bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Transformation from FK4 To FK5 and the Definition of UT
Authors: Xu B.X , Xia Y.F , Huang T.Y. , Han C.H. 
Published: July 2016

AbstractThe different procedures of the transforation from FK4 to FK5 are reviewed. With these procedures some numerical examples for selected FK4 stars are given. Basing on the original work of Fricke (1985), we prefer to select the procedure developed by Standisti (1982). One of the main reasons for the procedure of Aoki et al. (1983) is to consist with the new definition of UT. Since the corrections “FK5 - FK4” for many stars are significant, even if adopting this procedure, it is still impossible to avoid the effect of the right ascension discontinuities on UT.
The Use of the Nonrotating Origin in the Computation of Apparent Places of Stars for Estimating Earth Rotation Parameters
Authors: Capitaine N. , Chollet F. 
Published: July 2016

AbstractA new procedure has been devised for computing apparent places of stars in the intermediate frame (Capitaine 1990) linked to the nonrotating origin (Guinot 1979) for estimating the Earth rotation parameters (ERP) from astrometric observations. The latitude and time parameters as derived by this procedure have been compared to the parameters as derived from the classical procedure used for the reduction of Paris astrolabe observations (Chollet 1984). The consistency between the two procedures has been found to be of the order of a few 10−4ʺ, which is under the order of precision of the computations in the classical procedure. The new procedure, which is more directly related to the Earth rotation, is proposed to be used for the derivation of the ERP in the Hipparcos frame from existing astrometric observations, which is planned for the near future (IAU WG on “Earth Rotation in the Hipparcos Reference Frame”).
Digital Image Processing in the Analysis of Astrometric Plates
Authors: Garcia A.Lopez , Valdes J.L. , Orti J.A.Lopez , Machi R.Lopez. , Perez G.J. 
Published: July 2016

AbstractIn this paper, we display an improvement to our process of semi-automatic measuring of astrometric plates, in which the photometric sensor is substituted by a CCD system of image getting and digitalization. The advantages of this method are analyzed taking into account the possibilities of the image analysis in the space and frequency domain.
The Approach of Improvement to Stellar Coordinate
Authors: Ma W.Z. 
Published: July 2016

AbstractThis article presents a new method for observing minor planets. The observation is operated with a photo–electronic imaging devise CCD and a lower latitude meridian circle.The CCD is mainly used except it is during the favourable opposition of the minor planet when the meridian circle is mainly used in this method. The method can improve precision of observation of planetary position and enlarge scope of observation of planetary orbit. Therefore, the measured precision of zero point of stellar coordinate could be increased. The key of succeeding is that more precise result is got using the CCD.The experiment in this article indicates that this method is a good way:While a minor planet and calibration stars locate in the same image of the CCD, the measured precisions of the minor plant areσα = ±0″.03, σ´ ±0″.035;While the minor planet and calibration stars are located in different images of the CCD, the precisions areσα = ±0″.06, σδ = ±0″.08.
Comparison of the FK5 Proper-Motion System with a Kinematic Distribution Function
Authors: Ratnatunga Kavan U. , Warren Wayne H. 
Published: July 2016

AbstractA model for the kinematic distribution function of our Galaxy can be used as an independent confirmation that a reference system is free of Earth motions and retains the true kinematics of the stars. Maximum likelihood can simultaneously estimate the parameters required to calibrate distances to the stars, represent the kinematic distribution function, and check on residual Earth rotations in the proper-motion system. The global maximum-likelihood analysis uses all available information: photometry, trigonometric parallax, proper motion, and line-of-sight velocity for a well-defined catalog of stars. Awaiting observations from HIPPARCOS, preliminary testing of the algorithm on available ground-based observations is discussed.
Results from Kodaikanal Synoptic Observations
Authors: Sivaraman K. R. 
Published: July 2016

AbstractThe synoptic observations of Kodaikanal form one of the longest unbroken solar data from the beginning of the 20th century to the present day, and consists of the white light and monochromatic images of the sun. In this review, I shall discuss the results of the investigations in two areas using these data: (i) Tilt angles of the magnetic axes of bipolar spot groups, and (ii) structure and dynamics of large scale unipolar magnetic regions on the solar surface.The observed properties and patterns of behaviour of the tilt angles can be used as effective diagnostics to infer the physical conditions in the subsurface layers of the sun, and thus get an insight into the physical effects that act on the rising magnetic flux tubes during their journey through the convection zone to the surface.The second topic of discussion here, namely, the studies of the dynamics of unipolar regions over several solar cycles, show that the global solar activity has a high latitude component which manifests in the form of polar faculae, in addition to the well known sunspot activity at the middle and low latitudes. This raises the question about the origin of this high latitude component.
22-Year Periodicity in the Solar Differential Rotation
Authors: Javaraiah J. 
Published: July 2016

AbstractUsing the data on sunspot groups compiled during 1879–1975, we determined variations in the differential rotation coefficientsAandBduring the solar cycle. The variation in the equatorial rotation rateAis found to be significant only in the odd numbered cycles, with an amplitude ∼ 0.01μrads−1. There exists a good anticorrelation between the variations of the differential rotation rateBderived from the odd and even numbered cycles, suggesting existence of a ‘22-year’ periodicity inB. The amplitude of the variation ofBis ∼ 0.05μrads−1.
Coronal Structures as Tracers of Sub-Surface Processes
Authors: Pevtsov Alexei A. , Canfield Richard C. 
Published: July 2016

AbstractThe solar corona – one of the most spectacular celestial shows and yet one of the most challenging puzzles – exhibits a spectrum of structures related to both the quiet Sun and active regions. In spite of dramatic differences in appearance and physical processes, all these structures share a common origin: they are all related to the solar magnetic field. The origin of the field is beneath the turbulent convection zone, where the magnetic field is not a master but a slave, and one can wonder how much the coronal magnetic field “remembers” its dynamo origin. Surprisingly, it does. We will describe several observational phenomena that indicate a close relationship between coronal and sub-photospheric processes.
Analysis of the 9th November 1990 flare
Authors: Joshi Anita , Uddin Wahab 
Published: July 2016

AbstractIn this paper we present complete two-dimensional measurements of the observed brightness of the 9th November 1990Hαflare, using a PDS microdensitometer scanner and image processing software MIDAS. The resulting isophotal contour maps, were used to describe morphological-cum-temporal behaviour of the flare and also the kernels of the flare. Correlation of theHαflare with SXR and MW radiations were also studied.
Tessellation of SoHO Magnetograms
Authors: Srikant R. , Singh Jagdev 
Published: July 2016

AbstractA gradient based algorithm which divides arbitrary images into non-overlapping surface filling tiles of opposite polarity is used to study the flux and size distributions of large scale magnetic flux concentrations in solar and heliospheric observatory (SoHO) magnetograms. The mean absolute flux and size of the concentrations at the considered scale is found to be about 1.7 × 1018Mx and 5.2 Mm for both polarities. The form of the flux distribution is characterized by a skewness ofα3= 4.9 and a kurtosis ofα4= 42.8. The fall in the distribution in the range 6.5 × 1017Mx to 5 × 1018Mx is described by an exponential fit, in agreement with a model for the sustenance of quiet region flux.
Magnetoconvection and the Solar Dynamo
Authors: Nordlund Å. , Dorch S. B. F. , Stein R. F. 
Published: July 2016

AbstractWe review current understanding of the interaction of magnetic fields with convective motions in stellar convection zones. Among the most exciting recent results is the discovery that magnetic fields need not primarily be confined to the stable layer below the convection zone; numerical simulations have shown that surprisingly, strong magnetic fields can be maintained in the interior of the convection zone.
Large-scale Flow and Transport of Magnetic Flux in the Solar Convection Zone
Authors: Ambrož P. 
Published: July 2016

AbstractHorizontal large-scale velocity field describes horizontal displacement of the photospheric magnetic flux in zonal and meridian directions. The flow systems of solar plasma, constructed according to the velocity field, create the large-scale cellular-like patterns with up-flow in the center and the down-flow on the boundaries. Distribution of the largescale horizontal eddies (with characteristic scale length from 350 to 490 Mm) was found in the broad equatorial zone, limited by 60° latitude circles on both hemispheres. The zonal averages of the zonal and meridian velocities, and the total horizontal velocity for each Carrington rotation during the activity cycles no. 21 and 22 varies during the 11-yr activity cycle. Plot of RMS values of total horizontal velocity is shifted about 1.6 years before the similarly shaped variation of the magnetic flux.
Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo
Authors: Belvedere Gaetano , Pipin V. V. , Rüdiger G. 
Published: July 2016

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg &amp; Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg &amp; Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).
Exploring Coronal Structures with SOHO
Authors: Karovska M. , Wood B. , Chen J. , Cook J. , Howard R. 
Published: July 2016

AbstractWe applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board SOHO: LASCO and EIT.
Solar Wind Variation with the Cycle
Authors: Veselovsky I. S. , Dmitriev A. V. , Suvorova A. V. , Tarsina M. V. 
Published: July 2016

AbstractThe cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density, velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics of the solar wind are reviewed with the emphasis on the cycles.
Remote Sensing of the Heliospheric Solar Wind using Radio Astronomy Methods and Numerical Simulations
Authors: Ananthakrishnan S. 
Published: July 2016

AbstractThe ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in the past 25 years, that while coronal holes give rise to stable, recurring high speed solar wind streams during the minimum of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods. Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation of these disturbances throughout the solar system.
The Onset of Coronal Transients
Authors: van Tend W. 
Published: July 2016

Recently Anzer (1978) has discussed a model for the motion of transients in the high corona. In this model the transient is pictured as a circular current loop with a changing radius r, and having two fixed footpoints separated by a distance 2r0at the solar surface. The transient starts off with zero velocity at the point where r = r0. At that point however the acceleration, which is given byis generally non-zero. In (1) M⊙is the solar mass; G is the gravitational constant; b (which equals a/4, where a was introduced by Anzer (1978)) is a constant on a short time scale, which however may change on a long time scale when mass or electric current is supplied to or lost by the system; f is a function describing the distribution of mass and magnetic flux, qualitatively displayed in Figure la; R is the distance of the top of the current circuit to the solar center; r2/R2as a function of R is shown in Figure lb.
On the Role of Chaos and Instability in the Evolution of Nonlinear Nonstationary Stellar Systems
Authors: Nuritdinov S.N. 
Published: July 2016

AbstractThe role of chaos and instability in evolution of nonlinear, non-stationary stellar system have been discussed. It is possible to distinguish between the only two different cases (i) strongly non-stationary stage when we have the violent relaxation accompanied by the compulsive mixing (ii) weakly non-stationary state or quasilinear case, when the quasidiffusion mixing takes place. In case (i), the chaos and chaotic motion g stars play very important role and in case (ii) the role of any type of instability is important.
Ergodity of the Motions in the Dynamical Systems with Two Degrees of Freedom
Authors: Agekian T.A. , Mylläri A.A. , Orlov V.V. 
Published: July 2016

AbstractWe study a process of stochastization of the motions in an example of the Henon-Heiles model. We propose a new method to study this process a method of the field of directions of motion in the meridional plane. A numerical integration of the equation for the derivative of this field ∂f/∂n to the normal to a trajectory has been made. We denote the points in which ∂f/∂n → ± ∞, and derive the contours of orbit and folds of directions. The growth of ergodity is connected with the increase of a number and an area of the folds. May be, a successive doubling of a number of folds takes place that results in a chaos. In the transition region we found a complex periodical orbit. The interpretation of this fact may be made as an example of cantori. A transition region has very small sizes about 10−4
The In-Plane Motion of a Geosynchronous Satellite Under the Gravitational Attraction of the Sun, the Moon and the Oblate Earth
Authors: Bhatnagar K.B. , Kaur Manjeet 
Published: July 2016

AbstractThe in-plane motion of a Geosynchronous satellite under the gravitational effects of the sun, the moon and the oblate earth has been studied. The radial deviation (Δr) and the tangential deviation (rcΔθ) have been determined. Here rc represents the synchronous altitude. It has been seen that the sum of the oscillatory terms in Δr for different inclinations is a small finite quantity whereas the sum of oscillatory terms in rcΔθ for different inclinations is quite large due to the presence of the low-frequency terms in the denominator.
Astrophysical Interesting Compound Grains Produced by a Gas Evaporation Method
Authors: Kaito C. , Saito Y. 
Published: July 2016

AbstractProduction methods of Fe3O4grain and MgS grain have been introduced. Fe3O4grain was produced in an Ar gas pressure range of 25 to 100 Torr by evaporating FeO powder. The growth of Fe3O4have been discussed as the result of oxidation of Fe grains. MgS grain produced by the reaction of Mg and S vapors grew in the coagulation of tiny cubic sulfide.
Laboratory Spectra of Amorphous and Crystalline Olivine: An Application to Comet Halley IR Spectrum
Authors: Blanco A. , Orofino V. , Bussoletti E. , Fonti S. , Colangeli L. , Stephens J. R. 
Published: July 2016

AbstractAmong the various silicates proposed as components of cosmic dust grains, olivine is considered one of the most likely materials. In this work we present the infrared spectra of three different types of olivine grains: crystalline, amorphous and synthetic (also amorphous). While the first and second sample derive from the same natural mineral, the third one has been prepared in the laboratory according to the relative cosmic abundances of the elements. The experimental data are used to fit the emission feature observed in the comet Halley spectrum between 8 and 13μm.Satisfactory results are obtained by using synthetic olivine mixed with a small amount (5%) of crystalline grains.
The Optical Properties of Interplanetary Dust
Authors: Lamy P.L. , Perrin J.M. 
Published: July 2016

AbstractAfter briefly evaluating the observations of the Zodiacal Light and F-corona, we review the laboratory results on the light scattering by dust particles and the various theories which have been recently proposed. We then discuss the optical properties of the dust with emphasis on the phase function, the polarization, the color, the albedo and the local enhancement in the Gegenschein.
The Dust in the Coma of Comet Halley
Authors: Hage Joniek I. , Greenberg J. Mayo 
Published: July 2016

AbstractThe interstellar dust model of comets is numerically worked out to satisfy several basic constraints provided by observations of comet Halley and to derive the porosity of coma dust. The observational constraints are: (1) the strengths of the 3.4 μm and 9.7 μm emission bands; (2) the relative amount of silicates to organic materials; (3) the mass distribution of the dust. The results indicate that coma dust has a porosity in the range 0.93 &lt; P &lt; 0.975. Preliminary calculations concerning the observed linear polarization of comet Halley are presented.
Polarimetric Properties of Halley’s Dust
Authors: Sen A.K. , Deshpande M.R. , Joshi U.C. 
Published: July 2016

Abstract:Comet P/Halley was observed polarimetrically for seven nights in IHW and other continuum filters, during the pre and post perihelion passages. The polarimetric observations have been combined with the observations taken by other investigators, to get a complete picture of phase angle and wavelength dependence of polarization of comet P/Halley. Assuming Mie type scattering by cometary grains, the observed polarization data were fitted for a set of complex refractive indices which are (1.387, .032), (1.375, .040) and (1.374, .052) at .365, .484 and .684μm respectively.
Electrostatic Fragmentation of Irregularly Shaped Particles
Authors: Mukai Tadashi 
Published: July 2016

AbstractAn enhancement of the electrostatic stress forces due to the charge concentration on a position with small radius of curvature on the surface of irregularly shaped particle causes the fragmentation of fluffy particle more than expected for a spherical particle. This mechanism may act to produce “dust clusters” as detected in comet P/Halley by Simpsonet al.(1987) and also “dust swarms” near the Earth as reported in Fechtig(1982).
Velocity Distribution of Fragments in Collisional Breakup
Authors: Nakamura A. , Fujiwara A. 
Published: July 2016

AbstractOne of the key outcomes of collisional disruptions to the dust system is the velocity distribution of fragments. A series of laboratory impact experiments were carried out to obtain the mass-velocity and the position-velocity relation of the fragments by taking movie films, and films for tow impacts were completely analyzed.
Constraints on the Parent Bodies of Collected Interplanetary Dust Particles
Authors: Sandford S. A. 
Published: July 2016

AbstractSamples of interplanetary dust particles (IDPs) have now been collected from the stratosphere, from the Earth’s ocean beds, and from the ice caps of Greenland and Antarctica The most likely candidates for the sources of these particles are comets and asteroids. Comparison of the infrared spectra, elemental compositions, and mineralogy of the collected dust with atmospheric entry models and data obtained from cometary probes and telescopic observations has provided important constraints on the possible sources of the various types of collected dust. These constraints lead to the following conclusions. First, most of the deep sea, Greenland, and Antarctic spherules larger than 100 μm are derived from asteroids. Second, the stratospheric IDPs dominated by hydrated layer-lattice silicate minerals are also most likely derived from asteroids. Finally, the stratospheric IDPs dominated by the anhydrous minerals olivine and pyroxene are most likely from comets. The consequences of these parent body assignments are discussed.
Dynamics of the Gas in Spiral Galaxies
Authors: Roberts William W. 
Published: July 2016

AbstractThe dynamics of the gaseous component in disk-shaped galaxies is thought to play an important governing role in star formation, molecule formation, and the degree of development of spiral structure. The prospect that density waves and galactic shock waves are present on the large-scale has received support in recent years from a variety of observational studies. Large-scale shocks provide a most promising mechanism for driving star-forming and molecule-forming events on the scales of many kpc along spiral arms. Such shocks may also govern the kinematics and relative distribution of various galactic tracers. This is particularly apparent in M81 and other external spirals, because of our “bird’s-eye-view” perspective, and for the tracers of HI and CO in our own Galaxy. Comparison of the CO observations with model simulations based on the precepts of the density wave theory shows that these precepts are supported by several observational results.