Sazuna/UAT_keywords huggingface dataset:
Insights from Analytical Theory of Eccentric Circumbinary Disks. Eccentric cavities in circumbinary disks precess on timescales much longer than the binary orbital period. These long-lived steady states can be understood as trapped modes in an effective potential primarily determined by the binary quadrupole and the inner-disk pressure, with associated frequencies ωQ and ωP. Within this framework, we show that the ratio ωP/ωQ is the main parameter determining the mode spectrum, and obtain a thorough understanding of it by systematically solving this problem with various degrees of sophistication. We first find analytical solutions for truncated power-law disks and use this insight in disks with smooth central cavities. Our main findings are as follows: (i) The number of modes increases for thinner disks and more-equal-mass binaries. (ii) For 2D disks, the normalized ground-mode frequency, ω0/(ωQ + ωP), decreases monotonically with the ratio ωP/ωQ. (iii) For thin disks, ωP ≪ ωQ, the ground-mode frequency coincides with the maximum of the effective potential, which tracks the gravitational quadrupole frequency inside the inner-disk cavity, and is thus rather sensitive to the density profile of the cavity, where these modes are localized. (iv) For thick disks, ωP ≫ ωQ, increasing the pressure anchors the peak of the effective potential at the inner cavity radius as the ground-mode extends farther out and its frequency decreases. (v) In agreement with numerical simulations, with ωP/ωQ ≃ 0.1, we find that disk precession is rather insensitive to the density profile, and ground-mode frequencies for 3D disks are about half the value of those for 2D disks.

Keywords: Accretion, Binary stars, Planetary-disk interactions, Galaxy accretion disks, Protoplanetary disks, Perturbation methods, Astrophysical fluid dynamics
The Nature of Nitrogen-enhanced High-redshift Galaxies. Recent JWST observations have revealed a population of high-redshift galaxies (z ≳ 5) exhibiting unexpectedly bright ultraviolet (UV) nitrogen emission lines. The strong N III] and N IV] features imply nitrogen-to-oxygen abundance ratios (N/O) as high as  −0.8≲log(N/O)≲0.4  in these low-metallicity galaxies ( 12+log(O/H)≲8.2 ), compared to the local value of  log(N/O)≍−1.5 . If confirmed, this level of nitrogen enrichment challenges existing models of nucleosynthesis and galaxy evolution. However, the presence of active galactic nuclei (AGNs) can affect spectral diagnostics, and previous studies often excluded AGN contamination using photoionization models based on local N/O ratios. In this work, we compare nitrogen-enhanced AGN and H II region models to observed spectra of eight high-redshift galaxies to constrain their nitrogen abundance, excitation source, gas-phase metallicity, ionization parameter, and gas pressure simultaneously. We find seven galaxies (GHZ9, GS 3073, GN-z9p4, CEERS-1019, GHZ2, GN-z11, and GS-z9-0) are best described by nitrogen-enhanced AGN models, while RXCJ2248-ID is best reproduced by the nitrogen-enhanced H II model. The presence of AGN does not significantly impact (≲0.1 dex) the derived N/O ratio. We also find that equivalent width—based diagrams are the most robust UV diagnostic diagrams to distinguish AGNs and star-forming galaxies for situations where the nitrogen abundance varies. All nitrogen-enhanced galaxies have moderate-to-high gas pressure ( 7.0≤log(P/k)≤9.8 ) and a high-ionization parameter ( log(U)≳−2.0 ), indicating a dense and compact environment. We suggest that super star clusters containing Wolf─Rayet stars and massive stars are the most likely contributors to the elevated nitrogen abundance in these galaxies.

Keywords: AGN host galaxies, Chemical abundances, Interstellar medium
Time-dependent Modeling of the Subhour Spectral Evolution during the 2013 Outburst of Mrk 421. In 2013 April, the TeV blazar Markarian 421 underwent one of its most powerful emission outbursts recorded to date. An extensive multi-instrument campaign featuring MAGIC, VERITAS, and NuSTAR provided comprehensive very high-energy (VHE; E &gt; 100 GeV) and X-ray coverage over nine consecutive days. The VHE flux peaked at approximately 15 times that of the Crab Nebula, with rapid variability detected on timescales down to 15 minutes in both X-ray and VHE bands. This rich data set, characterized by its dense temporal coverage and high photon statistics, offers an unparalleled opportunity to probe the broadband emission dynamics in blazars. In this work, we perform a detailed spectral analysis of the X-ray and VHE emissions on subhour timescales throughout the flare. We identify several clockwise spectral hysteresis loops in the X-rays, revealing a spectral evolution more complex than a simple harder-when-brighter trend. The VHE spectrum extends beyond 10 TeV, and its temporal evolution closely mirrors the behavior in the X-rays. Crucially, we report the first evidence of VHE spectral hysteresis occurring simultaneously with the X-ray loops. To interpret these findings, we apply a time-dependent leptonic model to 240 broadband spectral energy distributions (SEDs) binned on a 15 minute scale, allowing us to self-consistently track the particle distribution's history. Our modeling shows that the majority of the subhour flux and spectral variations are driven by changes in the luminosity and slope of the injected electron distribution. The required variations in the electron slope are difficult to reconcile with magnetic reconnection, but they are consistent with a shock-acceleration scenario where the shock compression ratio evolves by a factor of ∼2. The model also points to a relatively stable magnetic field and emitting region size, favoring a scenario where the emission originates from a stationary feature in the jet, such as a recollimation shock. However, this scenario requires a jet Lorentz factor that significantly exceeds values from VLBI measurements to account for the high minimum electron energy implied by the lack of variability in the optical band.

Keywords: Gamma-ray astronomy, Non-thermal radiation sources, BL Lacertae objects, X-ray active galactic nuclei
Probing the Molecular Hearts of Extreme Bipolar Planetary Nebulae with ALMA. We present results from a program of Atacama Large Millimeter Array (ALMA) 1.3 mm (Band 6) molecular line mapping of a sample of nearby, bipolar/pinched-waist, molecule-rich planetary nebulae (PNs; NGC 6302, Hubble 5, NGC 2440, NGC 6445, NGC 2899, and NGC 2818). Maps of 12CO(2─1) and 13CO(2─1) emission as well as emission lines of HCN, HNC, HCO+, CN, and CS—many of these detected in these PNs for the first time—reveal the molecular mass distributions, compositions, and velocity fields of the equatorial and, in some cases, polar regions of the sample PNs. In each case, the bulk of the molecular gas traces an expanding equatorial torus, with torus expansion velocities ranging from ∼15 to ∼50 km s−1 and molecular masses from ∼0.002 to ∼0.1 M⊙. The inferred molecular torus dynamical ages, which span the range ∼500 yr (Hb 5) to ∼11,000 yr (NGC 2818), provide support for a model wherein molecular torus ejection precedes bipolar lobe formation. Collectively, these ALMA survey results provide insight into the rapid structural evolution as well as the zones of irradiated molecular gas within bipolar PNs that are descended from relatively massive progenitors, likely residing in interacting binary systems, over ∼10 kyr of the post-asymptotic giant branch evolution of such systems.

Keywords: Molecular gas, Stellar mass loss, Circumstellar matter, Planetary nebulae, Interferometry
Strategy for Identifying Vera C. Rubin Observatory Kilonova Candidates for Targeted Gravitational-wave Searches. Since the observation of the binary neutron star merger GW170817 and the associated kilonova AT2017gfo, the next joint gravitational-wave/optical kilonova has been highly anticipated. Overlapping observations between the Vera C. Rubin Observatory and the international gravitational-wave detector network are expected soon. Wide-field survey facilities, such as Rubin, can serve dual roles in gravitational-wave astronomy: conducting dedicated optical counterpart searches following gravitational-wave triggers and, through surveys such as the Legacy Survey of Space and Time, providing opportunities for fortuitous kilonova discoveries during routine operations. We use simulations to develop a strategy for identifying kilonova candidates observed by Rubin and processed by the FINK broker. These candidates can be used as astrophysical triggers for a targeted gravitational-wave search. We simulate kilonovae light curves for the first year of Rubin with the latest observing strategy for the Wide-Fast-Deep and the Deep Drilling Fields. Assuming a kilonova rate of 250 Gpc−3 yr−1, we find that Rubin should observe ∼40 kilonovae per year within the gravitational-wave detector horizon (∼500 Mpc). However, only ∼4 will be received by the brokers with a signal-to-noise ratio larger than 5. Most of these will be faint, and detected 1─2 days following the neutron star merger. Photometric and spectroscopic follow-up will be limited to large telescopes. Using archival data from the Zwicky Transient Facility and our proposed selection criteria, we estimate a minimum contamination of at least 30 events per month from other transients and variables, even under our strictest selection criteria. A deep gravitational-wave search targeting Rubin kilonova candidates may lead to the next multimessenger discovery.

Keywords: Neutron stars, Optical astronomy, Transient sources, Transient detection, Gravitational waves
Turbulent Modes in Slow, Alfvénic Slow, and Fast Solar Wind at 1 au. The characterization of solar wind fluctuations provides insight into magnetofluid turbulence. The slow solar wind with high Alfvénicity, the Alfvénic slow solar wind (ASSW), possesses a similar bulk speed as the slow wind, but with fluctuations largely similar to those found in the fast wind. ASSWs have attracted less attention from the turbulence community compared to fast wind flows. G. P. Zank et al. developed a linear mode decomposition (LMD) technique that identifies eight modes in the magnetized solar wind plasma, namely entropy, fast and slow (+/−) magnetosonic (MS), Alfvén (+/−), and magnetic island modes. Using the LMD technique, we present a comparative study of the characteristic modes found in the ASSW, classical slow solar wind (CSSW), and fast solar wind (FSW) events identified by the WIND spacecraft. We investigate the properties of the eight magnetohydrodynamic modes and their spectral characteristic differences in the three solar wind plasma environments at 1 au. We show that in the CSSW, ASSW, and FSW intervals (i) fast MS mode density fluctuations are dominant compared to entropy and slow MS modes, (ii) magnetic island modes clearly dominate Alfvén modes for the transverse fluctuating magnetic field, and (iii) slow MS modes show no significant power spectral density contribution compared to the Alfvén and fast modes in the frequency spectra for velocity fluctuations. The ASSW exhibits characteristics intermediate to the CSSW and FSW in entropy modes, compressibility, the magnetic island-to-Alfvén mode magnetic energy ratio, and kinetic variance anisotropy and magnetic energy variance anisotropy corresponding to Alfvén modes.

Keywords: Slow solar wind, Magnetohydrodynamics, Fast solar wind, Interplanetary turbulence, Solar wind, Alfven waves
Double Stars, Double Disks: Discovering the Young Companion of Herbig Be Star MWC 340. We present the discovery of a young, close-in companion to the early B-type Herbig Be star MWC 340 (V1685 Cyg), a rare system known to host a protoplanetary disk. Herbig Be stars often show complex circumstellar environments shaped by accretion and multiplicity. Using near-infrared (NIR) interferometric observations with the Center for High Angular Resolution Astronomy (CHARA) array over 5 yr in the H band (λ = 1.5─1.7 μm) and K band (λ = 2.1─2.4 μm), we resolve the binary and constrain its orbital and stellar properties through image reconstruction, model fitting, and spectral energy distribution analysis. Orbital modeling suggests a 16 yr minimum period and a 27.5 mas projected separation (≍25 au). Assuming an MA+B = 14.65 M⊙ total mass, we find a best-fit semimajor axis of 21 mas and eccentricity e = 0.69. The reconstructed images reveal a slightly elongated primary that is roughly 3 times brighter than the secondary (flux B/A = 0.28 in the H band, 0.3 in the K band), contributing 65% of the NIR flux. The secondary contributes 21%, with the remainder from extended emission. Stellar photospheres account for only ∼20% of total H- and K-band emission. Isochrone fitting yields masses and ages of 7.5─9 M⊙, 0.13─0.19 Myr for the primary, and 5.8─7 M⊙, 0.28─0.45 Myr for the secondary, suggesting non-coevality unless the secondary is more extinguished. The apparent age discrepancy and high eccentricity ruled out by mass constraints may reflect differential reddening or point to dynamical influence from an unresolved third component. Continued CHARA monitoring and Gaia astrometry will help clarify the system's architecture.

Keywords: Herbig Ae/Be stars, Binary stars, Protoplanetary disks, Interferometric binary stars, Planet formation
Kink Oscillations of Curved Arcade Loops with a Magnetic Shear. We considered the kink oscillations of coronal magnetic loops, which form a coronal loop arcade with a magnetic shear. In this structure, the magnetic field consists of helical lines. A semicircular magnetic slab model was used, and the corresponding dispersion relation was derived. To study oscillations of an individual sigmoid loop, we focused on the quasi-perpendicular propagation limit. Two fast surface waves, denoted FSW+ and FSW−, were found to couple with the Alfvén mode when the magnetic shear parameter α is nonzero. The FSW+ mode corresponds to the vertical kink mode and its frequency is close to the kink frequency. In the propagating regime, the frequency of the forward wave increases with increasing magnetic shear, and that of the backward wave has more complex behavior. The real frequencies of the forward and backward waves in the FSW+ mode exist up to certain values of the magnetic shear parameter. For a larger shear, the frequencies are complex values. The eigenfrequencies of the quasi-standing FSW+ mode were found to increase slightly as the shear parameter increases, and the effect is most prominent for the fundamental mode. The obtained results are relevant in the context of seismological use of the propagating and standing kink waves in sigmoid coronal loops.

Keywords: Solar coronal loops
Energetically Dominant Sunward-propagating Alfvén Waves near 1 au and Their Relation to Large-scale Magnetic Switchbacks. In this paper, we investigate the population of energetically dominant sunward-propagating Alfvén waves (SAWs) using more than 20 yr of data provided by the Wind spacecraft near 1 au. We refer to SAWs as energetically dominant sunward-propagating Alfvén waves within inertial range scales. Key parameters such as normalized cross helicity, plasma compressibility, and magnetic compressibility are used to determine the SAWs. Incorporating the polarity of the heliospheric magnetic field, Alfvén wave modes are identified, which enables the determination of the propagation direction. Occurrence rates of SAWs vary from 1% to 14% depending on the timescale and solar wind stream type considered. Particularly, the relationship between large-scale magnetic field switchbacks and SAWs (for a 1 hr long timescale) is investigated. A methodology utilizing pitch angle distributions of suprathermal electron strahl is employed to identify inverted magnetic field topology. The intervals containing SAWs are cross-referenced and examined with intervals identified as switchbacks . For a sample of 1636 1 hr SAW intervals, 17.5% are associated with magnetic field switchbacks occurring at scales larger than 1 hr. The analysis lends support to the idea of switchbacks as one of the candidate sources for a portion of the SAW population.

Keywords: Solar wind, Alfven waves, Heliosphere
Shock Wave Precursors in M33 Supernova Remnants. We present high-resolution profiles of the Hα, [N II], and [O III] lines of supernova remnants (SNRs) in M33. The 8 km s−1 resolution allows us to separate emission from the photoionized shock precursors from the emission from shocked gas. We find that there is considerable scatter in the ratios of precursor intensity to shock intensity and that the precursors account for up to 26% of the total Hα emission in SNRs in our sample and 35% of the total [N II] and [O III] emission. This is generally similar to what is predicted by steady-state precursor models from MAPPINGS for the shock speeds in the 150─180 km s−1 range, but it is unlikely that all the observed SNRs have shock speeds in this narrow interval. The ratios of precursor to shock emission in Hα indicate faster shocks (though selection effects may play a role). The discrepancies between observed and model ratios of precursor to shock emission may be because the precursors are not in steady state, because our fibers select only a portion of the SNRs, so that accidents of geometry can affect the ratio of precursor to shocked emission that we see, or because the plane-parallel MAPPINGS models do not account for geometrical dilution of the radiation field outside of the SNR. Regardless of the modeling issues, these observations point out that precursor emission needs to be taken into account when analyzing spectra obtained on SNRs, especially in galaxies more distant than the local group.

Keywords: Supernova remnants, Shocks, Triangulum Galaxy
Machine Learning Estimation of Energy Fractions in Magnetohydrodynamic Turbulence Modes. Magnetohydrodynamic (MHD) turbulence plays a central role in many astrophysical processes in the interstellar medium (ISM), including star formation and cosmic-ray transport and acceleration. MHD turbulence can be decomposed into three fundamental modes—fast, slow, and Alfvén—each contributing differently to the dynamics of the medium. However, characterizing and separating the energy fractions of these modes was challenging due to the limited 2D information available from observations. To address this difficulty, we use 3D isothermal and multiphase MHD turbulence simulations to examine how mode energy fractions vary under different physical conditions. Overall, we find that the Alfvén and slow modes carry comparable kinetic-energy fractions and together dominate the turbulent energy budget in multiphase media, while the fast mode contributes the smallest fraction. Relative to isothermal conditions, multiphase simulations exhibit an enhanced fast-mode energy fraction. We further introduce a machine learning─based approach that employs a conditional residual neural network to infer these fractions directly from spectroscopic data. The method leverages the fact that the three MHD modes imprint distinct morphological signatures in spectroscopic maps owing to their differing contributions to density and velocity fluctuations. Our model is trained on a suite of isothermal and multiphase simulations covering typical ISM conditions. We demonstrate that our machine learning model can recover the mode fractions from spectroscopic observables, achieving mean relative normalized errors of approximately 0 and standard deviations of 0.01─0.02 for seen data and 0.1─1.8 for unseen data.

Keywords: Neural networks, Radio astronomy, Interstellar medium, Magnetohydrodynamical simulations
Investigating the Anisotropy of Dispersion Measure Contribution from the Galactic Halo by Using Fast Radio Bursts. We propose a data-driven approach to reconstruct the all-sky distribution of the dispersion measure contribution from the Galactic halo (DMhalo) through a spherical harmonic expansion, enabling an investigation of its possible anisotropies. Based on the NE2001 model and using 92 localized and 574 unlocalized nonrepeating fast radio bursts (FRBs) at Galactic latitudes ∣b∣ &gt; 15°, we find a significant dipole anisotropy in DMhalo, pointing toward (l = 130°, b = +5°) with a 1σ uncertainty of approximately 28°. The DMhalo value in this direction is 63 ± 9 pc cm−3, exceeding the all-sky mean by about 2.6σ. This result is not significantly affected by the choice of Galactic interstellar medium models. Furthermore, even when using a refined sample of 62 localized FRBs (excluding CHIME detections, repeaters, and unlocalized events), the dipole anisotropic structure persists, with a direction of (l = 141°, b = +51°) and a larger 1σ uncertainty of ∼44°. Model comparisons using the Akaike information criterion and Bayesian evidence yield consistent preferences, and together they suggest that current FRB data slightly favor the existence of a dipole structure in DMhalo. If this feature is not a statistical fluctuation or systematic error, its physical origin requires further investigation. Future FRB samples with larger sizes and more complete sky coverage will be essential to confirm or refute this possible anisotropic structure.

Keywords: Cosmology, Circumgalactic medium, High energy astrophysics, Radio transient sources
Observation of the Forbush Decrease on 2024 May 10, Using the ALPAQUITA Air-shower Array at the 70─1000 GV Rigidity Range. The Andes Large area PArticle detector for Cosmic ray physics and Astronomy is a new air-shower array experiment under construction in the Bolivian Andes, and its prototype ALPAQUITA surface array has been operating since 2023 April. In addition to the traditional ≥ 3-hit or ≥ 4-hit coincidences to trigger recording air-shower events, ALPAQUITA records the counting rates of the ≥ 1-hit and ≥ 2-hit events (Any1 and Any2, respectively). We report a successful detection of a Forbush decrease (FD) that occurred on 2024 May 10 caused by a passage of an interplanetary shock formed ahead of the interplanetary coronal mass ejection. The amplitude detected in the Any1 rate is 4.26% ± 0.33% at the median primary rigidity of 76 GV, which is consistent with the observations with the worldwide neutron monitor and muon detector networks. Under the assumption of a power-law rigidity spectrum, we renormalized the errors of the observed amplitude (Aobs) and fitted them as a function of the median primary rigidity (Rm) of each detector and observational method. The result  Aobs=(10.9%±0.9%)×(Rm/10GV)−0.55±0.07  exhibits the hard nature of this event. Our nondetection in the Any2 rate decrease constrains the amplitude with a 2σ upper limit to be 0.95% at 960 GV. This marginally suggests an existence of a spectral softening between 100 and 1000 GV, as also suggested by the Misato underground muon detector at 145 GV. Although a strong geomagnetic storm was observed during this period, we conclude it does not impact our results. Our novel technique realizes a unique coverage to study the behavior of the FDs at the highest rigidity.

Keywords: Interplanetary shocks, Cosmic ray detectors, Forbush effect, Galactic cosmic rays, Solar coronal mass ejection shocks, Cosmic ray showers, Solar activity