CyberSec Research

The properties of stars and planets are shaped by the initial conditions of their natal clouds. However, the spatial scales over which the initial conditions can exert a significant influence are not well constrained. We report the first evidence for parsec-scale spatial correlations of stellar magnetospheric inclinations ($i_{\rm mag}$), observed in the Lupus low-mass star forming region. Applying consensus clustering with a hierarchical density-based clustering algorithm, we demonstrate that the detected spatial dependencies are stable against perturbations by measurement uncertainties. The $i_{\rm mag}$ correlation scales are on the order of ~3 pc, which aligns with the typical scales of the Lupus molecular cloud filaments. Our results reveal a connection between large-scale forces -- in the form of expanding shells from the Upper Scorpius and Upper-Centaurus-Lupus regions -- and sub-au scale system configurations. We find that Lupus has a non-uniform $i_{\rm mag}$ distribution and suggest that this results from the preferential elongation of protostellar cores along filamentary axes. Non-uniformity would have significant implications for exoplanet occurrence rate calculations, so future work should explore the longevity of these biases driven by the star-cloud connection.

We present AT2022kak, a rapidly evolving optical transient discovered by the KiloNova and Transients Program (KNTraP). This interesting burst exhibited extremely fast evolution, with a large amplitude blue outburst of m > 3.3 in a single night, and a rapid fade back to quiescence in the following two nights. We deployed a multi-wavelength follow-up campaign, monitoring the object for the next two months, but saw no recurrent burst. Three years later, while observing to get spectroscopy of the object in quiescence, there was a new outburst, enabling the collection of time-resolved spectra of the rise and fade of the outburst. The light curve properties of the first burst and spectra of the second burst are consistent with a dwarf nova. Its fast evolving behaviour makes it one of the fastest and faintest dwarf novae observed. The estimated distance of AT2022kak from the Galactic centre is ~6.6 kpc, with a scale height of ~2 kpc. This scale height places it in the Galactic thick disk, where only very few dwarf novae have been found, and is therefore a potential Population II dwarf novae system.

Mass loss shapes the fate of massive stars; however, the physical mechanism causing it remains uncertain. We present a comprehensive analysis of seven red supergiants, for which we searched evidence of episodic mass loss, in three low-metallicity galaxies: NGC~6822, IC~10, and WLM. Initially, the spectral classification of their optical spectra was refined and compared to previous reported classifications, finding four sources that display spectral variability. We derived the physical properties of five of them using the \textsc{marcs} atmospheric models corrected for nonlocal thermal equilibrium effects to measure stellar properties from our new near-infrared spectra, such as the effective temperature, surface gravity, metallicity, and microturbulent velocity. Additional empirical and theoretical methods were employed to calculate effective temperatures, finding consistent results. We constructed optical and infrared light curves, discovering two targets in NGC~6822 with photometric variability between 1 and 2.5 mag in amplitude in r and ~ 0.5 mag in the mid-infrared. Furthermore, we discovered a candidate-dimming event in one of these sources. Periods for three red supergiants were determined using epoch photometry, which were consistent with the empirical estimations from literature period-luminosity relations. Our comprehensive analysis of all the available data for each target provides evidence for episodic mass loss in four red supergiants.

We present a multi-spacecraft analysis of the 2024 July 16 Long-Duration Gamma-Ray Flare (LDGRF) detected by the Large Area Telescope on the Fermi satellite. The measured >100 MeV $\gamma$-ray emission persisted for over seven hours after the flare impulsive phase, and was characterized by photon energies exceeding 1 GeV and a remarkably-hard parent-proton spectrum. In contrast, the phenomena related to the coronal mass ejection (CME)-driven shock linked to this eruption were modest, suggesting an inefficient proton acceleration unlikely to achieve the energies well-above the 300 MeV pion-production threshold to account for the observed $\gamma$-ray emission. Specifically, the CME was relatively slow (~600 km/s) and the accompanying interplanetary type-II/III radio bursts were faint and short-duration, unlike those typically detected during large events. In particular, the type-II emission did not extend to kHz frequencies and disappeared ~5.5 hours prior to the LDGRF end time. Furthermore, the associated solar energetic particle (SEP) event was very weak, short-duration, and limited to a few tens of MeV, even at magnetically well-connected spacecraft. These findings demonstrate that a very-fast CME resulting in a high-energy SEP event is not a necessary condition for the occurrence of LDGRFs, challenging the idea that the high-energy $\gamma$-ray emission is produced by the back-precipitation of shock-accelerated ions into the solar surface. The alternative origin scenario based on local particle trapping and acceleration in large-scale coronal loops is instead favored by the observation of giant arch-like structures of hot plasma over the source region persisting for the entire duration of this LDGRF.

In this study we investigate the chemical enrichment of the rapid neutron-capture process in the Small Magellanic Cloud (SMC). We measure [Eu/Fe] abundance ratios in 209 giant stars that are confirmed members of the SMC, providing the first extensive dataset of Eu abundances in this galaxy across its full metallicity range, spanning more than 1.5 dex. We compare Eu abundances with those of Mg and Ba to evaluate the efficiency of the r-process relative to $\alpha$-capture and s-process nucleosynthesis. The SMC shows enhanced [Eu/Fe] values at all metallicities (comparable with the values measured in the Milky Way), with a clear decline as [Fe/H] increases (from $\sim$ -1.75 dex to $\sim$ -0.5 dex), consistent with the onset of Type Ia supernovae. In contrast, [Eu/Mg] is enhanced by about +0.5 dex at all [Fe/H], significantly above the values observed in Milky Way stars, where [Eu/Mg] remains close to solar, reflecting comparable production of r-process and $\alpha$-capture elements. Moreover, [Ba/Eu] increases with metallicity, beginning at [Fe/H] $\approx$ -1.5 dex, namely at a lower metallicity with respect to the Milky Way, where [Ba/Eu] starts to increase around [Fe/H] $\approx$ -1 dex. Our findings suggest the SMC has a higher production of Eu (with respect to the $\alpha$-elements) than the Milky Way but in line with what observed in other dwarf systems within the Local Group. We confirm that galaxies with star formation efficiencies lower than the Milky Way have high [Eu/$\alpha$], probably indicating a stronger efficiency of the delayed sources of r-process at low metallicities.

The Indian Pulsar Timing Array (InPTA) has recently published its second data release (DR2), comprising the timing analysis of seven years of data on 27 millisecond pulsars (MSPs), observed simultaneously in the 300-500 MHz (band 3) and 1260-1460 MHz (band 5), using the upgraded Giant Metrewave Radio Telescope (uGMRT). The low-frequency data, particularly in band 3, is highly sensitive to propagation effects such as dispersion measure (DM) fluctuations, which can be imprints of some astrophysical phenomena (scientific outliers). Here, we analyze the two outliers of possible astrophysical origin coming from the band 3 DM time series of two pulsars: PSR J1022+1001, with an ecliptic latitude of -0.06 degree , and PSR J2145-0750, one of the brightest MSPs, with multi-component profile morphology. Our study reveals compelling evidence for a coronal mass ejection (CME) event traced in the data of PSR J1022+1001, and reports evidence for a potential mode-changing event in PSR J2145-0750. Extending the analyses presented here to the full sample of InPTA-DR2 pulsars is expected to reveal additional CME events, and possible mode-changing events. Such detections will not only improve our understanding of solar and pulsar magnetospheric plasma interactions but will also enable more accurate modelling of DM variations, leading to improved pulsar timing solutions, which are crucial for high-precision Pulsar Timing Array (PTA) science.

The dipper subclass of YSOs are characterised by frequent dips in their light curves. Irregular dippers do not show periodic signatures and have dips accounting for significant proportions of their photospheric flux. Given the short timescales on which these dips occur, their driving mechanisms are linked to the inner circumstellar disc dynamics. We present the first multi-epoch analysis of 16 irregular dippers observed with X-Shooter. Investigating the properties of their dips, and in particular the analysis of the dust characteristics, we aim to understand the root of their variability, and get a glimpse of the inner disc behaviour. We employed a novel approach to measure the properties of the dips, by combining class III templates with Gaia photometry to construct the intrinsic photospheres. We measured several dip properties including the depth of the dips, near-infrared (NIR) excesses, and their optical depths as a function of wavelength. We record 20 significant dips that range in their dip properties and show no relation to one another. In almost all cases, the low optical depths and small NIR excesses are observed. Comparison of their optical depths with grain opacity models show that the dips can be explained by the presence of dust substructures containing processed grains obscuring their photospheres and/or their discs. These grain distributions can have maximum sizes as large as 20$\mu m$ and in many cases have almost grey-like extinction, while some require a strong scattering component. The findings highlight the extent of the irregularity of dippers, but also link it to the dust dynamics in the inner regions of circumstellar discs. The dust substructures causing the variability require processed dust grains to be lifted above the disc into the line of sight. Possible lifting mechanisms including disc winds, unstable accretion columns, and disc warps are discussed.

Neon (Ne) is the fifth most abundant element in the Universe. Because it is chemically inert, it has never been considered in astrochemical models that studied molecular evolution. In the cold dark environments of pre-stellar cores, where the temperatures are below 10 K, Ne can condense onto the surface of interstellar grains. We investigated the effect of Ne on the production of formaldehyde (H$_2$CO) and methanol (CH$_3$OH) through carbon monoxide (CO) hydrogenation on different cold surfaces. We highlight its role in conditions corresponding to pre-stellar cores. In an ultra-high vacuum system, we conducted two types of experiments. The first experiment involved the co-deposition of CO and H atoms with or without Ne. The second experiment involved depositing a monolayer of CO and separately a monolayer of Ne (or vice versa), followed by bombarding the layers with hydrogen atoms. Additionally, we used a gas-grain chemical code to simulate a pre-stellar core and determine where Ne can affect the chemistry. The presence of Ne on the surface significantly inhibits CO hydrogenation at temperatures below 12 K. In the co-deposition experiments, we observed a 38% decrease in the H$_2$CO production at 11 K when the quantity of Ne in the mixture was lower than a monolayer. At 10 K and with one monolayer in the mixture, the production decreased to 77%, and it reached 91% for a few monolayers of Ne in the mixture at 9 K. While the decrease in CH$_3$OH formation is still notable, it is less pronounced: 43% at 11 K, 61% at 10 K, and 77% at 9 K. Experiments with stacked layers revealed that the CO layer decay varies slightly when the Ne layer is positioned above or below it. This observation indicates that Ne and CO create a mixture in which Ne can diffuse and stabilize at the surface, which isolates CO molecules from the accreting H atoms.

A major challenge in modeling classical Cepheids is the treatment of convection, particularly its complex interplay with pulsation. This inherently three-dimensional process is typically approximated in one-dimensional hydrocodes using dimensionless turbulent convection (TC) free parameters. Calibrating these parameters is essential for reproducing key observational features such as light-curve amplitudes, secondary bumps, and the red edge of the instability strip. In this work, we calibrate TC parameters adopted in the publicly available MESA-RSP code through comparison with both observational data of classical Cepheids and stellar parameter constraints from the Stellingwerf code. We compute multi-band (V, I, and Ks) MESA-RSP light curves for 18 observed Large Magellanic Cloud Cepheids, using stellar parameters determined from the Stellingwerf code. By fine-tuning the mixing-length and eddy viscosity parameters, we calibrate the TC treatment in MESA-RSP. We then compare the resulting period-luminosity (PL), period-radius (PR), and period-mass-radius (PMR) relations with predictions from the Stellingwerf models. We successfully reproduce multi-band light curves and obtain PL, PR, and PMR relations consistent with Ragosta et al. (2019). While in broad agreement with previous work, we explicitly identify distinct mass-luminosity (ML) relations for fundamental-mode and first-overtone Cepheids for the first time. This suggests that the macroscopic processes affecting the ML relation depend on stellar mass and/or effective temperature range. Although our study focuses on the calibration of TC parameters, we do not find a single set of parameter values that reproduces all light curves. No statistically significant correlation is found between stellar properties and convection parameters, although subtle trends with period and effective temperature may be present.

As astronomy advances and data becomes more complex, models and inference also become more expensive and complex. In this paper we present {\sc ampere}, which aims to solve this problem using modern inference techniques such as flexible likelihood functions and likelihood-free inference. {\sc ampere}\ can be used to do Bayesian inference even with very expensive models (hours of CPU time per model) that do not include all the features of the observations (e.g. missing lines, incomplete descriptions of PSFs, etc). We demonstrate the power of \ampere\ using a number of simple models, including inferring the posterior mineralogy of circumstellar dust using a Monte Carlo Radiative Transfer model. {\sc ampere}\ reproduces the input parameters well in all cases, and shows that some past studies have tended to underestimate the uncertainties that should be attached to the parameters. {\sc ampere}\ can be applied to a wide range of problems, and is particularly well-suited to using expensive models to interpret data.

Unveiling massive stars' internal structure and the physical origin and efficiency of the internal mixing processes? It is now possible using the apsidal motion rate in close eccentric binaries! The apsidal motion rate depends on the tidal interactions occurring between the stars and is proportional to k2, a measure of the star's inner density profile. Confronting standard stellar models with observations reveals the famous k2-discrepancy: models predict too high a k2 for the stars, that is to say, stars with too low a density contrast between their core and envelope. We built bespoke GENEC stellar evolution models including tidal mixing for the twin massive binary HD 152248. The models reveal the instabilities allowing to reproduce the stellar density profiles: advecto-diffusive models better reproduce k2 than magnetic models. A large overshooting is necessary to converge towards the observed k2, yet alone is not sufficient. While a change in metallicity or mass-loss rate has no significant impact on k2, a larger initial helium abundance allows us to better reproduce the k2. Yet, a super-solar helium abundance is not observationally supported. Our analyses highlight the need for a process in the stars that slows down the radial expansion.

We present theoretical predictions of the born-again scenario for post-asymptotic giant-branch stars. An extensive model grid for born-again objects has been constructed, particularly including models for the Very Late Thermal Pulse with and without convective overshooting, and also including models for the Late Thermal Pulse. We constructed a large parameter space to analyze the dependencies of the born-again model on core mass, hydrogen-envelope mass, and overshoot parameters, and we analyzed how changes in these parameters affect the models' evolution. We applied our grid of models to interpret observations of DY\,Cen, a star exhibiting characteristics similar to confirmed born-again stars. We compared DY\,Cen with models from multiple aspects, including heating rate, evolutionary tracks, and surface abundances. Ultimately, we concluded that none of our born-again models could match all of the observed properties of DY\,Cen, especially its surface chemistry; DY\,Cen is therefore an unlikely born-again star.

In this study, we applied Al-Wardat's method to analyze the subgiant system HIP72217 for which we obtained accurate parameters including stellar masses, effective temperatures ($T_{\text{eff}}$) and system age.For the primary component we determined a stellar mass of $M_A = 1.14 \pm 0.15\,M_{\odot}$ and effective temperature $T_{\text{eff,A}} = 6125 \pm 50$\,K while for the secondary component we obtained the values of $M_B = 1.12 \pm 0.14\,M_{\odot}$ and $T_{\text{eff,2}} = 5950 \pm 50$\,K. The system's age was estimated to be $3.548 Gyr$, which is consistent with the predicted evolutionary period of a subgiant binary. The evolutionary timeline of HIP\,72217 becomes clearer through our study, which also demonstrates Al-Wardat's approach as an effective approach for binary star system characterization. These findings contribute to a better understanding of the physical mechanisms that control subgiant binary evolution and their broader role in stellar evolutionary processes.

The inclusion of convection in stellar evolution models lacks realism, especially near convective-radiative interfaces. Furthermore, the interaction of convection with oscillations prevent us from accurately predicting seismic frequencies, and therefore from fully exploiting the asteroseismic data of low-mass stars. We aim to develop a new formalism to model the one-point statistics of stellar convection, to implement it in a new numerical code, and to validate this implementation against benchmark cases. This new formalism is based on Lagrangian Probability Density Function (PDF) methods, where a Fokker-Planck equation for the PDF of particle-based turbulent properties is integrated in time. We then develop a Monte-Carlo implementation of this method, where the flow is represented by a large number of notional particles acting as realisations of the PDF. Notional particles interact with each other through the time- and space-dependent mean flow, which is estimated from the particle realisations through a scheme similar to Smoothed Particle Hydrodynamics. We establish a model for the evolution of turbulent properties along Lagrangian trajectories applicable to stellar turbulent convection, with only a minimal number of physical assumptions necessary to close the system. In particular, no closure is needed for the non-linear advection terms, which are included exactly through the Lagrangian nature of formalism. The numerical implementation of this new formalism allows us to extract time-dependent maps of the statistical properties of turbulent convection in a way which is not possible in grid-based large-eddy simulations, in particular the turbulent pressure, Reynolds stress tensor, internal energy variance and convective flux.

The discovery of hot Jupiters has challenged the classical planet formation theory. Although various formation mechanisms have been proposed, the dominant channel and relative contributions remain unclear. Furthermore, hot Jupiters offer a unique opportunity to test tidal theory and measure the fundamental tidal quality factor, which is yet to be well-constrained. In this work, based on a hot Jupiter sample around single Sun-like stars with kinematic properties, {we find that the declining trend of their frequency is broken with a ridge at about 2 Gyr, providing direct evidence that hot Jupiters are formed with multiple origins of different timescales. By fitting with the theoretical expectations, we provide a constraint of tidal factor for Sun-like stars, which aligns well with the detected number of hot Jupiters with orbital decay. Moreover, we simultaneously constrain the relative importance of different channels: although the majority of hot Jupiters are formed early, within several tenths of Gyr via 'Early' models (e.g., in-situ formation, disk migration, planet-planet scattering and Kozai-Lidov interaction), a significant portion (about 40%) should be formed late on a relatively long timescale extending up to several Gyr mainly via the secular chaos mechanism, further supported by the obliquity distribution of 'late-arrived' hot Jupiters. Our findings provide a unified framework that reconciles hot Jupiter demographics and long-term evolution with multichannel formation.

This study proposes a quantitative framework to enhance curriculum coherence through the systematic alignment of Course Learning Outcomes (CLOs) and Program Learning Outcomes (PLOs), contributing to continuous improvement in outcome-based education. Grounded in accreditation standards such as ABET and NCAAA, the model introduces mathematical tools that map exercises, assessment questions, teaching units (TUs), and student assessment components (SACs) to CLOs and PLOs. This dual-layer approach-combining micro-level analysis of assessment elements with macro-level curriculum evaluation-enables detailed tracking of learning outcomes and helps identify misalignments between instructional delivery, assessment strategies, and program objectives. The framework incorporates alignment matrices, weighted relationships, and practical indicators to quantify coherence and evaluate course or program performance. Application of this model reveals gaps in outcome coverage and underscores the importance of realignment, especially when specific PLOs are underrepresented or CLOs are not adequately supported by assessments. The proposed model is practical, adaptable, and scalable, making it suitable for academic programs. Its systematic structure supports institutions in implementing evidence-based curriculum improvements and provides a reliable mechanism for aligning teaching practices with desired learning outcomes. Ultimately, this framework offers a valuable tool for closing the feedback loop between instructional design, assessment execution, and learning outcomes, thus promoting greater transparency, accountability, and educational effectiveness. Institutions that adopt this model can expect to strengthen their quality assurance processes and help ensure that students graduate with the competencies required by academic standards and professional expectations.

We present a new spectroscopic pipeline designed to analyse large numbers of hot massive stars homogeneously. The pipeline has been developed to utilise large grids of FASTWIND non-LTE, line blanketed models in which spherical geometry is adopted, and uniquely incorporates model errors. The pipeline has been applied to three contemporary datasets involving Very Large Telescope spectroscopy of OB stars in the Magellanic Clouds, namely the VLT FLAMES Tarantula Survey (VFTS), XShooting-ULLYSES (XShootU) and Binaries at Low Metallicity (BLOeM). We find satisfactory agreement with previous detailed temperatures and surface gravities, although strong nebular contamination, binarity and disk emission from OBe stars are problematic for automatic pipelines, requiring visual inspection of fits. The tool has been incorporated into the pipeline for the VISTA/4MOST pipeline.

Precision UBVRI photometry of NGC 7789 is combined with Gaia data to map reddening variations across the cluster face. HYDRA spectra, Gaia astrometry, and isochrone fitting constrain the absolute reddening, apparent modulus, and age to E(B-V) = 0.30 +/- 0.02, (m-M)=12.51 +/- 0.06, and 1.46 +/- 0.02 Gyr for [Fe/H] between -0.2 and solar; the spectroscopic [Fe/H] = -0.13 +/- 0.068 (MAD) from 156 single-star members. Corrections for variable reddening reduce the scatter in the unevolved main sequence below the turnoff. A(Li) is derived for only single star members from the G-dwarf Li-Plateau to the tip of the red giant branch. Giants separate into two distinct groups, probable first-ascent giants with detectable Li that declines with evolution toward the red giant tip and stars within the clump and the asymptotic giant branch which only exhibit upper limits. A(Li) structure from the turnoff to the unevolved main sequence, including the Li-Dip, and the presence of an extended color spread among the upper main sequence stars are attributed to the V_ROT distribution, indicating the wall of the Li-Dip as the true hot boundary of the Kraft break. Differences in the color-magnitude diagram topology of NGC 7789 and NGC 752 are explored and attributed to differences in the individual cluster V_ROT distributions. Prior indications that main sequence stars more massive than the Li-Dip evolve redward across the Li-Wall, undergoing rotational spindown and Li depletion like stars within the Li-Dip, are confirmed.