bluuebunny/crossref_metadata_2025 huggingface dataset:
Circumstellar Matter in Algols and Serpentids
Authors: Plavec Mirek J.
Published: July 2016

A systematic search is reported for phenomena associated with circumstellar matter in interacting binary systems of the Algol and W Serpentis type. Ultraviolet emission lines have been detected by the author in 10 Algols and 6 Serpentids. No conspicuous difference exists between systems with disk accretion and those with direct stream impact. Evidence is indicated that the lines are formed predominantly by scattering in an induced stellar wind. Relative intensity of Fe II and Fe III emissions appears to be correlated with the spectral type of the gainer. It is suggested that in the Serpentids we see a thick disk nearly edge–on, but that the emission lines indicate the nature of the gainer inside.
The Relation Between RS CVn and Algol
Authors: Hall Douglas S.
Published: July 2016

Late-type secondaries in Algol binaries are rapidly rotating convective stars and thus should be chromospherically active (CA). They are examined with respect to observational manifestations which characterize already known CA stars: Ca II H and K emission cores, photometric variability attributable to starspots, soft x-ray emission, non-thermal radio emission, ultraviolet and infrared excess, and alternating period changes. The conclusion is that they can be regarded as another class of CA stars. In most respects they are literally indistinguishable from other CA stars. Ca II H and K emission cores are observed in the lobe-filling component of six semi-detached binaries: U Cep, RT Lac, RV Lib, AR Mon, S Vel, HR 5110. Alternating period changes are shown to occur only in Algols containing a late-type (convective) star. It is proposed, therefore, that the Matese-Whitmire mechanism explains these changes. Specifically, the interval from one increase (or decrease) to the next can be equated with the star’s magnetic cycle. Cycle lengths for 31 stars, derived in this way, range between 7 years and 109 years, with a median of 50 years.
A Photometric-Spectroscopic Analysis of the Algol-Type Binary U CRB
Authors: van Gent R.H.
Published: July 2016

U CrB is a well-known Algol-type eclipsing binary (P = 3ḍ522, spectrum B6 V + GO III-IV). Although the system has been closely observed since it’s discovery (Winnecke, 1870), progress in unraveling its true nature has been slow.

Early spectroscopic work suggested an early-type spectrum for the secondary which was in variance with the near absence of a secondary eclipse in the lightcurve. Rapid variations were also noted in the lightcurve (Lause, 1938; Batten, 1964; Piotrowski et al., 1974; Olson, 1982), which are only partly attributable to the variability of the commonly used comparison star HD 137147 (Olson, 1980; van Gent, 1982a).
A New Light Synthesis Optimization Program. Test on Simulated Algol Data
Authors: Linnell Albert P.
Published: July 2016

Simulation of light curve effects in Algol systems that are near contact or that may evolve into contact requires a different model than the tri-axial ellipsoid used in many current studies. A new light synthesis optimization program, based on the Roche model, satisfies the model requirements and determines system parameters with excellent accuracy, given a sufficiently large set of observations.

A widely used criterion for stopping iterative solutions is inadequate. A working criterion is proposed as a replacement.
Reverse Algols
Authors: Leung K.C.
Published: July 2016

An Algol is a binary system having a semidetached configuration where the less massive component is in contact with the critical equipotential surface. A reverse Algol is a binary system having a semidetached configuration where the more massive component is in contact with the critical equipotential surface. In 1985, Leung suggested 5 reverse Algol systems at the Beijing Colloquium. Two more such systems have been discovered recently. The spectral types of these systems range from early B to mid G. There is also a wide spread in mass ratio among these systems. There appear to be two types of reverse Algols, “hot” and “cool” systems. The hot systems have their more massive components as the hotter stars and the cool systems their more massive components as the cooler stars. The mass-radius relation of the reverse Algols is very similar to that of the contact and near-contact systems. It is believed that reverse Algols represent the pre-mass-reversal semidetached phase of close binary evolution. Since selection effects apply to both the regular Algols and reversed Algols in a similar manner, the evolutionary time scale between them would be simply the ratio of the number of confirmed systems of these two types of Algols.
The Effects of Magnetic Fields on Period Changes, Mass Transfer and Evolution of Algol Binaries
Authors: Bolton C. T.
Published: July 2016

Variations in the magnetic pressure and flux blocking by starspots during the magnetic cycle of the cool semidetached component of an Algol binary may cause cyclic changes in the quadrupole moment and moment of inertia of the star which can cause alternate period changes. Since several different processes and timescales are involved, the orbital period changes may not correlate strongly with the indicators of magnetic activity. The structural changes in the semidetached component can also modulate the mass transfer rate. Sub-Keplerian velocities, supersonic turbulence, and high temperature regions in circumstellar material around the accreting star may all be a consequence of magnetic fields embedded in the flow. Models for the evolution of Algols which include the effects of angular momentum loss (AML) through a magnetized wind may have underestimated the AML rate by basing it on results from main sequence stars. Evolved stars appear to have higher AML rates, and there may be additional AML in a wind from the accretion disk.
Epsilon Aurigae: A Supergiant and a Super Disk
Authors: Carroll Sean , Guinan Edward , McCook George , Donahue Robert
Published: July 2016

The eclipsing binary Epsilon Aurigae consists of an F0 supergiant and a cool, mysterious eclipsing companion with an orbital period of 27.1 years. The light curve of this system reveals two sources of variability: the eclipses themselves and the intrinsic variation of the supergiant. Multifilter photoelectric observations were made with the 38 cm reflector at the Villanova University Observatory. These data were analyzed along with other sources to reveal the nature of the components of the Epsilon Aurigae system. The system undergoes low-amplitude semi-regular light variations with a characteristic period of 110 days and perhaps a longer period of 500-600 days. The proximity of Epsilon Aur to the Cepheid instability strip on the H-R diagram suggests that the pulsation mechanism for this star may be similar to that of Cepheids.
The Algol-Type Binary QS AQL
Authors: Heintze J.R.W. , Hoekzema W. Spronk en N.
Published: July 2016

QS Aql is an eclipsing- and a (probably double-lined) spectroscopic binary with a period of 2.5133 days. However, from 1962 to 1968 the period was 2.5134 days. QS Aql is part of the visual double star Kui 93 with mA = 6.5 mag and mB = 6.7 mag or lA:lB = 1.2:1 (0). The system is also detected in X-rays (White & Marshall, 1983).
Synthetic Light Curve Analysis of the Close Binary Systems BX Andromedae and RR Leporis
Authors: Samec R.G. , Fuller R.E. , Kaitchuck R. H. , Bookmyer B. B. , Faulkner D. R.
Published: July 2016

Unpublished photoelectric observations of the systems BX And and RR Lep were subjected to light curve analysis using the Wilson-Devinney Code.

The short-period eclipsing binary system BX And was observed on five nights in 1976 at the Morgan-Monroe station of the Goethe Link Observatory of Indiana University. The observations covering the eclipse portions of the light curves yielded four times of minimum light. A period study covering 89 years of observations confirms that a major period change took place about 1950. The system is suspected of being quite active on a short time scale. Standard magnitudes were derived for BX And and for the comparison star. The corrected color indices indicate that BX And and the comparison star BD+39° 476 are in the spectral range of F3-F5. The light curves, defined by 1092 observations in B, 1097 in V and 971 in the U filter are symmetric. The difference in the eclipse depths are quite large averaging 0.m46. A distinct de-reddening of the light curves occurs during the secondary eclipse. The first synthetic light curve solutions of the system were obtained. The solution of BX And indicates that the system consists of an F-type primary and a K-type secondary component in a state of shallow contact. This result is supported by the location of BX And on the Eggen period-color diagram for contact binaries. The large mass ratio, temperature disparity and period increase are found to be consistent with an early contact phase of thermal relaxation oscillations.
KX Andromedae: Possibly a Strongly Interacting Binary
Authors: Stefl S. , Harmanec P. , Horn J. , Koubský P. , Kriz S. , Hadrava P. , Bozic H. , Pavlovski K.
Published: July 2016

Although KX And (HD 218393, MWC 397) has been observed since the beginning of our century, we have no reliable model of this peculiar emission-line object. Published papers (e.g. Plavec et al. 1982; Kriz and Harmanec 1975 and references therein) indicate that it is a B+K W Ser-type binary with a period of 38.9 days. This paper presents a summary of intensive observations carried out during the last fifteen years.

The observational material used consists of 65 coude spectra obtained with the Ondrejov 2-m telescope, UBV photometry obtained at Hvar Observatory and 28 archival IUE images. The radial-velocity and photometric data are combined with those found in the literature. A PDM period search over the interval 1 to 1000 days unambiguously indicates the 38.9-day period both in RV and photometric data.
Radio Emission from EA Eclipsing Binaries: Evidence for Kilogauss Early- and Late-Type Stars
Authors: Stewart R.T. , Slee O.B. , Budding E. , Coates D.W. , Thompson K. , Bunton John D.
Published: July 2016

A recent survey of EA eclipsing binaries by the Parkes 64-m telescope operating at 8.4 GHz detected 15 out of 47 systems on at least one out of the 10 nights surveyed. The detected systems were HD 6882 (ξ Phe), HD 36486 (δ Ori A), HD 39780 (TZ Men), HD 57167 (R CMa), HD 58713 (RY Gem), HD 74307 (S Cnc), HD 132742 (δ Lib), HD 147683 (V769 Sco), HD 161741 (V393 Sco), HD 163708 (V1647 Sgr), HD 16871Q(XZ Sgr), HD 183794 (V822 Aql), HD 187949 (V505 Sgr), HD 199005 (KZ Pav), and HD 207098 (δ Cap).

A full account of the observations and interpretation has been submitted to The Astrophysical Journal.

About one-half of the 15 detections refer to main-sequence pairs of spectral types earlier than F and the remainder are classical Algols.
Statistical Study of the Spin of Algols
Authors: Huisong Tan
Published: July 2016

Synchronous rotational velocities have been calculated for 91 Algol-type systems for which the radii of the components and orbital inclinations have been published. New values of V sin i have been measured for some of these systems. The frequency of components rotating near synchronism (F less than 1.5) is found to be higher for unevolved than for evolved systems. For Algols with periods less than 10 days and radii greater than 0.2, synchronous rotation is found to be the rule. There are 50 components of spectral type B and 44 of spectral type A in systems with periods shorter than 10ḍ The shortest period in which synchronism is found is 4 days for the A-type components and 2 days for the B-type.
Evidence for Transient Colour Changes of Algol in the Past
Authors: van Gent R.H.
Published: July 2016

Most Algol-type variables are believed to be close, semi-detached binaries which have evolved from a rapid mass-transfer phase, which reversed the initial mass-ratio, to a relatively quiescent stage where only small-scale transient events perturb the dynamical and the photo-metrical properties of the system.

Of all Algol-systems, only the prototype Algol (β Per) itself is bright enough to be traceable in astronomical records reaching back more than 2000 years. Evidence based on medieval stellar lists and 19th-century visual observations strongly suggest that the intrinsic colour of Algol has been subject to substantial variations within historical times. On a few occasions Algol was apparently observed as reddish, which is at variance with its present blue-white appearance (B-V = −0.05 to +0.10).
Evolution of Binary Systems and Their Generic Relations: Vainu Bappu Memorial Lecture
Authors: Kopal Zdeněk
Published: July 2016

Prologue: Irise to address you today with sadness in my heart - sadness which I trust is shared by all those here present; for as is underlined by its subtitle, our beloved colleague Vainu Bappu - past President of the International Astronomical Union, and life-long student of the subject of our Colloquium - is no longer in this world to take his rightful place among us; and, therefore, my remarks which follow can be dedicated only to his memory.
Radial Velocity and Profile Variations of the Ultraviolet Circumstellar Lines in ζ Tauri
Authors: Dawanas D. N. , Hirata R.
Published: July 2016

The radial velocity and profile variations of UV lines of the shell star ζ Tau have been examined in the IUE spectra obtained in 1978-1982. The neutral atoms, and once or twice-ionized ions (except C II, Al III, Si III resonance lines) follow the same velocity variations as in the visual spectra, while the Si IV and C IV resonance lines show a constant negative velocity (~ -50 km s− at the core). The Al III, C II resonance lines and probably Fe III (mult. No. 34) are formed in both regions, i.e., in lowly-ionized and highly-ionized regions and the Si III resonance line is formed in a highly-ionized region.
Wolf-Rayet Binaries: Evolutionary Causes for their Distribution in the Galaxy
Authors: Hidayat Bambang , Admiranto A. Gunawan , Van Der Hucht Karel A.
Published: July 2016

On the basis of the most recent data, the fraction of known Wolf-Rayet binaries is 0.22. In the solar neighbourhood (d < 2.5 kpc) this fraction is 0.34

In order to assess the relative importance of massive binary evolution as one of the ways to produce WR stars, the galactic distribution of WR binaries is compared with that of single WR stars using improved intrinsic parameters and new data for the fainter WR stars.

In the galactic plane the increase of the binary frequency with galactocentric distance is confirmed.

In a direction perpendicular to the galactic plane it is demonstrated at all distances from the Sun that the single-line spectroscopic WR binaries with small mass functions have definitely larger |z|-distances than the ‘single’ WR stars and the WR binaries with massive companions. This is consistent with the evolutionary scenario for massive binaries summarized by van den Heuvel (1976). Among the ‘single’ WR stars the fraction of those with large |z|-distances is increasing with galactocentric distance, like the fraction of the known binaries. This implies that among the high-ļzļ ‘single’ WR stars as well as among the WR stars with lower |z|-values many binaries are still to be discovered.

The total WR binary frequency in the Galaxy could be well above 50 %.
Steady Mass Loss Associated with Nova Outbursts
Authors: Kato Mariko
Published: July 2016

The structure of optically thick mass-losing envelopes of white dwarfs are studied in relation to nova outbursts. A sequence of steady mass-loss solutions is constructed for a nova outburst from the maximum photospheric radius to the disappearance. Much of mass of the envelope will be blown out.
The q-Log P Distribution of Classical Algols
Authors: Budding Edwin
Published: July 2016

Data on a large sample (∼400) of candidates for the classical Algol-type eclipsing binary configurations have been collected. The mass-ratio q has been calculated on the assumption of their semi-detached nature, and then compared with corresponding period for some subsets of the sample. The tendency to slight overluminosity (compared with corresponding MS stars) of the primaries in classical Algols is confirmed.

The role of the loss of angular momentum in classical Algol evolution is considered, together with a method for determining representative parameters to characterize such effects using the sample data. The possible existence of a class of post-contact classical Algols is noted.
Semi-Detached Binaries: The Origin and Present Status of TU Mon, SX Cas, and DM Per
Authors: De Grève J. P. , Packet W.
Published: July 2016

An attempt is made to trace back the possible progenitor systems of the Algol-type binaries TU Mon, SX Cas, and DM Per. The present characteristics are compared to the result of the evolution of 9 M0 + 5.4 M0. The position of the hot components in the HRD is discussed with regard to the theoretical models.
The Use of Asteroids for Determinations of Masses and other fundamental constants
Authors: Rabe Eugene
Published: July 2016

This report does not attempt to review all past and present work using asteroids for determinations of planetary masses and other fundamental constants. This would be a very large undertaking, and too extensively outside of the scope of a colloquium devoted to physical studies of minor planets. It seems preferable to concentrate more on principles involved, while mentioning only some of the various results obtained. At the same time, it will be appropriate to take note of the changed situation resulting from the recent development of certain modern methods and facilities that make it possible to determine some of the constants more accurately in other ways, thus partly eliminating the once dominant role of the minor planets.
Internal Constitution and Mechanisms of Asteroid Fragmentation
Authors: Brecher Aviva
Published: July 2016

It has been generally assumed in the past that the fragmentation of asteroidal bodies and the production of meteorites are solely the result of collision events. (See Dohnanyi, 1969; Hartmann and Hartmann, 1968; Wetherill, 1967.)

A possible mechanism of noncollisional fragmentation will be proposed below, its proper framework of applicability will be defined, and evidence suggesting and supporting its existence will be adduced. Briefly, it is shown that the presence of even trace amounts of hydrogen in meteoritic metal phases (Edwards, 1955) may have caused the parent bodies of iron meteorites to undergo, spontaneously, delayed brittle fracture under the action of prolonged slow stresses, the imprint of which has been recorded in the phase structure of meteorites (Baldanza and Pialli, 1969). This phenomenon, termed “hydrogen embrittlement,” has been amply documented in the literature on the metallurgy of ferrous metals (Bernstein, 1970;Tetelman, 1969).
Jetstream Formation through Inelastic Collisions
Authors: Baxter David C. , Thompson William B.
Published: July 2016

An inelastic collision integral is used in a Boltzmann-type equation for a distribution of particles in Kepler orbits. A Fokker-Planck equation is found that leads to radial density clustering.
Exploration in the Solar System with Electric Spacecraft
Authors: Stuhlinger Ernst
Published: July 2016

The landings of instrumented probes and astronauts on the Moon and the short glimpses at Venus and Mars that distinguished the spaceflight program of the last decade yielded such an impressive wealth of new knowledge that the President, in his programmatic speech of 1970, mentioned the continuing exploration of the solar system as one of the national goals during the decade of the seventies.

This exploration will be accomplished with unmanned spacecraft, except for the remaining three Apollo flights in 1971 and 1972 and Skylab in 1973. Planetary exploration will include photographic coverage of the surfaces of the celestial bodies; closeup pictures of specific surface features; magnetic and gravitational measurements; observations of atmospheres, ionospheres, and radiation belts; analysis of surface material in situ; and, as far as possible, the return of surface samples for careful chemical and mineralogical analyses and for age determinations.
Asteroid Rendezvous Missions
Authors: Bender D. F. , Bourke R. D.
Published: July 2016

The earliest flights to concentrate solely on the nature of particular asteroids will probably be of the simple flyby or rendezvous type. That is, data will be obtained by close investigation of these bodies without actually coming in contact with their surface. The technology of flyby missions to bodies at planetary distances is well established; there have been five successful Mariners to date and more flights are scheduled. Unfortunately, ballistic flyby missions suffer from the fact that the spacecraft is near the body of interest for a short period of time (relative velocities at asteroid encounters are 5 to 12 km/s). This problem is acute because spatial resolution of the onboard instruments must be very high, and typical flyby velocities will preclude detailed observations.
Manned Mission to an Asteroid
Authors: Hall Harvey
Published: July 2016

If manned missions to the planets are to be considered at some time in the future, as has long been imagined, it appears to be reasonable to explore the feasibility of carrying out a manned mission to an asteroid as an intermediate step between lunar and planetary missions. If study shows that it is possible to conduct such a mission with Apollo-type hardware, and if the answer to the first question is yes, then an asteroid flight should probably be considered while Apollo-type facilities are still in existence. Once these facilities have been dismantled, it may be many years, perhaps a generation, before a new era in space exploration would make such a manned flight possible.
Potentials of Asteroid Space Missions
Authors: Bratenahl A.
Published: July 2016

There is an important relation between the development of solar electric spacecraft and the possible inclusion within the space program of new missions devoted primarily to asteroid investigations. The notion that space missions to asteroids have a high potential to return critically needed data will be illustrated in some detail.
Discovery and Observation of Close-Approach Asteroids
Authors: Roemer Elizabeth
Published: July 2016

Close-approach asteroids, members of the so-called Apollo and Amor groups, are of considerable current interest as potential targets for probes and also in connection with the question of identification of the parent bodies of the meteorites. The possibility that some of these asteroids may be surviving comet nuclei has been suggested earlier. (See, e.g., Öpik, 1963.) Relatively few objects of this type are known; all are small bodies found accidentally in the course of work not always related to investigations of minor planets. The known Apollo and Amor asteroids, and notes as to their present observational status, are listed in table I. (See also table II of Marsden.) Except when they are relatively close to Earth (many can approach within 0.10 AU), these objects are faint and often in very awkward positions as well, low in the evening or morning sky at twilight.
Manmade Objects–A Source of Confusion to Asteroid Hunters?
Authors: Aksnes Kaare
Published: July 2016

On October 7, 8, and 9, 1970, Charles Kowal, in search of fast-moving asteroids, exposed three photographic plates of an area of the sky near the ecliptic with the 122 cm Schmidt reflector of the Hale Observatories. Several weeks later Eleanor Helin of the California Institute of Technology examined the plates under a blink microscope and discovered a fast-moving object of about 15 mag. During the 15 min exposures the object had left a slightly bumpy trail indicating light variations with a period of a few minutes.

Four positions of the object were reported to the author, who derived the heliocentric orbit defined in table I. From table II it is seen that the residuals of that orbit are not very satisfactory. Note that the third and the fourth position represent the end points of the same trail. There is a clear indication that after October 9, the predicted heliocentric positions would soon diverge from the actual positions. This circumstance, and the fact that the orbit is so similar to that of Earth, suggested that the object could actually be moving in an Earth-centered orbit.
The Photoionization Cross-Section of SI
Authors: Tondello G.
Published: July 2016

An experiment for the determination of the absorption spectrum of S i was performed using a flash-pyrolysis technique.

The material (pure Sulphur) was introduced by vacuum deposition into the absorption cell which was surrounded by a helical flash-lamp. A condensor bank of 120 μF charged to 10 kV was discharged through the flash-lamp. The absorption of the strong flux of light results in the evaporation of the material and in its dissociation. With delays of 100–500 μsec a Garton source was fired providing the background continuum.
Relation between Laser Flux, Temperature and Ionisation Equilibrium in Laser Produced Plasmas
Authors: Key M. H. , Hutcheon R. J. , Preston D.A. , Donaldson T.P.
Published: July 2016

Laser produced plasmas are a useful source of highly stripped ions for XUV spectroscopy and it is therefore important to understand the relation between the incident laser flux, plasma temperature and ionisation equilibrium.
A Universal Function for Ionization of Atoms by Structureless Charged Particles of Arbitrary Mass and Charge
Authors: Bely O. , Faucher P.
Published: July 2016

The collisional ionization of atomic systems by structureless charged particles of arbitrary mass and charge is considered. For the theoretical study, the classical impulse approximation is used. In this case, analytical expressions Q for the ionization cross-sections are given by Garcia et al. (1968). From these expressions, a reduced cross-section QR is obtained as a function of a scaled energy X. It is found that, for a particle of mass M, charge Z, and energy E, incident on a target having ξ equivalent electrons with a binding energy I, QR is given by:

where

IH is the hydrogen ionization potential and me is the electron mass.
Temperature Structure of the Chromosphere-Corona Transition Region
Authors: Elwert G. , Raju P. K.
Published: July 2016

Starting from the formula for line intensities E for a spherically symmetric atmosphere, considering the pressure parameter P0 = NeTe to be constant the inverse temperature gradient can be determined by taking it out from the integral for E. In this way Dupree and Goldberg (1967) found that the temperature gradient varies considerably whereas the conductive flux factor F=Te5/2(dTe/dh) is nearly constant for Te above 105 K. The best fit was obtained by using photospheric abundances. As the inverse temperature gradient varies considerably in the line forming region, it is, however, not satisfactory to take it out from the integral.
The Coronal X-Spectrum: Problems and Prospects
Authors: Walker A.B.C.
Published: July 2016

The coronal spectrum provides a unique opportunity to probe atomic processes in a high temperature plasma. The corona is optically thin, at low density, and the coronal ions are highly stripped. These characteristics result in an emission line spectrum with a rich multiplet structure, with forbidden lines prominent in the spectrum, and deexcitation of metastable states by two photon decay making significant contributions to the continuum. The multiplet structure is further complicated by the presence of satellite lines from autoionizing states formed during recombination. With few exceptions, the true coronal lines are below 300 Å, and the general necessity for and complexity of grazing incidence optics has made it difficult to obtain high resolution spectroheliograms.
Production of Different Non-Thermal Electron Groups in Small Solar Flares
Authors: Kane S. R.
Published: July 2016

Using the measurements of impulsive solar X-rays made with the OGO-5 satellite to identify the flash phase electron acceleration in solar flares of Hα-importance ≲ 1, the satellite and ground based observations are analyzed to study the origin of the different groups of non-thermal electrons responsible for the impulsive X-ray, impulsive microwave, type III radio and interplanetary electron emission.
The Transient Highly Excited Solar Flare Plasma
Authors: De Feiter L. D.
Published: July 2016

Recent observations of the energetic particles produced in solar flares indicate that the production of electrons, with energies up to about 100 keV, is a fairly common feature of small flares. In those flares the acceleration of protons and other nuclei does not extend beyond about 1 MeV.

The X-ray emission often exhibits two distinct components of which the first one is produced by non-thermal, the second by thermal electrons through bremsstrahlung collisions with the ambient ions. Along with these X rays, radio emission, in the microwave region, is observed. This radio emission is usually interpreted as due to gyrosynchrotron radiation from the same electrons.

In this review a discussion is presented of the processes occurring in solar flares with special reference to the acceleration and radiation processes.
Photometric and Spectroscopic Observations of the Cataclysmic Variable AC Cancri
Authors: Kitamura M. , Okazaki A. , Yamasaki A.
Published: July 2016

The eclipsing variable AC Cancri, recently identified as a cataclysmic variable by Shugarov (1981) and Okazaki, Kitamura and Yamasaki (1982), was further studied in detail on the bases of UBVcolours, multi-channel photoelectric light curves and image-tube spectrograms which were newly obtained at Tokyo Astronomical Observatory. The result of analysis of these materials for the nature of the cataclysmic variable is presented.
Infrared Observations of Nova Aquilae 1982
Authors: Bode M.F. , Davies J.K. , Evans A. , Whittet D.C.B.
Published: July 2016

We describe infrared photometry and spectroscopy of Nova Aquilae 1982. The broadband observations suggest that the dust shell of Nova Aquilae was anomalous, while the spectroscopic observations point to the presence of molecules in the nova environment.

Nova Aquilae was discovered (Honda 1982) on 1982 January 27th. The visual light curve, based on visual estimates (IAU circulars), IUE FES counts (derived assuming (B-V) = 0) and photometry at the South African Astronomical Observatory (SAA0), suggest a fast nova with visual decay rate mv = 0.3 mag d-1. Spectral development and outburst amplitude suggest that the nova was discovered at maximum.
The Continuum Energy Distribution of the Old-Nova GK Per (1901)
Authors: Bianchini A. , Sabbadin F.
Published: July 2016

The observed X-ray to IR continuum energy distribution of the old-nova GK Per, corrected for the contribution of the late-type secondary and for i.s. extinction,is found to be consistent with the model of an accreting magnetic white dwarf. Furthermore, we discuss plausible modifications of the standard disc structure caused by the presence of magnetic field lines threading the disc and evaluate the contribution to the observed radiation field from several physical mechanisms.
The ‘Isothermal’ Phase of Nova Dust Shells
Authors: Mitchel R.M. , Evans A. , Bode M.F.
Published: July 2016

We describe a model for the evolution of the infrared spectrum of the dust shell of nova NQ Vul. The effects of nucleation and grain growth, together with.extended, but diminishing, mass loss from the nova, are included. The variations in the effective temperature of the dust shell that occur near infrared maximum may be understood in terms of varying optical depth in a dust shell having significant temperature gradient. However, a more consistent picture is shown to combine interrelated optical depth and grain size variations.
Infrared Spectra of Nova Dust Shells
Authors: Bode M.F. , Evans A.
Published: July 2016

Results of fitting blackbqdy and pseudoblackbody functions to infrared photometry for three classical novae are briefly summarised.
Time Dependence in Accretion Onto Magnetic White Dwarfs
Authors: Langer Steven H. , Chanmugam G. , Shaviv G.
Published: July 2016

In this talk, we consider cataclysmic variable systems containing a white dwarf with a strong magnetic field. These include systems like AM Her (see, e.g., Chiappetti, Tanzi, and Treves 1981) in which the white dwarf rotates at the orbital period and systems such as AE Aquari in which the white dwarf rotates much faster than synchronously (see Patterson et al. 1980). The magnetic field in all of these systems is strong enough to disrupt the accretion disk at a point far above the surface of the white dwarf and may prevent the formation of a disk altogether. We will present theoretical models for the temperature, density, and velocity structure of the accretion flow in the region near the surface of the white dwarf where the kinetic energy of the flow is thermalized and radiated in the form of X-rays and ultraviolet radiation. This information is required to calculate accurate model spectra, and the results also have immediate consequences for the interpretation of observations.
Polarized Radiation from AM Herculis Stars
Authors: Barrett P. E. , Chanmugam G.
Published: July 2016

Calculations of polarized cyclotron radiation from magnetized hot plasmas are modified to include the effects of collisions and photon scattering. These effects produce a general reduction in both the linear and circular polarization. The background unpolarized flux which had previously been invoked, in an ad hoc manner for the collisionless case, is no longer required to bring agreement with observations. The most striking effect is at small viewing angles with the magnetic field, where the fractional circular polarization is reduced from nearly 100% to close to 0%. The calculations also show that the shape of the linear polarization pulse is essentially unchanged.
Fast Oscillations in Variable X-Ray Sources and X-Ray Bursters
Authors: Livio Mario
Published: July 2016

The properties of coherent oscillations with periods of tens of milliseconds that have been observed in seven variable X-ray sources and bursters are reviewed. Theoretical models for the generation of the oscillations are discussed. Difficulties with a magnetic rotator model are indicated. It is suggested that at least in several cases, g-mode oscillations of the neutron star provide a satisfactory explanation of the observations.
Introductory Comments
Authors: Bidelman William P.
Published: July 2016

The chairman has kindly encouraged, not to say entreated, me to write a few remarks concerning the subject of your symposium, which I was unfortunately unable to attend. This I am happy to do: the hydrogen-deficient stars are dear to my heart and even though I haven’t contributed anything to the subject for several years, it is certainly nice to be remembered. From an outsider, then, a few thoughts.

To quote from Miss Payne, in her classical study of 1925: The uniformity of composition of stellar atmospheres appears to be an established fact.” Certainly for the time that statement was beyond reproach. Yet even then the seeds of hydrogen deficiency had already been sown. Mrs. Fleming, in noting the presence of bright Hβ in u Sagittarii, in 1891, further states that its spectrum “is remarkable, since the hydrogen lines are very faint and of the same intensity as the additional dark lines.” Further, Ludendorff, in a paper written on Aug. 16, 1906, discovered the complete absence of the Hγ line in R Coronae Borealis (a similar situation with respect to Hβ and Hδ being confirmed by Frost). And by a remarkable coincidence, a Harvard objective-prism plate taken the very same day was described by Miss Cannon as showing very little absorption at the G band. Both HD 30353 and RY Sagittarii are stated in the Henry Draper Catalogue to show a spectral resemblance to R CrB. And finally, the non-typical weakness of the G band of the carbon star HD 182040 was pointed out by Rufus as early as 1923.
Emission Lines in High Resolution Spectra of Extreme Helium Stars
Authors: Heber U.
Published: July 2016

The occurrence of emission lines in high resolution blue spectra of four extreme helium stars is reported. This phenomenon is most apparent in the case of BD−9°4395 which displays emissions in He I, λ 3889 Å, C II, λ 4267 Å and in the C II multiplet No. 1 (λ 4740 Å). The latter is also present in LSE 78 and found to be variable. The C II emission lines are regarded as evidence for extended moving envelopes around BD−9°4395 and LSE 78. A possible relation to the hot R CrB star V348 Sgr is discussed.

HD 160641 and LSS 5121 show unidentified emission lines (λλ4485.6 Å, 4504.0 Å) which are also observed in some Of stars. No emission lines were found in the blue spectra of 12 extreme helium stars.
The Chemical Composition of Cool Stars: II - The Hydrogen Deficient Stars
Authors: Lambert David L.
Published: July 2016

The chemical composition of the R Coronae Borealis and cool hydrogen deficient carbon stars is reviewed. Similarities and differences between these stars and the hot He stars are noted. Proposed origins for the hydrogen deficient stars are sketched. Recent claims that normal (spectral type N) cool carbon stars are hydrogen deficient are shown to be unfounded. Attention is drawn to the curious case of pop. II variables (RV Tauri, W Virginis, and RR Lyrae stars) whose atmospheres show striking deficiencies of heavy elements and may be hydrogen deficient.
Intermediate Helium Stars: Atmospheric Parameters, Oblique Rotators and Shells
Authors: Hunger K.
Published: July 2016

Intermediate helium stars are defined by

nHe/nHbeing the number ratio of He over H. The upper bound which separates the intermediates from the extremes is well-defined (see Sect. 7), whereas the lower bound is rather soft.

The first intermediate helium star discovered was Sigma Ori E (Greenstein and Wallerstein, 1956). Since then, 23 intermediates with V ≤ 1lmhave been found (see the list of Walborn, 1983 and also the Annex), mostly through surveys such as that by McConnell et al. (1970) and McConnell (1972). (To this list, the newly discovered object SB 939, Langhans and Heber, 1985, should be added.) It is anticipated that a substantial fraction has as yet escaped detection. The spectral type centres around B2V while nHe/nHis typically of the order of unity.
Magnetic Fields and Winds of the Intermediate Helium Stars
Authors: Barker Paul K.
Published: July 2016

The intermediate helium stars are exceedingly rare hot analogs of the classical Ap stars, and are the earliest type stars to possess observable global ordered magnetic fields. A recent discovery is the existence of stellar winds which have large scale magnetospheric structure embedded within them. The nature and geometry of the detected fields are summarized, and the modulation of the circumstellar material by the field is illustrated for two examples: the rapid rotator σ Ori E, and the slow rotator HD 184927. The complex variety of stellar wind phenomenology which may be encountered is displayed by a sample of ten helium strong stars. A few of these objects show Hα emission, and thus are the only known magnetic Be stars.
Helium-Rich Stellar Atmosphere Models for B Stars
Authors: Odell Andrew P. , Voels Stephen A.
Published: July 2016

The hydrogen and helium line equivalent widths from stellar atmosphere models for early B stars are presented. The models, which range in helium number fraction from 0.10 to 0.85, result from the non-LTE statistical equilibrium code of Mihalas.
The Origin and Evolution of Helium-Rich White Dwarfs
Authors: Liebert James
Published: July 2016

White dwarfs with helium-rich atmospheres constitute about one fifth of the white dwarfs hotter than 12,000 K. They appear to have a mass distribution similar to the hydrogen atmosphere (DA) stars, and are similar in other properties. However, the temperature distribution exhibits a deficiency of DB/DO stars in the interval 25,000-45,000 K, which implies evolution in the dominant surface composition as the stars cool. The hottest group of transition DO white dwarfs are the pulsating objects of the PG1159 class. The central star of Kl-16 is a related object, as may be the newly discovered very hot star H1504+65, which shows no detected surface features of either hydrogen or helium.
Iras Results for Hydrogen Deficient Stars
Authors: Walker H.J.
Published: July 2016

The Infra-Red Astronomical Satellite, working at 12μm, 25μm, 60μm and 100μm, has observed stars in several subgroups of the hydrogen deficient stars. Observations of most known R CrB stars are reported here, as well as data for several HdC stars and other carbon-rich stars, together with some intermediate helium rich stars and related objects. Also given are LRS spectra of R CrB, RY Sgr, υ Sgr and some Carbon stars. Initial reductions of the additional observations from IRAS show an extended dust shell around R CrB, and probably also around SU Tau.
Diffusion and He Overabundances: Hydrodynamical Implications
Authors: Michaud G.
Published: July 2016

In the absence of mass loss, diffusion leads to underabundances of He in main sequence stars. Because of a very strong observational link with Ap and He weak stars, it has however been suggested that diffusion is the explanation for the He rich stars of the upper main sequence. This requires a mass loss rate of 10−12 Mo yr−1 or slightly lower. The mass loss rate must decrease as Teff increases. Magnetic fields must apparently be involved to reduce the mass loss rate. Since this model predicts that the CNO abundances should be normal in the cooler He rich stars, it leads to a clear observational test. Detailed calculations should be made to confirm the importance of this test. The effects of separation in the wind, the atmosphere and the envelope are discussed to conclude that separation in the atmosphere is likely to be most important. The importance of diffusion for He rich white dwarfs and horizontal branch stars are briefly discussed.
Appendix A: A Catalog of Hydrogen-Deficient Stars
Authors: Drilling J.S. , Hill P.W.
Published: July 2016

The following four tables were originally presented as part of the paper entitled ‘Basic Data on Hydrogen-Deficient Stars’ by J. S. Drilling, which appears earlier in this volume. A number of corrections and additions have been made by the participants, mostly by P. W. Hill using the SIMBAD data base. A much improved version of the catalog therefore follows. Helium-rich central stars of planetary nebulae, helium-rich white dwarfs, and Wolf-Rayet stars are not included. A complete list of helium-rich central stars is given by Mendez et al. elsewhere in this volume.
Origin of the Magnetic Field
Authors: Dolginov A.Z. , Ioffe A.F.
Published: July 2016

Some progress has been achieved in recent years in the theory of the stellar magnetic field generation but a lot of questions remain unanswered. I would like to give here a brief critical review of the current state of the problem.
Investigations of the Magnetic Fields of Chemically Peculiar Stars of Different Age
Authors: Glagolevskij Yu.V. , Klochkova V.G. , Kopylov I.M.
Published: July 2016

The program of comprehensive investigations of stellar magnetism in the Special Astrophysical Observatory of the USSR AS includes the study of origin and evolution of the stellar magnetic fields in open clusters and associations of different age. In the papers by Borra (1981), Brown et al. (1981) and North and Cramer (1984) have been found some indications on the evolutionary decay of the fossil stellar fields.
Application of Deutsch’S Method for 53 Cam
Authors: Vincze I.
Published: July 2016

53 Cam is a well-known magnetic, spectroscopic and photometric variable star of Ap-type. The line intensities of 53 Cam show a variation, which has a period of 8h. The oblique-rotator model, developed mathematically by Deutsch /1970/, has been applied for the spectral and magnetic variations. In this paper, using Deutsch’s method, the distribution of CrII, EuII, TiII, SrII on the stellar surface is analysed and the relation between the abundance of elements and the magnetic structure is studied. The Laplace and Fourier coefficients for each elements have been computed and also the distribution of the elements at the stellar surface has been drawn by a Sinclair ZX Spectrum personal computer.
A Search for Long-Term Photometric Variability in CP2-Stars
Authors: Hensberge H.
Published: July 2016

Southern bright CP2 stars mentioned in the literature to be constant in light are observed to search for possible variations over months or years. Presently (up to end of April, 1985) four candidate long-period CP2 stars are detected, one of which had already, been noticed in the literature as a slow spectroscopic variable.
Hd 24975: A New Delta Scuti Star? (Or A Mild Ap Star with Short Photometric Variations?)
Authors: Megessier C. , North P. , Burnet M.
Published: July 2016

Looking in the literature for short period variations of Ap stars, we found the puzzling case of HD 24975. Used as a comparison star by Weiss (1978), it had been found then to present variations with a peak-to-peak amplitude of 0.01 in U, B and V with a period of about 45mn, but with no clear correlation between the three passbands.

HD 24975 has the same spectral type A2 as 21 Com which seems to present photometric variations with P ⋍ 31mn and Δ V < 0,02m (Percy, 1973, 1975). Both stars are near the blue edge of the δ Scuti instability strip in the HR diagram. The lack of photo metric data, however, prevented the precise location of HD 24975 from being found on the HR diagram.
Hot Magnetic Stars
Authors: Hunger K.
Published: July 2016

The present discussion of hot magnetic CP stars is restricted to 17000 K < Teff < 30 000 K, the upper limit being the temperature up to which magnetic fields can be observed, the lower limit defining the boundary between He-rich and He-poor stars.

All of the hot magnetics belong to the class of intermediate helium stars which is defined by nH/nHe, < 3 (number ratio, Hunger 1975). Walborn (1983) lists 23 stars of this class, mostly with nH/nHe, ≈ 1, and of spectral type B2 V. Magnetic fields, so far, have been discovered in 7 of them (Borra et al. 1983). All but one of these are spectrum variables, with periods 0.9<P/day<1.7 (except one with P = 9.5 d), (Pedersen, 1979) and with rotational velocities of the order of v sin i ≈ 150 km/s which are compatible with the (P, v sin i)-relation of stars near the main sequence; i.e. these stars are oblique rotators.
Blanketing Hypothesis and Light Variations of HD 27309
Authors: Iliev I.Kh.
Published: July 2016

The influence of variable blanketing on the photometric variations of hot, silicon Ap star HD 27309 has been estimated. Spectrum variations in the visible are not the principal reason for the observed light variability, but flux redistribution from UV into visible fit well the observational data. An reference is made on the fulfillment of the variable blanketing assumptions at least for silicon Ap stars.
The Investigations of Variations in the Depression λ4200, λ5200 of the Magnetic Stars 53 Cam and Beta CrB
Authors: Burnashev V.I. , Malanushenko V.P. , Polosukhina N.S.
Published: July 2016

During many recent years, from 1973, the search for short-term variations in the spectrum of Ap-stars has been carried out at the Crimean Astrophysical Observatory. Some results are presented in the poster dedicated to 53CAM observations. Spectral observations of the magnetic star 53CAM with time resolution of about I min were supplemented by the narrow-band photometrical observations within the framework of the cooperative program of the magnetic stars observations, started in 1979.
Line Spectrum Variations in the Ap Star HD 51418
Authors: Iliev I.Kh. , Barzova I.S.
Published: July 2016

Line spectrum variations in Ap star HD 51418 were studied. The intensities of the Eu II lines wary by about three times. Radial velocity measurements show remarkable variability of the Eu II lines with an amplitude of 16 km/s, but the Sr II and Fe II lines do not show significant changes.
The Most Iron-Deficient Manganese Star HR562
Authors: Ptitsyn D.A. , Ryabchikova T.A.
Published: July 2016

Abundances of 11 elements are determined in the atmosphere of the manganese star HR562 = HD11905 (B8III, Te = 14000 K, log g=3.5). The deficit of iron of 0.9 dex is extreme among HgMn stars. The excess of mercury abundance amounts to 4.8 dex.