bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of the Cape Astrometric Survey of the Southern Hemisphere
Authors: Nicholson W. 
Published: July 2016

SummaryA routine has been developed for the processing of the 5820 plates of the survey. The plates are measured on the automatic measuring machine, GALAXY, and the measures are subsequently processed by computer, to edit and then refer them to the SAO catalogue. A start has been made on measuring the plates, but the final selection of stars to be made is still a matter for discussion.
The ESA Astrometry Satellite
Authors: Hog E. 
Published: July 2016

AbstractAn ESA study has demonstrated the feasibility of an Astrometry Satellite (AS) which will be able to obtain an accuracy of ±0002 for parallaxes, yearly proper motions and positions of 100 000 stars mostly brighter than mB= 11.It is emphasized that the scientific impact of these orders of magnitude improvements over present data will be multiplied if astrophysical data are also obtained for the selected stars by ground-based techniques.
Measurement Errors in Rotational Synthesis and their Effects in the Map Plane
Authors: Hamaker J.P. 
Published: July 2016

SummaryThe effect of errors in an aperture synthesis map is intimately related to the geometry of the synthesis instrument and the properties of the two-dimensional Fourier transformation. This paper concentrates on E-W rotational synthesis, the simple geometry of which allows a systematic treatment. After some preliminary remarks about error statistics and tolerances, the relevant properties of the Fourier transformation in polar coordinates are first reviewed. A classification of error types as “global”, “circular”, “radial” or “local” is introduced, based on the geometry of the area in the aperture over which they are coherent. A few special errors not fitting into this classification are also discussed. The characteristics of the corresponding patterns in the synthesized beam are described and illustrated with computer simulations and real-life examples.
“Kneading”: The Adjustment of Instrumental Phase and Gain Parameters to Suppress Error Patterns in a Synthesis Map
Authors: Hamaker J.P. 
Published: July 2016

SummaryOften, particular unnatural-looking patterns appear in a synthesis map. An experienced observer can recognize the type of error that produced them and may even be able to apply the corrections necessary to get a better-looking map. A systematic approach is described in this paper: A model of the errors most likely to occur is fitted to the patterns in the map, and the fitted parameters are used to apply corrections. The presence of a point source that can serve as a reference is required. This requirement limits the applicability of the method, but is met by quite a few objects of interest. Where interference from other sources would be too strong, their influence may be reduced by CLEANing the map prior to model fitting. One example of the results for atmospheric position scintillation and one for baseline calibration errors will be shown.
Processing and Display of Spectral Line Absorption Maps
Authors: Wright Melvyn 
Published: July 2016

AbstractWe describe the processing and display of aperture synthesis maps of the H I absorption against the radio source Cas A. Then data were obtained with the NRAO interferometer and constitute 384 narrow band maps of Cas A combined to produce a picture of the optical depth and mean velocity of the H I absorption due to the Perseus arm.Both digital and analogue data techniques have been used to Fourier transform, combine and display the data and the merits and usefulness of each are described.
Maximum Entropy Spectral Analysis – Some Comments
Authors: Bhandari Rajendra 
Published: July 2016

AbstractStudy of a model data analysis situation with the help of computer experiments reveals that the Maximum Entropy Method of Spectral Analysis owes its popularity to a peak-sharpening property which is found to be a strong function of the level of background white noise present in the spectrum. In one limit, misleading results may be obtained by this technique. Some suggestions for a more fruitful use of the technique are made.
Reconstruction from Projections in Medicine and Astronomy
Authors: Gordon Richard 
Published: July 2016

It is a great pleasure for me to address this colloquium of radio astronomers on reconstruction from projections, especially since this opportunity allows me to combine an early interest in astronomy with my current work.Some of you have been applying methods of reconstruction since the mid-1950’s. Radio astronomers formed a cohesive society then and the methods reached fruition and matured in a natural progression. Reconstruction from strip scans and then interferometer data has been so fundamental to the formation of images in radio astronomy that one may well say that the field could not have progressed without them.
On the Dynamics of the Solar Convection Zone
Authors: Durney Bernard R. , Spruit Hendrik C. 
Published: July 2016

AbstractWe derive expressions for the turbulent viscosity and turbulent conductivity applicable to convection zones of rotating stars. We assume that the dimensions of the convective cells are known and derive a simple distribution function for the turbulent convective velocities under the influence of rotation. From this distribution function (which includes, in particular, the stabilizing effect of rotation on convection) we calculate in the mixing-length approximation: i) the turbulent Reynolds stresstensor and ii) the expression for the heat flux in terms of the superadiabatic gradient. The contributions of the turbulent convective motions to the mean momentum and energy equation are treated consistently, and assumptions about the turbulent viscosity and heat transport are replaced by assumptions about the turbulent flow itself. The free parameters in our formalism are the relative cell sizes and their dependence on depth and latitude.
The Evolution of an Average Solar Granule
Authors: Altrock R.C. 
Published: July 2016

AbstractHigh-resolution photographic spectra of the center of the solar disk have been obtained with the Vacuum Tower Telescope at Sacramento Peak Observatory. Two weak iron lines and the neighboring continuum were recorded with 40 sec time resolutions and better than 1” spatial resolution over a period of 40 min. Intensity and velocity fluctuations were obtained in the two lines and continuum as a function of time and space, and 300 sec oscillations were filtered out. The resulting fluctuations, due solely to granulation, were assembled into an ensemble average of the center of a granule and the center of an intergranular lane, as a function of time. The intensity-fluctuation data have been analyzed through calculation of model line profiles to yield temperature fluctuations in a granule as functions of time and height. We find that the line parameters are distinctly out of phase with continuum brightness, so that, for example, maximum brightness at line center occurs approximately 100 sec prior to maximum continuum brightness. A series of one-dimensional model atmospheres representing the granule at various stages of its lifetime is presented.
Observed Solar Spectral Line Asymmetries and Wavelength Shifts Due to Convection
Authors: Dravins Dainis 
Published: July 2016

AbstractConvective motions are manifest in the solar spectrum as slight spectral line asymmetries and wavelength shifts. These have been studied for 311 Fe I lines. Most lines are blueshifted because the larger contribution of blueshifted photons from bright and rising granules statistically dominates over the contribution from dark and sinking intergranular lanes. Fainter lines (formed deeper) show larger blueshifts than strong lines; high-excitation lines usually are more blueshifted (preferentially formed in the hotter granules) and short-wavelength lines are more blueshifted because of increased granulation contrast there. Detailed studies of line bisector behavior as function of line parameters permit the construction of model atmospheres incorporating convective hydrodynamics. The method does not require spatially resolved observations and can be extended to studies of stellar convection.
Examples of Non-Thermal Motions as Seen on the Sun
Authors: Beckers Jacques M. 
Published: July 2016

SummaryOn the sun we can identify many of the motions derived from stellar spectral analysis. A summary is given of the observed solar velocity phenomena. Many of these (e.g. meridional flow, giant cells, solar differential rotation, supergranulation) are of great interest in astrophysics especially for interior structure and chromospheric and coronal structuring but contribute virtually nothing to the velocities derived from a solar irradiance spectrum analysis. Others (granulation, very small scale motions and to a lesser extent, oscillations) do contribute substantially to the integrated sun velocity analysis. Some of the properties of these motion fields are described.
Excitation Dependent Gf-Values and Depth Dependent Microturbulences
Authors: Hasegawa Toshio 
Published: July 2016

AbstractThe velocity of microturbulence is frequently determined from Fe I lines. Unfortunately classical gf-values of this element have excitation dependent errors. In the absolute curve of growth analysis of some F-type stars with new gf-values, the author found that a great part of the depth dependence (i.e. excitation dependence) of microturbulent velocity, which had been derived by many authors with old gf-values, is the consequence of these errors.The errors of old gf-values increased with excitation potential and the errors were compensated by adopting velocities of microturbulence decreasing with excitation potential. On the other hand, gf-values of ionized elements (e.g. Ti II and Fe II) are not changed as much as those of Fe I, accordingly the ionization dependence can also be eliminated.
Structure and Composition of White Dwarf Atmospheres and Convection Zones
Authors: Böhm K.H. 
Published: July 2016

SummaryWe present a brief review of the basic properties of white dwarf atmospheres) convection zones and corona models emphasizing qualitative and intuitive aspects.1. Atmospheres: We restrict our discussion essentially to very hot and very cool atmospheres since these are especially interesting. With regard to the first type of objects we study the fundamental differences between DA and non-DA models and between their surface fluxes. We discuss the important role of electron scattering in determining the EUV spectra of these objects. The differences between DAs and non-DAs with regard to backwarming effect and surface cooling are summarized.In our discussion of very cool non-DA atmospheres we emphasize the importance of the additional energy transport mechanisms convection and conduction which should both be very effective for Teff < 4000K and which lead to a very flat temperature gradient. This small gradient must lead to a rather featureless surface flux.2. Convection Zones. After a survey of the basic numerical results in this field we investigate the question whether convection in white dwarfs has the same basic properties as convection in other stars. We find that contrary to intuitive expectations the Rayleigh number in very cool non-DAs is higher than in the sun (indicating very turbulent convection). The Prandtl number in these objects is 6 to 7 orders of magnitude higher than in the sun.3. Coronae. The basic methods of the calculation of coronae for white dwarfs are very briefly discussed. We present some results for DA and non-DA stars from unpublished work by D.O. Muchmore and the author. It uses revised values for the emissivities. Only non-DA coronae are of practical interest. DA coronae have much lower densities and temperatures. White dwarf coronae do not generate a stellar wind.
Vibrational Instabilities and Pulsational Properties of Cool White Dwarfs
Authors: Dziembowski W. 
Published: July 2016

AbstractAttention is focused on those aspects of the theory that may be relevant in understanding the nature of ZZ Ceti-type variable white dwarfs. Recent calculations show that the opacity mechanism can drive a large variety of oscillation modes, including the ones that fit observed periods. An estimate of nonlinear effects shows that resonant mode coupling plays a dominant role in determining the finite amplitude behaviour of oscillations and is also probably responsible for rapid amplitude changes observed in these variables.
WZ Sge: Recent Observations Leading to a Model for Superhump Phenomena
Authors: Gilliland R. L. , Kemper E. 
Published: July 2016

AbstractThe short period eclipsing binary system and recurrent nova WZ Sge (1913, 1946, 1978) was observed spectroscopically during its renewed, December 1978 outburst. Absorption line radial velocities and Hα emission profiles suggest a clrcumblnary gaseous disk. A schematic model is presented to explain both the observed radial velocities and the photometric properties of WZ Sge during outburst. The model also accounts for ‘superhump’ phenomena in SU UMa type dwarf novae.
Comments on the Evolution and Origin of cataclysmic Binaries
Authors: Whyte Charles A. , Eggleton Peter P. 
Published: July 2016

AbstractSome aspects of the observational data on cataclysmic binaries are discussed and some possible correlations between type of behaviour and binary period are noted. A gap between 2 and 3 hours in the histogram of binary periods is estimated to be real. A numerical procedure for following the evolution of Roche-lobe-fiUing stars using simplified equations is described. This procedure Is applied to white/red dwarf binaries for a variety of initial conditions, and of mass loss and angular momentum loss mechanisms. The results of these calculations, in which we ignore the short timescale behaviour of the systems, are classified into four modes of evolution: normal, nuclear evolution dominated, angular momentum loss dominated and hydrodynamical. The results are discussed in connection with cataclysmic binaries. The clustering in period below 2 hours is Interpreted in terms of evolution following the hydrodynamical mode, and it is suggested that such systems contain low mass white dwarfs as well as low mass secondaries. These may be the most common type of cataclysmic binary. A possible explanation of the clustering of classical novae systems to binary periods of 3 to 5 hours is mentioned, and evolutionary scenarios for cataclysmic binaries are outlined. We suggest, following Ritter and Webbink, that the short period systems (≲ 2 hrs) arise mainly from late Case B mass transfer in the original binary (original primary mass 1.5 to 3M⊙) and the longer period systems arise mainly from Case C mass transfer.Full text to be published in Monthly Notices of the Royal Astronomical Society.
The Astro-D Mission
Authors: Tanaka Y. 
Published: July 2016

AbstractAstro-D, the fourth X-ray astronomy mission of ISAS following Ginga, is a high-throughput imaging and spectroscopic X-ray observatory, scheduled for launch in early 1993. It utilizes multilayer conical X-ray mirrors which provide a large effective area over a wide range energy range up to 12 keV. The focal plane instruments comprize a set of CCD cameras and Imaging gas scintillation proportional counters. Main features of Astro-D are described, and the important astrophysical objectives are discussed.
The Sax Mission For X-Ray Astronomy
Authors: Butler R.C. , Scarsi L. 
Published: July 2016

AbstractThe satellite for X-ray astronomy SAX, to be launched at the end of 1993, is devoted to systematic, integrated and comprehensive, studies of galactic and extra-galactic sources in the energy band 0.1–200 keV, and is under joint development by the Italian Space Agency (ASI) and the Netherlands Agency for Aerospace programs (NIVR), with the participation of SRU/SRON and SSD/ESTEC. The basic scientific objectives can be summarized as follows:– Broad band spectroscopy (E/Δ E=12) from 0.1–10 keV with imaging resolution of 1 arcmin.– Continuum and line spectroscopy (E/Δ E=5–20) in the energy range 3–200 keV.– Variability studies of bright source energy spectra on timescales from milliseconds to days and months.– Systematic long term variability studies over the entire sky down to a source intensity of 1 mCrab.
The Extreme Ultraviolet Explorer Mission
Authors: Bowyer Stuart 
Published: July 2016

AbstractThe Extreme Ultraviolet Explorer mission is described. The satellite is now scheduled to be launched in September, 1991. For the first six months, an all sky survey will be carried out covering 90 to 820 Å, or essentially the entire EUV bandpass. This EUV survey will be made in four bands, or colors, λλ90–150 Å; 170–250 Å, 400–600 Å and 550–750 Å. A portion of the sky which is free from the normally intense 304 Å geocoronal helium background will be surveyed at greater sensitivity; the wavelength coverage of this band is from 90 to 400 Å. Following the sky survey portion of the mission, spectroscopy of individual sources will be carried out. Three spectrometers employing novel variable line spaced gratings will provide spectra with ~1 Å resolution over the band from 90 to 800 Å. This spectroscopy will be carried out by guest observers chosen by NASA in a manner roughly analogous to the IUE guest observer program.
The Spectrum-UV Project/The Spectrum-UV Team
Authors:   The Spectrum-UV Team
Published: July 2016

AbstractThe Ultra-Violet Space Telescope “SPECTRUM-UV” consists of a 170-cm diffraction limited telescope for spectroscopy and imaging at λ ≥ 912 Å and a co-aligned assembly of two 50-cm telescopes for imaging and spectroscopy in the 400 to 1200 Å range and of four 20-cm, multilayer coated telescopes for narrow band imaging in the 100 to 400 Å range. The Observatory is an international facility to be launched in a highly eccentric orbit in the mid-1990s.
Launch Vehicles of ISAS
Authors: Tanaka Yasuo 
Published: July 2016

AbstractThe Institute of Space and Astronautical Science (ISAS) has developed a series of launch vehicles for delivering modest scale scientific satellites into space. This capability is unique for an inter-university research institute. The present ISAS launch vehicle, M-3S II, carries a 770 kg payload into a low earth orbit (LEO). A new program for the development of a more capable vehicle, M-V, started recently, which will have a LEO capability three times that of M-3S II. The enhanced launch capability will further expand the scope of the ISAS missions to include planetary explorations.
Does Theory Advance with Technology?
Authors: Arp Halton 
Published: July 2016

Observational technology in astronomy moves ahead. We can see a thousand times fainter and ten to a hundred times more detail than 40 years ago. But does our application to research match the engineering progress? Most of us make the easy assumption that theory is right at the cutting edge, waiting to gobble up each new fact into an even deeper, more detailed insight into the universe. But humans frequently misunderstand the real problems and misapply technology - making everything worse for agonizingly long times.Is it possible that extragalactic astronomy has serious misconceptions? The key point to appreciate is that its whole structure rests on the belief that we know the distances to objects in the universe. The simple shift to the red of the spectrum of any observed object is assumed to measure its distance. But for 25 years evidence has been increasing that drastically incorrect distances can result. Unfortunately, not only quasar distances but the distances to the vast majority of galaxies also depend on redshifts.
The X-Ray Large Array
Authors: Wood K. S. , Hertz P. , Norris J.P. , Michelson P. F. 
Published: July 2016

AbstractThere is a conspicuous gap in plans for X-ray timing after the X-ray Timing Explorer (XTE). Timing science has played a critical role in the development of X-ray astronomy. The need now is to move into a new domain of shorter timescales and weaker modulation, one that can be reached only with very large aperture instruments. XLA is an X-ray facility with an aperture substantially greater than 1 m2, nominally 100 m2. Most of this area is devoted to a large array of collimated proportional counters. There is also a ~ 1 m2 coded aperture. It extends observational parameter space by several orders of magnitude in timing resolution, sensitivity to variability, and angular resolution. This will lead to a qualitatively new kind of X-ray astrophysics that can be applied to the study of a broad range of astrophysical objects. XLA is thus both an advanced timing mission and a general purpose facility whose principal uses are in areas that are not well covered in other aspects of the planned High Energy Astrophysics program.
Limitations of Observational Cosmology
Authors: Kafatos Menas 
Published: July 2016

AbstractUnlike the usual situation with theoretical physics which is testable in the laboratory, in cosmological theories of the universe one faces the following problems: The observer is part of the system, the universe, and this system cannot be altered to test physical theory. Even though one can in principle consider any part of the observable universe as separate from the acts of observation, the very hypothesis of big bang implies that in the distant past, space-time regions containing current observers were part of the same system. One, therefore, faces a situation where the observer has to be considered as inherently a part of the entire system. The existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself. For example, in the big bang cosmology the universe becomes opaque to radiation early on, and the images of extended distant galaxies merge for redshifts, z, of the order of a few. Moreover, in order to measure the distance of a remote galaxy to test any cosmological theory, one has to disperse its light to form a spectrum which would cause confusion with other background galaxies. Since the early universe should be described in quantum terms, it follows that the same problems regarding quantum reality and the role of the observer apply to the universe as a whole. One of the most fundamental properties of quantum theory, non-locality, may then apply equally well to the universe. Some of the problems facing big bang cosmology, like the horizon and flatness problems, may not then be preconditions on theoretical models but may instead be the manifestations of the quantum nature of the universe.