bluuebunny/crossref_metadata_2025 huggingface dataset:
The Magnetic Fields and the Polarization of Radio Emission in the Active Center of October 1968
Authors: Erushev N. , Severny A. B. , Tsap T.
Published: July 2016

During the period of strong flare activity of the active center McMath No. 9740, from October 25 to November 2, 1968, 32 magnetograph records of longitudinal H∥ and 20 of transverse fields, H⊥, were obtained for this center with the Crimean magnetograph. Sometimes 5–7 daily records were made. Hα and K spectroheliograms, Hα cine film and routine determinations of sunspot magnetic fields were also obtained frequently. However the most important point is that all these optical observations were accompanied by simultaneous and continuous measurements of intensity and polarization of radio emission from this active center at a wavelength of 3 cm, recorded with the aid of the big 22-m radiotelescope of the Crimean Observatory (the resolution is 8′ for this wavelength), (Erushev and Zvetkov, 1970).
The Relation Between Dashes and Flares (Physical Nature of the Dash Phenomena)
Authors: Kuznetsov D. A. , Shpitalnaya A. A.
Published: July 2016

The phenomenon of dashes in the eruptive loop prominences is found to represent the part of the solar flare process which includes all the levels of the Sun's atmosphere. For 75% of observations a coincidence of dashes and flares in space and time was discovered. The rest of the dash observations may be interpreted as the excitation of dashes by the flares arising outside the limb.

Following the solar flare theory of Alfvén and Carlquist, the possibility to interpret the dashes as the eruptive instability of the pinch-effect is discussed. The computation of flare-current magnetic field gives the value H ∼ 3·104 oersted, its order being in agreement with the observed value.
Sunspot Magnetic Fields and Umbral Dots
Authors: Wilson P. R.
Published: July 2016

The fine structure features of the umbral magnetic fields (i.e. large field gradients and changes of polarity in local regions) are considered as evidence of strong non-linear interactions between magnetic and thermal or mechanical forces in the umbra. It is suggested that the umbral dots observed in white light are the optical manifestation of these interactions. A three-dimensional radiative transfer analysis of possible models for these bright features is discussed and this enables one to place limits on the geometry of these features and on the non-radiative energy requirements of the models. Of the several models considered those which were compatible with convection as the source of this energy were found to be quite inconsistent with the available data. The most likely model was found to have a diameter of 200 km, a height of 50 km and an average emission of non-radiative energy of 4 × 103 erg s−1/cm−3 throughout this region. It is shown that this is two orders of magnitude greater than the energy available from Joule heating by locally twisted magnetic fields. However, if the energy flux transported through the umbra by Alfvén waves is partially dissipated in regions of locally twisted fields it is shown that the emission into a volume of the above dimensions is of the right order of magnitude.
Distribution of the Magnetic Force in the Surface Layers of Sunspots
Authors: Jakimiec J.
Published: July 2016

At the beginning the problem of constructing the three-dimensional magnetohydrostatic models of the photospheric layers in sunspots is discussed in some detail. It is pointed out that the construction of such models by solving the set of equations of magnetohydrostatics cannot be effectively carried out.

In order to solve the difficulties a suitable method of determining the distribution of the magnetic force in sunspots from measurements of the magnetic field has been worked out. Tentative results of the computations are presented.

General features of the distribution of the magnetic force in the photospheric layers of stable sunspots are discussed. It is pointed out that significant magnetic forces are necessary in the penumbra; they secure its transversal equilibrium, but are rather unimportant for its vertical structure. And it is quite probable that the magnetic field in the umbras of stable spots is nearly potential or force-free down to the photospheric level.
Optical and Radio Observations of Large Scale Magnetic Fields on the Sun
Authors: Daigne G. , Lantos-Jarry M. F. , Pick M.
Published: July 2016

It is possible to deduce information concerning large scale coronal magnetic field patterns from the knowledge of the location of radioburst sources.

As the method concerns active centers responsible for corpuscular emission, the knowledge of these structures may have important implications in the understanding of corpuscular propagation in the corona and in the interplanetary medium.
Preliminary Results of Spectroscopic Determination of the Coronal Rotation
Authors: Stepanov V. E. , Tjagun N. F.
Published: July 2016

Coronal rotation is determined by means of the spectroscopic method. The mean value of the rotation rate vs. the heliographic latitude is found. At high latitudes the corona rotates much faster than the underlying photosphere. This fact confirms Waldmeier's and Billing's hypothesis that the high-latitude phenomena should depend on the magnetic fields of low latitudes and that the interchange of the matter between the active zone and polar coronal region along the field lines should take place.
Theories of Large Scale Fields and the Magnetic Activity Cycle
Authors: Weiss N. O.
Published: July 2016

The magnetic field is effectively frozen into the ionized gas in the Sun and it is therefore necessary first to describe the motion in the convective zone. Large scale motion in giant cells is strongly affected by Coriolis forces, giving a radial shear in the angular velocity, while the interaction of convection and rotation leads to the equatorial acceleration. Many hydromagnetic dynamo mechanisms have been proposed in the last few years. In particular, meridional fields can be generated from azimuthal fields owing to a preferred sense of helicity in the motionSuch regeneration is included in Leighton's phenomenological model, which reproduces many features of the solar cycle. More detailed models will have to treat the concentration of magnetic flux into ropes by individual convection cells.
The Redshifts of Extragalactic Objects
Authors: Sargent Wallace L. W.
Published: July 2016

We review the evidence for a general shift-distance law for galaxies. This is shown directly by a redshift-distance diagram recently prepared by Sandage and Tammann for Sc I galaxies. The distances are measured from H II region diameters and from the diameters of the Sc 1 galaxies themselves for the more distant systems. We also show the redshift-apparent magnitude diagrams for several objects which are identifiable over a large range in distance and which prove to have a small range in absolute magnitude: these are supernovae of type I (Kowal and Sargent, 1973, unpublished), brightest cluster galaxies (Sandage, 1972a), and radio galaxies (excluding N-type galaxies) (Sandage, 1972b). Plots of redshift versus angular size for brightest cluster galaxies (Sandage, 1972c) also have the correct slope for this to be a distance effect. In summary, the tightness of the correlations for the various diagrams listed implies that there is a very close correlation between distance and redshift for galaxies out to at least z = Δλ/λ~0.2 and that there is no evidence for redshift anomalies among the objects in these diagrams.
Observational Evidence for Non-Velocity Redshift in Stephan's Quintet
Authors: Balkowski C. , Bottinelli L. , Chamaraux P. , Gouguenheim L. , Heidmann J.
Published: July 2016

Distance determinations of the high-redshift galaxy NGC 7319 in Stephan's Quintet, based on 21-cm line observations, yield a value much smaller than the cosmological distance. At the 98.7 % level, a part of the redshift of this galaxy which could amount to 5000 km s−1 is anomalous.
Optical Observations of Nuclei of Galaxies
Authors: Ulrich Marie-Helene
Published: July 2016

Several problems concerning the nuclei of galaxies are particularly interesting at present, either because new data have become available from advances in observational techniques, or else because recent observations suggest that earlier conclusions should be revised. These problems are discussed in this article.

Spectrophotometry in the near infrared shows that the late-type stars in the nucleus of M31 are mostly late giants; the M/L ratio in the nucleus is approximately 15, a value in agreement with that calculated independently from the velocity dispersion of the stars.

Infrared emission at 10µ has now been detected in 50 galaxies; the Seyfert-type galaxies are the brightest at 10 µ and there is evidence of variations of the 10 µ flux in NGC 4151, which rules out re-radiation by dust as the mechanism of infrared emission. In each of the galaxies NGC 253 and NGC 3034 an infrared source of dimension ~ 200 pc is present in the centre which coincides in position and dimension with the central component of the radio source at 1415 MHz; since both galaxies are rich in dust and in early-type stars it is plausible that, in these cases, re-radiation by dust is the origin of the infrared emission. Most of the other galaxies detected at 10 µ are spirals with intense and narrow emission lines.

Comparison of the optical and radio properties of nuclei of galaxies show that galaxies with compact nuclear radio sources are more likely to have optical spectra with emission lines than are galaxies without central radio sources. This correlation holds for elliptical and spiral galaxies. Its cause is not understood at present.

The relatively accurate profiles now available for the permitted lines of several Seyfert galaxies show that mass motions are the main broadening agent for these lines. Variations of line intensities have been observed in several Seyfert galaxies. The most likely explanation of these variations is that they are due to the variations of the photoionizing flux; in some cases, however, weakening of the permitted lines could be caused by high-velocity mass motions present in the region emitting the broad component of these lines.

From the investigation of the relatively nearby galaxies it is estimated that at least 5 % of galaxies have expansion motions or non-thermal optical fluxes.
Variability of the Emission Line Spectrum of the Nucleus of Seyfert Galaxy NGC 1275
Authors: Pronik I.
Published: July 2016

Recent spectroscopic observations of the nucleus of NGC 1275, together with results from earlier workers, confirm the variability of the emission lines and indicate corresponding variations in the electron temperatures and densities of different zones. These changes may be associated with the microwave outbursts from this source.
Recent Radio Studies of Bright Galaxies
Authors: Oort J. H.
Published: July 2016

Some results are discussed of recent – still largely unpublished – high-resolution studies of bright spirals, both in the radio continuum and in the 21-cm line radiation. Special emphasis is given to observations of M51, M81 and NGC 4258.

The most important new data are (1) Estimates of the contrast in gas density between arms and interarm regions (M81 and M101); the contrast appears to be quite strong. It provides an important parameter for the density wave. (2) Evidence for a pronounced decrease of gas density along the arms when these are followed towards the centre. Considerable line radiation is observed from outer regions where the optical intensity of the arms is very low. (3) Extension of rotation curves to larger distances from the centre. (4) Data on the motions in the spiral waves. (5) Determination of the shift between synchrotron and optical arms, providing direct evidence for the formation of stars as a consequence of the passage of the interstellar gas through the spiral density wave. From the shift measured in M51 the formation time is found to be roughly ten million years. If the data for (2) are ascribed to the depletion of the gas by star formation, the average net fraction of the gas consumed in star formation is found to be between 2% and 3% per passage through the spiral wave (Table I). (6) Separation of nuclear and disk synchrotron radiation in spirals. (7) Evidence for a recent expulsion of about 108 solar masses from the nuclear region of NGC 4258.
The Spectrum of Mars in the Region 1800–3200 cm−1
Authors: Beer Reinhard
Published: July 2016

During the 1971 opposition of Mars, new infrared spectra covering the region 1800–3200 cm−1 (3.1–5.6μ) were taken at a resolution of 0.095 cm−1 using a Connes'-type Fourier spectrometer on the 2.7 m telescope, McDonald Observatory. Spectra were obtained near 6° and 33° phase and were calibrated against the Sun, standard stars and an internal black body.

No new trace constituents have, as yet, been found in the spectra, but several previously unobserved combination and isotopic bands of CO2 are visible. It has also been found possible to fit fairly well defined kinetic temperatures and Bond albedos to the two sets of data. The kinetic temperatures have been determined by a new technique. It is found that the albedo at 33° phase, which was determined a few days after the onset of the great dust storm of 1971, was significantly higher than for the clear atmosphere. The explanation for this phenomenon must await detailed radiative transfer calculations for a dust-laden atmosphere.
The Hydrogen to Helium Mixing Ratio in the Giant Planets
Authors: Gautier Daniel
Published: July 2016

The theoretical bases for deducing the solar abundance of helium from the determination of the H2/He mixing ratio in the giant planets are examined. The present state of the determination of the helium abundance is given. Experimental methods used to evaluate the H2/He ratio in the giant planets are critically reviewed. Methods in prospect are also briefly exposed.
Observations of Spatial and Temporal Variations of the Jovian H2 Quadrupole Lines
Authors: Carleton N. P. , Traub W. A.
Published: July 2016

We have made high resolution scans of the Jovian H2 4–0 S(1) line at 6367.75 Å and the 3–0 S(1) line at 8150.67 Å, in an attempt to establish improved equivalent widths and to measure any spatial-temporal variations across the disc. Preliminary analysis indicates that temporal changes in the 3–0 S(1) line can be as large as about 40% over a period of about a week; furthermore, this line is systematically weaker at the limb (about 10%) and stronger at the poles (about 20%) than it is at the center of the disc. The 4–0 S(1) line shows very little temporal change, but does have a similar center to limb variation. Current theoretical models of line formation and cloud structure on Jupiter are not able to explain the observed variations although it is clear that some sort of two-layer model is necessary.
On the Microwave Spectrum of Methane in the Atmospheres of the Outer Planets
Authors: Fox Kenneth
Published: July 2016

The existence of a small dipole moment in the vibronic ground state of methane leads to transitions in the microwave spectral range. Frequencies and line strengths appropriate to the atmospheres of the outer planets are presented.
Analysis of Spectroscopic Observations of Jupiter and the Variability of the Structure of the Visible Clouds
Authors: Hunt G. E. , Bergstralh J. T.
Published: July 2016

Realistic inhomogeneous models of Jupiter's lower atmosphere are used to interpret recent observations of the (3–0) and (4–0) H2 quadrupole lines at different portions of the visible disc of the planet. The time variations of these observations are analysed in terms of changes in the cloud structure.
Motions in Jupiter's Atmosphere
Authors: Hide R.
Published: July 2016

Recent contributions to the dynamics of Jupiter's atmospheres were reviewed under the following headings: (a) general magnitude of winds and temperature fluctuations; (b) cloud bands and zonal velocity profile (including equatorial jet); (c) transient non-axisymmetric features (spots, and irregular markings); (d) the Great Red Spot.
A Study of the Outermost Ring of Saturn
Authors: Bobrov M. S.
Published: July 2016

The attention is called to the fact that the discovery by Feibelman (1967) of the rarefied outer ring of Saturn is confirmed by the observations of Kuiper (1972). It is proposed to designate this object as E-ring (exterior) in order to avoid confusion with the innermost, also rarefied, D-ring observed by Guérin (1970) and earlier by Barabashov and Semejkin (1933). The effects of the interaction of E-ring with inner Saturn's satellites are briefly discussed. The conclusion is drawn that in cosmogonic time scale these effects are small. It is also shown that the optical thickness of E-ring is lower than 1/20000; the available photometric estimations of the geometric thickness of A- and B-rings need not be corrected for the light scattering and absorption by E-ring.
The Saturnian ‘Gas-Doughnut’ Hypothesis
Authors: McDonough Thomas R. , Brice Neil
Published: July 2016

It is hypothesized that constituents escaping the atmosphere of Titan are unlikely to have sufficient velocity to escape from Saturn. Thus most of the material will enter into elliptical orbits which, at some point, cross Titan's orbit at a small angle. In total, this matter will form a ‘doughnut’ shaped feature, roughly centered on Titan's orbit and having dimensions of about 20 Rs (Saturn radii) in the Saturnian-equatorial plane and 10 Rs normal to this plane. It is assumed that the material is lost from the doughnut when it is ionized or is recaptured by Titan's atmosphere. The upper limit on the density of hydrogen in the ring is estimated to be about 103 cm−3, with up to 99% of the particles in the doughnut being recaptured by Titan.

A brief summary of the work which has been done on this problem is given, and areas needing further research are suggested.
Neptune: Observations of the H2 Quadrupole Lines in the (4–0) Band
Authors: Trafton L.
Published: July 2016

The first measurement of Neptune's quadrupole H2 lines is reported. The equivalent widths of the S(0) and S(1) lines of the (4–0) band are given along with the corresponding widths measured from comparison spectra of Uranus taken on the same nights. These are interpreted in terms of both an inhomogeneous atmosphere overlying a reflecting layer and a homogeneous, semi-infinite, scattering atmosphere. Only the scattering model proves to be consistent with Neptune's spectrum in this wavelength region. The H2 abundance along the scattering mean free path is found to be less than the value for Rayleigh scattering in pure H2. This result is interpreted in terms of the presence of H2, CH4 and at least one other gas, instead of the more conventional interpretation in terms of the presence of an aerosol mixed with H2. Weak features in the continuum were observed. Their widths and the strength of the H2 features indicate that H2 is more abundant than the sum of the remaining gases in these atmospheres.
Relation Between Light Variations of Solar System Satellites and Their Interaction with Interplanetary Medium
Authors: Blanco C. , Catalano S.
Published: July 2016

The behaviour of the available light curves of Jupiter and Saturn satellites is shown to change steadily from inner to outer satellites.

The change in reflectivity of satellites with orbital motion could be explained assuming that dark meteoroidal material accumulates on a given portion of the satellite's surface, which was once mainly covered with ice or snow. The preferential impact location on the satellite's surface could be a consequence of the perturbing action of the planet on the motion of interplanetary material.
Spectroscopic Observation of Venus
Authors: Monfils A. , Gérard J. C.
Published: July 2016

The interest of a spectroscopic investigation of the upper atmosphere of Venus in the ultraviolet is briefly shown. The conditions for the observations to be made are defined and the main properties of the necessary instrument are deduced and described. The proposed package is a quadruple miniature spectrometer covering the entire spectral range extending from 1200 Å to 8000 Å with a resolving power of 500.
On the role of diffuse emission nebulae in galaxies
Authors: Shajn G. A.
Published: July 2016

The emission nebulae, as more or less compact gaseous or gas-and-dust formations, belong to a rather widespread type of population in our Galaxy. Though, for well-known reasons, we are able to penetrate into the depth of the Galaxy no further than 2–3 kpc for H 11 regions, several hundred nebulae have already been recorded (predominantly in the spiral arms). Sometimes the emission nebulae almost entirely occupy large regions of the sky, as, for instance, in the region of ρ, γ and o1 Cygni. In addition, in the area within latitudes ± 5°, we observe a nearly continuous faint emission background.
Variable stars and problems of general structure of galaxies
Authors: Kukarkin B. V.
Published: July 2016

The general structure of the galaxies is extremely diverse and can be described by Hubble's classification only in the first approximation. In fact, the differences in the distribution of gas and dust in some galaxies which have been established recently, the evident dissimilarity of the intensity of the radio emission in individual galaxies, as well as other facts, suggest definite differences even among galaxies belonging to the same type according to Hubble. Hubble's classification gives a sufficiently exhaustive description of the diversity of the optical forms of galaxies and unites them in a single sequence, which, in the case of spirals, branches into two parallel sequences (ordinary and barred spirals). The interpretation of Hubble's sequence as an evolutionary one became rather popular. In this case usually either the Eo form is considered as the initial stage (Jeans, Hubble) or, conversely, the irregular galaxies and late spirals are considered as the initial stage with the elliptical galaxies being the late stage of evolution (Shapley and many others).
The Galactic Electron Distribution from a Pulsar Survey
Authors: Lyne A. G.
Published: July 2016

The recent high-sensitivity pulsar survey at Jodrell Bank has allowed a statistical study of more distant objects. The longitude distribution suggests that many of the pulsars observed have distances greater than 5 kpc, leading to an upper limit of about 0.03 cm-3 for the mean electron density. The electron density averaged over distances of a few hundred parsecs seems to be very constant. The width of the electron distribution in the z-direction appears to be greater than about 600 pc.
Expanding Shells of Neutral Hydrogen as Birthplaces of Stellar Associations
Authors: Sancisi R.
Published: July 2016

Expanding shells of neutral hydrogen have been found connected with the associations Per OB2 and Sco OB2. The shells also contain dust and molecules. A model of the spatial configuration and the kinematics of gas, dust and stars is discussed. The stars of the associations lie outside, close to the shells; gas and stars move outward from a common centre of expansion. If the shells are interpreted as old supernova remnants which have been strongly decelerated by the interstellar medium, ages of the order of 1 × 106 yr are obtained. A genetic relationship between stars and shells is suggested. The stars formed in the densest gas shell; afterwards they separated from the gas, as the shell was further slowed down by intervening interstellar matter. Limits are set on the time scale of star formation. The geometry and the motion of the shell at the moment of star formation account also for the kinematics of Per OB2 and Sco OB2.
Distribution of Dust in the Orion Nebula
Authors: Smith Lindsey F.
Published: July 2016

The distribution of the dust is found by comparing 3-cm brightness temperatures, Hα surface brightness, and Hβ surface brightness. The dust is probably mixed with the gas. The Balmer radiation originates in front of the dark bay.
Maser Sources in H ii Regions
Authors: Burke B. F.
Published: July 2016

When OH and H2O sources are found in Hii regions, a compact source of radio continuum and infrared emission is usually, perhaps always, found nearby, < 1017 cm away (approximately the conjectured size of a prestellar condensation). Whether the masers are self-excited, are amplifying the background radiation, or are themselves associated with an exciting star is clearly model-dependent, and observations have not yet given the answer. H2O masers occur less frequently than OH masers. When they occur together they appear as a cluster of compact sources of line radiation, exhibiting the same range of radial velocities, The OH sources nearly always are strongly polarized, while the H2O maser is not. Both classes of maser are probably saturated, and some care is needed in inferring the maser geometry from the observations. The period of stability of neither OH nor H2O can be much more than 103 yr, and this fact can be used as an estimator of stellar formation rate.
Supernova Remnants: Can a Fossil Hii Region be Formed as the Result of a Supernova Explosion?
Authors: Kahn F. D.
Published: July 2016

An estimate of the amount of ionizing radiation available in a supernova explosion falls far short of the amount needed in the standard model of the Gum nebula. The only possibility left is radiation from the pulsar.
21-Cm Line Absorption Study of Extended Supernova Remnants
Authors: Sato Fumio
Published: July 2016

By using the Maryland-Green Bank Galactic 21-cm Line Survey, a series of equal-velocity contour diagrams has been constructed for the regions of the extended sources W51 and W44. The non-thermal component of W51 has no absorption features above 53 km s-1, but its thermal components have clear absorption features up to much higher velocities. From this fact, the association of the thermal and nonthermal components of W51 is rejected. Absorption features toward W44 cannot be seen above 50 km s-1. Kinematic distances to the nonthermal component of W51 and to W44 are 4.4 kpc and 3.5 kpc, respectively. From peculiar brightness distributions in the equal-velocity contour diagrams I conclude that a dense Hicloud, as well as clouds of OH and H2CO, is associated with W44.
The Birthplaces of Pulsars
Authors: Lyne A. G.
Published: July 2016

With the refinement of the estimates of electron density in the Galaxy it is clear that pulsars have z distances away from the galactic plane of a few hundred parsec. There is now a very strong indication that young pulsars lie at small z distances, suggesting that pulsars originate in a small z population and are given velocities of about 100 km s-1 at birth.
Radio Continuum Observations of Stellar Sources
Authors: Braes L. L. E.
Published: July 2016

Thirty optically visible stellar sources have been observed in the radio continuum: four red dwarf flare stars, three novae, two red supergiants, eight binary systems, and 13 related peculiar objects. The observations of red dwarfs, novae, and supergiants are briefly reviewed. Their emission seems reasonably well understood. Binary systems such as Algol show erratic flaring; consistent explanations have not yet been given. The related peculiar objects, such as V1016 Cyg and MWC 349, are even less well understood. Some of them may have just arrived on the main sequence; others may be planetary nebulae in an early stage of formation.
Radio Outbursts from Cygnus X-3
Authors: Hughes V. A. , Viner M. R. , Woodsworth A.
Published: July 2016

The variation in flux density obtained at 10522 MHz for Bursts 2, 3, and 4 is compared with that obtained by others at frequencies down to 365 MHz. The bursts appear to have a quasi-periodic modulation with a period of 3–4 h, which is different from the 4.8-h periodicity observed at X-ray and infrared wavelengths. The modulation is attributed to a fluctuation in the size of the expanding cloud of particles produced by either an instability in the atmosphere of Cygnus X-3 or by a built-in instability in the cloud itself.
Measurements on Planetary Nebulae
Authors: Milne D. K. , Aller L. H.
Published: July 2016

165 planetary nebulae south of +27° declination have been observed with the Parkes 64 m telescope. These nebulae were chosen to include most of those for which Hβ flux densities are available. Radio positions and flux densities (generally with probable errors of only a few millijanskies) obtained from the survey must represent the most reliable and homogeneous radio data currently available for the class of object. The data have been used to obtain distances and optical extinctions for these nebulae.
Radio Continuum and Recombination Line Studies of the Galactic Center
Authors: Gordon M. A.
Published: July 2016

This review discusses unsuccessful searches for electromagnetic bursts accompanying gravitational events observed to come from the galactic center, radio observations of continuum emission and recombination lines from the region of the galactic center.
Progress Report on the Maryland-Green Bank Galactic 21-cm Line Survey
Authors: Westerhout Gart
Published: July 2016

The survey has been completely re-observed using the resurfaced NRAO 300-ft telescope. It covers the latitude ranges b = − 1.5° to + 1.6° from l = 11° to 60°, b = − 2.2° to + 2.4° from l=60° to 132°, and b = − 1.9° to + 2.4° from l = 132° to 235°. Both the new survey and the old survey are available on magnetic tape and 70-mm film.
Low- and Intermediate-Velocity Hydrogen at Positive Galactic Latitudes
Authors: Takakubo K.
Published: July 2016

Low- and intermediate-velocity Gaussian components of hydrogen emission profiles observed at positive galactic latitudes are investigated. The low-velocity hole, as called by Wesselius and Fejes (1973), is a phenomenon which appears in the layer composed of the gas emitting narrow Gaussian components but does not in that of wide components. Both Models I and II suggested by Wesselius and Fejes contradict this result. A hypothesis is proposed that a stream motion in the layer emitting wide Gaussian components, which may be identified with the intercloud medium, swept away the interstellar clouds emitting narrow Gaussian components in the region of the hole.
Evolutionary Tracks of Extended Radio Sources
Authors: Baldwin J. E.
Published: July 2016

We know almost nothing about the evolutionary tracks of extragalactic radio sources but those tracks are, however, strongly constrained by the distribution of sources in the radio luminosity, P, overall physical size, D, diagram. This is the radioastronomer's H-R diagram, an analogy which two lines of algebra shows is exact. Fig. 1 is the P-D diagram for the 3CR 166 source sample of Jenkins et al. (1977) with later additions. Most of the sources are identified and have known redshifts. It is a flux density limited sample so that the numbers at any P are weighted relative to the true space density by P3/2 because of the differing volumes of space sampled. The important feature of the diagram is the lack of sources greater than 1 Mpc in size. Because of doubts about the completeness of the sample in this region, we have made searches in the 6C 151MHz survey for sources having surface brightnesses lying between the two lines of slope 2 on the right of Fig.1. The numbers found to a limiting flux density of 1–2 Jy suggest that there is no serious underestimate of the numbers in the 166 source sample.
Aperture Synthesis Observations of Cygnus A at 86.2 Ghz
Authors: Birkinshaw M. , Wright M.C.H.
Published: July 2016

Recent observations of Cygnus A with the Hat Creek interferometer at 86.2 GHz limit the spectral curvature of the hotspots and show that the diffuse lobe emission has a spectral index of about 1.5. The central component is, at most, weakly variable and its spectrum shows a distinct break to a spectral index near 0.65 at about 20 GHz.
What Bends Wide-Angle Tailed Radio Sources?
Authors: Burns Jack O. , Eilek Jean A. , Owen Frazer N.
Published: July 2016

It has been generally assumed that wide-angle tailed (WAT) sources like 3C465 are formed in a manner similar to that of the more strongly bent U-shaped sources such as NGC 1265, i.e., by ram pressure arising from galaxy motion through a dense intracluster medium (ICM). The WAT sources were thought to be less strongly bent because of the smaller ratio of tail plasma flow momentum flux to galaxy velocity. However, as noted recently by Burns (1981), there is a serious discrepancy between the ram pressure model requirements for bending WATs and the dynamics of the associated radio galaxy. To bend the tails, we calculate that the galaxy must typically move at velocities of 0.7–1×103 km s−1 for distances comparable to the length of the radio tails (∼200 kpc for 3C465). This implied galaxy motion is inconsistent with the nature of the massive cD galaxies generally associated with WATs. Cluster galaxy velocity data, X-ray observations, and recent models suggest that these giant galaxies are nearly at rest at the bottoms of cluster potential wells, at most moving ∼200 km s−1 in an oscillatory motion of small amplitude (<0.3 of a core radius, Malumuth, 1981, private communication). Thus it appears that some other mechanism is responsible for bending WAT sources.
Studies of a Complete Sample of Abell Clusters at 1400 MHz
Authors: White Richard A. , Owen Frazer N. , Hanisch Robert J.
Published: July 2016

We present here analyses of a radio survey of Abell clusters at 1400 MHz using the NRA0 91-m telescope. Details will appear in a paper to be submitted to the Astronomical Journal where we present two lists. The first contains sources within 0.5 of an Abell radius (hereafter Ra, 3 Mpc if H=50) of the center of an Abell cluster. The second contains those clusters for which there were no sources within that limit. The flux limit is 100 mJy, the beam size ∼10 1/2 arcmin, and the declination limit −19°30′. For consistency we use Corwin's (1974) m10 − z calibration throughout. The errors in m10 and therefore z and Ra, combined with a beam large compared to galaxy and cluster size (preventing identifications) preclude all but the simplest analyses which we present here.
Stephan's Quintet Revisited
Authors: van der Hulst J. M. , Rots A. H.
Published: July 2016

VLA observations at 1465 MHz of the Stephan's Quintet region reveal that the arc-shaped area of emission discussed by Allen and Hartsuiker (1972) breaks up into several components. The idea that NGC 7318b is a recent interloper in the group and that the interaction resulting from this event causes the enhanced activity at the east side of NGC 7318b is adopted as still the most reasonable explanation. The results are discussed in more detail in another paper (van der Hulst and Rots, 1981).
Emission Regions in Centaurus A
Authors: Price R. M. , Graham J. A.
Published: July 2016

Centaurus A, at an estimated distance of five megaparsecs, is the closest radio galaxy. It presents the best opportunity to examine in detail the physical mechanisms and resulting structures that are to be found in radio galaxies. Centaurus was first studied in detail at radio wavelengths by Cooper, Price and Cole (1965), hence CPC. Many of the comments, interpretations, and conclusions recorded in that paper remain valid today and provide the broader framework in which the more detailed studies using today's more powerful instrumentation can be understood. Historically, it is also interesting to note that Centaurus A was the first extragalactic radio source in which linear polarization and Faraday rotation were discovered and extensively studied.
X-Ray Emission from Centaurus A
Authors: Terrell James
Published: July 2016

Observations of 3–12 keV X-ray emission from NGC 5128 (Cen A) were made by Vela spacecraft over the period 1969–1979. These data are in good agreement with previously reported data, but are much more complete. Numerous peaks of X-ray intensity occurred during the period 1973–1975, characterized by rapid increases and equally rapid decreases (in less than 10 days). Thus it seems probable that most of the X-ray flux from the nucleus of Cen A came from a single source of small size.
4C 18.68: A QSO with Precessing Radio Jets?
Authors: Gower Ann C. , Hutchings J. B.
Published: July 2016

The radio source 4C 18.68, identified with the 16.5 m QSO 2305+187 (z = 0.313), was observed at 20 cm and 6 cm with the VLA in its highest-resolution configuration (A) on April 25, 1981, as part of a programme to map the radio structure of quasars for which optical structure has been mapped using the Canada-France-Hawaii telescope. The radio structure is remarkable, showing complex, curved structure at 6 cm resolution embedded in a halo ∼ 60 kpc across (HO = 100 km/sec/Mpc, qO = 0) seen most clearly in the 20 cm map. The polarisation is low (∼ 8% maximum at 6 cm) and follows the curved structure quite closely, showing the magnetic field direction to be along the curved structure. The central source has a flat spectrum, while the spectrum of the structure generally steepens with distance from the centre.
NGC 4258: A Bent Jet in a Spiral Galaxy
Authors: Sanders R. H.
Published: July 2016

The remarkable continuum arms in the spiral galaxy NGC 4258 are suggestive of some form of ejection from the nucleus of this galaxy (Van der Kruit, Oort and Mathewson, 1972). To summarize the observations (see Oort, Figure 2, this volume), the “anomalous spiral arms” are clearly distinct from the normal spiral arms, although wound in the same sense; there is a sharp gradient of the continuum emission on the leading edge of the arms, and an indication that the arms split on the western side; the arms go directly into the nucleus and coincide with Hα emitting filaments (Courtes, Viton and Veron, 1965).
The Arcsecond Morphology of Compact Radio Sources
Authors: Perley R. A.
Published: July 2016

As part of the VLA calibration program, 404 small angular size sources have been observed in the “A” array at both 6 and 20 cm with resulting resolutions of 0.4′ and 1.2′ respectively. Use of self-calibration techniques has allowed a search for associated extended structure to a level of ∼0.3% of the peak. Here we report preliminary analysis of the results.
Radiative Acceleration of Astrophysical Jets: Line-Locking in SS 433
Authors: Shapiro Paul R. , Milgrom Mordecai , Rees Martin J.
Published: July 2016

Observations of SS433 are consistent with the view that the Doppler-shifted line emission originates in a pair of oppositely-directed, precessing jets in which a gas outflow is maintained at the remarkably time- and space-invariant speed of 0.26c. A radiative acceleration mechanism is described for the jets and a detailed, numerical, relativistic flow calculation presented which explain this terminal velocity as the result of “line-locking”. The “line-locking” mechanism suggested here for SS433 may be important as well in extra-galactic radio sources in which the radio luminosity is similarly weak compared with the kinetic energy and optical luminosities.
Viscous Dissipation in Jets
Authors: Begelman Mitchell C.
Published: July 2016

The slow decline of surface brightness along many large-scale jets indicates that their internal pressures are determined largely by dissipation. If dissipation arises from a viscous interaction between a jet and its environment, then the observed degree of collimation enables one to constrain the nature of the viscous stress. Simple phenomenological models of the stress account for the frequently observed “gaps” and provide a means of slowing down jets without their becoming decollimated.
The Nature of the Energy Source in Radio Galaxies and Active Galactic Nuclei
Authors: Pacini F. , Salvati M.
Published: July 2016

For more than 20 years it has been known that extragalactic radio sources contain up to 1060–1062 ergs in the form of relativistic electrons and magnetic fields. One arrives at these figures if one assumes that the radio emission is due to the synchrotron process and the source contains an equal amount of energy in electrons and fields (Burbidge 1956). Any deviation from the postulated equipartition increases the energy required to account for the observed luminosities. Some authors believe that the real demands on the energy source may be still higher because of the probable presence of high energy protons. The ratio Ep/Ee is determined by the way in which particles gain and lose energy, and it is impossible to estimate it a priori. Observationally one has two conflicting lines of evidence: (a) in galactic cosmic rays one measures (Ep/Ee) ≃ 102; (b) in the Crab Nebula one infers (Ep/Ee) ≲ 1 (otherwise the dynamical pressure of the proton gas would cause a nebular expansion much faster than observed).
The Milliarcsecond Structure of Radio Galaxies and Quasars
Authors: Readhead A.C.S. , Pearson T. J.
Published: July 2016

Hybrid maps of the nuclei of radio galaxies and quasars show a variety of morphologies. Among compact sources, two structures are common: an asymmetric, “core-jet” morphology (eg, 3C 273), and an “equal double” morphology with two separated, similar components (eg, CTD 93). The nuclei of extended, double radio galaxies generally have a core-jet morphology with the jet directed toward one of the outer components.
A Millimetre/Submillimetre Study of Optically Selected Quasars
Authors: Sherwood W. A. , Schultz G. V. , Kreysa E. , Gemünd H.-P.
Published: July 2016

During the past decade many kinds of optical surveys have discovered hundreds of quasars most of which (∼90 %) are radio quiet (<10 mJy at 5 GHz). We have observed two samples of quasars brighter than 17m.6 found by their emission lines and by their ultraviolet excess. We have also selected quasars with redshifts known to be greater than 3.00. A brief description of the observing technique is given by Sherwood et al. (1981b). We have compared our millimetre photometry of flat radio spectrum quasars with that of Ennis and Werner and find excellent agreement. For four of the 8 sources in common the data have been published: Kreysa et al. (1980) and Jones et al. (1981). In addition, analysis of our “noise” shows it to be white, gaussian distributed about zero. The three samples are summarized as follows.
Broadband Studies of Compact Sources
Authors: Jones T. W. , Rudnick L.
Published: July 2016

Progress is reported on a program to study the polarization, spectral and variability properties of compact sources at centimeter and millimeter wavelengths. Source characteristics divide according to the broadband shapes of their spectra.
Superluminal Radio Sources
Authors: Cohen M. H. , Unwin S. C.
Published: July 2016

Several compact radio sources studied with VLBI show apparent transverse velocities much greater than the speed of light. This review is a summary of VLBI observations of these “superluminal” sources as of August 1981. The physical models proposed to explain this phenomenon are also discussed.
Compton Rockets: Radiative Acceleration of a Relativistic Fluid
Authors: O'Dell S. L.
Published: July 2016

Unless a plasma moves at relativistic bulk speeds, the Compton radiative lifetime for relativistic electrons near a luminous object is less than the transit time from the source. Acceleration by adiabatic decompression is too slow to preserve much of the electrons' energy. However, the Compton-rocket thrust and the radiatively induced pressure gradient can accelerate a relativistic fluid to relativistic bulk speeds on a time scale comparable to that for radiative loss. Consequently, severe Compton losses are not only reduced by relativistic bulk motion, but can in fact effect such motion.
Optical Spectra and Radio Properties of Quasars
Authors: Wills Beverley J.
Published: July 2016

Relations between observed optical and radio properties can, in principle, constrain the geometry and physical conditions of the broad-line regions in quasars and active nuclei. Osterbrock and colleagues (see this symposium) and J.E. Steiner (preprint) have noted differences between Hα/Hβ, [0III]/Hβ and optical Fe II emission for Seyfert 1 galaxies, broad-line radio galaxies (BLRG's) and quasars. Stockman et al. (1979) discovered a tendency for optical continuum polarization angles for quasars to be aligned with the direction of the outer radio lobes. Setti and Woltjer (1977) and Miley and Miller (1979) noted that the quasars with strongest Fe II are among the most compact radio sources (e.g. 3C 48, 0736+01, 1510–08), and Miley and Miller also note that the distribution of line widths is narrower for the more compact than for extended radio sources.
Evidence for Relativistic Motion in the Millisecond Structure of BL Lac
Authors: Mutel R. L. , Phillips R. B.
Published: July 2016

After several years of relative quiescence, the flux of BL Lac has increased dramatically at centimeter wavelength, starting about epoch 1979.9 (Fig. 1). We have begun a series of VLBI observations to monitor the milliarcsecond structure at λ6 and λ2.8 cm wavelengths, using a five element VLBI array consisting of telescopes at Bonn, West Germany; Westford, MA; Green Bank, WV; Ft. Davis, TX; and Owens Valley, CA. The first two observations, in 1980 May and September, were at 5 GHz and were not of sufficient resolution to distinguish individual components in the source (Mutel, Phillips and Aller 1981). They did show, however, that the source was highly elongated along position angle ∼ 10° and was expanding that axis with a velocity of ∼4 c. The position angle is the same as several previous VLBI observations of this source, both during quiet periods and during previous flux outbursts (Pearson and Readhead 1981; Shaffer 1978 and references therein).
Mark III VLBI Observations of the Nucleus of M81 at 2.3 and 8.3 GHz
Authors: Bartel N. , Corey B. E. , Shapiro I. I. , Rogers A. E. E. , Whitney A. R. , Graham D. A. , Romney J. D. , Preston R. A.
Published: July 2016

The normal spiral galaxy M81, which has some characteristics of a Seyfert (Peimbert, Torres-Peimbert, 1981), has a flat spectrum in the radio range (de Bruyn et al., 1976), variable on the time scale of days (Crane et al., 1976), and detectable radiation at infrared (Rieke, Lebofsky, 1978) and X-ray wavelengths (Elvis, van Speybroeck, 1981). At a distance of ∼3.3 Mpc, M81 is the nearest extragalactic object with a nucleus detectable with VLBI (Kellermann et al., 1976). We report here on simultaneous VLBI observations made with the Mark III system at 2.3 and 8.3 GHz. Observations on 14 and 16 March 1981 utilized the 100 m diameter telescope in Effelsberg, W. Germany (MPIR); the 43 m telescope at Green Bank, WV (NRAO); and the 40 m telescope near Big Pine, CA (OVRO).
The Angular Size Distribution of Radio Sources at Low Flux Densities
Authors: Downes Ann
Published: July 2016

Observations of complete samples of extragalactic radio sources at low and intermediate flux densities are described. Many types of source are found. The angular sizes form a smooth extrapolation from higher flux densities, and can be predicted from the known properties of samples at high flux density either with linear size evolution (for Ω = 1 or Ω = 0 Universes) or without linear size evolution (for Ω = 0). The question of whether such evolution is required therefore remains open.
A Study of Small Angular Size Ooty Sources
Authors: Menon T. K.
Published: July 2016

Recent theoretical models of radio radiation from central cores of radio sources invoke axial relativistic beaming of the radiation and predict significant enhancement of the radiation from the central cores when viewed at small angles to the direction of the beam. Investigations of the angular diameter distributions of radio sources by Swarup (1975) has shown that the median angular size of radio sources below 4 Jy at 327 MHz is about 10 arc seconds. Hence a sample of sources, with angular sizes substantially less than the above median, chosen from the Ooty occultation survey may be expected to contain a large fraction of double sources viewed along the axis of the double structure.
Cosmological Evolution of QSOs and Radio Galaxies from Radio — Selected Samples
Authors: Wall J. V. , Benn C. R.
Published: July 2016

We describe recent advances in observation and analysis which lead to improved understanding of the spatial distribution of QSOs and radio galaxies.