Sazuna/UAT_keywords huggingface dataset:
The Cumulation of Debris Clouds around a Fast-rotating Asteroid. The rotational mass loss has been realized to be a prevalent mechanism to produce low-speed debris near the asteroid, and the size composition of the asteroid's surface regolith has been closely measured by in situ explorations. However, the full-scale evolution of the shedding debris has not been examined using the observed particle sizes, which may hold vital clues to the initial growth of an asteroid moonlet and help us to understand the general mechanisms that dominate the formation of asteroid systems. This paper presents our study on the cumulative evolution of the debris cloud formed by a rotationally unstable asteroid. A semianalytical model is developed to characterize the spatiotemporal evolution of the debris cloud posterior to a shedding event. Large-scale discrete element method (DEM) simulations are performed to quantify the clustering behavior of the debris particles in the mechanical environment near the asteroid. As a result, we found that the cumulation of a steady debris cloud is dominated by large pieces of debris, and the shedding particles follow a common migration trend, which fundamentally determines the mass distribution of the debris cloud. For the accretion analysis, we sketched the life cycle of a debris cluster and showed its dependency on particle size. The DEM simulations adopt physical parameters estimated from observations and asteroid missions. The results confirm that porous fluffy cluster structures can form shortly after a shedding event with magnitudes the same as the observed shedding activities. Measurements of these structures show that they themselves possess a certain strength and have the capacity to collisions to absorb dissociative particles that collide with them.

Keywords: Accretion, Asteroid dynamics, Asteroid satellites, Asteroid rotation, Planetesimals, Debris disks
Systematically Measuring Ultradiffuse Galaxies. VII. The H I Survey Overview. We present the results from the neutral hydrogen (H I) follow-up survey of 378 optically detected ultradiffuse galaxy (UDG) candidates from the Systematically Measuring Ultra-Diffuse Galaxies survey using the Robert C. Byrd Green Bank Telescope. We detect H I in 110 targets and determine 37 to be UDGs and 73 to be low-surface-brightness (LSB) dwarfs based on their effective radii and central surface brightnesses. In line with previous studies, we find that: (i) our H I detections have on average bluer g ‑ r colors and more irregular morphologies than our H I nondetections, (ii) our H I detections populate the tail end of the star-forming main sequence from the ALFALFA catalog with marginally lower specific star formation rates, and (iii) H I detections are mostly in relatively isolated (i.e., field) environments, while most nondetections have at least one nearby neighbor in projection. We find that the H I mass to stellar mass ratios (i.e., gas richnesses) scale with the physical sizes for UDGs and LSB dwarfs alike, suggesting that mechanisms other than bursty star formation feedback may be at play for UDGs. However, we find a stronger trend between gas richnesses and physical sizes if we define UDGs using their effective surface brightness instead of their central surface brightness. We are in the process of using this unprecedented sample of UDG candidates to carry out detailed follow-up studies (i.e., star formation and environmental analysis, comparisons to simulations) and are obtaining resolved H I observations for several of them.

Keywords: Galaxy formation, Surveys, Dwarf galaxies, Cold neutral medium, Galaxy evolution, Low surface brightness galaxies
Mass-transfer Outbursts Reborn: Modeling the Light Curve of the Dwarf Nova EX Draconis. EX Draconis is an eclipsing dwarf nova that shows outbursts with moderate amplitude (≃2 mag) and a recurrence timescale of ≃20–30 days. Dwarf novae outbursts are explained in terms of either a thermal-viscous instability in the disc or an instability in the mass-transfer rate of the donor star (MTIM). We developed simulations of the response of accretion discs to events of enhanced mass transfer, in the context of the MTIM, and applied them to model the light curve and variations in the radius of the EX Dra disc throughout the outburst. We obtain the first modeling of a dwarf nova outburst by using χ 2 to select, from a grid of simulations, the best-fit parameters to the observed EX Dra outbursts. The observed time evolution of the system brightness and the changes in the radius of the outer disc along the outburst cycle are satisfactorily reproduced by a model of the response of an accretion disc with a viscosity parameter α = 4.0 and a quiescent mass-transfer rate  Ṁ2(quiescence)=4.0×1016  g s‑1 to an event of width Δt = 6.0 × 105 s (∼7 days) where the mass-transfer rate increases to  Ṁ2(outburst)=1.5×1018  g s‑1.

Keywords: Interacting binary stars, Dwarf novae, Eclipsing binary stars, Stellar accretion disks, Cataclysmic variable stars, Astronomical simulations
Electron Acceleration in Magnetic Islands in Quasi-parallel Shocks. We report new theories and simulations for electron acceleration in magnetic islands generated by magnetic reconnection in the shock turbulence in a quasi-parallel shock, using a 2 and 1/2 dimensional particle-in-cell simulation. When an island is moving, unmagnetized electrons are accelerated by the Hall electric field pointing toward the island center. In a stationary island, some electrons are energized by "island betatron acceleration" due to the induction electric field when the island core magnetic field changes with time. In the simulation, almost all of the high-energy electrons in the shock transition region that show a power-law distribution are accelerated in ion-skin-depth-scale magnetic flux ropes, and about half of them are accelerated by the Hall electric field and island betatron acceleration. These mechanisms can produce a power-law electron distribution, and also inject electrons into the diffusive shock acceleration. The mechanisms are applicable to quasi-parallel shocks with high Alfvén Mach numbers (M A &gt; 10), including planetary bow shocks and shocks in astrophysical objects such as supernova remnants.

Keywords: Interplanetary particle acceleration, Planetary bow shocks, Solar magnetic reconnection
Evolution of Tidal Disruption Event Disks with Magnetically Driven Winds. We present a time-dependent, one-dimensional, magnetically driven disk wind model based on magnetohydrodynamic (MHD) equations, in the context of tidal disruption events (TDEs). We assume that the disk is geometrically thin, is gas pressure dominated, and explicitly accounts for magnetic braking and turbulent viscosity through an extended α-viscosity prescription. We find a particular wind solution for a set of basic equations that satisfies the necessary and sufficient conditions for vertically unbound MHD flows. The solution shows that the disk evolves with mass loss due to wind and accretion from the initial Gaussian density distribution. We confirm that the mass accretion rate follows the power law of time t ‑19/16 at late times in the absence of wind, which matches the classical solution of J. K. Cannizzo et al. We find that the mass accretion rate is steeper than the t ‑19/16 curve when the wind is present. Mass accretion is also induced by magnetic braking, known as the wind-driven accretion mechanism, which results in a faster decay with time of both the mass accretion and mass-loss rates. In the disk emission, the ultraviolet (UV) luminosity is the highest among the optical, UV, and X-ray luminosities. While the optical and X-ray emission is observationally insignificant without magnetic braking, the X-ray emission is brighter at late times, especially in the presence of magnetic braking. This provides a possible explanation for observed delayed X-ray flares. Our model predicts that late-time bolometric light curves steeper than t ‑19/16 in UV-bright TDEs are potentially compelling indicators of magnetically driven winds.

Keywords: Accretion, Tidal disruption, High energy astrophysics, Magnetohydrodynamics
Topological Approach to Void Finding Applied to the SDSS Galaxy Map. The structure of the low redshift Universe is dominated by a multiscale void distribution delineated by filaments and walls of galaxies. The characteristics of voids, such as morphology, average density profile, and correlation function, can be used as cosmological probes. However, their physical properties are difficult to infer due to shot noise and the general lack of tracer particles used to define them. In this work, we construct a robust, topology-based void-finding algorithm that utilizes Persistent Homology to detect persistent features in the data. We apply this approach to a volume-limited subsample of galaxies in the SDSS I/II Main Galaxy catalog with the r-band absolute magnitude brighter than M  r  = ‑20.19, and a set of mock catalogs constructed using the Horizon Run 4 cosmological N-body simulation. We measure the size distribution of voids, their averaged radial profile, sphericity, and the centroid nearest neighbor separation, using conservative values for the threshold and persistence. We find 32 topologically robust voids in the SDSS data over the redshift range 0.02 ≤ z ≤ 0.116, with effective radii in the range 21‑56 h ‑1 Mpc. The median nearest neighbor void separation is found to be ∼57 h ‑1 Mpc, and the median radial void profile is consistent with the expected shape from the mock data.

Keywords: Cosmology, Galaxy distances, Voids, Redshift surveys
Collisions Between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud. II.. We present high-resolution simulations of high velocity clouds (HVCs) colliding with the outer part of the Galactic disk. All of the simulations include a 3 × 108 M ⊙ dark matter subhalo. Three simulations model a dark matter subhalo without a gaseous component, while eight simulations model a dark matter subhalo accompanied by a gaseous cloud of mass 2–8 × 106 M ⊙. Half of the simulations include the coherent component of the Galaxy's magnetic field. Each simulation spans ∼40 million years before the collision and ∼40 million years after the collision. The collisions between the gas cloud and disk splash gas into the halo, punch half-kiloparsec-size holes in the disk, and form long-lived, multi-kiloparsec-size shells. Each shell encloses a bubble of relatively cool gas. Holes and shells of these scales would be observable, and some have been observed in the past. We determine the fate of the HVC gas, temperature, composition, and ionization state of the bubble and shell gas, size and longevity of the holes, and effects of cloud density. Simulations show that the clouds do not survive the chaos of passage through the disk, but instead become part of the splash, bubble, and shell. Some dark matter clouds may appear to carry material with them long after the collision, but this material is shell gas that was captured by the dark matter subhalo. These results have ramifications for the Smith Cloud and other clouds hypothesized to have hit the Galactic disk.

Keywords: Hydrodynamical simulations, High-velocity clouds, Dark matter
Filamentary Molecular Cloud Formation via Collision-induced Magnetic Reconnection in a Cold Neutral Medium. We have investigated the possibility of molecular cloud formation via the collision-induced magnetic reconnection (CMR) mechanism of the cold neutral medium (CNM). Two atomic gas clouds with conditions typical of the CNM were set to collide at the interface of reverse magnetic fields. The cloud─cloud collision triggered magnetic reconnection and produced a giant 20 pc filamentary structure that was not seen in the control models without CMR. The cloud, with rich fiber-like substructures, developed a fully molecular spine at 5 Myr. Radiative transfer modeling of dust emission at far-infrared wavelengths showed that the middle part of the filament contained dense cores over a span of 5 pc. Some of the cores were actively forming stars and typically exhibited both connecting fibers in dust emission and high-velocity gas in CO line emission, indicative of active accretion through streamers. Supersonic turbulence was present in and around the CMR filament due to inflowing gas moving at supersonic velocities in the collision midplane. The shocked gas was condensed and transported to the main filament piece by piece by reconnected fields, making the filament and star formation a bottom-up process. Instead of forming a gravitationally bounded cloud that then fragments hierarchically (top-down) and forms stars, the CMR process creates dense gas pieces and magnetically transports them to the central axis to constitute the filament. Since no turbulence is manually driven, our results suggest that CMR is capable of self-generating turbulence. Finally, the resulting helical field should show field reversal on both sides of the filament from most viewing angles.

Keywords: Interstellar filaments, Molecular clouds, Star formation, Magnetic fields, Magnetohydrodynamical simulations
Origin of Line Broadening in Fading Granules: Influence of Small-scale Turbulence. In the quiet region of the solar photosphere, turbulent convective motions of the granular flows naturally drive the subgranular-scale flows. However, evaluating such small-scale velocities is challenging because of the limited instrumental resolution. Our previous study, R. T. Ishikawa et al., found line-broadening events during the fading process of granules; however, their physical mechanism has remained unclear. In the present study, we observed the fading granules with the Hinode-SOT/SP and performed spectral line inversions. Moreover, we investigated the broadening events of synthesized spectra in fading granules reproduced by the MURaM simulation. Our results demonstrated that the small-scale turbulent motions are excited in the fading process, and such turbulent flows contribute to line broadening. The spectral line widths can be potential tracers of the photospheric turbulent flows.

Keywords: Solar granulation, Spectropolarimetry, Solar photosphere
SPYGLASS. V. Spatially and Temporally Structured Star-forming Environments in the Cepheus-Hercules Complex. Young associations record complete histories of star-forming events through their demographics and dynamics, and Gaia has greatly expanded our knowledge of these associations. We present the first structural and dynamical overview study of the Cep-Her Complex, which has recently emerged as the largest stellar population within 500 pc that still lacks substantial follow-up. We reveal that Cep-Her is not a singular association, but rather an amalgam of four, consisting of the older (τ &gt; 100 Myr) open cluster Roslund 6, in addition to three dynamically coherent and highly substructured young associations that we focus on: Orpheus (25─40 Myr), Cinyras (28─43 Myr), and Cupavo (54─80 Myr). With 9552 ± 960 stars in Orpheus, 3872 ± 455 stars in Cinyras, and 8794 ± 1827 stars in Cupavo, all three are among the largest young associations within 500 pc, rivalling major associations like Sco-Cen. Our novel view of the ages and dynamics of these associations reveals evidence for sequential star formation in Cinyras, in addition to a multiorigin pattern of stellar dispersal in Orpheus that may hint to the presence of multiple clouds at formation. Dynamical simulations indicate that, while some embedded open clusters and central components of these associations are converging, they likely lack the mass necessary to capture one another and undergo hierarchical cluster assembly. Our results provide our first view of the complex star-forming environments that gave rise to the associations of Cep-Her, which will serve as important laboratories for future studies of star and planet formation.

Keywords: Young star clusters, Pre-main sequence stars, Star formation, Planet hosting stars, Stellar associations
On the Corotation of Milky Way Satellites: LMC-mass Satellites Induce Apparent Motions in Outer Halo Tracers. Understanding the physical mechanism behind the formation of a corotating thin plane of satellite galaxies, like the one observed around the Milky Way (MW), has been challenging. The perturbations induced by a massive satellite galaxy, like the Large Magellanic Cloud (LMC), provide valuable insight into this problem. The LMC induces an apparent corotating motion in the outer halo by displacing the inner regions of the halo with respect to the outer halo. Using the Latte suite of Feedback In Realistic Environments cosmological simulations of MW-mass galaxies, we confirm that the apparent motion of the outer halo induced by the infall of a massive satellite changes the observed distribution of orbital poles of outer-halo tracers, including satellites. We quantify the changes in the distribution of orbital poles using the two-point angular correlation function and find that all satellites induce changes. However, the most massive satellites with pericentric passages between ≈30 and 100 kpc induce the largest changes. The best LMC-like satellite analog shows the largest change in orbital pole distribution. The dispersion of orbital poles decreases by 20° during the first two pericentric passages. Even when excluding the satellites brought in with the LMC-like satellite, there is clustering of orbital poles. These results suggest that in the MW, the recent pericentric passage of the LMC should have changed the observed distribution of orbital poles of all other satellites. Therefore, studies of kinematically coherent planes of satellites that seek to place the MW in a cosmological context should account for the existence of a massive satellite like the LMC.

Keywords: Milky Way dark matter halo, Milky Way stellar halo, Milky Way dynamics, Milky Way Galaxy
Toward a Self-consistent Evaluation of Gas Dwarf Scenarios for Temperate Sub-Neptunes. The recent JWST detections of carbon-bearing molecules in a habitable-zone sub-Neptune have opened a new era in the study of low-mass exoplanets. The sub-Neptune regime spans a wide diversity of planetary interiors and atmospheres not witnessed in the solar system, including mini-Neptunes, super-Earths, and water worlds. Recent works have investigated the possibility of gas dwarfs, with rocky interiors and thick H2-rich atmospheres, to explain aspects of the sub-Neptune population, including the radius valley. Interactions between the H2-rich envelope and a potential magma ocean may lead to observable atmospheric signatures. We report a coupled interior-atmosphere modeling framework for gas dwarfs to investigate the plausibility of magma oceans on such planets and their observable diagnostics. We find that the surface─atmosphere interactions and atmospheric composition are sensitive to a wide range of parameters, including the atmospheric and internal structure, mineral composition, volatile solubility and atmospheric chemistry. While magma oceans are typically associated with high-temperature rocky planets, we assess if such conditions may be admissible and observable for temperate sub-Neptunes. We find that a holistic modeling approach is required for this purpose and to avoid unphysical model solutions. Using our model framework, we consider the habitable-zone sub-Neptune K2-18 b as a case study and find that its observed atmospheric composition is incompatible with a magma ocean scenario. We identify key atmospheric molecular and elemental diagnostics, including the abundances of CO2, CO, NH3, and, potentially, S-bearing species. Our study also underscores the need for fundamental material properties for accurate modeling of such planets.

Keywords: Exoplanet atmospheres, Planetary interior, Exoplanets
Multiple New or Updated Satellite Total Solar Irradiance (TSI) Composites (1978–2023). Several total solar irradiance (TSI) satellite missions have been carried out since 1978. None of these missions have lasted more than one to two solar cycles (SCs), and each mission implies a slightly different absolute TSI baseline. Nonetheless, several satellite composites have been developed by compositing satellite data from different missions to form an almost continuous daily record for the satellite era. However, disconcertingly, each mission has implied slightly different changes in TSI between consecutive solar minima and solar maxima. Some groups have developed adjustments to individual missions that have substantially reduced these differences. Others prefer to use the original data published by the satellite science teams. Some TSI composites average together conflicting records, while others prioritize specific records over others. Here, we compare four existing composites to 17 new alternative series based on the available satellite data. These 21 TSI series are statistically sorted into six groups of three to four series each. We found that the six groups suggest different intercycle trends between solar minima. We compare the groups to eight daily resolved solar proxy-based TSI reconstructions and to daily sunspot numbers. Excellent agreement is obtained over one to two SCs, but significant differences are observed over longer timescales for each group. Therefore, we have assembled all these time series (old and new) into a large and new TSI data set for use by the scientific community. Versions scaled to 1 au (for studying solar variability) or in situ values at Earth (for studying solar/terrestrial interactions) are provided at daily, monthly, and yearly resolutions.

Keywords: Solar activity, Solar spectral irradiance, Sunspot cycle, Solar cycle
The Faraday Rotation Measure of the M87 Jet at 3.5 mm with ALMA. Faraday rotation is an important probe of the magnetic fields and magnetized plasma around active galactic nuclei jets. We present a Faraday rotation measure (RM) image of the M87 jet between 85.2 and 101.3 GHz with a resolution of ∼2″ with the Atacama Large Millimeter/submillimeter Array. We found that the RM of the M87 core is (4.5 ± 0.4) × 104 rad m−2 with a low linear polarization fraction of (0.88 ± 0.08)%. The spatial RM gradient in the M87 jet spans a wide range from ∼ −2 × 104 rad m−2 to ∼3 × 104 rad m−2 with a typical uncertainty of 0.3 × 104 rad m−2. A comparison with previous RM measurements of the core suggests that the Faraday rotation of the core may originate very close to the supermassive black hole. Both an internal origin and an external screen with a rapidly varying emitting source could be possible. As for the jet, the RM gradient indicates a helical configuration of the magnetic field that persists up to the kiloparsec scale. Combined with the kiloparsec-scale RM measurements at lower frequencies, we found that RM is frequency-dependent in the jet. One possible scenario to explain this dependence is that the kiloparsec-scale jet has a trumpet-like shape, and the jet coil unwinds near its end.

Keywords: Relativistic jets, Low-luminosity active galactic nuclei, Radio galaxies, Radio continuum emission, Radio interferometry, Polarimetry, Extragalactic magnetic fields