Sazuna/UAT_keywords huggingface dataset:
SOFIA/HAWC+ Far-infrared Polarimetric Large Area CMZ Exploration Survey. V. The Magnetic Field Strength and Morphology in the Sagittarius C Complex. We present an analysis of the magnetic field strength and morphology in the Sagittarius C complex (Sgr C; G359.43-0.09) in the Milky Way's Central Molecular Zone (CMZ), using the 214 μm polarimetry data acquired with the High-resolution Airborne Wide-band Camera instrument on board the Stratospheric Observatory for Infrared Astronomy. We conduct a modified Davis─Chandrasekhar─Fermi analysis of individual clouds and find that the sky-plane magnetic field strength varies from highly turbulent regions having inferred strengths of ∼30 μG to regions of relatively uniform field orientation having strengths of ∼400 μG. Several hundred magnetic field pseudovectors in the Sgr C region were measured to trace the projected magnetic field orientation within cold molecular clouds, and as is the trend throughout the CMZ, they show a higher polarization fraction toward the periphery of the clouds. The magnetic field orientations suggest that outflows from active star-forming regions, such as the G359.43-0.10 extended green object and the protostellar source FIR-4 (G359.43+0.02), cause high turbulence in their vicinity. The magnetic field direction is found to be tangential to the surface of the Sgr C H II region, which displays spatial correspondence with two [C II] emission cavities reported in the H II region, signifying a compression front between the H II region and the surrounding dense clouds. Several other features in the vicinity of Sgr C, especially numerous nonthermal radio filaments and a diffuse source of X-ray emission to the immediate southwest of the H II region, are discussed with regard to the magnetic field measurements.

Keywords: Galactic center, Polarimetry, Infrared astronomy, Interstellar medium, Magnetic fields
Polytropic Analysis of Large-scale Compressive Fluctuations in the Solar Wind: Fluid and Kinetic Behavior. Large-scale compressive plasma fluctuations in the solar wind are typically characterized by an anticorrelation between the plasma density and the magnitude of the magnetic field, and thus share polarization properties with slow waves. The nature of the slow modes in the solar wind with respect to the polarization properties of the plasma has been found to be in better agreement with the magnetohydrodynamic (MHD) slow mode predictions compared to that of the kinetic slow mode. The polytropic behavior of the plasma in compressive fluctuations may provide further insight into the nature of the slow mode, since the MHD, Chew–Goldberger–Low (CGL), and kinetic slow modes predict different proton polytropic indices (γ). Using Solar Orbiter observations, we identify two 1–2 hr intervals of compressive fluctuations with a low probability of streamline crossings, determine the effective polytropic index of protons and electrons for both events, and compare them with the theoretical expectations of MHD, CGL, and kinetic slow modes. One interval exhibits characteristics of the MHD slow mode having a clear isotropic closure for the protons with γp ≈ 1.7, while the other interval is more consistent with the kinetic slow mode. The calculated electron polytropic index is γe ≈ 0.7 for both events. We decompose the signals into three different frequency bands and repeat our analysis, finding a similar difference in the proton polytropic behavior between the two events. A scale dependence is also observed, suggesting that kinetic effects become more prominent at smaller scales.

Keywords: Space plasmas, Magnetohydrodynamics, Solar wind, Plasma physics
Formation of the Two-armed Phase Spiral from Multiple External Perturbations. Recent studies using the Gaia DR3 data have revealed a two-armed phase spiral in the Z–VZ phase space in the inner disk. In this study, we present new features of the two-armed phase spiral revealed by the Gaia data and a new mechanism to explain such features with multiple external perturbations. By segmenting the Gaia DR3 Radial Velocity Spectrometer (RVS) catalog based on Jϕ (or Rg) and θϕ, we confirm the existence of a clear two-armed phase spiral in the inner disk. Moreover, we identify a different two-armed phase spiral pattern at slightly larger radii, resembling a weak secondary branch along with the prominent major branch. At a given radius, with the azimuthal angle increasing, we observe a systematic transition of the two-armed phase spiral, with the significance of one branch weakened and another branch enhanced. This two-armed phase spiral may be due to the overlapping of distinct one-armed phase spirals. At different radii, the perturbation times estimated from each branch of the two-armed phase spiral are ∼320 and ∼500 Myr, respectively, suggesting that the Galactic disk could be impacted by double external perturbers separated by ∼180 Myr. We also performed test-particle simulations of the disk perturbed by two satellite galaxies, which successfully generated a two-armed phase spiral similar to the observation. Both the observation and simulation results suggest that the signature in the Z–VZ phase space of earlier perturbations may not be completely erased by the more recent one.

Keywords: Stellar kinematics, Milky Way dynamics
Acceleration and Transport of the Unstable Cosmic-Ray Isotope <SUP>60</SUP>Fe in Supernova-enriched Environments. The unstable isotope 60Fe, with a half-life of 2.6 million years, is produced primarily in supernova explosions. The observed presence of 60Fe in cosmic rays and its detection in deep-sea crusts and sediments suggest two possible scenarios: either the direct acceleration of 60Fe from supernova ejecta or its enrichment in the circumstellar material surrounding supernova progenitors, which indicates cosmic ray production in clusters of supernovae. Focusing on the latter scenario, we consider an environment shaped by successive supernova explosions, reminiscent of the Local Bubble around the time of the most recent supernova explosion. We independently tracked the evolution of the 60Fe mass ratio within the Local Bubble using passive scalars. To investigate the spectra of protons and 60Fe, we explicitly modeled cosmic-ray acceleration and transport at the remnant of the last supernova by simultaneously solving the hydrodynamical equations for the supernova outflow and the transport equations for cosmic rays, scattering turbulence, and large-scale magnetic field, using the time-dependent acceleration code Radiation Acceleration Transport Parallel Code. The main uncertainty in our prediction of the local 60Fe flux at about pc = 1 GeV nuc‑1 is the magnetic-field structure in the Local Bubble and the cosmic-ray diffusion beyond the approximately 100 kyr of evolution covered by our study. We found that if the standard galactic propagation applies, the local 60Fe flux would be around 3% of that measured. If there is a sustained reduction in the diffusion coefficient at and near the Local Bubble, then the expected 60Fe flux could be up to 30% of that measured.

Keywords: Supernova remnants, Superbubbles, Cosmic rays
Cosmic-Ray Propagation in Young Embedded Clusters. This paper constructs a quantitative description for the geometrical properties of young stellar clusters using a Delaunay mesh. This approach defines the paths that connect cluster members and can be used to characterize the distribution of path lengths and other geometrical properties of these systems. As an application, we use this characterization to study the propagation of cosmic rays through the cluster, and estimate the resulting enhancement of cosmic-ray energy density. In the limit where magnetic fields are strong enough to confine cosmic rays, the magnetic field lines provide paths between neighboring stellar members, so that particles must travel along the paths defined by the Delaunay mesh. As a result, cosmic rays, which are locally accelerated by young stellar objects in the cluster, must random walk through the mesh in order to escape. For young stellar clusters with the properties found in the solar neighborhood, we find that once the gas has been dispersed (so that particle attenuation is insignificant), the increased escape time due to the random walk enhances the energy density in cosmic rays by a factor of ∼100 over the background on size scales of circumstellar disks.

Keywords: Star forming regions
Magnetic Activities of Wolf 359: Starspot Distribution and Quasiperiodic Pulsation Using TESS Data. Wolf 359 is the fifth closest (∼2.4 pc) star to Earth and a candidate exoplanet-hosting M6 dwarf. We studied the distribution of starspots and flaring activities of Wolf 359 to understand its stellar atmosphere and magnetic activities. Using 2 minute short-cadence Transiting Exoplanet Survey Satellite (TESS) data on this highly active star, we found 48, 46, and 32 flares in Sectors 45, 46, and 72, respectively. The rotation period from TESS is estimated to be 2.69 days with negligible error, which matches well with the previous literature values. We estimated the bolometric flare energy in the range of 1030–1032 erg, including a high flare event of 4.2 ± 0.5 × 1032 erg with a duration of 244.8 minutes. A high magnetic field strength of 0.18 kG is required to produce such a high flare. Interestingly, we first detect two complex flare events with oscillation periods of 104.56 ± 0.59 minutes and 39.22 ± 0.42 minutes in Sectors 45 and 46, probably caused by periodic motions of the emitting plasma or oscillatory reconnection. We estimated the mean spot temperature to be 2772 ± 100 K and the spot area to be 1.30% of the area of the star. We also correlate the duration of a flare event with its energy,  △t∝Ebol0.55±0.01 , and this steeper slope likely reflects differences in magnetic field topology, atmospheric cooling behavior, and possibly multi-loop flare complexity compared to other M dwarfs. We noticed the deviation in flare rate distribution and orbital phases, indicating the presence of highly active regions, or it might be a star–planet interaction.

Keywords: M dwarf stars, Starspots, Stellar flares, Star-planet interactions, Magnetic fields, Habitable planets
Probing the Internal Structure of Neutron Stars: A Comparative Analysis of Three Different Classes of Equations of State. Sound speed can be an important tool in unravelling the nature of matter at the cores of neutron stars. In this study, we investigate three major classes of equations of state: monotonic, nonmonotonic, and discontinuous, depending on the nature of the sound speed in neutron stars. The monotonic equation of state refers to hadronic models, the nonmonotonic refers to the quarkyonic or smooth crossover models, and discontinuous refers to the first-order phase transition models. We generate a large ensemble of equations of state for three classes with the model-agnostic speed of sound interpolation approach. Further, we find the Bayesian posterior distribution employing the recent astrophysical and gravitational wave constraints. Our main aim is to identify which class of equation of state is most favored by present astrophysical and gravitational wave bounds. The analysis with posterior distribution fails to provide a satisfactory result with the usual neutron star observations like mass–radius and f-mode oscillations. Universal relations are seen as not being really universal, as they show considerable spread and significant overlaps among the different classes. The Bayesian evidence also fails to provide definitive discrimination between the models, though the astrophysical data slightly favors the nonmonotonic equation of state, while the particular gravitational-wave constraints favor the monotonic one.

Keywords: Neutron stars, Neutron star cores, Pulsars
Low-mass Eclipsing Binaries KIC 4908495, KIC 6466939, and KIC 9474485: Isolated Pre-main-sequence Systems?. We present a detailed analysis of three Kepler eclipsing binaries, KIC 4908495, KIC 6466939, and KIC 9474485. Our analysis reveals that these systems are composed of components possessing a lower mass than our Sun with slight subsolar metallicities. Individual analysis of the evolutionary status of each system interestingly suggests that all component stars in all three systems are pre-main-sequence (PMS) stars that have already developed a radiative core and are on the way to the zero-age main sequence in the Hertzsprung–Russell diagram. Estimated ages are 25 ± 5, 22 ± 6 and 25 ± 15 Myr for KIC 4908495, KIC 6466939 and KIC 9474485, respectively. However, none of these systems is a cluster or association member, indicating that the targets might be isolated eclipsing binaries possessing PMS components. Kepler light curves show noticeable wave-like variability at out-of-eclipse parts, suggesting a considerable magnetic activity manifesting as the rotational modulation of cool surface spots or spot groups. Projected rotational velocities of the components and amplitude spectrum of out-of-eclipse variability suggest either asynchronous rotation of the component stars or the surface differential rotation of the magnetically active component.

Keywords: Eclipsing binary stars, Fundamental parameters of stars, Detached binary stars, Stellar activity
Energy Budget in the 2017 September 7 "Cold" Solar Flare. A subclass of early impulsive solar flares, cold flares, was proposed to represent a clean case, where the release of the free magnetic energy (almost) entirely goes to the acceleration of the nonthermal electrons, while the observed thermal response is entirely driven by the nonthermal energy deposition to the ambient plasma. This paper studies one more example of a cold flare, which was observed by a unique combination of instruments. In particular, this is the first cold flare observed with the Expanded Owens Valley Solar Array and, thus, for which the dynamical measurement of the coronal magnetic field and other parameters at the flare site is possible. With these new data, we quantified the coronal magnetic field at the flare site but did not find statistically significant variations of the magnetic field within the measurement uncertainties. We estimated that the uncertainty in the corresponding magnetic energy exceeds the thermal and nonthermal energies by an order of magnitude; thus, there should be sufficient free energy to drive the flare. We discovered a very prominent soft-hard-soft spectral evolution of the microwave-producing nonthermal electrons. We computed energy partitions and concluded that the nonthermal energy deposition is likely sufficient to drive the flare thermal response similarly to other cold flares.

Keywords: Solar flares, Non-thermal radiation sources, Solar magnetic fields, Solar x-ray flares, Solar activity, Solar radio flares
A Theoretical Three-dimensional Diagram to Separate Star Formation, Active Galactic Nuclei, and Shocks in Galaxies. The excitation sources in galaxies are frequently mixed owing to active galactic nucleus (AGN) and stellar feedback, including star formation, AGN, and shock excitation. Disentangling the star formation, AGN, and shocks in galaxy integral field unit (IFU) spectra at optical wavelengths is crucial to expanding the galaxy sample for AGN and stellar feedback studies, given the lack of multiwavelength observations for most of the galaxies that are observed in optical wavelengths. Previous methods to address this issue either have a limited application range or are highly uncertain in separating AGN from shock excitation. Here we propose a theoretical three-dimensional (3D) diagram. This theoretical 3D diagram overcomes the limitations of previous methods and can simultaneously separate star formation, AGN, and shocks in active galaxies. Along with the separation, the new theoretical 3D diagram also constrains the gas metallicity, ionization parameter, and gas pressure within the galaxy. By applying the Very Large Telescope/MUSE IFU data and the Wide Field Spectrograph IFU data for NGC 5728 on the theoretical 3D diagram, we find a star-forming ring surrounding the galaxy center with a projected radius of ∼1 kpc in the sky plane, an AGN ionized bicone extended up to ∼2 kpc from the nuclear center, and a fast-shock-dominated disk region at the base of the AGN outflow, which is likely associated with a nuclear accretion disk or the result of jet─interstellar medium interaction. The theoretical 3D diagram opens a new window in which to study the interplay among star formation, AGN, and shocks in active galaxies.

Keywords: Active galactic nuclei, Emission line galaxies
Solar Modulation of Galactic Cosmic Rays from Hydrogen to Nickel Based on a Modified Force-field Approach. Galactic cosmic rays (GCRs), consisting predominantly of fully stripped nuclei, are significantly modulated by solar activity and represent a major radiation hazard for long-duration human space exploration. This study presents a comprehensive GCR modulation model based on a modified force-field approach, extending previous work by Z. Shen et al. to heavier nuclei. The local interstellar spectra (LIS) for elements from hydrogen to nickel are derived by fitting observations from Voyager, Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics, Alpha Magnetic Spectrometer-02, Advanced Composition Explorer Cosmic Ray Isotope Spectrometer, HEAO3-C2, and others. The solar modulation potential ϕ(E) is described by a double power-law function with an exponential tail. Due to differences in LIS spectral shapes and mass-to-charge ratio-dependent modulation effects, protons and helium have distinct ϕ values, while heavier nuclei share the same ϕ as helium. The time-dependent parameters within the ϕ expression are determined by fitting selected GCR measurements and subsequently reconstructed using sunspot number, heliospheric current sheet tilt angle, and heliospheric magnetic field polarity, enabling the development of a predictive GCR model. The results successfully reproduce the 11 and 22 yr GCR cycles, with good agreement with observations since Solar Cycle 19 across different particle species and energies. Additionally, this study investigates long-term solar modulation over millennial timescales utilizing cosmogenic 14C isotope records and assesses radiation dose rates relevant for deep space missions, showing good agreement with Cosmic Ray Telescope for the Effects of Radiation/D1D2 measurements. This work thus provides a new framework for predicting GCR fluxes and associated radiation exposure in deep space.

Keywords: Galactic cosmic rays, Solar activity, Heliosphere
Diffuse X-Ray-emitting Gas in the Central Region of Star-forming Galaxies. The interstellar medium of galaxies, with temperatures reaching several million degrees, provides a pivotal perspective for understanding the physical and chemical properties of star formation, galactic evolution, and their associated feedback mechanisms. We use archival data from Chandra observations to extract the diffuse X-ray emission from 23 nearby star-forming galaxies and study its correlation with star formation activity in the central region of these galaxies. The surface brightness profile of each galaxy presents a sharp decrease in the central region of ∼0.3−2 kpc and then varies slowly outside this range. Compared to the global relation between the diffuse thermal X-ray luminosity from hot gas ( L0.5−2keVgas ) and the star formation rate (SFR), we found a superlinear relation of  log(Lgas0.5−2keV/ergs−1)  =  1.34log(SFR/M⊙yr−1)+40.15  for the center of these sample galaxies. This result suggests that more intense stellar feedback is associated with stronger star formation activity in the central region of star-forming galaxies, where more energy output from supernovae and stellar winds is converted into X-ray flux. Furthermore, the slope of the  L0.5−2keVgas ─SFR relation anticorrelates with spatial scale in the galactic central region. This indicates that the characteristics of central hot gas emission are gradually averaged over larger areas. The diffuse X-ray luminosity also shows a good correlation with molecular gas, stellar mass, and midplane pressure traced by the baryonic mass, although these relations show relatively large scatter.

Keywords: Spiral galaxies, Star formation, Interstellar medium, Scaling relations
Explaining JWST Counts with Galaxy Formation Models. A distinct power-law break is apparent at mAB ∼ 21 in the deep near-infrared PEARLS-JWST galaxy counts. The break becomes more pronounced at longer wavelengths, with the slope flattening smoothly with apparent magnitude in the shortest band used at 0.9 μm, and trending toward an increasingly broken slope by the longest wavelength passband of JWST's Near Infrared Camera, 4.4 μm. This behaviour is remarkably well predicted by the GALFORM semi-analytical model of galaxy formation. We use the model to diagnose the origin of this behaviour. The features that are responsible for the break are (1) the inherent break in the luminosity function (LF); (2) the change in the volume element with redshift; (3) the redshift-dependent nature of the k-correction (with 1 contributing to the existence of the break and 2–3 contributing to its shape). We study the contribution to these effects by their morphology using the bulge-to-total stellar mass ratio. The way in which bulge-dominated galaxies populate the bright end of the LF while disk-dominated galaxies dominate the faint end is preserved in the galaxy number counts, with a characteristic stellar mass at a break of ∼1010M⊙. The shape of the number counts is mainly driven by galaxies with relatively low redshift (z ≲ 2) for a limit of mAB ≲ 28. We give a comprehensive description of why the galaxy number counts in the near-infrared PEARLS-JWST observation look the way they do and which population of galaxies is dominant at each apparent magnitude.

Keywords: Galaxy formation, Cosmological models, Observational cosmology, James Webb Space Telescope, Galaxy evolution, Galaxy counts, Hierarchical models, Astronomical simulations
A Statistical Analysis of Magnetic Parameters in Solar Source Regions of Halo Coronal Mass Ejections with and without Solar Energetic Particle Events. Large solar energetic particles (SEPs) can cause adverse space weather hazards to human technology, and such events are especially associated with halo coronal mass ejections (CMEs). But in turn, a significant portion of halo CMEs are not associated with large SEPs. The objective of this study is to gain an understanding of the source region distinctions between halo CMEs in SEP and non-SEP events. Among the 176 halo CMEs observed from 2010 to 2024, we screen out 45 large SEP events and 131 non-SEP events from this data set. It is revealed that CME speed is a good discriminator between SEP and non-SEP events. Through classifying the source regions of all the halo CMEs, we find that 53% of SEP events originate from "single AR (active region)," and 47% from "multiple ARs" or "outside of ARs." The corresponding proportion for non-SEP events is 70% and 30%. This suggests that SEP source regions are more likely to originate from large-scale sources. We have also calculated the relevant magnetic parameters of the source regions and found that SEP source regions have higher magnetic free energy and reconnection flux compared to non-SEP source regions. However, SEP source regions are smaller in terms of the intensive magnetic parameters such as mean characteristic magnetic twist α and mean shear angles. Our statistical results can provide new potential variables for forecasting SEPs.

Keywords: Solar active region magnetic fields, Solar flares, Solar energetic particles, Solar coronal mass ejections, Solar activity