Sazuna/UAT_keywords huggingface dataset:
Hybrid Simulations of Interstellar Pickup Protons Accelerated at the Solar-wind Termination Shock at Multiple Locations. We estimate the intensity of interstellar pickup protons accelerated to ∼50 keV at various locations along the solar-wind termination shock, using two-dimensional hybrid simulations. Parameters for the solar wind, interstellar pickup ions (PUIs), and magnetic field just upstream of the termination shock at one flank of the heliosphere, and at the location in the downwind (or tail-ward) direction are based on a solar-wind/pickup-ion/turbulence model. The parameters upstream of the shock where Voyager 2 crossed are based on observations. The simulation is limited in size, and therefore cannot accurately model the distribution to energies much beyond ∼50 keV. This is sufficient to study the origin of the high-energy tail of the distribution, which is the low-energy portion of the anomalous cosmic-ray spectrum. We also extrapolate our results to other locations along the termination shock, such as the other flank, and the poles of the heliosphere. We find that the intensity of ∼10-50 keV accelerated pickup protons is remarkably similar at all three locations we simulated, suggesting that particles in this energy range are relatively uniformly distributed along the termination shock, and are likely quite uniform throughout the entire heliosheath. In addition, we find significant differences in the distribution in the 0.5-1 keV energy range for energetic neutral atoms coming from the tail region of the heliosphere compared to that at the nose or flank look directions. This is because the peak in the PUI distribution is at a higher energy there.

Keywords: Termination shock, Heliosphere, Pickup ions
The Milky Way Project: Probing Star Formation with First Results on Yellowballs from DR2. Yellowballs (YBs) were first discovered during the Milky Way Project (MWP) citizen science initiative. The MWP users noticed compact, yellow regions in Spitzer Space Telescope mid-infrared (MIR) images of the Milky Way plane and asked professional astronomers to explain these "yellow balls." Follow-up work by Kerton et al. determined that YBs likely trace compact photodissociation regions associated with massive and intermediate-mass star formation. The YBs were included as target objects in a version of the MWP launched in 2016, which produced a listing of over 6000 YB locations. We have measured distances, cross-match associations, physical properties, and MIR colors of ∼500 YBs within a pilot region covering the l = 30°-40°, b = ±1° region of the Galactic plane. We find that ∼20%-30% of YBs in our pilot region contain high-mass star formation capable of becoming expanding H II regions that produce MIR bubbles. A majority of YBs represent intermediate-mass star-forming regions whose placement in evolutionary diagrams suggest they are still actively accreting and may be precursors to optically revealed Herbig Ae/Be nebulae. Many of these intermediate-mass YBs were missed by surveys of massive star formation tracers; thus, this catalog provides information for many new sites of star formation. Future work will expand this pilot region analysis to the entire YB catalog.

Keywords: Surveys, Star formation, Catalogs
The TW Hya Rosetta Stone Project IV: A Hydrocarbon-rich Disk Atmosphere. Connecting the composition of planet-forming disks with that of gas giant exoplanet atmospheres, in particular through C/O ratios, is one of the key goals of disk chemistry. Small hydrocarbons like C2H and C3H2 have been identified as tracers of C/O, as they form abundantly under high C/O conditions. We present resolved c-C3H2 observations from the TW Hya Rosetta Stone Project, a program designed to map the chemistry of common molecules at 15-20 au resolution in the TW Hya disk. Augmented by archival data, these observations comprise the most extensive multi-line set for disks of both ortho and para spin isomers spanning a wide range of energies, Eu = 29-97 K. We find the ortho-to-para ratio of c-C3H2 is consistent with 3 throughout extent of the emission, and the total abundance of both c-C3H2 isomers is (7.5-10) × 10-11 per H atom, or 1%-10% of the previously published C2H abundance in the same source. We find c-C3H2 comes from a layer near the surface that extends no deeper than z/r = 0.25. Our observations are consistent with substantial radial variation in gas-phase C/O in TW Hya, with a sharp increase outside ∼30 au. Even if we are not directly tracing the midplane, if planets accrete from the surface via, e.g., meridional flows, then such a change should be imprinted on forming planets. Perhaps interestingly, the HR 8799 planetary system also shows an increasing gradient in its giant planets' atmospheric C/O ratios. While these stars are quite different, hydrocarbon rings in disks are common, and therefore our results are consistent with the young planets of HR 8799 still bearing the imprint of their parent disk's volatile chemistry.

Keywords: Exoplanet atmospheric composition , Protoplanetary disks, Astrochemistry
Radio Spectral Index Analysis of Southern Hemisphere Symbiotic Stars. Symbiotic stars show emission across the electromagnetic spectrum from a wide array of physical processes. At centimeter waves, both synchrotron and thermal emissions are seen, often highly variable and associated with outbursts in the optical and X-rays. Most models of the radio emission include an ionized region within the dense wind of the red giant star that is kept ionized by activity on the white dwarf companion or its accretion disk. In some cases, there is ongoing shell burning on the white dwarf due to its high mass accretion rate or a prior nova eruption; in other cases, nuclear fusion occurs only occasionally as recurrent nova events. In this study, we measure the spectral indices of a sample of symbiotic systems in the Southern Hemisphere using the Australia Telescope Compact Array. Putting our data together with results from other surveys, we derive the optical depths and brightness temperatures of some well-known symbiotic stars. Using parallax distances from Gaia Data Release 3, we determine the sizes and characteristic electron densities in the radio emission regions. The results show a range of a factor of 104 in radio luminosity and a factor of 100 in linear size. These numbers are consistent with a picture where the rate of shell burning on the white dwarf determines the radio luminosity. Therefore, our findings also suggest that radio luminosity can be used to determine whether a symbiotic star is powered by accretion alone or also by shell burning.

Keywords: Stellar accretion disks, White dwarf stars, Symbiotic binary stars, Interacting binary stars
Infrared Echoes of Optical Tidal Disruption Events: ∼1% Dust-covering Factor or Less at Subparsec Scale. The past decade has experienced an explosive increase of optically discovered tidal disruption events (TDEs) with the advent of modern time-domain surveys. However, we still lack a comprehensive observational view of their infrared (IR) echoes in spite of individual detections. To this end, we have conducted a statistical study of the IR variability of the 23 optical TDEs discovered between 2009 and 2018 using the full public data set of the Wide-field Infrared Survey Explorer. The detection of variability is performed on the difference images, yielding 11 objects with significant (&gt;3σ) variability in at least one band, while dust emission can be only fit in 8 objects. Their peak dust luminosity is around 1041-1042 erg s-1, corresponding to a dust-covering factor fc ∼ 0.01 at a subparsec scale. The only exception is the disputed source ASASSN-15lh, which shows an ultra-high dust luminosity (∼1043.5 erg s-1), and this makes its nature even more elusive. Other nondetected objects show even lower fc, which could be lower by one more order of magnitude. The derived fc is generally much lower than those of dusty tori in active galactic nuclei, suggesting either a dearth of dust or a geometrically thin and flat disk in the vicinity of supermassive black holes. Our results also indicate that the optical TDE sample (post-starburst galaxies overrepresented) is seriously biased to events with little dust at subparsec scale, while TDEs in dusty star-forming systems could be more efficiently unveiled by IR echoes.

Keywords: Supermassive black holes, Tidal disruption, Galaxy nuclei, Infrared astronomy, Active galactic nuclei, Time domain astronomy, Dust continuum emission, Interstellar medium
Research on Multiwavelength Isolated Bright Points Based on Deep Learning. Multiwavelength bright points (BPs) are taken to be cross sections of magnetic flux tubes extending from the surface of the photosphere upward to the higher photosphere. We aim to study the characteristics of isolated multiwavelength BPs using the cotemporal and cospatial TiO band and Hα line wings from the Goode Solar Telescope at Big Bear Solar Observatory. A deep-learning method, based on Track Region-based Convolutional Neural Networks, is proposed to detect, segment, and match the BPs across multiple wavelength observations, including the TiO, Hα + 1 Å, Hα - 1 Å, Hα + 0.8 Å, and Hα - 0.8 Å line wings. Based on the efficient detection and matching result with a precision of 0.98, 1283 groups of BPs matched in all five wavelengths are selected for statistics analysis. The characteristic values of the BPs observed at the same red and blue line wings are averaged. For the BPs of the TiO, averaged Hα ± 1 Å, and averaged Hα ± 0.8 Å line wings, the mean equivalent diameters are 162 ± 32, 254 ± 33, and 284 ± 28 km, respectively. The maximum intensity contrasts are 1.11 ± 0.09, 1.05 ± 0.03, and 1.05 ± 0.02 $\left\langle {I}_{\mathrm{QS}}\right\rangle $ , respectively. The mean eccentricities are 0.65 ± 0.14, 0.63 ± 0.11, and 0.65 ± 0.11, respectively. Moreover, the characteristic ratios of each Hα ± 1 Å and Hα ± 0.8 Å BP to its corresponding TiO BP are derived. Hα ± 1 Å and Hα ± 0.8 Å line wings BPs show 60% and 80% increases compared to TiO BPs, respectively. With increasing height, most BPs almost keep their shapes. This work is helpful for modeling the three-dimensional structure of flux tubes.

Keywords: Astronomical methods, Quiet sun, Convolutional neural networks, Solar photosphere
Direct Observation of a Large-scale CME Flux Rope Event Arising from an Unwinding Coronal Jet. Coronal mass ejections (CMEs) and coronal jets are two types of common solar eruptive phenomena, which often independently happen at different spatial scales. In this work, we present a stereoscopic observation of a large-scale CME flux rope arising from an unwinding blowout jet in a multipolar complex magnetic system. Based on a multiband observational analysis, we find that this whole event starts with a small filament whose eruption occurs at a coronal geyser site after a series of homologous jets. Aided by magnetic field extrapolations, it reveals that the coronal geyser site forms above an elongate opposite-polarity interface, where the emergence-driven photospheric flux cancellation and repetitive reconnection are responsible for those preceding recurrent jets and also contribute to the ultimate filament destabilization. By interacting with overlying fields, the erupting filament breaks one of its legs, and results in an unwinding blowout jet. Our estimation suggests that around 1.4-2.0 turns of twist release in its jet spire. This prominent twist transport in the jet spire rapidly creates a newborn larger-scale flux rope from the jet base to a remote site. Soon after its formation, this large-scale flux rope erupts toward the outer coronae causing an Earth-directed CME. In its source region, two sets of distinct postflare loops form in succession, indicating this eruption involves two stages of flare magnetic reconnection. This work not only reveals a real magnetic coupling process between different eruptive activities but provides a new hint for understanding for the creation of large-scale CME flux ropes during the solar eruption.

Keywords: Solar activity, Solar coronal mass ejections, Solar magnetic reconnection, Solar filament eruptions
Constraints on the Mass Accretion Rate onto the Supermassive Black Hole of Cygnus A Using the Submillimeter Array. We present the first detailed polarimetric studies of Cygnus A at 230 GHz with the Submillimeter Array (SMA) to constrain the mass accretion rate onto its supermassive black hole. We detected the polarized emission associated with the core at a fractional polarization of $0.73\pm 0.15 \% $ . This low fractional polarization suggests that the polarized emission is highly depolarized. One of the possible explanations is due to a significant variance in the Faraday rotation measure within the synthesized beam. By assuming the Faraday depolarization caused by inhomogeneous column density of the magnetized plasma associated with the surrounding radiatively-inefficient accretion flow within the SMA beam, we derived the constraint on the mass accretion rate to be larger than 0.15 ${M}_{\odot }$ yr-1 at the Bondi radius. The derived constraint indicates that an adiabatic inflow-outflow solution or an advection-dominated accretion flow should be preferable as the accretion flow model in order to explain the jet power of Cygnus A.

Keywords: Radio astronomy, Galaxy physics, Galaxy accretion disks, Active galaxies, Astronomical techniques, Radio galaxies, Active galactic nuclei, Galaxy accretion, Submillimeter astronomy, Polarimetry
Correcting Doppler Shifts in He II 30.38 nm Line by Using the EVE and AIA Data from Solar Dynamics Observatory. The Extreme-ultraviolet Variability Experiment (EVE) onboard the Solar Dynamics Observatory detects the solar EUV spectra with high temporal cadence and spectral resolution. The wavelength shifts of emission lines provide key information of the dynamics of the Sun. However, some of EVE spectral observations are influenced by the non-uniformly distributed irradiance on the Sun, which may prevent us from correctly understanding the physical processes happening in the solar corona. Here, based on the only published on-orbit calibration data of EVE He II 30.38 nm line on 2011 January 27, we develop a method to correct the He II 30.38 nm line by using AIA 304 imaging data. This correction method is then applied to EVE He II 30.38 nm data from 2010 October 29 to 2011 March 3 to study the Doppler oscillations of the solar He II 30.38 nm line, in which we show that the half-month periodic Doppler oscillation is caused by non-uniformly distributed irradiance mainly due to the presence of active regions. Other EVE coronal lines also present similar Doppler oscillations, suggesting that an appropriate correction must be implemented before interpreting the oscillation phenomena appearing in these lines.

Keywords: Solar rotation, Solar extreme ultraviolet emission, Solar spectral irradiance, Solar active regions, Doppler shift
Anisotropies in Compressible MHD Turbulence: Probing Magnetic Fields and Measuring Magnetization. Probing magnetic fields in the interstellar medium (ISM) is notoriously challenging. Motivated by the modern theories of magnetohydrodynamic (MHD) turbulence and turbulence anisotropy, we introduce the Structure Function Analysis (SFA) as a new approach to measure the magnetic-field orientation and estimate the magnetization. We analyze the statistics of turbulent velocities in three-dimensional compressible MHD simulations through the second-order structure functions in both local and global reference frames. In the sub-Alfvénic turbulence with the magnetic energy larger than the turbulent energy, the SFA of turbulent velocities measured in the directions perpendicular and parallel to the magnetic field can be significantly different. Their ratio has a power-law dependence on the Alfvén Mach number MA, which is inversely proportional to the magnetic-field strength. We demonstrate that the anisotropic structure functions of turbulent velocities can be used to estimate both the orientation and strength of magnetic fields. With turbulent velocities measured using different tracers, our approach can be generally applied to probing the magnetic fields in the multiphase ISM.

Keywords: Interstellar magnetic fields, Interstellar dynamics, Interstellar medium
OH Megamasers in H I Surveys: Forecasts and a Machine-learning Approach to Separating Disks from Mergers. OH megamasers (OHMs) are rare, luminous masers found in gas-rich major galaxy mergers. In untargeted neutral hydrogen (H I) emission-line surveys, spectroscopic redshifts are necessary to differentiate the λrest = 18 cm masing lines produced by OHMs from H I 21 cm lines. Next-generation H I surveys will detect an unprecedented number of galaxies, most of which will not have spectroscopic redshifts. We present predictions for the numbers of OHMs that will be detected and the potential "contamination" they will impose on H I surveys. We examine the Looking at the Distant Universe with the MeerKAT Array (LADUMA), a single-pointing deep-field survey reaching redshift zH I = 1.45, as well as potential future surveys with the Square Kilometre Array (SKA) that would observe large portions of the sky out to redshift zH I = 1.37. We predict that LADUMA will potentially double the number of known OHMs, creating an expected contamination of 1.0% of the survey's H I sample. Future SKA H I surveys are expected to see up to 7.2% OH contamination. To mitigate this contamination, we present methods to distinguish H I and OHM host populations without spectroscopic redshifts using near- to mid-IR photometry and a k-Nearest Neighbors algorithm. Using our methods, nearly 99% of OHMs out to redshift zOH ∼ 1.0 can be correctly identified. At redshifts out to zOH ∼ 2.0, 97% of OHMs can be identified. The discovery of these high-redshift OHMs will be valuable for understanding the connection between extreme star formation and galaxy evolution.

Keywords: Radio spectroscopy, Spiral galaxies, Surveys, Hydroxyl masers, H I line emission, Megamasers, Galaxy mergers, Galaxy evolution
Propagation of Torsional Alfvén Pulses in Zero-beta Flux Tubes. In this study, we investigate analytically the generation of mass flux due to a torsional Alfvén pulse. We derive that the presence of torsional Alfvén waves, which have been observed in, e.g., photospheric magnetic bright points (MBPs), can result in vertical plasma motions. The formation of this mass flux may even be a viable contribution to the generation of chromospheric mass transport, playing potential roles in the form of localized lower solar atmospheric jets. This relationship is studied using a flux tube model, with the waves introduced at the lower boundary of the tube as a magnetic shear perturbation. Due to the nature of MBPs we simplify the model by using the zero-beta approximation for the plasma inside the tube. The analytical results are demonstrated by an example of the type of Alfvén wave perturbation that one might expect to observe, and comparison is made with properties of spicules known from observations. We find that field-aligned plasma flux is formed nonlinearly as a result of the Lorentz force generated by the perturbations, and could be consistent with jet formation, although the current model is not intended to determine the entire evolution of a jet. Critical discussion of the model follows, including suggestions for improvements and for high-resolution proposed observations in order to constrain the driving magnetic and velocity shear.

Keywords: Magnetohydrodynamics, Solar spicules, Solar physics, Alfven waves, Solar magnetic fields, Solar chromosphere, Solar magnetic bright points
UV Extinction as a More Fundamental Measure of Dust than E(B - V) or A<SUB>V</SUB>. The gas-to-dust ratio of reddened stars in the Milky Way (MW), the Magellanic Clouds, and in general, is usually expressed as a linear relation between the hydrogen column density, N(H), and the reddening, E(B - V), or extinction in the V-band (AV). If the extinction curve were truly universal, the strength of the relationship and the linearity would naturally be maintained for extinction at any wavelength, as well as for N(H) versus E(B - V). However, extinction curves vary within the MW, and there is no reason, except by chance, why either E(B - V) or AV would be the most physical measure of dust column density. In this paper, we utilize for the first time full extinction curves to 41 MW sightlines, finding that the scatter between N(H) and extinction is minimized—and the relation becomes linear—for extinction at 2900 ± 160 Å. Scatter and nonlinearity increase at longer wavelengths, and are especially large for near-IR extinction. We conclude that near-UV extinction is a superior measure of the dust column density for MW dust. We provide new, nonlinear gas-to-dust relations for various dust tracers. We also find that the very large discrepancy between MW and SMC gas-to-dust ratios of 0.9 dex in N(H)/E(B - V) is reduced to 0.7 dex for far-UV extinction, which matches the difference in cosmic abundances of carbon between the two galaxies, and therefore confirms that N(C) is the preferred measure for gas in the gas-to-dust ratio, even though it may not be a convenient one.

Keywords: Interstellar dust, Gas-to-dust ratio, Interstellar dust extinction, Extinction, Interstellar extinction
Emergence of Internetwork Magnetic Fields through the Solar Atmosphere. Internetwork (IN) magnetic fields are highly dynamic, short-lived magnetic structures that populate the interior of supergranular cells. Since they emerge all over the Sun, these small-scale fields bring a substantial amount of flux, and therefore energy, to the solar surface. Because of this, IN fields are crucial for understanding the quiet Sun (QS) magnetism. However, they are weak and produce very small polarization signals, which is the reason why their properties and impact on the energetics and dynamics of the solar atmosphere are poorly known. Here we use coordinated, high-resolution, multiwavelength observations obtained with the Swedish 1 m Solar Telescope and the Interface Region Imaging Spectrograph (IRIS) to follow the evolution of IN magnetic loops as they emerge into the photosphere and reach the chromosphere and transition region. We studied in this paper three flux emergence events having total unsigned magnetic fluxes of 1.9 × 1018, 2.5 × 1018, and 5.3 × 1018 Mx. The footpoints of the emerging IN bipoles are clearly seen to appear in the photosphere and to rise up through the solar atmosphere, as observed in Fe I 6173 Å and Mg I b2 5173 Å magnetograms, respectively. For the first time, our polarimetric measurements taken in the chromospheric Ca II 8542 Å line provide direct observational evidence that IN fields are capable of reaching the chromosphere. Moreover, using IRIS data, we study the effects of these weak fields on the heating of the chromosphere and transition region.

Keywords: Solar magnetic flux emergence, Solar photosphere, Solar magnetic fields, Solar transition region, Solar chromosphere