When metre wavelength radars were first operated in the 1940s, echoes were obtained which could be attributed to backscatter from ionised trains produced by the ablation of meteroids in the upper atmosphere at altitudes near 100 km. Modern over-the-horizon skywave radars operating in the HF (High Frequency) band employ digital techniques for both radar control and signal processing and are aided by frequency management subsystems for the selection of appropriate frequencies for meteor detection based on real-time monitoring of the HF signal environment.

This paper describes the results of using such a radar for meteor observations. We report the detection of the Eta Aquarid meteor shower and demonstrate that a large increase in the echo rate due to sporadic meteors is obtained as frequencies are reduced below 15 MHz and the underdense echo ceiling rises in altitude. Finally, we present preliminary observations of highly Doppler shifted echoes which travel at meteoric velocities and which we identify as meteor ‘head echoes’.

We present a multi-frequency study of the intermediate spiral SAB(r)bc type galaxy NGC 6744, using available data from the Chandra X-Ray telescope, radio continuum data from the Australia Telescope Compact Array and Murchison Widefield Array, and Wide-field Infrared Survey Explorer infrared observations. We identify 117 X-ray sources and 280 radio sources. Of these, we find nine sources in common between the X-ray and radio catalogues, one of which is a faint central black hole with a bolometric radio luminosity similar to the Milky Way’s central black hole. We classify 5 objects as supernova remnant (SNR) candidates, 2 objects as likely SNRs, 17 as H ii regions, 1 source as an AGN; the remaining 255 radio sources are categorised as background objects and one X-ray source is classified as a foreground star. We find the star-formation rate (SFR) of NGC 6744 to be in the range 2.8–4.7 M⊙~yr − 1 signifying the galaxy is still actively forming stars. The specific SFR of NGC 6744 is greater than that of late-type spirals such as the Milky Way, but considerably less that that of a typical starburst galaxy.

Active galactic nuclei (AGN) have been observed as far as redshift $z \sim 7$. They are crucial in investigating the early Universe as well as the growth of supermassive black holes at their centres. Radio-loud AGN with their jets seen at a small viewing angle are called blazars and show relativistic boosting of their emission. Thus, their apparently brighter jets are easier to detect in the high-redshift Universe. DES J014132.4–542749.9 is a radio-luminous but X-ray weak blazar candidate at $z = 5$. We conducted high-resolution radio interferometric observations of this source with the Australian Long Baseline Array at $1.7$ and $8.5$ GHz. A single, compact radio-emitting feature was detected at both frequencies with a flat radio spectrum. We derived the milliarcsecond-level accurate position of the object. The frequency dependence of its brightness temperature is similar to that of blazar sources observed at lower redshifts. Based on our observations, we can confirm its blazar nature. We compared its radio properties with those of two other similarly X-ray-weak and radio-bright AGN, and found that they show very different relativistic boosting characteristics.

Gamma-ray bursts (GRBs) and double neutron star merger gravitational-wave events are followed by afterglows that shine from X-rays to radio, and these broadband transients are generally interpreted using analytical models. Such models are relatively fast to execute, and thus easily allow estimates of the energy and geometry parameters of the blast wave, through many trial-and-error model calculations. One problem, however, is that such analytical models do not capture the underlying physical processes as well as more realistic relativistic numerical hydrodynamic (RHD) simulations do. Ideally, those simulations are used for parameter estimation instead, but their computational cost makes this intractable. To this end, we present DeepGlow, a highly efficient neural network architecture trained to emulate a computationally costly RHD-based model of GRB afterglows, to within a few percent accuracy. As a first scientific application, we compare both the emulator and a different analytical model calibrated to RHD simulations, to estimate the parameters of a broadband GRB afterglow. We find consistent results between these two models, and also give further evidence for a stellar wind progenitor environment around this GRB source. DeepGlow fuses simulations that are otherwise too complex to execute over all parameters, to real broadband data of current and future GRB afterglows.

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.

It is more than 120 years since the discovery of spiral galaxies, and naturally there has been much speculation on their origin. The vital clue is the composition of the arms, and it is now known that the arms are patterns of newly formed, and hence very luminous, stars. Thus the problem of spiral arms is only part of the broader problem of the origin of stellar systems in general. The various galactic forms of the Hubble morphological classification are differentiated by their different stellar systems, and so the problem of spiral arms is part of the basic problem of the origin of the Hubble types. For this reason the potential significance of any theory of spiral arms is vastly extended.

Sir William Herschel and his sister, Caroline, had swept the skies over England as members of the court of George III. They had made amazing discoveries: a new planet in our solar system, the movement of the solar system with respect to the fixed stars, and hundreds of new nebulae and star clusters.

Then Sir William’s son John swept the southern skies from Cape Town, South Africa (1834 to 1838), mapping and sketching many more stars and nebulae.

Work on the development and use of optical fibres as light guides in astronomical spectroscopy has been underway at the AAO for over a year now. The fibres used are step-index polymer-clad silica with a core size of 200 microns giving an aperture size of 1.3 arcsec at the AAT f/8 focus. They are optimised for data transmission with losses below 5dB/km at a wavelength of 800 nm. The blue transmission is somewhat lower, typically 500dB/km at 300nm and 90dB/km at 400nm but over the short 2m length used these attenuations give transmissions of 79% and 96% respectively.

Evidence has recently been put forward that Jupiter might be modulating the intensity of cosmic radiation observed at the earth (Pizzella and Venditti 1973; Cini-Castagnoli et al. 1973). It therefore seemed worthwhile to analyse underground meson data in Jovian time for any evidence of an effect at the higher energies over a complete orbital period.

Very long baseline interferometry (VLBI) polarisation measurements provide information about the parsec-scale magnetic field structures in compact active galactic nuclei (AGN), as well as the densities of relativistic and thermal electrons in the radio emitting regions. This paper reviews the role of polarisation VLBI in studies of AGN variability on both relatively long and short (intraday) timescales.

Using both a theoretical and an empirical approach, we have investigated the frequency of low redshift galaxy-galaxy lensing systems in which the signature of 3D weak lensing might be directly detectable. We find good agreement between these two approaches. Using data from the Galaxy and Mass Assembly redshift survey we estimate the frequency of detectable weak lensing at low redshift. We find that below a redshift of z ~ 0.6, the probability of a galaxy being weakly lensed by γ ⩾ 0.02 is ~ 0.01. We have also investigated the feasibility of measuring the scatter in the M* − Mh relation using shear statistics. We estimate that for a shear measurement error of Δγ = 0.02 (consistent with the sensitivity of the Direct Shear Mapping technique), with a sample of ~$50,000 spatially and spectrally resolved galaxies, the scatter in the M* − Mh relation could be measured. While there are currently no existing IFU surveys of this size, there are upcoming surveys that will provide this data (e.g The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), surveys with Hector, and the Square Kilometre Array (SKA)).

We have completed a 21-cm survey of a 600 square degree region of the Centaurus A group of galaxies at a redshift of ∼500 km s−1 as part of a larger survey of the entire southern sky. This group of galaxies was recently the subject of a separate and thorough optical survey (Côté et al. 1997), and thus presented an ideal comparison for us to test the survey performance. We have identified 10 new group members to add to the 21 already known in our survey area. Six of the new members are previously uncatalogued galaxies, while four were catalogued but assumed not to be group members. Including the seven known members outside of our survey area, this brings the total known number of Cen A members to 38. All of the new HI detections have optical counterparts, most being intrinsically very faint (MB > –13·0), late-type low surface brightness dwarfs. Most of the new members have HI masses only a few times our survey limit of 107M☉ at an assumed distance for the group of 3·5 Mpc, and are extremely gas-rich, with a median MHI/LB > 1. Our limiting HI sensitivity was actually slightly worse than the HI follow-up observations of the Côté et al. optical survey, yet we have already increased the known number of group members by 50% using an HIsurvey technique. While we have increased the known number of members by ∼50%, these new members contribute <4% to its light.

We present long slit spectrophotometric emission line fluxes of bright and extended (< 5 arcsec in diameter) planetary nebulae (PNe), selected from a catalogue with suitable equatorial coordinates for northern hemisphere. In total, 17 planetary nebulae have been chosen and observed in 2008–2010. To measure absolute fluxes, broad slit sizes, ranging from 3.5 to 7.5 arcsec were used and thus equivalent widths (EW) of all observable emission line fluxes were also calculated. Among 17 planetary nebulae observed, line flux measurements of 12 of them were made for the first time. This work also aims to extend the sky coverage of emission line flux standards in northern hemisphere (52 planetary nebulae in southern hemisphere; 6 planetary nebulae in northern hemisphere). Electron temperatures and densities, and chemical abundances of these planetary nebulae were also calculated in this work. These data are expected to lead the photometric or spectrometric further work for absolute emission line flux measurements needed for H ii regions, supernova remnants etc.

This document is the final Phase A Science Report of the Australian LYMAN Science Working Group, and describes in detail the scientific objectives, technical feasibility, and engineering implementation of the LYMAN mission as developed in the Australian studies.

The tropopause, typically at 16 to 18 km altitude at the lower latitudes, dips down to only 8 km in the polar regions, allowing access to the cold, dry and nonturbulent lower stratosphere by tethered aerostats. These can float as high as 12 km, have long operating lifetimes, and are extremely reliable. In contrast to free-flying balloons, they can stay on station for weeks at a time, and payloads can be safely recovered for maintenance and adjustment and relaunched in a matter of hours. We propose to use such a platform, located first near Fairbanks, Alaska, and later in the Antarctic, to operate a new-technology 4 m telescope with diffraction-limited performance in the near infrared. Thanks to the low ambient temperature (~200 K), thermal emission from the optics is of the same order as that of the zodiacal light in the 2–3 μm band. Since this wavelength interval is the darkest part of the zodiacal light spectrum from optical wavelengths to 100 μm, the combination of high-resolution images and a very dark sky make it the spectral region of choice for observing galaxies, QSOs and clusters of galaxies at the formation epoch of galaxies.

The Sydney University one mile cross-type radio telescope at the Molonglo Radio Observatory has been used to study the 30 Doradus nebula with high resolution (~3´ arc) at 408 MHz. This preliminary report compares these observations with Balmer line isophotes published by Faulkner. A description of the calibration procedures used in the present observations, an analysis of the various radio features in the 30 Doradus region, and a comparison with previous observations at other frequencies, will be described in a later paper.

This paper describes the first results from a 20 deg2 mosaic of the Small Magellanic Cloud (SMC) in the λ21-cm line of neutral hydrogen. The mosaic consists of 320 separate pointings with the 375-m array of the Australia Telescope Compact Array. The angular resolution is 1′· 5 (26 pc, for a distance of 60 kpc) and the velocity resolution is l·6kms−1. The images reveal a structure of remarkable complexity, with much of the spatial power contained in high-brightness temperature compact knots and filaments. Numerous wind-blown ‘bubbles’ and ‘supershells’ are evident in the data, both inside and outside the stellar confines of the SMC. Some high-density H I regions are seen to correlate with Hα regions, indicating sites of current star formation. However, many high-column-density H I regions are devoid of optical emission and may represent regions of future star formation. These regions may be under-abundant in diffuse molecular gas due to the high radiation field and low metallicity of the SMC.

Following the detection of a high flux density from Saturn at 21.2 cm by Davies and Williams and the confirmation by Kellermann, it has been known that the radio emission from Saturn is enhanced at long wavelengths. The Molonglo cross telescope has searched for this emission at 73.5 cm on two occasions, the first in 1967 November when the planet was stationary, and the second during the opposition of 1968 October. Between these dates, installation of preamplifiers on the EW arm doubled the sensitivity of the cross so that although the same procedures were used on both occasions, this paper is based almost entirely on the recent results.

We shall examine the question of whether the concentration of magnetic field, the downward motion and the temperature excess observed at the boundaries of supergranules can be interpreted consistently in terms of a steady flow along the magnetic lines of force. Before doing so, however, we shall first consider the development of the magnetic configuration driven by a supergranular convection overshooting into the photosphere.

The Windsor amateur astronomer, John Tebbutt, had a ceased observing in 1907. However, in 1909, at the age of 75, he came out of retirement to observe Halley’s comet and his astrometric positions were published in the Monthly Notices of the Royal Astronomical Society. These data were used, together with most published observations from the 1835 and 1910 apparitions, for the computation of Halley’s orbit for ESA’s Halley intercept spacecraft, Giotto. A detailed analysis of the observations have shown minor imperfections that, when corrected, gave rms errors of 3''.5 arc in right ascension and 2''.8 in declination. His systematic errors are negligible at the 0''.2 level.