bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractOn 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 0.34In 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 %.
The q-Log P Distribution of Classical Algols
Authors: Budding Edwin 
Published: July 2016

AbstractData 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

AbstractAn 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.
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).
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.
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

AbstractLaser 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:whereIH is the hydrogen ionization potential and me is the electron mass.
The Transient Highly Excited Solar Flare Plasma
Authors: De Feiter L. D. 
Published: July 2016

AbstractRecent 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

ABSTRACTThe 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

AbstractWe 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

ABSTRACTThe 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

AbstractWe 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.
Polarized Radiation from AM Herculis Stars
Authors: Barrett P. E. , Chanmugam G. 
Published: July 2016

ABSTRACTCalculations 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

ABSTRACTThe 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

AbstractThe 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

AbstractThe 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 bynHe/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

AbstractThe 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.
The Origin and Evolution of Helium-Rich White Dwarfs
Authors: Liebert James 
Published: July 2016

AbstractWhite 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

AbstractThe 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

AbstractIn 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.
Application of Deutsch’S Method for 53 Cam
Authors: Vincze I. 
Published: July 2016

Abstract53 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

AbstractSouthern 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

AbstractThe 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.
Line Spectrum Variations in the Ap Star HD 51418
Authors: Iliev I.Kh. , Barzova I.S. 
Published: July 2016

AbstractLine 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

AbstractAbundances 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.