bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recently Developed Distance Criteria
Authors: Paturel G. 
Published: March 2016

The problem of the determination of distances in astronomy (the so-called problem of the distance scale) is a very old and important problem. About 280 BC Aristarchus of Samos, the famous greek astronomer of the Alexandrian school, already devised a method to find the relative distances to the Sun and Moon in terms of the size of the Earth. Later, Eratosthenes (about 200 BC), another greek astronomer, measured the Earth’s diameter; so the zero-point of this first distance scale was fixed.Now we are interested by extragalactic distances but the same approach is made : (i) determination of relative distances (ii) determination of the zero-point to obtain absolute distances.Some distance criteria can be used to determine the zero-point. These criteria cannot generally be used at a great distance. They permit a comparison between galactic objects, like Cepheids, Novae, Supergiants ..., globular clusters..., and the same counterparts recognized in external galaxies. Often application is limited to nearby galaxies. In a first section we will briefly present this kind of distance criteria. For more distant galaxies other criteria must be employed, the zero-point being here fixed with nearby galaxies whose distances are known from the preceding step. We will discuss these criteria in a second section.
Some Features of Evolution of Meteor Streams
Authors: Babadzhanov P.B. , Obrubov Yu.V. 
Published: March 2016

AbstractIt is shown that a number of features of meteor showers such as the correlation of orbital semimajor axes and longitudes of the ascending nodes with meteor magnitudes, the restriction of visibility periods and the displacement of maximum activity dates is explained by the joint influence of planetary perturbations, the Poynting-Robertson effect and its corpuscular analogue, light pressure and ejection velocities of different mass meteoroids from cometary nuclei.
Small-Scale Radio Jets
Authors: Wilkinson P.N. 
Published: March 2016

Here I shall interpret ‘small-scale’ to mean a few kpc or less. Such jets occur over a wide range of emitted energies (e.g. 1039erg s–1 in M87, 1046 in 3C273) and we do not know if they are manifestations of the same basic phenomenon or whether Nature is fooling us in some way despite the morpholigicaI similarities. For the moment, it seems sensible to assume an underlying unity and to use the observations to explore the jet phenomenon in different guises.With the highest resolutions obtainable with VLBI, our goal is to elucidate the nature and properties of the central energy source. To this end, we can ask various questions which our observations are expected to bear upon both now and in the future. How do jets form and propagate from the energy source? Are the jets ccnfined/colIimated or ballistic? Why are some jets much stronger than others - is this intrinsic or an evolutionary or relativistic effect - or all three? Why are only some sources superlumina Is? Why are most jets ore-sided? Does the relativistic velocity implied by super I urninaI motion on the pc-scale continue into the kpc-scale jets?
NLTE Masking and the Kiev Fe I Oscillator Strengths
Authors: Rutten Robert J. 
Published: March 2016

This contribution serves to advertise the empirical solar-spectrum determinations of the oscillator strengths of 860 Fe I lines by Gurtovenko and Kostik (1981), by showing that these Kiev data contain just the lines needed in cool-star abundance analyses, and by explaining why they are so good. For details, see Rutten and Kostik (1982) and Rutten and Zwaan (1983).Figures 1 and 2 show why the Kiev gf-values are so useful. While the precise Oxford measurements (see Simmons and Blackwell, 1982, for references) cover the low-excitation lines (Fig. la) which are mostly too violet and too strong for abundance studies, the Kiev workers have added the best lines in the solar visual, thus precisely the weaker lines of higher excitation one needs (Fig. 1b). Figure 2 demonstrates this for the solar Fe I curve of growth: the Doppler part, which is the only really useful part, is made up of Kiev lines (dots).
Recent Advances in X-Ray Astronomy
Authors: Tanaka Yasuo 
Published: March 2016

X-ray astronomy was born in June 1962 with a totally unexpected discovery of a bright X-ray source (presently known as Sco X-1) in a historic rocket flight conducted by Riccardo Giacconi, Herb Gursky, Frank Paolini and late Bruno Rossi. In the last 30 years, astronomy through the newly opened window has made a dramatic expansion.The universe contains enormously rich varieties which had been left unexplored until recent times. From 40’s through 60’s, new wavelength windows, radio, infrared and X-rays successively opened. As a result, the presence of objects and regions distributed over an extremely wide temperature range from a few Kelvin through hundreds of millions of Kelvin were discovered. A burst of surprising discoveries made in 60’s marked the opening of a whole new era of multi-wavelength astronomy.
Report of the IAU WGAS Sub-group on Numerical Standards
Authors: Standish E.M. 
Published: March 2016

AbstractThe Report of the Sub-Group on Numerical Standards of the IAU Working Group on Astronomical Standards (WGAS) is presented. The report is intended to incorporate the majority of the responses received from the e-mail recipients of the series of WGAS Circulars. The report proposes to retain the present (1976) IAU System of Astronomical Constants and also proposes to establish a IAU File of Current Best Estimates. Further, the report proposes the establishment of a Maintenance Committee, governed by a set of proposed by-laws, in order to oversee the maintenance of the new file.
Current Status of Geophysical Models of Nutation
Authors: Mathews P.M. , Dehant V. 
Published: March 2016

Geophysical modeling of nutations involves (a) the formulation of a general theory of the forced nutations of an idealized Earth (spheroidal, oceanless, elastic), supplemented by separate theoretical treatments of the effects of the oceans, anelasticity, and other deviations from the ideal, and (b) fitting of the theoretical expressions to VLBI-estimated amplitudes of the various spectral components of the nutations. The aim is to obtain best-fit estimates of Earth parameters which influence the nutations; and the degree of success of the modeling is judged by the precision of the estimates obtained, as well as the quality of the fit as measured by χ2red, the chisquared per degree of freedom.We present here our findings from two types of fits using, for the observational input, the nutation amplitude estimates for seven important pairs (retrograde and prograde) of circular nutations, together with their standard errors and mutual correlations, which were kindly furnished by T.A. Herring (private communication, 1993). The theoretical framework employed was that of Mathews et al. (1991), hereinafter referred to as MBHS, together with the Zhu and Groten (1989) rigid Earth nutation series modified to take account of the recently-estimated correction of −0.3mas/cyto the precession constant. Estimates of ocean tide effects, and of anelasticity effects based on Wahr and Bergen’s (1986) results for model QMU with α = 0.15 (hereafter abbreviated to WB), were taken from Herring et al. (1991). Alternative estimates of anelasticity effects (DZ, due to Dehant (1990) based on the Zschau model), were also considered.
Progress in Realization of the Time Unit and Scales
Authors: Kovalevsky J. 
Published: March 2016

AbstractThe establishment of the TAI is done in two steps: the construction of the EAT from clocks in laboratories, then its steering by primary frequency standards. Great progress in the precision and stability of EAL was made by the generalized use of GPS time transfer and by the introduction of hydrogen masers and new very performant clocks. Only two primary frequency standards are sufficiently accurate to steer the frequency of TAI, but new standards are now being assessed. The present stability of TAI is 5.10−15 and the accuracy 2.10−14. Improvements should occur in the years to come.The establishment of the International Atomic Time (TAI) and the resulting Coordinated Universal Time (UTC) by the time section of BIPM is done in two steps (Guinot and Thomas, 1988). At first, a free atomic scale, EAL (Echelle atomique libre) is built in two month blocks combining data from about 200 atomic clocks kept by 60 laboratories and regularly reported to the BIPM by 45 centres which maintain a local coordinated universal time, UTC(k). Then, the duration of the scale interval of EAL is compared with data from primary caesium standards producing the SI second which, in turn, is converted on the rotating geoid as the unit scale of TAL A linear function of time with the necessary slope is added to EAL to ensure the accuracy of the TAI scale interval.
The Variation of UT from 700 BC to the Present
Authors: Stephenson F.R. , Morrison L.V. 
Published: March 2016

AbstractRecords of solar and lunar eclipses in the period 700 BC to AD 1600 originating from the ancient and medieval civilisations of Babylon, China, Europe and the Arab world are amassed and critically appraised for their usefulness in answering questions about the long-term variability of the Earth’s rate of rotation. Results from previous analyses of lunar occultations in the period AD 1600-1955.5 and from high-precision data in AD 1955.5-1990 are included in the dataset considered in this paper.
Joint Discussion 6: Sun and Heliosphere - Challenges for Solar-Terrestrial Physics, Magneto-and Hydrodynamics
Authors: Huber Martin C.E. , Pedersen Arne , Fröhlich Claus 
Published: March 2016

There is one astrophysical system, where the sites of a star’s mass loss can be localised and observed in detail, and where the behaviour of the resulting stellar wind in the star’s environment and around orbiting obstacles can be investigated in situ: it is the Sun, the heliosphere and the surroundings of planets — among the latter most prominently the terrestrial magnetosphere. Indeed, within a year or so a fleet of satellites equipped with sophisticated remote-sensing and in-situ instruments will make this astronomical paradigm, or more precisely, the solar-terrestrial system accessible to intensive, multi-disciplinary study.Four identical CLUSTER spacecraft, orbiting the Earth within the magnetosphere, the surrounding space and the particularly interesting plasma boundary layers will perform a three-dimensional in-situ study of plasma-heating, particle-acceleration and other small-scale plasma processes (Schmidt and Goldstein,1988). A number of other missions — some of them already in orbit, like GEOTAIL and WIND, some to be launched within one or two years, like INTERBALL and POLAR — will provide information about the Earth’s magnetosphere and the solar wind on larger spatial scales. These missions are described in a Brochure issued jointly by the European Space Agency, NASA, the Japanese Institute of Space and Astronomical Science and the Rssian Space Agency, which can be obtained from A. Pedersen at the above address.
Observable Signals of Coronal Heating Processes
Authors: Venkatakrishnan P. 
Published: March 2016

AbstractThe solar corona is thought to be sustained by waves, currents, turbulence or by velocity filtration. For efficient wave heating of the corona, only the Alfven waves seem to survive the effects of steepening and shock dissipation in the chromosphere (Zirker, 1993, Solar Phys. 148,43) and these can be dissipated in the corona by mode conversion or phase mixing (Priest, 1991 in XIV Consultation on Solar Physics, Karpacz). Enhanced line width of 530.3 nm coronal line seen within closed structures (Singh et al., 1982, J. Astrophys. Astron. 3,248), association of enhanced line width of HeI 1083 nm line with enhanced equivalent width (Venkatakrishnan et al., 1992, Solar Phys. 138,107), and gradients seen in the MgX 60.9 and 62.5 nm coronal line width (Hassler, et al., 1990, Astrophys. J. 348, L77), are possibly some examples of the observed signals of wave heating. Current sheets, produced in a variety of ways (Priest and Forbes, 1989, Solar Phys. 43,177; Parker, 1979, Cosmical Magnetic Fields, Ox. Univ. Press), can dissipate and provide heat. The properties of current sheets can be inferred from fill factors, emission measures (Cargill, 1994, in J.L. Burch and J.H. Waite, Jr. (eds.) Solar System Plasma Physics: Resolution of Processes in Space and Time, AGU Monograph), hard xrays (Lin et al., 1984, Astrophys. J. 283,421), and radio bursts (Benz, 1986, Solar Phys. 104,99). The association of large scale currents with enhanced transition region (deLoach et al., 1984, Solar Phys. 91,235.) and regions of enhanced magnetic shear with brighter corona (Moore et al., 1994, Proc. Kofu Symp) are of some possible interest in this context. Self consistent calculations of the turbulent cascade of energy from the scales of photospheric motions down into dissipative scales (Heyvaerts and Priest, 1992, Astrophys. J. 390,297) predict the width of coronal lines as a function of the properties of the forcing flows. Velocity filtration caused by free streaming effects off a non maxwellian boundary distribution of particles may well result in a plasma having coronal properties (Scudder, 1992a, Astrophys. J. 398,299; 1992b, Astrophys.J.11 398,319). The observable signals are the variation of line shapes with altitude.
Fractionation of the Solar Wind
Authors: Von Steiger R. 
Published: March 2016

The composition of the solar wind (SW) is not a true sample of the solar composition, but it is fractionated with respect to the solar photosphere. This fractionation follows the well-known first ionization potential (FIP) pattern: When plotting the SW abundances with respect to the solar abundances as a function of FIP, a step function is obtained (Fig. 1). The step at ∼ 10eV has a height of 3-5 in the slow SW, but this is reduced to 1.5-2 in the fast streams, which originate in the coronal holes. The data given in Fig. 1 are collected and discussed in von Steiger & Geiss (1994), including the “FIP exceptions”, Kr and Xe.The process leading to the observed overabundance of the low-FIPs has been located to operate by atom-ion separation across magnetic field lines in the chromosphere (Geiss, 1982), because this is the only region of the solar atmosphere where a significant fraction of the gas is neutral. The fractionated abundances observed in the S W are thus important tracers for processes and conditions at this site.
Network of Oriental Robotic Telescopes
Authors: Querci François R. 
Published: March 2016

We should like to report on the Network of Oriental Robotic Telescopes, otherwise the ORT network. Our objective is non-stop observations of variable stars by collaboration with other networks of automated photometric telescopes, complementary to the ORT network in longitude and latitude intervals, such as the GNAT in the U.S.A., the Chilean cordillera stations, the South African stations, etc. As a first step we will deal with photometric telescopes, then we will extend them to spectroscopy.From 12-year archives of meteorological satellites, it appeared that sites located around the north latitude from 15° to 35° and from 10° west to 110° east in longitude have high-quality astronomical conditions with a significant annual number of clear nights. Such sites involve Islamic countries from Morocco to the western deserts of China. In addition to their astronomical history, the Islamic countries are suitable because they have high mountains in semi-desert areas, i.e. a clear sky with low telluric absorption. The final site selection will be based upon local astronomical tests, such as seeing and scintillation measurements.
Analysis of the Residuals between Theoretical Nutations and VLBI Observations
Authors: Dehant V. , Feissel M. , de Viron O. , Yseboodt M. , Bizouard Ch. 
Published: March 2016

The recent theoretical developments have provided accurate series of nutations, which are close to the Very Long Baseline Interferometry (VLBI) data. At the milliarcsecond (mas) level, three series are available: MHB2000 (Mathews et al. 2000), FG2000 (Getino and Ferrándiz 2000), and SF2000 (Shirai and Fukushima 2000a,b) (see Dehant 2000, and in this volume, for more information and for a short description of these models).In the first part of our work we have compared these models with the (VLBI) observations (Ma et al. 2000) by computing rms of the residuals for several time intervals of measurements. We have concluded that these series have comparable precision.
Scattering of Planetesimals from Young Planetary Disks: Application to the β Pictoris System
Authors: Beust Hervé , Thébault Philippe 
Published: March 2016

AbstractTransient redshifted events monitored in the spectrum of β Pictoris have been interpreted as resulting from the evaporation of numerous comet-like bodies in the vicinity of this star. The dynamical origin for this phenomenon is attributed to mean-motion resonances (4:1 and 3:1) with a Jovian-like planet. Numerical simulations of this phenomenon are able to correctly reproduce the dynamical characteristics of the star-grazers observed. The numerical study allows to estimate the density of the planetesimal disk from which the bodies are supposed to originate, i.e. ∼ a few 108 bodies per AU. A key issue with this model is the refilling of the resonances, as without refilling they should be cleared within a few 105 yr and the observed phenomenon should stop. Collisions among planetesimals are a plausible mechanism. Collisional simulations show that collisions are able to sustain the observed phenomenon over much more than 106 yr, provided the population of the disk is high enough. The mass density of this population is estimated to a few tens of Earth masses per AU, which is only marginally realistic. However, the mass estimate is very poorly constrained.
Comets and Circumstellar Dust
Authors: Waelkens C. , Waters L.B.F.M. 
Published: March 2016

AbstractSpectra obtained with the Infrared Space Observatory ISO of the dusty disks surrounding young stars display several characteristics which suggest the presence of large amounts of cometary material during these early stages. Of special interest are crystalline silicates and hydrated silicates, which surprisingly appear to be present already in cool material surrounding young objects. Another surprise is the occurrence of cometary features in the disks surrounding some binary post-AGB stars.
The Importance of Spatial Information in Sunspot Records
Authors: Brooke John M. , Pelt Jaan , Pulkkinen Pentti , Tuominen Ilka 
Published: March 2016

AbstractWe show that the spatial information in historical sunspot records, in particular the latitude of the spots, can be of great importance in determining the long term behaviour of the solar magnetic cycle. We examine a continuous record of sunspots with full spatial data from 1853-1996 compiled from the records of Carrington, Spörer, the GPR and SOON. Analysis of the latitudinally-weighted observations indicates that there is a previously unremarked oscillation of the solar magnetic equator with a period of approximately 90 years.
Driving Layer of Solar Activity
Authors: Wang Jingxiu 
Published: March 2016

AbstractThere should be a driving layer on the Sun, in which the interaction between magnetic field and plasma motion would provide enough magnetic energy and necessary topology for the explosion of solar activity in the corona.Although the exact location of the driving layer is not known, phenomenologically, the photosphere is acting, in many aspects, as the driving layer. Vector magnetic field measurements on the photosphere are greatly needed in clarifying the nature of the driving. Two elementary processes, flux emergence and cancellation, and one basic structure, magnetic interface between topology-independent magnetic loops, are key elements in the driving.
X-Ray Substructures of BCS, NORAS, REFLEX, Radio Halos/Relics and Cooling Flow Clusters of Galaxies
Authors: Schuecker Peter , Böhringer Hans , Feretti Luigina 
Published: March 2016

AbstractThe results of a systematic study of substructures in X-ray surface brightness distributions of BCS, NORAS, REFLEX, radio halo, relic, and cooling flow clusters of galaxies based on RASS data are presented. At least 40 percent of the clusters show substructure. Indications for a cluster morphology-density relation are found. The fraction of clusters with substructure seems to be higher for halo and relic clusters and lower for clusters with cooling flow signature.
Radio Sources and Their Environment
Authors: Owen Frazer , Ledlow Mike , Eilek Jean 
Published: March 2016

AbstractThe properties of radio sources in and outside of Abell clusters are reviewed. The properties of sources in and out of Abell clusters are shown to be surprisingly similar. However, sources in dense cluster cores do not fit this pattern and, as in Virgo A (M87), have a significant, sometimes dominant input of energy into the “cooling core” environment.
The Mars Global Surveyor Mission: Description, Status, and Significant Results
Authors: Albee Arden 
Published: March 2016

AbstractThe Mars Global Surveyor (MGS) spacecraft entered an elliptical orbit at Mars on September 11,1997. Until March 1999 it acquired scientific data from decreasing-sized orbits as it alternated between aerobraking and nadir-pointing modes. This time period provided tremendous advances in our knowledge of the shape and topography, the gravity field, the magnetic field, and the atmospheric structure and dynamics of Mars. In April 1999 MGS entered its planned two years in the mapping mode. In this mode the high-gain antenna tracks Earth so that the instruments can take data continuously and so that the camera system can return high-resolution data in real-time. IR spectral and temperature data, as well as high-resolution images are providing new insight into the geologic evolution of Mars. All data is being archived at about six month centers so that it is available in electronic format to the international community.
Black Hole Binary Mergers
Authors: Makino Junichiro 
Published: March 2016

AbstractI overview the current understanding of the evolution of massive black hole (MBH) binaries in the center of the host stellar system. One of the main questions is whether the stellar dynamical effect can make the MBH binary hard enough that they can merge through gravitational wave radiation. So far, theories and numerical simulations suggested otherwise, since the hardening time scale becomes very long once ”loss cone” is depleted. I’ll present the result of recent simulations on this hardening time scale, and discuss its implication on the formation history of massive black holes.
The Early Chemical Evolution of Dwarf Irregular Galaxies
Authors: Hensler Gerhard , Recchi Simone , Köppen Joachim , Rieschick Andreas 
Published: March 2016

AbstractInvestigations have been performed to understand the age of dwarf irregular galaxies from the point of view of their presently low chemical abundances and the enhanced star-formation rate. While for a few objects, like e.g. I Zw 18, their assumed relative youth can be verified by models taking a double-starburst behavior into account, those dlrrs with old underlying stellar populations have passed the regime of observed N/O-0 values within almost 2 Gyrs after their formation even with gas loss by means of supernova-driven galactic winds. Therefore alternative processes like gas infall must be invoked.