Sazuna/UAT_keywords huggingface dataset:
What is the Solar Wind Frame of Reference?. Various solar wind ion species move with different speeds and theoretical considerations as well as limited observations in a region close to the Sun show that heavy solar wind ions tend to flow faster than protons, at least in less-aged fast solar wind streams. The solar wind flow carries the frozen-in interplanetary magnetic field (IMF) and this situation evokes three related questions: (I) what is the proper solar wind speed, (II) is this speed equal to the speed of the dominant component, whatever that may be, and (III) what is the speed of the magnetic field? We show that simple theoretical considerations based on the MHD approximation as well as on the dynamics of charged particles in electric and magnetic fields suggest that the IMF velocity of motion (de Hoffmann-Teller (HT) velocity) would be deliberated as the velocity appropriate for solar wind studies. Our analysis based on the Wind, Helios, ACE, and SOHO observations of differential streaming of solar wind populations shows that their energy is conserved in the HT frame. On the other hand, the noise and temporal resolution of the data do not allow us to decide whether the total momentum is also conserved in this frame.

Keywords: Slow solar wind, Fast solar wind, Solar wind, Alfven waves, Interplanetary magnetic fields
NuSTAR Perspective on High-redshift MeV Blazars. With bolometric luminosities exceeding 1048 erg s-1, powerful jets, and supermassive black holes at their center, MeV blazars are some of the most extreme sources in the universe. Recently, the Fermi-Large Area Telescope detected five new γ-ray emitting MeV blazars beyond redshift z = 3.1. With the goal of precisely characterizing the jet properties of these extreme sources, we started a multiwavelength campaign to follow them up with joint Nuclear Spectroscopic Telescope Array, Swift, and the Southeastern Association for Research in Astronomy's optical telescopes. We observe six high-redshift quasars, four of them belonging to the new γ-ray emitting MeV blazars. Thorough X-ray analysis reveals spectral flattening at soft X-ray for three of these objects. The source NVSS J151002+570243 also shows a peculiar rehardening of the X-ray spectrum at energies E &gt; 6 keV. Adopting a one-zone leptonic emission model, this combination of hard X-rays and γ-rays enables us to determine the location of the Inverse Compton peak and to accurately constrain the jet characteristics. In the context of the jet-accretion disk connection, we find that all six sources have jet powers exceeding accretion disk luminosity, seemingly validating this positive correlation even beyond z &gt; 3. Our six sources are found to have ${10}^{9}\,{M}_{\odot }$ black holes, further raising the space density of supermassive black holes in the redshift bin z = [3, 4].

Keywords: Blazars, Jets, Active galactic nuclei, High energy astrophysics
Implications from Late-time X-Ray Detections of Optically Selected Tidal Disruption Events: State Changes, Unification, and Detection Rates. We present Chandra X-ray observations of four optically selected tidal disruption events (TDEs) obtained 4-9 yr after discovery. Three sources were detected with luminosities between 9 × 1040 and 3 × 1042 erg s-1. The spectrum of PTF09axc is consistent with a power law of index 2.5 ± 0.1, whereas the spectrum of PTF09ge is very soft. The power-law spectrum of PTF09axc and prior literature findings provide evidence that TDEs transition from an early-time soft state to a late-time hard state many years after disruption. We propose that the time to peak luminosity for optical and X-ray emission may differ substantially in TDEs, with X-rays being produced or becoming observable later. This delay helps explain the differences in observed properties such as Lopt/LX of optically and X-ray-selected TDEs. We update TDE rate predictions for the eROSITA instrument: it ranges from 3 to 990 yr-1, depending sensitively on the distribution of black hole spins and the time delay between disruption and peak X-ray brightness. We further predict an asymmetry in the number of retrograde and prograde disks in samples of optically and X-ray-selected TDEs. The details of the observational biases can contribute to observed differences between optically and X-ray-selected TDEs (with optically selected TDEs being fainter in X-rays for retrograde TDE disks).

Keywords: High energy astrophysics, Tidal disruption, X-ray transient sources, Active galactic nuclei, Astrophysical black holes
Deciphering the Local Interstellar Spectra of Secondary Nuclei with the Galprop/Helmod Framework and a Hint for Primary Lithium in Cosmic Rays. Local interstellar spectra (LIS) of secondary cosmic-ray (CR) nuclei, lithium, beryllium, boron, and partially secondary nitrogen, are derived in the rigidity range from 10 MV to ∼200 TV using the most recent experimental results combined with state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. The lithium spectrum appears somewhat flatter at high energies compared to other secondary species, which may imply a primary lithium component. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. An iterative maximum-likelihood method is developed that uses GALPROP-predicted LIS as input to HelMod, which provides the modulated spectra for specific time periods of the selected experiments for the model-data comparison. The proposed LIS accommodates the low-energy interstellar spectra measured by Voyager 1, the High Energy Astrophysics Observatory-3 (HEAO-3), and the Cosmic Ray Isotope Spectrometer on board of the Advanced Composition Explorer (ACE/CRIS), as well as the high-energy observations by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), Alpha Magnetic Spectrometer-02 (AMS-02), and earlier experiments that are made deep in the heliosphere. The interstellar and heliospheric propagation parameters derived in this study are consistent with our earlier results for propagation of CR protons, helium, carbon, oxygen, antiprotons, and electrons.

Keywords: Interplanetary medium, Isotopic abundances, Heliosphere, Interstellar medium, Particle astrophysics, Cosmic rays
Gamma Rays from Kilonova: A Potential Probe of r-process Nucleosynthesis. The mergers of compact binaries with at least one neutron star component are the potential leading sites of the production and ejection of r-process elements. Discoveries of galactic binary pulsars, short gamma-ray bursts, and gravitational-wave detections have all been constraining the rate of these events, while the gravitational wave plus broadband electromagnetic coverage of binary neutron star merger (GW170817) has also placed constraints on the properties (mass and composition) of the merger ejecta. But uncertainties and ambiguities in modeling the optical and infrared emission make it difficult to definitively measure the distribution of heavy isotopes in these mergers. In contrast, gamma rays emitted in the decay of these neutron-rich ejecta may provide a more direct measurement of the yields. We calculate the gamma production in remnants of neutron star mergers, considering two epochs: a kilonova epoch, lasting about two weeks, and a much later epoch of tens and hundreds of thousands of years after the merger. For the kilonova epoch, when the expanding ejecta is still only partially transparent to gamma radiation, we use 3D radiative transport simulations to produce the spectra. We show that the gamma-ray spectra associated with beta- and alpha-decay provide a fingerprint of the ejecta properties and, for a sufficiently nearby remnant, may be detectable, even for old remnants. We compare our gamma spectra with the potential detection limits of next generation detectors, including the Lunar Occultation Explorer (LOX), the All-sky Medium Energy Gamma-ray Observatory (AMEGO), and the Compton Spectrometer and Imager (COSI). We show that fission models can be discriminated via the presence of short-lived fission fragments in the remnant spectra.

Keywords: Neutron stars, Explosive nucleosynthesis, Gamma-ray lines, Gamma-ray sources, R-process
Gamma-Ray Emission of <SUP>60</SUP>Fe and <SUP>26</SUP>Al Radioactivity in Our Galaxy. The isotopes 60Fe and 26Al originate from massive stars and their supernovae, reflecting ongoing nucleosynthesis in the Galaxy. We studied the gamma-ray emission from these isotopes at characteristic energies 1173, 1332, and 1809 keV with over 15 yr of SPI data, finding a line flux in 60Fe combined lines of $(0.31\pm 0.06)\times {10}^{-3}\,\mathrm{ph}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ and the Al line flux of $(16.8\pm 0.7)\times {10}^{-4}\,\mathrm{ph}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ above the background and continuum emission for the whole sky. Based on the exponential disk grid maps, we characterize the emission extent of 26Al to find scale parameters ${R}_{0}={7.0}_{-1.0}^{+1.5}$ and ${z}_{0}={0.8}_{-0.2}^{+0.3}$ kpc; however, the 60Fe lines are too weak to spatially constrain the emission. Based on a point-source model test across the Galactic plane, the 60Fe emission would not be consistent with a single strong point source in the Galactic center or somewhere else, providing a hint of a diffuse nature. We carried out comparisons of emission morphology maps using different candidate source tracers for both 26Al and 60Fe emissions and suggest that the 60Fe emission is more likely to be concentrated toward the Galactic plane. We determine the 60Fe/26Al γ-ray flux ratio at 18.4% ± 4.2% when using a parameterized spatial morphology model. Across the range of plausible morphologies, it appears possible that 26Al and 60Fe are distributed differently in the Galaxy. Using the best-fitting maps for each of the elements, we constrain flux ratios in the range 0.2-0.4. We discuss the implications for massive star models and their nucleosynthesis.

Keywords: Gamma-ray sources, Gamma-ray astronomy, Gamma-rays
Flash Ionization Signatures in the Type Ibn Supernova SN 2019uo. We present photometric and spectroscopic observations of the type Ibn supernova (SN) 2019uo, the second ever SN Ibn with flash ionization (He II, C III, N III) features in its early spectra. SN 2019uo displays a rapid post-peak luminosity decline of 0.1 mag day-1 similar to most of the SNe Ibn, but is fainter ( ${M}_{\max }^{V}=-18.30\pm 0.24$ mag) than a typical SN Ibn and shows a color evolution that places it between SNe Ib and the most extreme SNe Ibn. SN 2019uo shows P-cygni He I features in the early spectra which gradually evolve and become emission dominated post peak. It also shows faster evolution in line velocities as compared to most other members of the type Ibn subclass. The bolometric light curve is fairly well described by a 56Ni + circumstellar interaction model.

Keywords: CCD photometry, Core-collapse supernovae, Astronomical techniques, Photometry, Spectroscopy, Supernovae
Diversity of Kilonova Light Curves. We perform radiative transfer simulations for kilonova in various situations, including the cases of prompt collapse to a black hole from neutron star mergers, high-velocity ejecta possibly accelerated by magnetars, and a black hole-neutron star merger. Our calculations are done employing ejecta profiles predicted by numerical-relativity simulations and a new line list for all the r-process elements. We found that: (I) the optical emission for binary neutron stars promptly collapsing to a black hole would be fainter by ≳1-2 mag than that found in GW170817, while the infrared emission could be as bright as that in GW170817 if the post-merger ejecta is as massive as ≈0.01 M⊙; (II) the kilonova would be brighter than that observed in GW170817 for the case that the ejecta is highly accelerated by the electromagnetic energy injection from the remnant, but within a few days it would decline rapidly and the magnitude would become fainter than in GW170817; and (III) the optical emission from a black hole-neutron star merger ejecta could be as bright as that observed in GW170817 for the case that sufficiently large amount of matter is ejected (≳0.02 M⊙), while the infrared brightness would be brighter by 1-2 mag at the same time. We show that the difference in the ejecta properties would be imprinted in the differences in the peak brightness and time of peak. This indicates that we may be able to infer the type of the central engine for kilonovae by observation of the peak in the multiple band.

Keywords: Neutron stars, Radiative transfer equation, Gravitational waves
Resolving Linear Polarization due to Emission and Extinction of Aligned Dust Grains on NGC 1333 IRAS4A with JVLA and ALMA. We report high angular resolution observations of linearly polarized dust emission toward the Class 0 young stellar object NGC1333 IRAS4A (hereafter IRAS4A) using the Karl G. Jansky Very Large Array at K (11.5-16.7 mm), Ka (8.1-10.3 mm), and Q bands (6.3-7.9 mm), and using the Atacama Large Millimeter Array (ALMA) at Band 6 (1.3 mm) and Band 7 (0.85-0.89 mm). On 100-1000 au scales, all of these observations consistently trace the hourglass-shaped magnetic field topology as shown in the previous studies. In the innermost 100 au region of IRAS4A1, the polarization position angles (E field) detected at 6.3-16.7 mm are consistent; however, they are nearly 90° offset from those detected at 1.3 mm and 0.85-0.89 mm. Such a 90° offset may be explained by the inner ∼100 au area being optically thick at wavelengths shorter than ∼1.5 mm, whereby the observations probe the absorption of aligned dust against the weakly or unpolarized warm dust emission from the innermost region. This can also consistently explain why the highest angular resolution ALMA images at Band 7 show that the polarization percentage increases with dust brightness temperature in the inner ∼100 au region of IRAS4A1. Following this interpretation and assuming that the dust grains are aligned with the magnetic fields, the inferred magnetic field position angle based on the 90° rotated at 6.3-7.9 mm in the central peak of IRAS4A1 is ∼-22°, which is approximately consistent with the outflow direction of ∼-9°.

Keywords: Polarimetry, Star formation, Interstellar medium, Protostars, Magnetic fields
The Gas Accretion History of Low-mass Halos within the Cosmic Web from Cosmological Simulations. Using high-resolution hydrodynamical cosmological simulations, we study the gas accretion history of low-mass halos located in a field-like, low-density environment. We track their evolution individually from the early, pre-reionization era, through reionization, and beyond until z = 0. Before reionization, low-mass halos accrete cool cosmic-web gas at a very rapid rate, often reaching the highest gas mass they will ever have. But when reionization occurs, we see that almost all halos lose significant quantities of their gas content, although some respond less quickly than others. We find that the response rate is influenced by halo mass first, and secondarily by their internal gas density at the epoch of reionization. Reionization also fully ionizes the cosmic-web gas by z ∼ 6. As a result, the lowest mass halos (M ∼ 106 h-1 M⊙ at z = 6) can never again re-accrete gas from the cosmic web, and by z ∼ 5 have lost all their internal gas to ionization, resulting in a halt in star formation at this epoch. However, more massive halos can recover from their gas mass loss, and re-accrete ionized cosmic-web gas. We find the efficiency of this re-accretion is a function of halo mass first, followed by local surrounding gas density. Halos that are closer to the cosmic-web structure can accrete denser gas more rapidly. We find that our lower mass halos have a sweet spot for rapid, dense gas accretion at distances of roughly 1-5 virial radii from the most massive halos in our sample (&gt;108 h-1 M⊙), as these tend to be embedded deeply within the cosmic web.

Keywords: Galaxy formation, Dwarf galaxies, Galaxy evolution
6.7 GHz CH<SUB>3</SUB>OH Absorption toward the N3 Galactic Center Point Source. We present evidence of 6.7 GHz methanol (CH3OH) and 4.8 GHz formaldehyde (H2CO) absorption toward the Galactic Center (GC) point source "N3." Both absorption features are unresolved and spatially aligned with N3. The 6.7 GHz CH3OH contains a single-velocity component (centered at ∼10 km s-1), while the 4.8 GHz H2CO shows two-velocity components (centered at ∼-3 and +8 km s-1). We find that the velocities of these absorption components are similar to that of emission lines from other molecules (e.g., SiO and HC3N) detected toward this compact source (-13 to +25 km s-1; "N3 cloud"). The detection of these absorption features is a firm indication that some of the molecular gas in the N3 molecular cloud is on the near side of the continuum source. Analysis of the CH3OH absorption kinematics shows a relatively large velocity dispersion (3.8 km s-1) for the size scale of this feature (&lt;0"1, &lt;0.01 pc at the GC), when compared with other similarly sized GC clouds in the Larson line width-size relationship. Furthermore, this line width is closer to velocity dispersion measurements for size scales of 1.3 pc, which is roughly the width of the N3 cloud (25″; 1.0 pc). We argue that this relatively broad line width, over a small cross-sectional area, is due to turbulence through the depth of the cloud, where the cloud has a presumed line-of-sight thickness of ∼1 pc.

Keywords: Molecular gas, Galactic center, Interstellar clouds
Dynamical Masses of Young Stars. II. Young Taurus Binaries Hubble 4, FF Tau, and HP Tau/G3. One of the most effective ways to test stellar evolutionary models is to measure dynamical masses for binary systems at a range of temperatures. In this paper, we present orbits of three young K+M binary systems in Taurus (Hubble 4, FF Tau, and HP Tau/G3) with very long baseline interferometry parallaxes. We obtained precision astrometry with Keck II/NIRC2, optical photometry with Hubble Space Telescope/Wide Field Camera 3, and low-resolution optical spectra with WIFeS on the ANU 2.3 m telescope. We fit orbital solutions and dynamical masses with uncertainties of 1%-5% for the three binary systems. The spectrum, photometry, and mass for Hubble 4 are inconsistent with a binary system, suggesting that it may be a triple system where the primary component consists of two stars. For HP Tau/G3 and FF Tau, model masses derived from spectral energy distribution-determined component temperatures and luminosities agree with the dynamical masses, with a small offset toward larger model masses. We find model ages for the primary components of these systems of ∼3 Myr, but find that the secondaries appear younger by a factor of two. These estimates also disagree with the age of the physically associated G-type star HP Tau/G2, which is older (∼5 Myr) according to the same models. This discrepancy is equivalent to a luminosity underprediction of 0.1-0.2 dex, or a temperature overprediction of 100-300 K, for K/M-type stars at a given model age. We interpret this as further evidence for a systematic error in pre-main-sequence evolutionary tracks for convective stars. Our results reinforce that the ages of young populations determined from the locus of M-type members on the HR diagram may require upward revision.

Keywords: Binary stars, Fundamental parameters of stars, Star forming regions, Pre-main sequence stars, Interferometry
WISE 2150-7520AB: A Very Low-mass, Wide Comoving Brown Dwarf System Discovered through the Citizen Science Project Backyard Worlds: Planet 9. We report the discovery of WISE 2150-7520AB (W2150AB): a widely separated (∼341 au) very low-mass L1 + T8 co-moving system. The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99-75:20:54.6 (MJD = 57947) using Wide-field Infrared Survey Explorer data via the Backyard Worlds: Planet 9 citizen science project. We present Spitzer ch1 and ch2 photometry (ch1-ch2 = 1.41 ± 0.04 mag) of the secondary and Folded-port InfraRed Echellette prism spectra of both components. The sources show no peculiar spectral or photometric signatures, indicating that each component is likely field age. Using all observed data and the Gaia DR2 parallax of 41.3593 ± 0.2799 mas for W2150A we deduce fundamental parameters of log(Lbol/L⊙) = -3.69 ± 0.01, Teff = 2118 ± 62 K, and an estimated mass = 72 ± 12 MJup for the L1 and log(Lbol/L⊙) = -5.64 ± 0.02, Teff = 719 ± 61 K, and an estimated mass = 34 ± 22 MJup for the T8. At a physical separation of ∼341 au this system has Ebin = 1041 erg, making it the lowest binding energy system of any pair with Mtot &lt; 0.1 MSun not associated with a young cluster. It is equivalent in estimated mass ratio, Ebin, and physical separation to the ∼2 Myr M7.25 + M8.25 binary brown dwarf 2MASS J11011926-7732383AB (2M1101AB) found in the Chameleon star-forming region. W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later.

Keywords: Brown dwarfs, Substellar companion stars, Stellar kinematics, L dwarfs, Star formation, Astrometry, Late-type dwarf stars, T dwarfs
Elemental Abundances in M31: A Comparative Analysis of Alpha and Iron Element Abundances in the the Outer Disk, Giant Stellar Stream, and Inner Halo of M31. We measured [Fe/H] and [α/Fe] using spectral synthesis of low-resolution stellar spectroscopy for 70 individual red-giant-branch stars across four fields spanning the outer disk, Giant Stellar Stream (GSS), and inner halo of M31. Fields at M31-centric projected distances of 23 kpc in the halo, 12 kpc in the halo, 22 kpc in the GSS, and 26 kpc in the outer disk are α-enhanced, with $\langle $ [α/Fe] $\rangle $ = 0.43, 0.50, 0.41, and 0.58, respectively. The 23 and 12 kpc halo fields are relatively metal-poor, with $\langle $ [Fe/H] $\rangle $ = -1.54 and -1.30, whereas the 22 kpc GSS and 26 kpc outer disk fields are relatively metal-rich with $\langle $ [Fe/H] $\rangle $ = -0.84 and -0.92, respectively. For fields with substructure, we separated the stellar populations into kinematically hot stellar halo components and kinematically cold components. We did not find any evidence of a radial [α/Fe] gradient along the high surface brightness core of the GSS between ∼17 and 22 kpc. However, we found tentative suggestions of a negative radial [α/Fe] gradient in the stellar halo, which may indicate that different progenitor(s) or formation mechanisms contributed to the build up of the inner versus outer halo. Additionally, the [α/Fe] distribution of the metal-rich ([Fe/H] &gt; -1.5), smooth inner stellar halo (rproj ≲ 26 kpc) is inconsistent with having formed from the disruption of a progenitor(s) similar to present-day M31 satellite galaxies. The 26 kpc outer disk is most likely associated with the extended disk of M31, where its high α-enhancement provides support for an episode of rapid star formation in M31's disk possibly induced by a major merger.

Keywords: Local Group, Galaxy stellar disks, Galaxy formation, Stellar abundances, Galaxy stellar halos, Andromeda Galaxy