One of the most puzzling discoveries by JWST is the population of high-redshift, red, and compact galaxies dubbed little red dots (LRDs). Based on broad-line diagnostics, these galaxies have been argued to host accreting $10^7-10^8$ M$_\odot$ supermassive black holes (SMBHs), a claim with crucial consequences for our understanding of how the first black holes form and grow over cosmic time. A key feature of LRDs is their extreme X-ray weakness: analyses of individual and stacked sources have yielded non-detections or only tentative, inconclusive X-ray signals, except for a handful of individual cases. As the most natural explanation, high obscuration, is disfavored by JWST spectroscopic evidence, several authors have suggested that the X-ray weakness of LRDs is intrinsic, due to super-Eddington accretion rates. In this work, we test that scenario by stacking X-ray data for 55 LRDs in the Chandra Deep Field South, accumulating a total exposure time of nearly 400 Ms. Despite reaching unprecedented X-ray depths, our stack still yields a non-detection. The corresponding upper limits are deep enough to rule out current super-Eddington accretion models, and are compatible only with extremely high levels of obscuration ($N_H\gtrsim10^{25}$~cm$^{-2}$). To explain the X-ray weakness of LRDs, we therefore speculate that the SMBHs in these systems are neither as massive nor as luminous as currently believed.

We present the results of four three-dimensional radiation magnetohydrodynamic simulations of accretion disks around a $10^8$ solar mass black hole, which produce the far ultraviolet spectrum peak and demonstrate a robust physical mechanism to produce the extreme ultraviolet to soft X-ray power-law continuum component. The disks are fed from rotating tori and reach accretion rates ranging from $0.03$ to $4$ times the Eddington value. The disks become radiation pressure or magnetic pressure dominated depending on the relative timescales of radiative cooling and gas inflow. Magnetic pressure supported disks can form with or without net poloidal magnetic fields as long as the inflowing gas can cool quickly enough, which can typically happen when the accretion rate is low. We calculate the emerging spectra from these disks using multi-group radiation transport with realistic opacities and find that they typically peak around $10$ eV. At accretion rates close to or above the Eddington limit, a power-law component can appear for photon energies between $10$ eV and 1 keV with a spectral slope varying between $L_\nu\propto\nu^{-1}$ and $\nu^{-2}$, comparable to what is observed in radio quiet quasars. The disk with $3\%$ Eddington accretion rate does not exhibit this component. These high energy photons are produced in an optically thick region $\approx 30^{\circ}-45^{\circ}$ from the disk midplane by compressible bulk Comptonization within the converging accretion flow. Strongly magnetized disks that have a very small surface density will produce a spectrum that is very different from what is observed.

We investigate the X-ray emission from the Galactic Centre (GC) region, focusing on the 6.4 keV fluorescent line of neutral or weakly ionised iron, which is commonly attributed to X-ray reflection from dense molecular clouds. Our goal is to separate the reflection signal from other physical X-ray components. We aim to produce a clean map of the 6.4 keV emission, thus providing a better understanding of the X-ray reflection processes in the GC. We utilised a deep mosaic of all available XMM-Newton observations, encompassing the central 40 square degrees of the Galaxy. The mosaics of two narrow bands centred at 6.7 keV and 6.4 keV, and a broader continuum band at lower energies (5-6.1 keV), provided valuable spatial and spectral information on the X-ray emission. These combined with the stellar mass distribution of our Galaxy enabled us to decompose the observed signal into physically meaningful components. Our analysis shows that the cleaned 6.4 keV band map, free from the contribution of bright and unresolved point sources, is predominantly shaped by X-ray reflection from dense molecular clouds. The spatial distribution of this emission, which strongly correlates with the molecular gas distribution in the Central Molecular Zone (CMZ), supports the interpretation that this map provides the best estimate of the X-ray reflection signal averaged over the last two decades. The cleaned reflection map produced could serve as a tool for future studies to quantify upper limits on the reflection contribution from low-energy cosmic rays in unilluminated regions. Moreover, we estimate that, on average within the CMZ, approximately 65% of the ridge emission contributes to the observed 6.4 keV emission, a factor that should be incorporated into upcoming investigations of the GC, such as polarisation studies of the reflected X-ray continuum from molecular clouds.

Modern cosmological surveys cover extremely large volumes and map fluctuations on scales reaching gigaparsecs. As a result, it is no longer a valid assumption to ignore cosmological evolution along the line of sight from one end of the survey to the other. When extracting cosmological information, the power spectrum becomes suboptimal because it relies on the assumption of translational invariance of the observed field. For example, during the Epoch of Reionization (EoR), the 21cm brightness temperature field on the nearby (low-redshift) end of a large survey volume exhibits statistical properties that differ significantly from those at far (high-redshift) end. To overcome these limitations, we have developed a eigen decomposition-inspired non-Fourier basis that captures evolution effects. Our work demonstrates that using this new basis integrated in a new summary statistic yields tighter constraints on astrophysical parameters compared to the traditional power spectrum. Additionally, we provide an illustrative example and a practical guide for applying this basis in the context of a realistic forecast for interferometers such as the Hydrogen Epoch of Reionization Array (HERA).

The overionized regions surrounding high-redshift quasars, known as proximity zones, provide a window into the interaction between supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). We present new homogeneous measurements of proximity zone sizes ($R_{\mathrm{p}}$) for a sample of $59$ quasars spanning redshifts $5.77 \leq z \leq 7.54$ (median $z = 6.59$). For $15$ of these sources, we measure $R_{\mathrm{p}}$ for the first time. The quasars in our catalog have absolute magnitudes at rest-frame $1450$ \r{A} in the range $-29.13 \leq M_{1450} \leq -25.20$ (median $M_{1450} \simeq -26.49$), providing one of the most extensive data sets for exploring $R_{\mathrm{p}}$ at these epochs. The distribution of $R_{\mathrm{p}}$ values shows a large scatter at fixed redshift and luminosity, likely reflecting variations in quasar lifetimes ($t_{\mathrm{Q}}$), IGM density fluctuations, and IGM neutral fraction. We fit a bivariate power-law model to a large sample of $100$ objects to study the dependence of $R_{\mathrm{p}}$ with both $M_{1450}$ and $z$: we find that the evolution of $R_{\mathrm{p}}$ with luminosity is in agreement with the models ($R_{\mathrm{p}} \propto 10^{-0.4 M_{1450}/2.87}$), while the evolution of $R_{\mathrm{p}}$ with $z$ is steeper than previous works ($R_{\mathrm{p}} \propto (1+z)^{-2.44}$). We identify $13$ quasars with small proximity zone size, defined using the residuals of our fit. In all cases, except for J2211$-$6320, we rule out the presence of associated dense absorbers that prematurely truncate $R_{\mathrm{p}}$, and suggest a short $t_{\mathrm{Q}}$ ($\lesssim 10^4$ yr) as a possible explanation for their small proximity zone sizes.

The latest results from the Atacama Cosmology Telescope Collaboration have moved the preferred perturbation spectral index $n_{\rm s}$ towards one. We reanalyse constraints on the simplest version of the curvaton model, using $n_{\rm s}$ and the tensor-to-scalar ratio $r$. We show that in the massless curvaton case the model gives the same locus of $n_{\rm s}$-$r$ predictions as the power-law model $V(\phi) \propto \phi^p$, but with a different and more elegant physical interpretation. The model gives an excellent account of current observational data, both in the regime where the curvaton dominates the observed perturbations and with an admixture of inflaton-originated perturbations of up to about one-third of the total. Forthcoming large-scale structure surveys, such as that of the recently-launched SPHEREx probe, could discriminate between curvaton and single-field inflation models using the bispectrum.

This study examines the period variation of the eclipsing binary system KR Cyg, a near-contact binary characterized by its short orbital period and significant stellar interactions. The precise orbital parameters of the system have been determined through light curve data collected periodically since 1999 and were published in our previous studies. Additionally, minimum light observations have been continuously monitored to analyze the period variation of the system. In our earlier work, the masses of the primary and secondary components were determined as $2.88\pm0.20 M_{\odot}$ and $1.26\pm 0.07 M_{\odot}$, with corresponding radii of $2.59\pm 0.06 R_{\odot}$ and $1.80\pm 0.04 R_{\odot}$. The bolometric albedo and effective temperature of the less massive star were also investigated, and deviations caused by mutual illumination effects were identified. These results provide valuable insights into the evolutionary status of KR Cyg and shed light on the dynamic processes that occur in near-contact binary systems. Using updated eclipse timings, an (O-C) diagram was constructed, revealing both long-term trends and periodic oscillations. These cyclical variations are thought to indicate the presence of a tertiary component affecting the system via the light-time effect. Additional observations and modeling are recommended to confirm the tertiary hypothesis and further refine the parameters of the system.

The formation of supermassive black holes (SMBHs) in early-type galaxies (ETGs) is a key challenge for galaxy formation theories. Using the monolithic collapse models of ETGs formed in Milgromian Dynamics (MOND) from Eappen et al. (2022), we investigate the conditions necessary to form SMBHs in MOND and test whether these systems adhere to observed SMBH-galaxy scaling relations. We analyse the evolution of the gravitational potential and gas inflow rates in the model relics with a total stellar mass ranging from 0.1 to 0.7 times 10^11 solar masses. The gravitational potential exhibits a rapid deepening during the initial galaxy formation phase, accompanied by high gas inflow rates. These conditions suggest efficient central gas accumulation capable of fueling SMBH formation. We further examine the MBH - sigma relation by assuming that a fraction of the central stellar mass contributes to black hole formation. Black hole masses derived from 10 to 100 percent of the central mass are comparable with the observed relation, particularly at higher central velocity dispersions (sigma greater than 200 km/s). This highlights the necessity of substantial inner mass collapse to produce SMBHs consistent with observations. Our results demonstrate that MOND dynamics, through the rapid evolution of the gravitational potential and sustained gas inflows, provide a favorable environment for SMBH formation in ETGs. These findings support the hypothesis that MOND can naturally account for the observed SMBH-galaxy scaling relations without invoking cold dark matter, emphasizing the importance of early gas dynamics in determining final SMBH properties.

We present WNTR23bzdiq/WTP19aalzlk, a slow eruption of an early-asymptotic giant branch (AGB) star in M31 identified by the Wide-field Infrared Transient Explorer (WINTER) near-infrared and the NEOWISE mid-infrared surveyors. This source brightened gradually over seven years: a 0.5-mag optical rise (2018-2021), a 1-mag optical outburst lasting $\sim$1000 days (2021-2023), and another 1-mag optical rebrightening in 2024. This was accompanied by a steady mid-IR brightening of 1-mag over ten years in NEOWISE data. Archival optical data show only erratic, small amplitude ($<0.3$\,mag) brightness variations from 2003 to 2015, revealing a progenitor star with T$_{\rm{eff}} \approx 3500$K and L $\approx1.6\times10^{4}$L$_{\odot}$ - consistent with a 7$\pm$2M$_{\odot}$ star in its early-AGB phase. During the eruption, the luminosity rose to $\approx5\times10^{4}$L$_{\odot}$ with slow photospheric expansion ($\approx5$km-s$^{-1}$) and constant temperatures ($\approx3600$K) inferred from the spectral energy distribution. Optical and NIR spectra of the eruption resemble late M-type stars, with a mixed-temperature behavior - transitioning from M1 in the optical to M7/M8 in the NIR. These properties of WNTR23bzdiq resemble those of stellar merger transients, particularly the giant star merger OGLE-2002-BLG-360, but on longer timescales. As such, WNTR23bzdiq potentially marks the onset of common-envelope evolution (CEE) in a binary with an AGB primary, and is possibly a member of the emerging population of infrared transients from CEE in giant stars. Continued multiwavelength monitoring, particularly mid-IR observations with JWST to quantify dust production, will shed further light on WNTR23bzdiq.

Although the X-ray spectra of Seyfert 1 galaxies exhibit absorption lines of He-like iron and H-like iron at blue-shifted velocities of approximately $500 \ \mathrm{km} \ \mathrm{s}^{-1}$, the physical origin of these absorption lines remains uncertain. In this study, we performed X-ray radiative transfer based on the sub-parsec-scale thermally driven outflows. The initial step involved calculating the photoionization equilibrium using the Cloudy code, which is based on three-dimensional radiative hydrodynamic simulations. Subsequently, X-ray radiative transfer was performed using the Monte Carlo simulation for astrophysics and cosmology code. Our findings indicate that when the angle of inclination ranges from $55 \ \mathrm{degrees}$ to $65 \ \mathrm{degrees}$, the transmitted component of the X-ray spectrum displays absorption lines of He-like and H-like iron, exhibiting a blue shift of approximately $500 \ \mathrm{km} \ \mathrm{s}^{-1}$. The results suggest that the absorption lines are generated by a photoionized gas within $0.005 \ \mathrm{pc}$. Additionally, the results indicate that the scattered component of the X-ray spectrum exhibits emission lines originating from neutral iron fluorescence, He-like iron, and H-like iron. The emission lines are broadened by approximately $7000 \ \mathrm{km} \ \mathrm{s}^{-1}$ due to the Keplerian rotation. Furthermore, the model reproduced the H-like iron and H-like iron absorption lines in NGC 3783 observed by the Chandra High Energy Transmission Grating.

The role of dust in the cosmic star formation budget remains highly uncertain, especially at $z>4$, where accurate bookkeeping of the dust-obscured component proves difficult. We address this shortcoming with SCUBADive, a compilation of the \jwst\ counterparts of (sub-)millimeter galaxies, in order to further analyze the distribution and properties of massive dust-obscured galaxies at early times. In this paper, we present a subset of SCUBADive, focusing on 60 ``dark'' galaxies that dropout at 1.5\micron. Motivated by \jwst\ observations of AzTECC71, a far-infrared bright F150W-dropout with $z_{\rm phot}=5.7^{+0.8}_{-0.7}$, we complete a systematic search of F150W-dropouts with SCUBA-2 and ALMA detections to find the highest redshift dusty galaxies. Within our subsample, 16 are most similar to AzTECC71 due to faint F444W magnitudes ($>24$\,mag) and lack of counterparts in COSMOS2020. Despite high star formation rates ($\langle$SFR$\rangle=550^{+500}_{-360}$\,\mdot\,yr$^{-1}$) and large stellar masses ($\langle$log$_{10}$(\mstar)$\rangle=11.2^{+0.5}_{-0.4}$\,\mdot), these galaxies may not be particularly extreme for their presumed epochs according to offsets from the main sequence. We find that heavily obscured galaxies, which have inadvertently been omitted by past galaxy evolution studies, comprise roughly 20\% of their host population by mass. This population may, however, contribute significantly to the high mass end (log$_{10}$(\mstar/\mdot)$>11$) of the $z>4$ stellar mass function as up to 60\% could have been missed from previous studies.

We describe our approach to solve the problem of ensuring the solenoidality of the magnetic field vector in three-dimensional (3D) inversions, as well as the estimation of the uncertainty in the inferred magnetic field. The solenoidality of the magnetic field vector is often disregarded in the inversion of spectropolarimetric data due to limitations in the traditional one-dimensional inversion techniques. We propose a method to ensure the solenoidal condition in 3D inversions based on our meshfree approach. The increase in dimensionality with respect to the 1D inversion techniques is such that some of the traditional methods to determine the uncertainties become unfeasible. We propose a method based on a Monte Carlo approach to determine the uncertainty of the magnetic field inference. Due to the physics of the problem, we can compute the uncertainty increasing the total required computational time by just a factor of about two. We also propose a metric to quantify the uncertainty to describe the degree of confidence of the magnetic field inference. Finally, we perform a numerical experiment to demonstrate the feasibility of both the method and the metric proposed to quantify the uncertainty.

We report the detection of a spatial variation of X-ray polarization in the southwestern shell of SN 1006 (SN 1006 SW) using IXPE. The shell has an average X-ray polarization degree (PD) of $21.6\%\pm 4.5\%$ and polarization angle (PA) of $-48^\circ \pm 5^\circ$ in the 2--4 keV energy band, similar to those in the northeastern shell. The PD varies along SN 1006 SW, with a peak PD$= 40\%\pm 8\%$ in the south and a significantly lower PD $\lesssim 27\%$ (99\% upper limit) in the west where the shell has been proposed to be interacting with an interstellar cloud. The correlation between the PD, which reflects the magnetic orderliness, and the preshock density provides observational evidence that magnetic turbulence and amplification are environment-dependent. The high PD detected in the southern region of the shell constrains the magnetic turbulence scale of $\lesssim 0.1$~pc. Moreover, by comparing the IXPE X-ray and MeerKAT radio polarization measurements for SN 1006 SW, we found that magnetic fields traced by X-ray polarization are nearly radially distributed, whereas those traced by radio polarization tend to follow a direction parallel to the Galactic plane. This suggests that the X-ray polarization probes freshly amplified magnetic fields from small-scale structures in the immediate postshock region, while the radio traces more extended regions influenced by the pre-existing ambient magnetic fields.

Trumpler 5 is a moderately old, dust-obscured metal-poor open cluster. In this study, high-resolution near-infrared spectroscopic data of seven giant stars from the Trumpler 5 cluster were analyzed to derive chemical abundances for 20 elements and $^{12}C/^{13}C$ ratios. Color-magnitude diagram (CMD) analysis of BV and Gaia photometry has also been performed for a comprehensive study of the cluster. Thanks to the methodology employed, some targets are studied for the first time. Additionally, it provides a detailed color-magnitude diagram analysis using photometric and spectroscopic data. We gathered high-resolution spectra for seven Trumpler 5 red giants in the near-infrared H and K wavelength domains, using the Immersion Grating INfrared Spectrometer (IGRINS). We introduced a method to initially estimate the stellar surface gravity (log g) by using calibrated equivalent widths of the Ti II line at 15873 {\AA} from a large sample. We performed standard spectroscopic analyses to refine the model atmospheric parameters of our targets and determined the chemical abundances primarily through spectrum synthesis. We also performed color-magnitude diagram analyses to extract differential reddening correction to compare cluster parameters both with and without corrections. We derived stellar parameters for seven members of Trumpler 5 with our method and the results are consistent with both the literature and other methods. We also inferred elemental abundances for more than 20 species, along with the $^{12}C/^{13}C$ ratios. The elemental abundances are in good agreement with the literature values for similar targets. Through CMD analysis, we found the reddening value, E(B-V)$\simeq$0.76 and estimated the age of the cluster to be approximately 2.50 Gyr.

We present high-resolution and spatially-matched observations with JWST and ALMA of a starburst galaxy (PACS-830) at $z=1.46$. The NIRCam observations mainly trace the stellar light while the CO ($J$=5--4) observations map the dense molecular gas at kpc scales. Both datasets reveal the morphology to be that of a gas/dust rich bulge with two extending arms, together resembling a grand-design spiral galaxy. The more pronounced arm contributes 21 $\pm$ 6\% of the total CO emission. These results demonstrate that starburst activity at high redshift can be triggered, without undergoing a highly disruptive major merger. We assess the strength and distribution of star formation using two tracers: (1) Polycyclic Aromatic Hydrocarbons (PAHs) emission detected at $8~\mu$m ($L_8$) with a MIRI/F1800W image, and (2) $L_\mathrm{IR}$, inferred from the CO ($J$=5--4) map. The spatial profiles of the $L_\mathrm{IR}$ and $L_8$ are dissimilar, thus leading to a significant deficit of mid-IR ($L_8$) emission in the nucleus. We hypothesize that this is due to the destruction of PAH molecules by the intense ionizing radiation field or decreased emission in the photodissociation region, as seen in nearby star-forming regions and consistent with the galaxy-wide properties of distant starbursts. This study reveals spatial variations in the $L_8$ to $L_\mathrm{IR}$ ratio for the first time at $z>1$, in agreement with expectations from theory. Our analysis underscores the pivotal role of joint high-resolution observations with JWST and ALMA in discerning the different phases of the interstellar medium (ISM) and revealing internal physics in galaxy substructures.

This review article delves into the study of low-mass exoplanets: super-Earths, mini-Neptunes and the new categories within and between that we are starting to discover. We provide an overview of current exoplanet observational capabilities, their limitations, and what they are allowing us to learn about low-mass planets. We briefly summarize the most important aspects of planet formation, with an emphasis on processes that may be testable with small exoplanets, in particular those that affect their composition. We also describe the observed compositional diversity of low-mass exoplanets and what it teaches us about planet formation pathways. We finish this review summarizing the study of the composition of small exoplanets during the very last stage of stellar evolution, by studying white dwarfs. This review is written as the JWST is making its first contributions to small planet characterization, rapidly opening new lines of inquiry.

In March of 2024 the AAS formed our Graduate Admissions Task Force (GATF), asking us to produce recommendations aimed at improving the state of graduate admissions in astronomy. The task was a timely one, as the past decade has seen dramatic shifts that are currently being exacerbated by rapidly-shifting funding and policy challenges. The GATF surveyed recent applicants to astronomy graduate school and admissions leaders in degree-granting graduate programs, held in-depth conversations with select programs, and explored how other fields approach admissions. Based on this work, we have quantified recent changes in the astronomy graduate admissions landscape, addressed mismatches between perception and reality, and identified several key ways to address some of our current challenges. In this report we summarize the results of this work and the four main recommendations we believe the AAS should take to make lasting positive changes. We emphasize that the goal of our report, and the GATF's work, is not to help programs select students, or to help applicants get into graduate school. Instead, we have focused on ways to make the admissions process itself more streamlined, fair, and efficient for everyone involved.

Quasars, powered by accretion onto supermassive black holes (SMBHs), exhibit significant variability, offering insights into the physics of accretion and the properties of the central engines. In this study, we analyze photometric variability and its correlation with key quasar properties, including black hole mass ($M_{\mathrm{BH}}$) and nuclear luminosities, using 915 quasars with $0\leq z<3.0$ from the AQMES sample monitored within SDSS-V. Variability metrics were derived from approximately 6-year light curves provided by the Zwicky Transient Facility -- ZTF, while SMBH masses and luminosities were obtained from the SDSS DR16 quasar catalog of \citet{wu2022catalog}. We identify a strong anti-correlation between variability amplitude and luminosity, which strengthens with redshift, and a redshift-dependent trend for $M_{\mathrm{BH}}$: a positive correlation at low redshifts, no significant correlation at intermediate redshifts, and an anti-correlation the highest redshifts. Our main finding is a robust anti-correlation between photometric variability amplitude and Eddington ratio, consistent across redshift bins. We present a general equation encapsulating this relationship, that appears to be almost free of redshift dependence, enabling predictions of quasar variability based on accretion parameters {\bf or vice-versa}. The derived relation with the Eddington ratio provides a unified framework for interpreting variability in active galactic nuclei (AGN) and facilitates future studies of quasar variability using high-cadence surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time -- LSST.

High-resolution cross-correlation spectroscopy (HRCCS) is a technique for detecting the atmospheres of close-in planets using the change in the projected planet velocity over a few hours. To date, this technique has most often been applied to hot Jupiters, which show a large change in velocity on short timescales. Applying this technique to planets with longer orbital periods requires an improved understanding of how the size of the velocity shift and the observational signal-to-noise ratio impact detectability. We present grids of simulated Keck/KPIC observations of hot Jupiter systems, varying the observed planet velocity shift and signal-to-noise ratio (SNR), to estimate the minimum thresholds for a successful detection. These simulations realistically model the cross-correlation process, which includes a time-varying telluric spectrum in the simulated data and data detrending via PCA. We test three different planet models based on an ultra-hot Jupiter, a classical hot Jupiter, and a metal-rich hot Saturn. For a ${6}\sigma$ detection suitable for retrieval analysis, we estimate a minimum velocity shift of $\Delta v_\text{pl} \sim {30, 50, 60}$ km/s, compared to an instrumental resolution of 9 km/s, and minimum SNR $\sim 370, 800, 1200$ for the respective planet models. We find that reported KPIC detections to-date fall above or near the ${6}\sigma$ limit. These simulations can be efficiently re-run for other planet models and observational parameters, which can be useful in observation planning and detection validation.

The Virgo Filament Survey (VFS) is a comprehensive study of galaxies that reside in the extended filamentary structures surrounding the Virgo Cluster, out to 12 virial radii. The primary goal is to characterize all of the dominant baryonic components within galaxies and to understand whether and how they are affected by the filament environment. A key constituent of VFS is a narrowband H$\alpha$ imaging survey of over 600 galaxies, VFS-H$\alpha$. The H$\alpha$ images reveal detailed, resolved maps of the ionized gas and massive star-formation. This imaging is particularly powerful as a probe of environmentally-induced quenching because different physical processes affect the spatial distribution of star formation in different ways. In this paper, we present the first results from the VFS-H$\alpha$ for the NGC~5364 group, a low-mass ($\log_{10}(M_{dyn}/M_\odot) < 13)$ system located at the western edge of the Virgo~III filament. We combine H$\alpha$ imaging with resolved H~I observations from MeerKAT for eight group members. These galaxies exhibit peculiar morphologies, including strong distortions in the stars and the gas, truncated H~I and H$\alpha$ disks, H~I tails, extraplanar H$\alpha$ emission, and off-center H$\alpha$ emission. These signatures are suggestive of environmental processing such as tidal interactions, ram pressure stripping, and starvation. We quantify the role of ram pressure stripping expected in this group, and find that it can explain the cases of H~I tails and truncated H-alpha for all but one of the disk-dominated galaxies. Our observations indicate that multiple physical mechanisms are disrupting the baryon cycle in these group galaxies.

Strontium (Sr) emissions have been observed across a wide range of astrophysical phenomena, from kilonovae (KNe) events to white dwarf (WD) stars. Precise and extensive atomic data for low ionisation stages of Sr is required for accurate theoretical modelling and to improve our understanding of evolutionary pathways. We calculated energy levels, Einstein A coefficients and electron-impact excitation collision strengths for Sr I, Sr III, Sr IV and Sr V at the temperature and density ranges of interest in KNe and WD research. We developed new target structures using the GRASP0 and AUTOSTRUCTURE packages. The energies and A-values arising from the new structures were found to be in good agreement with experimental and theoretical equivalents reported in the literature. Maxwellian averaged electron impact collision strengths were calculated using the R-matrix approach, as applied through the DARC and RMBP coding packages. These are presented in adf04 file format. The new data sets allowed us to construct synthetic spectra for the first five ionisation stages of Sr and probe possible density and temperature diagnostic lines. The synthetic spectra within the KNe regime revealed possible Sr IV and Sr V candidate lines at 1027.69nm and 1203.35nm respectively. These may provide useful benchmarks for determining the extent of Sr ionisation that can be reached in an evolving KNe event. Additional diagnostic lines were found to be poor across the Sr ion stages for both KNe and WD regimes due to most levels being in either coronal or Local Thermodynamic Equilibrium (LTE) conditions.

Reverberation mapping is a technique in which the mass of a Seyfert I galaxy's central supermassive black hole is estimated, along with the system's physical scale, from the timescale at which variations in brightness propagate through the galactic nucleus. This mapping allows for a long baseline of time measurements to extract spatial information beyond the angular resolution of our telescopes, and is the main means of constraining supermassive black hole masses at high redshift. The most recent generation of multi-year reverberation mapping campaigns for large numbers of active galactic nuclei (e.g. OzDES) have had to deal with persistent complications of identifying false positives, such as those arising from aliasing due to seasonal gaps in time-series data. We introduce LITMUS (Lag Inference Through the Mixed Use of Samplers), a modern lag recovery tool built on the "damped random walk" model of quasar variability, built in the autodiff framework JAX. LITMUS is purpose built to handle the multimodal aliasing of seasonal observation windows and provides evidence integrals for model comparison, a more quantified alternative to existing methods of lag validation. LITMUS also offers a flexible modular framework for extending modelling of AGN variability, and includes JAX-enabled implementations of other popular lag recovery methods like nested sampling and the interpolated cross correlation function. We test LITMUS on a number of mock light curves modelled after the OzDES sample and find that it recovers their lags with high precision and a successfully identifies spurious lag recoveries, reducing its false positive rate to drastically outperform the state of the art program JAVELIN. LITMUS's high performance is accomplished by an algorithm for mapping the Bayesian posterior density which both constrains the lag and offers a Bayesian framework for model null hypothesis testing.

We constrain the evolution of dark matter energy density over time, specifically focusing on deviation from the standard model represented by the equation $\rho_{m}\propto(1+z)^{3-\varepsilon}$, where $\varepsilon$ is a constant parameter. Utilizing a diverse array of observational datasets, including baryon acoustic oscillations (BAO) data from the first release of the Dark Energy Spectroscopic Instrument (DESI), distance priors derived from cosmic microwave background (CMB) observations by the Planck satellite, Hubble rate data obtained through the cosmic chronometers (CC) method, type Ia supernova (SNIa) data from the Panthon sample, and the data from the redshift space distortion (RSD) measurements ($f\sigma_8$), we derive stringent constraints on the deviation parameter. We find that for the model under consideration, the deviation parameter is constrained to be $\varepsilon = -0.0073^{+0.0029}_{-0.0033}$, indicating a deviation of approximately $2.4\sigma$ from the scenario where dark matter and vacuum dark energy do not interact. When compared with previous studies and alternative analyses, our findings provide corroborative evidence for an interaction between dark matter and vacuum dark energy, particularly in light of the release of BAO data from DESI.

The interplay between radiation chemistry and sublimation dynamics of condensed organic compounds on cold grains is fundamental to describe observed gas-phase and ice-phase molecular abundances in the ISM. Infrared measurements are generally used to identify molecules synthesized in irradiated ices in lab experiments, while mass spectrometric techniques have been used to monitor the products following temperature programmed desorption. The IR measurements are often used quantitatively to monitor chemical transformation of ices during the course of irradiation, but the gas phase methods applied with TPD generally do not permit quantitative branching determination. Here we combine reflection-absorption infrared spectroscopy (RAIRS) of ices with broadband rotational spectroscopy of the sublimed products, to study the branching of photoproducts produced by the VUV irradiation of condensed CH3CN and CH3CH2CN ices. This permits direct comparison between the ice-phase and gas-phase branching following temperature programmed desorption. This comparison is analogous to astronomical observations of ices in protostellar disks such as by the James Webb Space Telescope employed in conjunction with ALMA observations in the corresponding warm-up regions of the same objects. In the condensed CH3CN VUV processed ices we quantified the HCN, CH3NC, CH2CCNH, CH3NH2, and CH4 abundances. The CH3CH2CN ices also readily produced the corresponding isocyanide and HCN in addition to a significant yield of CH2CHCN. The ethyl cyanide ice produced CH3CHNH rather than CH3NH2 and no CH4 formation was observed. In the gas phase we detected the isocyanides, HCN and vinyl cyanide. The ice and gas phase relative abundances could be brought into agreement if the unknown IR band strength of the isocyanides C-N stretch is assumed to be ~3 times larger than that of the cyanides.

To understand physical processes such as mass transfer and binary evolution in X-ray binaries, the orbital parameters of the system are fundamental and crucial information. Cygnus X-3 is a high-mass X-ray binary composed of a compact object of unknown nature and a Wolf-Rayet star, which is of great interest in the context of wind-fed mass accretion and binary evolution. Here we present XRISM/Resolve high-resolution spectroscopy focusing on the Fe Ly$\alpha$ lines in its hypersoft state. We perform an orbital phase-resolved spectral analysis of the lines to study the orbital modulation of the emission and absorption lines. It is found that the emission lines reflect the orbital motion of the compact object whose estimated velocity amplitude is $430^{~~+150}_{~~-140}~~\mathrm{km\,s^{~-1}}$, while the absorption lines show a variation that can be interpreted as originating from the stellar wind. We discuss possible mass ranges for the binary components using the mass function with the estimated value of the velocity amplitude in this work, combined with the relation between the mass loss rate and the orbital period derivative and the empirical mass and mass loss rate relation for Galactic Wolf-Rayet stars. They are constrained to be $(1.3\text{-}5.1)\,M_\odot$ and $(9.3\text{-}12)\,M_\odot$ for the assumed inclination angle of $i = 25$ deg, which becomes more relaxed to $(1.3\text{-}24)\,M_\odot$ and $(9.3\text{-}16)\,M_\odot$ for $i = 35$ deg, respectively. Thus, it remains unclear whether the system harbors a black hole or a neutron star.

We present an updated reconstruction of the various dark energy equation of state (EoS), $w(a)$, employing the newly released DESI DR2 Baryon Acoustic Oscillation data. This analysis constrains the cosmological scenarios influenced by these equations through the joint examination of a range of recently available cosmological probes, specifically the Pantheon+ sample and the DESY5 sample of Type Ia Supernovae, baryon acoustic oscillations, Hubble parameter measurements derived from cosmic chronometers, and cosmic microwave background distance priors based on the Planck 2018 data. Furthermore, we provide a concise perspective on the dynamical evolution of all models and the interrelations among them. A Bayesian inference procedure is adopted to estimate the model parameters that yield the best fit to the data. The EoS remains within the phantom regime at higher redshifts, while favoring the quintessence regime in the current epoch. In this context, we propose a new Gaussian form EoS, termed BellDE, which avoids phantom behavior (\(w \geq -1\)) at higher redshifts while remaining precisely calibrated at lower redshifts. Interestingly, BellDE exhibits a transient phantom nature (\(w < -1\)) only around the transition redshift \(z \sim 0.5\), subsequently evolving into a quintessential regime (\(w > -1\)), as indicated by comparisons with the Chevallier-Polarski-Linder (CPL) and other parameterized EoS forms.

High-resolution spectroscopy (R > 25,000) has opened new opportunities to characterize exoplanet atmospheres from the ground. By resolving individual lines in planetary emission and transmission spectra, one can sensitively probe the chemical inventory and temperature structure of exoplanets. However, a significant challenge to reliable and reproducible atmospheric inferences from high-resolution datasets has been the lack of open source codes for high-resolution retrievals. Here, we present a unified high-resolution retrieval framework, for both emission and transmission spectroscopy, made publicly available within the open source POSEIDON retrieval code. Our high-resolution retrieval framework is fast (typically < 12 hours), accessible (no GPUs required), and well-documented via Python notebooks. We validate our framework by reproducing previous emission retrievals of the hot Jupiter WASP-77Ab and transmission retrievals of the ultra-hot Jupiter WASP-121b. Our results are broadly consistent with those of published works when making the same data detrending assumptions, but we demonstrate that user choices can subtly propagate into retrieved chemical abundances.

Planets undergoing convergent migration can be captured into mean-motion resonance (MMR), in which the planets' periods are related by integer ratios. The dynamics of MMR are typically considered in isolation, including only the forces between the planets and with the central star. However, the planets are often subjected to external forces that induce apsidal precessions, which may split the MMR into two sub-resonances and give rise to chaotic motion due to resonance overlap. In this study, we investigate how such externally induced differential apsidal precession affects capture into first-order $j:j+1$ MMRs. We study the restricted three-body problem for a test particle outside of an eccentric planet, with the planet undergoing outward migration. We find that capture can be sensitive to the differential apsidal precession, even when the precession rate is much smaller than the resonance overlap criterion. We identify two critical precession frequencies -- related to resonance overlap and secular apsidal resonance -- around which capture is disrupted even for very small planet eccentricity. Our results may help clarify the capture process of resonant trans-Neptunian objects by outward-migrating Neptune in early Solar System.

We present accurate mass measurements of the central supermassive black hole (SMBH) in NGC 4736 (M 94).\ We used the ``gold-standard" stellar absorption features (CO band heads) at $\sim$2.3 ${\rm \mu m}$, as opposed to gas emission lines, to trace the dynamics in the nuclear region, easily resolving the SMBH's sphere of influence. The analysis uses observations made with the integral field unit of the Near-Infrared Spectrograph (NIRSpec) on the {\it James Webb} Space Telescope and a surface brightness profile derived from {\it Hubble} Space Telescope archival images. We used Jeans anisotropic models within a Bayesian framework, and comprehensive Markov chain Monte Carlo optimization, to determine the best-fit black hole mass, orbital anisotropy, mass-to-light ratio, and nucleus kinematical inclination. We obtained a SMBH mass $M_{\rm BH}=(1.60\pm0.16)\times10^7$ M$_\odot$ (1$\sigma$ random error), which is consistent with the $M_{\rm BH}$-$\sigma$ and $M_{\rm BH}$-$M_\star$ relations. This is the first dynamical measurement of a $M_{\rm BH}$ in NGC 4736 based on the stellar kinematics observed with NIRSpec. We thus settle a longstanding inconsistency between estimates based on nuclear emission-line tracers and the $M_{\rm BH}$-$\sigma$ relation. Our analysis shows that NIRSpec can detect SMBHs with $M_{\rm BH,min}\approx 5\times10^6$ M$_\odot$ in galaxies within 5 Mpc and $\sigma\approx100$ km s$^{-1}$

In this paper, we study the dust dynamics in the molecular outflow using an analytical magnetohydrodynamical outflow model. Specifically, we investigate the maximum size of dust grains $a_{\rm d,max}$ that can be lifted by the outflow and whether they can escape into interstellar space. We also investigate the dependence of the maximum size of the dust grains on various outflow parameters, such as the mass ejection rate of the outflow $\dot{M}$, the disk size $r_{\rm disk}$, the mass of the central protostar $M_{*}$ and the internal dust density $\rho_{\rm mat}$. We find the empirical formula for the maximum dust size as a function of the outflow parameters. $a_{\rm d,max}$ depends on the parameters as $a_{\rm d,max}$ $\propto$ $\dot{M}^{1.0}$ $r_{\rm disk}^{-0.44}$ $M_{*}^{-0.82}$ $\rho_{\rm mat}^{-1.0}$. We also find that the dust grains with size of 100 $\rm \mu$m to 1 mm can be lifted by the outflow and can distribute in the well outside of the disk when the mass ejection rate of the outflow has the value of $10^{-7}\,M_{\odot}\rm \,yr^{-1}$ to $10^{-6}\,M_{\odot}\rm \,yr^{-1}$. This result is consistent with recent observations that show a correlation between the mass ejection rate of the outflow and the spectral index $\beta$ of the dust opacity at the envelope scale.

Dark matter (DM) remains one of the most significant open questions in modern physics, with its nature and interactions largely unexplored. In this study, we investigate the behavior of massive fermionic DM particles in the context of neutron stars (NSs), extending prior studies which focused on the bosonic DM. By incorporating the motion of NSs in the Galaxy and considering scenarios with and without DM self-annihilation, we demonstrate their impact on the DM capture rate and the accumulation process inside NSs. Observational data from pulsars in the Milky Way are used to place constraints on DM properties, including the mass and the DM-nucleon scattering cross-section, offering a more comprehensive picture in probing DM interactions in astrophysical environments.

The recently discovered spectroscopic binary $\rho$ Oph A is a rare magnetic hot binary system composed of two early B-type stars, comprising a non-magnetic primary (Aa) and a slightly less massive magnetic secondary (Ab). Using near-IR interferometry, we aim to resolve the system's astrometric orbit. The high-spectral resolution VLTI/GRAVITY data also enables obtaining further information about the two stellar components, and about the centrifugal magnetosphere orbiting the magnetic star. We obtained a time-series of $K$-band interferometric data from VLTI/GRAVITY, and analyzed them with the geometrical model-fitting tool PMOIRED. The continuum was used to derive the relative astrometry and relative fluxes of the two components, leading to the astrometric orbital solution. Spectro-interferometry covering the Br$\gamma$ line was then used to obtain high-angular-resolution information about the dominant magnetospheric cloud in corotation with the magnetic Ab component. The combination of the astrometric orbital solution with the published radial velocities for both components led to a 3-dimensional orbital solution, dynamical masses, and a dynamical parallax, revealing a good agreement with previous estimates and confirming the previously inferred alignment of the orbital axis and the rotation axis of the Ab component, albeit at a much higher precision. Detailed analysis of the Br$\gamma$ spectrointerferometry then revealed the changing position of the magnetospheric cloud relative to the Ab component. Comparison to the location of the cloud predicted from $\rho$ Oph Ab's oblique rotator model and H$\alpha$ emission properties demonstrated excellent agreement. We are additionally able to demonstrate that the magnetic star exhibits prograde rotation. This represents the first time that the motion of a centrifugal magnetosphere has been detected in angularly resolved observations.

Hierarchical triple systems play a crucial role in various astrophysical contexts, and therefore the understanding of their stability is important. Traditional empirical stability criteria rely on a threshold value of $Q$, the ratio between the outer orbit's pericenter distance and the inner orbit's semi-major axis. However, determining a single critical value of $Q$ is impossible because there is a range of the value of $Q$ for which both stable and unstable systems exist, referred to as the mixed-region. In this study, we introduce a novel method to assess the stability of triple systems within this mixed-region. We numerically integrate equal-mass, coplanar hierarchical triples within the mixed-region. By performing Fourier analysis of the time evolution of the semi-major axes ratio during the first 1000 inner orbital periods of the systems, we find notable features in stable systems: if the main peaks are periodically spaced in the frequency domain and the continuous components and irregularly spaced peaks are small, the system tends to be stable. This observation indicates that the evolution of stable triples is more periodic than that of unstable ones. We quantified the periodicity of the triples and investigated the correlation between the Fourier power distribution and the system's lifetime. Using this correlation, we show that it is possible to determine if a triple system in the mixed-region is stable or not with very high accuracy. These findings suggest that periodicity in orbital evolution can serve as a robust indicator of stability for hierarchical triples.

To investigate the star-forming process in nearby dwarf galaxies, we present Integral Field Units (IFU) observation of the star-forming dwarf galaxy, NGC 1522, with the Very Large Telescope (VLT)/Multi Unit Spectroscopic Explorer (MUSE) as a part of Dwarf Galaxy Integral Survey (DGIS). Our observation reveals the presence of a star-forming clumpy ring in its central region. We identify nine distinct star-forming clumps based on extinction-corrected H$\alpha$ emission-line map, with the total star formation rate (SFR) of about 0.1 $M_\odot$ yr$^{-1}$. The nine clumps are considered to be starbursts, which represent an extreme case in the local universe, without invoking major merging. We investigate the properties of ionized gas using the strong emission lines and `BPT' diagrams, in conjunction with the velocity mapping. Our analysis unveils intriguing patterns, including the positive metallicity gradient and low N/O abundance ratio. This peculiar distribution of metallicity may signify external gas accretion. Our results suggest that the ongoing star formation in NGC 1522 might be triggered and sustained by the inflow of external metal-poor gas.

Radio-loud active galactic nuclei, in particular radio-loud quasars, are fueled by accretion onto supermassive black holes and are among the most energetic sources in the Universe. While their impact on their surroundings - from the interstellar medium to the circumgalactic medium - is well recognized, the specific mechanisms remain uncertain. In this study we analyze deep Keck Cosmic Web Imager observations of the Lyman-alpha (Lya) halo surrounding the radio-loud quasar at the center of the cluster CARLA J1017+6116 at redshift z = 2.8. As is known from previous observations, the cluster hosts a high fraction of early-type galaxies, and the star formation of its spectroscopically confirmed cluster members is typical of or higher than that of galaxies on the main sequence. We find that the Lya halo extends at least 16 arcsec (128 pkpc) down to a surface brightness level of 1e-19 erg/s/cm^2/arcsec^2, with a total observed Lya luminosity of log10(L/Lsun) = 43.35 +- 0.05. The halo has distinct kinematic regions with asymmetries suggestive of complex interactions between the quasar and the intracluster medium, possibly driven by a combination of biconical feedback and episodic activity. Despite the quasar classification, our reanalysis of very long baseline interferometry data finds no evidence of extended jet structures; we instead find compact and variable radio emission that could indicate episodic jet activity or suppression by the dense interstellar medium. Combining these observations with imaging obtained with the Hubble Space Telescope, we identified one Lya-emitting source within the quasar halo. While mechanical feedback from a jet appears limited or episodic, radiative feedback likely plays a dominant role in shaping the extended Lya halo, highlighting the complex interplay between quasar-driven processes and the surrounding dense environment.

We compare the efficiency and ease-of-use of the Sparse Identification of Nonlinear Dynamics (SINDy) algorithm and Sparse Physics-Informed Discovery of Empirical Relations (SPIDER) framework in recovering the relevant governing equations and boundary conditions from data generated by direct numerical simulations (DNS) of turbulent convective flows. In the former case, a weak-form implementation pySINDy is used. Time-dependent data for two- (2D) and three-dimensional (3D) DNS simulation of Rayleigh-Benard convection and convective plane Couette flow is generated using the Dedalus PDE framework for spectrally solving differential equations. Using pySINDy we are able to recover the governing equations of 2D models of Rayleigh-Benard convection at Rayleigh numbers, R, from laminar, through transitional to moderately turbulent flow conditions, albeit with increasing difficulty with larger Rayleigh number, especially in recovery of the diffusive terms (with coefficient magnitude proportional to 1/R^0.5). SPIDER requires a much smaller library of terms and we are able to recover more easily the governing equations for a wider range of R in 2D and 3D convection and plane flow models and go on to recover constraints (the incompressibility condition) and boundary conditions, demonstrating the benefits and capabilities of SPIDER to go beyond pySINDy for these fluid problems governed by second-order PDEs. [We] demonstrat[e] the potential of machine-learning methods to validate numerical solvers and solutions for such flow problems. We also find that properties of the flow, specifically the correlation time and spatial scales, should inform the initial selection of spatiotemporal subdomain sizes [abbreviated]

Neptune-sized exoplanets are key targets for atmospheric studies, yet their formation and evolution remain poorly understood due to their diverse characteristics and limited sample size. The so-called "Neptune desert", a region of parameter space with a dearth of short-period sub- to super-Neptunes, is a critical testbed for theories of atmospheric escape and migration. The HONEI program aims to confirm and characterize the best Neptune-sized candidates for composition, atmospheric and population studies. By measuring planetary masses with high precision, we want to provide the community with optimal targets whose atmosphere can be effectively explored with the JWST or by ground-based high-resolution spectroscopy. For this purpose, we started a radial velocity follow-up campaign, using the twin high-precision spectrographs HARPS and HARPS-N, to measure the masses of TESS Neptune-sized candidates and confirm their planetary nature. In this first paper of the series, we confirm the planetary nature of two candidates: TOI-5800b and TOI-5817b. TOI-5800b is a hot sub-Neptune ($R_p=2.44\pm0.29$ $R_\oplus$, $M_p=9.4\pm1.8$ $M_\oplus$, $T_{eq} = 1108\pm20$ K) located at the lower edges of the Neptune desert ($P=2.628$ days) and is the most eccentric planet ($e\sim0.3$) ever found within $P<3$ d. TOI-5800b is expected to be still in the tidal migration phase with its parent star, a K3 V dwarf ($V=9.6$ mag), although its eccentricity could arise from interactions with another object in the system. Having a high-transmission spectroscopy metric ($TSM\sim103$), it represents a prime target for future atmospheric characterization. TOI-5817b is a relatively hot sub-Neptune ($R_p=3.08\pm0.14$ $R_\oplus$, $M_p=10.3\pm1.4$ $M_\oplus$, $T_{eq}=950\pm21$ K) located in the Neptune savanna ($P=15.610$ d) [...]

We investigate nonradial $f$-mode oscillations of protoneutron stars in full general relativity, employing equations of state described by the Brueckner-Hartree-Fock theory or the relativistic mean field model, while assuming isentropy and fixed lepton fractions for the internal structure. The validity of various universal relations for cold neutron stars involving $f$-mode characteristics and macroscopic properties of the star is confirmed for those isentropic protoneutron stars. Prospects of observations are also discussed. According to simulation results, we then model details of the thermal and trapping profiles in a PNS with the canonical mass. The corresponding $f$-mode frequencies and gravitational-wave strain amplitudes are presented. The validity of the universal relations during the evolution to the formation of a cold neutron star is confirmed.

Previous studies showed evidence of a dearth of close-in exoplanets around fast rotators, which can be explained by the combined action of intense tidal and magnetic interactions between planet and their host star. Detecting more exoplanets experiencing such interactions, with orbits evolving on short timescales, is therefore crucial to improve our understanding of the underlying physical mechanisms. For this purpose, we perform a new search for close-in non-transiting substellar companions in the Kepler data, focusing on orbital periods below 2.3 days. We focus on main-sequence solar-type stars and subgiant stars for which a surface rotation period was measured. For each star, we look for an excess in the power spectral density of the light curve, that could correspond to the signature of a close-in non-transiting companion. We compare our candidates with existing catalogues to eliminate potential contaminants in our sample, and we visually inspect the phase-folded light curve and its wavelet decomposition. We identify 88 stars, exhibiting a signature consistent with the presence of a close non-transiting substellar companion. We show that the objects in our sample are located mostly within the dearth zone, emphasising the importance of performing follow-up of such systems in order to gather observational evidence of star-planet interactions.

Lunar mean-motion resonances (MMRs) significantly shape cislunar dynamics beyond GEO, forming stable-unstable orbit pairs with corresponding intermingled chaotic and regular regions. The resonance zone is rigorously defined using the separatrix of unstable resonant periodic orbits surrounding stable quasi-periodic regions. Our study leverages the planar, circular, restricted three-body problem (PCR3BP) to estimate the (stable) resonance widths and (unstable) chaotic resonance zones of influence of the 2:1 and 3:1 MMRs across various Jacobi constants, employing a Poincar\'e map at perigee and presenting findings in easily interpretable geocentric orbital elements. An analysis of the semi-major axis versus eccentricity plane reveals broader regions of resonance influence than those predicted by semi-analytical models based on the perturbed Kepler problem. A comparison with high-fidelity 3-dimensional ephemeris propagation of several spacecraft - TESS, IBEX, and Spektr-R - in these regions is made, which shows good agreement with the simplified CR3BP model.

Vela.jl is a package for performing Bayesian pulsar timing & noise analysis written in Julia and Python. In the wideband paradigm of pulsar timing, simultaneous time of arrival and dispersion measure measurements are derived from a radio observation using frequency-resolved integrated pulse profiles and templates without splitting the observation into multiple frequency sub-bands. We describe the implementation of the wideband timing paradigm in Vela.jl, and demonstrate its usage using the NANOGrav 12.5-year wideband data of PSR J1923+2515. Vela.jl is the first software package to provide this functionality.

The wind-fed accretion of gas with an intrinsic magnetic field onto neutron stars in high-mass X-ray binaries (HMXBs) is discussed. The criteria for the implementation of quasi-spherical accretion in the system, the formation of a Keplerian accretion disk and a non-Keplerian magnetically arrested disk (MAD-accretion scenario) are formulated. It is shown that the period of the equilibrium rotation of a neutron star in the MAD-accretion scenario, in addition to the parameters of the binary system, is also determined by the velocity, temperature, and degree of magnetization of the stellar wind of its massive companion. Within the hypothesis of the equilibrium rotation, we have estimated the parameters of the stellar wind for the most fully-studied quasi-equilibrium accreting pulsars in the HMXBs corresponding to the criteria for the MAD-accretion scenario implementation. We show that the period of the equilibrium rotation of a neutron star in the system, all other things being equal, increases with the growth of the magnetization degree of the stellar wind component of its massive companion flowing out in the plane of the system's orbit. Therefore, the periods of accreting pulsars in systems with similar parameters can differ from each other by several orders of magnitude and, under favorable conditions, reach values of several thousand and even tens of thousands of seconds.

The recent detections of bright optical/infrared kilonova signals following two long-duration gamma-ray bursts (LGRBs), GRB 211211A and GRB 230307A, have significantly challenged the traditional classification of GRBs. These merger-driven LGRBs may represent a distinct GRB population. Since traditional GRB classification methods often struggle to distinguish merger-driven LGRBs from traditional merger-driven short-duration GRBs resulting from compact object mergers and collapse-driven LGRBs produced by massive stars, this work aims to explore the shared properties in terms of hardness, energy, and duration among currently observed merger-driven LGRB events, thereby identifying their observed differences from the traditional GRB population. We collect a sample of merger-driven LGRBs with known redshifts, including observed information on their main emission (ME) and whole emission (WE) phases. Treating ME and WE properties as two independent sets of information, we apply several GRB classification methodologies to explore their potential shared properties. Using the phenomenologically defined Energy-Hardness (EH) parameter, we identify a probable universal linear correlation across merger-driven LGRBs, regardless of whether their ME or WE phases are considered. We propose that such shared properties of merger-driven LGRBs are unlikely to arise from the low-redshift selection effect and they become particularly intriguing when compared with the relatively weak correlations or lack of correlation observed in traditional merger-driven short-duration GRBs (with or without extended emissions) and collapse-driven LGRBs. Our newly proposed correlation highlights the necessity for further investigation into the observations of merger-driven LGRBs and the physical mechanisms underlying the empirical correlation.

Numerical simulations predict that clumps ($\sim$1 pc) should form stars at high efficiency to produce bound star clusters. We conducted a statistical study of 17 nearby cluster-forming clumps to examine the star formation rate and gas mass surface density relations (i.e. $\Sigma_{\rm{SFR}}$ vs. $\Sigma_{\rm{gas}}$) at the clump scale. Using near-infrared point sources and Herschel dust continuum analysis, we obtained the radius, age, and stellar mass for most clusters in the ranges 0.5$-$1.6 pc, 0.5$-$1.5 Myr, 40$-$500 M$_\odot$, respectively, and also found that they are associated with $\Sigma_{\rm{gas}}$ values ranging from 80$-$600 M$_\odot$ pc$^{-2}$. We obtained the best-fit scaling relations as $\Sigma_{\rm{SFR}}$ $\propto$ $\Sigma_{\rm{gas}}^{1.46}$ and $\Sigma_{\rm{SFR}}$ $\propto$ $(\Sigma_{\rm{gas}}/t_{\rm{ff}})^{0.80}$ for the studied sample of clumps. Comparing our results with existing scaling relations at cloud and extragalactic scales, we found that while the power-law exponent obtained in this work is similar to those found at these scales, the star formation rate surface densities are relatively higher for similar gas mass surface densities. From this work, we obtained instantaneous median star formation efficiency (SFE) and efficiency per free-fall time ($\epsilon_{\rm{ff}}$) of $\sim$20% and $\sim$13%, respectively, for the studied clumps. We discuss the cause of the obtained high SFE and $\epsilon_{\rm{ff}}$ in the studied clumps and also discuss the results in the context of bound cluster formation within molecular clouds. We conclude that our results do not favour a universal scaling law with a constant value of $\epsilon_{\rm{ff}}$ in star-forming systems across different scales.

We present full-polarization observations at $\lambda = 0.87$ mm (345 GHz) conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) toward Messier 87 (M87) and seven other radio-loud active galactic nuclei (AGN). We determine polarization and Faraday properties of the targets, with linear polarization (LP) fractions spanning 1\% to 17\%, and Faraday rotation measures (RMs) exceeding $10^{5}$ rad m$^{-2}$. These RM values, 1-2 orders of magnitude higher than typically observed at $\lambda > 3$ mm, suggest denser Faraday screens or stronger magnetic fields in the (sub)millimeter emission regions. Additionally, we present the first submillimeter polarized images of the M87 jet and the observed AGN. In the M87 jet, we identify RM gradients and sign reversals, suggestive of a helical magnetic field structure extending over kiloparsec scales. These observations were part of the ALMA Band~7 Very Long Baseline Interferometry (VLBI) commissioning during the April 2021 Event Horizon Telescope (EHT) campaign. The results provide essential constraints for calibrating, analyzing, and interpreting VLBI data from the EHT at 345 GHz, representing a critical step toward submillimeter VLBI imaging.

The GeV-TeV {\gamma}-ray emission is observed from the direction of the source Sgr A^*, which is identified with the SMBH in the centre of our Galaxy. According to some models this {\gamma}-ray emission might originate in the very compact, central region identified with the direct surrounding of the SMBH. Sgr A^* is surrounded by a massive nuclear star cluster. Occasionally these stars might pass close to the line of sight of the observer, resulting in partial absorption of the sub-TeV {\gamma}-ray emission. We investigate the conditions at which an absorption feature appears in the {\gamma}-ray light curves from the Galactic Centre or nuclei of other galaxies containing SMBHs. The detection of such features would allow to obtain constraints on the emission site of {\gamma} rays in active galaxies. We calculate the optical depths for {\gamma} rays in the radiation of individual massive stars, or from the whole population of stars for different parameters of the star cluster. We show that the observer with a line of sight close to the orbital plane of the star can register a {\gamma}-ray absorption dip lasting from a fraction of a day up to a few tens of days. The combined effect of the bulk absorption on the whole population of stars instead can produce a flickering of the observed emission of a red-noise type in the power spectrum of the emission. Predicted absorption features in the sub-TeV {\gamma}-ray light curves from galaxies with SMBHs should be easily detectable by the Large-Sized Telescopes of the Cherenkov Telescope Array Observatory. The discovery of such absorption features provides a unique indication that the {\gamma}-ray production is occurring in a compact region, close to the horizon of the SMBH.

Evidence suggests that the Milky Way (MW) underwent a major collision with the Gaia-Sausage/Enceladus (GSE) dwarf galaxy around cosmic noon. While GSE has since been fully disrupted, it brought in ex-situ stars and dynamically heated in-situ stars into the halo. In addition, the gas-rich merger may have triggered a burst of in-situ star formation, potentially giving rise to a chemically distinct stellar component. We investigate the region of phase space where stars formed during the GSE merger likely reside, and retain distinct chemical and dynamical signatures. Building on our previous investigation of metallicity ([Fe/H]) and vertical angular momentum ($L_Z$) distributions, we analyse spectroscopic samples from GALAH, APOGEE, SDSS, and LAMOST, combined with Gaia kinematics. We focus on high proper-motion stars as effective tracers of the phase-space volume likely influenced by the GSE merger. To correct for selection effects, we incorporate metallicity estimates derived from SDSS and SMSS photometry. Our analysis reveals that low-$\alpha$ stars with GSE-like kinematics exhibit bimodality in [Na/Fe] and [Al/Fe] at $-1.0 \lesssim {\rm [Fe/H]} \lesssim -0.4$. One group follows the low light-element abundances of GSE stars, while another exhibits enhanced values. These low-$\alpha$, high-Na stars have eccentric orbits, but are more confined to the inner MW. A subset of these stars overlaps with the Eos population, representing only the high-eccentricity portion of a broader structure. After correcting for sampling biases, we find that the population comprises $\sim7\%$ relative to the GSE debris. These results suggest that the low-$\alpha$, high-Na stars formed in a compact region, likely fueled by gas from the GSE progenitor, analogous to clumpy star-forming clouds seen in high-redshift galaxies. Such stars may trace the first sparks of more extensive merger-driven starburst activity.

Very massive stars (VMS) play a fundamental role in astrophysics due to their winds and supernovae (SN), and their role as massive black hole (BH) progenitors. However, their origin and evolution remain a significant challenge. Recent theoretical work and observations suggest that VMS approaching the Eddington limit may experience mass loss above the standard wind predictions. This study investigates how enhanced winds influence single and binary VMS evolution, observable properties, and resulting BH populations. New stellar wind prescriptions, sensitive to the Eddington parameter ($\Gamma_e$) and the luminosity-to-mass ratio, were implemented into the stellar evolution code PARSEC v2.0. These updated single-star tracks (100 - 600 M$_{\odot}$ at Z=0.006) were used to model the VMS population in the Tarantula Nebula and integrated into the SEVN binary evolution code. The $\Gamma_e$-enhanced single-star tracks match observed VMS properties better than standard models. Explaining the most massive star, R136a1, through a single-star origin suggests a zero-age main sequence (ZAMS) mass limit of $<$ 400 M$_{\odot}$ regardless of the wind recipe used. However, binary stellar mergers also offer a suitable origin for R136a1 and other observed VMS, potentially lowering the upper ZAMS mass limit by ~100 M$_{\odot}$. In binaries, enhanced winds inhibit main-sequence stellar mergers and limit BH production above the pair-instability mass gap's lower edge (~50 M$_{\odot}$). Binary BHs merging in a Hubble time with enhanced winds yield more primary BHs above 30 M$_{\odot}$ and enable secondary BHs between 30-40 solar masses, a range not found with standard stellar winds at LMC metallicity. This study highlights the crucial role that stellar winds and binary interactions play in VMS evolution and offers predictions relevant for interpreting VMS observations and gravitational wave source origins.

The fundamental plane (FP) relation connects gamma-ray luminosity to intrinsic pulsar properties, offering the potential to estimate distances for radio-quiet (RQ) gamma-ray pulsars, where direct measurements are often unavailable. The Fermi Third Pulsar Catalog presents spectral data for 294 gamma-ray pulsars, including 72 RQ pulsars, of which only 9 have known distances. This study investigates the FP relation's potential to predict distances for RQ gamma-ray pulsars using machine learning (ML) approaches. Ordinary least-squares regression was employed alongside ML methods, including random forest and support vector regression, to predict RQ gamma-ray pulsar distances. To ensure robustness, the analysis considered spectral cutoff significance and outlier data. Results confirm that the FP relation is valid only for pulsars exhibiting significant gamma-ray cutoffs, with FP exponents closely matching theoretical expectations. It was shown that gamma-ray emission origins significantly favor the curvature radiation regime over the synchrotron regime at the 4.2 sigma level. The distances for 62 RQ pulsars, for which no traditional measurements exist, are predicted for the first time. The luminosity and spatial distributions of the considered RQ pulsar population match known pulsar distributions. Predictions for RQ pulsars with known distances are consistent with measured data. This study provides a proof of principle that the FP relation, combined with ML methods, is a promising tool for distance estimation in RQ gamma-ray pulsars, using gamma-ray emission directly for the first time in pulsar distance estimates. Future improvements can be achieved with larger data sets, precise spectral cutoff determinations, and corrections for key factors like the beaming factor.

We present a $z=0$ census of nuggets -- compact galaxies that form via gas-rich violent disk instability -- within the luminosity- and volume-limited REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntext (ECO) surveys. We use random forest (RF) models to predict near-ultraviolet (NUV) magnitudes for ECO galaxies that lack high-quality NUV magnitudes, thereby doubling the number of ECO galaxies with reliable extinction-corrected star formation rates (SFRs) and red/green/blue classifications based on specific SFRs (sSFRs). The resulting RF-enhanced RESOLVE+ECO nugget sample allows us to analyze rare subpopulations -- green nuggets and nuggets with active galactic nuclei (AGN) -- likely associated with quenching. Green nuggets are more similar to red nuggets than to blue nuggets in halo mass ($M_{\text{halo}}$) distribution, with both red and green nuggets being found mainly at $M_{\text{halo}} \ge 10^{11.4} M_\odot$, where permanent halo quenching is predicted. At these masses, the AGN frequency for green nuggets is higher ($\text{48.2\%}^{+5.3\%}_{-5.3\%}$) than for either blue ($\text{39.2\%}^{+2.9\%}_{-2.8\%}$) or red ($\text{29.3\%}^{+3.0\%}_{-2.8\%}$) nuggets. Between $M_{halo} = 10^{11.4}-10^{12} M_\odot$, at the onset of permanent quenching, the AGN frequency for green nuggets is nearly double the frequency for blue or red nuggets, implying AGN are associated with this transition. At $M_{halo} < 10^{11.4} M_\odot$, where temporary cyclic quenching is expected, the AGN frequency for blue nuggets ($\text{7.5\%}^{+1.4\%}_{-1.2\%}$) is lower than for either green ($\text{31.3\%}^{+8.7\%}_{-7.5\%}$) or red ($\text{18.8\%}^{+11.5\%}_{-7.8\%}$) nuggets. At all masses, nuggets with AGN have reduced sSFRs and likely also atomic gas content compared to nuggets without AGN, but the quenching is more extreme below $M_{halo} = 10^{11.4} M_\odot$.

Correlated time-of-arrival measurements by pulsar timing arrays (PTAs) have provided a new means of constraining astrophysical or cosmological models that produce a gravitational wave (GW) background. For this work, we discuss the implications of PTA observations for Gauss-Bonnet (GB) inflationary models through the production and propagation of inflationary GWs. We show that our GB inflationary scenario is consistent with present PTA and cosmological data. A blue-tilted tensor power spectrum supported by PTAs can be naturally accommodated in GB inflation. Using observational constraints, we derive general conditions for the inflaton potential and the GB coupling function, suggesting that in GB inflation, the inflaton must climb up the potential before rolling downhill and reaching the end of inflation. We provide two concrete GB inflationary models to demonstrate the viability of this mechanism.

Type II solar radio bursts are generated by electrons accelerated by coronal shock waves. They appear in dynamic spectra as lanes drifting from higher to lower frequencies at the plasma frequency and its harmonic. These lanes can often be split into two or more sub-bands that have similar drift rates. This phenomenon is called band-splitting, and its physical origins are still under debate. Our aim is to investigate the origin of band-splitting using novel imaging and spectropolarimetric observations of a type II solar radio burst from the Low Frequency Array (LOFAR). We used LOFAR imaging at multiple frequencies and time steps to track the locations of the radio sources corresponding to the two components of the band-split emission lane. In addition, we estimated the degree of circular polarisation (dcp) for both components using LOFAR's full Stokes dynamic spectra. From the imaging of the type II burst, we found two close but clearly separated emission regions clustered over several frequencies spanning each split band. One emission region corresponds to the lower frequency band and the other to the higher frequency band of the split lane. Using the full Stokes dynamic spectra, we also found the dcp to be very similar for both bands. The two distinct emission regions suggest that the split bands originate from two separate regions at the shock. The similar values of dcp for both sub-bands correspond to similar values of magnetic field strength in the two regions and indicate little to no change in the emission region plasma. Thus, our findings are in contradiction with previous theories, which have suggested that split bands originate in the same region but upstream and downstream of the shock. Instead, our results suggest that both bands originate in two separate upstream regions since we find a clear separation in locations and no magnetic compression.

The Atacama Cosmology Telescope (ACT) has recently reported updated measurements of the scalar spectral index $n_s$, which exhibit tension with predictions from many conventional inflationary models when combined with other observational data. In this work, we adopt a parameterization of the spectral index of the form $n_s = 1 - p/(N + \alpha)$ and reconstruct an inflationary potential that is consistent with the latest ACT data. The resulting potential takes the form of an inverse-power plateau, $V(\phi)=V_0[1-(M/\phi)^n]$, where the power index is given $n = 2(p-1)/(2-p)$. To match ACT constraints, $n$ can be chosen as $1$, $2$, $3$, $4$, or $5$. The corresponding tensor-to-scalar ratio is $r \approx 16(p-1)/[C (N+\alpha)^p]$ with $C= 2^{2p-1} \left[\sqrt{p-1}/(2-p)\right]^{2p-2} /M^{2p-2}$. The reconstructed potential corresponds to the form of the Polynomial $\alpha$-attractor potential. Since the reconstruction is model-independent, any inflationary model yielding predictions of the form $n_s = 1 - p/(N + \alpha)$ and satisfying observational constraints will exhibit a potential profile at the slow-roll region closely resembling that of the Polynomial $\alpha$-attractor.

Recent pulsar timing array (PTA) observations have reported evidence of a gravitational wave background (GWB). If supermassive black holes (SMBHs) are indeed the primary source of this signal, future PTA observations, such as those from the Square Kilometer Array (SKA), are expected to simultaneously capture multiple continuous gravitational waves (CGWs) emitted by bright individual SMBH binaries alongside a gravitational wave background (GWB). To address this anticipated scenario in the SKA era, we revisit the F-statistic, a detection method for single source signals in PTA datasets, and introduce a new modeling that accounts for unresolved GWs as a stochastic GWB. Here, we applied this improved F-statistic to the mock datasets that include both CGW and GWB and evaluated how accurately F-statistic can identify the parameters of CGW. As a result, we demonstrate that our approach can successfully improve the estimation of the sky position and the amplitude of CGW, particularly when the GWB is dominant over white noise. This work serves as an initial step toward developing an efficient and robust algorithm based on the F-statistic for future PTA observations.

Precise and accurate estimation of cosmological parameters is crucial for understanding the Universe's dynamics and addressing cosmological tensions. In this methods paper, we explore bio-inspired metaheuristic algorithms, including the Improved Multi-Operator Differential Evolution scheme and the Philippine Eagle Optimization Algorithm (PEOA), alongside the relatively known genetic algorithm, for cosmological parameter estimation. Using mock data that underlay a true fiducial cosmology, we test the viability of each optimization method to recover the input cosmological parameters with confidence regions generated by bootstrapping on top of optimization. We compare the results with Markov chain Monte Carlo (MCMC) in terms of accuracy and precision, and show that PEOA performs comparably well under the specific circumstances provided. Understandably, Bayesian inference and optimization serve distinct purposes, but comparing them highlights the potential of nature-inspired algorithms in cosmological analysis, offering alternative pathways to explore parameter spaces and validate standard results.

Understanding exoplanet interiors is crucial for interpreting atmospheric observations and constraining their evolution and formation. However, due to limited observational constraints, interiors structures remain poorly understood. In this work, we investigate how new observational constraints, such as the Love number and atmospheric metallicity, improve our ability to characterize the interiors of hot Jupiters, planets for which Love number measurements are most feasible. We assess the precision required in Love number measurements to derive interior properties using both a simple two-layer homogeneous model and a more complex dilute core model. To account for observational uncertainties, we implement a retrieval framework. Our results show that accurately constraining core mass and bulk metallicity requires a high-precision Love number measurement, better than 40% for a homogeneous model and 15% for a dilute core model, along with an atmospheric metallicity measurement. We apply our retrieval framework to five planets with observed Love numbers, of which only WASP-19Ab has both an atmospheric metallicity constraint and a highly precise Love number measurement, with a precision of 12%. For this flagship planet, both models confirm the presence of a core, although we cannot yet distinguish between a compact core or diluted core. With the homogeneous model, we find a core mass fraction of $0.21^{+0.05}_{-0.04}$, corresponding to $79^{+21}_{-18}$ $M_\mathrm{earth}$. Upcoming JWST observations are expected to provide high-precision Love number measurements and precise atmospheric data, offering new insights into the structure and composition of gas giant interiors.

Early-type stars are key drivers of Galactic chemical evolution, enriching the interstellar medium with alpha elements through powerful stellar winds and core-collapse supernovae, fueled by their short lifetimes and high masses. However, their spectra remain challenging to analyse due to rapid rotation, weak metal lines, and non-LTE effects. While large spectroscopic surveys provide extensive low-resolution data, extracting reliable parameters remains difficult due to methodological limitations for hot stars. Our goal is to develop a unified framework combining data-driven and synthetic spectral approaches to determine atmospheric parameters and abundances for hot stars using low-resolution spectra, addressing limitations in current methodologies while retaining critical spectral information. We present a hybrid approach integrating the Stellar LAbel Machine (SLAM) and the Payne frameworks, for low-resolution ($R\sim 1800$) spectra from LAMOST DR9. Our method preserves full spectral information including Balmer series and metal-line blends, employing neural-network interpolation for efficient parameter estimation ($T_\mathrm{eff}$, $\log g$, and $v\sin i$) and abundance determination for O, Mg, Si, and Fe, across 8000 - 20000 K. We derive stellar parameters and abundances for 315,822 stars with $\mathrm{SNR} \geqslant 10$ in the $r$-band. Additionally, we detect abundance trends ([$\alpha$/Fe]-[Fe/H]) that exhibit temperature-dependent systematics and a distinct $\alpha$-poor stellar population within $0.0 \leqslant \mathrm{[Fe/H]} \leqslant 0.5$ dex. The radial abundance gradients are negative and consistent with that derived from Cepheids, with a slope of $-0.070\pm0.007$ in \feh in the region $6 \leqslant R_\mathrm{GC}\leqslant 15$ kpc.

In the context of a new systematic study of the properties of the most compact and massive star clusters in the Large Magellanic Cloud (LMC), here we present the determination of the chronological age, the structural parameters, and the dynamical age of NGC 1754. We used high-resolution images taken with the WFC3/HST instrument, both in optical and near-ultraviolet filters. The high quality of the images made it possible to construct the star density profile from resolved star counts, and to fit the observed profile with an appropriate King model to obtain the structural parameters (e.g. core, half-mass, and tidal radii). Our findings confirm that NGC 1754 is a very compact globular cluster with a core radius of only 0.84 pc. The analysis of the same dataset allowed us to confirm a very old age ($t=12.8\pm0.4$ Gyr) for this system, thus further consolidating the indication that the process of globular cluster formation started at the same cosmic time both in the LMC and in the Milky Way, independently of the characteristics of the host environment. We have also used the empirical method called ``dynamical clock'' to estimate the dynamical age of the system. This consists of quantifying the degree of central segregation of blue straggler stars (BSSs) using the $A^+_{rh}$ parameter, which is defined as the area enclosed between the cumulative radial distribution of BSSs and that of a reference (lighter) population. This method yielded a value of $A^+_{rh}=0.31\pm0.07$, which is the highest measured so far for LMC clusters, pointing to an advanced dynamical age for the cluster, possibly on the verge of core collapse. The results presented here for NGC 1754 confirm that the natural dynamical evolution of globular clusters plays a role in shaping the age-core radius distributions observed in the LMC.

Though missions such as Kepler, K2, and TESS have discovered $>$2,000 sub-Neptune and Neptunian planets, there is a dearth of such planets at close-in (P$\lesssim$3 days) orbits. This feature, called the Neptune desert or the evaporation desert, is believed to be primarily shaped by planetary migration and photoevaporation. However, this region is not completely devoid of planets--a small number of very hot Neptunes reside within the desert. These planets provide an opportunity to directly probe the effects of migration and photoevaporation. We present confirmation of TOI-5800 b, an eccentric sub-Neptune on a $\approx$2.6 day period that is likely actively undergoing tidal migration. We use radial velocity measurements from the Carnegie Planet Finder Spectrograph (PFS) to constrain TOI-5800 b's mass and eccentricity. We find that it has an unusually high eccentricity (0.39$\pm$0.07) for its short orbit. TOI-5800 is therefore currently experiencing high levels of tidal heating as it moves into the desert. Ranked as a top candidate for transmission and emission spectroscopy within its temperature and radius regime, TOI-5800 b is a prime target for atmospheric characterization with JWST. TOI-5800 b presents a unique opportunity to study the atmosphere of a planet undergoing tidal heating and to probe the composition of sub-Neptune planets.

Recent analyses on the properties of the central compact object in the HESS J1731-347 remnant and the PSR J1231-1411 pulsar indicated that these two compact objects are characterized by similar (low) masses and possibly different radii. This paper aims at reconciling the aforementioned measurements by utilizing the widely employed color-flavor locked (CFL) MIT bag model. The main objective is related to the examination of the acceptable values for the color superconducting gap $\Delta$ and the bag parameter $B$. Furthermore, our analysis involves two distinct hypotheses for the nature of compact stars. Firstly, we considered the case of absolute stability for strange quark matter and we found that it is possible to explain both measurements, while also respecting the latest astronomical constraints on the masses and radii of compact stars. Secondly, we studied the case of hybrid stellar matter (transition from hadrons to quarks), and concluded that, when early phase transitions are considered, the simultaneous reconciliation of both measurements leads to results that are inconsistent to the existence of massive compact stars. However, we showed that all current constraints may be satisfied under the consideration that the HESS J1731-347 remnant contains a slow stable hybrid star.

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87*, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT) 2018 array, including improved $(u,v)$-coverage from the Greenland Telescope, we measure the ring's ellipticity using five independent imaging methods, obtaining a consistent average value of $\tau = 0.08_{-0.02}^{+0.03}$ with a position angle $\xi = 50.1_{-7.6}^{+6.2}$ degrees. To interpret this measurement, we compare against General Relativistic Magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including thermal or non-thermal electron distribution function, spins, and ion-to-electron temperature ratios in both low and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in non-thermal models and models with higher jet emission. These results indicate that the ellipticity measured from the \m87 emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.

Polars and low-accretion rate polars (LARPs) are strongly magnetic cataclysmic variables. Mediated by the magnetic field of the white dwarf, their spin and binary orbit are (mostly) synchronized. They play an important role in our understanding of close binary evolution and the generation of strong magnetic fields in white dwarfs. Thanks to X-ray all-sky surveys, optical variability, and spectroscopic surveys, the number of polars and LARPs has grown from just a few in the 1980s to more than 200 today. Follow-up studies are facilitated by the systematic compilation of these systems presented here, which is also made available as an online resource. Yearly updates are planned, and community input is highly appreciated.

Coronal mass ejections (CMEs) and coronal jets are two of the best-studied forms of solar eruptions, with the same underlying physics. Previous studies have presented partial eruptions producing coronal jets. We report, for the first time, a detailed analysis of three partial eruptions that segmented after the eruption began and produced CMEs. We use multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar TErrestrial RElations Observatory, and Solar Orbiter to reconstruct the three-dimensional evolution of the events. The magnetic field extrapolations indicated that the initial filaments were overlaid by pseudostreamer structures, and the splitting occurred after the interaction between the filament-supporting flux and external open field through their null points. The breakout mechanism seems to play a key role in both halting the system and splitting it. However, this initial evolution and consequent splitting into an erupting flux rope above the prominence segment that failed to erupt poses severe challenges to theories of solar eruptions.

The rotational evolution of stars is still an open question of stellar physics because of the numerous phenomena that can contribute to the distribution of angular momentum. This paper aims at determining the time scale over which a rotating early-type star relaxes to a steady baroclinic state or, equivalently, in which case its nuclear evolution is slow enough to let the evolution of the star be modelled by a series of quasi-steady states. We investigate the damping time scale of baroclinic and viscous eigenmodes that are potentially excited by the continuous forcing of nuclear evolution. We first investigate this problem with a spherical Boussinesq model. Since much of the dynamics is concentrated in the radiative envelope of the star, we then improve the realism of the modelling by using a polytropic model of the envelope that takes into account a realistic density profile. The polytropic model of the envelope underlines the key role of the region at the core-envelope interface. The results of evolutionary models recently obtained with two-dimensional axisymmetric ESTER models turn out to be a consequence of the slow damping of viscous modes. Using a vanishing Prandtl number appears to be too strong an approximation to explain the dynamics of the models. Baroclinic modes previously thought as good candidates of this relaxation process turn out to be too quickly damped. The dynamical response of rotating stars to the slow forcing of its nuclear evolution appears as a complex combination of non-oscillating eigenmodes. Simple Boussinesq approach are not realistic enough to explain this reality. The present work underlines the key role of layers near the core-envelope interface in an early-type star and also the key role of any angular momentum transport mechanism, here played by viscosity, for early-type stars to reach critical rotation, presumably associated with the Be phenomenon.

The rotation period of a star is an important quantity that provides insight into its structure and state. For stars with surface features like starspots, their periods can be inferred from brightness variations as these features move across the stellar surface. TESS, with its all-sky coverage, is providing the largest sample of stars for obtaining rotation periods. However, most of the periods have been limited to shorter than the 13.7-day TESS orbital period due to strong background signals (e.g., scattered light) on those timescales. In this study, we investigated the viability of measuring longer periods (> 10 days) from TESS light curves for stars in the Northern Continuous Viewing Zone (NCVZ). We first created a reference set of 272 period measurements longer than 10 days for K & M dwarfs in the NCVZ using data from the Zwicky Transient Facility (ZTF) that we consider as the "ground truth" given ZTF's long temporal baseline of 6+ years. We then used the unpopular pipeline to de-trend TESS light curves and implemented a modified Lomb-Scargle (LS) periodogram that accounts for flux offsets between observing sectors. For 179 out of the 272 sources (66%), the TESS-derived periods match the ZTF-derived periods to within 10%. The match rate increases to 81% (137 out of 170) when restricting to sources with a TESS LS power that exceeds a threshold. Our results confirm the capability of measuring periods longer than 10 days from TESS data, highlighting the dataset's potential for studying slow rotators.

Mitigating risks posed by solar energetic particles (SEPs) to operations and exploration in space and Earth's atmosphere motivates the development of advanced, synergistic approaches for monitoring, modeling, and analyzing space weather conditions. The consequences of SEPs and their interactions with the near-Earth space environment are numerous, including elevated radiation levels at aviation altitudes during major events, satellite damage, and health risks to astronauts, resulting in economic impacts and potential hazards for space exploration. This contribution will present a high-level overview of the operational requirements and research capabilities for SEP event environment monitoring and forecasting that were highlighted during a workshop at Georgia State University, held on October 16-19, 2024. Specifically, it summarizes the presented activities concerning the following: (1) Identifying needs for SEP event forecasting and nowcasting, including practical forecast timeframes; (2) Reviewing availability and coverage of the current observational data and identifying tangible data resources for research, operations and the R2O2R loop; (3) Mapping existing forecast capabilities and identifying meaningful modeling advances for research and operations.

Recently, the gravitational wave (GW) event for black hole (BH)-BH mergers, S241125n, has been reported to be associated with a short gamma-ray burst (GRB) and X-ray afterglow emission. Such an association could potentially unveil the environments of mergers and provide attractive targets for multi-messenger observations. We summarize these observations and model it as a binary BH merger occurring within an active galactic nucleus (AGN), where the merger remnant accretes disk material at hyper-Eddington rates. The resulting jet could lead to the GRB associated with the GW event. The GRB, detected by Swift-BAT, exhibits a Comptonized spectrum with an unusually soft photon index, which is consistent with emission from the jet interacting the emission associated with the dense AGN disk environment. Its X-ray afterglow shows an unusually hard spectrum, indicating possible strong absorption by a high column density typical of AGN disks. We highlight the importance of identifying the host galaxy and conducting more sensitive infrared observations to test the model.

With the goal of searching for very low modulation amplitudes among fundamental mode RR Lyrae stars and assess their incidence rate, we performed a survey of 36 stars observed by the Kepler satellite during the entire four-year period of its mission. The search was conducted by a task-oriented code, designed to find low-amplitude signals in the presence of high-amplitude components and instrumental systematics. We found 7 new modulated stars and negate one earlier claimed star, whereby increasing the number of known Blazhko stars from 17 to 24 and yielding an observed occurrence rate of 67% for the Kepler field. Six of the new stars have the lowest modulation amplitudes found so far, with ~250 ppm Fourier side-lobe amplitudes near the fundamental mode frequency. Because of the small sample size in the Kepler field, we extended the survey to 12 campaign fields observed by K2, the ``two-wheeled'' mission of Kepler. From the 1061 stars we found 514 Blazhko stars. After correcting for the short duration of the time spent on each field, and for the noise dependence of the detections, we arrived at an underlying occurrence rate of ~75% - likely a lower limit for the true rate of Blazhko stars in the K2 fields.

Aims: The precision of cosmological constraints from imaging surveys hinges on accurately estimating the redshift distribution $ n(z) $ of tomographic bins, especially their mean redshifts. We assess the effectiveness of the clustering redshifts technique in constraining Euclid tomographic redshift bins to meet the target uncertainty of $ \sigma ( \langle z \rangle ) < 0.002 (1 + z) $. In this work, these mean redshifts are inferred from the small-scale angular clustering of Euclid galaxies, which are distributed into bins with spectroscopic samples localised in narrow redshift slices. Methods: We generate spectroscopic mocks from the Flagship2 simulation for the Baryon Oscillation Spectroscopic Survey (BOSS), the Dark Energy Spectroscopic Instrument (DESI), and Euclid's Near-Infrared Spectrometer and Photometer (NISP) spectroscopic survey. We evaluate and optimise the clustering redshifts pipeline, introducing a new method for measuring photometric galaxy bias (clustering), which is the primary limitation of this technique. Results: We have successfully constrained the means and standard deviations of the redshift distributions for all of the tomographic bins (with a maximum photometric redshift of 1.6), achieving precision beyond the required thresholds. We have identified the main sources of bias, particularly the impact of the 1-halo galaxy distribution, which imposed a minimal separation scale of 1.5 Mpc for evaluating cross-correlations. These results demonstrate the potential of clustering redshifts to meet the precision requirements for Euclid, and we highlight several avenues for future improvements.

Physical properties of galaxies are correlated with their local environment. Quantifying these environmental correlations is crucial for a better understanding of galaxy formation and evolution. In this work, we investigate how galaxy properties are correlated with the environment through spatial clustering measurements of galaxies. Using two-point correlation functions and marked correlation functions, we measure and compare the environmental dependence of colour, stellar mass, luminosities in the $u$, $g$, $r$, $J$, and $K$ bands, star formation rate, and specific star formation rate. We use galaxy samples from the southern (G02 and G23) regions of the Galaxy and Mass Assembly (GAMA) survey. Furthermore, we explore how redshift completeness affects clustering measurements by comparing different subsets of the G02 region with varying redshift completeness. We show that the $u-r$ and $g-r$ colours correlate the most with the local environment, with stellar mass being the next most reliable indicator of the environment. We also demonstrate that redshift completeness has a significant effect on clustering measurements.

Near infrared (NIR) 0.9--2.5$\mu$m spectra of the remarkable recurrent nova M31N 2008-12a were obtained on days 6.3 and 10.3 after discovery of its 2024 outburst, and are the first NIR spectra of this object. The only prominent line seen in the spectra is that of HeI 1.083$\mu$m, on day 6.3. Apart from this HeI line, there are only two other weak emission features: one at 1.0786$\mu$m, suggested to be the [FeXIII] 1.075$\mu$m coronal line, and one unidentified feature at 1.0969$\mu$m. The observed full width at half maximum of the HeI line on day 6.3 (1350 km s$^{-1}$) is consistent with the behaviour of optical HeI lines during earlier eruptions of this RN, which show that the nova ejecta decelerate as they interact with the secondary's wind. The HeI 1.083$\mu$m line faded rapidly, and was absent in the day 10.3 spectrum, along with any other emission lines. We use the relative strengths of optical He and H lines in previous eruptions to estimate the expected strengths of the HeI 1.083$\mu$m line and of other infrared (including coronal) lines at 6.3 days after eruption. Our findings are consistent with the infrared spectra we observed during the 2024 eruption. We apply our analysis to account for the relative weakness of NIR coronal emission in known Galactic recurrent novae with giant secondaries.

Solar eruptive behavior is often modeled with magnetohydrodynamic simulations of magnetic flux emergence. The usual geometry considered is that of a horizontal cylindrical magnetic flux tube. An alternative is the toroidal tube geometry which has some advantages over the cylindrical one, namely, that the emerging bipolar pair of sunspots do not drift apart indefinitely. In addition to the toroidal tube, we include an oblique, ambient field in the simulation, which leads to the production of increased activity from the interaction of ambient and emerging fields. Letting the simulation run for a long time reveals that six eruptive jets take place after an initial reconnection jet. In an attempt to better understand the eruptive activity we examine the evolution of free energy and relative helicity of the coronal volume, as well as, the magnetic tension forces acting on the magnetic system. We find that all quantities decrease in magnitude during the eruptive jets and rebuild afterwards. This recurrent activity continues even after flux emergence ceases and stops once the examined quantities saturate to nearly constant values.

Genetic algorithm (GA) belongs to a class of nature-inspired evolutionary algorithms that leverage concepts from natural selection to perform optimization tasks. In cosmology, the standard method for estimating parameters is the Markov chain Monte Carlo (MCMC) approach, renowned for its reliability in determining cosmological parameters. This paper presents a pedagogical examination of GA as a potential corroborative tool to MCMC for cosmological parameter estimation. Utilizing data sets from cosmic chronometers and supernovae with a curved $\Lambda$CDM model, we explore the impact of GA's key hyperparameters -- such as the fitness function, crossover rate, and mutation rate -- on the population of cosmological parameters determined by the evolutionary process. We compare the results obtained with GA to those by MCMC, analyzing their effectiveness and viability for cosmological application.

Interpreting the data from radio detectors for extensive air showers typically relies on Monte-Carlo based simulation codes, which, despite their accuracy are computationally expensive and present bottlenecks for analyses. To address this issue we developed a novel method called template synthesis, which synthesises the radio emission from cosmic ray air showers in seconds. This hybrid approach uses a microscopically simulated, sliced shower (the origin) as an input. It rescales the emission from each slice individually to synthesise the emission from a shower with different properties (the target). In order to be able to change the arrival direction during synthesis, we adjust the phases based on the expected geometrical delays. We benchmark the method by comparing synthesised traces to CoREAS simulations over a wide frequency range of [30, 500] MHz . The synthesis quality is primarily influenced by the difference in $X_{max}$ between the origin and target shower. When $\Delta X_{max} \leq 100 g/cm^2$ , the scatter on the maximum amplitudes of the geomagnetic traces is at most 4%. For the traces from the charge-excess component this scatter is smaller than 6%. We also observe a bias with $\Delta X_{max}$ up to 5% for both components, which appears to depend on the antenna position. Since the bias is symmetrical around $\Delta X_{max} = 0 g/cm^2$, we can use an interpolation approach to correct for it. We have implemented the template synthesis algorithm in a Python package called \texttt{SMIET}, which includes all the necessary parameters. This package has been successfully tested with air showers with zenith angles up to $50^{\circ}$ and can be used with any atmosphere, observation level and magnetic field. We demonstrate that the synthesis quality remains comparable to our main benchmarks across various scenarios and discuss use cases, including machine-learning-based analyses.

We investigate the generation of magnetic fields above black hole accretion discs due to the non-zero curl of the disc radiation field. By self consistently computing the components of the radiation flux and their curl, we show that the rotational nature of the radiation field induces charge separation, leading to magnetic field generation in the plasma above the disc. Solving the magnetohydrodynamic equations, we derive the time evolution of these fields and demonstrate that they grow over astrophysically relevant timescales. For a standard Keplerian accretion disc, the produced magnetic fields remain weak, on the order of a few Gauss, consistent with previous predictions. However, when a luminous corona is present in the inner disc region ($r_d < 3-10 r_g$), the generated fields reach dynamically significant strengths of up to $10^5$ Gauss where the magnetic energy density approaching few percentage of equipartition with the gas pressure. These fields develop within realistic growth timescales (such as viscous timescale) and can be dynamically significant in governing disc and jet evolution. Our findings suggest that radiation-driven magnetic fields play a crucial role in accretion flow magnetization, influencing both disc dynamics and observational signatures. The predicted field strengths could affect the thermal emission, synchrotron radiation, and polarization properties of black hole accretion systems, with implications for X-ray binaries, AGN, and jet formation. Future numerical simulations and high-resolution polarimetric observations, such as those from IXPE, eXTP, and EHT, may provide observational confirmation of our findings.

Fast radio bursts (FRBs) are mysterious millisecond-duration radio transients from the distant universe. Some of them repeat, while others do not. In order to explore their origin, periodic examinations have been conducted on repeating FRBs. Most of them show irregular properties, including burst rate, dispersion measure (DM), and rotation measure (RM). A notable exception is FRB~20180916B, which shows a significant 16-day periodic burst rate. Possible periodic activities have also been reported in FRB~20121102A and FRB~20240209A. However, periodic studies of other properties are sparse. FRB~20220529 was monitored by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) for nearly three years, enabling periodic examinations of its properties. Here we report a possible period of $\sim 200$ days in the RM evolution, with a significance of 4.2 $\sigma$ estimated via the Lomb-Scargle algorithm and 3.5 $\sigma$ with a phase-folding method. The burst rate was also examined for periodicity. This is consistent with the binary origin indicated by the significant RM increase and its prompt recovery.

Compact binaries with accreting white dwarfs, neutron stars, or black holes are crucial for understanding accretion physics. In this study, we identify accreting compact binary candidates in the eROSITA DR1 by combining Gaia astrometry and ZTF time-domain photometry. We select accreting compact binary candidates whose X-ray emission is likely accretion-driven, based on their X-ray-to-optical flux ratios and optical colors, and further identify systems with short-period ZTF light curves, thereby ruling out AGNs. The resulting 22 candidates, including two known compact binaries, represent promising candidates for spectroscopic follow-up to confirm their accreting nature and explore their physical properties. Our results demonstrate the effectiveness of combining X-ray-to-optical flux ratio and optical color, and time-domain photometry in selecting accreting compact binaries. The method is scalable and adaptable to future multi-wavelength sky surveys, offering a promising path toward a more complete census of compact binaries in the Galaxy.

We present an investigation into an apparent relationship between white-light coronal brightness and the kinematics of flare-associated CMEs. Using a unique dataset known as the LASCO Coronal Brightness Index (CBI), we conduct a study that explores the brightness in the lower solar corona and its relationship to the velocity of flare-associated coronal mass ejections (CMEs). We analyze all M- and X-class flares that take place on or near the limbs of the Earth-facing disk of the Sun between 1996 and 2022, determine if these flares are associated with CMEs, and record the projection-corrected velocity of the eruptions if they occurred. Using the CBI dataset, we evaluate the brightness in the corona directly overlying the flare source locations between 2.4 and 6.2 solar radii, and find that above a certain level of coronal brightness, the likelihood of a high-velocity CME significantly decreases. This result implies coronal brightness could be an important indicator of the kinematics of solar CMEs. We also highlight and discuss the unique nature of Active Region (AR) 12192 in 2014, observing that its unprecedented overlying coronal brightness may be related to the low CME productivity of that region.

One of the main bottleneck in assessing the accuracy of Mars orbit is the unknown value of the asteroids in the Main Asteroid Belt. Nowadays a modeling with 343 asteroids as point masses is used, with the relative masses fitted to observational data. In the current work we propose an innovative methodology to reduce the number of asteroids implemented as point masses, thus reducing the number of parameters to be fitted, without a significant degradation of the postfit residuals.

Recent X-ray observations have discovered a class of periodic X-ray flares in galactic nuclei known as quasi-periodic eruptions (QPEs). A promising explanation of QPEs is an emission produced when a stellar-mass object orbiting a central supermassive black hole crosses an accretion disk. If the companion is a compact object, such systems would be a prospective multi-messenger target for the space-based observatory LISA and its successors. Here we quantify the prospects for joint X-ray and GW detection of QPEs with orbital frequency in the mHz band using a minimal flare-emission model. Our analysis shows that X-ray observations are most effective at orbital frequencies up to roughly 1 mHz, whereas LISA is sensitive chiefly above about 1 mHz. Because the optimal sensitivity windows overlap only marginally, we predict at most one joint detection during LISA's nominal mission lifetime. Extending GW sensitivity into the sub-millihertz regime (< 0.1 mHz) would raise the possibility of the joint detection by an order of magnitude, enabling QPEs as an interesting multi-messenger target.

Stars with outflows interacting with ambient gas experience accelerations arising from the gravitational feedback induced by the interaction structure. In this work, three-dimensional (3D) local shearing box simulations are performed to investigate the dynamical evolution of a star with outflows embedded in the outer regions of an active galactic nucleus (AGN) disk. Two types of stellar wind are considered: isotropic winds and axisymmetric jets, along with variations in the radial pressure gradient profile. The results show that anti-friction enables AGN stars to acquire angular momentum from the ambient gas, resulting in outward migration away from the disk center. The formation and stability of the head-wind structure, which is crucial for maintaining anti-friction, are sensitive to both the strength of the stellar outflow and the radial pressure gradient of the disk gas. Once the head-wind structure is disrupted, the anti-friction effect ceases to operate effectively. A case study is also presented, focusing on a stellar-mass black hole (sBH) in an AGN disk. It is shown that jet material launched along the z-axis is confined to the trailing side of the object's motion by high gas inflow velocities, thereby activating anti-friction and inducing outward migration. If such an sBH migrates inward initially, the interplay between inward and outward migration may trap it at an equilibrium radius, potentially facilitating the formation and merger of black hole binaries.

We investigate a class of slow roll inflationary models in the light of the recent Cosmic Microwave Background constraints from Planck 2018, ACT DR6, DESI DR1, and BICEP/\textit{Keck} 2018. The combined dataset favors a higher value of the scalar spectral index $n_{_\mathrm{S}}=0.9743 \pm 0.0034$, which places increased pressure on several conventional inflationary scenarios. In this study, we analyze the observational viability of various well-motivated models, including the $\alpha$-attractor E- and T-models, chaotic inflation, hilltop inflation, and natural inflation. We incorporate the effects of a post-inflationary phase of reheating and examine how the dynamics of reheating influence the predictions in the $n_{_\mathrm{S}}-r$ plane. We also impose a lower bound on the reheating temperature based on the constraint from the effective number of relativistic species ($\Delta{N}_{\mathrm{eff}}$) arising from primordial gravitational waves. While reheating improves agreement with observations for some models, significant regions of parameter space remain disfavored. Finally, we explore the impact of a non Bunch-Davies initial state and demonstrate that it can substantially improve the fit to the $n_{_\mathrm{S}}-r$ data across a broader class of inflationary models, thereby offering a potentially viable mechanism for reconciling theory with the latest observations.

We present an overview and catalogue of all known mass-transferring binary systems that have white dwarf accretors and orbital periods shorter than 70 minutes, including the AM CVn-type binary systems and a number of related objects. In this paper, we provide an overview of the literature background and describe recent breakthroughs, open questions, and connections to other fields. This overview is intended to provide a starting point for researchers who are relatively new to the fields of ultracompact binaries or AM CVn-type binaries. We define the scope of the catalogue (the criteria for inclusion) and describe its format and contents (what data have been included for each target). We also summarise the observed properties of the known mass-transferring ultracompact binaries, including their orbital periods and component stellar masses and radii. The catalogue presented here aims to provide a central resource to enable researchers to track the current status of the known sample. At the time of writing, the catalogue includes 123 confirmed binaries and 29 candidates. The catalogue is hosted on a public platform (Zenodo) with version control, and will be updated regularly.

The first transmission spectrum of the habitable-zone sub-Neptune K2-18 b with JWST has opened a new avenue for atmospheric characterisation of temperate low-mass exoplanets. The observations led to inferences of methane and carbon dioxide, as well as of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), both potential biosignatures. However, robust identification of DMS and/or DMDS requires further observations to increase the detection significances. More theoretical studies are also needed to identify potential false positives and possible abiotic sources for these molecules. In the present work we demonstrate the next step in this direction with a comprehensive and agnostic search for other chemical species in the atmosphere of K2-18 b. Our exploration includes 650 molecules, spanning a wide range of trace gases, including biotic, abiotic, and anthropogenic gases on Earth. We investigate possible evidence for any of these gases using three metrics: (a) evidence in the JWST mid-infrared spectrum, (b) evidence in the JWST near-infrared spectrum, and (c) plausible sources of production. We find three molecules, including DMS, which appear promising across the datasets considered. The two molecules besides DMS are diethyl sulfide and methyl acrylonitrile, which are more complex than DMS, biogenic on Earth, and have no significant sources known beyond Earth. A few other gases also provide comparable fits to a subset of the data considered but again with limited known plausible sources. Our study highlights the need for further observations to distinguish between possible trace gases in K2-18 b and theoretical work to establish their plausible sources if confirmed on this planet.

Studies of young planets help us understand planet evolution and investigate important evolutionary processes such as atmospheric escape. We monitored IRAS 04125+2902, a 3 Myr-old T Tauri star with a transiting planet and a transitional disk, with the SPIRou infrared spectropolarimeter on the Canada-France-Hawaii Telescope. Using these data, we constrained the mass and density of the Jupiter-size companion to <0.16 M_J and <0.23 g/cm^3, respectively (90\% upper limits). These rule out a Jovian-like object and support the hypothesis that it is an ancestor to the numerous sub-Neptunes found around mature stars. We unambiguously detect magnetic fields at the stellar surface, small-scale fields reaching 1.5 kG and the large-scale field mostly consisting of a 0.80-0.95 kG dipole inclined by 5-15deg to the rotation axis. Accretion onto the star is low and/or episodic at a maximum rate of ~10^{-11} Msun/yr, indicating that IRAS 04125+2902 is most likely in a magnetic 'propeller' regime, possibly maintaining the star's slow rotation (11.3~d). We discover persistent Doppler-shifted absorption in a metastable He I line, clear evidence for a magnetized wind from a gaseous inner disk. Variability in absorption suggests structure in the disk wind that could reflect disk-planet interactions.

Sufficiently strong and long-lasting first-order phase transitions can produce primordial black holes (PBHs) that contribute substantially to the dark matter abundance of the Universe, and can produce large-scale primordial magnetic fields. We study these mechanisms in a generic class of conformal U(1)' models that also explain active neutrino oscillation data via the type-I seesaw mechanism. We find that phase transitions that occur at seesaw scales between $10^4$ GeV and $10^{11}$ GeV produce gravitational wave signals at LISA/ET that can be correlated with microlensing signals of PBHs at the Roman Space Telescope, while scales near $10^{11}$ GeV can be correlated with Hawking evaporation signals at future gamma-ray telescopes. LISA can probe the entire range of PBH masses between $1\times 10^{-16}M_\odot$ and $8\times 10^{-11}M_\odot$ if PBHs fully account for the dark matter abundance. For Z' masses between 40 TeV and $10^4$ TeV, and 10 TeV right-handed neutrinos, helical magnetic fields (with magnitudes $\gtrsim 0.5$ pG and coherence lengths $\gtrsim 0.008$ Mpc above current blazar lower bounds can be produced.

We investigate the capabilities of upcoming kiloton-scale neutrino detectors, such as Hyper-Kamiokande, in determining the primary cosmic ray spectrum. These detectors provide full-sky coverage and long-term monitoring, unlike traditional satellite and balloon experiments that measure cosmic ray flux at specific altitudes and locations. By analyzing the atmospheric neutrino flux generated by cosmic ray interactions, we demonstrate that future detectors can differentiate between various cosmic ray models with high statistical significance, even when accounting for uncertainties in neutrino cross sections and hadronic interactions. We introduce a technique for reconstructing the primary cosmic ray spectrum using neutrino measurements, which reduces the flux uncertainty from approximately 20\% to about 7\%. We then show that Hyper-K has the potential to increase sensitivity to neutrino oscillation parameters, such as $\sin^2\theta_{23}$, by a factor of 2. Our results highlight the complementary role of neutrino detectors in cosmic ray physics and their critical importance for precision measurements in particle astrophysics.

The formation of primordial black holes (PBHs) during a first-order phase transition (FOPT) in a dark sector has been of recent interest. A quantity that characterizes a black hole is its spin. We carry out the first step towards determining the spin of such PBHs, by calculating the spin of spherical false vacuum bubbles induced by cosmological perturbations. The angular momentum is given by the product of density and velocity perturbations. We carefully track the evolution of background quantities and calculate the transfer functions during the FOPT. We find that the dimensionless spin parameter $s = J/(G_{\rm N} M^2)$ of false vacuum bubbles of mass $M$ and angular momentum $J$, take a wide range of values from ${\cal{O}}(10^{-3})$ to ${\cal{O}}(10^3)$ for FOPTs between 10 keV and 100 GeV and a dark sector that is 0.1 to 0.4 times cooler than the visible sector. We also find a scaling relation between the root-mean-square value of the spin, the FOPT time scale, the bubble wall velocity, and the dark sector-to-visible sector temperature ratio.

Dark matter accumulates in the center of the Earth as the planet plows through the dark matter halo in the Milky Way. Possible annihilation of dark matter to Standard Model particles can be probed in indirect dark matter searches. Among possible messengers, neutrinos are uniquely ideal as they can escape dense regions. Therefore, neutrino telescopes, with their large volume and broad energy exposures, offer new opportunities to search for dark matter signals from the center of the Earth. However, such studies have been restricted to dark matter masses below $\sim$ PeV as the Earth becomes opaque to very-high-energy neutrinos. In this study, we demonstrate that neutrino telescopes operating at TeV-PeV energies can probe very heavy dark matter particles if they annihilate to tau neutrinos or tau leptons. Here, we report upper limits on the spin-independent dark matter-nucleon cross section for masses between $10^5$ GeV and $10^{10}$ GeV by using 7.5 years of IceCube high-energy starting event observations. Our results motivate detailed analyses in IceCube and other upcoming neutrino telescopes in the Northern Hemisphere.

Ultralight bosons (ULBs) can form macroscopic superradiant clouds around spinning black holes. We show that for scalar ULB masses $\mu \sim 10^{-22}-10^{-21}$ eV boson cloud dynamical friction drives supermassive black hole (SMBH) final-parsec evolution in $\lesssim 1$ Gyr and suppresses the nanohertz gravitational wave background with turnover. Considering century-monitored OJ287 system, we place novel bounds restricting ULB mass range $\mu \simeq (8.5-22) \times 10^{-22}$ eV independent of any dark matter assumptions and show ULB drag can also efficiently reconcile any future confirmations of the debated orbital decay excess. Forthcoming pulsar timing array data and precise SMBH orbital timings will decisively test this scenario.

Our current understanding of the Universe relies on the hypothesis that, when observed at sufficiently large scales, it looks statistically identical regardless of location or direction of observation. Consequently, the Universe should exhibit mirror-reflection symmetry. In this essay, we show that gravitational-wave astronomy provides a unique, observer-independent test of this hypothesis. In particular, we analyze the average circular polarization emitted by an ensemble of binary black hole mergers detected by LIGO-Virgo, which we compute using a novel geometric and chiral observable in general relativity. We discuss current results and future prospects with upcoming detections and technical advancements. Moreover, we show that this circular polarization and the helicity of the remnant black hole are linearly correlated, drawing a conceptual parallel with Wu experiment in particle physics.

Simulations of relativistic plasmas traditionally focus on the dynamics of two-species mixtures of charged particles under the influence of external magnetic fields and those generated by particle currents. However, the extreme conditions of astrophysical plasmas near compact objects such as black holes and neutron stars are often characterized by mixtures of electrons, protons, and positrons, whose dynamics can differ significantly because of the considerable mass contrast. We present the first two-dimensional particle-in-cell (PIC) simulations of relativistic turbulence and magnetic reconnection in a three-species plasma, varying the relative abundance of electrons, protons, and positrons while employing realistic mass ratios to achieve unprecedented accuracy. We find that turbulence leads to the formation of magnetic islands, current sheets, and plasmoids. Reconnection occurs between these structures, with plasma composition playing a key role in determining the number of reconnection sites and their energy-conversion efficiency. In particular, as the proton fraction increases, very small-scale features of the turbulence are washed out, while global dissipative effects are amplified. Finally, using a novel generalization of Ohm's law for a relativistic multi-species plasma, we find that the reconnection rate is primarily governed by the electric fields associated to the divergence of the positron and electron pressure tensors. These results provide new insights into dissipation and particle acceleration in turbulent relativistic plasmas, such as those near black holes and neutron stars, and can be used to interpret their high-energy emission and phenomenology.

Future mHz gravitational wave (GW) interferometers will precisely probe massive black hole environments, such as accretion discs, cold dark matter overdensities, and clouds of ultralight bosons, as long as we can accurately model the dephasing they induce on the waveform of extreme mass-ratio inspirals (EMRIs). Most existing models rely on extrapolations from Newtonian results to model the interaction of the small black hole in an EMRI system with the environment surrounding the massive black hole. Here, we present a fully relativistic formalism to model such interaction with collisionless environments, focusing on the case of cold dark matter overdensities, like 'spikes' and 'mounds'. We implement our new formalism in the FastEMRIWaveforms framework and show that the resulting waveforms are significantly different from those based on a Newtonian treatment of environmental effects. Our results indicate that a fully relativistic treatment is essential to capture the environmental dephasing of GW signals from EMRIs accurately.

Two maximum likelihood-based algorithms for unfolding or deconvolution are considered: the Richardson-Lucy method and the Data Unfolding method with Mean Integrated Square Error (MISE) optimization [10]. Unfolding is viewed as a procedure for estimating an unknown probability density function. Both external and internal quality assessment methods can be applied for this purpose. In some cases, external criteria exist to evaluate deconvolution quality. A typical example is the deconvolution of a blurred image, where the sharpness of the restored image serves as an indicator of quality. However, defining such external criteria can be challenging, particularly when a measurement has not been performed previously. In such instances, internal criteria are necessary to assess the quality of the result independently of external information. The article discusses two internal criteria: MISE for the unfolded distribution and the condition number of the correlation matrix of the unfolded distribution. These internal quality criteria are applied to a comparative analysis of the two methods using identical numerical data. The results of the analysis demonstrate the superiority of the Data Unfolding method with MISE optimization over the Richardson-Lucy method.

The evolution of density perturbations is analysed in a modified theory of gravity with a nonminimal coupling between curvature and matter. We consider the broken degeneracy between the choices of matter Lagrangian for a perfect fluid, $\mathcal{L}_m=-\rho$ and $\mathcal{L}_m=p$, and determine the differences between their effects on the effective gravitational constant. We review the result for $\mathcal{L}_m=-\rho$ in the quasistatic approximation and show how it can lead to unphysical singular behaviour for late-time dominating models. This divergent regime can be avoided when considering the fully non-quasistatic perturbative equations, although the higher-order nature of the nonminimally coupled theory and the requirement of a physically viable effective gravitational constant strongly constrains the magnitude of these modifications to the action. We find that both of these issues can be removed when considering $\mathcal{L}_m=p$ at late times due to the pressureless nature of non-relativistic matter and provide predictions for inverse power-law models.

Self-interactions facilitate inter-particle redistribution of energy within the dense regions of galactic halos, implying modifications in the density and velocity distribution of dark matter. Simulating dark-matter only isolated halos for a wide range of mass and specific self-scattering cross-sections, we make a systematic study of the impact of self-scattering on the velocity distribution profiles. We report a conservative bound on $\sigma/m$ $\leq 2.7 \rm cm^2/gm$ at $95\%$ C.L. from observations of rotation curves in Milky-Way size galaxies. Sub-leading bounds from LSB galaxy and clusters are also presented.