto M. , Suzuki S. 
Published: July 2016

AbstractAutomated photoelectric meridian circles are able nowadays to have the full set of graduation errors of the decimation circle determined within a few days. Thus, the modern meridian circles can be monitored, and the annual and secular changes of the graduations can be easily detected to provide the graduation corrections at any date. In order to remove systematic declination errors in the form Δδα from absolute catalogs, these continuous changes should be taken into account.
Evidence of Systematic Errors in FK5
Authors: Morrison L.V. , Argyle R.W. , Requième Y. , Helmer L. , Fabricius C. , Einicke O.H. , Buontempo M.E. , Muinñs J.L. , Rapaport M. 
Published: July 2016

The primary purpose of the FK5 is to provide an absolute optical reference frame against which to measure the positions and motions of other objects. One of the main tasks of meridian circles is to check and improve that reference frame by repeated observation of the fundamental stars. The meridian circle at Bordeaux, France and the Carlsberg Automatic Meridian Circle (CAMC) at La Palma are carrying out programmes of observation of FK5 stars partly with this aim in view.The positions from which the systematic differences are derived are the means of at least 10, but normally about 30 (Bordeaux) and 50 (CAMC), independent observations of each FK5 star made in the period 1984–87. The systematic differences are displayed in pairs of 3-dimensional plots, Bordeau–FK5 and CAMC–FK5. The similarities of the corresponding pairs of plots is striking, particularly in declination. This implies that systematic errors exist in the FK5 which reach about in places at the epoch 1986.0.
A Note on the Astrometric Precision of Minor Planet Observations
Authors: Pascu D. 
Published: July 2016

AbstractFor years, interest in precise positions of minor planets has centered on tying the dynamical reference frame with the stellar frame and determining catalog zone errors. Photographic methods are generally used in obtaining observed spherical equatorial coordinates (R.A., Dec.) or crossing-point observations. Estimates of the external precision of the equatorial coordinates are overly pessimistic, while those for crossing-point observations, too optimistic.It is estimated that equatorial positions for the brighter (m < 11) minor planets can be determined with an external precision not worse than +/−0.2 arcsec (m.e.), and perhaps as low as +/−0.1 arcsec (m.e.), depending on the reference catalog zonal errors.Intersatellite observations are a type of crossing-point observation in which the images of two different objects appear in the same exposure. This is the most precise type of crossing-point observation and gives an estimate for the lower limit to the external precision of this observation type. Recent studies of satellite observations indicate that this lower limit is in the +/−0.05 to +/−0.08 arcsec (m.e.) range.
Optical Positions of Radiostars by the Danjon Astrolabe at Cagliari and Further Projects
Authors: Poma A. , Zanzu T. 
Published: July 2016

AbstractPrecise positions of optical counterparts of radiosources are needed in connecting optical and radio reference frames. The Cagliari Astronomical Observatory has planned systematic observations with the Danjon astrolabe of objects from the high priority Hipparcos radio-stars list. A preliminary result of the position of radiosource HR 5110 is presented.
Intermediate Star Reference Systems in the Vicinity of Radio Sources
Authors: Tel’nyuk-Adamchuk V.V. , Kumkova I.I. , Sadzakov S. , Toma E. , Volianska M.Yu. 
Published: July 2016

AbstractIn the framework of CONFOR program the formation of star lists of two intermediate reference star systems is being carried out. The first list, RRS2, contains meridian stars in the fields centered at extragalactic radio/optical sources. The second one is formed on the base of 12-14 magnitude stars. The observations are in progress now. The main purpose of this program is to form a base for investigation of mutual orientation of fundamental reference system and new ones.
Long-Term Nutation and the Length Day Variation from VLBI Observations
Authors: Yagudina E.I. , Sudnik I.S. 
Published: July 2016

AbstractThe shift of the celestial pole with respect to its 1980 position in longitude (Δψ) and obliquity (Δε) from the available VLBI measurement of 1984 year within IRIS project is estimated. Formal uncertainties of the angles Δψ and Δε are 5.9 mas and 2.7 mas respectively. The day length variation was obtained from the same data. Then attempt was made to obtain annual and semiannual nutation amplitudes. The values are in reasonable agreement with the determinations of other workers.
Improvement of the Optical Reference System by Photographic Astrometry: First Results of Simulations with Global Block Adjustment Methods
Authors: Zacharias N. 
Published: July 2016

AbstractBlock adjustment (BA) simulations of an entire hemisphere show major improvements in individual as well as systematic accuracy of star positions obtained by photographic astrometry, independent of systematic errors of the reference star catalog used. Results for the accuracy estimates obtained from a patch-like plate pattern in the sky are not valid for closed plate pattern. The importance of BA methods for the realisation of a reference system is stressed.
Active Region Magnetic Fields
Authors: Howard Robert F. 
Published: July 2016

AbstractThe tilt angles of sunspot groups are defined, using the Mount Wilson data set. It is shown that groups with tilt angles greater than or less than the average value (≈5 deg) show different latitude dependences. This effect is also seen in synoptic magnetic field data defining plages. The fraction of the total sunspot group area that is found in the leading spots is discussed as a parameter that can be useful in studying the dynamics of sunspot groups. This parameter is larger for low tilt angles, and small for extreme tilt angles in either direction. The daily variations of sunspot group tilt angles are discussed. The result that sunspot tilt angles tend to rotate toward the average value is reviewed. It is suggested that at some depth, perhaps 50 Mm, there is a flow relative to the surface that results from a rotation rate faster than the surface rate by about 60 m/sec and a meridional drift that is slower than the surface rate by about 5 m/sec. This results in a slanted relative flow at that depth that is in the direction of the average tilt angle and may be responsible for the tendency for sunspot groups (and plages) to rotate their magnetic axes in the direction of the average tilt angle.
Sunspot Groups as Tracers of Sub-Surface Processes
Authors: Gokhale M. H. 
Published: July 2016

AbstractData on sunspot groups have been quite useful for obtaining clues to several processes on global and local scales within the sun which lead to emergence of toroidal magnetic flux above the sun’s surface. I present here a report on such studies carried out at Indian Institute of Astrophysics during the last decade or so.
Cyclical Variability of Prominences, CMEs and Flares
Authors: Ballester J. L. 
Published: July 2016

AbstractSolar flares, prominences and CMEs are well known manifestations of solar activity. For many years, qualitative studies were made about the cyclical behaviour of such phenomena. Nowadays, more quantitative studies have been undertaken with the aim to understand the solar cycle dependence of such phenomena as well as peculiar behaviour, such as asymmetries and periodicities, occurring within the solar cycle. Here, we plan to review the more recent research concerning all these topics.
Temporal Variation of Large Scale Flows in the Solar Interior
Authors: Basu Sarbani , Antia H. M. 
Published: July 2016

AbstractWe attempt to detect short-term temporal variations in the rotation rate and other large scale velocity fields in the outer part of the solar convection zone using the ring diagram technique applied to Michelson Doppler Imager (MDI) data. The measured velocity field shows variations by about 10m/s on the scale of few days.
Observation of Hysteresis between Solar Activity Indicators and p-mode Frequency Shifts for Solar Cycle 22
Authors: Tripathy S. C. , Kumar Brajesh , Jain Kiran , Bhatnagar A. 
Published: July 2016

AbstractUsing intermediate degreep-mode frequency data sets for solar cycle 22, we find that the frequency shifts and magnetic activity indicators show a “hysteresis” phenomenon. It is observed that the magnetic indices follow different paths for the ascending and descending phases of the solar cycle while for radiative indices, the separation between the paths are well within the error limits.
The Role of Magnetic Buoyancy in a Babcock-Leighton Type Solar Dynamo
Authors: Nandy Dibyendu , Choudhuri Arnab Rai 
Published: July 2016

AbstractWe study the effects of incorporating magnetic buoyancy in a model of the solar dynamo—which draws inspiration from the Babcock-Leighton idea of surface processes generating the poloidal field. We present our main results here.
Lyα and β of H I, h and k of Mg II, H and K of Ca II Profiles of a Quiescent Prominence Obtained with the LPSP Instrument of OSO 8
Authors: Vial J.C. , Lemaire P. , Gouttebroze P. 
Published: July 2016

Simultaneous spectra have been recorded in the six lines, with a 1″ × 40″ entrance slit and a spectral resolution of 60 mÅ in Lyβ, 30 mÅ in Lyα, 85 mÅ in Mg II and 60 mÅ in Ca II.Lyβ and Lyα lines are reversed: peak to peak distances are 0.31 Å and 0.34 Å, peak-to-center intensity ratios are 2 and 1.4 for Lyβ and Lyα, respectively.Inferred opacities at line centers are of the order of 105. Prominence intensities are 0.4 times disk intensities in both lines (Lyα is in the range of computed models by Heasley and Milkey, 1978).
On the Measure-Preserving Mappings with Three-Dimensions
Authors: Sun Yi-Sui 
Published: July 2016

AbstractWe have systematically made the numerical exploration about the perturbation extension of area-preserving mappings to three-dimensional ones, in which the fixed points of area preserving are elliptic, parabolic or hyperbolic respectively. It has been observed that: (i) the invariant manifolds in the vicinity of the fixed point generally don’t exist (ii) when the invariant curve of original two-dimensional mapping exists the invariant tubes do also in the neighbourhood of the invariant curve (iii) for the perturbation extension of area-preserving mapping the invariant manifolds can only be generated in the subset of the invariant manifolds of original two-dimensional mapping, (iv) for the perturbation extension of area preserving mappings with hyperbolic or parabolic fixed point the ordered region near and far from the invariant curve will be destroyed by perturbation more easily than the other one, This is a result different from the case with the elliptic fixed point. In the latter the ordered region near invariant curve is solid. Some of the results have been demonstrated exactly.Finally we have discussed the Kolmogorov Entropy of the mappings and studied some applications.
Dynamical Mechanisms for Transferring Comets In and Out of the Oort Cloud
Authors: Valtonen M.J. , Zheng J.Q. 
Published: July 2016

AbstractWe study scenarios where comets are not original members of the Solar System but have been acquired from the surrounding medium through dynamical evolution. This leads to estimates of the present day number density of comets in the interstellar medium which are not in contradiction with observational upper limits. We also consider the dynamical transfer of Oort Cloud comets into short period comets. The process is very sensitive to the inclination of the comet orbit which leads to strong bias in favour of low inclinations in short comet orbits.