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The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance., Comment: Accepted for publication in the A&A special issue`Euclid on Sky'

Inducing and leveraging sparse activations during training and inference is a promising avenue for improving the computational efficiency of deep networks, which is increasingly important as network sizes continue to grow and their application becomes more widespread. Here we use the large width Gaussian process limit to analyze the behaviour, at random initialization, of nonlinear activations that induce sparsity in the hidden outputs. A previously unreported form of training instability is proven for arguably two of the most natural candidates for hidden layer sparsification; those being a shifted ReLU ($\phi(x)=\max(0, x-\tau)$ for $\tau\ge 0$) and soft thresholding ($\phi(x)=0$ for $|x|\le\tau$ and $x-\text{sign}(x)\tau$ for $|x|>\tau$). We show that this instability is overcome by clipping the nonlinear activation magnitude, at a level prescribed by the shape of the associated Gaussian process variance map. Numerical experiments verify the theory and show that the proposed magnitude clipped sparsifying activations can be trained with training and test fractional sparsity as high as 85\% while retaining close to full accuracy., Comment: Published in the International Conference on Learning Representations (ICLR) 2024

AT 2019azh is a H+He tidal disruption event (TDE) with one of the most extensive ultraviolet and optical data sets available to date. We present our photometric and spectroscopic observations of this event starting several weeks before and out to approximately two years after the g-band peak brightness and combine them with public photometric data. This extensive data set robustly reveals a change in the light-curve slope and a possible bump in the rising light curve of a TDE for the first time, which may indicate more than one dominant emission mechanism contributing to the pre-peak light curve. Indeed, we find that the MOSFiT-derived parameters of AT 2019azh, which assume reprocessed accretion as the sole source of emission, are not entirely self-consistent. We further confirm the relation seen in previous TDEs whereby the redder emission peaks later than the bluer emission. The post-peak bolometric light curve of AT 2019azh is better described by an exponential decline than by the canonical t^{-5/3} (and in fact any) power-law decline. We find a possible mid-infrared excess around the peak optical luminosity, but cannot determine its origin. In addition, we provide the earliest measurements of the Halpha emission-line evolution and find no significant time delay between the peak of the V-band light curve and that of the Halpha luminosity. These results can be used to constrain future models of TDE line formation and emission mechanisms in general. More pre-peak 1-2 days cadence observations of TDEs are required to determine whether the characteristics observed here are common among TDEs. More importantly, detailed emission models are needed to fully exploit such observations for understanding the emission physics of TDEs., Comment: Submitted to ApJ

Objectives: To examine sex differences in the associations between vascular risk factors and 6-year changes in the volume of white matter hyperintensities (WMH), and between changes in WMH volumes and changes in cognitive performance, in a cohort of non-demented older adults. Methods: WMH volumes at 3 time-points (baseline, and 2- and 6-year follow-up) were automatically quantified in participants of Sydney Memory and Ageing Study (N = 605; age range = 70-92 years; 54.78% female). Linear mixed models were applied to examine the effects of vascular risk factors and cognitive consequences of the progression of WMH, as well as the sex moderation effects in the associations. Results: Total (TWMH), periventricular (PVWMH), and deep (DWMH) WMH volumes increased by 9.47%, 7.70%, and 11.78% per year, respectively. No sex differences were found in WMH progression rates. After Bonferroni correction, increases in PVWMH volumes over time were associated with decline in global cognition, especially in visuospatial and memory domains. Men with more increases in PVWMH volumes over time had greater declines in visuospatial abilities. Moreover, higher average TWMH volumes across time-points were associated with poorer average performance in processing speed and executive function domains across time. Higher average PVWMH volumes across time-points were also associated with worse average performance in the executive function domain over time, among women but not men. Conclusion: The findings highlighted sex differences in the associations between WMH progression and cognition decline over time, suggesting sex-specific strategies in managing WMH accumulations in ageing. Keywords: Cerebral small vessel disease, white matter hyperintensities, sex differences, brain ageing, cognitive decline.

We search the archival Zwicky Transient Facility public survey for rapidly evolving transient (RET) candidates based on well-defined criteria between 2018 May and 2021 December. The search yielded 19 bona-fide RET candidates, corresponding to a discovery rate of $\sim 5.2$ events per year. Even with a Galactic latitude cut of $20^\circ$, 8 of the 19 events ($\sim 42$%) are Galactic, including one with a light-curve shape closely resembling that of the GW170817 kilonova (KN). An additional event is a nova in M31. Four out of the 19 events ($\sim 21$%) are confirmed extragalactic RETs (one confirmed here for the first time) and the origin of 6 additional events cannot be determined. We did not find any extragalactic events resembling the GW170817 KN, from which we obtain an upper limit on the volumetric rate of GW170817-like KNe of $R \le$ 2400 Gpc$^{-3}$ yr$^{-1}$ (95% confidence). These results can be used for quantifying contaminants to RET searches in transient alert streams, specifically when searching for kilonovae independently of gravitational-wave and gamma-ray-burst triggers., Comment: 16 pages, 7 figures, submitted to AAS Journals

AT 2021loi is an optical-ultraviolet transient located at the center of its host galaxy. Its spectral features identify it as a member of the ``Bowen Fluorescence Flare'' (BFF) class. The first member of this class was considered to be related to a tidal disruption event, but enhanced accretion onto an already active supermassive black hole was suggested as an alternative explanation. AT 2021loi, having occurred in a previously-known unobscured AGN, strengthens the latter interpretation. Its light curve is similar to those of previous BFFs, showing a rebrightening approximately one year after the main peak (which was not explicitly identified, but might be the case, in all previous BFFs). An emission feature around 4680 A, seen in the pre-flare spectrum, strengthens by a factor of $\sim$2 around the optical peak of the flare, and is clearly seen as a double peaked feature then, suggesting a blend of NIII $\lambda 4640$ with HeII $\lambda4686$ as its origin. The appearance of OIII $\lambda$3133 and possible NIII $\lambda\lambda4097,4103$ (blended with H$\delta$) during the flare further support a Bowen Fluorescence classification. Here, we present ZTF, ATLAS, Keck, Las Cumbres Observatory, NEOWISE-R, $Swift$, AMI and VLA observations of AT 2021loi, making it one of the best observed BFFs to date. AT 2021loi thus provides some clarity on the nature of BFFs but also further demonstrates the diversity of nuclear transients., Comment: Submitted to ApJ. This version addresses comments from the referee

From data collection to photometric fitting and analysis of white dwarfs to generating a white dwarf luminosity function requires numerous Astrophysical, Mathematical and Computational domain knowledge. The steep learning curve makes it difficult to enter the field, and often individuals have to reinvent the wheel to perform identical data reduction and analysis tasks. We have gathered a wide range of publicly available white dwarf cooling models and synthetic photometry to provide a toolkit that allows (1) visualisation of various models, (2) photometric fitting of a white dwarf with or without distance and reddening, and (3) the computing of white dwarf luminosity functions with a choice of initial mass function, main sequence evolution model, star formation history, initial-final mass relation, and white dwarf cooling model. We have recomputed and compared the effective temperature of the white dwarfs from the Gaia EDR3 white dwarf catalogue. The two independent works show excellent agreement in the temperature solutions., Comment: 18 pages, 12 figures, 2 tables. Accepted for publication in RAS Techniques and Instruments

Objective: To examine the moderation effects of hormonal factors on the associations between vascular risk factors and white matter hyperintensities (WMH) in men and women, separately. Methods: WMH were automatically segmented and quantified in the UK Biobank dataset (N = 18,294). Generalised linear models were applied to examine 1) the main effects of vascular (body mass index, hip to waist ratio, pulse wave velocity, hypercholesterolemia, diabetes, hypertension, smoking status) and hormonal (testosterone levels, contraceptive pill, hormone replacement therapy, menopause) factors on WMH, and 2) the moderation effects of hormonal factors on the relationship between vascular risk factors and WMH volumes. Results: In men with testosterone levels one standard deviation (SD) higher than the mean value, increased body mass index and pulse wave velocity, and smoking were associated with higher WMH volumes. The association between body mass index and WMH was more significant in the periventricular white matter regions, whilst the relationship between pulse wave velocity and WMH was restricted to deep white matter regions. Men with low testosterone levels (one SD below the mean level) showed a significant association between hypercholesterolemia and higher deep WMH volumes. Hypertensive women showed higher WMH volumes than women without hypertension regardless of whether hormone replacement therapy was used. However, higher WMH volumes, especially in the deep white matter regions, were found in women who did not use hormone replacement therapy or use it for a shorter duration. Conclusion: These findings highlighted the importance of considering hormonal risk factors in the prevention and management of WMH.

Even before COVID-19, school districts wanted to understand if school-based telemedicine services met student health needs during the school day and helped keep students in school all day, every day. Specifically, districts were interested in knowing if telemedicine enabled students with a school-day health issue to return to class instead of being sent home, preventing the loss of instruction. This study examined students' use of school-based telemedicine in all five of the schools in urban Robla Elementary School District in California during the first two years of implementation (2017/18 and 2018/19). The study also examined how students' use of services varied by grade level and by race/ethnicity. Districtwide, 26 percent of students used telemedicine services at least once over the two years, with 9 percent of students using telemedicine multiple times. The reasons students used telemedicine services varied, with the most frequent reasons being for noncommunicable health conditions(44 percent) and communicable illnesses(19 percent). Nearly all telemedicine visits (94 percent) resulted in students returning to class. This resulted in these students receiving, on average, approximately 3 hours of instruction remaining in that school day. Students in lower and upper elementary grades did not differ in their use of telemedicine services, though there were some differences by student race/ethnicity. Black students had the highest use of telemedicine and Asian students had the lowest use. This suggests that needs, awareness, level of comfort, or rate of parent/guardian consent for receiving school-based telemedicine services may vary across student groups. Compared to visits made by students of other race/ethnicity groups, a higher percentage of the telemedicine visits by Hispanic students were for preventative/wellness reasons. Telemedicine services may hold promise to help students stay healthy and in school, and is adaptable for students at home during the pandemic and when school buildings reopen. Results indicate that telemedicine can treat students during the school day, enabling them to attend their classes for the remainder of instruction that day.

Blue Large Amplitude Pulsators (BLAPs) are hot, subluminous stars undergoing rapid variability with periods of under 60 mins. They have been linked with the early stages of pre-white dwarfs and hot subdwarfs. They are a rare class of variable star due to their evolutionary history within interacting binary systems and the short timescales relative to their lifetime in which they are pulsationally unstable. All currently known BLAPs are relatively faint (15-19 mag) and are located in the Galactic plane. These stars have intrinsically blue colours but the large interstellar extinction in the Galactic plane prevents them from swift identification using colour-based selection criteria. In this paper, we correct the Gaia $G$-band apparent magnitude and $G_{\mathrm{BP}}-G_{\mathrm{RP}}$ colours of 89.6 million sources brighter than 19 mag in the Galactic plane with good quality photometry combined with supplementary all-sky data totalling 162.3 million sources. Selecting sources with colours consistent with the known population of BLAPs and performing a cross-match with the Zwicky Transient Facility (ZTF) DR3, we identify 98 short period candidate variables. Manual inspection of the period-folded light curves reveals 22 candidate BLAPs. Of these targets, 6 are consistent with the observed periods and light curves of the known BLAPs, 10 are within the theoretical period range of BLAPs and 6 are candidate high-gravity BLAPs. We present follow-up spectra of 21 of these candidate sources and propose to classify 1 of them as a BLAP, and tentatively assign an additional 8 of them as BLAPs for future population studies., Comment: 11 pages, 5 figures, 2 tables, accepted to MNRAS

We present the photometric analysis of Gaia19bld, a high-magnification ($A\approx60$) microlensing event located in the southern Galactic plane, which exhibited finite source and microlensing parallax effects. Due to a prompt detection by the Gaia satellite and the very high brightness of $I = 9.05~$mag at the peak, it was possible to collect a complete and unique set of multi-channel follow-up observations, which allowed us to determine all parameters vital for the characterisation of the lens and the source in the microlensing event. Gaia19bld was discovered by the Gaia satellite and was subsequently intensively followed up with a network of ground-based observatories and the Spitzer Space Telescope. We collected multiple high-resolution spectra with Very Large Telescope (VLT)/X-Shooter to characterise the source star. The event was also observed with VLT Interferometer (VLTI)/PIONIER during the peak. Here we focus on the photometric observations and model the light curve composed of data from Gaia, Spitzer, and multiple optical, ground-based observatories. We find the best-fitting solution with parallax and finite source effects. We derived the limit on the luminosity of the lens based on the blended light model and spectroscopic distance. We compute the mass of the lens to be $1.13 \pm 0.03~M_{\odot}$ and derive its distance to be $5.52^{+0.35}_{-0.64}~\mathrm{kpc}$. The lens is likely a main sequence star, however its true nature has yet to be verified by future high-resolution observations. Our results are consistent with interferometric measurements of the angular Einstein radius, emphasising that interferometry can be a new channel for determining the masses of objects that would otherwise remain undetectable, including stellar-mass black holes., Comment: accepted to Astronomy&Astrophysics

We provide a suite of public open-source spectral data-reduction software to rapidly obtain scientific products from all forms of long-slit-like spectroscopic observations. Automated SpectroPhotometric REDuction (ASPIRED) is a Python-based spectral data-reduction toolkit. It is designed to be a general toolkit with high flexibility for users to refine and optimize their data-reduction routines for the individual characteristics of their instruments. The default configuration is suitable for low-resolution long-slit spectrometers and provides a quick-look quality output. However, for repeatable science-ready reduced spectral data, some moderate one-time effort is necessary to modify the configuration. Fine-tuning and additional (pre)processing may be required to extend the reduction to systems with more complex setups. It is important to emphasize that although only a few parameters need updating, ensuring their correctness and suitability for generalization to the instrument can take time due to factors such as instrument stability. We compare some example spectra reduced with ASPIRED to published data processed with iraf-based and STARLINK-based pipelines, and find no loss in the quality of the final product. The Python-based, iraf-free ASPIRED can significantly ease the effort of an astronomer in constructing their own data-reduction workflow, enabling simpler solutions to data-reduction automation. This availability of near-real-time science-ready data will allow adaptive observing strategies, particularly important in, but not limited to, time-domain astronomy., Comment: 23 pages, 10 figures, 1 table, 1 appendix

Air pollution has long been a serious environmental health challenge, especially in metropolitan cities, where air pollutant concentrations are exacerbated by the street canyon effect and high building density. Whilst accurately monitoring and forecasting air pollution are highly crucial, existing data-driven models fail to fully address the complex interaction between air pollution and urban dynamics. Our Deep-AIR, a novel hybrid deep learning framework that combines a convolutional neural network with a long short-term memory network, aims to address this gap to provide fine-grained city-wide air pollution estimation and station-wide forecast. Our proposed framework creates 1x1 convolution layers to strengthen the learning of cross-feature spatial interaction between air pollution and important urban dynamic features, particularly road density, building density/height, and street canyon effect. Using Hong Kong and Beijing as case studies, Deep-AIR achieves a higher accuracy than our baseline models. Our model attains an accuracy of 67.6%, 77.2%, and 66.1% in fine-grained hourly estimation, 1-hr, and 24-hr air pollution forecast for Hong Kong, and an accuracy of 65.0%, 75.3%, and 63.5% for Beijing. Our saliency analysis has revealed that for Hong Kong, street canyon and road density are the best estimators for NO2, while meteorology is the best estimator for PM2.5.

We are reporting the updates in version 0.2.0 of the Automated SpectroPhotometric REDuction (ASPIRED) pipeline, designed for common use on different instruments. The default settings support many typical long-slit spectrometer configurations, whilst it also offers a flexible set of functions for users to refine and tailor-make their automated pipelines to an instrument's individual characteristics. Such automation provides near real-time data reduction to allow adaptive observing strategies, which is particularly important in the Time Domain Astronomy. Over the course of last year, significant improvement was made in the internal data handling as well as data I/O, accuracy and repeatability in the wavelength calibration., Comment: 4 pages, 2 figures, conference proceeding article for the ADASS XXX to be published in ASP Conference Series