We present UBVRI photometry of the faint and highly erratic cataclysmic variable discovered by Hawkins (1983) from a sequence of U.K. Schmidt plates. Observations using the ANU 2.3 m telescope over two nights in September 1986 show pronounced and repeatable modulation at a binary period of 108.6 min. Dramatic colour differences are evident in the folded UBVRI light curves: in the U band, a single sinusoidal peak is present, while at longer wavelengths, a second red peak dominates at a phase separation of Δϕ = 0.5. This behaviour is strongly suggestive of cyclotron emission from two magnetic accretion funnels in an AM Herculis binary system. Furthermore, the binary period lies in the narrow range of 100-115 minutes that characterizes most of the AM Herculis variables lying on the short side of the 2-3 hour period gap. We conclude therefore that the object is almost certainly a new AM Herculis system, and develop a model in which the blue and red components originate from two non-diametrically opposed cyclotron regions that are characterized by differing electron temperatures and opacities. Predictions are made regarding the linear and circular polarization properties of this important new magnetic variable.

The Molonglo Observatory Synthesis Telescope (MOST), operating at a frequency of 843 MHz, is currently surveying the southern galactic plane between 245° <l<360° and −1.5°<b<1.5°. The resolution of the survey is 43″ (HPBW), providing radio continuum maps of unprecedented resolution and sensitivity (1 mJy/beam) in this part of the sky. The survey involves 12-hour synthesis observations of over four hundred fields, each extending over one degree. Eighty of these have been mapped in the past year, bringing the number now completed to three hundred. The survey is revealing many faint structures with intriguing morphology, including filamentary emission associated with the Vela supernova remnant, and a number of very weak (<5 mJy/beam) disc-like objects.

This paper is a preliminary account of the calculation of the circularly polarized synchrotron radiation received from a distribution of electricallycharged particles confined to a thin shell in the magnetic field of a dipole. Calculations of the total radiation and the degree of linear polarization have previously been carried out, and these calculations are duplicated in part.

Large outbursts from the Sun which are widely extended over centimetre and decimetre ranges and show smooth time variations in intensity have been called microwave type IV bursts (μ-IV). Those bursts generally consist of more than two successive components, the spectra of which move progressively towards the lower frequencies. Furthermore there is a tendency for the decay times, which are defined as the times occupied by the decreasing parts of the bursts, to become successively longer. It seems worth while to make a quantitative study of the time variation of the decay times and flux densities of μ-IV burst spectra and to infer how the physical conditions in the source change with time.

The energy passing through the boundaries of a convective zone in a star, in an outward radial direction per second, must in total be equal to the luminosity of the star, provided of course that this zone does not encompass nuclear energy producing regions. If, in an endeavour to establish the nature of the convective motions in this zone, a section of the zone is modelled by considering steady cellular convection in a horizontal layer of Boussinesq fluid, it is on the basis of an average energy flux being imposed. Moreover, the sum of the conductive and convective heat fluxes is represented by the Nusselt number, which is specified and constant for the zone.

Most extra-galactic radio sources show angular structure over a wide range of size. Long-baseline interferometers and scintillation observations have shown that resolved sources extending over 10′ arc can have significant contributions from components <1″ arc. Observations at low frequency with the Molonglo cross telescope show also that a large fraction of the emission can come from halo, bridge or extended regions which may form a diffuse ridge or arc structure extending well beyond the small diameter components. However the majority of sources exhibit a basic double structure, and this has led to the adoption of two extended (Gaussian) components as an initial model for the interpretation of brightness distribution in most papers on the structure of extra-galactic sources. Parameters based on such a model will usually match the observed distribution quite well, but because of confusion, there is a danger in using intensity parameters for a model component to derive the spectral index for part of the source.

We present the results of a photometric survey for variability in ten X-ray-emitting low-mass stars in the Chamaeleon region. Eight of the stars we observed are bona fide pre-main-sequence members of the ∼2 Myr-old Chamaeleon I star-forming cloud. The other two stars are young with high levels of relative X-ray emission, but with discordant proper motions they are probable non-members of the cloud. In six of the stars we monitored, periodic variations on timescales of 2.5–11.5 d were detected, that we ascribe to stellar rotation and the presence of cool starspots. Two other stars, CHXR 20 and CHXR 85, show large amplitude variations at visual and near-infrared wavelengths and are candidate eclipsing binaries. Compared to the rotational properties of low-mass stars in the ≈8 Myr-old η Chamaeleontis cluster, we find that the older η Chamaeleontis stars have several times higher surface specific angular momentum than the younger Chamaeleon I stars. The apparent increase in angular momentum between ∼2 and 8 Myr might be due to changes in stellar internal structure as the stars evolve, or evidence for a different rotational history between members of the two star-forming regions.

One of the major problems in the theory of type III solar radio bursts concerns the development of the two-stream instability. On the one hand, Sturrock (1964) argued that one expects the instability to develop rapidly, and if it does it should prevent the stream from propagating through the corona, contrary to observation. On the other hand, one appears to require that the instability develop partially, in the sense that there is some significant amplified emission of Langmuir waves, in order to account for the observed emission.

Clusters of galaxies appear to contain much more mass than just that of the galaxies which provide most of their optical luminosity. There are two important ways to investigate the structure of their gravitational potential wells, firstly by an analysis of the radial velocities of the cluster galaxies, and secondly by a study of the X-ray emission from the hot gas which forms part of the intra cluster medium. We present new samples of radial velocity data for three clusters, and discuss some simple types of models of the X-ray sources.

Transit observations of the Sun can be made with the Molonglo radio telescope which is now in full operation at 408 MHz. Thus the Sun can be scanned once per day by eleven separate beams evenly spaced in declination. Because of foreshortening of the north-south arm with increasing zenith angle, the total coverage varies and in winter about 28′ arc can be covered by the eleven beams, whereas only 15′ is covered in mid-summer. This also means that the beamwidth in declination changes from 2′.9 at the zenith to about 5′.8 for the mid-winter sun. The beam is 2′.8 wide in right ascension. A further complication is the fact that the positions of the eleven beams cannot be chosen arbitrarily but can only be selected from a predetermined set of beam positions. These latter have been fixed by the phasing connections built into the telescope and cannot be changed easily. Hence for all the above reasons the strip of Sun which can be scanned will vary from day to day.

Observations of galactic HII regions in the longitude range 280° to 300° have recently been made at the OH-line frequencies 1612.231, 1665.402 and 1667.358 MHz using the Parkes radio telescope. Strong emission was observed at 1612 and 1665 MHz from a source near the regions of Hα emission RCW 48 and RCW 49 (Rodgers, Campbell and Whiteoak).

Compact radio sources have been observed over several years at 2.3 GHz by interferometers of the NASA-JPL Deep Space Network with trans- or inter-continental baselines to study the secular behaviour of fine structure appearing in these sources. A comparison of the variation in flux density of components of diameter < 0.001 arcsec with the corresponding variation in total flux density of the source at the same frequency indicated that variations could be wholly ascribed to components of this order of magnitude.

We present UBV photometry of SW Lac and analyse its light–curve to deduce starspot parameters for this star.

Rich clusters of galaxies are a common feature of the large-scale structure of the Universe. Those studied so far, show striking regularities with

1. (a) a smooth radial gradient of number density.

2. (b) ’isothermal’ distributions, which according to Bahcall (1975) have a scatter of only ±15% in the size of their characteristic core radii.

3. (c) their limiting structural diameters are ~50 Mpc (cf. Abell, 1975), if they are identified with superclusters.

4. (d) the magnitude of the velocity dispersion about their centres is generally 600-1000 km s-1, and the velocities are cpnsistent with a gaussian distribution (Yahil and Vidal, 1976; also Faber and Dressier, 1976).

5. (e) The extreme velocities are generally within ±3000 km s-1, and for Coma are ∼2400 km s-1 (Tifft and Gregory, 1976).

6. (f) elliptical galaxies tend to predominate near the centre, spirals in the surrounding loose groups.

In April 1967 the British and Australian Governments agreed jointly to build and operate a 150-inch (3.8m) optical telescope on Siding Spring Mountain, 16 miles west of Coonabarabran, N.S.W., where the Australian National University has an established observatory. To direct the construction and subsequent operation of the new telescope it was decided to create a statutory authority to be known as the Anglo-Australian Telescope Board. Pending the formation of this board, the two Governments, acting through the Department of Education and Science in Canberra and the Science Research Council in London, set up a joint policy committee to initiate the project.

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.

The Fleurs Synthesis Telescope (FST) has been used to map a number of bright, southern galactic HII regions at 1415 MHz. Descriptions of the FST can be found in Christiansen (1973) and associated papers. For the observations reported here, both the east-west and the north-south arms of the cross were used resulting in beamshapes which are nearly circular with half-power widths of 50” arc. The maps have been “cleaned” using a standard process (Högbom 1974).

The Lyman mission will undertake the first sensitive high resolution spectroscopic observations in the largely unexplored 912-1216Å region. This astrophysically critical wavelength interval is exceedingly rich in diagnostic spectral lines such as the Lyman series of atomic hydrogen and deuterium, the Lyman and Werner bands of molecular hydrogen and deuterium, and the resonance lines of numerous important species including CIII, NI-III and OVI. Lyman will have a major impact in all areas of modern astrophysics, with the most fundamental contribution being the determination of light element abundances in the local interstellar medium and in the intergalactic medium at low redshift. The mapping of hot gas (T ∼ 3 × 105K) and molecular hydrogen and HD in the disk and halo of our galaxy represent additional major objectives for which Lyman is uniquely qualified.

The Lyman payload will comprise a grazing incidence telescope and three spectroscopic instruments: the prime spectrograph operating between 912-1250Å with a resolution of λ/ Δλ ∼ 30,000, a far ultraviolet spectrograph (1200-2000Å;λ/ Δλ ∼ 10,000), and an extreme ultraviolet spectrograph (100-900Å; λ /Δλ ∼ 300). Observations will be conducted from a highly efficient 48 hour elliptical orbit which will allow long un-interrupted exposures and real time operations. It is anticipated that Lyman will be launched by Ariane in 1996, and will have an operational lifetime of at least 5 years. Data reception and spacecraft control will be undertaken from ground stations in Spain and in Australia.

Lyman is currently being studied at Phase-A level by Australia in close coordination with the European Space Agency. The scientific involvement is the responsibility of the Lyman Science Working Group, composed of members representing the various astronomical institutions in Australia. Funding to support the technical and scientific aspects of the mission is provided via the Australian Space Board and the Department of Industry, Technology and Commerce in recognition of the major opportunity that Lyman presents to the Australian aerospace industry.

The long-standing enigma of audible sound production simultaneous with the distant flight of large meteor fireballs is becoming increasingly well understood. Utilising Keay’s model linking the production of ELF/VLF electromagnetic radiation with turbulence in the fireball’s plasma trail, it has proved possible to adapt Ceplecha’s fireball model to include the criteria for turbulence and the consequent production of electrophonic sounds, yielding an excellent match with observations. It is becoming apparent that other geophysical phenomena also have the capacity to produce electrophonic sounds. These include aurorae, lightning and earthquakes.