bluuebunny/crossref_metadata_2025 huggingface dataset:
Future Research Directions: Theoretical Approach and Perspective
Authors: Weiss N.O.
Published: July 2016

It is difficult to provide a comprehensive theoretical explanation for the activity of red dwarf stars. Among particular problems that are ripe for further investigation are: the production of steady, cyclic or irregular patterns of activity by nonlinear dynamo action in stars; the effect of magnetic buoyancy in producing photospheric magnetic fields; the formation of isolated flux tubes and their interaction with convection. These topics are discussed and some future lines of research are suggested.
Summary of the Colloquium
Authors: Goldberg L.
Published: July 2016

I have rarely had the pleasure of attending a conference in which the sheer volume of information has been so impressive and the contributions have been so diversified. Ordinarily, an I.A.U. colloquium is quite specialized, but this one might easily have been sponsored by half a dozen commissions and several international scientific unions. Astronomers from many sub-disciplines, atomic physicists, plasma physicists, aerodynamicists and applied mathematicians have come together to unite solar and stellar physics and to learn one another's scientific language. In principle, my task is to summarize more than 100 papers, which is clearly impossible even if I had had two evenings to prepare instead of one. The best I can do is to mention a few of the papers which seem to me to have conveyed the flavor of the conference and to ask the forgiveness of the remaining authors.
High Order Resonances in the Evolution of the Lunar Orbit
Authors: Kovalevsky J.
Published: July 2016

This paper deals with the long term evolution of the motion of the Moon or any other natural satellite under the combined influence of gravitational forces (lunar theory) and the tidal effects. We study the equations that are left when all the periodic non-resonant terms are eliminated. They describe the evolution of the-mean elements of the Moon. Only the equations involving the variation of the semi-major axis are considered here. Simplified equations, preserving the Hamiltonian form of the lunar theory are first considered and solved. It is shown that librations exist only for those terms which have a coefficient in the lunar theory larger than a quantity A which is function of the magnitude of the tidal effects. The solution of the general case can be derived from a Hamiltonian solution by a method of variation of constants. The crossing of a libration region causes a retardation in the increase of the semi-major axis. These results are confirmed by numerical integration and orders of magnitude of this retardation are given.
The Study of Planetary Secular Perturbations
Authors: Jia-xiang Zhang
Published: July 2016

The methods of the first-order planetary secular perturbations are discussed in this paper. On the basis of Gauss' method, some concrete applicable formulae are derived. And then, orbital evolutions of the nine major planets in solar system during about 2,100,000 years are investigated numerically. The method applied here is in principle suitable for the orbits of arbitrary eccentricities and inclinations.
Physical Processes Affecting the Motion of Small Bodies in the Solar System and their Application to the Evolution of Meteor Streams
Authors: Williams Iwan P.
Published: July 2016

In addition to planetary perturbations, the small particles which make up a meteor stream are subject to outward radiation pressure and the Poynting-Robertson effect. New particles can also be generated in a stream through being released from the nucleus of a comet. We summarise the main physical effects, discuss models for meteor stream evolution and give a brief account of the observational data available.
Analytical Theory of A Trapping. In A Two-Body Problem of Variable Mass
Authors: Omarov T.B. , Minglibaev M.J.
Published: July 2016

The new nonstationary model problem is considered. Its solution generalizes by form the known particular Mestschersky-Vinti solution in a two-body problem of variable mass. The equations of the corresponding perturbed motion are deduced. In the case of a two-body problem of variable mass μ. the perturbing force is proportional to second temporal derivative from the value μ-1 . It is possible to describe with a good approximation such qualitative effects in this problem as a trapping and disintegration on a basis of properties of the model problem. Let us consider the example of a trapping.
Degenerate Dynamical Systems and the Disappearance of (K.A.M.-Type) Integrals of Motion
Authors: Varvoglis H.
Published: July 2016

The problem of constructing the stochasticity criterion of a degenerate near-integrable dynamical system is considered. We show that in certain cases the above criterion can be found as the limit of the corresponding stochasticity criteria of a family of non-degenerate systems, whose limit is the degenerate one.
Photographic infrared spectra of symbiotic stars
Authors: Andrillat Y. , Houziaux L.
Published: July 2016

Relatively few spectra of symbiotic stars have been recently published in the photographic infrared. We have observed six objects during the period 1962-1977 with a grating spectrograph attached to the newtonian focus of the 120-cm telescope at Observatoire de Haute Provence. The reciprocal dispersion is 230 A.mm-1 and the region 5800 to 8800 A has been covered using hypersensitized IN plates. The minimum equivalent width for an emission line to be seen is about 0.5 A. The spectra are displayed on plates I and II. We now briefly review the main spectral characteristics.
UV line emission of symbiotic stars
Authors: Nussbaumer H.
Published: July 2016

General characteristics of emission line spectra from symbiotic stars are outlined. Data from some special line ratios in the 1000 Å - 3000 Å range, and others connecting the visual and the far UV lines are presented, and their application to symbiotic stars is discussed. Integrated fractional abundances for ions easily observed in the far UV are given to facilitate abundance determinations for nebular conditions. It is found that the physical conditions of the regions emitting the emission line spectra differ considerably among different symbiotic stars.
Ultraviolet properties of the symbiotic stars
Authors: Slovak Mark H. , Lambert David L.
Published: July 2016

Prior to the launch of the IDE satellite in early 1978, the only symbiotic star previously detected in the ultraviolet by earlier UV satellites, such as the 0A0-2, TD-1 and ANS experiments, was AG Pegasi = HD 207757 (Gallager et al. 1979). These broad-band observations indicated that the symbiotics as a class may show a significant ultraviolet flux and thus they became natural candidates for a survey with the IUE satellite. The following is an interim report on a survey of the symbiotics, both at low and, for AG Pegasi and CH Cygni, at high resolution.
X-ray observations of symbiotic stars
Authors: Allen David A.
Published: July 2016

Observations are reported of 19 symbiotic stars made with the imaging proportional counter of the Einstein Observatory. Three of the objects (HM Sge, V 1016 Cyg and RR Tel) were detected as soft X-ray sources. All three have shown slow-nova eruptions in the past 40 years. The data are interpreted as support of a model for slow novae involving thermonuclear events on white dwarfs which accrete from M giant companions. Symbiotic stars in their steady state, not being detected X-ray sources, are presumed to be powered by the accretion process alone.
Z Andromedae: the prototype?
Authors: Viotti R. , Giangrande A. , Ricciardi O. , Cassatella A.
Published: July 2016

Z And is considered as the “prototype” of the symbiotic stars. Besides its symbiotic spectrum, the star is also known for its characteristic light curve (and for the related spectral variations). Since many theoretical speculations on Z And and similar objects have been based on the luminosity and spectral variations of this star, it is important to make a critical analysis of the observational data concerning it.
Polarimetry of CH Cygni
Authors: Piirola V.
Published: July 2016

Variable linear polarization has been detected in CH Cyg. Observations in 1977–79 (UBV) and 1979–80 (UBVRI) are presented. The amount of polarisation increases towards ultraviolet and the observed values range from 0.34 to 1 .85 % in the ultraviolet, and 0.04 to 0.68 % in the yellow light. In the red and infrared observations the polarizationwas typically less than 0.1 %. During the interval September 1977 – February 1978 and in May 1980 a second component of polarization, with different direction and wavelength dependence, was present, resulting in a strong rotation of the position angle as a function of wavelength. The R and I observations of May 1980 (PR ≅ 0.4 %, PI ≅ 0.5%) showed that the second component was increasing towards the infrared. The peculiar wavelength dependence of polarization and position angle could be explained by variations in particle size and scattering geometry in a complicated dust envelope around the M giant. Another hypothesis is that the component of polarization increasing towards the ultraviolet is produced by electron scattering in an extended envelope of a hot companion and the second component by transient dust envelope of the M giant.
Variation spectrale de CI Cygni en 1975
Authors: Fehrenbach Ch.
Published: July 2016

En 1971 et 1972, cette étoile présentait un spectre d’émission comorenant des raies de l’hvdrogène et les métaux ionisés Call. Fell, etc… se superposant sur un fond continu sans raie d’absorption, [Fell] est présent par deux raies faibles, les raies de l’hydrogène, de Fell et de CrII présentaient un profil P Cyg.

Le 4 Juillet 1975, Madame Y. Andrillat a sienalé la disparition de la raie de Hel 10830. Nous avons obtenu immediatement un spectre à 20 A mm-1 au télescope de 152 cm. Ce spectre est un spectre d’absorption où seules les raies de l’hydrogène présentent des émissions à structures complexes.
Spectral variations of CI Cyg between 1980 and 1981
Authors: Chang-Chun Huang
Published: July 2016

In our paper (Ch. Fehrenbach and C.C. Huang, 1981) we have described the details of our spectroscopic observations of CI Cyg in 1980. In that year, the star showed a fair presence of bright forbidden lines of [FeV ]and very strong emission lines of high and low excitation, including forbidden [0 III ] , [Ne III], [Fe II ] and [S II] and permitted 0 III, N III as well as He I and Fe II … etc … The He II 4686 A was very strong. The Balmer lines were the strongest emission features in the spectrum and Hα and Hβ were double. There were two groups of velocities in 1980, one was positive for forbidden lines and the other was negative for the permitted lines. The displacements of Balmer lines showed a regression.
Physical properties of V1329 Cygni
Authors: Iijima T.
Published: July 2016

In this paper, I shall present another model for V1329 Cyg. Grygar et al. (1979) proposed a long period eclipsing binary model consisting of a massive M giant and a hot component. Some problems, however, have remained on the binary model. Namely, the mass function is too large, the amplitude of the light variations changes from period to period, the light curve differs from that of Algol type systems and is similar to long period binaries, and so on (Iijima et al. 1981). It has been believed that some peculiarities in the system could explain those problems. Recently however, some phenomena which are inconsistent with the binary model were observed (Iijima and Mammano 1981).
Spectral evolution of HBV 475 (= V1329 Cygni) in the ultraviolet
Authors: Kindl Ch. , Nussbaumer H.
Published: July 2016

Figure 1 shows the low resolution IUE spectra of HBV 475 during 1979-81. Whereas the May 1981 spectrum looks very similar to that of June 1979, there is a clear difference in the August 1980 spectrum when the star was brighter. The strength of the NV multiplet at 1240 A surpasses those of the preceeding and succeeding years by at least a factor 4. A first glance at the continuum and the strongest lines suggests a strong activity increase between June 1979 and August 1980, followed by a decrease to the 1979 level by May 1981. Closer inspection shows that neither CIII]λ1908 nor NIII]λl750 followed that activity pattern, but rather decreased steadly in their fluxes. Thus in June 1979 CIII]λ1908 showed the same flux as HeIIλ1640, whereas in May 1980 CIII] was weaker by a factor two. The 0Iλ1304 and MgIIλ2800 multiplets show the same behaviour as HeII, CIV and NV.
AR Pavonis: the Rosetta stone of the symbiotics
Authors: Slovak Mark H.
Published: July 2016

With Mayall’s discovery of the eclipsing nature of AR Pavonis = CD-66°3307, a nearby unique opportunity to directly probe the structure of the symbiotic binary became available. Few eclipsing systems have been detected among the symbiotics and AR Pav is fortunately bright enough to be observed spectroscopically at Coudé dispersions.
HM Sagittae – A most remarkable star
Authors: Kwok Sun
Published: July 2016

HM Sagittae is one of the most unusual objects in the Galaxy for it displays activity in every spectral band from x-ray to radio. Its present variable-star designation was given after the discovery of its optical brightening from 16m to 12m between April and September 1975 (Dokuchaeva and Balazs 1976). It was soon found to have a rich emissionline spectrum similar to that of a planetary nebula (Stover and Sivertsen 1977). Post-brightening monitoring of the object by Ciatti, Mammano and Vittone (1977, 1978) found the B and V magnitudes to be variable with amplitudes of at least one magnitude. Evidence for increasing excitation was found by Ciatti, Mammano and Vittone (1979) with Hell 4686 emerging in October 1978. Wolf-Rayet features of velocities up to 2000 km s-1 have also been seen (Belyakina, Gershberg and Shakhovskaya 1978, 1979; Brown et al. 1978; Ciatti et al. 1978; Wallerstein 1978; Allen 1980; Andrillat and Swings 1982). Analysis of the forbidden line ratios gives an estimated nebula density of 106-107 cm-3 and a gas temperature >104K (Ciatti et al. 1977; Arkhipova and Dokuchaeva 1978; Davidson, Humphreys and Merrill 1979; Arkhipova, Dokuchaeva and Esipov 1979).
Changes of LISM Characteristics in the Heliospheric Interface
Authors: Ripken Hartmut W. , Fahr Hans J.
Published: July 2016

It is possible to deduce LISM properties from observations of interstellar neutral gases in the inner solar system. Parameters accessible by this method are the interstellar wind vector and the densities and temperatures of hydrogen and helium, implying also the deduction of the relative abundance ratios and the degree of ionization in the LISM. Direct inference from observations, for example resonance luminescence measurements of Ly-alpha and He-58.4 nm radiation, yields values appropriate only for the inner solar system, i.e. for the regions within the heliopause dominated by the solar wind plasma.

Particularly the subsonic LISM plasma interface ahead of the heliopause causes profound changes in the properties of the neutral LISM gas traversing this region. Mainly p-H charge exchange processes give rise to the destruction of primary hydrogen and the production of secondary hydrogen atoms, the net effect being a depletion of the neutral hydrogen component of the LISM by about 50%.

Details on the depletion mechanisms, the hydrogen and oxygen extinctions, and the consequences for the Ly-alpha resonance luminescence intensity interpretations are presented.
Non-Local Origin of a Substantial Portion of the Soft X-Ray Background
Authors: Clark George W.
Published: July 2016

Comparison of the SAS-3 soft X-ray sky survey (F. Marshall and G. Clark 1984) with the 21-cm neutral hydrogen survey of Stark et al. (1984) confirms the well-known anticorrelation between the counting rates in the C-band (0.10-0.28 keV) and the column density of neutral hydrogen, and demonstrates that this anticorrelation is significant on all angular scales ranging from that of the general trend from the galactic equator to the poles down to the angular resolution of the detector (2°.7 FWHM). Included in this general anticorrelation are numerous instances of what appear to be soft X-ray “shadows” of nearby (100-300 pc) 21-cm features, and several bright X-ray regions coincident with “holes” in the ISM.
Inverse Relations between 0.25 keV counts and local interstellar dust
Authors: Knude J. , Jakobsen P. , Labov S. , Bowyer S.
Published: July 2016

A preliminary comparison of color excesses and HEA0-1, A2 0.25 keV counts have been performed on two angular levels in order to search for indications of local photoelectric absorption.

a. Color excesses and background counts are smoothed to a common 1.5 1.5 sq.deg. beam. Although distance information on the color excesses are available it is not used in this first attempt. The lines of sight to which the excesses pertain have however a length comparable to the expected viewing distance at these energies in the local medium. Figure 1 displays the resulting average counts/pixel versus average excess/pixel for the five areas investigated. A general decrease of the counts with excess is apparent. The wide scatter in the individual regions is probably due to excess variations on scales smaller than the collimated beam. The minimum counts on the diagram come from a region where an almost coherent sheet of dust is present within a distance ~200 pc. The constancy of the minimum counts in this particular direction indicates that the soft X-ray emission probably originate exclusively in front of the matter observed to be present. Note that the SGP counts show a shallow inverse dependence on excess. The latitude distribution of the five areas assures that the general inverse relation of the 0.25 keV counts on color excesses is not a latitude effect.
The Parallax of Pulsar 0950+08 and the Local Free Electron Density
Authors: Gwinn C.R. , Taylor J.H. , Weisberg J.M. , Rawley L.A.
Published: July 2016

We report a parallax of 7.9±0.8 mas for PSR 0950+08, corresponding to a distance of 130±15 pc. The measured pulse dispersion of this pulsar implies an average free electron density of 0.023±0.002 cm-3 along the line of sight. This parallax measurement is subject to systematic errors and questions of interpretation which have not yet been fully explored.
The CFA System for Digital Correlations
Authors: Wyatt William F.
Published: July 2016

Our spectral reduction and analysis system has undergone many modifications and Improvements since 1979, when it was described in a paper by Tonry and Davis (1979). The system’s flexibility and power allows analysis of spectra from all our spectrographs (high dispersion to low), easy creation of templates, many correlations per object, and a very useful display of the correlation results. Several changes in filtering and correlation techniques have resulted in the improved reanalysis of old observations.
A New Halo Survey
Authors: Carney Bruce W. , Latham David W.
Published: July 2016

We describe a new survey of proper motion stars now nearing completion. We briefly discuss the survey’s completeness and our data analysis methods. We present preliminary results for the motion of the Local Standard of Rest (LSR) with respect to the most extreme velocity stars and the possible presence of a metallicity gradient amongst the halo stars.
Kinematics of Halo Red Giants
Authors: Carney Bruce W. , Latham David W. , Straižys V.
Published: July 2016

We discuss results from radial velocity data for a sample of metal-poor kinematically-unbiased red giants. We determine the motions of the stars with respect to the Local Standard of Rest, and estimate their velocity dispersions.
The Hyades: Membership and Convergent Point from Radial Velocities
Authors: Stefanik Robert P. , Latham David W.
Published: July 2016

Multiple radial velocities of 212 proper motion and/or photometric Hyades candidates have been obtained in the magnitude range 5 < V < 15 with an accuracy of ± 0.7 km s−l for an individual observation. These observations have been used to establish cluster membership, to identify binary star candidates, to derive a convergent point solution and to determine the cluster distance.
Internal Dynamics of Globular Clusters
Authors: Freeman K.C.
Published: July 2016

The purpose of this review is to discuss why stellar radial velocities are so important for globular cluster dynamics.

Globular clusters are structurally fairly simple. They are almost spherical and almost entirely stellar. Hany of them are close enough to allow really detailed observations of their stellar content, structure and internal motions. They give us a unique opportunity to acquire an understanding of the present dynamical state of real self-gravitating systems of interacting stars, at a level of detail that will probably never be possible for any galaxy. This would be an excellent starting point for the theory of the formation and dynamical evolution of globular clusters, which is now a very active area of research.
Radial Velocity Studies of the Internal Kinematics of Open Clusters
Authors: Mathieu Robert D.
Published: July 2016

The internal kinematics of open clusters are a particularly challenging subject for study with radial velocities. Our present sitate of knowledge concerning the structure and kinematics of open clusters has recently been reviewed (Mathieu 1985), so I will only summarize here several of the essential concerns. The most basic goal is to measure a central or global velocity dispersion. Comparison of such measured dispersions with dynamical models fit to the cluster structure is a direct test of our understanding of the dynamics of open clusters. Far more difficult but of great importance to our understanding of cluster dynamics is the observation of assorted differential effects in these clusters. Open clusters provide a unique opportunity to study velocity distributions as a function of stellar mass. Radial velocity studies of nearby clusters can in themselves span a factor 2 in stellar mass; when combined with proper-motion studies which include the earlier stars inaccessible to high-precision radial velocities, a mass spectrum of up to an order of magnitude can be studied. Also, as with globular clusters, anisotropie velocity distributions are to be expected in the halos of those open clusters which are more than a few relaxation times old. Proper-motion studies (Jones 1970, 1971; van Leeuwen 1983) have found that anisotropy exists to within 1 pc of the centers of the Pleiades and Praesepe, much nearer the center than has so far been found in globular clusters. Independent confirmation of these findings as well as an increase in the sample of clusters studied would be of real value. And finally, the very youngest open clusters allow us to study the state of clusters at formation and indeed the star-formation process itself.
Dynamics of NGC 188
Authors: Harris Hugh C. , McClure Robert D.
Published: July 2016

Radial velocities have been obtained of 48 stars (33 member giants) in NGC 188 to investigate the internal dynamics. The velocity dispersion drops from the center outward, but the observed central dispersion is undoubtedly inflated by undetected binaries. The binaries concentrate toward the center, but models of the binary population show that corrections for their effect on the dispersion of any small sample are uncertain. The dispersion in the outer ring indicates a cluster mass in agreement with the mass of visible stars.
Coravel Measurements of IAU and Southern Potential Radial-Velocity Standard Stars. A Zero Point Discussion
Authors: Mayor M. , Maurice E.
Published: July 2016

Radial velocity measurements have been carried out since 1981 with the spectrometer CORAVEL at ESO, La Silla. Almost one thousand measurements of IAU radial velocity standard stars and of potential southern standard stars have been acquired by the different observers (mean precision per measurement 0.2 km/s).

Among the measured IAU standard stars, at least four have shown clear radial-velocity variations from 1981 to 1984 (HD 36673, 156014, 44131, 115521).

The comparison between CORAVEL mean velocities and IAU values reveals a difference of approximately 0.8 km/s between bright (mv <4.3) and faint IAU (mv >4.3) standards (Vr(IAUB) - Vr(IAUF) = +0.8 km/s). A similar difference also appears when comparing IAU standard velocities and those measured with the Victoria spectrometer, Fletcher et al. (1982).

Thus, IAU standard stars not only include radial-velocity variable stars (intrinsic variables and SB) but they also present zero-point systematic effects.

In the present paper we correct the radial velocities of the bright IAU standard stars so that they now belong to the same system as the faint ones. After elimination of variable velocity stars and stars showing large differences between IAU values and recent radial-velocity determinations, an homogeneous list of 34 IAU standard stars is obtained. These revised radial velocities are based on IAU values and new determinations obtained with the Victoria spectrometer and with CORAVEL at La Silla. These stars are distributed between the declinations δ = -82° and δ = +28°.

This paper uses observational data in advance of the publication by CORAVEL observers of the 7th of the series of papers: “Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL”.
Stellar Lineshifts Induced by Photospheric Convection
Authors: Dravins Dainis
Published: July 2016

Effects of stellar atmospheres on measured radial velocities are examined. Surface convection (“stellar granulation”) causes photo-spheric line asymmetries and wavelength shifts of ≃ 100 - 500 m/s. Cyclic changes in the convection patterns, such as observed during the solar 11-year cycle, may mimic radial velocity variations of perhaps 30 m/s. The study of stellar atmospheres would benefit from accurate (< 100 m/s) differential radial velocity measurements among lines of different parameters (strength, excitation potential, wavelength region) in the same star. To minimize convective perturbations, the flanks of very strong photospheric lines should probably be used, at least in stars with weak chromospheres. To disentangle cyclic variations due to stellar motion, several different groups of lines should be monitored, together with the Ca II K chromospheric emission.
DDO Standard Velocity Star Measures 1968–1984
Authors: Kamper Karl W.
Published: July 2016

The current Cassegrain spectrograph on the DDO 1.9m telescope was first used in 1966, but came into regular service in 1968. It is a fairly standard configuration with a Cassegrain collimnator and f/2 and f/5 Schmidt cameras. In practice, the f/5 camera with gratings which yield dispersions of 8A/mm and 12A/mm In the blue have been used almost exclusively, with the latter the more common. Interchangeable red- and blue-enhanced collimnators and Richardson image slicers were added in June, 1978.

More than 1200 plates of IAU standard velocity stars have been taken with this spectrograph, of which measures of 956 were made by us, or were available from the DDO archives or were made available by other investigators. Ten of these plates were not used because they were taken with unusual grating and tilt combinations. Some of the plates left unmeasured were simply broken or of poor quality, but a depressingly large number were simply missing. Most of the stars of spectral type M have also not been measured, since a line list for this class has only recently been created. Of the plates used in this study 810 were with the 12A/mm dispersion, 110 with the 8A/mm, and 26 were taken at 16A/mm in the red. The latter are of less use in studying the IAU stars themselves, but are essential in calibrating the rather considerable number of velocities measured here in the red.
Bibliographic Catalogue
Authors: Barbier M.
Published: July 2016

The increasing number of stellar radial velocity determinations and their publication in many journals necessitates the compilation of a continuously evolving bibliographic catalogue.

The first stellar radial velocity catalogue was compiled by H. A. Abt and E. S. Biggs in 1972. It is complete up to 1970. At the Marseille Observatory, Mme. M. Petit and myself have undertaken a follow-up of this catalogue. Our presentation is nearly the same.

We systematically examine all reviews of possible interest received in our library. Our bibliography does not include papers which do not publish new data on radial velocities. The first part of our catalogue, including about 5000 references between 1970 to 1975, was published on microfiche in 1979. This microfiche was prepared by the Strasbourg Stellar Data Center. The catalogue is available on magnetic tape from the Stellar Data Center. This first part was not complete and several corrections have been made.
A Search with Reticon and CCD Detectors for New Spectroscopic Components of Binary and Multiple Stars
Authors: Fekel Francis C.
Published: July 2016

A search for binary and multiple star components previously undetected spectroscopically was initiated in 1976. This was the result of the availability of solid state Reticon and CCD detectors which have high quantum efficiency at red and infrared wavelengths. Such detectors enable high signal-to-noise observations to be made in search of weak secondary or tertiary features from cooler stars. Some of the work on multiple systems has been reported previously by Fekel, Lacy, and Tomkin (1980) and Fekel (1983). Emphasis most recently has been placed on a search for the secondaries of single-lined solar-type binaries.
Mass Distribution and Luminosity Function of White Dwarfs
Authors: Weidemann Volker , Yuan Jie W.
Published: July 2016

Ever since Graham’s Strömgren photometry (1972) demonstrated the existence of a single well defined cooling sequence of DA white dwarfs the question of the mass dispersion (or the width of the number-mass distribution) has been in the foreground of my studies (Weidemann, 1970, 1977).

Indeed it turned out that the shape of the white dwarf mass distribution provides strong constraints on the theory of stellar evolution with mass loss, a fact which will be demonstrated again in the following lecture. It therefore seems worthwhile to dwell in some detail on the methods of its determination. For the benefit of the non-specialists I shall first present some of the historical results and then continue to discuss the present situation.
The Luminosity Function of White Dwarfs in the Local Disk and Halo
Authors: Liebert James , Dahn Conard C. , Monet David G.
Published: July 2016

The luminosity function (LF) and total space density of white dwarfs in the solar neighborhood contain important information about the star formation history of the stellar population, and provide an independent method of measuring its age. The first empirical estimates of the LF for degenerate stars were those of Weidemann (1967), Kovetz and Shaviv (1976) and Sion and Liebert (1977). The follow-up investigations made possible by the huge Luyten Palomar proper motion surveys, however, added many more faint white dwarfs to the known sample. While the number of known cool white dwarfs grew to nearly one hundred, these did not include any that were much fainter intrinsically than the coolest degenerates found from the early Luyten, van Biesbroeck and Eggen-Greenstein lists.
On the Structure of Pre-White Dwarfs
Authors: Schönberner D. , Tylenda R.
Published: July 2016

White dwarfs (WD) are the final configurations of all stars up to initial masses between 5 and 9 M⊙. Two feeder channels for the creation of single WDs can be distinguished: Either evolution through the asymptotic giant branch (AGB) and the following planetary-nebula (PN) phase, or evolution from the horizontal branch through the hot subdwarf region. Prelimary estimates by Drilling and Schönberner (1985) and Heber (1986) indicate that the creation of WDs via the horizontal–branch channel is rather insignificant (few percent of the total WD birthrate) and can be neglected. Thus the evolution through the AGB determines the internal structure of single WDs, and the study of the PN stage serves to elucidate the inital conditions for the white-dwarf evolution.
Transport Processes and Neutrino Emission Processes in the Interior of White Dwarfs
Authors: Itoh Naoki
Published: July 2016

Recent developments in the studies of the transport processes and the neutrino emission processes in the interior of white dwarfs are reviewed. Special emphasis is placed upon the accuracy of the calculations. Ionic correlation effects play an essential role in the transport processes and the neutrino bremsstrahlung process. The Weinberg-Salam theory is the basis for the calculation of the neutrino emission processes.
Rosat - An All-Sky X-Ray and EUV Survey of White Dwarfs
Authors: Barstow M.A.
Published: July 2016

The West German astronomy satellite ROSAT comprises two imaging telescopes - an X-ray instrument covering the energy band 0.15-2keV and an EUV instrument (provided by the UK) covering the range 0.02-0.21keV. A primary aim of the mission is to perform a sensitive all-sky survey with both telescopes (two ‘colours’ in the EUV) in the first 6 months. This will be followed by a least one year of pointed observations at specific targets. This paper briefly describes the ROSAT instrumentation and discusses the likely impact of the survey on white dwarf studies.
Low Mass Hydrogen Envelopes and the DB Gap
Authors: MacDonald James
Published: July 2016

The existence of a gap in the distribution of helium atmosphere white dwarfs at the effective temperature interval 30,000 K ≤ Te ≤ 45,000 K is well documented (Wesemael, Green and Liebert 1985; Liebert et al 1986; Green and Liebert 1987).

To explain the presence of this gap and other variations of the non-DA to DA ratio, it has been proposed (Fontaine and Wesemael 1987; Liebert, Fontaine and Wesemael 1987) that the helium-rich PG 1159 stars are the progenitors of essentially all white dwarfs. Some minute quantity of hydrogen of total mass, MH, is assumed to be mixed in the outer helium envelope, and settle upward as the star cools from the PG 1159 stage. Eventually enough hydrogen is at the surface to make the star appear a DA. The star has to become DA before it cools down to ≈ 45,000 K and cools to ≈ 30,000 K as a DA. At this temperature, depending on MH, the underlying helium convection zone may break into the hydrogen layer, diluting it and making the star a DB.
Optical Frequencies in V471 TAU
Authors: Winget D. E. , Claver C. F.
Published: July 2016

V471 Tau is a spectroscopic and eclipsing binary system located in the Hyades cluster. The binary consists of a K2V and a hot DA white dwarf star (Nelson and Young 1970). Soft x-ray observations reveal strong modulation at periods of 554.7 ± 0.3s and 277.5 ± 0.1s (Jensen 1985, Jensnen et al. 1986).

Robinson et al. (1988) reported the detection of the 555 s period in the optical. This period was about a factor of 20 reduced in mean amplitude in their data relative to the soft x-ray amplitude. They also found that it varied in amplitude from run to run by more than a factor of 2.5, dropping below detectability on several runs. They found some evidence for the 277.5 s period in several runs, but never at high enough amplitude to measure reliably. In addition, they noted that several of their runs had statistically significant power at other frequencies, but noted that in their six runs none of the additional frequencies repeated themselves. Robinson et al. also used observations near the eclipse of the white dwarf to demonstrate that most of the pulsed light is coming from the white dwarf.
The Search for Close Binary Evolved Stars
Authors: Saffer Rex A. , Liebert James
Published: July 2016

We report on a search for short-period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Hα observations of the suspected white dwarf/brown dwarf system G 29–38.
White Dwarfs in Globular Clusters
Authors: Fahlman G.G. , Richer H.B.
Published: July 2016

Surrounding the galaxy,with an aloofness appropriate to their great age,the globular clusters have played a starry role in the development of much of modern astronomy. In particular,they continue to be vital laboratories for testing our ideas of stellar evolution (Renzini and Fusi Pecci 1988). Through the study of cluster color-magnitude diagrams (CMD’s),all the major phases in the life of a common low mass star can be traced,save one. The final sequence, the locus of cooling white dwarfs, remains unexplored. We are forced to glean our knowledge of this evolutionary phase from the study of a heterogeneous sample of relatively nearby stars. Although remarkable progress has been made, the prospect of observing white dwarfs in globular clusters offers the potential for new insights into old problems; e.g., the DA/DB dichotomy, and perhaps a resolution of some of the outstanding issues connected with the clusters themselves.
A Limit on the Space Density of Short-Period Binary White Dwarfs
Authors: Robinson Edward L. , Shafter Allen W.
Published: July 2016

We infer that detached binary white dwarfs with orbital periods of a few hours exist because we observe both their progenitors and their descendents. The binary LB 3459 has an orbital period of 6.3 hr and contains a pair of hot subdwarfs that will eventually cool to become white dwarfs (Kilkenny, Hill, and Penfold 1981). L870-2 is a pair of white dwarfs and, given enough time, its 1.55 d orbital period will decay to shorter periods (Saffer, Liebert, and Olszewski 1988). GP Com, AM CVn, V803 Cen, and PG1346+082 are interacting binary white dwarfs with orbital periods between 1051 s for AM CVn and 46.5 min for GP Com (Nather, Robinson, and Stover 1981; Solheim et al. 1984; Wood et al. 1987; O’Donoghue and Kilkenny 1988). These ultrashort period systems must be descendents of detached pairs of white dwarfs. We also expect short-period binary white dwarfs to exist for theoretical reasons. All calculations of the evolution of binary stars show that main-sequence binaries can evolve to binary white dwarfs (e.g., Iben and Tutukov 1984). Among Population I stars, 1/2 to 2/3 of all main-sequence stars are binaries and about 20% of these binaries should become double white dwarfs with short orbital periods (Abt 1983, Iben and Tutukov 1986). Thus, about 1/10 of all white dwarfs could be close binaries (Paczynski 1985). Nevertheless, no detached binary white dwarfs with extremely short periods have yet been found.
On the Masses of the White Dwarfs in Classical Nova Systems
Authors: Truran James W. , Livio Mario
Published: July 2016

Significant progress in our understanding of the nature of the outbursts of the classical novae has occurred over the past two decades (see, e.g., reviews by Truran 1982; Starrfield 1986). Their outbursts are now understood to be driven by thermonuclear runaways proceeding in the accreted hydrogen-rich shells on the white dwarf components of close binary systems. Critical parameters which serve to dictate the varied characteristics of the observed outbursts include the intrinsic white dwarf luminosity, the rate of mass accretion, the composition of the envelope matter prior to runaway, and the white dwarf mass.
White Dwarf – Accretion Disk Boundary Layers
Authors: Regev Oded
Published: July 2016

The method of matched asymptotic expansions is used to calculate the detailed structure of white dwarf- accretion disk boundary layers. Both optically thick and thin boundary layers are investigated for various values of the relevant parameters, as long as the layer’s vertical extension remains very much smaller than the white dwarf’s radius. Detailed, self consistent solutions for the boundary layer’s and disk’s structure are calculated and used to find the amount of energy radiated onto the accreting white dwarf (recently recognized to be an important factor in nova outburst modelling).
High Resolution Optical Spectra of 120 White Dwarfs
Authors: Tytler David , Rubenstein Eric
Published: July 2016

High quality optical spectra of 120 white dwarfs have been obtained to search for double degenerate systems, some of which might become type I supernovae. No systems with high amplitude velocity variations have been found. However several exceptionally cool DA white dwarfs have been found to show weak Helium absorption lines, and four stars have split H-alpha line cores indicative of binary systems.
On the Internal Structure of Main-Sequence Stars
Authors: Giménez Alvaro , García-Pelayo José M.
Published: July 2016

We present the main results of a study of the observed internal structure constants, k2, for a wide set of eclipsing binaries. From the analysis of the variations in relative positions of the eclipses and the comparison with different theoretical models, we could deduce that the discrepancy, previously reported by several authors between theory and observations, is no longer supported. Moreover, a strong correlation has been found between the evolution of the parameter k2 and the gravity at the surface of the star, g.
Properties of Relativistic Linear Stellar Models
Authors: Ureche V.
Published: July 2016

In the late stages of stellar evolution, relativistic objects are formed, such as neutron stars or black holes. These relativistic stars possess a strong gravitational field, therefore their structure and their space-time geometry can be described only in the frame of GRT (Zeldovich and Novikov, 1971; Misner, Thorne and Wheeler, 1973). For this purpose, the following four-dimensional interval is used (spherical gravitational field), (Zeldovich and Novikov, 1971).
A Mass-Eccentricity Correlation in Spectroscopic and Visual Binary Orbits
Authors: Dommanget J.
Published: July 2016

Looking for a possible explanation for the debated existence of a correlation between period and eccentricity in binary orbits [of which a diagramme is given in fig. 1.) we made the assumption that the orbital evolution of the binaries could be the consequence of a substantial mass-loss of their components even when these components are late type main sequence stars.

This led first to the consideration of various classes of the areal constant. But it.immediately appeared much better to consider for each of such classes, the total mass of each system instead of its orbital eccentricity and thus to consider the mass-period diagramme rather than the period-eccentricity diagramme. Eleven such diagrammes were considered.
Double Stars: The Closest and the Most Distant Systems
Authors: Herczeg Tibor J.
Published: July 2016

Review and comments on two extremely different samples of binary and multiple stars: systems within 10 parsecs of the sun and systems discovered in galaxies of the Local Group.
Quasi-Simultaneous Photometric and Polarimetric Observations of T Tau And Ry Tau
Authors: Red’kina N.P. , Chernova G.P.
Published: July 2016

Quasi-simultaneous photometric and polarimetric observations of T Tau and RY Tau show that the proper polarization of these stars barises in the visual region in their gaseous emitting envelopes. The polarization of T Tau shows cyclic variations with a period of 5h18. That of RY has two different modes of variation at brightnesses V > 11m and V < 11m; it is possibly connected with the suspected binary nature of this star.
Evolutionary Effects in Contact Binaries
Authors: Mauder H.
Published: July 2016

The structure and evolution of contact binaries is an extremely difficult problem in theoretical astrophysics.Several attempts have been made to set up a satisfactory model, see e.g. Lucy,1976, Flannery, 1976, Shu, Lubow and Anderson, 1976, Robertson and Eggleton, 1977, Rahunen and Vilhu, 1977 and others. There are, roughly, two lines of sight: Shu, Lubow and Anderson postulate the existence of a contact discontinuity in one of the two components of a contact binary (DSC Theory); in this case age zero models in thermal equilibrium are possible. The other authors find that unevolved contact binaries cannot achieve thermal equilibrium; therefore, relaxation oscillations on a thermal time scale are expected (TRO Theory). For a detailed discussion of the different effects see Lucy and Wilson,1979.
A Possible Explanation of Distortions in the Light Curves of VW Cep By Starspots
Authors: Yamasaki A.
Published: July 2016

An attempt is made to explain the variations in the light curve of VW Cep in terms of a starspot model. Based upon Kwee's (1966) observations, an unperturbed light curve without spots is constructed and analysed for the geometrical elements of VW Cep. Then, by assuming that starspots exist on the surface of the primary component, Kwee's individual light curves are further analysed for locations and intensities of the starspots.
The IUE Observations Of W UMa
Authors: Rucinski S.M. , Pringle J.E. , Whelan J.A.J.
Published: July 2016

The low resolution, phase averaged SWP spectra reveal the trend of increased transition-region line intensities for higher temperatures of ion formation which was previously observed for other active systems. Two series of low resolution LWR spectra covering two full orbital periods have been used to check the photometric results from the ANS satellite and a good agreement is found for the 2200 Å band. Wavelength shifts and changes in the intensity of the blended Mg II emission feature are not inconsistent with the ANS result that the more massive component is the more active one in the W UMa system.
Recent Observational Evidence on W Ursae Majoris Stars
Authors: Rovithis-Livaniou H. , Rovithis P.
Published: July 2016

During the four last years (1978–1981), some close binaries of W Ursae Majoris type have been observed from the National Observatory of Athens.

In all cases a two-beam, multi-mode, nebular-stellar photometer has been used, attached to the 48-inch Cassegrain reflector at the Kryonerion Station.

The observed systems are: 44i Boo, VW Cep, AB And, BV Dra, BW Dra, U Peg, V508 Oph. Especially VW Cep and 44i Boo, are very interesting objects; in addition to the light curves that have already been published (Rovithis and Rovithis-Livaniou, 1980–1981), other observations were obtained during the last year and are now at computational stage. The observations of these two systems will be continued during the next years.
Time Resolved Circular Polarimetry of White Dwarf Pulsars
Authors: Krzeminski W. , Landstreet J.D. , Thompson I.
Published: July 2016

There are two recognized subsets of cataclysmic binaries that contain white dwarfs: the AM Her stars, whose white dwarf components are sufficiently magnetized to ensure synchronous rotation with the orbital period, and the DQ Her stars, which do not maintain synchronism and probably have been spun up by mass accretion. Both groups of stars, recognized also as X-ray sources, are important as probes of the accretion process, and the radiation mechanisms in the vicinity of the white dwarf. So far, we know five objects belonging to the former group (AM Her, AN UMa, VV Pup, 2A 0311-227, and PG 1550+191), and seven falling into the latter: WZ Sge, AE Aqr, V533 Her, DQ Her, V1223 Sgr, H2252-035, and EX Hya, with the corresponding rotation periods of their white dwarf primaries of 28, 33, 64, 71, 794, 805, and 4020 s, respectively. While the main observational and theoretical efforts have been focussed on the AM Her class, the DQ Her binaries have been investigated to much lesser extent. This is probably because the DQ Her stars have been recognized only very recently as a homogeneous class.
Abundance Peculiarities in White Dwarf Atmospheres as a Result of Binary Evolution?
Authors: Bues I.
Published: July 2016

We investigate metal abundances in helium-rich white dwarf atmospheres and check the possibility of variations due to binary evolution.