bluuebunny/crossref_metadata_2025 huggingface dataset:
Radial Velocity Measurements with Objective Prisms for the Hipparcos Program
Authors: Fehrenbach Ch.
Published: July 2016

In 1986, the European Space Agency (ESA) will launch an astrometrie satellite, Hipparcos (see ESA SP-177) with the objective of measuring positions for 200,000 stars. Proper motions will be determined with an accuracy of 0.002 "/yr. It is also very important to have radial velocities for the program stars.

We will show here that an accuracy of 4 to 5 km/s for the radial velocity is good enough for a number of studies. For stellar studies, we need highly accurate radial velocities, and correlation methods (Griffin, Mayor et al.) allow that but are restricted to cool stars. Radial velocities are also needed for studies of stellar dynamics. In the case of star clusters (open and globular) we need a high accuracy, however the study of motions of stars in our galaxy do not require such a high accuracy. Only by increasing the sample can we improve our knowledge. In Table I we give data for the velocity ellipsoid. Kinematical data are from Allen and we have added absolute magnitudes and distances for stars having mv = 7.5. From an examination of this table we see that an accuracy of 4-5 km/s is good enough to study B star motions. The last column gives the dispersion in proper motion, and some of the values are astonishing, but it is well known that the proper motions for the nearby stars show a very high dispersion.
Radial Velocity Variations in Cool Supergiants
Authors: Harris Hugh C.
Published: July 2016

A survey of F, G, and W supergiants has been carried out with the DAO radial velocity spectrometer, an efficient instrument for detecting low-amplitude velocity variations in cool stars. Observations of 78 stars over five seasons show generally good agreement with OORAVEL results for spectroscopie binaries. The majority of supergiants show low-amplitude variability, with amplitudes typically 1 to 2 km s−1. The width of the cross-correlation profile has been measured for 58 supergiants. It reveals 14 stars with unusually broad lines, indicative of rotation velocities of 15 to 35 km s−1. Several have short-period binary companions and may be in synchronous rotation. The other broad-lined stars are apparently single or with long orbital periods; they may be making their first transition from the main sequence to become red supergiants.
Coravel Radial-Velocity Curves for Cepheids in the Large Magellanic Cloud
Authors: Imbert M. , Andersen J. , Ardeberg A. , Bardin C. , Benz W. , Lindgren H. , Martin N. , Maurice E. , Mayor M. , Nordström B. , Prevot L.
Published: July 2016

Radii and luminosities for Cepheid variables provide fundamental information on stellar evolution. Such data, obtained by the Baade-Wesselink method, are available and have been used for a number of galactic Cepheids. It is of particular interest to obtain corresponding data for Cepheids in the Magellanic Clouds. Firstly, this allows a comparative study of stellar evolution between the Galaxy and the Magellanic Clouds. Secondly, it provides data for an independent determination of the distance to the Magellanic Clouds.

Radial-velocity observations have been made for a total of around 20 Cepheid variables in both the LMC and the SMC. All measurements were made with the photoelectric scanner CORAVEL attached to the Cassegrain focus of the Danish 1.54-m telescope at European Southern Observatory, La Silla, Chile. Observations were made from January 1981 through October 1983. The accuracy of individual radial-velocity observations is of the order of 1 km s−1. The B magnitudes of the six Cepheids presented range from 13.0 to 15.5.
White Dwarf Evolution in Real Time: What Pulsating White Dwarfs Teach us About Stellar Evolution
Authors: Kawaler Steven D. , Hansen Carl J.
Published: July 2016

The variable white dwarfs repeatedly force theory to conform to their observed properties so that further progress can be made in understanding the structure and evolution of all white dwarfs. We use the term “understanding” in a loose sense here because, as we will show, both observational constraints and interpretation of the observations vis-à-vis theory contribute to uncertainties in our understanding at this time. In any case, recent progress in this field (sometimes called white dwarf seismology) has provided some fascinating insights into the evolutionary and structural properties of white dwarfs and their progenitors. This short review is our attempt to describe recent progress made in the interaction of theory with observations.
The Bologna/ESO Search for Double Degenerates
Authors: Bragaglia Angela , Greggio Laura , Renzini Alvio , D’Odorico Sandro
Published: July 2016

In 1984 a program has been set up for a systematic search of double degenerates (DD) among spectroscopically confirmed white dwarfs. For each WD at least two CCD spectra are obtained, which are then cross-correlated in order to get a radial velocity difference, if any. For this purpose we have used the ESO Faint Object Spectrograph and Camera (EFOSC) attached at the ESO 3.6m telescope. Exposure times are typically in the range 5–15 min, and the typical error in the radial velocity difference (Δυx) is ∼ 20 km s−1.

Until now we had two observing runs, respectively in September 1985 and January 1988, for a total of 5 usable nights. For 20 WDs we have obtained more than one spectrum. Among them we have singled out two DD candidates. The first object (WD0957–666) has shown Δυr values up to ∼ 220 km s−1 and three other spectra were kindly taken for us in April 1988 by Stefano Cristiani. These also showed Δυr,’s up to ∼ 140 km s−1. Another object (WD0954–710) exhibits a Δυr ≃ 70 km s−1. The two DD candidates will be observed again in the next observing run in order to confirm their binarity and in case determine the periods.
Non-LTE Spectral Analysis of PG 1159–035
Authors: Werner K. , Heber U. , Hunger K.
Published: July 2016

We present first preliminary results from an exploratory spectral analysis of PG1159-035. An effective temperature of 120000 K (±20000 K) and a surface gravity of about log g=7 are derived from optical and ultraviolet profiles of carbon and helium lines. NLTE model atmospheres are used which are composed of H (1%), He (19%), C (40%) and O (40%, mass fractions). The abundances adopted are in accordance with predictions of stellar pulsation theory. A direct spectroscopic determination is under way. The analysis of optical CIV lines is rendered difficult due to the lack of a reliable line broadening theory which would have to account for a gradual change to broadening by linear Stark effect. Due to the complexity of the spectral analysis, reliable abundance ratios can only be derived from a systematic investigation employing a large grid of models.
Hervy Element Abundances Predicted by Radiative Support Theory in the Atmospheres of Hot White Dwarfs
Authors: Chayer P. , Fontaine G. , Wesemael F.
Published: July 2016

The surface composition of a white dwarf evolves as a result of the interaction of several mechanisms, the most important of which being gravitational settling. In the early phases of the evolution, theory shows that selective radiative levitation can occasionally defeat settling and, thus, prevent the formation of a pristine pure hydrogen (helium) atmospheric layer in a hot DA (non-DA) white dwarf (Fontaine and Michaud 1979; Vauclair, Vauclair, and Greenstein 1979). The exciting discovery of sharp metallic features in the ultraviolet spectra of several hot DA and non-DA stars alike resulting from the work of several investigators has provided the essential motivation for further theoretical investigations of radiative levitation in the atmospheres of white dwarfs. Additionnal impetus comes from the continuing investigations of hot DA white dwarfs carried out by Bruhweiler and Kondo which have already revealed a most interesting observational pattern of heavy elements in these stars (Bruhweiler 1985). Moreover the recent availability of theoretical equivalent widths of selected astrophysically important ultraviolet metal lines in hot DA white dwarfs (Henry, Shipman, and Wesemael 1985) makes a comparison between theory and observations -in at least this type of stars- a timely and useful exercise.
A Variational Approach to Understanding White Dwarf Evolution
Authors: Wood M. A. , Winget D. E.
Published: July 2016

The observed falloff in the white dwarf luminosity function at log (L/L⊙) ≈ −4.5 (Liebert, Dahn, and Monet 1988) is most easily explained as a result of the finite age of the Galactic disk. Using a simple perturbation approach as our method and a white dwarf evolution code as our tool, we have mapped the sensitivity of the ages of the model sequences in this low-luminosity regime to the uncertainties in the input physics and model parameters. We present here a preliminary overview of what we’ve learned.

We have updated the White Dwarf Evolution Code of Lamb and Van Horn (1975) to include both carbon and oxygen in the core. We interpolate to the mixture composition using our pure-C and pure-O tables and the additive-volume technique (Fontaine, Graboske, and Van Horn 1977). The envelope subroutines calculate stratified H/He/C envelopes of essentially arbitrary layer masses within the range 0 to ∼ 10−2M*, and treat the composition transition zones as discontinuities. Because the equation of state tables referenced by the envelope routines do not include crystallization, a given sequence ends when the crystallization front reaches the core/envelope boundary.
A New Hydrogen Equation of State for Low Mass Stars
Authors: Saumon D. , Chabrier G.
Published: July 2016

Studies of the structure and evolution of low mass stars, brown dwarfs and giant planets require an equation of state (EOS) that includes a detailed, accurate model of the strongly non-ideal behavior of matter in these cool, compact objects [Fig. (1)]. Physical processes in the outer layers of white dwarfs, especially the analysis of the pulsation properties of ZZ Ceti stars, depend sometimes critically on the thermal properties of partially ionized hydrogen. In view of the substantial developments in the statistical physics of dense fluids and plasmas over the past decade, the computation of a new, independent EOS for astrophysical applications is justified. The statistical mechanical models which we present for hydrogen can be adapted to treat both pure helium and hydrogen-helium mixtures.
On the Formation of Close Binary White Dwarfs
Authors: Iben Icko , Webbink Ronald F.
Published: July 2016

Single stars of initial main-sequence mass larger than about 0.8-1.0⊙ and less than approximately 6-8M⊙ evolve into carbon-oxygen white dwarfs of mass in the range 0.55-1.1M⊙ in less than the Hubble time. Single stars do not make helium white dwarfs in a Hubble time. These statements are based on both observational and theoretical considerations. It is not yet established, but there are suspicions that single stars of initial mass in the range 8-10M⊙ may evolve into oxygen-neon white dwarfs of mass in the range 1.1-1.4M⊙. As a single star of the appropriate initial mass develops a hot, electron-degenerate core composed of carbon and oxygen or of oxygen and neon, it becomes large (R > 200R⊙) and luminous (L > 6000L⊙), with the luminosity being generated most of the time by hydrogen burning, interrupted quasiperiodically by a helium shell flash. The star is said to be an asymptotic giant branch (AGB) star. Within 105 - 106yr after arriving on the AGB, an envelope instability, whose nature is still being explored observationally and theoretically, leads to the ejection of most of the hydrogen-rich envelope of the star. The remnant shortly becomes the central star of a planetary nebula composed of the ejected material, and then cools into a white dwarf configuration.
The Coalescence of White Dwarfs And Type I Supernovae
Authors: Mochkovitch Robert , Livio Mario
Published: July 2016

In the context of the white dwarf coalescence model for type la supernovae, we compute post-coalescence configurations involving a thick disk, rotating around a central white dwarf (the original primary), having the same total mass, angular momentum and energy as the initial system. We show that carbon ignition in rather low density material (105 – 10° g.cm−3) can be triggered during the merging process itself or later, by dissipation due to turbulence in the disk. The evolution of the object following carbon ignition is very uncertain.
Evolutionary Trends in Wide Binary Systems
Authors: van de Kamp Peter
Published: July 2016

Zdenek Kopal has kindly invited me, and I have accepted, to “instruct the theoreticians on known facts”. He also asked me to express my opinion on the relative evolutionary stages of components.

I am essentially an observing astronomer, occupied with stars in our immediate neighborhood, say within 10 or at most some 25 parsec, i.e., the lower main sequence and the white dwarf degenerate branch.

I hope that I may perhaps contribute by surveying and reporting some relevant data. I shall touch on a number of topics, limited because of selection and lack of knowledge. My contributions to binary stars lie in the realm of parallaxes, mass-ratios and masses, – and for the past half century, perturbations, interpreted as unseen companions, stellar and otherwise. I shall briefly report on some results, and I shall be wondering and hoping that some trace of stellar evolution may possibly be present in these results. After having witnessed for more than half a century my own astronomical evolution, the time has come for me to become more aware of theoretical, evolutionary and cosmological aspects of the cosmic material, I have been playing with so long.
The Evolutionary State of Zeta Aurigae
Authors: Chapman Robert D.
Published: July 2016

Ultraviolet studies, originally undertaken to ascertain the state of the atmosphere of the K-supergiant component of the zeta Aurigae system, have been sidetracked by the discovery of significant accretion effects. An analysis of the phase dependence of the profiles of resonance lines in Mg II and C IV has led to a qualitative model of the wind flow from the K star. At the position of the B star, the flow velocity is about 100 km/sec and the density is 3 x 10-6 cm-3 , leading to a mass loss rate of 2 x 10-8 solar masses per year. This wind interacts with the B star in a shock, which will be described, leading to accretion on the B star at a rate of 4 x 10-10 solar masses per year.
Evolution of Close Binary Stars: Observational Aspects
Authors: Plavec Mirek J.
Published: July 2016

Detached close binary systems define the main sequence band satisfactorily, but very little is known about the masses of giants and supergiants. High-dispersion IUE observations promise an improvement, since blue companions are now frequently found to late-type supergiants. The Interesting cases of μ Sagittarii and in particular of ε Aurlgae are discussed in more detail. The barium star abundance anomaly appears now to be due to mass transfer in interacting systems. The symbiotic stars are another type of binary systems containing late-type giants; several possible models for the hotter star and for the type of Interaction are discussed. The W Serpentis stars appear to be Algols in the rapid phase of mass transfer, but a possible link relating them to the symbiotics is also indicated. Evidence of hot clrcumstellar plasmas has now been found in several ordinary Algols; there may exist a smooth transition between very quiescent Algols and the W Serpentis stars. β Lyrae Is discussed in the light of new spectrophotometry results.
Evolutionary Possibilities and Impossibilities for Solar Type Contact Binaries in NGC 188
Authors: Van ’T Veer Frans
Published: July 2016

We give a great number of arguments for the hypothesis that several epochs of star formation have taken place at different times in the old galactic cluster NGC 188.

From the last burst of star formation in this cluster, not more than a few times 108 years ago, 4 contact binaries are still now visible as W UMa stars. With the aid of a simplified probability calculation we argue that these 4 contact binaries are physically related and that the alignment of the orbital axes is not accidental.
Did SU UMa Undergo a Classical Nova Outburst?
Authors: Bode M.F. , Evans A. , Bruch A.
Published: July 2016

Recent observations of an apparent soft X-ray halo around the dwarf nova SU UHa have led to speculation that this may well be evidence of the object having undergone a classical nova-like outburst within historical times (Cordova and Mason 1980). By combining the relationship between quiescent X-ray luminosity and speed class for classical novae and the observed X-ray luminosity of SU UMa we derive a distance dependent apparent magnitude at outburst for the object. Distance estimates for SU UMa and absolute magnitude ranges for classical novae then determine the apparent magnitude of an outburst more exactly. From the angular size of the halo and the absolute magnitude - ejection velocity relationship for classical novae we derive the approximate date of any outburst. Comparison with historical records does not reveal any promising candidates. An alternative interpretation of the halo in terms of scattering of soft X-rays from dwarf nova outbursts by interstellar grains is suggested.
Azimuthal variations in Saturn’s A ring
Authors: Lumme Kari , Irvine Willian M.
Published: July 2016

The observations defining the azimuthal brightness variations in ring A are reviewed. This phenomenon is entirely separate from the “spokes” which are present in ring B. An explanation in terms of scattering by “density wakes” produced by large ring particles seems most reasonable.
Saturn rings: divisions, gaps and ringlets from ground-based telescopes
Authors: Dollfus Audouin
Published: July 2016

The high magnification visual telescopic observation of Saturn’s rings exhibits divisions, gaps and bright sub-rings. B. Lyot gave a first description of these features. Later, with still more resolving telescopes, we improved the analysis of the ring features. Some gaps and concentric bright or dark sub-rings are phase angle dependent; the steep luminance peaks of their light curves around zero phase angle are volume-density dependent (opposition effect); the overall result produces changes in the shapes and intensities of these features at small phase angles, which are analysed.
The rings of Uranus
Authors: Elliot James L.
Published: July 2016

The Uranian ring system consists of nine, narrow rings that have an average geometric albedo of 0.02. Since their discovery in 1977, the rings have been regularly observed with the technique of stellar occultations, which provides a spatial resolution of about 0.1 km in the positions of ring segments and about 4 km resolution in their structural details. The occultation data are well fitted by a kinematic model that describes the rings as ellipses, which are inclined to the equatorial plane of Uranus and precess due to harmonic terms in the Uranian potential field. The main characteristics of the Uranian ring system that need a confirmed theoretical explanation are: narrow rings, sharp edges, uniform orbital precession, origin of the eccentricities and inclinations, the structure of the e ring, the structure of the η ring and the origin of the ring system.
The Jovian ring
Authors: Burns Joseph A.
Published: July 2016

Lying in Jupiter's equatorial plane is a diaphanous ring having little substructure within its three components (main band, faint disk, and halo). Micron-sized grains account for much of the visible ring, but particles of centimeter sizes and larger must also be present to absorb charged particles. Since dynamical evolution times and survival life times are quite short (≲102-3yr) for small grains, the Jovian ring is being continually replenished; probably most of the visible ring is generated by micrometeoroids colliding into unseen parent bodies that reside in the main band.
Future studies of planetary rings by spaceprobes
Authors: Stone E.C.
Published: July 2016

In the second half of this decade. Voyager 2 will encounter Uranus and Neptune and Galileo will orbit Jupiter, returning new information on those planetary ring systems. The opportunities and capabilities for ring studies are briefly discussed.
Asymmetrical Ejection of Matter in a Thermonuclear Model of a Supernova Explosion
Authors: Chechetkin V.M. , Denisov A.A. , Koldoba A.V. , Poveschenko Yu.A. , Popov Yu.P.
Published: July 2016

With the recent Supernova 1987a in the LMC, new and interesting possibilities have arisen for the solution of a problem relating to the explosion mechanism of supernovae. The presupernova was probably a B3Ia, the blue supergiant, and not a red giant as it was earlier thought likely. Calculations of the evolution, which have been made recently, show that the loss of hydrodynamical stability may be connected with carbon burning in the stellar core during the blue giant stage. This loss of stability of the CO core is the main factor in our explanation of the recent event of SN 1987a.

Before we consider the thermonuclear model of a supernova based on a thermal flash in the degenerate CO core, let us dwell on the present situation in the theory of supernovae. The main problem in supernova theory is the simultaneity of births of a compact remnant and an expelled envelope. The compact remnant later becomes a neutron star. The expelled envelope determines the curve of brightness. Now, it is clear that a supernova explosion may result in either the total disruption of a star or in the simultaneous production of a compact remnant and an expelled envelope.
The Reionization of Unshocked Ejecta in SN1006
Authors: Hamilton A.J.S. , Fesen R.A.
Published: July 2016

The fortuitous positioning of the Schweizer and Middleditch OB subdwarf behind SN1006 has permitted the detection and subsequent confirmation by IUE of broad (±5000 km/s) Fe II absorption features which probably arise from unshocked iron ejecta in the center of SN1006. The mass of detected Fe II, ∽0.012 M⊙, is however only 1/25 of the ∽0.3 M⊙ of Fe within ±5000 km/s predicted by carbon deflagration models. IR and optical observations exclude any appreciable iron in grains or Fe I, but high ion stages, Fe III and up, oould be present. Promising mechanisms for ionizing the unshocked iron in SN1006 include the radioactive decay of 44Ti, and photoionization by UV and X-ray emission from the reverse shock. Although the photoionization model works, insofar as it permits as much as 0.2 M⊙ of unshocked iron in the center of SN1006, agreement with the IUE data requires that the ejecta density profile be flatter, less centrally concentrated, than the W7 deflagration model of Nomoto, Thielemann, and Yokoi.
A Model for the Interaction between Stars and Gas in the Interstellar Medium
Authors: Chiang Wei-Hwan , Bregman Joel N.
Published: July 2016

A global model for the ISM is described in which separate fluids of stars and gas interact through star formation, mass loss, stellar heating, and gaseous cooling processes. In all simulations, a steady state develops in which rarefied ionized regions separate ridges of neutral gas.
The Influence of Equilibration on the X-ray Intensity of Sedov Models
Authors: Jerius D. , Teske R.G.
Published: July 2016

We have synthesized a set of SNR X-ray and coronal iron surface brightness profiles to determine observational constraints to help distinguish how the remnants’ ion-electron energy equilibration time-scales compare to their ionization time-scales. The profiles are based on Sedov-Taylor blast wave models under the two scenarios (1) equal Tion and Te or (2) Coulomb equilibration of Te and Tion. Resultant spectra were convolved with Einstein HRI and IPC sensitivity curves to simulate satellite observations of actual remnants.
Long Slit Echelle Spectroscopy of Supernova Remnants in M33
Authors: Blair William P. , Chu You-Hua , Kennicutt Robert C.
Published: July 2016

We have obtained long slit echelle spectroscopy for 10 of the brightest supernova remnants in M33 using the KPNO 4 m telescope. The profiles at Hα indicate bulk motions in the range 100–350 km s−1 in these remnants. Nearly all of the objects show signs of contamination by low velocity H II emission at some level. This affects the line intensities measured from low resolution data and may affect diameter measurements of these remnants.
VLA Observations of SNRs in M33
Authors: Duric N.
Published: July 2016

The results of a VLA study of the radio continuum properties of supernova remnants in the nearby spiral galaxy M33 are presented. It is shown that a relationship exists between the radio surface brightnesses and the diameters of the 13 detected supernova remnants. The significance of the relation and the constraints it imposes on models of SNR evolution are discussed.
New Supernova Remnants from Deep Radio Continuum Surveys
Authors: Reich, W. , Fürst E. , Reich P. , Junkes N.
Published: July 2016

Based on radio continuum surveys of the Galactic plane at wavelengths of 21 cm and 11 cm we have so far identified about 32 new supernova remnants in the area 357°.4 ≤ℓ≤ 76°. |b| ≤ 5°. This increases the number of known objects in this field by about 68%. Most of them are in the Galactic latitude range |b| 〉 0°.5. Some implications are discussed.
Supernova Remnants and the ISM: Constraints from Cosmic-Ray Acceleration
Authors: Wandel Amri
Published: July 2016

Supernova remnants can reaccelerate cosmic rays and modify their distribution during the cosmic ray propagation in the galaxy. Cosmic ray observations (in particular the boron-to-carbon data) strongly limit the permitted amount of reacceleration, which is used to set an upper limit on the expansion of supernova remnants, and a lower limit on the effective density of the ISM swept up by supernova shocks. The constraint depends on the theory of cosmic ray propagation: the standard Leaky Box model requires a high effective density, > 1cm−3, and is probably inconsistent with the present picture of the ISM. Modifying the Leaky Box model to include a moderate amount of weak-shock reacceleration, a self consistent solution is found, where the effective density in this solution is ≈ 0.1 cm−3, which implies efficient evaporation of the warm ISM component by young supernova remnants, during most of their supersonic expansion.
Infrared Spectroscopy of Supernova Remnants
Authors: Moorwood A.F.M. , Oliva E. , Danziger I.J.
Published: July 2016

Spectra of several galactic and LMC supernova remnants have been obtained at R ~ 1500 in the 1−2.5 µm region with the cooled grating/array spectrometer, IRSPEC, on the ESO 3.6m telescope. The brightest lines observed are from [FeII]. In RCW 103, which exhibits the highest surface brightness, H (Brγ at 2.17µm) and H2 (1−0 S(1) at 2.12µm) lines have also been detected. A good correlation is found between [FeII] (1.64µm) and Hβ implying similar ionization structures and Fe abundances in a wide variety of remnants. The actual [FeII](1.64µm)/Hβ ratio of ~0.2 also implies a high depletion factor (>0.9) for Fe. Electron densities, extinctions and [FeII] luminosities derived from these data are presented and discussed and attention drawn to a potentially interesting discrepancy between H(Brγ) and Hβ fluxes.
Molecular Clouds Associated with H I Shells
Authors: Koo B-C. , Heiles C.
Published: July 2016

We report the detection of molecular clouds associated with three giant galactic H I shells.
Multifrequency Observations of Symbiotic Stars
Authors: Kenyon Scott J.
Published: July 2016

This paper reviews the discovery of symbiotic stars, and introduces multifrequency observations made during the past two decades.
Infrared Observations of Symbiotic Miras
Authors: Whitelock Patricia
Published: July 2016

Symbiotic Miras are identified by their infrared characteristics. It is shown how an understanding of the evolutionary position of normal Mira variables together with the empirically established period luminosity relation can be used to derive various physical parameters for similar objects in symbiotic systems. The pulsation periods of symbiotic Miras measured so far fall between 280 and 580 days, their ages must be in the 5–10 Gyr range while main sequence masses of the order 1 to 1.5 M⊙ are indicated. The obscuration events seen in the IR light curves of several symbiotic Miras are highlighted as potentially important and possible causes are discussed.
Ionization models of symbiotic stars
Authors: Nussbaumer H.
Published: July 2016

A model of a symbiotic system is outlined. We present evidence that the main ionization mechanism responsible for the symbiotic nebula is radiative and not collisional. For calculating fractional ionization throughout the emission region we take either a blackbody source or an accreting system. If the ionizing radiation is due to accretion, the boundary layer between accreting star and disc provides the bulk of the ionizing photons. The possibility for distinguishing between different ionization sources are briefly discussed. C/N and O/N abundance ratios, calculated with the outlined ionization model places HM Sge, RS Oph, and T CrB among the novae and not among the symbiotic stars.
The Decay Time after a Thermonuclear Flash
Authors: Orio Marina
Published: July 2016

The drag luminosity produced by a secondary embedded in a nova envelope is calculated and it is assumed to liberate gravitational energy. The results of a preliminary calculation show that the time for envelope ejection and therefore for the light decay varies sharply with the binary distance. It would be considerably reduced if the binary distance is a < 2 RO. It is suggested that this is the main difference between the thermonuclear runaway of symbiotic stars and nova systems, instead of other physical parameters.
CI Cygni – The Well Understood Symbiotic Binary ?
Authors: Mikolajewska J. , Mikolajewski M.
Published: July 2016

The observed properties of CI Cyg are reviewed. Spectroscopic and photometric changes due to orbital effects as well as intrinsic variability of the components are discussed.
A P Cygni Profile for the He 10830 A line of CI Cyg in Eclipse
Authors: Bensammar S. , Friedjung M. , Letourneur N. , Maillard J.P.
Published: July 2016

Infrared spectroscopic observations of CI Cyg in eclipse show a P Cygni profile for He I 10830 Å, with a wind velocity of the order of 150 km/s, not seen in hydrogen Brackett and Paschen emission lines, which are single peaked.
Symbiotic Eclipsing Binary Star CI CYG. The Cold Component Variability
Authors: Belyakina T.S.
Published: July 2016

It has been shown that the cold component of CI Cyg eclipsing binary system is a variable star. The amplitude of its light variations is close to with the time interval of 40–60 days.This star being the red giant M4 can be attributed as SR type variability. The light variations is caused by its temperature variations.
The Spectrum of CH Cygni - a Search for Rapid Line Variations
Authors: Tomov T. , Raikova D.
Published: July 2016

The spectacular changes of CH Cyg spectrum during the last period of activity and the flickering in short wavelength light suggest the possibility of rapid line variations (Walker et al.,1969). In November 1982 a series of spectral observations has been accomplished at Rozhen Observatory to investigate the subject.

In that period the spectrum of CH Cyg is dominated by type A shell lines. They are supposed to originate in an accretion disk surrounding the hot star of the binary system. The flickering in the optical wavelengths is characteristic for CH Cyg during periods of activity. Evidently it is related with the mass transfer. The investigation of its origin and relations with the other observational characteristics of the star could elucidate the accretion mechanism in this system.
A Model for RX Puppis
Authors: Allen David , Wright Alan
Published: July 2016

The dust-rich (D-type) symbiotic stars appear always to comprise a mira variable and a star of temperature ∼ 105 K which ionizes the mira’s circumstellar envelope. On timescales of decades they change little, save for the slow pulsation of the mira at infrared wavelengths. RX Puppis is a striking exception to this generalization, however, since it undergoes extraordinary changes.

RX Pup drifts between two extremes, exhibiting intermediate states. Table I summarises the known characteristics in the extreme states. Because of its variability, models of RX Pup are more highly constrained, giving us a chance to understand one of the D-type symbiotics.

Optical spectra of RX Pup from the Anglo-Australian Telescope. Tie breadth of the lines in 1976 may be due to lower spectral resolution.
A New Absorption-Line Orbit for the Symbiotic Nova AG Pegasi
Authors: Slovak M.H. , Lambert D.L.
Published: July 2016

Precise cross-correlation absorption-line velocities have been derived using high resolution near infrared coude’ spectra for the symbiotic nova AG Pegasi. A revised weighted orbital solution is presented based on both extant photographic and the new absorption-line velocities.
Spectroscopic Variations of the Symbiotic Nova PU VUL
Authors: Hric L. , Chochol D. , Kovachev B.
Published: July 2016

Evidence for formation and subsequent expansion of an A–F supergiant envelope in the very slow symbiotic nova PU Vul caused by quasiperiodic injections of matter from M giant to the A–F supergiant is given.
IUE and Optical Observations of HE 2-104
Authors: Lutz Julie H.
Published: July 2016

He 2-104 has been classified as both a planetary nebula and as a symbiotic star. Optical and ultraviolet spectra and CCD images have been obtained in order to learn more about the evolutionary state of this object. The spectra of the object indicate that it could be either a symbiotic star or a very high excitation planetary nebula. The CCD images show a nebulosity with a radius of about 4 seconds of arc and faint bipolar outer structures extending out approximately 25 seconds of arc from the center of the nebula.
Unravelling the Multiple Component Radio Emission of RS OPH in Outburst
Authors: Taylor A.R. , Bode M.F. , Davis R.J. , Porcas R.W.
Published: July 2016

VLBI observations of RS Ophiuchi during its 1985 outburst enable us to start to disentangle the multiple component radio emission. It appears that the emission at low frequencies was predominantly non–thermal, whereas at high frequencies the emission is most likely thermal. It is then possible to probe the physical properties of the remnant.
Criteria and Applications of the MK Classification (Early Type Stars)
Authors: Lodén Kerstin
Published: July 2016

The fundamental characteristic of the MK classification system is the definition of an array of standard stars, arranged in two dimensions. New techniques and an enormous increase in observational and theoretical work since the original catalog in 191+3 have in various ways complicated the problem of spectral classification. Problems discussed are: 1.) The re-examination of standard stars; 2.) The optimum dispersion and the limits of dispersion for MK classification; and 3.) Some groups of peculiar objects.
Les Étoiles Supergéantes Dans le Grand Nuage de Magellan. La Signification des Classes de Luminosite I
Authors: Fehrenbach Ch.
Published: July 2016

Les classes de luminosité de Keenan et Morgan sont une subdivision très commode pour caractériser les étoiles d’une même classe spectrale. Les classes V et III paraissent bien définir un type d’étoiles; leurs paramètres principaux (MB et Te ou pe et Te) sont déterminés par le type spectral et la classe de luminosité. Les classes IV et II sont mal définies, leur existence n’est pas assurée. L’ensemble des étoiles supergéantes est encore plus mal défini, elles remplissent complètement la partie supérieure de diagramme de Russell-Hertzspung. Une étude de ce diagramme pour les étoiles supergéantes du Grand Nuage de Magellan montre que les subdividions IaO, la, lab et Ib correspondent à une variation continue de la magnitude absolue qui va par exemple des étoiles AO de -9.6 à -5. La valeur souvent admise -7 pour la magnitude absolue des supergéantes est une simplification abusive. D’autre part, la classification exacte des luminosités est difficile et une mesure d’une quantité physique (rapport d’intensité de raies, ou intensité de raies) devrait permettre une meilleure classification de ces étoiles.
Spectral Classification, Photometry and Statistical Analysis
Authors: Heck A.
Published: July 2016

Sophisticated algorithms of modern statistical analysis are not yet widely applied to astronomical data. For the moment, these methods are mainly used by scientists in fields where the physical basis is less well determined than in astronomy. The algorithms could however be quite useful in new fields of our science where the physics is still being investigated. In more classical applications we have found them quite useful in the study of the relationship between photometric and spectroscopic data.
Automatic Spectral Classification - Present State and Future Developments
Authors: Schmidt-Kaler Th.
Published: July 2016

A survey is given of the present state of digitization and automation of spectral classification from low and intermediate dispersion objective prism plates and an outlook to automatic classification work by a photoelectric multi-element detector scanning system.
Spectral Classification from a Theoretical Point of View
Authors: Bohm-Vitense Erika
Published: July 2016

We study the conditions under which a two-dimensional spectral classification according to Teff and ne is possible and when 3- or It-dimensional spectral classification is necessary because the classification criteria are unavoidably influenced by the metal and helium abundances. For late type stars, where molecular absorption becomes important for the continuum a seven-or more- dimensional classification may be necessary. At this point spectral classification may not be useful any more. We find generally that a derivation of the gravitational acceleration from the spectroscopically determined electron density is only possible if the helium abundance is known.
Ultraviolet Spectrometry of Peculiar Stars
Authors: Baratta G. B. , Cassatella A. , Viotti R.
Published: July 2016

The standard classification criteria, when applied to peculiar objects, such as emission line and shell stars, cannot easily be interpreted in terms of their intrinsic physical characteristics. Observations outside the optical spectral region may provide complementary information on their nature leading to a better spectral classification.
A Deep Objective Prism Survey of Two Regions in the Large Magellanic Cloud for Ob and Supergiant Stars
Authors: Davis Philip A. G. , Sanduleak N.
Published: July 2016

Two regions in the Large Magellanic Cloud (centered atα = 5h 11m, δ= -66° 08’ (34B), α = 5h 27m, δ= -72° 15’ (47B) have been searched for OB and supergiant stars. A catalogue of 312 stars is presented in which objective prism spectral types, positions (1975), approximate B magnitues and cross identifications are given. About half the stars catalogued in each area are OB stars, the remainder are supergiants. The region at δ=-72° has two to three times as many F and G-type supergiants as the region at δ= -66°.
Two Dimensional Spectral Classification of Early Type Stars by Narrow Band Photometry
Authors: Gerbaldi M. , Morguleff N.
Published: July 2016

Spectrophotometry data of 775 early type stars in a narrow band photometric system are analyzed, looking for the best parameters for a two dimensional spectral classification in the spectral region 3575 Å - 6000 Å. A correlation is established with the MK classification. The statistical technique of Principal Componant Analysis is applied to determine the number of linearly independent parameters among the data.
The Formation and Evolution of Low-Mass Close Binaries with Compact Components
Authors: Tutukov A.V. , Yungelson L.R.
Published: July 2016

We discuss the formation and evolution of interacting low-mass close binaries with a He-ICO- or ONe-dwarf neutron star or a black hole as a compact component. Mass exchange leads to cataclysmic events in such systems. The rate of semidetached low-mass close binary formation is 5×10−3 yr−1 if the accreting component is a He degenerate dwarf, 5×10−3 yr−1 if it is a CO-dwarf and 3×10−8 yr−1 if it is a neutron star. Systems with compact accretors arise as the result of the common envelope phase of close binary evolution or due to collisions of single neutron stars or dwarfs with low-mass single stars in dense stellar clusters. Evolution of LMCB to the contact phase in semi-detached stages is determined mainly by the angular momentum losses by a magnetic stellar wind and radiation of gravitational waves. Numerical computations of evolution with momentum loss explain observed mass exchange rates in such systems, the absence of cataclysmic variables with orbital periods 2h−3h, the low number and the evolutionary status of systems with orbital periods shorter than 80m. In conclusion we list unsolved problems related to magnetic stellar wind, the distribution of young close binaries over main initial parameters, stability of mass exchange.
Echelle-Mepsicron Time-Resolved Spectroscopy of the Dwarf Nova SS Cygni
Authors: Echevarría J. , Diego F. , Tapia M. , Costero R.
Published: July 2016

High dispersion time-resolved spectrograms of the dwarf nova SS Cygni, obtained with the Echelle-Mepsicron system, show double peaked emission lines with a complex profile. The intensity of the Hβ line appears to be modulated by the orbital period. Radial velocity measurements of the wings of Hβ and of the absorption line system of the late-type star yield semiamplitude values of Kem = 101 ± 6 km s−1 and Kab = 151 ± 7 km s−1, respectively. Radial velocity measurements of the blue and red peaks and of the central absorption of Hβ reveal a synchronous movement with the broad wings, although there is some evidence of a narrow component probably associated with a hot spot in the disk or a chromospheric emission line from the secondary star. The Hβ modulation, the double profile and recently discovered UBV light variations support an inclination angle i ~ 50°. The masses of the primary and secondary stars using this angle and the observed semiamplitudes are Mp = 0.60 M⊙ and Ms = 0.40 M⊙, respectively. A detailed analysis of the absorption lines reveals a spectral type of K2V.
Some Notes on SS Cygni
Authors: Mirzoyan L.V.
Published: July 2016

The results of photoelectric and spectral observations of SS Cyg are briefly discussed. Some features of the spectral variations observed during a large outburst of SS Cyg can probably be explained using a model of a double star which is surrounded by an absorbing gaseous shell. It is noted that the existing data are not numerous enough for the explanation of the SS Cyg variability, in particular, its short-term variations.

SS Cyg is a spectroscopic binary star with a 0.d276 period. The components of this system are dwarf stars (M ≈ 5.m5 for both stars), with dG5 and sdBe spectra; they probably show eruptive activity (Joy, 1956). In the spectrum of the B-component strong emission lines are observed. The dG5 spectrum is observed only in the minimum of SS Cyg.

There are various investigations of SS Cyg, but up to now the cause of its variability, in particular, its rapid variability has not been determined. In addition, there are many other observations which have not been explained.
Photometry of TT Arietis
Authors: Semeniuk I. , Schwarzenberg-Czerny A. , Duerbeck H. , Hoffmann M. , Smak J. , Stepień K. , Tremko J.
Published: July 2016

An analysis of data spanning 24 years shows that a secondary 20m periodicity is a persistent feature in photometric observations of TT Ari. This period decreases from 27m in 1961 to 17m in 1985. The 4d beat period of photometric and spectroscopic periods is also apparent in observations of 1966.
Preliminary Results of Improved Model Fits to the Extreme and Far UV Observations of Cataclysmic Variables
Authors: Carone T.E. , Polidan R.S. , Wade R.A.
Published: July 2016

We present the first results of a study which will attempt to analyze the combined Voyager and IUE observations of cataclysmic variables using steady-state accretion disk models. Initially we use flux ratio diagrams to determine if a combination of models will suffice or if new ingredients are necessary.
New Exosat Observations of TV Columbae: Preliminary Results
Authors: Schrijver J. , Brinkman A.C. , Van Der Woerd H.
Published: July 2016

The first results of the analysis of new EXOSAT observations of the DQ Her type cataclysmic variable TV Col are presented. The period of the 1–10 kev X-ray pulsation associated with the white-dwarf rotation is now established as 1911 s. The pulsations are most pronounced in the lower energy channels (1–3.5 keV). The X-ray light curve shows absorption features associated with the orbital period of the system.
Periodic Variabilities in the IUE Spectra of SS Cygni
Authors: Lombardi R. , Giovannelli F. , Gaudenzi S.
Published: July 2016

The analysis of the IUE low resolution spectra of SS Cyg in quiescence clearly shows modulations with the orbital phase of the continuum and the emission lines total area. The shape of such modulations is depending on the type of the optical outburst preceding the quiescent phase in which the UV spectra were collected. This behaviour, together with those in other wavelength regions, could be explained within the framework of the intermediate polar models.
Accretion Disk Evolution
Authors: Bath G.T.
Published: July 2016

Three aspects of mass transfer instability models of dwarf novae are examined. The hydrodynamic development of instabilities in the secondary are examined within Roche geometry and shown to extend at least a few degrees away from the line of centres. The form of the outburst light curves observed in SS Cygni are shown to be a natural consequence of mass transfer bursts with a duration either less than, or greater than, the disk viscous timescale. Finally the two-dimensional structure of the disc in the plane of the orbit is studied. As with α-disks the viscous evolution time following a burst of mass transfer determines the size of viscosity within the disk. Significant deviations from axial symmetry are found to be present.
Accretion Disk Boundary Layers: Their Structure and Stability
Authors: Stanley G.Q.G. , Papaloizou J.C.B.
Published: July 2016

The importance of the boundary layer has been known for some time, (see Lynden-Bell and Pringle. 1974). Yet this region of the disc has never been studied in great depth. We present here some calculations which are undertaken in order to explore some of the complex processes which can go on in this region. It is shown how the structure of the boundary layer is affected by viscosity, how oscillations can occur in the outer disk and boundary layer regions. We also show how they disperse and dissipate.
Nucleation in Novae
Authors: Callus C.M. , Albinson J.S. , Evans A.
Published: July 2016

We consider the possibility that dust grains in novae could nucleate on ions. We examine how different ejected masses and different elemental abundances effect the availability of nucleation centres, and we show how this model could explain why only novae of intermediate speed classes form dust.
X-Ray and Optical Observations of the AM Her Star H0139−68
Authors: Schwope A. , Beuermann K.
Published: July 2016

We summarize results of our ongoing analysis of optical and X-ray data on the AM Herculis type binary H0139−68 (see also Beuermann et al., 1984; Schwope and Beuermann, 1985).