Sazuna/UAT_keywords huggingface dataset:
Binary Evolution, Gravitational-wave Mergers, and Explosive Transients in Multiple-population Gas-enriched Globular Clusters. Most globular clusters (GCs) show evidence for multiple stellar populations, suggesting the occurrence of several distinct star formation episodes. The large fraction of second population (2P) stars observed requires a very large 2P gaseous mass to have accumulated in the cluster core to form these stars. Hence, the first population of stars (1P) in the cluster core has had to become embedded in 2P gas, just prior to the formation of later populations. Here we explore the evolution of binaries in ambient 2P gaseous media of multiple-population GCs. We mostly focus on black hole binaries and follow their evolution as they evolve from wide binaries toward short periods through interaction with ambient gas, followed by gravitational-wave (GW) dominated inspiral and merger. We show that this novel GW merger channel could provide a major contribution to the production of GW sources. We consider various assumptions and initial conditions and calculate the resulting gas-mediated change in the population of binaries and the expected merger rates due to gas-catalyzed GW inspirals. For plausible conditions and assumptions, we find an expected GW merger rate observable by aLIGO of the order of up to a few tens of Gpc-3 yr-1 and an overall range for our various models of 0.08-25.51 Gpc-3 yr-1. Finally, our results suggest that the conditions and binary properties in the early stage of GCs could be critically affected by gas interactions and may require a major revision in the current modeling of the evolution of GCs.

Keywords: Globular star clusters, Gravitational waves, Gravitational wave sources
Time-dependent Numerical Model for Studying the Very-high-energy Emissions of Distant Gamma-Ray Burst GRB 201216C. Recently, the MAGIC Collaboration reported a ~5σ statistical significance of the very-high-energy (VHE) emission from a distant gamma-ray burst (GRB), GRB 201216C. Such distant GRB may be effectively absorbed by the extragalactic background light (EBL). The origin of the VHE emission from such distant objects is still unknown. Here, we propose a numerical model for studying the afterglow emission of this distant GRB. The model solves the continuity equation governing the temporal evolution of electron distribution, and the broadband observed data can be explained by the synchrotron plus synchrotron self-Compton (SSC) radiation of the forward shock. The predicted observed 0.1 TeV flux can reach ~10-9-10-10 erg cm-2 s-1 at t ~ 103-104 s, even with strong EBL absorption, such strong sub-teraelectronvolt (sub-TeV) emissions still can be observed by the MAGIC telescope. Using this numerical model, the shock parameters in the modeling are similar to two other sub-TeV GRBs (i.e., GRB 190114C and GRB 180720B), implying that the sub-TeV GRBs have some commonalities: they have energetic burst energy, low circumburst medium density, and a low magnetic equipartition factor. We regard GRB 201216C as a typical GRB, and estimate the maximum redshift of GRB that can be detected by the MAGIC telescope, i.e., z ~ 1.6. We also find that the VHE photon energy of such distant GRB can only reach ~0.1 TeV. Improving the low energy sensitivity of the VHE telescope is very important to detect the sub-TeV emissions of these distant GRBs.

Keywords: Shocks, Gamma-ray bursts
Study of Transverse Oscillations in Coronal Loops Excited by Flares and Eruptions. We present measurements of periodicity for transverse loop oscillations during the periods of activity of two remote and separated (both temporally and spatially) flares. The oscillations are observed in the same location more than 100 Mm away from the visible footpoints of the loops. Evidence for several possible excitation sources is presented. After close examination, we find that the eruptions during the flaring activities play an important role in triggering the oscillations. We investigate periodicities using time-distance, fast Fourier transform, and wavelet techniques. Despite different excitation sources in the vicinity of the loops and the changing nature of amplitudes, the periodicity of multiple oscillations is found to be 4-6 min.

Keywords: Solar coronal loops, Solar flares
The In Situ Origins of Dwarf Stellar Outskirts in FIRE-2. Extended, old, and round stellar halos appear to be ubiquitous around high-mass dwarf galaxies (108.5 &lt; M ⋆/M ⊙ &lt; 109.6) in the observed universe. However, it is unlikely that these dwarfs have undergone a sufficient number of minor mergers to form stellar halos that are composed of predominantly accreted stars. Here, we demonstrate that FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulations are capable of producing dwarf galaxies with realistic structures, including both a thick disk and round stellar halo. Crucially, these stellar halos are formed in situ, largely via the outward migration of disk stars. However, there also exists a large population of "nondisky" dwarfs in FIRE-2 that lack a well-defined disk/halo and do not resemble the observed dwarf population. These nondisky dwarfs tend to be either more gas-poor or to have burstier recent star formation histories than the disky dwarfs, suggesting that star formation feedback may be preventing disk formation. Both classes of dwarfs underscore the power of a galaxy's intrinsic shape-which is a direct quantification of the distribution of the galaxy's stellar content-to interrogate the feedback implementation in simulated galaxies.

Keywords: Galaxy structure, Hydrodynamical simulations, Dwarf galaxies, Astronomical simulations
Constraints on the Explosion Timescale of Core-collapse Supernovae Based on Systematic Analysis of Light Curves. The explosion mechanism of core-collapse supernovae is not fully understood yet. In this work, we give constraints on the explosion timescale based on 56Ni synthesized by supernova explosions. First, we systematically analyze multiband light curves of 82 stripped-envelope supernovae (SESNe) to obtain bolometric light curves, which is among the largest samples of the bolometric light curves of SESNe derived from the multiband spectral energy distribution. We measure the decline timescale and the peak luminosity of the light curves and estimate the ejecta mass (M ej) and 56Ni mass (M Ni) to connect the observed properties with the explosion physics. We then carry out one-dimensional hydrodynamics and nucleosynthesis calculations, varying the progenitor mass and the explosion timescale. From the calculations, we show that the maximum 56Ni mass that 56Ni-powered SNe can reach is expressed as M Ni ≲ 0.2 M ej. Comparing the results from the observations and the calculations, we show that the explosion timescale shorter than 0.3 s explains the synthesized 56Ni mass of the majority of the SESNe.

Keywords: Type Ib supernovae, Type Ic supernovae, Supernovae, Core-collapse supernovae
Exploring Changes in Quasar Spectral Energy Distributions across C IV Parameter Space. We examine the UV/X-ray properties of 1378 quasars in order to link empirical correlations to theoretical models of the physical mechanisms dominating quasars as a function of mass and accretion rate. The clarity of these correlations is improved when (1) using C IV broad emission line equivalent width (EQW) and blueshift (relative to systemic) values calculated from high signal-to-noise ratio reconstructions of optical/UV spectra and (2) removing quasars expected to be absorbed based on their UV/X-ray spectral slopes. In addition to using the traditional C IV parameter space measures of C IV EQW and blueshift, we define a "C IV ∥ distance" along a best-fit polynomial curve that incorporates information from both C IV parameters. We find that the C IV ∥ distance is linearly correlated with both the optical-to-X-ray slope, α ox, and broad-line He II EQW, which are known spectral energy distribution indicators, but does not require X-ray or high spectral resolution UV observations to compute. The C IV ∥ distance may be a better indicator of the mass-weighted accretion rate, parameterized by L/L Edd, than the C IV EQW or blueshift alone, as those relationships are known to break down at the extrema. Conversely, there is only a weak correlation with the X-ray energy index (Γ), an alternate L/L Edd indicator. We find no X-ray or optical trends in the direction perpendicular to the C IV distance that could be used to reveal differences in accretion disk, wind, or corona structure that could be widening the C IV EQW-blueshift distribution. A different parameter (such as metallicity) not traced by these data must come into play.

Keywords: Black hole physics, X-ray active galactic nuclei, Spectral energy distribution, Quasars
A Multiwavelength Study of the Sgr B Region: Contiguous Cloud-Cloud Collisions Triggering Widespread Star Formation Events?. The Sgr B region, including Sgr B1 and Sgr B2, is one of the most active star-forming regions in the Galaxy. Hasegawa et al. originally proposed that Sgr B2 was formed by a cloud-cloud collision (CCC) between two clouds with velocities of ~45 km s-1 and ~75 km s-1. However, some recent observational studies conflict with this scenario. We have reanalyzed this region, by using recent, fully sampled, dense-gas data and by employing a recently developed CCC identification methodology, with which we have successfully identified more than 50 CCCs and compared them at various wavelengths. We found two velocity components that are widely spread across this region and that show clear signatures of a CCC, each with a mass of ~106 M ☉. Based on these observational results, we suggest an alternative scenario, in which contiguous collisions between two velocity features with a relative velocity of ~20 km s-1 created both Sgr B1 and Sgr B2. The physical parameters, such as the column density and the relative velocity of the colliding clouds, satisfy a relation that has been found to apply to the most massive Galactic CCCs, meaning that the triggering of high-mass star formation in the Galaxy and starbursts in external galaxies can be understood as being due to the same physical CCC process.

Keywords: Galactic center, Molecular clouds, Star formation, Interstellar medium, CO line emission
3D Morphology of Open Clusters in the Solar Neighborhood with Gaia EDR 3. II. Hierarchical Star Formation Revealed by Spatial and Kinematic Substructures. We identify members of 65 open clusters in the solar neighborhood using the machine-learning algorithm StarGO based on Gaia EDR3 data. After adding members of 20 clusters from previous studies we obtain 85 clusters, and study their morphology and kinematics. We classify the substructures outside the tidal radius into four categories: filamentary (f1) and fractal (f2) for clusters &lt;100 Myr, and halo (h) and tidal tail (t) for clusters &gt;100 Myr. The kinematical substructures of f1-type clusters are elongated; these resemble the disrupted cluster Group X. Kinematic tails are distinct in t-type clusters, especially Pleiades. We identify 29 hierarchical groups in four young regions (Alessi 20, IC 348, LP 2373, LP 2442); 10 among these are new. The hierarchical groups form filament networks. Two regions (Alessi 20, LP 2373) exhibit global orthogonal expansion (stellar motion perpendicular to the filament), which might cause complete dispersal. Infalling-like flows (stellar motion along the filament) are found in UBC 31 and related hierarchical groups in the IC 348 region. Stellar groups in the LP 2442 region (LP 2442 gp 1-5) are spatially well mixed but kinematically coherent. A merging process might be ongoing in the LP 2442 subgroups. For younger systems (≲30 Myr), the mean axis ratio, cluster mass, and half-mass-radius tend to increase with age values. These correlations between structural parameters may imply two dynamical processes occurring in the hierarchical formation scenario in young stellar groups: (1) filament dissolution and (2) subgroup mergers.

Keywords: Stellar kinematics, Young star clusters, Stellar dynamics, Astrostatistics, Open star clusters
WO-type Wolf-Rayet Stars: The Last Hurrah of Massive Star Evolution. Are WO-type Wolf-Rayet (WR) stars in the final stage of massive star evolution before core-collapse? Although WC- and WO-type WRs have very similar spectra, WOs show a much stronger O VI λλ3811,34 emission-line feature. This has usually been interpreted to mean that WOs are more oxygen rich than WCs, and thus further evolved. However, previous studies have failed to model this line, leaving the relative abundances uncertain, and the relationship between the two types unresolved. To answer this fundamental question, we modeled six WCs and two WOs in the LMC using UV, optical, and NIR spectra with the radiative transfer code CMFGEN in order to determine their physical properties. We find that WOs are not richer in oxygen; rather, the O VI feature is insensitive to the abundance. However, the WOs have a significantly higher carbon and lower helium content than the WCs, and hence are further evolved. A comparison of our results with single-star Geneva and binary BPASS evolutionary models show that, while many properties match, there is more carbon and less oxygen in the WOs than either set of evolutionary model predicts. This discrepancy may be due to the large uncertainty in the 12C+4He → 16O nuclear reaction rate; we show that if the Kunz et al. rate is decreased by a factor of 25%-50%, then there would be a good match with the observations. It would also help explain the LIGO/VIRGO detection of black holes whose masses are in the theoretical upper mass gap. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Wolf-Rayet stars, Massive stars, WC stars, Stellar evolution
Constraining the Time of Gravitational-wave Emission from Core-collapse Supernovae. The advent of sensitive gravitational-wave (GW) detectors, coupled with wide-field, high-cadence optical time-domain surveys, raises the possibility of the first joint GW-electromagnetic detections of core-collapse supernovae (CCSNe). For targeted searches of GWs from CCSNe, optical observations can be used to increase the sensitivity of the search by restricting the relevant time interval, defined here as the GW search window (GSW). The extent of the GSW is a critical factor in determining the achievable false alarm probability for a triggered CCSN search. The ability to constrain the GSW from optical observations depends on how early a CCSN is detected, as well as the ability to model the early optical emission. Here we present several approaches to constrain the GSW, ranging in complexity from model-independent analytical fits of the early light curve, model-dependent fits of the rising or entire light curve, and a new data-driven approach using existing well-sampled CCSN light curves from Kepler and the Transiting Exoplanet Survey Satellite. We use these approaches to determine the time of core-collapse and its associated uncertainty (i.e., the GSW). We apply our methods to two Type II SNe that occurred during LIGO/Virgo Observing Run 3: SN 2019fcn and SN 2019ejj (both in the same galaxy at d = 15.7 Mpc). Our approach shortens the duration of the GSW and improves the robustness of the GSW compared to the techniques used in past GW CCSN searches.

Keywords: High energy astrophysics, Core-collapse supernovae, Type II supernovae, Gravitational wave astronomy, Gravitational waves
Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z &gt; 6.5 Universe. The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous star-forming galaxies known in the z &gt; 6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest UV-selected galaxies identified over a 7 deg2 area for bright [C II]158 μm and [O III]88 μm lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at z &gt; 6.5 by ~4-5× to &gt;30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the first-year observations, 18 highly significant ≥ 7σ [C II]158 μm lines have already been discovered, the bulk of which (13/18) also show ≥3.3σ dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the z &gt; 6.5 universe, such that the number of ALMA-derived redshifts at z &gt; 6.5 rival Lyα discoveries. An analysis of the completeness of our search results versus star formation rate (SFR) suggests an ~79% efficiency in scanning for [C II]158 μm when the SFRUV+IR is &gt;28 M ☉ yr-1. These new LP results further demonstrate ALMA's efficiency as a "redshift machine," particularly in the Epoch of Reionization.

Keywords: Dust continuum emission, High-redshift galaxies, Far infrared interferometry, Far infrared astronomy
Static Thin Disks with Power-law Density Profiles. The task of finding the potential of a thin circular disk with power-law radial density profile is revisited. The result, given in terms of infinite Legendre-type series in the above reference, has now been obtained in closed form thanks to the method of Conway employing Bessel functions. Starting from a closed-form expression for the potential generated by the elementary density term ρ 2l , we cover more generic-finite solid or infinite annular-thin disks using superposition and/or inversion with respect to the rim. We check several specific cases against the series-expansion form by numerical evaluation at particular locations. Finally, we add a method to obtain a closed-form solution for finite annular disks whose density is of "bump" radial shape, as modeled by a suitable combination of several powers of radius. Density and azimuthal pressure of the disks are illustrated on several plots, together with radial profiles of free circular velocity. * Dedicated to our teacher, Professor Jiří Bičák, on the occasion of his 80th birthday. For O.S., Jiří's interest in thin disks was, 30 yr ago (Bičák et al. ), the first motivation to study the topic.

Keywords: Black holes, Relativistic disks
Birthplaces of Extreme Ultraviolet Waves Driven by Impingement of Solar Jets upon Coronal Loops. Solar extreme ultraviolet (EUV) waves are large-scale propagating disturbances in the corona. It is generally believed that a vital key to the formation of EUV waves is the rapid expansion of the loops that overlie erupting cores in solar eruptions, such as coronal mass ejections (CMEs) and solar jets. However, the details of the interaction between the erupting cores and overlying loops are not clear because the overlying loops always instantly open after energetic eruptions. Here, we present three typical jet-driven EUV waves without CMEs to study the interaction between the jets and the overlying loops that remained closed during the events. All three jets emanated from magnetic flux cancellation sites in the source regions. Interestingly, after the interactions between the jets and overlying loops, three EUV waves respectively formed ahead of the top, the near end (close to the jet source), and the far (another) end of the overlying loops. According to the magnetic field distribution of the loops extrapolated through the potential field source surface method, it is confirmed that the birthplaces of three jet-driven EUV waves were around the parts of the overlying loops with the weakest magnetic field strengths. We suggest that the jet-driven EUV waves preferentially occur at the weakest part of the overlying loops, and the location can be subject to the magnetic field intensity around the ends of the loops.

Keywords: Solar activity, Beta Cephei variable stars, Solar coronal waves, Solar magnetic fields
Predicting Solar Flares Using CNN and LSTM on Two Solar Cycles of Active Region Data. We consider the flare prediction problem that distinguishes flare-imminent active regions that produce an M- or X-class flare in the succeeding 24 hr, from quiet active regions that do not produce any flares within ±24 hr. Using line-of-sight magnetograms and parameters of active regions in two data products covering Solar Cycles 23 and 24, we train and evaluate two deep learning algorithms-a convolutional neural network (CNN) and a long short-term memory (LSTM)-and their stacking ensembles. The decisions of CNN are explained using visual attribution methods. We have the following three main findings. (1) LSTM trained on data from two solar cycles achieves significantly higher true skill scores (TSSs) than that trained on data from a single solar cycle with a confidence level of at least 0.95. (2) On data from Solar Cycle 23, a stacking ensemble that combines predictions from LSTM and CNN using the TSS criterion achieves a significantly higher TSS than the "select-best" strategy with a confidence level of at least 0.95. (3) A visual attribution method called "integrated gradients" is able to attribute the CNN's predictions of flares to the emerging magnetic flux in the active region. It also reveals a limitation of CNNs as flare prediction methods using line-of-sight magnetograms: it treats the polarity artifact of line-of-sight magnetograms as positive evidence of flares.

Keywords: Solar active region magnetic fields, Solar flares, Classification, Neural networks, Astronomy data analysis
Comets in Context: Comparing Comet Compositions with Protosolar Nebula Models. Comets provide a valuable window into the chemical and physical conditions at the time of their formation in the young solar system. We seek insights into where and when these objects formed by comparing the range of abundances observed for nine molecules and their average values across a sample of 29 comets to the predicted midplane ice abundances from models of the protosolar nebula. Our fiducial model, where ices are inherited from the interstellar medium, can account for the observed mixing ratio ranges of each molecule considered, but no single location or time reproduces the abundances of all molecules simultaneously. This suggests that each comet consists of material processed under a range of conditions. In contrast, a model where the initial composition of disk material is "reset," wiping out any previous chemical history, cannot account for the complete range of abundances observed in comets. Using toy models that combine material processed under different thermal conditions, we find that a combination of warm (CO-poor) and cold (CO-rich) material is required to account for both the average properties of the Jupiter-family and Oort cloud comets, and the individual comets we consider. This could occur by the transport (either radial or vertical) of ice-coated dust grains in the early solar system. Comparison of the models to the average Jupiter-family and Oort cloud comet compositions suggests the two families formed in overlapping regions of the disk, in agreement with the findings of A'Hearn et al. and with the predictions of the Nice model.

Keywords: Interstellar molecules, Solar nebulae, Astrochemistry, Protoplanetary disks, Comet origins