The tortuous journey from theoretical suspicions to direct detection of gravitational waves took a hundred years and followed a crooked course. The field equations of general relativity evidently have wave-like solutions, but physical reality of these implied waves was doubted by many — including Einstein himself — for nearly fifty years. The question of physical reality was settled theoretically by the late 1950s, but for several more decades serious questions remained about what types of astrophysical systems might generate gravitational waves, and with what energies. The discovery of binary pulsar PSR B1913+16 led to dedicated development of much more accurate pulsar timing techniques, and results of these experiments motivated further theoretical work to clear up the quantitative questions about energy generation. By the late 1980s the generation of gravitational waves by the Hulse-Taylor binary pulsar was firmly established to be in quantitative agreement with general relativity. This experimental proof was almost surely a prerequisite for the funding of LIGO, the Laser Interferometer Gravitational-Wave Observatory, in 1992, which after nearly another quarter century achieved the first direct detection of gravitational waves.

We have started survey observations of the 22 GHz water maser sources associated with high-mass young stellar objects (HM-YSOs) as a part of the KaVA (KVN and VERA Array) large program (LP). The aim of our LP is to understand dynamical evolution of jets/outflows from HM-YSOs by analyzing 3D velocity structures of water maser features. In the first year (2016-2017), an imaging survey toward 25 HM-YSOs has been conducted and the 22 GHz water masers are detected toward 21 sources. Spatial distributions of maser features for individual sources are mapped. To complement physical properties in the vicinity of HM-YSOs, we have carried out ALMA cycle 3 observations of thermal molecular lines and continuum emissions toward 11 selected samples. Summary of the KaVA first year observations and the initial results from the ALMA toward one of our targets, G25.82-0.17, are reported.

Gamma-ray observations by the Fermi Large Area Telescope (LAT) have been used very successfully in the last 9 years to detect more than 200 gamma-ray pulsars. Sixty of these have been found by directly searching for pulsations in the gamma-ray data, but only one binary MSP has been found this way. Pulsars in binaries are often difficult to detect in radio data because of large eclipses, and some binary MSPs may even be radio quiet. For those, a gamma-ray blind search might be the only possibility for detection. While searches for isolated pulsars up to kilohertz frequencies are already computationally very challenging, blind searches for binary gamma-ray pulsars are simply infeasible without further knowledge of their orbital parameters. Here we present methods with which we can conduct searches for candidate binary gamma-ray pulsars for which orbital constraints are known from optical observations of a likely companion star. We also highlight some example sources where these methods have been used.

In this fifth paper of the series, we examine the spectroscopy and morphology of four southern Galactic planetary nebulae Hen 2-141, NGC 5307, IC 2553, and PB 6 using new integral field spectroscopy data. The morphologies and ionisation structures of the sample are given as a set of emission-line maps. In addition, the physical conditions, chemical compositions, and kinematical characteristics of these objects are derived. The results show that PB 6 and Hen 2-141 are of very high excitation classes and IC 2553 and NGC 5307 are mid to high excitation objects. The elemental abundances reveal that PB 6 is of Type I, Hen 2-141 and IC 2553 are of Type IIa, and NGC 5307 is of Type IIb/III. The observations unveil the presence of well-defined low-ionisation structures or ‘knots’ in all objects. The diagnostic diagrams reveal that the excitation mechanism of these knots is probably by photoionisation of dense material by the nebular central stars. The physical analysis of six of these knots show no significant differences with their surrounding nebular gas, except their lower electron densities. In spite of the enhancement of the low-ionisation emission lines of these knots, their chemical abundances are nearly comparable to their surrounding nebulae, with the exception of perhaps slightly higher nitrogen abundances in the NGC 5307 knots. The integrated spectrum of IC 2553 reveals that nearly all key lines that have led researchers to characterise its central star as a weak-emission line star type are in fact of nebular origin.

Most optical and IR spectra are now acquired using detectors with finite-width pixels in a square array. Each pixel records the received intensity integrated over its own area, and pixels are separated by the array pitch. This paper examines the effects of such pixellation, using computed simulations to illustrate the effects which most concern the astronomer end-user. It is shown that coarse sampling increases the random noise errors in wavelength by typically 10–20 % at 2 pixels per Full Width at Half Maximum, but with wide variation depending on the functional form of the instrumental Line Spread Function (i.e. the instrumental response to a monochromatic input) and on the pixel phase. If line widths are determined, they are even more strongly affected at low sampling frequencies. However, the noise in fitted peak amplitudes is minimally affected by pixellation, with increases less than about 5%. Pixellation has a substantial but complex effect on the ability to see a relative minimum between two closely spaced peaks (or relative maximum between two absorption lines). The consistent scale of resolving power presented by Robertson to overcome the inadequacy of the Full Width at Half Maximum as a resolution measure is here extended to cover pixellated spectra. The systematic bias errors in wavelength introduced by pixellation, independent of signal/noise ratio, are examined. While they may be negligible for smooth well-sampled symmetric Line Spread Functions, they are very sensitive to asymmetry and high spatial frequency sub-structure. The Modulation Transfer Function for sampled data is shown to give a useful indication of the extent of improperly sampled signal in an Line Spread Function. The common maxim that 2 pixels per Full Width at Half Maximum is the Nyquist limit is incorrect and most Line Spread Functions will exhibit some aliasing at this sample frequency. While 2 pixels per Full Width at Half Maximum is nevertheless often an acceptable minimum for moderate signal/noise work, it is preferable to carry out simulations for any actual or proposed Line Spread Function to find the effects of various sampling frequencies. Where spectrograph end-users have a choice of sampling frequencies, through on-chip binning and/or spectrograph configurations, it is desirable that the instrument user manual should include an examination of the effects of the various choices.

We describe the design and performance of the Engineering Development Array, which is a low-frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased array. The Engineering Development Array was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array precursor technology and expertise, specifically from the Murchison Widefield Array radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the Engineering Development Array’s receiver temperature as a function of frequency. The Engineering Development Array is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the Engineering Development Array in interferometric mode with the Murchison Widefield Array, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using Murchison Widefield Array-style precursor technology for Square Kilometre Array-scale stations. The modular architecture of the Engineering Development Array allows upgrades to the array to be rolled out in a staged approach. Future improvements to the Engineering Development Array include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

The current generation of experiments aiming to detect the neutral hydrogen signal from the Epoch of Reionisation (EoR) is likely to be limited by systematic effects associated with removing foreground sources from target fields. In this paper, we develop a model for the compact foreground sources in one of the target fields of the MWA’s EoR key science experiment: the ‘EoR1’ field. The model is based on both the MWA’s GLEAM survey and GMRT 150 MHz data from the TGSS survey, the latter providing higher angular resolution and better astrometric accuracy for compact sources than is available from the MWA alone. The model contains 5 049 sources, some of which have complicated morphology in MWA data, Fornax A being the most complex. The higher resolution data show that 13% of sources that appear point-like to the MWA have complicated morphology such as double and quad structure, with a typical separation of 33 arcsec. We derive an analytic expression for the error introduced into the EoR two-dimensional power spectrum due to peeling close double sources as single point sources and show that for the measured source properties, the error in the power spectrum is confined to high k ⊥ modes that do not affect the overall result for the large-scale cosmological signal of interest. The brightest 10 mis-modelled sources in the field contribute 90% of the power bias in the data, suggesting that it is most critical to improve the models of the brightest sources. With this hybrid model, we reprocess data from the EoR1 field and show a maximum of 8% improved calibration accuracy and a factor of two reduction in residual power in k-space from peeling these sources. Implications for future EoR experiments including the SKA are discussed in relation to the improvements obtained.

We present photometric observations of WD 1145+017 during six nights in early 2017. They exhibited asymmetric transits with durations of 10–50 mins and depths up to 50% in flux. We managed to track two deep features that drift in phase during 2.5-month season. This effect may be explained by period decreasing of the transiting formations due to their slow spiralling to the white dwarf. One of them seems to fragment in several smaller parts within a month. The structures causing the two deep transits have elongated shape whose sizes perpendicular and along the orbit are of the order of 1 R⊕ and 100 R⊕. They are parts of geometrically thin inhomogeneous disk (ring) around the white dwarf that is well within its Roche radius. This explains the observed dip activity of WD 1145+017 during the year 2017.

Observations of the most luminous quasars at redshift z > 6 reveal the existence of numerous supermasssive black holes (>199 M⊙) already in place about 12 billion years ago. In addition, the interstellar medium of the galaxies hosting these black holes are observed to be chemically mature systems, with metallicities (Z > Z⊙) and dust masses (>108 M⊙) similar to that of more evolved, local galaxies. The connection between the rapid growth of the first supermassive black holes and the fast chemical evolution of the host galaxy is one of the most puzzling issues for theoretical models. Here, we review state-of-the-art theoretical models that focus on this problem with particular emphasis on the conditions that lead to the formation of quasar seeds and their subsequent evolution at z ⩾ 6.

The SkyMapper 1.3 m telescope at Siding Spring Observatory has now begun regular operations. Alongside the Southern Sky Survey, a comprehensive digital survey of the entire southern sky, SkyMapper will carry out a search for supernovae and other transients. The search strategy, covering a total footprint area of ~2 000 deg2 with a cadence of ⩽5 d, is optimised for discovery and follow-up of low-redshift type Ia supernovae to constrain cosmic expansion and peculiar velocities. We describe the search operations and infrastructure, including a parallelised software pipeline to discover variable objects in difference imaging; simulations of the performance of the survey over its lifetime; public access to discovered transients; and some first results from the Science Verification data.

The results are presented for eclipsing binary KIC 2557430. The mass ratio was computed as 0.868 ± 0.002, while the inclination (i) was found as 69°.75 ± 0°.01 with T 2 = 6271±1 K. 50 frequencies were found in the period analysis. 48 frequencies of them are caused due to the primary component, a γ Doradus star, while two of them are caused by the cool spots. 69 flares were detected in the analyses. Two OPEA models were derived for flares, which indicates that the flares were come from two different sources. The Plateau value was found to be 1.4336 ± 0.1104 s for Source 1, which is seen as possible the secondary component and 0.7550 ± 0.0677 s for Source 2, which is seen as possible third body. The half-life value was computed as 2278.1 s for Group 1 and 1811.2 s for Group 2. The flare frequency N 1 was found to be 0.02726 h −1 and N 2 was computed as 0.00002 for Group 1, while N 1 was found to be 0.01977 h −1 and N 2 was computed as 0.00001 for Group 2. In a results, KIC 2557430 is a possible triple system consisting of a γ Doradus-type star, a chromospherically active star, and also a flaring third body.

Interest to lateral details of the solar filament shape named barbs, motivated by their relationship to filament chirality and helicity, showed their different orientation relative to the expected direction of the magnetic field. While the majority of barbs are stretched along the field, some barbs seem to be transversal to it and are referred to as anomalous barbs. We analyse the deformation of helical field lines by a small parasitic polarity using a simple flux rope model with a force-free field. A rather small and distant source of parasitic polarity stretches the bottom parts of the helical lines in its direction creating a lateral extension of dips below the flux-rope axis. They can be considered as normal barbs of the filament. A stronger and closer source of parasitic polarity makes the flux-rope field lines to be convex below its axis and creates narrow and deep dips near its position. As a result, the narrow structure, with thin threads across it, is formed whose axis is nearly perpendicular to the field. The structure resembles an anomalous barb. Hence, the presence of anomalous barbs does not contradict the flux-rope structure of a filament.

We have observed the Vela pulsar for 1 year using a phased array feed receiver on the 12-m antenna of the Parkes Test-Bed Facility. These observations have allowed us to investigate the stability of the phased array feed beam weights over time, to demonstrate that pulsars can be timed over long periods using phased array feed technology and to detect and study the most recent glitch event that occurred on 2016 December 12. The beam weights are shown to be stable to 1% on time scales on the order of three weeks. We discuss the implications of this for monitoring pulsars using phased array feeds on single dish telescopes.

During 2016 February, CSIRO Astronomy and Space Science and the Max-Planck-Institute for Radio Astronomy installed, commissioned, and carried out science observations with a phased array feed receiver system on the 64-m diameter Parkes radio telescope. Here, we demonstrate that the phased array feed can be used for pulsar observations and we highlight some unique capabilities. We demonstrate that the pulse profiles obtained using the phased array feed can be calibrated and that multiple pulsars can be simultaneously observed. Significantly, we find that an intrinsic polarisation leakage of −31 dB can be achieved with a phased array feed beam offset from the centre of the field of view. We discuss the possibilities for using a phased array feed for future pulsar observations and for searching for fast radio bursts with the Parkes and Effelsberg telescopes.

Advanced forecasting of space weather requires prediction of near-Earth solar-wind conditions on the basis of remote solar observations. This is typically achieved using numerical magnetohydrodynamic models initiated by photospheric magnetic field observations. The accuracy of such forecasts is being continually improved through better numerics, better determination of the boundary conditions and better representation of the underlying physical processes. Thus it is not unreasonable to conclude that simple, empirical solar-wind forecasts have been rendered obsolete. However, empirical models arguably have more to contribute now than ever before. In addition to providing quick, cheap, independent forecasts, simple empirical models aid in numerical model validation and verification, and add value to numerical model forecasts through parameterization, uncertainty estimation and ‘downscaling’ of sub-grid processes.

We use low frequency geomagnetic field measurements at two Antarctic stations to statistically investigate the longitudinal location of the polar cusp. The two stations are both located in the polar cap at a geomagnetic latitude close to the cusp latitude; they are separated by one hour in magnetic local time. At each station the Pc5 power maximizes when the station approaches the cusp, i.e. around magnetic local noon. The comparison between the Pc5 power at the two stations allows to determine the longitudinal location of the cusp. Our analysis is conducted considering separately different orientation of the interplanetary magnetic field. The results, which indicate longitudinal shifts of the polar cusp depending on the selected conditions, are discussed in relation to previous studies of the polar cusp location based on polar magnetospheric satellite data.

The morphological and chemical structure of the Milky Way today is an important constraint on models of the formation and evolution of the Galaxy. We use H ii regions, the sites of recent massive star formation, to probe both the Galactic spiral structure and the Galactic metallicity structure. H ii regions are the brightest objects in the Galaxy at radio wavelengths and are detected across the entire Galactic disk. We derive the distances to H ii regions using parallax measurements or by deriving kinematic distances. Here we summarize ongoing work to assess the accuracy of kinematic distances and to complete the census of Galactic H ii regions in the Southern sky.

A major avenue in the study of the Galaxy is the investigation of stellar populations and Galactic chemical evolution by stellar spectroscopy. Due to the dust obscuration, stars in the centre of the Galaxy can only be observed in the near-IR wavelength region. However, existing line lists in this wavelength region are demonstratively not of good enough quality for use in stellar spectroscopy. In response to this, we have developed an empirical astrophysical line list in the K-band based on modelling against the Sun and testing against Arcturus. Of ca. 700 identified interesting lines about 570 lines have been assigned empirically determined values.

We live on a very special planet in a very special solar system. Our planet has a benign climate. Our star has several habitable planets and is not so active as to inhibit the exploration and future colonization of these planets. In this short paper we review how the solar wind interacts with the planets, what factors matter in this interaction, and how active is our star.

Cepheids are excellent stellar tracers: they are bright enough to be observed even at large distances; their distances can be accurately determined via period-luminosity relations; their spectra contain numerous lines that enable us to derive abundances for many α, iron-peak or neutron-capture elements. Classical Cepheids are yellow supergiants that trace the young populations (⩽ 300 Myr); Type II Cepheids are post Horizontal Branch, low-mass, Population II stars (⩾ 10 Gyr). Both can be used for many purposes in Milky Way archaeology.