bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection of Stellar Flickering using Arrays of Telescopes
Authors: Edwards P.J. , Allen W. , Thomas M.
Published: July 2016

Rapid stellar variability of a stochastic type is characteristic of a variety of irregular variables including dwarf novae, x-ray binaries and nova-like variables. Rapid, small amplitude variability is often difficult to observe because of scintillation and photon statistics. Irregular variability is particularly difficult to observe because the power spectrum of the flickering is often not readily distinguishable from the spectra of atmospheric noise and shot noise. However, simultaneous observations of a variable with an array consisting of two or more telescopes separated by a distance exceeding the noise correlation length allows the intrinsic variability to be distinguished from noise.
A Remarkable Change in Period of SV Centauri
Authors: Irwin John B. , Landolt Arlo U.
Published: July 2016

SV Centauri (= HD 102552; 11h43m05s, -60°00.6 (1900)) is a contact binary showing the largest known variation of period. The system, which shows double lines at quadratures, consists of Bl and B2 components of 9.4 and 11.1 solar masses respectively (Irwin, J.B. and Landolt, A.U.,P.A.S.P. 84, 686. 1972). Recent observations (Eggen, O.J.,A.J. 83, 288, 1978) indicate that the eclipses are considerably shallower than found in 1970.
Systematic errors and the formation of a parallax catalogue
Authors: van de Kamp P.
Published: July 2016

I assume that we are restricting ourselves to photographic, trigonometric, annual parallax determinations. There is a long history on the subject of sytematic errors, and there are numerous aspects to the subject.
Requirements for a radio coordinate reference frame for the determination of Earth rotation parameters
Authors: Johnston K. , Spencer J. , Mayer C. , Klepczynski W. , Kaplan G. , McCarthy D. , Westerhout G.
Published: July 2016

The requirements for a radio reference frame to be used for the determination of Earth rotation parameters are given. The use of the NRAO interferometer at Green Bank, West Virginia for the initial radio interferometric studies of Earth rotation on a regular basis is also described. A catalog of accurate radio source positions will result from this study.
The Carlsberg Automatic Meridian Circle and the plans for Anglo-Danish collaboration
Authors: Olsen H. J. Fogh , Helmer L.
Published: July 2016

The Brorfelde meridian circle has been automated. This incorporates a telescope setting system, a new type of photoelectric slit micrometer, improved photoelectric circle reading system, met. data reading system with rain detector and photoelectric collimation micrometer all controlled by an HP 2100 minicomputer. The setting system can do the setting within 10 sees to an accuracy of ±2.”. The circle reading system with an accuracy of ±.”04 is more reliable than the original system. These systems have been tested and used for data collection for determination of diam. cor. This includes 1080 readings which are performed automatically in about 9 hours. The remaining equipment has been built and is being tested during the year 1978. After final tests it is planned to move the telescope to La Palma in collaboration with RGO and IAC. It is hoped to erect the instrument at La Palma at the end of 1980. At least 100 000 o bs. per year with an m. s.e. of.”20 are expected. In ten years time proper motions for at least 200 000 stars with an accuracy of .”014 will be available besides the fundamental work which will include observations of all traditional solar system objects and also day time observations.
Astrometrical software at the Pulkovo Observatory
Authors: Varin M. P. , Polozhentsev D. D.
Published: July 2016

Modern computing techniques are widely used in astrometry for reduction of astrometrical observations, theoretical studies and for gathering and storing measurements and observational data. At present the Pulkovo Observatory has a 3rdgeneration Soviet-Bulgarian computer ES-1020. It is similar to IBM computers in programming languages, magnete tapes, punch-cards and formats. ES-1020 can be used for a single-program and concurrent processing because it is supplied with a disc operating system(DOS). As its components DOS has the following translators: ASSEMBLER, BASIC, FORTRAN IV, PL/1, COBOL, etc., and also a programming library of mathematical and astrometrical modules. The library of sub-routines has a module principle which permits changing its contents and including new modules, e.g. astronomical programs.
Positions from objective prism spectra
Authors: Stock J.
Published: July 2016

Methods for the determination of radial velocities from objective prism plates have been elaborated by a number of authors. K. Schwarzschild was probably the first to analyze the mathematical problems of the method. Fehrenbach has used the radial velocity method extensively, and also Stock and Osbom. A discussion of the possibility of determining accurate positions from the same observational material, however, has been left aside. It is the purpose of this work to show not only that positions of astrometric accuracy can obtained from objective prism plates, but also that such a method offers certain advantages over the more conventional ones.
Fundamental observations made at Breslau in 1922-1925
Authors: Schmeidler F.
Published: July 2016

Meridian observations of fundamental stars were made at Breslau Observatory in 1922 to 1925. The observations in right ascension were made by W.Rabe with the 6-inch transit instrument, whereas the declinations were observed by A.Wilkens with the vertical circle. In both coordinates, observations of the Sun were also made.
Huit campagnes d’observations de Saturne a l’Astrolabe Danjon a San Fernando
Authors: Sanchez M.
Published: July 2016

This paper contains an analysis of Saturn observations with Danjon astrolabe at San Fernando. These observations were obtained during eight winter campaigns (1970-1978). Table 1 gives the mean values for each of the quantities Δα and Δδ (astrolabe - American Ephemeris) and the mean square errors. Figure 1 to 8 shows the results (right ascension and declination) and the corresponding smoothing curves. The accuracy of these curves is also given in table 1. The analysis of the values Δα and Δδ seem to show that there are differences, between the theoretical development of ephemeris and the observations, of periodical character.
A uniform system of designation of catalogues and surveys of star position
Authors: Teleki G. , Sevarlic B.
Published: July 2016

Introduction of an uniform digital system of designations of catalogues and surveys (lists) of star positions is proposed. The designations should comprise: 16 information groups with a total of 50 digits for observational catalogues and 10 groups with a total of 36 digits for other catalogues (derived, fundamental) and surveys of star positions.
Measurements of the Cape Astrometric Survey of the Southern Hemisphere
Authors: Nicholson W.
Published: July 2016

A 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

An 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.
Fundamentals and Deficiencies of Aperture Synthesis
Authors: Fomalont Edward B.
Published: July 2016

Aperture synthesis is the method used by astronomers to determine the accurate brightness distribution of the radio sky with a resolution much better than that possible with a single large antenna. The technique, now over a decade old, utilizes a large number of connected radio antennas, some of them physically moveable, to follow a region of sky for many hours or days in order to sample the spatial coherence function of the radiation field over a sufficiently large area and with a reasonable filling factor. Landmark references for aperture synthesis are McCready et al. (1947), Stanier (1950), Christiansen and Warburton (1955), Lequeux et al. (1962), Read (1961) and Ryle and Hewish (1960).
Measurement Errors in Rotational Synthesis and their Effects in the Map Plane
Authors: Hamaker J.P.
Published: July 2016

The 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

Often, 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.
A Proposal to Obtain Short Spacing Information by Interpolation
Authors: Rots A.H.
Published: July 2016

For a short description of the problem posed by missing information at short interferometer spacings in aperture synthesis we would like to refer to the introduction of the previous paper by Ekers and Rots. The solution that is suggested in this paper is not a true interpolation but somewhat intermediate between interpolation and Clean.
Analogue Processing Methods for Synthesis Observations
Authors: Cole T.W.
Published: July 2016

In aperture synthesis the formation of an image involves the two steps of spatial correlation across an aperture and transformation to the image. This is closely related to conventional imaging with a lens (Cole, 1977a), which Abbé interpreted as two successive transformations at the surfaces of the lens. With the simple lens the image is the light intensity in the output plane (Figure 1(a)). In aperture synthesis (Figure 1(b)) the image is the transform of the correlation but no detection takes place. The image corresponds to the ‘light’ amplitude rather than intensity.
Processing and Display of Spectral Line Absorption Maps
Authors: Wright Melvyn
Published: July 2016

We 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

Study 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.
An Optimum Deconvolution Method
Authors: Subrahmanya C.R.
Published: July 2016

An optimum solution to a deconvolution problem has to fulfil three general criteria: (a) an explicit recognition of the smoothing nature of convolution; (b) a statistical treatment of noise, e.g., using the least-squares criterion; and (c) requiring the solution to conform to all our prior knowledge about it. In the usual least-squares method, one minimises a variance of ‘residuals’, or the departures of the observed data from the values expected according to the recovered solution. However, this condition does not lead to a stable solution in the case of deconvolution, since the only stable solutions are those conforming to a criterion of ‘regularisation’ or smoothness (see, e.g., Tikhonov and Arsenin 1977). In our method, the stability is achieved by minimising the variance of the second-differences of the solution simultaneously with the fulfilment of the least-squares criterion. Such a procedure was first used by Phillips(1962). However, the solution thus obtained is still unsatisfactory since it usually does not conform to oura prioriinformation. When we seek the brightness distribution of an object, the most frequent violation of our prior knowledge is that of positiveness. This motivated us to develop an Optimum Deconvolution Method (ODM) which constrains the solution to satisfy prior knowledge while retaining the features of least-squares and smoothness criteria.
Formation of Acoustic Images from Spatial Coherence Functions: Processing by Superresolution Techniques
Authors: Biraud Y. , Escudié B. , Hellion A. , Munier J.
Published: July 2016

Radioastronomy deals with radiowaves emitted by different kinds of sources. These sources are very far from the receiving antenna; the distance R is very large compared with the wavelength. In acoustic imagery of noise sources the conditions are quite different.
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.
Stellar Convection Theory
Authors: Zahn Jean-Paul
Published: July 2016

This meeting, which deals with turbulence in stars, opens with a review on thermal convection. There is no better way to state from the start that among all instabilities that are likely to arise in stars, it is thermal convection which is the most firmly established as a cause for the turbulence that we observe on their surface. Our confidence in this comes mainly from the theoretical prediction that convective instability sets in whenever the density stratification becomes superadiabatic, as is expected in late type stars whose outer layers are very opaque, due to the ionization of the two most abundant elements, hydrogen and helium. And, in these stars at least, thermal convection occurs close enough to the photosphere to influence, be it indirectly, the profile of spectral lines.
On the Dynamics of the Solar Convection Zone
Authors: Durney Bernard R. , Spruit Hendrik C.
Published: July 2016

We 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

High-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

Convective 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

On 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.
Depth-Dependence of Turbulence in Stellar Atmospheres
Authors: Stencel Robert E.
Published: July 2016

I am very pleased to have this opportunity to present some recent observational work bearing on the depth dependence of motions in stellar atmospheres. I thank Dr. Gray for this invitation and also wish to acknowledge the patronage of the NAS-NRC.
Stellar Chromospheres
Authors: Linsky Jeffrey L.
Published: July 2016

Important progress in our understanding of stellar chromospheres has occurred in the past few years as a result of new observations, developments in spectral line formation theory, and the application of that theory to the construction of detailed model chromospheres. Significant trends are beginning to emerge from such analyses, and we are on the threshold of a meaningful confrontation between purely theoretical models and the data. The range of stars thought to possess chromospheres may be widening, and we now have a better understanding of the enigmatic problem of why the Wilson-Bappu relation between Ca II emission core widths and stellar absolute visual magnitudes actually works.
Excitation Dependent Gf-Values and Depth Dependent Microturbulences
Authors: Hasegawa Toshio
Published: July 2016

The 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.
Carbon in the Envelopes of White Dwarfs
Authors: D’Antona Francesca
Published: July 2016

Current theory of stellar evolution predicts that stars of initial masses up to 4-6 M⊙ evolve into Carbon-Oxygen White Dwarfs surrounded by a Helium envelope and, possibly, by a Hydrogen envelope. It also predicts that the mass of the Helium envelope which remains on the star at the end of its double shell burning evolution is a function of the Carbon-Oxygen core mass (Paczynski 1975). It can be shown that this mass can be reduced – but only slightly – during the following evolution of the star towards the White Dwarf region, either by nuclear burning or by mass loss (D’Antona and Mazzitelli 1979). During the White Dwarf stage, Helium convection grows into White Dwarfs having Helium atmospheres. The maximum extension of Helium convective mass is a function of the mass of the star (Fontaine and Van Horn 1976; D’Antona and Mazzitelli 1975,1979). It turns out that the Helium envelope remnant mass is always at least three orders of magnitude larger than the maximum Helium convective mass, whatever the mass of the star may be. This statement is unlikely to be changed by refinements either in the theory of double shell burning or in the theory of White Dwarf envelope convection.
Diffusion of Heavy Ions in Convective Envelopes, with Implications for the Masses of White Dwarfs
Authors: Alcock Charles
Published: July 2016

Heavy ions rapidly sink out of the base of a white,, dwarf convective zone, and a balance is set up between accreting interstellar material and this sedimentation flux. The heavy element abundances are lower than they would be in the absence of convection. The accretion process is responsible for any gross departures from the cosmic abundance ratios among the heavy ions. A chemically pure white dwarf must have mass greater than 0.2 M⊙. The DB stars have masses lower than 0.4 M⊙.
Structure and Composition of White Dwarf Atmospheres and Convection Zones
Authors: Böhm K.H.
Published: July 2016

We 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.
White Dwarf Candidates in the Globular Cluster NGC 6752
Authors: Richer Harvey B.
Published: July 2016

In a recent paper (Richer 1978, hereafter Paper I) the results of a search for faint blue objects in and around the globular cluster NGC 6752 were reported. The aim of the program was to isolate a sample of white dwarf candidates in this cluster which could then be studied in further detail. The plate material for this survey consisted of a set of deep UBV plates (only one in each color) obtained at the prime focus of the Cerro Tololo Interamerican Observatory 4-meter telescope. Limiting magnitudes reached by the plates were about U=22.4, B=23.0, V=22.0. A reanalysis of the photometry presented in Paper I (using a reduction program supplied by W. Harris [see Stetson and Harris 1977]) has now yielded a total of 68 candidate objects within 20′ of the cluster center having B≤22.7 and (U–B) ≤ –0.4. Although the accuracy of the photometry is low (about ±0.2 magnitudes), it seems clear that the preponderance of the objects do not have UBV colors typical of white dwarfs. Of the 68 candidate objects, 36 had a measurable V magnitude, and only 11 of these lay in the area of the color-color diagram known to be occupied by white dwarfs (Eggen and Greenstein 1965). The remaining 25 were generally well above the black body line in the two-color diagram and are probably QSO’s or peculiar blue stellar objects. Among these 11 good candidates, 7 are within 14’ of the cluster center and hence have a probability of greater than 50% of being cluster members according to the star counts of King et al (1968) assuming that white dwarfs have a radial distribution in NGC 6752 similar to other cluster members.
Nova Outbursts Due to Accretion from Rotating H-Rich Disks onto White Dwarfs
Authors: Sparks Warren M. , Siegfried Kutter G.
Published: July 2016

In this paper we discuss the third stage of our research on the nova outburst as described in the preceeding paper (Kutter and Sparks, page 290), i.e. we accrete hydrogen-rich material (normal solar composition) with Keplerian velocity onto a helium white dwarf at a rate of 10-8 M⊙/yr. When material with high angular momentum from a circumstellar disk is accreted onto a white dwarf with negligible angular momentum, a tremendous shear instability is created, and hydrogen-rich material is mixed with helium-rich material of the white dwarf on a scale that is short compared to the accretion time scale. Following Kippenhahn and Thomas (1978), we assume that in the mixing region marginal stability is established. Mathematically this is expressed by setting the Richardson number (the ratio of the work done against buoyancy to the kinetic energy of the turbulence) equal to ¼.
Photometry of AM Her Stars – Line and Continuum Emission
Authors: Szkody Paula
Published: July 2016

The 4 known AM Her stars or polars (AM Her, ANUMa, W Pup, and 2A0311-227) are characterized by large circular polarizations of 10-35%, (Tapia 1977a, b, Krzeminski and Serkowski 1977), an emission line spectrum with strong H and He lines (Crampton and Cowley 1977, Greenstein et al. 1977), complex photometric variations (Szkody 1978, Priedhorsky and Krzeminski 1978, Warner & Nather 1972), long term high and low states and short orbital periods (80-180 min.). Models of these systems envision a close binary containing a magnetic white dwarf primary (B ~ 108G) and late type main sequence secondary transferring material into an accretion funnel over one or both poles of the white dwarf (Stockman et al. 1977, Lamb & Masters 1979, Liebert et al. 1978).
Cyclotron Emission from the Shock-Heated Region of AM Herculis
Authors: Chanmugam G.
Published: July 2016

There has been considerable interest recently in the AM Herculis binaries, which are believed to contain a strongly magnetic white dwarf accreting matter from a lower-main-sequence companion (Tapia 1977, Chanmugam and Wagner 1977, Stockman et al. 1977). Models for these systems feature an accretion column above a magnetic pole of the white dwarf. A shock-heated region, with a temperature kT ≈ 20 keV (Raymond et al. 1979) and a height h – 106cm (Masters 1978), believed to be formed in AM Her just above the magnetic pole is likely to be responsible for the emission of the hard X-rays observed (Swank et al. 1977). It has been further suggested that this region should emit optically thick cyclotron emission in the ultraviolet because of the presence of the strong magnetic field ~ 108 gauss (Masters 1978, Lamb and Masters 1979). Such UV emission has not been observed (Raymond et al. 1979).
The Observational Properties of the ZZ Ceti Stars
Authors: Robinson Edward L.
Published: July 2016

The ZZ Ceti stars are the pulsating white dwarfs lying within a narrow instability strip, extending in temperature from 13,500 to 10,500 K, on the white dwarf cooling sequence. That white dwarfs should be pulsationally unstable cannot be considered surprising, since theoretical investigations of white dwarf pulsations began at least as early as 1949 (Sauvenier-Goffin 1949). As the predicted pulsation periods demonstrate, however, the nature of the pulsations was not correctly foreseen. With very few exceptions (e.g. Harper and Rose 1970) the early investigations assumed that the most likely pulsations to be excited were radial pulsations. Thus, the calculated periods were quite short, typically 2-10 seconds. The first of the pulsating white dwarfs actually to be observed was HL Tau-76 (Landolt 1968). A portion of its light curve is shown in Figure 1. The typical interval between successive pulses is about 750 seconds, not 2-10 seconds. This is a serious discrepancy, and one that exists for all of the ZZ Ceti stars discovered since HL Tau-76. Clearly, then, the observational data requires us to modify our understanding of pulsating white dwarfs. A considerable body of this observational data now exists. The purpose of the present paper is to present the data, and to show that it provides a reasonably coherent picture of the pulsating white dwarfs.
Vibrational Instabilities and Pulsational Properties of Cool White Dwarfs
Authors: Dziembowski W.
Published: July 2016

Attention 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.
White Dwarfs in Cataclysmic Binaries
Authors: Warner Brian
Published: July 2016

For isolated stars, identification as a white dwarf may be effected in several ways. The fundamental property of abnormally low luminosity can be detected through direct measurement of trigonometric parallax or indirectly through large proper motion (accompanied by appropriate photometric properties). The presence of greatly pressure broadened absorption lines is another unambiguous criterion. Rapid light oscillations of the kind reviewed by Robinson are another hallmark of a select group of white dwarfs. Any or all of these criteria may be used to classify a star as a white dwarf and in general can be applied to members of wide binary systems.
WZ Sge: Recent Observations Leading to a Model for Superhump Phenomena
Authors: Gilliland R. L. , Kemper E.
Published: July 2016

The 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

Some 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.
X-Ray Emission from Degenerate Dwarfs
Authors: Kylafis N. D. , Lamb D. Q. , Masters A. R.
Published: July 2016

Accreting degenerate dwarfs comprise an important class of galactic X-ray sources. This has become evident with the recent discovery of soft and hard X-ray emission from accreting magnetic degenerate dwarfs such as AM Her, AN UMa, and 2A0311-23, and from nonmagnetic or weakly magnetic cataclysmic variables such as SS Cyg, U Gem, EX Hya, and GK Per (for an observational review, see Garmire 1979). Previously known low mass X-ray binaries such as Cyg X-2 and Sco X-1, as well as some of the “bulge” sources, may also be moderate luminosity nonmagnetic degenerate dwarfs (Kylafis and Lamb 1979; Branduardi et al. 1979). Finally, theory predicts (Fabian, Pringle and Rees 1976; Katz 1977; Kylafis and Lamb 1979) an as yet undiscovered class of low luminosity nonmagnetic degenerate dwarf X-ray sources having hard (Tobs ≳ 30–50 keV) spectra.
A Spectroscopic Survey of Cataclysmic Variables
Authors: Bond Howard E.
Published: July 2016

The writer has undertaken a survey of cataclysmic variables (CV’s) with the image-dissector scanner on the Kitt Peak 2.1-m reflector. A resolution of 7 Å is obtained, and the wavelength interval 3500–5300 Å is covered. Generally only one or two observations of each object are made, with a typical integration time of 10 min. To date, about 100 objects have been observed; most of them are classified in the GCVS as U Gem, Z Cam, or Nl variables or old novae, but a number of irregular variables (types Is, L, ?, or RCB) that appear blue on the Palomar Sky Survey prints have also been included.
Z Cam at Standstill and in Eruption
Authors: Kiplinger Alan L.
Published: July 2016

Absolute spectrophotometric observations of the prototype dwarf nova Z Cam have been obtained at standstill and during the course of an eruption. Optical continuum slopes during the final stages of the rise to maximum appear steeper (bluer) than those observed during decline and at standstill. The Balmer jump is observed to be in shallow absorption during decline and in deeper absorption during the rise to maximum and at standstill. A composite energy distribution constructed for Z Cam at standstill is compared with fluxes derived from steady state (a-raodel) accretion disk models which utilize a grid of stellar energy distributions to synthesize the disk fluxes. The most reasonable accretion disk fit to the observations at standstill suggests a mass transfer rate of ~3 × 1017 g sec-1. The steady state model does not fit the observations of Z Cam during decline, nor does any arbitrary linear combination of stellar energy distributions. The results suggest that the accretion disk of decline is time dependent and exhibits an emission character which differs from that seen at standstill.
Radial Velocity Variations of the Secondary Star in U Geminorum
Authors: Wade Richard A.
Published: July 2016

We have used a photon-counting array detector at the coudé spectrograph of the Mt. Wilson 2.5-m reflector to follow changes in the near-infrared spectrum of U Geminorum around most of the orbit. A preliminary analysis of two series of exposures shows radial velocity variations in the Na I absorption doublet at λ8183 and λ8195, at the orbital frequency and with the orbital phase appropriate for the M5-type secondary star. A first attempt to detect the K I line at λ7699 was unsuccessful.
Recurrence of Nova Explosions
Authors: Nariai Kyoji , Nomoto Ken’ichi
Published: July 2016

It has been shown by many computations that a nova explosion is triggered by mass accretion onto a white dwarf in a close binary system. Such nova explosions will recur many times in the following way. When a certain amount of hydrogen-rich gas has been accreted on the white dwarf, a hydrogen-shell flash is ignited. Then the hydrogen-rich envelope expands greatly, which, in some cases, grows into a nova explosion. Almost all envelope mass is ejected into space or at least overflows its Roche lobe. After that the mass of the envelope increases again by accretion and the shell flash is ignited again. The period of such recurrence is given by τrec = ΔMH/(dM/dt), where dM/dt and ΔMH are the rate of accretion and the mass contained in the hydrogen-rich envelope at the ignition point.
Accreting Double Shell Source Degenerate Stars
Authors: Sion Edward M.
Published: July 2016

Ultraviolet photometry from the OAO-2 satellite supports the white dwarf thermonuclear runaway model for the symbiotic star AG Peg (Gallagher et al. 1979). Massive white dwarfs (M>1.1M⊙) burning hydrogen in a steady state with accretion (Sion et al. 1979) undergo either repetitive hydrogen shell flashes (Ṁ ≲1.03×10-7M⊙/yr), burn hydrogen stably in a steady state with accretion (1.03≲Ṁ≲2.7×10-7M⊙/yr) or evolve into a red giant structure (Ṁ≳2.7×10-7M⊙/yr). The nuclear reactions do not “shut off” between outbursts and mass is not ejected. If these models represent the behavior of the hot component of symbotic variable stars, the high luminosities and masses lead to the possibility that helium shell burning should be important as an additional energy source. The behavior of double shell burning near the surface of a white dwarf of any luminosity has not been explored (Webbink et al. 1978); Models have been constructed to represent such stars having (1) M=1M⊙, Ṁ=1.25×10-7M⊙/yr (L=104L⊙), log Te=5.70 and log R=8.965 and (2) M=1M⊙, Ṁ=1.26×10-8 M⊙/yr (L=103L⊙), log Te=5.52 and log R=8.85. Evolutionary sequences using these initial double shell source models are being constructed.
The Astro-D Mission
Authors: Tanaka Y.
Published: July 2016

Astro-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

The 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

The 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

The 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

The 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

There 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.