Astronomy Australia

Abstract Colliding winds in massive binaries generate X-ray-bright shocks, synchrotron radio emission, and sometimes even dusty “pinwheel” spirals. We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27 yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf–Rayet wind self-absorption and near-transparent O-star wind foreground each 20 yr orbit, producing phase-locked radio and X-ray variability. This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to ∼1350 km s−1 in about one orbital cycle, naturally matching the IR spiral from 5″ down to within 0 . ″ 1, while also fitting the phase of the radio brightening. These kinematic constraints supply critical boundary conditions for future hydrodynamic simulations, which can link hot-plasma cooling, nonthermal radio emission, X-ray spectra, and dust formation in a self-consistent framework. WR 112 thus joins WR 140, WR 104, and WR 70-16 (Apep) as a benchmark system for testing colliding-wind physics under an increasingly diverse range of orbital architectures and physical conditions.

Abstract We use data from the Evolutionary Map of the Universe (EMU) and Polarization Sky Survey of the Universe’s Magnetism (POSSUM) radio southern sky surveys, conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) to compile a catalog of Galactic supernova remnants (SNRs) and candidate SNRs within the region of 277 . ° 5 ≤ ℓ ≤ 311 . ° 7 Galactic longitude, ∣b∣ ≤ 5 . ° 4 Galactic latitude, as well as an additional field along the Galactic plane, approximately 315 . ° 5 ≤ ℓ ≤ 323 . ° 0 Galactic longitude, −4.5 ≤ b ≤ 1.5 Galactic latitude. In the areas studied, there are 44 known SNRs and 46 SNR candidates that have been previously identified in the radio. We confirm eight of these candidates as SNRs based on evidence of linear polarization or through the calculation of nonthermal spectral indices. Additionally, we identify possible radio counterparts for seven SNR candidates that were previously only identified in X-rays (four) or optical (three). We also present six new SNRs and 37 new SNR candidates. The results of this study demonstrate the utility of ASKAP for discovering new and potential SNRs and refining the classification of previously identified candidates. In particular, we find that the EMU and POSSUM surveys are particularly well suited for observing high-latitude SNRs and confirming SNR candidates with polarization. The region studied in this work represents approximately one-quarter of the Galactic plane, by longitude, that will eventually be surveyed by EMU/POSSUM, and we expect that the ongoing surveys will continue to uncover new SNRs and SNR candidates.

Abstract We have searched for anomalous events using 2,520 hours of archival observations from Murriyang, CSIRO’s Parkes radio telescope. These observations were originally undertaken to search for pulsars. We used a machine-learning algorithm based on ResNet and Uniform Manifold Approximation and Projection (UMAP) in order to identify parts of the data stream that potentially contain anomalous signals. Many of these anomalous events are radio frequency interference, which were subsequently filtered using multibeam information. We detected 202 anomalous events and provide their positions and event times. Our results show that the UMAP unsupervised machine learning pipeline effectively identifies anomalous signals in high-time-resolution datasets, highlighting its potential for use in future surveys. However, the pipeline is not applicable for standard searches for dispersed single pulses. We classify the detected events and, in particular, we are currently unable to determine the possible origin of events that last multiple seconds. For these we encourage follow-up observations.

In the era of climate change concerns, global pandemics, decreasing funding availability and increasing restrictions on travel, the issue of online access to events has become an important topic of discussion. The importance of online access is rarely disputed, with surveys taken during the COVID-19 pandemic demonstrating the substantial increase in diversity across factors such as geographical location, gender, race and sexual orientation. However, the online experience is still usually considered subpar compared to attending a physical venue, and hybrid events that combine both groups often struggle to offer online attendees the same level of experience as the in-person crowd. Part of the answer to this challenge may be found in the utilisation of 3D virtual spaces, which can add a far greater sense of presence to an event, and also offer experiences that are not achievable at a physical venue. To explore the possibility for improving interactions between people online, we developed a virtual exhibit focussed on radio astronomy science and technology in the context of the CSIRO ASKAP radio telescope. As with many instruments in planetary science and astronomy, ASKAP consists of cutting-edge technology with a large physical footprint that cannot be transported to events for demonstrations. Moreover, the ASKAP site at Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory, is located in a remote area with restricted access to protect the telescope from radio interference. Bringing visitors onto the site is therefore rarely possible, presenting a problem in common with remote observatories as to how to share the experiences of scientific investigation.We demonstrated the virtual exhibit at a booth equipped with two virtual reality (VR) headsets at three primarily in-person scientific conferences: the 2023 Astronomical Society of Australia Annual Science Meeting in Sydney, Australia (ASA2023), the 2023 Asia Pacific Regional International Astronomical Union Meeting in Koriyama, Japan (APRIM2023) and the 2023 Union Radio-Scientifique Internationale General Assembly and Scientific Symposium in Sapporo, Japan (URSI2023). The aim was to showcase the capabilities of a virtual space in communicating science in an impactful and innovative way, and to demonstrate the strength of virtual platforms to connect and meet with people.The virtual space was hosted on the VR social network platform, “Spatial”. Spatial can be accessed from the Meta Quest VR headset, computers, and smartphones, providing cross-platform access that allows nearly any person with an internet-ready device to join the space. Visitors joining from their computer can access Spatial from the web browser, further lowering the barrier for entry by not requiring a dedicated application to be installed.From the left: examining the PAF inside the virtual exhibit, stepping into the 360 degree view of the ASKAP site, at the in-person booth at the URSI conference (final image from CAPjournal, in press.)The virtual exhibit design resembled a museum, with several rooms containing exhibits with accompanying written and audio information. This was a design choice chosen to give a feeling of familiarity to visitors who may not have previously tried virtual reality. Walking through the exhibit, visitors could chat to one another or receive a guided tour from our team. Only one member of our team was physically on-site at the conference venue, with other team members joining from their home country to meet with exhibit visitors. This emphasised the huge advantage of virtual spaces in bringing people easily together, regardless of their physical location. Visitors join the exhibit as an avatar, whose location within the virtual space allows for directional audio and audio fall-off. This enables a large group of people to potentially be in the space at the same time and easily hold simultaneous and overlapping conversations as in a physical event hall. Walking through the virtual exhibit moves you naturally between conversations, promoting interactions and networking.The virtual exhibit included a number of displays that would either be very difficult or not possible in a physical exhibition space. These included animated models of the ASKAP radio antenna and a full-scale model of the Phased Array Feed (PAF) receiver that increases the antenna’s field of view by a factor of 36. Upon approaching the PAF, the receiver expands outwards to reveal the internal components, and a holographic animation of a CSIRO staff member appears next to the model and describes the now visible parts. Visitors could also step inside a 360-degree view of the ASKAP site, providing a view of the antennas as if they were a scientist visiting on location. This year, we have extended on the initial project, developing an immersive multi-room virtual venue for online and hybrid conference applications. The venue includes galleries for displaying posters, interaction spaces, and exhibit halls, designed around providing familiar and personal experiences that will facilitate effective networking. The virtual venue is planned for use at three conferences to be held in 2024, including the Astronomical Society of Australia Annual Science Meeting and the International Astronomical Union General Assembly, and is intended to enable online participants, via a greater sense of presence, to engage more organically with meeting content and other attendees.This contribution will present an overview of our experience with the design, construction and demonstration of the virtual exhibits and spaces, with an emphasis on the current technological readiness of virtual reality approaches to augment interactions such as those that take place in conferences and exhibit halls. It is our goal to emphasise that the creation of this kind of virtual experience is not limited to experts in technology, but can be realised similarly with a modest amount of technical expertise combined with readily available hardware. The use of VR for online events has the potential to bring an audience together to share experiences that have the social strengths of a physical location, but provide sights and opportunities that go “beyond being there”. 

We report the Australian Square Kilometre Array Pathfinder discovery of a new Galactic supernova remnant (SNR) candidate G308.73+1.38, which we name Raspberry. This new SNR candidate has an angular size of 20.′7 × 16.′7, and we measure a total integrated flux of 407 ± 50 mJy. We estimate Raspberry’s most likely diameter of 10–30 pc which would place it at a distance 3–5 kpc, in the near side of the Milky Way’s Scutum–Centaurus Arm. We also find a Stokes-V point source close to the center of Raspberry with a ∼5σ significance. This point source may be the remaining compact source, a neutron star, or possibly a pulsar, formed during the initial supernova event.

ABSTRACT Using the Lyman Dropout technique, we identify 148 candidate radio sources at z ≳ 4–7 from the 887.5 MHz Australian Square Kilometre Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112 radio sources are currently known beyond redshift z ∼ 4. However, simulations predict that hundreds of thousands of radio sources exist in that redshift range, many of which are probably in existing radio catalogues, but do not have measured redshifts, either because their optical emission is too faint or because of the lack of techniques that can identify candidate high-redshift radio sources (HzRSs). Our study addresses these issues using the Lyman Dropout search technique. This newly built sample probes radio luminosities that are 1–2 orders of magnitude fainter than known radio-active galactic nuclei (AGN) at similar redshifts, thanks to ASKAP’s sensitivity. We investigate the physical origin of radio emission in our sample using a set of diagnostics: (i) radio luminosity at 1.4 GHz, (ii) 1.4 GHz to 3.4 μm flux density ratio, (iii) Far-IR detection, (iv) WISE colour, and (v) SED modelling. The radio/IR analysis has shown that the majority of radio emission in the faint and bright end of our sample’s 887.5 MHz flux density distribution originates from AGN activity. Furthermore, ∼10 per cent of our sample are found to have a 250 μm detection, suggesting a composite system. This suggests that some high-z radio-AGNs are hosted by SB galaxies in contrast to low-z radio-AGNs, which are usually hosted by quiescent elliptical galaxies.

ABSTRACT We have searched for weak fast radio burst (FRB) events using a data base containing 568 736 756 transient events detected using the Parkes radio telescope between 1997 and 2001. In order to classify these pulses, and to identify likely FRB candidates, we used a machine-learning algorithm based on ResNet. We identified 81 new candidate FRBs and provide details of their positions, event times, and dispersion measures. These events were detected in only one beam of the Parkes multibeam receiver. We used a relatively low S/N cut-off threshold when selecting these bursts and some have dispersion measures only slightly exceeding the expected Galactic contribution. We therefore present these candidate FRBs as a guide for follow-up observations in the search for repeating FRBs.

Abstract At least half of the local galaxies reside in galaxy groups, which indicates that the group is the common environment where galaxies evolve. Therefore, it is important to probe how significantly galaxies are affected by group environmental processes, in order to obtain a better understanding of galaxy evolution. We carried out a new CO imaging survey for 31 galaxies in the IC 1459 and NGC 4636 groups, using the Atacama Compact Array, to study the effect of the group environment on the molecular gas properties and the star formation activity. With our resolved CO data, combined with high-resolution H i images, we find asymmetric CO and H i distributions in the group galaxies. Compared to isolated galaxies, group members have relatively low molecular gas fraction and low star formation rate. These results suggest that the group environment can change the properties of cold gas components and star formation in group galaxies.

We report the first detection of a magnetic field in a star of the FS CMa type, a subgroup of objects showing the B[e] phenomenon. These stars are surrounded by an extended circumstellar medium, which is responsible for emission lines from both permitted and forbidden transitions, a large infrared excess due to dust, and a very complicated variability. The split of magnetically sensitive lines in the spectra of IRAS 17449+2320 unexpectedly revealed a strong magnetic field with strength of 6.2+/-0.2 kG. Our discovery indicates the importance of considering magnetic fields in studies of FS CMa stars, whose evolutionary status is still unknown. We found that IRAS 17449+2320 has an effective temperature of ~10,000 K. Several spectral lines affected by the circumstellar medium (e.g., O I 7772–7775 AA, Balmer lines) regularly exhibit redshifted absorption components with a period of 36.13 days. The same periodicity shows up in the equivalent width of the Halpha line. The analysis of our data suggests three possible scenarios for the nature and evolutionary status of the object: i) a magnetic A-type star primary with a hot dwarf secondary, ii) a binary merger, or iii) a magnetic Ap star near the terminal age main sequence. The latter one may represent an object which has been sought for decades and fills the gap in the observations and theory of magnetic Ap stars.