Sazuna/UAT_keywords huggingface dataset:
Distances to Galactic OB Stars: Photometry versus Parallax. For application to surveys of interstellar matter and Galactic structure, we compute new spectrophotometric distances to 139 OB stars frequently used as background targets for UV spectroscopy. Many of these stars have updated spectral types and digital photometry with reddening corrections from the Galactic O-Star (GOS) spectroscopic survey. We compare our new photometric distances to values used in previous International Ultraviolet Explorer and Far Ultraviolet Spectroscopic Explorer surveys and to parallax distances derived from Gaia-DR2, after applying a standard (0.03 mas) offset from the quasar celestial reference frame. We find substantial differences between photometric and parallax distances at d &gt; 1.5 kpc, with increasing dispersion when parallax errors exceed 8%. Differences from previous surveys arise from new GOS stellar classifications, especially luminosity classes, and from reddening corrections. We apply our methods to two OB associations. For Perseus OB1 (nine O stars) we find mean distances of 2.47 ± 0.57 kpc (Gaia parallax) and 2.99 ± 0.14 kpc (photometric) using a standard grid of absolute magnitudes. For 29 O stars in Car OB1 associated with Trumpler 16, Trumpler 14, Trumpler 15, and Collinder 228 star clusters, we find 2.87 ± 0.73 kpc (Gaia) and 2.60 ± 0.28 kpc (photometric). Using an alternative grid of O-star absolute magnitudes shifts these photometric distances ∼7% closer. Improving the distances to OB stars will require attention to spectral types, photometry, reddening, binarity, and the grid of absolute magnitudes. We anticipate that future measurements in Gaia-DR3 will improve the precision of distances to massive star-forming regions in the Milky Way.

Keywords: Interstellar medium, Photometric parallax, Stellar parallax, O stars
A Catalog of Hyper-luminous X-Ray Sources and Intermediate-mass Black Hole Candidates out to High Redshifts. Hyper-luminous X-ray sources (HLXs; L X &gt; 1041 erg s-1) are off-nuclear X-ray sources in galaxies and strong candidates for intermediate-mass black holes (IMBHs). We have constructed a sample of 169 HLX candidates by combining X-ray detections from the Chandra Source Catalog (Version 2) with galaxies from the Sloan Digital Sky Survey and registering individual images for improved relative astrometric accuracy. The spatial resolution of Chandra allows for the sample to extend out to z ∼ 0.9. Optical counterparts are detected among one-fourth of the sample, one-third of which are consistent with dwarf galaxy stellar masses. The average intrinsic X-ray spectral slope indicates efficient accretion, potentially driven by galaxy mergers, and the column densities suggest one-third of the sample has significant X-ray absorption. We find that 144 of the HLX candidates have X-ray emission that is significantly in excess of the expected contribution from star formation and hot gas, strongly suggesting that they are produced by accretion onto black holes more massive than stars. After correcting for an average background or foreground contamination rate of 8%, we estimate that at least ∼20 of the HLX candidates are consistent with IMBH masses, and this estimate is potentially several times higher assuming more efficient accretion. This catalog currently represents the largest sample of uniformly selected, off-nuclear IMBH candidates. These sources may represent scenarios in which a low-mass galaxy hosting an IMBH has merged with a more massive galaxy and provide an excellent sample for testing models of low-mass BH formation and merger-driven growth.

Keywords: AGN host galaxies, Intermediate-mass black holes, Dwarf galaxies, X-ray quasars, X-ray active galactic nuclei, Active galactic nuclei, Galaxy mergers
Earth as an Exoplanet: A Two-dimensional Alien Map. Resolving spatially varying exoplanet features from single-point light curves is essential for determining whether Earth-like worlds harbor geological features and/or climate systems that influence habitability. To evaluate the feasibility and requirements of this spatial-feature resolving problem, we present an analysis of multi-wavelength single-point light curves of Earth, where it plays the role of a proxy exoplanet. Here, ∼10,000 Deep Space Climate Observatory/Earth Polychromatic Imaging Camera frames collected over a two-year period were integrated over the Earth’s disk to yield a spectrally dependent point source and analyzed using singular value decomposition. We found that, between the two dominant principal components (PCs), the second PC contains surface-related features of the planet, while the first PC mainly includes cloud information. We present the first two-dimensional (2D) surface map of Earth reconstructed from light curve observations without any assumptions of its spectral properties. This study serves as a baseline for reconstructing the surface features of Earth-like exoplanets in the future.

Keywords: Extrasolar rocky planets, Exoplanets, Exoplanet atmospheric variability, Exoplanet surface composition, Exoplanet astronomy, Exoplanet surface variability, Exoplanet surface characteristics, Exoplanet detection methods, Exoplanet atmospheres
Active Asteroid (6478) Gault: A Blue Q-type Surface below the Dust?. We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m Near Earth Environment Monitoring T05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. We confirm that Gault is a silicate-rich (Q- or S-type) object likely linked to the (25) Phocaea collisional family. The asteroid exhibits substantial spectral variability over the 0.75-2.45 μm wavelength range, from unusual blue (s‧ = -13.5 ± 1.1% μm-1) to typical red (s‧ = +9.1 ± 1.2% μm-1) spectral slope, that does not seem to correlate with activity. Spectral comparisons with samples of ordinary chondrite meteorites suggest that the blue color relates to the partial loss of the asteroid dust regolith, exposing a fresh, dust-free material at its surface. The existence of asteroids rotating close to rotational break-up limit and having similar spectral properties as Gault further supports this interpretation. Future spectroscopic observations of Gault, when the tails dissipate, will help further testing of our proposed hypothesis.

Keywords: Photometry, Asteroids, Spectroscopy
Fermi-LAT Stacking Analysis Technique: An Application to Extreme Blazars and Prospects for their CTA Detection. We present a likelihood profile stacking technique based on the Fermi-Large Area Telescope (LAT) data to explore the γ-ray characteristics of Fermi-LAT undetected astrophysical populations. The pipeline is applied to a sample of γ-ray unresolved extreme blazars, i.e., sources with the highest synchrotron peak frequencies ({ν }Syn}peak}≥slant {10}17 {Hz}), and we report a cumulative γ-ray detection with more than 32σ confidence for 2 degrees of freedom. Comparing the generated stacked γ-ray spectrum with the sensitivity limits of the upcoming Cherenkov Telescope Array (CTA), we find that the Fermi-LAT undetected population of such extreme blazars, on average, may remain well below the CTA detection threshold due to their faintness and extragalactic background light (EBL) absorption. However, γ-ray detected blazars belonging to the same class are promising candidates for CTA observations. The EBL-corrected stacked spectra of these sources do not show any softening up to 1 TeV. This finding suggests the inverse Compton peak of extreme blazars lies above 1 TeV, thus indicating a hard intrinsic TeV spectrum. Our analysis also predicts that at 100 GeV, at least ∼10% of the diffuse extragalactic γ-ray background originates from the γ-ray undetected extreme blazars. These results highlight the effectiveness of the developed stacking technique to explore the uncharted territory of γ-ray undetected astrophysical objects.

Keywords: Active galaxies, BL Lacertae objects
A Mass-accreting Gamma Doradus Pulsator with a Synchronized Core in Kepler Eclipsing Binary KIC 7385478. The short-period (P ≈ 1.7 days), Algol-type eclipsing binary KIC 7385478 consists of an F-type primary star (M 1 ≈ 1.71M ⊙) and an evolved K-type secondary (M 2 ≈ 0.37M ⊙). We study the variability of the Kepler light curve and attribute many frequency peaks in the Fourier spectrum to the spot modulation. These frequencies are in the form of orbital harmonics and are highly variable in amplitude. They are most likely from the mass-accreting primary star. In addition, we identify a series of prograde dipole g modes from the primary star that show a quasi-linear period spacing pattern and are very stable in amplitude. The period spacing pattern reveals an asymptotic period spacing value in agreement with fundamental parameters of the primary star and also implies that the near-convective-core rotation rate is almost the same as the orbital period. Thus, both the surface and the core of this Gamma Dor pulsator have synchronized with the binary orbit. We find that a lower stellar mass ≈1.50M ⊙ and higher effective temperature are needed in order to be compatible with the asteroseismic constraints from single-star evolutionary models.

Keywords: Close binary stars, Stellar oscillations, Stellar rotation
Pure Rotational Spectrum of CN<SUP>+</SUP>. The pure rotational spectrum of the elusive CN+ cation has been observed for the first time using a cryogenic ion trap apparatus and applying an action spectroscopy scheme. For the 12C14N+ species, the three lowest rotational transitions have been observed, each of which exhibits hyperfine structure from the presence of the 14N nucleus. The rare C15N+ isotopologue has been studied up to the J = 4 - 3 transition. The observations conclusively confirm that CN+ occupies a 1Σ+ electronic ground state. Given the ubiquity of the CN radical in space, CN+ is an appealing candidate for future radio astronomical searches.

Keywords: Interstellar molecules, High resolution spectroscopy, Spectral line identification, Laboratory astrophysics, Molecular physics
Atomic Hydrogen in Star-forming Galaxies at Intermediate Redshifts. We have used the upgraded Giant Metrewave Radio Telescope to carry out a deep (117 on-source hours) L-band observation of the Extended Groth Strip, to measure the average neutral hydrogen (H I) mass and median star formation rate (SFR) of star-forming galaxies, as well as the cosmic H I mass density, at 0.2 &lt; z &lt; 0.4. This was done by stacking the H I 21 cm emission and the rest-frame 1.4 GHz radio continuum from 445 blue star-forming galaxies with M B ≤ -17 at z mean ≈ 0.34. The stacked H I 21 cm emission signal is detected at ≈7σ significance, implying an average H I mass of &lt; {M}{{H}{{I}}} &gt; =(4.93+/- 0.70)× {10}9 {M}⊙ . We also stacked the rest-frame 1.4 GHz radio continuum emission of the same galaxies to obtain a median SFR of (0.54 ± 0.06) M ⊙ yr-1 this implies an atomic gas depletion timescale of Δt H I  = (≈9) Gyr, consistent with values in star-forming galaxies in the local universe. This indicates that the star formation efficiency does not change significantly over the redshift range 0-0.4. We used the detection of the stacked H I 21 cm emission signal to infer the normalized cosmic H I mass density (ρ H I /ρ c,0) in star-forming galaxies at z ≈ 0.34. Assuming the local relation between H I mass and absolute B-magnitude, we obtain ρ H I /ρ c,0 = (4.81 ± 0.75) × 10-4, implying no significant evolution in ρ H I /ρ c,0 from z ≈ 0.4 to the present epoch.

Keywords: Radio spectroscopy, H I line emission, Star formation, Galaxy evolution, Radio interferometry, High-redshift galaxies
Distinct Properties of the Radio Burst Emission from the Magnetar XTE J1810-197. XTE J1810-197 (PSR J1809-1943) was the first magnetar that was found to emit transient radio emission. It has recently undergone another radio and high-energy outburst. This is only the second radio outburst that has been observed from this source. We observed J1810-197 soon after its recent radio outburst at low radio frequencies using the Giant Metrewave Radio Telescope. We present the 650 MHz flux density evolution of the source in the early phases of the outburst, and its radio spectrum down to frequencies as low as 300 MHz. The magnetar also exhibits radio emission in the form of strong, narrow bursts. We show that the bursts have a characteristic intrinsic width of the order of 0.5-0.7 ms, and discuss their properties in the context of giant pulses and giant micropulses from other pulsars. We also show that the bursts exhibit spectral structures that cannot be explained by interstellar propagation effects. These structures might indicate a phenomenological link with the repeating fast radio bursts that also show interesting, more detailed frequency structures. While the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures.

Keywords: Neutron stars, Radio transient sources, Rotation powered pulsars, Pulsars, Radio bursts, Non-thermal radiation sources, Interstellar medium, Interstellar scintillation, Interstellar scattering, Magnetars, Radio pulsars
Time-varying Polarized Gamma-Rays from GRB 160821A: Evidence for Ordered Magnetic Fields. GRB 160821A is the third most energetic gamma-ray burst observed by the Fermi gamma-ray space telescope. Based on the observations made by the Cadmium Zinc Telluride Imager on board AstroSat, here we report the most conclusive evidence to date of (i) high linear polarization ({66}-27+26 % ;5.3σ detection), and (ii) variation of polarization angle with time, occurring twice during the rise and decay phase of the burst at 3.5σ and 3.1σ detections, respectively. All confidence levels are reported for two parameters of interest. These observations strongly suggest synchrotron radiation produced in magnetic field lines that are highly ordered on angular scales of 1/Γ, where Γ is the Lorentz factor of the outflow.

Keywords: Gamma-ray bursts, Magnetic fields, High energy astrophysics
Long-lived Eccentricities in Accretion Disks. Accretion disks can be eccentric: they support m = 1 modes that are global and slowly precessing. But whether the modes remain trapped in the disk—and hence are long-lived—depends on conditions at the outer edge of the disk. Here we show that in disks with realistic boundaries, in which the surface density drops rapidly beyond a given radius, eccentric modes are trapped and hence can live for as long as the viscous time. We focus on pressure-only disks around a central mass, and show how this result can be understood with the help of a simple second-order WKB theory. We show that the longest-lived mode is the zero-node mode in which all of the disk’s elliptical streamlines are aligned, and that this mode decays coherently on the viscous timescale of the disk. Hence, such a mode, once excited, could live as long as the lifetime of the disk. It may be responsible for asymmetries seen in recent images of protoplanetary disks.

Keywords: Hydrodynamics, Protoplanetary disks, Eccentricity, Circumstellar disks
Do Androids Dream of Magnetic Fields? Using Neural Networks to Interpret the Turbulent Interstellar Medium. The interstellar medium (ISM) of galaxies is composed of a turbulent magnetized plasma. In order to quantitatively measure relevant turbulent parameters of the ISM, a wide variety of statistical techniques and metrics have been developed that are often tested using numerical simulations and analytic formalism. These metrics are typically based on the Fourier power spectrum, which does not capture the Fourier phase information that carries the morphological characteristics of images. In this work we use density slices of magnetohydrodynamic turbulence simulations to demonstrate that a modern tool, convolutional neural networks, can capture significant information encoded in the Fourier phases. We train the neural network to distinguish between two simulations with different levels of magnetization. We find that, even given a tiny slice of simulation data, a relatively simple network can distinguish sub-Alfvénic (strong magnetic field) and super-Alfvénic (weak magnetic field) turbulence &gt;98% of the time, even when all spectral amplitude information is stripped from the images. In order to better understand how the neural network is picking out differences between the two classes of simulations we apply a neural network analysis method called “saliency maps.” The saliency map analysis shows that sharp ridge-like features are a distinguishing morphological characteristic in such simulations. Our analysis provides a way forward for deeper understanding of the relationship between magnetohydrodynamic turbulence and gas morphology and motivates further applications of neural networks for studies of turbulence. We make publicly available all data and software needed to reproduce our results.

Keywords: Interstellar magnetic fields, Computational methods
Limits on the Weak Equivalence Principle and Photon Mass with FRB 121102 Subpulses. Fast radio bursts (FRBs) are short-duration (∼millisecond) radio transients with cosmological origin. The simple sharp features of the FRB signal have been utilized to probe two fundamental laws of physics, namely, testing Einstein’s weak equivalence principle and constraining the rest mass of the photon. Recently, Hessels et al. found that after correcting for dispersive delay, some of the bursts in FRB 121102 have complex time-frequency structures that include subpulses with a time-frequency downward drifting property. Using the delay time between subpulses in FRB 121102, here we show that the parameterized post-Newtonian parameter γ is the same for photons with different energies to the level of ≤ft|{γ }1-{γ }2\right|&lt; 2.5× {10}-16, which is 1000 times better than previous constraints from FRBs using similar methods. We also obtain a stringent constraint on the photon mass, m  γ  &lt; 5.1 × 10-48 g, which is 10 times smaller than previous best limits on the photon mass derived through the velocity dispersion method.

Keywords: Radio transient sources
SN 2018hna: 1987A-like Supernova with a Signature of Shock Breakout. High-cadence ultraviolet, optical, and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early-phase multiband light curves (LCs) exhibit the adiabatic cooling envelope emission following the shock breakout up to ∼ 14 days from the explosion. SN 2018hna has a rise time of ∼ 88 days in the V band, similar to SN 1987A. A 56Ni mass of ∼0.087 ± 0.004 M ⊙ is inferred for SN 2018hna from its bolometric LC. Hydrodynamical modeling of the cooling phase suggests a progenitor with a radius ∼50 R ⊙, a mass of ∼14-20 M ⊙, and an explosion energy of ∼1.7-2.9 × 1051 erg. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A subsolar metallicity (∼0.3 Z ⊙) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.

Keywords: Type II supernovae, Supernovae, Core-collapse supernovae
Role of Planetary Obliquity in Regulating Atmospheric Escape: G-dwarf versus M-dwarf Earth-like Exoplanets. We present a three-species (H+, O+ and e-) multi-fluid magnetohydrodynamic model, endowed with the requisite upper-atmospheric chemistry, that is capable of accurately quantifying the magnitude of oxygen ion losses from “Earth-like” exoplanets in habitable zones, whose magnetic and rotational axes are roughly coincidental with one another. We apply this model to investigate the role of planetary obliquity in regulating atmospheric losses from a magnetic perspective. For Earth-like exoplanets orbiting solar-type stars, we demonstrate that the dependence of the total atmospheric ion loss rate on the planetary (magnetic) obliquity is relatively weak; the escape rates are found to vary between 2.19 × 1026 s-1 to 2.37 × 1026 s-1. In contrast, the obliquity can influence the atmospheric escape rate (∼1028 s-1) by more than a factor of 2 (or 200%) in the case of Earth-like exoplanets orbiting late-type M-dwarfs. Thus, our simulations indicate that planetary obliquity may play a weak-to-moderate role insofar as the retention of an atmosphere (necessary for surface habitability) is concerned.

Keywords: Stellar winds, Astrobiology, Magnetic fields, Habitable planets, Exoplanet atmospheres, Magnetohydrodynamical simulations
Lunar Xenon and the Origin of the Indigenous Component. Lunar indigenous Xe isotopic abundances provide crucial information on relationships not only between gas reservoirs in the solar protoplanetary disk but also regarding planetary fractionation processes and possible space weather effects due to an active young Sun. The indigenous lunar Xe isotopic composition is not yet firmly established. A verification of previously inferred lunar Xe signatures using rocks of varying compositions from Apollo 16 and 17 missions is made here. Ancient lunar highland rocks carry cosmic-ray-produced spallation and neutron-capture products, fission components due to 244Pu and 238U, as well as terrestrial contamination gas, all complicating the identification of the indigenous lunar Xe component. The present study reveals light and heavy isotopic abundances compatible with terrestrial Xe composition. We conclude that in order to firmly establish indigenous lunar Xe signatures in situ, Xe measurements on the moon in interior samples of anorthositic ejecta from very recent craters should be performed.

Keywords: Solar abundances, Isotopic abundances, Planetary atmospheres, Lunar origin
CHIME/FRB Detection of the Original Repeating Fast Radio Burst Source FRB 121102. We report the detection of a single burst from the first-discovered repeating fast radio burst (FRB) source, FRB 121102, with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope, which operates in the frequency band 400-800 MHz. The detected burst occurred on 2018 November 19 and its emission extends down to at least 600 MHz, the lowest frequency detection of this source yet. The burst, detected with a significance of 23.7σ, has fluence 12 ± 3 Jy ms and shows complex time and frequency morphology. The 34 ms width of the burst is the largest seen for this object at any frequency. We find evidence of subburst structure that drifts downward in frequency at a rate of -3.9 ± 0.2 MHz ms-1. Our best fit tentatively suggests a dispersion measure of 563.6 ± 0.5 pc cm-3, which is ≈ 1% higher than previously measured values. We set an upper limit on the scattering time at 500 MHz of 9.6 ms, which is consistent with expectations from the extrapolation from higher-frequency data. We have exposure to the position of FRB 121102 for a total of 11.3 hr within the FWHM of the synthesized beams at 600 MHz from 2018 July 25 to 2019 February 25. We estimate on the basis of this single event an average burst rate for FRB 121102 of 0.1-10 per day in the 400-800 MHz band for a median fluence threshold of 7 Jy ms in the stated time interval.

Keywords: Radio bursts, Radio transient sources