bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cloud Formation in a Galactic Fountain Resulting from Rayleigh-Taylor Instabilities
Authors: Berry D.L. , de Avillez M.A. , Kahn F.D. 
Published: July 2016

AbstractIntermediate and high velocity clouds are produced in a Galactic fountain as a result of Rayleigh-Taylor instabilities that grow at the interface separating the cool descending gas and the hot ascending gas within the fountain flow. It is proposed here that there is no need to introduce any initial perturbation to the system in order to trigger such instabilities. They will arise naturally as a result of the difference in the adiabatic parameters above and below the interface. A three-dimensional study of the unstable layer and the resulting cloud formation is presented.
Radio and Polarization Properties in the Disk and Halo of Edge-On Spirals
Authors: Dumke M. , Krause M. 
Published: July 2016

AbstractWe have observed a small sample of edge-on galaxies in total and linearly polarized radio continuum emission at λ6.2 cm, using the Effelsberg 100m telescope. The resulting maps were combined with available VLA data in order to obtain high-sensitivity radio images which have a sufficient angular resolution and do not suffer from the so-called missing-spacing problem.From an analysis of these images (together with 2.8cm and 20cm data) we get the following results: 1. The radio emission perpendicular to the plane can be described by a two-component exponential distribution with scale-heights of ~ 300 pc and ~ 1.8 kpc, independently of the star forming activity and interaction state. 2. In the disk of the non-interacting galaxies of our sample the thermal fraction of the emission seems to be higher than usually deduced from observations of face-on galaxies. 3. The fractional polarization p increases with increasing galactic height, reaches a maximum at h ~ 1 – 3 kpc, and decreases again. In general p is lower in actively star forming galaxies.
Anisotropic Outflows from LBVs and Ofpe/WN9 Stars
Authors: Nota Antonella 
Published: July 2016

AbstractIn the past decade, the increasing sophistication of the high resolution techniques from the ground, and the advent of HST have allowed a systematic study of the outflows around evolved massive stars. It has been established (Nota & Clampin 1997) that most LBVs and Ofpe/WN9 stars are surrounded by associated circumstellar nebulae which have been ejected in some previous phase of their evolution. These nebulae are the fossil record of the interactions of previous winds and of the violent ejections in which the stars most likely have shed their outer layers. The study of the morphology, kinematics and chemical composition of the ejected material has allowed us to gain deep insight in the ejection and shaping mechanism.
Extremely Luminous Atmospheres
Authors: Shaviv Nir J. 
Published: July 2016

AbstractWe present the effects that inhomogeneities have on radiating atmospheres. It is shown that nonuniformities in a medium induce a reduction of the effective opacity which subsequently increases the Eddington Luminosity. The most striking effect however that arises from the dependence of the opacity on the inhomogeneities, is the possibility of a phase transition, where the atmosphere energetically favors exciting horizontally propagating waves due to large fluxes.
The Effects of Magnetic Fields on the Winds from Luminous Hot Stars
Authors: Cassinelli Joseph P. , Miller Nathan A. 
Published: July 2016

AbstractHere we explore three types of models in which the combination of magnetic fields with line driving forces leads to faster winds than line forces alone. The fields can change the flow geometry; they can couple with rotation and transmit angular momentum; and they can carry transverse Alfvén waves. All three can lead to a deposition of momentum beyond the critical point and accelerate winds. Some history of the attempts to use magnetic fields to understand hot star winds is discussed and several new models for magnetic rotator B[e] winds are presented.
O-Star Wind Variability in the Ultraviolet and Optical Range
Authors: Kaper Lex 
Published: July 2016

AbstractVariability is a fundamental property of O-star winds. One of the major breakthroughs in this field of research has been the recognition that wind variability is cyclical in nature. This suggests that stellar rotation is an important piece in the unsolved puzzle of the wind-variability mechanism. The current idea is that Corotating Interacting Regions (CIRs) are responsible for the observed wind variability. These conclusions are based on detailed and extensive monitoring of ultraviolet resonance lines formed throughout the stellar wind, and subordinate lines like Hα which probe the regions close to the star.
Dusty LBV Nebulae: Tracing the Mass Loss History of the Most Massive Stars
Authors: Waters Laurens B.F.M. , Voors Robert H.M. , Morris Patrick W. , Trams Norman R. , de Koter Alex , Lamers Henny J.G.L.M. 
Published: July 2016

AbstractWe present spectra obtained with the Infared Space Observatory (ISO) of the dust shells surrounding several Luminous Blue Variables (LBVs), both in our galaxy and in the LMC. The 20-45 μm spectra of R71, AG Car and Wra 751 show prominent emission features from crystalline silicates. The composition of the crystalline silicates in LBV dust shells is compared to that found in other types of objects, such as (post)-AGB stars and red supergiants (RSG). Both Wra 751 and AG Car have a high ratio of pyroxenes to olivines. This suggests that the grains in both stars experienced very similar processing, but that this processing has lead to a higher abundance of pyroxenes compared to RSG. The dust composition of the three LBVs discussed here suggests dust formation in a cool outflow not unlike those of RSG.
Do Average Hamiltonians Exist?
Authors: Ferraz-Mello S. 
Published: July 2016

AbstractThe word “average” and its variations became popular in the sixties and implicitly carried the idea that “averaging” methods lead to “average” Hamiltonians. However, given the Hamiltonian H = H0(J) + ϵR(θ,J),(ϵ ≪ 1), the problem of transforming it into a new Hamiltonian H* (J*) (dependent only on the new actions J*), through a canonical transformation given by zero-average trigonometrical series has no general solution at orders higher than the first.
The Separatrix Algorithmic Map: Application to The Spin-Orbit Motion
Authors: Shevchenko Ivan I. 
Published: July 2016

AbstractThe planar rotational motion of a non-symmetric satellite in an elliptic orbit is considered. A two-dimensional map is constructed, describing the motion in a vicinity of the separatrix of the synchronous spin-orbit resonance. This map is a generalization of Chirikov’s separatrix map, in the sense that the asymmetry of perturbation is taken into account. Phase portraits of the generalized map perfectly reproduce well-known examples of surfaces of section (first computed by Wisdom et al. (Wisdom et al., 1984), Wisdom (Wisdom, 1987)) of the phase space of spin-orbit coupling for non-symmetric natural satellites. Moreover, it provides a straightforward analytical description of the phase space: analysis of properties of the map allows one to precalculate, by means of compact analytical relations, the locations of resonances and chaos borders, the emergence of marginal resonances, and even to describe bifurcations of the synchronous resonance’s center, though far from the separatrix.
Mean Motion Resonances in The Asteroid Belt
Authors: Nesvorný D. , Morbidelli A. 
Published: July 2016

The Kirkwood gaps in the main asteroidal belt (2 – 3.5 AU) coincide with the mean motion resonances with Jupiter (4/1, 3/1, 5/2, 7/3, 2/1). Similarly, several narrower gaps are observed in the outer asteroid belt (3.5 – 4 AU) at places of 11/6, 9/5, 7/4 and 5/3 Jovian resonances (Holman and Murray 1996). As it is now generally accepted, the formation and preservation of these gaps is due to the chaos of the resonant space and efficient ejection of the primordial and collisionaly injected bodies towards high eccentricities and planet-crossing orbits.The Jovian mean motion resonances are not the most important in what concerns the chaos of the observed (i.e. remaining) asteroid population. It was estimated by Šidlichovský and Nesvorný (1998) that about 40% of known objects have the Lyapunov time less than 105 years. It was later found (Nesvorný and Morbidelli 1998, 1999; Morbidelli and Nesvorný 1999) that the resonances responsible for this chaos are, in decreasing order of importance: 1) three-body resonances with Jupiter and Saturn, 2) exterior resonances with Mars, 3) moderate order Jovian resonances, and 4) three-body resonances with Mars and Jupiter.
A Necessary Condition to the Simultaneous Correction of Celestial Reference Frames and Minor Planets Orbital Elements
Authors: Martínez Usó M.J. , Marco Castillo F. , López Ortí J.A. 
Published: July 2016

AbstractIn order to obtain corrections to orbital elements of minor planets and to determine parameters of rotation of a reference frame, a geometrical model with restrictions in the declination, longitude of the ascending node and argument of the perihelion to minimize a residual function involving all named parameters was presented (Marco et al., 1996, 1997). On the other hand, such rotational model of correction should not modify the semiaxis, eccentricity nor the mean anomaly, so new restrictions on these parameters seem to be necessary. These conditions should reflect the invariability in the size of the orbit and they should be included in the model to complete a consistent set of restrictions.
Observations and Interpretation of Cataclysmic Variables
Authors: Warner Brian 
Published: July 2016

AbstractRecent observations pertaining to the structure of cataclysmic variables (CVs) are reviewed. Detection of X-rays from CVs, and their behaviour during outbursts, has opened new possibilities of studying the innermost regions of accretion discs. Studies of rapid oscillations continue to be an important source of information (and problems) on the white dwarf and accretion disc.Several major reviews of the properties of cataclysmic variables have appeared in recent years (Gorbatsky 1975; Warner 1976; Robinson 1976; Wolf 1977; Payne-Gaposchkin 1977a, b; Mallama and Trimble 1978; Gallagher and Starrfield 1978) so there would be no justification at this date in another survey of the entire field of CVs. This review is therefore confined to a discussion of some of the recent observations and their relevance to the problems of understanding the structure and mechanisms in novae and related stars. I have omitted AM Herculis stars as they are discussed by Tapia later in this Conference.
VW Hydri: Photo-Electric Observations during the 1977 May Supermaximum
Authors: Marino B. F. , Walker W.S.G. 
Published: July 2016

SummaryPhoto-electric observations of VW Hydri during the 1977 May supermaximum are presented in the context of an observational model in which supermaxima are triggered by a normal outburst. Two new hump features are identified. A possible explanation of the various superhump types is suggested.
Spectroscopic Observations of Dwarf Novae
Authors: Whelan J.A.J. , Rayne M.W. , Brunt C.C. 
Published: July 2016

Abstract.Dwarf novae spectroscopic work is briefly reviewed and the radiation emitted by the components of the system is discussed. The reasons why the broad, shallow absorption lines arise in the disc, and not in the white dwarf, are assembled. Results are presented for: (a) outburst and quiescent spectra of V436 Cen and VW Hyi; and (b) Z Cha throughout its binary orbit.
Stellar Magnetism: Some Observable, Expected and Suggested Effects of Magnetic Field in Eruptive Varaibles
Authors: Gershberg R.E. 
Published: July 2016

AbstractConsideration of main stellar-statistical and astrophysical features of th UV Cet-type flare stars leads to a conclusion that the evolution of these variables, as well as other stars, is determined by their masses and chemical composition; a third essential evolution factor is the magnetic field which is responsible for all manifestations of flare activity.The main physical features of the T Tau-type stars can be understood in the framework of a hypothesis that these stars have large scale magnetic fields. Their strengths are close to a critical level at which the magnetic field and subphotospheric convection begin to interact strongly causing a significant decrease of the photospheric brightness, as in sunspots. Physical and genetic similarities of the UV Cet and T Tau stars are discussed withinth the framework of the idea of the essential role of stellar magnetism.
A Search for TcO in S-Type Long Period Variables
Authors: Davis-Locanthi D. 
Published: July 2016

There are still several unidentified bands in S -star spectra, especially at minimum light. Since most S spectra exhibit strong Tel lines, compounds with 0, N, and H might be expected to form in-S star atmospheres. Although much oxygen is already bound with carbon, titanium, and zirconium, to mention a few known compounds, there might also be enough TcO to produce visible absorption.The spectrum of TcO was, however, unknown until recently (Cherniawsky, 1977). After considerable experimentation with the related spectra of MnO and ReO, Tatum and Cherniawsky succeeded in producing from ammonium pertechnate, NH4TcO4, a molecular spectrum in the 500-720 nm. region. which they believe is due to TcO. Unfortunately, like ReO, this spectrum has a strong continuum. Still, more than a dozen bandheads show on their plates.
A New Approach to the Determination of the Intrintic Colours of the Cepheid Variable Stars
Authors: Kron Gerald E. , Roach Franklin E. 
Published: July 2016

SummaryIntrinsic colours have been determined for 247 of the 275 variable stars listed in the “Catalogue of the Light and Colour Curves of Cepheids in the UBV System” by N. Nikolov. Algorithms for computing intrinsic colour are derived from 59 standard stars. The intrinsic colours of the standards were derived from four sets of data from colour excesses deemed reliable in four references. The colours of the standard stars indicate a need for revival of Eggen’s concept of discretee classes of Cepheid Variables. A new principle of least reddening is used to improve the accuracy of the intrinsic colours of normal supergiants, where these are needed, and to test our derived colour excesses for the 247 Cepheids.
Production of New and Revised A.A.V.S.O. Charts
Authors: Ford Clinton B. 
Published: July 2016

A “new charts program” for the Americal Association of Variable Star Observers was instigated in 1966 via the gift to the Association of the complete variable star observing records, charts, photographs, etc. of the late Prof. Charles P. Olivier of the University of Pennsylvania (USA). Adequate material covering about 60 variables, not previously charted by the AAVSO, was included in this original data, and was suitably charted in reproducible standard format.Since 1966, much additional information has been assembled from other sources, three Catalogs have been issued which list the new or revised charts produced, and which specify how copies of same may be obtained. The latest such Catalog is dated June 1978, and lists 670 different charts covering a total of 611 variables none of which was charted in reproducible standard form previous to 1966.
The Eclipsing Binary WX Eridani
Authors: Sarma M.B.K. , Abhankar K.D. 
Published: July 2016

AbstractThe Algol-type eclipsing binary WX Eridani was observed on 21 nights on the 48-inch telescope of the Japal-Rangapur Observatory during 1973-75 in B and V colours. An improved period of P = 0.82327038 days was obtained from the analysis of the times of five primary minima. An absorption feature between phase angles 50-80, 100-130, 230-260 and 280-310 was present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with primary to be transit and secondary, an occultation. Elements derived from the solution of the light curve using Russel-Merrill method are given. From comparison of the fractional radii with Roche lobes, it is concluded that none of the components have filled their respective lobes but the primary star seems to be evolving. The spectral type of the primary component was estimated to be F3 and is found to be pulsating with two periods equal to one-fifth and one-sixth of the orbital period.
Photoelectric astrometry: a comparison of methods for precise image location
Authors: Lindegren L. 
Published: July 2016

AbstractSeveral techniques for obtaining the precise location of a noisy image (of a star, spectral line, solar limb, etc.) are described by means of characteristic “weighting functions”. The imprecision of an image location estimate can be expressed in terms of the weighting function and the image shape and noise covariance. It is limited by the intrinsic imprecision of the image, which is attained with an optimum weighting function, computable from the image characteristics. The hypothetical optimum method is compared with some commonly used location methods, such as computing the median or centre of gravity, least-squares fitting and cross correlating, and hardware techniques including the quadrant detector and rotating knife-edge. One- and two-dimensional Gaussian images are considered as well as diffraction and seeing images. The general results apply also to photographic astrometry, measurement of radial velocities, timing of pulses, etc.
Accuracy of binary star speckle interferometry
Authors: McAlister H. A. 
Published: July 2016

AbstractNearly 400 speckle interferometric observations of binary stars with separations between 0033 to 325 obtained with the 4 meter Mayall telescope at Kitt Peak have been analyzed for accidental and systematic errors in order to determine the reliability of the error estimates assigned to single measurements and to develop schemes for correcting for possible systematic effects. The calibration technique currently in use limits the accuracy to ±0.6% of the angular separation and to ±02 in position angle. Comparison of 101 observations to published orbits of high quality gives mean residuals and r.m.s. errors of &lt;Δθ&gt; = -00005±00072 and &lt;Δρ&gt; = 00051±0158. Small systematic errors can be introduced into separation measurements unless the spatial frequency power spectrum for a single, unresolved star is subtracted from the two dimensional power spectra for binary stars. Residuals to published orbits have been compared to magnitude differences and angular separations in order to search for systematic dependences on these parameters. It is generally concluded that the published error estimates for the author’s speckle observations are realistic estimates of their accuracies.
High Luminosity F-K Stars Motions and Hα Emissions
Authors: Smolinski J. , Climenhaga J.L. , Harris B.L. 
Published: July 2016

AbstractChanges and differences in radial velocities between neutral and ionized metals have been found for three F5-type supergiants: HD 231195, HD 10494, and HD 17971. Fifteen high dispersion coudé spectrograms (6 Å/mm) were used and 33 to 165 lines were measured on each. Semi-regular time variations up to about 8 km s-1 in radial velocity have been found. In addition, Hα line profiles for 8 high luminosity F-K stars have been analyzed. All of the stars show Ha emissions, variable in time, which is probably a common phenomenon in very luminous stars. Metallic emission lines with low excitation potentials, in particular the Ca I 6572.8 and the Fe I 6574.2 lines, are present in 5 of these stars.
Small-Scale Versus Large Scale Motions in the Solar Atmosphere Derived from A Non-Lte Calculation of Multiplet 38 of Ti I
Authors: Cayrel R. , Dumont S. , Martin P. 
Published: July 2016

AbstractA non-LTE computation of multiplet 38 of Ti I (11 lines) has been undertaken in order to determine small and large scale unresolved motions contributing to the Doppler broadening of solar lines at the centre of the disk (vertical motions) and at the edge of the disk (horizontal motions).The abundance of Titanium and the total Doppler velocity (all scales) are determined by fitting observed and computed profiles of weak unsaturated lines (W < 12 mÅ) of the multiplet. Then saturated lines having the same lower level as the weak lines are computed for a variety of partitions of the total kinetic energy between the small scale and the large scale modes going from 0% small scale to 100% small scale. Oscillator strengths with internal accuracies of about 2% from Wahling (1977) have been used. The location of the observed profile (taken from Delbouille et al. for the centre of the disk and from Brault and Testerman, KPNO for μ 0.2) among the computed profiles yields the partition of the energy between the two modes.The computations done so far with 4 levels and continuum give less than 20% of the energy in the small scale mode. Further computations with more levels are needed to establish this ratio with better accuracy. The total energy for vertical motions has a root square velocity of about 1.4 km/sec whereas the same quantity is 2.2 km/sec for horizontal motions.
Summary
Authors: Böhm-Vitense Erika 
Published: July 2016

AbstractLet me start by saying that we have heard some excellent review papers and I doubt very much that I can contribute much of importance in addition to what we have heard already.1 also wish to apologize to all those who have made important contributions during this meeting and who will not be mentioned in this 30-minute summary. If I wanted to mention everybody I would just have enough time to read the program.
Collapse of Accreting White Dwarf to Form a Neutron Star
Authors: Nomoto Ken’ichi , Miyaji Shigeki , Sugimoto Daiichiro , Yokoi Koichi 
Published: July 2016

AbstractIn a close binary system with a primary star in the mass range 8-12 M⊙, the primary star leaves a white dwarf composed of 16O, 20Ne, and 24Mg as a result of mass exchange. When the companion star, fills its Roche lobe, overflowing matter accretes onto the white dwarf. We have computed the evolution of such an accreting O-Ne-Mg white dwarf and found that electron captures on 24Mg and 20Ne trigger the collapse when the mass reaches 1.38 M⊙. As a result of the collapse, oxygen begins to deflagrate but the effects of electron captures dominate over the oxygen deflagration. The white dwarf collapses to form a neutron star.
IUE Observations of White Dwarfs and Hot Subdwarfs
Authors: Oke J. B. 
Published: July 2016

The International Ultraviolet Explorer (IUE) has been used by Greenstein and Oke to obtain low resolution spectra from 1150 to 3200 Å of a selection of white dwarfs and hot subdwarfs.The observations can be converted to absolute fluxes so that, by including energy distributions measured with the multichannel spectrometer on the Hale telescope, fluxes can be derived between 1150 and 11000 Å. The IUE absolute fluxes show erratic level shifts of up to 20 percent and probably also smaller changes in the slope. These shifts are probably associated with the level of the radiation induced background coupled with uncertainties in the calibration of the non-linear detectors. In many cases, these anomalies in the fluxes are obvious, but they do decrease the accuracy with which temperatures and gravities can be determined.