A condensed summary of molecular cloud astrophysics is presented. Some examples of the power of combining near-IR and mm molecular line observations are given.

This paper presents evidence for the existence of a previously unobserved X-ray source in the constellation Cetus. The astronomical significance of an intense X-ray object located so far from the galactic disk has prompted this preliminary report.

Our current understanding of Herbig-Haro objects and their relationship with outflows and Pre-Main-Sequence objects is limited. Although the general mechanism of outflows is understood, the detailed questions concerning the outflowing material’s origin and the collimation mechanisms remain largely unanswered. The role of multi-waveband observations (visible, infrared and radio) is vital to our understanding of the shock dynamics of outflows.

This paper discusses high spatial resolution near infrared maps of three outflow complexes, HH34, HH46/HH47 and HH54, made using the Anglo Australian Observatory’s infrared camera, IRIS. For the first time molecular hydrogen emission is observed associated with the edges of outflow cavities. In the cases of HH46/47 and to a lesser extent HH34 molecular emission is seen coincident with highly collimated jets feeding the outflow cavities.

Tananbaum et al. (1976) have recently added to the Uhuru catalogue 4U1608-52, a source varying by over an order of magnitude in a time span of some months. They identified the object with MXB1608-52, a highly variable X-ray source of flares and bursts. (Kaluzienski et al. 1976; Belian et al. 1976; Grindlay and Gursky 1976a, b; Li 1976). There have been a number of earlier X-ray observations of sources very close to 4U1608-52 (Cooke and Pounds 1971; Luyendyk et al. 1973; Thomas et al. 1975; Grindlay and Gursky 1976b; Ricker et al. 1976), and in this paper we propose the identification of these earlier sources with 4U1608-52. We thereby obtain additional spectral information and can now rule out a globular cluster as the optical counterpart of the object.

In the usual model of discrete cosmic X-ray sources, it is assumed that a massive star loses matter to a companion neutron star, either through a stellar wind, or by means of Roche lobe overflow into an accretion disk around the neutron star (Pines 1980). The irifalling matter becomes ionized and is channelled along the magnetic field lines of the neutron star, so that it is accreted onto the star in a very small region at the magnetic polar caps. The physical conditions at these points are assumed to be: magnetic field B ~ 1012 G, plasma temperature ~107-108 K, and infall plasma velocity ~ 0.3 c-0.5 c.

The encounter of the spacecraft Voyager 2 with Neptune and its large satellite Triton in August 1989 will provide a crucial test of ideas regarding the origin and chemical composition of the outer solar system. In this pre-encounter paper we quantify the possibility that Triton is a captured moon which, like Pluto and Charon, originally condensed as a major planetesimal within the gas ring that was shed by the contracting protosolar cloud at Neptune’s orbit. Ideas of supersonic convective turbulence are used to compute the gas pressure, temperature and rate of catalytic synthesis of CH4, CO2 and solid carbon within the protosolar cloud, assuming that all C is initially present as CO. The calculations lead to a unique composition for Triton, Pluto, and Charon: each body consists of, by mass, 18.5% solid CO2 ice, 4% graphite, 0.5% CH4 ice, 29% methanated water ice and 48% anhydrous rock. This mix has a density consistent with that of the Pluto-Charon system and yields a predicted mean density for Triton of 2.20±0.05 g cm−3, for satellite radius equal to 1750 km.

The design and construction of the 30 m2 Bicentennial Gamma Ray Telescope at Woomera South Australia is described. This novel instrument is now completed and commissioning is underway. It is designed to observe astronomical sources at energies greater than ∼ 500 GeV by means of atmospheric Cerenkov light. It contains 55 spherical, glass mirrors of focal length 2.66 m arranged in three groups of 10 m2, to focus the light onto three sets of detectors operated in fast co-incidence. The recording electronics includes a rubidium clock to enable pulsars to be studied.

I am reporting here work done recently by the astrophysics group at the University of Queensland (notably G. D. Finn and R. L. Young). We are interested in the detailed formation of the profiles of the sodium-D solar absorption lines. These lines are very strong with extended wings and the object of the exercise is to determine how closely, under the physical conditions assumed to exist in the solar atmosphere, we can theoretically reproduce the detailed line profile which is observed.

Coudé spectra were obtained for a selection of giant and supergiant stars having spectral types in the range A9 to F2 to determine their atmospheric characteristics. The 12 members of Table 1 were compiled from The Catalogue of Bright Stars. This group of stars includes all known supergiants south of declination −15° and brighter than mv = 5.0 with spectral type between F5 and A5. Delta Canis Majoris (F81a) which has been the subject of many detailed investigations, was also observed to check for possible systematic errors in our equivalent widths. The spectra were obtained using the Coudé spectrograph of the 40 cm reflector at the University of Tasmania Observatory. Linear dispersions of 1.8Å mm−1 (0.12Å resolution) in the range 3600 to 4000Å and 2.4Åmm−1 (0.18Å resolution) in the range 4000 to 5000Å were used for stars brighter than third magnitude; 9Å mm−1 (0.4Å resolution) was used for stars fainter than third magnitude. The classification of 196 Car. was observed to be later (F8III) than the listed value and the spectrum of this star was not analysed further.

The Molonglo Observatory synthesis telescope has been used to obtain twelve observations of a 23′ arc field containing the active star AB Dor. On each occasion, an unresolved source close to the optical position of AB Dor was observed. The source exhibits day-to-day variations of flux density, with a mean value of ∼4 mJy. The identification of the source with the star and the variations in emission are discussed.

When the separation between two stars becomes sufficiently small, tidal forces may cause one or both stars to disrupt. Roche (1850) studied the problem of the stability of a liquid in synchronous, circular orbit with a point mass, and predicted an instability of the liquid star for separations ≤ 2.5 r S ⅓ where R is the initial radius of the liquid star, and S is the ratio of the mass of the point to the mass of the liquid star. Darwin generalized the problem to allow for two liquid stars in circular orbit. The whole of the classical research has been systematically analysed by Chandrasekhar (1969) using the tensor virial method. An error in Chandrasekhar’s analysis was corrected by Tassoul (1975).

Current observations and theories of solar bursts of types I, II and III suggest that the observed radiation may be emitted at a frequency close to the (fundamental) plasma frequency or its second harmonic. Refraction in a spherically symmetric corona would prevent radiation at the plasma frequency from reaching the observer except when the source is near the centre of the solar disk. However, it is found that fundamental frequency bursts are observed from anywhere on the disk. Recent analyses by Steinberg et al. and Riddle, in which the scattering of the radiation by coronal inhomogeneities was considered (in addition to refraction in an otherwise spherically symmetric corona), show that the radiation can escape from the plasma level and be observed for sources positioned almost anywhere on the disk. In addition, these authors and Fokker showed that a point source of radiation at the plasma frequency, or its harmonic, would be observed as an extended source with dimensions comparable with those observed. One implication was that the true source size is much smaller than the observed size.

Optical spectra of the ejecta of SN 1987A taken at the AAT now cover seven years of evolution. In recent years, SN 1987A has been in a phase known as freeze-out. The timescales for recombination have exceeded those of energy deposition, and the ionisation structure has become fixed. During this phase, cooling is slow and the optical spectrum has been extremely stable. Our latest spectrum, however, shows significant change. [FeI] and [FeII] emission from iron-rich clumps has dominated the optical emission from the supernova over the last four years. All the [FeII] features have disappeared in our latest spectrum from December 1993 and model fits of [FeI] features indicate that these clumps have cooled to the critical temperature of 1000 K. They may be entering a phase of rapid cooling known as the infrared catastrophe. In addition, emission at high velocities has strengthened, in line with the predictions of freeze-out. SN 1987A may be entering a new, and previously unobserved, phase in supernova evolution.

Recent modifications to the Fleurs digital receiver enable the additional correlations between the six 13.7 m dishes to be measured. Previously, only those correlations formed between the four east-west 13.7 m dishes and the thirty-two 5.7 m dishes were measured. This enables the production of three type of maps; each with full 20 arc second resolution but with properties which suit differing astronomical applications.

Gravitational lensing can significantly magnify the images of astrophysical sources, but only if the source lies within the Einstein ring of the lens. In consequence the chance of any Galactic star magnifying a more distant source is extremely small—much less than one in a million. However, the extra light travel time (‘Shapiro delay’) introduced by the presence of a lens can be large even when there is negligible effect on the image magnification, and as the relative positions of source and lens change so does the delay. In this paper we quantify these changes and the corresponding influence on apparent timing properties of pulsars. While the total Shapiro delay can be large, it is the temporal variations in this quantity which are measurable with pulsar timing. We find that the magnitude of the expected delay variations is too small to be detectable except during strong lensing events, which are extremely rare. Even in the case of a high-velocity pulsar in the Galactic Plane, the stochastic Shapiro delay is typically expected not to have a substantial influence on the timing properties. In consequence the viability of a pulsar-based time standard is not adversely affected by gravitational lensing.

The twenty years following the Second World War saw great changes in the research interests of the Observatory at Mount Stromlo, with the early emphasis on solar and geophysical phenomena giving way to stellar and galactic astrophysics. This paper traces the development of the astrophysical research work during the directorships of Woolley, who initiated the change of direction, and of Bok, who continued it. Apart from the shift in the Observatory’s research interests, these years were distinguished by (i) an outstanding period of telescope acquisition, which saw the commissioning of the 74 inch reflector, the 50 inch (formerly the Great Melbourne Telescope), the Yale/Columbia refractor (relocated from South Africa), and the Uppsala Schmidt; (ii) an Australia-wide site-testing programme and the consequent establishment of Siding Spring Observatory with the 40 inch, 24 inch and 16 inch reflectors (the site has subsequently, of course, also become the home of the Anglo-Australian Telescope, the U.K. Schmidt, and the ANU 2.3 m Advanced Technology Telescope); (iii) the incorporation of several major technological developments into the instrument complement of the Observatory, including photo-electric photometry, coudé spectroscopy, spectrum scanners, polarization instruments, and digital computers; (iv) the establishment of the link with the Australian National University and the consequent transformation of the Commonwealth Observatory into the Mount Stromlo Observatory; and (v) the setting up of a large and vigorous graduate school, comprising, at Bok’s departure, about fifteen PhD students on course.

In a previous paper (Van der Borght 1979) the techniques developed for studying finite amplitude convection in a compressible medium were applied to an investigation of super-granulation in the Sun. Assuming that the instability is due to He+ recombination, a model was derived which seems to indicate that convection in the upper 8000 km of the Sun may occur as an overtone and not as a fundamental mode. This investigation yielded results which were very close to those obtained from standard mixing-length theory.

The University of Tasmania has been operating muon telescopes since mid-1971 in an underground power station operated by the Hydro-Electric Commission at Poatina in Northern Tasmania. The equipment is located beneath ~ 150 m of rock, corresponding to a total absorption depth of ˜ 365 hg cm-2. The initial pilot experiment was reported (Fenton and Fenton 1972) at the May 1972 meeting of A.S.A., and results from the first two full years of operation were presented to the Hobart meeting of A.S.A. two years later (Fenton and Fenton 1974). We now have complete data for the 5-year period 1972-1976, together with provisional data for 1977.