bluuebunny/crossref_metadata_2025_split huggingface dataset:
Turbulent Convection: A New Model
Authors: Canuto V. M. 
Published: July 2016

AbstractWe use the latest models of turbulence to compute a new expression for the turbulent convective flux, Fc. The new values of Fc are up to ten times larger than those given by the mixing length theory, MLT. Astrophysical considerations indicate that the new model fares better with observational data than the MLT.
Large Scale Convection in Stars : Towards a Model for the Action of Coherent Structures
Authors: Rieutord Michel , Zahn Jean-Paul 
Published: July 2016

AbstractWe show that, representing the descending fluid in a convection zone by a porous medium, the differential rotation of the (rising) fluid is very close to that in an axisymmetric model of the convection zone with anisotropic viscosity.
Convective Cores in Stellar Models
Authors: Roxburgh I.W. , Monteiro M. 
Published: July 2016

AbstractThe condition for homogeneous radiative stellar models to be marginally stable to convection at the centre is investigated for the family of models where the opacity к and energy generation ε are given by power laws in temperature and density κ = κo ρα T−β, ε = εo ρ Tη. The Naur-Osterbrock (1953) condition 6η > 6 + 10β − 15α is a necessary but not sufficient condition. A better estimate is obtained by taking the effective polytropic index n = dlogP/dlogT - 1 to be a linear function of temperature T throughout the model. This gives the conditionThe predictions of this condition agree well with results for a set of stellar models 0 ≤ α ≤ 1, 0≤ β ≤ 5.
The Solar Dynamo
Authors: Brandenburg Axel , Tuominen Ilkka 
Published: July 2016

AbstractThe traditionalαΩ-dynamo as a model for the solar cycle has been successful in explaining the butterfly diagram, phase relations between poloidal and toroidal field, and polar branch migration features. Observational and theoretical achievements in recent years have however shaken this picture. The current trend is towards dynamos operating in the overshoot region of the convection zone. Nevertheless, there are many open questions and a consistent picture has not been established. In this paper we compare recent approaches and discuss remaining problems.
Dynamo Action in Evolved Stars
Authors: Gray David F. 
Published: July 2016

AbstractEvolved stars tell us a great deal about dynamos. The granulation boundary shows us where solar-type convection begins. Since activity indicators also start at this boundary, it is a good bet that solar-type convection is an integral part of dynamo activity for all stars. The rotation boundary tells us where the magnetic fields of dynamos become effective in dissipating angular momentum, and rotation beyond the boundary tells us the limiting value needed for a dynamo to function. The observed uniqueness of rotation rates after the rotation boundary is crossed can be understood through the rotostat hypothesis. Quite apart from the reason for the unique rotation rate, its existence can be used to show that magnetic activity of giants is concentrated to the equatorial latitudes, as it is in the solar case. The coronal boundary in the H-R diagram is probably nothing more than a map of where rotation becomes too low to sustain dynamo activity.
Long-term Polarimetric Activity of the Cool Supergiant μ Cephei
Authors: Arsenijević J. , Jankov S. 
Published: July 2016

AbstractThe intrinsic polarisation parameters P, θ, Q and U of the star μ Cep, in the V spectral region during the period 1979-1989, are presented. The data were obtained from the Belgrade polarimetric observational program. The polarization percentage of the star exhibits change is of about 2.5% during this interval and the position angles change by about 90 degrees. These very large long-term changes of polarization parameters are discussed briefly.
Ca II H High-Resolution Spectral Monitoring of Active Late-type Dwarfs
Authors: Beckman J. E. , López R. J.García , Rebolo R. , Crivellari L. 
Published: July 2016

AbstractWe have monitored Ca II H with a spectral resolution of 8 × 104, in asimple of late-type MS stars over a four-year period. The high resolution enables us to add information on velocity fields to the usual flux monitoring. We detect changes in wavelength of different parts of the Ca II H feature, which can be interpreted as velocity fields in the lower chromosphere, with downflow and upflow of order 0.5 km s−1, depending on the star. Flux variations in Ca II H emission can be ascribed, via velocity tagging, to long-term change in plage cover rather than short-term modulation by (incompletely sampled) rotation cycles.
The Onset of Chromospheres in A-type Stars: The Altair Affair
Authors: Catalano S. , Gouttebroze P. , Marilli E. , Ferrero R. Freire 
Published: July 2016

AbstractHere we present preliminary results on the study of the chromosphere of Altair from Lα high dispersion profiles. We report also the detection of Lα chromospheric emission from α Cep (A7V) and β TrA (F0 V) with the IUE. We show that chromosphere may exist up to B – V = 0.22. The possible heating mechanism, magnetic or nonmagnetic, for the chromosphere of these stars is also discussed.
On the Coronal Activity of RS CVn Systems
Authors: Demircan Osman , Derman Ethem 
Published: July 2016

An analysis of the X-ray emission of a large sample of single MS stars shows that X-ray luminosity is strongly correlated with the photospheric radius (Fleming et al., 1989) which implies the dependence of activity on bolometric luminosity Lbol, effective temperature Teff, and thus stellar mass M (Micela et al., 1985; Bookbinder et al., 1986). The role of the emission area on the coronal activity of RS CVn systems has been noted independently by Majer et al. (1986), and Demircan (1986).By using new data on some well known RS CVn systems, we produce new evidence that above idea is indeed valid. A plot of X-ray luminosity Lx versus (B – V) for the sample of well known RS CVn systems in Fig. 1 shows that cooler, long period, more evolved systems with larger surface area have stronger X-ray emission.
The Distribution of The Periods of the Hagnetic Variable Stars
Authors: Catalano F.A. , Strazzulla G. 
Published: July 2016

SummaryThe distribution of the periods of about 80 of the known variable Ap stars is studied in the framework of the oblique rotator model. It is shown that for the long period variables (P &gt; 100 days) the oblique rotator has trouble in explaining the observed variations.
Kinematic and Dynamic Reference Frames
Authors: Gaposchkin E. M. 
Published: July 2016

AbstractThe fundamental properties of kinematic and dynamic reference frames are defined, first as an abstract concept and second in a practical (although idealized) thought experiment. A four dimensional spacetime description in coordinate free notation illustrates the properties, limitations, and relationships between kinematic and dynamic reference frames. Kinematic reference frames can be defined quite rigorously. Dynamic reference frames cannot be defined so well, but are nonetheless very useful. In practice a combination has been generally adopted. Presently we can materialize purely kinematic terrestrial and celestial reference frames.
A New Parameterization of Polar Motion
Authors: Papo Haim B. 
Published: July 2016

AbstractThe rotational motion of the earth is decomposed into spin, polar motion and local motions. The rotation vector components are associated to phenomena such as precession, nutation, diurnal spin, polar motion and local motions. The above decomposition is accomplished without refering to an earth-fixed CIO pole or BIH zero meridian. The time-like variations of the coordinates of a surface point in a geocentric equatorial reference frame are presented as a function of the rotation vector components. In the rigid earth approximation three scalar parameters are necessary for evaluating point coordinate variations, namely spin rate of the earth, polar motion magnitude and spin rate of the polar motion vector. Two numerical examples are given as an illustration.
The Stellar Reference Frame from Space Observations
Authors: Murray C. A. 
Published: July 2016

Abstract:The HIPPARCOS Satellite, to be launched by the European Space Agency, will provide a stellar reference frame over the whole celestial sphere with an average accuracy of ± 0002 in each coordinate and component of annual proper motion, for some 100,000 stars.The origin of coordinates will be arbitrary. Absolute rotation of the system of proper motions can be obtained by measuring quasars relative to stars in the HIPPARCOS catalogue, either with the NASA Space Telescope or by conventional ground based astrometric observations.
An Attempt to Compare the Radio Astronomical System of Coordinates of Quasars With FK4
Authors: Kumkova I. I. 
Published: July 2016

AbstractA method of comparison of the FK4 system to a system based on extragalactic sources is tested on actual data for 140 sources observed by radio-interferometric and whose optical counterparts have positions referred to FK4. The difference of coordinates is analyzed in spherical harmonics series. The computation show that the method gives satisfactory results. However, the precision of the data prevents from any interpretation in terms of systematic errors of the FK4.
X-Ray Burst Sources - A Simple Two Zone Model
Authors: Buchler J. Robert , Barranco Manuel , Livio Mario 
Published: July 2016

AbstractWith the help of a very simple two zone model, we demonstrate the possibility of periodic thermal relaxation (limit cycle) oscillations in the helium burning envelope of accreting neutron stars. Physically reasonable model parameters can be chosen which yield agreement with the observed features of x-ray bursts and we suggest that this limit cycle is operative in neutron stars which have an accretion rate in a specific range. For hydrogen burning a similar cycle is possible, but it operates at such high temperatures that an unrealistically large accretion rate would be required.
Rotational Modes in A Uniformly Rotating Star
Authors: Smeyers P. 
Published: July 2016

AbstractThe linear adiabatic oscillations of a uniformly rotating star are examined with respect to a co-rotating frame of reference. It is shown that time-independent displacement fields are allowed and can be represented as toroidal fields. The time-dependent oscillation modes are governed by a system of differential equations of the fourth order in time for axisymmetri’c perturbations, and of the fifth order for non-axisymmetric perturbations. Therefore, in comparison to a non-rotating spherical star, a rotating star allows a new class of non-axisymmetric oscillation modes with non-zero frequencies. These modes correspond to the r-modes, which originate from purely toroidal displacement fields in a non-rotating spherical star.
Towards effective data processing: portable software models
Authors: Mistrik I. 
Published: July 2016

AbstractIn many application fields a need for more effective data processing has been identified. There are various means to achieve this goal: 1) new technological developments; 2) new information management and organizational techniques; 3)new methods and tools for systems development; 4) greater awareness of economic, legal, and social aspects of data processing. An attempt is being made to integrate these means into the “optimal solution” of effectiveness problem. The approach taken is to develop flexible software models in order to test for applicability in the real-world environment. Major characteristics of such software models are: 1) portability; 2) modifiability; 3) functionality; 4) operationality.
Aids to the retrieval and evaluation of astronomical data
Authors: Wilkins G.A. 
Published: July 2016

AbstractAuthors, editors and data centres should ensure that data on astronomical objects and systems can be readily located and that their accuracy can be properly judged by the user. In particular, authors and editors should endeavour to ensure that the title, abstract and other retrieval aids are accurate and informative and that the procedures used are described in sufficient detail to allow a proper evaluation of the results. Data centres should, where appropriate, provide additional aids to allow the users to find data efficiently and should, in all cases, ensure that each datafile contains adequate information about the sources of the data and about the significance of the fields in the records of the file.
Dictionnaire de la nomenclature des objets celestes
Authors: Fernandez A. , Lortet M.C. , Spite F. 
Published: July 2016

AbstractThe confusing situation of the nomenclature of the astronomical objects led us to build, as a first step, a dictionary of the designations presently used. The future publication of this work is supported by Commission 5 of IAU. A brief description of this dictionary, as well as a sample of it, is given here. The designations (acronyms) will be given, together with the format, the total number of objects, the type of objects, the code for the complete bibliographical reference, the signification of acronym… Nomenclature for X and γ-ray sources, designations by constellations and descriptive designations will be dealt with as well. Good compilations are a considerable help in nomenclature problems; every effort should be made in order of : 1) urging specialists to build compilations 2) announce compilations in progress to Astronomical Data Centers and to the present authors.
Large scale photometric surveys using archival plates
Authors: Janes Kenneth 
Published: July 2016

AbstractModern microdensitometers and image processing software suggest the possibility that it may soon be feasible to utilize the enormous amount of photometric and positional data potentially available on existing photographic plates. This paper describes the possibility of large-scale surveys and outlines a method for densitometric calibration of plates from an analysis of the detailed structure of the star images on the plate.
The new catalogue of optical HII-Regions
Authors: Polechova P. 
Published: July 2016

AbstractThe principles of the work on the new catalogue of the optical HII-regions are described.On the basis of thirteen catalogues and lists of the optical HII-regions the catalogue of these objects had been compiled by me (Marsalkova, 1974). The main source of the objects on the northern sky was the catalogue of Sharpless (1959) which up to now is the only one in computer-readable form, the southern sky being characterized by a larger number of smaller catalogues represented in first place by that of Rodgers et al (1960) and that of Gum (1955). For this already published catalogue (now referred to as the “old” one) only optical data were taken into account. The catalogue was supplemented by a list of excluded HII-regions like supernova remnants, planetary nebulae and galaxies.
Two-Dimensional Television System: Application for Direct Acquisition of Images and Speckle Interferometry
Authors: Balega Yu.Yu. , Somov N.N. , Fomenko A.F. 
Published: July 2016

AbstractA two-dimensional photon counting and analog television system has been developed at the Special Astrophysical Observatory of the Academy of Sciences, USSR, for morphological investigations and
photometry of faint extended objects, spectrophotometry and speckle interferometry.
TV Spectrum Scanner of the 6-Meter Telescope
Authors: Somova T.A. , Somov N.N. , Markelov S.V. , Nebelitskii V.B. , Spiridonova O.I. , Fomenko A.F. 
Published: July 2016

AbstractThe television multichannel spectrophotometer of the BTA (SAO, USSR AS), used for accumulating and recording the spectra of faint astronomical objects, is described. The Soviet image detection system comprises a three-stage image tube (UM-92) optically coupled to a high sensitivity SIT TV tube. The system operates in a photon counting mode with digital definition of the centres of photoelectron events. The spectrophotometer operates on-line with a minicomputer which exercises control of the system and performs primary reductions of the data collected. Illustrations of scans obtained during observations are given.
An efficient integrator that uses Gauss-Radau spacings
Authors: Everhart Edgar 
Published: July 2016

AbstractThis describes our integrator RADAU, which has been used by several groups in the U.S.A., in Italy, and in the U.S.S.R. over the past 10 years in the numerical integration of orbits and other problems involving numerical solution of systems of ordinary differential equations. First- and second-order equations are solved directly, including the general second-order case. A self-starting integrator, RADAU proceeds by sequences within which the substeps are taken at Gauss-Radau spacings. This allows rather high orders of accuracy with relatively few function evaluations. After the first sequence the information from previous sequences is used to improve the accuracy. The integrator itself chooses the next sequence size. When a 64-bit double word is available in double precision, a 15th-order version is often appropriate, and the FORTRAN code for this case is included here. RADAU is at least comparable with the best of other integrators in speed and accuracy, and it is often superior, particularly at high accuracies.
Do comet groups exist?
Authors: Lindblad B.A. 
Published: July 2016

AbstractThe phenomena of comet groups, i.e. sets of comets that exhibit similarity in their orbital elements, is investigated. A computer program based on the D-criterion of orbital similarity is used to search for comet pairs and groups. The reality of the groups is tested by making computer searches in random samples of comet orbits.The data base for the study is 599 long-period comet orbits. The degree of orbital similarity within a comet group was first assumed to be identical to that encountered in meteor streams. The computer search at this level produced five comet pairs plus two groups with four and seven members, respectively. The latter two represented the eleven known members of the Kreutz group of sun-grazing comets. A comparison with searches in random samples showed that the two Kreutz groups were significant. There is a probability of 0.2 that the five comet pairs found in the real sample could be accidental formations.In a second study the orbital similarity parameter Ds was varied and the number of comet groups found in the real and synthetic comet populations was compared at each level of Ds. Apart from the Kreutz group of comets, the number of groups detected in the real comet sample was for all levels of orbital similarity only slightly higher than the average found in the random samples. At the 2σ confidence level we conclude that comet groups exhibit similarity in their orbital elements, that is no greater than might be expected by chance.
Influence op non-gravitational forces on the orbital evolution of the short-period comets
Authors: Belyaev N.A. , Ivanovskaya K.P. 
Published: July 2016

AbstractThis paper is concerned with the influence of non-gravitational forces on the orbital evolution of the short-period comets. This influence is variable for different comets and is especially noticeable for those comets which undergo approaches with Jupiter. When studying the dynamic evolution it is desirable to take into account the non-gravitational effects.
On the nongravitational effects in the comet Encke motion
Authors: Batrakov Yu.V. , Chernetenko Yu.A. 
Published: July 2016

AbstractA factor depending on geomagnetic index was introduced in the B. Marsden’s formula for the nongravita-tional force. The orbit of the cornet Encke covering seven apparitions (1895-1914) obtained with this modified formula shows better residuals than that obtained with the non-modified one.
The F-Corona and the Circum-Solar Dust Evidences and Properties [G. Nikolsky Memorial Lecture]
Authors: Koutchmy S. , Lamy P.L. 
Published: July 2016

AbstractThis review deals with the main properties of the F-corona. Analysis of its morphology and photometry allows to derive a new axisymmetric, non-spherical model. Polarization, color and infra-red properties are further considered. We suggest the existence of a variable “local” component surperimposed on a quasi-stationnary “far” component.
Doppler Shifts Measurements of the Zodiacal Light at the Pic Midi Observatory
Authors: Robley R. , Bücher A. , Koutchmy S. , Lamy Ph. 
Published: July 2016

AbstractAt the Pic-du-Midi Observatory, we have started a program to observe the spectrum of the zodiacal light in the region of the b absorption lines of MgI. We use a 1 meter spectrograph with a holographic grating followed by a focal reducer to obtain a 19 Å/mm dispersion over the micro-channel plate camera. Calibrated spectra obtained with an exposure time of 10 minutes systematically show earth atmospheric emission lines attributed to both NI and OH. The temporal variability of these emissions prevents an accurate determination of the line profiles. Our best processed measurements of Doppler shifts obtained during five nights do not allow to descriminate between circular and hyperbolic orbits of the interplanetary dust.
Explorer 46 Meteoroid Bumper Experiment: Earth Orbital Debris Interpretation
Authors: Kessler D.J. 
Published: July 2016

AbstractThe Meteoroid Bumper Experiment on Explorer 46 (launched 1972) was placed in Earth orbit to evaluate the effectiveness of using double-wall structures against meteoroids. This paper re-examines the data from this experiment. Certain sets of sensors were found to be penetrated much more frequently than other sets. The most plausible explanation is that nearly all of the penetrations were from an Earth orbiting population of particulates. In addition, because a large percentage of the penetrations occured soon after solid rocket motors were fired in space, the particulates are most likely 75 μm diameter aluminum oxide. Aluminum oxide particulates are a major exhaust product from solid rocket motors. The size of particulates from most current solid rocket motors is found to range between 0.1 μm to 20 μm. Modeling the orbits of particulates from these rockets predicts that measurements in Earth orbit of interplanetary dust in this size range are also likely to include Earth orbiting particulates from solid rocket motors.
Prospects for Cosmic Dust Experiments on the Planned Reflight of LDEF
Authors: Walker R.M. , Zinner E. 
Published: July 2016

AbstractThe Long Duration Exposure Facility (LDEF-I), which contains a number of cosmic dust experiments, is due to be launched in the spring of 1984 and recovered about a year later. Current plans call for re-fitting the LDEF spacecraft with a large area of plastic nuclear track detectors and relaunching (LDEF-II) for a flight that will last about 2 years. The main purpose of the mission is to extend primary cosmic ray abundance measurements to the actinide region. A meeting was held at Washington University in December 1983 to discuss the problems and prospects for cosmic dust experiments on LDEF-II. Most participants were drawn from the LDEF-I community of investigators. The meeting resulted in a report which treated the scientific rationale for LDEF-II dust experiments, discussed various implementation options, and concluded with a set of summary recommendations. We discussed this report and summarized the status of LDEF-II as of this meeting. It is important to note that the report serves equally well as a basis for discussion of dust experiments on future space stations.