Papers for Tuesday, Aug 19 2025

Fast radio bursts (FRBs) are millisecond-duration extragalactic transients characterized by ultrahigh brightness temperatures, suggesting coherent emission mechanisms in extreme astrophysical processes. In this paper, we extend the bunched coherent Cherenkov radiation (CChR) framework by incorporating bunch inclination and geometric configuration parameters, enabling it to more rigorously model FRB emission and tera-Hertz (THz) emission from magnetars. When relativistic bunches are injected into the magnetized plasma of a magnetar's magnetosphere at the Cherenkov angle, their emitted waves achieve phase coherence through constructive interference. Furthermore, the three-dimensional geometry of the bunches plays a crucial role in influencing the coherence of the radiation. Within the framework of CChR, we predict the existence of THz emission counterparts associated with FRBs and explain the observed characteristics of the THz-emitting magnetar SGR J1745-2900. Detections of such counterparts by upgraded millimeter telescopes (e.g., Atacama Large Millimeter/submillimeter Array, IRAM) would be expected to provide new insights into the potential physical connection between FRBs and magnetars.

Accurate correction for extinction by Galactic dust is essential for studying the extragalactic sky. In the low-extinction regions of the Ursa Major molecular cloud complex, we demonstrate that Galactic dust reddening maps constructed from observations of far-infrared emission are insensitive to variations in the abundance of polycyclic aromatic hydrocarbons (PAHs), and, as a result, to PAH-induced variations in reddening. Using galaxy counts to validate various reddening maps, we find evidence that maps based on far-infrared emission erroneously under-predict reddening compared to stellar reddening maps. This underestimation by far-infrared emission based reddening maps -- representing the largest discrepancy between maps of up to $E(B-V)=0.08$ mag -- is correlated with the relative brightness of PAH emission. Furthermore, we demonstrate theoretically that changes in PAH abundance via accretion from the gas phase is capable of altering extinction significantly with only minor changes to far-infrared emission. We show that modeling the extinction of Ursa Major using both far-infrared and mid-infrared emission more accurately traces dust extinction variations due to changes in PAH abundance. Finally, we discuss how SPHEREx observations of the 3.3 $\mu$m PAH feature are a promising way to overcome this limitation of far-infrared emission.

We present multi-wavelength observations of the type II supernova (SN II) 2023ixf during its first two years of evolution. We combine ground-based optical/NIR spectroscopy with Hubble Space Telescope (HST) far- and near-ultraviolet spectroscopy and James Webb Space Telescope (JWST) near- and mid-infrared photometry and spectroscopy to create spectral energy distributions of SN 2023ixf at +374 and +620 days post-explosion, covering a wavelength range of ~0.1-30 $\mu$m. The multi-band light curve of SN 2023ixf follows a standard radioactive decay decline rate after the plateau until ~500 days, at which point shock powered emission from ongoing interaction between the SN ejecta and circumstellar material (CSM) begins to dominate. This evolution is temporally consistent with 0.3-10 keV X-ray detections of SN 2023ixf and broad ''boxy'' spectral line emission from reprocessing of shock luminosity in a cold dense shell located between forward and reverse shocks. Using the expected absorbed radioactive decay power and the detected X-ray luminosity, we quantify the total shock powered emission at the +374 and +620 day epochs and find that it can be explained by nearly complete thermalization of the reverse shock luminosity as SN 2023ixf interacts with a continuous, ''wind-like'' CSM with a progenitor mass-loss rate of $\dot M \approx 10^{-4}$ M$_{\odot}$ yr$^{-1}$ ($v_w = 20 \pm 5$ km/s). Additionally, we construct multi-epoch spectral models from the non-LTE radiative transfer code CMFGEN, which contain radioactive decay and shock powers, as well as dust absorption, scattering, and emission. We find that models with shock powers of $L_{sh} = (0.5-1) \times 10^{40}$ erg s$^{-1}$ and $(0.5 - 1) \times 10^{-3}$ M$_{\odot}$ of silicate dust in the cold dense shell and/or inner SN ejecta can effectively reproduce the global properties of the late-time (>300 days) UV-to-IR spectra of SN 2023ixf.

We develop a model for supermassive black hole binaries (SMBHBs) accreting below their Eddington limit, focusing on systems where hot, advection-dominated flows become viable. We specifically explore the spectral appearance of multi-component accretion flows where the solution can independently transition between cold, thin disks and hot, advection-dominated torii depending on the local accretion rate. Using a three-disk model, we compute spectral energy distributions for four possible accretion configurations and assess their observational signatures, including which frequencies might reflect variability at the binary orbital period. The spectral modeling reveals that binary accretion can self-consistently account for many of the properties of standard AGN, while the variability analysis shows that hydrodynamic modulation at the binary period is most likely in the thermal emission and low-frequency synchrotron components. Doppler boosting of emitting material bound to a single binary component would also induce periodic variability. We apply our model to the SMBHB candidate PG1302-102 and demonstrate that a mixed-component accretion state (plus a jet feature) can self-consistently capture the observed broadband spectrum. Our model offers a framework for interpreting candidate SMBHBs and motivates future multi-wavelength follow-up of potential multi-messenger sources, as well as more detailed future modeling of multi-component binary accretion.

Based on the Kolmogorov-Arnold Network (KAN), we present a novel emulator of the global 21 cm cosmology signal, $\texttt{21cmKAN}$, that provides extremely fast training speed while achieving nearly equivalent accuracy to the most accurate emulator to date, $\texttt{21cmLSTM}$. The combination of enhanced speed and accuracy facilitated by $\texttt{21cmKAN}$ enables rapid and highly accurate physical parameter estimation analyses of multiple 21 cm models, which is needed to fully characterize the complex feature space across models and produce robust constraints on the early universe. Rather than using static functions to model complex relationships like traditional fully-connected neural networks do, KANs learn expressive transformations that can perform significantly better for low-dimensional physical problems. $\texttt{21cmKAN}$ predicts a given signal for two well-known models in the community in 3.7 ms on average and trains about 75 times faster than $\texttt{21cmLSTM}$, when utilizing the same typical GPU. $\texttt{21cmKAN}$ is able to achieve these speeds because of its learnable, data-driven transformations and its relatively small number of trainable parameters compared to a memory-based emulator. We show that $\texttt{21cmKAN}$ required less than 30 minutes to train and fit these simulated signals and obtain unbiased posterior distributions. We find that the transparent architecture of $\texttt{21cmKAN}$ allows us to conveniently interpret and further validate its emulation results in terms of the sensitivity of the 21 cm signal to each physical parameter. This work demonstrates the effectiveness of KANs and their ability to more quickly and accurately mimic expensive physical simulations in comparison to other types of neural networks.

Exozodiacal dust disks (exozodis) are populations of warm (~300K) or hot (~1000K) dust, located in or interior to a star's habitable zone, detected around ~25% of main-sequence stars as excess emission over the stellar photosphere at mid- or near-infrared wavelengths. Often too plentiful to be explained by an in-situ planetesimal belt, exozodi dust is usually thought to be transported inwards from further out in the system. There is no consensus on which (if any) of various proposed dynamical models is correct, yet it is vital to understand exozodis given the risk they pose to direct imaging and characterisation of Earth-like planets. This article reviews current theoretical understanding of the origin and evolution of exozodi dust. It also identifies key questions pertinent to the potential for exozodis to impact exoplanet imaging and summarises current understanding of the answer to them informed by exozodi theory. These address how exozodi dust is delivered, its size and spatial distribution, and the effect of its composition on exozodi observability, as well as the connection between hot and warm exozodis. Also addressed are how common different exozodi levels are and how that level can be predicted from system properties, as well as the features that planets impart in dust distributions and how exozodis affect a planet's physical properties and habitability. We conclude that exozodis present both a problem and an opportunity, e.g., by introducing noise that makes planets harder to detect, but also identifying systems in which ingredients conducive to life, like water and volatiles, are delivered to the habitable zone.

We present far- and near-ultraviolet (UV) spectra of the Type II supernovae (SNe) SN~2023ixf from days 199 to 722 and SN~2024ggi at days 41 and 232. Both supernovae show broad, blueshifted, and asymmetric UV emission lines with an initial maximum velocity of $\sim9000\,km\,s^{-1}$ and narrow unresolved emission in CIV. We compare the optical and UV emission-line profiles, showing that they evolve from two distinct velocity profiles to a single profile tracing the UV emission. We interpret this as shock power from interaction with circumstellar material coming to dominate over the radioactive-decay power from the inner ejecta. Comparing our observations to radiative transfer models with injected shock power, we find SN~2024ggi is best matched by $P_{\mathrm{shock, abs}}=1\times10^{41}\,erg\,s^{-1}$ at day 40, SN~2023ixf at day 300 and SN~2024ggi at day 200 are best matched by $P_{\mathrm{shock,abs}}=1\times10^{40}\,erg\,s^{-1}$, and SN~2023ixf at day 600 is best matched by $P_{\mathrm{shock,abs}}=5\times10^{39}\,erg\,s^{-1}$. From these models, we find the mass-loss rate of both supernovae increased just before explosion. For SN~2023ixf our mass-loss rates go from $4\times10^{-5}\,M_{\odot}\,yr^{-1}$ at 600 yr before explosion to $2\times10^{-2}\,M_{\odot}\,yr^{-1}$ at 15 yr prior to explosion. For SN~2024ggi, we find a mass-loss rate of $9\times10^{-5}\,M_{\odot}\,yr^{-1}$ at 150 yr before explosion and $1\times10^{-3}\,M_{\odot}\,yr^{-1}$ at 30 yr before explosion.

Context: Magnetic fields play a pivotal role in dynamics of black hole accretion flows and formation of relativistic jets. Observations by the Event Horizon Telescope (EHT) provided unprecedented insights into accretion structures near black holes. Interpreting these observations requires a theoretical framework linking polarized emission to underlying system properties and magnetic field geometries. Aims: We investigate how system properties, particularly magnetic field geometry in the event horizon scale region, influence the structure of the observable synchrotron emission in M87*. Specifically, we aim to quantify the sensitivity of observables used by the EHT to black hole spin, plasma dynamics, accretion disk thickness, and magnetic field geometry. Methods: We adopt a semi-analytic radiatively inefficient accretion flow model in Kerr spacetime. We vary magnetic field geometry, black hole spin, accretion disk dynamics, and geometric thickness of the disk. We perform general relativistic ray tracing with a full polarized radiative transfer to obtain synthetic images of M87*. We extract EHT observables, such as disk diameter, asymmetry, and polarimetric metrics from synthetic models. We also consider a number of general relativistic magnetohydrodynamics simulations and compare them with the semi-analytical models. Results: We see limited impact of the disk thickness on observables. On the other hand, toroidal field dominated and poloidal field dominated magnetic configurations can be distinguished reliably. The flow dynamics, in particular presence of radial inflow, also significantly impacts the EHT observables. Conclusions: The M87* system is most consistent with a poloidal magnetic field dominated flow with partially radial inflow. While the spin remain elusive, moderate or large positive values are preferred.

JWST is discovering a plethora of species in planet-forming disks around very low-mass stars such as C2H2, C6H6, C4H2, CH3 etc. The column densities of these species retrieved from 0D slab models are very large, e.g. of the order of $10^{20}$\,cm$^{-2}$. This is indicating a carbon-dominated chemistry in a gas with a high C/O ratio. The disk around 2MASS-J1605321-1993159 (M4.5) is one such source showing a molecular pseudo-continuum of C2H2. Still two oxygen-bearing molecules, CO and CO2 are also detected in this source. We aim to take the next step beyond 0D slab models to interpret the spectrum. We examine whether 2D thermo-chemical disk models can produce the large inferred column densities of \ce{C2H2} in the inner regions of the disk and produce a pseudo-continuum in the mid-IR spectrum. We also want to constrain whether depletion of oxygen or enrichment of carbon is causing the high C/O ratio triggering a carbon-dominated chemistry. We utilize the radiative thermo-chemical disk model P{\tiny RO}D{\tiny I}M{\tiny O} to identify a disk structure which is capable of producing the observed molecular emission of species such as CO, CO2, C2H2, and H2O simultaneously. The spectrum is generated using the fast line tracer FLiTs. We derive the gas temperature $\langle T \rangle$, column density $\langle$ log$_{\rm {10}} N\rangle$ and the emitting area $\langle r_{\rm{1}} - r_{\rm{2}} \rangle$ for these molecules from the 2D disk model and compare them to the parameters retrieved originally from 0D slab models. We use the different effect that changing the O or C abundance has on CO and C2H2 respectively to discriminate between O depletion and C enhancement. We find that a disk structure characterised by the presence of a gap can best explain the observations. The inner disk is strongly depleted in dust, especially small grains ($<5\,\mu$m), and ..

The Compton Spectrometer and Imager (COSI) is a gamma-ray survey telescope utilizing a compact Compton imager design, enabled by an array of 16 high-resolution germanium cross-strip detectors. After its launch into an equatorial Low Earth Orbit (LEO) in 2027, COSI will experience radiation damage primarily due to energetic protons, with the proton fluence dominated by the passage of COSI through the edge of the South Atlantic Anomaly (SAA) for a few minutes each orbit. We have developed a comprehensive program focused on the modeling, characterization, data correction, and physical repair of radiation damage effects in the COSI detectors. We have performed energetic proton beam irradiations of a spare COSI detector at a proton synchrotron, with proton fluences consistent with multiple years of exposure to the COSI space radiation environment. These exposures allow us to characterize the relationship between proton fluence and induced charge trapping. We demonstrate our techniques to correct for trapping effects, as well as characterize the effectiveness of high-temperature annealing on correcting this damage, as characterized by the resulting spectral performance of the detector. We will present our efforts to characterize the effects of radiation damage in the COSI detectors, as well as our techniques for correcting these effects in the data analysis pipeline and ultimately repairing the detectors on orbit every few years through high-temperature annealing.

Data on five Washington Double Star catalog binaries were collected from the Dimension Point Observatory (Mayhill, New Mexico) and Las Cumbres Observatory (Cerro Tololo, Chile) on February 19, 2025, and March 5, 2025, respectively. Student researchers participating in the Four Corners Research Seminar measured the position angle (theta/deg) and separation (rho/arcsec) of each target using AstroImageJ and an author-created script utilizing the Astropy module in Python3. Each target was imaged using a variety of instruments, filters, and exposure times. Compared to the extrapolated 6th Orbit Catalog estimates, measurements using AstroImageJ were within 1.52% of theta and 14.87% of rho, while the author's automated code method provided measurements within 4.09% of theta and 16.59% of rho.

Constraints on local primordial non-Gaussianity (LPnG) obtained from galaxy power spectra are limited by the perfect degeneracy between the LPnG parameter $f_{\rm NL}$ and the bias parameter $b_{\phi}$ which encodes the response of galaxy clustering to a change in the amplitude of primordial curvature fluctuations. For galaxies observed by galaxy surveys, the relation between $b_{\phi}$ and the galaxy bias $b_{g}$ is poorly understood and differs significantly from the universal mass function ansatz. In this paper, we investigate this non-universality in the context of dark-matter halos using the Separate Universe framework, focussing on dark-matter halos selected by mass and/or concentration. We show that the Separate Universe framework provides a natural explanation of the observed universality in the bias of dark-matter halos selected purely by their mass, independent of the spherical collapse picture of halo formation. We further propose an explanation for the observed non-universality in halos selected by concentration and corroborate it with $N$-body simulations in scale-free (EdS) and $\Lambda\text{CDM}$ cosmologies. In particular, we show that the relation between $b_{\phi}$ and halo bias $b_{h}$ for halos selected by concentration in matter-dominated cosmologies tends towards universality at the highest halo masses due to such halos gravitationally dominating their environment throughout their evolution. We also argue that concentration-selected halos of lower masses exhibit non-universality due to their mass accretion being significantly affected by the gravitational influence of neighbouring, more massive halos. Our results suggest that any non-universality in high redshift ($z\gtrsim 3$), high-bias objects observed by realistic galaxy surveys is entirely an artifact of the associated selection function.

We perform a frequentist analysis using the standard profile likelihood method for clustering measurements from Data Release 1 of the Dark Energy Spectroscopic Instrument (DESI). While Bayesian inferences for Effective Field Theory models of galaxy clustering can be highly sensitive to the choice of priors for extended cosmological models, frequentist inferences are not susceptible to such effects. We compare Bayesian and frequentist constraints for the parameter set $\{\sigma_8, H_0, \Omega_{\rm{m}}, w_0, w_a\}$ when fitting to the full-shape of the power spectrum multipoles, the post-reconstruction Baryon Acoustic Oscillation (BAO) measurements, as well as external datasets from the CMB and type Ia supernovae measurements. Bayesian prior effects are very significant for the $w_0w_a$CDM model; while the $1 \sigma$ frequentist confidence intervals encompass the maximum a posteriori (MAP), the Bayesian credible intervals almost always exclude the maximum likelihood estimate (MLE) and the MAP - indicating strong prior volume projection effects - unless supernovae data are included. We observe limited prior effects for the $\Lambda$CDM model, due to the reduced number of parameters. When DESI full-shape and BAO data are jointly fit, we obtain the following $1\sigma$ frequentist confidence intervals for $\Lambda$CDM ($w_0w_a$CDM): $\sigma_8 = 0.867^{+0.048}_{-0.041} , \ H_0 = 68.91^{+0.80}_{-0.79} \ \rm{km \ s^{-1}Mpc^{-1}} , \ \Omega_{\rm{m}} = 0.3038\pm0.0110$ ($\sigma_8 = 0.793^{+0.069}_{-0.048} , \ H_0 = 64.9^{+4.8}_{-2.8} \ \rm{km \ s^{-1}Mpc^{-1}} , \ \Omega_{\rm{m}} = 0.369^{+0.029}_{-0.059}$ , $w_0 = -0.24^{+0.17}_{-0.64}$ , $w_a = -2.5^{+1.9}_{}$), corresponding to 0.7$\sigma$, 0.3$\sigma$, 0.7$\sigma$ (1.9$\sigma$, 3.4$\sigma$, 5.6$\sigma$, 5.5$\sigma$, 5.6$\sigma$) shifts between the MLE relative to the Bayesian posterior mean for $\Lambda$CDM ($w_0w_a$CDM) respectively.

Using a 90 ks Chandra ACIS-S observation in the 0.3--7 keV band, along with complementary Low-Frequency Array and Karl G.~Jansky Very Large Array data in the 120--168 MHz and 1--2 GHz ranges, we study the diffuse emission around the nearby dwarf galaxy KUG~1138+327. Our analysis reveals a diffuse X-ray feature on the southern side, disconnected from the galactic disk. This feature exhibits a hard X-ray spectrum, which is highly unusual for an outflow from a dwarf galaxy. We interpret the irregularly shaped feature as hot plasma in a young galaxy cluster at redshift 0.5, supported by X-ray spectral fitting and consistent with the optical redshift of the central elliptical galaxy of a known cluster identified by a red sequence. Additionally, we detect a radio lobe east of the X-ray feature, likely produced by an AGN offset from the cluster center and confined primarily by ram pressure from the ambient medium. The lobe shows a steep nonthermal radio spectrum, suggesting a cosmic-ray age of $\gtrsim 5 \times 10^{7}$~yr. Assuming energy equipartition between cosmic rays and magnetic fields, we estimate the lobe's total energy to be $\sim 9 \times 10^{56}~\mathrm{erg}$, comparable to the thermal energy in the same volume. This study thus identifies a background young cluster projected next to KUG~1138+327 and highlights the potentially significant role of off-center AGN feedback in shaping the intracluster medium.

We present a quantitative spectroscopic study of 13 blue supergiant stars in the Pinwheel Galaxy M101, based on data obtained with the Low Resolution Imaging Spectrometer available at the Keck I telescope. The average stellar metallicity decreases from ~1.9 Zsun near the center of the galaxy to ~0.3 Zsun at the optical outskirts. The galactocentric radial metallicity gradient is statistically consistent with previous studies of the gas-phase oxygen abundance from H II regions using the direct method. The H II region-based Cepheid metallicities used by Riess et al. in their determination of the Hubble constant H_0 are in substantial agreement with our measurements. The direct method gas-phase metallicities of the 18 star-forming galaxies we have analyzed so far, when adjusted upward for a mean ~0.15 dex oxygen dust depletion factor, are in good agreement with those we infer from the supergiants, over a factor of 50 in metallicity. From the same data, we derive an expression for the metal-dependent depletion of oxygen in photoionized nebulae. Utilizing the flux-weighted gravity - luminosity relationship (FGLR) of blue supergiants, we measure a distance to M101, D=6.5 +\- 0.2 Mpc (m-M = 29.06 +\- 0.08), which is within 1 sigma from determinations based on the tip of the red giant branch and Cepheids. With M101 as a nearby SN Ia host and using the observed standardized B-band magnitude of the supernova, our FGLR distance yields an independent value H_0 = 72.5 +\- 4.6 km/s/Mpc.

Next-generation gamma-ray observatories aim to enable precision measurements in high-energy astrophysics using advanced semiconductor detector technologies. Meeting the scientific requirements of modern instruments demands detector systems that provide high spatial and spectral resolution across large detection areas, with strict limits on power consumption and mass. These needs drive innovation in front-end electronics and mixed-signal processing to support compact detector electrode geometries. Application-specific integrated circuits (ASICs) are essential in front-end readout electronics, enabling high-channel-density and low-power systems, while maintaining low-noise performance suitable for space-based instruments and balloon-borne payloads. The NRL4 (Naval Research Laboratory 4) is a recently developed 32-channel front-end ASIC featuring low-power, low-noise channels consisting of charge-sensitive preamplifiers, 4 configurable gain settings, dual configurable shapers for optimized timing and energy resolution, trimmable per-channel discrimination, time-to-analog conversion, and peak-detect output. The NRL4 has been integrated with a high-purity germanium (HPGe) dual-sided strip detector with a 1.16 mm strip pitch. Energy resolution of 3 keV full width at half maximum (FWHM) at 59.54 keV was achieved with a gain of 18.4 mV/fC and a slow shaper peaking time of 2 {\mu}s. Preliminary results from ongoing research demonstrate the suitability of the NRL4 for high-resolution, low-power gamma-ray spectroscopy for ground and space-based missions.

Light curve analysis of W UMa-type contact binary systems using MCMC or MC methods can be time-consuming, primarily because the repeated generation of synthetic light curves tends to be relatively slow during the fitting process. Although various approaches have been proposed to address this issue, their implementation is often challenging due to complexity or uncertain performance. In this study, we introduce the BSN application, whose name is taken from the BSN project. The application is designed for analyzing contact binary system light curves, supporting photometric data, and employing an MCMC algorithm for efficient parameter estimation. The BSN application generates synthetic light curves more than 40 times faster than PHOEBE during the MCMC fitting process. The BSN application enhances light curve analysis with an expanded feature set and a more intuitive interface while maintaining compliance with established scientific standards. In addition, we present the first light curve analyses of four contact binary systems based on the TESS data, utilizing the BSN application version 1.0. We also conducted a light curve analysis using the PHOEBE Python code and compared the resulting outputs. Two of the target systems exhibited asymmetries in the maxima of their light curves, which were appropriately modeled by introducing a cold starspot on one of the components. The estimated mass ratios of these total-eclipse systems place them within the category of low mass ratio contact binary stars. The estimation of the absolute parameters for the selected systems was carried out using the $P-a$ empirical relationship. Based on the effective temperatures and masses of the components, three of the target systems were classified as A-subtype, while TIC 434222993 was identified as a W-subtype system.

We investigate the growth of supermassive black holes (SMBHs) at high redshift ($z \ge 10$) from a combination of dark matter capture, black-hole mergers, and gas accretion. It has previously been shown that SMBHs can form by $z \approx 10$ via black-hole mergers, Eddington-limited Bondi gas accretion and tidal disruption events with stars within dense nuclear clusters. Here, we show that the capture of collisionless dark matter by a growing SMBH also substantially contributes, in some cases by an order of magnitude to the final SMBH mass. In particular, we show that a small seed stellar-remnant black hole can more easily reach $> 10^7$ M$_{\odot}$ by $z = 10$ in the core of dense nuclear star clusters when dark matter is included. This remains true for either cold dark matter or ultralight dark matter if the mass of the ULDM particle is $^>_\sim 10^{-20}$ eV. We highlight the unique evolution of ULDM capture by the growing SMBH when the ULDM de Broglie wavelength exceeds the initial nuclear star cluster half-mass radius.

We investigate the constraints on the neutron star equation of state (EoS) and nuclear properties achievable with third-generation gravitational wave detectors using the Fisher information matrix approach. Assuming an optimistic binary neutron star (BNS) merger rate, we generate synthetic inspiral gravitational wave (GW) signals corresponding to one year of observation. From these simulated data, we compute the covariance matrix and posterior distributions for nuclear properties and EoS. Our results show that the EoS can be tightly constrained, particularly in the density range between one and four times nuclear saturation density. However, due to the scarcity of of low-mass neutron stars in the GW sample, the EoS at sub-saturation densities remains poorly constrained. Thus, in turn, leads to weaker constraints on neutron star radii, as the radii are sensitive to the low-density EoS. Additionally, We note that the nuclear properties are degenerate in their influence on the EoS, making them difficult to be constrained through GW observations alone. These highlights inherent limitations of inspiral GW signals in probing dense matter properties. Therefore, precise radius measurements, post-merger GW observations, and supplementary constraints from terrestrial nuclear experiments remain essential for a comprehensive understanding of dense matter.

This study provides the first comprehensive analysis of eight total-eclipse W Ursae Majoris-type contact binary systems. Ground-based photometric multiband observations were conducted at a Mexican observatory, and new times of minima were extracted. The O-C analysis reveals that four of our target binaries exhibit a long-term increase in their orbital periods, while the others show a long-term decrease in their orbital periods. We analyzed the light curves using the PHOEBE Python code and BSN application. Among the target systems, two required the inclusion of a cold starspot on one of the components to achieve an adequate fit. The light curve analysis revealed that the target systems exhibit a shallow fillout factor. Absolute parameters were estimated using the Gaia DR3 parallax and astrophysics equations. Considering the effective temperatures and component masses, each system was classified as either the A- or W-subtype. The stellar evolution of the systems was represented through the mass-radius and mass-luminosity diagrams. Additionally, we calculated the initial masses of the companion stars and the total mass lost for each target system.

Understanding the behavior of the water-ammonia system at high pressure-high temperature conditions is important for modeling the internal dynamics of exoplanet icy mantles. Conventionally, mixtures of ammonia hemihydrate AHH (2:1 ammonia-water molar ratio) and H2O ice VII have been regarded as the ultimate solid phase assembly in the system. Here we report evidence for chemical reactions between AHH and ice VII above 750 K and 16 GPa that stabilize water-rich ammonia hydrates, including a novel ultra-water rich hydrate NH3.6H2O (1:6 ratio) coexisting with ammonia dihydrate ADH (1:2 ratio) and excess ice VII. This assembly is stable up to at least 30 GPa and 1600 K and can be quenched to room temperature. Our results demonstrate that water-rich ammonia hydrates are favored in the icy mantle of 1-2 MEarth exoplanets regardless of the ammonia content of the hydrate crystallized during accretion and/or evolution as long as excess H2O ice is available. The buoyancy contrast between water-rich hydrates and ice VII may lead to chemical stratification in exoplanet icy mantles, hence affecting their thermal evolution.

We present a study of quasar host galaxy 3C 297 which is home to a powerful bent-jet radio source suggesting vigorous interaction with a dense ISM and/or jet precession. Archival HST imaging showed interestingly perturbed morphology of the host with a bright ~30 kpc arc feature, extended filamentary structure of line-emitting gas and clumpy blue excess emission co-spatial with the radio hotspots. Our VLT/SINFONI integral-field observations reveal complex, spatially-resolved H{\alpha}+[NII] emission in this source. A prominent blue-shifted wing in H{\alpha} indicates an ionized gas flow extending out to ~18 kpc from the nuclear region. Combining our SINFONI narrow-H{\alpha} data with archival HST/UV and VLA imaging, we map the young stellar population in the host and compare the spatial distribution of star-forming regions with the ionized gas motion and jet structure. In the attempt to characterize the feedback mechanisms in this chaotic system, we suggest that the powerful radio source dominates the feedback with possible contribution from radiation pressure due to AGN accretion. We also propose that the expanding jet cocoon likely shocked the ISM, triggering a kpc-scale ionized gas outflow and new starbursts that enhanced ongoing merger-induced star formation.

All the four giant planets in our Solar System have rings, but their characteristics are very different. The rings consist of a number of small particles, although individual particles have not been directly imaged. Near the central planet, colliding particles bounce off each other in low-velocity impacts but cannot gravitationally merge due to the effect of the tidal force, resulting in the formation of rings, whereas in more distant regions particles can gravitationally accrete to form satellites. Rings exhibit various types of fine structure, and the mutual gravitational forces between particles and the gravity from satellites play an important role in rings of macroscopic particles, while non-gravitational forces are important for dusty rings. There are several theories about the origin of rings, and formation mechanisms are likely to be different among different ring systems. The rings of small Solar System bodies were discovered through observations of occultations of stars by these bodies. It is natural to expect that some exoplanets should also have rings, but their detection remains challenging. Future discovery of more ring-moon systems around small bodies and exoplanets will provide clues to understanding the formation and evolution of the central bodies that host them.

Classifying variable stars is crucial for advancing our understanding of stellar evolution and dynamics. As large-scale surveys generate increasing volumes of light curve data, the demand for automated and reliable classification techniques continues to grow. Traditional methods often rely on manual feature extraction and selection, which can be labor-intensive and less effective for managing extensive datasets. In this study, we present a convolutional neural network (CNN)-based method for classifying variable stars using raw light curve data and their known periods. Our approach eliminates the need for manual feature extraction and preselected preprocessing steps. By applying phase-folding and interpolation to structure the light curves, the model learns variability patterns critical for accurate classification. Trained and evaluated on the All-Sky Automated Survey for Supernovae (ASAS-SN) dataset, our model achieves an average accuracy of 90% and an F1 score of 0.86 across six well-known classes of variable stars. The CNN effectively handles the diverse shapes and sampling cadences of light curves, offering a robust, automated, data-driven solution for classifying variable stars. This automated, data-driven method provides a robust solution for classifying variable stars, enabling the efficient analysis of large datasets from both current and future sky surveys.

When 3D relative displacement $\mathbf{r}$ and velocity $\mathbf{v}$ between the pair in a gravitationally-bound system are precisely measured, the six measured quantities at one phase can allow elliptical orbit solutions at a given gravitational parameter $G$. Due to degeneracies between orbital-geometric parameters and $G$, individual Bayesian inferences and their statistical consolidation are needed to infer $G$ as recently suggested by a Bayesian 3D modeling algorithm. Here I present a fully general Bayesian algorithm suitable for wide binaries with two (almost) exact sky-projected relative positions (as in the Gaia data release 3) and the other four sufficiently precise quantities. Wide binaries meeting the requirements of the general algorithm to allow for its full potential are rare at present, largely because the measurement uncertainty of the line-of-sight (radial) separation is usually larger than the true separation. As a pilot study, the algorithm is applied to 32 Gaia binaries for which precise HARPS radial velocities are available. The value of $\Gamma \equiv \log_{10}\sqrt{G/G_{\rm N}}$ (where $G_{\rm N}$ is Newton's constant) is $-0.002_{-0.018}^{+0.012}$ supporting Newton for a combination of 24 binaries with Newtonian acceleration $g_{\rm N}>10^{-9}$m s$^{-2}$, while it is $\Gamma=0.063_{-0.047}^{+0.058}$ or $0.134_{-0.040}^{+0.050}$ for $7\text{ or }8$ binaries with $g_{\rm N}<10^{-9}$m s$^{-2}$ (depending on one system) showing tension with Newton. The Newtonian ``outlier'' is at the boundary set by the Newtonian escape velocity, but can be consistent with modified gravity. The pilot study demonstrates the potential of the algorithm in measuring gravity at low acceleration with future samples of wide binaries.

Extreme nitrogen enhancement relative to oxygen, recently found in very high-redshift galaxies, has been seen in local star-forming galaxies displaying high log(N/O) values ($\geq\!-1.1$) at relatively low O abundances, 12+log(O/H)$\leq$8. Understanding the physical origins of these extreme N-emitters at low redshifts enables us to better constrain chemical enrichment mechanisms that drove such high log(N/O) values in the early Universe. With direct N and O abundances derived for 944 SFGs with spectroscopic observational data from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI DR1), we report the discovery of 19 extreme N-emitters at low-z (z$<$0.5). Our sample of N-emitters represents a five-fold increase in their known number at low-z with 12+log(O/H)$\leq$8, and statistically, $2.21\pm0.91$\% of DESI DR1 SFGs with reliable O and N abundances obtained directly, are extreme N-emitters. The sample spans a mass range of $\sim 10^7$ - $10^{10}$~M$_{\odot}$ with 12+log(O/H) range of $\sim$7.1 - 8.2, and the N-emitter fraction is found to increase with increasing stellar mass and decreasing metallicity. The most extreme N-emitter in our sample has log(N/O)=$-0.53\pm0.13$, while also having the lowest 12+log(O/H)=$7.08\pm0.09$ and the highest stellar mass, log(M$_{*}$/M$_{\odot}$)=$9.95\pm0.13$ among our sample. With galactic chemical evolution models, we show that sustained N-enhancement by asymptotic giant branch stars, in conjunction with presence of outflows, can well explain the high log(N/O) of low-z extreme N-emitters. While single starbursts with outflow are sufficient to explain lower-mass N-emitters, more massive ones require a dual starburst scenario where a secondary starburst is triggered by inflow of gas.

Observations of Cosmic Microwave Background (CMB) B-mode polarization provide a way to probe primordial gravitational waves and test inflationary predictions. Extragalactic point sources become a major source of contamination after delensing and can bias estimates of the tensor-to-scalar ratio $r$ at the $10^{-3}$ level. We introduce Generalized Point Spread Function Fitting (GPSF), a method for removing point-source contamination in polarization maps. GPSF uses the full pixel-domain covariance, including off-diagonal terms, and models overlapping sources. This allows accurate flux estimation under realistic conditions, particularly for small-aperture telescopes with large beams that are more susceptible to source blending. We test GPSF on simulated sky maps, apply foreground cleaning using the Needlet Internal Linear Combination (NILC) method, and compare its performance with standard masking and inpainting. The results show GPSF reduces point-source contamination without significantly affecting the background signal, as seen in both the maps and their power spectra. For the constraint on $r$, GPSF reduces the bias from $1.67 \times 10^{-3}$ to $2.9 \times 10^{-4}$, with only a 2% increase in standard deviation. Compared to inpainting and masking, GPSF yields lower bias while maintaining comparable variance. This suggests that it may serve as a promising method for future CMB experiments targeting measurements of $r \sim 10^{-3}$.

We present a framework that combines physics-informed neural networks (PINNs) with Markov Chain Monte Carlo (MCMC) inference to constrain dynamical dark energy models using the Pantheon+ Type Ia supernova compilation. First, we train a physics-informed neural network to learn the solution of the Friedmann equation and accurately reproduce the matter density term x_m(z) = Omega_m,0 (1+z)^3 across a range of Omega_m,0. For each of five two-parameter equation-of-state (EoS) forms: Chevallier-Polarski-Linder (CPL), Barboza-Alcaniz (BA), Jassal-Bagla-Padmanabhan (JBP), Linear-z, and Logarithmic-z, we derive the analytic dark energy factor x_de(z), embed the trained surrogate within a GPU-accelerated likelihood pipeline, and sample the posterior of (h0, Omega_m,0, w0, wa, M0) using the emcee ensemble sampler with the full Pantheon+ covariance. All parameterizations remain consistent with a cosmological constant (w0 = -1, wa = 0) at the 95% credible level, with the tightest bounds from the CPL form. While the surrogate does not reduce computation time for a single run in simple models, it becomes advantageous for repeated analyses of the same EoS or for models with expensive likelihood evaluations, and can be shared as a reusable tool with different datasets within the training range of SNe redshifts. This flexibility makes the approach a scalable tool for future cosmological inference, especially in regimes where conventional ODE-based methods are computationally prohibitive.

Cygnus X-1 is a persistent, high-mass black hole X-ray binary (BHXRB) which in the hard state shows many similar properties to transient BHXRBs, along with intriguing differences, such as the lack of quasi-periodic oscillations. Here, we compare for the first time the detailed spectral-timing properties of Cyg X-1 with a transient BHXRB, MAXI J1820+070, combining data from XMM-Newton and NICER with contemporaneous INTEGRAL data to study the power spectra, rms spectra and time-lags over a broad 0.5 - 200 keV range. We select bright hard state MAXI J1820+070 data with similar power-spectral shapes to the Cyg X-1 data, to compare the source behaviours while accounting for the evolution of spectral-timing properties, notably the lags, through the hard state. Cyg X-1 shows no evidence for soft lags in the 1 - 10 Hz frequency range where they are clearly detected for MAXI J1820+070. Furthermore the low-frequency hard lags and rms-spectra evolve much more strongly during the hard state of Cyg X-1 than for MAXI J1820+070. We argue that these differences cannot be explained by the different black hole masses of these systems, but may be related to their different accretion rates and corresponding locations on the hardness-intensity diagram. We conjecture that there is a significant luminosity-dependence of coronal geometry in the hard state of BHXRBs, rather than an intrinsic difference between Cyg X-1 and transient BHXRBs. This possibility has also been suggested to explain a common time-lag feature that appears in the hard intermediate states of Cyg X-1 and transient BHXRBs.

A damped random walk (DRW) process is often used to describe the temporal UV/optical continuum variability of active galactic nuclei (AGN). However, recent investigations have shown that this model fails to capture the full spectrum of AGN variability. In this work, we model the 22-year-long light curves of $21,767$ quasars, spanning the redshift range $0.28 < z < 2.71$, as a noise-driven damped harmonic oscillator (DHO) process. The light curves, in the optical $g$ and $r$ bands, are collected and combined from the Sloan Digital Sky Survey, the Panoramic Survey Telescope and Rapid Response System, and the Zwicky Transient Facility. A DHO process can be defined using four parameters, two for describing its long-term behavior/variability, and the other two for describing its short-term behavior/variability. We find that the best-fit DHO model describes the observed variability of our quasar light curves better than the best-fit DRW model. Furthermore, the best-fit DHO parameters exhibit correlations with the rest-frame wavelength, the Eddington ratio, and the black hole mass of our quasars. Based on the power spectral density shape of the best-fit DHOs and these correlations, we suggest that the observed long-term variability of our quasars can be best explained by accretion rate or thermal fluctuations originating from the accretion disk, and the observed short-term variability can be best explained by reprocessing of X-ray variability originating from the corona. The additional information revealed by DHO modeling emphasizes the need to go beyond DRW when analyzing AGN light curves delivered by next-generation wide-field time-domain surveys.

Recent work has successfully achieved sub-arcsecond wide-field imaging with high-band observations from the Low Frequency Array (LOFAR). However, the scalability of this work remains limited due to the need for manual intervention, poor calibration solutions for the Dutch LOFAR stations, and high computational costs. We address these issues by: (1) improving automated self-calibration using a signal-to-noise metric and a neural network for image artefact detection; (2) implementing a refined calibration strategy for the Dutch LOFAR stations; and (3) cutting computational costs by optimising the data processing strategy. We demonstrate the effectiveness of our automated processing strategy by reprocessing one previously reduced dataset and a new dataset from the ELAIS-N1 deep field, which features more severe ionospheric conditions. We find calibration artefacts across facet boundaries to be reduced with our improved automated calibration strategy and achieve a computational cost reduction of about a factor of 4 to 6 compared to previous work, where the exact factor depends on whether a single observation is processed or multiple observations of the same sky area are combined. Further optimisation and improved handling of data with baseline-dependent averaging could reduce this in the near future by another factor of two, bringing the total cost for an 8-hour observation below 30,000 CPU core hours. This work enables ultra-deep imaging at sensitivities on the order of a few $\mu$Jy/beam. Furthermore, it also lays the foundation for a fully automated survey pipeline for sub-arcsecond wide-field imaging of the northern sky with LOFAR.

The association between FRB 20200428D and the Galactic magnetar SGR J1935+2154 makes magnetars the leading engine of cosmological fast radio bursts (FRBs). However, there is a list of puzzles for this magnetar-for-all-FRBs scenario: known Galactic magnetars are all isolated and none of them are active repeaters; some cosmological repeaters have extremely high repetition rates but without any measurable spin-related periodicity; some show long-term periodic active windows; and some show diverse rotation measure (RM) evolution patterns, such as quasi-periodic fluctuations, sign reversals, and abrupt RM flares. Here we propose a unified theoretical framework for FRBs within the framework of magnetar engine: Most active repeating FRBs originate from magnetars in binary systems with nearly aligned rotation and magnetic axes, some of which with a triple-aligned geometry, i.e. with an alignment with the orbital axis as well; whereas apparent non-repeaters and inactive repeaters originate from magnetars in isolated systems or in binaries with a misaligned geometry. By studying various magnetar formation channels using population syntheses, we show that a few percent of magnetars in the universe can be in binary systems, most with a massive star companion and some with aligned geometry. We suggest that such binary systems can account for the rich phenomenology of active repeaters. We suggest that the existence of a companion helps to maintain the aligned geometry and that the companion may play an active role in triggering FRBs in an active repeater source.

Comparing the dynamical and stellar masses of Milky Way (MW) globular clusters (GCs) reveals a discrepancy exceeding a factor of two. Since this substantial invisible mass is concentrated in the cluster centre, it is attributed to stellar remnants. The majority of mass in remnants consists of white dwarfs (WDs). Allocating over half of a GC's current mass to WDs could significantly restrict the dynamical evolution scenarios governing stellar clusters. As the most massive stars in GCs, black holes (BHs) exert a substantial effect on the escape rate of lower mass stars, such as WDs. This paper aims to identify which scenarios of BH natal kicks can accurately reproduce the notable dark remnant fraction observed in MW GCs. We compare the observed remnant fraction of MW GCs with a comprehensive grid of direct \Nbody simulations while adjusting the natal kick received by BHs. Our results reveal that simulations employing low natal kicks to BHs are the only ones capable of mirroring the remnant fraction of MW GCs. According to the Spitzer instability, the presence of a BH population prompts the formation of a BH sub-system (BHSub) at the centre of a star cluster. The BHSub serves as an energetic power plant, continually releasing kinetic energy through few-body encounters between single and binary BHs, and transferring the generated energy to the entire stellar population. This energy induces a significant difference in the ejection rate of stellar remnants and luminous stars, ultimately increasing the fraction of dark remnants within the star cluster.

LDN 1616 is a cometary globule located approximately 8 degrees west of the Orion OB1 associations. The massive OB stars in the Orion belt region act as catalysts, triggering the star formation activity observed in the L1616 region, which is a photodissociation region (PDR). This paper provides an in-depth analysis of gas kinematics within the L1616 PDR, leveraging the Heterodyne Array Receiver Program (HARP) on the James Clerk Maxwell Telescope (JCMT) to observe 13CO and C18O (3-2) emissions. Employing the Clumpfind algorithm on the C18O emission data, we identify three distinct clumps within this PDR. For each of these clumps, we derive key physical parameters, including the mean kinetic temperature, optical depth, and velocity dispersion. In addition, we compute the non-thermal velocity dispersion and Mach number, providing critical insights into the turbulent dynamics of the gas. A comprehensive evaluation of mass, including virial and energy budget evaluations, is conducted to assess the gravitational stability and star-forming potential of the identified clumps. While previous studies have proposed that radiation-driven implosion (RDI) is the dominant mechanism initiating star formation in LDN 1616, our results suggest that the clumps may represent pre-existing substructures within the PDR. This interpretation is supported by our estimation of a relatively low interstellar radiation field, which, although insufficient to form clumps independently, may enhance gravitational instability through additional compression. Thus, our findings offer a more nuanced perspective on the role of RDI, highlighting its capacity to trigger star formation by amplifying the instability of pre-existing clumpy structures in PDRs like LDN 1616.

We report a numerical discovery that the formations of cosmic voids are closely linked with the mechanism through which the giant galaxies on void surfaces establish elliptical shapes, redder colors, and lower sSFR. Identifying the voids from the TNG300-1 simulations via the Void-Finder algorithm, we explore if and how the shapes of the TNG galaxies located on void surfaces are aligned with the directions toward the void centers. Noting that only the giant void-surface galaxies with stellar masses $M_{\star}\ge 10^{10.5}\,h^{-1}\,M_{\odot}$ exhibit significant tendency of perpendicular alignments, we dichotomize them into two $M_{\star}$-controlled samples according to their morphologies (elliptical or spiral), colors (redder or bluer), sSFR (lower or higher) and stellar ages (older or younger). It is found that the void-galaxy perpendicular alignment becomes stronger for the cases that the void-surface galaxies have elliptical shapes, redder colors, and lower sSFR. The numerical results are also shown to be well described by the analytical one-parameter model derived under the assumption of the existence of a linear scaling between the covariance matrices of galaxy shape axes and local tidal tensors. Our result implies that the compression of adjacent matter due to the formation and rapid expansion of cosmic voids prevent them from radial infall/accretion, which in turn contribute to stalling and quenching the giant void-surface galaxies. Given that the formation epochs and expansion rates of cosmic voids depend sensitively on the dark energy equation of state, we also discuss a possibility of using the abundance of elliptical void-surface galaxies as a probe of dark energy.

Core-collapsed globular clusters are ideal targets to explore the presence of stellar collision products. Here, we have studied seventeen FUV bright white dwarf members in the globular cluster NGC 362 using data obtained from the Ultra Violet Imaging Telescope (UVIT) mounted on AstroSat and from HST. Multi-wavelength spectral energy distributions (SEDs) are analyzed using UV and optical data sets to characterize and determine the parameters of white dwarfs. Fourteen of the white dwarfs fit single-component SEDs well, while three showed a good fit with a two-component SED model,indicating a binary system comprising a white dwarf and a low-mass main-sequence star. The effective temperature, radius, luminosity, and mass of white dwarfs range between 22000 - 70000 K, 0.008 - 0.028 Rsun, 0.09 - 3.0 Lsun, and 0.30 - 1.13 Msun, respectively. The effective temperature, radius, luminosity, and mass of the companions (low-mass main-sequence stars) are 3500 - 3750 K, 0.150 - 0.234 Rsun,0.003 - 0.01 Lsun, and 0.14 - 0.24 Msun, respectively. The three binary systems (WD-MS), along with the massive WDs may have formed through dynamical processes that occurred during the core collapse of the cluster. This is the first evidence of a massive WD formation in a core-collapsed cluster, which is the missing link in the formation of a fast radio burst (FRB) progenitor in a globular cluster. This study provides evidence that NGC 362 hosts stellar systems that may evolve into exotic stars such as Type Ia supernovae, and/or FRBs in the future. *This is paper VI of the Globular Cluster UVIT Legacy Survey.

The stochastic self-propagating star-formation (SSPSF) model is an important theoretical framework for explaining how localised star-formation events trigger subsequent activity across galactic discs. While widely used to interpret spiral and irregular structures, its probabilistic rules have lacked a formal statistical foundation. In this work, we establish a connection between the SSPSF model and spatio-temporal point processes (STPP), which describe events in space and time through history-dependent intensities. We show that the SSPSF update law is equivalent to a separable spatio-temporal Hawkes process, and we derive a simple likelihood function that recovers SSPSF parameters from historical star-formation event data under simplifying assumptions. Beyond the statistical formulation, the framework provides a new approach to analysing the propagation of star formation in galaxies, enabling observational surveys of star-forming regions to be interpreted within the STPP framework. Furthermore, the approach naturally extends to continuous-time models, offering a more realistic representation of galactic dynamics.

We re-investigate the HD208487 system to test the reality of the proposed HD208487c world. We also search for additional companions using applied Bayesian statistics and 15+ years of new RV data from the HARPS and the PFS instruments that were taken post-discovery of HD208487b. The RV data was analyzed with GLS Periodograms, followed by Bayesian analysis using the EMPEROR code. We scrutinised various stellar activity indices to search for any corresponding peaks in the power spectra, correlations with the RV measurements, or significant signals from a Bayesian analysis methodology. Finally, photometric data was checked to test for any transits or possible activity manifestations that could lead to possible false RV signals or excess noise. Our analysis points towards a candidate second planet in the system, positioned near the period of a previously proposed and subsequently challenged signal. This signal, HD208487c, would relate to a cool Saturn with an orbital period of 923.06 +2.02 -2.76 d and a minimum mass of Mj sini = 0.32 +/- 0.01Mj. Our analysis also gives rise to a newly discovered candidate planet, HD208487d, which would be the result of a cool super-Neptune/sub-Saturn with a period of 1380.13 +19.20 -8.25 d and a minimum mass of Mj sini = 0.15 +/- 0.01Mj. Neither stellar activity indices nor photometric data show signals statistically matching these periods. We have uncovered a candidate three planet system that would consist of an inner gas giant, a central Saturn and an outer super-Neptune/sub-Saturn. A dynamical analysis suggests that gravitational scattering of an initially ordered, equally-spaced system in a long resonant chain of six Neptunes can explain the current proposed architecture of HD208487. More RVs may also shed light on the reality of a fourth Doppler signal uncovered in the data that sits close to the 2:1 period-ratio with signal of HD208487c.

We use subsurface-flow velocity maps inferred by time--distance helioseismology from Doppler measurements with the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) to investigate variations of large-scale convection during Solar Cycles 24 and 25 in the 19-Mm-deep layer. The spatial power spectra of the horizontal-flow divergence reveal well-defined characteristic scales of solar supergranulation in the upper 4 Mm layer, while the giant-cell scale is prominent below levels of d ~ 8 Mm. We find that the characteristic scales of supergranulation remain stable while the giant scales increase during the periods of the 11-year activity cycle maxima. The power of the giant-cell scales increases with the enhancement of solar activity. This may be due to large-scale flows around active regions and, presumably, solar-cycle variations of the convection-zone stratification.

We report first results from the JWST Rocky Worlds Director's Discretionary Time program. Two secondary eclipses of the terrestrial exoplanet GJ 3929b were recently observed using MIRI photometric imaging at 15 um. We present a reduction of these data using the updated SPARTA pipeline. We also refine the planet mass, radius, and predicted time of secondary eclipse using a new sector of TESS data and new, high-precision radial velocities from the MAROON-X spectrograph. For the two JWST observations, we recover secondary eclipse depths of 177+47-45ppm and 143+34-35ppm at times consistent with a nearly circular orbit, as expected from the radial velocity data. A joint fit of the two visits yields a dayside brightness temperature Tp,dayside = 782+/-79K for GJ 3929b, which is consistent with the maximum brightness temperature Tmax = 737+/-14K for a bare, black rock (i.e., assuming zero Bond albedo and no heat redistribution). These results rule out CO2-rich atmospheres thicker than 100mbar at >3sigma, suggesting that GJ 3929b has lost any significant secondary atmosphere. The radial velocity data also indicate two additional non-transiting planets in the system: a previously-identified planet in a 15.0d orbit, and a newly-identified planet candidate in a 6.1d orbit.

Following a type Ia supernova (SN Ia) in a double white dwarf (WD) binary, a surviving WD companion leaves at its orbital velocity $\approx 1$,000 - 3,000 km/s. The Gaia mission has discovered seven such hypervelocity WDs with inflated radii indicative of shock heating by SN ejecta. We study the interaction between SN ejecta and Roche lobe-filling 0.08 - 0.45 $M_{\odot}$ helium WD companions using three-dimensional hydrodynamical simulations with Athena++. Given the importance of the later thermal evolution, we include an accurate equation-of-state for the degenerate helium WD donor. We show that a lower-mass, larger-radius WD companion is more strongly impacted by SN ejecta and undergoes substantial mass loss. We find a tight relation between the fractional mass loss and the ratio between the ejecta ram pressure and donor volume-averaged pressure, which can be used for predicting mass loss in other systems. In the most extreme case, the companion becomes a very inflated $\approx0.02\,M_{\odot}$ object. We find helium mass loss $\approx 0.005 - 0.06\,M_{\odot}$ with velocities $\approx $ 1,000$-$4,000 km/s, which may lead to emission lines in the nebular phase. The surviving helium WD receives a kick velocity, but its final velocity is essentially determined by its orbital velocity $\lesssim$ 1,600 km/s. We model the post-explosion evolution of the shock-heated companions using MESA, and find reasonable agreement with the hypervelocity stars D6-2, J0546+0836, J1332-3541 & SDSS J1637+3631. A surviving $\gtrsim 0.3\,M_{\odot}$ helium WD can be ruled out in SN1972E & SN2011fe, and any surviving helium WD is likely ruled out in SN remnants 0509-67.5 & SN1006.

Accurate estimation of dark matter halo masses for galaxy groups is central to studies of galaxy evolution and for leveraging group catalogues as cosmological probes. We present a calibration and evaluation of two complementary halo mass estimators: a dynamical estimator based on the virial theorem, and an empirical relation between the sum of the stellar masses of the three most massive group galaxies and the halo mass (SHMR). Using state-of-the-art semi-analytic models (SHARK, SAGE, and GAEA) to generate mock light-cone catalogues, we quantify the accuracy, uncertainty, and model dependence of each method. The calibrated virial theorem achieves negligible systematic bias (mean $\Delta$ = -0.01 dex) and low scatter (mean $\sigma$ = 0.20 dex) with no sensitivity to baryonic physics. The calibrated SHMR yields the highest precision (mean $\Delta$ = 0.02 dex, mean $\sigma$ = 0.14 dex) but shows greater model dependence due to sensitivity to baryonic physics across the models. We demonstrate applications to observational catalogues, including the empirical halo mass function and mapping quenched fractions in the stellar mass-halo mass plane. We provide guidance: the virial theorem is recommended for GAMA-like surveys (i < 19.2) at z < 0.1 where minimal model dependence is required, while the SHMR is optimal for high-precision halo mass estimates across diverse catalogues with limits of z < 0.3. These calibrated estimators will aid upcoming wide-area spectroscopic surveys in probing the connection between galaxies and their host dark matter halos.

Crust quakes are frequently invoked as a mechanism to trigger sudden transients in the magnetospheres of magnetars. In this picture, a mechanical failure of the crust excites seismic motions of the magnetar surface that launch force-free waves into the magnetosphere. We first investigate this problem analytically and then perform three-dimensional numerical simulations. Our simulations follow the propagation of high-frequency magneto-elastic waves in the entire crust, and include magnetic coupling to the dipolar magnetosphere and liquid core through simplified radiation boundary conditions. We observe seismic waves bouncing between the crust-core interface and the surface with a characteristic frequency $\sim 1$ kHz, which could appear as a modulation of the magnetospheric radiation. Both the star quake and its associated magnetospheric wave emission are strongly damped on a timescale $\sim 10 \ \rm ms$ by magnetic coupling to the liquid core. Since seismic waves are significantly damped before they can spread laterally around the crust, magnetospheric wave emission occurs primarily near the initial epicenter of the quake. Our simulations suggest that non-axisymmetric quakes will launch a mixture of Alfvén and fast magnetosonic waves into the magnetosphere. The results will be important for interpreting magnetar bursts and understanding the possible trigger mechanisms of fast radio bursts.

The high-mass (M$>$2 \Msolar{}) Kepler red giant stars are less well-studied than their lower-mass counterparts. In the previous article, we presented a sample of 48 high-mass Kepler red giants and measured their asteroseismic parameters. This article presents spectroscopic measurements from the same sample, using high-resolution Keck/HIRES spectra to determine \Teff{}, [Fe/H], \logg{}, and $v \sin i$. We refined our previous estimates of the stellar masses and radii based on the new \Teff{}. We also examined spectral features that could indicate binary activity, such as the Li line and [C/N] ratios. We found no Li-rich stars or clear [C/N] anomalies, but we observed a correlation between [C/N] and [Fe/H]. We measured chromospheric activity using the $S$-index of the Ca II H \& K lines and found no correlation with internal magnetic fields. However, we confirmed an anti-correlation between surface chromospheric activity and radial mode oscillation amplitudes, which indicates that strong surface magnetic fields weaken stellar oscillations. Finally, we used the Gaia DR3 astrometric data to show that our sample of stars have orbits consistent with all three Galactic kinematic regions. Although these stars are quite young, their orbits carry them into the thick disk and even the halo, raising questions about the accuracy and viability of kinematics in unravelling Galactic history. In future work, we plan to use the spectroscopic parameters measured here to provide better constraints for boutique frequency modelling, which will allow us to test the asteroseismic scaling relations at the high-mass regime.

We present the second data release of the Systematic Mid-Infrared Instrument (MIRI) Legacy Extragalactic Survey (SMILES), focusing on JWST/NIRSpec medium-resolution spectroscopy of galaxies across cosmic time. This release includes spectroscopic observations of 166 galaxies spanning $0 < z < 7.5$, sampling star-forming galaxies, quiescent systems, and active galactic nuclei (AGN), with an emphasis on galaxies at cosmic noon ($z \sim 1$-3). We describe the target selection strategy, the observational setup with the G140M/F100LP and G235M/F170LP gratings, and the data calibration process. The final data products include the reduced spectra, redshift catalog, emission-line catalogs produced with \texttt{GELATO} for emission-line galaxies and \texttt{pPXF} fits for quiescent systems, and ancillary spectral energy distribution (SED) fit results derived from multi-band photometry. The SMILES NIRSpec dataset enables investigations of obscured AGN, multi-phase outflows, ionizing properties, and the role of environment in galaxy evolution.

After carbon and oxygen, $^{22}$Ne is the most abundant element in white dwarf interiors. As C/O white dwarfs (WDs) crystallize, they are predicted to go through a distillation process in the central layers if they have a sufficiently high $^{22}$Ne mass fraction of $\gtrsim2.5$\%. Observational evidence for distillation comes from an over-density of WDs on the Q-branch in Gaia color-magnitude diagrams, which indicates that $\sim6$\% of massive WDs are delayed in their cooling by as much as $\sim10$ Gyr. However, it is unclear how these stars end up with such a high concentration of $^{22}$Ne and if a significant fraction of the more common average-mass WDs go through distillation. We argue that a significant metal-rich stellar population in the solar neighborhood should lead to distilled WDs, without requiring a binary merger. We use MESA along with the CNO abundances derived from high-resolution spectroscopy of stars included in the Hypatia catalog to predict the $^{22}$Ne mass fraction in their descendant WDs. We find that 0.6-2.5\% of the WDs in the solar neighborhood have sufficient $^{22}$Ne in their interiors to go through multi-Gyr cooling delays, which could significantly inflate their numbers in the observed samples. Hence, $^{22}$Ne distillation and long-lived habitable zones around WDs should be relatively common in the solar neighborhood. We also use a Galactic model to predict the fraction of WDs that go through distillation as a function of Galactocentric distance. The fraction of distilled WDs is $\sim2$-8\% near the Galactic center, and declines steadily toward the outer disk.

Infrared spectra of hydrocarbon dust absorption bands toward the bright hypergiant Cygnus OB2-12 are compared to published spectra of the Quintuplet Cluster, a sightline to the Galactic center. The Cyg OB2-12 data include a new ground-based 2.86-3.70 microns spectrum and a previously published, but here further analyzed, spectrum of the 5.50-7.34 microns region. Higher spectral resolution data for the Cyg OB2-12 sightline in the 3 micron region allows a detailed comparison of the 3.4 micron aliphatic bands to those observed toward the Quintuplet. Despite differences in interstellar environments along each sightline, strong similarities are observed in the central wavelengths and relative strengths for bands at 3.3, 3.4, 5.85, 6.2, and 6.85 microns. Analysis of these bands, produced by aromatic, aliphatic, olefinic, hydrogenated, and oxygenated components, shows that carbonaceous dust is a significant component of the diffuse interstellar medium, second in abundance only to silicates, and is primarily aromatic in nature. The grains producing these bands likely consist of large aromatic carbon cores with thin aliphatic mantles composed of hydrogenated amorphous carbon (HAC). Laboratory analog spectra reproduce the observed aliphatic absorption bands well, supporting the presence of such mantles. We present evidence that the carriers of both the 3.4 micron aliphatic and the 3.3 micron aromatic bands reside exclusively in the diffuse ISM, and that the 3.3 micron bands observed in the diffuse ISM differ from those seen in dense clouds, implying chemically distinct carriers.

Massive stars play a critical role in the evolution of galaxies, but their formation remains poorly understood. One challenge is accurate measurement of the physical properties of massive protostars, such as current stellar mass, envelope mass, outflow cavity properties, and system orientation. Spectral energy distribution (SED) fitting is widely-used to test models against observations. The far-infrared SED traces cold dust in envelopes, while the near- and mid-infrared (MIR) probes emission from outflow cavities and/or the inner envelope. However, SED fitting has degeneracy limiting its ability to yield accurate measurements of protostellar properties. Here, we develop image profile (IMPRO) fitting as a method to improve the characterization of protostars. We utilize brightness distributions from multi-wavelength MIR images of massive protostars taken by SOFIA/FORCAST as part of the SOFIA Massive Star Formation (SOMA) survey to constrain protostellar properties via comparison to a grid of radiative transfer models. We develop a fitting pipeline to extract information along the outflow axis, which is then combined with the SED fitting to yield improved constraints on protostellar properties. We apply the IMPRO fitting method on the nearby massive protostar Cepheus A, finding that its properties become more tightly constrained compared to SED fitting, especially in the inclination of the source. However, for the more distant G35.20-0.74N, we find that the spatial resolution of SOFIA/FORCAST limits the utility of this combined fitting pipeline. However, higher resolution MIR observations, e.g., with JWST, are expected to greatly expand the applicability of this fitting technique to protostars across the Galaxy.

Stripped-envelope supernovae (SESNe) mark the deaths of massive stars without hydrogen-rich envelopes. Most SESNe likely originate from binary systems where a companion stripped the progenitor of its envelope. Years of HST imaging of nearby SESNe sites have produced a statistically meaningful sample of constraints on surviving binary companions. We assemble the current sample of six companion detections and six non-detections from the literature, re-analyzing whenever needed. We then conduct the first statistical comparison with binary population-synthesis predictions, primarily based on new calculations performed with the POSYDON framework. Across a metallicity range, our models predict that 80-90% of Type Ib/c and 60-85% of IIb SNe explode with a rapidly rotating, main-sequence companion. The observed luminosity distribution favors fairly inefficient mass accretion and failed explosions of the most massive stripped stars. The companion detection fraction broadly matches predictions, given the imaging depth, but appears elevated for Type IIb SNe. In all but one non-detection, a faint, undetected companion is the most likely scenario. The red, apparently evolved companions in a few Type Ib/c SNe may result from strong interaction with the ejecta, expected in $\sim$12% of them. Companion demographics offer a powerful, independent probe of SESN progenitor systems, with the current sample disfavoring efficient accretion and supporting Wolf-Rayet non-explodability. Larger companion samples and follow-up studies will further clarify binary pathways to SESNe, serving as benchmarks for transient surveys.

The LIGO-Virgo-KAGRA consortium has sporadically detected purely inspiral gravitational-wave events like GW170817 and GW190425. These events offer an opportunity to constrain the presence of possible initial (residual) orbital eccentricities while using purely inspiral template families. We detail the implementation of a LSC Algorithm Library Suite approximant, TaylorF2Ecck, which models analytically inspiral gravitational waves from non-spinning compact binaries in Post-Newtonian accurate eccentric orbits while restricting the initial-eccentricity contributions to its leading order. Specifically, our frequency domain approximant consistently incorporates the orbital, advance of periastron, and gravitational-wave emission effects fully up to the 3PN order. We pursue detailed parameter estimation studies of GW170817 and GW190425 using TaylorF2Ecck, after performing comprehensive sanity checks to validate the model's performance and investigate the influence of periastron advance in the relevant parameter space. The results indicate that initial-eccentricity at 20 Hz is essentially zero (less than 0.011 for GW170817 and less than 0.028 for GW190425) at a 90 percent confidence level. We compare posteriors for these two events that arise from a few purely inspiral eccentric approximants and point out certain subtle effects arising due to the inclusion of periastron advance. Additionally, these detailed studies reveal the importance of incorporating initial eccentricity contributions at least up to 3.5PN-order and discuss its implications. We substantiate this inference by employing versions of quasi-circular TaylorF2 approximant that incorporate Fourier phase contributions beyond the conventional 3.5PN order.

Context. A significant fraction (~30%) of massive stars in our Galaxy are moving supersonically through the interstellar medium, which strongly governs their location at the time they end their lives, e.g. die as a supernova and give birth to a supernova remnant (SNR). These dead stellar environments accelerate particles, emitting by non-thermal mechanisms up to the TeV range, and they are considered as a major contributor to the very-high-energy band of the local cosmic-ray spectrum. Aims. This study investigates the effect of the runaway motion of supernova progenitors on the spatial distribution of SNRs in the Milky Way and how this influences the deduced properties of the population. Methods. We construct Galactic populations of SNRs by Monte Carlo simulation, taking into account the bulk motion and the evolution history of their progenitor stars once ejected from their parent clusters. The gamma-ray domain emission of each population is then calculated, to be compared with the High Energy Stereoscopic System (H.E.S.S.) Galactic Plane Survey. Results. We find that including the runaway motion of supernova progenitors strongly modifies the detectability of the simulated emission of their remnants in the very-high-energy band. Particularly, our best fit model using a Reid Milky Way model for core-collapse supernova progenitors requires 33% of massive runaway stars, which is close to the known fraction of runaway high-mass stars, to be in accordance with the H.E.S.S. Galactic Plane Survey data. Conclusions. Our results show that the runaway nature of supernova progenitors must be taken into account in the study of the Galactic population of SNRs within the H.E.S.S. Galactic Plane Survey and the forthcoming Galactic Plane Survey of the Cherenkov Telescope Array Observatory, as it is a governing factor of the detectability of non-thermal emission of their subsequent SNRs.

Utilizing high-resolution imaging and spectroscopic observations from the New Vacuum Solar Telescope (NVST), the Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO), we investigated the nature and origin of counter-streaming flows within a forming active region filament. The ever-present counter-streaming flows observed within the filament are identified as interleaved unidirectional mass flows in opposing directions occurring in neighboring threads. Multi-wavelength observations corroborate the multi-thermal nature of these counter-streaming flows: the cool H$\alpha$ component flows at about 10--20 km s$^{-1}$, while the warm ultraviolet and extreme ultraviolet components reach 40--70 km s$^{-1}$. The Si~{\sc iv} 1400~Å line reveals significant micro-turbulence in the filament's counter-streaming flows, with a nonthermal velocity width of 40 km s$^{-1}$. These multi-thermal flows emanate from compact brightenings at the filament's ends, manifesting as small-scale, collimated upflows at their nascent phase. They continuously inject both chromospheric and transition region plasma into the filament channel, thereby feeding the counter-streaming flows. At their base, the Si~{\sc iv} and C~{\sc ii} spectral lines show pronounced line broadening and intensity enhancements, indicating significant localized chromospheric heating. Additionally, numerous small-scale photospheric flux emergence and cancellation events, with magnitude of $10^{17}$~Mx, are detected near their base. We suggest such weak magnetic-field activities, possibly associated with unresolved magnetic reconnection events, drive these persistent upflows and localized footpoint heating. This work elucidates the multi-thermal origin of counter-streaming flows within a forming filament and provides evidence of localized chromospheric heating at the filament footpoints.

Two main models coexist for the environment in which stars form. The clustered model stipulates that the bulk of star formation occurs within dense embedded clusters, but only a minority of them survive the residual gas expulsion phase caused by massive stellar feedback unbinding the clusters. On the other hand, the hierarchical model predicts that star formation happens at a range of scales and densities, where open clusters (OCs) only emerge from the densest regions. We aim to exploit a recent catalog of compact OCs, corrected for completeness, to obtain an updated estimation of the surface density star formation rate within OCs ($\sum_{\rm SFR,OC}$), which we compare with recent estimates of $\sum_{\rm SFR}$ to determine which model is more likely. We have applied two methods. The first one consisted of integrating over the power law that was fit for the mass function of the youngest OCs using a MC sampling. The second one consisted of counting the total compact mass within these youngest OCs within 1 kpc, so that the result could be directly compared with local values of $\sum_{\rm SFR}$. We estimated new $\sum_{\rm SFR,OC}$ values between $736^{+159}_{-176}$ and $875^{+34}_{-35}$ M$_{\odot}$ Myr$^{-1}$ kpc$^{-2}$, depending on the methodology. These results are significantly higher than previous $\sum_{\rm SFR,OC}$ estimates, which we attribute to the incompleteness of past catalogs, and are consistent with the majority ($\geq$ 50 \%) or even the vast majority ($\geq$ 80 \%) of the star formation occurring in initially compact clusters, through comparisons with $\sum_{\rm SFR}$ from the recent literature. Our new $\sum_{\rm SFR,OC}$ values are consistent with clustered formation being the most dominant mode of star formation.

We perform a comprehensive study of thermonuclear bursts from the neutron star low-mass X-ray binary 4U 1702-429 detected with NICER and XMM-Newton. The thermonuclear burst detected with NICER shows clear evidence of a photospheric radius expansion (PRE) event and a distinct feature in the burst profile. The burst profiles demonstrate significant energy dependence, with the hardness ratio varying notably during the PRE phase. The radius of the neutron star photosphere expanded to a maximum of $23.1_{-3.2}^{+3.8}$ km while its temperature reached a minimum of 1.4 keV. The time-resolved burst spectra can be modeled using variable persistent emission method, indicating that the soft excess may arise from enhanced mass accretion onto the neutron star, potentially due to the Poynting-Robertson drag. Alternatively, the disk reflection model can be used to explain the soft excess emission during a burst. The time-resolved spectral study is performed for three thermonuclear bursts detected with XMM-Newton. The XMM-Newton time-resolved burst spectra can be modeled using an absorbed blackbody model, without any signatures of the PRE. We conduct a detailed spectral analysis of the 2025 NuSTAR observation of 4U 1702-429, revealing a broad iron line at 6.4 keV and a Compton hump around 20 keV, indicating X-ray reflection features. The disk reflection model relxill provides an inner disk radius of 12 $R_g$ and an inclination angle of $\sim39^{\circ}$. The magnetic field strength at the pole of the neutron star is estimated to be 5.1 $\times10^8$ G, assuming that the accretion disk is truncated at magnetosphere boundary.

The transition from a once-dense Martian atmosphere to the thin one observed today implies a substantial loss of carbon, either through atmospheric escape or surface deposition. Accurately modeling this carbon escape necessitates accounting for collisions between energetic carbon atoms and the primary atmospheric constituents, including oxygen. To this end, we computed a highly accurate and comprehensive set of potential energy curves (PECs) for the C($^3$P) + O($^3$P) system. Based on these PECs, we derived statistically averaged total elastic and differential cross sections. Comparison with literature data for O($^3$P) + O($^3$P) collisions reveals that cross sections involving carbon can differ by up to a factor of two, indicating that oxygen is not a good proxy for modeling carbon escape. Furthermore, we evaluated the impact of all possible isotopic combinations in C($^3$P) + O($^3$P) collisions and found variations in cross sections of up to 8\%. Given the observed isotopic enrichment of carbon and oxygen in the Martian atmosphere, even such moderate differences can have a significant effect on escape models and the interpretation of planetary evolution.

JWST/NIRCam 0.9 to 2.0 micron images reveal a population of point sources around the major galaxies in the El Gordo cluster at redshift z=0.87. Their distribution in the color--magnitude diagrams shows a narrow sequence well separated from field-galaxy contamination and consistent with their identification as ultra-compact dwarf galaxies (UCDs) or luminous globular clusters (GCs). The point-source sequence is more luminous by almost a magnitude than the corresponding sequence in Abell 2744 at z=0.31, matching the predicted evolutionary change for GC/UCDs over the 4-Gyr difference in lookback time between these two clusters. Deeper observations should allow direct JWST imaging of GC/UCD populations, even without the help of lensing, up to z ~ 1.4, a lookback time of more than 9 Gyr. Such observations would directly reveal the evolution of these compact stellar systems two-thirds of the way back to the Big Bang.

The Cosmic Shoreline concept was introduced as a way to separate planets with and without atmosphere, based on the relationship between the cumulative instellation and the escape velocity observed in the Solar System. The exoplanet community has tried to refine the way we understand the cosmic shoreline in order to provide a consistent tool for establishing the hierarchy for exoplanet observations. This is particularly relevant when trying to unveil small exoplanet atmospheres with the JWST or the upcoming ELTs. Here, our goal is to use an empirical approach to refine the Cosmic Shoreline concept. In particular, we used the data provided by the ExoAtmospheres database, using the largest available sample of exoplanets with confirmed atmospheric detections. We reconcile limitations in the classical shoreline definition by anchoring our Empirical Cosmic Shoreline (ECS) to both Mars and the irradiated super-Earth 55 Cnc e. The resulting relation exhibits a significantly steeper slope than previously theorized. Applied to planets orbiting M dwarfs, prime targets for habitable-zone studies, the ECS suggests that a larger fraction retain atmospheres than predicted by classical models when using standard Ixuv estimates. However, incorporating revised XUV fluence histories for low-mass M dwarfs (M< 0.35 Ms) reveals severe atmospheric vulnerability: only seven small planets (R<1.7 Re) orbit securely within the retention zone of these stars. We finally identify high-priority targets for the JWST Rocky Worlds survey and future ELT observations based on their ECS positioning and Transmission Spectroscopy Metrics. Future efforts must focus on expanding the empirical validations of the ECS, particularly through high-precision observations of borderline candidates and systems with well-constrained XUV histories. [Abridged]

Both star clusters and variable stars are sensitive laboratories of stellar astrophysics and evolution: cluster member stars provide context for interpreting cluster populations, whereas variability reveals the nature of individual stellar systems. The European Space Agency's Gaia mission has revolutionized the census of star clusters in the Milky Way, while simultaneously providing an unprecedented homogeneous all-sky catalog of variable stars. Here, we leverage the third Gaia data release to obtain an empirical bird's eye view of stellar evolution based on 34760 variable stars residing in 1192 Galactic open clusters (OCs) containing 173294 members (variable member fraction 20.0%). Using precise OC distances, dereddened magnitudes, and consistently determined ages, we a) pinpointed regions of pulsational instability across the color-absolute magnitude diagram (CaMD); b) traced the occurrence rate of variables as a function of age, and c) considered the evolution of rotation periods and photometric activity (gyrochronology). The occurrence of pulsating stars can serve as a model- and reddening-independent age estimator. Our results underline that jointly considering stellar variability and OC membership enables a plethora of further applications, such as age dating or dereddening OCs based on expected CaMD locations of variable stars. Upcoming Gaia data releases and the Vera C. Rubin Observatory will vastly increase the extent to which the details of variable stars in OCs can empirically unravel the astrophysics and evolution of stellar populations.

The "dirty" image made by direct Fourier inversion of visibility data is an important first step in inteferometric imaging. This is where the "deconvolution problem" is defined and the degree to which that problem is either well- or ill-conditioned has direct consequences for the ultimate image fidelity that is achieved in practise. An under-utilised degree of freedom during Fourier imaging is the relative weights that are assigned to the visibility data. We explore the circumstances under which some adjustment of the relative weights might provide improvements to the "dirty" image, and consequently the ultimate post-deconvolution image fidelity. We develop a method to calculate a distinct effective local density estimate for each data point. When used in conjunction with a "uniform" weight correction and the desired clean beam (eg. Gaussian) tapering, it provides a significant improvement in the image quality over that provided by the current pixel-based density estimate. In many cases, particularly spectral-line observations and those with only limited sidereal tracking, this adaptive approach improves the beam quality by a factor of 2 to 10, as measured by the RMS residual relative to the best-fitting clean beam, providing an improvement in final image fidelity that is similar in magnitude.

The TIRAMISU code, a new program for computing on-the-fly non-LTE molecular spectra and opacities for solving self-consistent radiative transfer problems in exoplanet atmospheres, is presented. The ultra-hot Jupiter KELT-20 b is used as a case study to identify the wavelength regions at which non-LTE effects may be detectable. It is shown that upper atmospheric OH in vibrational non-LTE should be observable primarily via hot bands in the mid-infrared and enhanced photodissociation in the visible. Varying the abundance of OH in non-LTE demonstrates a non-linear relationship between the abundance and the strength of non-LTE effects. Using recent calculations of the photodissociation probabilities of OH it is shown that non-LTE effects can increase the total photodissociation rate by two orders of magnitude in the upper atmosphere, which is likely to have a significant impact on atmospheric and chemical modelling. Increases and reductions in the molecular opacities under non-LTE conditions may lead to the mischaracterisation of molecular abundances in retrievals that only consider opacities computed under LTE. Collisional data requirements to support future non-LTE modelling for a variety of exoplanet atmospheres and across a wide range of wavelengths are discussed.

Some planetary nebulae (PNe) host X-ray-emitting hot bubbles shaped by stellar wind interactions and/or harbor X-ray-emitting central stars due to accretion, shocks within their fast stellar winds, or even chromospheric emission from binary companions. In both cases, the properties of the X-ray emission critically probe late-stages of stellar evolution for such low- and intermediate-mass stars. While extant Chandra and XMM-Newton observations have detected X-ray emission in PNe, the numbers known remain very small ($\sim40$) compared to the overall Galactic PNe population ($\sim4000$). We have initiated a project aimed at increasing the sample of known PNe with X-ray emission using both current and new space-based X-ray telescopes such as the Einstein probe. To further investigate their X-ray properties to elucidate what drives current X-ray PN detections, we have cross-searched the SRG {\it eROSITA-DE} eRASS1 source catalogue and Hong Kong (HASH) PNe Database. Five known X-ray PNe have been detected (Abell\,30, NGC\,2392, NGC\,3242, NGC\,5315, and LoTr\,5), two new X-ray PNe are revealed (IC\,1297 and NGC\,2867), one (K\,1-27) is removed from previous X-ray compilations, and another 11 previously detected X-ray emitting PNe are not recovered. A comparison of the X-ray flux of detected and undetected X-ray PNe reveals that eROSITA eRASS1 is sensitive to PNe with X-ray fluxes larger than $\approx2\times10^{-14}$ erg~cm$^{-2}$~s$^{-1}$. The frequency of occurrence is $\simeq$0.5\% among the 1430 HASH True PNe in the eRASS1 footprint.

Core-collapse supernovae (CCSNe) are among the primary sources of dust in galaxies. In this study, we derive theoretical upper limits on dust masses as a function of supernova (SN) progenitors with initial masses between 9 and 120 Msun, based on previously established models of dust formation chemistry in CCSNe. We find that O-rich dust, particularly silicates, dominates the dust budget, with masses ranging from 0.02 to 0.9 Msun, and that the total mass of O-rich dust increases with progenitor mass. C-rich amorphous carbon dust is significant for lower-mass progenitors (up to 15 Msun), but its mass never exceeds 0.05 Msun. For progenitors up to 30 Msun, we provide best-fit functions describing the masses of O-rich dust, C-rich dust, and CO molecules. A large stochastic variation is found in the predicted masses of silicate dust, which correlates with the randomness of shell-merger events in the pre-explosion phases of massive stars. Furthermore, we show that the dust mass for a given progenitor can vary by a factor of 2-5, reflecting differences in pre-explosion abundance profiles predicted by the stellar evolution codes KEPLER and MESA. We emphasize that the final dust yield in CCSNe is primarily determined by stochastic stellar yields and uncertainties in pre-explosion nucleosynthesis, while explosion properties mainly influence the timescales of dust formation.

The energy that heats the magnetically closed solar corona originates in the complex motions of the massive photosphere. Turbulent photospheric convection slowly displaces the footpoints of coronal field lines, causing them to become twisted and tangled. Magnetic stresses gradually build until reaching a breaking point when the field reconnects and releases a sudden burst of energy. We simulate this basic picture of nanoflares using a high-fidelity, three-dimensional, multi-stranded magnetohydrodynamic simulation that starts with a fully stratified atmosphere. This simulation includes the effects of field-aligned thermal conduction and optically thin radiation and uses the state-of-the-art Transition Region Adaptive Conduction (TRAC) method to capture the response of the plasma to the nanoflare heating. We find that our physical model supports a unified explanation for both the diffuse emission observed in active regions and the bright coronal loops. Specifically, our results suggest that the diffuse emission originates from spatially and temporally uncorrelated nanoflares, whereas coherent clusters of nanoflares - nanoflare storms - are responsible for the formation of bright coronal loops. Quantitative comparisons between the simulated emission and observed characteristics of coronal loops show that key observed properties - such as loop widths, lifetimes and cross sections - are reasonably well reproduced by the model. The idea that avalanche spread naturally leads to circular cross sections in coronal loops is strongly supported. Our results also suggest that phase differences in heating and cooling events across neighboring magnetic flux strands are a plausible explanation for the anomalous cross-field motions of coronal loops that were recently reported in high-resolution observations.

Doppler Imaging (DI) is a well-established technique to map a physical field at a stellar surface from a time series of high-resolution spectra. In this proof-of-concept study, we aim to show that traditional DI algorithms, originally designed for rapidly-rotating stars, have also the ability to model the activity of Sun-like stars, when observed with new-generation highly-stable spectrographs, and search for low-mass planets around them. We used DI to retrieve the relative brightness distribution at the surface of the Sun from radial velocity (RV) observations collected by HARPS-N between 2022 and 2024. The brightness maps obtained with DI have a typical angular resolution of about 36 degrees and are a good match to low-resolution disc-resolved Dopplergrams of the Sun at epochs when the absolute, disc-integrated RV exceeds ~2 m/s. The RV residuals after DI correction exhibit a dispersion of about 0.6 m/s, comparable with existing state-of-the-art activity correction techniques. Using planet injection-recovery tests, we also show that DI can be a powerful tool for blind planet searches, so long as the orbital period is larger than ~100days (i.e. 3 to 4 stellar rotation periods), and that it yields planetary mass estimates with an accuracy comparable to, for example, multi-dimensional Gaussian process regression. Finally, we highlight some limitations of traditional DI algorithms, which should be addressed to make DI a reliable alternative to state-of-the-art RV-based planet search techniques.

Recent observations and simulations indicate that solar flares undergo extremely complex three-dimensional (3D) evolution, making 3D particle transport models essential for understanding electron acceleration and interpreting flare emissions. In this study, we investigate this problem by solving Parker's transport equation with 3D MHD simulations of solar flares. By examining energy conversion in the 3D system, we evaluate the roles of different acceleration mechanisms, including reconnection current sheet (CS), termination shock (TS), and supra-arcade downflows (SADs). We find that large-amplitude turbulent fluctuations are generated and sustained in the 3D system. The model results demonstrate that a significant number of electrons are accelerated to hundreds of keV and even a few MeV, forming power-law energy spectra. These energetic particles are widely distributed, with concentrations at the TS and in the flare looptop region, consistent with results derived from recent hard X-ray (HXR) and microwave (MW) observations. By selectively turning particle acceleration on or off in specific regions, we find that the CS and SADs effectively accelerate electrons to several hundred keV, while the TS enables further acceleration to MeV. However, no single mechanism can independently account for the significant number of energetic electrons observed. Instead, the mechanisms work synergistically to produce a large population of accelerated electrons. Our model provides spatially and temporally resolved electron distributions in the whole flare region and at the flare footpoints, enabling synthetic HXR and MW emission modeling for comparison with observations. These results offer important insights into electron acceleration and transport in 3D solar flare regions.

The Unification Model of AGN suggests that all AGN galaxies should exhibit similar line ratios in their spectra. NGC 5548, a Seyfert I, underwent obscuration -- similar to naturally obscured Seyfert II galaxies -- due to an outflowing accretion wind, resulting in absorption. As per the Model, a Seyfert I and a Seyfert II should show similar flux ratios during their respective obscuration states. In this note, we present a comparison of emission fluxes between NGC 5548 and NGC 1068, a Seyfert II. We present the CLOUDY prediction of NGC 5548, which underpredicts the line ratios compared to observations, likely due to SED choices. The differing observed line ratios of NGC 5548 and NGC 1068 suggest additional unknown factors in the unification model.

Solar flare ribbons are believed to map the footpoints of newly reconnected magnetic flux tubes, therefore shedding light on the reconnecting current sheet, which is rarely observed by direct imaging or spectroscopy. Here we study the detailed evolution of flare ribbons down to the arcsecond scale for 10 flares characterized by the classic double ribbons. Identifying the flaring pixels by combining the intensity variances of the UV filter ratio and intensity threshold, we found that the waiting time distributions of the flaring pixels are well described by power laws, distinct from those in the preflare or quiet-Sun regions, and that the power-law slopes are generally consistent with those predicted by nonstationary Poisson processes in the nonlinear regime or by the 2D/3D self-organized criticality (SOC) model. The size distributions for flaring duration also follow power laws but the slopes are more scattered. In contrast, the size distributions for other parameters, including peak intensity, energy, and radial magnetic field strength of the flaring pixels, deviate from power laws, and the estimated slopes significantly differ from the SOC predictions. These results suggest that a nonstationary Poisson process or an avalanche-like process might be ongoing in the temporal dimension in the reconnecting current sheet, but in other aspects, e.g., space- and energy-wise, the avalanche is likely modulated by other physical processes or the fine structures of the reconnecting current sheet.

The serendipitous discovery of the M31 globular cluster (GC) EXT8 has presented a significant challenge to current theories for GC formation. By finding other GCs similar to EXT8, it should become clear if and/or how EXT8 can fit into our current understanding of GC formation. We aim to test the potential of integrated-light narrow-band Ca II H & K photometry as a proxy for the metallicity of GCs to be able to provide effective candidate selection for massive GCs below the GC metallicity floor ([Fe/H] $\leq$ -2.5), such as EXT8. We investigate the behaviour of two colours involving the CaHK filter employed by the Pristine survey, CaHK-u and CaHK-g, as a function of metallicity through CFHT MegaCam imaging of EXT8 and a wide set of M31 GCs covering the metallicity range of -2.9 $\leq$ [Fe/H] $\leq$ +0.4. Additionally, we investigate if the CaHK colours are strongly influenced by horizontal branch morphology through available morphology measurements. In both of the CaHK colours, EXT8 and two other potential GCs below the metallicity floor can be selected from other metal-poor GCs ([Fe/H] $\leq$ -1.5) with CaHK-g showing the larger metallicity sensitivity. The RMS of linear fits to the metal-poor GCs show an uncertainty of 0.3 dex on metallicity estimations for both colours. Comparisons with u-g and g-z/F450W-F850L colours reinforce the notion that CaHK photometry can be used for effective candidate selection as they reduce false positive selection rates by at least a factor of 2. We find no strong influence of the horizontal branch morphology on the CaHK colours that would interfere with candidate selection, although the assessment is limited by quantity and quality of available data.

Fast X-ray Transients (FXTs) are short-lived extra-galactic X-ray sources. Recent progress through multi-wavelength follow-up of Einstein Probe discovered FXTs has shown that several are related to collapsars, which can also produce gamma-ray bursts (GRBs). In this paper we investigate the nature of the FXT EP250207b. The VLT/MUSE spectra of a nearby (15.9 kpc in projection) lenticular galaxy reveal no signs of recent star formation. If this galaxy is indeed the host, EP250207b lies at a redshift of z=0.082, implying a peak observed absolute magnitude for the optical counterpart of M_r=-14.5. At the time when supernovae (SNe) would peak, it is substantially fainter than all SN types. These results are inconsistent with a collapsar origin for EP250207b. The properties favour a binary compact object merger driven origin. The X-ray, optical and radio observations are compared with predictions of several types of extra-galactic transients, including afterglow and kilonova models. The data can be fit with a slightly off-axis viewing angle afterglow. However, the late-time (~30 day) optical/NIR counterpart is too bright for the afterglow and also for conventional kilonova models. This could be remedied if that late emission is due to a globular cluster or the core of a (tidally disrupted) dwarf galaxy. If confirmed, this would be the first case where the multi-wavelength properties of an FXT are found to be consistent with a compact object merger origin, increasing the parallels between FXTs and GRBs. We finally discuss if the source could originate in a higher redshift host galaxy.

Understanding the cold atomic hydrogen gas (HI) within cosmic filaments has the potential to pin down the relationship between the low density gas in the cosmic web and how the galaxies that lie within it grow using this material. We report the discovery of a cosmic filament using 14 HI-selected galaxies that form a very thin elongated structure of 1.7 Mpc. These galaxies are embedded within a much larger cosmic web filament, traced by optical galaxies, that spans at least $\sim 15$~Mpc. We find that the spin axes of the HI galaxies are significantly more strongly aligned with the cosmic web filament ($\langle\lvert \cos \psi \rvert\rangle = 0.64 \pm 0.05$) than cosmological simulations predict, with the optically-selected galaxies showing alignment to a lesser degree ($\langle\lvert \cos \psi \rvert\rangle = 0.55 \pm 0.05$). This structure demonstrates that within the cosmic filament, the angular momentum of galaxies is closely connected to the large-scale filamentary structure. We also find strong evidence that the galaxies are orbiting around the spine of the filament, making this one of the largest rotating structures discovered thus far, and from which we can infer that there is transfer of angular momentum from the filament to the individual galaxies. The abundance of HI galaxies along the filament and the low dynamical temperature of the galaxies within the filament indicates that this filament is at an early evolutionary stage where the imprint of cosmic matter flow on galaxies has been preserved over cosmic time.

Gamma-ray bursts early afterglows are important tracers for determining the radial structure and magnetization of the ejecta. In this paper, we focus on GRB 110213A that shows double-peaked optical afterglow lightcurves and the shallow decay feature of the X-ray afterglow. We adopt a semi-analytic model for the dynamics of forward and reverse shocks generated through an interaction between an arbitrary magnetized ejecta with a finite thickness and a stratified circumstellar medium. Multiwavelength radiation from forward and reverse shocks seen from an arbitrary viewing angle is calculated under a thin-shell approximation. Our analysis with multimodal nested sampling methods for GRB 110213A suggests that the thick shell ejecta naturally explains the shallow decay feature of the X-ray afterglow. The combination of the reverse shock emission in the strongly magnetized jet and forward shock emission in the weakly magnetized circumstellar medium makes the double peak feature of the optical afterglows. The estimated low radiative efficiency in the prompt phase may be a consequence of the high magnetization of the jet in this case. A multi-messenger emission simulator based on the magnetic bullet afterglow model is publicly available as the open source Julia package "Magglow".

Simulations predict that circumgalactic hydrogen gas surrounding massive ($M_{\rm{halo}}^{z=1}=10^{12}-10^{13}\ M_{\odot}$) galaxies at $z\sim4$ may be predominantly neutral, and could produce damped Ly$\alpha$ absorbers (DLAs) along sight-lines to background quasars \citep{Stern2021}. A circumgalactic medium (CGM) origin for DLAs naturally explains high redshift HI absorption-selected galaxy detections at physical separations much greater than the likely extents of the galaxy disks \citep{Neeleman2017, Neeleman2019}. The observed $z\sim 4$ DLA HI column densities are large and comparable to interstellar (ISM) gas columns at which substantial molecular hydrogen (H$_2$) abundances occur. We therefore investigate the possible molecular content of high-redshift CGM gas, and its potential detectability via (rest-frame) far-ultraviolet (UV) absorption line studies. For this purpose we develop an analytic sub-grid model for HI-to-H$_2$ transitions and incorporate the model with zoom-in FIRE-2 simulations of evolving high-$z$ galaxies. We include dust absorption and scattering computations for the transfer of photodissociating Lyman-Werner (LW) band radiation. We find that the typical extents of detectable H$_2$ sightlines are $\approx 0.1\, R_{\rm vir}$, independent of redshift from $z=2.5$ to 5. We argue that a CGM origin for DLAs naturally explains the low detection rates of H$_2$ in DLA observations, as the low CGM densities and relatively strong far-UV fields lead to molecular fractions much lower than observed in the ISM at comparable HI columns.

This study presents all available, multi-epoch 3.6 and 4.5 $\mu$m photometry from Spitzer Space Telescope observations of white dwarf debris disks, including weekly cadence observations of 16 relatively bright systems, and 5 h staring-mode observations for five of these. Significant variability is detected in 85 per cent of disks and across all timescales probed, from minutes to weeks to years, where the largest flux changes correlate with the longest time baselines, and the infrared excesses persist utterly. While each source is idiosyncratic, the overall results indicate the most variable disks correlate with those that are the brightest (dustiest), and also among those with detected gas, demonstrating both dust and gas are produced via ongoing collisions. There is a correlation between flux and colour changes, where disks tend to appear redder when dimmer and bluer when brighter, consistent with an excess of small dust grains produced in collisions, followed by a gradual return to equilibrium. The overall results are a drastic departure from the predictions of the canonical - geometrically thin, optically thick - disk in both flux and colour, but are broadly consistent with collisional evolution based on a simple model. The data presented herein constitute a legacy resource that can inform time-series studies of polluted and dusty white dwarfs, and importantly serve as a basis for future disk modelling, beyond the pioneering canonical framework.

Star formation governs galaxy evolution, shaping stellar mass assembly and gas consumption across cosmic time. The Kennicutt-Schmidt (KS) relation, linking star formation rate (SFR) and gas surface densities, is fundamental to understand star formation regulation, yet remains poorly constrained at $z > 2$ due to observational limitations and uncertainties in locally calibrated gas tracers. The [CII] $158 {\rm \mu m}$ line has recently emerged as a key probe of the cold ISM and star formation in the early Universe. We investigate whether the resolved [CII]-SFR and KS relations established at low redshift remain valid at $4 < z < 6$ by analysing 13 main-sequence galaxies from the ALPINE and CRISTAL surveys, using multi-wavelength data (HST, JWST, ALMA) at $\sim2$ kpc resolution. We perform pixel-by-pixel spectral energy distribution (SED) modelling with CIGALE on resolution-homogenised images. We develop a statistical framework to fit the [CII]-SFR relation that accounts for pixel covariance and compare our results to classical fitting methods. We test two [CII]-to-gas conversion prescriptions to assess their impact on inferred gas surface densities and depletion times. We find a resolved [CII]-SFR relation with a slope of $0.87 \pm 0.15$ and intrinsic scatter of $0.19 \pm 0.03$ dex, which is shallower and tighter than previous studies at $z\sim5$. The resolved KS relation is highly sensitive to the [CII]-to-gas conversion factor: using a fixed global $\alpha_{\rm [CII]}$ yields depletion times of $0.5$-$1$ Gyr, while a surface brightness-dependent $W_{\rm [CII]}$, places some galaxies with high gas density in the starburst regime ($<0.1$ Gyr). Future inputs from both simulations and observations are required to better understand how the [CII]-to-gas conversion factor depends on local ISM properties. We need to break this fundamental limit to properly study the KS relation at $z\gtrsim4$.

Hot Jupiters (HJs) are $2-3\times$ less common around early M dwarfs than around AFGK stars, suggesting that HJs may form and/or migrate via distinct pathways around different types of stars. One source of insight into HJ formation mechanisms is to trace their dynamical histories through measurements of host stellar obliquities via the Rossiter-McLaughlin (RM) effect. Here we present measurements of the RM effect for the HJs TOI-3714 b and TOI-5293 A b using the Gemini-North/MAROON-X spectrograph. Our measurements represent just the second and third hot Jupiters around M dwarfs (HJMD) with a detection of the RM effect. We find that both systems are well-aligned with sky-projected obliquities of $\lambda = 21^{+14}_{-11}$$\mathrm{^{\circ}}$ and $-12^{+19}_{-14}$$\mathrm{^{\circ}}$ and deprojected obliquities of $\psi = 26^{+11}_{-10}$$\mathrm{^{\circ}}$ and $24^{+11}_{-10}$$\mathrm{^{\circ}}$ for TOI-3714 and TOI-5293 A, respectively. Both stars are in wide binary systems. We refine the stellar parameters by decontaminating their unresolved $K_s$-band photometry and constrain the binary orbits using Gaia DR3 astrometry. We find that the minimum mutual inclination of the planet and binary companion in the TOI-5293 system is sufficiently large to drive Kozai-Lidov (KL) migration while the result for TOI-3714 is inconclusive. We present a population-level analysis of HJs around AFGK versus early M dwarfs and argue that KL migration is more efficient around the latter, which is expected to produce misaligned stellar obliquities in HJMD systems in the absence of efficient tidal damping. The emerging population of well-aligned HJMD hosts supports the expectation that M dwarfs, with their deep convective envelopes, do efficiently dampen misaligned obliquities.

We study the impact of non-thermal leptogenesis on the spectrum of gravitational waves (GWs) produced by a strong first-order phase transition in the early Universe. We consider a scenario in which a heavy scalar field, $\phi$, dominates the energy density of the early Universe and decays into heavy right-handed neutrinos (RHNs). The subsequent decay of RHNs generates a lepton asymmetry, which is partially converted into the observed baryon asymmetry via the sphaleron process. The $\phi$-dominated era and the entropy injection from the decays of $\phi$ and RHNs leave characteristic imprints on the GW spectrum, such as damping and modified frequency dependence, that distinguish it from the standard cosmological evolution. We identify the parameter space in which non-thermal leptogenesis is successful, leading to distinctive GW spectral features. We show that these GW signals can fall within the sensitivity ranges of future detectors such as ET, DECIGO and BBO. If observed, they would provide valuable insights into the thermal history and dynamics of the early Universe.

Testing General Relativity (GR) is a key science goal of much of modern physics, and usually results in constraints that are either theory or context specific. We present an holistic framework that we dub `Parametrized Post-Newtonian Cosmology' (PPNC), which can be used for obtaining theory-agnostic constraints on deviations from GR using a single unified set of parameters that apply on all astrophysical and cosmological scales. Our approach is based on the formalism and philosophy of the highly successful Parametrized Post-Newtonian (PPN) framework, but allows us to combine observations of the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAOs) with Solar System observations of the Cassini probe and ephemeris of Mars. The full combination of these data sets constrains average deviations from GR over the history of the Universe to be less than $\sim 10\%$, with PPNC parameter values $\bar{\alpha}=0.97^{+0.06}_{-0.07}$ and $\bar{\gamma}=0.97^{+0.05}_{-0.05}$ at the $68\%$ confidence level (GR corresponds to $\bar{\alpha}=\bar{\gamma}=1$). We find that these gravitational parameters have a strong mutual degeneracy, and are constrained to be within $1\%$ of each other for all of cosmic history. Our results demonstrate the ability of the PPNC framework to combine astrophysical, Solar System and cosmological tests of gravity into a single set of unified constraints. We expect our approach to be particularly useful for upcoming missions in both cosmology and astrophysics, which ultimately seek to constrain the same underlying gravitational interaction.

We develop the spacetime approach to gravitational lensing by spherically symmetric perturbations of flat, cosmological constant-dominated Friedman-Robertson-Walker metrics. The geodesics of the spacetime are expressed as integral expressions which are used to examine the formation of multiple images and the observed shapes of non-point sources. We develop the lens mapping from the spacetime perspective, and use the Jacobian of the mapping to explain the observed image shapes. Approaching the geodesic equations as ordinary differential equations, we demonstrate the development of wave front singularities and time delays between light ray signals. This work demonstrates that the widely used thin lens approximation can be replaced with more robust techniques aligned with general relativity.

Cosmic rays scattering with neutrinos produced in supernovae induce a flux of supernova neutrinos boosted to high energies. We calculate the neutrino flux arising from this new mechanism in environments with large cosmic-ray and supernova densities, such as some Active Galactic Nuclei. Under plausible astrophysical conditions, this flux may be detectable with high-energy neutrino telescopes, just considering the proton-neutrino scattering cross section expected in the Standard Model. Furthermore, the center of mass energy of such scatterings can reach $ \sqrt{s} \sim 10-100$ TeV, where the proton-neutrino cross section may be enhanced by new physics such as extra-dimensional theories. The boosted neutrino signal benefits from such an enhancement in the cross section not only at the detection point on Earth, but also at production in astrophysical sources, which allows us to set novel constraints on the ultra-high energy proton-neutrino cross section with neutrino telescopes.

Based on the magnetic reconnection mechanism, this study investigates how to extract energy effectively from an accelerating Kerr black hole in the plunging region and circular orbit region. After introducing the properties of accelerating black holes, including the event horizon, ergosphere, circular orbits, and innermost stable circular orbit, we investigate the magnetic reconnection process in the plunging region. Specifically, we analyze variations of the azimuthal angle with respect to the acceleration, examine changes in energy per enthalpy of decelerated plasma, and plot energy extraction efficiency along with permissible energy extraction regions. Results show that in the plunging region, at larger radii of reconnection locations, the accelerating black hole exhibits higher energy extraction efficiency than a Kerr black hole. Away from extremality, the acceleration parameter impedes energy extraction, while near extremality, it enhances extraction. We also study energy extraction in circular orbit region by plotting energy extraction efficiency within permissible regions. We find that the permissible energy extraction area is reduced and the efficiency exceeds that of Kerr black holes due to the existence of acceleration parameter. Larger acceleration parameters yield more effective energy extraction regardless of extremality, which is different from that in the plunging region. Additionally, energy extraction efficiency in the plunging region surpasses that in the circular orbit region, aligning with prior conclusions.

Power spectral density (PSD) estimation is a critical step in gravitational wave (GW) detectors data analysis. The Welch method is a typical non-parametric spectral estimation approach that estimates the PSD of stationary noise by averaging periodograms of several time segments, or by taking the median of periodograms to adapt to non-stationary noise. In this work, we propose a wavelet-based approach for fast PSD estimation of both stationary and non-stationary noise. For stationary noise, we apply wavelet smoothing to the periodogram, avoiding the segmentation step in the Welch method, and enabling PSD estimates with high frequency resolution and low variance. The wavelet smoothing PSD outperforms Welch PSD in matched filtering and parameter estimation. For non-stationary noise, we estimate the PSD by taking the median of wavelet packet coefficients in each frequency bin, which offers greater robustness than the traditional median periodogram method. This work introduces a new PSD estimation approach for GW data analysis and expands the application of wavelet methods in this field.

GW200105_162426 is the first neutron star-black hole merger to be confidently confirmed through either gravitational-wave or electromagnetic observations. Although initially analyzed after detection, the event has recently gained renewed attention following a study, Morras et al. (2025), that employed a post-Newtonian inspiral-only waveform model and reported strong evidence for orbital eccentricity. In this work, we perform a detailed analysis of GW200105 using state-of-the-art effective-one-body waveform models. Importantly, we present the first study of this event utilizing a physically complete model that incorporates both orbital eccentricity and spin precession across the full inspiral, merger, and ringdown stages, along with higher-order gravitational wave modes. Our results support the presence of eccentricity in the signal, with zero eccentricity excluded from $99\%$ credible interval, but yield a mass ratio closer to the original LIGO-Virgo-KAGRA analysis, differing from the findings of Morras et al. (2025). Additionally, similar to previous eccentric-only analysis Planas et al. (2025), we observe a multimodal structure in the eccentricity posterior distribution. We conduct targeted investigations to understand the origin of this multimodality and complement our analysis with numerical relativity simulations to examine how the inclusion of eccentricity impacts the merger dynamics.

Compact stars in scalar-tensor gravity have been extensively investigated, but relatively few studies have focused on highly relativistic neutron stars (NSs) with an extremely dense core region where the trace of the energy-momentum tensor reverses its sign. In this regime, we identify the origin of the phenomenon where {\it multiple} scalarized solutions exist for a {\it fixed} central density, arising from the oscillatory profile of the scalar field inside the star. This origin further indicates that the multi-branch structure emerges for both negative and positive $\beta$, the quadratic-term coefficient in the effective coupling function between the scalar field and conventional matter in the Einstein frame. By comparing the Damour--Esposito-Farèse and Mendes-Ortiz models of the scalar-tensor gravity, we demonstrate that their distinct scalarization behaviors stem from whether the effective coupling function is bounded. We also compute for scalarized NSs with a highly relativistic dense core in scalar-tensor theories the moment of inertia and tidal deformability that are relevant to pulsar-timing and gravitational-wave experiments.

We present a neural-network framework designed to reconstruct the properties of cosmic-ray nuclei traversing the scintillating-fiber tracking calorimeter of the RadMap Telescope. Employing the Geant4 simulation toolkit and a simplified model of the detector to generate training and test data, we achieve the spectroscopic capabilities required for an accurate determination of the biologically relevant dose that astronauts receive in space. We can reconstruct a particle's trajectory with an angular resolution of better than $1.4^\circ$ and achieve a charge separation of better than $95\%$ for nuclei with $Z\leq8$; specifically, we reach an accuracy of $99.8\%$ for hydrogen. The energy resolution is $<20\%$ for energies below 1 GeV/n and elements up to iron. We also discuss the limitations of our detector, the reconstruction framework, and this feasibility study, as well as possible improvements.

In this work, we present the refinement of axion double level crossings within the context of multi-axion mass mixing, specifically focusing on cases where the number of axions exceeds two. Our investigation reveals that double level crossings are a common phenomenon in the mass mixing of the $Z_{\mathcal N}$ axion and axion-like particles. We introduce the general model for double level crossings, along with several toy examples, and redefine the light and heavy axion scenarios. In the light axion scenario, double level crossings can occur multiple times in the large ${\mathcal N}$ limit. However, excessively large values of ${\mathcal N}$ may also prevent the occurrence of double level crossings. Conversely, in the heavy axion scenario, excessively small ${\mathcal N}$ may similarly prevent their occurrence. Our findings also have some intriguing implications for axion cosmology.

We present an application of computer vision methods to classify the light curves of eclipsing binaries (EB). We have used pre-trained models based on convolutional neural networks ($\textit{ResNet50}$) and vision transformers ($\textit{vit\_base\_patch16\_224}$), which were fine-tuned on images created from synthetic datasets. To improve model generalisation and reduce overfitting, we developed a novel image representation by transforming phase-folded light curves into polar coordinates combined with hexbin visualisation. Our hierarchical approach in the first stage classifies systems into detached and overcontact types, and in the second stage identifies the presence or absence of spots. The binary classification models achieved high accuracy ($>96\%$) on validation data across multiple passbands (Gaia~$G$, $I$, and $TESS$) and demonstrated strong performance ($>94\%$, up to $100\%$ for $TESS$) when tested on extensive observational data from the OGLE, DEBCat, and WUMaCat catalogues. While the primary binary classification was highly successful, the secondary task of automated spot detection performed poorly, revealing a significant limitation of our models for identifying subtle photometric features. This study highlights the potential of computer vision for EB morphological classification in large-scale surveys, but underscores the need for further research into robust, automated spot detection.

We present a simple, analytically solvable MHD model of current sheet formation through X-point collapse under optically thin radiative cooling. Our results show that cooling accelerates the collapse of the X-point along the inflows, but strong cooling can arrest or even reverse the current sheet elongation in the outflow direction. Hence, we detail a modification to the radiatively-cooled Sweet-Parker model developed by Uzdensky & McKinney (2011) to allow for varying current sheet length. The steady-state solution shows that when radiative cooling dominates compressional heating, the current sheet length is shorter than the system size, with an increased reconnection rate compared to the classical Sweet-Parker rate. The model and subsequent results lay out the groundwork for a more complete theoretical understanding of magnetic reconnection in regimes dominated by optically thin radiative cooling.