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Abstract In an effort to search for faint sources of emission over arbitrary timescales, we present a novel method for analyzing forced photometry light curves in difference imaging from optical surveys. Our method “ATLAS Clean,” or ATClean, utilizes the reported fluxes, uncertainties, and fits to the point-spread function (PSF) from difference images to quantify the statistical significance of individual measurements. We apply this method to control light curves across the image to determine whether any source of flux is present in the data for a range of specific timescales. From ATLASo-band imaging at the site of the Type II supernova (SN) 2023ixf in M101 from 2015–2023, we show that this method accurately reproduces the 3σflux limits produced from other, more computationally expensive methods. We derive limits for emission on timescales of 5 days and 80–300 days at the site of SN 2023ixf, which are 19.8 and 21.3 mag, respectively. The latter limits rule out variability for unextinguished red supergiants with initial masses >22M_⊙, comparable to the most luminous predictions for the SN 2023ixf progenitor system. We also compare our limits to short-timescale outbursts, similar to those expected for Type IIn SN progenitor stars or the Type II SN 2020tlf, and rule out outburst ejecta masses of >0.021M_⊙, much lower than the inferred mass of circumstellar matter around SN 2023ixf in the literature. In the future, these methods can be applied to any forced photometry on difference imaging from other surveys, such as Rubin optical imaging. 

Thanks to its exceptional near-infrared photometry, JWST can effectively contribute to the discovery, characterisation, and understanding of multiple stellar populations in globular clusters, especially at low masses where theHubbleSpace Telescope (HST) faces limitations. This paper continues the efforts of the JWST GO-1979 programme in exploring the faintest members of the globular cluster NGC 6397. In this work, we show that the combination of HST and JWST data allows us to identify two groups of MS stars: MSa, the first-generation group, and MSb, the second-generation group. We measured the ratio between the two groups and combined it with measurements from the literature focused on more central fields and more massive stars compared to our study. Our findings suggest that the MSa and MSb stars are present in a ≈30−70 ratio regardless of the distance from the centre of the cluster and the mass of the stars used so far. However, considering the limited areal coverage of our study, a more comprehensive spatial analysis is necessary to definitively confirm complete spatial mixing. 

The fixed preemption point (FPP) model has been studied as an alternative to fully preemptive and non-preemptive models, as restricting preemptions to specific, predictable locations within a task’s execution can simplify overhead analysis without disallowing preemptions entirely. Prior work has produced response-time analyses for global Earliest Deadline First (G-EDF) scheduling under the FPP model. However, scheduling decisions based solely on task deadlines may be too coarsegrained and may not lead to the lowest response times. In this paper, we propose global FPP EDF-like (G-FPP-EL) scheduling, which assigns a priority point in time for each non-preemptive region of a task. We adapt compliant-vector analysis (CVA) to our model and present general response-time bounds for G-FPPEL schedulers. We then demonstrate that it is possible to design G-FPP-EL schedulers acheiving response-time bounds optimal under CVA and argue that such schedulers should replace global FPP EDF. 

Practical reproducibility is the ability to reproduce results is a manner that is cost-effective enough to become a vehicle of mainstream scientific exploration. Since computational research artifacts usually require some form of computing to interpret, open and programmable infrastructure, such as a range of NSF-supported testbeds spanning infrastructure from datacen- ter through networks to wireless systems, is a necessary – but not sufficient – requirement for reproducibility. The question arises what other services and tools should build on the availability of such programmable infrastructure to foster the development and sharing of findable, accessible, integrated, and reusable (FAIR) experiments that underpin practical reproducibility. In this paper, we propose three such services addressing the problems of packaging for reuse, findability, and accessibility, respectively. We describe how we developed these services in Chameleon, an NSF-funded testbed for computer science research which has supported the research of a community of 8,000+ users, and discuss their strengths and limitations. 

Context.High-precision pulsar timing is highly dependent on the precise and accurate modelling of any effects that can potentially impact the data. In particular, effects that contain stochastic elements contribute to some level of corruption and complexity in the analysis of pulsar-timing data. It has been shown that commonly used solar wind models do not accurately account for variability in the amplitude of the solar wind on both short and long timescales. Aims.In this study, we test and validate a new, cutting-edge solar wind modelling method included in theenterprisesoftware suite (widely used for pulsar noise analysis) through extended simulations. We use it to investigate temporal variability in LOFAR data. Our model testing scheme in itself provides an invaluable asset for pulsar timing array (PTA) experiments. Since, improperly accounting for the solar wind signature in pulsar data can induce false-positive signals, it is of fundamental importance to include in any such investigations. Methods.We employed a Bayesian approach utilising a continuously varying Gaussian process to model the solar wind. It uses a spherical approximation that modulates the electron density. This method, which we refer to as a solar wind Gaussian process (SWGP), has been integrated into existing noise analysis software, specificallyenterprise. Our Validation of this model was performed through simulations. We then conduct noise analysis on eight pulsars from the LOFAR dataset, with most pulsars having a time span of ∼11 years encompassing one full solar activity cycle. Furthermore, we derived the electron densities from the dispersion measure values obtained by the SWGP model. Results.Our analysis reveals a strong correlation between the electron density at 1 AU and the ecliptic latitude (ELAT) of the pulsar. Pulsars with |ELAT|< 3° exhibit significantly higher average electron densities. Furthermore, we observed distinct temporal patterns in the electron densities in different pulsars. In particular, pulsars within |ELAT|< 3° exhibit similar temporal variations, while the electron densities of those outside this range correlate with the solar activity cycle. Notably, some pulsars exhibit sensitivity to the solar wind up to 45° away from the Sun in LOFAR data. Conclusions.The continuous variability in electron density offered in this model represents a substantial improvement over previous models, that assume a single value for piece-wise bins of time. This advancement holds promise for solar wind modelling in future International Pulsar Timing Array (IPTA) data combinations.