Sazuna/UAT_keywords huggingface dataset:
Three-dimensional Structure and Dust Extinction in the Small Magellanic Cloud. We examine the three-dimensional structure and dust extinction properties in a ∼200 pc × 100 pc region in the southwest bar of the Small Magellanic Cloud (SMC). We model a deep Hubble Space Telescope optical color-magnitude diagram (CMD) of red clump and red giant branch stars in order to infer the dust extinction and galactic structure. We model the distance distribution of the stellar component with a Gaussian and find a centroid distance of 65.2 kpc (distance modulus μ = 19.07 mag) with an FWHM ≈ 11.3 kpc. This large extent along the line of sight reproduces results from previous studies using variable stars and red clump stars. Additionally, we find an offset between the stellar and dust distributions, with the dust on the near side relative to the stars by 3.22 ${}_{-1.44}^{+1.69}$ kpc, resulting in a 73% reddened fraction of stars. Modeling the dust layer with a log-normal AV distribution indicates a mean extinction ⟨AV⟩ = 0.41 ± 0.09 mag. We also calculate AV/NH = 3.2-4.2 × 10-23 mag cm2 H-1, which is significantly lower than the Milky Way value but is comparable to previous SMC dust-to-gas ratio measurements. Our results yield the first joint dust extinction and 3D geometry properties in a key region in the SMC. This study demonstrates that CMD modeling can be a powerful tool to simultaneously constrain dust extinction and geometry properties in nearby galaxies.

Keywords: Interstellar dust, Red giant branch, Red giant clump, Distance measure, Dwarf galaxies, Small Magellanic Cloud, Galaxy structure, Interstellar dust extinction, Interstellar medium, Magellanic Clouds
The First Mid-infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment toward the Orion Hot Core. We present the first mid-infrared (MIR) detections of HNC and ${{\rm{H}}}^{13}\mathrm{CN}$ in the interstellar medium, and numerous resolved HCN rovibrational transitions. Our observations span 12.8-22.9 μm toward the hot core Orion IRc2, obtained with the Echelon-Cross-Echelle Spectrograph aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). In particular, ∼5 km s-1 resolution distinguishes individual rovibrational transitions of the HNC and HCN P, Q, and R branches; and the ${{\rm{H}}}^{13}\mathrm{CN}$ R branch. This allows direct measurement of the species' excitation temperatures, column densities, and relative abundances. HNC and ${{\rm{H}}}^{13}\mathrm{CN}$ exhibit a local standard of rest velocity of -7 km s-1 that may be associated with an outflow from nearby radio source I and an excitation temperature of about 100 K. We resolve two velocity components for HCN, the primary component also being at -7 km s-1 with a temperature of 165 K. The hottest component, which had never before been observed, is at 1 km s-1 with a temperature of 309 K. This is the closest component to the hot core's center measured to date. The derived ${}^{12}{\rm{C}}{/}^{13}{\rm{C}}=13\pm 2$ is below expectation for Orion's Galactocentric distance, but the derived HCN/HNC = 72 ± 7 is expected for this extreme environment. Compared to previous sub-millimeter and millimeter observations, our SOFIA line survey of this region shows that the resolved MIR molecular transitions are probing a distinct physical component and isolating the chemistry closest to the hot core.

Keywords: Spectral line identification, Molecular spectroscopy, Infrared astronomy, Molecular physics, Star formation, Interstellar medium
The Early Discovery of SN 2017ahn: Signatures of Persistent Interaction in a Fast-declining Type II Supernova. We present high-cadence, comprehensive data on the nearby (D ≃ 33 Mpc) Type II supernova (SN II) 2017ahn, discovered within about one day of the explosion, from the very early phases after explosion to the nebular phase. The observables of SN 2017ahn show a significant evolution over the ≃470 days of our follow-up campaign, first showing prominent, narrow Balmer lines and other high-ionization features purely in emission (i.e., flash spectroscopy features), which progressively fade and lead to a spectroscopic evolution similar to that of more canonical SNe II. Over the same period, the decline of the light curves in all bands is fast, resembling the photometric evolution of linearly declining H-rich core-collapse SNe. The modeling of the light curves and early flash spectra suggests that a complex circumstellar medium surrounds the progenitor star at the time of explosion, with a first dense shell produced during the very late stages of its evolution that is swept up by the rapidly expanding ejecta within the first ∼6 days of the SN evolution, while signatures of interaction are observed also at later phases. Hydrodynamical models support the scenario in which linearly declining SNe II are predicted to arise from massive yellow super- or hypergiants depleted of most of their hydrogen layers.

Keywords: Type II supernovae, Supernovae, Core-collapse supernovae
Gaia Gaps and the Physics of Low-mass Stars. I. The Fully Convective Boundary. The Gaia M-dwarf gap is a significant underdensity of stars observed near MG = 10.2 in a color-magnitude diagram for stars within 200 pc of the Sun. It has been proposed that the gap is the manifestation of structural instabilities within stellar interiors due to nonequilibrium 3He fusion prior to some stars becoming fully convective. To test this hypothesis, we use Dartmouth stellar evolution models, MARCS model atmospheres, and simple stellar population synthesis to create synthetic MG-(GBP - GRP) color-magnitude diagrams. We confirm that the proposed 3He instability is responsible for the appearance of the M-dwarf gap. Our synthetic gap shows qualitatively similar features to the observed gap, including its vertical extent in MG, its slope in the color-magnitude diagram, and its relative prominence at bluer colors as compared to redder colors. Furthermore, corresponding overdensities of stars above the gap are reproduced by the models. While qualitatively similar, the synthetic gap is approximately 0.2 magnitudes bluer, and when this color offset is accounted for, it is 0.16 magnitudes brighter than the observed gap. Our results reveal that the Gaia M-dwarf gap is sensitive to conditions within cores of M-dwarf stars, making the gap a powerful tool for testing the physics of M-dwarf stars and potentially using M dwarfs to understand the local star formation history.

Keywords: M dwarf stars, Stellar interiors, Main sequence, Stellar evolutionary models, Hertzsprung Russell diagram, Stellar evolution
Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding. The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions.

Keywords: Astrostatistics tools, Astronomy databases, Astronomy data analysis, Radiative transfer, Spectroscopy, Solar chromosphere
Three-dimensional Simulations of the Inhomogeneous Low Solar Wind. In the near future, the Parker Solar Probe will put theories about the dynamics and nature of the transition between the solar corona and the solar wind to stringent tests. The most popular mechanism aimed to explain the dynamics of the nascent solar wind, including its heating and acceleration, is magnetohydrodynamic (MHD) turbulence. Most of the previous models focused on nonlinear cascade induced by interactions of outgoing Alfvén waves and their reflections, ignoring effects that might be related to perpendicular structuring of the solar coronal plasma, despite overwhelming evidence for it. In this paper, for the first time, we analyze through 3D MHD numerical simulations the dynamics of the perpendicularly structured solar corona and solar wind, from the low corona to 15 R⊙. We find that background structuring has a strong effect on the evolution of MHD turbulence, on much faster timescales than in the perpendicularly homogeneous case. On timescales shorter than nonlinear times, linear effects related to phase mixing result in a 1/f perpendicular energy spectrum. As the turbulent cascade develops, we observe a perpendicular (parallel) energy spectrum with a power-law index of -3/2 or -5/3 (-2), a steeper perpendicular magnetic field than velocity spectrum, and a strong build-up of negative residual energy. We conclude that the turbulence is most probably generated by the self-cascade of the driven transverse kink waves, referred to previously as "uniturbulence," which might represent the dominant nonlinear energy cascade channel in the pristine solar wind.

Keywords: Interplanetary turbulence, Solar coronal waves, Magnetohydrodynamical simulations, Fast solar wind
Non-Boussinesq Low-Prandtl-number Convection with a Temperature-dependent Thermal Diffusivity. In an attempt to understand the role of the strong radial dependence of thermal diffusivity on the properties of convection in Sun-like stars, we mimic that effect in non-Oberbeck-Boussinesq convection in a horizontally extended rectangular domain (aspect ratio 16) by allowing the thermal diffusivity κ to increase with the temperature (as in the case of stars). Direct numerical simulations (i.e., numerical solutions of the governing equations by resolving up to the smallest scales without requiring any modeling) show that, in comparison with Oberbeck-Boussinesq simulations (two of which we perform for comparison purposes), the symmetry of the temperature field about the mid-horizontal plane is broken, whereas the velocity and heat flux profiles remain essentially symmetric. Our choice of κ(T), which resembles the variation in stars, results in a temperature field that loses its fine structures toward the hotter part of the computational domain, but the characteristic large scale of the turbulent thermal "superstructures," which are structures whose size is typically larger than the depth of the convection domain, continues to be largely independent of the depth.

Keywords: Solar convective zone, Stellar convective zones
Data-driven Stellar Models. We developed a data-driven model to map stellar parameters (Teff, $\mathrm{log}g$ , and $\left[\mathrm{Fe}/{\rm{H}}\right]$ ) accurately and precisely to broadband stellar photometry. This model must, and does, simultaneously constrain the passband-specific dust reddening vector in the Milky Way, R. The model uses a neural network to learn the (de-reddened) absolute magnitude in one band and colors across many bands, given stellar parameters from spectroscopic surveys and parallax constraints from Gaia. To demonstrate the effectiveness of this approach, we train our model on a data set with spectroscopic parameters from LAMOST, APOGEE, and GALAH, Gaia parallaxes, and optical and near-infrared photometry from Gaia, Pan-STARRS 1, Two Micron All Sky Survey and Wide-field Infrared Survey Explorer. Testing the model on these data sets leads to an excellent fit and a precise—and by construction—accurate prediction of the color-magnitude diagrams in many bands. This flexible approach rigorously links spectroscopic and photometric surveys, and also results in an improved, Teff-dependent R. As such, it provides a simple and accurate method for predicting photometry in stellar evolutionary models. Our model will form a basis to infer stellar properties, distances, and dust extinction from photometric data, which should be of great use in 3D mapping of the Milky Way. Our trained model can be obtained at doi:10.5281/zenodo.3902382.

Keywords: Stellar photometry, Interstellar dust extinction, Astrostatistics, Neural networks
1000 Days of the Lowest-frequency Emission from the Low-luminosity GRB 171205A. We report the lowest-frequency measurements of gamma-ray burst (GRB) 171205A with the upgraded Giant Metrewave Radio Telescope (uGMRT) covering a frequency range of 250-1450 MHz and a period of 4-937 days. It is the first GRB afterglow detected in the 250-500 MHz frequency range and the second brightest GRB detected with the uGMRT. Even though the GRB was observed for nearly 1000 days, there is no evidence of a transition to a nonrelativistic regime. We also analyzed the archival Chandra X-ray data on day ∼70 and day ∼200. We also found no evidence of a jet break from the analysis of combined data. We fit synchrotron afterglow emission arising from a relativistic, isotropic, self-similar deceleration as well as from a shock breakout of a wide-angle cocoon. Our data also allowed us to discern the nature and the density of the circumburst medium. We found that the density profile deviates from a standard constant density medium and suggests that the GRB exploded in a stratified wind-like medium. Our analysis shows that the lowest-frequency measurements covering the absorbed part of the light curves are critical to unraveling the GRB environment. Our data combined with other published measurements indicate that the radio afterglow has a contribution from two components: a weak, possibly slightly off-axis jet and a surrounding wider cocoon, consistent with the results of Izzo et al. The cocoon emission likely dominates at early epochs, whereas the jet starts to dominate at later epochs, resulting in flatter radio light curves.

Keywords: Extragalactic radio sources, Gamma-ray bursts, Gamma-ray transient sources
The Relativistic Jet Orientation and Host Galaxy of the Peculiar Blazar PKS 1413+135. PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object—objects that have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet and the host galaxy. Answering these two questions is important because they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range 0.247 &lt; z &lt; 0.5. The intervening spiral galaxy at z = 0.247 provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission.

Keywords: Blazars, Strong gravitational lensing, Relativistic jets, Seyfert galaxies, Radio active galactic nuclei, Apparent superluminal motion
Rise of the Titans: Gas Excitation and Feedback in a Binary Hyperluminous Dusty Starburst Galaxy at z ∼ 6. We report new observations toward the hyperluminous dusty starbursting major merger ADFS-27 (z = 5.655), using the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). We detect CO (J = 2 → 1), CO (J = 8 → 7), CO (J = 9 → 8), CO (J = 10 → 9), and H2O (312 → 221) emission, and a P Cygni-shaped OH+ (11 → 01) absorption/emission feature. We also tentatively detect H2O (321 → 312) and OH+ (12 → 01) emission and CH+ (J = 1 → 0) absorption. We find a total cold molecular mass of Mgas = (2.1 ± 0.2) × 1011 (αCO/1.0) M☉. We also find that the excitation of the star-forming gas is overall moderate for a z &gt; 5 dusty starburst, which is consistent with its moderate dust temperature. A high-density, high kinetic temperature gas component embedded in the gas reservoir is required to fully explain the CO line ladder. This component is likely associated with the "maximum starburst" nuclei in the two merging galaxies, which are separated by only 140 ± 13 km s-1 along the line of sight and 9.0 kpc in projection. The kinematic structure of both components is consistent with galaxy disks, but this interpretation remains limited by the spatial resolution of the current data. The OH+ features are only detected toward the northern component, which is also the one that is more enshrouded in dust and thus remains undetected up to 1.6 μm even in our sensitive new Hubble Space Telescope Wide Field Camera 3 imaging. The absorption component of the OH+ line is blueshifted and peaks near the CO and continuum emission peak, while the emission is redshifted and peaks offset by 1.7 kpc from the CO and continuum emission peak, suggesting that the gas is associated with a massive molecular outflow from the intensely star-forming nucleus that supplies 125 M☉ yr-1 of enriched gas to its halo.

Keywords: Starburst galaxies, Interstellar line emission, Millimeter astronomy, Active galaxies, Infrared excess galaxies, Galaxy evolution, Submillimeter astronomy, High-redshift galaxies
The Multipolar Magnetic Field of the Millisecond Pulsar PSR J0030+0451. Modeling of the NICER X-ray waveform of the pulsar PSR J0030+0451, aimed at constraining the neutron star mass and radius, has inferred surface hot spots (the magnetic polar caps) that imply significantly nondipolar magnetic fields. To this end, we investigate magnetic field configurations that comprise offset dipole-plus-quadrupole components using a static vacuum field and force-free global magnetosphere models. Taking into account the compactness and observer angle values provided by Miller et al. and Riley et al., we compute geodesics from the observer plane to the polar caps to compute the resulting X-ray light curve. We explore, through Markov Chain Monte Carlo techniques, the detailed magnetic field configurations that can reproduce the observed X-ray light curve and have discovered degeneracies, i.e., diverse field configurations, which can provide sufficient descriptions of the NICER X-ray waveforms. Having obtained the force-free field structures, we then compute the corresponding synchronous γ-ray light curves following Kalapotharakos et al.; these we compare to those obtained by Fermi-LAT, to provide models consistent with both the X-ray and the γ-ray data, thereby restricting further the multipole field parameters. An essential aspect of this approach is the proper computation of the relative phase between the synchronous X- and γ-ray light curves. We conclude with a discussion of the broader implications of our study.

Keywords: X-ray astronomy, Millisecond pulsars, Space telescopes, Stellar magnetic fields, Pulsars, General relativity, Markov chain Monte Carlo, Gamma-ray astronomy
Stratified and Vertically Shearing Streaming Instabilities in Protoplanetary Disks. Under the right conditions, the streaming instability between imperfectly coupled dust and gas is a powerful mechanism for planetesimal formation as it can concentrate dust grains to the point of gravitational collapse. In its simplest form, the streaming instability can be captured by analyzing the linear stability of unstratified disk models, which represent the midplane of protoplanetary disks. We extend such studies by carrying out vertically global linear stability analyses of dust layers in protoplanetary disks. We find that the dominant form of instability in stratified dust layers is the one driven by the vertical gradient in the rotation velocity of the dust-gas mixture, but also requires partial dust-gas coupling. These vertically shearing streaming instabilities grow on orbital timescales and occur on radial length scales ∼ 10-3Hg, where Hg is the local pressure scale height. The classic streaming instability, associated with the relative radial drift between dust and gas, occurs on radial length scales ∼ 10-2Hg, but has much smaller growth rates than vertically shearing streaming instabilities. Including gas viscosity is strongly stabilizing and leads to vertically elongated disturbances. We briefly discuss the potential effects of vertically shearing streaming instabilities on planetesimal formation.

Keywords: Hydrodynamics, Protoplanetary disks, Planetesimals, Astrophysical fluid dynamics, Planet formation
The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Radio Source Properties. The shape of bent, double-lobed radio sources requires a dense gaseous medium. Bent sources can therefore be used to identify galaxy clusters and characterize their evolutionary history. By combining radio observations from the Very Large Array Faint Images of the Radio Sky at Twenty centimeters (VLA FIRST) survey with optical and infrared imaging of 36 red sequence selected cluster candidates from the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey (0.35 &lt; z &lt; 2.2), we find that radio sources with narrower opening angles reside in richer clusters, indicating that the cluster environment impacts radio morphology. Within these clusters, we determine 55.5% of our radio host galaxies are brightest cluster galaxies (BCGs) and that the remainder are associated with other luminous galaxies. The projected separations between the radio sources and cluster centers and the sizes of the opening angles of bent sources follow similar distributions for BCG and non-BCG host populations, suggesting that COBRA host galaxies are either BCGs or galaxies that may evolve into BCGs. By measuring the orientation of the radio sources relative to the cluster centers, we find between 30% and 42% of COBRA bent sources are outgoing and have passed through the cluster center, while between 8% and 58% of COBRA bent sources are infalling. Although these sources typically do not follow directly radial paths, the large population of outgoing sources contrasts what is observed in low-z samples of bent sources and may indicate that the intracluster medium is less dense in these high-z clusters.

Keywords: Galaxy clusters, High-redshift galaxy clusters, Extragalactic radio sources, Radio galaxies, Tailed radio galaxies, Galaxy evolution, Fanaroff-Riley radio galaxies, Infrared galaxies