Sazuna/UAT_keywords huggingface dataset:
A Bright First Day for Tidal Disruption Events. Stream-stream collision may be an important prepeak energy dissipation mechanism in tidal disruption events (TDEs). We perform local three-dimensional radiation hydrodynamic simulations in a wedge geometry including the gravity to study stream self-crossing with an emphasis on resolving the collision and following the subsequent outflow. We find that the collision can contribute to prepeak optical emissions by converting ≳5% of the stream kinetic energy to radiation, yielding prompt emission of ~1042-44 erg s-1. The radiative efficiency is sensitive to stream mass fallback rates and strongly depends on the downstream gas optical depth. Even for a sub-Eddington (10%) mass fallback rate, the strong radiation pressure produced in the collision can form a local super-Eddington region near the collision site, where a fast, aspherical outflow is launched. A higher mass fallback rate usually leads to more optically thick outflow and lower net radiative efficiency. For $\dot{M}\gtrsim 0.1{\dot{M}}_{\mathrm{Edd}}$ , the estimated photosphere size of the outflow can expand by 1-2 orders of magnitude, reaching ~1014 cm. The average gas temperature at this photospheric surface is a few × 104 K, roughly consistent with inferred prepeak photosphere properties for some optical TDEs. We find that the dynamics is sensitive to the collision angle and radius, but the radiative efficiency or outflow properties show more complex dependency than is often assumed in ballistic models.

Keywords: Accretion, Tidal disruption, Astrophysical black holes, Astronomical radiation sources
The Circumgalactic Medium of Extreme Emission Line Galaxies at z∼2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyα Emission in the KBSS-KCWI Survey. The resonantly scattered Lyα line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. We present integral field Keck Cosmic Web Imager observations of double-peaked, spatially extended Lyα emission in 12 relatively low-mass (M ⋆ ∼ 109 M⊙) z ∼ 2 galaxies characterized by extreme nebular emission lines. Using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the Lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. We use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. These models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from Lyα and absorption lines. The galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (ICM), whose residual neutral content produces absorption at the systemic redshift. The peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the H I column density, and the residual neutral density in the ICM respectively. The azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the H I column density in the outer halos. *Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

Keywords: Galaxy evolution, Circumgalactic medium, Radiative transfer simulations, Galaxy spectroscopy, High-redshift galaxies
Rapid Quenching of Galaxies at Cosmic Noon. The existence of massive quiescent galaxies at high redshift seems to require rapid quenching, but it is unclear whether all quiescent galaxies have gone through this phase and what physical mechanisms are involved. To study rapid quenching, we use rest-frame colors to select 12 young quiescent galaxies at z ~ 1.5. From spectral energy distribution fitting, we find that they all experienced intense starbursts prior to rapid quenching. We confirm this with deep Magellan/FIRE spectroscopic observations for a subset of seven galaxies. Broad emission lines are detected for two galaxies, and are most likely caused by active galactic nucleus (AGN) activity. The other five galaxies do not show any emission features, suggesting that gas has already been removed or depleted. Most of the rapidly quenched galaxies are more compact than normal quiescent galaxies, providing evidence for a central starburst in the recent past. We estimate an average transition time of 300 Myr for the rapid quenching phase. Approximately 4% of quiescent galaxies at z = 1.5 have gone through rapid quenching; this fraction increases to 23% at z = 2.2. We identify analogs in the TNG100 simulation and find that rapid quenching for these galaxies is driven by AGNs, and for half of the cases, gas-rich major mergers seem to trigger the starburst. We conclude that these young massive quiescent galaxies are not just rapidly quenched, but also rapidly formed through a major starburst. We speculate that mergers drive gas inflow toward the central regions and grow supermassive black holes, leading to rapid quenching by AGN feedback.

Keywords: Galaxy quenching, Galaxy formation, Galaxy evolution
Mass Distribution for Single-lined Hot Subdwarf Stars in LAMOST. Masses for 664 single-lined hot subdwarf stars identified in LAMOST were calculated by comparing synthetic fluxes from spectral energy distribution with observed fluxes from a Virtual Observatory service. Three groups of hot subdwarf stars were selected from the whole sample according to their parallax precision to study the mass distributions. We found that He-poor sdB/sdOB stars present a wide mass distribution from 0.1 to 1.0 M ☉ with a sharp mass peak at around 0.46 M ☉, which is consistent with canonical binary model prediction. He-rich sdB/sdOB/sdO stars present a much flatter mass distribution than He-poor sdB/sdOB stars and with a mass peak at around 0.42 M ☉. By comparing the observed mass distributions to the predictions of different formation scenarios, we concluded that the binary merger channel, including two helium white dwarfs (He-WDs) and He-WD + main-sequence mergers, cannot be the only main formation channel for He-rich hot subdwarfs, and other formation channels, such as the surviving companions from Type Ia supernovae, could also make impacts on producing this special population, especially for He-rich hot subdwarfs with masses less than 0.44 M ☉. He-poor sdO stars also present a flatter mass distribution with an inconspicuous peak mass at 0.18 M ☉. The similar mass- ${\rm{\Delta }}{{RV}}_{\max }$ distribution between He-poor sdB/sdOB and sdO stars supports the scenario that He-poor sdO stars could be the subsequent evolution stage of He-poor sdB/sdOB stars.

Keywords: B subdwarf stars, Spectral energy distribution, Stellar masses
Sequential Small Coronal Mass Ejections Observed In Situ and in White-Light Images by Parker Solar Probe. We reconstruct the morphology and kinematics of a series of small transients that erupted from the Sun on 2021 April 24 using observations primarily from Parker Solar Probe (PSP). These sequential small coronal mass ejections (CMEs) may be the product of a continuous reconnection at a current sheet, which is a macroscopic example of the more microscopic reconnection activity that has been proposed to accelerate the solar wind more generally. These particular CMEs are of interest because they are the first CMEs to hit PSP and be simultaneously imaged by it, using the Wide-field Imager for Solar Probe (WISPR) instrument. Based on imaging from WISPR and STEREO-A, we identify and model six discrete transients, and determine that it is the second of them (CME2) that first hits PSP, although PSP later more obliquely also encounters the third transient. Signatures of these encounters are seen in the PSP in situ data. Within these data, we identify six candidate magnetic flux ropes (MFRs), all but one of which are associated with the second transient. The five CME2 MFRs have orientations that are roughly consistent with PSP encountering the right-hand sides of roughly E-W oriented MFRs, which are sloping back toward the Sun.

Keywords: Interplanetary physics, Solar wind, Interplanetary magnetic fields, Solar coronal mass ejections
Reprocessing Models for the Optical Light Curves of Hypervariable Quasars from the Sloan Digital Sky Survey Reverberation Mapping Project. We explore reprocessing models for a sample of 17 hypervariable quasars, taken from the Sloan Digital Sky Survey Reverberation Mapping project, which all show coordinated optical luminosity hypervariability with amplitudes of factors ≳2 between 2014 and 2020. We develop and apply reprocessing models for quasar light curves in simple geometries that are likely to be representative of quasar inner environments. In addition to the commonly investigated thin-disk model, we include the thick-disk and hemisphere geometries. The thick-disk geometry could, for instance, represent a magnetically elevated disk, whereas the hemisphere model can be interpreted as a first-order approximation for any optically thick out-of-plane material caused by outflows/winds, warped/tilted disks, and so on. Of the 17 quasars in our sample, 11 are best-fitted by a hemisphere geometry, five are classified as thick disks, and both models fail for just one object. We highlight the successes and shortcomings of our thermal reprocessing models in case studies of four quasars that are representative of the sample. While reprocessing is unlikely to explain all of the variability that we observe in quasars, we present our classification scheme as a starting point for revealing the likely geometries of reprocessing for quasars in our sample and hypervariable quasars in general.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, Quasars
An Ongoing Tidal Capture in the Large Magellanic Cloud: The Low-mass Star Cluster KMK 88-10 Captured by the Massive Globular Cluster NGC 1835?. In the context of a project aimed at characterizing the dynamical evolution of old globular clusters in the Large Magellanic Cloud, we have secured deep HST/WFC3 images of the massive cluster NGC 1835. In the field of view of the acquired images, at a projected angular separation of approximately 2' from the cluster, we detected the small stellar system KMK 88-10. The observations provided the deepest color-magnitude diagram ever obtained for this cluster, revealing that it hosts a young stellar population with an age of 600-1000 Myr. The cluster surface brightness profile is nicely reproduced by a King model with a core radius r  c  = 4″ (0.97 pc), a half-mass radius r  hm  = 12″ (2.9 pc), and a concentration parameter c ~ 1.3 corresponding to a truncation radius r  t  ~ 81″ (19.5 pc). We also derived its integrated absolute magnitude (M  V  = -0.71) and total mass (M ~ 80-160 M ⊙). The most intriguing feature emerging from this analysis is that KMK 88-10 presents a structure elongated in the direction of NGC 1835, with an intracluster overdensity that suggests the presence of a tidal bridge between the two systems. If confirmed, this would be the first evidence of a tidal capture of a small star cluster by a massive globular. * Based on observations collected at the Hubble Space Telescope under proposal GO16361 (PI: Ferraro).

Keywords: Stellar photometry, Young star clusters, Large Magellanic Cloud
The X-Ray Binary-star Cluster Connection in Late-type Galaxies. We conduct one of the largest systematic investigations of bright X-ray binaries (XRBs) in both young star clusters and ancient globular clusters (GCs) using a sample of six nearby star-forming galaxies. Combining complete CXO X-ray source catalogs with optical Physics at High Angular Resolution in Nearby Galaxies-Hubble Space Telescope cluster catalogs, we identify a population of 33 XRBs within or near their parent clusters. We find that GCs that host XRBs in spiral galaxies appear to be brighter, more compact, denser, and more massive than the general GC population. However, these XRB hosts do not appear to be preferentially redder or more metal-rich, pointing to a possible absence of the metallicity-boosted formation of low-mass X-ray binaries (LMXBs) that is observed in the GCs of older galaxies. We also find that a smaller fraction of LMXBs is found in spiral GC systems when compared with those in early-type galaxies: between 8% and 50%, or an average of 20% across galaxies in our sample. Although there is a non-negligible probability of a chance superposition between an XRB and an unrelated young cluster, we find that among clusters younger than 10 Myr, which most likely host high-mass XRBs, the fraction of clusters associated with an XRB increases at higher cluster masses and densities. The X-ray luminosity of XRBs appears to increase with the mass of the cluster host for clusters younger than ~400 Myr, while the inverse relation is found for XRBs in GCs.

Keywords: Globular star clusters, X-ray binary stars, Young star clusters, Late-type galaxies
Using the Gaia Excess Uncertainty as a Proxy for Stellar Variability and Age. Stars are known to be more active when they are young, resulting in a strong correlation between age and photometric variability. The amplitude variation between stars of a given age is large, but the age-variability relation becomes strong over large groups of stars. We explore this relation using the excess photometric uncertainty in Gaia photometry (VarG, VarBP, and VarRP) as a proxy for variability. The metrics follow a Skumanich-like relation, scaling as ≃t -0.4. By calibrating against a set of associations with known ages, we show how the Var of population members can predict group ages within 10%-20% for associations younger than ≃2.5 Gyr. In practice, age uncertainties are larger, primarily due to the finite group size. The index is most useful at the youngest ages (&lt;100 Myr), where the uncertainties are comparable to or better than those derived from a color-magnitude diagram (CMD). The index is also widely available, easy to calculate, and can be used at intermediate ages where there are few or no pre- or post-main-sequence stars. We further show how Var can be used to find new associations and test if a group of comoving stars is a real coeval population. We apply our methods to Theia groups within 350 pc and find ≳90% are inconsistent with drawing stars from the field and ≃80% have variability ages consistent with those derived from the CMD. Our findings suggest the great majority of these groups contain real populations.

Keywords: Stellar rotation, Young star clusters, Stellar ages, Stellar evolution
Exploring the Evolution of Massive Clumps in Simulations That Reproduce the Observed Milky Way α-element Abundance Bimodality. The Milky Way (MW) stellar disk has both a thin and a thick component. The thin disk is composed mostly of younger stars (≲8 Gyr) with a lower abundance of α-elements, while the thick disk contains predominantly older stars (≳8-12 Gyr) with a higher α abundance, giving rise to an α-bimodality most prominent at intermediate metallicities. A proposed explanation for the bimodality is an episode of clumpy star formation, where high-α stars form in massive clumps that appear in the first few billion years of the MW's evolution, while low-α stars form throughout the disk and over a longer time span. To better understand the evolution of clumps, we track them and their constituent stars in two clumpy MW simulations that reproduce the α-abundance bimodality, one with 10% and the other with 20% supernova feedback efficiency. We investigate the paths that these clumps take in the chemical space ([O/Fe]-[Fe/H]) as well as their mass, star formation rate (SFR), formation location, lifetime, and merger history. The clumps in the simulation with lower feedback last longer on average, with several lasting hundreds of millions of years. Some of the clumps do not reach high-α, but the ones that do on average have a higher SFR, longer lifetime, greater mass, and form closer to the Galactic center than the ones that do not. Most clumps that reach high-α merge with others and eventually spiral into the Galactic center, but shed stars along the way to form most of the thick-disk component.

Keywords: Hydrodynamical simulations, Galaxy formation, Galaxy structure, Galaxy disks, Galaxy abundances, Galaxy evolution
Differences between the Pierre Auger Observatory and Telescope Array Spectra: Systematic Effects or Indication of a Local Source of Ultra-high-energy Cosmic Rays?. The Pierre Auger Observatory (PAO) and Telescope Array (TA) collaborations report significant differences in the observed energy spectra of ultra-high-energy cosmic rays (UHECRs) above 30 EeV. In this work we present a joint fit of TA and PAO data using the rigidity-dependent maximum energy model, including a full marginalization over all relevant parameters. We test two possible scenarios to explain these differences. One is that they are due to complex energy-dependent experimental systematics; the other is the presence of a local astrophysical source in the Northern Hemisphere, which is only visible by the TA experiment. We show that the astrophysical and systematic scenarios improve the explanation of the data equally well, compared to the scenario where both experiments observe the same UHECR flux from a cosmological source distribution and have energy-independent systematics. We test different mass compositions emitted from the local source and conclude that the data are best described by a source lying at a distance below 26 Mpc that emits cosmic rays dominated by the silicon mass group. We also discuss possible source candidates and the possible role of the putative local UHECR source in the observed TA anisotropy and in the differences in TA spectral data from different decl. bands.

Keywords: Neutrino astronomy, High energy astrophysics, Cosmic rays
The Spectacular Tidal Tails of Globular Cluster M3 (NGC 5272). We provide a detailed analysis of the tidal tails of the globular cluster M3 (NGC 5272). We first discover clear extratidal structures with a slight S shape near the cluster. This inspires us to examine the existence of its long tidal tails. We highlight potential stream stars using the proper motions (PMs) of a model stream combined with the cluster's locus in a color-magnitude diagram (CMD). A 35° long leading tail and a 21° long trailing tail are successfully detected at the same time. Their corresponding overdensities can be recognized in CMD and PM space after subtracting the background. We estimate the stream width, star number density, and surface brightness for both tails, as well as the distance variation along the entire stream. We then verify the connection of M3 and the Svöl stream. Finally, we tabulate 11 member stars belonging to the M3 tidal stream with available spectroscopic observations.

Keywords: Globular star clusters, Milky Way stellar halo, Stellar streams
Near-infrared Spectroscopy of Dense Ejecta Knots in the Outer Eastern Area of the Cassiopeia A Supernova Remnant. The Cassiopeia A supernova remnant has a complex structure, manifesting the multidimensional nature of core-collapse supernova explosions. To further understand this, we carried out near-infrared multiobject spectroscopy on the ejecta knots located in the northeastern (NE) jet and Fe K plume regions, which are two distinct features in the outer eastern area of the remnant. Our study reveals that the knots exhibit varying ratios of [S II] 1.03, [P II] 1.189, and [Fe II] 1.257 μm lines depending on their locations within the remnant, suggesting regional differences in elemental composition. Notably, the knots in the NE jet are mostly S-rich with weak or no [P II] lines, implying that they originated below the explosive Ne-burning layer, consistent with the results of previous studies. We detected no ejecta knots exhibiting only [Fe II] lines in the NE jet area that are expected in the jet-driven supernova explosion model. Instead, we discovered a dozen Fe-rich knots in the Fe K plume area. We propose that they are dense knots produced by a complete Si burning with α-rich freeze-out in the innermost region of the progenitor and ejected with the diffuse X-ray-emitting Fe ejecta but decoupled after crossing the reverse shock. In addition to these metal-rich ejecta knots, several knots emitting only He I 1.083 μm lines were detected, and their origin remains unclear. We also detected three extended H emission features of circumstellar or interstellar origin in this area and discuss their association with the supernova remnant.

Keywords: Supernova remnants, Supernovae, Core-collapse supernovae
Monte Carlo Radiation Transport for Astrophysical Transients Powered by Circumstellar Interaction. In this paper, we introduce SuperLite, an open-source Monte Carlo radiation transport code designed to produce synthetic spectra for astrophysical transient phenomena affected by circumstellar interaction. SuperLite utilizes Monte Carlo methods for semi-implicit, semirelativistic radiation transport in high-velocity shocked outflows, employing multigroup structured opacity calculations. The code enables rapid post-processing of hydrodynamic profiles to generate high-quality spectra that can be compared with observations of transient events, including superluminous supernovae, pulsational pair-instability supernovae, and other peculiar transients. We present the methods employed in SuperLite and compare the code's performance to that of other radiative transport codes, such as SuperNu and CMFGEN. We show that SuperLite has successfully passed standard Monte Carlo radiation transport tests and can reproduce spectra of typical supernovae of Type Ia, Type IIP, and Type IIn.

Keywords: Stellar-interstellar interactions, Monte Carlo methods, Transient sources, Circumstellar shells, Radiative transfer, Supernovae
A Three-dimensional Model for the Evolution of Magnetohydrodynamic Turbulence in the Outer Heliosphere. We present a time-dependent, three-dimensional single-fluid model for the transport of magnetohydrodynamic (MHD) turbulence that is self-consistently evolving with a dynamic large-scale solar wind in the outer heliosphere. The emphasis is on the region beyond the termination shock, where the solar wind expands subsonically, as well as sub-Alfvénically and nonradially. In extension of earlier work, we refine the treatment of turbulence by considering, in addition to the Elsässer energies, a nonconstant energy difference (or residual energy) and by allowing each of these quantities its own characteristic correlation length scale. While the nonlinear effects in the equations for the Elsässer energies and their length scales are implemented using familiar von Kármán-Howarth style modeling of homogeneous MHD turbulence, the energy difference, which is not conserved in the absence of dissipation, and its length scale are modeled using distinct approaches. We also clarify the impact of the choice of measurement direction for correlation functions associated with two-dimensional fluctuations in transport models. Finally, we illustrate and study the solutions of the resulting six-equation model in detail.

Keywords: Interplanetary turbulence, Heliosheath, Solar wind termination