The mean abundances of Mg, Si, Ca, Ti, Cr, and Fe based on both strong and weak lines of α Cen A are determined by matching the observed line profiles with those synthesised from stellar atmospheric models and comparing these results with a similar analysis for the Sun. There is good agreement between the abundances from strong and weak lines.

Strong lines should generally be an excellent indicator of abundance and far easier to measure than the weak lines normally used. Until the development of the Anstee, Barklem, and O'Mara (ABO) theory for collisional line broadening, the uncertainty in the value of the damping constant prevented strong lines being used for abundance determinations other than in close differential analyses.

We found that α Cen A has a mean overabundance of 0.12 ± 0.06 dex compared to solar mean abundances. This result agrees remarkably well with previous studies that did not use strong lines or the ABO theory for collisional line broadening. Our result supports the conclusion that reliable abundances can be derived from strong lines provided this new theory for line broadening is used to calculate the van der Waals damping.

Recent history in South Africa has created unique problems in many areas. As a result of an unequal educational structure, particularly in science, there is a general lack of science literacy and awareness. Some years ago the South African Astronomical Observatory started a Science Education Initiative as a contribution to addressing this problem by using astronomy as a vehicle to stimulate an interest in science amongst teachers and students. This programme was given a boost by the South African government in 1998 and the construction of the Southern African Large Telescope will provide further stimulus to the Science Education Initiative.

The TAURUS Tunable Filter (TTF) affords a new approach to observational cosmology, allowing a wide field (10 arcmin) to be imaged monochromatically in contiguous wavelength intervals (6–60 Å bandpass) over the R and I bands. In a 200 s exposure with the AAT, the TTF can detect Hα emission powered by star formation rates as low as 0·1 M⊙ yr−1 at z = 0·08 and 1 M⊙ yr−1 at z = 0·24 in 2 arcsec seeing (cf. 0·26 M⊙ yr−1 for the LMC). In this paper we describe an emission-line survey currently under way using the TTF on the AAT to detect redshifted Hα over the ranges z = 0·06–0·1 and z = 0·22–0·26. Such detections will be of timely interest to the Southern HI Sky Survey which is motivated along similar lines.

We present simulated AXAF spectra of accreting white dwarfs, using parameters appropriate for magnetic cataclysmic variables. The very high spectral resolution that can be obtained with the High-Energy Transmission Grating of AXAF can resolve the keV X-ray emission lines that characterise the temperature, density and velocity profiles of the shock-heated emission regions of these systems. These simulations demonstrate that actual spectra will allow us to place constraints on the white-dwarf mass and the accretion rate of the systems. The high-resolution spectra also allow the measurement of the velocity of the accretion flow in regions close to the white-dwarf surface.

Recently Vernstrom et al. (2021, MNRAS) claimed the first definitive detection of the synchrotron cosmic web, obtained by ‘stacking’ hundreds of thousands of pairs of close-proximity clusters in low-frequency radio observations and looking for a residual excess signal spanning the intracluster bridge. A reproduction study by Hodgson et al. (2022, PASA, 39, e013), using both the original radio data as well as new observations with the Murchison Widefield Array, failed to confirm these findings. Whilst the detection remains unsure, we here turn to stacking a simulated radio sky to understand what kind of excess radio signal is predicted by our current best cosmological models of the synchrotron cosmic web. We use the FIlaments & GAlactic RadiO (FIGARO; Hodgson et al. 2021a, PASA, 38, e047) simulation, which models both the synchrotron cosmic web as well as various subtypes of active galactic nucleii and star-forming galaxies. Being a simulation, we have perfect knowledge of the location of clusters and galaxy groups which we use in our own stacking experiment. Whilst we do find an excess radio signature in our stacks that is attributable to the synchrotron cosmic web, its distribution is very different to that found by Vernstrom et al. (2021, MNRAS). Instead, we observe the appearance of excess emission on the immediate interiors of cluster pairs as a result of asymmetric, ‘radio relic’-like shocks surrounding cluster cores, whilst the excess emission spanning the intracluster region—attributable to filaments proper—is two orders of magnitude lower and undetectable in our experiment even under ideal conditions.

It has recently been shown that the abundance of cold neutral gas may follow a similar evolution as the star formation history. This is physically motivated, since stars form out of this component of the neutral gas and if the case, would resolve the long-standing issue that there is a clear disparity between the total abundance of neutral gas and star-forming activity over the history of the Universe. Radio-band 21-cm absorption traces the cold gas and comparison with the Lyman-α absorption, which traces all of the gas, provides a measure of the cold gas fraction, or the spin temperature, Tspin. The recent study has shown that the spin temperature (degenerate with the ratio of the absorber/emitter extent) appears to be anti-correlated with the star formation density, ψ*, with 1/Tspin undergoing a similar steep evolution as ψ* over redshifts of 0 ≲ z ≲ 3, whereas the total neutral hydrogen exhibits little evolution. Above z ∼ 3, where ψ* shows a steep decline with redshift, there are insufficient 21-cm data to determine whether 1/Tspin continues to follow ψ*. Knowing this is paramount in ascertaining whether the cold neutral gas does trace the star formation over the Universe’s history. We explore the feasibility of resolving this with 21-cm observations of the largest contemporary sample of reliable damped Lyman-α absorption systems and conclude that, while today’s largest radio interferometers can reach the required sensitivity at z ≲ 3.5, the Square Kilometre Array is required to probe higher redshifts.

We present H-band observations of the elliptical galaxy NGC 4696, the brightest member of the Centaurus cluster of galaxies. We have measured its light profile, using a two-dimensional fitting algorithm, out to a radius of 180 arcsec (37 h70−1 kpc). The profile is well described by a de Vaucouleurs law, with an effective radius of 35.3 ± 1.0 h70−1 kpc. There is no need for the extra free parameter allowed by a Sérsic law. Allowing for a variation of 0.3% in the sky level, the profile obtained is compatible with data from the Two-Micron All Sky Survey (2MASS). The profile shows no sign of either a truncation or an extended halo.

We use Gemini Multi-Object Spectrograph integral Field Unit observations of the inner 285 × 400 pc2 region of the Seyfert 2 galaxy NGC 5643 to map the [S iii]λ9069 emission line flux distribution and kinematics, as well as the stellar kinematics, derived by fitting the Ca iiλλλ8498,8542,8662 triplet, at a spatial resolution of 45 pc. The stellar velocity field shows regular rotation, with a projected velocity of 100 km s−1 and kinematic major axis along a position angle of –36°. A ring of low stellar velocity dispersion values (∼70 km s−1), attributed to young/intermediate age stellar populations, is seen surrounding the nucleus with a radius of 50 pc. We found that the [S iii] flux distribution shows an elongated structure along the east–west direction and its kinematics is dominated by outflows within a bi-cone at an ionised gas outflow rate of 0.3 M⊙ yr−1. In addition, velocity slices across the [S iii]λ9069 emission line reveal a kinematic component attributed to rotation of gas in the plane of the galaxy.

A study has been made of the upper main-sequence stars in several young clusters, in an attempt to determine a well-defined effective temperature scale for the B stars, and to compare the observed atmospheric parameters with the recent theoretical evolutionary tracks in the H-R diagram (Iben, 1965, Hofmeister et al, 1964, Kippenhahn et al., 1965). Each of the clusters studied contains at least one peculiar A star of the Si λ-4200 type, and this afforded an excellent opportunity for a study of the evolution of these stars.

We consider the effect of a velocity gradient on the source function for a spectral line formed in an atmosphere in non local thermodynamic equilibrium, a problem examined previously by Kulander and Hummer and Rybicki. A numerical method is used which extends the Feautrier technique.

Ten years ago I put forward the suggestion that the Sun may possess a small burnt-out helium-rich core covering some 2-3% of its mass (Prentice 1973a,b). The purpose of this chemically inhomogeneous solar model was to account for the anomalously low flux of neutrinos being emitted by the Sun, as observed by Davis et al. (1971).

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.

At previous meetings of the A.S.A., brief reports have been made of a new theory for the formation of the solar system which is being developed at Monash University (Prentice 1972, 1977, 1978a, b; Hourigan 1977). This work is nearing completion and on this occasion an outline of the whole theory is presented.

It is now generally accepted that the remnants of supernovae (SNRs) are of two types, recognizable by their radio structure and spectral index. To date most of the radio sources identified as SNRs are of the easily identified shell type. These have spectral indices a of -0.5 ±0.2 and exhibit some degree of annular brightness distribution — the projection of the radio shell. The second type, e.g. the Crab Nebula, have filled structures and relatively flat (a = -0.1 ±0.1) spectral indices. The relatively strong radio polarization exhibited by some members of this class has led to their identification but generally they tend to be hidden amongst the HII regions in our galaxy.

Crannell et al. (1978) have reported an observed correlation between the time profiles and flux densities of impulsive hard X-ray and microwave solar bursts. We report here on a significant correlation between the flux density of extended bursts of hard X-rays and micowaves. These extended events follow after impulsive bursts and last much longer (see e.g. Fig. 1, Frost and Dennis 1971). However, as extended bursts only occur during very large flares the number of cases available for study is small. The significance of our observations follows from the suggestion of Wild et al. (1963) that the extended bursts are evidence for a second-phase acceleration process in the corona. We show that the observed characteristics of these extended microwave bursts (viz. a rather flat spectrum below a turnover frequency which is independent of intensity) can be explained by gyro-synchrotron radiation from the same population of energetic (E ≈ 100 keV) electrons as those emitting (thin-target) X-ray bremsstrahlung. A detailed source model is discussed in a companion paper (Nelson and Stewart 1979 — Paper B).

The Llanherne telescope is a meridian transit instrument with an instantaneous bandwidth of two octaves in the range 35 to 150 MHz, and was constructed primarily for studying the low frequency properties of pulsars. The antenna is a 78 × 156 metre filled aperture phased array comprising 4096 wire dipole elements arranged in a 64 × 64 matrix. Uniform illumination of the elements produces a single pencil beam response which is scanned electronically along the meridian from Declination -90° to +30°. The beamwidth at 100 MHz is 1 degree in right ascension and two degrees sec(Dec.) in declination and varies proportionally with wavelength, giving a transit time of 4 sec(Dec) × 100/f(MHz) minutes between half power points.

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).

Compton scattering in the bulk accretion flow of the accretion column in magnetic cataclysmic variables can significantly shift photon energies in the X-ray emission lines resulting from accretion shocks. In particular, Compton recoil can potentially broaden the 6.7 and 6.97 keV Fe Kα emission lines produced in the post-shock region, and contaminate the fluorescent 6.4 keV neutral Fe Kα line reflected off the white dwarf surface. We present nonlinear Monte Carlo simulations demonstrating these effects, and we discuss the interpretation of observed Fe Kα linewidths in magnetic cataclysmic variables in light of these new results. The implications for other accreting compact objects are also discussed.

We presented the first photometric and orbital period investigations for four W Ursae Majoris-type binaries: V473 And, V805 And, LQ Com, and EG CVn. The photometric solutions suggested that V805 And and LQ Com are two total-eclipse contact binaries, while V473 And and EG CVn are partial-eclipse ones. V473 And and LQ Com belong to the A-subtype contact binaries, while V805 And and EG CVn belong to the W subtype. The O’Connell effects found in the light curves of V805 And, LQ Com, and EG CVn can be interpreted as a result of a cool spot on the surface of their less massive and hotter primary components. Based on two different methods, the absolute physical parameters were properly determined. Combining the eclipse timings derived from our observations and survey’s data with those collected from literature, we investigated their orbital period variations. The results show that the orbital periods of V473 And, V805 And, and EG CVn are undergoing a secular decrease/increase superposed a periodic variation, while LQ Com exhibits a possible cyclic period variation with a small amplitude. The secular period changes are caused mainly by the mass transfer between two components, while the cyclic period oscillations may be interpreted as the results of either the light-time effect due to the third body or the cyclic magnetic activity. Finally, we made a statistical investigation for nearly 200 contact binaries with reliable physical parameters. The statistical results suggested that the W-subtype systems are more evolved than the A-subtype ones. Furthermore, the evolutionary direction of A-subtype into W-subtype systems is also discussed. The opposite evolutionary direction seems to be unlikely because it requires an increase of the total mass, the orbital angular momentum, and the temperature differences between two components of a binary system.

We present an analysis of the scientific (refereed) paper productivity of the current largest (diameter > 8m) ground-based optical (and infrared) telescopes during the ten-year period from 2000 to 2009. The telescopes for which we have gathered and analysed the scientific publication data are the two 10-m Keck telescopes, the four 8.2-m Very Large Telescopes (VLT), the two 8.1-m Gemini telescopes, the 8.2-m Subaru telescope, and the 9.2-m Hobby–Eberly Telescope (HET). We have analysed the numbers of papers published in various astronomical journals produced by using these telescopes. While the total numbers of papers from these observatories are largest for the VLT, followed by Keck, Gemini, Subaru, and HET, the number of papers produced by each component of the telescopes is largest for Keck, followed by VLT, Subaru, Gemini, and HET. In 2009, each telescope of the Keck, VLT, Gemini, Subaru, and HET observatories produced 135, 109, 93, 107, and 5 refereed papers, respectively. We have shown that each telescope of the Keck, VLT, Gemini, and Subaru observatories is producing 2.1 ± 0.9 Nature and Science papers annually and these papers make up 1.7 ± 0.8% of all refereed papers produced by using each of those telescopes. Extending this relation, we propose that this ratio of the number of Nature and Science papers to the total number of refereed papers that will be produced by future extremely large telescopes (ELTs) will remain similar. From a comparison of the publication trends of the above telescopes, we suggest that (i) having more than one telescope of the same kind at the same location and (ii) increasing the number of instruments available at the telescope are good ways to maximize the paper productivity.