bluuebunny/crossref_metadata_2025_split huggingface dataset:
Image Tube Radial Velocities of Southern Stars
Authors: Lu Phillip K. 
Published: July 2016

AbstractRadial velocities have been determined for 243 southern barium and high proper motion stars based on 346 image-tube (IT) spectra. These spectra were obtained using the Yale 1-m telescope at CTIO with a dispersion of 43A/mm near H-gamma. All spectra were widened to 0.3 mm for MK spectral classification. Analysis of the measurements yields the following results:1.Of the 91 spectra scanned and reduced using the Yale PDS and cross-correlation (CC) procedures, the internal standard errors for stars of similar spectral type to the template or standard star are ±12 km/sec.2.Spectra of 130 southern high proper motion stars measured with a PSK-2 and a Grant comparator, the linear least squares solution yielded a mean internal error of ±7.5 km/sec.3.For the 125 IT spectra of southern barium stars scanned using a PDS at KPKO, radial velocities obtained using the linear portion of the s-curve and a Gaussian line fit procedure, the accuracy is about ±5.5 km/sec.4.Using standard stars and some published radial velocities, the comparison has shown that no systematic error exists between this study and those published data.
Mean Stellar Radial, Velocities Catalogue
Authors: Barbier M. 
Published: July 2016

The accumulation of new data requires that the existing catalogues (Wilson 1951 - Evans * 1970, still not completed) be supplemented by a new mean radial velocities catalogue; a need which is particularly pressing for astronomers, especially statisticians.Today, such work cannot be done by one person only, as has been done previously. Therefore¿ in 1976, during the IAU General Assembly at Grenoble, Commission 30 made up a working-group (consisting of J. Andersen, M. Barbier, A. H. Batten, M. Duflot, D. S. Evans, R. Griffin), under my responsibility, with a mandate to examine the possibility of making a new mean radial velocities catalogue using computers, so that the catalogue could regularly be brought up to date. In 1982, at Patras, our working-group submitted the results of its work and proposed the following set of rules to plan their catalogue. Commission 30 asked us to test them. This work has been done at the Marseille Observatory by M. Duflot and myself in collaboration with P. Figon, who worked on the programming for the catalogue.
Pre-White Dwarf Evolution: Up to Planetary Nebulae
Authors: Mazzitelli Italo 
Published: July 2016

AbstractThe main evolutionary phases having some interest for the formation of the remnant white dwarf are discussed, starting from the core helium burning phase, in the attempt of evaluating a theoretical relation between initial main sequence mass and final white dwarf mass. Several difficulties, mainly due (but not only) to uncertainties in the theory of mass loss, have been met, so that only a fiducial bona fide correlation can be drawn. The mass function of population I white dwarfs has probably a secondary maximum at M = 0.9 – 1 Me.
Helium Abundance in the Photospheres of Hot Da White Dwarfs
Authors: Holberg J. B. , Kidder K. , Liebert J. , Wesemael F. 
Published: July 2016

AbstractWe have used optical and UV spectroscopy to determine He abundances and upper limits to He abundances in the photospheres of a selected sample of very hot hydrogen-rich white dwarfs. He abundances in the range log(He/H) -3 to -1.5 are observed in several of these DAs and upper limits of -3 determined for the remainder. In apparent contradiction to the relatively large He abundances inferred from soft X-ray observations for the hot DA G191 B2B, we find no evidence of He in the optical and UV.
Thermonuclear Explosion in Binaries: White Dwarf Helium Star
Authors: Ergma E. , Fedorova A.V. , Khohlov A.M. 
Published: July 2016

AbstractEvolutionary sequences of a binary system consisting of a helium star in the stage of core helium burning and a white dwarf are presented. Different ways of He burning in the envelope of a dwarf are discussed. Incomplete helium burning is discussed with relation to occurence of possible observational features.
Phase Correlated Spectra of Magnetic White Dwarfs
Authors: Bues I. , Pragal M. 
Published: July 2016

AbstractNew photometric and polarimetric observations of the magnetic white dwarfs G 99–37 and G 99–47 are in accordance with a period of 4.117h and 0.97h respectively. Spectra taken at various phases could be correlated and analyzed by model atmosphere technique.
The Nearby Binary, Stein 2051 (G175–34AB)
Authors: Strand K. Aa. , Kallarkal V. V. 
Published: July 2016

AbstractPhotographic observations of the large proper motion binary, Stein 2051, extended over the period 1966–87, do not support that it is a triple system as previously reported (Strand, 1977). The orbital motion is nearly linear over this interval? however, when results of plates from the Vatican Astrographic Zone from 1908–11 are included, a mass ratio is obtained, leading to a mass of 0.50©for the white dwarf component, given the calculated mass of 0.24© for the red dwarf component.
Time Resolved Spectroscopy of AM CVn
Authors: Lázaro C. , Solheim J.-E. , Arévalo M.J. 
Published: July 2016

AbstractThe preliminary results of time resolved spectroscopy of the He White Dwarf system AM CVn are presented. We have searched for spectral variations at different photometric periods. These are found at different time scales although this does not particularly favour any of the searched periods.
Binary, Pulsating, and Irregular Variables Among Planetary Nuclei
Authors: Bond Howard E. , Ciardullo Robin 
Published: July 2016

For the past two years, the authors have been carrying out a program of CCD photometry of planetary-nebula nuclei (PNNs), using the 0.9-m telescopes at Kitt Peak National and Cerro Tololo Inter-American Observatories. The aim of this program is to investigate the variability of PNNs on timescales of minutes to days, in order to search for close binaries and pulsators, as well as unexpected new classes of variable stars.The program represents an extension of the photoelectric photometry of PNNs carried out by Bond and Grauer (1987). Use of the two-dimensional CCD detector allows us to model and subtract the nebulosity surrounding a PNN, in addition to providing exactly simultaneous observations of the PNN and several nearby comparison stars. The latter allow us to compensate for variable atmospheric transparency, permitting accurate differential photometry to be obtained even when the observing conditions are not photometric.
Disk Instabilities in Hubble-Sandage Variables?
Authors: Meyer F. , Meyer-Hofmeister E. 
Published: July 2016

The brightest individual objects in extragalactic nebulae are the Hubble-Sandage variables. They were first investigated by Hubble and Sandage (1953). Observations by Tamman and Sandage (1968) and Rosino and Bianchini (1973) followed. The main characteristics are high luminosity (L/Lʘ ≈ 105), blue color indices, F type spectra and irregular variability.Bath (1979) has suggested that the Hubble-Sandage variables contain an accreting main-sequence star with a Roche Lobe filling companion in a wide binary system. Based on this model we derive theoretical color indices for disks and determine the mass in the disk for different mass accretion rates. Further we discuss an instability of the disk which could explain the change in the color index observed for Var A in M33.
A Note about Multiple Systems of Dense Molecular Clouds
Authors: Vanýsek Peter 
Published: July 2016

AbstractThe space distribution of some small dense clouds with point-like IR sources, resembles the clustering of young OB stars. It can be assumed that such objects contain heavy obscured high-luminosity stars on the ZAMS. From the comparison of infrared and radio data it follows that in typical cases, only one B star is the source of the radiation of the cloud. The total mass of the cloud is of the order of one solar mass. If the individual fragments of the cloud are gravitationally unstable, then in the later stage of the evolution only low-mass stars are formed. One can therefore expect that young OB stars are most frequently accompanied by low-mass pre-Main Sequence stars.
Observational Selection in Spectroscopic Binary Eccentricities
Authors: Staniucha M.S. 
Published: July 2016

AbstractThe discovery-and-identification probability for different shaped orbits of spectroscopic binary stars is estimated. The eccentricity distribution observed in the sample of ~1000 binaries with known orbits and appearing as strongly peaked toward e=0 is corrected for observational selection effects. The resulting e-distribution seems to be flat for e in the range ~0.05-0.6 with some excess of circular (or almost circular) orbits and a deficiency of orbits with e ≲ 0.6.
Ultraviolet Light Curves Of U Geminorum and VW Hydri
Authors: Wu Chi-Chao , Panek R.J. , Holm A.V. , Schiffer F.H. 
Published: July 2016

AbstractUltraviolet light curves have been obtained for the quiescent dwarf novae U Gem and VW Hyi. The amplitude of the hump associated with the accretion hot spot is much smaller in the UV than in the visible. This implies that the bright spot temperature is roughly 12000 K if it is optically thick. A hotter spot would have to be optically thin in the near UV. The flux distribution of U Gem in quiescence cannot be fitted by model spectra of steady state, viscous accretion disks. The absolute luminosity, the flux distribution, and the far UV spectrum suggest that the primary star is visible in the far UV. The optical-UV flux distribution of VW Hyi could be matched roughly by our model accretion disks, but the fitting is poorly constrained due to the uncertainty in its distance.
Numerical Calculations for Accretion Disks in Close Binary Systems
Authors: Hensler G. 
Published: July 2016

AbstractA numerical method for 3D magnetohydrodynamical investigations of accretion disks in close binary systems is presented, which allows for good spatial resolution of structures (hot spot, accretion column). The gas is treated as individual gas cells (pseudo-particles) whose motion is calculated within a grid consisting of one spherical inner part for 3D MHD and two plane outer parts. Viscous interactions of the gas cells are taken into account by a special treatment connected with the grid geometry.We present one result of 2D hydrodynamical calculations for a binary applying the following parameters which are representative for Cataclysmic Variables: M1= 1 Mʘ, r1= 10-2Rʘ, M2= 0.5 Mʘ, p = 0.2 d, M = 10-9Mʘy-1.Column density and radiative flux distributions over the disk are shown and briefly discussed by comparison with the theoretical understanding of these Dwarf Novae drawn from observations.
S Cnc as a Case Study of Classical Algol Evolution
Authors: Awadalla N.S. , Budding E. 
Published: July 2016

AbstractBasic information on empirical determinables for the system S Cnc are reviewed. Whilst the photometric information can be clearly analysed along well known lines, the spectrographic information is far from clear and requires further study, though a semi-detached configuration, at least, can be confidently deduced.The potentially important question of some physical relationship of the variable to the open cluster Praesepe is considered, but the result is in the negative.The evolutionary status of the binary is examined in a general way by making use of some summary formulae, some guidelines for which were taken from previous more general work of Refsdal and Weigert. S Cnc is in good overall agreement with the low mass Case B theoretical mode of binary evolution, and even the absence of a detectable rate of period variation is shown to be not in serious conflict with this picture. Interesting close comparisons with the well known example AS Eri are possible.
The Very Unusual Ultraviolet Spectra of R Arae
Authors: Kondo Yoji , McCluskey George E. 
Published: July 2016

AbstractThe high resolution ultraviolet spectra of the 4.4-day period binary R Arae, observed in 1980 with the International Ultraviolet Explorer (IUE), show that its continuum flux level varied outside of eclipse by more than a factor of two in ten days, and by over 50 percent within a same orbital cycle. The flux level varied non-monotonically at different wavelengths. The resonance lines of Mg II and Si IV exhibited shortward–shifted absorption components near phase 0.4, indicating the presence of a gas stream toward the observer at a velocity of some –450 to –500 km s–1. Our observations of R Arae with the Einstein satellite show it to be an X–ray source.
The Short-Period Non-Contact Binary Systems UU Lyn and GR Tau
Authors: Yamasaki A. , Okazaki A. , Kitamura M. 
Published: July 2016

AbstractTwo binary systems UU Lyn (P = 0d.468) and GR Tau (P = 0d.430) are discussed on the basis of BV photoelectric observations and spectroscopic observations which were made between 1980 and 1981 at the Tokyo Astronomical Observatory. The component stars in both systems are found to be still inside their Roche lobes but very close to them.
Observations of Secular Changes in the Kinematic Model of SS433
Authors: Collins G.W. , Newsom G.H. 
Published: July 2016

AbstractIn this paper we present evidence that several of the defining parameters of the Kinematic Model for SS433 are not constant but rather exhibit long term systematic changes. Recent data confirm the existence of the previously reported decrease in the precessional period. The value for this period change, when combined with the observed change in the period of the synodic spectral variations, implies that the orbital period is not significantly changing on a time scale less than 1000 years.In addition we find mounting evidence for a statistically significant (40) secular change in the cone angle θ at a rate of about -1.5 x 10-3 deg/day. However, t the surprisingly short time scales implied by the observed values of P and θ when combined with estimates of the system age suggest the possible existence of detectable higher time derivatives. This view is supported by the most recent data which suggest a value for P ~ 10-5 (days)-1. It is possible to understand these secular changes in terms of the motions to be expected from an object exhibiting classical precession in response to an external torque.
The Formation of Massive White Dwarfs in Cataclysmic Binaries
Authors: Law Wai-Yuen , Ritter Hans 
Published: July 2016

AbstractIn contrast to the mass spectrum of single white dwarfs which has a single narrow peak at ~0.6 M⊙, the observed mass spectrum of white dwarfs of cataclysmic binaries (CB's) shows a rather uniform distribution of the masses in the range ~0.3 M⊙, to ~1.3 M⊙. The formation of CB's with white dwarfs of less than about 0.8 M⊙ can be understood as the result of a binary evolution according to low mass Case B or Case C with a subsequent spiraling-in in a common envelope. On the other hand the formation of massive white dwarfs of M ≲ 1 M⊙, can be explained as the result of a massive Case B mass transfer yielding a helium star which subsequently undergoes a second Case B mass transfer (so called Case BB evolution). The ultimate product of such an evolution is either a CO-white dwarf with a mass up to the Chandrasekhar limit or a neutron star. The formation of CB's via Case BB evolution requires the binary to undergo at least one, most probably two separate phases of spiraling-in in a common envelope.
A model containing “blobs” for the A ring of Saturn
Authors: Thompson Willian , Blerkom David van , Irvine William 
Published: July 2016

ABSTRACTObservations of the brightness distribution of Saturn’s ring A from four separate years, including specifically the azimuthal variations, are calibrated and interpreted through the use of a scattering model. In this model the A ring is composed of elongated density enhancements (“blobs”) embedded in a ring of uniform density. The blobs are approximated by biaxial ellipsoids. Intensity observations at one tilt angle can be used in the context of the model to predict the intensity at other tilt angles. The analysis shows that there must be matter between blobs characterized by an optical thickness τo≃0.45 and single scattering albedo ωo≃0.70. A rough estimate, based on what appears to be shadowing of one bfob by another, gives the ring area occupied by blobs as 5%.
Solved and unsolved problems in planetary ring dynamics
Authors: Borderies N. , Goldreich P. , Tremaine S. 
Published: July 2016

ABSTRACTWe discuss a number of new ideas related to planetary ring dynamics and apply them to Saturn's rings. The topics are ordered in terms of increasing spatial scale. For simplicity, the ring particles are taken to be identical, smooth, spheres composed of dense and chemically pure ice.
Diffusion of dust around a central body
Authors: Barge P. , Millet J. , Pellat R. 
Published: July 2016

ABSTRACTThe dynamics of particles moving in an external field of force and submitted to a stochastic perturbative force is relevant to a number of astrophysical problems. The Fokker-Planck equation describing the evolution of the distribution function of particles in phase space can be reduced to a diffusion equation through a formalism coming from the quasi-linear theory in plasma physics, (Laval and Pellat, 1974). The diffusion coefficients, expressed in terms of power spectral densities of the fluctuating quantity, are shown to have a resonant behaviour. This aspect of the diffusion and the simplifications due to the formalism could be interesting in the study of planetary rings.
Saturn's E, G and F rings: modulated by the plasma sheet
Authors: Grün E. , Morfill G.E. , Johnson T.V. , Schwehm G.H. 
Published: July 2016

ABSTRACTSaturn's broad E ring, the narrow G ring and the structured and apparently time variable F ring(s), contain many micron and sub-micron sized particles, which make up the “visible” component. These rings (or ring systems) are in direct contact with magnetospheric plasma. Fluctuations in the plasma density and/or mean energy, due to magnetospheric and solar wind processes, may induce stochastic charge variations on the dust particles, which in turn lead to an orbit perturbation and spatial diffusion. It is suggested that the extent of the E ring and the braided, kinky structure of certain portions of the F rings as well as possible time variations are a result of plasma induced electromagnetic perturbations and drag forces. The G ring, in this scenario, requires some form of shepherding and should be akin to the F ring in structure. Sputtering of micron-sized dust particles in the E ring by magnetospheric ions yields lifetimes of 102to 104years. This effect as well as the plasma induced transport processes require an active source for the E ring, probably Enceladus.
Statistical theory of the planet growth
Authors: Hornung P. , Pellat R. 
Published: July 2016

ABSTRACTWe compute analytically the main average parameters &lt;e2&gt;½, &lt;i2&gt;½= β&lt;e2&gt;½necessary for understanding the planet growth. We take into account simultaneously the inelastic hard sphere collisions (including gravitational focusing) and the long distance self gravitational interaction between the planetesimals orbiting around the Sun.
Rendez vous with Saturn's rings
Authors: Nock Kerry T. 
Published: July 2016

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.
Concluding remarks on the planetary rings conference
Authors: Stone E.C. 
Published: July 2016

ABSTRACTIn the past five years ring systems have been discovered around Uranus and Jupiter and a wealth of new data acquired about Saturn’s rings. This vigorous observational program has been accompanied by renewed theoretical interest in ring systems. Although all of these topics have been addressed in papers at this first conference on planetary rings, these concluding remarks are focused on some of the key aspects of Saturn’s rings about which more needs to be understood through further data analysis, calculations, and observations.
The Circumstellar Structure Around Supernovae
Authors: Lundqvist P. , Fransson C. 
Published: July 2016

AbstractThe time dependent ionization and temperature structure of the circumstellar medium around supernovae has been calculated, in order to interpret recent supernova radio observations. For a stellar wind origin of the circumstellar medium, we relate the time of radio turn-on to the progenitor mass loss rate. We also show that large column densities for the UV resonance lines are expected. The results are applied to SN 1979c, SN 1980k and SN 1987A.
Analysis of the Spectrum of the Type V Supernova SN1986J
Authors: Hamilton A.J.S. , Vacca W.D. , Pradhan A.K. , Rupen M. P. , Gunn J. E. , Schneider D. P. 
Published: July 2016

AbstractThe supernova SN1986j resembles the prototypical Type V supernova SN1961v in the relatively slow ∼1000km/s expansion velocity, the slow light curve, and also in the Hα dominated spectrum. The optical spectrum is similar to the spectra of some novae, and some OB stars with massive winds, being characteristic of a nebular plasma at about 1010cm−3 and 104K. What makes SN1986j exceptional is its tremendous radio luminosity, the brightest radio supernova observed to date. The radio emission indicates the presence of a massive circumstellar wind, with which the SN ejecta are now colliding. Since the cooling time of the optically emitting gas is about an hour, a heat source is required to power the light curve. Shocks moving back into the ejecta offer a natural heat source, and account quantitatively for the observed luminosity and spectral character of SN1986j. The large Hα/Hβ ratio is attributed to trapping of Ly α, which pumps the n = 2 level of hydrogen, causing a finite optical depth in Balmer lines, and converting Hβ to Pα and Hα. The ratio of the derived H(n = 2) density and column density yields a size for the Hα emitting region consistent with the thickness of a cooling shock, but less than 10−7 of the 1017cm VLBI size. An important discriminant between shock models and photoionization models of the spectrum is that shocks predict Lyman 2-photon emission. The mass of the optically emitting material in SN1986j is about 1M⊙, substantially less than the 2000 M⊙ argued in the case of SN1961v by Utrobin. However, there may be, and probably is, considerably more unobserved ejecta. This material should reveal itself as the remnant of SN1986j continues to evolve.
Nova GK Persei – A Miniature Supernova Remnant?
Authors: Seaquist E.R. , Frail D.A. , Bode M.F. , Roberts J.A. , Whittet D.C.B. , Evans A. , Albinson J.S. 
Published: July 2016

AbstractWe present radio and optical images of the shell-like remnant of the 1901 outburst of Nova GK Persei. The behaviour of this object is remarkably similar to supernova remnants. The synchrotron radiation-emitting shell is polarized with the magnetic field oriented radially, as in young SNR’s. This similarity plus extensive data we have acquired on the expansion and the interstellar environment of GK Per indicate that the nova shell is colliding with ambient gas whose density is substantially higher than the ISM.Furthermore, there is strong evidence that the ambient gas is circumstellar rather than interstellar, and that this material is the shell of an ancient planetary nebula associated with the white dwarf companion of GK Per.