We present a new radio detection from the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe (EMU) survey associated with the Reflection Nebula (RN) VdB-80. The radio detection is determined to be a previously unidentified Hii region, now named Lagotis. The RN is located towards Monoceros, centred in the molecular cloud feature known as the ‘Crossbones’. The 944 MHz EMU image shows a roughly semicircular Hii region with an integrated flux density of 30.2$\pm$0.3 mJy. The Hii region is also seen at 1.4 GHz by NRAO VLA Sky Survey (NVSS), yielding an estimated spectral index of 0.65$\pm$0.51, consistent with thermal radio emission. Gaia Data Release 3 (DR3) and Two Micron All Sky Survey (2MASS) data give a distance to the stars associated with the Hii region of $\sim$960 pc. This implies a size of 0.76$\times$0.68($\pm$0.09) pc for the Hii region. We derive an Hii region electron density of the bright radio feature to be 26 cm$^{-3}$, requiring a Lyman-alpha photon flux of $10^{45.6}$ s$^{-1}$, which is consistent with the expected Lyman flux of HD 46060, the B2 ii type star which is the likely ionising star of the region. The derived distance to this region implies that the Crossbones feature is a superposition of two filamentary clouds, with Lagotis embedded in the far cloud.

The 2175Å bump is a prominent absorption feature at ultraviolet (UV) wavelengths in dust extinction and attenuation curves. Understanding the relative strength of this feature is important for making accurate dust corrections at both low- and high-redshift. This feature is postulated to arise from polycyclic aromatic hydrocarbon (PAH) dust grains; however, the carrier has not been definitively established. We present results on the correlation between the 2175Å feature and PAH abundances in a spatially-resolved manner for 15 local galaxies in the PHANGS-JWST survey that have NUV and mid-IR imaging data from Swift/UVOT and JWST/MIRI, respectively. We find a moderate positive correlation between the 2175Å feature strength and PAH abundance (Spearman’s coefficient, $0.3 \lesssim \rho \lesssim 0.5$), albeit with large intrinsic scatter. However, most of this trend can be attributed to a stronger negative correlation of both quantities with SFR surface density and specific-SFR (proxies of ionising radiation; $\rho\sim-0.6$). The latter trends are consistent with previous findings that both the 2175Å carrier and PAHs are small grains that are easily destroyed by UV photons, although the proxy for PAH abundance (based on photometry) could also be influenced by dust heating. When controlling for SFR surface density, we find weaker correlations between the 2175Å feature and PAH abundances ($\rho \lesssim 0.3$), disfavouring a direct link. However, analyses based on spectroscopic (instead of photometric) measurements of the 2175Å feature and PAH features are required to verify our findings. No significant trends with gas-phase metallicity or galactocentric radii are found for the 2175Å feature and PAHs; however, the metallicity range of our sample is limited ($8.40 \lt 12+\log[\mathrm{O/H}] \lt 8.65$). We provide prescriptions for the strength of the 2175Å feature and PAHs in local massive (metal-rich) galaxies with SFR surface density and specific-SFR; however, the former should be used with caution due to the fact that bump strengths measured from Swift/UVOT are expected to be underestimated.

The data volumes generated by theWidefield ASKAP L-band Legacy All-sky Blind surveY atomic hydrogen (Hi) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) necessitate greater automation and reliable automation in the task of source finding and cataloguing. To this end, we introduce and explore a novel deep learning framework for detecting low signal-to-noise ratio (SNR) Hi sources in an automated fashion. Specifically, our proposed method provides an automated process for separating true Hi detections from false positives when used in combination with the source finding application output candidate catalogues. Leveraging the spatial and depth capabilities of 3D convolutional neural networks, our method is specifically designed to recognize patterns and features in three-dimensional space, making it uniquely suited for rejecting false-positive sources in low SNR scenarios generated by conventional linear methods. As a result, our approach is significantly more accurate in source detection and results in considerably fewer false detections compared to previous linear statistics-based source finding algorithms. Performance tests using mock galaxies injected into real ASKAP data cubes reveal our method’s capability to achieve near-100% completeness and reliability at a relatively low integrated SNR $\sim3-5$. An at-scale version of this tool will greatly maximise the science output from the upcoming widefield Hi surveys.

We carry out timing and spectral studies of the Be/X-ray binary pulsar GX 304-1 using NuStar and XMM-Newton observations. We construct the long-term spin period evolution of the pulsar which changes from a long-term spin-up ($\sim1.3 \times 10^{-13}$ Hz s$^{-1}$) to a long-term spin-down ($\sim-3.4 \times 10^{-14}$ Hz s$^{-1}$) trend during a low luminosity state ($\sim10^{34-35}$ erg s$^{-1}$). A prolonged low luminosity regime ($L_X \sim 10^{34-35}$ erg s$^{-1}$) was detected during 2005–2010 and spanning nearly five years since 2018 December. The XMM-Newton and NuStar spectra can be described with a power law plus blackbody model having an estimated luminosity of $\sim2.5 \times 10^{33}$ and $\sim3.6 \times 10^{33}$ erg s$^{-1}$, respectively. The inferred radius of the blackbody emission is about 100–110 m which suggests a polar-cap origin of this component. From long-term ultraviolet observations of the companion star, an increase in the ultraviolet signatures is detected preceding the X-ray outbursts. The spectral energy distribution of the companion star is constructed which provides a clue of possible UV excess when X-ray outbursts were detected from the neutron star compared to the quiescent phase. We explore plausible mechanisms to explain the long-term spin-down and extended low luminosity manifestation in this pulsar. We find that sustained accretion from a cold disc may explain the prolonged low luminosity state of the pulsar since December 2018 but the pulsar was undergoing normal accretion during the low luminosity period spanning 2005–2010.

Asymptotic giant branch (AGB) stars play a significant role in our understanding of the origin of the elements. They contribute to the abundances of C, N, and approximately 50% of the abundances of the elements heavier than iron. An aspect often neglected in studies of AGB stars is the impact of a stellar companion on AGB stellar evolution and nucleosynthesis. In this study, we update the stellar abundances of AGB stars in the binary population synthesis code binary_c and calibrate our treatment of the third dredge-up using observations of Galactic carbon stars. We model stellar populations of low- to intermediate-mass stars at solar-metallicity and examine the stellar wind contributions to C, N, O, Sr, Ba, and Pb yields at binary fractions between 0 and 1. For a stellar population with a binary fraction of 0.7, we find $\sim$20–25% less C and s-process elements ejected than from a population composed of only single stars, and we find little change in the N and O yields. We also compare our models with observed abundances from Ba stars and find our models can reproduce most Ba star abundances, but our population estimates a higher frequency of Ba stars with a surface [Ce/Y] > $+0.2\,$dex. Our models also predict the rare existence of Ba stars with masses $ \gt 10\,\textrm{M}_{\odot}$.

The initial mass function (IMF) is a construct that describes the distribution of stellar masses for a newly formed population of stars. It is a fundamental element underlying all of star and galaxy formation and has been the subject of extensive investigation for more than 60 yr. In the past few decades, there has been a growing, and now substantial, body of evidence supporting the need for a variable IMF. In this light, it is crucial to investigate the IMF’s characteristics across different spatial scales and to understand the factors driving its variability. We make use of spatially resolved spectroscopy to examine the high-mass IMF slope of star-forming galaxies within the SAMI survey. By applying the Kennicutt method and stellar population synthesis models, we estimated both the spaxel-resolved ($\alpha_{res}$) and galaxy-integrated ($\alpha_{int}$) high-mass IMF slopes of these galaxies. Our findings indicate that the resolved and integrated IMF slopes exhibit a near 1:1 relationship for $\alpha_{int}\gtrsim -2.7$. We observe a wide range of $\alpha_{res}$ distributions within galaxies. To explore the sources of this variability, we analyse the relationships between the resolved and integrated IMF slopes and both the star formation rate (SFR) and SFR surface density ($\Sigma_{\textrm{SFR}}$). Our results reveal a strong correlation where flatter/steeper slopes are associated with higher/lower SFR and $\Sigma_{\textrm{SFR}}$. This trend is qualitatively similar for resolved and global scales. Additionally, we identify a mass dependency in the relationship with SFR, though none was found in the relation between the resolved slope and $\Sigma_{\textrm{SFR}}$. These findings suggest an scenario where the formation of high-mass stars is favoured in regions with more concentrated star formation. This may be a consequence of the reduced fragmentation of molecular clouds, which nonetheless accrete more material.

We have conducted a widefield, wideband, snapshot survey using the Australian SKA Pathfinder (ASKAP) referred to as the Rapid ASKAP Continuum Survey (RACS). RACS covers $\approx 90$% of the sky, with multiple observing epochs in three frequency bands sampling the ASKAP frequency range of 700–1 800 MHz. This paper describes the third major epoch at 1 655.5 MHz, RACS-high, and the subsequent imaging and catalogue data release. The RACS-high observations at 1 655.5 MHz are otherwise similar to the previously released RACS-mid (at 1 367.5 MHz) and were calibrated and imaged with minimal changes. From the 1 493 images covering the sky up to declination $\approx +48^\circ$, we present a catalogue of 2 677 509 radio sources. The catalogue is constructed from images with a median root-mean-square noise of $\approx 195$ $\unicode{x03BC}$Jy PSF$^{-1}$ (point-spread function) and a median angular resolution of $11{\stackrel{\prime\prime}{\raise-0pt\hbox{.}}}8 \times 8{\stackrel{\prime\prime}{\raise-0pt\hbox{.}}}1$. The overall reliability of the catalogue is estimated to be 99.18%, and we find a decrease in reliability as angular resolution improves. We estimate the brightness scale to be accurate to 10%, and the astrometric accuracy to be within $\approx 0{\stackrel{\prime\prime}{\raise-0pt\hbox{.}}}6$ in right ascension and $\approx 0{\stackrel{\prime\prime}{\raise-0pt\hbox{.}}}7$ in declination after correction of a systematic declination-dependent offset. All data products from RACS-high, including calibrated visibility datasets, images from individual observations, full-sensitivity mosaics, and the all-sky catalogue are available at the CSIRO ASKAP Science Data Archive.

We have carried out a detailed investigation of eclipsing binary star NT Aps using high cadence photometric observations from the TESS satellite and time-series spectra from EFOSC2 at ESO’s New Technology Telescope.a We have, for the first time, determined precise system parameters for this W UMa-type late-type contact binary. Our analysis indicates that the system is composed of two solar-like stars with mass ratio of $q=0.31$ and orbital period of 0.29475540 $\pm$ 0.00000035 days. These values are typical for common envelope contact binaries. However, the system does not exhibit strong magnetic activity in the form of frequent flaring and large starspots, even if large flare rates have been earlier predicted for this system. This lack of strong magnetic activity further strengthens the earlier indications that the contact binaries are less magnetically active than those of detached chromospherically active binaries with similar parameters.