Sazuna/UAT_keywords huggingface dataset:
Transition Region Contribution to AIA Observations in the Context of Coronal Heating. We investigate the ratio of coronal and transition region intensity in coronal loops observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Using Enthalpy-based Thermal Evolution of Loops (EBTEL) hydrodynamic simulations, we model loops with multiple lengths and energy fluxes heated randomly by events drawn from power-law distributions with different slopes and minimum delays between events to investigate how each of these parameters influences observable loop properties. We generate AIA intensities from the corona and transition region for each realization. The variations within and between models generated with these different parameters illustrate the sensitivity of narrowband imaging to the details of coronal heating. We then analyze the transition region and coronal emission from a number of observed active regions and find broad agreement with the trends in the models. In both models and observations, the transition region brightness is significant, often greater than the coronal brightness in all six "coronal" AIA channels. We also identify an inverse relationship, consistent with heating theories, between the slope of the differential emission measure (DEM) coolward of the peak temperature and the observed ratio of coronal to transition region intensity. These results highlight the use of narrowband observations and the importance of properly considering the transition region in investigations of coronal heating.

Keywords: Observational astronomy, Astronomical models, Astronomy data modeling, Solar extreme ultraviolet emission, Solar coronal loops, Solar transition region, Solar observatories, Solar electromagnetic emission
A Unified Model for Bipolar Outflows from Young Stars: The Interplay of Magnetized Wide-angle Winds and Isothermal Toroids. Large-scale morphology and time evolution are investigated for the unified model of bipolar outflows outlined in Shang et al. (2006), where an outflow forms by a radially directed, wide-angle magnetized wind interacting with magnetized isothermal toroids in various quasistatic states. The primary wide-angle wind is toroidally magnetized and maintains a cylindrically stratified density profile, mimicking the asymptotic solution of the cold X-wind model. We explore the interplay between the toroidally magnetized primary wind and the surrounding toroids threaded by poloidal magnetic fields and examine how the jet and shell morphology and fine structures within them vary with the physical parameters. The variation in flatness of the density distribution in the ambient isothermal toroids helps shape the varieties of lobe morphology and collimation. The presence of a stronger ambient poloidal field helps shape the outflow, forming a magnetic cocoon and nested multilayered cavities surrounding the wind-filled lobe, which is most evident in the more open configurations of the ambient toroids. The wind-toroid interface is prone to substantial shear and thus unstable to the Kelvin-Helmholtz instability. Magnetic forces in the compressed toroidally magnetized high-velocity wind can generate vorticity, leading to nonlinear patterns within the extended magnetized mixing layers. Magnetic disturbances generated by the interplay could modulate lobe shapes, density, and velocities, giving rise to visual impressions of thicker and rugged shells and apparent episodic distribution of matter. The system maintains a quasi-self-similar evolution in time, which serves as a proxy for understanding the underlying physical mechanisms driving it.

Keywords: Magnetohydrodynamics, Stellar-interstellar interactions, Jets, Stellar jets, Stellar mass loss, Young stellar objects, Stellar winds, Star formation, Low mass stars, Protostars, Magnetic fields, Magnetohydrodynamical simulations
Outflows in the Presence of Cosmic Rays and Waves. Plasma outflow or wind against a gravitational potential under the influence of cosmic rays is studied in the context of hydrodynamics. Cosmic rays interact with the plasma via hydromagnetic fluctuations. In the process, cosmic rays advect and diffuse through the plasma. We adopt a multi-fluid model in which, besides thermal plasma, cosmic rays and self-excited Alfvén waves are also treated as fluids. We seek possible, physically allowable steady-state solutions of three-fluid (one Alfvén wave) and four-fluid (two Alfvén waves) models with given boundary conditions at the base of the potential well. Generally speaking, there are two classes of outflows—subsonic and supersonic (with respect to a suitably defined sound speed). A three-fluid model without cosmic-ray diffusion can be studied in the same way as the classic stellar wind problem, and is taken as a reference model. When cosmic-ray diffusion is included, there are two categories of solutions. One of them resembles the three-fluid model without diffusion, and the other behaves like thermal wind at large distances when the waves wither and cosmic rays are decoupled from the plasma. We also examine the effect of wave damping mechanisms (such as nonlinear Landau damping). Roughly speaking, the effect is much smaller in supersonic outflow than in subsonic outflow.

Keywords: Galactic winds, Hydrodynamics, Stellar winds, Alfven waves, Cosmic rays
Star Formation in Splash Bridges. Splash bridges are created from the direct collision of two gas-rich disk galaxies. These direct collisions can eject gas masses on the order of 1010 M⊙ stripped from the stellar disks of each galaxy. The Taffy Galaxy system (UGC 1294/5) is a prototypical example of a splash bridge system. CO observations of the Taffy revealed that its splash bridge contains a mass of H2 equal to the Milky Way's H2 mass. However, the little visible star formation occurring within the bridge highlights the need for models of direct gas-rich disk collisions. The Arp 194 system displays what may be another splash bridge resulting from the collision between two disk galaxies. The region between the two stellar disks contains bright clumps of active star formation. We aim to better understand the conditions for star formation in splash bridges by employing a Jeans criterion to determine where gravitational instabilities occur in the shocked and cooling gas of gas-rich disk collisions. The splash bridge results are obtained from our previous work using a sticky particle code and post-processed. We find that the inclination between the gas disks and the collision velocity with which the gas collides strongly affects the fraction of gas that will become gravitationally unstable. Low inclinations between gas disks produce starbursts whereas high inclinations result in steady-rate star formation. The offset of the gas disks at impact will determine how many gas elements directly collide but does not strongly affect the resulting star formation.

Keywords: Hydrodynamical simulations, Astronomical models, Galaxy collisions, Hydrodynamics, Galaxy dynamics, Intergalactic gas, Star formation, Galaxy mergers, Interacting galaxies
The Herschel Orion Protostar Survey: Far-infrared Photometry and Colors of Protostars and Their Variations across Orion A and B. The degree to which the properties of protostars are affected by environment remains an open question. To investigate this, we look at the Orion A and B molecular clouds, home to most of the protostars within 500 pc. At ∼400 pc, Orion is close enough to distinguish individual protostars across a range of environments in terms of both the stellar and gas projected densities. As part of the Herschel Orion Protostar Survey (HOPS), we used the Photodetector Array Camera and Spectrometer to map 108 partially overlapping square fields with edge lengths of 5' or 8' and measure the 70 and 160 μm flux densities of 338 protostars within them. In this paper we examine how these flux densities and their ratio depend on evolutionary state and environment within the Orion complex. We show that Class 0 protostars occupy a region of the 70 μm flux density versus 160 μm/70 μm flux density ratio diagram that is distinct from their more evolved counterparts. We then present evidence that the Integral-Shaped Filament (ISF) and Orion B contain protostars with more massive inner envelopes than those in the more sparsely populated LDN 1641 region. This can be interpreted as evidence for increasing star formation rates in the ISF and Orion B or as a tendency for more massive inner envelopes to be inherited from denser birth environments. We also provide technical details about the mapmaking and photometric procedures used in the HOPS program. * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Keywords: Protostars, Star formation, Infrared sources
A Dust Trap in the Young Multiple System HD 34700. Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700: two Herbig Ae stars in a close binary system (Aa/Ab, ∼0.25 au), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower-mass companions. These observations include 1.3 mm continuum emission and the 12CO 2-1 line at ∼0"5 (178 au) resolution. They resolve a prominent azimuthal asymmetry in the continuum and Keplerian rotation of a circumbinary disk in the 12CO line. The asymmetry is located at a radius of 155+11-7 au, consistent with the edge of the scattered-light cavity, being resolved in both radius (72 +14-15 au) and azimuth (FWHM = 64°+8-7). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of 12CO emission and small grains. We hypothesize an unseen circumbinary companion responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of 12CO and nondetection of 13CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation ∼1850 au), which we explain through a circumstellar disk.

Keywords: Planetary system formation, Protoplanetary disks, Circumstellar disks, Submillimeter astronomy, Circumstellar dust, Interferometry
Hunting Gravitational Wave Black Holes with Microlensing. Gravitational microlensing is a powerful tool to search for a population of invisible black holes (BHs) in the Milky Way (MW), including isolated BHs and binary BHs at wide orbits that are complementary to gravitational wave observations. By monitoring highly populated regions of source stars like the MW bulge region, one can pursue microlensing events due to these BHs. We find that if BHs have a Salpeter-like mass function extended beyond 30M⊙ and a similar velocity and spatial structure to stars in the Galactic bulge and disk regions, the BH population is a dominant source of microlensing events at long timescales of the microlensing light curve ≳100 days. This is due to a boosted sensitivity of the microlensing event rate to lens mass, given as M2, for such long-timescale events. A monitoring observation of 2 × 1010 stars in the bulge region over 10 yr with the Rubin Observatory Legacy Survey of Space and Time (LSST) would enable one to find about 6 × 105 BH microlensing events. We evaluate the efficiency of potential LSST cadences for characterizing the light curves of BH microlensing and find that nearly all events of long timescales can be detected.

Keywords: Gravitational microlensing, Gravitational wave sources, Microlensing event rate, Microlensing optical depth
Physical Conditions of Gas Components in Debris Disks of 49 Ceti and HD 21997. Characterization of the gas component in debris disks is of fundamental importance for understanding their origin. To address this goal, we have conducted non-LTE (local thermodynamic equilibrium) analyses of the rotational spectral lines of CO including those of rare isotopologues (13CO and C18O) that have been observed toward the gaseous debris disks of 49 Ceti and HD 21997 with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Compact Array (ACA). The analyses have been carried out for a wide range of H2 density, and the observed line intensities are found to be reproduced as long as the H2 density is higher than 103 cm-3. The CO column density and the gas temperature are evaluated to be (1.8-5.9) × 1017 cm-2 and 8-11 K for 49 Ceti and (2.6-15) × 1017 cm-2 and 8-12 K for HD 21997, respectively, where the H2 collision is assumed for the rotational excitation of CO. The results do not change significantly even if electron collision is considered. Thus, CO molecules can be excited under environments containing no H2 or a small number of H2 molecules, even where collisions with CO, C, O, and C+ would make an important contribution to the CO excitation in addition to H2. Meanwhile, our result does not rule out the case of abundant H2 molecules. The low gas temperature observed in the debris disks is discussed in terms of inefficient heating by interstellar and stellar UV radiation.

Keywords: Observational astronomy, Astrochemistry, Submillimeter astronomy, Debris disks, Circumstellar gas
The Pairing Probability of Massive Black Holes in Merger Galaxies in the Presence of Radiative Feedback. Dynamical friction (DF) against stars and gas is thought to be an important mechanism for orbital evolution of massive black holes (MBHs) in merger remnant galaxies. Recent theoretical investigations, however, show that DF does not always lead to MBH inspiral. For MBHs evolving in gas-rich backgrounds, the ionizing radiation that emerges from the innermost parts of their accretion flow can affect the surrounding gas in such a way to cause the MBHs to accelerate and gain orbital energy. This effect was dubbed "negative DF." We use a semianalytic model to study the impact of negative DF on pairs of MBHs in merger remnant galaxies evolving under the combined influence of stellar and gaseous DF. Our results show that for a wide range of merger galaxy and MBH properties negative DF reduces the MBH pairing probability by ∼46%. The suppression of MBH pairing is most severe in galaxies with one or more of these properties: (1) a gas fraction of fg ≥ 0.1; (2) a galactic gas disk rotating close to the circular velocity; (3) MBH pairs in prograde, low eccentricity orbits; and (4) MBH pairs with mass &lt;108 M⊙. The last point is of importance because MBH pairs in this mass range are direct progenitors of merging binaries targeted by the future space-based gravitational wave observatory the Laser Interferometer Space Antenna (LISA).

Keywords: Supermassive black holes, Galaxy dynamics, Gravitational interaction, Galaxy mergers, Galaxy evolution, Dynamical friction
Nonlinear Color-Metallicity Relations of Globular Clusters. IX. Different Radial Number Density Profiles between Blue and Red Clusters. The optical colors of globular clusters (GCs) in most large early-type galaxies are bimodal. Blue and red GCs show a sharp difference in the radial profile of their surface number density in the sense that red GCs are more centrally concentrated than blue GCs. An instant interpretation is that there exist two distinct GC subsystems having different radial distributions. This view, however, was challenged by a scenario in which, due to the nonlinear nature of the GC metallicity-to-color transformation for old (≳10 Gyr) GCs, a broad unimodal metallicity spread can exhibit a bimodal color distribution. Here we show, by simulating the radial trends in the GC color distributions of the four nearby giant elliptical galaxies (M87, M49, M60, and NGC 1399), that the difference in the radial profile between blue and red GCs stems naturally from the metallicity-to-color nonlinearity plus the well-known radial metallicity gradient of GC systems. The model suggests no or little radial variation in GC age even out to ∼20 Reff. Our results provide a simpler solution to the distinct radial profiles of blue and red GCs that does not necessarily invoke the presence of two GC subsystems and further fortify the nonlinearity scenario for the GC color bimodality phenomenon.

Keywords: Globular star clusters, cD galaxies, Giant elliptical galaxies, Galaxy evolution, Elliptical galaxies
Faint Quasars Live in the Same Number Density Environments as Lyman Break Galaxies at z ∼ 4. Characterizing high-z quasar environments is key to understanding the coevolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout galaxy overdensity distribution around 570 faint quasar candidates at z ∼ 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, ${0.7}_{-0.4}^{+0.4}$ $({3.9}_{-0.8}^{+0.8}) \% $, are found to be associated with the &gt;4σ overdense regions within an angular separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at this epoch. This is similar to the fraction of g-dropout galaxies associated with the &gt;4σ overdense regions. This result is consistent with our previous work in which ${1.3}_{-0.9}^{+0.9} \% $ and ${2.0}_{-1.1}^{+1.1} \% $ of luminous quasars detected in the Sloan Digital Sky Survey exist in the &gt;4σ overdense regions within 1'8 and 3'0 separations, respectively. Therefore, we suggest that the galaxy number densities around quasars are independent of their luminosity, and most quasars do not preferentially appear in the richest protocluster regions at z ∼ 4. The lack of an apparent positive correlation between the quasars and the protoclusters implies that (i) the gas-rich major merger rate is relatively low in the protocluster regions, (ii) most high-z quasars may appear through secular processes, or (iii) some dust-obscured quasars exist in the protocluster regions.

Keywords: Galaxy formation, Quasars, Protoclusters, Galaxy evolution, Lyman-break galaxies
High-resolution He I 10830 Å Narrowband Imaging for an M-class Flare. III. EUV Late Phase. In this paper, we report the EUV late phase for the M1.8 class flare on 2012 July 5 in the active region (AR) 11515. The late phase is shown by the prominent appearance of EUV emission at 131 Å of two additional flare loop systems (flare arcades 2 and 3, as named in this paper) other than the main flare loop (flare arcade 1), as observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). Three sets of flare arcades connect four flare ribbons, which forms an asymmetric quadrupole magnetic field configuration. While the emission from flare arcade 2, linking the pair of secondary flare ribbons, and arcade 3, linking one of the main flare ribbons and one of the secondary flare ribbons, conjointly contributes to the EUV late phase, their heating mechanisms are quite different. While the brightening of flare arcade 2 is the result of disturbance created by the eruption of EUV hot channels to the overlying coronal magnetic field, the heating of flare arcade 3 was closely associated with two rapid contractions of the overlying filament threads during the partial eruption of the filament. The contractions are discernible in He I 10830 Å images and have signatures in the EUV wavelengths of AIA. The two rapid contractions are the result of a sudden drop in magnetic pressure after the eruption of two hot channels. Clear evidence suggests that magnetic reconnection may occur between the contracting filament threads and the low-lying magnetic field.

Keywords: Solar flares, Solar extreme ultraviolet emission, Solar filaments
Constraints on Primordial Non-Gaussianity Using the Multitracer Technique for Skew Spectra. Extracting the bispectrum information from large-scale structure observations is challenging due to the complex models and the computational costs involved in measuring the signal and its covariance. Recently, the skew spectrum was proposed to access parts of the bispectrum information in a more effective manner and was confirmed to provide complementary information to that available in power spectrum measurements. In this work, we generalize the theory to apply the multitracer technique and explore its ability to constrain the local-type primordial non-Gaussianity. Using the spectra and their covariance estimated from N-body simulations, we find that the multitracer approach is effective in reducing the cosmic variance noise. The 1σ marginalized errors for ${b}_{1}^{2}{A}_{s},{n}_{s}$, and ${f}_{\mathrm{NL}}^{\mathrm{loc}}$ are reduced by 50%, 52%, and 73% compared with the results achieved using only the power spectrum obtained from a single tracer. These results indicate that both the skew spectrum and the multitracer technique are useful in constraining the primordial non-Gaussianity with the forthcoming wide-field galaxy surveys.

Keywords: Non-Gaussianity, Cosmological parameters from large-scale structure
The Betelgeuse Project. III. Merger Characteristics. We previously proposed that Betelgeuse might have been spun up by accreting a companion of about 1 M⊙. Here we explore in more detail the possible systematics of such a merger and a larger range of accreted masses. We use the stellar evolutionary code MESA to add angular momentum to a primary star in core helium burning, core carbon burning, or shell carbon burning. Our models provide a reasonable "natural" explanation for why Betelgeuse has a large, but sub-Keplerian equatorial velocity. They eject sufficient mass and angular momentum in rotationally induced mass loss to reproduce the observed ratio of the equatorial velocity to escape velocity of Betelgeuse, ≈0.23, within a factor of 3 nearly independent of the primary mass, the secondary mass, and the epoch at which merger occurs. Our models suggest that merger of a primary of somewhat less than 15 M⊙ with secondaries from 1 to 10 M⊙ during core helium burning or core carbon burning could yield the equatorial rotational velocity of ∼15 km s-1 attributed to Betelgeuse. For accreting models, a wave of angular momentum is halted at the composition boundary at the edge of the helium core. The inner core is thus not affected by the accretion of the companion in these simulations. Accretion has relatively little effect on the production of magnetic fields in the inner core. Our results do not prove, but do not negate, that Betelgeuse might have ingested a companion of several M⊙.

Keywords: Post-asymptotic giant branch stars, Late stellar evolution, Stellar mergers, Asymptotic giant branch stars, Supernovae