Sazuna/UAT_keywords huggingface dataset:
Dynamics of Star Cluster Formation: The Effects of Ongoing Star Formation and Stellar Feedback. We perform a high-resolution zoomed-in simulation of star cluster assembly including the merger of two subclusters with initial conditions taken from previous large-scale giant molecular cloud (GMC) simulations. We couple hydrodynamics to N-body dynamics to simulate the individual stars themselves, and the gas-rich environment in which they evolve. We include prescriptions for star formation and stellar feedback and compare them directly to previous simulations of the same region without these prescriptions to determine their role in shaping the dynamics inherited from the cluster assembly process. The stellar mass of the cluster grows through star formation within the cluster and accretion of new stars and star-forming gas from a nearby filament. This growth results in an enhancement in the cluster's rotation and anisotropic expansion compared to simulations without star formation. We also analyze the internal kinematics of the cluster once it has lost most of its gas and find that the rotational velocity and the velocity anisotropy profiles are qualitatively similar to those expected of clusters that have undergone violent relaxation. Additionally, rotation and anisotropic expansion are still present by the time of gas removal. This implies that evolution within the GMC was unable to completely erase the kinematics inherited by the merger.

Keywords: Star formation, Stellar dynamics, Hydrodynamics, Star clusters
A Unified Model of Kilonovae and Gamma-Ray Bursts in Binary Mergers Establishes Neutron Stars as the Central Engines of Short GRBs. We expand the theoretical framework by O. Gottlieb et al., which connects binary merger populations with long and short binary gamma-ray bursts (lbGRBs and sbGRBs, respectively), incorporating kilonovae (KNe) as a key diagnostic tool. We show that lbGRBs, powered by massive accretion disks around black holes (BHs), should be accompanied by bright, red KNe. In contrast, sbGRBs—if also powered by BHs—would produce fainter, red KNe, potentially biasing against their detection. However, magnetized hypermassive neutron star (HMNS) remnants that precede BH formation can produce jets with power (PNS ≈ 1051 erg s‑1) and Lorentz factor (Γ &gt; 10) likely compatible with sbGRB observations, and would result in distinctly bluer KNe, offering a pathway to identifying the sbGRB central engine. Recent modeling by J. C. Rastinejad et al. found luminous red KNe consistently accompany lbGRBs, supporting their origin in BH-massive disk systems, likely following a short-lived HMNS phase. The preferential association of sbGRBs with comparably luminous KNe argues against the BH engine hypothesis for sbGRBs, while the bluer hue of these KNe provides additional support for an HMNS-driven mechanism. Within this framework, BH–NS mergers likely contribute exclusively to the lbGRB population with red KNe. Our findings suggest that GW170817 may, in fact, have been an lbGRB to on-axis observers. Finally, we discuss major challenges faced by alternative lbGRB progenitor models, such as white dwarf–NS or white dwarf–BH mergers and accretion-induced collapse forming magnetars, which fail to align with observed GRB timescales, energies, and KN properties.

Keywords: Neutron stars, Gamma-ray bursts, Jets, Gamma-ray sources, Relativistic jets, Gamma-ray bursters, Compact binary stars, Stellar mass black holes, Gamma-ray transient sources, Astrophysical black holes
Magnetic Helicity Fluxes in Dynamos from Rotating Inhomogeneous Turbulence. We analyze direct numerical simulations of large-scale dynamos in inhomogeneous nonhelically driven rotating turbulence with and without shear. The forcing is modulated so that the turbulent intensity peaks in the middle of the computational domain and drops to nearly zero at the two ends above and below the midplane. A large-scale dynamo is driven by an α effect of opposite signs in the two hemispheres. In the presence of shear, the hemispheric magnetic helicity flux from small-scale fields becomes important and can even overcompensate for the magnetic helicity transferred by the α effect between large and small scales. This effect has not previously been observed in nonshearing simulations. Our numerical simulations show that the hemispheric magnetic helicity fluxes are nearly independent of the magnetic Reynolds number, but those between large and small scales, and the consequent dynamo effect, are still found to decrease with increasing Reynolds number—just like in nonshearing dynamos. However, in contrast to nonshearing dynamos, where the generated mean magnetic field declines with increasing magnetic Reynolds number, it is now found to remain independent of it. This suggests that catastrophic dynamo quenching is alleviated by the shear-induced hemispheric small-scale magnetic helicity fluxes that can even overcompensate the fluxes between large and small scales and thereby cause resistive contributions.

Keywords: Astrophysical magnetism
Chandra Discovery of a Candidate Hyperluminous X-Ray Source in MCG+11-11-032. We present a multiwavelength analysis of MCG+11-11-032, a nearby active galactic nucleus (AGN), with a unique classification as being both a binary and a dual AGN candidate. With new Chandra observations, we aim to resolve any dual AGN system via imaging data and search for signs of a binary AGN via analysis of the X-ray spectrum. Analyzing the Chandra spectrum, we find no evidence of the previously suggested double-peaked Fe Kα lines; the spectrum is instead best fit by an absorbed power law with a single Fe Kα line, as well as an additional line centered at ≍7.5 keV. The Chandra observation reveals faint, soft, and extended X-ray emission, possibly linked to low-level nuclear outflows. Further analysis shows evidence for a compact hard source—MCG+11-11-032 X2—located 3 3 from the primary AGN. Modeling MCG+11-11-032 X2 as a compact source, we find that it is relatively luminous (  erg s−1), and the location is coincident with a compact and off-nuclear source resolved in Hubble Space Telescope infrared (F105W) and optical (F621M, F547M) bands. Pairing our X-ray results with a 144 MHz radio detection at the host galaxy location, we observe X-ray and radio properties similar to those of ESO 243-49 HLX-1, suggesting that MCG+11-11-032 X2 may be a hyperluminous X-ray source. This detection with Chandra highlights the importance of a high-resolution X-ray imager as well as how previous binary AGN candidates detected with large-aperture instruments can benefit from high-resolution follow-up. Future spatially resolved optical spectra, and deeper X-ray observations, can better constrain the origin of MCG+11-11-032 X2.

Keywords: Supermassive black holes, Intermediate-mass black holes, X-ray active galactic nuclei, Galaxy mergers
Using Two-frequency Dust Spectral Matching to Separate Galactic Synchrotron and Free–Free Temperature Foregrounds from the Cosmic Microwave Background. We introduce a method for removing cosmic microwave background (CMB) and anomalous microwave emission (AME, or spinning dust) intensity signals at high to intermediate Galactic latitudes in temperature sky maps at frequencies roughly between 5 and 40 GHz. The method relies on the assumption of a spatially uniform combined dust (AME and thermal) rms spectral energy distribution for these regions but is otherwise model independent. A difference map is produced from input maps at two different frequencies in thermodynamic temperature: the two frequencies are chosen such that the rms AME signal in the lower-frequency (∼5‑40 GHz) map is equivalent to the thermal dust emission rms in the higher-frequency (∼95‑230 GHz) map. Given the high spatial correlation between AME and thermal dust, the resulting difference map is dominated by synchrotron and free–free foreground components and can thus provide useful insight into the morphology and possible spectral variations of these components at high latitudes. We show examples of these difference maps obtained with currently available WMAP and Planck data and demonstrate the efficacy of CMB and dust mitigation using this method. We also use these maps, in conjunction with Haslam 408 MHz and Wisconsin H-Alpha Mapper Hα observations, to form an estimate of the diffuse synchrotron spectral index in brightness temperature on degree scales. The hybrid analysis approach we describe is advantageous in situations where frequency coverage is insufficient to break spectral degeneracies between AME and synchrotron.

Keywords: Diffuse radiation, Interstellar dust, Observational cosmology, Interstellar synchrotron emission
GRB 170519A: Thermal Radiation in an X-Ray Flare and Decaying Magnetic Fields for the Early-time Afterglow. GRB 170519A was discovered by the Swift Burst Alert Telescope (BAT) and then observed by the Swift X-Ray Telescope, Swift UltraViolet and Optical Telescope, and ground-based telescopes. We report Lick Katzman Automatic Imaging Telescope observations of GRB 170519A and make temporal analysis and spectral joint fits of its multiwavelength light curves. The observations present a relatively complete afterglow structure, including two X-ray flares (Flares I and II), optical onset (Slice 1), normal decay (Slices 2 and 3), and a possible jet break. The spectrum of the bright X-ray flare (Flare II) indicates that a thermal component exists at t = 190–240 s. The blackbody (BB) emits in the photospheric radius Rph ∼ 1011 cm, and its temperature (kT) decreases with time from 1.08 to 0.37 keV, while its Lorentz factor of BB (ΓBB) decreases with time from 67.71 to 46.70. The luminosity of the BB (LBB), kT, and ΓBB follows the relations LBB ∝ kT2.49±0.03 and  . In the optical light curves, there is an onset bump in the early-time afterglow, rising with an index αO,1 ≈ ‑0.43 and peaking ∼1174.9 s since the BAT trigger. The bump then decays with αO,2 ≈ 0.88 in the normal decay phase, and the X-ray flux decays with a similar index of αX,1 ≈ 0.95. There is no obvious spectral evolution in the normal decay phases, with photon index   and 1.92 in Slices 2 and 3, respectively. We find that the multiwavelength light curves of the GRB 170519A afterglow can be well fitted by an external shock with time-dependent ϵB. In the early afterglow, the value of ϵB decays rapidly from 4.29 × 10‑2 to 8.23 × 10‑3.

Keywords: Gamma-ray bursts
Closeby Habitable Exoplanet Survey (CHES). III. Retrieval of Planetary Masses in Binaries Using the N-body Model with Radial Velocity and Astrometry Synergy. Given that secular perturbations in a binary system not only excite high orbital eccentricities but also alter the planetary orbital inclination, the classical Keplerian orbital model is no longer applicable for orbital retrieval. The combination of a dynamical model and observational data is essential for characterizing the configuration and planetary mass in close binaries. We calculate the theoretical radial velocity (RV) signal in the N-body framework and observe a drift in the RV semiamplitude, which leads to a reduction in the msini detection threshold by 20 M⊕, with ∼100% detection probability in the m1sini1─a1 parameter space. High-precision RV data with an accuracy of 1 m s−1 can detect such dynamical effects. For four close-in binaries—GJ 86, GJ 3021, HD 196885, and HD 41004—the deviation between the minimum mass derived from the Keplerian and N-body models is found to be &gt;0.2 MJup. High-precision astrometric data are also necessary to resolve the 3D orbits and true masses of exoplanets. We generate astrometric simulation data with accuracies corresponding to Gaia (57.8 μas) and the Closeby Habitable Exoplanet Survey (CHES; 1 μas), respectively. Joint orbit fitting is performed for RV+Gaia and RV+CHES synergy methods. Compared with the fitting results from the astrometry-only model, the synergy models more effectively constrain the range of orbital inclinations. Using simulation data, we derive precise uncertainties for the true planetary mass, which are critical for determining the evolution of planets around binary stars and multiplanet systems.

Keywords: Radial velocity, Binary stars, Astrometry, Exoplanets
Vortex Avalanches and Collective Motion in Neutron Stars. We simulate the dynamics of about 600 quantum vortices in a spinning-down cylindrical container using a Gross–Pitaevskii model. For the first time, we find convincing spatial-temporal evidence of avalanching behavior resulting from vortex depinning and collective motion. During a typical avalanche, about 10–20 vortices exit the container in a short period, producing a glitch in the superfluid angular momentum and a localized void in the vorticity. After the glitch, vortices continue to depin and circulate around the vorticity void in a similar manner to that seen in previous point-vortex simulations. We present evidence of collective vortex motion throughout this avalanche process. We also show that the effective Magnus force can be used to predict when and where avalanches will occur. Finally, we comment on the challenge of extrapolating these results to conditions in real neutron stars, which contain many orders of magnitude more vortices.

Keywords: Neutron stars, Hydrodynamical simulations, Pulsars
Analysis of X-Ray Surface Brightness Radial Profiles in Several Relatively Symmetric Young Supernova Remnants. Based on observations from XMM-Newton, we analyze the surface brightness radial profiles of several young supernova remnants (SNRs) with relatively symmetric structures. The surface brightness data are obtained from the MOS1, MOS2, and PN instruments. We fit these profiles using a phenomenological model combining Gaussian and β models. Our results reveal a significant difference between SNRs with bright shell edges and those with faint shell edges. SNRs with bright shell edges exhibit a surface brightness peak within a certain range. In contrast, SNRs with faint shell edges show a gradual decrease in brightness, indicating differences in the physical mechanisms driving their evolution. Subsequently, we use the Gaussian and β models to fit these profiles. The results effectively reflect their evolutionary trends and brightness distribution, indicating that the internal part of the profiles is generally expressed by the Gaussian models, while the external part is characterized by the β model. Notably, the β-values in our model closely approximate the expansion parameters of the SNRs. This intriguing similarity suggests that detailed analyses of surface brightness radial profiles may provide valuable insights into the expansion dynamics of SNRs.

Keywords: Supernova remnants, Astronomy data analysis, X-ray sources
CO Observations of the SMC-N66 H II Region with ALMA: Properties of Clumps Along Filamentary Molecular Clouds and Possible Expansion Motion. The star-forming region N66, as a host of the majority of OB stars in the Small Magellanic Cloud, provides a unique opportunity to enhance our understanding of the triggers of high-mass star formation. We investigate the properties of the molecular cloud in N66 using the 12CO(1–0) data obtained with the Atacama Large Millimeter/submillimeter Array. A cloud decomposition analysis identified 165 independent cloud structures and substructures. The size–linewidth scaling relation for the entire region exhibits an index of 0.49, indicating that the region is in a state of virial equilibrium. In contrast, a detailed analysis of the central N66 region revealed a size–line width scaling relation with an index of 0.75, suggesting that distinct factors are influencing the dynamics of this central area. Averaging the spectra in the central N66 region revealed three distinct velocity peaks at 145, 152, and 160 km s‑1, indicating that some kinds of interactions are occurring within the cloud. The analysis of the position–velocity diagrams in the central region revealed a ring-like structure, indicating the presence of an expanding bubble. The bubble exhibits supersonic characteristics, with an expansion velocity of   km s‑1, and an overall systemic velocity of vsys ≈ 151 km s‑1. The radius is estimated to be in the range of r ≈ [9.8‑12.9] ± 0.5 pc and is approximately 1.2 Myr old.

Keywords: Local Group, Small Magellanic Cloud, Molecular clouds, Young stellar objects, Star formation, Interstellar medium
Theoretical Foundation of Black Hole Image Reconstruction Using PRIMO. A new image-reconstruction algorithm, Principal-component Interferometric Modeling (PRIMO), applied to the interferometric data of the M87 black hole collected with the Event Horizon Telescope (EHT), resulted in an image that reached the native resolution of the telescope array. PRIMO is based on learning a compact set of image building blocks obtained from a large library of high-fidelity, physics-based simulations of black hole images. It uses these building blocks to fill the sparse Fourier coverage of the data that results from the small number of telescopes in the array. In this paper, we show that this approach is readily justified. Since the angular extent of the image of the black hole and of its inner accretion flow is finite, the Fourier space domain is heavily smoothed, with a correlation scale that is at most comparable to the sizes of the data gaps in the coverage of Fourier space with the EHT. Consequently, PRIMO or other machine learning algorithms can faithfully reconstruct the images without the need to generate information that is unconstrained by the data within the resolution of the array. We also address the completeness of the eigenimages and the compactness of the resulting representation. We show that PRIMO provides a compact set of eigenimages that have sufficient complexity to recreate a broad set of images well beyond those in the training set.

Keywords: Principal component analysis, Black hole physics, Long baseline interferometry, Black holes
The Struggles of Developing an Operational Machine Learning Model for Flare Forecasting: Recasting the Problem as a Regression onto X-Ray Flux. Complex machine learning (ML) models do not seem to have improved solar flare forecasting. Despite many efforts to apply deep neural network architectures, it is unclear whether these models truly offer improvements compared to classical statistical and ML techniques because consistent benchmark test sets are underused and few papers offer comparisons to baseline models. In particular, predicting the onset and decline of flaring activity is an unsolved challenge. One possibility for the lack of improvement in performance is that the flare forecasting problem has been cast as one of binary classification, which forces models to try to distinguish between flares below and above an arbitrary intensity threshold. Here, we define a fully regression-based forecasting task and present results for full-disk forecasts of the maximum X-ray flux within a given forecast window using models trained on historical magnetogram data. We compare various ML architectures and show that a hybrid convolutional neural network only offers comparable performance to a simple random forest model. This demonstrates the continued value of a small set of predictive scalar features in flare forecasting and the importance of comparing to a baseline. By showing how performance varies depending on the choice of test set, we also emphasize the need to simulate operational conditions when evaluating forecasting models. We do not claim to have developed a more skillful flare forecasting model in this work; rather, we seek to highlight key challenges and best practices within the context of investigating a regression task for flare prediction.

Keywords: Solar cycle, Solar flares, Space weather, Convolutional neural networks, Solar magnetic fields, Solar activity
Helicity Effect on Turbulent Passive and Active Scalar Diffusivities. Turbulent flows are known to produce enhanced effective magnetic and passive scalar diffusivities, which can fairly accurately be determined with numerical methods. It is now known that, if the flow is also helical, the effective magnetic diffusivity is reduced relative to the nonhelical value. Neither the usual second-order correlation approximation nor the various τ approaches have been able to capture this. Here we show that the helicity effect on the turbulent passive scalar diffusivity works in the opposite sense and leads to an enhancement. We have also demonstrated that the correlation time of the turbulent velocity field increases with the kinetic helicity. This is a key point in the theoretical interpretation of the obtained numerical results. Simulations in which helicity is being produced self-consistently by stratified rotating turbulence resulted in a turbulent passive scalar diffusivity that was found to be decreasing with increasing rotation rate.

Keywords: Magnetic fields, Hydrodynamics
Period–Luminosity Relations for Double-mode δ Sct Stars. Previous studies of the period–luminosity relations (PLRs) of Delta Scuti (δ Sct) stars have focused on those with a single pulsation mode. However, for δ Sct stars with many different pulsation modes, classifying a single mode is difficult. In this study, an all-sky data set is constructed using double-mode δ Sct stars from the Zwicky Transient Facility and Optical Gravitational Lensing Experiment and is used to determine fundamental (F)-mode and first-overtone (1O)-mode PLRs for eight single bands and six Wesenheit bands. In the W1 band, the PLR dispersion is about 0.171 mag, and the total zero-point error is 1%. Our results show that to accurately classify the 1O modes of δ Sct stars requires authentication based on multiple modes. Classification based on amplitude alone leads to impure 1O-mode δ Sct stars and significant deviations in the PLRs. We compare the PLRs of the different sequences in the Petersen diagram and find that they are consistent after a strict criterion filtering, suggesting that their evolutionary state is similar. In addition, we find a weak period–metallicity relation for double-mode δ Sct stars, unlike double-mode RR Lyrae stars. As distance tracers, large-amplitude F-mode δ Sct and double-mode δ Sct stars are the most suitable of the δ Sct family.

Keywords: Double periodic variable stars, Periodic variable stars, Delta Scuti variable stars, Distance indicators
The Effects of Kinematic Magnetohydrodynamics on the Atmospheric Circulation of Eccentric Hot Jupiters. Hot Jupiters are typically considered to be tidally locked due to their short orbital periods. The extreme irradiation can result in atmospheric species becoming thermally ionized on the dayside, which then interact with the planet's magnetic field by resisting flow across magnetic field lines, shaping the atmospheric structure. However, an eccentric orbit results in temporally dependent irradiation and a nonpermanent dayside, as the planet─star distance can change drastically during its orbit. In this paper, we present 3D atmospheric models of TOI-150b, an eccentric (e = 0.26), Jupiter-mass (∼1.75MJup) planet whose equilibrium temperature varies from 1300 to 1700 K. We conduct simulations for magnetic field strengths ranging from 0 to 30 Gauss using the kinematic magnetohydrodynamics (MHD) approach. When compared with simulations of the planet assuming a circular orbit, we find that the eccentric orbit results in a strengthened and narrowed equatorial jet, westward winds at midlatitudes, and a phase-dependent thermal inversion. The strength and magnitude of these effects scale with the chosen global magnetic field strength. We also generate high-resolution (R = 100,000) emission spectra to study net Doppler shifts and find interorbit spectroscopic variability at moderate magnetic field strengths, as well as decreased Doppler broadening as magnetic field strengths increase. This work represents the first time that the kinematic MHD approach has been applied to an eccentric hot Jupiter and highlights the importance of a locally calculated, temperature-dependent magnetic drag prescription for predicting atmospheric structure and resulting spectra.

Keywords: Hydrodynamical simulations, Exoplanet atmospheric dynamics, Exoplanet atmospheric variability, Exoplanet atmospheres, Extragalactic magnetic fields