bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation, Equilibrium and Stability of Jets
Authors: Norman Colin A.
Published: June 2019

Consideration of the many observed types of jets on scales ranging from parsecs to megaparsecs seen in radio, optical, infrared and X-ray wavebands with a variety of morphologies both in galactic and extragalactic systems leads to some constraints on their fundamental nature. Jet formation is introduced with the concept of the Laval nozzle and related points include the problem of maintaining the nozzle, Mach disk effects due to under and over-expansion and the potential importance of magnetic confinement and focussing. Current ideas on jet formation at the black hole and accretion disk are given with emphasis on the plasma physics associated with black-hole electrodynamics, thermal and magnetically driven winds and thick disks. Stability of jet propagation is reviewed with emphasis on magnetised and unmagnetised Kelvin-Helmholtz instabilities and the various dominant modes. The particle acceleration physics of shocks, wave-particle interactions and turbulence is summarised while noting some outstanding plasma physics problems. Jet equilibrium associated with the non-linear saturation of instabilities, the formation of cocoons, shock stabilisation and magnetic fields is discussed. Detailed plasma physics studies that could significantly clarify jet physics are indicated.
Links Between Jet Instabilities, Radiation and Propagation in Astrophysics
Authors: Benford Gregory
Published: June 2019

At the head of a jet the confining medium of plasma frequency νp is compressed, so that streaming instabilities between relativistic electrons and this plasma produce waves at νp′ > νp. Considerable power can be lodged in these electrostatic waves, and conversion to electromagnetic waves allows them to propagate far beyond the jet. Emission at ν ≈ νp′ or Compton boosted radiation at ν ≲ γ2 νp′ yields a cone of radiation of angle ~ 1/γ, which illuminates the region directly in front of the jet. This emission is not absorbed by the surrounding plasma unless a cloud blocks the jet. Absorption in a cloud can lead to tunneling through large clouds, or propelling of smaller clouds out of the jet path. In this fashion jets may clear their way through an inhomogeneous medium, avoiding lateral disturbances and preheating their path.
Observational Evidence for Magnetic Reconnection in Microwave Solar Bursts
Authors: Kundu M. R.
Published: June 2019

In this paper, we first discuss a set of 6 cm observations made with the NRAO Very Large Array (VLA) (spatial resolution ~ 2″) that pertain to changes in the coronal magentic field configurations that took place before the onset of an impulsive burst observed on 14 May 1980. We also discuss a second set of 6 cm VLA observations (spatial resolution 18″ arc) where several interacting loops were involved in triggering the onset of an impulsive burst observed on June 24, 1980, 19:57:00 UT. Both sets of observations are examples of magnetic reconnection process being involved in accelerating microwave emitting electrons.
3D Simulation of Externally Driven Reconnection
Authors: Sato T.
Published: June 2019

A 3D magnetohydrodynamic simulation is presented. The essential conclusions obtained by the previous 2D model, such as the slow shock formation and the strong plasma jet generation, are reconfirmed. In addition, several new findings pertinent to three dimensionality are obtained. Among them, particularly interesting and important is the generation of field aligned currents at the slow shock associated with a local interruption of the neutral sheet current. It is also interesting to observe the generation of super–magnetosonic flows with the Mach number of 2.
Energy Dissipation Mechanisms in Flare Stars
Authors: Mullan D. J.
Published: June 2019

Flare stars derive their name from intermittent increases in luminosity which have certain characteristics reminiscent of solar flares (e.g. enhanced strengths of emission lines in the stellar spectrum during the outbursts). When a flare star is observed in a filter which transmits, say, the violet part of the visible spectrum, the increase in luminosity during a flare may range from noise level up to perhaps 100 times the quiescent brightness. During a flare, certain spectral features of the quiescent star (e.g. molecular bands) remain visible, indicating that the flare occupies only a fraction of the visible disk. Thus, analagous to a solar flare, a stellar flare is confined to a single active region. However the total power is large enough to affect the integrated light from the stellar disk. In contrast, the largest solar flare (Etot ≈ 1032 ergs) has a rate of energy release (L ≈ 1029 erg/sec) which is so small that a distant observer would record such a flare as a luminosity increase of less than 10−4Lsun. However, even apart from the flares themselves, it has become apparent in recent years that flare stars in their “quiescent state” provide some extreme contrasts with the sun.
Magnetodynamical Processes in Interacting Magnetospheres of RS CVn Binaries
Authors: Uchida Yutaka , Sakurai Takashi
Published: June 2019

Magnetodynamical processes in RS CVn binaries are discussed in the scheme of Active-Longitude-Belt picture (Uchida and Sakurai, 1983) in which the “photometric wave” is due to a number of spot pairs which emerge, drift across, and submerge in the “active longitude belt” on the K-star. The formation of the corona and the origin of flares in these close binary systems having starspots are interpreted in terms of the reconnections of the magnetic flux tubes of the companion star with the emerging and submerging pairs of spots on the K star. The injection of the hot plasma into the large scale pole-to-spot connections is required to explain the extended corona with large emission measure, and we attribute this to the “sweeping-pinch” mechanism (Uchida and Shibata, 1984) associated with the relaxation of the toroidal component in the twisted magnetic flux tubes which emerge and reconnect with the flux tubes connecting pole and spots.
Energy Release in Solar Flares
Authors: Sturrock P. A. , Kaufmann P. , Smith D. F.
Published: June 2019

In early research on solar flares, attention was focused on the impulsíve or flash phase, and it was assumed implicitly that virtually all the energy of a flare is released during that short phase. In recent years, however, it has been realized that the long-lived soft X-ray emission which follows the impulsive phase may require a separate energy-release process, which has been termed the “gradual phase” (Kane 1974). The fact that the impulsive phase is often preceded by soft X-ray emission has also led to the suggestion that there may be a third phase of energy release, which might be termed the “onset phase” (Sturrock 1980). It has long been realized that filament eruptions frequently precede flares, and it has been suggested (Kiepenheuer 1964) that the two should be regarded as parts of the same process. For these and other reasons, it is appropriate to question how many phases of energy release are involved in flares and what are their characteristics.
Nonlinear Effects and the Limitation of Electron Streaming Instabilities in Astrophysics
Authors: Spangler Steven R. , Sheerin James P.
Published: June 2019

Nonlinear effects, such as soliton collapse, will result in evolution of hydromagnetic waves excited by a field-aligned charged particle beam. If the time scale for such evolution is comparable to, or shorter than, linear time scales such as those for wave growth or pitch angle isotropization, then nonlinear effects may limit the instability. For conditions appropriate to relativistic electron streaming in a radio galaxy, the nonlinear time scale may be comparable to the linear time scales.
Bursting Particle Acceleration in Radio Jets
Authors: Henriksen R. N.
Published: June 2019

This work follows on the papers by Henriksen, Bridle and Chan (1982) (HB) and by Eilek and Henriksen (1983). These papers introduced a comprehensive model of (hydrodynamic) turbulence driven Alfven wave, resonant, particle acceleration. Very similar ideas were introduced independently by Fedorenko (1980), but the details were sketchy and the universality of the resulting spectral index was not realized. Eichler (1979) has come closest to these ideas previously (again independently) in a very original paper directed at ion acceleration in solar flares. He includes a back reaction on the turbulent eddies however which requires an adhoc treatment and is probably unnecessary (we replace this by the Lighthill noise analysis: HBC) and he omits synchrotron and adiabatic losses. Moreover, the quasi-linear theory is not used in calculating the distribution function. Nevertheless, it is reassuring that the same intuitive physics, even to the self-similar universality, should arise independently.
Accretion Disk Electrodynamics
Authors: Coroniti F. V.
Published: June 2019

Accretion disk electrodynamic phenomenae are separable into two classes: 1) disks and coronae with turbulent magnetic fields; 2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an α - ω dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.
Ultra-High Energy Cosmic Ray Production by Current Disruption in Active Galactic Nuclei
Authors: Lake George , Pudritz R. E.
Published: June 2019

Electrodynamic models for the activity of galactic nuclei are shown to be current systems which can be examined in terms of equivalent circuits. The resulting inductive circuit which describes the coupling of the generator (black-hole and accretion disk) to the distant load (jet plasma) is prone to various instabilities. We consider the disruption of this current system and propose that ultra-energetic cosmic rays (E~1019–1021 eV) could be produced during the discharges, which occur at distances of ~1016–1018 cm from the central massive hole (M~108 M). Such discharges will also produce variable γ-ray and X-ray activity and we discuss observations of Cen A in this regard.
Magnetic Field Reconnection in Differentially Rotating Accretion Disks
Authors: Gilden David , Tajima T.
Published: June 2019

Differentially rotating accretion disks threaded by a uniform magnetic field have been numerically simulated. Fast reconnection followed by coalescence allows the magnetic field to drive small amplitude radial oscillations in the disk. These oscillations may be observable as the viscous stresses cause the disk to brighten and fade as the disk expands and contracts. Episodes of reconnection may also be observable as hot spots produced locally at the sites of coalescence. Cataclysmic variables, and in particular dwarf novae, provide a natural interpretation for these calculations.
Coronal Arcades in the Sun and Their Hydromagnetic Stability
Authors: Ray A.
Published: June 2019

Two ribbon flares on the sun are sometimes preceded by luminous arcade like structures in the corona with fillament activity. The arcades which are associated with the coronal magnetic field are sometimes without these fillaments when they are found to be relatively long lived. The reasons underlying the stability and instability of these structures may be relevant in understanding the basic mechanism of two ribbon flares. Here we present results on the equilibrium structure of coronal arcades and their hydromagnetic stability taking into account the effects of magnetic field line-tying on the photosphere.
Bending Waves on Current Sheets
Authors: Bertin G. , Coppi B.
Published: June 2019

Current sheets are found to be subject to bending waves described by a dispersion relation indicating that these are, essentially, modified surface Alfvén waves. Applications to the observed magnetic polarity sectors in the solar wind and to other astrophysical environments, such as planetary magnetospheres, are suggested.
Current Status of the Dissipative Thermal Model for Solar Hard X-Ray Bursts
Authors: Smith Dean F.
Published: June 2019

Up until about five years ago all models for hard X-ray bursts consisted of streaming nonthermal electrons interacting with an ambient plasma (Brown 1975). Even in its most efficient form of thick-target emission in which electrons are stopped in the ambient plasma, this type of model is very inefficient because the electrons lose about 105 times more energy in Coulomb collisions with the ambient plasma than in X-rays resulting from bremsstrahlung. As a result, according to the latest estimates, at least 20% of the dissipated flare energy must go into accelerated electrons at the peak of the impulsive phase (Duijveman et al. 1982). Stimulated by observations of hard X-rays with thermal spectra (Crannel et al. 1978; Elcan 1978), analysis of a thermal model in which all the electrons in a given volume are heated to a temperature Te = 108K was begun (Brown et al. 1979; Smith and Lilliequist 1979; Vlahos and Papadopoulos 1979). It was recognized from the beginning that some electrons in the tail of the distribution would escape through the conduction fronts formed and mimic nonthermal streaming electrons. This thermal model with loss of electrons or dissipation became known as the dissipative thermal model (Emslie and Vlahos 1980). If the escaping electrons are not replenished, they will cease to make a contribution after a fraction of a second and the source will become a pure thermal source. It will be shown below that collisional replenishment (Smith and Brown 1980) is too slow.
Optical Counterparts of Extragalactic Radio Sources in the Southern Sky: Positions Obtained from Schmidt Plates
Authors: Walter H. G.
Published: June 2019

The usefulness of Schmidt plates for measuring astrometric positions of extragalactic radio sources with an average uncertainty of less than 0.3 arcseconds is emphasized in the discussion of the results on 50 optical counterparts and by the comparison with corresponding positions obtained through radio interferometry.
Astrometry with the Lowell PDS
Authors: Wasserman L. , Bowell E.
Published: June 2019

The Lowell Observatory PDS is currently used in several projects which necessitate astrometric reduction of photographic plates. To meet this need, we have developed a series of computer programs for astrometric data reduction which enable the user to obtain maximum flexibility from the PDS while at the same time retaining ease of use. In its simplest form our astrometric “package” consists of four separate programs. The first two constitute the “data taking” part of the process and reside on a DEC PDP 11/34, the computer which controls the PDS. The second two programs handle “data reduction” and reside on Lowell's general purpose computer, a DEC PDP 11/55.
First Results from the New GSU CCD Speckle Camera
Authors: Hartkopf William I.
Published: June 2019

The CCD speckle camera now in use at Georgia State University has brought about considerable improvement in limiting magnitude and photometric accuracy over the old photographic system, but has also necessitated considerable changes in data storage and reduction. These new data handling techniques are outlined, with a few words about overall accuracy and a brief description of new equipment which should further improve our speckle program at GSU.
The Bordeaux Automatic Transit Circle: First Catalogues, Current and Future Programs
Authors: Requième Y. , Mazurier J. M.
Published: June 2019

The Bordeaux automatic meridian circle has been used for routine differential observations for three years. Current programs concern NPZT stars, faint nearby stars from the Gliese catalogue, Mars, Uranus, Neptune, Jupiter and Saturn satellites, and minor planets. From 1984 on, 5000 faint stars from the HIPPARCOS Input Catalogue will be observed.
The Use of Astrometric Instruments in Vacuum Chambers
Authors: Hu Ningsheng
Published: June 2019

This paper discusses the effect of using a vacuum chamber with a horizontal entrance window to eliminate astronomical refraction, dispersion and irregular refraction in a telescope tube. Some engineering problems arising in connection with the entrance window are dealt with. The actual results obtained by vacuum photoelectric astrolabes and a vacuum photographic zenith tube are presented.
A Multislit Photoelectric Star Micrometer for the Meridian Circle of the Nikolayev Astronomical Observatory
Authors: Konin V. V. , Pogonij A. D.
Published: June 2019

In the course of the cooperation between the Nikolaev and the Pulkovo Observatories, a photoelectric micrometer, similar to that proposed by E. Høg, was designed and installed on the Repsold meridian circle.
HIPPARCOS Satellite and the Organization of the Project
Authors: Kovalevsky J.
Published: June 2019

The HIPPARCOS satellite is an approved project of the European Space Agency since 1980. A sketch of the past and future development of the project is given. The resulting astrometric parameters and magnitudes of 100 000 stars should be available circa 1993. Many astronomical groups are involved in the preparation of the mission together with ESA bodies and industry. Their functions and mutual interfaces are described.

The main features of the satellite are presented. While observing out of the atmosphere removes most of the effects that limit the accuracy of ground based astrometry, new causes of systematic or random errors appear in an instrument designed for a millisecond of arc level of precision. The main limitations that have been identified are discussed: basic angle unstability, mechanical jitter, grid irregularity, diffraction chromatism, shape of the image dissector sensitivity profile. The consequence is that the presently expected basic measurement precision is limited not only by the photon count errors. However, all these effects are taken into account when assessing a final accuracy of 0″.002 for the astrometric parameters of a 9-th magnitude star.
The New Index Catalog of Visual Double Stars-WDS
Authors: Worley Charles E. , Douglass Geoffrey G.
Published: June 2019

A new index catalog of visual double stars, the Washington Double Star Catalog (WDS), 1984.0, is now available in tape form. All of the double star data has been updated, as well as the notes to the catalog. This report summarizes the contents of the WDS and describes its compilation.
Objets Accessibles aux Astrolabes de Haute Precision: Etoiles et Radioetoiles Brillantes, Planetes, Soleil
Authors: Chollet F. , Débarbat S.
Published: June 2019

Capabilities of the Danjon astrolabe and its transformations (with full pupil, photoelectric device, for Sun) are examined regarding both fields of instrumental modifications and improvement of the reduction techniques. For bright objects (stars and radiostars, planets, galilean satellites, Sun) these instruments will insure a valuable contribution to results obtained by the other techniques.
Astrometry in China
Authors: Shu-Hua Ye
Published: June 2019

The space age and modern technology have opened a new era for astrometry. A great amount of modern, precise astrometric data and approaches is urgently needed not only for astrophysics but also for Earth Science research. The Astrometric Community looks forward to establishing a precisely specified uniform celestial frame of reference for all purposes, which will link the bright stars, faint stars, and galaxies, down to the remote radio sources, and to establish a terrestrial frame of reference as well as to specify a precise transformation between these two frames. Effective international cooperation is the goal of all astrometrists. The Chinese astronomers are ready to join and play an active part in this cooperation.
The Need for Better Co-Operation and Intercomparison in Fundamental Astrometry
Authors: Teleki G.
Published: June 2019

The present status and practice in the fundamental astrometry are analysed, and relying upon the findings the author suggests the organization of an international action aimed achieving better co-operation in the star position observations and celestial reference system determinations, as well as performing the intercomparison of the different techniques and methods.
How to Choose a Randomly Oriented Sample
Authors: Cawthorne Tim
Published: June 2019

Efficient VLBI tests of relativistic models for superluminal motion require a complete sample of sources free from selection effects in orientation, coupled with an observational requirement for bright cores. Probably the best way to construct such a sample is to extract from a low frequency sample those sources with the highest radio luminosity, since these tend to have the strongest cores. One must then ask whether there are any sources included which would not be if they were differently oriented; that is, either the flux or the power falls below the limit for the sample when the core and jet flux is removed.
3C205 - A Source with Extraordinary Alignment and a VLBI Hotspot
Authors: Lonsdale C. J.
Published: June 2019

High resolution maps of 3C205 using MERLIN and the European VLBI network (EVN), some of which are shown in Fig.1, reveal unusual characteristics in this high redshift (z = 1.534) source. The most striking of these are as follows:

1)

The hotspots A and B, and the core C are aligned to within 0″.05 (at the hotspot), as measured on the MERLIN 6 cm map.

2)

The compact feature in the southern hotspot (A1) has projected dimensions of ~0″.03 x ~0″.015 (see Fig.1d). The corresponding minimum internal energy density of this feature is ≳2.3 × 10−6 erg cm−3.

3)

There is a continuous zig-zag ridge in the southern component, which starts with a definite spur of emission extending in a south-east direction from the compact feature A1 (see Fig.1b). The magnetic field in A1 is in approximately the same position angle as this spur and the VLBI elongation, which both point towards a bright secondary peak in the southern lobe (1a and 1b).
Multifrequency Observations of the BL Lac Object 1219+28
Authors: Weistrop Donna , Shaffer David B. , Hintzen Paul
Published: June 2019

The BL Lac object 1219+28 has been observed at visible wavelengths and at 2.3 GHz, 5.0 GHz and 8.3 GHz using the VLBI network.
Optically Quiet Quasars
Authors: Cotton W. D.
Published: June 2019

The study of steep spectrum sources containing compact components has become increasingly popular as the number of papers on the topic in this volume indicates. I wish to discuss the properties of a number of steep spectrum sources which are dominated by compact components whose spectra remain steep to quite low frequencies. Most of the known sources of this type do not have optical counterparts to the limit of the Palomar Sky Survey prints and thus, with the implicit assumption that they are extragalactic, have been referred to as “Optically Quiet Quasars”.
VLBI Observations of the Superluminal Sources 3C 273 and 3C 279
Authors: Unwin S. C. , Biretta J. A.
Published: June 2019

Monitoring of the radio structure in the core of 3C 273 has yielded a series of hybrid maps in which substantial source evolution can be seen. We discuss the superluminal motion of components in the jet of 3C 273, and the evolution of their flux densities and spectra. For 3C 279 we identify a new epoch of superluminal expansion with v/c = 6.5.
The Radio Polarization of BL Lacertae: Shocks in a Jet
Authors: Aller Hugh D. , Aller Margo F.
Published: June 2019

The behavior of the linear polarization of BL Lacertae during the recent series of radio bursts indicates the presence of Faraday rotation in the vicinity of the source and the formation of an axial compression in the radio jet.
Observations of Superluminal Motions in 3C 120
Authors: Walker R. C. , Benson J. M. , Seielstad G. A. , Unwin S. C.
Published: June 2019

Superluminal motions were first seen in 3C 120 between 1972.5 and 1974.4 (Seielstad et al. 1979 and references therein). Between 1975 and 1980, the source was monitored along with 3C 273 and 3C 345 by the Caltech group. One reasonably clear episode of expansion was seen in 1979 (Walker et al. 1982) but, for most of the time, the source evolution was so rapid that it was difficult to relate the structures seen at successive epochs.
VLBI Monitoring of BL Lac-Objects
Authors: Bååth Lars B.
Published: June 2019

This is a report on an ongoing project designed to study structural variations on the milliarcsecond scale in four BL Lac-type objects. The observations are made at λ6 cm with a global VLBI network consisting of the combined US and European networks and with some additional antennae like one in South Africa and one in Finland. A typical experiment involves 7–9 stations and produces maps with a resolution (FWHM) of 1–1.5 m.a.s depending on the declination of the source. Seven experiments have been made since the start in 1978, resulting in hybrid maps at three epochs for each of the four main sources: A0 0235+164,0735+178,Mk 421, and 1749+701. The same restoring beam has been used for each source at all epochs. The epoch March 1979 is an exception though, the maps from then were restored with a larger beam corresponding to the resolution on the European baselines only. The results from the epochs 1978–1979 have already been published (Bååth et al. 1981), and papers describing the results from the later epochs are in preparation.
The Radio Jet in 3C418
Authors: Muxlow T.W.B. , Jullian M. , Linfield R.
Published: June 2019

Models are here presented interpreting the arcsecond radio structure found in the quasar 3C418 as a precessing jet. No simple solution exists and it has been found necessary to complicate the model geometry by allowing the precession cone-angle to increase with time. The timescales suggest the presence of a close binary black-hole system within the quasar core. The modelled behaviour of the precession cone close to the core is explained either by interaction of the jet with the surrounding galactic material or by the observation of the source during the capture of one black-hole by the other.
The Structural Variations of 3C454.3 and 2134+004
Authors: Pauliny-Toth I.I.K. , Porcas R. W. , Zensus A. , Kellermann K. I.
Published: June 2019

3C454.3 has a core-jet structure on the milliarcsec scale. Following a flux density outburst, the core showed a “superluminal brightening”. Comparison with older observations suggests superluminal motion in the jet. 2134+004, in contrast, is a double source, with no significant (v/c < 1) relative motion of the components.
Evidence for Relativistic Motion Based on Arcsecond Structure
Authors: Perley R. A.
Published: June 2019

Observations with arcsecond-resolution interferometers can be used to detect motion or changes of the large scale structure associated with core dominated objects. If these arcsecond structures are expanding at relativistic velocities, detectable changes should be measureable within a few years. Indirect estimates of jet velocities can be made by a number of arguments, but none are model independent or free of dependence upon poorly established parameters. Application of some of these methods are given on sources with established VLB structure.
The Low Frequency Variability of Extragalactic Radio Sources
Authors: Padrielli L.
Published: June 2019

The flux variability of extragalactic radio sources at decimetric wavelengths (L.F.V.) is now considered a classical astrophysical subject connected with compact radio sources.
Daily Radio Frequency Observations of Selected Objects
Authors: Geldzahler B. J. , Johnston K. J. , Spencer J. H. , Waltman E. B. , Klepczynski W. J. , Angerhofer P. E. , Florkowski D. R. , McCarthy D.D. , Matsakis D. N.
Published: June 2019

In Table I we present the list of 38 celestial objects that have been observed since January 1978 at 2.7 and 8.1 GHz with the Green Bank interferometer. The sources fall naturally into three categories: radio stars, possibly Galactic sources, and extragalactic sources. SS433, Cyg X-3, and each extrgalactic source is measured several times per day while the other sources are measured once every three days. Reports on the entire program will be found in Geldzahler et al. (1983a), and on specific sources: SS433—Johnston et al. (1983a), BL Lac—Johnston et al. (1983b), Cyg X-3—Geldzahler et al. (1983b) and elsewhere in this volume), and CTA 26—Spencer et al. (1983).
Evidence of Doppler Beaming in Variable Radio Sources
Authors: Legg T. H.
Published: June 2019

Total flux observations of variable sources (Andrew et al. 1978) have been re-examined to test their consistency, or lack of it, with the Doppler beaming hypothesis of Scheuer and Readhead (1979).
VLBI Observations of the Gravitational-Lens Images of Q0957+561
Authors: Gorenstein M. V. , Shapiro I. I. , Cohen N. L. , Bonometti R. J. , Falco E. E. , Rogers A. E. E. , Marcaide J. M.
Published: June 2019

We have conducted a series of VLBI observations of the gravitational-lens images of the quasar Q0957+561 (Walsh et al., 1979), utilizing the Mark III VLBI data acquisition system (Rogers et al., 1983). The goals of our observations are to (1) map the milliarcsecond structure of the A and B images, (2) detect the predicted third image of the quasar, and (3) determine the time delay between the images. We will use these results to constrain the mass distribution of the lens and, possibly, cosmological constants.
Radio Nuclei in Nearby Galaxies
Authors: Preuss E.
Published: June 2019

This review is an attempt to summarize VLBI continuum observations at cm- and dm-wavelengths of active galactic nuclei at distances ≲ 100 Mpc (Ho = 50 km s−1 Mpc−1). ‘Nearby galaxies’, thus defined, are close enough for achieving the highest possible spatial resolution. Galaxies at these distances, however, typically do not show extreme and rare forms of nuclear activity such as powerful radio sources, the cores of which are relatively easy to map with VLBI, and which are therefore the subject of most of the VLBI work done so far (see e.g. Preuss, 1983). Nearby active galaxies show rather more ‘ordinary’ forms of nuclear activity; they include a few of the weaker classical ‘radio galaxies’, but most of them are Seyfert galaxies and mildly active ‘normal galaxies’. Their total radio emission is typically weak (P(5 GHz) ≲ 1031 erg s−1 Hz−1) and so are their compact radio nuclei (if any). The highest available sensitivity is therefore required for their study and the current instrumental performance is just becoming sufficient to tackle the strongest of them in the hope of obtaining maps.
Sub Arc Second Components in Nearby Bright Galaxies at Metre-Wavelengths
Authors: Bagri D. S. , Ananthakrishnan S.
Published: June 2019

150 nearby bright galaxies have been observed for compact components at 327 MHz by the method of Interplanetary Scintillation (IPS) using the Ooty radio telescope; scintillation was detected in 28 of these galaxies indicating compact components with size < 30 mas to 300 mas having flux density > 100 mJy. Comparison of our data with other results at high frequencies indicates that these compact components are associated with the central regions of the galaxies.
The Rate of Component Separation in SCO X-1
Authors: Geldzahler B. J. , Fomalont E. B. , Hjellming R. M. , Wade C. M.
Published: June 2019

Sco X-1 was observed in the A configuration of the VLA on 4 Feb. 1981 and 18 Mar. 1982 (Fomalont et al. 1983). The radio map at 1.5 GHz, made with the 1982 data, is shown in Figure 1. The central component is nearly coincident with the binary and has an angular size of less than 0″.1. A 0″.5-resolution map of the SW component of Sco X-1, shown in Figure 2, displays only the brightest peaks in the two emission regions. The brightest part of the emission is located at the extreme edge of the component, and its location and shape are reminiscent of hot spots in radio lobes associated with luminous extragalactic radio sources. Although the NE component is only slightly resolved at this resolution, it is extended in approximately the same position angle as that of the entire source and that of the SW component.
Thermal Radio Stars and High-Resolution Radio Observations
Authors: Wright Alan E.
Published: June 2019

The main purpose of this talk is to outline a few of the problems in our understanding of thermal radio stars that may be resolved by the large arrays. Several radio telescopes in operation (such as the VLA and MERLIN arrays) or under construction (such as the Australia Telescope) have both the required resolution and sensitivity.
Interstellar Broadening of Compact Low Galactic Latitude Radio Sources
Authors: Dennison Brian , Thomas M. , Broderick J. J. , Booth R. S. , Brown Robert L. , Condon J. J.
Published: June 2019

Scattering of radio waves off inhomogeneities in electron density in the interstellar medium can produce an apparent broadening in the angular diameter of an intrinsically compact background radio source. The magnitude and distribution of this effect at low galactic latitudes (|b|<5°) is not well known, although several cases suggest substantial broadening in certain directions, such as the Cygnus X region (Anderson et al. 1972), and the galactic center (Davies, Walsh, and Booth 1976). Large scattering in the plane is consistent with the scintillation properties of pulsars seen through substantial thicknesses (≳ 1 kpc) of the galactic disk.
Observations of Excited State OH Masers at 6.0 and 13.4 GHz
Authors: Baudry A. , Guilloteau S. , Walmsley M. , Wilson T. L. , Winnberg A.
Published: June 2019

This is a brief report on a sensitive search for excited OH absorption and emission sources made with the Effelsberg 100 m telescope towards several compact HII regions. Our data are discussed elsewhere (Guilloteau et al., 1983) and we mainly present here our II3/2, J = 5/2 and 7/2 OH narrow emission results (masers). In the J = 5/2 state, 14 sources were observed with a typical 1 σ sensitivity of 0.2 Jy. Among 13 positive detections, 4 and may be 5 are new maser sources: G43.1, W48, K3-50, ON3 and G34.3 (?). With the exception of W3 (OH) the 6035 MHz line is always much stronger than the 6030 MHz line. Comparison with spectra published by others suggests time variability in M17, W51 and Orion A. In W3 (OH) a weak broad emission was also detected at 6049 MHz. In our j = 7/2 observations the peak to peak noise was the range 0.1 to 1 Jy. No masers were detected even in the strong 6035 MHz sources associated with M17 and W33 cont. Thus the F = 4−4 emission line in W3 (OH) seems to be really exceptional (Baudry et al., 1981).
Merlin Observations of the OH Maser Emission from IRC+10420
Authors: Diamond P. J.
Published: June 2019

MERLIN observations of the 1612 and 1665 Mhz OH masers from the supergiant IRC+10420 reveal several major departures from the usual morphology of OH/IR stars.

IRC+10420 is one of the most unusual OH maser sources yet found. It is an F8 supergiant with strong OH maser emission at 1612, 1665 and 1667 Mhz. A north-south optical nebulosity with an angular size of 2 arcsec has been detected (Thompson and Boroson,1977) and its peculiar IR properties are reminiscent of Eta Carina. These characteristics make IRC+10420 unique among Type II OH/IR stars.
VLBI Synthesis Observations of Circumstellar OH Masers
Authors: Norris R.P. , Booth R.S. , Diamond P.J. , Graham D.A. , Nyman L-A.
Published: June 2019

A technique for mapping spectral line sources using closure phase VLBI techniques is described, and some initial results on circumstellar shell sources are presented. The maps show an unresolved point source on the nearside of the shell, but no corresponding source on the far-side of the shell. This is interpreted in terms of amplification of the stellar thermal emission. Preliminary results are also presented on another source, OH17.7, which show correlated flux outside the velocity range of the known OH masers, and it is suggested that this represents high velocity (~600 km s−1) violent motions around the central star. If confirmed, this may represent a new class of source, representing violent phenomena associated with red giant stars.
The Spatial Structure of Silicon Monoxide Masers
Authors: Lane Adair P.
Published: June 2019

VLBI observations of stellar masers provide important constraints on models for maser excitation and for the dynamics and physical conditions in circumstellar envelopes. The spatial distribution and apparent sizes of Si0 masers toward several late type variable stars and toward the star-forming region in Orion have been measured using the 75 km baseline between the 37 m telescope of Haystack Observatory and the 14 m telescope of the Five College Radio Astronomy Observatory. The fringe spacing is 0.02 arcsec and the transitions observed were the v = 1, J = 1 - 0 and v = 2, J = 1 - 0 lines at 43 GHz. The data were obtained in September 1979 and April 1982.
Proper Motions and Distances of Water Maser Complexes
Authors: Schneps M. H. , Reid M. J. , Moran J. M. , Genzel R. , Downes D. , Rönnäng B.
Published: June 2019

We report preliminary results of a long term spectral line VLBI experiment to observe internal proper motions of water maser sources in the vicinity of newly formed stars. This technique yields a picture of the three-dimensional kinematics of the region and a measure of the distance to the source. First results from the galactic center source SGR B2 are presented.
A New Way of Tying Together the Hipparcos Frame to the VLBI Extragalactic Frame: Astrometric Observations of Stellar Maser Sources
Authors: Baudry A. , Mazurier J. M. , Requième Y.
Published: June 2019

The Hipparcos (H) reference system will contain 100 000 stars whose positions and proper motions will be known with an accuracy of 0″.002 and 0″.002/yr respectively. Because a residual rotation of the H system may exist and because a VLBI extragalactic frame is being constructed one must (i) determine an eventual rotation of the H rigid frame, (ii) link the H system to the VLBI extragalactic frame. VLBI observations at JPL (Fanselow et al., 1981) have provided a catalogue of about 100 quasars with internal accuracy of' ~ 0″.001.
The VLB Array+
Authors: Kellermann K. I.
Published: June 2019

The VLB Array (VLBA) is a synthesis radio telescope which has been designed to extend the resolution of the VLA in order to allow sub-milliarcsec studies of compact galactic and extragalactic radio sources over a wide range of wavelengths and spectral resolution.
The Canadian Long Baseline Array
Authors: Legg T. H.
Published: June 2019

On 1983 May 31, the National Research Council of Canada gave formal approval to a new national facility, the ‘Canadian Long Baseline Array’. The instrument will be made up of eight radio telescopes spaced across southern Canada, with a ninth antenna, primarily for geophysics, in the north. Though the project is still some way from being funded, the NRC approval was an important and encouraging step in a process that started five years ago.
Orbiting VLBI: A Survey
Authors: Burke Bernard F.
Published: June 2019

The Very-Long-Baseline Interferometry technique is not limited by the size of the Earth. Near-Earth-orbiting space vehicles can carry radio telescopes that can serve as VLBI stations using existing technology. By proper use of ground VLB arrays, a single orbiting VLBI satellite can yield radio maps with 2-dimensional coverage and high dynamic range at all declinations. A single orbiter can be used out to orbits that yield an effective aperture greater than two Earth diameters. Interstellar scintillations are a limiting factor only in the micro-arc-second range.
Orbiting Very Long Baseline Interferometer Demonstration Using the Tracking and Data Relay Satellite System
Authors: Levy G. S. , Christensen C. S. , Jordan J. F. , Preston R. A. , Burke B. F.
Published: June 2019

A proposal has been made to use the Tracking and Data Relay Satellite System (TDRSS) as an orbiting element for a very long baseline interferometry (VLBI) demonstration. The TDRSS is a satellite system designed to coherently track and relay data between other satellites and the central ground station. This system could also be used to coherently observe a celestial radio source. A ground-based frequency standard would be used to coherently drive the spacecraft receiver local oscillator and transmitter. The data will be telemetered to a ground station, where it will be recorded on a Mark III terminal.
Trigonometric Parallaxes and Their Calibration
Authors: Upgren Arthur R.
Published: June 2019

The precision obtained in equating a very precise linear dimension to a very small and imprecise angular dimension sets a limit on the precision of the distance scale of the Universe. Within the Solar System, errors in distances are of the order of one part in one hundred million, but beyond its limits only a single star, Barnard's star, has a distance known to better than one part in one hundred, and distances known to one part in twenty from parallaxes are limited to only a few hundred nearby stars. Yet most other distance methods and results must ultimately be calibrated against distances to nearby stars derived from the heliocentric parallax method and its observations and uncertainties.
Masses, Radii and Luminosities from Analysis of Eclipsing Binaries
Authors: Popper Daniel M.
Published: June 2019

The reliability of values of the fundamental properties of stars derived from eclipsing binary analysis is discussed in terms of general concepts. Since the principles involved in the determination of masses and radii are simple, the heart of the matter is the care and judgment with which the relevant spectrographic and photometric observations are obtained and analyzed. Problems in the evaluation of the radiative properties require special attention.
Measuring Stars with High Angular Resolution: Current Status and Future Prospects
Authors: Davis John
Published: June 2019

The current state of knowledge of angular diameters of stars is reviewed and, based on this review and the requirements for the determination of surface fluxes, effective temperatures, radii and masses, targets of sensitivity, angular resolution and accuracy for future programs of stellar angular diameter measurements are established. Long baseline interferometry is the only technique with the potential to meet all the targets. The necessary improvements in sensitivity, angular resolution and accuracy are promised by the approach adopted in the modern Michelson stellar interferometer under development at the University of Sydney and the prototype instrument, which is currently nearing completion, is briefly described to illustrate how the atmospheric and mechanical problems which have inhibited the development of amplitude interferometry may be overcome using modern technology. This program together with the developments taking place at CERGA lead to the conclusion that the prospects for contributions by high angular resolution measurements to the determination of fundamental stellar quantities during the next decade are excellent.
The Calibration of Photometric Determinations of Abundance
Authors: Straižys V.
Published: June 2019

Photometric abundance determinations using blanketing in the ultraviolet and violet spectral regions as well as the intensity of strong lines and bands is the most important tool in the study of chemical composition of faint and distant stars. However, this method requires the calibration of different photometric quantities in terms of abundance at given temperatures and luminosities. Two principal methods of calibration are in use. One of them uses stars with abundances determined from high dispersion spectra by curve of growth or model atmosphere analysis of the spectral lines. The other one uses synthetic spectra based on model atmospheres which are integrated to imitate the narrow band photometric indices. This paper will summarize the results of the application of both of these methods to calibrate a number of the important photometric systems. Most attention will be given to the late-type stars, which demonstrate the strongest photometric abundance effects.
The Microfiche of Standard Stars
Authors: Philip A. G. Davis , Egret Daniel
Published: June 2019

We are preparing a microfiche, at the Stellar Data Center in Strasbourg, concerning standard stars in various systems which will be included with the proceedings of this meeting. In the first part of the microfiche we will present a list of stars which are standards in spectroscopic, photometric systems or for which fundamental determinations of temperature, gravity, radius or mass have been made or for which spectrophotometry has been done, fluxes measured or [Fe/H] determined. If a star is a standard in one of these systems an X will be placed in the column opposite its name.
The Open Cluster M67 as a Fundamental Standard of Reference for Stellar Properties
Authors: Janes Kenneth
Published: June 2019

With the possible exception of the Hyades, M67 is the best-studied star cluster. Accurate photoelectric photometry exists well down onto the main sequence and proper motion studies have isolated cluster stars from the field. From photometry and spectroscopy, its composition is determined to be almost exactly the same as the Sun, with an age about one-half billion years less. This similarity to the Sun permits an accurate determination of distance to M67 independently of other distance measurements. Using the Sun as a reference, the distance modulus of M67 is found to be 9.48 mag. An extensive analysis of possible sources of error leads to an uncertainty (standard error) of ± 0.15 mag., with the chief sources of error being the color index of the Sun, the composition of the cluster, and its age. The M67 distance uncertainty compares favorably with Hanson's (1975) Hyades modulus of 3.29 ± 0.08.
The Relation Between the Anomalous CN Strength, δ CN, and [FE/H] Abundances
Authors: Fracassini M. , Pasinetti L. E. , Pastori L. , Pironi R.
Published: June 2019

Following a previous study of stellar abundances (Pasinetti 1980), a relation has been derived between the DDO cyanogen-strength index and values of [Fe/H] reported in the catalog of Cayrel de Strobel, et al. (1980). From this relation we obtain [Fe/H] = 0.08 for the Hyades. This value is slightly lower than that given by Janes (1979), [Fe/H] = 0.13, and is in better agreement with other recent estimates of the Hyades metallicity (Cayrel de Strobel 1980). This improvement is due to the larger quantity of more precise spectroscopic data used in our correlation.
On the Gravity Determination from Carbon Star Spectra
Authors: Gass H.
Published: June 2019

Spectra of carbon dwarf and giant stars may look very similar, as is demonstrated, e. g., by TT CVn and G77-61. Model calculations show that the bands of C2, CN and CO cannot be used in the range log g = 0……6 for log g determinations, since they are affected by abundance. If, moreover, lines of two ionization stages cannot be observed in any element, the only log g indicator would seem to be the ratio of the MgH band and the Mg I b lines. Simple analytic expressions are derived which demonstrate the relation between spectral appearance, abundances and gravity.
The BE II λ 3130 Å Region in the Spectra of Vega and Sirius
Authors: Griffin R. F. , Griffin R. E. M.
Published: June 2019

Spectrograms of very high quality have been obtained of Vega and Sirius with the Mount Wilson 100-inch (2.5-m) telescope and coudé spectrograph. Examples of these plates, showing the Be II region in the ultraviolet, are exhibited. The reciprocal dispersion is 0.83 Å/mm (83 nm/m) and the FWHM is about 19 mÅ (1.9 pm). The spectrograms have a trailed width of 3 mm and are on IIa or IIIa emulsions.
A Comparison of Direct and Indirect Methods of Determination of Stellar Angular Diameters
Authors: Pastori L. , Pasinetti L. E. , Antonello E.
Published: June 2019

Several direct and indirect methods for the determination of stellar apparent diameters have been developed in the past; they are summarized in Table 1 by Fracassini, et al. (1981) with a code number and references. So far, no detailed comparison of the methods has been carried out, the main difficulty being the extremely small number of common stars. Nevertheless, from the stars listed in CADARS (Fracassini, et al. 1981), we have obtained some correlations in order to test the reliability of some methods and to define the regions of the HR diagram where they can be applied.