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.

We present BVR observations of DK CVn from 2007 and 2008. We analysed the BVR light curves of the system and obtained the system's parameters. Using the ‘q-search’ method, we measured the mass ratio of the system (q) as 0.55. Taking the temperature of the primary component as 4040 K, the temperature of the secondary was found to be 3123 K. Several flares were detected, and the distributions of flare equivalent duration versus flare total duration were modelled using the One-Phase Exponential Association Function for these flares. The parameters of the model demonstrated that the flares are the same as those detected from UV Ceti stars. We also demonstrate that the variation at out-of-eclipse must be caused by some cool spot(s) on one of the components. The star is found to show two active longitudes in which the spots are mainly formed. Consequently, this study reveals that DK CVn should be a chromospherically active binary star.

Planetary nebulae (PNe) can be roughly categorized into several broad morphological classes. The high quality images of PNe acquired in recent years, however, have revealed a wealth of fine structures that preclude simplistic models for their formation. Here we present narrow-band, sub-arcsecond images of a sample of relatively large PNe that illustrate the complexity and variety of small-scale structures. This is especially true for bipolar PNe, for which the images reveal multi-polar ejections and, in some cases, suggest turbulent gas motions. Our images also reveal the presence or signs of jet-like outflows in several objects in which this kind of component has not been previously reported.

V- and I-band observations were taken over 9 months to study the RR Lyrae population in the metal-poor diffuse globular cluster NGC 6101. We identify one new variable, which is either a potential long-period red giant variable or eclipsing binary, and recover all previously identified RR Lyraes. One previously studied RR Lyrae is reclassified as an RRc type, while two period estimations have been significantly refined. We confirm that NGC6101 is Oosterhoff type II with a high ratio of n(c)/n(ab + c) = 0.833 with a very long mean RRab period of 0.86 d. By using theoretical RRLyrae period-luminosity-metallicity relations, we use our V- and I-band RR Lyrae data to gain an independent estimate of the reddening towards this cluster of E(B − V) = 0.15 ± 0.04 and derive a distance of 12.8 ± 0.8 kpc. The majority of the work in this study was undertaken by upper secondary school students involved in the Space to Grow astronomy education project in Australia.

Surface Brightness Fluctuations (SBFs) are one of the most powerful techniques to measure the distance and to constrain the unresolved stellar content of extragalactic systems. For a given bandpass, the absolute SBF magnitude M depends on the properties of the underlying stellar population. Multi-band SBFs allow scientists to probe different stages of the stellar evolution: ultraviolet and blue wavelength band SBFs are sensitive to the evolution of stars within the hot horizontal branch and post-asymptotic giant branch phases, whereas optical SBF magnitudes explore the stars within the red giant branch and horizontal branch regimes. Near- and far-infrared SBF luminosities probe the important stellar evolution stage within the asymptotic giant branch and thermally pulsating asymptotic giant branch phases. Since the first successful application by Tonry and Schneider, a multiplicity of works have used this method to expand the distance scale up to 150 Mpc and beyond. This article gives a historical background of distance measurements, reviews the basic concepts of the SBF technique, presents a broad sample of investigations and discusses possible selection effects, biases, and limitations of the method. In particular, exciting new developments and improvements in the field of stellar population synthesis are discussed that are essential to understand the physics and properties of the populations in unresolved stellar systems. Further, promising future directions of the SBF technique are presented. With new upcoming space-based satellites such as Gaia, the SBF method will remain as one of the most important tools to derive distances to galaxies with unprecedented accuracy and to give detailed insights into the stellar content of globular clusters and galaxies.

We review the importance of Centaurus A in high-energy astrophysics as a nearby object with many of the properties expected of a major source of very high-energy cosmic rays and gamma rays. We examine observational techniques and the results so far obtained in the energy range from 200 GeV to above 100 EeV and attempt to fit those data to expectations of Centaurus Aas an astrophysical source from very high to ultra-high energies.

The discovery of the radio source Centaurus A and its optical counterpart NGC 5128 were important landmarks in the history of Australian astronomy. NGC 5128 was first observed in August 1826 by James Dunlop during a survey of southern objects at the Parramatta Observatory, west of the settlement at Sydney Cove. The observatory had been founded a few years earlier by Thomas Brisbane, the new governor of the British colony of New South Wales. Just over 120 years later, John Bolton, Gordon Stanley and Bruce Slee discovered the radio source Centaurus A at the Dover Heights field station in Sydney, operated by CSIRO's Radiophysics Laboratory (the forerunner to CSIRO Astronomy and Space Sciences). This paper will describe this early historical work and summarize further studies of Centaurus A by other Radiophysics groups up to 1960.

In wavelength calibration using arc lines, the normal approach is to use the strongest unsaturated lines, leaving weak lines unused. A new method is proposed in this paper, which not only utilizes the strong spectral lines, but also makes most use of weak spectral lines. In order to validate the effectiveness of the method we propose, experiments are performed on simulated spectra. Firstly, two kinds of spectra are generated: one with a short exposure and another with a long exposure. Secondly, calibration lines are chosen from the short exposure and long exposure spectra separately according to some rules. Thirdly, the initial wavelength calibration is completed by using the selected short-exposure lines. Fourthly, the approximate centroids of the selected long-exposure lines are obtained by utilizing the result of the initial wavelength calibration. These are then adjusted iteratively to obtain the centroids. Finally, the selected lines from the short- and long-exposures are combined to obtain the final wavelength calibration. Compared with traditional calibration methods which only use short exposures and strong lines, the proposed method is shown to be more accurate.

We have recently confirmed the planetary nebula (PN) nature of PM 1–242, PM 1–318 and PM 1–322. Here we present high-resolution long-slit spectra of these three PNe in order to analyze their internal kinematics and to investigate their physical structure. PM 1–242 is a tilted ring and not an elliptical PN as suggested by direct images. The object is probably related to ring-like PNe and shows an unusual pointsymmetric brightness distribution in the ring. PM 1–318 is a pole-on elliptical PN, instead of a circular one as suggested by direct images. PM 1–322 is spatially unresolved and its spectrum shows large differences between the forbidden lines and Hα profiles, with the latter showing a double-peaked profile and relatively extended wings (FWZI ~325 km s−1). These properties are found in other PNe that are suspected to host a symbiotic central star.

Since the IUE satellite produced a vast collection of high-resolution UV spectra of the central stars of planetary nebulae (CSPNe), there has not been any further systematic study of the stellar winds of these stars. The high spectral resolution, sensitivity and large number of archival observations in the FUSE archive allow the study of the stellar winds of CSPNe in the far-UV domain where lines of species spanning a wide excitation range can be observed. We present here a preliminary analysis of the P Cygni profiles of a sample of ∼60 CSPNe observed by FUSE. P Cygni profiles providing evidence for fast stellar winds with velocities between 200 and 4300 km s−1 have been found in 40 CSPNe. In many cases, this is the first time that fast stellar winds have been reported for these planetary nebulae (PNe). A detailed study of these far-UV spectra is on-going.

We discuss the optimal detection of point sources from multiwavelength imaging data using an approach, referred to as MDET, which requires no prior knowledge of the source spectrum. MDET may be regarded as a somewhat more general version of the so-called ‘chi-squared’ technique. We describe the theoretical basis of the technique, and show examples of its performance with four-channel infrared broadband imaging data from the WISE mission. We also discuss the potential benefits of applying it to the multifrequency data cubes of the ASKAP surveys, and suggest that it could increase the detection sensitivity of searches for neutral hydrogen emission at moderately high redshifts.

We are developing a purely commensal survey experiment for fast (<5 s) transient radio sources. Short-timescale transients are associated with the most energetic and brightest single events in the Universe. Our objective is to cover the enormous volume of transients parameter space made available by ASKAP, with an unprecedented combination of sensitivity and field of view. Fast timescale transients open new vistas on the physics of high brightness temperature emission, extreme states of matter and the physics of strong gravitational fields. In addition, the detection of extragalactic objects affords us an entirely new and extremely sensitive probe on the huge reservoir of baryons present in the IGM. We outline here our approach to the considerable challenge involved in detecting fast transients, particularly the development of hardware fast enough to dedisperse and search the ASKAP data stream at or near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of the key technologies and survey modes proposed for high time resolution science with the SKA.

Due to its proximity, the neutral hydrogen belonging to Cen A can be observed at high resolution with good sensitivity. This allows us to study the morphology and kinematics in detail, in order to understand the evolution of this radio-loud source (e.g. merger history, AGN activity). At the same time, it is important to compare results to other sources of the same class (i.e. early-type galaxies in general and radio galaxies in particular) to see how Cen A fits into the global picture of early-type/radio galaxy evolution. The amount of Hi, the morphology of a warped disk with Hi clouds surrounding the disk and the regular kinematics of the inner part of the Hi disk are not unusual for early-type galaxies. The growing evidence that mergers are not necessarily responsible for AGN activity fits with the observational result that the recent merger event in Cen A is not directly connected to the current phase of activity. Based on these results, we conclude that Cen A has typical neutral hydrogen properties for an early-type and radio galaxy and it can therefore — from the perspective of Hi — be seen as a typical example of its class.

Cen A, at a distance of less than 4 Mpc, is the nearest radio-loud AGN. Its emission is detected from radio to very-high energy gamma-rays. Despite the fact that Cen A is one of the best studied extragalactic objects the origin of its hard X-ray and soft gamma-ray emission (100 keV <E< 50 MeV) is still uncertain. Observations with high spatial resolution in the adjacent soft X-ray and hard gamma-ray regimes suggest that several distinct components such as a Seyfert-like nucleus, relativistic jets, and even luminous X-ray binaries within Cen A may contribute to the total emission in the MeV regime that has been detected with low spatial resolution. As the Spectral Energy Distribution of Cen A has its second maximum around 1 MeV, this energy range plays an important role in modeling the emission of (this) AGN. As there will be no satellite mission in the near future that will cover this energies with higher spatial resolution and better sensitivity, an overview of all existing hard X-ray and soft gamma-ray measurements of Cen A is presented here defining the present knowledge on Cen A in the MeV energy range.

Dependences of electron and proton impact Stark width on the upper level ionization potential within different series of the neutral calcium spectral lines have been evaluated and discussed. The similar dependences previously found for the electron impact contribution were also obtained for the proton impact contribution to the Stark broadening. The emphasis is on the term structure influence on the studied Stark width dependences. The influence of the lower transition level and transition term is higher at low temperatures. After establishing these dependences, predictions were made for Stark widths of neutral calcium spectral lines not measured experimentally or calculated theoretically until now.

Cosmic radioactivity represents a cross-disciplinary theme and an interesting alternate viewpoint on cosmic nuclear astrophysics. Radioactive isotopes and their decay provide unique messages from sites of cosmic nucleosynthesis, as the decay is mediated by weak interaction physics and independent of environmental conditions. The radioactive clock of various isotopes traces stellar mixing processes and the process of solidification of bodies when the solar system was formed. Isotopic abundances directly reflect the conditions of their formation in the nucleosynthesis site, which is unobservable otherwise. Measurements range from meteorites and their included stardust grain compositions through to cosmic rays and electromagnetic radiation from infrared to gamma ray wavelengths. Thus, various astronomical disciplines with their different messengers of cosmic nucleosynthesis as seen through unstable, decaying isotopes are linked to the physics of nuclear reactions, and to theories and models of the variety of cosmic nucleosynthesis sites and of cosmic isotopic evolution.

This is a design study into the capabilities of the Australian Square Kilometre Array Pathfinder in performing a full-sky low redshift neutral hydrogen survey, termed WALLABY, and the potential cosmological constraints one can attain from measurement of the galaxy power spectrum. We find that the full sky survey will likely attain 6 × 105 redshifts which, when combined with expected Planck CMB data, will constrain the Dark Energy equation of state to 20%, representing a coming of age for radio observations in creating cosmological constraints.

Atmospheric modelling of the components of the visually close binary systems Hip70973 and Hip72479 was used to estimate the individual physical parameters of their components. The model atmospheres were constructed using a grid of Kurucz solar metalicity blanketed models and used to compute a synthetic spectral energy distribution for each component separately, and hence for the combined system. The total observational spectral energy distributions of the systems were used as a reference for comparison with the synthetic ones. We used the feedback modified parameters and iteration method to obtain the best fit between synthetic and observational spectral energy distributions. The physical parameters of the components of the system Hip70973 were derived as = 5700 ± 75 K, = 5400 ± 75 K, log ga = 4.50 ± 0.05, log gb = 4.50 ± 0.05, Ra = 0.98 ± 0.07 R⊙, Rb = 0.89 ± 0.07 R⊙, and π = 26.25 ± 1.95 mas, with G4 and G9 spectral types, and those of the system Hip72479 as = 5400 ± 50 K, = 5180 ± 50 K, log ga = 4.50 ± 0.05, log gb = 4.60 ± 0.05, Ra = 0.89 ± 0.07 R⊙, Rb = 0.80 ± 0.07 R⊙, and π = 23.59 ± 1.00 mas, with G9 and K1 spectral types.

The total number of true, likely and possible planetary nebulae (PN) now known in the Milky Way is nearly 3000, double the number known a decade ago. The new discoveries are a legacy of the recent availability of wide field, narrowband imaging surveys, primarily in the light of H-alpha. In this paper, we summarise the various PN discovery techniques, and give an overview of the many types of objects which mimic PN and which appear as contaminants in both Galactic and extragalactic samples. Much improved discrimination of classical PN from their mimics is now possible based on the wide variety of high-quality multiwavelength data sets that are now available. We offer improved taxonomic and observational definitions for the PN phenomenon based on evaluation of these better diagnostic capabilities. However, we note that evidence is increasing that the PN phenomenon is heterogeneous, and PN are likely to be formed from multiple evolutionary scenarios. In particular, the relationships between some collimated symbiotic outflows and bipolar PN remain uncertain.

The process of determining the number and characteristics of sources in astronomical images is so fundamental to a large range of astronomical problems that it is perhaps surprising that no standard procedure has ever been defined that has well-understood properties with a high degree of statistical rigour on completeness and reliability. The Evolutionary Map of the Universe (EMU) survey with the Australian Square Kilometre Array Pathfinder (ASKAP), a continuum survey of the Southern Hemisphere up to declination +30°, aims to utilise an automated source identification and measurement approach that is demonstrably optimal, to maximise the reliability, utility and robustness of the resulting radio source catalogues. A key stage in source extraction methods is the background estimation (background level and noise level) and the choice of a threshold high enough to reject false sources, yet not so high that the catalogues are significantly incomplete. In this analysis, we present results from testing the SExtractor, Selavy (Duchamp), and SFIND source extraction tools on simulated data. In particular, the effects of background estimation, threshold and false-discovery rate settings are explored. For parameters that give similar completeness, we find the false-discovery rate method employed by SFIND results in a more reliable catalogue compared to the peak threshold methods of SExtractor and Selavy.