bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Art of Surface Imaging
Authors: Piskunov N.E. 
Published: July 2016

AbstractWe intend to analyze the reliability of surface imaging of stars based on high resolution spectroscopy and the technique of inverse problem solution. Both astrophysical and mathematical aspects including different regularization methods are reviewed. The influence of the different factors on the resulting map is discussed and it is shown that the simultaneous use of different kinds of observational data (spectroscopy, photometry, polarimetry etc.) is very useful in providing additional constraints for the solution. The recent results in the surface imaging of Cp- and late-type stars show the way for further progress: the use of more adequate mathematical description of the stellar atmosphere and the simultaneous consideration of various surface inhomogeneities.
Surface Imaging of El Eri
Authors: Hackman T. , Piskunov N.E. , Poutanen M. , Strassmeier K.G. , Tuominen I. 
Published: July 2016

AbstractWe present maps of the temperature distribution on the spotted RS CVn-type binary EI Eri (HD 26337), obtained by means of the surface imaging technique described in the Colloquium (Piskunov, 1991). Images were calculated for two separate lines for two epochs of observation. For one epoch we also calculated an image using a blend of several lines. The reliability of the maps is confirmed by comparing the simultaneous photometric observations with the light curves calculated from the temperature maps.
Linear Polarization and Magnetic Fields in Cool Stars
Authors: Huovelin J. , Saar S. H. 
Published: July 2016

AbstractObservations and theoretical models of broadband linear polarization (BLP) in cool stars are discussed. Two effects, 1) differential saturation in magnetically sensitive absorption lines and, 2) Rayleigh and Thomson scattering are considered as the possible causes of the BLP. Results of theoretical models, and comparisons with observations are summarized.
Activity of Relatively Close Binaries
Authors: Schrijver Carolus J. , Zwaan Cornelis 
Published: July 2016

AbstractWhereas the rotation-activity relationship for single cool stars can be described in terms of fundamental stellar properties, the activity in relatively close binaries is enhanced with respect to that of single stars by an amount which depends strongly on the properties of the companion. We consider mechanisms which could cause an excess in activity of binaries, and conclude that it is likely that the presence of a companion affects the interior structure of the stars in such a way that either the efficiency of the dynamo or of the atmospheric heating is enhanced.
Recent Advances in our Understanding of Chromospheric and Coronal Heating Mechanisms
Authors: Linsky Jeffrey L. 
Published: July 2016

AbstractI will summarize some of the principal scientific results presented at the Conference on “Mechanisms of Chromospheric and Coronal Heating” held on 5-8 June 1990 in Heidelberg, Germany. The Conference included invited and contributed papers on observations that point to specific heating mechanisms and theoretical papers on the heating mechanisms themselves. There were many opportunities for useful interaction between proponents of these two approaches to understanding stellar chromospheres and coronae. I will concentrate on what is being learned from the empirical side, and then summarize the heating mechanisms discussed and for which types of stars they may be applicable.
On Equatorially Symmetric Models for Magnetic Stars as Suggested by Dynamo Theory
Authors: Krause F. , Oetken L. 
Published: July 2016

SummaryDynamo theory suggests that an equatorially symmetric structure of the magnetic field holds for single stars. Assuming that the distribution of elements is connected with the magnetic field, an equatorially symmetric concentration of elements in rings was constructed, which can represent the observed quantities W(t), vr(t), and Heff(t) of the periodic magnetic variable stars. Especially for α2CVn, a model has been found which represents the main features of this star as well as that which pyper derived by harmonic analysis. Generally no severe objections against equatorial symmetry of the physical parameters of magnetic stars have been found.
On The Radii of Ap Stars
Authors: Catalano F.A. , Strazzulla G. 
Published: July 2016

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.
Hd 101065 - An Astronomical Enigma
Authors: Przybylski A. 
Published: July 2016

SummaryHD 101065 is a very peculiar star whose spectrum is dominated entirely by the numerous lines of the rare earths. The only other metals seen in the spectrum are strontium, yttrium, zirconium and barium and traces of calcium.The effective temperature of the star is 6075° ± 200°K or about 1000°K lower than that of the coolest Ap stars known to date.HD 101065 is a suitable testing ground for the theories on the formation of Ap stars. The absence of “normal” elements in the atmosphere of the star puts stringent limitations on the choice of the available theories.
Light Variations of Ap Stars: 10-Colour Photometry and its Interpretation by a Magnetic Spot Model
Authors: Schöneich W. , Staude J. 
Published: July 2016

SummaryAmplitude-wavelength relations obtained by a multicolor photometry of 16 Ap stars are represented. Model calculations show that the characteristic observed features may be explained by assuming, relative to the undistributed photosphere, a different depth dependence of the temperature in a spot caused by the magnetic field.
Photometry of Five Southern Magnetic Stars
Authors: Bartolini C. , Scardovi S. 
Published: July 2016

SummaryPhotoelectric observations carried out in 1970 at Siding Spring Observatory are presented. HD 45677, observed also at Bologna, presents in the time interval 1970-1975 variations of 0m.4; the hypothesis of eclipsing binary is considered. Light variations of 0m.026 with a possible period of about 30dhave been detected in HD 168814. HD 184552 seems to vary with an amplitude of 0m.015 in about 10d, but rapid variations could be present. HD 187474 and HD 204075 stayed constant.
The Sun as a Magnetic Star
Authors: Wilcox John M. , Svalgaard Leif 
Published: July 2016

SummaryThe sun as a magnetic star is described on the basis of recent work on solar magnetism. Observations at an arbitrary angle to the rotation axis would show a 22-year polar field variation and a 25-day equatorial sector variation. The sector variation would be similar to an oblique rotator with an angle of 90° between the magnetic and rotational axis.
Abundance Studies of Peculiar B Stars
Authors: Vilhu O. , Tuominen I.V. , Boyarchuk A.A. 
Published: July 2016

SUMMARYSpectroscopic investigation of some peculiar B stars has been carried out. The whole α Scl-group of weak-helium-line stars was analysed. The stars studied (Table) represent a sample of Bp stars in the overlapping region, where several peculiarity phenomena (weak-helium-line, Mn, Si λ 4200) are found at the same effective temperature.
The Ultraviolet Variations of ι Cas
Authors: Molnar M.R. , Mallama A.D. , Soskey D.G. , Holm A.V. 
Published: July 2016

SummaryThe Ap variable star ι Cas was observed with the photometers on OAO-2 covering the spectral range λλ 1430-4250. The ultraviolet light curves show a double wave with primary minimum and maximum at ϕ = 0.00 and 0.35, respectively. Secondary minimum light is at ϕ = 0.65 with secondary maximum at ϕ = 0.85. The light curves longward of λ3150 vary in opposition to those shortward of this “null region”.Ground-based coude spectra show that the Fe II and Cr II line strengths have a double-wave variation such that maximum strength occurs at minimum ultraviolet light. We suggest that the strong ultraviolet opacities due to photoionization and line blanketing by these metals may cause the observed photometric variations.We have also constructed an oblique-rotator model which shows iron and chromium lying in a great circle band rather than in circular spots. These elements have been observed to lie in bands along the magnetic equator in several other Ap stars such as α2CVn, HD 173650, and 108 Aqr. Thus, we predict that the inclination of the magnetic dipole field with respect to the axis of rotation is about 84°.
Reference Coordinate Systems for Earth Dynamics: A Preview
Authors: Mueller Ivan I. 
Published: July 2016

AbstractA common requirement for all geodynamic investigations is a well-defined coordinate system attached to the earth in some prescribed way, as well as a well-defined inertial coordinate system in which the motions of the terrestrial system can be monitored. This paper deals with the problems encountered when establishing such coordinate systems and the transformations between them. In addition, problems related to the modeling of the deformable earth are discussed.
Celestial Reference Frames
Authors: Kovalevsky J. 
Published: July 2016

AbstractA celestial reference frame is based on some dynamical or kinematic approximation of an absolute coordinate system and is materialized by a fundamental catalogue of stars. It is characterized by the accuracy of the system and the precision of its stellar realization.The present situation, marked by the construction of the FK5 system and catalogue, is briefly described. It will be an hybrid system based on the discussion of all existing observations. The prospects for improvement in accuracy are good using lunar laser observations or VLBI determination of the positions of extra-galactic radio-sources. Three procedures that may be used to link such a system to a star catalogue are given. A major improvement in precision is expected from the Hipparcos programme and further extensions include essentially the densification of catalogues with stars of magnitudes 10 to 14 using photoelectric automatic meridian instruments.
Some Geodetic Aspects of the Plate Tectonics Hypothesis
Authors: Lambeck Kurt 
Published: July 2016

AbstractGeodetic observations of gravity, body tides, the Earth’s rotation and crustal motion and deformation potentially provide important constraints in the general inversion of geophysical data for determining the structure and evolution of the Earth. More specifically, the geodetic data provide constraints on the rheology of the planet in the frequency range intermediate between geological and seismic frequencies, on the geologically instantaneous kinematics of the Earth and on the mechanisms responsible for the motions within the Earth, results that are intimately related to the plate tectonics hypothesis. The discussion is limited here to only a few aspects of these “geodetic” aspects of this hypothesis, including deformation along plate boundaries, intraplate tectonics and vertical motions.
Comments on the Terrestrial Pole of Reference, the Origin of the Longitudes, and on the Definition of UT1
Authors: Guinot Bernard 
Published: July 2016

AbstractThe definition of a terrestrial reference pole (TRP) and of a Terrestrial Longitude Origin (TLO), by fixing the stations coordinates of an adopted network seems unrealistic. It is proposed that TRP and TLO be the realized origins of some specified service working in accordance with some stated principles. It is also proposed to clarify the definition of UT1 and to base it on some physical properties.
Local Geometric and Gravimetric Datum and Its Relation to the Global Terrestrial Reference System
Authors: Kelm R. 
Published: July 2016

AbstractIn active tectonic zones relative earth surface displacements of mm-order and, relative gravity disturbances of 0.1 mgal size may be expected between two survey epochs. To monitor and separate these small effects significantly special local free networks have to be designed which are measured by relative observations of highest accuracy (mm-and ygal-level). For the connection of the local nets to a global terrestrial reference system a suitable local datum for point coordinates (geometric datum) and gravity field parameters (gravimetric datum) has to be defined within the terrestrial reference system.
Errors in Pole Coordinate Obtained by the Doppler Satellite Positionings
Authors: Takagi S. 
Published: July 2016

AbstractThe pole coordinate obtained by the Doppler observation of Earth satellite shows good results, but there are some important difference from those of the astronomical observation, for example, that of the IPMS.The Doppler observation of the Navy Navigation satellite has proved to be precise enough to supersede the astronomical observation in the geodynamics. (Anderle, 1965, 1966, 1970, 1971a, 1971b, 1971c, 1974). Yumi et al. (1979) showed that the local terms in the astronomical observation was not found in the Doppler latitude obtained at Mizusawa. This shows the superiority of the Doppler observation to the astronomical one.
Planetary Ephemerides
Authors: Lieske Jay H. , Standish E. Myles 
Published: July 2016

AbstractIn the past twenty years there has been a great amount of growth in radiometric observing methods, as well as in classical optical observations. Through radar ranging and Doppler observations of the planets and spacecraft, we have been able to improve our knowledge of the location and motion of the planets by several orders of magnitude and have succeeded in planning and executing space missions which would have been difficult if not impossible to plan and to perform utilizing the classical ephemerides. We will outline the goals and methods employed by the Jet Propulsion Laboratory in its effort to develop improved ephemerides which accurately reflect the motions of planets in an inertial system.
Contribution des Astrolabes au Raccordement des Systemes de Reference “Optique” et “Radio”.
Authors: Débarbat Suzanne 
Published: July 2016

AbstractTwenty-two radio sources, being bright objects of the Galaxy are observable with astro labe (plus six for those having photoelectric devices). It is about half of the total number (forty-six, figure 2) of objects of the list of galactic objects given by the working group of Commission six of the IAU. Seventeen astro labe stations (figure 2) are interested in a cooperation which final objective is to link the radio and optical reference systems.
Collapse, Equilibrium, and Fragmentation of Rotating, Adiabatic Clouds
Authors: Boss A. P. 
Published: July 2016

AbstractNumerical calculations of the collapse of adiabatic clouds from uniform density and rotation initial conditions show that when restricted to axisymmetry, the clouds form either near-equilibrium spheroids or rings. Rings form in the collapse of low thermal energy clouds and have β = T/|w|≳ 0.43. When the axisymmetric constraint is removed and an initial m=2 density variation is introduced, clouds either collapse to form near-equilibrium ellipsoids or else fragment into binary systems through a bar phase. Ellipsoids form in the collapse of high thermal energy clouds and have β ≲ 0.27. The results are consistent with the critical values of β for instabilities in Maclaurin spheroids, and suggest that protostellar clouds may undergo a dynamic fragmentation in the nonisothermal collapse regime.
Pulsation Modes and Luminosities of the β Cephei Staks
Authors: Jerzykiewicz M. , Sterken C. 
Published: July 2016

AbstractAssuming that frequencies observed in multiperiod β Cephei variables correspond to normal pulsation modes leads to the following conclusions: (1) a variety of low Z oscillations are excited in these stars, (2) at most one radial mode is seen in any of them.Pulsation constants can be derived for two β Cephei stars without recourse to photometric calibrations. In both cases a 0.5 mag. downward revision of the Balmer line absolute magnitudes is indicated. Implications of this result for Stellingwerf’s opacity bump mechanism are briefly considered.The text of the paper will appear in Proceedings of the Fifth European Regional Meeting of the IAU.
Recent Work on Cepheid Variables
Authors: Cox J. P. 
Published: July 2016

AbstractRecent work on Cepheids is reviewed in the areas of (1) the large-amplitude mode behavior, (2) convection, and (3) Cepheid masses. Initial-value type nonlinear calculations have not yet yielded true double-mode behavior. Yet we have the beginnings of a promising theory of modal selection. Theoretical calculations also yield reasonably located red edges to Cepheid (and Cepheid-like) instability regions.
The Unusual Classical Cepheid Hr 7308: 1966-1969
Authors: Breger Michel 
Published: July 2016

AbstractThe small-amplitude classical cepheid HR 7308 has the shortest period known in our Galaxy for a classical cepheid. 1966-1969 photoelectric observations together with more recent data show a period of 1d.49078 with sinusoidal light variations. Except for the presence of the beat period, no secondary period can be found in the extensive 1966 data. The lack of a secondary period near Pi/Po = 0.7 sets HR 7308 apart from many other short-period classical cepheids.
RR Lyrae AND BL Herculis Variables
Authors: Cox Arthur N. 
Published: July 2016

AbstractThe RR Lyrae variables are currently believed to have masses between about 0.5 and 0.8 M⊙, effective surface temperatures between 6350 and 7500K, radii from about 4.0 to 6.0 R⊙ and luminosities between log L/L⊙ of 1.5 and 2.0. Since they are found in population II locations, they generally have Y = 0.3 and Z = 10−3 , but there are exceptions for both higher Z like the sun and lower Z like 0.0002. In globular clusters the periods range from 0.25 - 0.45 day for the first overtone pulsators and 0.40 - 0.80 day for those in the fundamental mode, depending on their luminosity. At transition lines, to be discussed in detail below, the switch from fundamental to first overtone, or maybe vice versa, involves a period change factor of about 0.74 - 0.75.
Low-Mass Evolution from He Ignition to Beyond the Horizontal Branch
Authors: Despain Keith 
Published: July 2016

AbstractThe evolution of an 0.6 M⊙ stellar model during core helium burning is presented. Following the off-center ignition of helium in the “core” flash, the star remains on the red giant branch for > 106 years, undergoing twelve additional flashes. After leaving the giant branch, the star evolves on the horizontal branch for 8.15×107 years before returning to the giant branch and undergoing strong helium-shell flashes. The implications for horizontal branch and RR Lyrae stars are discussed.
The Absolute Magnitudes of RR Lyrae Stars
Authors: Manduca A. , Bell R. A. 
Published: July 2016

AbstractA theoretical counterpart to the Barnes-Evans relation between stellar surface brightness and V-R color has been calculated from model atmospheres for parameters appropriate to RR Lyrae stars. Such a relation can be used to derive stellar angular diameters from V,R photometry and, when applied to variable stars and combined with a radial velocity curve,, to derive radii, distances, and absolute magnitudes by the method of Barnes et al. (1977, MNRAS,178, 661). This was done for RR Lyr and X Ari using the photometry of Moffett and Barnes (1980, private communication) and radial velocities from the literature. The resulting absolute magnitudes are <MV> ± + 0.59 + 0.25 for X Ari and <MV> = 0.61 + 0.35 for RR Lyr. The method is shown to be a very accurate way of determining radii, distances, and absolute magnitudes for RR Lyrae stars which compares very favorably to the variations of the Baade-Wesselink technique currently in use.
Blazhko Effect in the RR Lyrae Variables as a Result of Double Mode Pulsation
Authors: Borkowski K.J. 
Published: July 2016

AbstractOn the basis of a frequency analysis of light variations of AR Her a double-mode pulsation is proposed as an explanation of the Blazhko effect. The analysis revealed a number of components, which can all be interpreted as a result of nonlinear superposition of the fundamental mode, and a mode with period P = 1/(2/P0 + 1/PB) ~ P0/2, where P0 = 0d.470 and Pb = 31d.55 denote the fundamental and the Blazhko effect periods, respectively.The P ⋍ P0/2 mode can be identified as the second or the third radial overtone. In both these cases the “beat” masses derived from a comparison of the calculated (nonadiabatic) and observed period ratios for RR Lyrae variables with Blazhko effect are different from their evolutionary masses.
Pulsations of the R Coronae Borealis Stars
Authors: Cox J. P. , King D. S. , Cox A. N. , Wheeler J. C. , Hansen C. J. , Hodson S. W. 
Published: July 2016

AbstractThe radial pulsations of very luminous, low-mass models (L/M ˜ 104, solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadia–batic. We find that there are in some cases at least one extra (“strange”) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars.
Internal Structure of Uranus
Authors: MacFarlane J. J. , Hubbard W. B. 
Published: July 2016

AbstractWe present an updated study of Uranus interior models using current information about the planet’s gravity field and rotation rate. The most plausible model, both from the point of view of recent data and cosmogony, has a central core of iron and magnesium silicates, an outer envelope of liquid water, methane, and ammonia, and a deep “atmosphere” of almost four earth masses of hydrogen, helium, and methane. The “atmosphere” contains a gravit at ionally nonnegligible amount of methane — about 40% by mass. All plausible models are most consistent with a rotation period of ~15 to 16 hours.
Data on Time and Polar Motion: Immediate Accessibility
Authors: McCarthy Dennis D. , Westerhout Gart 
Published: July 2016

AbstractUsers of time and polar motion information have requirements for data which are somewhat different from those usually considered for astronomical data files. Because of these requirements, it is necessary to provide immediate access to the latest information on Earth orientation and even predictions of future orientation. For other applications where data of the highest accuracy is required with little concern for the delay between observations and the determination o f the required information, a more traditional approach may be used. To meet all of these needs a versatile automated data retrieval system is demanded. The U. S. Naval observatory is now implementinq such a system in the area of Earth orientation information and for precise time and time interval applications. Data are available through a series of weekly, monthly, and annual reports, as well as through a digital communications link to Time Service machine-readable files.
The International URSIGRAM and World Days Service
Authors: Simon P.A 
Published: July 2016

Broad outlines of a permanent service involved in the prompt dissemenition of solar and geophysical data.The Solar Activity has an effect on several modern technics. For instance, during a transient increase of solar UV flux, the trajectory of a low perigee satellite can slightly change, a ionospheric communication link can fade out or some scientific program can only be carried out during some outburst of the solar activity.
System software approaches to the Analysis of Multidimensional Data Structures
Authors: Albrecht Rudolf 
Published: July 2016

AbstractIn this review paper on software techniques, the concepts of “software system” and “data base interface” are defined in the context of astronomical data analysis requirements. Principles of software desiqn and maintainance over are discussed.A deliberate effort was made to stay as close as possible to the astronomical application and not deviate too much into computer science.