Showing papers in "Publications of the Astronomical Society of Australia in 1968"
TL;DR: In this paper, a pinhole camera with resolutions better than 10−3 rad is presented. But the apertures are very small, not greater than about 10−4 cm2.
Abstract: In comparison with all other branches of astronomy, X-ray astronomy suffers from a relative dearth of image forming devices. No X-ray lens is known and image formation by reflection requires glancing incidence optics which have small fields of view and are extremely difficult to fabricate, even for the small apertures (about 2 cm2) now employed. The only other imaging device which has been successfully employed is the simplest of all, the pinhole camera. Pinhole cameras with resolutions better than 10−3 rad are easily constructed, but the apertures are very small—not greater than about 10−4 cm2. The new instrument described here is closely related to the pinhole camera and may be viewed as an attempt to overcome the aperture restrictions of this simple device.
144 citations
18 citations
12 citations
11 citations
TL;DR: In this paper, the primordial solar system chemical composition for studies of origin and evolution, compiling solar composition data is presented, which is used for the study of origins and evolution of the solar system.
Abstract: Primordial solar system chemical composition for studies of origin and evolution, compiling solar composition data
11 citations
TL;DR: In this article, the authors observed a flare event with the 80 MHz Culgoora radioheliograph consisting of a sequence of two type II bursts followed by enhanced emission possibly of type IV.
Abstract: On 17 June 1968 we observed a flare event with the 80 MHz Culgoora radioheliograph consisting of a sequence of two type II bursts followed by enhanced emission possibly of type IV. In this paper we shall attempt to summarize some ofthe profuse data collected by the radioheliograph during this event and relate it to data from the radiospectrograph and Hα films of the associated flare (the Hα films were kindly made available by the Division of Physics, CSIRO).
7 citations
6 citations
6 citations
6 citations
TL;DR: In this article, the Henyey method was used to obtain the evolution of stellar models for stars of mass 0.8 M, 0.9 M and 1.0 M. The starting point of each sequence is a star with a core of carbon and oxygen, comprising 25% of the star's mass, surrounded by helium-rich material.
Abstract: Evolutionary sequences of stellar models have been obtained, using the Henyey method, for stars of mass 0.8 M⊙, 0.9 M⊙ and 1.0 M⊙. The starting-point of each sequence is a star with a core of carbon and oxygen, comprising 25% of the star’s mass, surrounded by helium-rich material. It is assumed that any remaining hydrogen-rich material has been ejected in the form of the planetary shell. The star contracts gravitationally until helium ignites in a shell at the composition discontinuity, and the subsequent evolution of the shell burning has been followed. No neutrino-loss processes have been considered in this investigation.
5 citations
TL;DR: The most plausible hypothesis is that we are dealing with naturally occurring interstellar gas masers as mentioned in this paper, and some of the latest evidence we have in favour of the maser action is presented in this paper.
Abstract: Since 1965 we have been unravelling the curious properties of the intense 18 cm emission lines observed from OH molecules. We are still without a quantitative theory of the emission that might tie the threads together and provide guidelines for the observational work. The most plausible hypothesis is that we are dealing with naturally occurring interstellar gas masers. I want to present some of the latest evidence we have in favour of the maser action, and to indicate where it is inadequate. I will concentrate on work done in 1967, as the earlier work has been discussed in detail elsewhere.
TL;DR: In this article, a preliminary series of observations of the Sun made at a frequency of 80 MHz with the 3 km radioheliograph of the Culgoora Observatory is described.
Abstract: This paper describes a preliminary series of observations of the Sun made at a frequency of 80 MHz with the 3 km radioheliograph of the Culgoora Observatory. The instrument records, at one-second intervals, pictures of the solar image in the form of 60 (E-W) × 48 (N-S) points, each separated in angle by half the Rayleigh limit (2’ arc in the zenith). At the time of the present observations the instrument was incomplete in three main respects : (a) the facilities for recording opposite senses of circular polarization were not available; (b) the automatic image compensation for zenith-angle foreshortening was not available—hence the optical disk of the Sun appears elliptical; and (c) the phase and amplitude calibration procedures had not been fully established, resulting in a higher sidelobe level than that specified in the design—the effects are sometimes evident in the pictures as spoke-like brightenings.
TL;DR: In this article, a radio-astronomical observation in its most complete form is a determination of intensity and polarization as functions of frequency /, time t, and position in the sky.
Abstract: A radio-astronomical observation in its most complete form is a determination of intensity and polarization as functions of frequency / , time t, and position in the sky. An actual observation is usually much less complete. Apart from the well-reviewed spectral lines radiated by bound electrons in neutral atoms or molecules, the electromagnetic radiations observed by radio astronomers are the distant fields due to currents in astrophysical plasmas. The macroscopic currents consist of moving electrons, or other microscopic charges. A moving electron radiates in proportion to the square of its acceleration; it is also accompanied by a radiation cone for any wave mode in which its instantaneous velocity, v, exceeds the phase velocity vPb i and it radiates at any velocity when it crosses a rapid change in dielectric constant. The radiation processes at uniform velocity are called Cerenkov and transition radiation respectively. Since /? = v/c < 1 and the real refractive index /i = c/vPb, the former occurs only when /j, > 1; the plasma may be uniform. The latter, on the other hand, requires for its existence a plasma of irregular dielectric structure, such as may be due to statistical fluctuations in electron density. These same fluctuations can scatter Cerenkov plasma waves, thereby allowing energy in longitudinal waves to escape from the plasma as transverse, electromagnetic radiation. In such plasmas the contribution from transition radiation is likely to be negligible. The radiation processes due to electron acceleration are called bremsstrahlung when the Coulomb force of individual ions deflects the electron in electron-ion encounters, and gyro and synchrotron radiation when the centripetal force experienced by a moving electron makes the charged particle gyrate about magnetic field lines. The radiation from electrons in general helical orbits in a magneto-plasma contains contributions from all radiation mechanisms. Which mechanism dominates depends on various factors, especially the electron energy E = wc/(l — /J)*, the pitch angle between the magnetic field B and the velocity v, the angle of observation 0 between the propagation vector k of plane waves oc exp i(k • r cot) and B, and the relative magnitude of hi ft > where / p = (eW/»)* is the plasma frequency (N being the particle density) and fB = eB/2nmc is the gyro frequency. When one mechanism clearly dominates, the radiation may properly be described as gyro radiation (E ;> we), synchrotron radiation (E > mc) or plasma radiation, which is understood to refer to electromagnetic radiation extracted from Cerenkov plasma waves (v > vPh) through scattering or wave-mode coupling. Bremsstrahlung, while accounting for practically all radiation from thermal plasmas in which/g < fv, is not likely to dominate in the more interesting non-thermal situations. It is not an efficient radiation process for energetic electrons because the faster the electron, the shorter the time spent in each encounter and the longer the mean free path.' For non-thermal electron distributions, say F(p, r, t), in phase-space and time the intensity of radiation may be far greater than the thermal component. In particular in the case of 'double-humped' distributions, such as may correspond to transient electron streams through an equilibrium background plasma, Cerenkov and gyroresonance radiation may be emitted coherently with the possibility of wave amplification which is limited only by non-linear wave-wave and wave-particle interactions.
TL;DR: In this article, a number of strong radio sources have been examined for structure with the 3'.5 beam of the 80 MHz radioheliograph at the CSIRO Solar Observatory, Culgoora, Australia.
Abstract: A number of strong radio sources have been examined for structure with the 3’.5 beam of the 80 MHz radioheliograph at the CSIRO Solar Observatory, Culgoora Contour maps of brightness distribution are presented here for the galactic source W44, and the extra-galactic sources Fornax A, Pictor A and 3C353; they are compared, where possible, with maps at other frequencies.
TL;DR: In this article, the authors considered the effect of rotation on relativistic stellar dynamics and found analogues of the Newtonian polytropic models and of Woolley's truncated Maxwellian systems.
Abstract: Recently the possibility has been raised of using general relativistic star clusters as models for quasi-stellar sources. The theory of static, spherically symmetric, collisionless star clusters has been developed within the framework of general relativity. In particular, analogues have been found of the Newtonian polytropic models and of Woolley’s truncated Maxwellian systems. However, in view of the importance of rotation on stability in relativistic astrophysical problems, it is of considerable interest to include the effect of rotation in relativistic stellar dynamics.
TL;DR: A survey of clusters of galaxies from Abell's catalogue has been carried out using the Mk II 11 cm receiver recently installed at Parkes as mentioned in this paper, although the sensitivity limit of the receiver is about one-sixth of that value.
Abstract: A survey of clusters of galaxies from Abell’s catalogue has been carried out using the Mk II 11 cm receiver recently installed at Parkes. For the present preliminary report only sources with flux densities down to about 0.3 f.u. will be considered, although the sensitivity limit of the receiver is about one-sixth of that value.
TL;DR: In this paper, the authors considered a very slow pulsar with a period of about 10 h or 35 000 s. Like pulsars, this emission period is known to a high order of accuracy (about 1 in 106).
Abstract: A precedent to the recently-discovered pulsed radio sources or ‘pulsars’ exists in our own solar system. Jupiter could be thought of as a very slow ‘pulsar’ having a period of about 10 h or 35 000 s. Like pulsars, this emission period is known to a high order of accuracy (about 1 in 106). One difference is that Jupiter emission is received over an appreciable part of this period (1/4 to 1/2 or more) compared with about 1/30 of a typical pulsar period (about 40 ms in 1.3 s). Both pulsar and Jupiter bursts have a microstructure of the order of milliseconds, suggesting similar sizes of instantaneous emission regions. In both, the intensity observed varies from period to period. Emissions from both have relatively strong circular-polarization components at times.
TL;DR: A review of the progress in the solar modulation of galactic cosmic rays can be found in this article, where the authors set out some of the advances in the basic theories and indicated why certain disagreements between convection-diffusion theory and observations are to be expected.
Abstract: This review is concerned mainly with the solar modulation of galactic cosmic rays and the progress that has been made since the Tenth International Conference on Cosmic Rays (Calgary, June 1967), My aim is to set out some of the advances in the basic theories; to indicate why certain disagreements between convection-diffusion theory and observations (noted in Webber’s invited review at Calgary) are to be expected; and to indicate some of the currently emerging areas of interest.
TL;DR: A natural introduction to this topic is a brief discussion of two phenomena observable in interplanetary space near Earth: the energetic storm particle event (ESPE) and the recurrent Forbush decrease as discussed by the authors.
Abstract: A natural introduction to this topic is a brief discussion of two phenomena observable in interplanetary space near Earth—the energetic storm particle event (ESPE), and the recurrent Forbush decrease.
TL;DR: The Molonglo fan-beam survey is a digitized survey carried out in March and April 1966, using the 1 mile E-W arm of the Molongla cross operating at 408 MHz.
Abstract: The Molonglo fan-beam survey is a digitized survey carried out in March and April 1966, using the 1 mile E-W arm of the Molonglo cross operating at 408 MHz. Three 1´.5 fan beams separated by 1´.5 in right ascension were used. The survey covered the region in right ascension from 10 h 30 m to 18 h 30 m and in declination from +18° to —40°. The region common to the 4C survey has been analysed and we have obtained right ascensions for the 4C sources.