bluuebunny/crossref_metadata_2025 huggingface dataset:
Succession to Treaties in New States
Authors: Udokang Okon
Published: June 2019

For our present purpose it is useful to divide the Commonwealth countries into two categories according to the circumstances under which they achieved international recognition as subjects of international law: first, the older Dominions of Canada, Australia, New Zealand, Irish Free State and South Africa which acquired international identity through a gradual process of constitutional transition from Crown colony systems to responsible governments; and, second, the colonial territories that have become independent states since 1945.
Theory of Photospheric Magnetic Fields
Authors: Spruit H.C.
Published: June 2019

In this review I discuss from a theoretical point of view the magnetic fields seen at the solar (stellar) surface. Since magnetic field lines have no ends, and the photospheric fields are mostly vertical, the discussion necessarily includes some of the properties of the fields above and below the photosphere. A more general discussion of the theory of solar magnetic fields can be found in Priest (1982).
Time-Dependent Convective Collapse of Flux Tubes
Authors: Hasan S. Sirajul
Published: June 2019

The time-dependent collapse of a slender flux tube extending vertically in the convection zone of the Sun is modelled. Starting from an initial state in which the flux tube is in hydrostatic equilibrium, the non-linear MHD equations are used to examine its temporal evolution. A detailed study of the flow variables and magnetic field within the tube is presented. It is seen that asymptotically in time a unique state of dynamic equilibrium is established, irrespective of the value of βo (the ratio of the thermal to magnetic pressure at the initial epoch).
The Magnetic Field Configuration in Solar and Stellar Chromospheres
Authors: Anzer U. , Galloway D.J.
Published: June 2019

Calculations are presented for the inhomogeneous magnetic field structure above a stellar photosphere which has magnetic flux tubes located at the downdraughts of its supergranulation pattern. Regions can be delineated where the ambient magnetic energy density is large or small compared with the thermal energy density derived from a model atmosphere. This enables the relative importance of magnetic versus non-magnetic heating mechanisms to be assessed. For the quiet Sun, over half the chromospheric emission must be supplied non-magnetically, whilst the network and active regions require a magnetic supply. For other late-type stars, a simple working rule suggests that when the magnetic field is strong enough to be directly observable, the chromosphere will be magnetically dominated.
Coronal and Chromospheric Structures in AR LAC: I. Data and Models
Authors: Gibson D.M. , Walter F.M. , Basri G.S.
Published: June 2019

Traditionally stellar sizes and shapes have been determined by analyzing the optical light curves of eclipsing binaries. Now it is possible to extend our knowledge to structures above the photosphere by making similar observations at X-ray, UV, and radio wavelengths. We report the first such observations, together with their geometrical and physical interpretation, which allow us to determine coronal and chromospheric properties of the stars in the RS CVn binary AR Lac. In this paper we discuss the properties of the system, Einstein observations which provide a reasonably good X-ray light curve, IUE data which enable us to tie the inferred coronal features to the surfaces, and radio observations which allow us to separate geometric and intrinsic variations by acting as a flare monitor. We also discuss the construction of simple coronal model which, when applied to the X-ray light curve, yields the sizes and shapes of the coronae in this system. In another paper (Paper II: Walter, Gibson, and Basri, 1982), the geometrical properties of the coronae are discussed and used to determine the physical conditions within.
Electrodynamic Coupling in Magnetically Confined Stellar X-Ray Loops
Authors: Ionson James A.
Published: June 2019

The solar-coronal complex is the only astrophysical system whose X-ray structure has to some degree been spatially resolved. The most important lesson that we have learned from these relatively high-resolution observations is that the corona is highly structured, comprising a variety of closed, loop-like regions of enhanced radiative output. Furthermore, coronal radiation loops are now known to be spatially coincident with magnetic loops which confine the radiating plasma.
Theoretical Problems
Authors: Stix M.
Published: June 2019

The purpose of theoretical work is twofold: we want to understand physical mechanisms — and we want to predict numbers which can be compared with observations. In the field of solar and stellar magnetism much of the work still belongs to the first category.
Color-Magnitude Diagram Morphology of the Oldest Star Clusters in the Large Magellanic Cloud
Authors: Hesser James E. , McClure Robert D. , Harris William E.
Published: June 2019

We summarize B,V imagery results from the CTIO 4-m telescope and two electronic detectors: (1) The SIT vidicon at the R-C focus yielded pixels in the 0.82 or 1.1 arcmin2 frames (Harris, Hesser and Atwood 1983). (2) KPNO's P-F CCD (used by McClure and Hesser) gave 0.6 pixels in 3×5′ fields. (The latter data are being analyzed in cooperation with Stryker and Nemec, who observed some of the same objects.) Zero points for the CCD data are set by observations of E region standards and of giants in Galactic star clusters.
JHK Observations of Magellanic Cloud Cepheids
Authors: Welch D. L. , Madore B. F.
Published: June 2019

The pioneering work of McGonegal et al. (1982), originally employing random-phase data for the LMC near-infrared period-luminosity (P-L) relation, is refined to mean light and extended to the SMC using new observations. We use a procedure for reducing single-phase infrared observations to mean light to obtain JHK magnitudes for Magellanic Cloud Cepheids. The new  P-L relations are presented and discussed.
Spectroscopy of Overluminous Cepheids in the Magellanic Clouds
Authors: Smith Horace A. , Connolly Leo
Published: June 2019

The Small Magellanic Cloud is known to contain types of short period Cepheid variable stars not yet discovered in either the Large Magellanic Cloud or, with the exception of a single star, in the Galaxy. These variables can be divided into two categories: anomalous Cepheids and Wesselink-Shuttleworth (WS) stars. The former, which have also been found in dwarf spheroidal systems and in the globular cluster NGC 5466, have periods of 0.4–3 days, but average 0.7–1.0 mag. brighter than RR Lyrae and BL Her stars of equal period. The stars we call WS stars have periods less than about 1.1 day and, at MV = −1 to −2, are brighter than anomalous Cepheids of equal period.
Statistical Problems Encountered in Using Trigonometric Parallaxes
Authors: Lutz Thomas E.
Published: June 2019

The importance of understanding the properties of a data sample which is to be used for calibrating luminosities can hardly be overemphasized. In an earlier paper (Lutz 1983) I pointed out the methods for dealing with two well-defined cases. In this paper I will elaborate further on the same topic.
Instrument and Method for Determination of High-Precision Coordinates of Geostationary Artificial Satellites
Authors: Duma D.P. , Kizjun L.N. , Laptienko N.I. , Mel'nikov M.A. , Safronov Yu. I.
Published: June 2019

One of the promising ways for improving the precision of the angular coordinates (positions) of geostationary artificial satellites is the application of the long-focus astrograph, equiped with special equipment for tracking the satellites and recording the instants of exposure.
Speckle Interferometry in Astrometry
Authors: McAlister Harold A.
Published: June 2019

Speckle interferometry, which is characterised by diffraction limited resolution and enhanced accuracy, offers a wide range of possibilities for astrometry. Speckle applications are limited by the constraint of isoplanicity with the result that only differential rather than absolute astrometry can be carried out with the technique. Nevertheless, potentially important applications exist in solar system and stellar astrometry, but speckle interferometry has so far made significant contributions only in binary star astrometry.
Formation of Organic Molecules by Formaldehyde Reactions in Astrophysical Ices at Very Low Temperatures
Authors: Schutte W. A. , Allamandola L J. , Sandford S. A.
Published: June 2019

Warm-up of astrophysical ice analogues containing formaldehyde produced organic residues in large abundances. It is argued that formaldehyde reactions at very low temperatures could be an important source of interstellar and cometary organic molecules.
Deuterium in the Diffuse Interstellar Medium
Authors: Ferlet R.
Published: June 2019

We review the observational status in evaluating the interstellar deuterium abundance and show that the most reasonable value is of the order of 10−5. Although in general agreement with the standard Big Bang nucleosynthesis, the situation is still unclear and deserves much more observations.
A 158μm [CII] Map of NGC 6946: Detection in Extragalactic Atomic and Ionized Gas
Authors: Madden S. C. , Geis N. , Genzel R. , Herrmann F. , Poglitsch A. , Jackson J. , Stacey G. J. , Townes C. H.
Published: June 2019

The first observations of the [CII] line toward the nuclei of gas-rich external galaxies, showed that the far-infrared line emission contributes up to 1% of the total luminosity and most likely originates from dense photon-dominated regions (PDRs) associated with the surfaces of molecular clouds exposed to FUV from external or embedded OB stars (Crawford et al. 1985, Lugten et al. 1986, Stacey et al. 1991). We have mapped the [CII] emission toward NGC 6946 over an 8' × 6' (23 × 17 kpc) (Madden et al. 1991) using the Max-Planck Instutute/U.C.Berkeley Far-Infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory (KAO).
The Structure of Quiescent Clouds
Authors: Falgarone E.
Published: June 2019

Several tracers of the cold interstellar medium in its quiescent phase reveal common unexpected properties: the fractal nature of the emission contour levels, the self-similar brightness distribution, the existence of small unresolved fragments of dense gas in various environments, and a highly turbulent velocity field. In spite of the difficulties met in interpreting these data, they are important bearings in our understanding of the structure, the physics and the chemistry of this medium.
Results from a Three Position Spectral Scan in the Sgr B2 Molecular Cloud Core
Authors: Bergman P. , Hjalmarson Å. , Friberg P. , Irvine W. M. , Millar T. J. , Ohishi M. , Saito S.
Published: June 2019

We report on results from an ongoing spectral scan of four nearby positions in the Sgr B2 molecular cloud using SEST (Swedish-ESO Submillimeter Telescope). The antenna beam size is approximately 22″ in the frequency range 226-245 GHz presently covered. This high angular resolution allows detailed studies of the physical and chemical conditions in the warm and compact cores discovered (Vogel et al. 1987, Goldsmith et al. 1987) inside the region previously surveyed in the 3 mm band with lower angular resolution (Cummins et al. 1986, Turner 1989, beam sizes of 1.5-2.9′ and 1-2′, respectively). The Sgr B2(OH) position used by these investigators is located about 30″ south of our M position, and hence the cores M and N will contribute to the observed spectral line emissions to a larger or lesser extent.
Carbon Isotopic Chemistry
Authors: Langer W. D.
Published: June 2019

Isotopic molecular abundances are used to interpret Galactic chemical evolution and the properties of interstellar clouds. The isotopic chemistry of carbon plays an important role in the interpretation of these measurements. This paper reviews the recent measurements of the carbon twelve to thirteen ratio across the Galaxy and the isotopic chemistry.
Nitrogen Sulfide (NS) in Star Forming Regions
Authors: Mcgonagle Douglas , Irvine William , Minh Young
Published: June 2019

Gas phase models of ion molecule chemistry have been rather successful in matching the observed abundances of small interstellar molecules containing carbon, hydrogen, and oxygen. However, the situation is somewhat less clear for nitrogen-containing species, partly because the important initiating reaction N+ + H2 is slightly endothermic; and for sulfur-containing molecules, where it remains uncertain whether it is necessary to invoke surface reactions on grains to match the observed abundances. As a relatively simple species, the abundance of nitrogen sulfide should provide a good test of the models of the coupled chemistry of nitrogen and sulfur. Until very recently only two molecules containing both these elements were known in the interstellar medium, NS and HNCS, and both have been observed only in Sgr B2. We have therefore undertaken a survey for interstellar NS in Galactic molecular clouds using the FCRAO 14-meter telescope. The 2Π1/2, J = 5/2 → 3/2, transition has in fact been detected in many regions of massive star formation (see table).
Preliminary Observations of the Galaxy with a 7° Beam by the Cosmic Background Explorer (COBE)
Authors: Wright Edward L.
Published: June 2019

The FIRAS instrument on COBE has mapped almost the entire sky with a 7° beam and a spectral resolution of about 1 cm−1 over the 1-100 cm−1 range. Maps showing the strengths of the three main components: dust continuum, [C II] and [N II] are presented. A mean spectrum of the galactic emission is found. These results are used to compare the Milky Way to other galaxies.
Molecular Studies of Herbig-Haro Objects
Authors: Curiel Salvador
Published: June 2019

Recent ultraviolet, infrared, millimeter and centimeter-wavelength observations have revealed that HH objects are also sources of molecular line emission. Infrared observations have shown that H2 line emission in HH objects presents a wide and complex variety of morphologies, being in most of the cases similar to that observed at optical wavelengths. New high-angular resolution radio observations of molecular lines have revealed that small high-density condensations are frequently found in association with HH objects. Below, a brief review of molecular emission in HH objects is presented.
Interstellar and Meteoritic Organic Matter at 3.4 μm
Authors: Ehrenfreund P. , Robert F. , d'Hendecourt L. , Behar F.
Published: June 2019

The 3 micron spectrum of the galactic center source IRS 7 is compared to a spectrum obtained on the deuterium-rich organic polymer extracted from the Orgueil carbonaceous meteorite. The almost perfect match between the two spectra in the 3.4 μm region suggests that the chemical composition of the interstellar organic matter resembles that of the meteoritic macromolecule.
Mass Loss Rates of Three Comets
Authors: Singh P.D. , Huebner W.F. , Boice D.C. , Konno I. , Scalise E.
Published: June 2019

Emission features of C2, C3, CN, and dust in Comets Thiele (1985m), Hartley-Good (1985l), and Giacobini-Zinner (1984e) have been analyzed and their mass loss rates of about 0.5, 1.1, and 0.8 Mg s−1 have been determined.
Stability of Asteroid Motions
Authors: Kozai Y.
Published: June 2019

In this paper the author presents evidences showing that for most of the asteroids the motions are stable in the sense that they never approach major planets very closely and explains about mechanisms to avoid very close approaches by investigating the variations due to the secular perturbations of the eccentricities as functions of the arguments of perihelion, particularly, for asteroids with high eccentricities and inclinations. It is believed that some kinds of dynamical evolution processes have made the asteroid motions stable. The author shows also that there were some kinds of collisions among asteroids in the past which produced families and present distribution of asteroids as there are very faint asteroids only near Kirkwood gaps.
Proper Elements of the Asteroids: A Semi - Analytical Method
Authors: Lemaitre Anne
Published: June 2019

We propose here the first results of the semi analytical method of Henrard(1990) applied to the calculation of proper elements for the asteroids.
Generalized Canonical Systems. Formal Solutions and the Main Problem of Satellite Theory
Authors: Fernandes Sandro Da Silva
Published: June 2019

The generalized canonical version of Hori's method is discussed using some properties of generalized canonical system and, then, applied in solving the main problem of satellite theory.
On the Relationship Between Comet P/Machholz and the Quadrantid Meteor Stream
Authors: Gonczi R. , Rickman H. , Froeschlé C.
Published: June 2019

The Quadrantid meteor shower has been recognized for more than 150 years. The dynamics of the corresponding stream is peculiar due to the high orbital inclination and, for some particles, the closeness of the 2/1 mean motion resonance with Jupiter. It has been the subject of many investigations relating to the structure of the stream and its nodal retrogression as well as its long-term history and its likely cometary origin. Thus Hamid and Youssef (1963) found that the jovian secular perturbations lead to very large changes in the inclination and perihelion distance of typical stream particles with a period around 4000 yrs. From a more extensive study by Williamset al.(1979) it was obvious that this period is not unique but may vary considerably between different particles. Related to this behaviour is also the investigation by Froeschlé and Scholl (1982) who performed an extensive study of three-dimensional orbits at the 2/1 resonance. The orbits remain confined in the resonance zone and are stable in Hill's sense. Close encounters with Jupiter are avoided through the action of three main protection mechanisms:σlibration around 0,ωlibration aroud 90°, ande–ωcoupling, although most orbits exhibit large variations in inclination and eccentricity. Investigating in more detail a Quadrantid-like meteor stream, Froeschlé and Scholl (1986) also found a nonuniform nodal retrogression and an unusual progression. This behaviour causes a formation of arcs which was not found for other meteor streams in resonance with Jupiter – however, almost never having large inclinations.
The Quadrantid Stream, Chaos or Not?
Authors: Wu Zidian , Williams Iwan P
Published: June 2019

The Quadrantid stream covers a region of space which contains many strong resonances and commensurabilities with the Jovian orbit. We have numerically integrated the orbital evolution of over one hundred actual meteoroids backwards to BC 5000. The evolution is quit complex, but most of the meteoroids are quite well behaved with rapid but smooth changes in the orbital elements. One meteoroid however shows sharp sudden changes in its orbital parameters and these changes are generally indicative of the presence of chaos.
Plans and Objectives of the Remaining Apollo Missions
Authors: Scherer L. R.
Published: June 2019

The three remaining Apollo missions will have significantly increased scientific capabilities. These result from increased payload, more time on the surface, improved range, and more sophisticated experiments on the surface and in orbit. Landing sites for the last three missions will be carefully selected to maximize the total scientific return.
Maria Lavas, Mascons, Layered Complexes, Achondrites and the Lunar Mantle
Authors: Biggar G. M. , O'hara M. J. , Humphries D. J. , Peckett A.
Published: June 2019

Experimental data show Apollo 11 and 12 lava compositions to be controlled by fractional crystallization close to the lunar surface, in a process which yields achondrite-like igneous rocks as underlying complementary crystal accumulates. Volatilization losses during eruption can account for most other chemical differences between lunar lavas and common terrestrial magmas. No specific hypotheses of the composition, mineralogy, or origin of lunar interior can be sustained until the extent of these processes is known. A terrestrial upper-mantle-type lunar interior cannot yet be excluded. The assumption that maria surface lavas are primary partial melts is unjustified and leads to a postulated lunar interior with too low Mg/Mg+Fe to serve as a source for Apollo 14 and other igneous liquids. Other workers' uncontrolled visual estimates of crystallinity in experimental charges, purporting to show that maria lavas were not modified by low pressure fractionation, are irreconcilable with the chemistry of the residual liquids developed in our ‘reversed’ equilibrium experiments. The undesirability of using glass as a starting material for this type of experiment is re-emphasized.
Interferometric Studies on Apollo 11 and Apollo 12 Lunar Glass Objects
Authors: Tolansky S.
Published: June 2019

A review of results obtained by an examination with optical interferometry of a variety of glassy objects found in lunar fines from Apollo 11 and 12. Glassy spheres, cylinders, chips and fragments have been examined. It is established that many spherules show

(a) evidence of shock;

(b) evidence of impact with a small particle;

(c) very high specularity.

Some small pieces of lunar glass reveal the characteristic step pattern shown by glass shattered in the laboratory.
Convection in the Moon
Authors: Runcorn S. K.
Published: June 2019

It is natural to inquire whether thermal convection is occurring in the Moon through solid state creep processes. The primary evidence is the departure of the Moon from the figure of hydrostatic equilibrium, but certain difficulties in the thermal history of the Moon are eased by assuming heat transfer by convection. If convection exists in the Moon it must have a second harmonic pattern, otherwise the lunar moments of inertia would not differ.

Two important predictions of the marginal theory of convection: the existence of a core of radius 0.06–0.3 of the lunar radius (for a second ergee harmonic) and the value of 0.4 for the ratio of the dynamical to surface ellipticities now have support, the latter from the data of the heights of the lunar surface. The former prediction is compatible with the value of the moment of inertia factor now found if the Moon's interior is ‘hot’.

Further the existence of a fluid iron core 3400 m.y. ago seems required as a result of the remanent magnetization of the crystalline rocks of the maria basins inferred from the remanent magnetization of the returned Apollo samples and the fields measured by the Apollo 12 and Explorer magnetomers.
Fluidization on the Moon and Planets
Authors: Mills A. A.
Published: June 2019

A dual origin of lunar formations by both exogenous and endogenous mechanisms is now generally accepted. These processes are normally equated with impact and volcanism respectively, but many aspects of the latter cannot be readily identified with present-day terrestrial volcanism. It is proposed that lunar volcanism involved large volumes of gases and volatiles, so that ‘fluidization’ of particulate systems occurred. Terrestrial fluidization structures and model studies are described and illustrated. Certain lunar rilles and transient phenomena are also suggested to result from degassing of the interior. Some possible applications of fluidization to Mars and the synthesis of electropolymers are mentioned.
Summary-Introduction
Authors: Underhill A. B.
Published: June 2019

The term ≪ astronomical turbulence ≫ may be interpreted in a variety of ways. For the purposes of this paper, it is assumed that this expression is equivalent to the term ≪ velocity fields ≫. Thus this paper will summarize our knowledge of (i) the magnitudes of the velocities occurring in the atmospheres of reasonably stable stars, (ii) the time-dependence, and (iii) the directional characteristics of the velocity fields that exist. Neither motions in the atmospheres of explosive variables, nor motions in the atmospheres of strictly periodic variables, nor solar phenomena will be discussed. This summary is restricted to spectrographic observations of stars that have not changed their character radically since they were first observed some fifty or sixty years ago. The stars which are studied can hardly all be classified as stable stars, for changes do occur in their light and spectrum, but in no case are the changes catastrophic.
Summary-Introduction
Authors: Severny A. B.
Published: June 2019

Speaking on localized velocity fields on the Sun, we mean the velocity fields in active regions on the disk. The experimental data used to picture these fields are based mainly on 1) the observations of Doppler shifts of spectral lines, 2) the form (asymmetry) of line profiles, 3) moving picture process in monochromatic, mainly Hα and H or K, light. However the big skin-time of solar plasma makes these data insufficient to get an adequate and complete idea about the motions in active regions, and we must also take into account the available observational data about magnetic fields in these regions. Somewhere the state of affairs permits one to disregard the possible influence of magnetic fields on the picture of velocity fields But these occasions are comparatively rare, because the main source of solar activity is closely, but in a not quite recognized way, connected with magnetic activity of the Sun. This is why we should in our talk consider as closely as possible both subjects—the motions in active regions and their magnetic fields. The best illustrations of the necessity of such a mode of consideration are the velocity fields in sunspots.
Summary-Introduction: Collision-Free Plasmas
Authors: Petschek H. E.
Published: June 2019

In many cases, the outer atmosphere or corona regions of stars are not dominated by the ordinary process of collisions between ions. Very roughly, collision-free phenomena become of interest when the mean free path for interparticle collisions is larger than the region of space being considered. For solar corona conditions, if we consider a density of 107 particles per cubic centimeter and a typical particle velocity of 500 kilometer per second, the mean free path is a few times the solar diameter. At the same velocity for a density of 100 particles per cubic centimeter, corresponding to the interplanetary density, the mean free path would be a thousand astronomical units. Since in both of these regions, we are interested in smaller dimensions, it is of interest to consider the properties of a plasma in which collisions are very rare.
OH/IR stars as tracers of Galactic populations
Authors: Habing H.J.
Published: June 2019

I discuss observable quantities of OH/IR stars and their interpretation. The strong 1612 MHz maser is found in about 1/2 of all the stars that reach the AGB and then have the following properties: they are oxygen–rich, of high–luminosity (3,000 → 30,000L⊙), vary in luminosity with a long period (P>500 d), lose mass rapidly and have a metallicity high enough to form sufficient amounts of dust (the metallicity of the LMC is probably the lowest value sufficient to produce OH/IR stars). OH/IR stars can be several Gyr old. There are at least three different populations each characterized by different galactic orbits. (1) OH/IR stars in the galactic disk on almost circular orbits; (2) OH/IR stars in the galactic bulge on orbits of lower angular momentum; (3) OH/IR stars within 150 pc from the galactic center forming a rapidly rotating system.
MgI triplet lines in composite systems
Authors: Barbuy B. , Souza R.E. De , Anjos S. Dos
Published: June 2019

We use information contained in CMDs of metal-rich globular clusters, in order to compute a grid synthetic spectra for 10 evolutionary stages. These synthetic spectra are added up to reproduce the composite spectra of S0/E galaxies.
Metallicity of two stars in Baade's window
Authors: Castro S. , Barbuy B. , Richtler T.
Published: June 2019

Low resolution spectra of two stars of the Baade Window were obtained with the 1.5m telescope at ESO. Their temperatures and gravities are obtained by using their location in colour magnitude diagrams of bulge clusters, and through synthetic spectra fitting, their metallicities are derived.
The Bulge-Halo transition region
Authors: Ibata Rodrigo , Gilmore Gerard
Published: June 2019

The Baade's Window bulge is a metal-rich, rotationally supported entity, whereas the solar neighbourhood halo is metal-poor and non-rotating; what is the connection between these two spheroid components?

We present results of a spectroscopic survey of 847 K-giants from 3 low absorption windows at (5,-12), (-5,-12) and (-25,-12). This is a seven times larger sample than has been previously studied in this region.
Kinematical features of the main Bulge in a multi-component galactic model
Authors: Cubarsi Rafael , Hernandez-Pajares Manuel
Published: June 2019

The present state of the Galaxy can be idealized as a stellar system with several components: inner bulge, main bulge, thin disk, thick disk, stellar halo, corona, etc. In the regions where the diffusion phenomena are negligible, the dynamics can be determined from a conservative dynamic system, according to the superposition principle with a common potential. Here we describe the kinematical behavior of the main bulge, thin and thick disks, and stellar halo, depending on the cylindrical galactocentric coordinates r and z, under axisymmetric conditions. The angular dependence is treated in the work by Sanz-Subirana & Juan-Zornoza (1992).
Two-integral distribution functions for axisymmetric galaxies
Authors: Hunter C. , Qian E.
Published: June 2019

We present a new method for finding a distribution function f, which depends only on the two classical integrals of energy E and angular momentum J about the axis of symmetry, for a stellar system with a known axisymmetric potential and density.
Tumbling instability in oblate rotating stellar systems
Authors: Szuszkiewicz E. , Papaloizou J.C.B. , Allen A. J. , Palmer P.L.
Published: June 2019

We present evolutionary calculations which show the tumbling instability found in spherical stellar systems by Allen et al. (1992) also occurs in some initially oblate rotating systems.
Investigating a self-consistent galactic potential with central mass
Authors: Hasan H. , Sellwood J. A. , Norman C. A.
Published: June 2019

The evolution of a barred galactic potential containing a central mass concentration is examined by means of a self-consistent 2-D N-body simulation. It is found that the bar weakens as the central mass grows and eventually dissolves, in agreement with earlier orbital studies of this problem.
Photometric and kinematic properties of disky elliptical galaxies
Authors: Scorza Cecilia
Published: June 2019

New insights in the structure of elliptical galaxies have been obtained indicating the presence of faint stellar disks in some of these systems. Clear correlations between the isophotal shapes, the kinematic, radio and X-ray properties of disky E's were found, suggesting that these galaxies form together with SO's a continuous transition of D/B ratio in the Hubble sequence (Bender et al. 1989). The isophotal shapes of these galaxies have been quantified by the fourth cosine coefficient a4 of the Fourier expansion of the deviations from perfect ellipses, which yields positive values when the isophotes are pointed along the major axis (Carter 1987, Lauer 1985, Jedrzewski 1987, Bender and Möllenhoff 1987).
Abundance jump in the inner bulges of galaxies
Authors: Chenko O. K. Sil'
Published: June 2019

The metallicity difference of about an order between the kinematically decoupled nuclei and the surrounding bulges is found in 3 spiral galaxies possessing an axisymmetric potential in their centres.
Observations of HII Regions and Planetary Nebulae: the Infrared Emission Bands
Authors: Bregman Jesse D.
Published: June 2019

Advances in infrared spectrometers and the theory that PAHs are responsible for the infrared emission bands have led to a wealth of new information in recent years. High quality data have shown many weak emission bands which are diagnostic of the material producing the bands. While correlations of the strengths of the narrow bands indicate that a single material can account for all of the narrow bands, independent spatial behavior of the narrow and broad components show that they have different origins. Predictions of the behavior of the spectra based on laboratory data have been confirmed observationally, strengthening the theory that PAH molecules are the origin of the infrared emission bands.
The PAH Hypothesis and the Extinction Curve
Authors: Léger A. , Verstraete L. , D'Hendecourt L. , Défourneau D. , Dutuit O. , Schmidt W. , Lauer J. C.
Published: June 2019

The Polycyclic Aromatic Hydrocarbon (PAH) hypothesis states that a mixture of free PAH molecules is an ubiquitous and abundant component of the interstellar matter. It has been first formulated by Léger and Puget (1984) on the basis of molecular stability that made PAHs good candidates for the very small grains proposed by Sellgren (1984). Then, they obtained strong, although not final, support from spectroscopy.
5 Years of VLBI and X-Ray Observations of NRAO 140
Authors: Marscher Alan P.
Published: June 2019

The author and his collaborators have observed NRAO 140 twice at X-ray energies and numerous times with multifrequency VLBI. The VLBI observations reveal a knotty jet structure with superluminal motion of the innermost two knots relative to the core. The VLBI core decreased by about a factor of 2 in flux density between 1980 and late 1984. The X-ray flux also declined by about the same factor during this period. Monitoring at 18 cm during periods of low-frequency variability has revealed pronounced changes in the relative brightnesses of the components of the source while the total flux density has varied by ≲ 10%.
Superluminal Behaviour of the Double-Lobed Radio Galaxy 3C111
Authors: Preuss Eugen , Alef Walter , Kellermann Kenneth I.
Published: June 2019

Due to sensitivity problems only about a dozen of the powerful double-lobed radio galaxies have so far been mapped with VLBI. Even less is known about the time dependence of the small scale structure in these objects (Preuss and Alef, 1987). We have recently reported the first results of our monitoring program of classical double sources. We observed strong changes of the pc-scale structure in 3C111 (Götz et al., 1987) and 3C390.3 (Alef et al., 1987) implying “superluminal behaviour” in both sources. This is the first time that such a phenomenon has been found in lobe-dominated radio galaxies. Both objects are Broad Line Radio Galaxies of type N, and their radio emission from m to cm wavelengths is dominated by their outer lobes which are ∼300 kpc apart (H0 = 50 km/s/Mpc).
VLBI Structure of the QSO 3C286
Authors: Kus A. J. , Marecki A. , Neff S. , van Ardenne A. , Wilkinson P. N.
Published: June 2019

The steep, small angular size QSO 3C286 (z = 0.846, mv = 17m) (Burbidge and Burbidge 1969) is a bright object in the radio band, which has a steep spectrum (α = −0.65, S ∼ fα) from 1 GHz, peak in spectrum at about 100 MHz, and self-absorption below 50 MHz. 3C286 is a member of a well established class of radio sources (the CSSQSO) and is similar to 3C147, 3C309.1, and 3C380 in general.
Evolution of the Milliarcsecond Polarization Structure of the Superluminal Quasar 3C345
Authors: Wardle J. F. C. , Roberts D. H. , Brown L. F. , Gabuzda D. C.
Published: June 2019

The λ6 cm milliarcsecond polarization structure of 3C345 has been determined at three epochs between December 1981 and March 1984. The knots C2, C3, and C4 all showed changes as they moved away from the core, which remained virtually unpolarized.
Physics of Cosmic Masers
Authors: Strelnitskij V. S.
Published: June 2019

Natural masers, which emit powerful narrow-band radiation in molecular microwave lines, were discovered about 20 years ago. They draw the astrophysicist's attention in two ways: 1) as a unique physical phenomenon and 2) as very informative probes of physical conditions in those astrophysical objects (very young and very old stars) with which they are intimately connected. In this paper, the first aspect of masers will be stressed, though some consideration will be given to the astrophysical aspect as well. The limited space here will not allow a complete discussion. For a more systematic account, refer to reviews on astrophysical masers by Litvak 1974; Strelnitskij 1974; Kegel 1975; Cook 1977; Moran 1976; Reid and Moran 1981; Elitzur 1982. I shall limit myself only to several topics of general character, which, to me personally, seem to be particularly important for understanding the fundamental principles of cosmic maser physics. I shall then try to illustrate these general principles by the example of H2O masers in star formation regions. These masers, in my opinion, are the most intriguing of all the cosmic masers known at present. And (to make the subjectivity of the report complete!) I shall lay special stress on the results obtained by our group in the last few years.
VLBI Observations of the H2O Maser Outburst in Orion KL
Authors: Matveyenko L. I. , Graham D. A. , Diamond P. J.
Published: June 2019

We present preliminary results from a seven year VLBI study of the H2O maser outburst in Orion-KL. Our results reveal changes in the profile, in the spatial structure and in the polarization characteristics of the H2O masers. We interpret our data in terms of edge-on rings rotating about a protostellar object.
SiO Maser Observations - VLBI and Polarimetry
Authors: McIntosh G.C. , Predmore C. R. , Moran J. M. , Greenhill L. J. , Reid M. J. , Rogers A.E.E. , Barvainis R. E.
Published: June 2019

The spatial distribution and polarization characteristics of the SiO (v=1, J=1-0) maser emission from several late type stars have been observed. The spatial distribution, derived from VLBI observations, generally shows a number of emitting regions but no clear velocity pattern or geometry. Some of these regions have well defined polarization characteristics. The results of high spatial resolution polarization measurements of RCas are similar to the lower spatial resolution polarimetry performed on this source.
VLBI Observations of an Expanding Jet in Cygnus X-3
Authors: Molnar Lawrence A. , Reid M. J. , Grindlay J. E.
Published: June 2019

The X-ray binary Cyg X-3 offers a rare opportunity to study the physical conditions of the formation of a relativistic jet. While the central engines of extragalactic jets are generally poorly understood, the infrared and X-ray data on Cyg X-3 allow detailed modelling of the conditions in the inner disk and corona, the source of the jet energy. Study of the periodic nature of particle injection into the jet may yield an important clue to the nature of the particle injection mechanism. And the time scale of jet evolution is much shorter than for extragalactic sources, allowing the possibility of observing a large number of flares to determine general characteristics.
The Long Term Stability of VLBI Earth Orientation Measurements
Authors: Eubanks T. M. , Steppe J. A.
Published: June 2019

Tectonic motions will, in general, change the orientation as well as the length of baselines used in Very Long Baseline Interferometry (VLBI), and will thus cause slow divergences between Earth orientation results obtained with different VLBI networks, as well as between VLBI results and those obtained by Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR). Such drifts (on the order of a milliarcsecond /year) are inherently interesting as well as being significant in combinations of orientation results from different sources. The geodetic study of tectonic motions is also closely connected to research into the nature and causes of systematic errors in data from the modern techniques of space geodesy. We describe both a special coordinate system found to be of use in the analysis of VLBI data and tectonic motion estimates for a VLBI baseline stretching from California to Australia.
URAN, A Decameter Band VLBI System
Authors: Braude S. J. , Litvinenko L. N. , Megn A. V.
Published: June 2019

Until recently, regular interferometric measurements were not performed at decameter wavelengths. The reasons are well known, i.e., effects of the ionosphere and the interplanetary plasma, the inherently high level of interference and of the galactic background, and the necessity to have very large antennas. Yet, because of the considerable interest in such observations, the Ukrainian SSR Academy of Sciences has started a project aimed at the development and construction of a system of decameter band interferometers (project URAN, from the “Ukrainian Radio Interferometers of Academy of Sciences (Nauk)”). By 1989, the system will involve four interferometers with baseline lengths between 40 and 900 km. The basic instrument of all these is the N–S arm of the large UTR-2 radio telescope operated by the Institute of Radio Astronomy in Kharkov. The antenna is an electrically controlled phased array of broad band dipoles (total length about 1800 m). At the other sites, the antennas are smaller phased arrays (maximum length about 230 m) consisting of crossed dipoles.
The Australia Telescope Long Baseline Array
Authors: Norris R. P.
Published: June 2019

Progress on the Australia Telescope, due for commissioning in 1988, is on schedule. When complete, the Australia Telescope will consist of a 6-km compact array and a Long Baseline Array which will, in collaboration with the University of Tasmania and NASA, use baselines up to 1400 km. Here I focus on the novel features of the Long Baseline Array, which is planned to use satellite linked local oscillators and VLBA data acquisition terminals to provide a VLBI network capable of expansion both within Australia and overseas.
The Development of the Torun VLBI Station
Authors: Gorgolewski Stanislaw
Published: June 2019

The Torun VLBI Station is situated in Piwnice near the site of the Torun Radio Astronomical Observatory on the Nicolaus Copernicus University Land Estate, about 10 km north of Torun. The VLBI station development started in 1976, when the rubidium frequency standard was ordered and the ground was broken for the foundation of the 15-m equatorially mounted dish. The construction of the Mark II-C VLBI system began in 1977, and the completed VLBI station was first tested in 1980. The first fringes were obtained on May 31, 1981, with the Effelsberg 100-m dish. This experiment started our work with the European VLBI Network (EVN), and later in 1984 with the Global VLBI Network. We now have five radiometers and have received funding for the construction of a new VLBI station, with a 32-m dish, which is now in the final design stage.
Compact Cryogenic Receivers for the 1.3 to 43 GHz Range
Authors: Weinreb S. , Norrod R. , Pospieszalski M. W.
Published: June 2019

A series of front-ends utilizing small closed-cycle refrigerators and very low-noise, high-electron-mobility transistor (HEMT) amplifiers have been developed for use in the Very Long Baseline Array (VLBA). The frequency bands, amplifier noise temperatures, expected system temperatures, and current status are shown in Table I. The receivers are designed to be light weight (∼ 55 pounds except for 105 pounds at 1.5 GHz) for ease of installation and maintenance, are easily remotely controlled and monitored, and provide dual-channel circular polarization capability. Detailed descriptions of some of the front-ends are given in VLBA technical reports.
Quasar Emission - Line Strengths
Authors: Green Richard , Osmer Patrick , Porter Alain
Published: June 2019

The strongest lines have been measured in 73 quasar spectra from the archives of the International Ultraviolet Explorer Satellite. The optically bright quasars observed with IUE were typically discovered by powerful radio emission or ultraviolet excess. They therefore should not be biased directly by observational selection with respect to ultraviolet line strength.
The Shape of Soft X-ray Spectra of Quasars
Authors: Schwartz D. A. , Qian Y. , Tucker W. H.
Published: June 2019

Several lines of evidence suggest that the x-ray spectra of quasars are not simple, exact power laws: 1. when Wilkes and Elvis (1987) analyzed quasars as power laws they found an absorption less than that due to our galaxy; 2. The mean 0.3 to 3.5 keV spectral index is steeper than the mean for the 2 to 20 keV range; 3. although several lines of evidence argue that AGN provide a significant portion (perhaps all) of the x-ray background, the diffuse background spectrum does not agree with the x-ray power-law indices measured for quasars or Seyfert galaxies. Schwartz and Tucker (1988) have suggested that all the above conflicts are reconciled if the slope in the Log(flux density) vs. Log(energy) plot flattens continuously with increasing energy. In this paper we utilize one particular parameterization suggested for the flux density, which we call the “log-slope” model:

where f is the flux density, K a normalization parameter which is not of interest here, and a and b are the two parameters of our fit.
An X-ray Spectral Survey of BL Lac Objects
Authors: Barr P. , Giommi P. , Pollock A. , Tagliaferri G. , Maccagni D. , Garilli B.
Published: June 2019

A wide variety of X-ray spectral forms has been reported in BL Lac objects. Concave spectra, i.e. a steep soft X-ray spectrum with a flat high energy tail, have been reported in a few of the brightest BL Lacs (e.g Urry 1986). Conversely, convex spectra (steep hard X-rays, flat soft X-ray spectrum) have also been reported, sometimes in the same objects (Madejski 1985, Barr et al 1988, George et al 1988). The high energy tails have usually been invoked as a signature of synchrotron-self-Compton emission. Two conflicting interpretations of the convex spectra have been made. Urry et al (1986) suggest absorption by a partially ionised medium, probably intrinsic to the BL Lac object, following the identification of an Oxygen absorption trough in the Einstein OGS spectrum of PKS 2155-304 by Canizares and Kruper (1984). Conversely, Barr et al (1988) attribute the hard X-ray steepening to energy loss mechanisms operating on a synchrotron source.
X-ray Background Constraints on the Log N–Log S Relation for AGN
Authors: Boldt Elihu
Published: June 2019

The most definitive information presently available on X-ray source populations comes from surveys carried out with the HEAO program (i.e., the all-sky HEAO-1 mission and the HEAO-2 Einstein Observatory) and EXOSAT. The large-sky/low-sensitivity survey (LSS) at high galactic latitudes performed with the HEAO-1 A2 experiment (Piccinotti et al. 1982) is complete and optically identified down to the level of about a millicrab. The LSS overlaps in spectral coverage (2–50 keV) with observations of the cosmic X-ray background (CXB) obtained with the same detectors (Boldt 1987). CXB surface brightness fluctuations observed in this band have been used to set constraints on the Log N–Log S relation for sources an order of magnitude fainter than those resolved in the LSS (Shafer 1983).
Quasar Evolution and the Growth of Black Holes in the Nuclei of Active Galaxies
Authors: Blandford R. D.
Published: June 2019

The observed evolutionary behavior of active galactic nuclei is compatible with a model in which black holes form in the nuclei of new-born galaxies and then grow at a rate limited by both radiation pressure and the supply of gas. Individual sources become more luminous with time as long as they are being fueled. However, the rapid decrease in the mean rate of supply of gas causes a strong decline in the space density of active objects. Nearby galaxies should harbor modest size (∼ 106 – 108 M⊙) black holes. It is suggested that the gas that fuels high redshift quasars is mostly derived from the host galaxy.
Line Emission from Accretion Disks in Active Galactic Nuclei
Authors: Collin-Souffrin S. , Dumont A.M.
Published: June 2019

If accretion disks are present in AGN and extend to large radii they should contribute substantially to the Broad Line emission. The outer regions of the disk are indeed illuminated by a small amount of ionizing radiation. X-rays are emitted by the central inner region near the black hole, and they are either received directly by the outer disk, owing to its “flaring” shape (Cunningham, 1976), or partly reflected towards the disk by a hot Compton thin medium (Begelmann and McKee, 1983). X-ray photons are also produced through the Inverse Compton mechanism in compact radio sources located above the disk(“jet model”).