bluuebunny/crossref_metadata_2025_split huggingface dataset:
Line-Driven Ablation by External Irradiation
Authors: Gayley Kenneth G. , Owocki Stanley P. , Cranmer Steven R. 
Published: July 2016

AbstractThe Sobolev approximation for supersonic flows creates an effective opacity distribution that is nonisotropic, because the line-of-sight velocity gradient is different in different directions. To better understand the importance of this phenomenon in a simplified geometry, we consider line-driven flows in the plane-parallel zero-sound-speed limit, and solve for the wind driven by radiation with an arbitrary angular distribution. One conclusion, surprising at first glance, is that the acceleration component normal to the surface is independent of both the strength and angular profile of the driving radiation field. The flow tilt and overall mass-loss rate do depend on the character of the radiation field. Also interesting is that mass loss through a surface may be generated or enhanced by irradiation that originates above the surface.
Disks formed by Rotation Induced Bi-stability
Authors: Lamers Henny J.G.L.M. , Vink Jorick S. , de Koter Alex , Cassinelli Joseph P. 
Published: July 2016

AbstractWe discuss the evidence for the existence of bi-stable stellar winds of early type stars, both theoretically and observationally. The ratio between the terminal wind velocity and the escape velocity drops steeply from about 2.6 for stars with Teff > 21 000 K to about 1.3 at Teff < 21 000 K. This is the bi-stability jump, which is due to a change in the ionization of the wind and in the wind driving lines. The mass loss rate increases across the jump by about a factor 2 to 5 from the hotter to the cooler stars. The mass flux from rapidly rotating stars can also show the bi-stability jump at some lattitude between the pole and the equator, with a slow high density wind in the equatorial region and a faster low density wind from the poles. This might explain the disks of rapidly rotating B[e] stars, formed by the Rotation Induced Bi-stability mechanism. We discuss the RIB mechanism and its properties. We also describe some future improvements of the model.
X-Ray Emission from Magnetically Confined Winds
Authors: Babel Jacques 
Published: July 2016

AbstractWe consider the effect of large scale magnetic fields on the circumstellar environment of hot stars. In these stars, magnetic fields of order of 100 G lead to magnetically confined wind shocks (MCWS) and then to the existence of large X-ray emitting region. MCWS lead also to the presence of corotating cooling disks around hot stars.We discuss the case of θ1 Ori C, which is perhaps the hottest analog to Bp stars and consider the effect from rotation and instabilities. We finally discuss the case of the Herbig Ae-Be HD 104237 and show that MCWS might also explain the X-ray emission from this star.
On the Variable Winds of BA Supergiants
Authors: Chentsov Eugene 
Published: July 2016

AbstractThe manifestation of instability and nonhomogeneity of the atmospheres and winds of β Ori, HD 168607, 6 Cas and other highly luminous B7–A3 stars are considered on the basis of visible and near-infrared spectra obtained with CCD–echelle spectrometers of the 1–m and 6–m telescopes SAO RAS. Changes in the profile shapes, radial velocities and differential shifts of lines create an impression that unstable disk– or ring–shaped structures may exist at the wind bases of super-giants such as β Ori. In the process of destruction they occasionally produce more or less radial flows of escaping and infalling gas. It looks that, as the luminosity increased, the geometry and kinematics of the wind simplify. The wind becomes more symmetrical, the sings of compression diappear and even in the lower layers steady (at least over an interval of several years), although unstable expansion is observable.
Spectral Analyses of Wolf-Rayet Stars: The Impact of Clumping
Authors: Hamann Wolf-Rainer , Koesterke Lars 
Published: July 2016

AbstractInhomogeneities are accounted for in our non-LTE stellar wind models in a first-order approximation. When applied for spectral analyses, clumpy models yield lower mass-loss rates than homogeneous models, while other parameters are not affected. For representative WR stars, we determine the density contrast from the electron-scattering line wings and obtain mass-loss rate reductions by a factor of two, typically.
Evidence for Wind Anisotropies from Dust Formation by Wolf-Rayet Stars
Authors: Williams Peredur M. 
Published: July 2016

AbstractThe formation and survival of dust around stars requires a physical environment very different from that believed to hold anywhere in a Wolf-Rayet stellar wind. The observed facts of dust formation by Wolf-Rayet stars force the conclusion that their winds are not homogeneous. They also allow us to deduce the types of inhomogeneity, including clumps and large-scale high-density wakes produced in colliding-wind binaries, that allow the formation of dust.
Impact of The Quadrupole Moment of The Sun on The Dynamics of The Earth-Moon System
Authors: Bois E. , Girard J.F. 
Published: July 2016

AbstractRange of values of the Sun’s mass quadrupole moment of coefficient J2 arising both from experimental and theoretical determinations enlarge across literature on two orders of magnitude, from around 10−7 until to 10−5. The accurate knowledge of the Moon’s physical librations, for which the Lunar Laser Ranging data reach an outstanding precision level, prove to be appropriate to reduce the interval of J2 values by giving an upper bound of J2. A solar quadrupole moment as high as 1.1 10−5 given either from the upper bounds of the error bars of the observations, or from the Roche’s theory, is not compatible with the knowledge of the lunar librations accurately modeled and observed with the LLR experiment The suitable values of J2 have to be smaller than 3.0 10−6.As a consequence, this upper bound of 3.0 10−6 is accepted to study the impact of the Sun’s quadrupole moment of mass on the dynamics of the Earth-Moon system. Such an effect (with J2 = 5.5 ± 1.3 × 10−6) has been already tested in 1983 by Campbell & Moffat using analytical approximate equations, and thus for the orbits of Mercury, Venus, the Earth and Icarus. The approximate equations are no longer sufficient compared with present observational data and exact equations are required. As if to compute the effect on the lunar librations, we have used our BJV relativistic model of solar system integration including the spin-orbit coupled motion of the Moon. The model is solved by numerical integration. The BJV model stems from general relativity by using the DSX formalism for purposes of celestial mechanics when it is about to deal with a system of n extended, weakly self-gravitating, rotating and deformable bodies in mutual interactions.The resulting effects on the orbital elements of the Earth have been computed and plotted over 160 and 1600 years. The impact of the quadrupole moment of the Sun on the Earth’s orbital motion is mainly characterized by variations of , and Ė. As a consequence, the Sun’s quadrupole moment of mass could play a sensible role over long time periods of integration of solar system models.
A Dynamical Survey of Inner Solar System Asteroids
Authors: Murison Marc A. 
Published: July 2016

AbstractResults from a numerical integration survey of all 179 currently-known inner solar system asteroids with a ≤ aMars, q ≥ aMercury are presented. A surprising number of asteroids are currently in, or very near, mean-motion resonances with Mercury, Venus, Earth, or Mars. Some of the resonance associations are of high order. Most of the resonance associations are relatively short-lived, with the asteroids wandering in and out of resonance on timescales of hundreds to several thousand years.
Perturbations of Small Moons Orbits due to their rotation: The Model Problem
Authors: Goździewski K. , A.J. Maciejewski  
Published: July 2016

We consider here the spin—orbit coupling influence on the relative orbital motion of two bodies interacting gravitationally. We assume that one of the bodies is spherically symmetric and the other possesses a plane of dynamical symmetry. In the full non-linear settings, this problem permits coplanar motion when the mass center of the spherically symmetric body moves in the plane. We used this simple model for a qualitative estimation of the changes of the relative orbit in two cases: A) the Sun-asteroid case (the fast rotating rigid body), B) a small satellite of a big planet in resonant rotation.The motion is described in the rigid body fixed frame. An appropriate change of physical units (Goźdiewski,1998a) leads to nondimensional dynamical variables and parameters. After that the Hamiltonian of the problem, written in polar variables, is the followingwhere (I1, I2, I3) are the principal moments of inertia, (r, φ) are the relative polar coordinates of the point mass in the body frame, (Pr, pφ) are the canonical momenta, (G3 represents the constant of total angular momentum, ε = (ro/r)2, and ro is the mean radius of the body.
Modelling Very-High-Eccentricity Asteroidal Librations with the Andoyer Hamiltonian
Authors: Simula A. , Ferraz-Mello S. , Giordano C. 
Published: July 2016

High-eccentricity asteroidal librations are modelled using the high-eccentricity non-planar asymmetric expansion (Roiget al1997). This second-degree expansion gives us the potential of the perturbing forces acting on a resonant asteroid in a first order resonance in explicit form, as a quadratic polynomial in the canonical non-singular variables. Secular and short periodic perturbations are introduced in the model, giving a more realistic description of the dynamics.The reducing Sessin’s transformation (Sessin, 1981; Sessin & Ferraz-Mello, 1984) is used to include the main effect of Jupiter’s ecc entricity in the main part of the Hamiltonian. It leads to an integrable first-order approximation known as the second fundamental model for resonance (Henrard & Lemaitre 1983) or Andoyer Hamiltonian (Andoyer 1903).
HST-FGS Astrometry of the Low Mass Binary L722-22
Authors: Taff L.G. , Hershey John L. 
Published: July 2016

The M dwarf L722-22 (= LHS 1047) was discovered to be a binary system by Ianna 20 years ago. The analysis of the ground- based data indicated a mass 0.06M⊙ for the secondary. This is below the nominal stellar mass limit of 0.08M⊙. The importance of potential “brown-dwarf” candidates, and the fact that the masses of both components place them near the end of the main sequence, made this system a prime object for further, intensive, study.This close (separation 0."3), faint (V = 11.m5, 14.m4) binary was near the limit for ground-based work. The residuals of an individual night’s photographic data were typically at the 50% level. Also, the photographic images are completely blended. The few one-dimensional speckle data points yielded a merged, asymmetric image profile. Finally, this system is too faint for HIPPARCOS. Our proposal for Hubble Space Telescope Fine Guidance Sensor (FGS) observing was approved in 1992.
Moon’s Planetary Perturbations
Authors: Bidart P. , Chapront J. 
Published: July 2016

In ELP, the computation of planetary perturbations is about 20 years old. A better knowledge of lunar and planetary parameters, new planetary solutions under construction and progresses in numerical tools, are factors that should contribute to their improvements. The construction of planetary perturbations takes widely its inspiration from Brown’s method. In a first step, we only consider the main problem (Earth, Moon, and Sun with a Keplerian motion). The solution of the main problem is actually of a high precision and is used as a reference (Chapront-Touzé, 1980). This solution is expressed in Fourier series of the 4 Delaunay arguments, with numerical coefficients, and partials with respect to integration constants.The method based on the variation of arbitrary constants is described in (M.Chapront-Touzé, J.Chapront, 1980). Equations of Moon’s motion are written in a rotating frame where the reference plane is the mean ecliptic. In this frame, the absolutec acceleration is expressed by means of disturbing forces acting on the Moon, by the Sun, the Earth and a planet. It is the gradient of F which can be divided into several components: Fc related to the main problem, FD and FI giving rise to direct and indirect planetary perturbations.
Dynamics of Fictitious Earth’s Satellites with Possible Past Values of the Ecliptic
Authors: Callegari N. , Yokoyama T. , Marinho E.P. 
Published: July 2016

AbstractAccording to many authors, there is no reason to believe that inner planets never had satellites in the past. Indeed, Alfvén and Arrhenius (1972), Burns (1973), Ward and Reid (1973), etc, explain their disappearance using essentially tidal effects which cause secular variations in the semimajor axes. Here, taking into account only gravitational forces, we show that the extinction or the non existence of Earth’s satellites could also be related to some strong instabilities which increase the eccentricities e to prohibitive values.
An Intermediary Periodic Orbit for Hyperion
Authors: Stellmacher I. 
Published: July 2016

AbstractWe have seen (Stellmacher, 1996) that the long-period terms for Hyperion’s motion are very well represented by a second kind and second genius periodic orbit, after Poincaré’s classification.We have shown how to construct such an orbit with, as only data, the observed periods, which characterise the resonance of the Titan-Hyperion couple, and the Titan’s motion which is an elliptical one. The physical quantities as the masses and the J2 term of Saturn’s flattening are given. We will present the results that we obtained, and compare them with those that other authors obtained by fitting the series to the observations.
Study of the Normal Variational Equation in an Homogeneous Field of Degree Five
Authors: Makhlouf A. , Debbah N. 
Published: July 2016

We study the normal variational equation of degree five:where λ is a parameter and C5(t) verifiesThe solution C5(t) of (1.2) is the inverse function ofWe prove that the pole t5 of C5(t) defined by is given bywhere
Theoretical Continuum and Line Spectra of Accretion Discs
Authors: Mayo S.K. , Wickramasinghe D.T. , Whelan J.A.J. 
Published: July 2016

Abstract.Theoretical continuum and Balmer line spectra have been computed for steady-state accretion discs. Models can be found which are in good general agreement with the observed colours and hydrogen absorption line profiles of dwarf novae in outburst and UX UMa-type objects.
Characteristics of the AM Herculis Type Stars and Review of proposed Interpretations
Authors: Tapia S. 
Published: July 2016

Consider a close binary system where mass transfer is underway from a relatively normal star to a highly magnetic degenerate dwarf. The magnetic field is strong enough that the magnetic pressure balances the ram pressure of the infalling plasma at a distance comparable with the separation of the two stars. Under these conditions accretion takes place along the magnetic lines of force, channeling the inflow of plasma towards the magnetic polar caps. Confined to a narrow column the plasma develops a standing shock at some distance above the surface of the degenerate dwarf. Due to its gravitational energy the infalling plasma can reach very high temperatures below the shock, then very efficient cooling effects ensue. Most of our information on such binary systems will be contained in cooling mechanisms involving radiation.Current theoretical trends identify three sources of radiation linked to the accretion column: 1) electron-ion bremsstrahlung in the hot plasma below the shock, 2) thermal emission from the heated surface of the degenerate dwarf, around the magnetic polar caps, and 3) optically thick electron cyclotron emission.
Models of Cataclysmic Variables from Photometric and Spectroscopic Data
Authors: Fabian A.C. , Pringle J.E. , Whelan J.A.J. , Bailey J.A. 
Published: July 2016

Abstract.Recent photometric and spectroscopic observations of the dwarf nova system Z Cha are discussed. Methods for constraining the system parameters are applied and the disc emissivity is deduced as a function of radius. Indications are found that the disc shrinks in size with increasing time after outburst.
UBV Observations of Some Long Period Variable Stars
Authors: Marino B.F. , Walker W.S.G. , Beuning J.A. , Blow G. 
Published: July 2016

Summary.Three colour UBV observations made at the Auckland Observatory are presented for the stars R Cen, CR Mus, SY For, and for Eta Car. An epoch and period are given for SY For. A period of Eta Car is discussed.
Spectroscopy and Narrow Band Polarimetry of Red Long Period Variables
Authors: Magalhães A.M. , Codina - Landaberry S.J. , Coyne G.V. 
Published: July 2016

AbstractA set of narrow band filters for studying variations in the intrinsic polarization across spectral features in late type variables stars is presented. The primary purpose is to study TiO bands and Hydrogen Balmer lines in the spectrum of such variables. These observations should help in distinguishing the role of the various sources of polarization in the extended atmospheres of the Mira and Semi-regular variables.
Short Term Variations in the Spectrum of the T Tauri Star DI Cep
Authors: Mundt R. , Bastian U. 
Published: July 2016

AbstractExtended spectroscopic observations of the T Tauri star DI Cep with a time resolution of 10 to 15 minutes have been carried out. On 2 of 6 observing nights the star showed significant variations of the strengths of its emission lines on time scales down to the time resolution of the observations. The most drastic event is shown in Figure 1. The equivalent width of the Hα line increased by a factor of 7 within two hours. Even faster variations, but of smaller amplitude, were observed in the strengths of the Hβ and Till 82 (λ 4572 Å) lines on another night. Obviously strong short time variations are not always present in DI Cep, as in 4 nights no significant variations could be detected.
Magnitude-Air Mass Loops as A Diagnostic by-Product of the Photometry of Variable Stars
Authors: Kvíz Z. 
Published: July 2016

If a variable star is observed with a photoelectric photometer during the whole night or at least for several hours both east and west from the meridian, the measurements of the brightness of the comparison star may yield useful information about the atmospheric extinction and about the performance of the photoelectric equipment as well. The extinction coefficients are valuable for the reduction of the data concerning the variable star itself and also for the study of the variation of atmospheric extinction at the observatory site. One of the most annoying characteristics of the photometric device is the zero-point drift during the night as a consequence of the change of the sensitivity of the photometer.The influence of the zero-point drift and the changes of extinction during the night on the Bouguer line (observed magnitude against air mass) was studied separately in a previous paper (Kviz, 1978, hereafter referred to as Paper I). In the present paper the simultaneous effects of both the zero-point drift and the changes of the extinction on the Bouguer plots are investigated.
A survey of trigonometric parallaxes and proper motions with the UK Schmidt Telescope: I. Methods and first results for stars brighter than B = 14 in a field near the South Galactic Pole
Authors: Murray C. A. , Corben P. M. 
Published: July 2016

AbstractIn an attempt to investigate the statistics of stars in the solar neighbourhood, independent of the bias toward high velocity stars introduced by selection of stars with large proper motion, a major astrometric investigation is being carried out at RGO using U.K. Schmidt plates measured on the GALAXY machine.So far more than 15000 objects brighter than B = 18 in a field near the South Galactic Pole have been measured on more than 50 plates taken between 19 74 and 1977.This paper describes the methods of analysis and the results of a pilot investigation on nearly 900 stars with B &lt; 14. The measurements show a very high degree of internal consistence, demonstrating the astrometric excellence of the U.K. Schmidt telescope and the GALAXY machine; random errors of measurement are found to be about ±0075 (=1.1.μm) per coordinate over the whole area (4° x 4°) measured, using a simple linear plate constant model for all plates. The external error of a single component of proper motion is estimated to be ± 0013 which is exactly consistent with the internal measurement error. The external error of a parallax in the present data is about ± 0018 whereas that predicted from the errors of measurement, and the self-consistency of two subsets of the data, is ± 0013; it is shown that the discrepancy can be largely accounted for by the random errors (± O11) in the B-V colours used in computing the effect of atmospheric dispersion, and should be reduced when better photometry becomes available.
The combined Herstmonceux Cambridge Program of optical positions of radio sources
Authors: Argue A. N. , Clements E. D. , Harvey G. M. , Murray C. A. 
Published: July 2016

SummaryAGK3-based optical positions are presented for 38 counterparts of radio sources selected from the catalogue of Elsmore &amp; Ryle. The measurements were made from plates taken with the 13-inch Astrograph, the 26-inch refractor and the 2.5 m (INT) reflector at Herstmonceux, and the 17-inch Schmidt at Cambridge. The standard error for a mean position of unit weight is 0”.11, and the weights range from 3.0 for the brightest sources to 0.5 for the faintest. Comparison with the radio positions shows no significant differences. The effects of applying the Brorfelde corrections to AGK3 are discussed.
On the Danger of Applying Statistical Reconstruction Methods in the Case of Missing Phase Information
Authors: Dainty J.C. , Fiddy M.A. , Greenaway A.H. 
Published: July 2016

The use of entropy as a basis for object/image reconstruction procedures is not new, but with the appearance of new, faster algorithms the actual use of these algorithms for the reconstruction of objects from ‘real’ data is likely to increase.The purpose of this contribution is not to discourage such applications, but to illustrate that, under certain circumstances, there is a need for caution in interpreting the results obtained from such algorithms. Specifically, we shall show that the application of statistical methods to problems of object reconstruction, in situations where only the modulus of the object Fourier transform is known, could lead to wholly false conclusions. Indeed, we shall primarily be concerned here with situations for which there is no ‘correct’ solution. In such situations it is pointless to speak of ‘safe’ object reconstruction algorithms. The important point here is that the user of a statistically based ‘object reconstruction algorithm’ may be totally ignorant of whether or not he is working in this régime.
Numerical Simulations of the Solar Granulation
Authors: Nordlund Åke 
Published: July 2016

AbstractNumerical simulations of the convective granular motions in the solar photosphere are presented. Realistic background physics allows a detailed comparison with observed characteristics of the solar granulation. The numerical methods are based on a bivariate Fourier representation in the horizontal plane, combined with a cubic spline representation in the vertical direction. Using a numerical grid with 16×16×16 grid points, which cover a unit cell of dimension ⋍ 3600×3600×1500 km, granular motions have been followed over several turnover times. The simulated motion shows the characteristics of granular motion. The evolution of large granules into bright rings (“Exploding granules”) is a consequence of the accumulating excess pressure at the granule center, necessary to support the horizontal velocities required by the continuity equation. The increasing pressure evenutally inhibits further upward motion at the granule center, which cools radiatively and shows up as a dark center in the expanding granule.