bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Forbush-type Cosmic Ray Intensity Decreases Observed During Solar Cycle 21
Authors: Fenton A. G. , Fenton K. B. , Humble J. E.
Published: July 2016

Although transient decreases in cosmic ray intensity of the type first reported by Forbush (1937) have been observed and studied for more than 40 years using a variety of detectors at many locations, from medium depths underground to those on spacecraft far from Earth, the precise nature of the physical process causing these events is not yet clear (see, for example, McKibben 1981).
A Study of the Rapidly Rotating Variable Star HD 36705 (AB Doradus)
Authors: Innis J. L. , Robinson R. D. , Coates D. W. , Thompson K.
Published: July 2016

Photoelectric B and V light curves and high dispersion spectroscopic observations were obtained in 1985 February for the rapidly rotating spotted star HD 36705. The visual light range was about 0.09 magnitude, with a well correlated B-V change of approximately 0.04 magnitude, the star being redder when faintest. There is evidence for a broadband flare of ~0.05 magnitude in V and 0.07 magnitude in B. This occurred near maximum light.

Spectroscopic observations show a variation in the equivalent width of the Ca K emission by a factor of about two in antiphase with the photometric variations, maximum emission corresponding to minimum brightness. This is probably due to bright plages and enhanced chromospheric heating associated with the photospheric starspots.

High dispersion, high signal-to-noise spectroscopic observations confirm the presence of lithium λ 6708 as reported by Rucinski (1982, 1985).

Several interpretations of the nature of HD 36705 are discussed; however at present none is completely satisfactory and further observations are required. As the star is probably at less than 100 pc, a parallax determination may be possible, and could help answer many of the questions concerning HD 36705.
Interstellar Nal Absorption Towards the Stellar Association Ara OB1
Authors: Whiteoak J. B. , Gardner F. F.
Published: July 2016

Observations have been made of the interstellar D-line absorption of Nal towards a loose grouping of OB stars (containing the association Ara OB1 and probably the Hα emission regions RCW 107 and 108) centred at 1 = 337°.5 and b= -0°.5. The individual absorption spectra contain several velocity components which show well-defined groupings at –37, –18 and 0 km s-1. The corresponding median optical depths are 2, 7 and 6. The evidence indicates that both the –37 and –18 km s-1 Nal clouds are located in the Carina-Sagittarius spiral arm. Several HII regions are located at similar longitudes, but most are close to zero latitude and are more distant than the arm.

The association contains the galactic cluster NGC 6193. The results suggest that the turbulence seen optically towards this cluster has been caused by the interaction between two cloud groups moving towards each other at velocities of 10 to 15 km s-1.
Sky Brightness and Atmospheric Extinction at A.N.R.A.O., Parkes and Siding Spring Observatory
Authors: Payne Paul
Published: July 2016

In May 1984 site testing began for the Automated Patrol Telescope. A series of atmospheric extinction and night sky brightness measurements were made over the following year at Parkes and Siding Spring Mountain using B and V filters. Parkes revealed an extinction greater than that of Siding Spring and more prone to variation. Results for the night sky brightness indicated Parkes has a sky slightly brighter than that at Siding Spring. The paper discusses the procedures used for obtaining the results and their limitations.
An Australian Broad-band Satellite for X-ray Astronomy
Authors: Greenhill J. G. , Fenton K. B. , Sood R. K. , Tuohy I. R.
Published: July 2016

A broad-band (2-190 keV) Australian X-ray satellite could provide a spectral sensitivity substantially better than HEAO-1 or any presently approved spacecraft. It would be virtually unique by providing simultaneously data over a wide energy range with high sensitivity and energy resolution in the little measured region above 30 keV. These measurements are vital to our understanding of such diverse topics as the cyclotron line production mechanism in binary sources, the structure of the magnetosphere of neutron stars, the origin of the diffuse cosmic X-ray background and the nature of the giant power sources in active galaxies and stellar black holes. Details of the proposed spacecraft and scientific objectives are given.
Preferred Horizontal Scale for Thermal Convection
Authors: Fiedler R. , Murphy J. O.
Published: July 2016

Linear stability theory for Rayleigh-Benard convection shows that for a specified Rayleigh number, greater than some critical value, only a finite range of horizontal wave numbers support convective instability in a horizontal layer of fluid heated from below. However, it is not possible to predict the preferred horizontal scale of established motions from this approach although it is clear from observations, particularly of the solar surface, that a preferred cell size does prevail. In an endeavour to establish a preferred horizontal scale appropriate non-linear modal equations have been integrated forward in time, initially incorporating a discrete band of wave numbers equally spaced across the range that supports convection, for a specific Rayleigh number. The horizontal resolution was improved in subsequent integrations by first deleting modes that had substantially decayed and then introducing new modes on a finer horizontal mesh in the vicinity of what appeared to be the evolutionary dominant mode. Finally, the multimode integrations were continued in time until the evolution of a dominant horizontal mode from within the restricted range was evident. Both the model characteristics and numerical scheme adopted placed limits on the degree of horizontal refinement that could be undertaken with confidence.
The Source of Free Energy for Type II Solar Radio Bursts
Authors: Cairns Iver H.
Published: July 2016

A theory for the source of free energy for the Langmuir waves producing Type II bursts is presented. It is shown that electrons accelerated at the Type II shock naturally develop a distribution function with an abrupt cutoff at a characteristic minimum parallel velocity (a ‘cutoff distribution) in a limited spatial volume ahead of the shock, irrespective of the acceleration process active at the shock. The long duration, narrow bandwidth Type II radiation is then explained in terms of Langmuir waves produced by a cutoff distribution. The theory also accounts in a natural way for split-band Type II bursts and herringbone bursts.
The Parkes Radio Telescope — 1986
Authors: Ables J. G. , Jacka C. E. , McConnell D. , Schinckel A. E. , Hunt A. J.
Published: July 2016

The Parkes radio telescope was commissioned in 1961, with an anticipated operational life of 15 years. Twentyfive years later the telescope has been refurbished with the aim of extending its life yet another decade or two. A major undertaking has been the complete replacement of the drive and control System. This presentation outlines the main features of the new System and its effect on the observing facilities offered at the observatory.
X-Ray Observations of Supernova Remnants from the Einstein Observatory
Authors: Tuohy Ian R.
Published: July 2016

The most extensive studies of supernova remnants (SNRs) in the past have taken place at radio and optical wavelengths.
A Small Computer System for Radio Astronomy at the Tidbinbilla Tracking Station
Authors: Rayner P. T. , Batty M. J.
Published: July 2016

The Tidbinbilla NASA Deep Space Network tracking station near Canberra employs 64-m and 34-m antennas for deep space vehicle communication. Regular use is made of the facilities for radio astronomy via a host country agreement between the United States and Australia. To support the expanding astronomical use of the station, and in particular for the Tidbinbilla two-element interferometer (Batty et al. 1977), a small computer was installed early in 1980 to control observations. The system will also be used for as much data analysis as possible to minimize off-site computing.
The Polarization of Metre-Wave Solar Emission
Authors: Suzuki S. , Sheridan K. V.
Published: July 2016

Sources of the Type I storms are thought to lie on closed magnetic loop systems above bipolar sunspots. Usually one sunspot is stronger than the other in the bipolar magnetic structure, and accordingly only one radio source associated with the stronger sunspot is usually observed. Occasionally however a double radio source is observed in conjunction with the bipolar sunspots. In such a case the double radio source should be intrinsically bipolar, viz. the two components should emit opposite senses of circular polarization (in this paper we use the word polarity for simplicity).
Fine Spectral Structure of Solar Radio Storms
Authors: McConnell D.
Published: July 2016

As part of an investigation of solar radio bursts at high time (≈ 1 msec) and frequency (≈ 10 kHz) resolution, observations have been made between 30 MHz with the Llanherne broadband radio telescope (Ferris 1980). The radio frequency signals in the six frequency ranges 30-33, 33-36, 38-41, 54-57 and 79-82 MHz were recorded on six video tape recorders for about 10 minutes each day near solar transit.
The Emission Mechanism of Solar Moving Type IV Metre-Wave Radio Sources
Authors: Duncan R. A.
Published: July 2016

The term ‘moving Type IV’ denotes a spectacular class of solar event in which the radio source, beginning low in the corona, moves outward, typically at hundreds of kilometres per second (Wild et al. 1963).
Spectroscopic Abundance Determinations in M Supergiants
Authors: McGregor P. J.
Published: July 2016

The M supergiants are rare objects in the solar neighbourhood and consequently until recently their importance has been largely overlooked. It is now being realized that these stars hold the key to extragalactic distance determinations since they can be detected at large distances while the maximum luminosity they attain seems to be remarkably constant and independent of galaxy type (Sandage and Tammann 1974; Humphreys 1978, 1979a, 1979b; Humphreys and Davidson 1979). They are also important in their own right since they are massive stars in the late stages of their evolution and undoubtedly suffer from mass loss and chemical enrichment due to the mixing of processed materials to their surfaces. In this light they can be considered as precursors of the luminous carbon stars and supernovae.
Preliminary Observations of Interstellar Sodium D-Line Absorption towards the Carina Nebula
Authors: Whiteoak J. B. , Gardner F. F.
Published: July 2016

As part of a general investigation of interstellar clouds associated with southern HII regions we have begun a high-resolution study of the sodium D-line absorption in the directions of early-type stars that are likely to be associated with or located behind the clouds.
Observations of the 89 GHz Transition of HCO+ in Orion
Authors: Batchelor R. A. , McCulloch M. G. , Whiteoak J. B.
Published: July 2016

Observations of CO emission (Kutner et al. 1977) have delineated a molecular cloud extending over several square degrees in the Orion region, and extensive surveys have been made of several other molecules (e.g. CN, CS, HCN, H2CO, H2H+) in the densest regions of this cloud.
Comparison of the X-Ray Sources CIR X-1. GX301-2 and 2S0535-668
Authors: Duldig M. L. , Thomas R. M. , Haynes R. F.
Published: July 2016

There is reasonably strong evidence to suggest that the periodic X-ray, radio and optical variable Cir X-1 is a highly eccentric orbit (e ~ 0.8), binary system comprising an OB supergiant primary and a compact object, probably a neutron star (Whelan et al. 1977; Haynes, Lerche and Murdin 1980).
The Solar-stellar Connection: Magnetic Braking and Stellar Activity
Authors: Mestel L.
Published: July 2016

The theory of coronal structure and of the associated angular momentum transport by magneto-thermo-centrifugal winds is reviewed, with reference to recent observations of rapidly rotating late-type stars. In particular, the combined optical and X-ray studies of AB Doradus are consistent with the predicted picture of a hot, magnetically-controlled ‘dead zone’ in near corotation with the star, and of cooler wind-emitting regions (analogues of the solar coronal holes). The standard theory predicts a rate of angular momentum transport that depends on the extent of the wind zone, the relative importance of thermal and centrifugal driving, and the variation of the dynamo-built surface field with rotation. For stars like the Sun, with approximately one tenth of the mass in the convective envelope, detailed comparison of the theory with the observed rotations of stars in clusters of different ages is sensitive to the strength of the coupling between the envelope and the radiative core, and is constrained by helioseismological limitations on rotational shear within the present-day Sun. An inferred strong braking during the early epochs may hint at a non-standard braking model, with the Maxwell stresses dominant far from as well as near the stellar surface.
The Effect of Helium Shell Flashes on Asymptotic Giant Branch Evolution
Authors: Vassiliadis E. , Wood P.R.
Published: July 2016

Mass-loss has been incorporated into a series of evolutionary calculations of low to intermediate mass stars during Asymptotic Giant Branch (AGB) evolution. When helium shell flashes occur a superwind phase is a natural consequence of the mass-loss process. The structure of the stellar wind envelopes that result has been computed. The models may explain some previously curious features seen in OH/IR and CO line emission spectra.
Energy Dissipation due to Mass Loss in a Rotating System
Authors: Melrose D.B.
Published: July 2016

When a rotating magnetised system (angular speed Ω), such as a planet or star, loses mass there is necessarily an energy dissipation associated with the mass loss. Consider mass loss at rate M, such that the matter is flung off with the orbital speed ΩR1, at a radius R1 ≫ R0, where R0 is the radius of the planet or star. The power released is approximately equal to the power Prot = 1/2MΩ2R2 carried off in rotational kinetic energy. Part of the energy released is carried off as magnetic energy in the escaping plasma, and the remainder is released through dissipation of currents. Such dissipation plausibly leads to the acceleration of particles. The power released should be important for Jupiter and for some rapidly rotating stars. For most stellar systems, the power released is small compared to that required to drive a wind.
A Model for Intermediate Temperature Solar Coronal Loops
Authors: Brown S.F.
Published: July 2016

Simple hydrostatic equilibrium models have been very successful at describing the physical conditions in hot coronal loops (T > 106 K). However, equilibrium models of cooler loops predict densities that are much lower than observed. We follow the evolution of a hot loop which undergoes a sudden reduction in heat input. The physical conditions in the cooling loop show significant departures from equilibrium. Such models appear to be able to reproduce the physical conditions observed in intermediate temperature loops (105 < T < 106 K).
Proxy Data from Tree-ring Time Series for the Eleven-year Solar Cycle
Authors: Murphy J.O. , Veblen T.T.
Published: July 2016

Over past decades many attempts have been undertaken to detect a statistically significant 11-year variation in tree-ring widths and thereby provide direct evidence for the influence of solar cycle activity on growth. The data were generally associated with arid sites and were found to contain no signal of any consequence at the equivalent frequency. However, our recent analysis of a tree-ring chronology established from spruce trees growing at a very high sub-alpine site in Colorado, has revealed the presence of a dominant 11-year spectral periodicity over the last 200 years. These growth cycles could arise from temperature changes due to variations in insolation and climate or from variations in direct radiation within a specific band.
Redesigning a Baker-Nunn Camera for CCD Imaging
Authors: Carter B. D. , Ashley M. C. B. , Sun Y-S. , Storey J. W. V.
Published: July 2016

The University of NSW’s Automated Patrol Telescope is a modified Baker-Nunn satellite tracking camera, now used for CCD imaging of astronomical objects. The f/1 Baker-Nunn optical design gives a 30° field of view with an approximately spherical focal surface of radius ≈500 mm. While the focal plane curvature is tolerable across the 1.4° × 1.0° field of the present CCD, it becomes unacceptable when a larger CCD is used. In addition, the use of glass filters in the highly convergent beam produces intolerable spherical aberration. We present a design modification to the original Baker-Nunn which enables a 5° diameter flat field to be produced when using B, V, R or I filters. By making this modification, we plan to perform multicolour imaging, using a new large-format CCD with a 2.9° × 1.9° field of view.
The Laboratory Astrophysics Facility at University College
Authors: Hyland A.R. , Smith R.G. , Robinson G.
Published: July 2016

A laboratory astrophysics facility for the study of the terrestrial analogues of interstellar dust grains is being developed in the Physics Department, University College, Australian Defence Force Academy. The facility consists of a gas handling system for the preparation of samples, a closed-cycle cooler and specimen chamber, and a Fourier Transform Infrared (FTIR) Spectrometer capable of high resolution (0.3 cm−1) and high sensitivity measurements, currently from 1-25 μm. The layout and construction of the laboratory are described, and the proposed initial experimental program aimed at determining the optical constants of ices over a wide wavelength range for comparison with astronomical observations is discussed.
Towards a Unified Model of Active Galactic Nuclei
Authors: Coleman C.S. , Dopita M.A.
Published: July 2016

Active Galactic Nuclei (AGN) occur with widely differing characteristics of luminosity, variability and non-thermal emission. Although it is generally accepted that all such objects are powered by the accretion of matter to a super-massive black hole, no convincing model has been proposed which accounts for the diversity of observed phenomena. The model described here is based upon the hypothesis that shear flows in a misaligned accretion disc around a Kerr black hole lead to the growth of dynamical instabilities which disrupt the disc near the Bardeen-Petterson radius. Resulting clouds of disc material are fragmented by collisions and ablated by radiation from the compact core to produce a hot Parker wind which is optically thick to electron scattering. Within this wind, many fragments of disc material are entrained and photoionised to produce the broad emission lines, while some are accreted to power the system. Usually the wind impedes jet flows, in which case the object is radio quiet. When the disc and black hole are only slightly misaligned, however, the wind is equatorially biased and collimated axial jets may form. Such objects will be radio loud, and may exhibit superluminal phenomena if the jet is oriented close to the line of sight.
A New Infrared Camera Optical Design
Authors: Sun Y-S. , Ashley M.C.B. , Storey J.W.V.
Published: July 2016

We have designed a novel all-reflective optical system for an infrared camera. The camera gives a flat 5 arcminute field with a final focal ratio of f/2.5 when used at the f/15 focus of the Anglo-Australian Telescope (AAT). A 70mm diameter Fabry-Perot filter can be accommodated in a collimated beam, thereby giving narrow-band imaging capability. The design could readily be adapted to other telescopes and focal ratios. Its advantages are no chromatic aberration, no vignetting, no ghost images, low light-loss and excellent image quality.
Solar Radio Astronomy at the University of Western Australia, 1946-48
Authors: Burman R.R. , Jeffery P.M.
Published: July 2016

A small radio astronomy group led by S.E. Williams in the Department of Physics at the University of Western Australia operated in the pioneering days. Observations were made of solar radiation at 75 Mc/s (4 m), using a polar-mounted Yagi antenna on the University campus in the Perth suburb of Nedlands. The group produced four papers, three in Nature and a longer one published locally. Although the work was noticed internationally, its influence on the course of radio astronomy seems to have been slight, and even the existence of the group has been almost forgotten outside of its home department.
An Automatic Electronic Combined Blink-comparator and Measuring Engine
Authors: Thomas G. , Jones E. , Jones K. L. , Francis G. M. , Kingshott F. , O’Mara B. J. , Page A. A.
Published: July 2016

We have designed and manufactured a multi-purpose electronic, computer-operated blink-comparator and measuring engine. It has been specifically designed to facilitate the examination of stellar images on Uppsala Schmidt photographic plates, identify and establish coordinates of new suspect variable stars appearing on the plates being examined, and also to derive photometric values for those stars manifesting variability.
The Head—Tail Radio Galaxy B1610—605
Authors: Jones Paul A. , McAdam W. Bruce
Published: July 2016

The radio galaxy B1610–605 within the Abell cluster A3627 has a low-brightness tail extending at least 26 arcmin from the nucleus of the 14 · 5m galaxy. The structure of this tail has been explored using observations with the Molonglo Observatory Synthesis Telescope (MOST) and the Australia Telescope Compact Array (ATCA). We present details of the brightness, width and alignment of the tail. The single tail expands and brightens rapidly within 2 arcmin of the nucleus. Confinement by the pressure of the cluster medium maintains a low but constant brightness for the tail between 10 and 25 arcmin. There are indications of turbulence down the tail but the position of the ridge remains within 1 · 6 arcmin of the initial alignment throughout its length.
Supernova Remnants in the Large Magellanic Cloud
Authors: Dickel John R. , Milne D. K.
Published: July 2016

Twelve supernova remnants in the Large Magellanic Cloud have now been observed with the Australia Telescope. These were all imaged in total intensity and where possible the linear polarisation was also mapped. In many respects this survey is similar to previous single-dish observations of Galactic supernova remnants, and comparisons are made with these results. Preliminary images are shown for several sources. The survey is continuing with additional array configurations and at other wavelengths.
Peculiar Gas Dynamics in the Starburst Galaxy NGC 253
Authors: Koribalski Bärbel , Whiteoak John B. , Houghton Sally
Published: July 2016

Here we present our first results of a study of the neutral hydrogen gas (HI) in the southern spiral galaxy NGC 253 with the Australia Telescope Compact Array. The relative proximity of NGC 253 makes it a very suitable object for detailed studies of large-scale, as well as nuclear, gas dynamics. Several peculiar features have been found. The HI distribution is asymmetric in the outer regions, probably as a result of the strong warping of the spiral arms. A bar associated with the disc, clearly visible in the optical and near-infrared, also reveals its signature in the neutral hydrogen gas. HI absorption measurements reveal unusual motions of the gas in the nuclear region which seem to indicate a fast-rotating ring of cold gas as well as outflow of gas. Similar features have been found in other starburst galaxies, such as M 82, NGC 1808 and NGC 4945, and are interpreted in terms of bar-induced gas dynamics and star formation.
Feedback Mass Transfer in Cataclysmic Variables: An Explanation of the Behaviour of VY Scl Stars
Authors: Wu Kinwah , Wickramasinghe Dayal T. , Warner Brian
Published: July 2016

We investigate irradiation-driven mass transfer in cataclysmic variables in the presence of shielding of the radiation by an accretion disk. We have shown that the shielding can cause a temporal drop of 3–5 magnitudes in the brightness of systems with orbital periods shorter than about 4 hr. This provides a possible explanation for the brightness variations in the VY Scl stars.
The Magnetic Field of 1H1752+08
Authors: Ferrario Lilia , Wickramasinghe Dayal T. , Bailey Jeremy , Buckley David
Published: July 2016

We present spectropolarimetric observations of the eclipsing cataclysmic variable 1H1752+08. Modelling of the line intensity and polarisation spectra of 1H1752+08 shows that the magnetic field structure of the white dwarf is off-centre and the mean photospheric field strength is about 7 MG, the lowest measured in a cataclysmic variable (CV). We argue that 1H1752+08 is most probably a low-field AM Herculis system.
Effects on Seeing at the Anglo-Australian Telescope of Temperature Differences between Outside Air, Dome Air and Mirror
Authors: Wood P. R. , Ryan S. G.
Published: July 2016

Seeing measured in the open air with a differential image motion monitor (DIMM) is compared with seeing measured simultaneously at the Cassegrain focus of the Anglo-Australian Telescope (AAT). It is shown that when the mirror is hotter than the dome air, the AAT’s seeing is degraded by ~1 arcsec per Celsius degree of excess mirror temperature. The consequence of this is that mirror seeing currently contributes significantly to the seeing at the AAT on many nights. A mirror colder than the dome air does not seem to degrade seeing, and neither does an internal-to-external air temperature difference of up to at least 3°C when the venting fans are on.
Dark Matter: Abstracts from a Two-day Workshop held in February 1994 by the Australia Telescope National Facility
Authors: Koribalski Bärbel
Published: July 2016

A Dark Matter Workshop was held at the CSIRO Radiophysics Laboratory in Marsfield, Sydney, on 24–25 February 1994. The workshop, sponsored by the Australia Telescope National Facility (ATNF), was a meeting of dark matter (DM) specialists as well as astronomers interested in the field, and attracted about 80 participants from nine institutions. The program consisted of 22 oral contributions (15–45 minutes), followed by lively discussions, as well as podium discussions at the end of each day. Abstracts of most of the contributions are presented here, arranged by subject groups which range from ‘Gravitational Lensing and DM in Clusters’, ‘DM in Elliptical Galaxies’, ‘The Nature of DM’, and ‘The Shapes of Dark Halos’ to ‘Alternatives to DM’.
Visualisation of Radio Data
Authors: Oosterloo Tom
Published: July 2016

Radio astronomy software has not quite kept up with recent developments for the display of, and interaction with, data. At the Australia Telescope National Facility we are trying to catch up by investigating how useful visualisation techniques and approaches like visual computing are for the reduction of radio data. I will discuss a few techniques that we have applied to radio data and comment briefly on their merits.
JACARA’s Plans
Authors: Burton Michael G. , Ashley Michael C.B. , Storey John W. V. , Dopita Michael A. , Lançon Adriane , Mould Jeremy , Wood Peter R. , Hall Peter , Duldig Marc
Published: July 2016

The plans of JACARA, the Joint Australian Centre for Astrophysical Research in Antarctica, for Australian involvement in future astronomical activities on the antarctic plateau, are outlined.
An Automated Astrophysical Observatory for Antarctica
Authors: Storey J. W. V. , Ashley M.C.B. , Burton M. G.
Published: July 2016

Conditions on the high Antarctic Plateau would appear to be extremely favourable for a wide range of astronomical research. Before a decision can be made on constructing an observatory, data are required on site conditions at the most promising locations. To enable these data to be collected, a Lockheed Automated Geophysical Observatory is being purchased. This facility will be fitted with a suite of astronomical site-testing instruments, and deployed to several sites on the Antarctic Plateau. This program will allow a definitive assessment of the site conditions to be made by the end of this century.
Accretion Curtains in Magnetic CVs
Authors: Ferrario Lilia
Published: July 2016

We have carried out calculations to model the hydrogen emission line spectrum of intermediate polars with accretion disks. We show that we can explain most of the observed optical continuum and line fluxes in terms of hard and soft X-rays that originate from the accretion shocks and are reprocessed in curtains formed by magnetically channelled material.
Simulations of Quasi-periodic Oscillations in Accreting White Dwarfs
Authors: Wu Kinwah , Pongracic Helen , Chanmugam Ganesar , Shaviv Giora
Published: July 2016

The stability of accretion shocks in magnetic white dwarfs is investigated. Shock oscillations are simulated numerically, and in the simulations bremsstrahlung and cyclotron cooling are considered in an explicit form. We have found that for shocks with magnetic fields lower than 10 MG, shock oscillations can be sustained; while for magnetic fields greater than 20 MG, the oscillations are suppressed.
Langmuir Wave Emission by Neutrinos in a Medium
Authors: Hardy S. J. , Melrose D. B.
Published: July 2016

Expressions for the probability per unit time of the emission of a Langmuir wave by both massive and massless neutrinos moving in a medium are derived using finite-temperature field theory. A comparison between this process and the analogous emission from an electron is made, and possible implications of this process for the explosion mechanisms of type II supernovae are briefly discussed.
Axel: A Balloon-borne X-ray Astronomy Experiment
Authors: Sood R. K. , Panettieri J. , Grey D. , Woods G. , Hoffmann J. , Manchanda R. K. , Staubert R. , Kendziorra E. , Rochester G. K.
Published: July 2016

Following a successful program to investigate the physics of ultra-high-pressure proportional counters, a counter array has been developed for hard X-ray astronomy. A parallel investigation has evaluated the performance of a large-area phoswich scintillator detector for the same purpose. The two detectors have been integrated in a balloon-borne payload, the Astrophysical X-ray Experimental Laboratory (AXEL). This paper describes the instrumentation aboard the payload.
Millimetre-wave Astronomy: Abstracts from a One-day Workshop held on 19 April 1995 at the Australia Telescope National Facility
Authors: Koribalski Bärbel
Published: July 2016

A Millimetre-wave Astronomy Workshop was held at the CSIRO Radiophysics Laboratory in Marsfield, Sydney, on 19 April 1995. The workshop, sponsored by the Australia Telescope National Facility (ATNF), was a meeting of mm-wave specialists as well as astronomers and students interested in the field, and attracted about 80 participants from 13 institutions. The program consisted of 23 oral contributions (5–45 min) followed by lively discussions. Abstracts of most of the contributions are presented here, arranged by groups dealing with subjects such as ‘A Basic Introduction’, ‘Astronomy in the mm-range with Mopra’ and ‘Projects: Galactic and Extragalactic 3 mm-wave astronomy’.
Millimetre Continuum Observations of AGNs and IRAS Galaxies
Authors: Norris Ray
Published: July 2016

The 3 mm radio continuum emission from active galaxies consists of three components:

(1)

Synchrotron emission from the active galactic nucleus (AGN), which is over 1 Jy in 3C273 but which is not significant in most of the types of galaxy considered here.

(2)

Free–free emission from H II regions. The flux of this in a starburst galaxy is typically of the order of 10 mJy and could be imaged with a 3 mm-capable Australia Telescope Compact Array (ATCA).

(3)

Emission from the tail of the 50–100 K black-body spectrum of the dust. For example, the dust in Arp 220 (redshift of 0·02) at a temperature of 50 K has a flux of 30 mJy at 3 mm. Interestingly, this flux does not decrease substantially with redshift, as the decrease in brightness is compensated for by the redshifting of the steep edge of the blackbody curve, and so infrared-bright galaxies can be studied up to high redshifts with existing instruments.
Dust-reddened Quasars
Authors: Drinkwater M. J. , Webster R. L. , Francis P. J. , Wiklind T. , Combes F.
Published: July 2016

We have recently discovered evidence for a population of radio-loud quasars that is reddened by dust. The dust is either along the line of sight to the quasars or is associated with the quasars. In the latter case the dust may be in molecular clouds in the quasar’s host galaxy, or in a molecular torus around the nucleus. We are planning to use 3 mm observations to search for molecular absorption lines (CO and HCO+) associated with dust at the redshift of these quasars. If any absorption systems are detected we will be able to deduce detailed information about the physical state of the molecular gas, hopefully showing which of the proposed locations of the dust is most likely.
Elliptically Polarized Natural Modes in Pulsar Magnetospheres
Authors: Allen Michelle C. , Melrose D.B.
Published: July 2016

The most obvious feature of the polarization of the radio emission from most pulsars is the rotation of the plane of linear polarization across pulses. The original interpretation of this in terms of the magnetic pole model (Radhakrishnan 1969, Radhakrishnan et al. 1969, Radhakrishnan and Cooke 1969) accounts for the variation of position angle extremely well for some pulsars (e.g. Manchester and Taylor 1977, Manchester 1978). Conversely, this provides strong support for the magnetic pole model for pulsar emission. It also suggests that the emission is basically linearly polarized as implied by virtually all proposed emission mechanisms, e.g. the reviews by Ginzburg and Zheleznyakov (1975) and Arons (1979). However, there are two features of the polarization which require a separate explanation. First, some pulsars have a moderately high degree of circular polarization, even in the integrated pulse profile (Manchester 1971, Lyne, Smith and Graham 1971). In some pulsars the average degree of circular polarization can exceed the average degree of linear polarization, e.g. in PSR 0835-41 and 0959-54 (McCulloch et al. 1978). Second, some pulsars exhibit the phenomenon of transitions between orthogonal elliptical polarizations (Manchester, Taylor and Huguenin 1975, Backer, Rankin and Campbell 1976, Cordes and Hankins 1977, Cordes, Rankin and Backer 1978). In many pulsars the orthogonal polarizations have substantial circular components, e.g. in PSR 1133 + 16 (Manchester et al. 1975) and PSR 2020 + 28 (Cordes et al. 1978).
Correcting Low-Frequency Solar Radio Source Positions for Ionospheric Refraction
Authors: Stewart R.T. , McLean D.J.
Published: July 2016

We describe a method for reducing displacements in radio source positions caused by ionospheric refraction. Our method is an improvement on that used by Wild et al. (1959), who assumed all frequencies in the 40-70 MHz band came from the same position above the Sun and applied an f-2 correction for ionospheric refraction. Our method retains the dispersion of source position with frequency, which is inherent in the radio source, but allows for the f-2 ionospheric effect. We also discuss ways of estimating the absolute source positions from a knowledge of ionospheric density gradients. A typical example of ionospheric variations on solar records is shown in Figure 1(a). Here we have plotted the observed source positions on an f-2 scale. The measurements refer to a solar storm continuum burst which occurred on 1981 May 9 following an importance 2B flare at 08°N., 38°E., heliographic coordinates. From previous observations of such events we think it highly likely that the true source positions are stationary and displaced with decreasing frequency outwards along a line close to the radial direction above the flare. Figure 1(a) shows that: (a) the 160, 80 and 43 MHz source displacements vary as f-2; (b) there is a systematic slow drift of the source positions towards the south and east which increases with increasing hour angle; (c) superimposed on this steady drift is a quasi-periodic variation in source position with a period ~20 min.
The Main Sequence Evolution of Inhomogeneous Stars
Authors: Lattanzio J.
Published: July 2016

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.
Changing Depth of Minima of SV Cen
Authors: Kvíz Z.
Published: July 2016

The eclipsing variable SV Cen was observed differentially in the UBV system with the 60cm reflector at Perth Observatory (1974-75) and with the 41cm reflector at Siding Spring (1975-79). Individual measurements have either been published in the IBVS or will be published there soon.
The Light Variation of the Eclipsing Variable UX Eridani
Authors: Kennedy H.D.
Published: July 2016

The discovery of the variability of the eclipsing system UX Eri can be attributed to Soloviev (1937). Photographic observations were made by Zessewitsch (1934, 1954), Bodokia (1938) and Gaposchkin (1953). Photoelectric observations were obtained by Kitamura and Nakamura (1957). The most recent photoelectric data were obtained by Binnendijk (1967) who determined new orbital elements. During the 10-year period from 1967-1977 the variable appears to have received little attention.
Changes in the Period of the Eclipsing System AH Virginis
Authors: Kennedy H.D.
Published: July 2016

Guthnick and Prager (1929) were the discoverers of the variability of AH Virginis. Prager (1929) produced a photographic light curve the same year. Lause (1934, 1935, 1937) observed the system visually and improved the period as deduced by Prager. Further visual work on the system was done by Zessewitsch (1944). The first photoelectric observations came from Huruhata and Nakamura (1951), followed in 1952 by Kitamura, Tanabe and Nakamura (1957).

Lack of their data on ingress and egress at primary eclipse resulted in the mean curve showing a rounded bottom during minimum light. From this, an inclination of the system of 61° was derived by Kopal and Shapley (1956). Two years later, Kwee (1958) revealed primary minimum to be flat bottomed; the light remaining constant for some 40 minutes. This was confirmed by Binnendijk (1960), thus classifying AH Virginis as one of the few W UMa systems which display complete eclipses at an inclination likely to be closer to 90° then to 61°. Observations of the present study confirm constancy of light of 40 minutes duration during primary minimum. Assuming i = 90°, a new orbital solution was derived by Kitamura and Takahashi (1959) showing constant light for both minima. Binnendijk’s observation, however, showed a curved appearance at secondary minimum. The present observations indicate curved as well as flat secondary minima.
Global Value of Hubble Constant
Authors: Visvanathan N.
Published: July 2016

An accurate determination of the global Hubble Constant needs distance to objects well outside the Local Supercluster with redshift greater than ~ 2000 km/s. This is mainly to reduce the effect of the peculiar motion of the Local Group on the measured redshifts as well as to get away from the gravitational influence of the nearby high density regions.

The present practice of deriving distances involves identifying objects such as Cepheids and brightest red stars both in the Local Group galaxies as well as in the distant galaxies. This method cannot be used for galaxies at the large distances.
Spectra of Radio Galaxies in Clusters
Authors: Slee O. B. , Wilson I. R. G. , Siegman Betty C.
Published: July 2016

There has been considerable speculation in recent years about the evolution of radio galaxies in clusters. The discovery of powerful X-ray emission with an apparently thermal spectrum from a considerable number of clusters has been attributed to a hot (108K) intracluster gas with an electron density of ∼ 10-3 cm -3 at the cluster centre (see e.g. McHardy 1978). Such a gas surrounding a radio galaxy may conceivably retard the expansion or diffusion of the relativistic electrons and thus allow the source to retain its identity for longer intervals than is the case for field galaxies.
First Results Using a K-Band Maser Receiver on the Parkes 64-m Radio Telescope
Authors: Batchelor R. A. , Caswell J. L. , Forster J. R. , Wellington K. J.
Published: July 2016

A new maser receiver, operating between 20 and 24 GHz and constructed by the radiometer group at the CSIRO Division of Radiophysics, was first scheduled for astronomical observations in December 1981. In good observing conditions the system temperature was as low as 60 K. In conjunction with the versatility of the 1024-channel correlator and the large collecting area of the Parkes telescope (the central 37 m illuminated at 22 GHz yields a ratio of flux density to antenna temperature of 9∼ Jy K-1) the total system is a very powerful new tool. Here we report some observations of naturally occuring celestial H2O masers which we have studied with this system.
The UTIC Hard X-ray Balloon-borne Platform
Authors: Greenhill J. G. , Watts D. J. , Emery M. W. , Giles A. B. , Fenton K. B. , Ashton S. C.
Published: July 2016

Most of the recent advances in X-ray astronomy have resulted from satellite observations in the low energy (< 20 keV) range. The Einstein X-ray Observatory in particular has been responsible for a dramatic increase in our knowledge of the X-ray sky, in that all major classes of astronomical objects have been detected.
Global Oscillations in Late-Type Stars (Invited Paper)
Authors: Cram L. E.
Published: July 2016

The advent of new techniques to measure the global oscillation spectrum of the Sun has provided a new and powerful tool to investigate solar structure. One of the most challenging and potentially rewarding problems in contemporary astronomy is to devise techniques which will allow similar studies of other stars. This paper outlines the theory of global oscillations of late-type main-sequence stars, and summarises some of the achievements of global oscillation studies of the Sun. It then reviews the very few successful attempts that have been made to study stellar oscillations, and briefly discusses several apparently promising lines for further instrumental development.
The Cross-Field Resistance of the Solar Photosphere
Authors: Khan J. I.
Published: July 2016

The height-integrated Pedersen and Hall conductivities are calculated for the weakly ionized region of the solar atmosphere in the vicinity of a sunspot. The values obtained are much larger than previous authors have estimated. Dynamo theories for solar flares which rely on the photospheric region having a large resistance are untenable.
843 MHz Emission from the Active Star AB Dor
Authors: Beasley A. J. , Large M. I. , Vaughan A. E.
Published: July 2016

The Molonglo Observatory synthesis telescope has been used to obtain twelve observations of a 23′ arc field containing the active star AB Dor. On each occasion, an unresolved source close to the optical position of AB Dor was observed. The source exhibits day-to-day variations of flux density, with a mean value of ∼4 mJy. The identification of the source with the star and the variations in emission are discussed.
Evolution of the Precursor of SN1987A
Authors: Wood P. R. , Faulkner D. J.
Published: July 2016

Evolutionary calculations have been made for a star of initial mass 17.5 M⊙ in order to emulate the evolution of the precursor of SN1987A. The results give good agreement (i) with the observed properties of Sanduleak -69°202 (star 1) when the model reaches the supernova epoch, and (ii) with the observed distribution of red and blue supergiants in the LMC. Mass loss throughout the life of the star at rates reasonably consistent with observed values is required to produce these results. At the time of explosion, the supernova has a mass of only ∼ 5.4 M⊙ and it is surrounded by about 8 M⊙ of wind material in a shell of ∼0.4 pc radius.
The Stability of Rotating Stars
Authors: Brookshaw Leigh
Published: July 2016

It was first shown by von Zeipel (1924) that strict radiative equilibrium is impossible in the radiative zones of a uniformly rotating star. This result lead Eddington (1925) and Vogt (1925) to independently suggest the existence of large-scale meridional currents in the radiative zones of rotating stars. Eddington argued that since these currents will transport angular momentum, the condition of strict radiative equilibrium would result in meridional currents combined with differential rotation.
The Accuracy of Timing the Minima of Eclipsing Variables
Authors: Kviz Z. , Wong A. P. S.
Published: July 2016

It is shown that for the eclipsing variable stars MP Mus and SV Cen a least squares fitting procedure is more accurate when a linear (intensity) rather than a logarithmic (magnitude) scale is used.
The Effect of Magnetic Field Spread and Temperature and Density Variations in Cyclotron Emission Regions
Authors: Wickramasinghe D. T. , Ferrario Lilia
Published: July 2016

We discuss the properties of cyclotron radiation from accretion shocks located above the atmospheres of magnetic white dwarfs taking into account the effects of field spread and density and temparture structure. The models which are an improvement on previous point source models are shown to have characteristics that are in better overall agreement with the properties of AM Herculis type systems. Our calculations of the polarization properties of large polar cap emission regions are used to discuss the recent null measurements of circular polarization in DQ Herculis type systems.
Electron Scattering in Cyclotron Emission Regions
Authors: Meggitt S. M. A. , Wickramasinghe D. T.
Published: July 2016

The polarization properties of cylindrical magnetic accretion columns are calculated allowing for electron scattering within the emission region. The results are used to estimate the effects of electron scattering and geometry on the observed properties of AM Herculis type systems.
A Highly Excited Ammonia Cloud at least 300 pc from the Galactic Centre
Authors: Gardner F. F. , Boes F.
Published: July 2016

A cloud with a l.s.r. velocity of ∼ 160 km s-1 and a half-width of ∼ 25 km s-1 was mapped in the (1,1), (2,2) and (4,4) lines of para NH3 and the (3,3) and (6,6) lines of ortho NH3 using the 40″ arc beam of the 100-m Effelsberg telescope. The cloud was extended some 5′ in latitude and contained a central concentration ∼ 1′.5 in size at ℓ = 1°.59; b=0°.01. Line temperatures of the four higher transitions define a rotational temperature of ∼ 120 K, while the (1,1) and (2,2) alone yield the lower value of ∼ 40 K. The high temperatures, well above that of the dust, are too high to be caused by collisions with H2 molecules in the ground state, but might result from collisions with H2 in excited states. On a (ℓ, v) plot the cloud does not coincide with any generally accepted galactic centre feature but it is possibly located near the periphery of the ‘rotating nuclear disk’, where conditions would be favourable for the production of shocks, excited H2 and possibly high NH3 temperatures.
Ammonia Mapping of the Southern Molecular Cloud NGC 6334
Authors: Forster J. R. , Whiteoak J. B. , Gardner F. F. , Peters W. L. , Kuiper T. B. H.
Published: July 2016

The Parkes 64-m antenna has been used to map ammonia emission in the (J,K = 1,1) and (J,K = 2,2) transitions toward molecular cloud complex NGC 6334. This complex contains a number of OH and H2O masers, HII regions and IR sources, and is a rich source of molecular line emission.

Distributions of observed and derived quantities are presented with a linear resolution of ∼ 1 pc. Velocity anomalies are present near the two OH masers NGC 6334A and B, and the source of ammonia emission located near the northernmost H2O maser is one of the most intense sources of NH3 emission in the Galaxy.