Absorption limits the distances at which X-ray sources may be observed at low photon energies (≲3 keV). Several authors have estimated the X-ray absorption coefficients of the interstellar medium by assuming a chemical composition such as that given by Aller for the general abundances of the elements.

The OVV blazar 3C 446 was monitored over seven months in 1997 with ground based telescopes and instruments on ESA's Infrared Space Observatory (ISO). The aim was to try to detect variations in the IR and see if these were correlated with optical variations. The object varied in the optical and near-IR during this period, but did not vary in the far-IR. Despite being a factor of ten weaker than in 1983, the optical-IR SED exhibited the same slope. The new far-IR observations from ISO allow us to determine the location of the turnover in the spectrum, caused by synchrotron self-absorption. It occurs just longwards of 100 μm.

The ‘holographic’ technique for accurately measuring the surface figure of large reflector antennas, described by Bennet et al, (1976) and Scott and Ryle (1977), has many advantages over older conventional survey methods. These include high speed, low cost, and the absence of any need for additional complex mechanical or optical survey devices. In essence, the technique consists of measuring the complex far-field response of the antenna at a single frequency using a terrestrial, satellite-borne or celestial radiation source of small angular diameter. This two-dimensional pattern is then Fourier-transformed to yield the complex illumination function across the antenna aperture. Antenna surface deviations are manifested as phase fluctuations in this function. In practice, a second antenna is needed to provide a phase reference.

We report on an initial survey of the cores of the Rho Ophiuchus and R Coronae Australis clouds, made with the AAT’s new IR array camera, IRIS. No turnover is seen in the initial luminosity function for ρ Oph to the sensitivity limit of the survey. Some implications for the low mass end of the initial mass function are discussed.

Four years ago a Table was shown in which the sensitivity of the Fleurs Synthesis Telescope (F.S.T.) was compared with that of three other radiotelescopes of similar resolvingpower (Christiansen 1972). At that time the high sensitivities quoted for the F.S.T., like those for all but one of the comparison telescopes were only theoretical since only the eastwest array of the F.S.T. was in operation and low noise r.f. amplifiers had not been installed. Now the telescope is in operation with characteristics close to those given in the Table quoted. Sources are mapped separately with the eastwest and north-south arrays and the two maps are combined. The combination produces maps with a resolution that isapproximately the same in declination and right ascension. This is unique amongst existing rotational synthesis telescopes. Some of these maps will be shown in papers now in preparation.

We present IIIaJ, IIIaF and IVN band images of HH objects digitised from the ESO/SERC Southern Sky Survey plates. These form part of a digital image database of southern HH objects, which allows the identification of emission and reflection nebulosity and the location of the obscured sources of outflows.

We previously reported a putative detection of a radio galaxy at $z=10.15$ , selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), and Herschel Space Observatory in the infrared, as well as $<$ 10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at $z<3,$ then it has an extremely unusual nature, and that the more likely solution is that the source lies above $z=7$ .

Initially some simple analytical properties based on the annual Zürich relative sunspot number are established for the 22-year Hale solar magnetic cycle. Since about AD1850, successive maximum sunspot numbers in a Hale cycle are highly correlated. Also, a regression model for the reconstruction of the 22-year Hale cycle has been formulated from proxy tree-ring data, obtained from spruce trees growing at a high altitude site in White River National Forest in Colorado. Over a considerable fraction of the past 300 years to AD1986, the ring-index time series power spectrum exhibits a strong 22-year periodicity, and more recently a significant spectral peak (at the 95% confidence level) at approximately 11 years. The model shows that the greatest variation in ‘amplitude’ in the magnetic cycle occurs over the early decades of the eighteenth century, when the sample size is small. Thereafter, a nearly constant amplitude is maintained until about AD1880 when a break occurs in both phase correspondence and amplitude, extending over the next three cycles. From AD1950 the signal recovers phase with the solar cycle, with reduced but increasing amplitude.

It is usual to describe the motion of the planets around the sun in terms only of the gravitational forces between them. The purpose of this note is to point out that another form of interaction between bodies in the solar system is possible through the medium of the solar wind.

It is now firmly established that a small anisotropy of the galactic cosmic rays exists, observable from Earth as a variation of intensity in sidereal time. The problem now is to determine more clearly the characteristics of the anisotropy and, in particular, its detailed spatial structure and how it depends upon the energy and composition of the cosmic rays. This is a very difficult task and, in the final analysis, may not be fully achievable from Earth-based observations. The purpose of the present paper is to describe briefly an installation now operating in Tasmania to provide further information on the spatial structure of the anisotropy.

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 March 1963 a paper by Hazard, Mackey and Shimmins in Nature, announced an accurate position for the radio source 3C 273. This was subsequently identified as the first known quasar. Through an innocent editorial mistake, the affiliation of the first author was wrongly attributed. This caused long-term animosity between the Physics Department of the University of Sydney and the CSIRO Division of Radiophysics.

Plots of periods against (25μm – 12μm) colour of OH/IR stars suggest that four IRAS sources, that have been associated with known OH/IR stars, either provide anomalous identifications, or are weak rather than regular variables. It is argued here that only one of these cases is an association error. OH15.7+0.8 and OH37.1–0.8 are the new proto–planetary nebula candidates.

We demonstrate the presence of a cluster of hot, population I stars at the very centre of the Galaxy, using the depth of the first overtone band of CO and the presence of emission in He I 2 ·058 μm and [Fell] 1·644μm to identify stars. The cluster is very compact and comprises at least several hundred stars. They lie close to the nonthermal radio source Sgr A* and dominate the luminosity and mass loss of the Galactic core. Their presence suggests that a starburst occurred at the Galactic centre.

A considerable amount of observational interest in short timescale phenomena has developed in optical astronomy in recent years. This interest has stemmed primarily from search efforts directed towards optical pulsars and the study of rapid fluctuations in cataclysmic variable and flare stars. Such studies have been made feasible by the development of the necessary photon pulse-counting technology required for rapid data sampling.

There are three non-thermal sources in the Large Magellanic Cloud which are recognized as supernova remnants. They are N49, N63A and N132D in Henize’s catalogue; a summary of their observing history is given by Westerlund and Mathewson (hereinafter referred to as ‘WM’). They are rather important to our knowledge of supernovae, as there are only four galactic supernova remnants (Cas A, the Crab, the Cygnus Loop and Vela) whose distances are known approximately from independent evidence. Since the distance to the LMC is well-known, the distance to sources in it is also known quite accurately.

Globular clusters in the Galaxy are all old objects, with ages of about 1010 years. The LMC is quite different: its globular clusters have ages anywhere between about 5 × 106 years and 1010 years. It is important to find out why globular clusters can form now in the LMC but not in the Galaxy; the galactic globulars play a major role in our picture of the early history of the Galaxy, and it is obviously desirable that we should understand the conditions under which these clusters can form.

The classical model of the interstellar medium consists of cool clouds (typical temperature 80 K, number density 20-40 cm-3) moving through a warmer interstellar medium (104 K, 0.15-0.3 cm-3) at a rms velocity of ~ 10 km s-1. More recent models have included the coronal gas (106 K) as part of this medium. We consider the collisions of these clouds in order to determine whether these collisions initiate star formation and/or change the state of the interstellar medium.

I would like to begin by saying what a pleasure it is for me to be here. For my entire adult life I have wanted to come to Australia. Actually, I have been invited to visit here twice before, but each time I was thwarted by circumstances beyond my control. But this time I was determined to (a) prove that the third time is indeed the charm, and (b) pay homage to Walter Stibbs, who in my mind is the epitome of a scholar and a gentleman. I have known Walter as colleague, teacher, and friend, not to mention as an inspiration, both professional and personal. So I am here today to try to give some sense of progress in the study of stellar atmospheres, a field that Walter has graced with his virtuosic touch. I will follow an unabashedly personal path, describing the development as I experienced it. I will focus almost entirely on early-type stars, where we may reasonably expect the atmospheric layers to be homogeneous, and in radiative equilibrium. Only at the end will I mention our nearest stellar neighbor, the Sun, which, because we can study it in so much detail, offers counterexamples to almost all of the the theory that works so well for early-type stars. I offer apologies in advance to anyone this approach may offend.

The Astronomical Society of Australia was formally constituted at an Inaugural Meeting held at 2 p.m. on Wednesday, 30th November, 1966, in the Grounds of the University of Sydney.