We present three southern transiting giant planet candidates alerted by the Transiting Exoplanet Survey Satellite (TESS) mission and investigated at the University of Tasmania Greenhill Observatory (UTGO). The candidate planets are orbiting thin disk G-dwarf main-sequence stars with roughly solar metallicity, possessing orbital periods between 2.9 - 3.3 days and radii of 1.1 - 1.3 RJ. We performed ground-based follow-up photometry primarily with the UTGO Harlingten 50 cm, then gathered reconnaissance spectra, high angular resolution imaging and high-precision radial velocities to rule out false positive scenarios. We confirmed that two of these systems host true exoplanets and constrained their masses. TOI-3053b is a typical hot Jupiter, with M3053b = 0.85 ± 0.12 MJ and a bulk density of ρ3053b = 0.64 ± 0.10 g cm–3. TOI-3278b/HATS-78b is a hot Saturn-mass planet (M3278b = 0.30 ± 0.07 MJ) with a highly inflated atmosphere and a low density of ρ3278b = 0.21 ± 0.05 g cm–3. The other candidate (TOI-3272.01) remains unconfirmed, but appears consistent with being a hot Jupiter. TOI-3272.01 is notable as a candidate planet orbiting a potentially young to intermediate age star, with a rotational analysis indicating an age estimate of T3272 = 1.1 ± 0.2 Gyr. These systems add to a growing sample of hot giant planets from TESS that may provide constraints on the migration pathways and radius inflation of the broader close-in exoplanet population.

Veloce began operations in tandem with the Transiting Exoplanet Survey Satellite (TESS), at a time marked by rapid growth in the number of known exoplanets. This growth underscores Veloce’s core purpose: the detection of small planets orbiting cool stars. The spectrograph is mounted on the Anglo-Australian Telescope, and is a high-resolution, fibre-fed instrument that offsets the costs of instrument stabilisation onto data analysis. In order to achieve high resolution for the spectrograph, it was necessary to sub-sample the typical telescope seeing with multiple small fibres. Unfortunately, this complex optical design solution causes the images of different fibres to overlap. The overlapping images have limited the radial velocity precision of the spectra. The applicability of Veloce to general spectroscopy has been greatly improved by extending the wavelength range to cover green and blue ranges down to 396 nm. To date, the data are only available as raw images, with some data being custom reduced on a case-by-case basis, but no official general reduction pipeline is available. In this paper, we introduce a new, fully automated, end-to-end pipeline designed for both quick-look assessment during observations and the production of science-ready spectra. The pipeline is publicly available, and while its extraction method is intentionally simplified, the results are consistent and coherent for use in non-radial-velocity science, including stellar characterisation and elemental abundance work.

Multi-wavelength observations of low-mass X-ray binaries (LMXBs) during bright outbursts reveal many details about the coupling of their inflows and outflows. However, only high angular resolution radio observations are able to resolve and track the motion and variability of individual jet ejecta. We present the results of our intensive VLBI campaign on the black-hole low-mass X-ray binary (LMXB) Swift J1727.8-1613 during its 2023-2024 outburst. We observed the repeated quenching and re-establishment of the highly-extended continuous core jet during several transitions between hard-intermediate and soft-intermediate states, and the repeated ejection of transient jets. Using time-dependent visibility model fitting, we tracked the motion of nine discrete jet knots, obtaining some of the most precise measurements of transient jet proper motions and ejection dates in an LMXB. These ejecta were only detectable for a short time with VLBI, and some showed rapid intra-observation flux density variability that was not captured in image reconstructions. For the first time, we use time-dependent visibility modelling to fit a piecewise model for the jet knot flux densities, allowing us to create complex, non-parametric light curves of their intra-observation variability. We observed the launching of multiple ejecta across several state transitions, however, we could not identify a consistent signature of jet ejection in the available X-ray intensity or hardness data. We constrained the intrinsic speeds and bulk Lorentz factors of the jet knots, finding that Swift J1727.8-1613 launched both mildly relativistic (βΓ<1) and highly relativistic (βΓ>2) ejecta throughout its outburst. We used their proper motions to constrain a posterior distribution for the maximum inclination angle of the jet axis, which had 50th, 84th, and 99th percentiles of 40°, 50°, and 66°, respectively. These unique observations of the repeated ejection of transient jets by a single LMXB reveal that fixed parameters such as black-hole mass, black-hole spin, and spin-orbit misalignment do not uniquely determine the varying properties of transient jets, particularly their speeds and Lorentz factors.

We present results of a continuation of the search, started by Baran et al. (2023, 2024), for short-period pulsations in compact stellar objects observed during Sectors 61 – 97 of the TESS mission. We use newly collected and other unpublished spectroscopic data to confirm or determine spectral classification of many stars included in this work. From the TESS photometry, we identify 36 short-period hot-subdwarf pulsators, including 33 pulsators not known before the TESS mission. We present the results in a similar way to Baran et al. (2024). We provide an update on the instability strip and the evolutionary status of hot subdwarf stars with a more populated Kiel diagram. We discuss hybrid candidates as well as the results of testing correlations between theoretical predictions of the highest amplitude pulsation modes and spectroscopic parameters of stars found to be pressure-mode (p-mode) pulsators in the TESS mission. We report the discovery of the first p-mode dominated V366Aqr – type star, the first helium-enhanced hot subdwarf pulsator, and an unusual blue large-amplitude pulsator. We revise a classification of a previously reported BLAP star and correct the final TESS p-mode star statistics by accounting for a new spectral classification of two hot subdwarfs.

HLX-1 is a prominent intermediate-mass black hole (IMBH) candidate, historically exhibiting recur-rent X-ray outbursts with spectral state transitions analogous to those observed in stellar-mass black holes. Here, we present new Hubble Space Telescope, Chandra, and Swift observations from 2018–2022 to characterise the late-time flux decline. HLX-1 has persisted in a low X-ray luminosity state (LX ≈ a few ×1039 erg s−1) since the end of its last outburst in 2017. We observe a significant decoupling between the X-ray and optical/UV emission: while the X-rays have faded by at least two orders of magnitude from peak outburst luminosity (in 2010) to the current low state, the optical/UV flux has declined much more slowly over the same time. This results in an X-ray/optical luminosity ratio in-consistent with X-ray reprocessing in a standard accretion disk, as this would require an unphysical reprocessing fraction >100% at late times. Instead, we find that the optical/UV evolution is well-fit by a cooling, expanding photosphere (T ≈ 30, 000 K), similar to the late-stage evolution seen in tidal disruption events (TDEs). The redder component of the optical emission is instead consistent with the old stellar population of a massive star cluster (IMBH host). The pre-2017 X-ray bursting phase is consistent with simulations of disk instabilities in TDE evolution: this strengthens the scenario of HLX-1 as an IMBH TDE. Furthermore, our observations resolve the morphology and flux of the mysterious far-UV emitter, seen in projection next to HLX-1, into a ring-like star-forming structure. We re-assess the possibility that HLX-1 and its host star cluster are physically associated with this starburst dwarf, perhaps via a high-speed collision.

In this pilot study, we use data from the First Large Absorption Survey in HI (FLASH) to search for redshifted HI 21 cm absorption at 0.4 < z < 1 towards 157 bright radio sources with Interplanetary Scintillation (IPS) measurements at 820 MHz in a single field observed with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. The ASKAP IPS measurements, which use only 2.5 minutes of observing time in total, allow us to estimate the compactness of these radio sources on sub-arcsecond scales at a frequency within the 712–1000 MHz FLASH band. In particular, the Normalised Scintillation Index (NSI) for each source reflects the fraction of the flux density arising from compact components less than 0.1 arcsec in diameter. We find that 18 ± 5% of ASKAP sources with flux densities above 150 mJy are highly compact with NSI ≥ 0.8 – implying that at least 80% of their radio emission arises from a single region smaller than about 800 pc in size. The compactness of these sources makes them ideal probes for an HI absorption search, since the covering factor for any HI gas clouds along the line of sight is likely to be high. About half of the sources with NSI ≥ 0.8 also have peaked radio spectral energy distributions (SEDs), consistent with previous IPS studies at lower frequencies. These pilot results imply that IPS measurements with ASKAP can provide a simple and powerful tool for identifying uniform samples of compact radio sources at frequencies of a few hundred MHz across large areas of sky. With FLASH, we detect two new HI absorption lines against compact sources in the ∼ 30 deg2 region of sky covered by the IPS data; an associated HI line at redshift z = 0.9540 (with a matching optical redshift) in MRC 2125-237 (NSI = 0.98), and a likely intervening line at z = 0.4632 towards MRC 2131-241 (NSI = 0.84). The radio sources with these two detections are both bright and compact, with peaked radio SEDs.

Wind-fed accretion onto magnetised neutron stars drives long-term spin variability that can be used to trace angular-momentum transfer in structured stellar outflows. We analyse five years of TESS optical timing to measure the spin evolution of the wind-fed X-ray pulsar 4U 1954+319, which hosts the slowest known accretion-powered pulsar. Coherent hour-scale pulsations are detected in all eight TESS sectors. The optical spin period evolves non-monotonically from 5.51 ± 0.06 h to 5.72 ± 0.06 h and then returns to 5.55 ± 0.05 h, consistent with a mid-2023 break and a torque reversal from spin-down to spin-up (Ṗ1 = +0.68 ± 0.08 s d−1 to Ṗ2 = −2.16 ± 0.35 s d−1). The observed Ṗ corresponds to torques of N1 = (−1.2 ± 0.1) × 1032 dyn cm and N2 = (+3.6 ± 0.6) × 1032 dyn cm for a canonical moment of inertia I = 1045 g cm2, while the associated spin-down power remains negligible compared with the X-ray luminosity. Within the quasi-spherical settling accretion regime, a change in mass accretion rate by a factor of ∼ 3.6 is sufficient, at the order-of-magnitude level, to account for the measured torque ratio. The inferred torque scale is compatible with a surface dipole field B ≈ (0.5 − 5) × 1012 G, with the magnetospheric radius remaining well inside co-rotation and no requirement for a propeller transition at the inferred luminosities. No clear contemporaneous hard-X-ray brightening is apparent in the BAT monitoring, which is consistent with an origin of the optical pulsations in reprocessing of the pulsed high-energy emission. Overall, the data favour a picture in which 4U 1954+319 is a long-period, near-equilibrium wind-fed pulsar whose torque reversals can arise from moderate changes in settling accretion, without invoking magnetar-strength fields or persistent propeller transitions. They also show that long-baseline optical timing can provide useful constraints on torque balance in faint wind-fed pulsars.

We report the results of a four-epoch very long baseline interferometry experiment targeting seventeen water maser sources in the Magellanic Clouds with the Long Baseline Array. We have measured accurate proper motions for water masers associated with two star formation regions N180 and N157A, both in the Large Magellanic Cloud. The water masers have proper motions of (1.79 ± 0.13, 0.89 ± 0.03) milliarcseconds per year and (1.74 ± 0.29, 0.55 ± 0.08) milliarcseconds per year in right ascension and declination respectively. These results are consistent with the proper motions of nearby stars and the bulk motion of the Large Magellanic Cloud as measured by Gaia, providing independent non-optical evidence of the Large Magellanic Cloud’s motion.

Recent studies by B. Villarroel and colleagues have assembled and analysed datasets of unidentified features measured from digital scans of photographic plates captured by the first-epoch Palomar Observatory Sky Survey (POSS1) in the pre-Sputnik era. These studies have called attention to (i) a purported deficit of features within Earth’s shadow; (ii) the sporadic presence of linear clusters; and (iii) a positive correlation between the timing of feature observations and nuclear tests as well as Unidentified Aerial Phenomena (UAP) sighting reports. These observations were cited as evidence that some fraction of the unidentified features represent glinting artificial objects near Earth. We have examined these claims using two previously published datasets that are closely related to those used in the Villarroel et al. studies. For these datasets, the Villarroel et al. assumption of a spatially uniform-random background distribution of features, essential to the Earth shadow analysis, is shown to be false. After finding the null distribution of feature count deviations from the background, we find no statistically significant deficit in the shadow. We also determine that a third of the features in the reported linear clusters were not confidently distinguished from catalogue stars. We find that the reported correlation between the timing of feature observations and nuclear tests becomes insignificant after properly normalizing by the relevant number of observation days, and is almost completely determined by the observation schedule of the Palomar telescope. We uncover important inconsistencies in the definitions of the datasets used in these studies, as well as the use of unvalidated datasets containing catalogue stars, scan artefacts, and plate defects. It has not been shown that any of the features in these datasets represent optical transients. We examine the spatial distribution of the plate-derived features, finding an overall gradual increase in number density toward the corners and edges of plates, as well as examples of (i) empty north-south strips that span multiple plates; (ii) clusters and voids having geometric shapes; and (iii) amorphous clusters. We also highlight a circular argument used in these studies, that leverages the results of an inferential analysis to justify conclusions about the origin of the features as well as the validity of the measurements. Finally, we also review the literature concerning historical searches for optical transients in photographic plates corresponding to gamma ray bursts (GRBs); following decades of work, researchers were unable to make a confident identification of a GRB-associated optical transient.

Measurements of peculiar velocities in the local Universe are a powerful tool to study the nature of dark energy at low (z < 0.1) redshifts. Here we present the largest single set of z < 0.1 peculiar velocity measurements to date, obtained using the Fundamental Plane (FP) of galaxies in the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI).We describe the photometric and spectroscopic selection criteria used to define the sample, as well as extensive quality control checks on the photometry and velocity dispersion measurements. Additionally, we perform detailed systematics checks for the many analysis parameters in our pipeline. Our DESI DR1 catalogue contains FP-based distances and peculiar velocities for 98, 292 unique early-type galaxies, increasing the total number of z < 0.1 FP distances ever measured by a factor of ∼ 2. We achieve a precision of 26% random error in our distance measurements which is comparable to previous surveys. A series of companion DESI papers use the distances and peculiar velocities presented in this paper to measure cosmological parameters.

Over a hundred fast radio burst (FRB) host galaxies have now been identified, enabling both comparisons of host redshift with FRB dispersion measure to study the cosmological distribution of ionised gas, and analyses of host properties in order to identify FRB progenitors. The standard method for determining the most likely FRB host galaxy in an optical image is the Bayesian framework Probabilistic Association of Transients to their Hosts (PATH), which accounts for uncertainties in the radio localisation, and simplified prior distributions on the host being observable. In this work we extend PATH, incorporating physically-motivated priors that are based on expectations about FRB host galaxy magnitudes. We develop three different models for the apparent r-band magnitude distribution based on an FRB’s expected host galaxy redshift, P(mr|z) and combine these with expectations for redshift based on an FRB’s dispersion measure, P(z|DM). We fit the parameters of these prior models using host galaxy candidates for 32 FRBs detected by the Australian SKA Pathfinder (ASKAP) in incoherent sum (ICS) mode by the Commensal Real-time ASKAP Fast Transients (CRAFT) survey.

Employing PATH with the new priors on the host magnitudes, we find increased confidence in the most probable hosts of all ASKAP ICS FRB host galaxies. All three models predict similar distributions of FRB host magnitudes at low redshift (z ∼ 0.1), and we confirm previous results that the true FRB host galaxy distribution is fainter than expected for a star-formation-weighted distribution (p-value of 0.12%). However, a mass-weighted distribution provides an even worse fit (p-value of 10−9). Tests against more FRBs in the z > 0.5 range, where the models differ, and extensions of the models to account for e.g. host metallicity, may help to resolve these uncertainties in the FRB host distribution.

We present a detailed characterisation of radio frequency interference (RFI) in the 2.4 GHz band around Murriyang, CSIRO’s Parkes radio telescope. The dominant sources of interference are Wi-Fi and Bluetooth transmissions. We quantify how the intensity and directionality of this RFI vary with time of day and document its evolution over several years. Although most observers currently discard data within this band, our analysis shows that the interference is confined in both time and frequency and can be effectively mitigated. Using 10 seconds of 16-bit voltage data recorded during observations of the Vela Pulsar (PSR J0835—4510), we demonstrate that the majority of the channelised data remain unaffected by RFI. We compare three RFI detection and mitigation algorithms and evaluate their relative performance. All methods perform effectively, and any could be implemented in real time to enable productive use of this observing band. A real time implementation would allow the scientific use of this 128MHz observing band to increase, from almost 70% of the band being completely unusable all of the time, to over 90% of becoming accessible for science. Given its simplicity and efficiency, a basic power-threshold approach offers a relatively straightforward solution.