Spectropolarimetric observations of the 10 arc second region surrounding Eta Carinae have been made in the 8-13 μm wavelength band. The observed polarization, of a few percent, is due to emission of radiation from aligned grains. The radial position angle of the polarization suggests that gas streaming is responsible for the grain alignment.

In conjunction with the Stellar Interferometer project at Sydney University, a shearing interferometer system has been constructed to measure the atmospheric ‘seeing’ in real time using a portable telescope. The interferometric method allows direct measurement of the parameter ro, which derives from the theory of atmospheric turbulence. This permits reliable comparison with ‘seeing’ determinations by other methods. This paper briefly describes the instrument and presents initial results of the observing program.

Visual meteors, due to impinging meteoroids of radius about 1 cm, appear at a rate of a few per hour during non-shower periods. Smaller meteoroids (100 μm – 1 cm) give rise to less bright trails, but are much more abundant. These are usually detected by radars of about 10 m wavelength which, over the past 40 years, have produced a plethora of information concerning mass and height distributions, orbits, etc.

Using such ‘conventional radars’, the peak of the measured height distribution is found at about 95 km, with few meteors detected above 105 km. However, the flux detected is only a few percent of the total flux (a) measured using a large (10 m) optical collector, and (b) expected from a comparison with measurements by satellite impacts and zodiacal light observations (radii < 100 μm). One possibility is that the radars detect few low-velocity (V < ~25 km s-1) meteors since these produce little ionization and thus limit their detectability: the ionizing efficiency of meteors varies as ~ V7/2. In direct opposition, our alternative hypothesis is that the undetected flux is held in a faint high-velocity component which ablates at high altitude. These are not detected by conventional radars because meteor trails have ‘initial widths’ of about 3 m at 105 km; for a radar wavelength of 10 m, components scattered from different regions of the trail therefore destructively interfere, and the probability of detecting any meteor above 105 km is small.

In order to test our hypothesis we have measured the height distribution with a 150 m radar, and we are commencing ancillary observations at 50 m; compared to these wavelengths the initial width is small to at least 140 km. The results show a peak at 105 km with most meteors being above this, significant numbers occurring right up to 140 km. This suggests that the true flux is at least 10 or 20 times that previously deduced, having implications for the number of cornets in the recent past and the balance of material between the smaller bodies in the solar System.

A complete orbital light-curve of V2051 Oph in the IR H band is presented, together with a second eclipse in the J band. Simultaneous Rc band data were obtained. Eclipse depths in Rc, J and H are 1.8 mag, 1.0 mag and 0.8 mag respectively. No evidence for ellipsoidal variations due to the secondary was seen and constraints on the secondary are discussed.

We present preliminary results of a search for the optical counterparts of faint but energetic (1-13 keV) X-ray sources observed by the HEAO-1 satellite. The objects we have identified include Active Galactic Nuclei, Cataclysmic Variables, Be Binaries, and RS CVn Systems. A description is also given of the identification techniques and the X-ray database, which represents the most recent flux-limited all-sky survey of hard X-ray sources.

Linear stability theory for Rayleigh-Benard convection shows that for a specified Rayleigh number, greater than some critical value, only a finite range of horizontal wave numbers support convective instability in a horizontal layer of fluid heated from below. However, it is not possible to predict the preferred horizontal scale of established motions from this approach although it is clear from observations, particularly of the solar surface, that a preferred cell size does prevail. In an endeavour to establish a preferred horizontal scale appropriate non-linear modal equations have been integrated forward in time, initially incorporating a discrete band of wave numbers equally spaced across the range that supports convection, for a specific Rayleigh number. The horizontal resolution was improved in subsequent integrations by first deleting modes that had substantially decayed and then introducing new modes on a finer horizontal mesh in the vicinity of what appeared to be the evolutionary dominant mode. Finally, the multimode integrations were continued in time until the evolution of a dominant horizontal mode from within the restricted range was evident. Both the model characteristics and numerical scheme adopted placed limits on the degree of horizontal refinement that could be undertaken with confidence.

The star AB Dor (HD 36705) was first identified as an interesting object because of its strong Call H and K emission features (Bidelman and MacConnell 1973; Houk and Cowley 1975). It has a spectral class of G8 and appears to be a single star, since no radial velocity variations have thus far been detected, despite numerous attempts (e.g. Collier 1982; Innis et al. 1985a). Probably the most unusual and important feature about the star is its rapid rotational velocity, with a Vsini of 80 km s-1 (Collier 1982), which is more than 20 times that of a normal star of similar spectral class. AB Dor also shows a substantial photometric wave, commonly interpreted as indicating the presence of starspots. This wave has a typical amplitude of 0.05 to 0.15 magnitudes in V and a period of 0.514 days (e.g. Innis et al. 1985b). Combining this with the Vsini value gives a lower limit of 0.76 R⊙ for the stellar radius, while assuming the radius of a normal G8 dwarf yields an axial inclination of 60° ± 10°.

A proposal for a medium rigidity muon telescope system to be installed at the U.S. South Pole Station for observations of time variations of cosmic ray intensity is at present being prepared by Professor Pomerantz, Director of the Bartol Research Foundation, University of Delaware and Drs Jacklyn and Duldig of the Cosmic Ray Section, Antarctic Division, Department of Science. A novel approach to medium energy cosmic ray observations viewing in equatorial to mid-latitude directions is described. The absorber depth required for the proposed 50-1000 GV rigidity range would be achieved by locating the telescope system at a depth of approximately 7 metres water equivalent (MWE) in the ice and viewing at high zenith angles. Optimization techniques used in the telescope design are presented together with the unique advantages of the location. Justification for the experiment and comparison with important observatories in this rigidity range are also discussed.

We present a survey at J (1.25μm) and K (2.2μm) of 36 arcmin2 in the Bar and Inner Wing of the Small Magellanic Cloud. The (J-K) colour – bolometric magnitude diagram is constructed and compared with theory. For the first time a sparsely populated region of the diagram separating proposed carbon stars from oxygen rich stars has been identified. In addition large numbers of red sources have been found apparently fainter than the accepted limit for carbon star formation. These include extremely red sources which are good candidates for OH/IR sources and extreme carbon stars.

3C75 consists of a pair of twin-jetted radio galaxies near the centre of the cluster Abell 400 which is a strong extended X-ray source. Fibre spectroscopy from the AAT, combined with number counts of the galaxies in Abell 400 give the gravitational potential of the cluster which is used to model the X-ray source. The inferred pressure of the X-ray gas suggests that the lobes of the radio source are probably confined. Evidence of excess X-ray emission near the centre of the cluster is also found.

A theory for the source of free energy for the Langmuir waves producing Type II bursts is presented. It is shown that electrons accelerated at the Type II shock naturally develop a distribution function with an abrupt cutoff at a characteristic minimum parallel velocity (a ‘cutoff distribution) in a limited spatial volume ahead of the shock, irrespective of the acceleration process active at the shock. The long duration, narrow bandwidth Type II radiation is then explained in terms of Langmuir waves produced by a cutoff distribution. The theory also accounts in a natural way for split-band Type II bursts and herringbone bursts.

The single G8V active chromosphere star HD36705 (AB Dor) was observed at 8.4 GHz with the Parkes 64 m telescope during three observing sessions involving a total of 21 days in the interval 1985 December to 1986 February. Subsequent photometric observations were made of the star with the 0.25 m and 0.45 m telescopes of the Monash Observatory in 1986 March-April. Two strong radio flares, each lasting three days, were detected; they yielded peak radio powers of P8.4≈4×109 W Hz-1, comparable with the microwave power emitted by the RS CVn binaries. Significant circular polarization of 13% left-hand was measured on only one of the six active days. The 8.4 GHz flux density showed smooth variation over an interval of several hours, consistent with the flare source being partly occulted by the stellar disk as the star rotated. When all the radio data was phase-binned using the known rotation period of 0.514 day we found two radio maxima corresponding to radio sources at stellar longitudes ~180° apart. The subsequent photometric data showed intensity variations that were consistent with the starspots at the same approximate longitudes. We thus interpret our radio curve as showing the presence of comparatively small (<0.5 D*) radio sources in the corona above the star spots. The upper limit to source diameter gives a peak brightness temperature ≥2×l010 K, which can be achieved by gyro-synchrotron emission only if the source is optically thick and the electrons, with average energy ~ 2 MeV, have a hard energy spectrum. The observed radiation can be due only to very high harmonics of the gyro-frequency, leading to an estimate for the magnetic field strength of ~30G.

Many of the X-ray pulsars for which X-ray lightcurves have been presented in the literature exhibit asymmetric emission beams. We postulate the existence of an off-centre magnetic dipole field embedded in the rotating neutron star and show that such a field leads to varying rates of matter transfer between an accretion dise and the neutron star surface, over a rotation period. Assuming that the accretion rate onto the surface is simply related to the luminosity, we show that most of the observed asymmetries can be accounted for by this mechanism.

Properties of the microwave emission from HR1099 are examined in an attempt to determine whether the emission arises as gyro-synchrotron radiation from mildly relativistic electrons trapped in magnetic fields above starspots on the active K subgiant component. It is shown that radio curves do not exhibit a systematic variation in phase with the rotation rate, as one might expect for emission from a source situated above a long-lived starspot. However, there is some evidence that the radio flaring occurs at two preferred longitude zones. Whether these zones agree with starspot locations remains to be determined by light curve modelling. What we can say with confidence is that the measured spectral index of the microwave emission does not fit a simple gyro-synchrotron source model, such as that proposed to explain the observed reversal with frequency of the sense of circular polarization.

Photoelectric B and V light curves and high dispersion spectroscopic observations were obtained in 1985 February for the rapidly rotating spotted star HD 36705. The visual light range was about 0.09 magnitude, with a well correlated B-V change of approximately 0.04 magnitude, the star being redder when faintest. There is evidence for a broadband flare of ~0.05 magnitude in V and 0.07 magnitude in B. This occurred near maximum light.

Spectroscopic observations show a variation in the equivalent width of the Ca K emission by a factor of about two in antiphase with the photometric variations, maximum emission corresponding to minimum brightness. This is probably due to bright plages and enhanced chromospheric heating associated with the photospheric starspots.

High dispersion, high signal-to-noise spectroscopic observations confirm the presence of lithium λ 6708 as reported by Rucinski (1982, 1985).

Several interpretations of the nature of HD 36705 are discussed; however at present none is completely satisfactory and further observations are required. As the star is probably at less than 100 pc, a parallax determination may be possible, and could help answer many of the questions concerning HD 36705.

Angular diameters of Magellanic Cloud planetary nebulae obtained using speckle interferometry on the AAT are presented. The mass of ionized gas in each nebula is derived from the angular diameter and published Hβ line fluxes; the derived masses range from 0.005M⊙ to 0.19M⊙, with a mean value of 0.08M⊙. All the planetary nebulae observed are relatively small (diameter ≲0.13pc), young (age ≲ 2500 years), bright and dense. They are therefore almost certainly only partially ionized, so that the masses derived for the ionized parts of the nebula are lower limits to the total nebula mass.

The dynamics exhibited by systems, such as galaxies, are dominated by the isolating integrals of the motion. The most common are the energy and angular momentum integrals. The motions in a system with a full complement of isolating integrals are regular, that is, periodic or quasi-periodic. Such a system is integrable. If there is a deficiency in the number of integrals, then the motions are chaotic. There is a fundamental quantative difference in the motion, depending on the number of integrals. A technique, called Generalised Painlevé analysis, based on complex variable theory allows the user to determine if a system is integrable. Two new integrable cases of the Henon-Heiles system are presented, bringing the total number of such integrable potentials to five. It is highly probable that there are no further integrable cases of the Henon-Heiles potential. Five cases of the quartic Verhulst potential, defined by certain restrictions on the coefficients, which are found to be integrable are summarised.

Known Southern flare stars and RSCVn-like variables are being observed with the Molonglo Observatory Synthesis Telescope in an attempt to detect quiescent (non-flaring) emission. Two flare stars out of 7 and one RSCVn out of 8 have been detected. Quiescent emission has not been observed previously from these sources at such a low frequency. All sources so far detected have mean flux densities below 10 mJy and in at least two of them the emission varies with a time scale of about one day.

We present some preliminary results of an optical and radio study of the very active RS CVn binary HD 127535. Photometric measurements show the presence of a large amplitude wave which exhibits marked changes in shape and range on time scales as short as a few months. This photometric variation is almost certainly due to large cool starspots on the cooler, more luminous component. As part of a survey of southern active-chromosphere stars with the Parkes radio telescope, HD 127535 has been observed at 5, 8.4 and 22 GHz. No detection was made at 5 GHz, possibly because of confusion due to the angular proximity of the star to the galatic plane. However, it is one of the strongest sources detected in the 8.4 GHz survey, and is one of only two stars detected at 22 GHz. Photometry obtained two cycles before the 8.4 GHz observations suggest a possible correlation between the radio emission and the photometric wave, i.e. spot visibility, but more data are needed.

The SRC-J and ESO-B Sky Survey copy films are being used to compile a major new catalogue of apparent diameters, axis ratios, and relative bar/ring position angles of inner and outer rings in more than one thousand southern galaxies. This paper presents a preliminary analysis of the data for about two hundred SB rings of both types. It is concluded that the rings have a wide range of intrinsic eccentricities, and more importantly that they have preferred alignments, one mode for inner rings and two for outer rings, with respect to bars.