bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Heating in the Galactic Diffuse Ionized Gas
Authors: Minter Anthony , Balser Dana S.
Published: July 2016

The observed properties of the diffuse ionized gas (DIG) in our Galaxy are not easily reconcilable with simple photoionization models. This suggests that there are different or additional physical processes at work in the DIG. We have developed a model of the DIG whereby it is ionized by a relatively soft ionizing spectrum (Teff ≤ 32,000 K) and is also heated by an additional thermal mechanism: the dissipation of turbulence. This model predicts the same electron temperature, [N II] λ 6583/Hα ratio, [S II] λ 6716/Hα ratio and He I λ 5876/Hα ratio as observed in the DIG. Without the turbulent thermal heating term, this model will not reproduce the observed properties of the DIG. The dissipation of turbulence may also be important in other phases of the ISM.
Superbubbles in Dwarf Galaxies: Blown Out or Blown Away?
Authors: Low Mordecai-Mark Mac , Ferrara Andrea
Published: July 2016

We numerically model the impact of superbubbles produced by starbursts on the gas in dwarf galaxies, using realistic gravitational potentials including the contributions from dark matter haloes, and galaxy radii based on empirical laws. We find that the metal-rich gas is very efficiently ejected in many cases, contradicting previous results; the ambient gas is far more difficult to eject. X-ray emitting plumes can last more than 108 yr after the end of the active starburst.
Rotationally Modulated Winds of BA-Type Supergiants
Authors: Kaufer Andreas
Published: July 2016

Extended spectroscopic monitoring programs with high resolution and coverage in wavelength and time have revealed a new picture of the winds and the circumstellar environments of late B- and early A-type supergiants. Dramatic line-profile variations (LPV) of the wind-sensitive Hα line with characteristic cyclical V/R variations indicate the presence of deviations of the envelopes from spherical symmetry. Time-series analysis of these LPVs suggest that the wind variations are caused by rotating surface structures which modulate the lower wind region. Occasionally observed high-velocity absorptions (HVA) indicate the presence of rotating extended and dense streakline or loop structures in the envelopes. The potential use of these circumstellar features to determine the true stellar rotation periods is discussed.
Using Spectropolarimetry to Determine Envelope Geometry and Test Variability Models for Hot Star Circumstellar Envelopes
Authors: Bjorkman Karen S.
Published: July 2016

A survey and monitoring of the spectropolarimetric characteristics of hot stars over the entire visible wavelength range has been carried out over the past 8 years using the HPOL instrument at the Pine Bluff Observatory. Data from these projects is being used to derive physical characteristics of circumstellar envelopes. Quantitative modeling of the polarization, in combination with optical interferometry, has shown that the circumstellar disks of classical Be stars are geometrically thin, consistent with either the wind-compressed disk model or with hydrostatically supported Keplerian disks. Furthermore, spectropolarimetric variability, which is significant in a large fraction of the hot stars observed, provides information about changes occuring in the circumstellar envelope. For example, polarimetric changes provide a critical test of the one-armed density wave models proposed to explain observed V/R variations.
Disk Winds of B[e] Supergiants
Authors: Zickgraf Franz-Josef
Published: July 2016

The class of B[e] supegiants is characterized by a two-component stellar wind consisting of a normal hot star wind in the polar zone and a slow and dense disk-like wind in the equatorial region. The properties of the disk wind are discussed using satellite UV spectra of stars seen edge-on, i.e. through the equatorial disk. These observations show that the disk winds are extremely slow, v∞ ≃ 50 ‒ 90 km s−1, i.e. a factor of ~ 10 slower than expected from the spectral types. Optical emission lines provide a further means to study the disk wind. This is discussed for line profiles of forbidden lines formed in the disk.
Modeling Oblique Rotators: Magnetospheres and Winds
Authors: Shore Steven N.
Published: July 2016

The upper main sequence chemically peculiar (CP) stars display evidence of trapped circumstellar gas and nonspherical outflows. These stars are also known to possess strong magnetic fields that are often highly inclined to the rotational axis. Their phenomenology can be understood by using the oblique rotator model, which has successfully accounted for the observed behavior of the cooler CP stars. This paper reviews some features of the oblique rotator model, in which the magnetic field is assumed to provide a rigid framework for the structuring of the stellar and circumstellar gas. Corotation of circumstellar plasma is enforced out to the Alfven radius in the magnetic equatorial plane, while for the hotter stars, a radiatively driven wind emerges from the magnetic polar caps. Some observable consequences of the model are discussed, especially the Hα and ultraviolet resonance line absorption and emission periodic variability that has been observed in the He-peculiar stars and nonthermal radio emission. Magnetospheres may also be present in O stars, e.g. θ1 Ori C, and in the Herbig Ae/Be stars.
Wind Variations of Wolf-Rayet Stars
Authors: Moffat Anthony F.J.
Published: July 2016

What distinguishes WR stars from most of their progenitor phases is their dense winds, that often completely hide their small hydrostatic cores. Thus, to learn about these cores, which are especially important in an evolutionary context, we are generally limited to studying the winds only. One way to do this is to examine their ubiquitous variability. Variability studies of (single) WR stars using various techniques have revealed two main classes of wind variation: (1) large-scale and periodic, probably related to rotating disturbances (e.g. NRP or magnetic structures) close to the core surface, and (2) small (multi-) scale and stochastic, probably intrinsic to the winds themselves. The former is only seen rarely in WR stars, contrary to other hot stars. The latter appears to be universal in WR and probably (though less obvious) in all hot-star winds.
Non-radially Pulsating Hot Stars: Non-radial Pulsations and Be Phenomenon
Authors: Osaki Yoji
Published: July 2016

We discuss a possible role of non-radial oscillations as a cause of mass-loss in hot stars. In particular, we propose a working model for the episodic mass-loss in Be stars. In this model, equatorial mass loss is thought to be driven by wave-breaking phenomenon of large-amplitude non-radial waves and a circumstellar disk could thus be formed around the equatorial plane of a rapidly rotating star. A kind of relaxation-oscillation cycle could be established between the Be phase and non-Be phase, in which an interplay between non-radial oscillations in stellar atmosphere and the circumstellar disk is essential. We also discuss a viscous decretion-disk model for the circumstellar envelope around Be stars.
Linear Strange Modes in Massive Stars
Authors: Glatzel Wolfgang
Published: July 2016

The occurrence and properties of strange modes and associated instabilities in massive stars are reviewed. If applicable, strange modes may be classified by the maximum of the opacity they are associated with. Whether they are still present in the limit of vanishing or infinite thermal timescales – which corresponds to the NAR and adiabatic approximations respectively – is another criterion for classification. A model for the instability mechanism of strange mode instabilities is discussed.
Rotation and Wolf-Rayet Star Formation
Authors: Meynet Georges
Published: July 2016

New results for 60 M⊙ stellar models with different rotation rates are presented. Some effects of rotation on Wolf-Rayet star formation are discussed.
Conference Summary: The Demise of Spherical and Stationary Winds
Authors: Appenzeller Immo
Published: July 2016

The observational evidence and the theoretical work presented at this colloquium demonstrate that significant non-spherical effects and time variations are very common phenomena in the winds from hot stars. Hence, the assumptions of spherical symmetry and stationarity, while highly successful for the theory of stellar structure, appear to be inadequate for describing and understanding the winds of hot stars. This conclusion has significant consequences for the appearance and evolution of hot stars.
Bianchi Cosmologies as Dynamical Systems
Authors: Maciejewski Andrzej J. , Szydłowski Marek
Published: July 2016

We discuss specific properties of dynamical systems originating from cosmology and relativity. In particular, we present results of our study of the Bianchi class A cosmological models. We introduce new variables in which the Hamiltonian constraint for all the class A models is solved algebraically. We present results of dimension reduction of the investigated models.
Star Cluster Simulations: The State of The Art
Authors: Aarseth Sverre J.
Published: July 2016

This paper concentrates on four key tools for performing star cluster simulations developed during the last decade which are sufficient to handle all the relevant dynamical aspects. First we discuss briefly the Hermite integration scheme which is simple to use and highly efficient for advancing the single particles. The main numerical challenge is in dealing with weakly and strongly perturbed hard binaries. A new treatment of the classical Kustaanheimo-Stiefel two-body regularization has proved to be more accurate for studying binaries than previous algorithms based on divided differences or Hermite integration. This formulation employs a Taylor series expansion combined with the Stumpff functions, still with one force evaluation per step, which gives exact solutions for unperturbed motion and is at least comparable to the polynomial methods for large perturbations. Strong interactions between hard binaries and single stars or other binaries are studied by chain regularization which ensures a non-biased outcome for chaotic motions. A new semi-analytical stability criterion for hierarchical systems has been adopted and the long-term effects on the inner binary are now treated by averaging techniques for cases of interest. These modifications describe consistent changes of the orbital variables due to large Kozai cycles and tidal dissipation. The range of astrophysical processes which can now be considered by N-body simulations include tidal capture, circularization, mass transfer by Roche-lobe overflow as well as physical collisions, where the masses and radii of individual stars are modelled by synthetic stellar evolution.
Distribution of Kolmogorov-Sinaï Entropy in Self-Consistent Models of Barred Galaxies
Authors: Wozniak H. , Pfenniger D.
Published: July 2016

The properties of chaos in 2D self-consistent models of barred galaxies are investigated using Kolmogorov-Sinai entropy hKS. These models are constructed with Schwarzschild’s method which combines orbits as elementary building blocks.

Most models are dominated by chaos near the 2/3 of the length of the bar and close to corotation. These locations correspond to regions where star-forming HII regions are observed because gas clouds could shock, shrink and fragment such that star formation could be ignited.

The model the most similar to N-body models shows a peak of hKS between the corners of the rectangular-like x1 orbits and the maximum extension points of the Lagrangian orbits. This emphasizes the role of Lagrangian orbits in the morphology of bars. Most models essentially contain ‘semi-chaotic’ orbits confined inside the corotation.
Regular and Chaotic Motion in Globular Clusters
Authors: Carpintero Daniel D. , Muzzio Juan C. , Wachlin Felipe C.
Published: July 2016

As a first step towards a comprehensive investigation of stellar motions within globular clusters, we present here the results of a study of stellar orbits in a mildly triaxial globular cluster that follows a circular orbit inside a galaxy. The stellar orbits were classified using the frequency analysis code of Carpintero and Aguilar and, as a check, the Liapunov characteristic exponents were also computed in some cases.

The orbit families were obtained using different start spaces. Chaotic orbits turn out to be very common and while, as could be expected, they are particularly abundant in the outer parts of the cluster, they are still significant in the innermost regions. Their relevance for the structure of the cluster is discussed.
Periodic Orbits Around a Massive Straight Segment
Authors: Riaguas Andrés , Elipe Antonio , Lara Martín
Published: July 2016

In this paper, we consider the motion of a particle under the gravitational field of a massive straight segment. This model is used as an approximation to the gravitational field of irregular shaped bodies, such as asteroids, comet nuclei and planets’s moons. For tbis potential, we find several families of periodic orbits and bifurcations.
Canonical Variables of The Second Kind and The Reduction of The N-Body Problem
Authors: Bryant John G.
Published: July 2016

We introduce a new kind of canonical variables that prove very useful when the order of a Hamiltonian system can be reduced by one, as in the case of isoenergetic reduction, and of what we call homogeneous reduction. The Kepler Problem, Geometrical Optics and McGehee Blow-up are discussed as examples. Finally we carry out the isoenergetic reduction of the general N-Body Problem using the new variables, and briefly discuss its application to the problem of collision.
The Hamiltonian Dynamics of The Two Gyrostats Problem
Authors: Mondejar F. , Vigueras A.
Published: July 2016

The problem of two gyrostats in a central force field is considered. We prove that the Newton-Euler equations of motion are Hamiltonian with respect to a certain non-canonical structure. The system posseses symmetries. Using them we perform the reduction of the number of degrees of freedom. We show that at every stage of the reduction process, equations of motion are Hamiltonian and give explicit forms corresponding to non-canonical Poissson brackets. Finally, we study the case where one of the gyrostats has null gyrostatic momentum and we study the zero and the second order approximation, showing that all equilibria are unstable in the zero order approximation.
The Effect of C22 on Orbit Energy and Angular Momentum
Authors: Scheeres D.J.
Published: July 2016

The effect of the C22 gravity field term on a particle is evaluated analytically over one orbit to find the change in orbit energy and angular momentum as an explicit function of the orbital inclination, argument of pericenter, longitude of the ascending node, orbit parameter and eccentricity. Changes in orbit energy and angular momentum are shown to be proportional to a family of integrals which can be parameterized in terms of eccentricity and non-dimensional pericenter radius.
The Use of Lie Series in The Construction of a Perturbation Theory and some Recent Results in The Theory of The Motion ofd Hyperion
Authors: Message P.J.
Published: July 2016

This paper begins with a brief review of a form of the Lie series transformation, and then reports some new results in the study, using Lie series methods, of the orbit of Saturn’s satellite Hyperion. In particular, improved expressions are given for the long-period perturbations of the orbital elements which describe the motion in the orbit plane, and also first results for expressions for the short-period perturbations in the apse longitude, derived from the Lie series generating function.
Higher Order and Iterative Theories to Compute Asteroid Mean Elements
Authors: Knežević Z. , Milani A.
Published: July 2016

Mean orbital elements are obtained from their instantaneous, osculating counterparts by removal of the short periodic perturbations. They can be computed by means of different theories, analytical or numerical, depending on the problem and accuracy required. The most advanced contemporary analytical theory (Knežević 1988) accounts only for the perturbing effects due to Jupiter and Saturn, to the first order in their masses and to degree four in eccentricity and inclination. Nevertheless, the mean elements obtained by means of this theory are of satisfactory accuracy for majority of the asteroids in the main belt (Knežević et al. 1988), for the purpose of producing large catalogues of mean and proper elements, to identify asteroid families, to assess their age, to study the dynamical structure of the asteroid belt and chaotic phenomena of diffusion over very long time spans. In the vicinity of the main mean motion resonances, however, especially 2:1 mean motion resonance with Jupiter, these mean elements are of somewhat degraded accuracy.
The Asteroid Mass Determination Project at The U.S. Naval Observatory
Authors: Hilton James L. , Stone Ronald C.
Published: July 2016

Asteroid masses are the largest source of unmodeled forces in current planetary ephemerides research. Williams (1984) showed that the asteroids produce km size perturbations in the position of Mars. However, the masses of only three asteroids are known to better than 10%, and only six other asteroid masses have been determined at all.

Detecting the mass of an asteroid is difficult because the observed quantity is the change in the mean motion of a second, perturbed asteroid. Asteroid masses are small, so the change in the mean motion is typically on the order of 0."015 yr−1. Thus, excellent orbit determinations are needed both before and after the perturbing encounter. This requires high precision observations over as many oppositions as possible.

Hilton (1997) determined the mass of 15 Eunomia to within 25% by detecting perturbations of 1313 Berna. The greatest source of uncertainty in determining the mass of Eunomia was the very poor coverage and accuracy of pre-encounter observations. Hilton (1998) has determined the masses of 1 Ceres, 2 Pallas and 4 Vesta, all based on mutual interactions. The uncertainties in the masses are 1% for Ceres, 3% for Pallas, and 7% for Vesta. The masses of Ceres and Pallas are the best so far, and the mass for Vesta corroborates previous determinations of its mass.
The Asteroid Identification Problem
Authors: Sansaturio M.E. , Milani Andrea , La Spina A.
Published: July 2016

A large fraction of the asteroids observed so far are to be considered lost, that is they cannot be recovered by pointing the telescope at the predicted position only. The catalogues of asteroid orbits are therefore polluted by large numbers of low accuracy orbits, which cannot be easily improved by observation. Two of these inaccurate orbits can belong to the same physical object, and indeed identifications are regularly found when the orbital elements are close; an unknown number of real identifications have not been found in the existing catalogues because the orbital elements as computed are far apart. It is impossible to systematically check for possible identification of all the couples of orbital element sets; an algorithm is required to single out a comparatively small number of proposed identifications, and to find a suitable first guess within the region of convergence of the differential corrections procedure to be used to confirm the identification.

In the linear approximation the target function to be minimized is a quadratic form; thus a fully analytic algorithm can be given to compute both the first guess for an identification and the cost, that is the increase in the target function resulting from joining the two sets of observations. This allows to define a number of distances in the elements space, which are functions, not only of the two orbital element sets, but also of their uncertainties, as measured by the Gaussian covariance matrices. Tests on the values of these distances are used as preliminary filters, to allow more extensive computations to be performed on a fraction of the total number of possible couples.
Target Plane Confidence Boundaries: Mathematics of The 1997 XF11 Scare
Authors: Milani Andrea , Valsecchi Giovanni B.
Published: July 2016

The uncertainty of the close approach distance of a Potentially Hazardous Object (PHO), either an asteroid or a comet, can be represented on the Modified Target Plane (MTP), a modification of the one used by Öpik. The MTP is orthogonal to the geocentric velocity at the closest approach along the nominal orbit, solution of the least square fit to the observations. The confidence regions of this solution in the 6-D space of orbital elements (for an epoch close to the observations) are well approximated by a family of concentric ellipsoids, if the observed arc is not too short. In the linear approximation these ellipsoids are mapped on the MTP into concentric ellipses, which can be computed by solving for the state transition matrix.

For a PHO observed at only one opposition, with a close approach expected after many revolutions, the ellipses on the MTP become extremely elongated and the linear approximation may fail. In this case the confidence boundaries on the MTP, i.e. the nonlinear images of the confidence ellipsoids, may not be well approximated by the ellipses. The Monte Carlo method (Muinonen and Bowell, 1993) can be used to find nonlinear confidence regions, but the computational load is very heavy: to estimate a low probability event the number of test cases must be larger than the inverse of the probability. We propose a new method to compute semilinear confidence boundaries on the MTP (Milani and Valsecchi, 1998), based on the theory developed to compute confidence boundaries for predicted observations (Milani, 1999). This method is a good compromise between reliability and computational load, and can be used for real time risk assessment.
Periodic Orbits in Three-Armed Galaxies
Authors: Grosbøl Preben J. , Patsis Panos A.
Published: July 2016

Although interarm features in the Population I disk of spiral galaxies frequently give an impression of a three-fold symmetry (Patsis et al., 1997), true three-armed spiral structures in the old stellar disk are seldomly seen. Such systems are of special interest since they display unique conditions which favor the growth of m=3 modes. The face-on spiral NGC 7137 shows a clear three-armed pattern on K-band images and was used as a prototype for the potential of these systems.

A K-band map of NGC 7137 was decomposed in axisymmetric components and a synthetic rotation curve was generated [see (Grosbøl and Patsis, 1998)]. The maximum rotational velocity was taken to be ≈150 km sec−1 corresponding to the mean value given by (Rubin et al., 1982) for this type of galaxy.
Orbits of Hipparcos Metal-Poor Stars with Well-Defined Spectroscopic Abundances
Authors: Bancken F. , Jehin E.
Published: July 2016

Orbital characteristics of 80 HIPPARCOS mildly metal-poor stars are derived assuming a Galactic model slightly modified from that of Ostriker and Caldwell (1979). A comparison with other works is performed and a relationship between the dynamical properties of the stars and their well-determined spectroscopie abundances is investigated.
Second Order Perturbations of Elliptic Elements with Respect to the Initial Ones
Authors: Marco Castillo F.J. , Martínez Usó M.J. , López Ortí J.A.
Published: July 2016

The following paper is devoted to the theoretical exposition of the obtention of second order perturbations of elliptic elements and is a follow-up of previous papers (Marco et al., 1996; Marco et al., 1997) where the hypothesis was made that the matrix of the partial derivatives of the orbital elements with respect to the initial ones is the identity matrix at the initial instant only. So, we must compute them through the integration of Lagrange planetary equations and their partial derivatives.

Such developments have been applied to the individual corrections of orbits together with the correction of the reference system through the minimization of a quadratic form obtained from the linearized residual. In this state two new targets emerged:

1.

To be sure that the most suitable quadratic form was to be considered.

2.

To provide a wider vision of the behavior of the different orbital parameters in time.

Both aims may be accomplished through the consideration of the second order partial derivatives of the elliptic orbital elements with respect to the initial ones.
On the Model of WZ Sge
Authors: Smak J.
Published: July 2016

The following limiting relations between μ = m2/(m1+m2) and the dimensionless outer radius of the disk r, can be used to discuss the physical parameters of the system:
Recent and Future Radio Observations of Flare Stars
Authors: Slee O.B. , Page A.A.
Published: July 2016

Observations of flare stars began in Australia in 1962 soon after the commissioning of the Parkes 64-m reflector, which was successfully used to detect 408 MHz emission from V371 Orionis during an optical flare; this result was published by Slee et al. (1963) shortly after Lovell et al. (1963) reported their first successful observations of UV Ceti at 240 MHz. Thereafter a number of cooperative radio and optical studies were made with the large reflectors at Jodrell Bank and Parkes and more recently at Arecibo. Unfortunately the poor angular resolution (1° to 2°) of these large single reflectors at metre wavelengths did not permit the positioning of a weak radio source with an accuracy sufficient for positive identification of flare star emission - the observer had to rely on the presence of an optical flare to distinguish the flare deflections on the radio record from interference and baseline drifts. Naturally this resulted in general scepticism among astronomers concerning the reality of the flare star radio emission, especially as the radio luminosity of a typical event was shown to be several orders of magnitude higher than the most intense solar bursts. In addition, it is clear that the method of observing strongly favoured the detection of the shorter impulsive type of bursts lasting from seconds to a few minutes - this selection effect resulted from the difficulty in discriminating between weak, slowly varying flare-star emission and changes in the receiver baseline due to receiver instability.
Changing Periods of Long-Period Variables
Authors: Hoffleit Dorrit
Published: July 2016

A manuscript catalogue has been prepared listing all of the Mira-type and SRa variables reputed at one time or another to have changing periods (356 stars). The frequencies of the recorded changes are investigated and qualitatively discussed. For a selected list of 100 of these stars (Table III) the published JD0of maximum for successive time-intervals are examined to see if they cannot better be represented by constant periods. Such data are suggestive but inadequate for definitive conclusions. For many of these stars the AAVSO has accumulated observations spanning over one hundred years. Sophisticated analyses of these rich data are to be encouraged.
Polarimetric Observations of Red Variables: A Study of Gas and Particle Interactions
Authors: Coyne G. V. , McLean I. S.
Published: July 2016

In recent years the wavelength, dependence of the polarization in a number of Mira variables, semi-regular variables and red supergiants has been measured with resolutions between 0.3 and 300 A over the range 3300 to 11000 A. Variations are seen across molecular absorption bands, especially TiO bands, and across atomic absorption and emission lines, especially the Balmer lines. In most cases one can ignore or it is possible to eliminate the effects due to interstellar polarization, so that one can study the polarization mechanisms operating in the stellar atmosphere and environment. The stars Omicron Ceti. (Mira), V CVn (semi-regular variable) and Mu Cephei (M2 la), in addition to other stars similar to them, will be discussed in some detail.

Models to explain the observed polarization consider that the continuum flux is polarized either by electron, molecular and/or grain scattering or by temperature variations and/or geometrical asymmetries over the stellar photosphere. This polarized radiation is affected by atomic and molecular absorption and emission processes at various geometric depths in the stellar atmosphere and envelope. High resolution spectropolarimetry promises, therefore, to be a power-rul tool for studying stratification effects in these stars.
Variable Star Research at Los Alamos
Authors: Davis C. G. , Cox A. N. , Adams T. F.
Published: July 2016

We are at present engaged in three major areas of variable star research at Los Alamos: 1) A study using improved Cepheid light curves in order to define more precisely the Hertzsprung sequence, in collaboration with John Castor and John Cox, 2) The suggestion by A. Cox that helium enrichment occurs in the stellar envelope, by a stellar wind, which may explain many of the mass anomalies, this work being with G. Michaud, D. King, R. Deupree, and S. Hodson, and 3) The study of Cepheid and RR Lyrae colors to compare directly to the observations. A brief discussion of the present status of each of these research programs will be given.
Photographic Photometry in the Absence of Standard Stars
Authors: Gilmore Gerard
Published: July 2016

Photographic monitoring of the optical variability of a sample of southern quasars has been carried out by the author since early 1975. (Gilmore 1978). Observations are made with a 61 cm reflector and an unfiltered S20R photo-cathode image-intensifier. Because of the small usable field of view (~ 10 arcmins), and the non-standard filter system, observations are reduced using a generalised form of a technique developed by Penston and Cannon (1970) for the RGO quasar programme. This technique allows the detection of variability with an accuracy limited only by the detective quantum efficiency of the photographic plate, and without the need to establish a local photometric sequence, or to restrict observations to a standard photometric system.
A Search for β Cephei Stars in the Southern Hemisphere - Results
Authors: Jerzykiewicz M. , Sterken C.
Published: July 2016

In 1975 we started a photometric search program of examining for variability- the bright early B stars located south of -20° declination. The main purpose we had in mind was to look for hitherto undiscovered 6 Cephei variables. Therefore, we limited our program to objects spectroscopically similar to the B Cephei stars.
On the applicability of observatory corrections
Authors: Norgaard-Nielsen H. U.
Published: July 2016

I have a few comments on the use of photometric parallaxes for examining the differences between the trigonometric parallaxes determined by different observatories. Dr. Lutz argues that because we don’t know the cause of the observatory corrections we should not use them in forming a new parallax catalogue. I have compared the trigonometric parallaxes with photometric parallaxes determined by means of the Strömgren four colour photometry (Nørgaard-Nielsen). My conclusion is that the observatory corrections applied in the Jenkins catalogue, especially the difference between the northern and the southern observatories, are significant. Dr. Upgren has recently reviewed the discussion of the observatory corrections and concludes that the north- south discrepancy is real. Therefore, I think that you have to apply observatory corrections in some way in the new catalogue, regardless of not having a satisfactory explanation for them.
Trigonometric stellar parallaxes
Authors: Strand K. Aa.
Published: July 2016

I derive some satisfaction from the fact that the general judgment of astrometric work with reflectors as being inferior to that carried out with the long focus refractors, which existed for most of this century, is no longer generally accepted, and that the USNO 61-inch astrometric reflector has contributed to this.

If, however, van Maanen had continued his parallax work with the 60-inch Mt. Wilson reflector, or stayed within the small coma free field of the 100-inch telescope, his contributions to the parallax field would have been more justly appreciated.
Photometric and astrometric observations of close visual binaries
Authors: Rakosch K. , Albrecht R. , Jenkner H. , Kreidl T. , Michalke R. , Oberlerchner D. , Santos E. , Schnell A. , Weiss W.
Published: July 2016

Nearly 250 close visual binaries have been observed using the area scanner photometer since 1973. The observations were carried out at Figl-Observatory, Austria, Mauna Kea Observatory, Hawaii, and European Southern Observatory, Chile. Through the generous help of the Director of the Institute for Astronomy in Honolulu, Prof. Dr. John T. Jefferies, the 24 inch telescope on Mauna Kea was available for this program. Also the Directorate of ESO has kindly made available the 100 cm and 50 cm telescopes for this purpose.
Observations optiques de la radiosource β Persei
Authors: Débarbat S.
Published: July 2016

There will be a need for precise positions of optical counterparts of radio sources to be provided in the near future, so that the radio and optical position systems can be securely related. The available optical observations of β Persei are reviewed. The author will be glad to receive any unpublished observations of this star or of β Lyrae.
On possible improvment of fundamental star coordinate system using radiointerferometric and photographic Quasar observations
Authors: Gubanov V. S. , Kumkova I.I.
Published: July 2016

At present the astrometry possesses the new perspective measuring method namely very long baseline interferometry (VLBl).

Possibility of establishing inertial (unrotating) radio source coordinate system (IRCS) is one of VLBI technique advantages. This system may be useful as a reference system for studying of a wide range of geodynamic, ce -lestial mechanic, geophysic, navigational and other applied astrometry problems.
On the astrometric performance of the 60 inch L. Figl Telescope and results from a joint program of precise optical positions of radio sources in the FK4 System
Authors: Vegt Chr. de , Prochazka F. V.
Published: July 2016

The 60” R.C.Telescope of the Vienna University Observatory is located at the Schöpfl which is situated about 30 km west from Vienna in a height of about 900 m.

Fig.1 gives the optical data of the 60”.
Current results and developments in astrometric VLBI at the Jet Propulsion Laboratory
Authors: Purcell G. H. , Cohen E. J. , Fanselow J. L. , Rogstad D. H. , Skjerve L. J. , Spitzmesser D. J. , Thomas J. B.
Published: July 2016

The Jet Propulsion Laboratory is engaged in a program of astrometric VLBI as one element of a navigation system for interplanetary spacecraft. The program involves stations of the Deep Space Network in Spain, the United States, and Australia, and is now in an advanced stage of development.

As one part of this program we are developing a radioastrometric source catalog which at present contains about fifty sources with positions known to better than 0.”05. Our results agree well with those published by other groups.

We are continuing to refine our delay model, and we are improving our data reduction procedures to account better for the effects of instrumental and ionospheric delays. When the system becomes fully operational in July of 1979, we expect the catalog to contain at least a hundred sources with positions accurate to 0.”01.
Thermal and aerodynamical analysis of a meridian building
Authors: Hog E.
Published: July 2016

On a night with low wind speed, the refraction inside a conventional meridian dome can cause a systematic error about 0.”2. In view of the recent improvements of meridian techniques through photoelectric micrometers it is desirable to reduce also this remaining source of error. The present study gives a quantitative theory of the astrometric effect of insulation and ventilation of a meridian building, both for the closed and the open dome, and for daytime as well as for the night. The conclusions are formulated so that they can easily be applied to the design of new buildings and to improvement of existing ones. The design differs from current practice in that e.g. the basement should be well ventilated; the piers must therefore be insulated also in the basement. It is concluded that the slit width is not critical and that a rather narrow slit is therefore altogether preferable, quite opposite to the popular opinion that the roof ought to be completely removed during observation.

A building constructed according to these principles, including a slit of 1.4 m width, would have about 5 times smaller thermal effects than the present one in Brorfelde.

It would be interesting and simple to extend the methods and results to other astronomical domes in order to diminish seeing effects.
A general computer program for the extended plate overlap algorithm
Authors: de Vegt Chr. , Ebner E. , von der Heide K.
Published: July 2016

In contrast to the adjustment of single plates a block adjustment is a simultaneous determination of all unknowns associated with many overlapping plates (star positions and plate constants etc. ) by one large adjustment. This plate overlap technique was introduced by Eichhorn and reviewed by Googe et. al. The author now has developed a set of computer programmes which allows the adjustment of any set of contemporaneous overlapping plates. There is in principle no limit for the number of plates, the number of stars, the number of individual plate constants for each plate, and for the overlapping factor.
A comparative study of trigonometric parallax reduction techniques
Authors: Russell J. L.
Published: July 2016

Trigonometric parallaxes from measurements of photographic plates have always been reduced by some variant of the method of plate constants. From the dependences technique developed by Schlesinger (1910) to the full rigorous non-iterative approach, to be discussed below, all methods depend on the basic equations

to represent the relationship between a star’s standard coordinates (ξ, η) in the sky and its cartesian coordinates (x, y) obtained from measurements of a photographic plate. The quantities A through F are the plate constants. Besides allowing for the necessary affine transformation, these terms remove the first order effects of refraction, aberration, seeing, etc. Individual instruments may need additional terms on the right-hand side of eqs. (1) to account for errors introduced by the optical system.
Status of the Lick Proper Motion Program
Authors: Klemola A. R.
Published: July 2016

Second-epoch photographs have now been obtained for nearly 850 of the 1246 fields of the proper motion program with centers at declination -20° and northwards. For the sky at 0° and northward only 130 fields remain to be taken in the next year or two. The 270 southern fields with centers at -5° to -20° remain for the future.
Progress in the compilation of the FK5
Authors: Fricke W. , Gliese W.
Published: July 2016

Presented is a status report on work on FK5 giving information on the following items: (a) the intended increase of the number of fundamental stars and their magnitude range in FK5, (b) available material for the improvement of the system, (c) methods for the determination of systematic differences, (d) the determination of equator and equinox of FK5, and (e) the elimination of the motion of the FK4 equinox.
Relative determinations concerning the right ascensions of the FK 4 Supplementary Stars
Authors: Jackson P. , Polnitzky G. , Göbel E.
Published: July 2016

According to a recommendation of the Astronomisches Rechen-Institut Heidelberg continual observations of the FK4 and FK4 SUP stars were made at Vienna Observatory during the past ten years. The used transit instrument (Askania AP 70, 1960) was lent from the University of Technology in Vienna. It was equipped in the usual way with an impersonal contact micrometer. The aperture of 3 inches allows to reach most of the FK4 SUP stars; but only determinations of the right ascensions are possible. We also used several additional instruments, for example quartz clocks combined with digital equipments for time recording, a time signal receiver and so on. Furthermore we could get a permanent wire to an atomic clock, property of the Geodetic Department in Vienna (Bundesamt für Eich-und Vermessungswesen). Extensive and continual instrumental investigations were necessary.
Final results of relative declination observations made with the Repsold Meridian Circle at Cerro Calan
Authors: Carrasco G.
Published: July 2016

The final results of 1936 individual observations in declination of stars of the FK4 Catalogue along the whole meridian arc and 18583 individual observation of stars from the International Programme SRS and BS and FK4 in the declination zone -20° to -40° are given.

The systematic differences Δδδand Δδαand the comparison with other catalogues is presented too.
Space Telescope Astrometry
Authors: van Altena W.
Published: July 2016

The astrometric requirements for NASA’s Space Telescope were defined during the Phase B study by an astrometry team consisting of O.G.Franz, L.W.Fredrick, and W.F.van Altena (Team Leader). During the current Phase C the astrometric characteristics of the ST and its instruments are being monitored by a new team consisting of the above three and G.F. Benedict, R.L.Duncombe, P.D. Hemenway, W.H.Jefferys (Team Leader), and P.J. Shelus. Previous progress reports have been given by van Altena, et al (1974), Fredrick, et al (1975), and Jefferys (1978).
The contribution of Hipparcos to the study of open clusters
Authors: Feissel M. , Gómez A.
Published: July 2016

The observation by the projected ESA astrometric satellite Hipparcos (HIghPrecisionPARallaxesCOllectingSatellite) of stars in nearby open clusters is studied and the expected precision and accuracy of their parallax measurements are evaluated. The amplitude of local systematic errors will certainly be smaller than the precision of the results, a feature which is very seldom realized in global astrometric sets of data; this will have far-reaching consequences.

With the exception of Hyades, these measures will be the first trigonometric parallaxes ever obtained for open clusters. The precision of astronomical interferences from clusters properties will be greatly improved.
Map Making with Non-Phase Stable Interferometers
Authors: Wilkinson P. N. , Readhead A. C. S.
Published: July 2016

The ability to make reliable maps of radio sources at any available frequency and on all feasible angular scales is obviously a fundamental goal of observational radio astronomy. Unfortunately, until very recently, our map-making capability has been extremely restricted, limited in fact to those physical baselines and frequencies where phase-stable interferometers could be operated. However it is now becoming increasingly clear that phase stability is not an essential prerequisite for reliable mapping. The basic point is that whereas in principle there are an infinite number of brightness distributions which could give rise to the observed amplitudes of a set of Fourier components whose phases are unknown, in practice the a priori information that the required distribution is real and positive severely constrains the range of possibilities. Both Bates and his co-workers (e.g. Bates and Napier 1974) and Ross et al. (1978) have pointed out that the brightness distributions we are seeking are examples of ‘entire’ functions. In particular it is known that the real and imaginary parts of such functions are not independent (see references in Ross et al.) and that by studying the positions of their complex zeroes one may well be able to deduce the brightness distribution from knowing only the modulus of its Fourier transform. Unfortunately such a rigorous approach appears to be rather difficult to implement in practice. However the results of Napier and Bates (1974) have confirmed that in two dimensions reliable structure determinations can be made without phase information.
Image Reconstruction from VLBI Amplitude and Phase Closure Data
Authors: Cotton William D. , Wittels Jill J.
Published: July 2016

A two step procedure is developed for the determination of the angular structure of the compact components of radio sources from observations made with very long baseline interferometry (VLBI). The first step is to fit a model composed of circularly symmetric Gaussian components to the observations. Then this, or any other, model and closure phase information is used to predict visibility phases which, when paired with the corresponding visibility amplitude observation, are combined in a direct synthesis; the resulting map is deconvolved from the point source response by means of the “CLEAN” procedure. If necessary, the “cleaned” components can be used as a starting model to predict visibility phases and the process iterated. The initial model in many cases may be as simple as a point source. Convergence of this process appears to be quite rapid, requiring only a few iterations when the source is simple or the starting model is good. These two steps for source mapping can be used either together or separately. Examples are given using data generated from test models.
An Acousto-optical Image Processor and Its Application to a 160 MHz Interferometer
Authors: Kai Keizo , Kosugi Takeo
Published: July 2016

Radio emissions from the Sun are characterized by extremely rapid time variation. Although they are relatively strong, the signal to noise ratio becomes critical when we observe them with high resolution in space and time. To improve the S-N ratio, we have investigated the feasibility of an acousto-optical processing of interferometer images and applied it to the 160 MHz interferometer of the Nobeyama Solar Radio Observatory. We present here results of simulation experiments and preliminary solar observations with the new image processor.
Photospheric Macroturbulence in Late-Type Stars
Authors: Smith Myron A.
Published: July 2016

It is intimidating to attempt a review of the subject of late-type stars macroturbulence which follows so closely on the heels of David Gray’s (1978) fine review in Solar Physics. Therefore this paper will avoid many emphases of his review while filling in some areas where some progress has emerged in the last 1-1/2 years. My slant will come mainly from the standpoint of line broadening analysis.
Turbulence in the Atmosphere of B-Type Stars
Authors: Kodaira Keiichi
Published: July 2016

The stationary turbulent surface layer, whose depth is of the order of the pressure scale height in the subphotospheric layer, was investigated for B-type stars, using the momentum and the continuity equations with the inertia term neglected but the turbulence-viscosity term included. The mean velocity field is dominated by the horizontal component of the meridional circulation, driven by the pressure-density unbalance in the radiative envelope of the rotating star, and the differential rotation induced by the Coriolis force.

The model calculation for a B3IV-V star with the equatorial rotational velocity of 200 km/s led to the conclusions that the velocity field due to the differential rotation is of the order of 0.1-1 km/s, the velocity field of the meridional circulation itself is negligible, the velocity field of the three-dimensional shear turbulence is of the order of 0.1 km/s, and i t s scale is comparable to or less than the pressure scale height, the velocity field of the horizontal two-dimensional turbulence is of the order of 1-10 km/s, and i t s maximum scale ranges from a few times the pressure scale height to one-fiftieth of the stellar radius. If the index of the energy density law is close to 3.5, the turbulent surface layer may be dominated by the large scale (two-dimensional) barotropic eddies whose energy is fed by the small scale (three-dimensional) baroclinic turbulence in a way similar to the planetary atmospheres. In this case we may expect the tangential macroturbulence of the order of 1-10 km/s, though the interaction between this and the small-scale three-dimensional turbulence still remains to be investigated.