bluuebunny/crossref_metadata_2025 huggingface dataset:
The Galactic Fountain
Authors: Kahn F.D.
Published: July 2016

The Galactic fountain is driven by the hot inter-cloud medium (ICM). The ICM itself is heated by successive supernova explosions. This process introduces sufficient irregularities to prevent the fountain flow from being smooth. Instead it leads to the formation of a frothy medium above the disk (Avillez, Berry & Kahn 1997). This paper describes the effect of successive supernova explosions, in a rather idealised case. The real case is still more complicated, but the present approach shows why it is so.
The HI Supergiant Shells in the Large Magellanic Cloud
Authors: Kim S. , Staveley-Smith L. , Sault R.J. , Kesteven M.J. , McConnell D. , Dopita M.A. , Bessell M.
Published: July 2016

We present the result of an HI aperture synthesis mosaic of the Large Magellanic cloud (LMC), made recently with the Australia Telescope Compact Array (ATCA). The resolution of the mosaiced images is l′.0 (15 pc, using a distance to the LMC of 50 kpc). In contrast to its appearance at other wavelengths, the LMC is remarkably symmetrical in HI on the largest scales, with the bulk of the HI residing in a disk of diameter 8.°4 (7.3 kpc). Outer spiral structure is clearly seen, though the features appear to be due to differential rotation, therefore transient in nature. On small to medium scales, the combined action of numerous shells and supershells dominate the structures and motions of the HI gas in the LMC. A good correlation is seen between supershells previously identified in Hα (e.g. Meaburn 1980) and HI structures. We compare the results with a new wide-field Hα image.
Workshop for Continued Discussion of the Local Bubble
Authors: Sanders Wilton T. , Frisch Priscilla C.
Published: July 2016

At the end of the regularly scheduled conference, the organizers made available a large sunny conference room for the remaining participants to continue discussion. The main topics were the structure of the Local Bubble and the properties of the Galactic X-ray halo. Here we try to summarize the main points of those discussions.
Wolf-Rayet Wind Models: Photometric and Polarimetric Variability
Authors: Rodrigues Cláudia V. , Magalhães Antônio Mário
Published: July 2016

We have modelled the observed random variation in broad band intensity and polarization of some isolated Wolf-Rayet stars assuming that their winds have localized, enhanced density regions (blobs). Our model is based on a Monte Carlo code that treats all Stokes parameters of the radiation bundle. This study indicates that the blobs must have sizes comparable to the stellar dimension and be near the base of the envelope. These blobs can be interpreted as a variable structure of large geometric cross section causing the observed polarimetric and photometric variability.
Radio Evidence for Non-isotropic Outflows from Hot Stars
Authors: White Stephen
Published: July 2016

Radio diagnostics for outflows from hot stars are reviewed and three well–studied examples (WR 140, η Car and MWC 349) are discussed in some detail. The three systems are very different and their radio properties are diverse, but in each case, the radio data provide strong evidence for the presence of equatorially–enhanced outflows.
Direct Observational Evidence for Magnetic Fields in Hot Stars
Authors: Mathys Gautier
Published: July 2016

Attempts at achieving direct detections of magnetic fields in hot stars are reviewed. The techniques used in these observations and their analysis are described, with emphasis on the physical situations to which they are relevant. Results of projects carried out in the last couple of years are reported, and prospects for future investigations are briefly considered.
HST WFPCII Observations of the Inner HR Car Nebula
Authors: Hulbert Stephen , Nota Antonella , Clampin Mark , Leitherer Claus , Pasquali Anna , Langer Norbert , Schulte-Ladbeck Regina
Published: July 2016

We present Hα observations of the inner region of the HR Carinae nebula. The inner nebula looks clumpy and material appears to be present only to the east of the central star. A jet-like filament stretches away from the central star to the southeast.
Observing Hot Stars in all Four Stokes Parameters
Authors: Eversberg Thomas , Moffat Anthony F.J. , Debruyne Michael , Rice John B. , Piskunov Nikolai , Bastien Pierre , Wehlau William H. , Chesneau Olivier
Published: July 2016

We introduce a new polarimeter unit which, mounted at the Cassegrain focus of any telescope and fiber-connected to a fixed CCD spectrograph, is able to measure all Stokes parameters I, Q, U and V photon-noise limited across spectral lines of bright stellar targets and other point sources in a quasi-simultaneous manner. We briefly outline the technical design of the polarimeter unit and the linear algebraic Mueller calculus for obtaining polarization parameters of any point source. In addition, practical limitations of the optical elements are discussed. We present first results obtained with our spectropolarimeter for three prototype hot-star.
Non-spherical Radiation-Driven Wind Models
Authors: Puls Joachim , Petrenz Peter , Owocki Stanley P.
Published: July 2016

The present state of modelling radiatively driven stellar winds from rapidly rotating stars is reviewed. Various processes affecting the actual, still controversial wind structure are highlighted, in particular non-radial line-forces and gravity darkening, and useful scaling relations are provided. The importance of accounting for consistent NLTE line-forces depending both on the actual density structure and radiation field (as function of latitude and radius) is stressed, and some independent test calculations confirming earlier numerical results are reported.
Line-Driven Ablation by External Irradiation
Authors: Gayley Kenneth G. , Owocki Stanley P. , Cranmer Steven R.
Published: July 2016

The 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

We 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

We 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.
X-Ray Evidence for Wind Instabilities
Authors: MacFarlane Joseph J. , Cassinelli Joseph P. , Cohen D.H.
Published: July 2016

Hot stars are known to emit X-rays with LX/Lbol ~ 10−7 for O stars, falling to ~ 10−9 for B3 stars. These stars also lose mass at large rates through their high-speed winds. Over the years, several types of production mechanisms have been proposed to explain the X-ray emission from O stars, with source locations ranging from very near the stellar surface to very far from the star. A coronal X-ray source was originally proposed (Cassinelli and Olson 1979) to explain the presence of anomalously high ionization stages observed as P Cygni line profiles in the UV spectra of O stars. At the other extreme, Chlebowski (1989) suggested that the X-rays of O stars originate far from the star, and are produced by the interaction of the stellar wind with circumstellar matter. A model in which shocks forming due to instabilities in the line-driven winds of O stars was proposed by Lucy (1982), and studied in detail by Owocki et al. (1988), Cooper (1994), and Feldmeier (1996). In this case, the X-ray emission originates in a large number of shock-heated regions distributed throughout the wind. The shocked-wind model has also been shown to be consistent with the X-ray emission from early-B stars, such as τ Sco (MacFarlane and Cassinelli 1989). However, it appears difficult for shocked wind models to explain the X-ray emission from B3 and later stars because of their presumed low mass loss rates (Cohen et al.1997).
On the Variable Winds of BA Supergiants
Authors: Chentsov Eugene
Published: July 2016

The 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

Inhomogeneities 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

The 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

Range 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

Results 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.
Dynamical Behaviour of Asteroids in the 4:1 Resonance
Authors: López-García Francisco , Brunini Adrian
Published: July 2016

We study the dynamics of mean motion resonance with Jupiter in the 4:1 gap using only gravitational methods. This mechanism is capable of explaining this Kirkwood gap in an uniform way (see Ferraz-Mello, 1994; Ferraz-Mello et al., 1994; Moons, 1997; Yoshikawa, 1989). We considered the asteroidal motion in two and three dimensions and we carried out our investigations integrating numerically the full equations of motion and taking into account Mars, Jupiter and Saturn as disturbing planets. The orbital evolution of asteroids was obtained considering the elements variation. The numerical investigations were carried out using symplectic integrators. These integrations were stopped when the asteroid had close encouters with Mars or Jupiter, this occurs when the distance between the planet and the asteroid is of the order of 0.01 AU or less, or when the eccentricity increases up to 0.9. We studied real and fictitious asteroids on a time scale of 5 × 107 yr. The initial osculating elements of perturbing planets and their inverse masses were taken from the Ephemerides of Minor Planets (EMP) at the epoch of JD 2450000.5. The initial data corresponding to the real asteroids were also taken from the EMP. The starting elements of fictitious asteroids were, in all analyzed cases, a = acrit = 2.064; AU, i = 2°.5 and e = 0.01 (in the majority of cases). The other initial elements are shown in Table II. We have also studied fictitious asteroids with i = 0°, a = acrit and e = 0.01 (Table I). The present analysis leads to the following results: (1) The motions are unstable. The eccentricity, in the majority of cases, has very large increase. It may grow up to 0.9 in 106 yr. The semi major axis has large variations then, owing to both effects some fictitious asteroids reach the 3:1 resonance while others reach 7:2 resonance in a few million years, they are very chaotic regions. (2) The eccentricities of fictitious asteroids become large by the effect of the secular resonance v6, i.e. when (ϖ − ϖSat) ≅ 0, the rate of this resonance is 26.217”/year with period ~ 4.9 × 104 years (Bretagnon, 1974). (3) The fictitious asteroids studied with a = acrit, e < 0.05 and i < 3° are removed of this gap mainly by the effects of the secular resonances v6 and v16 (see Moons and Morbidelli, 1995; Williams, 1969). (4) There are close encounters with Mars or eventually with the Earth (not considered here) in a time scale of 106 - 107 yr. (5) For certain initial conditions some fictitious asteroids are temporally captured by Mars and in some cases for a long time. (6) If a = acrit,e = 0.3 and the inclination is less than 3°, Mars and asteroid’s perihelion are very close ( ~ 0.06AU ). This situation helps the capture. (7) The (a,e)-plane was used to determine the dynamical behaviour of all asteroids and we found that the 4:1 resonance is very strong. The Lyapunov times are very short.
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 following

where (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

According 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

We 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) verifies

The solution C5(t) of (1.2) is the inverse function of

We prove that the pole t5 of C5(t) defined by is given by

where
Theoretical Continuum and Line Spectra of Accretion Discs
Authors: Mayo S.K. , Wickramasinghe D.T. , Whelan J.A.J.
Published: July 2016

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

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.
Recent Observations of Dwarf Novae
Authors: Schoembs R. , Vogt N.
Published: July 2016

A supermaximum of VW Hydri was observed at the ESO site from Oct. 26 until Nov. 9» 1978. High time resolution polarimetrie and spectroscopic measurements have been obtained. This paper reports on some preliminary results.
Quasi-Periodic Oscillations in Dwarf Novae
Authors: Robinson Edward L.
Published: July 2016

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.
Novae in the Magellanic Clouds
Authors: Graham J.A.
Published: July 2016

During the past several years, a systematic search for novae in the Magellanic Clouds has been carried out at Cerro Tololo Inter-American Observatory. The Curtis Schmidt telescope, on loan to CTIO from the University of Michigan is used to obtain plates every two weeks during the observing season. An objective prism is used on the telescope. This provides additional low-dispersion spectroscopic information when a nova is discovered. The plates cover an area of 5°x5°. One plate is sufficient to cover the Small Magellanic Cloud and four are taken of the Large Magellanic Cloud with an overlap so that the central bar is included on each plate. The methods used in the search have been described by Graham and Araya (1971). In the CTIO survey, 8 novae have been discovered in the Large Cloud but none in the Small Cloud. The survey was not carried out in 1974 or 1976. During 1974, one nova was discovered in the Small Cloud by MacConnell and Sanduleak (1974).
UBV Observations of Some Long Period Variable Stars
Authors: Marino B.F. , Walker W.S.G. , Beuning J.A. , Blow G.
Published: July 2016

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.
Dust Alignement in Envelopes of Red Long Period Variables
Authors: Machado J.A. Marcondes
Published: July 2016

The intrinsic polarization of red long period variables has been the subject of various explanatory models. Donn et al. (1966, 1968) and Kruszewski (1971) proposed aligned dust grains in the star envelope as the polarizing agent. Harrington (1969) suggested photos-pheric scattering plus temperature and/or geometric asymmetry. Scattering in an asymmetrical circumstellar cloud of non-aligned grains has also been invoked (Shakhovskoi 1963, Serkowski 1971, Shawl 1975a, b). This last mechanism seems to have been the more elaborated, whereas Harrington’s have received strong support from recent observations (Landstreet and Angel 1977, Coyne and Magalhães 1977). As for the first model, it is faced with a problem: grains with the compositions thus far proposed (graphite, silicates) need a magnetic field much too strong in order to be aligned.
Spectroscopy and Narrow Band Polarimetry of Red Long Period Variables
Authors: Magalhães A.M. , Codina - Landaberry S.J. , Coyne G.V.
Published: July 2016

A 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.
Simultaneous Photometry and Spectroscopy of the B2(e) Variable Star HD 4567
Authors: Barbier R. , Klutz N. , Surdej A. , Surdej J. , Swings J.P.
Published: July 2016

Light variations are observed for HD 45677 in the visible, if they are due to obscuration by circumstellar patchy dust clouds, part of the stellar UV and visible radiations are back-scattered inside the extended atmosphere surrounding the star. The excitation of all atoms and ions in the envelope is thus affected, and the result is seen most for the atoms moving towards the observer: the intensity variations of the blue emission wings of the Balmer lines in opposite phase with simultaneous variations of the stellar flux are therefore understandable.
Short Term Variations in the Spectrum of the T Tauri Star DI Cep
Authors: Mundt R. , Bastian U.
Published: July 2016

Extended 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.
An Independent Distance Scale for Variable Stars
Authors: Barnes Thomas G.
Published: July 2016

For the past two years my collaborators and I at the University of Texas at Austin have worked toward establishing an independent distance scale for variable stars. The basis of our approach is to make use of the apparent magnitude and the visual surface brightness, inferred from an appropriate color index, to determine the angular diameter variation of the variable. When combined with the linear displacement curve, obtained from the integrated radial velocity curve, the distance and linear radius are determined. The great attractiveness of the method is its complete independence of all other stellar distance scales. At present a number of practical difficulties exist in implementing the technique, but the results to date are encouraging. In this discussion I will use Cepheid variables to demonstrate the method.
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.
Mode Discrimination in β Cephei Stars
Authors: Stamford P.A. , Watson R.D.
Published: July 2016

In an extension of previous work, we have compared observed 3 Cephei star light ranges [Δm(λ)] with model predictions, to assist in discriminating between proposed oscillation modes for their surfaces. Specifically we have considered the radial model and the non-radial form studied by Osaki (1971). Stars with published Δm(λ) extending from the satellite ultraviolet up to the visual were examined. For all eight singly-periodic stars examined, and for the line-broadening mode of a Sco, the Δm(λ) are only consistent with the radial model. An excellent model fit is achieved when the data are of uniformly high quality, as is the case for ξ’ CMa, BW Vul and β Cep. For the line-broadening modes of β CMa and 12 Lac, the visual data indicate that Δm(λ) depends only weakly on wavelength. These modes are not consistent with the radial interpretation and require an alternate explanation. They are consistent with the non-radial form of Osaki.
On the statistical use of trigonometric parallaxes random errors
Authors: Crézé M. , Turon-Lacarrieu C.
Published: July 2016

Among the various investigations of error analysis involved in the preparation of a new general catalog of trigonometric parallaxes, those in which spectroscopic or photometric measurements interact are often disregarded. Lutz(this colloquium) summarizes the reasons of such a neglect as follows: the basic idea of these methods is that stars with identical photometric indices or identical spectroscopic features have the same absolute magnitude. The criticism is that this astrophysical idea is subject to revision as astrophysics are progressing. Evaluation of errors depending on evolutive criteria can therefore not be included in a general catalogue.
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

In 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 < 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.
Stellar mass calibration
Authors: Heintz W. D.
Published: July 2016

Although mass results and their evolutionary connotations now largely stem from observational realms other than astrometry, it is the combination with proper motions, kinematics, and distance calibration which significantly enhances their usefulness.
Use of classical pertubation theories for the calculation of barycentric aberration and Doppler Effect
Authors: Stumpff P.
Published: July 2016

Modern techniques have considerably improved the accuracy of radioastronomical measurements. Examples are the high resolution in frequency, time and position for spectroscopic, pulsar, and VLBI observations. There is an increasing demand for accurate reduction of such measurements to an inertial frame of reference, preferably the barycenter of the solar system and the mean equator and equinox of a standard epoch. Reductions of this kind include the computation of general precession, nutation, aberration and Doppler effect. For general precession and nutation, there are internationally accepted algorithms which can be programmed in form of self-consistent subroutines. Aberration and Doppler shifts are determined by the barycentric velocity of the Earth and by diurnal effects. Until now, as far as I know, a self-consistent algorithm of sufficient accuracy for computation of the barycentric velocity components of the Earth has not been available. The need for such an algorithm is indicated by the recommendations of Commission 4 (Ephemerides) of the IAU (1976), that “stellar aberration shall be computed from the total velocity of the Earth …”, and that “reductions to apparent places should be computed rigorously …”. In practice, this can be done by reading and interpolating ephemerides obtained from numerical integrations.
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

AGK3-based optical positions are presented for 38 counterparts of radio sources selected from the catalogue of Elsmore & 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.
Absolute declination determinations with the Pulkovo Photographic Vertical Circle
Authors: Bagildinsky B. K.
Published: July 2016

The Pulkovo photographic vertical circle(PVC) designed and constructed under the supervision of Prof.Dr.M.S.Zverev (1) at the Pulkovo Observatory is used at present for determination of absolute declinations of bright and faint fundamental stars after its reconstruction and modernisation (2, 3). The main optical system of the PVC is the Maksutov meniscus cassegrain system (D = 200mm, f’ = 2000mm) with a photographic micrometer for star registrations. The limiting magnitude of ORWO NP - 27 plates is m=8.5 for zenith A special measuring machine is used for automatic measurements of star plates of the PVC (4-6). The Pulkovo PVC is equipped with two glass-circles with 4 photoelectric scanning microscopes for each circle. A description of the photoelectric reading system of the PVC is given in (7). The investigation shows that the mse of a single reading of one microscope is about + 005 (7). Observations of about 200 FK4 stars made in 1974-1977 show that the PVC instrumental system is sufficiently stable and ensures high precision as far as accidental errors are concerned. The mse of a single observation is δo= ± 018 at the zenith and no more than ± 030 at z = 50° (3) A special analysis of the observations made by the PVC showed the presence of chromatic refraction effects, particularly, at great zenith distances (8). The early type stars (0, B, A) are most affected by chromatic refraction. The refraction effects are northwards and southwards asymmetric relative to the zenith.
Short Spacing Synthesis from a Primary Beam Scanned Interferometer
Authors: Ekers R.D. , Rots A.H.
Published: July 2016

Aperture synthesis instruments providing a generally highly uniform sampling of the visibility function often leave an unsampled hole near the origin of the (u,v)-plane. One of the common configurations of the Westerbork Synthesis Radio Telescope (WSRT) provides sampling in concentric rings with radii of n × 18 m. However, the samples with n=0 and n=1 cannot be obtained directly with the instrument because of rather obvious physical constraints. This missing short spacing information causes a central depression of the synthesized beam pattern, resulting in large negative, bowl shaped areas around (especially) extended sources. Very large sources will only partially be present in the maps. Annoying as this can be for continuum observations, in the case of spectral line data it causes serious distortions of the individual line profiles.
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.
Digital Hardware Processing of Rotational Synthesis Data
Authors: Frater R.H.
Published: July 2016

Digital techniques for the direct transformation of rotational synthesis data are discussed with particular emphasis on current cost and technological limits. A prototype system designed to test various approaches will be described and its application to “clean” and maximum entropy reconstructions considered.
A Proposed Correlator Back-end for the Culgoora Radio-heliograph
Authors: McLean D.J.
Published: July 2016

The original design of the Culgoora radioheliograph (Wild, 1967; Sheridan et al., 1973) incorporated a number of features, such as high time resolution and limited declination coverage, which were particularly suited to its primary function of observing the Sun. Although some of these features are disadvantageous for cosmic work, the instrument has nevertheless proved useful for a variety of non-solar studies as well.
Towards Imaging of Star Clusters by Speckle Interferometry
Authors: Bates R.H.T. , Milner M.O.
Published: July 2016

Labeyrie’s (1970, 1976) speckle interferometry permits an astronomical object to be resolved to a limit approaching λ/D (where λ is the mid-band wavelength of the light accepted by a telescope having a pupil aperture of diameter D) in the presence of severe atmospheric seeing. As Dainty (1973) has pointed out, this resolution limit is virtually independent of the accuracy to which the telescope is figured – the seeing can actually improve a telescope’s resolution! Even though a true image of the object cannot usually be constructed by Labeyrie’s data reduction procedures, nevertheless the autocorrelation of (the distribution of brightness over) the object can always be reconstructed – provided the extent (width, apparent angular diameter) of the object does not exceed that of the isoplanatic patch (cf. Bates and Gough, 1975). The autocorrelation is useful because its extent is necessarily twice that of the object.
Resolution Enhancement; the ‘Maximum Entropy Method’ and the ‘High Resolution Method’
Authors: van Schooneveld C.
Published: July 2016

In image formation from coherence functions we start with a set of observed coherences (visibilities) R′ (uk, vk), measured at locations uk, vk in the u,v-plane:
Numerical Simulations of the Solar Granulation
Authors: Nordlund Åke
Published: July 2016

Numerical 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.