Sazuna/UAT_keywords huggingface dataset:
Stars Lensed by the Supermassive Black Hole in the Center of the Milky Way: Predictions for ELT, TMT, GMT, and JWST. Gravitational lensing is an important prediction of general relativity, providing both its test and a tool to detect faint but amplified sources and to measure masses of lenses. For some applications, (e.g., testing the theory), a point source lensed by a point-like lens would be more advantageous. However, until now only one gravitationally lensed star has been resolved. Future telescopes will resolve very small lensing signatures for stars orbiting the supermassive black hole (SMBH) in the center of the Milky Way. The lensing signatures, however, should be easier to detect for background stars. We predict that the Extremely Large Telescope (ELT), Thirty Meter Telescope (TMT), and Giant Magellan Telescope (GMT) will resolve the lensed images of around 100 (60) stars in the disk and 30 (20) stars in the bulge in the background of the SMBH, down to 28 (27) mag (Vega) limits at K-band, requiring 5 (1) hr of integration. In order to detect several such stars one needs the limit of at least 24 mag. With decade-long monitoring, one can also detect the rotation of the lensed images. The detection of elongated images will not be possible, because this would require a nearly perfect source-lens alignment. The James Webb Space Telescope (JWST) will likely be limited by the confusion caused by stars near the Galactic center. The detection of such lensed images will provide a very clean test of general relativity, when combined with the SMBH mass measurement from orbital motions of stars, and accurate measurements of the SMBH properties, because both the source and the lens can be considered point-like.

Keywords: Supermassive black holes, Strong gravitational lensing, Galactic center, Optical telescopes
A Red Giant Branch Common-envelope Evolution Scenario for the Exoplanet WD 1856 b. We propose a common-envelope evolution scenario where a red giant branch (RGB) star engulfs a planet during its core helium flash to explain the puzzling system WD 1856+534, where a planet orbits a white dwarf (WD) of mass MWD ≃ 0.52 M⊙ with an orbital period of Porb = 1.4 days. At the heart of the scenario is the recently proposed assumption that the vigorous convection that core helium flash of RGB stars drive in the core excite waves that propagate and deposit their energy in the envelope. Using the BINARY-MESA stellar evolution code we show that this energy deposition substantially reduces the binding energy of the envelope and causes its expansion. We propose that in some cases RGB stars might engulf massive planets of ≳0.01 M⊙ during their core helium flash phase, and that the planet can unbind most of the mass of the bloated envelope. We show that there is a large range of initial orbital radii for which this scenario might take place under our assumptions. This scenario is relevant to other systems of close sub-stellar objects orbiting white dwarfs, like the brown dwarf-WD system ZTFJ003855.0+203025.5.

Keywords: Star-planet interactions, Red giant branch, Exoplanet evolution
Evidence for Hierarchical Black Hole Mergers in the Second LIGO-Virgo Gravitational Wave Catalog. We study the population properties of merging binary black holes in the second LIGO-Virgo Gravitational-Wave Transient Catalog assuming they were all formed dynamically in gravitationally bound clusters. Using a phenomenological population model, we infer the mass and spin distribution of first-generation black holes, while self-consistently accounting for hierarchical mergers. Considering a range of cluster masses, we see compelling evidence for hierarchical mergers in clusters with escape velocities ≳100 km s-1. For our most probable cluster mass, we find that the catalog contains at least one second-generation merger with 99% credibility. We find that the hierarchical model is preferred over an alternative model with no hierarchical mergers (Bayes factor ${ \mathcal B }\gt 1400$ ) and that GW190521 is favored to contain two second-generation black holes with odds ${ \mathcal O }\gt 700$ , and GW190519, GW190602, GW190620, and GW190706 are mixed-generation binaries with ${ \mathcal O }\gt 10$ . However, our results depend strongly on the cluster escape velocity, with more modest evidence for hierarchical mergers when the escape velocity is ≲100 km s-1. Assuming that all binary black holes are formed dynamically in globular clusters with escape velocities on the order of tens of km s-1, GW190519 and GW190521 are favored to include a second-generation black hole with odds ${ \mathcal O }\gt 1$ . In this case, we find that 99% of black holes from the inferred total population have masses that are less than 49M⊙, and that this constraint is robust to our choice of prior on the maximum black hole mass.

Keywords: Gravitational wave astronomy, Hierarchical models, Gravitational wave sources, Astrophysical black holes
The Intriguing Behavior of Ultraviolet Photodesorption and Color Temperature of Astrophysical CO Ice Analogs: A Possible Indication of Molecular Disorder. Ejection of molecules from ice-covered dust exposed to ultraviolet photons, known as photodesorption, is summoned to account for gas abundances in cold regions. Carbon monoxide (CO) is the second most abundant ice component in interstellar clouds. Photon energy transfer between CO molecules can eventually excite molecules on the ice surface, allowing desorption. CO photodesorption drops linearly by a factor of 4 for increasing ice deposition temperature between 7 and 20 K. Because translation of molecules leading to crystallization occurs above 20 K, amorphous CO ice must hold another property that depends on deposition temperature and has an impact on photodesorption. CO ice molecules act as tiny dipoles weakly bonded to each other. We used colorimetry to trace variations of the relative orientations between CO molecules, a process not observed using other techniques. Color variations seen by eye at different deposition temperatures range from brown to translucent, or transparent when CO ice is deposited above 20 K and is nearly crystalline. As expected, apolar N2 ice did not display a visual color. Color temperature measurements allowed quantification of this phenomenon. The behavior of color temperature matches the photodesorption, allowing a better understanding of this process, and provides a method to monitor structural changes in molecular solids. An implication in astrophysics is that the albedo of icy bodies can be low in CO patches. A brownish color is not only indicative of organic matter, as it may be due to disordered solid CO, and allows to determine the build-up temperature of CO ice.

Keywords: Interstellar molecules, Interstellar dust processes, Dense interstellar clouds
A Search for the 3.5 keV Line from the Milky Way's Dark Matter Halo with HaloSat. Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark-matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way's galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report nondetections of a ~3.5 keV emission line in four HaloSat observations near the Galactic center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux for a field centered 18.6 degrees from the Galactic center and the corresponding 7.1 keV sterile neutrino mixing angle: F ≤ 0.077 ph cm-2 s-1 sr-1 and ${\sin }^{2}(2\theta )\leqslant 4.25\times {10}^{-11}$ . The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way's dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way's dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature.

Keywords: X-ray astronomy, Milky Way dark matter halo, Galactic center, Diffuse radiation, Neutrino astronomy, Dark matter, Particle astrophysics
The Low-redshift Lyman-continuum Survey: [S II] Deficiency and the Leakage of Ionizing Radiation. The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the [S II] nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the [S II] deficiency is an effective method to select LyC-leaking candidates using data from the Low-redshift LyC Survey, which has detected flux below the Lyman edge in 35 out of 66 star-forming galaxies with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We show that LyC leakers tend to be more [S II] deficient and that the fraction of their detections increases as [S II] deficiency becomes more prominent. Correlational studies suggest that [S II] deficiency complements other LyC diagnostics (such as strong Lyα emission and high [O III]/[O II]). Our results verify an additional technique by which reionization-era galaxies could be studied.

Keywords: Starburst galaxies, Interstellar medium, Circumgalactic medium, Extragalactic astronomy, Reionization
Quantifying Non-parametric Structure of High-redshift Galaxies with Deep Learning. At high redshift, due to both observational limitations and the variety of galaxy morphologies in the early universe, measuring galaxy structure can be challenging. Non-parametric measurements such as the CAS system have thus become an important tool due to both their model-independent nature and their utility as a straightforward computational process. Recently, convolutional neural networks (CNNs) have been shown to be adept at image analysis, and are beginning to supersede traditional measurements of visual morphology and model-based structural parameters. In this work, we take a further step by extending CNNs to measure well known non-parametric structural quantities: concentration (C) and asymmetry (A). We train CNNs to predict C and A from individual images of ~150,000 galaxies at 0 &lt; z &lt; 7 in the CANDELS fields, using Bayesian hyperparameter optimization to select suitable network architectures. Our resulting networks accurately reproduce measurements compared with standard algorithms. Furthermore, using simulated images, we show that our networks are more stable than the standard algorithms at low signal-to-noise. While both approaches suffer from similar systematic biases with redshift, these remain small out to z ~ 7. Once trained, measurements with our networks are &gt;103 times faster than previous methods. Our approach is thus able to reproduce standard measures of non-parametric morphologies and shows the potential of employing neural networks to provide superior results in substantially less time. This will be vital for making best use of the large and complex data sets provided by upcoming galaxy surveys, such as Euclid and Rubin-LSST.

Keywords: Convolutional neural networks, High-redshift galaxies, Galaxies
He I Spectropolarimetry of a Supersonic Coronal Downflow Within a Sunspot Umbra. We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. using observations acquired in the He I 10830 Å triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s-1 and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively controlled source function above the sunspot umbra. Strong emission profiles close to the rest wavelengths but with long redshifted tails are also observed at the downflow terminus. From the polarized spectra, we infer longitudinal magnetic field strengths of ~2.4 kG in the core portion of the He I strong emission, which we believe is the strongest ever reported in this line. Photospheric field strengths along the same line of sight are ~2.8 kG as inferred using the Ca I 10839 Å spectral line. The temperatures of the highest speed He I absorption and the near-rest emission are similar (~10 kK), while a differential emission measure analysis using Solar Dynamics Observatory/Atmospheric Imaging Assembly data indicates significant increases in radiative cooling for temperatures between ~0.5 and 1 MK plasma associated with the downflow terminus. Combined we interpret these observations in the context of a strong radiative shock induced by the supersonic downflow impacting the low sunspot atmosphere.

Keywords: Spectropolarimetry, Sunspots, Solar magnetic fields, Solar transition region, Solar chromosphere
Interstellar Cloud Conditions Based on 63 μm [O I] Emission and Absorption in W3. We investigate the origin of self-absorption in [O I] 63 μm line emission, which is very clearly seen in approximately half of the 12 Galactic giant molecular cloud (GMC)/H II regions observed. For this study, we observed velocity-resolved spectra of photon-dominated region (PDR) and H II region tracers, the [O I] 63 μm, [N II] 205 μm, and CO J = 5-4 and 8-7 lines, with the upGREAT instrument in the 4GREAT configuration on the NASA/DLR Stratospheric Observatory For Infrared Astronomy (SOFIA). To probe the origin of the [O I] absorption and line shape and what they tell us about the physical conditions, we focus on the W3 region, for which we obtained data for eight positions along a line near the H II region W3 A. We derive the foreground column density of low-excitation atomic oxygen to be in the range 2-7 × 1018 $\,{\mathrm{cm}}^{-2}$ . At the position of strongest [O I] emission and greatest absorbing column density, 24% of the oxygen in the PDR is in the form of low-excitation atomic oxygen. We employ the Meudon PDR code to study the chemical and thermal structure of the PDR and to understand the large column density of neutral oxygen throughout the PDR. The reduction in the integrated intensity of the [O I] 63 μm emission is a factor of ≃2-4 in directions with strong [O I] emission. The results from our sample, if general, would significantly impact the use of the [O I] 63 μm line as a tracer of massive star formation and could play a significant role in explaining the "63 μm [O I] deficit" seen in very luminous extragalactic sources.

Keywords: Dark interstellar clouds, Interstellar clouds, Dense interstellar clouds
Revisiting FUSE O VI Emission in Galaxy Halos. A significant fraction of baryons in galaxies are in the form of diffuse gas of the circumgalactic medium (CGM). One critical component of the multiphases of CGM, the so-called "coronal" warm-hot phase gas (105-106 K) traced by O VI 1031.93, 1037.62 Å resonance lines, has rarely been detected in emission from galaxy halos other than that of the Milky Way. Here we report four additional detections of O VI emission gas in the halos of nearby edge-on galaxies, NGC 4631 and NGC 891, using archival Far Ultraviolet Spectroscopic Explorer data and an updated data pipeline. We find the most intense O VI emission to be from fields forming a vertical line near the center of NGC 4631, despite the close proximity to the disk of two other fields. The detected O VI emission surface brightness is about (1.1 ± 0.3) × 10-18 to (3.9 ± 0.8) × 10-18 erg s-1 cm-2 arcsec-2. The spatial distribution of the five 30″ × 30″ O VI detection fields in NGC 4631 can be interpreted as the existence of filamentary structures of more intense O VI emission superimposed within a diffuse and faint O VI halo in star-forming galaxies. Volume-filled O VI emission mapping is greatly needed to determine the structure and prevalence of warm-hot gas and the role it plays in the cycling of gas between the galaxy disk and the halo. Finally, we present the sensitivity of future funded and proposed UV missions (LUVOIR-A, LUVOIR-B, CETUS, and Aspera) to the detection of diffuse and faint O VI emission in nearby galaxy halos.

Keywords: Extragalactic astronomy, Galaxy structure, Circumgalactic medium
Gaia EDR3 Proper Motions of Milky Way Dwarfs. I. 3D Motions and Orbits. Based on Gaia Early Data Release 3 (EDR3), we estimate the proper motions of 46 dwarf galaxies of the Milky Way (MW). The uncertainties in proper motions, determined by combining both statistical and systematic errors, are smaller by a factor of 2.5 when compared with Gaia Data Release 2. We have derived orbits in four MW potential models that are consistent with the MW rotation curve, with total mass ranging from 2.8 × 1011 M⊙ to 15 × 1011 M⊙. Although the type of orbit (ellipse or hyperbola) are very dependent on the potential model, the pericenter values are firmly determined, largely independent of the adopted MW mass model. By analyzing the orbital phases, we found that the dwarf galaxies are highly concentrated close to their pericenter, rather than to their apocenter as expected from Kepler's law. This may challenge the fact that most dwarf galaxies are MW satellites, or alternatively indicates an unexpectedly large number of undiscovered dwarf galaxies lying very close to their apocenters. Between half and two-thirds of the satellites have orbital poles that indicate them to orbit along the vast polar structure, with the vast majority of these co-orbiting in a common direction also shared by the Magellanic Clouds, which is indicative of a real structure of dwarf galaxies.

Keywords: Galaxy dynamics, Dwarf galaxies, Galaxy kinematics
Fast Multipole Methods for N-body Simulations of Collisional Star Systems. Direct N-body simulations of star clusters are accurate but expensive, largely due to the numerous ${ \mathcal O }({N}^{2})$ pairwise force calculations. To solve the post-million-body problem, it will be necessary to use approximate force solvers, such as tree codes. In this work, we adapt a tree-based, optimized Fast Multipole Method (FMM) to the collisional N-body problem. The use of a rotation-accelerated translation operator and an error-controlled cell opening criterion leads to a code that can be tuned to arbitrary accuracy. We demonstrate that our code, Taichi, can be as accurate as direct summation when N &gt; 104. This opens up the possibility of performing large-N, star-by-star simulations of massive stellar clusters and would permit large parameter space studies that would require years with the current generation of direct summation codes. Using a series of tests and idealized models, we show that Taichi can accurately model collisional effects, such as dynamical friction and the core-collapse time of idealized clusters, producing results in strong agreement with benchmarks from other collisional codes such as NBODY6++GPU or PeTar. Parallelized using OpenMP and AVX, Taichi is demonstrated to be more efficient than other CPU-based direct N-body codes for simulating large systems. With future improvements to the handling of close encounters and binary evolution, we clearly demonstrate the potential of an optimized FMM for the modeling of collisional stellar systems, opening the door to accurate simulations of massive globular clusters, super star clusters, and even galactic nuclei.

Keywords: Stellar dynamics, Star clusters
Born in a Pair (?): Pisces II and Pegasus III. We have used B, V time-series photometry collected with the Large Binocular Telescope to undertake the first study of variable stars in the Milky Way ultra-faint dwarf (UFD) satellites Pisces II and Pegasus III. In Pisces II we have identified an RRab star, one confirmed and a candidate SX Phoenicis star, and a variable with uncertain classification. In Pegasus III we confirmed the variability of two sources: an RRab star and a variable with uncertain classification, similar to the case found in Pisces II. Using the intensity-averaged apparent magnitude of the bona fide RRab star in each galaxy, we estimate distance moduli of (m - M)0 = 21.22 ± 0.14 mag (d = 175 ± 11 kpc) and 21.21 ± 0.23 mag (d = 174 ± 18 kpc) for Pisces II and Pegasus III, respectively. Tests performed to disentangle the actual nature of variables with an uncertain classification led us to conclude that they most likely are bright, long-period, and very metal-poor RRab members of their respective hosts. This may indicate that Pisces II and Pegasus III contain a dominant old stellar population (t &gt; 12 Gyr) with metallicity ⟨[Fe/H]⟩ - 1.8 dex along with, possibly, a minor, more metal-poor component, as supported by the V, B - V color-magnitude diagrams of the two UFDs and their spectroscopically confirmed members. The metallicity spread that we derived from our data sample is ≳0.4 dex in both systems. Lastly, we built isodensity contour maps that do not reveal any irregular shape, thus making the existence of a physical connection between these UFDs unlikely. * Based on data collected with the Large Binocular Cameras at the Large Binocular Telescope, PI: G. Clementini.

Keywords: Galaxy distances, Dwarf galaxies, Variable stars
HETDEX [O III] Emitters. I. A Spectroscopically Selected Low-redshift Population of Low-mass, Low-metallicity Galaxies. We assemble a sample of 17 low-metallicity (7.45 &lt; log(O/H)+12 &lt; 8.12) galaxies with z ≲ 0.1 found spectroscopically, without photometric preselection, in early data from the Hobby-Eberly Telescope Dark Energy Experiment. Star-forming galaxies that occupy the lowest-mass and lowest-metallicity end of the mass-metallicity relation tend to be undersampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high [O III]λ5007/[O II]λ3727, implying highly ionized nebular emission often indicative of low-metallicity systems. With the Second Generation Low Resolution Spectrograph on the Hobby-Eberly Telescope we acquired follow-up spectra, with higher resolution and broader wavelength coverage, of each low-metallicity candidate in order to confirm the redshift, measure the Hα and [N II] line strengths, and, in many cases, obtain deeper spectra of the blue lines. We find our galaxies are consistent with the mass-metallicity relation of typical low-mass galaxies. However, galaxies in our sample tend to have similar specific star formation rates as the incredibly rare "blueberry" galaxies found by Yang et al. We illustrate the power of spectroscopic surveys for finding low-mass and low-metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.

Keywords: Galaxy properties, Surveys, Optical astronomy, Emission line galaxies, Astronomical techniques, Galaxy abundances, Star formation, Galaxy evolution, Spectroscopy, Galaxies