bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooling of White Dwarfs with Account of Non-Equilibrium Beta-Processes
Authors: Bisnovatyi-Kogan G.S.
Published: July 2016

Non-equilibrium heating of white dwarfs during two-step neutronization and formation of small but finite core of the new phase is a main source of energy in these stars when the temperature is sufficiently small and Coulomb crystal becomes degenerate.

Existence of Chandrasekhar mass limit of white dwarfs Mch = 5.83 /μ2z, μz = A/z, is connected with the prevalence of the relativistic degenerate electrons in pressure. When neutronization is taken into account, the maximal value of mass is smaller and is reached at finite density (Schatzman, 1958). The central density of the white dwarf with limiting mass is larger than threshold density of neutronization. Such star has a small, but finite core of new phase (Seidov, 1967). The neutronization threshold for the iron is equal to ρ = 1.15 109 g/cm3 The neutronization goes through two steps
The Effect of Varying Helium and Hydrogen Layer Masses on the Pulsation Properties of White Dwarf Models
Authors: Bradley P.A. , Winget D.E. , Wood M.A.
Published: July 2016

Currently, there are disagreements on the theoretical pulsation properties of DA white dwarf models. Winget and his group (cf Winget 1981, Winget and Fontaine 1982, Winget et al. 1981, 1982) use 0.6M⊙ evolutionary white dwarf models, to find that (Teff)blue is sensitive to the mass of the hydrogen layer and very sensitive to the treatment of convective efficiency. However, (Teff)blue is relatively insensitive to the helium layer mass. Winget and collaborators also find that the hydrogen layer must be restricted to 10−8 > MH/M* > 10−12 for (Teff)blue to occur at ∼ 10,500K in models with ML1 convection (see below). More efficient (ML2) convection pushes the blue edge up to ∼ 12,200K, which is still short of the observed blue edge of ∼ 13,000K.
Pressure Shifts of Metal Lines in Cool White Dwarfs
Authors: Hammond Gordon L.
Published: July 2016

Model atmosphere techniques and an experimentally confirmed theory of collision broadening of CaII H and K by helium have been combined to shou that the difference in velocity shifts for the two lines is a sensitive diagnostic for the H/He abundance ratio in cool, metallic line uhite dwarfs.
The Detection of Ionized Helium and Carbon in the Pulsating DB Degenerate GD358
Authors: Sion Edward M. , Liebert James , Vauclair Gerard , Wegner Gary
Published: July 2016

Spectroscopic observations of hot white dwarfs utilizing the Explorer (IUE) high resolution spectrograph have led to the important discovery of ion absorption features (undetectable at low resolution) which have been ascribed to wind outflow in some cases (cf. Bruhweiler and Kondo 1983) and formation at the photosphere (cf. Sion and Guinan 1983; Bruhweiler and Kondo 1983; Dupree and Raymond 1982) in others. These line features, often weak and sharp, have presented a fundamental challenge to current understanding of the complex interplay of physical processes which control observed surface abundances in white dwarfs: gravitational/thermal diffusion, selective radiative support of ions, mass loss, convective dilution and mixing, and accretion (cf. the review by Vauclair, this volume and references therein).
An Explanation for the Euv Spectrum of Feige 24
Authors: Vennes S. , Chayer P. , Fontaine G. , Wesemael F.
Published: July 2016

Feige 24 is a bright DA white dwarf which has been studied extensively both from ground-based and space-borne observatories. The best determination of its fundamental atmospheric parameters are that of Holberg, Wesemael, and Basile (1986) who have used detailed model atmosphere analyses in conjunction with optical, IUE, and Voyager data. They give log g = 7.23±0.35 and Te(103K) = 55±5. The question of the atmospheric composition is more involved as small traces of heavy elements would not be observable in the optical spectrum of such a hot, hydrogen-dominated atmosphere. If it were isolated, Feige 24 would presumably only show the usual bland optical spectrum of a typical DA white dwarf, i.e. the hydrogen Balmer line series, but the presence of a M dwarf companion complicates its spectrum. On the other hand, Feige 24 belongs to a handful of hot DA white dwarfs sufficiently bright that ultraviolet spectroscopy in the high resolution mode of the IUE has been possible. Following the theoretical expectation of Vauclair, Vauclair, and Greenstein (1979), it was discovered that the photosphere of Feige 24 contains small amounts of C, N, and Si (Dupree and Raymond 1982). Spectral synthesis techniques used by Wesemael, Henry, and Shipman (1984) indicate the following abundances: log(C/H)=−6.4±0.6, log(N/H)=−5.3±1.0, and log(Si/H)=−6.3±0.9. The most plausible explanation to account for these small abundances is the influence of selective radiative forces possibly coupled to a weak wind (Chayer et al. 1987).
Gravitational Redshifts for Hyades White Dwarfs
Authors: Wegner G. , Reid I. N. , McMahan R. K.
Published: July 2016

Precise white dwarf gravitational redshifts can only be obtained utilizing systems of known distance and space velocity. Binaries with known orbits such as 40 Eri B are rare, and although common proper motion pairs have proven highly useful(Wegner 1973: Koester 1987: Wegner & Reid 1987), there are some problems in their interpretation. Another approach is to employ white dwarfs in open clusters; they not only have known systemic velocities, but also provide information on the progenitors of the white dwarfs. Of the nearby galactic clusters, the Hyades currently give the best information for achieving accurate gravitational redshifts: the members are relatively bright and nearby and their kinematics are well known.
Polarized Radiation from Inhomogeneous Accretion Columns in AM Herculis Binaries
Authors: Wu Kinwah , Chanmugam G.
Published: July 2016

The polarization of radiation emitted by inhomogeneous accretion columns is found to be significantly different from homogeneous columns. A good fit to the V-band circular polarization light curve of EF Eri is obtained using the two-core model with temperature &T=15keV, magnetic field B=26MG, and dimensionless plasma parameter Λ ≤ 106.
Constraints on the Atmospheric Parameters of the Binary DA White Dwarf L870-2 (EG11)
Authors: Bergeron P. , Wesemael F. , Liebert J. , Fontaine G. , Lacombe P.
Published: July 2016

The recent discovery that the cool DA white dwarf L870-2 (EG11, WD0135-052) is a double-lined spectroscopic binary composed of a detached pair of DA white dwarfs (Saffer, Liebert, and Olszewski 1988, SLO hereafter) has raised some challenging problems for stellar evolution theories of such binary systems. One first important step in the understanding of this short-period system is to establish the atmospheric parameters of each component. SLO have argued from previous determinations of the effective temperature and absolute magnitude of the system, and also from their own study of the composite Hα profile, that the two components should be similar. We wish here to reexamine this assertion by taking a new look at the constraints on the two components brought about by the available observational data.
The White Dwarf Mass and Orbital Period Distribution in Zero-Age Cataclysmic Binaries
Authors: Politano M. , Webbink R. F.
Published: July 2016

A zero-age cataclysmic binary (ZACB) we define as a binary system at the onset of interaction as a cataclysmic variable. We present here the results of calculations of the distributions of white dwarf masses and of orbital periods in ZACBs, due to binaries present in a stellar population which has undergone continuous, constant star formation for 1010 years.

Distributions of ZACBs were calculated for binaries formed t years ago, for log t = 7.4 (the youngest age at which viable ZACBs can form) to log t = 10.0 (the assumed age of the Galactic disk), in intervals of log t = 0.1. These distributions were then integrated over time to obtain the ZACB distribution for a constant rate of star formation. To compute the individual distributions for a given t, we require the density of systems forming (number of pre-cataclysmics forming per unit volume of orbital parameter space), n£(t), and the rates at which the radii of the secondary and of its Roche lobe are changing in time, s (t) and L, s (t), respectively. In calculating nf(t), we assume that the distribution of the orbital parameters in primordial (ZAMS) binaries may be written as the product of the distribution of masses of ZAMS stars (Miller and Scalo 1979), the distribution of mass ratios in ZAMS binaries (cf. Popova, et al., 1982), and the distribution of orbital periods in ZAMS binaries (Abt 1983). In transforming the the orbital parameters from progenitor (ZAMS) to offspring (ZACB) binaries, we assume that all of the orbital energy deposited into the envelope during the common envelope phase leading to ZACB formation goes into unbinding that envelope. R.L, s (t) is determined from orbital angular momentum loss rates due to gravitational radiation (Landau and Lifshitz 1951) and magnetic braking (γ = 2 in Rappaport, Verbunt, and Joss 1983). We turn off magnetic braking if the secondary is completely convective.
The Optical Spectra of V803 CEN
Authors: Kepler S.O. , Steiner J.E. , Jablonski F.
Published: July 2016

We obtained spectrophotometry of V803 Cen in both high state (B ≈ 13.5) and low state (B ≈ 17) from 3800 Å to 7100 Å and 5 Å resolution. Essentially all the observed absorption lines are due to He I. No emission lines in either high or low state were detected, as well as no significant departures from a Planck law distribution.
The Mass Spectrum of the White Dwarfs in Cataclysmic Binaries
Authors: Politano M. , Ritter H. , Webbink R. F.
Published: July 2016

Using the theoretically predicted mass spectrum of the white dwarfs (WDs) in zero-age cataclysmic binaries (ZACBs) by Politano and Webbink (1988), we examine to what extent observational selection can account for the observed high masses of the WDs in cataclysmic binaries (CBs).
Growth Rate of White Dwarf Mass in Binaries
Authors: Kato Mariko , Saio Hideyuki , Hachisu Izumi
Published: July 2016

The growth rate of a white dwarf which accretes hydrogen-rich or helium matter is studied. If the accretion rate is relatively small, unstable shell flash occurs and during which the envelope mass is lost. We have followed the evolutions of shell flashes by steady state approach with wind mass loss solutions to determined the mass lost from the system for wide range of binary parameters. The time-dependent models are also calculated in some cases. The mass loss due to the Roche lobe overflow are taken into account. This results seriously affects the existing scenarios on the origin of the type I supernova or on the neutron star formation induced by accretion.
Dynamic Mass Exchange in Doubly Degenerate Binaries. II. The Importance of Nuclear Energy Release
Authors: Benz W. , Cameron A.G.W. , Bowers R. L.
Published: July 2016

The hypothesis that Type I supernova explosions originate in binary stars, in which the secondary overflows its Roche lobe and causes a white dwarf primary to pass a critical threshold for dynamical collapse, has gained in popularity over the last decade and a half (Truran and Cameron 1971; Whelan and Iben 1973; Wheeler 1982). During this period attention has also focussed on double-degenerate binary precursors of such systems, in which gravitational radiation of orbital angular momentum causes two white dwarf stars to spiral slowly together until the less massive of the stars begins to overflow its Roche lobe (Tutukov and Yungelson 1979; Webbink 1979; Iben and Tutukov 1984; Paczyński 1985). Cameron and Iben (1986) discussed the stability of such systems as the threshold of Roche lobe overflow was approached and for low mass ratios in which gravitational radiation can maintain a low rate of such overflow. Benz, Bowers, Cameron, and Press (1988, hereafter BBCP) computed the actual merging of a binary system composed of a 1.2M© primary and a 0.9M© secondary using a fully three-dimensional SPH code. Their simulation did not include the effect of nuclear energy release despite the fact that the temperature in the accretion shock reached the carbon ignition threshold, and therefore their conclusions about the structure of the merged object remained uncertain.
A Study of the Orbital Periods of 22 Eclipsing Binaries
Authors: Panchatsaram T. , Abhyankar K.D.
Published: July 2016

Investigation of the variability of the orbital periods of eclipsing binaries is important not only from the evolutionary point of view but also for detecting additional components in them. Systematic study of the period changes in binary stars was started by Plavec (Plavec et al 1960) more than twenty years ago. Work on the same lines for 20 detached systems was reported by Herczeg (1980) at the I.A.U. Symposium No. 88 held in Toronto two years ago. Here we describe the study of 22 systems carried out by us at Hyderabad.
Trapezium Type Multiple Systems and Formation of Stars
Authors: Salukvadze G.N.
Published: July 2016

By a comparison of Trapezium-type multiple star systems in the Abastumani Catalogue and the famous Catalogue of Stellar Associations and Clusters, it is confirmed that the great number of Trapezium-type multiple stars, which belong mostly to spectral classes 0-B2, are found in associations and clusters.

In 13 T-associations, 120 Trapezium-type multiple systems and 182 common multiple and double stars could be detected.

Based on present-day observational data and the author's photographic observations, the kinematic of Trapezium-type multiple stars of spectral class 0-B2 is studied.
Statistical Models For Close Binaries
Authors: Halbwachs J.L.
Published: July 2016

Statistical models for binaries as a vhole were selected; then statistical properties of close binaries -the proportions of spectroscopic and eclipsing binaries and the distributions of the K velocities and of the depths of eclipse- were computed for each model.
Some Aspects of the Evolutionary Status Of W Ursae Majoris Binaries Deduced from Observational Data
Authors: Van Hamme Walter
Published: July 2016

We have developed a test for the evolutionary state of W Ursae Majoris binaries by comparing the observed spectral type of 31 of these systems (14 of type W and 17 of type A) with the expected one
when their primary component is an unevolved main sequence star. It appears that both the W- and A-type systems have a primary with a mass and radius too large to be compatible with the observed spectral
type,so there is no indication that each type should mark a different evolutionary stage.
Mass Flow due to Heating in a Binary System: Application to U Cephei
Authors: Kondo Yoji , Modisette Jerry L.
Published: July 2016

We have investigated the possibility of mass flow due to the heating of the cooler component in a close binary system. The heating may be caused by irradiation from the hotter companion or by other mechanisms such as the spacial coincidence of non-linear “g-mode” oscillations in the cooler star. The 2.4-day period binary U Cep, in which gas streaming has been observed, has been chosen for model calculations. Preliminary results show that such a heating of the lower atmosphere of the cooler star could lead to mass flow at an average rate of 10-9 to 10-7 solar mass per year without the star's necessarily filling its critical Roche surface.
On a Possible Linkage between W-Type WUMa Systems and the Short Period RSCVn-Like Binaries
Authors: Milano L. , Russo G. , Mancuso S.
Published: July 2016

We analize the general properties of a group of WUMa-type binaries, which show RSCVn-like activity. The position of these stars in the colour-density and mass-orbital momentum diagrams is studied, but no definite answer can be given on the linkage between short period RSCVn systems (SPG) and WUMa systems with RSCVn-like activity (WWG).
PU Vulpeculae (Object Honda-Kuwano 1979) - A Possible Short-Period Relative of the Symbiotic Stars
Authors: Chochol D. , Grygar J.
Published: July 2016

PU Vul was discovered by Honda (1979) and Kuwano (1979) due to its conspicuous increase of brightness in the years 1977-79. The analysis of the archive data by Liller and Liller (1979) revealed that the star was about 16.0m - 16.5m since the year 1898 until October 1977, with occasional brightening to 15m in 1926 and 1955. Since November 1977 it started to flare up by 5m until April 1979 when it reached a maximum of 9.0m. After the flat maximum lasting to June 1979, the brightness of the object started to diminish (Nakagiri and Yamashita, 1980). It reached 14.0m in the autumn of 1980, but then it flared up again, and was again of 9.0m in the summer of 1981 (Belyakina et al., 1981). The latter authors have found that the B-V index diminished in the 1980 minimum.
Saturn’s rings resolved by the VLA
Authors: Pater Imke de , Dickel John R.
Published: July 2016

High resolution radio data of Saturn have been obtained at 1.3, 2, 6 and 21 cm, at differentinclinationangles of the ring plane. Preliminary results on optical depth measurements in the rings are described.
Apparent thickness of Saturn’s rings from the observations of the ring plane crossing
Authors: Sicardy Bruno , Laques Pierre , Lecacheux Jean , Brahic André , Wlerick Gérard
Published: July 2016

The reductions of electronographic plates taken during ground-based observations of Saturn at the times of the transits of the Sun and the Earth through the ring plane (March 1980) are interpreted.

1. The variation of the ring’s brightness vs. elevation angle around Earth’s crossing is different from the variation around Sun’s crossing. Furthermore, the ring’s brightness increases with the distance to Saturn’s centre around Earth’s crossing and decreases around Sun’s crossing. This allows to derive the illumination of the Saturn’s disc on the rings and indicates that the rings do not behave like an homogeneous scattering layer when observed or lit almost edge-on.
Photometric study of the Saturn’s E ring
Authors: Laques Pierre , Sicardy Bruno , Brahic André , Lecacheux Jean
Published: July 2016

Observations of Saturn’s E ring at the Pic du Midi Observatory with an electronographic camera are presented. Faint material has been observed until the Dione’s orbit with a maximum of brightness near the Enceladus orbit.
The Saturn ring particles from optical reflectance polarimetry
Authors: Dollfus Audouin
Published: July 2016

The light reflected by the Saturn rings is polarized; the degree and azimuth of the polarization varies with the phase angle, the wavelength and the position on the ring.

For ring B, the polarization is the result of three combined effects which have been separated: – First, a polarization Poby the direct reflection of the sunlight on the ring particles; in the visible light, this polarization is compatible with the model of dirty-ice blocks, but in UV the scattering is dominated by a population of micron size particles. – Second, a polarization by the light which is reflected by the rings from the Saturn globe. – Third, a component with an azimuth always radial from the disk center and which varies with time, often significantly in a few days, in ways which are not predictable. An organized structure in or between the blocks making the rings is needed and suggested explanations are discussed.

For Saturn ring A, the component of polarization produced by direct reflection suggests ring particles of the same type as for the blocks in ring B. But, in addition, very variable polarizations are observed, with azimuths often tilted locally for several tens of degrees from the scattering plane; clear relationships are not yet identified.
Dynamics of spokes in Saturn's B ring
Authors: Eplee R.E. , Smith B.A.
Published: July 2016

An analysis of spoke behavior in the Voyager 2 low-resolution ring movie (resolution ⋍ 230 km/lp) has revealed the dynamical and morphological properties of several spokes. During this analysis, orbital velocities of individual spokes were determined by measuring the longitudinal positions of the leading and trailing edges of the spokes in successive images.
Voyager UVS observations of stellar occultations by the rings of Saturn
Authors: Holbelg J.B. , Forrester W.T.
Published: July 2016

During the Voyager 1 and 2 Saturn encounters the ultraviolet spectrometers observed three separate stellar occultations by Saturn's rings. Together these three observations, which sampled the optical depth of the rings at resolutions from 3 to 6 km. can be used to establish a highly accurate distance scale allowing the identification of numerous ring features associated with resonances due to exterior satellites. Three separate observations of an eccentric ringlet near the location of the Titan apsidal resonance are discussed along with other ringlet-resonance associations occurring in the C ring. Density waves occurring in the A and B rings are reviewed and a detailed discussion of the analysis of one of these features is presented.
Perturbed particle disks
Authors: Borderies N. , Goldreich P. , Tremaine S.
Published: July 2016

We solve the Boltzmann moment equations to determine the disk particle velocity ellipsoid near an isolated satellite resonance. In a coordinate frame which rotates with the pattern speed of the perturbation potential the solutions are stationary functions of the azimuthal angle. From the velocity ellipsoid we obtain the stress tensor due to particle collisions and consequently, the viscous angular momentum flux. We find that in sufficiently perturbed regions there are ranges of azimuthal angle within which the radial component of the angular momentum flux is negative. It is even possible for the angular momentum luminosity, the radial flux integrated over azimuth, to be negative. We also show that the magnitude of the rate of deformation tensor in a perturbed particle disk is bounded from above by Ω(1 + τ2)½, where Ω is the orbital angular velocity and τ Is the optical depth. These results are applied to sharp edges of planetary rings, the decay of density waves, and the damping of differential precession and eccentricity in narrow ringlets.
Sharp edges of planetary rings
Authors: Borderies N. , Goldreich P. , Tremaine S.
Published: July 2016

The ring systems of Saturn and Uranus exhibit a number of sharp edges across which the optical depth drops from order unity to near zero. At least two and perhaps all of these features are associated with the location of orbital resonances between a satellite and a ring particle. It is remarkable that the optical depth varies on a distance scale which is much finer than that over which angular momentum can be transferred between a satellite and the ring material. We illustrate here with qualitative argument the results of a numerical simulation concerning the outer edge of the B ring. More details can be found in Borderies, Goldreich and Tremaine (1982).
Size distribution in collisional systems distribution de tailles dans les systemes collisionnels
Authors: Clairemidi S.
Published: July 2016

The dynamical evolution of a three dimensional system of particles of different masses and sizes, orbiting in the gravitational field of a central body, and interacting through inelastic collisions is studied here. Recent fly-bys of planetary rings and observations of flat galaxies with modern receptors indicate that a number of structures discovered in collisional systems can be understood only of three ingredients are included in the models, namely interparticles collisions , distributions of particles sizes and self attraction of the particles.
Orbital elements of Saturn's F ring and its shepherding satellites
Authors: Synnott S.P.
Published: July 2016

The orbital parameters of Saturn's F-ring and the shepherding satellites have been estimated from Voyager images. The method, results and associated uncertainties are briefly described. In addition, we discuss the locations of the braids which were observed in a few Voyager frames.
Dynamics of charged small particles
Authors: Grün E.
Published: July 2016

Collisions of dust particles with magnetospheric electrons cause dust particles to become negatively charcied if the electron flux exceeds the photo-electron flux (2.5 x 1010r-2cm-2s-1) at the distance r (A.U.) from the sun. These charged dust particles interact with a planetary magnetic field via the Lorentz force. Only for very small particles (e.g. ~ .1 µm in Jupiter's magneto-sphere) the Lorentz force exceeds the gravitational force of the planet. In most observationally relevant cases (Jupiter's and Saturn's ring systems) elec-tromagnetic forces cause only small perturbations of the Keplerian orbits. Local fluctuations of the plasma parameters change the charge of the particles and lead to spatial diffusion. Small changes in the plasma environment of a ring of particulates may release large quantities of dust grains by electro-static blow-off. Drag forces induced by the magnetospheric plasma compete with the radiation pressure drag outside the synchrous orbit. Effects of these dust-magnetospheric interactions are observed in the ring systems of Jupiter and Saturn.
On the role of mother-planet magnetic field in spiral structure explanation of formation of spokes
Authors: Song G.X.
Published: July 2016

Some features about the spokes in B rings can be explained in terms of the electromagnetic effect. Due to the existence of the magnetic field in Saturn, plasma and micro-sized dust particles, the loosely spiral structure of magnetic field near Saturn, which is similar to that invoked to explain the sectoral structure of the interplanetary magnetic field in the solar system, may be induced.

The spiral structure is rotating with mother-planet and will gradually form at corotation circle, but the wave amplitude will grow outside the corotation and will decay gradually inside the corotation. Using the characteristics of this spiral structure, we have tried to attack the mechanism of the formation of spokes.
Formation of the solar system
Authors: Safronov V.S.
Published: July 2016

Kant-Laplace hypothesis of a common origin of the sun and the planets from a single nebula was rejected by astronomers on the verge of our century. Its main idea was renewed only six decades later. First models by Hoyle, Schatzman, Cameron were too simplified because there was no theory of star formation, and could not explain main features of the solar system. Much moresuccessful was the study of formation of planets by accumulation of solid particles and bodies in a circumsolar protoplanetary cloud. This idea was revived by O.Yu.Schmidt in 1944 on the basis of geophysical and geochemical data. Schmidt pointed out that the planetary cosmogony should be based not only on scarce astronomical data about the planetary system but also on the whole evidence from all earth sciences. Though he supposed that the protoplanetary cloud was captured by the sun he emphasized at the same time that the subsequent evolution of the cloud depended only weakly on the way of its formation. The initial conditions were forgotten with time and internal properties of the process became prevailing.
Tidal breakup and origin of the Uranian ring system
Authors: Farinella P. , Milani A. , Nobili A.M. , Paolicchi P.
Published: July 2016

The peculiar features of the Uranian ring system have posed several difficult dynamical problems. The mutual gravitational forces among the ring particles can ensure stability against the spreading due to differential precession of the orbits, but are not able to provide an effective confinement mechanism against dissipative processes like interparticle collisions (Farinella et al., 1978, 1980a). The existence of small undiscovered satellites inside the orbit of Miranda is not ruled out by the presently available observational data, and has been proposed by Goldreich and Tremaine (1979) as a possible solution for the confinement problem: each ring is supposed to lie between two different satellites exerting a gravitational torque which tends to repel ring material and prevents the collisional spreading.
Future observations of planetary rings from ground-based observatories and Earth-orbiting satellites
Authors: Smith Bradford A.
Published: July 2016

For the past several days we have been discussing observations of planetary rings and the models that have been developed to explain them. But where can we go from here? What new observations can we expect to help test the models now being developed? In order to shed some light on what the future may hold, Ed Stone and Kerry Knock will discuss furture observations by existing and proposed space probes, and I will say a few words about what we might expect to accomplish from the vicinity of the earth.
A priority of space exploration: observation of Saturn's rings from a Saturn orbiter
Authors: Brahic André
Published: July 2016

Observations of Saturn’s ring by Voyager spacecrafts have revealed a much more complex system than expected. So many basical physical meehanisms are involved that more data are required. The logical next step after Voyager is the launch of an orbiter around Saturn. Significant improvements of our knowledge about the ring system could be obtained with the highest possible resolution, with observations with a large variety otf phase angles, with multiple occultation experiments, with observations of the evolution of selected area with time, and with observations of small particles phenomena and electromagnetic properties of the spokes.
Recent X-ray Observations of Supernova Remnants and their Interpretation
Authors: Aschenbach B.
Published: July 2016

A review is given of recent observations of the X-ray emission from supernova remnants carried out on the Einstein, Tenma and EXOSAT satellites as well as from a few sounding rocket experiments. Our current interpretation of the high resolution images, high resolution energy spectra and the first few spectrally resolved images is discussed.
X-ray Images of Supernova Remnants
Authors: Seward Frederick D.
Published: July 2016

Einstein observations of supernova remnants have been reviewed and analyzed. Images of 44 galactic remnants have been reprocessed, merged when necessary, and collected into a catalog. Some bright remnants were viewed with both moderate and high resolution instruments (IPC with 1’ resolution and HRI with 4” resolution). Some IPC images of nearby remnants have been separated into 2 energy bands, 0.2–0.6 keV and 0.6–4.5 keV; whereas most images cover the band 0.2–4.5 keV. The catalog consists of 72 images of the 44 remnants.

These images will be published in the form illustrated here. Contour levels are spaced geometrically as indicated below the figures and show the faintest observable features. The pictures are more linear and generally show only the brighter regions. Images are
available now, however, in FITS format, on magnetic tape and may be obtained by writing to the author.
A Hydrodynamical Model of Kepler’s Supernova Remnant Constrained by X-ray Spectra
Authors: Ballet J. , Arnaud M. , Chieze J.P. , Magne B. , Rothenflug R.
Published: July 2016

We present NEI hydrodynamical models of Kepler’s SNR compared with the EXOSAT and EINSTEIN X-ray spectra.
Plasma Diagnostics with X-ray Lines of Oxygen in Puppis A
Authors: Fischbach Kathryn F. , Canizares Claude R. , Markert Thomas H. , Coyne Joan M.
Published: July 2016

High resolution X-ray spectral observations of Puppis A were performed with the FPCS on Einstein. We use plasma diagnostics of lines from OVII and OVIII to constrain the values of temperature, ionization timescale, and hydrogen column density.
X-ray Images of PKS1209-52 and its Central Compact X-ray Source
Authors: Matsui Yutaka , Long Knox S. , Tuohy Ian R.
Published: July 2016

A complete X-ray image of the SNR PKS1209-52 (= G296.5+10.0) was obtained with the IPC and HRI on the Einstein Observatory. The remnant has a shell-like X-ray morphology much like its appearance at radio wavelengths, while a compact X-ray source is clearly detected near the center of the remnant. The flux observed from the X-ray nebula F(0.1−4.5 keV) is 8 × 10−11 ergs cm−2 s−1, which corresponds to a luminosity L(0.1−4.5 keV) = 8 × 1035 ergs s−1 for a distance of 2 kpc. Applying a simple shell model to the X-ray emission distribution, we derived an ambient interstellar medium nO = 0.08 H atoms cm−3, total X-ray emitting plasma mass 150 M⊙, and thermal energy 1.2 × 1050 ergs. The flux from the compact X-ray source F(0.15−4.5 keV) is ~2 × 10−12 ergs cm−2 s−1. There are no obvious optical counterparts brighter than mv ~ 22 within the 3.3″ radius HRI error circle. If the object is a hot neutron star, the HRI/IPC count rate ratio implies a surface temperature of 1.6 × 106 K for NH = 3.2 × 1021 cm−2.
Supernova Remnants in Giant HII Regions
Authors: Chu You-Hua , Kennicutt Robert C.
Published: July 2016

Giant HII regions contain large numbers of massive stars, and hence are expected to contain large numbers of SNRs. Until recently, however, only a few SNRs have been identified in extragalactic giant HII regions. Moreover, most of these SNRs are located at the outskirts of HII regions, instead of the core where most of the stars are located. The low detection rate and the outlying locations of the SNRs may be due to: 1) observational difficulties - the background HII regions are much more luminous than the SNRs in both optical line emission and radio continuum; 2) intrinsic invisibility of SNRs - stellar wind and SNRs may have created a supershell (Mac Low and McCray 1987), and the core of a giant HII region is filled with hot tenuous coronal gas; or 3) a genuine deficiency of supernovae and SNRs in the HII regions (Sramek and Weedman 1986).
The Dominant Interactions Between SNR and the ISM
Authors: Braun Robert
Published: July 2016

The interactions of supernovae ejecta with the surrounding medium which have a dominant influence on the resulting SNR dynamics and brightness are considered for both young and evolved objects. The important roles of clumpy ejecta in determining the brightness of young SNR and of shock impingement on a pre-existing shell in influencing both the brightness and subsequent dynamics of evolved SNR are stressed.
A Model of SNR Evolution for an O-Star in a Cloudy ISM
Authors: Shull Peter , Dyson John , Kahn Franz
Published: July 2016

We present an analytical model of SNR evolution in a cloudy interstellar medium for a single progenitor star of spectral type 05 V. The model begins with the progenitor on the zero-age main sequence, includes the effects of the star’s wind and ionizing photons, and ends with the SNR’s assimilation by the ISM. We assume that the ISM consists of atomic clouds, molecular clouds, and a hot intercloud phase. The type of SNR that results bears a strong resemblance to N63A in the Large Magellanic Cloud.
Radio Emission from Young Supernova Remnants: Effects of an Inhomogeneous Circumstellar Medium
Authors: Dickel John R. , Eilek Jean A. , Jones Eric M.
Published: July 2016

The evolution of young supernova remnants has been modeled using a 1-dimensional hydrodynamic code. Turbulent dynamo amplification of magnetic fields and both turbulent and shock acceleration of relativistic electrons have been included macroscopically to produce synchotron radiation. The observed radio morphology cannot be reproduced by expansion into a homogeneous medium; it appears that many small cloudlets must be present in the circumstellar material.
HI Associated with Cas A
Authors: Goss W.M. , Kalberla P.M.W. , Schwarz U.J.
Published: July 2016

A small HI absorption feature has been detected in front of Cas A at a velocity of -66 km/s. This HI feature can probably be associated with a recombined high density QSF.
A CO (J = 1-0) Survey of Five Supernova Remnants at ℓ = 70° - 110°
Authors: Fukui Y. , Tatematsu K.
Published: July 2016

A program of CO observations of five selected supernova remnants is in progress on the 4-m radio telescope at Nagoya. Here, we report observations of two supernova remnants, G78.2+2.1 (the γ Cygni SNR) and HB21. In these two remnants we have obtained evidence for the interaction between the supernova remnants and molecular gas.
High Resolution Radio Observations of the SNR G160.9+2.6 (HB9)
Authors: Leahy D.A. , Roger R.S.
Published: July 2016

G160.9+2.6 (HB9) is a supernova remnant of large angular diameter and low radio surface brightness. We report new observations of the continuum emission from HB9 at 408 MHz and 1420 MHz with angular resolutions of 3.5’ and 1.0#x2019;, respectively, which reveal significant filamentary structure not previously detected. The 1420 MHz field covers only the central and eastern parts of HB9. The 408-1420 MHz spectral index (S∝vα) of regions common to both maps is α=-0.68, with no significant spatial variation. The radio filamentary structure closely follows the optical structure. X-ray emission from HB9 is more centrally concentrated than the radio or optical emission. The radio, optical, and particularly, the X-ray surface brightness are all diminished in the northern and northwestern portions of the remnant, in directions approximately coincident with an extensive molecular cloud detected in CO.
A Shell SNR Associated with PSR1930+22?
Authors: Routledge D. , Vaneldik J.F.
Published: July 2016

Observations at 408 and 1420 MHz are reported which show a large (1.7 degree diameter) faint shell of nonthermal emission partially surrounding PSR1930+22. This may be the SNR associated with the pulsar, whose spin-down age is only 40000 years.
The Rotation Measure of Background Radio Sources Seen Through the Supernova Remnant OA184 (G166.2+2.5)
Authors: Kim K.-T. , Kronberg P.P. , Landecker T.L.
Published: July 2016

Radio sources in the field of the extended SNR OA184 (G166.2+2.5) have been studied to determine the excess rotation measure (RM) arising from the SNR. Of a total of 32 radio sources observed with the VLA in the C configuration, eight are found to be polarized above 7σ The sources seen through the SNR show significantly high RM in comparison to background sources. The excess RM due to the Faraday active plasma in the SNR is estimated to be 150±20 rad m−2, which corresponds to . The sign of RMs of the sources within an area of about 2°×2° centred on the SNR shows a systematic longitudinal polarity change on either side of l ≈ 166°.2. Although a larger sample is needed to justify this, we tentatively interpret this “flip” as due to the reversal of an irregular component of the galactic magnetic field on a scale of order 100 pc.
Infrared Analysis of Supernova Remnants
Authors: Dwek Eli
Published: July 2016

Infrared observations of supernova remnants obtained with the Infrared Astronomical Satellite provide new insights into the dynamics and energetics of the remnants, and into their interaction with the ambient interstellar medium. In most remnants the infrared emission arises from dust that is collisionally heated by the X-ray emitting gas. The infrared observations can therefore be used as a diagnostic for the physical conditions of the shocked gas. In particular, it is shown that all the prominent X-ray remnants in the Galaxy and in the LMC cool mainly by dust grain collisions instead of atomic processes.
New Observations of Non-Radiative Shocks in the Cygnus Loop
Authors: Hester J.J. , Raymond J.C.
Published: July 2016

We present deep Hα and [O III] images and echelle spectra of non-radiative shocks in the NE Cygnus Loop. The contrast between the smooth Hα structure and the clumpier [O III] indicates that portions of the sheet-like front are beginning to go radiative. The column depth through the shock seems to be ≼ 1017.5 cm−2 for the entire region – a remarkable constraint for such a large structure.
A Perspective on the Symbiotic Stars
Authors: Allen David
Published: July 2016

I give a very brief summary of the state of our knowledge of the symbiotic stars, together with some of my hopes for how the field will develop.
Absolute Energy Distributions for Selected Quiescent Symbiotic Stars
Authors: Slovak M.H. , Code A.D.
Published: July 2016

Absolute continuum energy distributions for 1200 A to 100μ have been derived for eight quiescent symbiotics. These data are a combination of contemporaneous satellite and ground-based observations, including low resolution IUE and optical spectrophotometry, broadband JKLM infrared photometry and IRAS Point Source Catalogue fluxes. The resulting multifrequency energy distributions represent a merged, uniformly calibrated set of observations and provide a unique opportunity for comparison with quiescent theoretical models.
Radio Imaging of Symbiotic Stars
Authors: Taylor A.R.
Published: July 2016

A brief review of radio observations of individual symbiotic stars is presented, with emphasis on radio imaging of the circumstellar nebulae. The ionized nebulae are catagorized into two types: outburst ejecta and stellar winds. Among the ejecta-type there is a strong tendency for bipolar or jet morphology. In the case of the quiescent, stellar wind emitter, a few very wide binary systems (eg. Hl-36) offer the potential of directly viewing the effects of the binary interaction.
Optical Polarimetry of Symbiotic Stars
Authors: Magalhães Antonio Mârio
Published: July 2016

A review of some physical mechanisms that may give rise to detectable optical polarization in symbiotic stars is presented, emphasizing the ability of polarimetry in studying the evolution of dust envelopes, the atmospheric structure of the cool component and the geometry of these systems. A brief summary of the techniques is also given. General polarimetric properties of symbiotics as well as data for a few specific systems are discussed. Proposed models for symbiotics that include the prediction of their polarimetric properties are highly encouraged. Specific suggestions for future work from the ultraviolet through the infrared and which explore the potential of the technique are advanced.
On the outburst of symbiotic stars
Authors: Nussbaumer H. , Vogel M.
Published: July 2016

The most commonly advocated models for explaining the outburst of symbiotic systems are thermonuclear runaways, modulated mass accretion through a disc, or accretion disc instabilities. We show that the onset of a strong stellar wind on the cool component can also produce the observed increase in luminosity.
Z Andromedae: Quiescence and Activity
Authors: Cassatella A. , Fernandez-Castro T. , Oliversen N.
Published: July 2016

Z Andromedae, often considered as the prototype of symbiotic stars, experimented, after several years of quiescence, a small outburst in March-April 1984, followed by a larger one in September-October 1985. The imminence of a new activity phase was predicted by Viotti et al. (1982). Z And is, together with AG Draconis, the only symbiotic star observed both during quiescence and activity with the IUE satellite. The early photometric and spectroscopic history of Z And has been recently reviewed by Kenyon (1986).

The behaviour of Z And in the ultraviolet during quiescence has been studied by Fernåndez-Castro et al. (1988), on the basis of data obtained by the International Ultraviolet Explorer from 1978 to 1982. In that period of time, the UV continuum and the emission line fluxes varied quasiperidically with a period of about two years, in phase with the Hα variability found by Altamore et al. (1979), with the UBV photometry by Belyakina (1985) and also in agreement with the ephemeris given by Kenyon and Webbink (1984). The electron density derived from Si III/C III] flux ratio, also varied in phase with the UV flux. In particular, a correlation was found between the electron density variations, and the UV continuum flux at 2900 A. This fact, together with the presence of a Balmer jump in emission, indicates that the principal contributor at those wavelengths is nebular emission, mainly free-bound transitions.
Spectroscopic Orbit of the Eclipsing Symbiotic Star CH Cyg
Authors: Mikołajewski M. , Szczerba R. , Tomov T.
Published: July 2016

Mikołajewski et al.(1987) quoted convincing arguments that CH Cygni is eclipsing binary system:

1.

Photometric minima in U light were separated by 57004÷5780 days which is very close to the spectroscopic period (P=5750±250d) found by Yamashita and Maehara (1979).

2.

Variations of Hβ and Hγ profiles during both minima can be succesfully interpreted as an eclipse of a rotating disk or envelope from which these profiles originate (see also Fernie et al.,1986).

3.

The flickering activity was absent during the 1985 minimum while observed before and after the minimum.

4.

Only forbidden lines were unaffected by the minimum. Recently, additional arguments for the eclipsing nature of CH Cygni have been found:

5.

Deep minimum in the IUE integrated flux was coincided with the minimum detected in U light (Mikołajewska et al., 1987a).

6.

Changes of Balmer decrement and Balmer continuum emission measure suggest a presence of relatively small dense region occulted during the minimum and extended low density region coinciding with the radio jets (Mikołajewska et al., 1987b).

7.

Radial velocity of the jet spatially resolved by Solf (1987) in the [OIII]5007 line suggests the jet is practically perpendicular to the line of sight.
Polarization in CH Cygni During Quiet and Active Phases
Authors: Rodriguez M.H.
Published: July 2016

Our wide-band polarimetric observations of CH Cyg began in 1974 and continued In 1976 and 1984. During the first two observational seasons the star was in quiet phase between two outbursts, in 1984 the latest outburst that began in 1977 was declining. Figure shows mean values of the degree of polarization P and the position angle θ for the different observational periods. Standard errors calculated by photon noise statistics are 0.02–0.04% for P and 1–5% for θ.

In 1974 (October 12 - December 1) polarization parameters did not change significantly. Sharp increase of the degree of polarization in the shortwave region of the spectrum and change with wavelength of the degree of polarization are typical for many cool luminous stars and indicate existence of an asymmetric circumstellar envelope around CH Cyg. Interstellar polarization in the direction of CH Cyg should be quite small [1,2],as its distance is 330 pc and colour-excess EB-V does not exceed 0.07m.
An “Accretor-Propeller” Model of CH Cygni
Authors: Mikolajewski M. , Mikolajewska J.
Published: July 2016

The most spectacular episode in the history of CH Cyg was undoubtedly a sudden drop of brightness (by about 1 mag) during the last weak of July 1984, coinciding with the ejection of two collimated jets (Taylor et al. 1985) perpendicular to the line of sight (Solf 1987) and the orbital plane (Luud et al. 1986). Supercritical accretion cannot be responsible for the jet ejection mechanism, because the luminosity of the accreting component was always about 2 orders of magnitude lower than the Eddington limit (Mikolajewska et al. 1987). This mechanism is also inconsistent with the rapid drop of brightness coinciding with the ejection of material. Simultaneously, it is conspicuous that the increase of brightness to optical maximum was also rapid (∼1 mag from July to September 1981; e.g. Kaler et al. 1983).
Symbiotic Nova PU VUL (Kuwano-Honda Object): Some Results of Coordinated Investigations
Authors: Gershberg R.E. , Shakhovskoj N.M.
Published: July 2016

Since 1979 a team consisting of T.S.Belyakina, N.I.Bondar’, K.K.Chuvaev, Yu.S.Efimov, R.E.Gershberg, V.I.Krasnobabtsev, E.P.Pavlenko, P.P.Petrov, I.S.Savanov, N.I.Shakhovskaya, N.M.Shakhovskoj, A.G.Shcherbakov and V.I.Shenavrin from the Crimea, Dr. V.Piirola from Finland and Drs D.Chochol, L.Hric and J.Grygar from Czechoslovakia are carrying out a coordinated study of pecular Kuwano-Honda (PU Vul) object, and this short report is made on behalf of the team.

PU Vul flared up from 14m to 9m in 1978 and up to date maintains the high brightness. Our studies include the optical and IR photometry, spectroscopy, spectrophotometry, polarimetry and UV observations with the space station Astron. The general character of brightness variations and time distribution of our observations are given in Fig.1.