We re-evaluate the outer edge of orbital stability for possible exomoons orbiting the radial velocity planet discovered in the HD 23079 system. In this system, a solar-type star hosts a Jupiter-mass planet in a nearly circular orbit in the outer stellar habitable zone. The outer stability limit of exomoons is deduced using N-body and tidal migration simulations considering a large range of initial conditions, encompassing both prograde and retrograde orbits. In particular, we extend previous works by evaluating many values in the satellite mean anomaly to identify and exclude regions of quasi-stability. Future observations of this system can make use of our results through a scale factor relative to the currently measured minimum mass. Using a constant time lag tidal model (Hut 1981), we find that plausible tidal interactions within the system are insufficient to induce significant outward migration toward the theoretical stability limit. While current technologies are incapable of detecting exomoons in this system, we comment on the detectability of putative moons through Doppler monitoring within direct imaging observations in view of future research capacities.

We present the results of a search for additional exoplanets in all multiplanetary systems discovered to date, employing a logarithmic spacing between planets in our Solar System known as the Titius–Bode (TB) relation. We use the Markov Chain Monte Carlo method and separately analyse 229 multiplanetary systems that house at least three or more confirmed planets. We find that the planets in $\sim 53\%$ of these systems adhere to a logarithmic spacing relation remarkably better than the Solar System planets. Using the TB relation, we predict the presence of 426 additional exoplanets in 229 multiplanetary systems, of which 197 candidates are discovered by interpolation and 229 by extrapolation. Altogether, 47 predicted planets are located within the habitable zone of their host stars, and 5 of the 47 planets have a maximum mass limit of 0.1–2 ${\rm M}_{\oplus}$ and a maximum radius lower than 1.25 ${\rm R}_{\oplus}$ . Our results and prediction of additional planets agree with previous studies’ predictions; however, we improve the uncertainties in the orbital period measurement for the predicted planets significantly.

This paper is a preliminary report on the sky mapping being undertaken at the University of Tasmania using the Llanherne low frequency array. (Ellis 1972).

The observations are facilitated by the use of an on-line PDP-8 computer and the beam steering system described by Whitham (1975). In summary, a scanning system is used in which the computer is programmed to steer the telescope beam to a number of declinations with a time interval between settings such that a scan takes 5 minutes. Usually a scan of 12 declinations is chosen. Calibration levels obtained each hour and recorded on magnetic tape permit gain changes to be accounted for when the data is analysed from the tape.

During 1971/72 the radioheliograph at Culgoora, N.S.W. was used to observe 30 bright galaxies at 80 MHz.

A study has been made of the optical performance to be expected from an Antarctic Ritchey Chrétien telescope with a 2 m diameter primary mirror imaging directly onto a detector array in the K and L infrared windows. Near diffraction limited performance is provided across a flat 30 arcmin diameter field by compensating the astigmatism and field curvature with a meniscus lens which also serves as the Dewar window. With baffling inside and Narcissus mirrors outside the Dewar, extraneous radiation can be kept to a low level.

The Epoch of Reionisation (EoR) is the period within which the neutral universe transitioned to an ionised one. This period remains unobserved using low-frequency radio interferometers, which target the 21 cm signal of neutral hydrogen emitted in this era. The Murchison Widefield Array (MWA) radio telescope was built with the detection of this signal as one of its major science goals. One of the most significant challenges towards a successful detection is that of calibration, especially in the presence of the Earth’s ionosphere. By introducing refractive source shifts, distorting source shapes, and scintillating flux densities, the ionosphere is a major nuisance in low-frequency radio astronomy. We introduce sivio, a software tool developed for simulating observations of the MWA through different ionospheric conditions, which is estimated using thin screen approximation models and propagated into the visibilities. This enables us to directly assess the impact of the ionosphere on observed EoR data and the resulting power spectra. We show that the simulated data captures the dispersive behaviour of ionospheric effects. We show that the spatial structure of the simulated ionospheric media is accurately reconstructed either from the resultant source positional offsets or from parameters evaluated during the data calibration procedure. In turn, this will inform on the best strategies of identifying and efficiently eliminating ionospheric contamination in EoR data moving into the Square Kilometre Array era.

We present results, some preliminary, from a major new study of the star formation properties of a sample of nearby disk galaxies (Ferguson 1997). Our emphasis is on the faint outer regions of disks. Hα images, combined with broad-band images and spectroscopy of HII regions, constrain the present and past star formation rates and chemical enrichment. These data also allow study of faint diffuse ionised gas, which traces the influence of massive stars on their environment, and the structure of the interstellar medium.

HD 106515 AB (STF1619 AB) is a high common proper motion and common radial velocity binary star system composed of two G-type bright stars located at 35 pc and separated by about 7 arcsec. This system was observed by the Hipparcos satellite with a precision in distance and proper motion of 3 and 2%, respectively. The system includes a circumprimary planet of nearly 10 Jupiter masses and a semimajor axis of 4.59 AU, discovered using the radial velocity method. The observational arc of 21° shows a small curvature that evidences HD 106515 AB is a gravitationally bound system. This work determines the dynamical parameters for this system which reinforce the bound status of both stellar components. We determine orbital solutions from instantaneous position and velocity vectors. In addition, we provide a very preliminary orbital solution and a distribution of the orbital parameters, obtained from the line of sight (z). Our results show that HD 106515 AB presents an orbital period of about 4 800 years, a semimajor axis of 345 AU and an eccentricity of about 0.42. Finally, we use an N-body numerical code to perform simulations and reproduce the longer term octupole perturbations on the inner orbit.

Astonomy in Sydney predates Sydney Observatory by some 70 years. Lt William Dawes arrived with the First Fleet and set up an observatory at a place now called Dawes Point at the foot of the present Observatory Hill. His instructions were to observe a comet predicted by the famous astronomer, Edmund Halley, to return about 1790.

Microwave line investigations have shown that several bright southern galaxies contain dense molecular clouds overlying bright radio nuclei (see e.g. Whiteoak 1978). In terms of general kinematic models of galaxies the clouds have velocities that are anomalous, being consistent with radial motions both towards and away from the nucleus. To extend our knowledge of these motions we are investigating the distribution of optical spectral lines near the nuclei of the galaxies. We present here preliminary results for NGC 4945 and 5128.

A new surface installed recently over the central 16.7-m-diameter zone of the 64-m radio telescope at Parkes has extended the operating range of this instrument to millimetre wavelengths.

Using the SDSS and Pan-STARRS1 survey data, we found a likely companion of the recently discovered binary γ-ray radio-loud millisecond pulsar J0621+2514. Its visual brightness is about 22 mag. The broadband magnitudes and colours suggest that this is a white dwarf. Comparing the data with various white dwarfs evolutionary tracks, we found that it likely belongs to a class of He-core white dwarfs with a temperature of about 10 000 K and a mass of ≲ 0.5 M⊙. For a thin hydrogen envelope of the white dwarf, its cooling age is ≲ 0.5 Gyr which is smaller than the pulsar characteristic age of 1.8 Gyr. This may indicate that the pulsar age is overestimated. Otherwise, this may be explained by the presence of a thick hydrogen envelope or a low metallicity of the white dwarf progenitor.

Teaching an astronomy course online involves many challenges. One major challenge is the design of appropriate, practical and challenging forms of assessment which focus both on the astronomy content of the course and on the particular astronomy interests of the enrollees. This paper will discuss the assessment approaches we have chosen for our introductory-level subjects, the outcomes obtained and the reactions of the course participants. In particular, some of the wide variety of project work undertaken by the participants will be described.

Powerful water masers have been detected in 23 active galactic nuclei (AGN) to date. Most of the sources that have been monitored show evidence for variability, which may be either intrinsic (response of the masers to a time-varying pump or background source) or extrinsic (the effects of scintillation in the interstellar medium of the Galaxy). I briefly review the examples in which these mechanisms may be operating (interstellar scintillation in the Circinus galaxy, a time-varying background source in Mrk 348, and a time-varying AGN luminosity in NGC 1068).

The J = 1–0 rotational transition of carbon monoxide has been used to trace the molecular gas at five different positions in the Circinus galaxy using the Australia Telescope National Facility's 22 m radio telescope at Mopra. The intensity profile of the central CO emission has a full width at half maximum of 550 pc. The 12CO (1–0) spectrum at the centre of the galaxy has an integrated temperature of 145 K km S−1, with components peaking at 0·62 K and ranging in velocity from 200–600 km S−1. The total mass of molecular gas in the Circinus galaxy, assuming that the CO intensity profile of the galaxy is similar to the radio continuum, is at least 7·5±4·1 × 108 M⊙. This estimate, combined with previously published far infrared data, yields a value for the star-forming efficiency, SFE = 16±9 L⊙ M⊙‒1.

It is well known that interstellar travel is bounded by the finite speed of light, but on very large scales any rocketeer would also need to consider the influence of cosmological expansion on their journey. This paper examines accelerated journeys within the framework of Friedmann–Lemaître–Robertson–Walker universes, illustrating how the duration of a fixed acceleration sharply divides exploration over interstellar and intergalactic distances. Furthermore, we show how the universal expansion increases the difficulty of intergalactic navigation, with small uncertainties in cosmological parameters resulting in significantly large deviations. This paper also shows that, contrary to simplistic ideas, the motion of any rocketeer is indistinguishable from Newtonian gravity if the acceleration is kept small.

Comet C/1850 Q1 (Bond) is one of a number of comets catalogued with parabolic orbits. Given that there are sufficient observations, 104 in right ascension and 103 in declination, it proves possible to calculate a better orbit. Some of the difficulties of working with 19th century observations, which show considerable scatter, are discussed. Rectangular coordinates, both of the comet and the Sun, are interpolated by a recursive version of Aitken's method, rendering unnecessary the need to specify an order for the interpolation. Comet Bond's orbit is slightly hyperbolic.

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.

We present a comparison between the latest Parkes radio surveys (Filipović et al. 1995, 1996, 1997) and Hα surveys of the Magellanic Clouds (Kennicutt & Hodge 1986). We have found 180 discrete sources in common for the Large Magellanic Cloud (LMC) and 40 in the field of the Small Magellanic Cloud (SMC). Most of these sources (95%) are HII regions and supernova remnants (SNRs). A comparison of the radio and Hα flux densities shows a very good correlation and we note that many of the Magellanic Clouds SNRs are embedded in HII regions.

Evidence has been mounting for some years that cosmic rays have a dwell time in the disk of the Galaxy of 106-107 years. This evidence comes mainly from the study of the chemical composition of the cosmic rays, for if the particles were stored in the Galaxy for a longer time the heavy nuclei would suffer more collisions with interstellar matter and would be broken down into lighter nuclei or protons (see, for example, Shapiro).