Sazuna/UAT_keywords huggingface dataset:
BRITE Nanosat Photometry Reveals Bright Spots in the Single Wolf─Rayet Star EZ CMa That Can Drive Spectral-line-emitting Corotating Interaction Regions. We analyze an unprecedented 4.5 contiguous months of 2015─2016 BRITE nanosatellite precision optical photometry of the 7th mag Wolf─Rayet (WR) star EZ CMa = WR 6 = HD 50896. A Fourier transform (FT) of the light curve (LC) reveals a period of 3.751 ± 0.011 days (broadly consistent with all previous data and analyses), with five other harmonics at simple multiples of the fundamental frequency. All harmonics are used to determine the best period. The FT shows Lorentzian as opposed to Gaussian peaks that were a first hint that EZ CMa was behaving oddly. A more revealing 3D dynamical plot (rotation-cycle number versus rotation phase and color-coded intensity) of the LC further shows at least a dozen apparently independent bright spots over ∼35 rotations, each randomly starting in time and stellar azimuth and lasting FWHM ∼ 5 rotations, but always following the same rotation period. This randomness goes against any binary hypothesis. A model simulation suggests that we are likely seeing the bright rotating footprints of corotating interaction regions (CIRs). The model bright spots must be located above the hydrostatic radius to be compatible with the observed LC. While EZ CMa remains the key WR star showing this scenario, there are now five other WR stars claimed in the literature with CIRs, and more are likely to follow. This discovery opens the door to searching for local magnetic fields that may be needed to stabilize the bright spots.

Keywords: Stellar photometry, Wolf-Rayet stars, Starspots
Energy Bounds from Relative Magnetic Helicity in Spherical Shells. Relative magnetic helicity is commonly used in solar physics to avoid the well-known gauge ambiguity of standard magnetic helicity in magnetically open domains. However, its physical interpretation is challenging, owing to the invocation of a reference field. For the specific case of spherical-shell domains (with potential reference field), relative helicity may be written intrinsically in terms of the magnetic field alone, without the need to calculate the reference field or its vector potential. We use this intrinsic expression to prove that nonzero relative helicity implies lower bounds for both magnetic energy and free magnetic energy, generalizing the important Arnol'd inequality known for closed-field magnetic helicity. Further, we derive a stronger energy bound by spatially decomposing the relative helicity over a magnetic partition of the domain to obtain a new ideal invariant, which we call unsigned helicity. The bounds are illustrated with analytical linear force-free fields (that maximize relative helicity for given boundary conditions) as well as a nonpotential data-driven model of the solar corona. These bounds confirm that both relative helicity and the unsigned helicity can influence the dynamics in the solar corona.

Keywords: Solar magnetic fields
The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) Survey: 5σ Source Catalog and Redshift Distribution. One of the greatest challenges in galaxy evolution over the last decade has been constraining the prevalence of heavily dust-obscured galaxies in the early Universe. At z &gt; 3, these galaxies are increasingly rare, and difficult to identify, as they are interspersed among the more numerous dust-obscured galaxy population at z = 1─3, making efforts to secure confident spectroscopic redshifts expensive, and sometimes unsuccessful. In this work, we present the Extended Mapping Obscuration to Reionization with the Atacama Large Millimeter/submillimeter Array (ALMA; Ex-MORA) Survey—a 2 mm blank-field survey in the COSMOS-Web field, and the largest ever ALMA blank-field survey to date, covering 577 arcmin2. Ex-MORA is an expansion of the MORA survey designed to identify primarily z &gt; 3 dusty, star-forming galaxies while simultaneously filtering out the more numerous z &lt; 3 population by leveraging the very negative K-correction at observed-frame 2 mm. We identify 37 significant (&gt;5σ) sources, 33 of which are robust thermal dust emitters. We measure a median redshift of  &lt;z&gt;=3.8−1.52+1.7 , with two-thirds of the sample at z &gt; 3, and just under half at z &gt; 4, demonstrating the overall success of the 2 mm selection technique. The total integrated z &gt; 3 volume density of Ex-MORA sources is ∼1─3 × 10−5 Mpc−3, consistent with other surveys of infrared luminous galaxies at similar epochs. We also find that techniques using rest-frame optical emission (or lack thereof) to identify z &gt; 3 heavily dust-obscured galaxies miss at least half of Ex-MORA galaxies. This supports the idea that the dusty galaxy population is heterogeneous, and that synergies across observatories spanning multiple energy regimes are critical to understanding their formation and evolution at z &gt; 3.

Keywords: Submillimeter astronomy, Redshift surveys, High-redshift galaxies, Infrared galaxies
Far-infrared Emission Lines as Metallicity Diagnostic. The chemical abundance of the interstellar medium is a key tracer of galaxy evolution. Optical and ultraviolet emission lines are widely used to derive gas-phase metallicities, but suffer from uncertainties due to possible temperature fluctuations and extinction corrections. Far-infrared atomic fine-structure lines offer a promising alternative, penetrating dust without extinction correction and with minimal dependence on electron temperature. However, the far-infrared lacks useful hydrogen transitions and must be calibrated through other means, such as the N/O ratio. We use four far-infrared diagnostic emission lines, [O III]52 μm, [N III]57 μm, [O III]88 μm, and [N II]122 μm from archival Herschel/PACS and SOFIA/FIFI-LS data, coupled with a photoionization model to determine metallicity for a sample of local galaxies, ranging from dwarf irregular galaxies to ultraluminous infrared galaxies. We use a Bayesian framework, as well as simple emission-line ratios, to derive the O/H abundance ratio. The results are compared with results from optical diagnostics. After correcting for a slight difference between the calibrations used in the photoionization model used for the far-infrared emission lines, and the empirical calibration used for the optical emission lines, we find that far-infrared and optical diagnostics yield the same metallicity within the observational errors. Furthermore, we find no statistically significant difference between the N/O ratios derived from far-infrared emission lines and those derived using optical emission lines. Hence, the far-infrared methods provide robust metallicity estimates in the range 0.2 &lt; Z/Z⊙ &lt; 1.0. We apply our far-infrared techniques to Atacama Large Millimeter/submillimeter Array data for the A1689-zD1 galaxy at z = 7.1. We find a low electron density consistent with findings for local low-metallicity galaxies. Assuming an ionization parameter similar to those found locally, we infer a gas-phase metallicity in the range 0.2─0.3 Z⊙.

Keywords: Dwarf irregular galaxies, Metallicity, Emission line galaxies, Far infrared astronomy
EIGER. VIII. First Stars Signatures in the Connection between O I Absorption and Galaxies in the Epoch of Reionization. We investigate the association between galaxies and neutral O I absorption systems at z ∼ 6, which trace metal-enriched gas during the epoch of reionization. We identify 40 galaxies across six quasar fields, residing in 15 overdensities within 300 kpc of the background sight lines. Five O I absorption systems are associated with five of these overdensities, yielding a covering fraction of  0.27−0.10+0.13  within 300 kpc. The absorption occurs beyond typical virial radii, indicating that the gas traces extended overdensity environments rather than individual galaxy halos, unlike the z ∼ 0 circumgalactic medium (CGM), which is largely bound to halos. These galaxy-associated absorbers account for ∼35% of all O I systems seen in blind quasar surveys, implying the remainder arise in lower-mass galaxies below our detection threshold or in dense neutral intergalactic medium pockets. The CGM around these galaxies contains ≳ 2 × 106 M⊙ of oxygen, comparable to the interstellar medium oxygen mass of the galaxies themselves, suggesting that the surrounding environment holds as much metal mass as the galaxies. All five galaxy-associated systems show significantly higher  log(NCII/NOI)  ratios than absorbers lacking galaxy associations. Furthermore, relative abundance ratios ([Si/O], [C/O]) reveal that four of the five exhibit enrichment patterns consistent with Population III nucleosynthesis at the outskirts of galaxy overdensities. These rare systems offer a unique window into the role of first-generation stars in shaping the early metal enrichment of galaxies and their environments.

Keywords: Galactic and extragalactic astronomy, Galaxy evolution, Circumgalactic medium, Extragalactic astronomy, Reionization
Wave Generation via Oscillatory Reconnection at a Three-dimensional Magnetic Null Point. This work conducts a three-dimensional (3D), nonlinear magnetohydrodynamic (MHD) simulation to investigate wave-generating, time-dependent reconnection around a magnetic null point. A nonperiodic perturbation (in the xz-plane) triggers oscillatory reconnection (OR) at the 3D null, resulting in a self-sustained oscillation with a constant period P. We investigate the response of the system using three distinct wave proxies (compressible parallel, compressible transverse, and incompressible parallel) as well as spectral proper orthogonal decomposition for decoupling and analyzing the resultant MHD wave behavior. We find that OR generates a slow magnetoacoustic wave of period P that propagates outward in all directions along the spine and fan plane of the 3D null point. We also find the generation of a propagating Alfvén wave of period P, exclusively along the y-axis in the fan plane, i.e., in the direction perpendicular to the spine motion. These findings provide new insights into waves generated from a 3D null point and their implications for coronal seismology.

Keywords: Solar coronal transients, Magnetohydrodynamics, Solar magnetic reconnection, Solar physics, Alfven waves
Fastest or Significant: A Systematic Framework for Validating Global Minimum Variability Timescale Measurements of Gamma-Ray Bursts. The minimum variability timescale (MVT) is a key observable for probing the central engines of gamma-ray bursts, constraining both the emission region size and outflow Lorentz factor. However, its interpretation is often ambiguous: Statistical noise and analysis choices can bias measurements, making it difficult to distinguish genuine source variability from artifacts. Here, we perform a comprehensive suite of simulations to establish a quantitative framework for validating MVT measurements based on the Haar wavelet estimator. We show that in multicomponent light curves, the MVT returns the most statistically significant structure in the interval, which is not necessarily the fastest intrinsic timescale, and can therefore converge to intermediate values. Reliability is found to depend jointly on the MVT value and its signal-to-noise ratio (SNRMVT), with shorter intrinsic timescales requiring proportionally higher SNRMVT to be resolved. We use this relation to define an empirical MVT validation curve, and provide a practical workflow to classify measurements as robust detections or upper limits. Applying this procedure to a sample of Fermi Gamma-ray Burst Monitor bursts shows that several published MVT values are better interpreted as upper limits. These results provide a path toward standardizing MVT analyses, and highlight the caution required when inferring physical constraints from a single MVT measurement in complex events.

Keywords: Gamma-ray bursts, High time resolution astrophysics, Astronomy data analysis, Time domain astronomy, Gamma-ray astronomy, Time series analysis
The Phase Spiral's Origin and Evolution: Indications from Its Varying Properties across the Milky Way Disk. The phase spiral is a perturbation to the vertical phase-space distribution of stars in the Milky Way disk. We study the phase spiral's properties and how they vary with spatial position, in order to constrain its origin and evolution, as well as properties of the disk itself. We produce high-resolution maps using two complementary data processing schemes: (a) we bin the Gaia proper-motion sample in a disk-parallel spatial grid, reaching distances up to 4 kpc; and (b) we bin the spatially nearby line-of-sight velocity sample in terms of disk-parallel orbital parameters. We find complex structure, most significantly with respect to Galactocentric radius and guiding radius, but also in Galactic azimuth and epicyclic action and phase. We find that spiral winding and rotation phase vary smoothly across the disk, with close-to-flat radial profiles. This uniform structure, in particular for the rotation phase, disfavors small-scale perturbations as the primary source of the phase spiral, for example, from giant molecular clouds or dark matter subhalos. Curiously, these close-to-flat profiles also imply that the winding time has a strong slope with respect to Galactocentric radius, with low values for the inner disk. A uniform perturbation time cannot be reconciled by self-gravity effects that act only in the disk's vertical dimension, because this would delay winding but not the evolution of the rotation phase. This suggests that more complex self-gravity effects, acting also in dimensions parallel to the disk plane, are important for the spiral's formation and evolution.

Keywords: Milky Way disk, Milky Way dynamics, Astrometry
Early Stages of Protostellar Disk Evolution: A Link to the Initial Cloud Core. We study the structure and evolution of the very early protostellar disk ("protodisk") just after protostar formation, where disk self-gravity dominates and the stellar contribution is dynamically minor. The disk redistributes angular momentum outward through outflows and gravitational torques, thereby helping to resolve the angular momentum problem of star formation. We develop a self-similar model and carry out a parameter study that examines disk stability as a function of the key drivers of early evolution, notably the infall rate from the envelope and the strength of the gravitational torques. The mass-infall rate onto the disk is estimated to be that from the collapse of a Bonnor─Ebert sphere. Our results indicate that protostellar disks that form from more unstable initial cores are more likely to be Toomre unstable. We also find that the specific angular momentum of young protostellar disks lies in the range 1019─1020 cm2 s−1. We find distinct power-law profiles of physical quantities in the protodisk stage, including a rotation velocity profile that is shallower than the Keplerian profile that would be established at a later stage. As a rough validity window, our assumptions are most secure during the first ≲2 × 103 yr after protostar formation and may plausibly extend to ∼(0.5─1) × 104 yr under weak magnetic braking and strong infall.

Keywords: Hydrodynamics, Stellar winds, Star formation, Gravitational collapse, Interstellar medium, Circumstellar disks, Stellar accretion disks
Shock Acceleration in the Intracluster Medium: Implications of Micromirror Confinement. Merging galaxy clusters exhibit strong observational evidence for efficient particle acceleration in the intracluster medium (ICM), particularly in the form of synchrotron-emitting radio relics and halos. Cosmic-ray (CR) electrons are likely accelerated (or reaccelerated) at merger and accretion shocks via diffusive shock acceleration. However, in the presence of the large diffusion coefficients, one would naively expect in the rarefied, relatively unmagnetized ICM, this acceleration—in particular, the maximum proton energy ( Emax )—is limited by long acceleration times. On the other hand, recent work on CR transport suggests that the diffusion coefficient can be suppressed in ICM-like environments. In this picture, deviations from local thermodynamic equilibrium can trigger the mirror instability, creating plasma-scale magnetic structures, or "micromirrors," that efficiently scatter CRs. In this paper, we investigate the implications of micromirror confinement for shock acceleration in the ICM. We demonstrate that micromirrors enforce a minimum value of  Emax≳100  GeV that does not rely on CR-driven magnetic field amplification. We also discuss micromirror confinement in the context of cosmological simulations and γ-ray observations, and present a simulation of a Coma-like merging cluster that self-consistently includes CR acceleration at shocks, with an effective diffusion coefficient set by micromirrors. We show that the introduction of micromirrors yields simulated galaxy clusters that remain consistent with γ-ray observations.

Keywords: Galaxy clusters, Coma Cluster, Shocks, Intracluster medium, Cosmic rays
Planet Migration in Protoplanetary Disks with Rims. Complex structures, including sharp edges, rings, and gaps, have been commonly observed in protoplanetary disks with or without planetary candidates. Here we consider the possibility that they are the intrinsic consequences of angular momentum transfer mechanisms and investigate how they may influence the dynamical evolution of embedded planets. With the aid of numerical hydrodynamic simulations, we show that gas giants have a tendency to migrate away from sharp edges, whereas super-Earths embedded in the annuli tend to be retained. This implies that, observationally, Jupiters are preferentially detected in dark rings (gaps), whereas super-Earths tend to be found in bright rings (density bumps). Moreover, planets' tidal torque provides (not necessarily predominant) feedback on the surface density profile. This tendency implies that Jupiter's gap-opening process deepens and widens the density gap associated with the dark ring, while super-Earths can be halted by the steep surface density gradient near the disk or ring boundaries. Hence, we expect that there would be a desert for super-Earths in the surface density gap.

Keywords: Hydrodynamical simulations, Tidal interaction, Extrasolar gaseous giant planets, Protoplanetary disks
Multiwavelength Signatures of Supernova Shock Breakout from Red Supergiants in Two Dimensions. We present new two-dimensional radiation hydrodynamic simulations of supernova shock breakout from red supergiants (RSGs) using the CASTRO code. Our progenitors are 20 and 25 M⊙ solar-metallicity stars evolved from the zero-age main sequence with MESA and exploded in one dimension using FLASH. We consider a range of circumstellar media (CSMs) produced by stellar winds to investigate how preexplosion mass loss affects shock breakout. The multigroup flux-limited diffusion scheme in CASTRO captures the interaction between the explosion shock, its radiation precursor, and the surrounding CSM. We find that strong radiation precursors, generated by radiation leakage behind the shock, can drive fluid instabilities and move the effective photosphere outward before the shock reaches the stellar surface. The resulting breakout emission reaches peak luminosities of ∼1044 erg s−1 with FWHM durations of 1─3 hr, fainter and longer than previous one-dimensional models. The light-curve colors gradually evolve from blue to red after the peak. The 25 M⊙ model with explosion energy E ∼ 1.69 × 1051 erg produces an ∼10%─30% higher maximum luminosity than the 20 M⊙ model with E ∼ 1.09 × 1051 erg. The dense CSM further extends the breakout rise time by increasing the photon diffusion. These results provide new constraints on RSG atmospheres and mass-loss histories prior to core collapse. Although our selected wavelength ranges fall outside the observational bands of missions such as the Einstein Probe and ULTRASAT, our study still provides valuable insights into the color evolution of shock breakout and can help guide the interpretation of future observations.

Keywords: Massive stars, Radiative transfer simulations, Stellar mass loss, Stellar winds, Shocks, Supernovae
Persistence of Solar Wind Velocity along Radial, Longitudinal, and Latitudinal Spacecraft Separation. Recent missions, including the Parker Solar Probe, Solar Orbiter, and the Mars Atmosphere and Volatile EvolutioN (MAVEN), have probed a wide range of heliocentric distances, enabling new investigations of solar wind evolution. By comparing solar wind measurements from spacecraft located at different positions in the heliosphere (0.1─1.5 au), we study the persistence of solar wind velocity in longitude, latitude, and over radial distance. To this end, we introduce a new persistence model based on in situ observations being propagated across longitudes and radial distance, conserving latitude. The resulting time-dependent two-dimensional maps of projected solar wind parameters are then compared with in situ measurements from the OMNI database at 1 au and from MAVEN orbiting Mars. We find that the mean absolute error (MAE) of the solar wind velocity increases by 2.4 km s−1 for each degree of latitudinal spacecraft separation over a range of up to 14 .° 3. In addition, we identify a logarithmic relationship between persistence time and MAE, revealing spatial and temporal solar wind variability in the heliosphere. Over radial separation, we find no clear relationship based on current data coverage.

Keywords: Space plasmas, Heliosphere, Solar wind, Solar physics, Corotating streams
The Reliability of Local Correlation Tracking for Inferring Photospheric Intensity Vortices. Magnetoconvective simulations of the solar photosphere show ubiquitous formation of vortices in intergranular lanes, which are thought to contribute to the energy transfer between atmospheric layers. Observationally, these vortices are often reported as photospheric intensity vortices, with their flow field assumed parallel to the plane of sky, making their identification a challenge. The most common method to detect these vortices is to infer the photospheric velocity field using Fourier local correlation tracking (FLCT) and identifying vortical motions within. To validate FLCT as a tool for inferring photospheric intensity vortex flows, FLCT was performed on TiO 705.8 nm observations from the Visible Broadband Imager at the Daniel K. Inouye Solar Telescope, as well as on synthetic intensity images derived from the MURaM code. Using Γ-functions on velocity vectors, vortices were identified while characterizing their statistical properties. Vortices in MURaM FLCT velocity fields were then compared with those in the MURaM-simulated velocity field. It was found that the FLCT kernel size has a significant impact on recovered vortex properties and quantity. However, statistical distributions of the properties of vortex lifetimes and areas remain similar. Furthermore, vortices in the MURaM-simulated velocity field were found to be much smaller than those in MURaM FLCT-derived velocity fields, with their overlap in space being 0.4%─19.7%, depending on the FLCT kernel size. The vast majority of those that do match are coincidental and arise from particularly large choices of kernel size. Therefore, FLCT was determined to be unreliable for inferring photospheric intensity vortices in intergranular lanes.

Keywords: Solar photosphere, Solar physics, Solar optical telescopes, Solar atmospheric motions, Magnetohydrodynamical simulations