bluuebunny/crossref_metadata_2025 huggingface dataset:
Supergranulation at the Center of the Disk
Authors: Frazier Edward N.
Published: July 2016

The Kitt Peak multi-channel magnetograph was used to make raster scans of the supergranulation at the center of the disk. The scan pattern was arranged to largely cancel out the effects of the 5 min oscillations and the granulation and to enhance visible effects of the supergranulation.

The results show vertical supergranular motions. These motions consist of relatively isolated ‘patches’ of downward flowing material, or ‘downdrafts’, with an average speed of 0.1 km/s. These downdrafts coincide with patches of magnetic field, and the speed of the downdraft is linearly proportional to the magnetic field strength (50 to 100 G). These downdrafts are also regions of increased brightness in the chromosphere and photosphere.
The Magnetic and Velocity Fields and Brightness in the Solar Atmosphere
Authors: Gopasyuk S. I. , Tsap T. T.
Published: July 2016

Simultaneous observations of the magnetic fields, the line-of-sight velocities and brightness were made in active and quiet regions with the Crimean double-magnetograph in the following lines: Hα, K3 Ca II, Hβ, Hγ, Hδ, MgI λ 5184 Å, CaI λ 4227 Å, D1 NaI, BaII λ 4554 Å, CaI λ 6103 Å, FeI λ 5250 Å.

It is shown, that in the active regions the horizontal velocity is larger than the vertical one.

The mean velocities in the quiet solar photosphere have an isotropic distribution (Gopasyuk and Kalman, 1971).

The mean vertical velocities increase exponentially with height in active and quiet regions.

The correlation between velocities at different levels in active and quiet regions decreases with the distance between the levels of the formation of spectral lines, and it disappears for the velocities recorded in λ 6103 Å and Hβ, for λ 5184 and Hα lines in active regions and for the velocities recorded in λ 5250 Å and Hα lines in quiet regions.

The position of the maximal field strength within a magnetic hill coincides statistically with the zero line of the line-of-sight velocities for active as well as for quiet regions.
Magnetic Fields Measured with the 10830 Å HeI Line
Authors: Harvey J. , Hall D.
Published: July 2016

Several advantages of near infrared spectral lines for magnetic field measurements are listed. In particular, the 10830 Å multiplet of HeI is well suited for observations of chromospheric magnetic fields.

New photoelectric spectroheliograms made with the 10830 Å line reveal a large amount of filamentary fine structure in active regions. This fine structure has important consequences on the interpretation of 10830 Å magnetograms. Except for an association of 10830 Å disk filaments with polarity reversals there is little correlation between absorption features and the 10830 Å longitudinal field. Comparisons of chromospheric and photospheric observations show that the chromospheric field is spatially more diffuse and weaker than the photospheric field.
On the Reality of Magnetic Fine Structure
Authors: Sawyer Constance
Published: July 2016

On filter magnetograms of the Sun made at Lockheed Solar Observatory, small mottles create a salt-and-pepper appearance. Outside plages, the surface seems to be sprinkled with little magnetic elements, with opposite polarities intermingled. The many steps of the photographic subtraction process required to make these elements visible tend to cast doubt on their reality. Independent and stronger evidence for the quantization of magnetic field, recently presented by Livingston and Harvey (1969), stimulates an effort to define more carefully the characteristics of the elements seen on filter magnetograms. The purpose of this contribution is to show that these characteristics are compatible with those of the elements observed at Kitt Peak.
Interaction of Coronal Material with Magnetic Fields
Authors: Pneuman G. W. , Kopp Roger A.
Published: July 2016

The optical resolution in recent eclipse photographs is now sufficient to illustrate clearly many qualitative features of gas-magnetic field interactions in the solar corona. Close to the Sun where the field is strong, the coronal gas over certain regions of the solar surface can be contained within closed loop structures. However, since the field strength in these regions declines outward rapidly, the pressure and inertial forces of the solar wind eventually dominate and distend the field outward into interplanetary space. The overall configuration is determined by a complex interplay of inertial, pressure, gravitational, and magnetic forces. The present work is oriented toward the understanding of this interaction.

Of central importance to this general problem is the typical ‘helmet’ streamer generally overlying a large diffuse bipolar region on the solar surface. A helmet streamer consists of closed magnetic loops near the Sun and open field lines adjacent to and above the loops. The configuration possesses a ‘cusp-type’ neutral point (to be differentiated from a y-type neutral point) at the top of the closed loops. In addition to volume currents, a single sheet current separates the regions of opposite polarity above the neutral point. Below the neutral point, sheet currents also are present between the open and closed regions. These sheet currents are necessary to support the discontinuity in gas pressure which arises since the open region is expanding and the closed region is not. The neutral point problem is discussed in some detail and sample numerical examples are presented.
The Possibility of Magnetic Field Origin in Fine Structure Elements of Solar Features
Authors: Kopecký M. , Kuklin G. V.
Published: July 2016

It is demonstrated that in principle the magnetic field may originate in the fine structure elements of the photosphere and the sunspots as a result of lack of coincidence of isobaric and isothermic surfaces in those elements.
Observations of the Polar Magnetic Fields
Authors: Stenflo Jan Olof
Published: July 2016

Results from observations of the polar magnetic fields made in 1968 with the Mount Wilson magnetograph are reported. The field was of south polarity near the heliographic north pole and of north polarity near the south pole. The inversion line of the field was at latitude +70° in the north hemisphere and −55° in the south, which coincides with the position of the polar prominence zones at that time. Observations made simultaneously at the Crimean Astrophysical Observatory are in good agreement with the Mt. Wilson data and confirm the latitude variation of the field.

A few hundred of Hale's plates from 1914, which he had used to determine the Sun's general magnetic field, have been remeasured. The plates were automatically scanned with a digitized microphotometer, and the treatment of the data was made with a computer. While the visual measurements by Van Maanen had given a strong general field similar to that of a dipole, the computer reductions did not reveal any significant field (stronger than 5 G) at any latitude.
A Numerical Study of the Solar Cycle
Authors: Nakagawa Y.
Published: July 2016

Models relevant to numerical studies of the solar cycle are reviewed briefly with discussions of pertinent physical mechanisms. It is suggested that the observed surface activities are secondary in nature and an example of possible non-axisymmetric steady state solutions is given, together with the results of preliminary numerical computations.
Sector Structure of the Solar Magnetic Field
Authors: Wilcox John M.
Published: July 2016

The solar sector structure consists of a boundary in the north-south direction such that on one side of the boundary the large-scale weak photospheric magnetic field is predominantly directed out of the Sun, and on the other side of the boundary this field is directed into the Sun. The region westward of a solar sector boundary tends to be unusually quiet and the region eastward of a solar sector boundary tends to be unusually active. This tendency is discussed in terms of flares, coronal enhancements, plage structure and geomagnetic response.
Neutral Hydrogen at Large Distances from Parent Galaxies
Authors: Davies R. D.
Published: July 2016

High sensitivity measurements in the vicinity of nearby galaxies have shown the existence of appreciable quantities of neutral hydrogen at large distances (2 to 5 Holmberg radii) from the centre. The galaxies studied were the M81/M82/NGC 3077 system, M31, M33, IC 342 and M51. In all cases the gas is at velocities consistent with being bound to the parent galaxy. Of these the M81 system contains the most circum-galactic neutral hydrogen. In several galaxies there is as much neutral hydrogen outside the Holmberg dimensions as inside.
Dwarf Content of Old Galaxy Populations
Authors: Whitford A. E.
Published: July 2016

Scanner observations of five galaxies in the region near 9910 Å showed that the strength of the dwarf-sensitive Wing-Ford band is below the level of detection. This result is at variance with the predictions of strongly dwarf-enriched population models and in accord with the evidence for giant-dominated radiation at 2.3μ reported by Baldwin et al. (1973) on the basis of the strong CO band found in three galaxies. In the absence of any evidence for a power-law mass function, the consequences of a rounded function are examined.
Some Recent Developments in the Theory of Spiral Structure
Authors: Contopoulos G.
Published: July 2016

The particle resonance in a galaxy is of special interest because, according to the recent theory of Lynden-Bell and Kalnajs (1972), it provides the excitation of the density waves. In particular it is of interest to know if the density wave reaches the particle resonance, because the dispersion relation derived by Lin and Shu (1966) has a forbidden region if the parameter
where (with α0 the surface density and κ the epicyclic frequency), is larger than one. If Q= 1, Lin and Shu find two waves going through the resonance but the amplitude tends to infinity there.
Planetary Formation
Authors: Williams I.P.
Published: July 2016

Existing theories of planetary formation (based on a continuous solar nebula or on discrete objects) are briefly reviewed.
Nature of the Venus Clouds as Derived from Their Polarization
Authors: Hansen James E. , Hovenier J. W.
Published: July 2016

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of particles which have a narrow size distribution with a mean radius ~ 1 μ. The refractive index of the particles is 1.44 ± 0.015 at γ = 0.55 μ with a small normal dispersion, the refractive index decreasing from the ultraviolet toward the infrared. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb.

The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venus. A concentrated solution of sulfuric acid (H2SO4–H2O) provides good agreement with the polarization data.
Results from the Infrared Spectroscopy Experiment on Mariner 9
Authors: Pearl J. , Conrath B. , Curran R. , Hanel R. , Kunde V. , Pirraglia J.
Published: July 2016

Over 20000 thermal emission spectra of Mars have been obtained, providing extensive diurnal, seasonal and spatial coverage of the planet. Each spectrum covers the spectral range from 200 to 2000 cm−1 with an apodized spectral resolution of 2.4 cm−1; the noise equivalent radiance of the instrument is 0.5 × 10−7 W cm−2 sr−1 (cm−1)−1.
Theoretical Studies of an Atmosphere Around Saturn's Rings
Authors: Dennefeld M.
Published: July 2016

The subject of this paper is an attempt to predict what can be seen in the vicinity of Saturn through a UV photometer on board the Mariner-Jupiter-Saturn mission. We will restrict ourselves to the study of atomic hydrogen and OH and to H2O which can be the parent molecule and will consider only the particles ejected from the rings and from Titan.
Spectroscopic evidence bearing on the distribution of gas in extra-galactic systems
Authors: Mayall N. U.
Published: July 2016

Six years ago, in a joint paper with W. Baade, I presented certain spectrographic data bearing on the distribution and motions of gaseous masses in spiral nebulae. Since then progress in this special field has been unspectacular and relatively slow by conventional optical means, mainly because of the considerable faintness of the sources. Nevertheless, the optical data now seem sufficiently representative to warrant a review directed toward an eventual comparison of optical and radio results. For there can be little doubt that the new radio astronomy techniques give every indication of revolutionary new advances. Highly significant results have been obtained for the Magellanic Clouds, a beginning has been made in the local group spirals such as the Andromeda nebula, and it is reasonable to expect, as more powerful installations come into operation, that the nearer field and great cluster nebulae will come under detailed radio observation. But these matters have been considered at the recent Jodrell Bank symposium on radio astronomy, in Manchester. For this reason and because I am not a radio astronomer I shall proceed, without further discussion of these exciting new developments, to a description of the more prosaic optical data obtained from spectrographic observations.
A Modern Look at ‘Interstellar Clouds’
Authors: Heiles Carl
Published: July 2016

We compare past and present modes of investigation of the structure of the interstellar gas. Many aspects of the interstellar cloud model are invalid.

Interstellar optical absorption lines and Hi21-cm emission lines show a number of very large aggregates with properties similar to those of ‘cloud complexes’. At nonzero velocities especially for b<0°, exist optical lines which have no Hicounterparts. These are almost certainly produced in low-density gas clouds; perhaps the intercloud medium is itself cloudy.

Maps of Hicolumn density taken over large velocity ranges do not reveal much small-scale structure. This fact cannot easily be reconciled with the statistical analyses of interstellar reddening. The maps do reveal large, coherent gas structures which are often filamentary in shape and at least sometimes aligned parallel to the interstellar magnetic field.

Maps of Hicolumn density over small velocity ranges show much small-scale structure, often filamentary in shape. The filaments are almost universally oriented parallel to the interstellar magnetic field and have Doppler velocity gradients along their lengths. In one area the geometry of the field and gas almost exclusively suggests Alfvén-type motions.
Properties of Neutral Hydrogen Clouds
Authors: Schwarz Ulrich J. , van Woerden Hugo
Published: July 2016

In the region +19° <b< +30°, 122° <l< 143°, 21-cm line profiles were analyzed into Gaussian components, and these components combined into clouds, by means of computerized procedures. Maps of some of the clouds so defined are presented, and their properties discussed. Many clouds are elongated and/or irregular in shape. Histograms of cloud parameters are presented and subjected to statistical analysis. There is evidence for tenuous clouds of large angular extent but very low column density (NH<1019 cm-2).
Free Electrons Outside Hii Regions
Authors: Guélin M.
Published: July 2016

This paper reviews the recent observational results on the electron distribution outside the Hiiregions. The mean electron density in the solar neighbourhood is of the order of 0.03 cm-3, and does not seem to vary very much between the Hiclouds and the intercloud medium, or between the arms and the interarm region. The z thickness of the electron layer in the solar neighbourhood is found to be larger than or of the order of 0.8 kpc. No reliable figure of the electron distribution can be deduced for the moment in the inner parts of the Galaxy.
The Chemical Composition and Distribution of Interstellar Grains
Authors: Greenberg J. Mayo , Hong Seung-Soo
Published: July 2016

The chemical composition of interstellar grains is derived here on the basis of (1) the cosmic abundance of the elements; (2) the wavelength dependence of extinction and polarization; (3) the average total extinction; (4) the ratio of polarization to extinction; (5) the predominantly dielectric character of grains in the visible spectral region; and (6) infrared spectral characteristics of grains. It is indicated that the major portion of the grains, by mass, consist of core-mantle particles in the 0.1-µm size range, whose cores consist largely of silicates and whose mantles are a solid mixture of O, C, and N with H in a heterogeneous combination of simple and complex molecules with frozen free radicals. A minor constituent of the solid particles exist in the form of very small uncoated particles generally less than 10-6 cm in size whose precise composition is not certain. Inferences of the core-mantle model with respect to spatial distribution are consistent with the proposition that growth of the mantles occurs in the galactic shock region predicted by the density-wave theory. Estimates of the total visual extinction toward the galactic center and the consequent estimates of the total amount of far infrared radiation are shown to depend critically on the grain model. Variations of the ratio of far ultraviolet to visual extinction are correlated with the conditions for growth of mantles on the bare small particles which are generally prevented from accreting mantles primarily because of their extreme temperature fluctuations produced by the ultraviolet photons in the radiation field.
The Gas-to-Dust Ratio in the Galaxy
Authors: Kerr F. J. , Knapp G. R.
Published: July 2016

We have investigated the gas-to-dust ratio in the Galaxy by comparing 21-cm Hicolumn densities with the color excesses of globular clusters. We find a constant gas-to-reddening ratio in interstellar clouds and the intercloud medium. This ratio is also independent of galactic latitude.
The Brightness Distribution of Ori a at 4.1 Mm in the 101–000 Line of Para-Formaldehyde and in the Continuum
Authors: Kaifu Norio , Iguch Tetsuo , Morimoto Masaki
Published: July 2016

The 4.1-mm continuum emission shows a peak at the Trapezium stars and an extension to the west, where the molecular and IR sources are. The 4-mm line of para-formaldehyde has a similar distribution to that of the 3-mm line of HCN and extends more to the north than the 2-mm line of ortho-formaldehyde. This probably means a lower temperature in the northern part of the cloud.
Optical Observations of Ionized Gas in External Galaxies
Authors: Monnet G.
Published: July 2016

This paper reviews recent optical results on the large scale distribution of ionized gas in spiral galaxies, including our own. There is a diffuse, inhomogeneous emission in the arm region in spirals, including our Galaxy, and in gas-rich galaxies a fainter diffuse emission between the arms.
Infrared Emission from Hii Regions
Authors: Wynn-Williams C. G.
Published: July 2016

Most Hii regions emit large amounts of energy at infrared wavelengths. Dust grains absorb a major fraction of the total energy emitted by the O stars, and this is reradiated in the infrared. The dense Hiicondensations seen by aperture synthesis radio observations are strong 20-µm infrared sources. The dust is probably mixed with the ionized gas in these sources. There are also infrared sources that are not radio sources; these may be protostars. Infrared emission has also been found from many OH/H2O maser sources associated with Hiiregions.
Time Scales and Masses of OH-Emission Regions
Authors: Menon T. K.
Published: July 2016

The velocity structure of OH profiles of OH maser regions is used to estimate the time scales of the source distributions. Time scales are found to be of the order of a few thousand years in typical cases. The velocity dispersions and intensity distribution of components are interpreted in terms of a collapsing cloud model of the emission regions. The masses of the clouds are found to be in the range from a few solar masses to a few hundred solar masses for the well-known emission regions.
Oh Observations Near the Reflection Nebulae Ngc 2068 and Ngc 2071
Authors: Johansson L. E. B. , Höglund B. , Winnberg A. , Nguyen-Q-Rieu  , Goss W. M.
Published: July 2016

Narrow OH emission lines at 1667 MHz, apparently from a Class I source, have been observed near the reflection nebula NGC 2071. The region contains many T Tauri stars. OH emission corresponding to the dust cloud north and east of NGC 2024 is also seen. At 1720 MHz the dust cloud component appears in absorption; presumably the isotropic 2.7 K cosmic background is being absorbed.
High-Resolution Observations of Galactic Nonthermal Sources at 160 Mhz
Authors: Slee O. B. , Dulk G. A.
Published: July 2016

Preliminary maps of the brightness distributions of 11 supernova remnants are presented. The sources, with diameters ≲10′, were observed at 160 MHz with resolution better than 2′. Ten of the supernova remnants are significantly resolved, and at least six show evidence of a shell-like structure. For those sources where high-frequency maps are available with comparable resolution the brightness distributions are generally very similar.
Westerbork Observations of the Galactic Supernova Remnants IC 443 and Tycho
Authors: Duin R. M. , Strom R. G. , van der Laan H.
Published: July 2016

Continuum observations of IC 443 were made at 21 cm with a resolution of 23″×59″. The appearance in the radio continuum is very similar to the optical appearance. Since the radio emission is nonthermal, this requires a mechanism that can enhance the synchrotron volume emissivity within thermal filaments, which emit strong optical radiation. We suggest compression of gas and magnetic fields in a shock.

Tycho's remnant has been observed both at 21 cm (resolution 24″ × 27″) and at 6 cm (resolution 7″ × 8″). Most of the fine scale structure is resolved. The similarity at the two wavelengths indicates a remarkable constancy in the spectral index of features down to a scale of 20″.
Fine Structure in Planetary Nebulae
Authors: Terzian Yervant
Published: July 2016

A short report is presented on the aperture synthesis radio observations of planetary nebulae performed by Terzian et al. (1974). Examples of radio maps at 8085 MHz are shown with angular resolutions of the order of 2″ to 3″.
The Large-Scale Structure of Local Hi, Dust, and Galactic Radio Continuum
Authors: Heiles Carl E. , Heiles Carl
Published: July 2016

The correlation of Hiand dust at high latitudes gives different results depending on whether one uses galaxy or reddening data for the dust distribution. It is not certain to what extent this depends on differences in the gas to dust ratio or on difficulties in determining the amount of dust from the optical data. The correlation of Hiand continuum radiation shows Histructures associated with the large-scale loops. There is also a coincidence of a hole in both the Hiand continuum.
A Possible Evolutionary Feature in the Spectra of Radio Galaxies
Authors: Slee O. B.
Published: July 2016

A recent analysis (Slee, 1981) of the spectra of extragalactic sources derived by Slee et al. (1981) has revealed a relationship between spectral index and redshift in the sense that the spectra of identified radio galaxies steepen with increasing redshift; this behaviour is consistent with an effect first reported by Kellermann et al. (1969) that the average spectral index of identified radio galaxies is lower than that of sources in empty optical fields, which are now generally regarded as distant radio galaxies (rather than QSOs). However, because of the selection effects present in the sample, Slee was not able to decide whether the basic correlation is between spectral index and redshift (implying an evolutionary origin), between spectral index and radio power, or between spectral index and linear dimension.
A Preliminary Examination of the Effect of Cluster Gas on Tailed Radio Galaxies
Authors: Harris D. E.
Published: July 2016

From a comparison of X-ray and radio data for 20 clusters which contain tailed radio galaxies, we find evidence for the effects of buoyant forces on the low brightness parts of radio tails. In several cases, the width of the tail increases markedly in low gas density regions, strengthening the case for thermal gas confinement of radio tails. Three examples of enhanced X-ray emission around radio galaxies which are further than 2 Mpc from their cluster centers are found.
A Morphological Classification of Clusters of Galaxies from Einstein Images
Authors: Jones C. , Forman W.
Published: July 2016

The earliest Uhuru observations showed that cluster X-ray sources were not associated with single individual galaxies but were extended sources (Gursky et al. 1971, Kellogg et al. 1972, and Forman et al. 1972). The detection of iron line emission from X-ray spectroscopic observations (Mitchell et al. 1976 and Serlemitsos et al. 1977) showed both that the dominant X-ray emission process was thermal bremsstrahlung and that the gas had been processed through stellar systems before being injected into the intracluster medium.
VLBI Observations of the Nucleus of Centaurus A
Authors: Preston R. A. , Wehrle A. E. , Morabito D. D. , Jauncey D. L. , Batty M. , Haynes R. F. , Wright A. E. , Nicolson G. D.
Published: July 2016

VLBI observations of the nucleus of Centaurus A have been made at three southern hemisphere observatories. Since Centaurus A is the nearest active galaxy, VLBI investigations are important because the physical processes in the nucleus can be studied in greater linear detail than in other similar galaxies. Previous VLBI observations of Centaurus A have been hampered by its southerly declination (−43°) and the sparsity of VLBI capability in the southern hemisphere, leading to only scattered single point u, v coverage. This paper presents results from the early stages of development of a southern hemisphere VLBI network.
Bent Jets in Radio Quasars
Authors: Neff Susan G.
Published: July 2016

How is energy transported out from the central engine in quasars and radio galaxies to the distant radio lobes? This problem has been around since the early discovery of classical double radio sources, and is still not answered in detail. The idea of relativistic beams was first suggested by Martin Rees as a means of transporting plasma out of the nucleus (Rees, 1971, Blandford and Rees, 1974). This idea gained support first from the discovery of hot spots in the radio lobes of these large classical double sources, and later by observations of the beams themselves in radio galaxies. As more jets were observed, it became obvious that they were often curved, serpentine, or even sharply bent. This behavior has been modeled as precession of the central nozzle (Bridle et al., 1976, Ekers et al., 1978), as nuclear refraction (Henriksen et al., 1981), as a growing plasma instability (Hardee, 1981) and as various combinations of the above. At the present time, it seems safest to conclude that there are some examples of each of these processes known.
Morphology and Power of Radio Sources
Authors: Scheuer P.A.G.
Published: July 2016

I want to make two points:

1.

Observations suggest that the hot-spots move about either because the beam precesses (e.g. Ekers et al. 1978; Lonsdale & Morrison 1980) or more discontinuously, as in sources like 3C351 that have multiple hot-spots (Laing 1981). The natural interpretation is that the hot-spot at the end of the beam slides over the inner surface of a ‘cavity’ filled with very hot dilute ex-hot-spot material (Scheuer 1974), extending the cavity at various places at different times. Such a ‘dentist's drill’ model has various consequences:

(i)

The mean speed (length/age) at which the cavity elongates may be considerably smaller than the instantaneous speed V of the hot-spot, estimated in the customary way from pressure balance:

(ii)

Remark (i) raises the possibility that giant radio sources have become so long because their jets are unusually constant in direction. NGC6251, which is over 2 Mpc long, has a jet whose direction has not wavered by more than a few degrees in ∼ 107 years (Saunders et al. 1981).

(iii)

We should not be surprised by sources whose hot-spots lie some way behind the extreme ends of the source; this may merely mean that the beam at present impinges on one side of the ‘cavity’. 3C285 is a typical example; a more persuasive case is the Np component of 3C219 (Perley et al. 1980).

2.

Most of the radio emission of most really powerful radio sources comes from their hot spots. Contrariwise, straightforward equipartition calculations on models lead to at least as much emission from the ‘cavity’ as from the hot-spots (Scheuer 1974). While there are several possible explanations, one in particular is suggested by Laing's (1981) extensive data on 40 sources. He lists the synchrotron lifetimes in the hot-spots for electrons radiating at 15 GHz, and while these exceed the light crossing times, they do so by only one or two orders of magnitude. One expects flow through the hot spots at some fairly small fraction of the speed of light; the synchrotron loss cutoff in the hot-spot is then expected to appear in the mm or infra-red region. Expansion of the hot-spot material into the cavity shifts the loss cutoff to a much lower frequency. If the expansion is adiabatic (certainly an oversimplification) the ratio of loss cutoff frequencies is equal to the ratio of energy densities. We cannot use this relationship directly in the more interesting cases, as we cannot estimate the energy density (or even the size) of a ‘cavity’ that we cannot observe. However, we can estimate the cutoff frequency within the hot-spots (for some assumed streaming speed), and Figure 1 shows that the most powerful hot-spots have loss cutoff frequencies in the 10–100 GHz range, implying cutoff frequencies in the ‘cavity’ that could well be below 1 GHz.
Radio Continuum Observations of the Nuclei of Nearby Galaxies
Authors: Davies R.D. , Pedlar A. , Booler R. V.
Published: July 2016

A survey has been carried out at Jodrell Bank of the continuum radio emission from nearby galaxies. The objects include normal galaxies, Seyfert galaxies and others with nuclei active at optical and radio wavelengths.
Jets from Discs and Doughnuts
Authors: Allan P. M.
Published: July 2016

Various authors have suggested that there is a close connection between jets in radio galaxies and the precessing beams of SS433, and that the underlying mechanism for forming the jets is the same on both scales (Rees, 1981). We examine a possible model for generating gas jets close to the central object in either of these two cases.
Supercritical Accretion and its Possible Relation to Quasars and Radio Sources
Authors: Meier David L.
Published: July 2016

This paper reviews some of the properties of supercritical accretion which make it a possible model for the quasar optical central source and for producing the jet in radio sources. Some of the problems with this scenario can be remedied with alternative, but related, models.
Structural Evolution in the Nucleus of NGC 1275
Authors: Romney J. D. , Alef W. , Pauliny-Toth I.I.K. , Preuss E. , Kellermann K. I.
Published: July 2016

The extremely powerful compact radio nucleus of NGC1275 is perhaps the most complex structure seen at milliarcsecond scales. Early attempts to determine its structure (Schilizzi et al. 1975) were unsuccessful, although it was evident that the structure consisted of several bright regions whose relative positions remained fixed while their intensities varied. Later observations and analysis (Pauliny-Toth et al. 1976; Preuss et al. 1979) confirmed this inference and revealed a slow expansion in a direction transverse to the primary axis of alignment.
VLBI Observations of M87
Authors: Reid M. J. , Schmitt J.H.M.M. , Owen F. N. , Booth R. S. , Wilkinson P. N. , Shaffer D. B. , Johnston K. J. , Hardee P. E.
Published: July 2016

On 1980 February 20 we conducted an 8-station intercontental VLBI experiment in order to study the nucleus and jet of M87 at 1666.6 MHz in right circular polarization. Our array was sensitive to structures from 0.001 to 0.1 arcsec. We made a hybrid map of the nucleus of M87, and also searched for compact structures within the knots of the jet. The map (Figure 1) shows that the nucleus of M87 contains a one-sided jet. This morphology is similar to that observed in many compact extragalactic sources. The position angle of the nuclear jet is 290.5 (±1) degrees, which precisely matches that of the 20 arcsec jet. No bending of the jet through an angle greater than about 2 degrees is observed. The nucleus also contains a large component (>0.1 arcsec) which is elongated along the same position angle as the jet and has a flux density of roughly 1 Jy. This component is fully resolved by the vast majority of our (u, v) points, and we could not map it with standard techniques.
Polarization of the Compact Radio Structure of 3C 454.3
Authors: Cotton W. D. , Geldzahler B. J. , Shapiro I. I.
Published: July 2016

The polarization structure of synchrotron sources provides information about the magnetic field structure and thermal particle distributions near the source. Such information is critical to a full understanding of compact sources in the nuclei of galaxies and quasars. VLBI maps of these objects are frequently interpreted as showing jets even though the maps are dominated by a few bright regions. If these sources do indeed contain jets then the jet should have a relatively well-ordered component of the magnetic field. The presence of this ordered magnetic field, as well as the presence of thermal plasma in and around the jet, should be revealed by the polarized radiation. We present below the results of the first successful VLBI measurements of the polarized emission from an extragalactic compact radio source.
Changes in the HI Absorption Line Spectrum of AO 0235+164
Authors: Davis Michael M. , Wolfe Arthur M.
Published: July 2016

The BL Lac object AO 0235+164 is an extreme example of a QSO containing a compact, non-thermal energy source which is violently variable. In 1975 it brightened simultaneously at optical and radio frequencies, with a hundred-fold increase in optical brightness on a time scale of a few weeks (Rieke et al. 1976; Ledden, Aller and Dent 1976). During the outburst 0235 was among the most luminous objects in the universe. It exhibits longer term variations at meter wavelengths (Condon and Dennison 1978), and has experienced repeated optical and short wavelength radio outbursts since 1975 (Pica, Smith and Pollock 1979). Very long baseline interferometry shows it to be the most compact known extragalactic radio source.
Rotating Structures in Extragalactic Variable Radio Sources
Authors: Aller Hugh D. , Hodge Philip E. , Aller Margo F.
Published: July 2016

Four sources have now been found by the Michigan variability program which exhibit large amplitude rotations in polarization position angle with time. The most straightforward explanation for the phenomenon is a physical rotation in the radio emitting region.
Colors of Radio Galaxies at High Redshifts
Authors: Windhorst Rogier A. , Kron Richard G. , Koo David , Katgert Peter
Published: July 2016

In this paper we present the first results of the Westerbork-Berkeley Deep Survey, the purpose of which is to derive the epoch dependence of the radio luminosity function (RLF) and the optical spectral energy distribution (SED) of elliptical radio galaxies. From calibrated photographic photometry we conclude that no spectral evolution is seen for z ≲ 0.4, but that colors of radio galaxies are bluer for 0.4 ≲ z ≲ 0.9 than predicted from classical model spectra for ellipticals (with star formation only during the first 109 yrs after formation). First-ranked cluster radio galaxies may be slightly bluer than the average radio galaxy for z ≳ 0.6. The epoch dependence of the 1.4 GHz RLF is determined in a direct way. We find almost no population evolution for z ≲ 0.3, but strong evolution for 0.3 ≲ z ≲ 0.9 for all radio powers above the break in the RLF, with enhancement factors of ∼ 100 at z ∼ 0.8.
Modelling the Gravitational Lens of the Double Quasar
Authors: Moore P. K. , Harding S. M.
Published: July 2016

The discovery of the double quasar (Walsh ET AL. 1979) provides an opportunity to study the mass distribution of elliptical galaxies and clusters of galaxies. This has been done initially by Young ET AL. (1981) who produced a model to account for the image positions and intensities. Since then VLBI observations have been made of 0957+561A and B (Porcas ET AL. 1981) which show very similar core and jet structures in the nuclei of both images. In addition to providing further evidence in favour of the gravitational lens hypothesis, these new observations provide additional constraints on the mass distribution of the lensing galaxy and cluster. We have attempted to produce a model in the light of these new results.
Wolf-Rayet Phenomena
Authors: Conti P. S.
Published: July 2016

I have been asked to review in broad terms the concept of Wolf-Rayet (W-R) phenomena, that is, to outline what we currently know about the properties of stars showing such phenomena and to indicate the directions in which future work is leading. I thought I would begin by listing the characteristics of W-R spectra to which probably all the participants at this Symposium will be able to agree. These can readily be adapted from Thomas (1968) who discussed them at the Boulder W-R Symposium. The characteristics of W-R spectra are as follows:

(1)

They are primarily an emission line spectrum superimposed on a “hot” continuous spectrum.

(2)

P Cygni absorption components are observed for some lines in some stars; a fact not realized in 1968 was that a very few W-R stars have intrinsic absorption lines (e.g. The Balmer series in HD 92740 — Niemela (1973).

(3)

The emission lines represent a wide range of excitation and ionization. This level is often higher than indicated by simple modeling of the continuous spectrum.

(4)

The emission lines are broad, corresponding to widths of hundreds to thousands of kilometers per second; widths often differ among various ions in the same star.

(5)

The W-R stars can be divided into two subtypes: These are the WN types, in which the ions of nitrogen dominate, and the WC types, in which the ions of carbon (and oxygen) dominate. Both sub-types have strong lines of helium; in a few cases, hydrogen lines, in emission, are also observed (Underbill 1968).
Hot Mantles, Moderate Photospheres for Wolf-Rayet Stars
Authors: Underhill Anne B.
Published: July 2016

The amount of continuous energy from Wolf-Rayet stars and the shape of the continuous spectrum from the ultraviolet to the near infrared correspond to effective temperatures in the range 25000 to 30000 K. The value of log g is of the order of 4.0±0.5. Thus the photospheres of Wolf-Rayet stars correspond to those of moderately hot stars. The line spectra of Wolf-Rayet stars, however, indicate that electron temperatures greater than 30000 K occur in the outer atmospheres or mantles of these stars. Here outflow is important.
The Infrared Recombination-Line Spectra of Wolf-Rayet Stars
Authors: Hummer D. G. , Barlow M. J. , Storey P. J.
Published: July 2016

Effective recombination coefficients have recently been calculated for recombination lines of He I, He II and C IV (among other ions with up to three electrons) for densities and temperatures appropriate for Wolf-Rayet atmospheres. These have been applied to recently obtained infrared spectra of γ Vel in order to derive the He+/He+2 and C+4/He+ + He+2 ratios.
The Chemical Composition of the Wolf-Rayet Stars
Authors: Willis Allan J.
Published: July 2016

This review summarises current knowledge of the chemical composition of PopI WR stars, concentrating on work carried out in this area since the last IAU, No. 49, symposium devoted to this stellar class (Bappu & Sahade 1973). Earlier reviews of this topic are found in Gebbie & Thomas (1968). The dichotomy of the WR stars into the WN and WC sequences (Beals 1934) has generally been qualitatively interpreted as arising because of gross differences in the C and N abundances: WN stars which exhibit emission lines of predominantly He and N ions with little evidence for C, being inferred as C-poor objects, whilst WC stars, showing predominantly He and C lines and virtually no evidence for N being inferred as N-poor. In both sequences the visible spectra show little or no evidence for hydrogen. However, although the WR stars have been acknowledged as a class for over a century now, progress has been very slow in putting quantitative determinations of their physical and chemical properties on a firm basis, with the bulk of work in this area being conducted during the past decade. The chemical nature of the WR stars has always been a matter of considerable uncertainty, controversy and, quite often, passionate disagreement, arising from uncertainties in the interpretation of the, often ambiguous, observational material available, as well as from disagreements as to the reliability of the use of comparatively simple analytical models employed to date. Recent results strongly suggest that the WR stars are chemically evolved objects, with low H/He ratios and quite different C/N ratios in the WN and WC sequences, with some measure of agreement in these results with the chemistries predicted to arise at various stages of evolutionary theory for hot massive stars which, by one means or another, have shed much of their atmospheric material during their evolution. My purpose in this review is to summarise the investigations and results that lead to the above conclusions. §2 deals with an assessment of the atmospheric H/He ratio in both WN and WC stars: a parameter of fundamental importance in addressing their evolutionary status, as well as providing a base species with which to compare other derived chemical abundances. §3 briefly deals with the models generally employed and gives recent results for He, C and N abundances derived from both visible and UV line analyses. §4 summarises recent results from stellar evolutionary theory and in §5 compares these with those derived from observation, assessing the significance of these new results and their implications for the evolutionary status of the WR stars. Some areas for further advancement are identified.
Radio Emission from WR Stars
Authors: Hogg David E.
Published: July 2016

In principle radio observations of WR stars offer the best possibility of determining the rate of mass loss, since for a simple model of the extended atmosphere the mass loss rate depends primarily on quantities—the flux density, the velocity, and the distance—which are observable (Barlow 1979). Until now, detections of Wolf-Rayet stars have been limited by the sensitivity and resolution of available telescopes. The advent of the Very Large Array makes a search for emission from a large number of these stars feasible.
Wolf-Rayet Stars with Compact Companions
Authors: Moffat Anthony F.J.
Published: July 2016

Evidence is accumulating in favour of a heretofore missing link in the evolution of massive binary stars — a second WR phase in which the companion to the WR star is a neutron star of mass 1–2 M⊙, or in some cases a more massive black hole. The discovery of such objects is also important in assessing the role of duplicity in the formation of WR stars.
A Spectral Study of HD 50896
Authors: Niemelä V.S. , Méndez R.H.
Published: July 2016

ED 50896 (=EZ CMa) has long been known as a variable star. Recently, Firmani et al. (1980) derived a period of 3.763 days from spectral and photometric variations. This period was later confirmed by McLean (1980) and by Cherepashchuk (1981).
The Evolution of Massive Stars: The Production of “Single” WR Stars
Authors: Chiosi C.
Published: July 2016

In this paper we summarize the basic observational properties of WR stars, and the current status of the evolution of massive stars, giving particular emphasis to those physical mechanisms (mass loss, overshooting, turbulent diffusion…) that may lead O type stars to the WR stage. We consider only those scenarios for WR formation and evolution that have been developed during the last few years and that appear to be sufficiently substanciated by observational and theoretical arguments. Finally, the theoretical results are compared with the observations, pointing out several still unsettled aspects of the problem.
Properties of the Scenario for the Formation of WR Stars as Post-Red Supergiants
Authors: Maeder André
Published: July 2016

Grids of evolutionary models for single stars in the range 9–120 M⊙ have been computed up to the end of the central C-burning phase with up-to-date stellar physics. In addition to other results these models allow us to study the main properties of the formation of WR stars as post-red supergiants (Maeder, 1981c). Three grids of models have been computed: one for constant mass evolution (grid A) and the other two (B and C) with mass loss. As there exists no unique parametrization representing, over the various spectral types, the mass loss rates as a function of basic stellar parameters, we have used mass loss rates fitted on the observations, applying different laws for a) OB stars, b) B-G supergiants, c) red supergiants (RSG) and d) WR stars. At a given luminosity, the rates in grid C are twice as large as in grid B and both grids encompass the central bulk of the observed mass loss rates.
The WO Wolf-Rayet Stars
Authors: Barlow M. J. , Hummer D.G.
Published: July 2016

Sanduleak (1971) has listed five stars, not apparently associated with planetary nebulae, which show very strong 0 VI 3811,34 å emission. He pointed out that two of them are in the Magellanic Clouds and have absolute magnitudes comparable to those of classical (Population I) Wolf-Rayet stars. 0 VI emission is know to occur in some classical Wolf-Rayet stars, but not with the extreme strength shown by the Sanduleak stars. We have obtained absolute optical spectrophotometry (3100–7400å) of all five of these stars, using the UCL Image Photon Counting System and RGO Spectrograph on the Anglo-Australian Telescope. Figure 1 shows their relative flux distributions. Inspection shows that Sand 1 is very lightly reddened, Sand 2 and 3 have intermediate reddening, and Sand 4 and 5 are heavily reddened. IUE ultraviolet spectrophotometry has been obtained of the first three stars; Sand 4 and 5 are too heavily reddened for IUE spectra to be feasible.
Near Infrared Observations of Magellanic WN Stars
Authors: Andrillat Y. , Dennefeld M. , Vreux J.M.
Published: July 2016

November 27, 1980, we had the opportunity to make near infrared observations of a few WR stars of the Magellanic Clouds with the ESO reticon system attached to the Boller and Chivens spectrograph at the 3.6 m telescope. The observing conditions as well as the reduction procedure have been described in another paper of this symposium (Vreux et al., 1982). We will immediately show how the near infra-red can be useful to improve our knowledge of some WR stars.
NGC 604 — A Giant H II Region Dominated by Many WR Stars
Authors: Rosa M. , D'Odorico S.
Published: July 2016

NGC 604, the largest H II region in M 33, is comparable in many respects (eg. ionized mass, total extent of a few hundered pc) with the giant H II complex 30 Doradus of the LMC. Recently D'Odorico and Rosa (1981) discovered broad WR emission features at 4640 å, 4660 å, He II 4686 å and 5812 å in a number of the bright knots in the core of NGC 604. In that paper it was concluded, that about 50 WR stars, mainly of the transition type WN 7 but WC characteristica seen as well, are present in the H II region. These findings were confirmed by the observations by Conti and Massey (1981).