bluuebunny/crossref_metadata_2025 huggingface dataset:
The Frequency Splitting of Transient Solar Radio Bursts
Authors: Ellis G. R. A.
Published: July 2016

Observations of transient solar radio emissions lasting 0.2 to 2 s in the frequency range 25-50 MHz have demonstrated the existence of a characteristic and relatively common type of burst (the split pair) made up of two narrow band components separated in frequency by about 0.1 MHz.
A Search for Pulsed Gamma Emission from Two Pulsars
Authors: Ables J. G. , Durdin J. M. , Gregory A. G. , Stone B. J.
Published: July 2016

We have recently used the atmospheric air-shower Cerenkov technique in an attempt to observe pulsed gamma radiation from two southern pulsars, PSR 0833—45 and MP 0959. Northern hemisphere observers do not agree whether the pulsars CP 0950, CP 1133 and CP 1919 are sources of gamma emission, either pulsed or uniform in time.
Position Measurements of a Harmonic Type II Solar Burst
Authors: Riddle A. C.
Published: July 2016

Prior to the advent of the Culgoora 80 MHz radioheliograph position measurements on type II solar bursts were restricted to those made with one-dimensional interferometers. These measurements yielded conflicting evidence on the apparent positions of fundamental and harmonic emission observed at a given frequency; different observers reported the fundamental to be closer to and further from the centre of the Sun than the harmonic. Here we report on two-dimensional observations at 80 MHz made on both fundamental and harmonic emission of a type II event that occurred on 1969 March 2. The observations are shown to be consistent with the hypothesis that the emission is produced as the result of a disturbance moving out from the site of a flare and forming a shock front within an overlying coronal streamer. Both fundamental and harmonic are explained by ‘forward’ emission from the shock front. Observations of the harmonic emission at 158 MHz are also consistent with this model.
On the Radio Frequency Spectrum of Jupiter
Authors: Gleeson L. J. , Legg M. P. C. , Westfold K. C.
Published: July 2016

Recent observations of the radio-frequency flux spectrum of Jupiter in the frequency range 80-10 000 MHz suggest that the synchrotron component is not independent of frequency as has been generally accepted. Rather, the flux decreases at frequencies below 300 MHz and above 3000 MHz. In this paper we show that extensions and variations of the well-known dipolar model for this emission can account for the modified spectrum.
Adiabatic Oscillations of Stars
Authors: Van der Borght R.
Published: July 2016

In the past a number of analytical solutions have been found to the differential equation for small radial adiabatic oscillations of stars, with the aid of a series expansion of the form leading to a two-term recurrence relation.
Extra-galactic Radio Sources with Extended Structure
Authors: Schilizzi R. T. , McAdam W. B.
Published: July 2016

Most extra-galactic radio sources show angular structure over a wide range of size. Long-baseline interferometers and scintillation observations have shown that resolved sources extending over 10′ arc can have significant contributions from components <1″ arc. Observations at low frequency with the Molonglo cross telescope show also that a large fraction of the emission can come from halo, bridge or extended regions which may form a diffuse ridge or arc structure extending well beyond the small diameter components. However the majority of sources exhibit a basic double structure, and this has led to the adoption of two extended (Gaussian) components as an initial model for the interpretation of brightness distribution in most papers on the structure of extra-galactic sources. Parameters based on such a model will usually match the observed distribution quite well, but because of confusion, there is a danger in using intensity parameters for a model component to derive the spectral index for part of the source.
Frequency Dependence of 4C Source Positions
Authors: Munro R. E. B. , Hoskins D. G.
Published: July 2016

Recent accurate measurements at 408 MHz and 2700 MHz of the positions of 4C catalogue sources have allowed a comparison of the positions of radio sources measured at the two frequencies and an investigation of the frequency dependence of these positions.
Synchrotron Radiation from Mildly Relativistic Electrons
Authors: Wild J. P.
Published: July 2016

The exact formula for the intensity of synchrotron radiation emitted by a single charged particle in vacuo was given by Schott, for the case of circular orbits, and Takakura for the case of helical orbits. In the general case the radiated power is expressed in terms of four variables which appear in (among other places) the arguments or orders of a Bessel function and its first derivative; hence the general formula gives little insight into the interpretation of synchrotron radiation and allows evaluation only in particular cases. There is a particular need for approximate formulae that yield the spectrum of the radiation in explicit form. Such approximate formulae were found by Vladimirskii and Schwinger for the case of highly relativistic electrons. In the present paper we outline the derivation of approximate formulae applicable to mildly relativistic electrons, especially those with velocity βc such that 0 ≪ β ≲ O.9. These approximations are also relevant to the case of highly relativistic electrons in a plasma with refractive index appreciably less than unity.
Solar Magnetic Fields and Velocities
Authors: Giovanelli R. G.
Published: July 2016

It has long been known that Fraunhofer lines show variations in intensity from place to place over the Sun’s surface, these being particularly noticeable in spectroheliograms obtained in the strong chromospheric lines. An early account of the weaker Unes was given by d’Azam-buja. McMath, Mohler, Pierce and Goldberg attributed intensity increases in (or decreases in depth of) metallic spectral lines to local temperature increases. Sheeley used high-resolution spectra to study these line weakenings further, finding them where, and only where, strong non-spot magnetic fields occurred. He also reported that in many cases the continuum in such regions was of reduced intensity, suggesting that fields often occur in the dark lanes and pores in the granulation. Spectroheliograms obtained in the cores of the weakened lines (e.g., Fel 6302.5Å) by Chapman and Sheeley showed that the bright network which these weakenings form appears as a sequence of sharp, bright points in the cores of the fainter lines and the wings of stronger lines but is more diffuse in the cores of stronger lines. They found the bright network in Zeeman-insensitive Unes (e.g., 5123.7A) also, indicating that it is due, at least in part, to variations in physical conditions. Lines of low ionization and excitation are weakened more than those of high ionization and excitation, and they attributed this to a temperature increase by 100-200 °K in the region of formation of the line cores ; a similar increase of 250 °K was found by Harvey and Livingston.
Some Investigations of the Solar Corona: The First Two Years of Observation With the Culgoora Radioheliograph
Authors: Wild J. P.
Published: July 2016

The first meaningful observation with the 80 MHz Cul-goora radioheliograph was made on 2 September 1967, a few weeks before the instrument was officially commissioned. Systematic observations, normally for 4 to 6 hours per day, began late in February 1968 and the Sun has since been observed on 438 days. The remaining days and many nights have been used for investigations of radio sources and the interplanetary medium and for maintenance and instrumental extension. The standard of reliability thus achieved has been due to the sustained efforts of K. V. Sheridan, W. J. Payten, K. R. McAlister, M. Beard and their colleagues. These first two years have been a period mainly of exploration—a phase of great interest to those engaged in observing, though possibly bewildering to those not. The present review is a first attempt to collate and summarize what has so far been found and where possible to draw preliminary conclusions. The observations to be described and their discussion have been due to a joint effort on the part of a number of workers, particularly G. A. Dulk (on leave from the University of Colorado), K. Kai (on leave from the University of Tokyo), N. R. Labrum, D. J. McLean, A. C. Riddle, K. V. Sheridan, S. F. Smerd, R. T. Stewart, and the present writer. The period has also seen considerable development in the evolution of intricate computer programmes for analysing the data, particularly on the part of L. H. Heisler and D. J. McLean.
On the Polarization and Rapid Fade-out of Moving Type IV Solar Bursts
Authors: Dulk G. A.
Published: July 2016

Since the advent of the 80 MHz radioheliograph, precise position and polarization measurements have become available on several moving type IV bursts. Two of the more puzzling characteristics of these bursts are : (1) they exhibit strong circular polarization in parts or all of the source region ; (2) after moving outward to as much as 3 R⊙ with relatively constant intensity, they rapidly fade away. In this paper we discuss the polarization and intensity of synchrotron radiation from mildly relativistic electrons and suggest betatron deceleration as a mechanism to explain the rapid fade-out of the moving type IV sources. The results are applied to two examples of moving type IV bursts.
The Principle of Invariance and Non-coherent Scattering
Authors: Holt J. N.
Published: July 2016

The purpose of this paper is to obtain an expression for the reflecting properties of a semi-infinite, plane parallel, isothermal atmosphere of scattering factor λ. The absorption and scattering of the incident radiation is assumed to be entirely due to transitions in two-level atoms, and the absorption and emission profiles are given by (y), y being frequency from line centre in Doppler units.
Core Helium Burning Evolution at 15 M⊙
Authors: Robertson J. W.
Published: July 2016

The existence of red supergiants such as those in the clusters h and χ Persei has puzzled stellar evolution theoreticians for some time. Suggested explanations for them have included stars in a stage of gravitational contraction to the main sequence, or between nuclear burnings, core helium burning stars, and stars burning carbon or oxygen in the core, but it is now generally accepted that most red supergiants are core helium burning stars.
Core Helium Burning Evolution at 5M⊙
Authors: Robertson J. W.
Published: July 2016

Observations of the red giants in NGC 1866 in the Large Magellanic Cloud, made by Arp and Thackeray provide a strict test for core helium burning models of about 5M⊙. The main observational features to be reproduced theoretically are the luminosity of the red giants, the range in effective temperature that they occupy and the ratio of the number of giants near the blue end of this range to the number at the bottom of the red giant branch. Meyer-Hofmeister attempted a theoretical fit to these observations using the initial (X, Y, Z) composition (0.602, 0.354, 0.044) and assuming the stars to have formed uniformly over a period of 1.5 × 107 years about a mean age of 5.75 × 107 years. Although she was able to fit the luminosity and effective temperature spread of the red giants, her theory predicted far too many stars at the bottom of the red giant branch relative to the number of bluer giants.
Secondary Bumps in Cepheid Variables
Authors: Gascoigne S. C. B.
Published: July 2016

The Hertzsprung phenomenon, in which secondary bumps in the light or velocity curves of cepheid variables occur at systematically earlier phases as the period lengthens, has been known for about 50 years. As part of his programme on non-linear computations of cepheid models, Christie has interpreted the effect as a progressive wave which originates near the surface, travels to the core and is reflected back. He found that the phase varied with period in the correct sense, but to make his models fit both the Hertzsprung and period-luminosity relations he had to assign to them masses only about a half of those expected from evolutionary theory. The discrepancy is one of the outstanding problems in the field.
Asymptotic Methods in the Theory of Non-linear Convection
Authors: Borght R. Van Der
Published: July 2016

The effective Rayleigh number, in the solar convection zone, soon reaches a value of the order of 106 and, although considerable progress has been made in the numerical integration of the basic system of differential equations at high Rayleigh number, it is of interest to investigate more fully the application of asymptotic methods to such a problem.
An Improved Vitense Model of the Solar Convection Zone
Authors: van der Borght R.
Published: July 2016

Recently, Unno has proposed a new method for constructing models of convective non-grey atmospheres, making two substantial improvements to the mixing-length theory of Böhm-Vitense. His method, based on the variational technique of Glansdorff-Prigogine, enables the determination of the eddy-size and is no longer dependent on an ad hoc assumption of a constant mixing-length to scale height ratio. It also takes into account the effects of non-grey radiative transfer.
Non-linear Convection with Variable Viscosity and Thermal Conductivity
Authors: van der Borght R. , Waters B. E.
Published: July 2016

In his studies of the temperature fluctuation in the solar photosphere P. R. Wilson came to the conclusion that, in order to explain Edmond’s r.m.s. intensity fluctuation distribution against heliocentric angle, one is led, using two dimensional solutions for the equation of radiative transfer, to the existence of a sharp temperature fluctuation of about 660 K r.m.s. at a depth of 250 km below τ5000 = 0.03 and that this temperature fluctuation decreases sharply in the next 70 km. There also seems to be an indication that there exists a second temperature fluctuation maximum at a depth of approximately 100 km below the first one.
Possible Causes of Line Splitting in Drift Pair Solar Bursts
Authors: Melrose D. B. , Sy W.
Published: July 2016

In this paper possible causes of line splitting in emission near the local plasma frequency are considered in connection with drift pair solar radio bursts. The basic model envisaged for the bursts involves a bunch of electrons streaming through the solar corona at several times the thermal velocity of electrons. The emission process assumed is the transformation of coherently generated electron plasma waves (I-waves) into electromagnetic waves (t-waves) with little change in frequency.
Observations at 6 MHz of Radio Pulses from Extensive Air Showers
Authors: Felgate D. G. , Stubbs T. J.
Published: July 2016

Extensive air showers radiate because they are essentially sheets of charge moving through a medium at relativistic velocities. Of interest in the present experiment are their emissions in the optical and radio regions of the spectrum—the first long accepted as primarily of a Cerenkov origin, and the second very far from fully understood.
Effect of a Magnetic Field on Finite Amplitude Convection
Authors: Murphy J. O. , Spiegel E. A. , Van Der Borght R.
Published: July 2016

It is well known that a magnetic field has an inhibiting effect on thermal convection. It is also likely that a magnetic field might have a marked effect on the preferred cell-size and it is therefore of some importance to investigate the effect of such a field on finite amplitude convection. We restrict ourselves to fluids in which the Boussinesq approximation holds. For astrophysical application, especially in a study of the convective layer of the Sun, one should consider the compressible case but unfortunately the full compressible equations are much more difficult to handle numerically. In any case, the integration of the equations for the incompressible case will yield at least an indication of the effect of a magnetic field.
The Coronal Site of a Type III Burst as a Source of Interplanetary Electrons
Authors: Palmer I. D. , Lin R. P.
Published: July 2016

Although cosmic rays detected in interplanetary space have often been correlated with visible flares at the Sun, little is known about the transport of these particles through the corona. Lin demonstrated a good correlation between ≳20 keV electron events detected by spacecraft near the Earth and type III radio bursts at the Sun. In a detailed investigation of many of these electron events from one particular active region source, Lin proposed that the injection of electrons was characterized by a source region in the corona which extended over ~70° in longitude, such that in this region the electrons had direct access to an ‘open cone’ of propagation in interplanetary space. When the spacecraft was situated outside this open cone (by up to 15°), impulsive electron events were still recorded, but these were now modified by diffusion through the corona of the electrons from the 70° source region.
An X-Ray Observation of the Large Magellanic Cloud
Authors: Tuohy I. R. , Harries J. R. , Broderick A. J. , Fenton K. B. , Luyendyk A. P. J.
Published: July 2016

A Skylark rocket (SL727) carrying an X-ray astronomy experiment prepared by the University of Adelaide and Tasmania (UAT) was launched from Woomera at 0030 UT on July 10, 1970. The Large Magellanic Cloud (LMC) was detected during the flight, and the recent observation of structure within the Cloud is confirmed. In particular, the data support the suggestion of X-ray emission from the 30 Doradus (Tarantula) Nebula.
The New Fleurs Radiotelescope
Authors: Christiansen W. N.
Published: July 2016

The adjective ‘high’ when applied to the resolving power of radiotelescopes, has a meaning that has changed very rapidly during the last twenty-five years. In the late 1940s a resolving power of one degree was considered to be ‘high’.
The Llanherne Low Frequency Radio Telescope
Authors: Ellis G. R. A.
Published: July 2016

A large proportion of the easily accessible radio astronomy spectrum lies between 50 MHz and a lower limit of about 1 MHz set by interstellar absorption. The features of the spectrum in this frequency range, from sources such as the galaxy, extragalactic sources, pulsars, the Sun and Jupiter, remain only partially explored mainly owing to the large sizes of telescopes necessary to obtain adequate angular resolution and sensitivity. In addition, below 20 MHz, interference from man-made radiation and from the ionosphere severely hinders observations. At the lowest frequencies, the effects of the ionosphere can be overcome by using earth satellite telescopes at the expense of greatly increased difficulty in attaining sufficient telescope aperture.
On the Interpretation of Solar Radio-Burst Positions in a Scattering Corona
Authors: Riddle A. C.
Published: July 2016

Current observations and theories of solar bursts of types I, II and III suggest that the observed radiation may be emitted at a frequency close to the (fundamental) plasma frequency or its second harmonic. Refraction in a spherically symmetric corona would prevent radiation at the plasma frequency from reaching the observer except when the source is near the centre of the solar disk. However, it is found that fundamental frequency bursts are observed from anywhere on the disk. Recent analyses by Steinberg et al. and Riddle, in which the scattering of the radiation by coronal inhomogeneities was considered (in addition to refraction in an otherwise spherically symmetric corona), show that the radiation can escape from the plasma level and be observed for sources positioned almost anywhere on the disk. In addition, these authors and Fokker showed that a point source of radiation at the plasma frequency, or its harmonic, would be observed as an extended source with dimensions comparable with those observed. One implication was that the true source size is much smaller than the observed size.
Supersonic Convection and the Structure of T-Tauri Stars
Authors: Prentice A. J. R.
Published: July 2016

It is generally agreed that T-Tauri stars are very young stars of solar mass which are still engaged in the process of gravitational contraction toward the main sequence (Ambartzumian, Herbig).
The Evolution of Stars to the White Dwarf Stage
Authors: Wegner Gary
Published: July 2016

That the parent masses of white dwarf (WD) stars can exceed the Chandrasekhar limit of approximately 1.2 can be seen from star clusters that have turn-off points in excess of this mass and still contain WD. Auer and Woolf argued that WD in the Hyades and Pleiades is evidence that stars with masses larger than 2.5 can become WD. Sandage and Jones have used the luminosity function to compute the number of WD expected in several clusters. Jones estimated that the brighter of the two WD sequences arises from stars of mass greater than 1-9 Schwarzschild, for example, has stressed the importance of a knowledge of the resulting mass-loss. Deutsch has discussed mass-loss from red giants and Faulkner has summarized the relationship between the planetary nebulae and the WD. Nevertheless, the role of WD formation in the enrichment of the interstellar medium and the relationship between WD and their parent stars is unclear.
Dynamic Spectra of Jupiter Radio Bursts
Authors: Ellis G. R. A.
Published: July 2016

Extensive observations of the spectra of the decametric radio bursts for Jupiter have been made by Riihimaa, principally at frequencies between 18 and 23 MHz and with frequency resolution of 50 kHz. These showed much fine frequency-time structure in the bursts but pointed to the need for higher frequency resolution and greater antenna sensitivity. This paper reports the results of observations made of the Jupiter bursts between February and April, 1972, using the Llanherne low frequency telescope (Ellis,).
The Position of a Type I Storm Source in the Magnetic Field of an Active Region
Authors: Dulk G. A. , Nelson G. J.
Published: July 2016

Type I storms generally occur in association with large sun-spots and the radiation is usually circularly polarized. Statistically it has been found that the sense of polarization, right-hand (RH) or left-hand (LH), usually corresponds to the ordinary magneto-ionic mode in the field of the dominant spot of the active region; when a following spot dominates, the polarization tends to be determined by this spot rather than by the leading field. One-dimensional position measurements show that the type I sources are usually not radially above the active region but are displaced by a few minutes of arc. The source sizes are about l′.2 to 4′.5 at 169 MHz and the sources frequently contain double, multiple or bipolar structure at 80 and 160 MHz.
Supersonic Turbulent Stress and the Solar Neutrino Flux
Authors: Prentice A. J. R.
Published: July 2016

Some while ago (Prentice 1973a) I demonstrated that if the present Sun were to possess a small burnt out central core of mass 2-3% M⊙ its neutrino flux would be a factor 10 or so smaller than that of conventional homogeneously evolved solar models. It was not, however, conclusively shown what conditions might lead to the formation of such a core or indeed whether a burnt out core could be attained after 4.7 × 109 yr. of nuclear evolution. In this connection Demarque et al. (1973) has considered the evolution of an initially inhomogeneous model consisting of a hydrogen free core surrounded by a homogeneous envelope.
Cosmic Ray Stömer Cut-offs on the Surface of Jupiter
Authors: Cooke D. J.
Published: July 2016

It has recently been reported (Cini-Castagnoli et al. 1973; Jacklyn and Cini-Castagnoli, 1974) that Jupiter may be responsible for a modulation component in the counting rate of underground cosmic ray detectors on the earth. The evidence suggests that a screening mechanism is operating, in as much as the observed counting rates are diminished when Jupiter is within the field of view of these detectors. The magnitude of the effect is larger than can be accounted for by simple line-of-sight obscuration by the planet itself, and it has been suggested that the intense and extensive Jovian magnetic field is producing the effect.
The Solar Neutrino Problem
Authors: Faulkner D.J.
Published: July 2016

A few years ago Fowler (1972) published a paper in which he proposed two ‘desperate explanations’ for the solar neutrino problem. Desperation continues to be characteristic of the subject, for, in spite of many investigations over recent years, there is still no unambiguously successful model satisfying all the observational features of the Sun and giving a predicted neutrino count rate below the Davis (1972) experimental limit.
High-Resolution Observations of Centaurus-A and Pictor-A at 160 MHz
Authors: Slee O.B. , Sheridan K.V.
Published: July 2016

Since early 1974 the radioheliograph operated by the Division of Radiophysics at Culgoora, N.S.W. has been used in a 160 MHz study of ~2000 catalogued sources in the declination range -46° to +35°. In addition to measurements of flux densities and accurate positions at 160 MHz, brightness distributions are obtained for the sources that can be resolved by the 1’.9 × 1’.9 arc beams. A comparison of the brightness distributions at 160 MHz with those obtained from high-frequency measurements with similar angular resolution can yield valuable information about the energy distribution of the relativistic electrons, which are believed to be responsible for the radio emission from most nonthermal sources. Among the first objects to be examined were the strong southern radio galaxies Centaurus-A and Pictor-A.
Jupiter’s Rotation Period from Dekametric Observations 1951-1975
Authors: Duncan R.A.
Published: July 2016

Prompted by recent moves to ask the International Astronomical Union to redefine the System III rotation period, we have used all available dekametric observations from 1951 to 1975 and new analysis methods in an attempt to improve our estimate of the Jovian dekametric rotation period.
Cross Correlation Studies of Stellar Variability using two Telescopes
Authors: Edwards P.J. , Hurst R.B. , Christie G.
Published: July 2016

The study of short time scale phenomena of astronomical interest is often handicapped by the presence of wide band noise. In particular, in the study of the optical variability of stars, such noise arises from atmospheric scintillation, extinction variations, sky radiance variations and photon statistics. For example if in order to resolve rapid stellar variability we reduce the length (T) of the time intervals over which a photometric record is integrated and sampled, we find that the fractional noise fluctuations increase, eventually obscuring any intrinsic variability.
Multi-Frequency Heliograph Observations of Type II Bursts
Authors: Nelson G.J. , Robinson R. D.
Published: July 2016

Multi-frequency observations with the Culgoora radioheliograph (Wild 1967); Sheridan et al. 1973) of five solar bursts of spectral type II (Wild et al. 1954) have now been analysed. The spectra of all five bursts show split-banded harmonic structure. Each type II burst passed through only two of the heliograph’s three observing frequencies (160, 80 and 43.25 MHz). Relationships between the positions, sizes and brightness temperatures of the various sources in each burst are presented and summarized; their implications for the propagation of shock waves and radio waves in the solar corona are briefly discussed.
Solar Flare Continua at the Metre Wavelengths
Authors: Robinson R.D. , Smerd S.F.
Published: July 2016

The term ‘flare continuum’ (denoted by FC) was introduced by Wild (1970) to describe a strong, stationary continuum source at the metre wavelengths which occurs early in some flare events, particularly those of high energy. The flare continuum is distinct from the ‘storm continuum’ (SC), which occurs late in some flare events, becomes strongly circularly polarized and may continue as a ‘storm’. Both had previously been referred to as ‘stationary type IV’ bursts, to distinguish them from the original ‘moving type IV’ burst, IVM.
A Versatile Multi-Mode Fabry-Perot Instrument
Authors: Dopita Michael A. , Hart John A.
Published: July 2016

Fabry-Perot instruments have been extensively used for many years for the study of spatially extended emission nebulae because they offer a potential luminosity resolution product (L × Rpot) which exceeds by a high factor tha attainable by aerating spectrometer. Meaburn (1970) shows that this product is given by the relation

where P is the number of resolution elements each containing a maximum solid angle, Ω observed simultaneously, ti is the refractive index of the medium between the plates, A is the acceptance area of the device, εo is the transmission coefficient of the associated optics and εF the transmission coefficient of the Fabry-Perot (which if coated with dielectric multilayers can be very high).
Weak OH Masers in the Direction of H20 Masers
Authors: Haynes R. F. , Caswell J. L. , Goss W. M.
Published: July 2016

Most of the known 1.35 cm water vapour masers have been detected in the direction of known 18 cm OH masers. However, a small number have been found in the direction of HII regions where no OH maser is known. Several new examples of H20 masers with no known OH counterparts have recently been published by Kaufmann et d. (1976), who suggest that these constitute a new class of H20 maser.
First Results of a Survey of Neutral Hydrogen in 500 Southern Galaxies
Authors: Woerden Hugo van , Goss W. M. , Mebold U. , Siegman Betty , Hawarden T. G.
Published: July 2016

Observations of the 21 cm line of neutral hydrogen can provide several integral properties of galaxies. The systemic velocity Vsvs indicates the distance Δ via the Hubble relation or through group membership. The integral over velocity of the flux density profile, ∫S dV, immediately yields the amount of neutral hydrogen in the galaxy: MH ∝ Δ2∫S dV (neglecting optical-depth effects). The profile width W and the inclination i (derived from the optical axial ratio), together with the (optical) angular diameter a, supply the ‘indicative mass’ Mi ∝ (W/sin i)2 a △ (Bottinelli et al. 1968; Balkowski 1973), which is a fair estimate of the total mass of the system. In addition, as shown by Tully and Fisher (1976), the profile width is a good indicator of luminosity L. The quantities and L, which are (at least roughly) representative of the amounts of matter and of gaseous and luminous material in the system, give an indication of its composition. Together with the linear diameter a△, these quantities contain clues as to galaxy formation and evolution.
Deep Surveys with the Molonglo Radio Telescope
Authors: Robertson J. G.
Published: July 2016

Four catalogues based on the survey made with the Molonglo Cross-type radio telescope have so far been completed, the largest of which is MCI (Davies, Little and Mills,
1973). These catalogues were noise limited and had a 5α lower limit of about 0.3 Jy. This paper gives an outline of deep surveys that have been made in order to reach significantly fainter sources, but only in a small solid angle of sky.
Mass Loss from Stars
Authors: Morton Donald C.
Published: July 2016

The visual spectra of some hot stars, including P Cygni, have emission with associated absorption troughs ˜ 102 km s-1 on the short-wavelength side (Beals 1929, 1951). These P Cygni profiles are easily understood in terms of mass flowing away from the star. Later, rocket observations of the far-ultraviolet resonance lines (Morton 1967) showed that the phenomenon is rather common among hot stars and the velocity shifts could be from 1000 to 3000 km s-1, demonstrating that the mass must be escaping from the star. Resonance lines provide the strongest absorption in the shell where neither the density nor the radiation field is high enough to leave many ions in excited states. Since the ion stages likely to be present around a hot star have their resonance lines shortward of the atmospheric cutoff, space observations are essential in this investigation. Figure 1 shows the P Cygni profile of O VI in ς Pup obtained with Copernicus satellite spectrometer.
Fourier analysis of Beat Cepheids
Authors: Faulkner D. J.
Published: July 2016

The double-mode or beat Cepheids form a group of some 10 variables at the short period end of the classical Cepheid period range, which exhibit two (or three) simultaneous pulsations with remarkably constant period ratio (see Table I). If, as seems likely, the two periods (P0andP1,) are to be identified with fundamental and first-overtone radial oscillations, linear pulsation theory may be used to yield a mass and a radius estimate for each beat Cepheid(MbearandRbeat)based on period observations alone. The masses so obtained may be compared with two other Cepheid mass estimates: thepulsation mass, Mpuls, is derived by the application of pulsation theory tooneobserved stellar period (usuallyP0) and a radius calculated from the stellar luminosity and temperature; theevolutionary mass, Mevol, is inferred from the stellar luminosity by the application of stellar evolution results (without mass loss) for Population I stars in the core helium-burning phase. If a Cepheid is a member of a cluster or association whose distance and reddening have been determined, the Cepheid luminosity and temperature may be obtained observationally, yieldingMpuls, andMevolestimates directly. For other Cepheids, only indirect estimates may be made, based on the period-luminosity-colour relationship calibrated using the Cepheids with cluster membership.
The Possibility of Detecting DC
Authors: Witte N. S. , Brown R. D.
Published: July 2016

IRC + 10216, a bright infrared late type carbon star, is observed to have millimetre range line emission of the species 12CO, 13CO, CS, C2H, HC3N, CN, HCN, SiS and SiO in an extended envelope around the central infrared sources. The infrared emission arises from two concentric dust shells around the star: an inner 0”.2 arc radius shell of 600 K and optically thick, i.e. radiating as 600 K black body, and an outer shell 1″.0 arc radius at 375 K and optically thin for λ ≳ 2μ. A model explaining the line emission in terms of infrared pumping between the two lowest vibrational levels, first proposed by Morris (1975a) for IRC + 10216, was used to calculate antenna temperatures for various rotational transitions of HC3N; since there is a prima facie agreement between the calculated and observed values for HC3N we have attempted the same calculation for DC3N.
H2CO and OH Observations of a Molecular Cloud near RCW 36
Authors: Whiteoak J. B. , Gardner F. F.
Published: July 2016

Many cold molecular clouds have been detected as a result of their association with dense optical obscuration. The HII region RCW 36 is contained within a prominent dust lane extending several degrees along a line of almost constant right ascension (see e.g. Rodgers et al. 1960). By means of H2CO and OH observations we have found that this lane is associated with a dense elongated molecular cloud.
Entropy and the Spontaneous Emission of Plasma Waves
Authors: Grognard R. J. M.
Published: July 2016

The emission of plasma waves by beams of electrons travelling in a plasma is a phenomenon of critical importance in applied plasma physics (for instance in problems directly related to the achievement of controlled nuclear fusion) and also astrophysical research (e.g. in the theory of solar radio bursts). In principle, the mechanisms involved are all contained in the Boltzmann-Vlasov equation, where the field is the self-consistent electromagnetic field produced by the interaction between beam and plasma. Unfortunately this celebrated equation cannot be solved directly, because both the analytical and numerical methods that can deal with this equation are plagued by secular terms which restrict the time domain of validity of the solutions to a few thousand plasma periods. In all applications of interest this domain is far too small; indeed in all astrophysical cases it is quite negligible compared with the duration of the observed phenomena (it is even much shorter than the time resolution of present-day equipment, such as dynamic spectrographs).
Radio Evidence on the Particle Distribution Functions in the Corona following Flares
Authors: Dulk G. A. , Melrose D. B. , Smerd S. F.
Published: July 2016

In this paper we summarize the results of radio studies of the distribution functions (number, energy distribution and pitch angle distribution) of the energetic particles that are produced at the time of solar flares. We consider the clues and constraints they impose on the mechanisms of acceleration, bearing in mind that radio evidence implies that there are at least two stages of acceleration in many flares.

In the following sections we discuss the distribution functions of the particles resulting from (a) first phase acceleration, (b) first and/or second phase and (c) second phase acceleration. Table I summarizes the results.
The Measurement of f-values for Lines of Astrophysical Interest by Beam-Foil Spectroscopy
Authors: Ross J. E. , O’Mara B. J.
Published: July 2016

The necessity of having accurate oscillator strengths in astrophysical applications is well known. The apparent discrepancy which existed between the solar and meteoritic abundance of iron is just one example of the problems which can arise from poor f-values. An excellent critique of methods for determining both absolute and relative f-values has been given by Blackwell & Collins (1972). Their comments on life-time techniques provide a clear indication of both the advantages and difficulties associated with these techniques: “In principle, a life-time method, as exemplified by the technique of beam foil spectroscopy, described for example by Wiese (1970), has the fundamental advantage that in some restricted circumstances its application does not depend upon a temperature measurement or any assumption of themodynamic equilibrium in the source: in addition it gives an absolute result without the need of an absolute number density of atoms. The hope is sometimes expressed that the method of beam foil spectroscopy will yield oscillator strengths of the required accuracy. In practice, the technique suffers from the difficulty that although the life-time of an excited state can be measured with reasonable accuracy, it is also necessary to measure in a separate experiment the branching ratios for radiative de-excitation. As these ratios are usually measured by an arc method, the accuracy of the final oscillator strengths is limited by the deficiencies of this source. Also, some atoms in the beam may be excited to higher levels than the one being examined, and because of the nature of the initial excitation is unknown, radiative de-excitation (cascading) takes place to this lower level in a way that is wholly unpredictable. This difficulty is especially important for levels of low excitation.” In this talk techniques will be described for overcoming the cascading problem in beam foil spectroscopy and for measuring the associated branching ratios.
Voyager and the Origin of the Saturnian System
Authors: Prentice A. J. R.
Published: July 2016

As Voyager 1 sailed through Saturn’s system of moons and rings last November 1980 it revealed new worlds not seen by man before. For centuries, since Galileo’s first telescopic observations in 1610, the satellites of Saturn had been no more than pin points of light, whilst the structure of the rings was barely resolved beyond 3 principal bands. Yet, within the space of a few hours, that picture changed dramatically as the images of these objects grew through Voyager’s cameras from mere specks into full and wondrous worlds. These pictures contained features that were not only intricate and astonishing in detail but which were, in many cases, unfamiliar and unexpected. A composite view of the Saturnian system as seen by Voyager 1 appears in Figure 1. Saturn’s rings, once thought to be broad belts of particles spread uniformly thin through billions of years of evolution and interparticle collisions, were found to be divided into hundreds of individual ringlets (Figure 2). And Cassini’s Division, a region which had been previously thought to be empty because of a ‘sweeping’ influence of Mimas, was found to contain many ringlets itself! The appearance of light and dark radial spokes in the B ring, which rotated with a velocity contrary to the law expected of Keplerian orbits, was baffling. And the F ring (Figure 3) was found to contain knots, kinks and braids which probably indicated the presence of electro-magnetic forces as well as gravitational forces (Smith et al. 1981).
Are we falling into the Virgo Cluster?
Authors: Visvanathan N.
Published: July 2016

One of the important discoveries of astronomy is that the Universe expands: distant galaxies have large recession velocities in direct proportion to their distances. Attempts to determine a global value for the constant of proportionality between the velocity and the distance (Hubble constant) are met with difficulties by the presence of peculiar, random and streaming motions in the local region. These peculiar motions are either of primordial origin or the effect of density perturbations. These affect the mean velocity of the nearby groups in the level of 50-100 km/sec (Tammann, Sandage and Yahil 1980). However, the expected peculiar gravitationally induced motion of the Local Group towards the Virgo cluster, could be large due to the high density contrast in that direction (Sciama 1967; de Vaucouleurs and Peters 1968; Sandage, Tammann and Hardy 1972; Jones 1976). This infall motion could be as high as 500 km/sec if the anisotropy of the microwave background is interpreted to have a component of our peculiar motion towards the Virgo cluster (Peebles 1971, Boughn, Cheng and Wilkinson 1981; Gorenstein and Smoot 1981).
High Resolution 2-D Imaging Polarimetry of the Jet of M87, in the Light of U, B and V
Authors: Visvanathan N. , Pickles A. J.
Published: July 2016

The polarisation observations of the central region (containing the jet) of the galaxy M87 were obtained in May 1980, with the polarimeter (Visvanathan 1972) attached to the f/15 cassegrain focus of the AAT. The IPCS was used in direct mode to record the images of the field. Figure 1 shows a single, raw image of M87 in the light of B (the image shown is 90 arcsec square). The knots referred to in the text are marked. One complete observation consists of 12 images of the object field, corresponding to the 12 selected position angles of the polaroid filter, rotated from 0° to 330° in 30° increments. The Taurus software (Taylor and Atherton 1980) was used to increment the data to the relevant memory location. The data were stored on tape after a sufficient number of complete rotations of the polaroid were completed.
The Effect of Neutrinos on the Formation Time of Rich Clusters of Galaxies
Authors: Lewis B. M.
Published: July 2016

Both the radial and the velocity distributions of galaxies within rich clusters are well described by the isothermal distribution (e.g. Lewis 1978 and 1979). It is tempting to ascribe this apparently relaxed state to the operation of Lynden-BeU’s (1967) violent relaxation mechanism, during the initial coherent collapse on the proto-cluster, after it brakes itself against the universal expansion. This scenario explains the isothermal distribution observed in elliptical galaxies and globular clusters. When applied to a cluster of galaxies made up of baryons, however, the timescale for the scenario is comparable with the Hubble time H−1. The situation changes if most of the cluster mass is contributed by neutrinos.
The Neutrino Content of Elliptical Galaxies
Authors: Lewis B. M.
Published: July 2016

Current results from the experiment by Reines et al (1980) on the oscillation of neutrinos from one flavour to another, if confirmed, require a non-zero rest-mass for the neutrino. Corroborative evidence can be adduced from the astrophysical consequences. In particular, the long-standing ‘missing light’ paradox in rich clusters of galaxies is solved (c.f. Cowsik and McClelland 1973), and more recent difficulties in reconciling the chronology of the Universe with both the primordial abundance of He4 and the cosmological mass density are eased (c.f. Symbalisty et al 1980). Finally Lewis (1981) shows that the concept also solves the problem of obtaining dynamically relaxed clusters of galaxies with feasable formation times. As a result, elliptical galaxies are necessarily formed from the material of a proto-cluster amid a high density of low-velocity neutrinos. This paper makes a preliminary estimate of the maximum neutrino content of elliptical galaxies.
A Cyclotron Theory for the Beaming Pattern of Jupiter’s Decametric Radio Emission
Authors: Hewitt R. G. , Melrose D. B. , Rönnmark K. G.
Published: July 2016

Ground-based observations of Jupiter’s decametric radio emission (DAM) have been reviewed by Ellis (1965), Warwick (1967, 1970) and Carr and Gulkis (1969). A startling feature of DAM is the modulating effect of Io, and interpretation of the Io effect has dominated theoretical discussions of DAM until quite recently, specifically until the fly-by s of Voyagers 1 and 2. The Voyager data showed that the DAM appears as nested arcs in the frequency-Jovian longitude plane (Warwick et al. 1979, Boischot et al. 1981). The interpretation of this arc structure has been of primary theoretical interest over the past two years. The most widely adopted explanation is that the emission from each point is confined to the surface of a hollow cone (Goldstein and Thieman 1981). This idea is not new: emission on the surface of a cone was discussed by Ellis and McCulloch (1963); Dulk (1967) derived detailed parameters for the cone (half angle 79° width 1°) from the occurrence pattern of DAM; and Goldreich and Lynden-Bell (1969) presented a theoretical interpretation of it. More recently Goldstein et al. (1979) used observational data on the Jovian magnetic field in deriving properties of the required emission cone. It seems that one requires the properties of the emission cone to vary with position in the Jovian magnetosphere to account for the nested arc pattern (Goldstein and Thieman 1981; Gurnett and Goertz 1981).
Growth of Planetesimals in a Gaseous Ring
Authors: Hourigan K.
Published: July 2016

The aggregation of a large number of planetesimals into a single body is a problem that has proved to be a stumbling block for many theories of planetary formation. This difficulty has mainly arisen because of the tendency of an orbiting stream of bodies to disperse over the equatorial plane as a result of the combined effects of collisions and gravitational interactions (Trulsen 1972; Brahic 1975). Once such a chaotic distribution of orbiting bodies has developed, it is extremely difficult for these bodies to subsequently accumulate into a single entity. This problem does not arise, however, when aggregation takes place within a differentially rotating gaseous ring as proposed by Prentice (1978). It has been shown previously (Hourigan 1977) that the gas drag overcomes the disruptive nature of collisional interactions, resulting in the formation of a thin concentrated torus of orbiting bodies.
The Solar Neutrino Problem Revisited
Authors: Lattanzio J.
Published: July 2016

The discrepancy between the observed and predicted flux of neutrinos from the Sun is well known. Past attempts at reconciling this difference have been unconvincing (Kuchowicz 1976, Rood 1978), and hence investigations in this area continue.