bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activity Report of the IAU Working Group on Reference Systems Sub-Group on Astronomical Constants
Authors: Fukusfflma T. 
Published: July 2016

The IAU Working Group on Reference Systems (WGRS) Sub-Group on Astronomical Constants (SGAC) was established in June, 1989, as a consequence of resolutions adopted by Commissions 4, 7, 8 and 24 at the IAU General Assembly at Baltimore in 1988. The given missions of this sub-group were stated clearly by J. Hughes, the chairman of the WGRS, as:“Provide numerical values for the primary constants and specify the relationships between these and other, secondary constants within the framework of general relativity. This task will involve the documentation of the constants themselves as well as of the procedures and algorithms associated with their use. Recognition must be given to the fact that approaches which are specific to various techniques exist. The group must recommend the best estimates which can meet the varied requirements of astronomy. The apparent dichotomy between adopting fixed values for various quantities on the one hand, and the need for current, highly accurate values on the other hand, must be addressed by the group. Indeed, the crafting of effective procedures for incorporating new determinations into the values assigned to the constants, and the setting up of a mechanism for disseminating information regarding new determinations as an interim measure, are important tasks for this group.”This is a report of the activity of the SGAC prior to IAU Colloquium No.127. Section 2 summarizes the questionnaire prepared in trie course of discussion. In Section 3, the discussions on major issues are introduced. The drafts of Recommendations from the SGAC prepared before the Colloquium are shown in Section 4. Note that these drafts were very different from the final form as indicated in this Proceeding. Sections 5 and 6 deal with the current status of astronomical constants used widely now and the best estimates of some major constants which are available now, respectively. I believe these will serve as a guideline for current astronomical constants.
The Necessary Procedures to Reach an Agreeable Reference Frame: –Counter-Proposal to the Circular Letter N° 4 of Kovalevsky–
Authors: Aoki Shinko 
Published: July 2016

AbstractThe procedures are summarized in order to obtain a reference system which is available at the present moment and in the near future for the astronomical purposes. The target of the present discussions is the IAU General Assembly to be held in the summer of year 1991, in order to find out an agreeable result there. Discussions beyond this are postponed to a further occasion.
The Linkage Between Radio and Optical Coordinate Systems: Program Confor
Authors: Kumkova I.I. , Tel“njuk- Adamchuk V.V. , Bashtova L.I. , Dick W.R. , Inasariose R.Ya. , Irkaev B.N. 
Published: July 2016

AbstractThe present status and prospects of program CONFOR-Connection of Frames in Optic and Radio, are described. It is supposed that positions of extragiactic objects and intermediate stars in 200 areas will be obtained in FK5 system.
Stability of the Extragalactic Reference Frame Realized by VLBI
Authors: Ma C. , Shaffer D.B. 
Published: July 2016

AbstractThe 318 compact extragalactic radio sources with positions derived from dual frequency Mark III VLBI data acquired by the geodetic and astrometric programs of NASA, NOAA, NRL and USNO form a celestial reference frame with stability in orientation and relative position at the 1 mas level. This paper examines the reference frame realized using 461,000 observations from 1021 observing sessions between 1979 August and 1990 August in the NASA Crustal Dynamics Project VLBI data base. Catalogs of positions estimated from subsets of data (annual, seasonal, network) show differences in orientation typically less than 1 mas provided precession and nutation are adjusted using a reference day. For 17 sources with >5 year time span and >200 one-day position estimates, the rates of change of right ascension and declination are generally less than 5 mas/century, giving upper limits on real motion.
The Orientation of the Dynamical Reference Frame
Authors: Williams J.G. , Dickey J.O. , Newhall X X , Standish E.M. 
Published: July 2016

AbstractWe summarize the current status of the JPL ephemerides, focusing on the various data types utilized, especially the impact of the modern ranging data, and the resulting accuracies obtained. The dynamical equinox, as determined from the analysis of Lunar Laser Ranging data, is determined with an accuracy of 5 mas and the obliquity to a 2 mas level in ~1983, the weighted center of data. Knowledge of the lunar and planetary positions with respect to the dynamical equinox degrades to 10 mas at J2000. Twenty years of LLR data allow for the separation of the 18.6 yr nutation terms from the precession constant. The correction to IAU precession is found to be −2.7 ± 0.4 mas/yr, while the 18.6 yr nutation of the pole is 3.0 ± 1.5 mas larger in magnitude than the 1980 IAU series. The necessity of different reference systems and the accurate knowledge of the interconnections between frames is addressed.
A Terrestrial Reference System Consistent with WGRS
Authors: Boucher C. , Altamimi Z. 
Published: July 2016

AbstractThe IAU and IUGG has jointly established in 1988 an International Earth Rotation Service (IERS) which is in charge of the realization of conventional celestial and terrestrial reference systems, together with the determination of earth orientation parameters which connect them.The theoretical definition of the terrestrial reference system which is realized by IERS through a conventional terrestrial reference frame formed by SLR, LLR, VLBI and GPS stations is presented. In particular its origin, scale, orientation and evolution with time are reviewed, taking into account relativistic and deformation effects.
Present Status of Work on the FK5 Extension
Authors: Corbin Thomas E. , Schwan Heiner 
Published: July 2016

AbstractThe FK5 Extension, consisting of 3117 new fundamental stars selected from the FK4 Sup catalogue and the IRS list, will extend the FK5 system to about 9.5th visual magnitude. The construction of the FK5 Extension is briefly described and the main characteristics are given.
Optical Astrometry and the Global Positioning System
Authors: Kammeyer P.C. , Fliegel H.F. , Harrington R.S. 
Published: July 2016

AbstractAstrometric accuracies of a few tens of milliarcseconds are expected to be attainable within five years by calibrating astrograph plates with optical observations of Global Positioning System (GPS) satellites against a stellar background. The line of sight from an observer on the Earth’s surface to a GPS satellite may be calculated with high accuracy. Motion on each day of the line of sight to the satellite and changes from day to day in the apparent path of the satellite are sufficiently slow to make it possible to reduce atmospheric errors by averaging. Advanced ground-based optical sensors, probably using charge coupled device technology, will be required for GPS optical astrometry.
Third General Catalogue of Stars Observed with the Photoelectric Astrolabes
Authors: Lizhi Lu 
Published: July 2016

AbstractOn the basis of the data observed with the Photoelectric Astrolabes in China observed during the period from 1982 to 1990, the general catalogue is compiled. With magnitudes ranging from 0m.l to 7m.3, the general catalogue consists of 2577 stars spreading from δ=−3° to δ= 69°, in which 955 are FK5 stars and 1622 are GC stars. The mean precisions of 2577 Δα’s and 1892 Δδ’s are ±4.0 ms and ±0”.065, respectively. The mean epoch of the catalogue is 1987.4. Finally systematic corrections of (CAT—FK5) are given.
Precession Theory Using the Invariable Plane of the Solar System
Authors: Owen W.M. 
Published: July 2016

AbstractStandard precession theory builds up the precession matrix P, which rotates coordinates from the mean equator and equinox of epoch to the mean equator and equinox of date, by a sequence of three elementary rotations by the accumulated Euler angles ϚA, θA and zA: P = R3(−zA)R2(θA)R3(−ϚA). This scheme works well provided both the epoch and the date are within a few centuries of J2000. For long-term applications, the alternative formulation using the accumulated luni-solar and planetary precession, P = R3(ᵡA)R1(−ѡA)R3(−ψA)R1(ɛ), is more stable.Yet another formulation for P is possible, using the invariable plane of the Solar System as an intermediate plane: P = R3(−L) R1(−I) R3(−Δ) R1(I0) R3(L0). The angles I0 and L0 are the inclination and ascending node of the invariable plane at epoch; I and L are the same quantities at the date. Only the angle Δ is a function of both times. This scheme works for both short-term and long-term applications.For the short term, polynomial coefficients for I, L, and Δ are derived from the currently-accepted coefficients of the angles ϚA, θA and zA. For the long term, these angles are expressed as sums of Chebyshev polynomials obtained from analysis of a million-year numerical integration.If the intersection of the mean equator and the invariable plane were adopted as the origin of right ascensions, the theory would be simplified further: since L0 and L would no longer be required, P would again consist of the minimum three rotations.
New High Resolution Observations of the Solar Diameter from Space and Ground with the Microsatellite Program PICARD
Authors: Damé Luc 
Published: July 2016

AbstractThe PICARD microsatellite mission will provide 2 to 6 years simultaneous measurements of the solar diameter, differential rotation and solar constant to investigate the nature of their relations and variabilities. The 100 kg satellite has a 40 kg payload consisting of 3 instruments which will provide an absolute measure (better than 10 milliarcsec) of the diameter and the solar shape, a measure of total solar irradiance, and UV and visible flux in selected wavelength bands. Now in Phase B, PICARD is expected to be launched before mid-2003. The engineering model of the diameter telescope will be used on ground simultaneously with the satellite to investigate the atmospheric bias and state on the possible accuracy of the ground measurements carried up to now. We review the scientific goals linked to the diameter measurement, present the payload, and give a brief overview of the program aspects.
Solar Filaments as Tracers of Subsurface Processes
Authors: Rust D. M. 
Published: July 2016

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.
Polar Magnetic Field Reversals of the Sun in Maunder Minimum
Authors: Makarov V. I. , Tlatov A. G. 
Published: July 2016

AbstractA possible scenario of polar magnetic field reversal of the Sun during the Maunder Minimum (1645–1715) is discussed using data of magnetic field reversals of the Sun for 1880–1991 and the14Ccontent variations in the bi-annual rings of the pine-trees in 1600–1730 yrs.
On the Possibility of Radio Emission from Quasi-parallel and Quasi-perpendicular Propagation of Shocks
Authors: Shanmugaraju A. , Umapathy S. 
Published: July 2016

AbstractA set of 21 solar type II radio bursts observed using Hiraiso radio spectrograph have been analysed to study the direction of propagation of coronal shocks. A simple analysis is carried out to find the approximate angle between the shock normal and magnetic field by solving the Rankine-Hugoniot MHD relation with assumption of Alfven speed and plasma beta. From this analysis, it is suggested that both quasi-parallel shocks (favourable) and quasi-perpendicular shocks can generate type II bursts depending upon the circumstances of the corona.
Infrared Photometry of Solar Active Regions
Authors: Sobotka M. , Vázquez M. , Cuberes M. Sánchez , Bonet J. A. , Hanslmeier A. 
Published: July 2016

AbstractSimultaneous time series of broad-band images of two active regions close to the disk center were acquired at the maximum (0.80μm) and minimum (1.55μm) continuum opacities. Dark faculae are detected in images obtained as weighted intensity differences between both wavelength bands. The elements of quiet regions can be clearly distinguished from those of faculae and pores in scatter plots of brightness temperatures. There is a smooth transition between faculae and pores in the scatter plots. These facts are interpreted in terms of the balance between the inhibition of convective energy transport and the lateral radiative heating.
Electron Density and Temperature Measurements, and Abundance Anomalies in the Solar Atmosphere
Authors: Mohan Anita , Dwivedi Bhola N. , Landi Enrico 
Published: July 2016

AbstractUsing spectra obtained from the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory), we investigate the height dependence of electron density, temperature and abundance anomalies in the solar atmosphere. In particular, we present the behaviour of the solar FIP effect (the abundance enhancement of elements with first ionization potential &lt; 10 eV in the corona with respect to photospheric values) with height above an active region observed at the solar limb, with emphasis on the so-called transition region lines.
Ulysses Observations of Nonlinear Wave-wave Interactions in the Source Regions of Type III Solar Radio Bursts
Authors: Thejappa G. , MacDowall R. J. 
Published: July 2016

AbstractThe Ulysses Unified Radio and Plasma Wave Experiment (URAP) has observed Langmuir, ion-acoustic and associated solar type III radio emissions in the interplanetary medium. Bursts of 50–300 Hz (in the spacecraft frame) electric field signals, corresponding to long-wavelength ion-acoustic waves are often observed coincident in time with the most intense Langmuir wave spikes, providing evidence for the electrostatic decay instability. Langmuir waves often occur as envelope solitons, suggesting that strong turbulence processes, such as modulational instability and soliton formation, often coexist with weak turbulence processes, such as electrostatic decay, in a few type III burst source regions.
A Magneto-Hydrodynamic Study of Pre-Flare Loops
Authors: Hasan S.S. 
Published: July 2016

The aim of this paper is to discuss the equilibrium and stability of a configuration which may apply to pre-flare loops on the Sun. The analysis is based on the following working scenario:a)The loops exist much prior to the flare and in equilibrium with their surroundings.b)Gradually, starting probably a few hours before the flare, the configuration acquires energy in the form of currents.c)During the period of energy build-up, the loops are MHD stable.d)The flare occurs only after there is adequate energy in the currents.
Prominences and Solar Activity
Authors: Švestka Z. 
Published: July 2016

The following subjects were discussed:(1)Filament activation(2)Post-flare loops.(3)Surges and sprays.(4)Coronal transients.(5)Disk vs. limb observations.(6)Solar cycle variations of prominence occurrence.(7)Active prominences patrol service.Of all these items, (1) and (2) were discussed in most detail and we also pay most attention to them in this report. Items (3) and (4) did not bring anything new when compared with the earlier invited presentations given by RUST and ZIRIN and therefore, we omit them.
Algorithms for Controlling chaos: Application to BVP Oscillator
Authors: Rajeskar S. 
Published: July 2016

AbstractWe discuss how chaotic dynamics can be converted into regular motion in Bonhoeffer-van der Pol oscillator. Using a control signal proportional to the actual and desired outputs we study the control of fixed points and limit cycles by making time-dependent perturbations of amplitude of external force. We show the round-off induced periodicity in the digital computer simulations of orbits on chaotic attractor. We illustrate the stabilization of unstable periodic or bits by adding periodic pulses of small magnitude.
Chaotic Stellar Dynamics During Collective Interactions
Authors: Subbarao D. , Uma R. 
Published: July 2016

AbstractWe prove a basic result for collisionless galactic models that collective motion not only introduces Landau damping but also intrinsic chaos of typical star dynamics in the phase plane when a small perturbative wave disturbance is present. The Melnikov method is used; the consequences of the chaos and quasilinear diffusion are pointed out.
Dynamical Instability of Trapezium Type Multiple Stars
Authors: Mirzoyan L.V. 
Published: July 2016

AbstractThe properties of the Trapezium type multiple stars are discussed. The existing data confirm the dynamical instability of the Trapeziums. They show that because of the specific space configurations of components the Trapezium type multiple stars are disintegrated completely or partly (becoming ordinary systems with smaller number of components). The disintegration time is estimated some million years for Trapeziums with negative total energies and much shorter when their total energies are positive. There are some evidences in favour of the existence of Trapeziums possessing positive total energies.
The Effect of Multiplicity of Stellars Encounters and the Convergence of Collision Integral in the Stellar System
Authors: Petrovskaya Irina V. 
Published: July 2016

AbstractThe multiplicity factor of stellar encounters in the infinite homogeneous layer with the constant thickness H has been studied. It is seen that simultaneous effect of Chaotically distributed distant field stars leads to the convergence of the collision integral for the great distances in the plane disk and in the layer of the constant finite thickness.
On Gravothermal Instability of Anisotropic Self-Gravitating Gas Spheres: Singular Equilibrium Solution
Authors: Spurzem R. 
Published: July 2016

AbstractA reinvestigation of the linear perturbation theory is presented, which examines the hydrostatic readjustment of an isolated self-gravitating gas sphere to a redistribution of energy. The here presented model describes a stellar system by the common equations of gas in hydrostatic equilibrium but with the effect of the anisotropic velocity distribution on the pressure gradient. We take as equilibrium models the singular isothermal solution with and without anisotropy. The total variation of the Boltzmann entropy resulting from a perturbation of the system caused by a redistribution of heat (i.e. r.m.s. kinetic energy of the stars) is calculated for anisotropic solutions to first order as well as to second order for the isotropic equilibrium. The extremized eigenfunctions which represent the entropy and anisotropy perturbation functions, are determined analytically. They exhibit gravothermal behaviour in the central region where heat is removed. It is also found that the anisotropy readjusts non-thermally in the sense that the system departs from isotropy although the total entropy increases.
Stability of the Triangular Lagrangian Solutions of the Photo Gravitational Restricted Three-Body Problem in the Three-Dimensional Case
Authors: Murtuza Md. Ghulam , Kumar Vijay , Choudhry R.K. 
Published: July 2016

AbstractThe stability of the triangular Lagrangian solutions for the photo-gravitational restricted three-body problem in the three-dimensional case is investigated for the case when the resonances are absent and also when the resonances are present. Stability is proved for most (in the sense of Lebesgue) initial conditions for all μ < μ0 except for the resonance cases.
Tidal Force of Sun Due to Planetary Radial Alignment and Sun-Spot Cycle
Authors: Verma S.D. 
Published: July 2016

AbstractIt is well known that the Sun’s radiation and a large number of phenomena occurring on the sun have influence on the Earth’s near environment i.e. Atmosphere, Ionosphere, Magnetosphere, etc. These manifest themselves as day-night, seasons, tides and many changes in the neutral atmosphere; changes in meteorological parameters. These changes are directly or indirectly related to variations in solar parameters, such as solar flares, magnetic storms, variations in sunspot number occurring in solar photosphere. Sunsports are observed, their number counted and their accurate records maintained for long time (many centuaries). The sunspot number seems to follow periodic changes with several periods; mainly 11 years and 23.5 years. Recently it has been shown that the combined tidal force of the inner planets and two largest planets, Jupiter and Saturn, have periodic change of 11 and 23.5 years. It was proposed that this small force may be having a tiny influence on the surface of the Sun and causing some nonlinear effect which results into formation of sunspots and thus causes the variations in the number of sunspots. In the present work it is shown that whenever the combined tidal force on sun increases then sunspot number seems to increase and when force decreases sunspot number decreases. This is shown for Solar Cycle number 21.
Particulate Detection in the Near Earth Space Environment Aboard the Long Duration Exposure Facility Ldef: Cosmic or Terrestrial?
Authors: McDonnell J.A.M. , Sullivan K. , Stevenson T.J. , Niblett D.H. 
Published: July 2016

AbstractExamination of surfaces exposed for more than five and a half years, from detectors with unique attitude stabilisation relative to the orbital velocity vector, offers scope for examining definitively the sources of hypervelocity space particulates. Surfaces reveal discrete crater morphologies, crater size distributions and incident flux distributions. Discrete crater studies will later also reveal the chemistry of residues which can, especially via the capture cell principle, lead to elemental analysis of micron dimensioned particles.First analyses of the flux data from the thin foil perforation experiments (MAP) involve a study of the statistics of the forward (ram) direction, the rear (trailing) direction and the space pointing direction. Modelling of the dynamics of geocentrically bound and unbound orbits yields evidence that the characteristics of the particles, and hence probably their source, change over the particle size range measured by the experiment. Smaller particles (&lt; 1 μm diameter) have lower velocities which could include geocentrically bound particulates, whereas the larger particles (5-10 μm diameter) can be identified with “cosmic” particles of interplanetary or interstellar origin.