Some of the most interesting insights into solar physics and space weather come from studying radio emissions associated with solar activity, which remain inherently unpredictable. Hence, a real-time triggering system is needed for solar observations with the versatile new-generation radio telescopes to efficiently capture these episodes of solar activity with the precious and limited solar observing time. We have developed such a system, Solar Triggered Observations of Radio bursts using MWA and Yamagawa (STORMY) for the Murchison Widefield Array (MWA), the precursor for the low frequency telescope of upcoming Square Kilometre Array Observatory (SKAO). It is based on near-real-time data from the Yamagawa solar spectrograph, located at a similar longitude to the MWA. We have devised, implemented, and tested algorithms to perform an effective denoising of the data to identify signatures of solar activity in the Yamagawa data in near real-time. End-to-end tests of triggered observations have been successfully carried out at the MWA. STORMY is operational at the MWA for the routine solar observations, a timely development in the view of the ongoing solar maximum. We present this new observing framework and discuss how it can enable efficient capturing of event-rich solar data with existing instruments, like the LOw Frequency ARray (LOFAR), Owens Valley Radio Observatory - Long Wavelength Array (OVRO-LWA) etc., and pave the way for triggered observing with the SKAO, especially the SKA-Low.

We examine the potential improvements in constraints on the dark energy equation of state parameter w and matter density $\Omega_M$ from using clustering information along with number counts for future samples of thermal Sunyaev-Zel’dovich selected galaxy clusters. We quantify the relative improvement from including the clustering power spectrum information for three cluster sample sizes from 33 000 to 140 000 clusters and for three assumed priors on the mass slope and redshift evolution of the mass-observable relation. As expected, clustering information has the largest impact when (i) there are more clusters and (ii) the mass-observable priors are weaker. For current knowledge of the cluster mass-observable relationship, we find the addition of clustering information reduces the uncertainty on the dark energy equation of state, $\sigma(w)$, by factors of $1.023\pm 0.007$ to $1.079\pm 0.011$, with larger improvements observed with more clusters. Clustering information is more important for the matter density, with $\sigma(\Omega_M)$ reduced by factors of $1.068 \pm 007$ to $1.145 \pm 0.012$. The improvement in w constraints from adding clustering information largely vanishes after tightening priors on the mass-observable relationship by a factor of two. For weaker priors, we find clustering information improves the determination of the cluster mass slope and redshift evolution by factors of $1.389 \pm 0.041$ and $1.340 \pm 0.039$, respectively. These findings highlight that, with the anticipated surge in cluster detections from next generation surveys, self-calibration through clustering information will provide an independent cross-check on the mass slope and redshift evolution of the mass-observable relationship as well as enhancing the precision achievable from cluster cosmology.

The brown dwarf desert describes a range of orbital periods (<5 years) in which fewer brown dwarf-mass companions have been observed around Sun-like stars, when compared to planets and low mass stellar companions. It is therefore theorised that brown dwarf companions are unlikely to form or remain in this period range. The Gaia space telescope is uniquely sensitive to companions in this period range, making it an ideal tool to conduct a survey of the brown dwarf desert. In this study, we use Bayesian inference to analyse data from nearby (<200 pc) Sun-like stars in Gaia’s DR3 catalogue, assuming single companions. From this, we identify 2673 systems (2.41% of the sample) with possible brown dwarf companions in this period range. Accounting for observational biases, we find that of nearby Sun-like stars have astrometric errors consistent with a brown dwarf-mass companion with a period less than 5 years, significantly higher than previous studies which reported occurrence rates of <1 %. However, we acknowledge the limitations of DR3 and are unable to make a definitive statement without epoch data. By simulating epoch data with multiple companions, we find that, while some of the data can be explained by multiple low-mass brown dwarf companions and high-mass planets (>10MJ), high-mass brown dwarfs (>50MJ) in this period range are comparatively rare. Finally, we used our studies of the brown dwarf distribution to predict the number of companions in the brown dwarf desert we can expect to discover in DR4.

The mechanical feedback from the central active galactic nuclei (AGNs) can be crucial for balancing the radiative cooling of the intracluster medium (ICM) at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used the catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with radio observations from the Australian SKA Pathfinder (ASKAP). In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated the radio properties of the BCGs (radio luminosity, largest linear size/LLS, and BCG offset from the cluster centre) with the integrated X-ray luminosity of the host clusters. We utilised the concentration parameter, $c_{R_{500}}$, to categorise the clusters into cool cores (CCs) and non-cool cores (NCCs). By combining $c_{R_{500}}$ with the BCG offset, we assessed the dynamical states of the clusters in our sample. Furthermore, we analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, which may hint at an environmental influence on the morphology of central radio sources. We find a weak trend suggesting that more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Additionally, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity within the CC subsample. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation observed in our CC subsample indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},\,r} \lt \mathrm{R}_{\mathrm{cool}}\approx 5.50\times10^{43}\,\mathrm{erg\,s^{-1}}$, on average, AGN feedback appears to contribute only about $13\%-22\%$ of the energy needed to offset the radiative losses in the ICM.

With the installation of next-generation phased array feed (PAF) receivers on radio telescopes, there is an urgent need to develop effective and computationally efficient radio frequency interference (RFI) mitigation methods for large-scale surveys. Here, we present a new RFI mitigation package, called mRAID (multi-beam RAdio frequency Interference Detector), which uses the eigenvalue decomposition algorithm to identify RFI in cross-correlation matrix (CCM) of data recorded by multiple beams. When applied to high time-resolution pulsar search data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), mRAID demonstrates excellent performance in identifying RFI over short timescales, thereby enhancing the efficiency of pulsar and fast radio burst (FRB) searches. Since the computation of the CCM and the eigenvalue decomposition for each time sub-integration and frequency channel are independent, the process is fully parallelisable. As a result, mRAID offers a significant computational advantage over commonly used RFI detection methods.

The transient and variable optical sky is relatively poorly characterised on fast (${\lt}$1 h) timescales. With the dark energy camera (DECam), the Deeper, Wider, Faster programme (DWF) probes a unique parameter space with its deep (median of $g\sim22.2$ AB mag), minute-cadence imaging. In this work, we present DWF’s first data release which comprises high cadence photometry extracted from $\sim$12 000 images and 166 h of telescope time. We present a novel data processing pipeline, dwf-postpipe, developed to identify sources and extract their light curves. The accuracy of the photometry is assessed by cross-matching to public catalogues. In addition, we injected a population of synthetic GRB afterglows into a subset of the DWF DECam imaging to compare the efficiency of our pipeline with a standard difference imaging approach. Both pipelines show performance and reliably recover injected transients with peak magnitudes $g\lt22$ AB mag with an efficiency of $97.24^{+0.7}_{-1.0}$ percent for dwf-postpipe and $96.14^{+0.9}_{-1.1}$ percent for a difference imaging approach. However, we find that dwf-postpipe is less likely to recover transients appearing in galaxies that are brighter or comparable in brightness to the transient itself. To demonstrate the power of the data in this release, we conduct a search for uncatalogued variable stars in a single night of DWF DECam imaging and find ten pulsating variables, two eclipsing binaries and one ZZ ceti. We also conduct a search for variable phenomena in the Chandra Deep Field South, a Rubin deep drilling field, and identify two flares from likely UV ceti type stars.

The Experiment to Detect the Global Epoch of reionization 21 cm Signal (EDGES) has reported evidence for an absorption feature in the sky-averaged radio background near 78 MHz. A cosmological interpretation of this signal corresponds to absorption of 21 cm photons by neutral hydrogen at z ∼ 17. The large depth of the signal has been shown to require an excess radio background above the CMB and/or non-standard cooling processes in the IGM. Here, we explore the plausibility of a scenario in which the EDGES signal is back-lit by an excess radio background sourced from a population of radio-loud AGN at high redshift. These AGN could also explain the unexpected abundance of UV-bright objects observed at z > 10 by JWST. We find that producing enough radio photons to explain the EDGES depth requires that nearly all high-z UV-bright objects down to MUV ≳ –15 are radio-loud AGN and that the UV density of such objects declines by at most 1.5 orders of magnitude between z = 10 and 20. In addition, the fraction of X-ray photons escaping these objects must be ≲ 1% of their expected intrinsic production rate to prevent the absorption signal being washed out by early IGM pre-heating. Re-producing the sharp boundaries of the absorption trough and its flat bottom require that the UV luminosity function, the fraction of UV light produced by AGN, and the X-ray escape fraction have fine-tuned redshift dependence. We conclude that radio-loud AGN are an unlikely (although physically possible) candidate to explain EDGES because of the extreme physical properties required for them to do so.

Asymptotic giant branch (AGB) stars are important to chemical evolution at metallicity $Z \sim 0.0001$ ($\text{[Fe/H]} \approx -2.2$) as they contribute significantly to the production of nitrogen, lead, and dust in the early Universe. The contribution of AGB stars to the chemical evolution of the Universe is often quantified using the chemical yields from single AGB stars. Binary evolution challenges our understanding of chemical evolution as binary phenomena such as mergers and mass transfer episodes can significantly alter the stellar evolution pathways and yields. In this work, we use binary population synthesis code binary_c to model populations of low and intermediate-mass ($\sim 0.7$–$7\,\mathrm{M}_{\odot}$) stars at metallicity $Z = 0.0001$. Our binary star populations predict $\sim 37\%$ fewer thermally pulsing AGB stars than our single star populations, leading to a $\sim 40\%$ decrease in the amount of ejected C and a $\sim 35$–40% reduction in elements synthesised through the slow neutron capture process. The uncertainty introduced by the mass-loss from stellar winds on the AGB makes the impact of binary evolution on the total amount of ejected N uncertain. The total N yield ejected by our binary star populations ranges from a 17% to a 36% decrease compared to our single star populations. However, our binary populations overproduce N by over an order of magnitude during the period $300\text{--}700\, {\rm Myr}$ after formation.

Data from observations of pulsars made by Murriyang, the CSIRO Parkes 64-metre radio-telescope over the last three decades are more accessible than ever before, largely due to their storage in expansive long-term archives. Containing nearly 2 million files from more than 400 Parkes pulsar projects, CSIRO’s Data Access Portal is leading the global effort in making pulsar data accessible. In this article, we present the current status of the archive and provide information about the acquisition, analysis, reduction, visualisation, preservation, and dissemination of these datasets. We highlight the importance of such an archive and present a selection of new results emanating from archival data.

We present the discovery of PSR J1728$-$4608, a new redback spider pulsar identified in images from the Australian SKA Pathfinder telescope. PSR J1728$-$4608 is a millisecond pulsar with a spin period of 2.86 ms, in a 5.05 h orbit with a companion star. The pulsar exhibits a radio spectrum of the form $S_{\nu} \propto \nu^\alpha$, with a measured spectral index of $\alpha = -1.8(3)$. It is eclipsed for 42% of its orbit at 888 MHz, and multi-frequency image–domain observations show that the egress duration scales with frequency as a power law with index $n = -1.74$, where longer duration eclipses are seen at lower frequencies. An optical counterpart is detected in archival Gaia data within $0.5''$ of the radio position. It has a mean G-band magnitude of 18.8 mag, and its light curve displays characteristics consistent with a combination of ellipsoidal modulation and irradiation effects. We also report the nearest Fermi $\gamma$-ray source, located 2′ away from our source, as a possible association. A radio timing study constrains the intrinsic and orbital properties of the system, revealing orbital period variations that we attribute to changes in the gravitational quadrupole moment of the companion star. At the eclipse boundary, we measure a maximum dispersion measure excess of $2.0 \pm 1.2 \ \mathrm{pc\ cm^{-3}}$, corresponding to an electron column density of $5.9 \pm 3.6 \times10^{18} \ \mathrm{cm^{-2}}$. Modelling of the eclipse mechanism suggests that synchrotron absorption is the dominant cause of the eclipses observed at radio wavelengths. The discovery and characterisation of systems like PSR J1728$-$4608 provide valuable insights into pulsar recycling, binary evolution, the nature of companion-driven eclipses, and the interplay between compact objects and their plasma environments.

We search data from the GLEAM-X survey, obtained with the Murchison Widefield Array (MWA) in 2020, for the presence of radio frequency interference from distant Earth-orbiting satellites, in the form of unintended emissions similar to those recently seen from objects in Low Earth Orbits (LEO). Using the GLEAM-X $\delta=1.6^{\circ}$ pointing, which is stationary in azimuth (on the local Meridian) and elevation (near the celestial Equator), the very wide field of view of the MWA maintains custody of a large number of satellites in geostationary and geosynchronous (GEO) orbits in this direction for long periods of time. We use one night of GLEAM-X data in the 72–231 MHz frequency range to form stacked images at the predicted coordinates of up to 162 such satellites, in order to search for unintended radio emission. In the majority of cases, we reach 4$\sigma$ upper limits of better than 1 mW Equivalent Isotropic Radiated Power (EIRP) in a 30.72 MHz bandwidth (dual polarisation), with the best limits below 10 $\unicode{x03BC}$W. No convincing evidence for unintended emissions at these detection thresholds was found. This study builds on recent work showing an increasing prevalence of unintended emissions from satellites in LEO. Any such emission from objects in GEO could be a significant contributor to radio frequency interference experienced by the low frequency Square Kilometre Array and warrants monitoring. The current study forms a baseline for comparisons to future monitoring.

A coronal mass ejection (CME) was detected crossing the radio signals transmitted by the Mars Express (MEX) and Tianwen-1 (TIW) spacecraft at a solar elongation of $4.4^{\circ}$. The impact of the CME was clearly identifiable in the spacecraft signal SNR, Doppler noise, and phase residuals observed at the University of Tasmania’s Very Long Baseline Interferometry (VLBI) antenna in Ceduna, South Australia. The residual phases observed from the spacecraft were highly correlated with each other during the transit of the CME across the radio ray-path despite the spacecraft signals having substantially different Doppler trends. We analyse the auto- and cross-correlations between the spacecraft phase residuals, finding time-lags ranging between 3.18 and 14.43 seconds depending on whether the imprinted fluctuations were stronger on the uplink or the downlink radio ray-paths. We also examine the temporal evolution of the phase fluctuations to probe the finer structure of the CME and demonstrate that there was a clear difference in the turbulence regime of the CME leading edge and the background solar wind conditions several hours prior to the CME radio occultation. Finally, autocorrelation of the MEX two-way radio Doppler noise data from Ceduna and closed-loop Doppler data from ESA’s New Norcia ground station antenna were used to constrain the location of the CME impact along the radio ray-path to a region 0.2 AU from the Sun, at a heliospheric longitude consistent with CME origin at the Sun. The results presented demonstrate the potential of the multi-spacecraft-in-beam technique for studying CME structures in great detail and providing measurements that complement the capabilities of future solar monitoring instruments.

Common envelope (CE) evolution is largely governed by the drag torque applied on the in-spiralling stellar components by the envelope. Previous work has shown that idealized models of the torque based on a single body moving in rectilinear motion through an unperturbed atmosphere can be highly inaccurate. Progress requires new models for the torque that account for binarity. Towards this end, we perform a new 3D global hydrodynamic CE simulation with the mass of the companion point particle set equal to the mass of the asymptotic giant branch star core particle to maximize symmetry and facilitate interpretation. First, we find that a region around the particles of a scale comparable to their separation contributes essentially all of the torque. Second, the density pattern of the torque-dominating gas and, to an extent, this gas itself, is roughly in corotation with the binary. Third, approximating the spatial distribution of the torquing gas as a uniform-density prolate spheroid whose major axis resides in the orbital plane and lags the line joining the binary components by a constant phase angle reproduces the torque evolution remarkably well, analogous to studies of binary supermassive black holes. Fourth, we compare the torque measured in the simulation with the predictions of a model that assumes two weak point-mass perturbers undergoing circular motion in a uniform background without gas self-gravity and find remarkable agreement with our results if the background density is taken to be equal to a fixed fraction ($\approx0.44$) of the density at the spheroid surface. Overall, this work makes progress towards developing simple time-dependent models of the CE phase, for example by informing the development of drag force prescriptions for 1D spherically symmetric CE simulations, which could be used to explore the parameter space of luminous red novae or in binary population synthesis studies.

Astronomical objects that change rapidly give us insight into extreme environments, allowing us to identify new phenomena, test fundamental physics, and probe the Universe on all scales. Transient and variable radio sources range from the cosmological, such as gamma-ray bursts, to much more local events, such as massive flares from stars in our Galactic neighbourhood. The capability to observe the sky repeatedly, over many frequencies and timescales, has allowed us to explore and understand dynamic phenomena in a way that has not been previously possible. In the past decade, there have been great strides forward as we prepared for the revolution in time domain radio astronomy that is being enabled by the SKA Observatory telescopes, the SKAO pathfinders and precursors, and other ‘next generation’ radio telescopes. Hence, it is timely to review the current status of the field and summarise the developments that have happened to get to our current point. This review focuses on image domain (or ‘slow’) transients, on timescales of seconds to years. We discuss the physical mechanisms that cause radio variability and the classes of radio transients that result. We then outline what an ideal image domain radio transients survey would look like and summarise the history of the field, from targeted observations to surveys with existing radio telescopes. We discuss methods and approaches for transient discovery and classification and identify some of the challenges in scaling up current methods for future telescopes. Finally, we present our current understanding of the dynamic radio sky, in terms of source populations and transient rates, and look at what we can expect from surveys on future radio telescopes.

High-sensitivity observations of PSR J1919+1745 were conducted using the Five-hundred-metre Aperture Spherical Radio Telescope (FAST) at a central frequency of 1 250 MHz, enabling a detailed investigation of its single-pulse behaviour. Our research indicates that this pulsar is a normal pulsar, exhibiting null behaviour, subpulse drifting, and occasional bright pulses. Moreover, we observed that the null events tend to be of short duration, with an estimated overall null fraction of approximately $29.5\pm1.1\% $. Through Sliding Fluctuation Spectrum analysis, the modulation period of subpulse drifting is determined to be $P_3=(6.1 \pm 0.7)P_1$ (where $P_1$ denotes the pulsar rotation period), and a non-drifting behaviour is also observed besides this. Analysis using the Harmonic-Resolved Fourier Spectrum indicates that a combination of amplitude modulation and phase modulation causes the subpulse drifting behaviour of this pulsar. Furthermore, the value $P_2$, derived from phase modulation, is approximately $360^\circ / 21 = 17.1^\circ$. polarisation analysis shows a moderate degree of linear polarisation ($37.22\pm0.59\% $), an S-shaped swing in the polarisation position angle, and an approximate $90^\circ$ orthogonal polarisation jump. The radiation characteristics of PSR J1919+1745 will expand the sample of pulsars with pulse null and subpulse drifting, thus contributing to future systematic studies on the physical origins of pulse null and subpulse drifting phenomena.

We report the first observations in a rare family of class II methanol maser transitions in both CH$_3$OH and $^{13}$CH$_3$OH towards three southern high-mass star formation regions, along with the first maser detected in the $^{13}$CH$_3$OH line. The $8_2 \rightarrow 9_1 A^{-}$ methanol transition was observed in both CH$_3$OH and $^{13}$CH$_3$OH (at 28.9 GHz and 41.9 GHz, respectively) towards three sources; G358.93-0.03, NGC6334I, and G345.01+1.79, all of which are star formation regions with recent maser flaring events. We report the first maser detection of the 41.9 GHz line in $^{13}$CH$_3$OH towards G358.93-0.03 and the first confirmed maser detection of the 28.9 GHz line in CH$_3$OH towards NGC6334I. Additionally, we report a maser detection of the 28.9 GHz line in CH$_3$OH towards G358.93-0.03, meaning that with our detection of the 41.9 GHz line, this is the first isotopic detection of these lines towards G358.93-0.03. The newly detected maser transitions are associated with the primary millimetre continuum sources (MM1) in both G358.93-0.03 and NGC6334I, within the varying positional uncertainties.

Bars are ubiquitous morphological features in the observed distribution of galaxies. There are similarly many methods for classifying these features and, without a strict theoretical definition or common standard practice, this is often left to circumstance. So, we were concerned whether astronomers even agree on the bar which they perceive in a given galaxy and whether this could impact perceived scientific results. As an elementary test, we twenty-one astronomers with varied experience in studying resolved galaxies and circumstances, have each assessed 200 galaxy images, spanning the early phase of bar evolution in two different barred galaxy simulations. We find variations exist within the classification of all the standard bar parameters assessed: bar length, axis-ratio, pitch-angle and even whether a bar is present at all. If this is indicative of the wider community, it has implications for interpreting morphological trends, such as bar-end effects. Furthermore, we find that it is surprisingly not expertise but gender, followed by career stage, which gives rise to the largest discrepancies in the reported bar parameters. Currently, automation does not seem to be a viable solution, with bar classifications from two automated bar-finding algorithms tested and failing to find bars in snapshots where most astronomers agree a bar must exist. Increasing dependence on machine learning or crowdsourcing with a training dataset can only serve to obfuscate any existing biases if these originate from the specific astronomer producing the training material. On the strength of this small sample, we encourage an interim best practice to reduce the impact of any possible classification bias and set goals for the community to resolve the issue in the future.

Post-asymptotic giant branch (post-AGB) binary stars are evolved systems that host circumbinary discs formed through mass loss during late stage binary interactions. Their structural, morphological, kinematic, and chemical similarities to planet-forming discs suggest that these systems may act as sites of ‘second-generation’ planet formation. In this study, we assess whether the disc instability mechanism – a proposed pathway for rapid, giant planet formation in some protoplanetary discs - can operate in post-AGB discs; motivated by their short lifetimes ($10^{4-5}$ yr). Using the Toomre criterion under well motivated assumptions for disc structure and size, mass, and thermal properties, we assess the conditions for gravitational instability. We first benchmark our analytical framework using well studied protoplanetary disc systems (including HL Tauri, Elias 2-27, GQ Lupi) before applying the same analysis to observed post-AGB discs. We find that post-AGB discs are generally gravitationally stable at present, due primarily to their low masses. Using viscous disc theory, we find that the discs were stable against collapse even in the past, when their masses were potentially higher. In contrast, several protoplanetary discs analysed in the same way show that they likely experienced gravitationally unstable phases early on. We also find that higher viscosity parameters ($\alpha \sim 10^{-2}$) are better aligned with expected post-AGB disc lifetimes. Finally, we revisit the planet formation scenario proposed for the post-common envelope system NN Ser, first carried out by Schleicher and Dreizler, and we show that gravitational instability could be feasible under specific, high disc mass assumptions. Overall, our results provide the first systematic theoretical assessment of gravitational instability in post-AGB discs, demonstrating that this mechanism is unlikely to dominate second-generation planet formation in these systems and underscoring the need to explore alternative pathways – such as core accretion – in future studies.

With the growing number of gravitational wave detections, achieving a competitive measurement of $H_0$ with dark sirens is becoming increasingly feasible. The expansion of the LIGO-Virgo-KAGRA Collaboration into a four detector network will reduce both the localisation area and the luminosity distance uncertainty associated with each gravitational wave event. It is therefore essential to identify and mitigate other major sources of error that could increase the uncertainty in $H_0$. In this work, we explore three scenarios relevant to the dark siren method in future observing runs. First, we demonstrate that there is a precision gain offered by a catalogue of spectroscopic-like redshifts compared to photometric-like redshifts, with the greatest improvements observed in smaller localisation areas. Second, we show that redshift outliers (as occur in realistic photometric redshift catalogues), do not introduce bias into the measurement of $H_0$. Finally, we find that uniformly sub-sampling spectroscopic-like redshift catalogues increases the uncertainty in $H_0$ as the completeness fraction is decreased; at a completeness of 50% the benefit of spectroscopic redshift precision is outweighed by the degradation from incompleteness. In all three scenarios, we obtain unbiased estimates of $H_0$. We conclude that a competitive measurement of $H_0$ using the dark siren method will require a hybrid catalogue of both photometric and spectroscopic redshifts, at least until highly complete spectroscopic catalogues become available. This, however, will come at the cost of a more complex selection function.