bluuebunny/crossref_metadata_2025 huggingface dataset:
The Overall Abundances of Globular Clusters
Authors: Bell R. A.
Published: July 2016

At a meeting on globular clusters held five years ago, Zinn (1981) made the following comments:

“In summary, there are clearly large differences in metal line strength between 47 Tuc giants and the giants in the other clusters. These differences suggest that there are substantial differences in metal abundance, which conflicts with the measurements obtained from echelle spectrograms, and there appears to be no simple way of reconciling these results. Until this is done, the metallicity scale for globular clusters hangs in limbo.”
An Overview of Globular Cluster Systems in Distant Galaxies
Authors: Harris William E.
Published: July 2016

Information is currently available for globular cluster systems in almost 50 galaxies from the Milky Way to the Coma Cluster. The observed features of these systems are reviewed, with emphasis on (a) their total populations (specific frequencies), (b) spatial structures compared with the underlying halo light, (c) photometric characteristics (luminosity function and metallicity). The combined evidence suggests strongly that globular clusters are likely to have formed in a rather sharply defined epoch clearly before the bulk of the halo field stars, and that this epoch was more active in E galaxies, especially those in rich environments. Finally, the special role of the supergiant E's at the centers of rich galaxy clusters is reviewed.
The Origin of Globular Clusters
Authors: Fall S. Michael , Rees Martin J.
Published: July 2016

The purpose of this article is to review some recent attempts to understand the origin of globular clusters. To put this in perspective, it may help to recall the analogous problem of the origin of galaxies. This splits into two parts. First, given a proto-galaxy with a specified mass and radius, how does it collapse, form stars and settle into a state of dynamical equilibrium? Richard Larson explored these topics in an important series of numerical simulations in the 1970s. Progress in this area brings into sharper focus a second set of questions that really has precedence over the first. Why did proto-galaxies have properties like the initial conditions in the collapse calculations and what distinguishes galaxies from structures on much larger and much smaller scales? Similar questions face us when we consider the origin of globular clusters. First, how did stars form in a proto-cluster, what was the efficiency, the initial mass function and so forth? It is appropriate that Larson has discussed these topics in the preceding article but here we are mainly concerned with the second kind of question: What is special about objects with masses of order 105-106 M⊙ and dimensions of a few tens of parsecs?
Precollapse Evolution of Globular Clusters
Authors: Inagaki Shogo
Published: July 2016

Density profiles of most globular clusters are well fitted by a King (1966) model. The evolution of a King model in the tidal gravitational field of the Galaxy is first discussed. If the concentration parameter c (= log(rt/rc)) is small enough, the evolution is nearly along the King model sequence and c becomes larger. When c becomes large enough (about 2.1), gravothermal instability sets in. The basic properties of gravothermal instability is next discussed. The stability criterion and its interpretation are given. Globular clusters consist of stars with disparate masses, so that finally the evolution of multi-component clusters is discussed. Acceleration of evolution in multi-component clusters and equipartition of the kinetic energies among components are discussed, and conclusions and future problems are given.
After Core Collapse. What?
Authors: Cohn Haldan
Published: July 2016

As our understanding of core collapse in globular clusters has improved through detailed computer simulations, attention has naturally turned to dynamical evolution of globular clusters after core collapse. The results of recent simulations of post-collapse cluster evolution are reviewed. An assessment is given of progress towards the goal of developing astrophysically realistic models that cover all phases of globular cluster evolution. A focus of this review is the stability of the post-collapse expansion phase to the large amplitude core oscillations first observed in the simulations of Sugimoto and Bettwieser and now confirmed by several other studies. The implications of core oscillations for the observation of post-collapse clusters are discussed.
Interstellar Matter in Globular Clusters
Authors: Roberts Morton S.
Published: July 2016

“Is there any point to which you would wish to draw my attention?”

“To the curious incident of the dog in the night-time.”

“The dog did nothing in the night-time.”

“That was the curious incident,” remarked Sherlock Holmes.

Memoirs of Sherlock Holmes

The source for intracluster matter is seen in various mass loss processes ongoing within clusters and is supported by the theoretical need for mass loss to explain the morphology of cluster colormagnitude diagrams. A variety of techniques ranging from X-ray to radio wavelengths have been employed to search for such matter but with few exceptions has not been found. The amount of material expected to collect between cleansing passages through the galactic plane has variously been estimated at between ∼ 102 and ∼ 103 M⊙. In contrast, observed upper limits for many clusters are well below these values, often > 1 M⊙. The few detections are at levels of ≲10−2 M⊙.
Globular Clusters as Tracers of the Galaxy Mass Distribution
Authors: Innanen K. A.
Published: July 2016

This review will consist of two parts: (a) a brief description of a new method to determine Vo, the circular speed of the local standard of rest, and which, of course, plays a fundamental role in the mass distribution of the Galaxy, and (b) a review of the globular clusters as tracers of the mass distribution in the Galaxy.
Globular Clusters and Primordial Composition
Authors: Cayrel Roger
Published: July 2016

So much has been learned already, during these last four days, about globulars that I shall start by addressing the second part of my topic first: the primordial chemical composition. Then I shall review the abundance of the primordial elements in globulars, or more generally in Population II. Actually if the globulars are the oldest stars ever observed in the Universe one could hope that the subject is over and that there is no need to speak about elements synthesized in stellar interiors for globulars. Unfortunately these rascals show always some amount of stellar nucleosynthesis products and this may very well be the central problem raised by their chemical composition. We shall discuss in turn the amount of the stellar synthesized elements in globulars and then the clues given by the pecularities of the abundance ratios, which may help in understanding their origin. The last section summarized the present knowledge of the subject.
The Development of a Red-Giant Branch in Low to Intermediate Mass Stars
Authors: Sweigart A. V. , Greggio L. , Renzini A.
Published: July 2016

A new grid of evolutionary sequences has been computed for the main sequence and first red-giant branch (RGB) phases of low to intermediate mass stars. From these sequences we have obtained new intermediate age isochrones.
Axial Ratios and Orientations for 100 Galactic Globular Star Clusters
Authors: White Raymond E. , Shawl Stephen J.
Published: July 2016

The non-spherical appearance of globular clusters was first noted by Pease and Shapley (1917) and discussed in some detail by Shapley (1930) who analyzed cluster shapes determined from star counts made by Helen Sawyer on the Franklin-Adams star charts. This classic work has provided most of the data set used in all subsequent discussions of cluster shapes. A number of studies reporting cluster shapes have appeared in the years since we began this project, the most recent of which include Geyer, Hopp and Nelles (1983), Frenk and Fall (1982), and Kadla et al. (1976, 1977).
The Integrated Spectra of Metal-Rich Galactic Globular Clusters: A Two-Parameter Family
Authors: Rose James A. , Tripicco Michael J.
Published: July 2016

Integrated photographic image-tube spectra have been obtained for the central regions of a number of metal-rich Galactic globular clusters with a wavelength resolution of 2.5 å over the wavelength region λλ3400-4500 å. The spectra have been analyzed using a variety of quantitative spectral indices that compare the strengths of neighboring absorption features. Our main result is that two parameters are needed to describe the integrated spectra of metal-rich globular clusters. The second parameter is manifested in two ways:

(1) In a diagnostic diagram sensitive to surface-gravity the metal-rich clusters do not form a well-defined linear sequence. Instead, we find large differences from one cluster to another in the mean surface gravity of the stars contributing to the integrated light at 4000 å. It appears that the relative amounts of light contributed by dwarfs and giants varies considerably from one cluster to another.

(2) In a diagram that discriminates CN strength we find large differences from one cluster to another in the mean CN strengths of clusters having similar “spectral type”. It is inferred that the mean CN anomaly varies from one cluster to another and that the anomalous CN strengths are present in main sequence stars as well as in giants.

The above two second parameter effects are shown to be strongly correlated in the sense that the “dwarf-dominated” clusters have the largest CN anomalies. Hence, our study indicates that no more than two independent parameters are required to explain the integrated spectra of metal-rich globular clusters.

Details of the above findings can be found in Rose and Tripicco (1986, A.J. 92, 1610).
Four-Color Measures of BHB Stars in M 4, M 13 and M 55
Authors: Davis Philip A. G.
Published: July 2016

Strömgren four-color photometric measures have been made of blue horizontal-branch A stars in the globular clusters M 4, M 13 and M 55 with the Steward Observatory 90 inch telescope and with the 60 inch telescope at Cerro Tololo Inter-American Observatory. These stars are faint, ranging in V magnitude from 13.6 in M 4 to 15.5 in M 13 and the corresponding errors in the four-color indices are ± 0.04 to 0.06 in the c1 index, for one observation. The error of the mean value of the c1 indices is approximately ± 0.02 for most of the stars since they have been measured from 4 to 10 times each.
Astrometric Distances of Globular Clusters
Authors: Cudworth Kyle , Peterson Ruth C.
Published: July 2016

With high-precision radial velocities and proper motions, one can equate the proper motion and radial velocity dispersions to obtain astrometric distances independent of any standard candles. We discuss the method and the small distance it yields to M 22.
The Development of the Red Giant Branch in Magellanic Cloud Clusters: Progress Report
Authors: Buonanno R. , Corsi C. E. , Pecci F. Fusi , Greggio L. , Renzini A. , Sweigart A. V.
Published: July 2016

In close connection with a parallel theoretical study (see Sweigart, Greggio and Renzini 1987) CCD photometry in the B and V bands of star clusters in the LMC and SMC was started in 1983 using the ESO telescopes. To study the development of the red giant branch (RGB) we selected intermediate age clusters using the following criteria: 1) integrated (B-V) color between 0.3 and 0.6 and/or 2) membership in the type IV group of the Searle, Wilkinson and Bagnuolo (1980) classification (SWB). A few other clusters (e.g. NGC 121) were observed for calibration purposes. The observed clusters are NGC 121, 152, 1756, 1831, 1841, 1987, 2164, 2173, 2209, 2249, 1466, 1866, 2107, 2108 and 2134 and good or very good quality CM diagrams have been obtained for the first ten of them. Out of this list, those clusters with a well developed RGB are NGC 121, 152, 1841, 1987 and 2173. Using the CCD frames, integrated (B-V) colors have also been obtained for some of the clusters.
The Age Distribution and Age-Metallicity Relation of Star Clusters in a Northern Region of the LMC
Authors: Mateo Mario
Published: July 2016

CCD images and UBV integrated photometry of 31 clusters comprising a magnitude limited sample in a remote northern region of the LMC have provided reliable ages and consistent abundances using isochrone ‘fits’ to deep color-magnitude (CM) diagrams for the 15 clusters with CCD data. Ages for the remaining clusters have been inferred from their integrated colors. The resulting LMC cluster age distribution is markedly different from the age distribution of Galactic clusters suggesting a significant ‘burst’ in the cluster formation rate in the outer LMC 2-4 Gyr ago. The age-metallicity relation (AMR) for our LMC cluster sample is also presented.
Deep Photometry of the Draco Dwarf Spheroidal Galaxy
Authors: Carney Bruce W. , Seitzer P.
Published: July 2016

We report the results of deep CCD photometry of two overlapping fields in the Draco dwarf spheroidal galaxy. We find (B-V)o,g = m0.69, indicating a mean [Fe/H] = −2.0. The width of the giant branch below the horizontal branch is somewhat wider than our observational errors permit, from which we infer there is a spread in metallicities amongst the Draco giants, up to 0.8 dex, perhaps. Draco is found to contain numerous blue stragglers, like almost all other loosely bound halo systems. The number of such stars more massive than about 1.2 M⊙ is roughly consistent with the number of anomalous cepheids discovered previously. It is not clear whether the blue stragglers represent a large number of mass transfer binaries or an intermediate age population, or both. A younger population component would help explain the galaxy's red horizontal branch stars in spite of its low mean metallicity. Signs of a younger population are seen in the color magnitude diagram for the entire sample, and especially from the higher quality data from the smaller area observed in the overlap of the two fields.
A Candidate for the Recovered Nova of 1938 in the Globular Cluster M 14
Authors: Shara Michael M. , Potter Michael , Moffat Anthony F. J. , Hogg Helen Sawyer , Wehlau Amelia
Published: July 2016

Although close binaries are believed to be of importance in the dynamical evolution of globular clusters, searches for such binaries have produced mostly negative results, aside from x-ray sources. Two dwarf novae which are possible cluster members are known (Margon and Downes 1983) and two classical nova candidates have been found. The crowded field around the nova observed in 1860 close to the center of M80 makes ground-based recovery of that star impossible with present techniques. Here we report on our attempt to recover the star which erupted in 1938 about 30″ (0.8 core radii) from the center of M14.
The Globular Cluster System of M 87
Authors: Cohen Judith G.
Published: July 2016

Long exposures with the 4-Shooter at the Cassegrain focus of the 200-inch telescope at Palomar Observatory have been obtained for M87 (and two other giant ellipticals in Virgo). Ellipse fitting with a code specially developed to reject point sources has been carried out to determine the surface brightness in various bandpasses of the underlying galaxy. The color gradients in the galaxy are quite small over the entire regime between 2 and 350 arc-sec from the nucleus of M87. Also I find that there is no difference between the ellipse parameters (position angle and eccentricity) derived in the various colors, i.e. the isochromes and the isophotes coincide. Details of the study of the halo of M87 are described in a paper submitted to the Astronomical Journal.
U Photometry of Globular Clusters in the Central Region of M 87
Authors: Held E. V. , Nieto J. -L.
Published: July 2016

We present a photometric (U band) investigation of the globular clusters in the central region of M87 from deep calibrated photographic and electronographic material, obtained with the CFH telescope. The aim of this work is to complete previous photometric studies at longer wavelengths (Grillmair et al., 1986; Lauer and Kormendy, 1986).
High Precision Photometry of 10,000 Stars in M 3
Authors: Buonanno R. , Buzzoni A. , Corsi C. E. , Pecci F. Fusi , Sandage A. R.
Published: July 2016

A new color-magnitude diagram for M 3 is presented. 10,000 stars have been measured down to V = 22 with an internal accuracy better than 0.03 mag to get complete and very accurate samples over well defined areas.

More than 10,000 stars have been measured down to V = 22 in two different areas. In the first, with 3.5 < r < 6.0 arcmin, photometric completeness has been achieved down to V = 21.5 and an algorithm to correct for losses due to unrecoverable crowding and blending has been experimentally computed. In the second, within a square field of 15 × 15 arcmin, completeness has been extended only to V = 18, well below the horizontal branch.

Many tests made on the data guarantee an internal photometric accuracy better than 0.03 mag at V = 21. Therefore, both the total population of each branch and the relative star-number ratios are “bona fide” representatives of the corresponding evolutionary time-scales. Here we simply present: 1) the color-magnitude diagram (see Fig. 1) obtained from the reduction of a wide collection of Palomar plates; 2) a table which presents the contribution of the various branches to the integrated cluster light; 3) the preliminary indication that, within the annulus we have considered, the blue stragglers seem to be slightly less centrally concentrated than the subgiants in the same magnitude interval.
Deep CCD Photometry in M 5
Authors: Richer Harvey B. , Fahlman Gregory G.
Published: July 2016

Deep UBV CCD imagery has been obtained in three fields of the galactic globular cluster M5. The locations of these fields are at distances of 8, 21, and 58 core radii. In the middle field, which overlaps substantially with the deep photometry field of Arp, the CCD photometry reaches fainter than V = 26. Color-magnitude diagrams constructed from stars in the inner two fields are identical, to within the errors, and can be used to set an upper limit of 4% to any metallicity difference between these two fields. A U, (U - V) color-magnitude diagram is also shown for the inner field and compared with that of a more metal rich and more metal poor cluster. Major differences in the morphology of these three diagrams are present as a function of metal abundance. From the color-color diagram the reddening in the direction of M5 is determined (E(B - V) = 0.02) as well as its metallicity ([M/H] = −1.13). The distance to M5 is then established from fitting local subdwarfs to the lower main sequence of the cluster. This yields (m - M)V = 14.3. Using the observationally determined parameters, an overlay of the appropriate VandenBerg and Bell isochrones yields an age estimate of 18 Gyrs for M5. Luminosity functions constructed from the three fields show excellent agreement through the range V = 17 to 23. Fainter than V = 23 there is some evidence for mass segregation effects due to dynamical relaxation.
Deep CCD Photometry of Omega Centauri
Authors: Noble R. G. , Buttress J. , Griffiths W. K. , Penny A. J. , Dickens R. J. , Cannon R. D.
Published: July 2016

This paper presents a color magnitude diagram for the enigmatic cluster ω Centauri (NGC 5139 = C1328 − 472) tracing the main sequence down to V ~ 21.5. The spread in color on the upper main sequence is confirmed as intrinsic to the cluster. The CCD observations were made using the SAAO 1 m telescope with the UCL CCD camera and the RGO CCD camera at the prime focus of the AAT.
The Dynamics of Globular Cluster Systems
Authors: Ramamani Natarajan
Published: July 2016

This paper describes a project whose aim is to study the dynamics of a globular cluster system using an N-body code modified to include the gravitational field of an isothermal galaxy model. The galaxy and the globular cluster system have the same radii, are spherically symmetric and non-rotating. The evolution is to be followed up to a Hubble time.
Evolution of Globular Clusters Including a Degenerate Component
Authors: Lee Hyung Mok
Published: July 2016

Low mass X-ray sources observed in many globular clusters are usually interpreted as compact binaries with degenerate components (e.g., Hertz and Grindlay 1983). Degenerate stars can exist in globular clusters if the IMF contains a sufficiently large number of high mass stars. Since the main-sequence lifetime is a very steep function of stellar mass, most of degenerate stars can be regarded as primordial. If the typical mass of degenerate stars is higher than that of main-sequence stars, mass segregation makes the core crowded with degenerate stars. Tidally captured binaries between degenerates and main-sequence stars can abundantly form as the core density becomes very high.
Binary Interactions in Star Clusters
Authors: McMillan Stephen L. W.
Published: July 2016

Over the past decade, a very considerable amount of effort in stellar dynamics has gone into the study of interactions between binary systems and other stars. The asymptotic analytic results obtained by Heggie (1975) for binary-single star encounters have been largely confirmed and extended by later numerical experiments (Hills 1975, Hut and Bahcall 1983). Binary-binary interactions have been studied by Mikkola (1983).
The Effects of Stellar Evolution and Galactic Tides on Globular Cluster Evolution
Authors: Chernoff D. F. , Weinberg M. D. , Shapiro S. L.
Published: July 2016

We investigate the evolution of globular clusters in the Galactic tidal field prior to core collapse. These multimass models incorporate mass loss by stellar evolution.
New Methods for the Search for Hot Gas in Globular Clusters
Authors: Gnedin Yu. N. , Natsvlishvili T. M.
Published: July 2016

Two new methods for the detection of hot gas in globular clusters are proposed: 1. measurement of the position change of a radio source due to refraction and 2. determination of the concentration of hot gas using the Faraday rotation of the polarization plane of the background radio source radiation.
The Kuiper Belt
Authors: Luu Jane
Published: July 2016

The existence of a belt of comets in the outer solar system (the “Kuiper belt”) has been postulated for a variety of reasons, including the need for a source for the short-period comets. The existence of the belt seems supported by the discoveries of the trans-Neptunian objects 1992 QB1, 1993 FW, 1993 RO, 1993 RP, 1993 SB, and 1993 SC. If these objects are members of the Kuiper belt, crude lower limits on the belt population can be established from the discoveries. The Kuiper belt comets are likely to be primordial remnants of the disk from which the solar system accreted. According to the current theories of cometary nucleus evolution, these objects are expected to possess mantles (“irradiation mantles”) which are different from mantles of comets which have been heated to the point of sublimation (“rubble mantles”). Kuiper belt comets on their way to short-period comet orbits may exist among the Centaur objects.
Comets (Existing Populations)
Authors: Kresák Ľ.
Published: July 2016

The definition, population, extent, origin and evolution of the individual subsystems of comets and transitions between them are discussed, together with presentation of the relevant statistical data and their changes with time. The largest outer subsystems are unobservable, but their existence is documented by the necessity of progressive replenishment of the observable populations, with limited survival times. There is persuasive evidence for two different evolutionary paths, one from the Oort cloud and another from the Kuiper belt. While the extent and accuracy of the data available is increasing rapidly, the Jupiter family of comets is the only one for which the evolutionary time scales do not exceed by many orders of magnitude the history of astronomical observations. The individual comet populations differ from one another not only by the distribution of orbits, but also by the size distribution and aging rate of their members. Their dynamical evolution is coupled with disintegration processes, which make it questionable whether the present state can be interpreted as a long-term average.
9. A 21-cm. study of the Orion region
Authors: Menon T. K.
Published: July 2016

An analysis of the profiles of the 21-cm. radiation from neutral hydrogen promises to be of great importance for a study of the internal motions of specific regions of the Galaxy. The two factors which influence the shape of the profiles are the velocity distribution and the density distribution of the neutral hydrogen atoms in the line of sight. The velocity distribution is essentially determined by three factors (1) galactic rotation, (2) the random motions of the gases, and (3) local peculiar motions as, for example, expansion. In the plane of the Galaxy in any specific direction the isolation of a region of particular interest is made difficult because of the superposition of the radiation along the entire line of sight. Hence regions at intermediate galactic latitudes are more suitable for study of internal motions than regions on or near the galactic equator. Also, for the study of peculiar motions, regions with small galactic rotation terms have the distinct advantage that any prevailing preferential motion will be clearly indicated by the profiles. The Orion region satisfies most of the above requirements. The galactic latitude of the section under consideration falls between − 10° and − 25°, and at the mean galactic longitude of 170° the galactic rotation term in radial velocity amounts to 7 km./sec. at a distance of 500 parsecs. Moreover the Orion region contains many features of considerable interest like the Orion Nebula, the Orion Association, the great arc of ionized hydrogen and many smaller H II regions. The great arc of Barnard (1895) [1] forms part of an almost elliptical ring of emission nebulosity with dimensions 14 × 12°. At the distance of 500 parsecs for the Orion Association these dimensions are of the order of 120 × 105 parsecs. It is of interest to note that the major axis of this ellipse is parallel to the galactic equator. This ellipticity could presumably be caused by galactic rotation, by a galactic magnetic field with lines of force along the spiral arms, or by the rotation of the whole mass itself. Further investigation is necessary to decide which of the above effects is most important.
18. Current progress in development and results obtained with the ‘Mills Cross’ at the Radiophysics Laboratory
Authors: Pawsey J. L.
Published: July 2016

The study of continuous spectrum cosmic radio waves in the Radiophysics Laboratory is based mainly on two large ‘Mills Crosses’: one on 85 Mc./s. which has been in use for a year, and another on 20 Mc./s. which is under construction. The principle of this instrument has been described by Mills and Little (1953) [1]. It utilizes two long thin arrays arranged in the form of a cross and gives an effective ‘pencil-beam’ response which records both the background and discrete sources simultaneously. Essential data relating to these Crosses are given in Table 1.
23. Observations of discrete sources with the 22 Mc./s. Mills Cross
Authors: Burke B. F. , Franklin K. L.
Published: July 2016

The 22·2 Mc./s. crossed array of the Carnegie Institution of Washington has been in use since 20 July 1954. This antenna system consists of two linear arrays 2047 ft. in length, each composed of sixty-six half-wave folded dipoles. The amplitude gains of the two arrays are, in effect, multiplied together by a phase-switching system similar to that used in phase-switching interferometers (Ryle, 1952) [1]. The design differs somewhat from the arrangement first used by Mills (Mills and Little, 1953) [2] in that the arrays are arranged in the form of a slightly flattened X. The resulting pencil beam is slightly elliptical in cross-section, measuring 1°·6 by 2°·4 at half-power points, and is directed by inserting lengths of line into the feeder system of each array, phasing the dipoles such that the maximum response is at the desired zenith angle.
26. The radio frequency spectrum of Cassiopeia A: a Symposium summary
Authors: Seeger Ch. L.
Published: July 2016

Data presented at this symposium showed that there had been considerable progress during the previous year towards the solution of one of the basic problems in radio astronomy—the determination of the full radio frequency spectra of the discrete sources. The generally accepted plan is to establish the spectra of a few ‘reference sources’. At present, these reference objects must be chosen from among the most intense sources, Cassiopeia A, Cygnus A, Taurus A and Virgo A. The utility of both Cygnus A and Taurus A is impaired by their close proximity to other discrete sources of appreciable strength. If they are to be observed with small antennas, meticulous interferometry, employing both variable spacing and variable azimuth, will probably be required in order to obtain an accuracy of 10 %. Cassiopeia A and Virgo A appear to be sufficiently in the clear for present needs, though only the latter is visible in both hemispheres and it is about twenty times less bright than Cassiopeia A. However, Cassiopeia A has received most attention so far. The effects of radiometer non-linearity must be examined, particularly at the lower frequencies, when calibrating Virgo A in terms of Cassiopeia A.
29. The discrete source of radio waves at the galactic centre
Authors: Smith F. G. , O'Brien P. A. , Baldwin J. E.
Published: July 2016

The discrete source of radio emission in Sagittarius is among the most intense in the whole sky, but its situation in the belt of emission from ionized hydrogen and other sources associated with the galactic plane makes it difficult to observe. The observations described in this paper were made at frequencies of 38, 81·5, 210, and 500 Mc./s.; at these low frequencies it is particularly difficult to obtain sufficient aerial resolving power to distinguish the discrete source from the background. Interferometer aerials were therefore used, and at 38 and 210 Mc./s. spacings up to λ60 were used, sufficient to resolve the source completely. At 81·5 Mc./s. various sections of the large interferometer aerial were used.
30. Radio and optical intensity distributions in the Centaurus source (NGC5128)
Authors: De Vaucouleurs G. , Sheridan K. V.
Published: July 2016

(1) A preliminary determination of the apparent intensity distribution in the Centaurus source has been made with the 1500-ft. Mills' Cross at 3·5 metres wave-length. At the declination of the source the beam is nearly circular and has a half-power width of 0°·8. Fig. 1 shows contours of apparent equal intensity above a smooth interpolated reference level. The inner ‘point’ source[1] which is not resolved by the present equipment appears to be embedded in an extended source strongly elongated in position angle 12°. The secondary, isolated maxima and minima of intensity on the major axis of the extended source at distances greater than 1° from the central maximum are probably unreal and may represent side lobes in the diffraction image of the point source.
36. On the nature of the emission from the Galaxy NGC4486
Authors: Shklovsky I. S.
Published: July 2016

It is well known that the radio galaxy NGC4486 has as a striking peculiarity a small and very bright ‘jet’ in its central part. It seems to us that the key to the understanding of the nature of this radio galaxy is the purely continuous spectrum of the jet, where not even a slight trace of emission or absorption lines is present.
43. Some problems of meta-galactic radio-emission
Authors: Shklovsky I. S.
Published: July 2016

The observed cosmical radio-emission has to be divided into the galactic and metagalactic components. The separation of these components is a problem of first importance. It was shown by us (Shklovsky, 1952 [1]) that at least 75% of the observed intensity near the galactic poles is caused by sources located in our stellar system. These sources form an almost spherical sub-system. Another model of the distribution of the cosmical radio-emission sources (Westerhout and Oort, 1951 [2]) is popular in the western countries. The so-called ‘isotropic component’ of metagalactic origin used in that model was considered responsible for the greatest part of the intensity near the galactic poles.
46. The structure of the solar chromosphere from centimetre-wave radio observations
Authors: Hagen J. P.
Published: July 2016

The atmosphere of the sun is transparent to visible radiation, is nearly transparent to millimetre and centimetre radio radiation, and becomes opaque to the metre and longer wave radiation. Information about the chromosphere can then be given by observing the radiation from the sun at short radio wave-lengths. In its outer part, the atmosphere of the sun is highly ionized. Absorption in any region is directly proportional to the square of the density and the wave-length squared and inversely to the temperature to the three-halves power
This is the familiar equation for the absorption of radio waves in an ionized medium. By consequence of this, the longer wave radiation is absorbed in the outer layers of the sun's atmosphere and can escape only from these outer regions. The shorter wave-length radiation is absorbed very little in the outer part of the solar atmosphere where the density is quite low, and hence radiation from the chromosphere escapes as centimetre and millimetre radio waves. In fact, the principal radiation from the sun in the centimetre and millimetre region comes from the chromosphere.
60. Relation between optical solar features and solar radio emission
Authors: Dodson H. W.
Published: July 2016

During the last five years, we at the McMath-Hulbert Observatory have been attempting to determine the characteristics of radio-frequency radiation associated with certain of the transient solar features that we normally observe on monochromatic spectroheliograms or in integrated light. We have had the privilege of using the original 200 Mc./s. records at Cornell University and the 2800 Mc./s. records at the National Research Council in Ottawa.
A lunar radar study at 10-cm wavelength
Authors: Yaplee B. S. , Roman Nancy G. , Craig K. J. , Scanlan T. F.
Published: July 2016

In February 1957 the U.S. Naval Research Laboratory was successful in obtaining radar echoes from the moon by using a short-pulse radar [1]. Although the signal-to-noise ratio was not as large as desired, the leading edge of the echo was sufficiently well defined to make possible an accurate measurement of the radar distance to the moon. It was hoped that geodetic information could be extracted from such distance measurements. Hence in October and November, 1957, the radar distance to the moon was measured with a radar mounted in the 50-foot steerable parabola at NRL.
Radio observations of the lunar atmosphere
Authors: Elsmore B.
Published: July 2016

Observations of a lunar occultation of a radio source may provide information concerning both the distribution of radio “brightness” across the source and its accurate position. For sources of which these results are already fairly well known, observations at long wavelengths may be used to derive the density of the lunar atmosphere [1]. During recent years two such occultations have been observed at Cambridge: one, the occultation of IC 443, the large-diameter radio source in the constellation of Gemini, from which the density of the lunar atmosphere was estimated to be less than 10–12 of that of the density of the terrestrial atmosphere [2] and [3]; and two, the occultation of the Crab nebula on 1956 January 24 [4].
Observations of discrete sources at 3-cm wavelength using a maser
Authors: Alsop L. E. , Giordmaine J. A. , Mayer C. H. , Townes C. H.
Published: July 2016

The new types of low-noise radio-frequency amplifiers now under development hold great promise for improving and extending radio astronomical observations. A solid-state maser, designed and built at Columbia University, has been used with the U.S. Naval Research Laboratory's 50-foot reflector since 1958 April. The maser is the 3-level type [1], with ruby [2] as the paramagnetic medium. Initially, an rms radiometer output fluctuation of about 0.1 °K was realized with a 5s output time constant. Subsequent improvements of the maser and of the associated circuitry have made it possible to observe with an rms output fluctuation of 0.04 °K for a 5s output time constant. These figures represent improvement factors of about 5 and 13 respectively over the radiometer without the maser. These significant improvements in sensitivity have made possible continuum observations which could not previously have been made with the NRL apparatus except by unwieldy averaging techniques.
The structure of the chromosphere and the low corona
Authors: De Jager C.
Published: July 2016

The outer part of the sun consists of two main regions: (1) the convection zone, which extends from a depth of 105 km below the visible surface to 100 or 200 km below the surface, and in which the temperature decreases from about 106 °K near the lower limit to 6000 °K near the surface; and (2) the corona, which starts about 5000 km above the surface and extends very far, up to many solar radii, and in which the temperature is 106 °K in the low parts.
A model of the inner corona based on radio data
Authors: Panovkin B. N.
Published: July 2016

The work of Ginzburg, Shklovskiĭ, and Martyn (1946) showed that the upper layers of the solar atmosphere (chromosphere and corona) are responsible for the sun's thermal emission in the radio-emission range. This was confirmed by a number of observations.
Solar radio bright spots at 88-cm wavelength
Authors: Firor J.
Published: July 2016

During 1957 we studied the solar radio radiation at a wavelength intermediate between the centimeter region with its slowly varying bright spots and the meter-wavelength region with its noise storms. At this intermediate wavelength (88 cm) the slowly varying bright-spot and the noise-storm producing regions merge into two aspects of the same persistent, bright, solar radio regions.
Etude statistique de la composante lentement variable d'apres les observations entre 10,000 et 600 Mc/s
Authors: Vauquois B.
Published: July 2016

La composante lentement variable du rayonnement radioélectrique solaire provient de régions d'étendue finie de l'atmosphère du soleil, dans lesquelles la température et la densité électronique sont normalement élevées. Ces régions appelées “centres d'activité radioélectrique” (C.A.R.) ne sont pas connues directement par les observations. En effet, les mesures journalières effectuées avec un radiotélescope fournissent une valeur du rayonnement solaire sur une longueur d'onde qui est la somme du rayonnement de base d'origine thermique de l'atmosphère normale et de l'émission d'un nombre indéterminé de C.A.R. sur cette longueur d'onde.
A model of the electron corona by reference to radio observations
Authors: Newkirk G.
Published: July 2016

The K-coronameter developed at the High Altitude Observatory [1] to study the electron corona outside of eclipse has been in routine use since 1956 September. Up to the present date, usable observations have been obtained on some fifty-five days, and the accumulated information on the corona out to one solar radius from the limb has permitted the development of models of the electron corona above the quiet disk, the polar regions, and the active regions. The last of these, since it departs from the spherically symmetric model, should be of interest to radio astronomers.
Some characteristics of dynamic spectra of solar bursts
Authors: Haddock F. T.
Published: July 2016

The sun has been observed daily at the University of Michigan during the last year with three sweep-frequency receivers covering the 100 to 580 Mc/s band three times a second. The output is displayed as an intensity-modulated line on a precision cathode-ray tube that is photographed on a 35-mm film moving about one centimeter per minute, thereby producing a frequency-time record with solar intensities recorded as variations in photographic density. The combination of the film characteristic and the logarithmic response of the IF amplifier permits the recording of a wide range of intensities in greater detail than before. A number of typical radio events associated with solar flares have been obtained; a typical sequence is a short group of intense type III bursts (fast drifts) followed within minutes by a type II burst (slow drifts) lasting 10 to 30 minutes, and followed by a type I noise storm, with or without a continuum increase, continuing for hours or days. The type I event is usually confined to frequencies below about 200 Mc/s, whereas the type III and type II (bursts) have been recorded up to 580 Mc/s.
Some aspects of type II bursts
Authors: Roberts J. A.
Published: July 2016

The outstanding bursts of radio emission from the sun, which are termed spectral type II or “slow-drift” bursts, are a rare phenomenon. Even at sunspot maximum the average rate of occurrence is only about one burst every 50 hours, so that a long series of observations is needed to define the characteristics of the bursts. The present study uses the records made over the past 5½ years with the 40 to 240 Mc/s Dapto radio spectrograph. During this period, 65 bursts of this type were recorded.
Optical observations of solar disturbances causing type II radio bursts
Authors: Giovanelli R. G. , Roberts J. A.
Published: July 2016

During 1956-57, 15 type II radio bursts have been recorded on the Dapto radio spectrograph during times of observation with the Sydney Hα flare patrol camera. We believe that we have established identifications of the optical disturbances responsible for 13 of these bursts, and alternative identifications for the remaining two. As Table I shows, some of these were prominences ejected at the limb. Some were disappearing filaments that ejected matter and were accompanied by the development of two parallel lines of flares, one on either side of the position of the former filament. Others were flares, almost all being particularly bright and showing some evidence of dark-hydrogen activity.
The correlation of solar radio bursts by magnetic activity and cosmic rays
Authors: Thompson A. R.
Published: July 2016

The sweep-frequency equipment at the Harvard Radio Astronomy Station, Fort Davis, Texas, has now been running continuously since 1956 September, recording solar radio activity in the frequency range from 100 to 580 Mc/s. The following contribution describes preliminary investigations of the correlation of the radio data with solar corpuscular emissions. This work was initiated to examine the well-known suggestions that the origins of the type II and type III radio bursts are associated with the ejection of auroral particles and cosmic rays respectively.
The scattering of radio waves in the solar corona
Authors: Hewish A.
Published: July 2016

The angular diameter of the Crab nebula is considerably increased when it is viewed through the solar corona. This effect is due to the scattering of the waves by coronal irregularities and its study gives some indication of the nature of the outermost corona. This paper is a summary of observations carried out each year at Cambridge for the period 1952 to 1958 inclusive.
Eclipse de la nebuleuse du Crabe par la couronne solaire
Authors: Blum E. J. , Boischot A.
Published: July 2016

En 1957 et 1958 des observations de la nébuleuse du Crabe lors de son passage derrière la couronne solaire ont été effectuées sur 169 Mc/s à l'aide de l'interféromètre méridien à 32 antennes de Nançay [1, 2]. Cet appareil ayant un pouvoir séparateur de 3′.8 dans la direction est-ouest et un lobe principal tous les deux degrés, nous permet de distinguer le rayonnement de la radiosource même quand elle est très proche du soleil. Le flux maximum reçu lors du passage de la source non élargie atteignant 10 pour cent du flux donné par le soleil calme, la source sera très facile à distinguer sur les enregistrements.
The radio sources in the Cygnus loop and IC443
Authors: Burbidge E. Margaret , Burbidge G. R.
Published: July 2016

Within our Galaxy there are a number of nonthermal sources of radio emission. In the last few years a considerable amount of data has been collected about some of these sources, in particular the Crab nebula and the Cassiopeia A source. There is strong evidence now to suggest that all of the nonthermal radio sources emit by synchrotron radiation, or acceleration radiation as we shall describe it here. In this paper we want to discuss the physical conditions in two objects, the Cygnus loop and IC 443.
21-cm hydrogen-line absorption in the spectra of discrete sources
Authors: Muller C. A.
Published: July 2016

This paper is a short survey of the results obtained with the Dwingeloo 25-meter radio telescope (beamwidth 0°.56) and the 21-cm receiver on hydrogen-line absorption effects in the spectra of a number of strong point sources. Earlier work on this subject has been done by Hagen, Lilley, and McClain [1], and by Davies and Williams [2]. Some preliminary results of the first part of the present investigation were already published [3].
The problem of confusion in surveys of sources
Authors: Ryle M.
Published: July 2016

Dr. Pawsey has asked me to make some general remarks on the problem of confusion when the traces of adjacent radio sources overlap. This is a question that affects all surveys in which the observations are limited by resolving power and not by sensitivity; there is perhaps some misunderstanding about the relative performance of interferometers and pencil-beam systems of similar sizes, and there seems to be an impression that the former are more seriously affected than the latter.
Resultats preliminaires de l'observation des radiosources a l'aide de l'interferometre de Nancay
Authors: Boischot A.
Published: July 2016

Un des problèmes majeurs de l'étude des radiosources est leur identification avec des objets optiques. Cette identification est presque toujours rendue très difficile par l'imprécision des mesures de position des radiosources.
On the possibility of observing radio emission from flare stars
Authors: Schatzman E.
Published: July 2016

Strong radio emissions are associated with solar flares. It seems worth while, therefore, to examine whether radio emission associated with flares and eruptions in nonstable stars could be observed. The first problem in this respect is establishing the threshold of sensitivity necessary to receive anything during an eruption or a flare; the second one is naturally fixing the duration of the radio emission, which can be much shorter in a given wavelength than the optical emission.
Concluding lecture
Authors: Hoyle F.
Published: July 2016

Undoubtedly the outstanding advance of the last few years in theoretical radio astronomy has been the widespread recognition of the importance of synchrotron radiation by relativistic electrons. The possibility that high-speed electrons might be of importance in the solar problem was mentioned by Giovanelli [1] and by me [2] in 1948. But real quantitative development in this direction dated from the well-known paper of Schwinger [3] published in 1949. Schwinger's results were put into a form suited to the problems of radio astronomy by Alfvén and Herlofson in 1950, still from the point of view of emission from stellar surfaces, however. In 1953, Ginzburg [5] and Shklovskiì [6] took the additional step of suggesting that relativistic electrons exist in space and that they give rise to the emission from nonthermal sources.