Sazuna/UAT_keywords huggingface dataset:
An Anisotropic Plasma Model of the Heliospheric Interface. We present a pioneering model of the interaction between the solar wind and the surrounding interstellar medium that includes the possibility of different pressures in directions parallel and perpendicular to the magnetic field. The outer heliosheath region is characterized by a low rate of turbulent scattering that would permit development of pressure anisotropy. The effect is best seen on the interstellar side of the heliopause, where a narrow region develops with an excessive perpendicular pressure resembling a plasma depletion layer typical of planetary magnetospheres. The magnitude of this effect for typical heliospheric conditions is relatively small owing to proton–proton collisions. We show, however, that if the circumstellar medium is warm and tenuous, a much broader anisotropic boundary layer can exist, with a dominant perpendicular pressure in the southern hemisphere and a dominant parallel pressure in the north.

Keywords: Astrophysical fluid dynamics, Interstellar clouds, Heliosphere
Dependence of Planet Populations on Stellar Mass and Metallicity: A Pebble-accretion-based Planet Population Synthesis Model. The formation and evolution of planetary systems are linked to their host stellar environment. In this study, we employ a pebble-accretion-based planet population synthesis model to explore the correlation between planetary properties and stellar mass/metallicity. Our numerical results reproduce several main aspects of exoplanetary observations. First, we find that the occurrence rate of super-Earths, ηSE, follows an inverted V-shape in relation to stellar mass: it increases with stellar mass among lower-mass dwarfs, peaks at early M dwarfs, and declines toward higher-mass GK stars. Second, super-Earths grow ubiquitously around stars with various metallicities, exhibiting a flat or weak ηSE dependence on Z⋆. Third, giant planets in contrast form more frequently around stars with higher mass/metallicity. Lastly, we extend a subset of simulations to 1 Gyr to investigate the long-term evolution of the systems' architecture. By converting our simulated systems into synthetic observations, we find that the eccentricities and inclinations of single-transit systems increase with stellar metallicity, while these dependencies in multiplanet systems remains relatively weak. The alignment between our results and observations provides key insights into the connection between planet populations and stellar properties.

Keywords: Exoplanet dynamics, Exoplanet migration, Exoplanets, Exoplanet systems, Exoplanet formation
Asteroseismic Analysis of a Red Giant KIC 9145955 by Including the Small-scale Magnetic Fields in the Atmosphere. Recent convincing evidence is found within asteroseismology that suggests the magnetic fields exist in three red giants. Research on small-scale magnetic fields in the Sun and HD 49385 has shown that they have a certain corrective effect on the systematic discrepancies between observed and theoretical frequencies. Here we apply a similar method applied for the Sun to a red giant, KIC 9145955, to explore the impact of small-scale magnetic fields in the photosphere on its frequencies. We find that the calculated frequencies of our best-fit model, which simulates the effect of the magnetic fields by artificially modifying the Eddington T‑τ relation, perfectly match those of the observed l = 0, 1, and 2 modes, indicating the existence of small-scale magnetic fields with an upper strength limit of 65 G and concentrating at a height 13,100 km in the photosphere. Based on the best-fit model, we revise the stellar parameters of KIC 9145955 as M = 1.23 ± 0.04 M⊙, R = 5.57 ± 0.06 R⊙, L = 19.85 ± 0.5 L⊙, Age = 3.83 ± 0.5 Gyr, MHe = 0.2108 ± 0.0005 M⊙, and RHe = 0.0306 ± 0.0001 R⊙.

Keywords: Magnetohydrodynamics, Stellar cores, Stellar magnetic fields, Asteroseismology, Stellar atmospheres, Stellar evolution
Overall Ultra-high Energy Neutrino Emission from GRBs During Jet Expansion. The ultrarelativistic jet released in gamma-ray bursts (GRBs) is expected to produce ultra-high-energy cosmic rays (UHECRs), prompt gamma-ray emission, and hence prompt high-energy neutrinos by photopion interactions. In this work, we calculate the time-integrated neutrino spectrum during the expansion of jets by taking into account the time evolution of cosmic-ray and secondary spectra and neutrino production. We numerically solve the continuity equations for nucleons, pions, and muons for their spectral evolution. Since pion and muon damping weakens as the jet expands, the neutrino production at large radii at high energies may dominate that around the jet energy dissipation radius. Compared with the usually adopted approaches that only consider neutrino production around the energy dissipation radius, the overall UHE neutrino fluence integrated over time can be significantly larger, and the flavor fraction of electron neutrinos as function of neutrino energy is different at UHE, due to neutrino production at radii much larger than the energy dissipation radius. The faster magnetic field decay leads to larger UHE neutrino fluence, and the UHE neutrino spectra are weakly dependent on the energy dissipation radius and the jet Lorentz factor. Observations of prompt EeV neutrinos from GRBs by the next-generation neutrino telescopes, e.g., GRAND and IceCube-Gen2, will test the hypothesis of GRBs as UHECR sources and probe the physics of GRB jets.

Keywords: Neutrino astronomy, Gamma-ray bursts, Particle astrophysics, Cosmic rays
The Spheroidal Analog Method for Modeling Irregular Porous Aggregates. It is shown that the optical properties of an irregular porous grain with effective radius aeff ≲ 3λ (where λ is the wavelength) can be well approximated by a "spheroidal analog": a spheroid with appropriate axial ratio and size, with a dielectric function obtained from an effective medium theory. Prescriptions for specifying the axial ratio and porosity of the spheroidal analog, based on simple geometric properties, are given. The accuracy of the spheroidal analog method is studied for irregular grains with a range of structures and porosities. Different effective medium theories are compared; Bruggeman's theory is found to give the best results. The accuracy of the spheroidal analog method justifies the use of spheroids for modeling absorption, scattering, and polarization by interstellar, circumstellar, or interplanetary dust.

Keywords: Interstellar dust, Interstellar dust extinction, Starlight polarization, Radiative transfer, Interstellar scattering
A Detailed Single-pulse Study of Four-component Pulsar PSR J1239+0326 Discovered by FAST. We report on a single-pulse study of PSR J1239+0326 discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in the Commensal Radio Astronomy FAST Survey. The observations were conducted at a central frequency of 1.25 GHz. The integrated pulse profile of PSR J1239+0326 shows four distinct components, implying a central line of sight traversing a presumed double cone core emission beam. We found correlations between intensities of the first and fourth components and the second and the core components, indicating that the charges emitted between the correlated components may be related. Based on rotating vector model fitting, we estimated the inclination angle between the magnetic and the rotational axes to be 10°. No nulls, giant pulses, or giant micropulses were detected during observation sessions. Outer-cone components are observed to display "even-odd" subpulse modulation with quasiperiodicity around 2P, where P is the rotational period of the pulsar. The trailing component exhibits energy modulation with quasiperiodicities of 19P and 26P. This two-mode modulation could result from the combination of sub-pulse drifts and the feedback between the voltage difference across the polar gap and surface thermal emission by backflowing charges.

Keywords: Pulsars
On Neutron Star Natal Kicks in High-mass X-Ray Binaries: Insights from Population Synthesis. The motion of neutron stars (NSs) in the Galaxy is largely dependent on natal kicks received by the NSs during supernova explosions. Thus, the measured peculiar velocities of NS high-mass X-ray binaries (HMXBs) provide valuable clues to natal kicks, which also play an important role in the evolution of HMXBs. In this work, we collect proper motions, radial velocities, and parallaxes for 36 NS HMXBs to derive their peculiar velocities at the birth of the NSs. We then use binary population synthesis to simulate the velocities of NS HMXBs with various choices of the kick velocity distribution for both core-collapse and electron-capture supernovae. Comparing the simulated and measured velocities, orbital periods, and eccentricities, we show that the natal kick distribution that can best match the observations is characterized by a bimodal Maxwellian distribution with σ1 = 320 km s‑1 (for core-collapse supernovae) and σ2 = 80 km s‑1 (for electron-capture supernovae) and the He core mass for the latter in the range of (1.83–2.25) M⊙. Our findings provide useful insights for further population synthesis and binary evolution studies of NS binaries.

Keywords: Neutron stars, High mass x-ray binary stars, Supernovae
Estimating the Poynting Flux of Alfvénic Waves in Polar Coronal Holes across Solar Cycle 24. Alfvénic waves are known to be prevalent throughout the corona and solar wind. Determining the Poynting flux supplied by the waves is required for constraining their role in plasma heating and acceleration, as well as providing a constraint for Alfvén-wave-driven models that aim to predict coronal and solar wind properties. Previous studies of the Alfvénic waves in polar coronal holes have been able to provide a measure of energy flux for arbitrary case studies. Here, we build upon previous work and take a more systematic approach, examining if there is evidence for any variation in vertical Poynting flux over the course of the solar cycle. We use imaging data from the Solar Dynamics Observatory's Atmospheric Imaging Assembly to measure the displacements of the fine-scale structure present in coronal holes. It is found that the measure for vertical Poynting flux is broadly similar over the solar cycle, implying a consistent contribution from waves to the energy budget of the solar wind. There is variation in energy flux across the measurements (around 30%), but this is suggested to be due to differences in the individual coronal holes rather than a feature of the solar cycle. Our direct estimates are in agreement with recent studies by Z. Huang et al., who constrain the vertical Poynting flux through comparison of predicted wind properties from Alfvénic-wave-driven turbulence models to those observed with OMNI at 1 au. Taken together, both sets of results points toward a lack of correlation between the coronal Poynting flux from waves and the solar cycle.

Keywords: Solar coronal holes, The Sun, Solar coronal plumes, Solar corona
Cloud-scale Gas Properties, Depletion Times, and Star Formation Efficiency per Freefall Time in PHANGS─ALMA. We compare measurements of star formation efficiency to cloud-scale gas properties across the PHANGS─ ALMA sample. Dividing 67 galaxies into 1.5 kpc scale regions, we calculate the molecular gas depletion time   and the star formation efficiency per freefall time   for each region. Then we test how   and   vary as functions of the regional mass-weighted mean molecular gas properties on cloud scales (60─150 pc): gas surface density,  , velocity dispersion,  , virial parameter,  , and gravitational freefall time,  .   and   correlate positively, consistent with the expectation that gas density plays a key role in setting the rate of star formation. Our fiducial measurements suggest   and  , though the exact numbers depend on the adopted fitting methods. We also observe anticorrelations between   and   and between   and  . All three correlations may reflect the same underlying link between density and star formation efficiency combined with systematic variations in the degree to which self-gravity binds molecular gas in galaxies. We highlight the  ─  relation because of the lower degree of correlation between the axes. Contrary to theoretical expectations, we observe an anticorrelation between   and   and no significant correlation between   and  . Our results depend sensitively on the adopted CO-to-H2 conversion factor, with corrections for excitation and emissivity effects in inner galaxies playing an important role. We emphasize that our simple methodology and clean selection allow for easy comparison to numerical simulations and highlight this as a logical next direction.

Keywords: Molecular gas, Interstellar medium, Star formation, Disk galaxies
Mapping Galactic Dust Emission and Extinction with H I, H II, and H<SUB>2</SUB>. Neutral hydrogen (H I) emission closely traces the dust column density at high Galactic latitudes and is thus a powerful tool for predicting dust extinction. However, the relation between H I column density NHI and high-latitude dust emission observed by Planck has large-scale residuals at the level of ≲20% on tens of degree scales. In this work, we improve H I-based dust templates in the north/south Galactic poles covering a sky fraction of fsky = 13.5%/11.0% (5577/4555 deg2) by incorporating data from ionized (H II) and molecular (H2) gas phases. We make further improvements by employing a clustering analysis on the H I spectral data to identify discrete clouds with distinct dust properties. However, only a modest reduction in fitting residuals is achieved. We quantify the contributions to these residuals from variations in the dust-to-gas ratio, dust temperature and opacity, and magnetic field orientation using ancillary data sets. Although residuals in a few particular regions can be attributed to these factors, no single explanation accounts for the majority. Assuming a constant dust temperature along each line of sight, we derive an upper limit on the high-latitude dust temperature variation of σT &lt; 1.28 K, lower than the temperature variation reported in previous studies. Joint analysis of multiple existing and upcoming data sets that trace Galactic gas and dust properties is needed to clarify the origins of the variation of gas and dust properties found here and to significantly improve gas-based extinction maps.

Keywords: Interstellar dust, Molecular gas, Interstellar phases, Interstellar atomic gas, Interstellar thermal emission, Molecular clouds, Neutral hydrogen clouds, H I line emission, Warm ionized medium, Cold neutral medium, Interstellar medium, Diffuse interstellar clouds
Connecting a Magnetized Disk to a Convective Low-mass Protostar: A Global 3D Model of Boundary Layer Accretion. In the early stages of star formation, boundary layer accretion, where protostars accrete material from disks extending down to their surfaces, plays a crucial role. Understanding how a magnetorotational-instability (MRI)-active disk connects to a protostar's surface remains a significant challenge. To investigate the mechanisms of mass and angular momentum transfer, we develop a global, 3D magnetohydrodynamic model of boundary layer accretion around a magnetized, convective low-mass protostar. Our results reveal that angular momentum transport mechanisms transition significantly from the outer MRI-active disk to the protostellar surface. Various mechanisms—MRI, spiral shocks, coronal accretion, jets, and disk winds—contribute to angular momentum transfer, resulting in three distinct disk structures: (1) the MRI-active disk, (2) the transition layer, and (3) the boundary layer. The simulated protostar is strongly magnetized due to the accumulation of the disk fields, wrapping by disk toroidal fields, and stellar dynamo activity. Magnetic concentrations analogous to starspots form on the protostar and interact with the rotating disk gas to generate spiral shocks. These shocks play a key role in driving accretion. These findings demonstrate the necessity of global MHD models for a comprehensive understanding of angular momentum transport. Additionally, we identify explosive events triggered by magnetic reconnection in both the protostar and the disk atmosphere. We also find decretion flows in the disk midplane, which may be important for the radial transport of refractory materials, such as calcium-aluminum-rich inclusions precursor gas, to the outer disk.

Keywords: FU Orionis stars, Star formation, Protoplanetary disks, Protostars, Magnetohydrodynamical simulations
Sequential Ejections of Plasma Blobs Due to Unbraiding of Tangled Loops in the Solar Atmosphere. Nanoflares, which are consequences of braids in tangled magnetic fields, are an important candidate to heat the solar corona to a million degrees. However, their observational evidence is sparse, and many of their observational characteristics are yet to be discovered. With the high-resolution observations taken by the Extreme Ultraviolet Imager onboard the Solar Orbiter, here we study a series of ejections of plasma blobs resulting from braided magnetic loops in the upper transition region and reveal some critical characteristics of such processes. The cores of these ejections have a size of about 700 km, a duration of less than 1 minute, and a speed of about 90 km s‑1. An important characteristic is that these plasma blobs are apparently constrained by the postreconnection magnetic loops, along which they show an extension of up to about 2000 km. The propagation of unbraiding nodes along the main axis of the tangled loops has a speed of about 45 km s‑1. The separation angles between the postreconnection loops and the main axis of the tangled loops are about 30°. The observations from the Atmospheric Imaging Assembly reveal that the braiding loops are upper transition region structures. Based on these observations, the typical magnetic free energy producing a blob is estimated to be about 3.4 × 1023 erg, well in the nanoflare regime, while the kinematic energy of a blob is about 2.3 × 1023 erg, suggesting that a majority of magnetic free energy in a magnetic braid is likely transferred into kinematic energy.

Keywords: Solar atmosphere, Solar magnetic reconnection, Solar coronal loops, Solar coronal heating, Solar corona, Solar transition region
Theory of the Kinetic Helicity Effect on Turbulent Diffusion of Magnetic and Scalar Fields. Kinetic helicity is a fundamental characteristic of astrophysical turbulent flows. It is not only responsible for the generation of large-scale magnetic fields in the Sun, stars, and spiral galaxies, but it also affects turbulent diffusion, resulting in the dissipation of large-scale magnetic fields. Using the path integral approach for random helical velocity fields with a finite correlation time and large Reynolds numbers, we show that turbulent magnetic diffusion is reduced by the kinetic helicity, while the turbulent diffusivity of a passive scalar is enhanced by the helicity. The latter can explain the results of recent numerical simulations for forced helical turbulence. One of the crucial reasons for the difference between the kinetic helicity effect on magnetic and scalar fields is related to the helicity dependence of the correlation time of a turbulent velocity field.

Keywords: Cosmic magnetic fields theory
Impulsive Solar Flares in the Parker Solar Probe Era. I. Low-energy Electron, Proton, and Alpha Beams. Multiple instruments on board the Parker Solar Probe spacecraft have detected signatures of impulsive electron and ion beam events over the course of the first 20 encounters. The energy spectra of these events are characterized by a peak originating in the low-frequency bandwidth of the FIELDS sensor and descending over time in energy until it merges with the bulk of the solar wind as observed by the Solar Wind Electrons, Alphas, and Protons suite. All events are well associated with Type III radio bursts, and some are well correlated with soft and hard X-rays generated by impulsive solar flares. These dispersive energy beam phenomena are essential in understanding particle acceleration, transport, and energy partitioning between electrons and ions as a result of impulsive solar flares. In this work, we present an analysis of said events and leverage multiwavelength observations that are conducted by instruments on multiple platforms. Our results show, for the first time, that solar flares are observed to be the source of low-energy ions in interplanetary space. This discovery has never been previously observed at such low energies by instruments at 1 au.

Keywords: Solar particle emission
A Data-constrained Magnetohydrodynamic Simulation of Successive X-class Flares in Solar Active Region 13842. I. Dynamics of the Solar Eruption Associated with the X7.1 Solar Flare. We investigated the initiation and the evolution of an X7.1-class solar flare observed in NOAA Active Region 13842 on 2024 October 1, based on a data-constrained magnetohydrodynamic (MHD) simulation. The nonlinear force-free field (NLFFF) extrapolated from the photospheric magnetic field about 1 hr before the flare was used as the initial condition for the MHD simulations. The NLFFF reproduces highly sheared field lines that undergo tether-cutting reconnection in the MHD simulation, leading to the formation of a highly twisted magnetic flux rope (MFR), which then erupts rapidly, driven by both torus instability and magnetic reconnection. This paper focuses on the dynamics of the MFR and its role in eruptions. We find that magnetic reconnection in the preeruption phase is crucial in the subsequent eruption driven by the torus instability. Furthermore, our simulation indicates that magnetic reconnection also directly enhances the torus instability. These results suggest that magnetic reconnection is not just a by-product of the eruption due to reconnecting of postflare arcade, but also plays a significant role in accelerating the MFR during the eruption.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar flares, Magnetohydrodynamical simulations
EP240414a: Off-axis View of a Jet-cocoon System from an Expanded Progenitor Star. When a relativistic jet is launched following the core collapse of a star, its interaction with the stellar envelope leads to the formation of a hot cocoon, which produces various viewing-angle-dependent observational phenomena following the breakout from the surface. We study the observational signatures of fast X-ray transient (FXT) EP240414a, which may originate from a jet-cocoon system viewed slightly off-axis. In our model, (1) the prompt X-ray emission lasting ∼100 s is attributed to the cooling emission from the inner cocoon (shocked jet material); (2) the ∼0.1 day X-ray emission comes from the inner cocoon's afterglow; (3) the ∼0.4 day thermal-dominated optical emission arises from the cooling of the outer cocoon (shocked stellar material); (4) the ∼3 day nonthermal optical component and subsequent radio emission can be explained by the afterglow from a jet with a viewing angle of 10∘ ≲ θv ≲ 15∘; and (5) the associated broad-lined Type Ic supernova only dominates the optical emission after ∼7 days. Both the jet inferred from the off-axis afterglow and the inner cocoon constrained by the cooling emission are found to have similar kinetic energies, on the order of 1051 erg. We find that the progenitor's radius is ∼3 R⊙ as constrained by the inner cocoon's cooling emissions, indicating that the preexplosion star may be a massive helium star that is slightly inflated. More FXTs associated with off-axis jets and supernovae will be further examined by the Einstein Probe, leading to a deeper understanding of jet-cocoon systems.

Keywords: Type Ic supernovae, Gamma-ray bursts, High energy astrophysics, Massive stars, Relativistic jets