Sazuna/UAT_keywords huggingface dataset:
Search for Synchrotron Emission from Secondary Electrons of Proton–Proton Interactions in Galactic PeVatron Candidate HESS J1641–463. HESS J1641‑463 is an unidentified gamma-ray source with a hard TeV gamma-ray spectrum, and thus it has been proposed to be a possible candidate for a cosmic-ray (CR) accelerator up to PeV energies (a PeVatron candidate). The source spatially coincides with the radio supernova remnant G338.5+0.1 but has not yet been fully explored in the X-ray band. We analyzed newly taken NuSTAR data, pointing at HESS J1641‑463, with 82 ks effective exposure time. There is no apparent X-ray counterpart of HESS J1641‑463, while nearby stellar cluster, Mercer 81, and stray-light X-rays are detected. Combined with the archival Chandra data, partially covering the source, we derived an upper limit of ∼6 × 10‑13 erg cm‑2 s‑1 in 2–10 keV (∼3 × 10‑13 erg cm‑2 s‑1 in 10–20 keV). If the gamma-ray emission is originated from the decay of π 0 mesons produced in interactions between CR protons and ambient materials, secondary electrons in the proton–proton interactions can potentially emit synchrotron photons in the X-ray band, which can be tested by our X-ray observations. Although the obtained X-ray upper limits cannot place a constraint on the primary proton spectrum, it will be possible with a future hard X-ray mission.

Keywords: Galactic cosmic rays, Diffuse radiation, Gamma-ray sources, Gamma-rays
Strong Fractionation of Deuterium and Helium in Sub-Neptune Atmospheres along the Radius Valley. We simulate atmospheric fractionation in escaping planetary atmospheres using IsoFATE, a new open-source numerical model. We expand the parameter space studied previously to planets with tenuous atmospheres that exhibit the greatest helium and deuterium enhancement. We simulate the effects of extreme-ultraviolet-driven photoevaporation and core-powered mass loss on deuterium–hydrogen and helium–hydrogen fractionation of sub-Neptune atmospheres around G, K, and M stars. Our simulations predict prominent populations of deuterium- and helium-enhanced planets along the upper edge of the radius valley with mean equilibrium temperatures of ≈370 K and as low as 150 K across stellar types. We find that fractionation is mechanism dependent, so constraining He/H and D/H abundances in sub-Neptune atmospheres offers a unique strategy to investigate the origin of the radius valley around low-mass stars. Fractionation is also strongly dependent on retained atmospheric mass, offering a proxy for planetary surface pressure as well as a way to distinguish between desiccated enveloped terrestrials and water worlds. Deuterium-enhanced planets tend to be helium dominated and CH4 depleted, providing a promising strategy to observe HDO in the 3.7 μm window. We present a list of promising targets for observational follow-up.

Keywords: Exoplanet atmospheric composition , Isotopic abundances, Exoplanets, Super Earths, Exoplanet astronomy, Exoplanet evolution, Mini Neptunes, Exoplanet formation, Exoplanet atmospheres, Exoplanet atmospheric evolution
Autoencoding Labeled Interpolator, Inferring Parameters from Image and Image from Parameters. The Event Horizon Telescope (EHT) provides an avenue to study black hole accretion flows on event-horizon scales. Fitting a semianalytical model to EHT observations requires the construction of synthetic images, which is computationally expensive. This study presents an image generation tool in the form of a generative machine-learning model, which extends the capabilities of a variational autoencoder. This tool can rapidly and continuously interpolate between a training set of images and can retrieve the defining parameters of those images. Trained on a set of synthetic black hole images, our tool showcases success in interpolating both black hole images and their associated physical parameters. By reducing the computational cost of generating an image, this tool facilitates parameter estimation and model validation for observations of black hole systems.

Keywords: Accretion, Black hole physics, Computational astronomy, High energy astrophysics, Neural networks, Astronomy image processing, Convolutional neural networks, Astronomy data analysis, Computational methods, Radiative processes, GPU computing, Astrophysical black holes
Relation between the Local Width and Linear Halo Mass Density of Cosmic Filaments. Large-scale cosmic filaments may have played an important role in shaping the properties of galaxies. Meanwhile, cosmic filaments are believed to harbor a substantial portion of the missing baryons at redshift z &lt; 2. To inspect the role of filaments in these issues, many properties of filaments need to be examined, including their lengths, thicknesses, and density profiles. However, measuring some of these properties poses challenges. This study concentrates on estimating filament width/thickness, investigating potential correlations between the local width of filaments and the properties of dark matter halos within filaments. We find that the local width of filaments generally increases with the mass of dark matter halos embedded in filaments per unit length, roughly following a second-order polynomial, although with notable scatter. We probe and discuss means that may refine our findings. After further verification and improvements, this relation could be applied to filament samples constructed from the observed galaxy distribution, aiding in understanding the roles of cosmic filaments in galaxy evolution and uncovering the missing baryons.

Keywords: Hydrodynamical simulations, Cosmic web, Large-scale structure of the universe
The Metallicity Dependence and Evolutionary Times of Merging Binary Black Holes: Combined Constraints from Individual Gravitational-wave Detections and the Stochastic Background. The advent of gravitational-wave astronomy is now allowing for the study of compact binary merger demographics throughout the Universe. This information can be leveraged as tools for understanding massive stars, their environments, and their evolution. One active question is the nature of compact binary formation: the environmental and chemical conditions required for black hole birth and the time delays experienced by binaries before they merge. Gravitational-wave events detected today, however, primarily occur at low or moderate redshifts due to current interferometer sensitivity, therefore limiting our ability to probe the high-redshift behavior of these quantities. In this work, we circumvent this limitation by using an additional source of information: observational limits on the gravitational-wave background from unresolved binaries in the distant Universe. Using current gravitational-wave data from the first three observing runs of LIGO–Virgo–KAGRA, we combine catalogs of directly detected binaries and limits on the stochastic background to constrain the time-delay distribution and metallicity dependence of binary black hole evolution. Looking to the future, we also explore how these constraints will be improved at the Advanced LIGO A+ sensitivity. We conclude that, although binary black hole formation cannot be strongly constrained with today's data, the future detection (or a nondetection) of the gravitational-wave background with Advanced LIGO A+ will carry strong implications for the evolution of binary black holes.

Keywords: Gravitational waves
Exploring the Substructure of the Near-surface Shear Layer of the Sun. The gradient of rotation in the near-surface shear layer (NSSL) of the Sun provides valuable insights into the dynamics associated with the solar activity cycle and the dynamo. Results obtained with global oscillation mode splittings lack resolution near the surface, prompting the use of the local helioseismic ring-diagram method. While the Helioseismic and Magnetic Imager ring-analysis pipeline has been used previously for analyzing this layer, default pipeline parameters limit the accuracy of the near-surface gradients. To address these challenges, we fitted the flow parameters to power spectra averaged over one-year periods at each location, followed by additional averaging over 12 yr. We find that the NSSL can be divided into three fairly distinct regions: a deeper, larger region with a small shear, steepening toward the surface; a narrow middle layer with a strong shear, with a gradient approximately 3 times larger; and a layer very close to the surface, where the logarithmic gradient is close to zero but becomes steeper again toward the surface. The middle layer appears to be centered at 3 Mm, but the poor resolution in these layers implies that it is potentially located closer to the surface, around 1.5 Mm deep. While our analysis primarily focused on regions along the central meridian, we also investigated systematic errors at longitudes off the center. The east–west antisymmetric component of the gradient reveals a layer of substantial differences between the east and west longitude of around 1.7 Mm, and the amplitude of the differences increases with the longitude.

Keywords: Solar rotation, Solar interior, Helioseismology, The Sun, Solar oscillations
Thermal Structure and Millimeter Emission from a Protoplanetary Disk with Embedded Protoplanets from Radiative Transfer Modeling. The discovery of protoplanets and circumplanetary disks provides a unique opportunity to characterize planet formation through observations. Massive protoplanets shape the physical and chemical structure of their host circumstellar disk by accretion, localized emission, and disk depletion. In this work, we study the thermal changes induced within the disk by protoplanet accretion and synthetic predictions through hydrodynamical simulations with postprocessed radiative transfer with an emphasis on radio millimeter emission. We explored distinct growth conditions and varied both planetary accretion rates and the local dust-to-gas mass ratios for a protoplanet at 1200 K. The radiative transfer models show that beyond the effect of disk gaps, in most cases, the circumplanetary disk (CPD) and the planet's emission locally increase the disk temperature. Moreover, depending on the local dust-to-gas depletion and accretion rate, the presence of the CPD may have detectable signatures in millimeter emission. It also has the power to generate azimuthal asymmetries that are important for continuum subtraction. Thus, if other means of detection of protoplanets are proven, the lack of corresponding evidence at other wavelengths can set limits on their growth timescales through a combined analysis of the local dust-to-gas ratio and the accretion rate.

Keywords: Submillimeter astronomy, Planetary-disk interactions, Protoplanetary disks
Disk Wind Feedback from High-mass Protostars. IV. Shock-ionized Jets. Massive protostars launch accretion-powered, magnetically collimated outflows, which play crucial roles in the dynamics and diagnostics of the star formation process. Here we calculate the shock heating and resulting free─free radio emission in numerical models of outflows of massive star formation within the framework of the Turbulent Core Accretion model. We postprocess 3D magnetohydrodynamic simulation snapshots of a protostellar disk wind interacting with an infalling core envelope, and calculate shock temperatures, ionization fractions, and radio free─free emission. We find heating up to ∼107 K and near-complete ionization in shocks at the interface between the outflow cavity and infalling envelope. However, line-of-sight averaged ionization fractions peak around ∼10%, in agreement with values reported from observations of massive protostar G35.20-0.74N. By calculating radio-continuum fluxes and spectra, we compare our models with observed samples of massive protostars. We find our fiducial models produce radio luminosities similar to those seen from low- and intermediate-mass protostars that are thought to be powered by shock ionization. Comparing to more massive protostars, we find our model radio luminosities are ∼10─100 times less luminous. We discuss how this apparent discrepancy either reflects aspects of our modeling related to the treatment of cooling of the post-shock gas or a dominant contribution in the observed systems from photoionization. Finally, our models exhibit 10 yr radio flux variability of ∼5%, especially in the inner 1000 au region, comparable to observed levels in some hypercompact H II regions.

Keywords: Massive stars, Stellar jets, Stellar winds, Star formation, Radio continuum emission, Astronomical simulations, Magnetohydrodynamical simulations
Collective Neutrino Oscillations and Heavy-element Nucleosynthesis in Supernovae: Exploring Potential Effects of Many-body Neutrino Correlations. In high-energy astrophysical processes involving compact objects, such as core-collapse supernovae or binary neutron star mergers, neutrinos play an important role in the synthesis of nuclides. Neutrinos in these environments can experience collective flavor oscillations driven by neutrino–neutrino interactions, including coherent forward scattering and incoherent (collisional) effects. Recently, there has been interest in exploring potential novel behaviors in collective oscillations of neutrinos by going beyond the one-particle effective or "mean-field" treatments. Here, we seek to explore implications of collective neutrino oscillations, in the mean-field treatment and beyond, for the nucleosynthesis yields in supernova environments with different astrophysical conditions and neutrino inputs. We find that collective oscillations can impact the operation of the ν p-process and r-process nucleosynthesis in supernovae. The potential impact is particularly strong in high-entropy, proton-rich conditions, where we find that neutrino interactions can nudge an initial ν p-process neutron-rich, resulting in a unique combination of proton-rich low-mass nuclei as well as neutron-rich high-mass nuclei. We describe this neutrino-induced neutron-capture process as the "ν i-process." In addition, nontrivial quantum correlations among neutrinos, if present significantly, could lead to different nuclide yields compared to the corresponding mean-field oscillation treatments, by virtue of modifying the evolution of the relevant one-body neutrino observables.

Keywords: Supernova neutrinos, Nucleosynthesis, Core-collapse supernovae, Neutrino oscillations, R-process, P-process
Thirteen New M Dwarf + T Dwarf Pairs Identified with WISE/NEOWISE. We present the discovery of 13 new widely separated T dwarf companions to M dwarf primaries, identified using Wide-field Infrared Survey Explorer/NEOWISE data by the CatWISE and Backyard Worlds: Planet 9 projects (hereafter BYW). This sample represents an ∼60% increase in the number of known M + T systems, and allows us to probe the most extreme products of binary/planetary system formation, a discovery space made available by the CatWISE2020 catalog and the BYW effort. Highlights among the sample are WISEP J075108.79-763449.6, a previously known T9 thought to be old due to its spectral energy distribution, which was found by Zhang et al. (2021b) to be part of a common proper motion pair with L34-26 A, a well-studied young M3 V star within 10 pc of the Sun; CWISE J054129.32-745021.5 B and 2MASS J05581644-4501559 B, two T8 dwarfs possibly associated with the very fast-rotating M4 V stars CWISE J054129.32745021.5 A and 2MASS J05581644-4501559 A; and UCAC3 52-1038 B, which is among the widest late-T companions to main-sequence stars, with a projected separation of ∼7100 au. The new benchmarks presented here are prime JWST targets, and can help us place strong constraints on the formation and evolution theory of substellar objects as well as on atmospheric models for these cold exoplanet analogs.

Keywords: Brown dwarfs, Fundamental parameters of stars, Low mass stars, Visual binary stars, T dwarfs
First Extragalactic Detection of Thermal Hydroxyl (OH) 18 cm Emission in M31 Reveals Abundant CO-faint Molecular Gas. The most abundant interstellar molecule, molecular hydrogen (H2), is practically invisible in cold molecular clouds. Astronomers typically use carbon monoxide (CO) to trace the bulk distribution and mass of H2 in our galaxy and many others. CO observations alone fail to trace a significant component of molecular gas known as "CO-dark" molecular gas, which can be probed with molecules such as OH and CH. We present an extremely sensitive pilot search for the 18 cm hydroxyl (OH) lines in the Andromeda galaxy (M31) with the 100 m Robert C. Byrd Green Bank Telescope. We successfully detected the 1665 and 1667 MHz OH lines in faint emission. The 1665/1667 MHz line ratio displays the characteristic 5:9 ratio predicted under conditions of local thermodynamic equilibrium. To our knowledge, this is the first detection of nonmaser 18 cm OH emission in another galaxy. We compare our OH and H I observations with archival CO (1–0) observations. Our OH detection position overlaps with the previously discovered Arp Outer Arm in CO. Our best estimates show that the amount of H2 traced by OH is 100%–140% higher than the amount traced by CO in this sight line. The amount of dark molecular gas implied by dust data supports this conclusion. We conclude that the 18 cm OH lines hold promise as a valuable tool for mapping of the "CO-dark" and "CO-faint" molecular gas phase in nearby galaxies, especially with upcoming multibeam, phased-array feed receivers on radio telescopes, which will allow for drastically improved mapping speeds of faint signals.

Keywords: Interstellar molecules, Interstellar clouds, Interstellar medium, Andromeda Galaxy, Radio astronomy
An Informed and Systematic Method to Identify Variable Mid-L Dwarfs. Most brown dwarfs show some level of photometric or spectral variability. However, finding the most variable dwarfs more suited for a thorough variability monitoring campaign remained a challenge until a few years ago with the design of spectral indices to find the most likely L and T dwarfs using their near-infrared (NIR) single-epoch spectrum. In this work, we designed and tested NIR spectral indices to preselect the most likely variable L4–L8 dwarfs, complementing the indices presented by Ashraf et al. and Oliveros-Gomez et al. We used time-resolved NIR Hubble Space Telescope Wide Field Camera 3 spectra of an L6.0 dwarf, LP 261–75b, to design our novel spectral indices. We tested these spectral indices on 75 L4.0–L8.0 NIR SpeX/IRTF spectra, providing 27 new variable candidates. Our indices have a recovery rate of ∼80% and a false negative rate of ∼25%. All the known nonvariable brown dwarfs were found to be nonvariable by our indices. We estimated the variability fraction of our sample to be %, which agrees with the variability fractions provided by Buenzli et al., Radigan et al., and Metchev et al. for L4–L8 dwarfs. These spectral indices may support the future selection of the most likely variable directly imaged exoplanets for studies with the James Webb Space Telescope and as well as the 30 m telescopes.

Keywords: Spectral index, Brown dwarfs, L dwarfs, Atmospheric variability
Anisotropy of Density Fluctuations in the Solar Wind at 1 au. A well-known property of solar wind plasma turbulence is the observed anisotropy of the autocorrelations, or equivalently the spectra, of velocity and magnetic field fluctuations. Here we explore the related but apparently not well-studied issue of the anisotropy of plasma density fluctuations in the energy-containing and inertial ranges of solar wind turbulence. Using 10 yr (1998–2008) of in situ data from the Advanced Composition Explorer mission, we find that for all but the fastest wind category, the density correlation scale is slightly larger in directions quasi-parallel to the large-scale mean magnetic field as compared to quasi-perpendicular directions. The correlation scale in fast wind is consistent with isotropic. The anisotropy as a function of the level of correlation is also explored. We find at small correlation levels, i.e., at energy-containing scales and larger, the density fluctuations are close to isotropy for fast wind, and slightly favor more rapid decorrelation in perpendicular directions for slow and medium winds. At relatively smaller (inertial range) scales where the correlation values are larger, the sense of anisotropy is reversed in all speed ranges, implying a more "slablike" structure, especially prominent in the fast wind samples. We contrast this finding with published results on velocity and magnetic field correlations.

Keywords: Space plasmas, Magnetohydrodynamics, Plasma physics, Interplanetary turbulence, Solar wind
Kinematics and Star Formation in the Hub–Filament System G6.55-0.1. Hub–filament systems (HFSs) being the potential sites of formation of star clusters and high-mass stars, provide a testbed for the current theories that attempt to explain star formation globally. It is thus important to study a large number of HFSs using both intensity and velocity information to constrain these objects better observationally. Here, we present a study of the HFS associated with G6.55-0.1 using newly obtained observations of the radio continuum and the J = 2–1 transition of CO, 13CO, and C18O. The radio continuum maps show multiple peaks that coincide with far-infrared dust continuum peaks, indicating the presence of more than one young massive star in the hub of the HFS. We used the velocity information from the C18O(2–1) map to (a) show that the source G6.55-0.1 is not physically associated with the supernova remnant W28 and (b) disentangle and identify the velocity components genuinely associated with G6.55-0.1. Among the velocity-coherent structures identified in the region, we conclude that only the two filaments at 13.8 and 17.3 km s‑1 contribute a total mass accretion rate of 3000 M ⊙ Myr‑1 to the hub. Both the filaments also show a V-shaped structure, characteristic of gravitational collapse, in their velocity profile at the location of the hub. The estimated mass per unit length of the segments of the filaments is smaller than the critical line masses derived from virial equilibrium considerations. This suggests that the filaments are not gravitationally collapsing as a whole, although their inner parts clearly show evidence of collapse in the form of young star-forming cores. We further conclude that the observed velocity gradients are consistent with the gravitational collapse of the main source in the region as estimated from its mass and size.

Keywords: Star formation, Interstellar filaments, Interstellar medium