Sazuna/UAT_keywords huggingface dataset:
On the Origin of Late-time X-Ray Flares in UV/optically Selected Tidal Disruption Events. We propose a model to explain the time delay between the peak of the optical and X-ray luminosity, ΔtO-X hereafter, in UV/optically selected tidal disruption events (TDEs). The following picture explains the observed ΔtO-X in several TDEs as a consequence of the circularization and disk accretion processes as long as the sub-Eddington accretion. At the beginning of the circularization, the fallback debris is thermalized by the self-crossing shock caused by relativistic precession, providing the peak optical emission. During the circularization process, the mass fallback rate decreases with time to form a ring around the supermassive black hole (SMBH). The formation timescale corresponds to the circularization timescale of the most tightly bound debris, which is less than a year to several decades, depending mostly on the penetration factor, the circularization efficiency, and the black hole mass. The ring will subsequently evolve viscously over the viscous diffusion time. We find that it accretes onto the SMBH on a fraction of the viscous timescale, which is 2 years for the typical given parameters, leading to X-ray emission at late times. The resultant ΔtO-X is given by the sum of the circularization timescale and the accretion timescale and significantly decreases with increasing penetration factor to several to ~10 yr typically. Since the X-ray luminosity substantially decreases as the viewing angle between the normal to the disk plane and line of sight increases from 0° to 90°, a low late-time X-ray luminosity can be explained by an edge-on view. We also discuss the super-Eddington accretion scenario, where ΔtO-X is dominated by the circularization timescale.

Keywords: Accretion, Black hole physics, Supermassive black holes, High energy astrophysics, Tidal disruption, Galaxy accretion disks, Transient sources, Astrophysical black holes
Effect of Dust Rotational Disruption by Radiative Torques on Radiation Pressure Feedback from Massive Protostars. Radiation pressure on dust is thought to play a crucial role in the formation process of massive stars by acting against gravitational collapse onto the central protostar. However, dust properties in dense regions irradiated by the intense radiation of massive protostars are poorly constrained. Previous studies usually assume the standard interstellar dust model to constrain the maximum mass of massive stars formed by accretion, which appears to contradict dust evolution theory. In this paper, using the fact that stellar radiation exerts on dust simultaneous radiation pressure and radiative torques, we study the effects of grain rotational disruption by radiative torques (RATs) on radiation pressure and explore its implications for massive star formation. For this paper, we focus on the protostellar envelope and adopt a spherical geometry. We find that originally large grains of micron sizes presumably formed in very dense regions can be rapidly disrupted into small grains by RATs due to infrared radiation from the hot dust shell near the sublimation front induced by direct stellar radiation. Owing to the modification of the size distribution by rotational disruption, the radiation pressure opacity can be decreased by a factor of ~3 from the value expected from the original dust model. However, to form massive stars via spherical accretion, the dust-to-gas mass ratio needs to be reduced by a factor of ~5 as previously found.

Keywords: Stellar feedback, Massive stars, Astrophysical dust processes, Radiative processes, Star formation, Interstellar dust processes
Molecular Gas Filaments and Fallback in the Ram Pressure Stripped Coma Spiral NGC 4921. We investigate the effects of ram pressure on the molecular interstellar medium (ISM) in the disk of the Coma cluster galaxy NGC 4921 via high-resolution CO observations. We present 6″ resolution CARMA CO(1-0) observations of the full disk, and 0"4 resolution Atacama Large Millimeter/submillimeter Array CO(2-1) observations of the leading quadrant, where ram pressure is strongest. We find evidence for compression of the dense ISM on the leading side, spatially correlated with intense star formation activity in this zone. We also detect molecular gas along kiloparsec-scale filaments of dust extending into the otherwise gas stripped zone of the galaxy, seen in Hubble Space Telescope images. We find the filaments are connected kinematically as well as spatially to the main gas ridge located downstream, consistent with cloud decoupling inhibited by magnetic binding, and inconsistent with a simulated filament formed via simple ablation. Furthermore, we find several clouds of molecular gas ~1-3 kpc beyond the main ring of CO that have velocities that are blueshifted by up to 50 km s-1 with respect to the rotation curve of the galaxy. These are some of the only clouds we detect that do not have any visible dust extinction associated with them, suggesting that they are located behind the galaxy disk midplane and are falling back toward the galaxy. Simulations have long predicted that some gas removed from the galaxy disk will fall back during ram pressure stripping. This may be the first clear observational evidence of gas re-accretion in a ram pressure stripped galaxy.

Keywords: Galaxy clusters, Galaxy quenching, Galaxy evolution, Galaxy environments
A Wide-field CO Survey toward the California Molecular Filament. We present the survey of 12CO/13CO/C18O (J = 1 - 0) toward the California molecular cloud (CMC) within the region of 161°75 ≤ l ≤ 167°75, -9°5 ≤ b ≤ -7°5 using the Purple Mountain Observatory (PMO) 13.7 m millimeter telescope. Adopting a distance of 470 pc, the mass of the observed molecular cloud estimated from 12CO, 13CO, and C18O is about 2.59 × 104, 0.85 × 104, and 0.09 × 104 M⊙, respectively. A large-scale continuous filament extending about 72 pc is revealed from the 13CO images. A systematic velocity gradient perpendicular to the major axis appears and is measured to be ~0.82 km s-1 pc-1. The kinematics along the filament shows an oscillation pattern with a fragmentation wavelength of ~2.3 pc and velocity amplitude of ~0.92 km s-1, which may be related to core-forming flows. Furthermore, assuming an inclination angle to the plane of the sky of 45°, the estimated average accretion rate is ~101 M⊙ Myr-1 for the cluster LkHα 101 and ~21 M⊙ Myr-1 for the other regions. In the C18O observations, the large-scale filament could be resolved into multiple substructures, and their dynamics are consistent with the scenario of filament formation from converging flows. Approximately 225 C18O cores are extracted, of which 181 are starless cores. Roughly 37% (67/181) of the starless cores have αvir less than 1. Twenty outflow candidates are identified along the filament. Our results indicate active early-phase star formation along the large-scale filament in the CMC region.

Keywords: Giant molecular clouds, Star formation, Interstellar filaments, Interstellar medium
The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution. Since planet occurrence and primordial atmospheric retention probability increase with period, the occurrence-weighted median planets discovered by transit surveys may bear little resemblance to the low-occurrence, short-period planets sculpted by atmospheric escape ordinarily used to calibrate mass-radius relations and planet formation models. An occurrence-weighted mass-radius relation for the low-mass planets discovered so far by transit surveys orbiting solar-type stars requires both occurrence-weighted median Earth-mass and Neptune-mass planets to have a few percent of their masses in hydrogen/helium (H/He) atmospheres. Unlike the Earth that finished forming long after the protosolar nebula was dissipated, these occurrence-weighted median Earth-mass planets must have formed early in their systems' histories. The existence of significant H/He atmospheres around Earth-mass planets confirms an important prediction of the core-accretion model of planet formation. It also implies core masses Mc in the range 2 M⊕ ≲ Mc ≲ 8 M⊕ that can retain their primordial atmospheres. If atmospheric escape is driven by photoevaporation due to extreme-ultraviolet (EUV) flux, then our observation requires a reduction in the fraction of incident EUV flux converted into work usually assumed in photoevaporation models. If atmospheric escape is core driven, then the occurrence-weighted median Earth-mass planets must have large Bond albedos. In contrast to Uranus and Neptune that have at least 10% of their masses in H/He atmospheres, these occurrence-weighted median Neptune-mass planets are H/He poor. The implication is that they experienced collisions or formed in much shorter-lived and/or hotter parts of their parent protoplanetary disks than Uranus and Neptune's formation location in the protosolar nebula.

Keywords: Exoplanets, Super Earths, Exoplanet evolution, Mini Neptunes, Exoplanet formation, Exoplanet atmospheres
Effects of Spin-Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone. Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, including spin-orbit resonant configurations, particularly when higher eccentricity orbits can be maintained in a system. Additionally, the oscillating strain as a planet moves from periastron to apoastron results in friction and tidal heating, which can be an important energy source. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with the NASA GISS ROCKE-3D general circulation model, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 and 3000 K stars. This study is the first to use a 3D general circulation model that implements tidal heating to investigate habitability for multiple resonant states. We find that for reference experiments without tidal heating, the resonant state has little impact on the radial position of the inner edge because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, when strong tidal heating is present, the rotational component implies a strong dependence of habitable conditions on the system evolution and rotational state. Since tidal and stellar heating both decrease rapidly with orbital distance, this results in a compact orbital width separating temperate and uninhabitable climates. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge.

Keywords: Planetary atmospheres, Tidal interaction, Habitable zone, Habitable planets, Exoplanet atmospheres
Shock Properties and Associated Characteristics of Solar Energetic Particles in the 2017 September 10 Ground-level Enhancement Event. The solar eruption on 2017 September 10 was accompanied by a fast coronal mass ejection (~3000 km s-1) and produced a ground-level enhancement (GLE) event at Earth. Multiple-viewpoint remote sensing observations are used to find the three-dimensional (3D) structure of the shock. We determine the shock parameters by combining the 3D shock kinematics and the solar wind properties obtained from a global magnetohydrodynamic (MHD) simulation, in order to compare them with the characteristics of the solar energetic particles (SEPs). We extract the magnetic connectivities of the observers from the MHD simulation and find that L1 was magnetically connected to the shock flank (rather than the nose). Further analysis shows that this shock flank propagates through the heliospheric current sheet (HCS). The weak magnetic field and relatively dense plasma around the HCS result in a large Mach number of the shock, which leads to efficient particle acceleration even at the shock flank. We conclude that the interaction between the shock and HCS provides a potential mechanism for production of the GLE event. The comparison between the shock properties and the characteristics of SEPs suggests an efficient particle acceleration in a wide spatial range by the shock propagating through the highly inhomogeneous coronal medium.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Solar flares
Photochemistry and Spectral Characterization of Temperate and Gas-rich Exoplanets. Exoplanets that receive stellar irradiance approximately equal to Earth's or less have been discovered and many are suitable for spectral characterization. Here, we focus on the temperate planets that have massive H2-dominated atmospheres, and trace the chemical reactions and transport following the photodissociation of H2O, CH4, NH3, and H2S, with K2-18 b, PH2 b, and Kepler-167 e representing temperate/cold planets around M and G/K stars. We find that NH3 is likely depleted by photodissociation to the cloud deck on planets around G/K stars but remains intact in the middle atmosphere of planets around M stars. A common phenomenon on temperate planets is that the photodissociation of NH3 in the presence of CH4 results in HCN as the main photochemical product. The photodissociation of CH4 together with H2O leads to CO and CO2, and the synthesis of hydrocarbon is suppressed. Temperate planets with a supersolar atmospheric metallicity and appreciable internal heat may have additional CO and CO2 from the interior and less NH3, and thus less HCN. Our models of K2-18 b can explain the transmission spectrum measured by the Hubble Space Telescope, and indicate that future observations in 0.5-5.0 μm wavelength range would provide the sensitivity to detect the equilibrium gases CH4, H2O, and NH3, the photochemical gas HCN, as well as CO2 in some cases. Temperate and H2-rich exoplanets are thus laboratories of atmospheric chemistry that operate in regimes not found in the solar system, and spectral characterization of these planets in transit or reflected starlight promises to greatly expand the types of molecules detected in exoplanet atmospheres.

Keywords: Transmission spectroscopy, Extrasolar gaseous planets, Mini Neptunes, Habitable zone, Extrasolar ice giants, Exoplanet atmospheres
Three-dimensional Hydrodynamic Simulations of Convective Nuclear Burning in Massive Stars Near Iron Core Collapse. Nonspherical structure in massive stars at the point of iron core collapse can have a qualitative impact on the properties of the ensuing core-collapse supernova explosions and the multimessenger signals they produce. Strong perturbations can aid successful explosions by strengthening turbulence in the postshock region. Here we report on a set of 4π 3D hydrodynamic simulations of O- and Si-shell burning in massive star models of varied initial masses using MESA and the FLASH simulation framework. We evolve four separate 3D models for roughly the final 10 minutes prior to and including iron core collapse. We consider initial 1D MESA models with masses of 14, 20, and 25 M⊙ to survey a range of O/Si-shell density and compositional configurations. We characterize the convective shells in our 3D models and compare them to the corresponding 1D models. In general, we find that the angle-average convective speeds in our 3D simulations near collapse are three to four times larger than the convective speeds predicted by MESA at the same epoch for our chosen mixing length parameter of αMLT = 1.5. In three of our simulations, we observe significant power in the spherical harmonic decomposition of the radial velocity field at harmonic indices of ℓ = 1-3 near collapse. Our results suggest that large-scale modes are common in massive stars near collapse and should be considered a key aspect of presupernova progenitor models.

Keywords: Stellar convective zones, Late stellar evolution, Hydrodynamics, Massive stars, Supernovae
Do Coronal Loops Oscillate in Isolation?. Images of the solar corona by extreme-ultraviolet telescopes reveal elegant arches of glowing plasma that trace the corona's magnetic field. Typically, these loops are preferentially illuminated segments of an arcade of vaulted field lines and such loops are often observed to sway in response to nearby solar flares. A flurry of observational and theoretical effort has been devoted to the exploitation of these oscillations with the grand hope that seismic techniques might be used as probes of the strength and structure of the corona's magnetic field. The commonly accepted viewpoint is that each visible loop oscillates as an independent entity and acts as a one-dimensional wave cavity for magnetohydrodynamic kink waves. We argue that for many events, this generally accepted model for the wave cavity is fundamentally flawed. In particular, the 3D magnetic arcade in which the bright loop resides participates in the oscillation. Thus, the true wave cavity is larger than the individual loop and inherently multidimensional. We derive the skin depth of the near-field response for an oscillating loop and demonstrate that most loops are too close to other magnetic structures to oscillate in isolation. Further, we present a simple model of a loop embedded within an arcade and explore how the eigenmodes of the arcade and the eigenmodes of the loop become coupled. In particular, we discuss how distinguishing between these two types of modes can be difficult when the motions within the arcade are often invisible.

Keywords: Solar coronal seismology, Solar coronal loops, Solar coronal waves, Solar magnetic fields, Solar oscillations, Active solar corona
The Nature of High-frequency Oscillations Associated with Short-lived Spicule-type Events. We investigate high-resolution spectroscopic and imaging observations from the CRisp Imaging SpectroPolarimeter (CRISP) instrument to study the dynamics of chromospheric spicule-type events. It is widely accepted that chromospheric fine structures are waveguides for several types of magnetohydrodynamic (MHD) oscillations, which can transport energy from the lower to upper layers of the Sun. We provide a statistical study of 30 high-frequency waves associated with spicule-type events. These high-frequency oscillations have two components of transverse motions: the plane-of-sky (POS) motion and the line-of-sight (LOS) motion. We focus on single isolated spicules and track the POS using time-distance analysis and in the LOS direction using Doppler information. We use moment analysis to find the relation between the two motions. The composition of these two motions suggests that the wave has a helical structure. The oscillations do not have phase differences between points along the structure. This may be the result of the oscillation being a standing mode, or that propagation is mostly in the perpendicular direction. There is evidence of fast magnetoacoustic wave fronts propagating across these structures. To conclude, we hypothesize that the compression and rarefaction of passing magnetoacoustic waves may influence the appearance of spicule-type events, not only by contributing to moving them in and out of the wing of the spectral line but also through the creation of density enhancements and an increase in opacity in the Hα line.

Keywords: Solar atmosphere, Magnetohydrodynamics, Solar chromosphere
Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S<SUP>5</SUP>). We present new spectroscopic observations of the diffuse Milky Way satellite galaxies Antlia 2 and Crater 2, taken as part of the Southern Stellar Stream Spectroscopic Survey (S5). The new observations approximately double the number of confirmed member stars in each galaxy and more than double the spatial extent of spectroscopic observations in Antlia 2. A full kinematic analysis, including Gaia EDR3 proper motions, detects a clear velocity gradient in Antlia 2 and a tentative velocity gradient in Crater 2. The velocity gradient magnitudes and directions are consistent with particle stream simulations of tidal disruption. Furthermore, the orbit and kinematics of Antlia 2 require a model that includes the reflex motion of the Milky Way induced by the Large Magellanic Cloud. We also find that Antlia 2's metallicity was previously overestimated, so it lies on the empirical luminosity-metallicity relation and is likely only now experiencing substantial stellar mass loss. Current dynamical models of Antlia 2 require it to have lost over 90% of its stars to tides, in tension with the low stellar mass loss implied by the updated metallicity. Overall, the new kinematic measurements support a tidal disruption scenario for the origin of these large and extended dwarf spheroidal galaxies.

Keywords: Stellar streams, Stellar kinematics, Dwarf galaxies, Dark matter, Large Magellanic Cloud, Milky Way Galaxy
SOFIA-upGREAT Imaging Spectroscopy of the [C II] 158 μm Fine-structure Line of the Sgr B Region in the Galactic Center. We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158 μm spectral line, as well as a number of [O I] 63 μm spectra, across a 67 × 45 pc field toward the Sgr B region in our Galactic center. The fully sampled and velocity-resolved [C II] images have 0.55 pc spatial and 1 km s-1 velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C II] emission encompasses Sgr B1 (G0.5-0.0) and the G 0.6-0.0 H II region and passes behind and beyond the luminous star-forming cores toward Sgr B2 (G0.7-0.0). Sgr B is a major contributor to the entire Galactic center's [C II] luminosity, with surface brightness comparable to [C II] from the Arches region. [C II], 70 μm, and 20 cm emissions share nearly identical spatial distributions. Combined with the lack of [C II] self-absorption, this indicates that these probes trace UV on the near surfaces of more extended clouds visible in CO isotopologues and 160 μm continuum. Stars from regions of local star formation likely dominate the UV field. Photodissociation regions and H II regions contribute similar amounts of [C II] flux. The extreme star formation cores of Sgr B2 contribute negligible amounts to the total [C II] intensity from the Sgr B region. Velocity fields and association with a narrow dust lane indicate that they may have been produced in a local cloud-cloud collision. The cores are likely local analogs of the intense star formation regions where ideas to explain the "C+ deficit" in ultraluminous galaxies can be tested.

Keywords: High resolution spectroscopy, Galactic center, Star forming regions, Photodissociation regions, Interstellar medium
The Crab Nebula as a Calibrator for Wide-beam Cosmic Microwave Background Polarization Surveys. We analyze the effect of polarized diffuse emission in the calibration of wide-beam millimeter-wave polarimeters, when using the Crab Nebula as a reference source for both polarized brightness and polarization angle. We show that, for CMB polarization experiments aiming at detecting B-mode in a scenario with a tensor to scalar ratio r ~ 0.001, wide (a few degrees in diameter), precise ( ${\sigma }_{Q},{\sigma }_{U}\sim 20\,\mu {{\rm{K}}}_{\mathrm{CMB}}\mathrm{arcmin}$ ), high angular resolution (&lt;FWHM) reference maps are needed to properly take into account the effects of diffuse polarized emission and avoid significant bias in the calibration.

Keywords: Observational cosmology, Cosmic microwave background radiation, CMBR detectors, Dust continuum emission, Polarimetry