The question of modelling a wide variety of astrophysical phenomena is discussed. It is argued that the combination of new computing equipment and algorithms has created the opportunity for a concerted attack on problems ranging from star formation to the evolution of the universe.

The purpose of this paper is to review current and planned Space Astronomy missions from an international perspective, with principal attention to the programs of the USA, Europe, Japan and the USSR. The review focusses on extra-solar astrophysics, and the capabilities and broad research objectives of numerous individual spacecraft are described. These collectively span more than seventeen decades in wavelength and thus provide an essential complement to ground-based astronomy. Many of the missions offer significant opportunities for Australian participation via three complementary routes. First through Guest Investigator programs analogous to that offered for the Hubble Space Telescope (HST). Second, through the proposed establishment of an Australian Space Astronomy Data Centre to gain access to archival data from HST and other missions (the creation of such an archival facility in Canada is highlighted as a pertinent example). Third, via the contribution of instrumentation or ground support services. This latter category includes the Radioastron VLBI mission for which an agreement with the USSR has already been signed. In addition, an unprecedented opportunity has arisen for Australia to provide a ground station for the Infrared Space Observatory (ISO), due to be launched by ESA in 1993. In return for providing this service, the Australian astronomical community would receive a guaranteed share of the ISO observing time during the two year mission. Finally, Australian astronomers have been invited to contribute an advanced All-sky X-ray Monitor for the Soviet Spectrum-X-Gamma mission in 1993. This opportunity, and also the Radioastron initiative, have arisen under the USSR-Australia Space Research Agreement signed in December 1987.

A method for calculating the resultant probability distributions of orbital elements for a small body (a comet, asteroid or meteoroid) after a gravitational encounter with a planet is described. This technique incorporates the frequency of such encounters so that the chance of attaining a certain new orbit per unit time is derived. The use of this technique is then illustrated by considering the effect of Jupiter upon the orbits of near-parabolic comets with perihelia near that planet (q = 5.2 AU) and in the inner solar system (q = 1.0 AU), with prograde (i = 10°) and retrograde (i = 170°) paths. As indicated by previous authors the prograde comets are more easily captured into short-period (P< 20 yr) and intermediate-period (20<P<200 yr) orbits; however, in contradiction to most previous work but in agreement with the results of Stagg and Bailey (submitted to Mon. Not. R. Astron. Soc.) it is found that the comets with smaller perihelia, rather than those with perihelia near Jupiter, have higher capture probabilities. This is apparently due to the fact that a small deflection only is needed to sufficiently decelerate a comet onto a smaller orbit if it makes a near-perpendicular crossing of Jupiter’s path, whereas a larger deflection (to achieve a large orbital change) is needed if the paths are near-parallel. With comparatively modest amounts of computer time this method may be used to calculate the relative capture probabilities as a function of i and q for all values of interest, and is thus a useful precursor to integrations following orbital evolution, since it indicates the most likely avenues whereby shorter-period comets are derived from the near-parabolic flux.

Advances in digital computer technology since the middle decades of the twentieth century have transformed many subject areas in astrophysics. Topics which had previously been dealt with by analytic approximations (usually to a very limited number of special cases) suddenly became amenable to detailed numerical modelling for all cases. Frequently, insights derived from this modelling ran ahead of other techniques in predicting physical phenomena before they were either observed or discerned in purely analytic treatments.

It has sometimes been said that the second half of this century has seen the advent of a totally new modus operandi in scientific research, which ranks alongside the two traditional approaches–experimentation and theory. The most powerful computers now available have greatly accelerated these developments. They employ simultaneous computational techniques (either vector processing or parallel processing, or both), and their throughput is so large that, for most problems, the only way in which the human mind can fully appreciate the scientific content of the numerical results being calculated is by transforming those results into pictorial representations.

This paper draws on my experience as Academic Director of the ANU Supercomputer Facility during the first eighteen months of its operation, to describe the place which I believe super-computers will occupy in the development of astrophysics during the 1990s and into the next century.

Radio telescopes in more than 20 different countries on five continents are being used for VLBI observations of galactic and extragalactic radio sources, as well for applications to geodesy and geophysics. New radio telescopes and networks of radio telescopes dedicated to VLBI which are being built in the United States, the U.S.S.R., Italy, China, Poland, the U.K. as well as in Australia will greatly improve the sensitivity, resolution, image quality, and frequency coverage of the existing networks. The Mk II VLBI recording system, which is based on consumer type Video Tape Recorders, is widely used but the sensitivity is limited. Broad band recording systems are expensive, but are becoming more popular due to their much greater sensitivity. They are expected to dominate VLBI systems in the 1990s.

The first tests of an earth-to-space VLBI system took place in 1986, and by the mid 1990s dedicated VLBI antennas will be launched into earth orbit by the U.S.S.R. and by Japan in collaboration with Australia and other countries throughout the world. Space VLBI missions will give an order of magnitude improvement in resolution over the ground based VLBI networks operating at the same wavelengths.

Proxima Centauri was observed photoelectrically in the period July-September 1987 with a newly-installed computer-interfaced photometer. Four definite flares and six further possible events were recorded. The level of Proxima’s flaring activity was examined and no significant change since 1969 found.

Oscillatory convective motions have been observed in the umbrae of sunspots and, in the past, the linear theory of overstability has been used for sunspot models. Here a non-linear model for oscillatory convection has been used to investigate the possibility of a preferred horizontal cell size for these motions, in the presence of a magnetic field.

The integration forward in time, from the conductive state, of the non-linear multimode equations governing magnetoconvection when the magnetic Prandtl number is less than one portrays a complex interaction between the evolving magnetic and vertical velocity horizontal scales. Preferred horizontal scales for the convective cells have been established by identifying the modes that substantially contribute to the overall convective heat transport. All other modes, although initially perturbed, in time essentially decay to zero through self interaction.

Elliptical galaxies are at first sight a remarkably homogenous class of objects, yet some of them produce large and enormously powerful radio sources while others remain more or less quiescent. Why should this be so? What prompts the nucleus of an elliptical galaxy to become ‘active’? What, if anything, do elliptical galaxies have in common with the bulges of spirals? Here, I review some of the radio and optical properties of nearby elliptical galaxies, with special emphasis on events which take place within the central kiloparsec.

In science we have good, successful laboratories and scientists and we also have wasteful, inefficient and unproductive ones. The differences are not matters of chance.

It is not an accident that just one Cambridge College, Trinity, has achieved more Nobel Prizes than all of Japan. There was something in common amongst the Nobel prize winners Todd, Adrian, Perutz, Bragg, Crick, Ryle, Hewish and Mott that I was fortunate enough to meet and, in some cases, get to know well. Of course there was the personal and intellectual calibre of these people, their drive and determination. But also, there was the laboratory culture within which they worked, a culture still benefiting from the influence of Maxwell, Thomson and Rutherford.

The mass-fraction Y of helium in the interstellar medium is between 0.22 and 0.30 wherever it has been measured and it is believed to be the sum of two components: YP from Big Bang nucleosynthesis (BBNS) at about 100 s after the Big Bang (ABB) and a temperature near 0.1 MeV, and ΔY due to processing in stars. Precise measurements of Yp, along with balances of trace elements D, 3He, 7Li also resulting from BBNS, provide important tests of BBNS theory and of parameters of cosmology and particle physics, notably the contribution ΩBO of baryons to the mean density of matter in the universe (in units of the closure density), the number Nv of light neutrino flavours (or families of quarks and leptons) and the half-life т½ of the neutron (Shaver et al. 1983; Yang et al. 1984; Boesgaard and Steigman 1985). Figure 1 shows the predicted abundances from Standard BBNS theory (SBBN) as a function of η = μB/nλ the ratio of baryons to photons (unchanged since e± annihilation a few seconds ABB), which is proportional (through the known temperature of the microwave background) to ΩBOh20 where h0 is the Hubble constant in units of 100 km s−1 Mpc−1. SBBN theory (which assumes a homogeneous Friedmann universe and small lepton numbers), when combined with reasonable ideas on Galactic chemical evolution that predict a primordial (D + 3He)/H ratio below 10−4, imply that η ≥ 3 × 10−10 (shown by the tall vertical line in Fig. 1), which in turn implies YP≥0.210 if Nv = 3 and т½≥10.4 minutes. But this limit can be somewhat relaxed if т½ is smaller (current measurements permit values down to 9.0 minutes, e.g. Last et al. 1988) and/or if the quark-hadron phase transition around 200 MeV is first-order and leads to significant density fluctuations (Kurki-Sunonio et al. 1989; Reeves 1989).

A simple model for solar flares is described which invokes many ion-acoustic double layers in the source region. The ability of the model to explain some of the observed characteristics of solar flares is discussed, particular attention being paid to the well-observed high-energy flare examined by de Jager et al. (1987).

The binary flare star AT Mic has been observed with the VLA (5 GHz and 1.5 GHz) and, nearly simultaneously, with the MOST (0.843 GHz). There appears to be a slowly varying component of the radio intensity, with a flux density greater at 0.843 GHz than at higher frequencies. It is suggested that above 1 GHz the emission is possibly produced by incoherent gryosynchrotron radiation, whereas below 1 GHz a coherent mechanism predominates.

During routine monitoring of active-chromosphere stars in August 1987 an intense radio flare on the FK Comae star HD 32918 was detected by the Parkes radiotelescope. Other observatories were notified, enabling data to be collected at 843 MHz, 1.4 GHz, 8.4 GHz and optical frequencies.

The flare at radio frequencies was largely similar to a previous event on this star, reaching a peak radio power of 5 < 1012 W Hz−1 at 8.4 GHz. During the flare the spectrum varied as ∼ v1.4 and later flattened as the flare progressed. Compared to the previous flare, circular polarization was higher.

Ca II and Hα optical spectra taken at the AAO 3.9-metre telescope show the star to have a highly active chromosphere and a strong wind, with a terminal velocity of ≈230 km s−1. While much of this activity appears to be long lived, there is good evidence for an increase in the strength of the chromospheric lines during the radio flare event.

A survey of the optical spectra of IRAS galaxies, made with the AAT, has shown that the majority have strong emission lines. Ratios of the emission lines have been plotted on the Veilleux-Osterbrock diagram ([O III]/Hβ against [N II]/Hα); this shows that the IRAS galaxies comprise several classes. In our sample the majority appear to be starburst galaxies, but Seyfert, Liner and narrow-line galaxies are also represented. Co-added spectra of the galaxy classes are presented. On the basis of optical spectroscopy, it appears that the starburst phenomenon is capable of generating luminosities exceeding 1012L⊙.

The problem of the surface migration of solar magnetic fields is discussed. It is shown that, unless some form of reconnection takes place below the surface, magnetic tension should effectively prevent such migration and the possibility of U-loop formation and transport is considered. As a first step, the buoyancy of a magnetic ‘U-loop’ within an isothermal atmosphere is considered. It is shown that such a configuration may form by the reconnection of the arms of an Ω-loop associated with an active region, and is likely to be buoyant initially and rise through the region. However, as it rises, the net buoyancy decreases and, provided that the temperature within the loop is even marginally less than that outside, it will reach a sub-surface configuration in which the net buoyancy is zero. The significance of this result for solar magnetic fields is then assessed.

We question Newton’s inverse square law of universal gravitation in the light of recent, alternative formulations. In addition, we present numerical simulations of galaxy interactions which were used in an attempt to distinguish between an inverse square law and an inverse linear law. We conclude that an inverse linear relation is as compatible with the observational data on interacting galaxy systems as the inverse square law.

We present preliminary results from a number of deep radio polarization surveys being made of the Magellanic Clouds at 2.3 GHz, 4.75 GHz and 8.55 GHz. Extended and linearly polarized radio emission has been found at 2.3 and 4.75 GHz from both the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). However, as the analysis of these data is not yet complete we present only some of the 4.75 GHz results at this time.

The stability of a swirling cylindrical jet of compressible fluid is examined by performing a normal mode analysis and numerically solving the eigenvalue problem. Perturbations of the form f(r)exp[i(ωt-mϕ-kz)] are considered, where f is any fluid variable. Instabilities which are characteristic of both a non-swirling (top-hat) jet and a Rankine vortex are investigated for a particular axial wavenumber.

The vortex instabilities are weak, and are found to remain weak when axial flow is present. The jet instabilities are much stronger, but axial flow is a stabilizing influence. The positive helicity (km > 0) non-axisymmetric modes (m ≠ 0) are stabilized by a small component of azimuthal flow. The axisymmetric mode (m = 0) and the negative helicity non-axisymmetric modes persist in rapidly swirling jets, but with a greatly reduced growth rate.

Local large scale structure is best studied using statistically complete samples which cover the entire sky, and for which full redshift information is available. The optical galaxy redshift surveys which have been made to date involve many thousands of objects but cover only limited parts of the sky, and so provide only a fragmented picture of local large scale structure. Complete samples of radio and X-ray galaxies are available, however, with large sky coverage. While the number of objects is small, they may still suffice to define the dominant local structures, particularly as they may preferentially sample the deeper gravitational potentials and so provide a more efficient tracer of dominant structure.

We present observations of Hα and CaII resonance lines in 4 stars having Hα features which place them intermediately between the non-(e) and (e) classifications of dK/dM stars. There is considerable variety in the shape of the Hα line, presumably due in part to differences in rotation rates. As expected, the energy fluxes in the CaII emission lines lie between those typical of non-(e) and (e) stars. There is some evidence (especially from the binary Gl 876A) that the energy fluxes in the CaII and Hα emission lines do not vary from star to star according to a simple proportionality. An intriguing result is the apparent detection of spatially displaced chromospheric emission in Gl 907.1 and Gl 890.