bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for a Black Hole in LMC X-3
Authors: Cowley A. P. , Crampton D. , Hutchings J. B. , Remillard R.
Published: June 2019

The best X-ray position (Einstein Observatory HRI - Giacconi et al 1979) for LMC X-3 confirms its identification with the early type star first suggested by Warren and Penfold (1975). Our spectroscopic observations obtained with the CTIO 4–m telescope show the WP star is a slightly reddened B3 V star with mV ≈ 16.9. Large radial velocity variations (Δv ≈ 500 km s−1) reveal an orbital period of 1.7049 days. From the orbital elements (Table 1) one can determine the mass function f(M) = (Mx sin i)3/(Mopt + Mx)2 = 2.3 M⊙, which shows without any assumptions about the mass of the optical star, the orbital inclination, or the mass ratio the unseen X-ray object has a mass >2.3 M⊙. Detailed analysis of the HEAO–1 scanning modulation collimator X-ray data shows that the system does not eclipse, implying that the orbital inclination is ≤ 65°. Assuming the B star mass lies between 4 and 8 M⊙ (an average mass for a normal B3 V star would be about 6–7 M⊙), the mass of the unseen companion must lie between 7 and 13 M⊙ (see Fig. 4a - Hutchings, this volume). Smaller inclinations of course give even higher masses. An important point is that the unseen star must have a mass larger than that of the B star, and thus if it were any kind of normal star it should be easily seen in the spectrum. Thus the X-ray emitting object is a very good candidate for a black hole.
The Stellar Content of 30 Doradus
Authors: Walborn Nolan R.
Published: June 2019

The supergiant H II region 30 Doradus is placed in context as the optically most spectacular component in a much larger region of recent and current star formation in the Large Magellanic Cloud, as shown by deep Hα photographs and the new IRAS results. The current state of knowledge concerning the concentrated central cluster in 30 Dor is summarized. Spectroscopic information exists for only 24 of the brightest members, most of which are WR stars; however, photometry shows over 100 probable members earlier than BO. The spectral classification of these stars is a difficult observational problem currently being addressed; in the meantime their hypothetical ionizing luminosity is calculated from the photometry and compared with that suggested for the superluminous central object R136a alone, and with the H II region luminosity. With reference to related regions in the Galaxy, the likelihood that many of the brightest objects in 30 Dor are multiple systems is emphasized. An interpretation of R136a as a system containing a few very massive stars (as opposed to a single supermassive object) is in good accord with the observations, including the visual micrometer results. The study of 30 Dor and its central cluster is vital for an understanding of the numerous apparently similar regions now being discovered in more distant galaxies.
X-ray Surveys of the Magellanic Clouds
Authors: Helfand David J.
Published: June 2019

The proximity, well-determined distance, and low foreground obscuration of the Magellanic Clouds makes them an ideal target for the study of galactic X-ray source populations. Steady progress since the initial detection of X-rays from the LMC in 1968 culminated in the recent Einstein Observatory surveys from which over three dozen supernova remnants and ~10 compact binaries have been identified. In this review, we record the 15-year history of Magellanic Cloud X-ray research, summarize our current knowledge, and offer a brief prospectus of what the next 15 years may hold.
Coronae of the Magellanic Clouds
Authors: de Boer Klaas S.
Published: June 2019

A hot gaseous corona was postulated by Spitzer (1956) for the Milky Way as a consequence of the detection of cool interstellar clouds (seen in Call absorption) on paths to stars in the Milky Way halo. Halos around extra galactic systems were proposed by Bahcall and Spitzer (1969) as a possible explanation for the wealth of high redshift absorption line systems in the spectra of quasars. The recording with the International Ultraviolet Explorer (Boggess et al 1978) in 1978 of echelle spectra of R136 and HD38282 in the LMC showed strong absorption lines of the high ionization stage ions CIV and SiIV, due to material with velocities clearly pertaining to locations outside the Milky Way disk (Savage and de Boer 1979). Thus the reality of the galactic corona became established (review de Boer 1984). There is confusion with the words corona (gas – massive component) and halo (location – stars) and I (1984) proposed for the large mass from dynamics MASsive DArk Component, MASDAC.
Absolute Hα and Hβ Photometry of LMC HII Regions
Authors: Caplan J. , Deharveng L.
Published: June 2019

A nebular photometer equipped with a scanning Fabry-Perot interferometer has been used at the ESO 50-cm telescope to observe about 50 HII regions of the LMC (Caplan and Deharveng, 1983). This instrumentation gives the profiles of the observed lines, thus allowing discrimination against unwanted continuum and line emission. The integrated fluxes were measured with a 4.9′ diaphragm, to facilitate comparison with the 6-cm radio continuum fluxes obtained by McGee et al. (1972) with a similar resolution. Nebular reddening, from the Hα/Hβ ratio, is greatest for the 30 Doradus Nebula. Relatively high reddening was also observed for the following zones: N159 (at the border of the largest HI-molecular complex of the LMC) and N160; N79, N81 and N83; N48; N64. Reddening is rather low towards other HII regions, especially for those in the bar and for large bubble-shaped regions.
CO Observations in the Small Magellanic Cloud
Authors: Rubio M. , Cohen R. , Montani J.
Published: June 2019

The dwarf Magellanic irregular galaxies apparently have a very low molecular content compared to the Milky Way. In the LMC, molecular clouds are fairly common, but the ratio of molecular to atomic gas is at least 5 times lower than in the Galaxy (Cohen et al. 1984). Elmegreen et al. (1980) searched for CO in 6 dwarf galaxies and failed to detect any emission even though their sensitivity was adequate to detect galactic giant molecular clouds placed at the distance of these galaxies. Israel (1984) observed the J=2→1 transition of CO at 15 points in the Small Magellanic Cloud and detected CO emission from five of them, but at a level two to six times lower than typical galactic values.
Waves and Oscillations in the Non-Magnetic Photosphere
Authors: Deubner Franz - Ludwig
Published: June 2019

The solar photosphere is the outer boundary of the cavity which defines the spectrum of the global p-modes. It is also the lowest layer that permits direct observation of the boiling mixture of motions which eventually create the complex patterns apparent in the chromosphere and corona. Studies of the dynamical behaviour of this layer are therefore of paramount importance for an overall understanding of the dynamic sun.
Waves and Oscillations in Magnetic Fluxtubes
Authors: Ryutova M.P.
Published: June 2019

According to observational data solar magnetic fields have a pronounced filamentary structure. Theoretical investigations of plasmas containing structured magnetic fields, including the study of the properties of these structures and their interactions with associated gas flows, are of great importance for our understanding of the basic processes in the solar atmosphere, whose structure and dynamics are dominated by magnetic fields. In the present review theoretical models of thin magnetic fluxtubes and their behaviour in the ambient plasma are discussed.
Generators of Solar Differential Rotation and Implications of Helioseismology
Authors: Rüdiger G. , Tuominen I.
Published: June 2019

We interpret the helioseismological results for the solar rotation law as implying a uniform Ω0in depth, if the angular velocity Ω(θ) is expanded in series of orthogonal polynomials. One of the possibilities to ensure uniformity of Ω0is to exclude any anisotropy from the generating turbulence field, so that only the rotationally originated part of the heat conductivity tensor survive as a generator of meridional flow and consequently equatorial acceleration is produced. In addition to this simplest possible turbulence model, we discuss some possible forms of the nondiffusive parts of the Reynolds stresses which may be compatible with the uniformity of Ω0.
Generation of Torsional Oscillations in the Sun
Authors: Vandakurov Y.V.
Published: June 2019

The hypothesis is considered that the torsional wave observed on the Sun is an eigenmode oscillation excited in the presence of a weak poloidal magnetic field. We derive asymptotic linear equations for a perturbation with a large number of nodes along the radius, assuming the rotation to be slow and the characteristic perturbation period to be much longer than the rotational period. The results of a preliminary numerical study of the stability of the torsional mode indicate that the superadiabaticity of the solar convection may contribute to the excitation of this mode. In the present work the approximation of harmonic radial dependence of the perturbation has been used.
Results of Coordinated Multiwavelength Observations of Solar-Type Stars
Authors: Huovelin J. , Saar S.H.
Published: June 2019

We present results of nearly simultaneous polarimetric and Ca II(H+K) emission observations taken over a full rotation period for a sample of six solar-type stars. Significant variations are seen for two stars in polarization and four stars in Ca emission, which we interpret as due to rotational modulation of magnetic areas on the stellar surface. The irregularity of the variations suggest changes of the area size and/or distribution in time scales of the rotation period. Preliminary models (including rough surface maps of two stars) and future prospects are discussed.
A Decade of Wolf-Rayet Literature
Authors: van der Hucht Karel A.
Published: June 2019

To set the stage for the symposium, a brief overview is given of the main thrust of the about 1250 papers on Wolf-Rayet star research published in the past decade, broken down into inventory, basic parameters and galactic distribution, atmospheres, binaries, intrinsic variability, mass loss, enrichment and evolution.
The H/He Ratio of WN Stars
Authors: Crowther Paul A. , Smith Linda J. , Willis Allan J.
Published: June 2019

The observed He II Pickering decrement is modelled using the escape probability method developed by Castor & Van Blerkom (1970) to solve simultaneously the equations of radiative and statistical equilibrium for detailed model hydrogen and helium atoms. All important radiative and collisional processes are incorporated in this nLTE model. We confirm values of 0.0 ≤ H/He ≤ 0.5 for WNE stars and 0.0 ≤ H/He ≤ 3.0 for WNL stars with considerable spread in each subtype.
Diffuse C IV Emission Around the WO Star ST3
Authors: Polcaro V.F. , Giovannelli F. , Manchanda R.K. , Pollock A. , Norci L. , Rossi C.
Published: June 2019

A strong diffuse C IV (5801-12 A) emission has been discovered in Berkeley 87 cluster near to the WR (WO) star ST3 (Barlow and Hummer, 1982) using the Loiano 152 cm telescope equipped with a Boiler and Chivens 26767 spectrograph and a CCD RCA camera. The diffuse emission seems to interest all the core of the cluster Berkeley 87. In fact it is present around many cluster members sited near to the center.
The UV Variability of the WR Star HD 50896 – A One Day Recurrence Timescale
Authors: St-Louis N. , Willis A.J. , Smith L.J. , Garmany C.D. , Conti P.S.
Published: June 2019

The WN 5 star HD 50896 has been the subject of many variability studies in the optical. A period of 3.766 days is frequently associated with this variability although it is by no means clear whether it reflects, for example, binary motions or rotation.
The Structure of Colliding Stellar Winds
Authors: Pollock A. , Blondin J. , Stevens I.
Published: June 2019

We report on progress in the theoretical modelling of colliding winds in WR binary systems, concentrating on two WR+O systems, namely V444 Cygni, and HD 193793.
Stellar Evolution in the Upper HRD: Theory
Authors: Langer Norbert
Published: June 2019

Theoretical aspects of the modeling of observable evolutionary phases of massive single stars are reviewed. The SN 1987A progenitor evolution is considered in detail as an example for a star below the WR limit. Formation, structure, evolution, and mass loss of WR stars are discussed, and the impact of supernova research on stellar evolution theory is stressed.
A Deep Survey for Faint Galactic Wolf-Rayet Stars
Authors: Shara M.M. , Potter M. , Moffat A.F.J. , Smith L.F.
Published: June 2019

Surveys of the Galaxy for Wolf-Rayet (WR) stars are mostly based on objective prism searches, and are generally complete to only about 13th visual magnitude. We are using direct narrowband and broadband Schmidt plates to survey large areas of the southern Milky Way for WR stars to 17-18th magnitude. We expect to find more than 50 new WR stars. The newly detected stars should be among the most distant and/or reddened known in the Galaxy. The survey is also designed to test the completeness of previous bright WR star surveys, and thus to help settle debates over the Initial Mass Function of the most massive stars. We have now located 13 new WR stars in a 40 square degree region in Carina where 24 WR stars were already known. A 25% incompleteness in detection of WR stars as close as 2-3 kpc is suggested.
Massive Stars and Galactic Evolution
Authors: Matteucci Francesca
Published: June 2019

The evolution and nucleosynthesis in massive stars are briefly reviewed, and compared with the information derived from SN1987A in LMC. Most of the theoretical models agree with the measured abundances and they can be used in models of galactic evolution.

Models of chemical evolution of galaxies are presented and the role of massive stars in their evolution is discussed.

Finally, the role of Wolf-Rayet stars in galactic evolution is studied, particularly from the point of view of their final fate. It is shown that, if Wolf-Rayet were the progenitors of type Ib supernovae, the Galactic chemical evolution would not change substantially with respect to the case of white dwarfs being the progenitors of type Ib supernovae. However, the predicted frequency of type Ib supernovae in the Wolf- Rayet case would be far too low in comparison with observational estimates.
Attempt to Apply the U B V B1B2V1G Photometry to the Determination of the Distance of the Hyades
Authors: Golay M.
Published: June 2019

A photometric method, using the U B V B1B2V1G system, is suggested to determine the distance of clusters. This method based on the assumption that stars with same seven colours have also same absolute visual magnitude is applied, as an example, to Hyades and Praesepe.
The Calibration of Luminosity Criteria
Authors: Blaauw A.
Published: June 2019

Attention is drawn to important systematic effects in the calibration procedure due to the accidental errors in the measured luminosity criteria. The present state of the luminosity calibrations in the MK system is reviewed with reference to recent work based on proper motions and radial velocities, and on trigonometric parallaxes, resulting in evidence for corrections of about −0.4 mag. for the K0–K5, III stars. Brief reference is made to the developments with regard to the Mv(K) system.

The present report summarizes the principal elements of the review presented at the symposium.
A Preliminary Test of the Calibration of the Hβ System in Terms of Absolute Magnitudes and Intrinsic Colours for Early-Type Stars
Authors: Moffat A. F. J. , Schmidt-Kaler Th , Vogt N.
Published: June 2019

The dependency of the Hβ-index on two physical parameters is briefly discussed. The previous calibration of Mv(β) (Fernie, 1965 or Crawford, 1971) is confirmed for main sequence O and B stars; however, the β-values of the later B-supergiants tend to be too large for their absolute magnitudes. The problem of filtering out stars with marginal emission is emphasized.
Three-Dimensional Representation of A0–G5 Stars
Authors: Hauck B.
Published: June 2019

It is possible to obtain for the stars of the spectral type included between A0 and G5 three parameters respectively correlated with the effective temperature, the luminosity and the blanketing. A method to determine the absolute magnitude is given.
First Results of the Absolute Calibration of the u, v, b, y System of Filters
Authors: Tapia S. , Johnson H. L. , Crawford D. L.
Published: June 2019

Absolute flux densities for a zero magnitude A0V star at the effective wavelengths of the u, v, b, y spectral bands are presented.
Introduction
Authors: Davis Philip A. G.
Published: June 2019

A short introduction to the subject of the meeting, IAU Symposium No. 167, New Developments in Array Technology and Applications is given. CCD and Array detectors have become the detectors of choice at optical observatories all over the world. Direct imaging, photometry and spectroscopy are all vastly improved as a result. Thirteen IAU Commissions joined in sponsoring this meeting which indicates the wide interest in this subject. In the five days of the symposium the following topics were discussed: New Developments in CCD Technology, New Developments in IR Detector Arrays, Direct Imaging with CCDs and Other Arrays, Spectroscopy with CCDs and Other Arrays and Large Field Imaging with Array Mosaics. A few papers concerning Astrometry with CCDs were given in the poster sessions. Scientific results were also presented in the poster sessions.
Array Detectors and Instruments for the ESO VLT
Authors: D'Odorico Sandro
Published: June 2019

Two-D array detectors are one of the key components of the instruments being built for the four ESO 8-m telescopes, the VLT project. Three optical and two infrared instruments are under construction. One faint object imager and multi-slit spectrograph to operate in the spectral region 350–1000 nm (acronym FORS) is based on a 20482 high-efficiency CCD. A two-channel echelle spectrograph to work in the 300–1000 nm region (UVRS) is built around a mosaic of 20482, 15 μm CCDs. A multifiber, new spectrograph is based on a 4096 × 2048, 16 μm CCD. The two infrared high-resolution instruments, one imager/long-slit spectrometer (ISAAC) and one high-resolution camera are designed to work with adaptive optics and in the speckle mode (CONICA). Both are designed to incorporate IR arrays up to a format of 10242 and will work in the spectral region of 1–5 μm. The main properties of the instruments and of detectors are presented and their close interdependence is illustrated.
Infrared Arrays at the European Southern Observatory
Authors: Finger G. , Nicolini G. , Biereichel P. , Meyer M. , Moorwood A. F. M.
Published: June 2019

This paper gives an overview of infrared array detectors which have been tested and used at ESO. The performance of arrays using Reticon type readouts, CCD readouts and switched FET multiplexers have been evaluated for both InSb and Hg1−xCdxTe detectors. Performance limitations specific to the NICMOS3 256 × 256 Hg1−xCdxTe detector installed in the ESO infrared array camera IRAC2 are addressed. The first test results with a high well capacity SBRC 256 × 256 InSb array are also presented.

Advanced readout techniques for image sharpening tested on a 2.2-m telescope are discussed briefly. A new generation of instruments being built for the VLT, the very large telescope project of ESO, is designed to house large format 1024 × 1024 IR arrays. A fast data acquisition system is currently being developed at ESO. The system is capable of handling the high data rates generated in the thermal infrared by large format low well capacity arrays. It can also cope with the low read noise required for flux levels of ≤ one photon/sec. It will first be installed in ISAAC, the Infrared Array Camera and Spectrometer built for the VLT (Moorwood 1993). The present status of both the detector developments and the data acquisition system is reviewed.
CCD Photometry — Present and Future
Authors: Walker Alistair R.
Published: June 2019

I will briefly treat some of the developments relating to CCD photometry which have taken place over the last two to three years, and speculate on those which can be anticipated to take place in the near future. CCDs have been in widespread use as astronomical detectors for slightly more than a decade. For the majority of visual-light projects they have displaced the photographic plate and the photomultiplier as the detector-of-choice, except in applications requiring large area coverage or high time resolution, but even here the development of arrays and the use of more sophisticated electronics has permitted encroachment into these domains. The use of large, low-noise detectors for CCD photometry places stringent demands on telescope optics, instruments, controllers, calibration procedures, data reduction methods and data storage, and forces a holistic approach to managing the data flow from detector to final storage medium.

For an earlier review on this field see Walker (1993); other papers presented at IAU Colloquium No. 136 and IAU Symposium 167 (these proceedings) should be consulted for different topics, alternative viewpoints, and more in-depth discussions of specific subjects.
High Precision Stellar Photometry by CCDs. II
Authors: Bessell Michael S.
Published: June 2019

CCD photometry is capable of high internal precision, however there are several important requirements necessary to attain high precision in standardized photometry. Firstly, the CCD passbands must match as closely as possible the standard passbands; secondly, new faint standards must be set up in several declination zones and thirdly, for convenience a sufficient number of standards covering a good range in color should be obtained on a single CCD frame so that several different frames should suffice for standardization. Landolt has taken the first steps in defining several such fields. The small systematic differences between different UBVRI systems have been examined and transformations can be applied to the photometry of Landolt and Bessell to place it on the Cape — SAAO system.
Echelle Spectroscopy by a CCD at Low Signal-to-Noise Ratio
Authors: Queloz Didier
Published: June 2019

The measurement of some physical parameters of astronomical objects can only be carried out with high resolution spectra. Unfortunately the high dispersion of the light on the detector restricts such observations to relatively bright sources. However, some spectral information can be concentrated into a single spectral “line” by a cross-correlation algorithm, allowing the observation of fainter objects. Such a technique, taken from the CORAVEL optical correlation, is presented. A complete description of the errors of the correlation function parameters is given and the minimum signal-to-noise ratio is also discussed. Finally, a short investigation of the best resolution needed to observe efficiently radial velocities and velocity broadenings is made.
Magnetic Field Reconnection in Cosmic Plasmas
Authors: Sonnerup B. U. Ö.
Published: June 2019

A brief review is presented of the concept of magnetic field reconnection or merging. This process occurs whenever an electric field is present along a separator line in the magnetic field. The basic properties of reconnection are discussed in the context of the classical MHD models by Sweet and Parker and by Petschek. Attention is then focussed on reconnection in collision-free plasmas. The energization of charged particles during their interaction with the current layers associated with the reconnection geometry is discussed and the nature of the processes occurring in the so-called diffusion region which surrounds the separator is considered. Finally, comments are made on the nonsteady aspects of reconnection at the earth's magnetopause.
Laboratory Experiments on Reconnection in Current Sheets
Authors: Bratenahl A. , Baum P. J.
Published: June 2019

Laboratory reconnection experiments dedicated to problems of space and astrophysics are briefly reviewed with the purpose of demonstrating that such experiments can provide important insights of considerable value to the development of reconnection theory. Moreover, many of these insights are of a kind not likely to be perceived either when working directly with space observations or while pursuing a course of pure theoretical reasoning without reference to laboratory results.
The Coalescence Instability in Solar Flares
Authors: Tajima T. , Brunel F. , Sakai J.-I. , Vlahos L. , Kundu M. R.
Published: June 2019

The non-linear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic and emission as well as the characteristics of 2–D microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. We note that the presence of strong electric fields and super–Alfvenic flows during the course of the instability play an important role in the production of non–thermal particles. A qualitative explanation on the physical processes taking place during the non–linear stages of the instability is given.
Phase Mixing of Propagating Alfvén Waves
Authors: Nocera L. , Leroy B. , Priest E. R.
Published: June 2019

Among MHD waves, Alfvén waves have been proved to be the best candidates to reach the solar corona and, eventually, to be responsible for the heating of this outer part of the solar atmosphere. The problem arises, however, about the mechanism able to transform the energy stored in the waves into heat.
Variations in External Parallax Errors
Authors: Upgren A. R.
Published: June 2019

The present astrometric program of the Van Vleck Observatory began in 1967. Since then it has emphasized parallaxes and proper motions of stars of the lower main sequence which are not identified on the basis of proper motion and are therefore not biased towards high space velocity. Later an analysis was made from parallax and proper motion data from 70 stars in the spectral range dK3-M2 (Upgren 1973) which found the average external mean error in parallax to be 8.0 ± 1.7 mas (milliarcseconds). This external error was found to vary little from one parallax to another and to have no correlation with the formal internal errors for the individual parallax determinations. Hanson and Lutz (1983) confirm this result using the parallaxes of 14 members of the Hyades cluster also determined at Van Vleck. They find a mean external parallax error of 9.4 ± 1.8 mas and suggest that the proximity of the two determinations may be evidence that Van Vleck parallaxes may be characterized by a single external error. Their slightly larger figure may or may not reflect the relatively fewer plates and epochs of observation from which the Hyades parallaxes were determined.
Testing Schmidt Plates for Astrometric Purposes
Authors: Russell J. L. , Williams C. A.
Published: June 2019

The Guide Star Selection System for the Space Telescope is being developed to find positions (± 0.25 arcsec) and magnitudes (± 0.4 mag) for guide star pairs for every possible ST target. The data available for the astrometric portion of this task are measurements (±1 μm) of plate surveys from the Palomar and UK schmidt telescopes and positional data from the AGK3 and the SAOC. Astrometric testing to date has concentrated on whole plate reductions in the area of the astrometric standard region in Praesepe. Described here are the test procedures derived to measure the effect of the astrometric accuracy of the guide star positions on ST pointing success. The most critical item in the pointing procedure is that the separations of the guide stars and the target over the ST field of view (28 arcmin diameter) be well-known. Any small zero-point shift or rotation of the field relative to the absolute system is tolerable.
Astrometric Characteristics of the Abastumani Astrophysical Observatory 125 cm Reflector (AZT-11) of Ritchey-Cretien Optical System
Authors: Salukvadze G. N.
Published: June 2019

Quite a number of instances are known when Schmidt, mirror-lens system telescopes and generally reflectors are used for solving the problems of photographic astrometry.

This paper describes the use of the Ritchey-Cretien telescope (AZT-11) at the Abastumani Astrophysical Observatory for determining relative positions of the members of multiple systems.
Impersonal Techniques of Transit Circle Observations. “The Carlsberg Automatic Meridian Circle”
Authors: Helmer L.
Published: June 2019

The conventionel reversible meridian circle of Copenhagen University, has over the last years been fully automated, and equipped with a new photoelectrical transit micrometer and a revised photoelectric circle recording system. Setting, observation and data recording is completely controlled by two minicomputers, therefore the presence of an observer is needed only for emergency situations, and for the reduction procedure. The telescope has been succesfully tested over a two year period in Brorfelde, resulting in two published catalogues with mean errors similar to those previously obtained with the photographic micrometer. The magnitudes were also measured and the limiting magnitude in Brorfelde was mv = 12.

In the autumn of 1983 the telescope was moved to the Canarian island La Palma, where it is currently being installed.
The Seven-Inch Transit Circle and its New Zealand Program
Authors: Hughes J. A. , Robinson M. D. , Gauss F. S. , Stone R. C.
Published: June 2019

The modernization of the seven-inch transit circle is an important aspect of the envisioned Naval Observatory observing effort. This task has been carried out on the basis of the following desiderata:

1) The basic sensor should be photoelectric

2) Point sources observable at night down to at least m=10

3) Venus, Mercury and stars down to m=4 observable in the daytime

4) Mars, Jupiter, Saturn, Uranus, Neptune and the Moon observable

5) The Sun must be observable

6) The instrumental parameters: azimuth, level, collimation, nadir, and so on must be determined so as to allow absolute observations

7) The system should operate essentially autonomously, but an observer should be kept in the observing “loop”.

It appears that all of these objectives have been achieved by the system now to be briefly described.
Comparison of Tokyo PZT Catalogues with AGK3 and with Three Other Independent Catalogues
Authors: Sadžakov S. , Dačić M. , Fomin V. A.
Published: June 2019

Results are presented of the comparison of five Tokyo PZT cataloques with the AGK3 and three other independet catalogues obtained with meridian circles.
Preparation of the HIPPARCOS Input Catalogue. Astrometric Programs for HIPPARCOS. Preliminary Astrometric Observations
Authors: Turon-Lacarrieu C. , Réquième Y.
Published: June 2019

The various aspects of the preparation of the Hipparcos Input Catalogue are presented here. The astrometric parts of the work are pointed out in more details, especially the new observations and measurements already undertaken. The astrometric proposals submitted for observation with Hipparcos are also presented, as they will allow the link between Hipparcos, Space Telescope and ground-based astrometric programs.
Intermediate Scale Structure
Authors: Browne I.W.A.
Published: June 2019

What does intermediate (arcsecond) scale structure tell us about the activity deep in the VLBI cores of galaxies and quasars? There are certain key areas where a knowledge of this structure is particularly relevant. One is in defining the relationships between the various classes of objects leading to unified schemes. A second is in the understanding of jet physics. For the latter it is very important to know if the material in the jets supplied from the nucleus is heavy or light, slow or fast, ejected one side at a time or symmetrically. The optimum resolution to study jet material is on the arcsecond (≡ kiloparsec) scale where very high dynamic range maps are possible and where it becomes feasible to find out something about the physical conditions in the surrounding medium from optical and X-ray observations.
The Variable HI Absorption (z=0.524) in the Spectrum of AO 0235+164
Authors: Briggs F. H.
Published: June 2019

The spectrum of AO 0235+164 (z>0.85) reveals the presence of absorbing gas (z=0.524) which has been studied extensively at radio and optical wavelengths (See Wolfe, Davis and Briggs, 1982 for bibliography). A program by Wolfe et al. to monitor the radio absorption line at 932 MHz showed that the profile had changed during a 5 year period. The observation led to a tightly constrained model in which variations in the source continuum were capable of driving the HI hyperfine level populations (and hence the optical depths of the features in the absorption line) by virtue of the hypothesized close proximity of the source to the clouds. A continued monitoring program has not shown the predicted correspondence between the continuum variation and the behavior of the individual features, and this model has therefore been ruled out.
Spatial Structures of a Complete Sample of Extragalactic Radio Sources North of Declination 70°
Authors: Eckart A. , Witzel A.
Published: June 2019

With the aim of studying the spatial structures of a complete sample
of radio sources found at 6 cm wavelength we selected 13 sources from the
“S5–survey” (Kühr et al., 1981) which fulfil the following criteria

1) δ > 70°, |bII| > 10°

2) S5 GHz > 1 Jy (at the epoch of the S5–survey)

3) α5 GHz2.7 GHz > − 1.5 (S ∝ να)

6 of these sources are identified by means of optical spectroscopy with QSOs, 6 are BL Lac-type objects, and the identification of 1 source is presently unknown. Observations at frequencies ranging from radio to X-ray have been reported (Biermann et al., 1981; Biermann et al., 1982; Eckart et al., 1982).
Superluminal Acceleration of the New Component in 3C 345
Authors: Moore R. L. , Biretta J. A. , Readhead A. C. S. , Bååth L.
Published: June 2019

VLBI observations of 3C 345 at 10.8 GHz and 22.2 GHz show that the position angle of the new component is increasing as it separates from the core. Also, the apparent velocity of the component is increasing. This is the first clear evidence for non-radial motion and acceleration of an individual component in an extragalactic radio source.
Proper Motion of Components of the Quasar 3C 345
Authors: Bartel N. , Ratner M. I. , Shapiro I.I. , Herring T. A. , Corey B. E.
Published: June 2019

From five sets of VLBI observations spaced between 1972 and 1981, we estimated the positions of components of the superluminal quasar 3C 345 relative to the position of the single component of the quasar NRAO 512. The relative proper motion of the easternmost component of 3C 345, believed to be the “core”, was found to be 0.02±0.02 mas/yr. This result is consistent with the “core” being stationary and the “jet” components moving with respect to NRAO 512.
4C39.25 - a Contracting Source?
Authors: Shaffer David B.
Published: June 2019

The quasar 4C39.25, whose nuclear radio structure was stable for many years, now shows a contraction in the brightness distribution. Possible explanations are discussed.
Inner Oscillations in the M87 Jet
Authors: Nieto J.-L. , Lelièvre G. , Heudier J.-L. , Maury A.
Published: June 2019

Continuing a long project of investigations of the optical morphology of the M87 jet (see review in Nieto, 1983), we have obtained at the Cassegrainan focus of the CFH telescope in March 1983 three UV exposures with the wide-field electronographic camera (Lallemand et al., 1970). The aim was to achieve the same order of resolution as that of the photographic plates obtained by Nieto and Lelièvre (1982), but with a much higher signal to noise ratio.
Theoretical Models of Active Galactic Nuclei
Authors: Blandford R. D.
Published: June 2019

We review attempts to incorporate radio sources within the context of general models of active galactic nuclei. The behaviour of gas accreting onto a massive black hole depends upon its angular momentum and accretion rate. It is argued that radio galaxies, QSR's and QSO's (and Seyfert 1 galaxies) be associated with increasing mass accretion rates The classification of an active galaxy appears to be aspect-dependent. In particular BL Lac objects, OVV quasars and the superluminally expanding compact sources appear to be beamed towards us. We show how the choice of source model can influence the statistics of beaming.
Radio Activity in Bright E/SO Galaxies: NGC 3894
Authors: Wrobel J. M.
Published: June 2019

NGC 3894 is a 13th magnitude E/SO galaxy (de Vaucouleurs, de Vaucouleurs & Corwin 1976; Nilson 1973) whose recession velocity (Kelton 1980) implies a distance of 44 Mpc if Ho=75 km s−1Mpc−1. The radio emission from NGC 3894 is compact-core-dominated and, as shown in Fig. 1, this compact core is surrounded at 1.5 GHz by weak diffuse emission with a characteristic size of ~2 arcmin (26 kpc) (Wrobel & Heeschen 1983). If the compact core radiates isotropically, then its radio luminosity is ~1040 erg s−1.
The Evolution of the Compact Radio Structure in SS433 Over a 16-Day Period
Authors: Schilizzi R. T. , Romney J. D. , Spencer R. E.
Published: June 2019

SS433 has been under intensive study for the past five years in almost all wavelength bands of the electromagnetic spectrum. This peculiar object is generally regarded (Beer 1981) as being a binary system composed of a main sequence star losing mass via Roche lobe overflow to a massive accretion disk associated with a compact object, probably a neutron star. The binary period is 13.1 days. Supercritical accretion onto the disk causes about 10−6 M⊙/year of ionised matter to be ejected in the form of jets with a relatively constant velocity of 0.26 c along the disk axis. The disk (or the inner part of it) precesses with a period of about 164 days, although there is evidence that this may not be constant. The half angle of the precession cone is ~20° and its axis lies at an angle of ~80° to the line of sight. The main sequence star loses mass at a rate of 10−4 to 10−6 M⊙/yr into a stellar wind with the result that a relatively dense environment surrounds the binary system.
Jets in Molecular Clouds
Authors: Königl Arieh
Published: June 2019

There is now growing evidence that the cosmic jet phenomenon manifests itself in a remarkable way in regions of active star formation embedded in dense molecular clouds. The first indications for oppositely directed, supersonic outflows from young stars were provided by molecular line observations (most notably of CO) which detected spatially separated regions of redshifted and blueshifted emission in association with embedded infrared sources. About twenty sources of this kind have been identified so far, and more are continuously being discovered; they typically have radii ∼1018cm, velocities ∼10–50 km s−1, dynamical ages ∼104yr, and energies ∼1046-1047erg s−1(see Bally and Lada 1983 for a review). Statistical arguments indicate that energetic outflows of this type are probably a common feature in stellar evolution, and that they occur in both massive and low-mass stars. Direct evidence that the outflows in many cases are highly collimated was subsequently provided by the detection of high-velocity Herbig-Haro objects (optical emission clumps with typical masses ∼10−5M⊙) along the axes of the bipolar CO lobes. Proper-motion measurements are now available for a number of these objects (e.g., Herbig and Jones 1981), and they invariably reveal that the velocity vectors (of typical magnitudes 200–400 km s−1) point away from the central star. The clumps are often found to consist of many sub-condensations which move independently with disparate speeds, but which nevertheless travel in the same general direction with an angular spread ≲ 10°. Finally, radio continuum observations (e.g., Cohen et al. 1982) and deep CCD images (e.g., Mundt and Fried 1983) have shown that the collimation of the outflows is already well established on scales of ≲ 1015cm.
The Structure of OH Maser Clouds Associated with Late-Type Stars
Authors: Bowers P. F. , Johnston K. J. , Spencer J. H.
Published: June 2019

The absolute positions and the arcsec structure of OH maser clouds surrounding 20 Mira variables and late-type supergiant stars have been measured using the Very Large Array in a spectral line mode at 1612 MHz. The stars observed are listed in Table 1 which indicates that the angular radii θ of the maser clouds range up to 4″. The linear radii R range from < 100 AU for the Mira variable U Ori to 104 AU for the supergiant IRC+10420 and are correlated with the stellar mass loss rates.
Magnetic Field Structure of Star Forming Regions: VLBI Spectral Line Results
Authors: Garcia-Barreto J.A. , Burke B. F. , Reid M. J. , Moran J. M. , Haschick A. D.
Published: June 2019

Magnetic fields play a major role in the general dynamics of astronomical phenomena and particularly in the process of star formation. The magnetic field strength in galactic molecular clouds is of the order of few tens of μG. On a smaller scale, OH masers exhibit fields of the order of mG and these can probably be taken as representative of the magnetic field in the dense regions surrounding protostars. The OH molecule has been shown to emit highly circular and linearly polarized radiation. That it was indeed the action of the magnetic field that would give rise to the highly polarized spectrum of OH has been shown by the VLBI observations of Zeeman pairs of the 1720 and 6035 MHz by Lo et. al. and Moran et. al. VLBI observations of W3 (OH) revealed that the OH emission was coming from numerous discrete locations and that all spots fell within the continuum contours of the compact HII region. The most detailed VLBI aperture synthesis experiment of the 1665 MHz emission from W3 (OH) was carried out by Reid et. al. who found several Zeeman pairs and a characteristic maser clump size of 30 mas. In this work, we report the results of a 5 station VLBI aperture synthesis experiment of the 1665 MHz OH emission from W3 (OH) with full polarization information. We produced VLBI synthesis maps of all Stokes parameters of 16 spectral features that showed elliptical polarization. The magnitude and direction of the magnetic field have been obtained by the detection of 7 Zeeman pairs. The three dimensional orientation of the magnetic field can be obtained, following the theoretical arguments of Goldreich et. al., from the observation of π and σ components.
Pulsar Astrometry
Authors: Taylor Joseph H. , Gwinn Carl R. , Weisberg Joel M. , Rawley Lloyd A.
Published: June 2019

High precision measurements of the celestial coordinates of pulsars are desirable for a number of reasons. If carried out at several epochs, the measurements can yield angular proper motions; together with distance estimates based on dispersion measure, the proper motion of a pulsar reveals two of three components of its space velocity, and consequently provides important kinematic information on pulsar ages (see, for example, Manchester, Taylor and Van 1974; Lyne, Anderson and Salter 1982; and references therein). Direct measurements of annual parallaxes are also possible in principle, and are marginally feasible with present techniques for a few of the closest pulsars. Model independent distances obtained from parallax measurements, together with observed pulsar dispersion measures, yield the electron density along the line of sight to the pulsar. Knowledge of the interstellar electron density in the solar neighborhood provides a calibration of the dispersion-based distance scale that is complementary to the calibration derived from neutral hydrogen absorption measurements of more distant pulsars (Weisberg et al. 1980), and permits appropriate statistical analyses to be made of the local space density of pulsars and their birthrate (e.g. Taylor and Manchester 1977). Finally, pulsar astrometry can be expected to yield important information on the relative orientations of fundamental reference frames. In particular, pulse timing observations yield positions in a reference frame based on motions of the planets, while interferometric position measurements are based on an Earth-equatorial system. At present the relative orientation of these two coordinate systems is known to only accuracy, though the potential precision of both types of measurements is much higher.
The Calibration of Interferometrically Determined Properties of Binary Stars
Authors: McAlister Harold A.
Published: June 2019

With the advent of speckle interferometry, high angular resolution has begun to play a routine role in the study of binary stars. Speckle and other interferometric techniques not only bring enhanced resolution to this classic and fundamental field but provide an equally important gain in observational accuracy. These methods also offer the potential for performing accurate differential photometry for binary stars of very small angular separation. This paper reviews the achievements of modern interferometric techniques in measuring stellar masses and luminosities and discusses the special calibration problems encountered in binary star interferometry. The future possibilities for very high angular resolution studies of close binaries are also described.
The Role of Space Observations in The Calibration of Fundamental Stellar Quantities
Authors: Code Arthur D.
Published: June 2019

This paper summarizes the current status of ultraviolet spectrophotometry with emphasis on the instrumental characteristics unique to space observations and on the application of existing data to the calibration of stellar properties. The currently available data bases will be briefly reviewed. When combined with ground based data, ultraviolet observations provide information on effective temperatures and bolometric corrections for early type stars and on the nature of the intervening interstellar medium. The ultraviolet measurements are sensitive to chemical composition differences and provide a powerful tool in discussion of stellar evolution in composite systems. This review concludes with a brief discussion of future directions in instrumentation and analysis.
Standard Astronomical Sources for the Space Telescope
Authors: Bohlin Ralph C.
Published: June 2019

The Space Telescope (ST) will require many types of standard sources for a diverse range of calibrations to be performed after launch. The scientific instruments are sensitive to a wide range of wavelengths from 1050 to 11,000Å and encompass a broad range of measurement capabilities including astrometry, photometry, imaging, polarimetry, and spectroscopy. To verify proper operations of each instrument and to provide quantitative calibrations, a diverse range of standard sources and fields are required. In order to select targets that satisfy the requirements of the Instrument Definition Teams and the long term responsibilities of the Science Institute, six groups containing a total of 25 astronomers are defining the calibration targets to be observed after launch. The six categories of ST standard sources are:

1)

Ultraviolet Spectrophotometric

2)

Ground Based Spectrophotometric and Photometric

3)

Wavelength

4)

Astrometric

5)

Polarimetric

6)

Spatially Flat Field

The data in these categories will be collected from the literature or through new observing programs as appropriate. These six reports of the working groups outline the calibrations and proposed targets for all of the scientific instruments on ST. The collected data on each set of standard sources should be published in the refereed literature.
The Wilson-Bappu Effect for MG II K-Line Emission Widths
Authors: Parthasarathy M.
Published: June 2019

The existence of a tight linear correlation between the stellar absolute magnitude Mv and the Mg II k-line emission width log WMg II k (kms−1) is confirmed using IUE high-resolution (0.2A) data for 100 late-type stars. A least-squares fit to the data gives the relation: