The effect of varying magnetic field strength on the frequency of oscillatory motions for cellular multimode magnetoconvection has been investigated. In addition the influence of the thermal, viscous and magnetic diffusivities have been taken into account and the range of preferred horizontal scales established. The relationship between the period of oscillation and the magnetic field strength is determined.

The study of short time scale phenomena of astronomical interest is often handicapped by the presence of wide band noise. In particular, in the study of the optical variability of stars, such noise arises from atmospheric scintillation, extinction variations, sky radiance variations and photon statistics. For example if in order to resolve rapid stellar variability we reduce the length (T) of the time intervals over which a photometric record is integrated and sampled, we find that the fractional noise fluctuations increase, eventually obscuring any intrinsic variability.

We present near-infrared spectroscopic observations over the wavelength range 0·9 to 2·5 μm of the AM Herculis system BL Hyi. During these observations, broad and resolvable cyclotron emission harmonics were visible near 1·25, 1·60 and 2·20 μm. We have interpreted these features as arising from a cyclotron emission region located near the white dwarf’s polar cap of magnetic field strength B p = 23 MG.

We examine the production of cosmic ray positrons by photon-photon pair production of high-energy γ-rays on starlight photons. We start by calculating the production rate as a function of positron energy and distance from the Sun resulting from interactions with sunlight. The results are generalized to production on other types of star. We calculate the average production rate per unit volume averaged over the local region of the galaxy, and we estimate the contribution to the observed intensity from this process.

The third UHURU catalogue of X-ray sources lists 64 sources at galactic latitudes higher than 20°, many of which have been identified with galaxies and clusters of galaxies. One of the best criteria for identifying a cluster of galaxies with an X-ray source is the extended nature of the X-ray source. Table I is a compilation of all clusters of galaxies known to be within the boundaries of X-ray error boxes. Not all have measured X-ray angular sizes (see column 3). Since the southern sky has been inspected too (Vidal 1975a), we believe that this list may represent a complete sample (down to the sensitivity of the UHURU satellite and the completeness of the Abell catalogue and the southern survey). Column 1 gives the optical identification, column 2 the 3U designation, column 3 the X-ray angular radius, column 4 the radio spectral index (see below), column 5 the redshift (corrected for galactic rotation) and column 6 the X-ray luminosities assuming the Hubble law. Numbers in parentheses give the references for the entries. When no such references are given, the data have been taken from Kellogg et al. (1973) and Bancall (1974).

The purpose of this paper is to provide a new expression for < ṗ > the average time-rate-of-change of momentum of cosmic-ray particles propagating in the interplanetary region. The expression derived replaces the previously used adiabatic deceleration formula and it is arrived at by a rearrangement and reinterpretation of the well known equation of transport for cosmic-rays. Thus, although we provide a new expression for < ṗ > we maintain the equation of transport and do not render invalid results for differential intensity and differential current density of cosmic-ray particles obtained by its solution (Jokipii 1971; Gleeson 1972).

Some years ago the full non-linear equations, within the one mode approximation, describing finite amplitude convection in a compressive medium with polytropic structure were derived (Van der Borght 1977). It is the purpose of the present paper to report on the numerical integrations of these equations and to show how these can be used to construct a convective model of granulation. In this way one may gain some insight into the structure of the outer layers of the Sun.

This is a brief description of the way I see the Schmidt functioning through the next three years. There are four important functions which must be maintained: (a) The Science from the Schmidt material must continue to be of the same high quality as that on which the Schmidt’s reputation has been built; (b) The service we provide to the Australian and British communities must continue despite the new trim (slim) appearance of the Schmidt staff and budget; (c) We must maintain our links with ROE, its Plate Library, which is the archive for Schmidt plate material, and Photolabs which provide some of the survey atlases; (d) We are being actively encouraged to promote Australian and British usage of the UK’s large measuring machines APM and COSMOS. Additionally, we are continually being encouraged to improve our efficiency. There is still at least one area in which we can do this and this is discussed.

We compare observations of a large coronal streamer made with the 80 MHz Culgoora radioheliograph, the Kcoronameter on Mauna Loa and the white light coronagraph on Skylab. The various measurements are not in agreement, and this raises fundamental questions about the nature of the corona and wave propagation through a streamer structure. The comparisons also indicate how precise data from the heliograph may contribute to a better understanding of these processes.

It has been known for about 5 years that the flux densities at 408 MHz of some sources change over time scales of a few months, but discovery of these variable sources has been largely accidental during the intensity calibration of various observing programs at Molonglo. This paper describes some results from systematic observation of 254 sources over a 12 month period, through which we hope to better understand the telescope performance, find more identifications in the southern sky, and recognise variable sources. An improved calibration will be applied to digital data from Molonglo observations since 1967 (both surveys and individual source observations), now stored on magnetic tape.

The Parkes Interferometer was designed and constructed by the CSIRO Radiophysics Laboratory. It is unique in having continuously variable North-South and East-West baselines making possible plotting the visibility function of a source in a single observation. From an engineering point of view it is noteworthy in that the receivers, control circuits and computer employ semi-conductors exclusively.

Film copies of original astronomical plates taken with the 1.2-metre UK Schmidt Telescope (UKST) at Siding Spring Observatory, New South Wales have been used for several years at Edinburgh University. Two teaching packages are intended for undergraduate use; the educational packages are mainly designed as visual aids for colleges, schools and amateur groups.

Determination of the large-scale structure of flare-produced disturbances requires either multiple spacecraft observations or an ensemble averaging of single spacecraft observations of a number of events. There is currently some confusion in the results of studies of shock normals derived from spacecraft data. Chao and Lepping (1974) suggest that the average shock shape near 1 AU is essentially spherical while Bavassano et al. (1973) suggest that the disturbance corresponds closely to the shapes predicted in the numerical simulations of de Young and Hundhausen (1971).

This paper presents recent stellar evolutionary calculations of the Asymptotic Giant Branch evolution of a 5M ⊙ model. It is found that temperatures at the base of the convective envelope reach up to almost 100 million degrees, high enough for much nucleo-synthesis to occur. Some implications are discussed briefly.

We describe a versatile infrared camera/spectrograph, IRIS, designed and constructed at the Anglo-Australian Observatory for use on the Anglo-Australian Telescope. A variety of optical configurations can be selected under remote control to provide several direct image scales and a few low-resolution spectroscopic formats. Two cross-dispersed transmission echelles are of novel design, as is the use of a modified Bowen-Burch system to provide a fast f/ratio in the widest-field option. The drive electronics includes a choice of readout schemes for versatility, and continuous display when the array is not taking data, to facilitate field acquisition and focusing.

The linearity of the detector has been studied in detail. Although outwardly good, slight nonlinearities prevent removal of fixed-pattern noise from the data without application of a cubic linearising function.

Specific control and data-reduction software has been written. We describe also a scanning mode developed for spectroscopic imaging.

The AAT’S new IR array camera, IRIS, has been used to image the Galactic Centre in the He I (2.058μm), H+ Br γ(2.166μm) and H2 1-0 S(l) (2.122μm) emission lines. The case is presented for UV-excitation of the molecular gas, as opposed to shocks.

One of the factors determining system sensitivity in radio astronomy measurements of microwave emission and absorption spectra is the flatness of the spectrometer response in the absence of any spectral features. Ripple appears as a quasi-sinusoidal variation of this baseline and occurs whenever two or more components of the same signal reach the receiver by different paths and interfere.