Young supernova remnants are poorly understood and few are known. Further examples may be present, but unrecognised, within existing catalogues of radio sources. G274.68–2.84 was recently suggested as one such candidate but our new radio map from the Australia Telescope indicates that it is not a supernova remnant. Rather, it appears to be extragalactic with a strong, variable, flat-spectrum nucleus, and a bright X-ray counterpart.

Established techniques for inverting observed solar spectra rely on the use of centre to limb observations.

The University of Tasmania balloon-borne large area X-ray telescope was flown from Alice Springs on 20 November 1978. A number of known X-ray sources were observed and a transient increase believed to be a gamma ray burst was detected.

Some results of spot modelling for 18 light curves of AB Dor are presented, covering the period 1980-1992. Using the technique of Budding and Zeilik (1987) to determine spot parameters, it is shown that photospheric spots on this star tend to form in one of two longitude belts separated by approximately 180 degrees. This can be compared to the similar active longitudes proposed by Zeilik et al.(1988, 1989) for the RS CVn stars SV Cam and RT And. The change in overall light level of AB Dor over the past 12 years indicates the possibility of a solar-type spot cycle although more photometric observations will be needed to confirm this.

An HI survey of the Large Magellanic Cloud (LMC) has been reanalyzed to find the transverse velocity of the LMC, and derive an upper limit of 4.5 × 1011 M⊙ for the mass of our Galaxy out to 50 kpc. A rotation curve is derived for the LMC from the HI data giving a best mass estimate of (4.0±0.4)×109 M⊙. Velocity observations of 97 planetary nebulae (PN) in the Large Cloud are used to compare the old and young components. Our results are found to be at odds with an earlier sample of 9 old clusters, which is interpreted as being due to the low number of objects in that sample. The w-component of velocity dispersion of the PN population is 35 km s-1 and that of the HI 10 km s-1. If this difference is a result of stellar diffusion then the average age of the PN population is 1.3 × 109 yr, implying a precursor mass of 1.8 M⊙ and a remnant mass of 0.63 M⊙.

Our re-examination of the neutral hydrogen gas in the Small Magellan Cloud has led to four important results. Firstly, we find that Hindman’s (1967) total content HI map is a satisfactory representation of the gas in the line of sight. Secondly, we find that the HI gas in the SMC exists in four distinct large masses separated from one another in radial velocity by 20 to 30 km s−1. Thirdly, having made this division of the gas we show that there is good correlation between the radial velocities of HII regions, supergiant stars and HI. Finally, we believe that our observations reveal that the SMC is associated with an extremely large trailing halo of HI gas which forms the major component of the inter-cloud bridge region.

A unique data set of 160 MHz solar noise storm positions and polarizations covering a complete sunspot cycle interval from the Skylab period of 1973 through the Solar Maximum intervals of 1980 and 1984 is presented in the form of 27.28-day synoptic plots.

A new family of solutions for stationary convection (Murphy and Lopez 1984) has been established which exists within the astrophysical range of parameter values — large Rayleigh number and low Prandtl number. These single mode Type II solutions, which have a non-zero component of vertical vorticity, apparently do not exist at higher Prandtl numbers and are characterized by a lower vertical velocity and heat flux, when compared to the equivalent single mode Type I solutions for Rayleigh — Benard convection with zero vertical vorticity. In turn the vertical component of vorticity associated with Type II solutions is responsible for modifying the horizontal components of the velocity field to establish cyclonic or swirling type solutions within the hexagonal convection cell.

Meteor rates have been measured with a large HF Radar at a number of frequencies. At the top end of the HF band our results match those of Greenhow (1963). However at lower frequencies we find high echo rates which indicate that past observations measured only a few percent of the total meteor flux incident on the Earth’s atmosphere. This explains the ‘missing mass’ discrepancy observed when radar results are compared with satellite or visual data. Accounting for’this missing mass results in a four-fold increase in the calculated total meteoroid mass influx to the surface of the Earth from 4000 to 16,000 tonnes per year. Our results also imply that the majority of echoes originate from altitudes above 100 km.

Recent seeing measurements at the Anglo-Australian Telescope (AAT) point towards the thermal characteristics of the telescope itself, in particular the temperature difference between the mirror and the dome air, as the most important factor degrading the seeing, more so than the temperature difference between the inside and outside air. We present the findings, propose clarifying experiments, and discuss possible remedies. We set the realistic target for the AAT to achieve median seeing of 1·5″ rather than the current 1·8″.

The close association between flare events having metric radio type II and type IV bursts and the subsequent occurrence of sudden commencement geomagnetic storms is well known. In such cases it has been amply demonstrated (e.g. Malitson et al. 1973; Cane et al. 1982) that the sudden commencement (SC) is caused by the same magnetohydrodynamic shock which originates near the Sun and which produces the type II burst. Recently, a study of geomagnetic storms thought to be associated with the disappearance of filaments from quiet regions of the Sun (Joselyn and McIntosh 1981) showed that several of these storms began with marked sudden commencements.

From extensive spectroscopic observations we derive the three-dimensional structure of the Homunculus Nebula surrounding η Carinae. The analysis shows that the two lobes are hollow and incomplete, and that the gas was ejected at similar epoch. Consequently the distribution of material we see reflects its initial velocity. Using the observed expansion velocity, and the known time of ejection, we derive a distance to η Car of 2.2 ± 0.2 kpc.

In this paper the author describes the instrumentation for the Infrared Space Observatory to be launched in 1993.

The Division of National Mapping has received, on long term loan from NASA and in co-operation with the Smithsonian Astrophysical Observatory, a Lunar Laser Ranging instrument consisting of a gigawatt pulsed ruby laser, a 150 cm aspheric Ritchey-Chretien telescope, and associated electronic equipment. The instrument was formerly operated by the Air Force Cambridge Research Laboratories at Mount Lemmon in Arizona. Its principal use by National Mapping will be direct determination of the distance between the telescope and any of the three retro-reflector arrays placed on the Moon at Hadley’s Rille, Fra Mauro and Mare Tranquillitatis by Apollo astronauts. Full scale operation in conjunction with similar instruments well separated in latitude and longitude, in particular at Mount McDonald in Texas and Mount Haleakala in Hawaii, will permit determination of Earth rotation and polar motion, lunar ephemeris and libration, and tectonic plate movement or continental drift, which justifies its use in a geodetic environment.

Twelve supernova remnants in the Large Magellanic Cloud have now been observed with the Australia Telescope. These were all imaged in total intensity and where possible the linear polarisation was also mapped. In many respects this survey is similar to previous single-dish observations of Galactic supernova remnants, and comparisons are made with these results. Preliminary images are shown for several sources. The survey is continuing with additional array configurations and at other wavelengths.

A high-resolution image of the strong extragalactic source 1343–601 has been made with the Molonglo Observatory Synthesis Telescope (MOST) at 843 MHz. The source is identified with a 10 mag galaxy (M v = −24) which is heavily obscured through our Galaxy. A recent redshift (z = 0.01215) gives a distance of 73 Mpc and a corresponding radio luminosity of log P 843 = 24.9.

The MOST image shows a core linked by a double jet to asymmetric lobes which are surrounded by a confined balloon (400 × 200 kpc2) of low-brightness plasma. This has a complex network of ridges or flows which lead out into the wider cluster medium. If similar balloons exist around other double sources, they could provide the depolarising medium required by the Laing-Garrington effect.

Separate observations show the core is compact with strong X-ray emission.

Conner et al. have reported the sudden emergence of a strong X-ray source at 3-12 keV in a position well removed from any previously known X-ray source. This source has been confirmed by Kitamura et al. We wish to report the results of an attempt to detect the source during a balloon flight made from Mildura, Australia, on 1969 August 25.