Sazuna/UAT_keywords huggingface dataset:
Simulating Jellyfish Galaxies: A Case Study for a Gas-rich Dwarf Galaxy. We investigate the formation of jellyfish galaxies using radiation-hydrodynamic simulations of gas-rich dwarf galaxies with a multiphase interstellar medium (ISM). We find that the ram-pressure-stripped (RPS) ISM is the dominant source of molecular clumps in the near wake within 10 kpc from the galactic plane, while in situ formation is the major channel for dense gas in the distant tail of the gas-rich galaxy. Only 20% of the molecular clumps in the near wake originate from the intracluster medium (ICM); however, the fraction reaches 50% in the clumps located at 80 kpc from the galactic center since the cooling time of the RPS gas tends to be short owing to the ISM-ICM mixing (≲10 Myr). The tail region exhibits a star formation rate of 0.001-0.01 M ⊙ yr-1, and most of the tail stars are born in the stripped wake within 10 kpc from the galactic plane. These stars induce bright Hα blobs in the tail, while Hα tails fainter than 6 × 1038 erg s-1 kpc-2 are mostly formed via collisional radiation and heating due to mixing. We also find that the stripped tails have intermediate X-ray-to-Hα surface brightness ratios (1.5 ≲ F X/F Hα  ≲ 20), compared to the ISM (≲1.5) or pure ICM (≫20). Our results suggest that jellyfish features emerge when the ISM from gas-rich galaxies is stripped by strong ram pressure, mixes with the ICM, and enhances the cooling in the tail.

Keywords: Hydrodynamical simulations, Ram pressure stripped tails, Galaxy environments
The Role of Disk Tearing and Precession in the Observed Variability of Pleione. We acquired Hα spectroscopic observations from 2005 to 2019 showing Pleione has transitioned from a Be phase to a Be-shell phase during this period. Using the radiative transfer code HDUST, we created a grid of ~100,000 disk models for Pleione. We successfully reproduced the observed transition with a disk model that varies in inclination while maintaining an equatorial density of ${\rho }_{0}{(r)=3\,\times \,{10}^{-11}(r/{R}_{\mathrm{eq}})}^{-2.7}\,{\rm{g}}\,{\mathrm{cm}}^{-3}$ , and an Hα-emitting region extending to 15 R eq. We use a precessing disk model to extrapolate the changing disk inclination over 120 yr and follow the variability in archival observations. The best-fit disk model precesses over a line-of-sight inclination between ~25° and ~144° with a precessional period of ~80.5 yr. Our precessing models match some of the observed variability but fail to reproduce all of the historical data available. Therefore, we propose an ad hoc model based on our precessing disk model inspired by recent smoothed particle hydrodynamics simulations of similar systems, where the disk tears due to the tidal influence of a companion star. In this model, a single disk is slowly tilted to an angle of 30° from the stellar equator over 34 yr. Then, the disk is torn by the companion's tidal torque, with the outer region separating from the innermost disk. The small inner disk returns to the stellar equator as mass injection remains constant. The outer disk precesses for ~15 yr before gradually dissipating. The process repeats every 34 yr and reproduces all trends in Pleione's variability.

Keywords: Binary stars, Emission line stars, Massive stars, Spectroscopy, Circumstellar disks, Photometry, Be stars, Polarimetry
Signatures of a Surviving Helium-star Companion in Type Ia Supernovae and Constraints on the Progenitor Companion of SN 2011fe. Single-degenerate (SD) binary systems composed of a white dwarf and a nondegenerate helium (He)-star companion have been proposed as the potential progenitors of Type Ia supernovae (SNe Ia). The He-star companions are expected to survive the SN Ia explosion in this SD progenitor model. In the present work, we map the surviving He-star companion models computed from our previous three-dimensional hydrodynamical simulations of ejecta-companion interaction into the one-dimensional stellar evolution code Modules for Experiments in Stellar Astrophysics to follow their long-term evolution to make predictions of their post-impact observational properties, which can be helpful in searches for such surviving He-star companions in future observations. By comparing with the very-late-epoch light curve of the best observed SN Ia, SN 2011fe, we find that our surviving He-star companions become significantly more luminous than SN 2011fe about 1000 days after maximum light. This suggests that an He star is very unlikely to be a companion to the progenitor of SN 2011fe.

Keywords: Hydrodynamical simulations, Close binary stars, Helium-rich stars, Type Ia supernovae, Companion stars, Stellar evolution
Simulating the Space Weather in the AU Mic System: Stellar Winds and Extreme Coronal Mass Ejections. Two close-in planets have been recently found around the M-dwarf flare star AU Microscopii (AU Mic). These Neptune-sized planets (AU Mic b and c) seem to be located very close to the so-called "evaporation valley" in the exoplanet population, making this system an important target for studying atmospheric loss on exoplanets. This process, while mainly driven by high-energy stellar radiation, will be strongly mediated by the space environment surrounding the planets. Here we present an investigation of this last area, performing 3D numerical modeling of the quiescent stellar wind from AU Mic, as well as time-dependent simulations describing the evolution of a highly energetic coronal mass ejection (CME) event in this system. Observational constraints on the stellar magnetic field and properties of the eruption are incorporated in our models. We carry out qualitative and quantitative characterizations of the stellar wind, the emerging CMEs, as well as the expected steady and transient conditions along the orbit of both exoplanets. Our results predict extreme space weather for AU Mic and its planets. This includes sub-Alfvénic regions for the large majority of the exoplanet orbits, very high dynamic and magnetic pressure values in quiescence (varying within 102-105 times the dynamic pressure experienced by Earth), and an even harsher environment during the passage of any escaping CME associated with the frequent flaring observed in AU Mic. These space weather conditions alone pose an immense challenge for the survival of exoplanetary atmospheres (if any) in this system.

Keywords: Exoplanets, High energy astrophysics, Space weather, Plasma astrophysics, Stellar magnetic fields, Red dwarf flare stars, M stars, Stellar winds, Stellar coronal mass ejections, Star-planet interactions, Magnetohydrodynamical simulations
Numerical Convergence of 2D Solar Convection in Implicit Large-eddy Simulations. Large-eddy simulations (LES) and implicit LES (ILES) are wise and affordable alternatives to the unfeasible direct numerical simulations of turbulent flows at high Reynolds (Re) numbers. However, for systems with few observational constraints, it is a formidable challenge to determine if these strategies adequately capture the physics of the system. Here, we address this problem by analyzing numerical convergence of ILES of turbulent convection in 2D, with resolutions between 642 and 20482 grid points, along with the estimation of their effective viscosities, resulting in effective Reynolds numbers between 1 and ~104. The thermodynamic structure of our model resembles the solar interior, including a fraction of the radiative zone and the convection zone. In the convective layer, the ILES solutions converge for the simulations with ≥5122 grid points, as evidenced by the integral properties of the flow and its power spectra. Most importantly, we found that even a resolution of 1282 grid points, $\mathrm{Re}\,\sim \,10$ , is sufficient to capture the dynamics of the large scales accurately. This is a consequence of the ILES method allowing the energy contained in these scales to be the same in simulations with low and high resolution. Special attention is needed in regions with a small density scale height driving the formation of fine structures unresolved by the numerical grid. In the stable layer, we found the excitation of internal gravity waves, yet high resolution is needed to capture their development and interaction.

Keywords: Solar convective zone, Computational methods, Hydrodynamical simulations
Superrotation of Titan's Stratosphere Driven by the Radiative Heating of the Haze Layer. Titan's stratosphere has been observed in a superrotation state, where the atmosphere rotates many times faster than the surface does. Another characteristic of Titan's atmosphere is the presence of a thick haze layer. In this paper, we performed numerical experiments using a general circulation model to explore the effects of the haze layer on the stratospheric superrotation. We employed a semigray radiation model of Titan's atmosphere following McKay et al., which takes account of sunlight absorption by the haze particles. The phase change of methane or seasonal changes were not taken into account. Our model with radiation parameters tuned for Titan yielded a global eastward wind around the equator with larger velocities at higher altitudes, except at around 70 km, after 105 Earth days. Although the atmosphere is not in an equilibrium state, the zonal wind profiles are approximately consistent with the observed one. By changing the parameters of the radiation model, we found that the intensity and the location of the maximum zonal wind velocity highly depended on the optical thickness and the altitude of the haze layer, respectively. Analysis of our experiments suggests that the quasi-stationary stratospheric superrotation is maintained by the balance between the meridional circulation decoupled from the surface and the eddies that transport angular momentum equatorward. This is different from, but similar to, the so-called Gierasch mechanism, in which momentum is supplied from the surface. This structure may explain the no-wind region at about 80 km in altitude.

Keywords: Planetary atmospheres, Titan, Atmospheric circulation
Statistical Properties of the Nebular Spectra of 103 Stripped-envelope Core-collapse Supernovae. We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O I] λλ6300, 6363. The line profile and width of [O I] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the [O I]/[Ca II] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the [O I] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the ~1σ level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O I] width and [O I]/[Ca II] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O I]/[Ca II] increases, the fraction of objects with Gaussian [O I] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass. * This research is based (in part) on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: Transient sources, Core-collapse supernovae
Temporal Analysis of GRB Precursors in the Third Swift-BAT Catalog. We select 52 long gamma-ray bursts (GRBs) that have precursor activity in the third Swift-BAT catalog. Each episode shown in both the precursors and the main bursts is fitted by the Norris function. We systematically analyze the temporal properties for both the precursors and the main bursts. We do not find any significant difference between the temporal profile of the precursor and that of the main burst. The photon count of the precursor is related to that of the main burst. It is indicated that the precursor and the main burst might have the same physical origin, as the precursor and the main burst follow the same τ  p -ω relation. However, we do not find the explicit relation between the energy release of the precursor and the quiescent time. Some theoretical models, such as the fallback collapsar scenario and the jet-cocoon scenario, may be helpful to explain the GRB-precursor phenomena.

Keywords: Gamma-ray bursts
Quasiperiodic Microjets Driven by Granular Advection as Observed With High-resolution Imaging at He I 10830 Å. With high-resolution narrowband He I 10830 Å filtergrams from Goode Solar Telescope, we give an extensive analysis for four granule-sized microeruptions which appear as the gentle ejection of material in He I 10830 Å band. The analysis was aided with the EUV data from Atmospheric Imaging Assembly and line-of-sight magnetograms from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The microeruptions are situated on magnetic polarity inversion lines (PILs), and their roots are accurately traced down to intergranular lanes. Their durations are different: two microeruptions are repetitive microjets, lasting ~50 and 27 minutes respectively, while the other two events are singular, lasting ~5 minutes. For the two microjets, they are continuous and recurrent in the He I 10830 Å band, and the recurrence is quasiperiodic with a period of ~5 minutes. We found that only transient cospatial EUV brightenings are observed for the longer duration microjets and EUV brightenings are absent for the two singular microeruptions. What is essential to the longer duration microjets is that granules with the concentration of a positive magnetic field persistently transport the magnetic field to the PILs, canceling the opposite magnetic flux and making the base of the two microjets and the underlying granules migrate with the speed of ~0.25 and 1.0 km s-1. The observations support the scenario of magnetic reconnection for the quasiperiodic microjets and further show that the reconnection continuously generates multitemperature components, especially the cool component with chromospheric temperature. In addition, the ongoing reconnection is modulated by p-mode oscillations inside the Sun.

Keywords: Solar magnetic reconnection, Solar mottles
Coronal Mass Ejections and Dimmings: A Comparative Study Using MHD Simulations and SDO Observations. Solar coronal dimmings have been observed extensively in recent years. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings as well as their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-constrained global magnetohydrodynamics model (Alfvén-wave solar model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize the emissions of different EUV spectral bands/lines and compare with SDO/AIA and EVE observations. A detailed analysis of the simulation and observation data suggests that the transient dimming/brightening are related to plasma heating processes, while the long-lasting core and remote dimmings are caused by mass-loss process induced by the CME. Moreover, the interaction between the erupting flux rope with different orientations and the global solar corona could significantly influence the coronal dimming patterns. Using metrics such as dimming depth and dimming slope, we investigate the relationship between dimmings and CME properties (e.g., CME mass, CME speed) in the simulation. Our result suggests that coronal dimmings encode important information about the associated CMEs, which provides a physical basis for detecting stellar CMEs from distant solar-like stars.

Keywords: Solar corona, Solar wind, Solar coronal mass ejections
Exploring Features in the Binary Black Hole Population. Vamana is a mixture model framework that infers the astrophysical distribution of chirp mass, mass ratio, and spin component aligned with the orbital angular momentum for the binary black holes (BBH) population. We extend the mixing components in this framework to also model the redshift evolution of merger rate and report all the major one- and two-dimensional features in the BBH population using the 69 gravitational-wave signals detected with a false alarm rate &lt;1 yr-1 in the third Gravitational-Wave Transient Catalog (GWTC-3). Endorsing our previous report and a recent corroborating report from LIGO Scientific, Virgo, and KAGRA Collaborations, we observe the chirp mass distribution has multiple peaks and a lack of mergers with chirp masses 10-12 M ⊙. In addition, we observe that aligned spins show mass dependence with heavier binaries exhibiting larger spins, the mass ratio shows a dependence on the chirp mass but not on the aligned spin, and the redshift evolution of the merger rate for the peaks in the mass distribution is disparate. These features possibly reflect the astrophysics associated with the BBH formation channels. However, additional observations are needed to improve our limited confidence in them.

Keywords: Gravitational wave astronomy, Gravitational wave sources
The 3D Dust and Opacity Distribution of Protoplanets in Multifluid Global Simulations. The abundance and distribution of solids inside the Hill sphere are central to our understanding of the giant planet dichotomy. Here, we present a 3D characterization of the dust density, mass flux, and mean opacities in the envelope of subthermal and superthermal-mass planets. We simulate the dynamics of multiple dust species in a global protoplanetary disk model accounting for dust feedback. We find that the meridional flows do not effectively stir dust grains at scales of the Bondi sphere. Thus the dust settling driven by the stellar gravitational potential sets the latitudinal dust density gradient within the planet envelope. Not only does the planet's potential enhance this gradient, but also the spiral wakes serve as another source of asymmetry. These asymmetries substantially alter the inferred mean Rosseland and Planck opacities. In cases with moderate-to-strong dust settling, the opacity gradient can range from a few percent to more than two orders of magnitude between the midplane and the polar regions of the Bondi sphere. Finally, we show that this strong latitudinal opacity gradient can introduce a transition between optically thick and thin regimes at the scales of the planet envelope. We suggest that this transition is likely to occur when the equilibrium scale height of hundred-micron-sized particles is smaller than the Hill radius of the forming planet. This work calls into question the adoption of a constant opacity derived from well-mixed distributions and demonstrates the need for global radiation hydrodynamics models of giant planet formation that account for dust dynamics.

Keywords: Planetary atmospheres, Planet formation
Variation in Cosmic-Ray Intensity Lags Sunspot Number: Implications of Late Opening of Solar Magnetic Field. Galactic cosmic rays (GCRs), the highly energetic particles that may raise critical health issues for astronauts in space, are modulated by solar activity, with their intensity lagging behind the variation in sunspot number (SSN) by about one year. Previously, this lag has been attributed to the combined effect of outward convecting solar wind and inward propagating GCRs. However, the lag's amplitude and its solar-cycle dependence are still not fully understood. By investigating the solar surface magnetic field, we find that the source of heliospheric magnetic field-the open magnetic flux on the Sun-already lags behind SSN before it convects into the heliosphere along with the solar wind. The delay during odd cycles is longer than that during sequential even cycles. Thus, we propose that the GCR lag is primarily due to the very late opening of the solar magnetic field with respect to SSN, though solar wind convection and particle transport in the heliosphere also matter. We further investigate the origin of the open flux from different latitudes of the Sun and find that the total open flux is significantly contributed by that from low latitudes, where coronal mass ejections frequently occur and also show an odd-even cyclic pattern. Our findings challenge existing theories, and may serve as the physical basis of long-term forecasts of radiation dose estimates for manned deep-space exploration missions.

Keywords: Solar cycle, Solar magnetic fields, Heliosphere, Cosmic rays
Hubble Space Telescope Imaging of Luminous Extragalactic Infrared Transients and Variables from the Spitzer Infrared Intensive Transients Survey. The SPitzer InfraRed Intensive Transients Survey (SPIRITS) searched for luminous infrared (IR) transients and variables in nearly 200 nearby galaxies from 2014 to 2019, using the warm Spitzer telescope at 3.6 and 4.5 μm. Among the SPIRITS variables are IR-bright objects that are undetected in ground-based optical surveys. We classify them as (1) transients, (2) periodic variables, and (3) irregular variables. The transients include eSPecially Red Intermediate-luminosity Transient Events (SPRITEs), having maximum luminosities fainter than supernovae, red IR colors, and a wide range of outburst durations (days to years). Here we report deep optical and near-IR imaging with the Hubble Space Telescope (HST) of 21 SPIRITS variables. They were initially considered SPRITE transients, but many eventually proved instead to be periodic or irregular variables as more data were collected. HST images show most of these cool and dusty variables are associated with star-forming regions in late-type galaxies, implying an origin in massive stars. Two SPRITEs lacked optical progenitors in deep preoutburst HST images; however, one was detected during eruption at J and H, indicating a dusty object with an effective temperature of ~1050 K. One faint SPRITE turned out to be a dusty classical nova. About half the HST targets proved to be periodic variables, with pulsation periods of 670-2160 days; they are likely dusty asymptotic-giant-branch (AGB) stars with masses of ~5-10 M ⊙. A few of them were warm enough to be detected in deep HST frames, but most are too cool. Out of six irregular variables, two were red supergiants with optical counterparts in HST images; four were too enshrouded for HST detection. * Based in part on observations and archival data from the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; also in part on observations and archival data made with the Spitzer Space Telescope, operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Keywords: Red supergiant stars, Transient sources, Luminous blue variable stars, Infrared sources, Variable stars, OH/IR stars, Supernovae, Classical novae