Sazuna/UAT_keywords huggingface dataset:
Discovery of a Fast Iron Low-ionization Outflow in the Early Evolution of the Nearby Tidal Disruption Event AT 2019qiz. We report the results of ultraviolet (UV) and optical photometric and spectroscopic analysis of the tidal disruption event (TDE) AT 2019qiz. Our follow-up observations started &lt;10 days after the source began to brighten in the optical and lasted for a period of six months. Our late-time host-dominated spectrum indicates that the host galaxy likely harbors a weak active galactic nucleus. The initial Hubble Space Telescope (HST) spectrum of AT 2019qiz exhibits an iron and low-ionization broad absorption line (FeLoBAL) system that is seen for the first time in a TDE. This spectrum also bears a striking resemblance to that of Gaia16apd, a superluminous supernova. Our observations provide insights into the outflow properties in TDEs and show evidence for a connection between TDEs and engine-powered supernovae at early phases, as originally suggested by Metzger &amp; Stone. In a time frame of 50 days, the UV spectra of AT 2019qiz started to resemble those of previous TDEs with only high-ionization broad absorption lines. The change in UV spectral signatures is accompanied by a decrease in the outflow velocity, which began at 15,000 km s-1 and decelerated to ~10,000 km s-1. A similar evolution in the H&amp;agr; emission-line width further supports the speculation that the broad Balmer emission lines are formed in TDE outflows. In addition, we detect narrow absorption features on top of the FeLoBAL signatures in the early HST UV spectrum of AT 2019qiz. The measured H I column density corresponds to a Lyman-limit system, whereas the metal absorption lines (such as N V, C IV, Fe II, and Mg II) are likely probing the circumnuclear gas and interstellar medium in the host galaxy.

Keywords: Black hole physics, Galaxy accretion disks, High energy astrophysics
The NANOGrav 12.5 Year Data Set: Monitoring Interstellar Scattering Delays. We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program. Dynamic spectra for the observing epochs of each pulsar were used to obtain estimates of scintillation timescales, scintillation bandwidths, and the corresponding scattering delays using a stretching algorithm to account for frequency-dependent scaling. We were able to measure scintillation bandwidths for 28 pulsars at 1500 MHz and 15 pulsars at 820 MHz. We examine scaling behavior for 17 pulsars and find power-law indices ranging from -0.7 to -3.6, though these may be biased shallow due to insufficient frequency resolution at lower frequencies. We were also able to measure scintillation timescales for six pulsars at 1500 MHz and seven pulsars at 820 MHz. There is fair agreement between our scattering delay measurements and electron-density model predictions for most pulsars. We derive interstellar scattering-based transverse velocities assuming isotropic scattering and a scattering screen halfway between the pulsar and Earth. We also estimate the location of the scattering screens assuming proper motion and interstellar scattering-derived transverse velocities are equal. We find no correlations between variations in scattering delay and either variations in dispersion measure or flux density. For most pulsars for which scattering delays are measurable, we find that time-of-arrival uncertainties for a given epoch are larger than our scattering delay measurements, indicating that variable scattering delays are currently subdominant in our overall noise budget but are important for achieving precisions of tens of nanoseconds or less.

Keywords: Millisecond pulsars, Astronomy data analysis, Gravitational waves, Interstellar medium, Interstellar scattering
A Metallicity Study of F, G, K, and M Dwarfs in the Coma Berenices Open Cluster from the APOGEE Survey. We present a study of metallicities in a sample of main-sequence stars with spectral types M, K, G, and F (Teff ~3200-6500K and log g ~ 4.3-5.0 dex) belonging to the solar neighborhood young open cluster Coma Berenices. Metallicities were determined using the high-resolution (R = λ/Δ λ ~ 22,500) NIR spectra (λ1.51-λ1.69 μm) of the Sloan Digital Sky Survey IV APOGEE survey. Membership to the cluster was confirmed using previous studies in the literature along with APOGEE radial velocities and Gaia DR2. An LTE analysis using plane-parallel MARCS model atmospheres and the APOGEE DR16 line list was adopted to compute synthetic spectra and derive atmospheric parameters (Teff and log g) for the M dwarfs and metallicities for the sample. The derived metallicities are near-solar and are homogeneous at the level of the expected uncertainties, in particular when considering stars from a given stellar class. The mean metallicity computed for the sample of G, K, and M dwarfs is ⟨[Fe/H]⟩ = +0.04 ± 0.02 dex; however, the metallicities of the F-type stars are slightly lower, by about 0.04 dex, when compared to cooler and less massive members. Models of atomic diffusion can explain this modest abundance dip for the F dwarfs, indicating that atomic diffusion operates in Coma Berenices stars. The [Fe/H] dip occurs in nearly the same effective temperature range as that found in previous analyses of the lithium and beryllium abundances in Coma Berenices.

Keywords: M dwarf stars, Stellar diffusion, Infrared astronomy, Open star clusters, Metallicity, Stellar associations
How Metals Are Transported Into and Out of a Galactic Disk: Dependence on Hydrodynamic Schemes in Numerical Simulations. Metallicity is a fundamental probe for understanding the baryon physics in a galaxy. Since metals are intricately associated with radiative cooling, star formation, and stellar feedback, reproducing the observed metal distribution through numerical experiments will provide a prominent way to examine our understanding of galactic baryon physics. In this study, we analyze the dependence of the galactic metal distribution on numerical schemes and quantify the differences in metal mixing among modern galaxy simulation codes (the mesh-based code ENZO and the particle-based codes GADGET-2 and GIZMO-PSPH). In particular, we examine different stellar feedback strengths and an explicit metal diffusion scheme in particle-based codes, as a way to alleviate the well-known discrepancy in metal transport between mesh-based and particle-based simulations. We demonstrate that a sufficient number of gas particles are needed in the gas halo to properly investigate the metal distribution therein. Including an explicit metal diffusion scheme does not significantly affect the metal distribution in the galactic disk but does change the amount of low-metallicity gas in a hot diffuse halo. We also find that the spatial distribution of metals depends strongly on how the stellar feedback is modeled. We demonstrate that the previously reported discrepancy in metals between mesh-based and particle-based simulations can be mitigated with our proposed prescription, enabling these simulations to be reliably utilized in the study of metals in galactic halos and the circumgalactic medium.

Keywords: Cosmology, Hydrodynamical simulations, Galaxy chemical evolution, Galaxy dynamics, Stellar winds, Galaxy evolution, Interstellar medium
Periodic Fast Radio Bursts from Luminous X-ray Binaries. The discovery of periodicity in the arrival times of the fast radio bursts (FRBs) poses a challenge to the oft-studied magnetar scenarios. However, models that postulate that FRBs result from magnetized shocks or magnetic reconnection in a relativistic outflow are not specific to magnetar engines; instead, they require only the impulsive injection of relativistic energy into a dense magnetized medium. Motivated thus, we outline a new scenario in which FRBs are powered by short-lived relativistic outflows ("flares") from accreting black holes or neutron stars, which propagate into the cavity of the pre-existing ("quiescent") jet. In order to reproduce FRB luminosities and rates, we are driven to consider binaries of stellar-mass compact objects undergoing super-Eddington mass transfer, similar to ultraluminous X-ray (ULX) sources. Indeed, the host galaxies of FRBs, and their spatial offsets within their hosts, show broad similarities with ULXs. Periodicity on timescales of days to years could be attributed to precession (e.g., Lens-Thirring) of the polar accretion funnel, along which the FRB emission is geometrically and relativistically beamed, which sweeps across the observer line of sight. Accounting for the most luminous FRBs via accretion power may require a population of binaries undergoing brief-lived phases of unstable (dynamical-timescale) mass transfer. This will lead to secular evolution in the properties of some repeating FRBs on timescales of months to years, followed by a transient optical/IR counterpart akin to a luminous red nova, or a more luminous accretion-powered optical/X-ray transient. We encourage targeted FRB searches of known ULX sources.

Keywords: X-ray binary stars, High energy astrophysics, Plasma astrophysics, Burst astrophysics, X-ray transient sources, Ultraluminous x-ray sources, Shocks, Radio transient sources
The Lightweaver Framework for Nonlocal Thermal Equilibrium Radiative Transfer in Python. Tools for computing detailed optically thick spectral line profiles out of local thermodynamic equilibrium have always been focused on speed, due to the large computational effort involved. With the Lightweaver framework, we have produced a more flexible, modular toolkit for building custom tools in a high-level language, Python, without sacrificing speed against the current state of the art. The goal of providing a more flexible method for constructing these complex simulations is to decrease the barrier to entry and allow more rapid exploration of the field. In this paper we present an overview of the theory of optically thick nonlocal thermodynamic equilibrium radiative transfer, the numerical methods implemented in Lightweaver including the problems of time-dependent populations and charge-conservation, as well as an overview of the components most users will interact with, to demonstrate their flexibility.

Keywords: Computational methods, Stellar physics, Solar physics, Radiative transfer, Radiative transfer simulations
Observations and Analysis of CH<SUP>+</SUP> Vibrational Emissions from the Young, Carbon-rich Planetary Nebula NGC 7027: A Textbook Example of Chemical Pumping. We discuss the detection of 14 rovibrational lines of CH+, obtained toward the planetary nebula NGC 7027 with the iSHELL spectrograph on NASA's Infrared Telescope Facility (IRTF) on Maunakea. Our observations in the 3.49-4.13 μm spectral region, obtained with a 0"375 slit width that provided a spectral resolving power λ/Δλ ~ 80,000, have resulted in the unequivocal detection of the R(0)-R(3) and P(1)-P(10) transitions within the v = 1-0 band of CH+. The R-branch transitions are anomalously weak relative to the P-branch transitions, a behavior that is explained accurately by rovibronic calculations of the transition dipole moment reported in a companion paper. Nine infrared transitions of H2 were also detected in these observations, comprising the S(8), S(9), S(13), and S(15) pure rotational lines; the v = 1-0 O(4)-O(7) lines; and the v = 2-1 O(5) line. We present a photodissociation model, constrained by the CH+ and H2 line fluxes that we measured, that includes a detailed treatment of the excitation of CH+ by inelastic collisions, optical pumping, and chemical ("formation") pumping. The latter process is found to dominate the excitation of the observed rovibrational lines of CH+, and the model is remarkably successful in explaining both the absolute and relative strengths of the CH+ and H2 lines.

Keywords: Interstellar molecules, Interstellar line emission, Molecular spectroscopy, Planetary nebulae, Near infrared astronomy
Anomalous Intensities in the Infrared Emission of CH<SUP>+</SUP> Explained by Quantum Nuclear Motion and Electric Dipole Calculations. The unusual infrared emission patterns of CH+, recently detected in the planetary nebula NGC 7027, are examined theoretically with high-accuracy rovibrational wavefunctions and ab initio dipole moment curves. The calculated transition dipole moments quantitatively reproduce the observed J-dependent intensity variation, which is ascribed to underlying centrifugal distortion-induced interference effects. We discuss the implications of this anomalous behavior for astrochemical modeling of CH+ production and excitation, and provide a simple expression to estimate the magnitude of this effect for other light diatomic molecules with small dipole derivatives.

Keywords: Transition probabilities, Molecular spectroscopy, Line intensities
A Search for Wandering Black Holes in the Milky Way with Gaia and DECaLS. We present a search for "hypercompact" star clusters in the Milky Way using a combination of Gaia and the Dark Energy Camera Legacy Survey (DECaLS). Such putative clusters, with sizes of ~1 pc and containing 500-5000 stars, are expected to remain bound to intermediate-mass black holes (MBH ≈ 103-105 M⊙) that may be accreted into the Milky Way halo within dwarf satellites. Using the semianalytic model SatGen, we find an expected ~100 wandering intermediate-mass black holes if every infalling satellite hosts a black hole. We do not find any such clusters in our search. Our upper limits rule out 100% occupancy but do not put stringent constraints on the occupation fraction. Of course, we need stronger constraints on the properties of the putative star clusters, including their assumed sizes and the fraction of stars that would be compact remnants.

Keywords: Intermediate-mass black holes, Milky Way stellar halo, Star clusters
Threads, Ribbons, and Rings in the Radio Galaxy IC 4296. The nearby elliptical galaxy IC 4296 has produced a large (510 kpc) low-luminosity radio source with typical FR I core/jet/lobe morphology. The unprecedented combination of brightness sensitivity, dynamic range, and angular resolution of a new 1.28 GHz MeerKAT continuum image reveals striking new morphological features, which we call threads, ribbons, and rings. The threads are faint narrow emission features originating where helical Kelvin-Helmholtz instabilities disrupt the main radio jets. The ribbons are smooth regions between the jets and the lobes, and they appear to be relics of jets powered by earlier activity that have since come into pressure equilibrium. Vortex rings in the outer portions of the lobes and their backflows indicate that the straight outer jets and ribbons are inclined by $i=60^\circ \pm 5^\circ $ from the line of sight, in agreement with photometric, geometric, and gas-dynamical estimates of inclination angles near the nucleus.

Keywords: Interstellar magnetic fields, Radio galaxies, Elliptical galaxies, Radio jets
A Self-similar Solution of Hot Accretion Flow: The Role of the Kinematic Viscosity Coefficient. We investigate the dependency of the inflow-wind structure of a hot accretion flow on the kinematic viscosity coefficient. In this regard, we propose a model for the kinematic viscosity coefficient to mimic the behavior of the magnetorotational instability that would be maximal at the rotation axis. Then, we compare our model with two other prescriptions from numerical simulations of the accretion flow. We solve two-dimensional hydrodynamic equations of hot accretion flows in the presence of thermal conduction. The self-similar approach is also adopted in the radial direction. We calculate the properties of the inflow and the wind such as velocity, density, and angular momentum for three models of the kinematic viscosity prescription. On inspection, we find that in our suggested model the wind is less efficient at extracting the angular momentum outward where the self-similar solutions are applied than it is in two other models. The solutions obtained in this paper might be applicable to hydrodynamical numerical simulations of hot accretion flows.

Keywords: Accretion, Low-luminosity active galactic nuclei, Hydrodynamics
Evidence Suggesting That 'Oumuamua Is the  30 Myr Old Product of a Molecular Cloud. The appearance of interstellar objects (ISOs) in the solar system-and specifically the arrival of 1I/'Oumuamua-points to a significant number density of free-floating bodies in the solar neighborhood. We review the details of 'Oumuamua's pre-encounter Galactic orbit, which intersected the solar system at very nearly its maximum vertical and radial excursion relative to the Galactic plane. These kinematic features are strongly emblematic of nearby young stellar associations. We obtain an a priori order-of-magnitude age estimate for 'Oumuamua by comparing its orbit to the orbits of 50,899 F-type stars drawn from Gaia DR2; a diffusion model then suggests a ~35 Myr dynamical age. We compare 'Oumuamua's orbit with the trajectories of individual nearby moving groups, confirming that its motion is fully consistent with membership in the Carina (CAR) moving group with an age of ~30 Myr. We conduct Monte Carlo simulations that trace the orbits of test particles ejected from the stars in the CAR association. The simulations indicate that in order to uniformly populate the ~106 pc3 volume occupied by CAR members with the inferred number density, n = 0.2 au-3, of ISOs implied by Pan-STARRS's detection of 'Oumuamua, the required ejection mass is M ~ 500 MJup per known star within the CAR association. This suggests that the Pan-STARRS observation is in significant tension with scenarios that posit 'Oumuamua's formation and ejection from a protostellar disk.

Keywords: Asteroids, Asteroid dynamics, Orbits, Molecular clouds, Interstellar objects, Comets, Milky Way Galaxy
Evidence for Radial Expansion at the Core of the Orion Complex with Gaia EDR3. We present a phase-space study of two stellar groups located at the core of the Orion Complex: Briceño-1 and Orion Belt Population-near (OBP-near). We identify the groups with the unsupervised clustering algorithm, Shared Nearest Neighbor (SNN), which previously identified 12 new stellar substructures in the Orion Complex. For each of the two groups, we derive the 3D space motions of individual stars using Gaia EDR3 proper motions supplemented by radial velocities from Gaia DR2, APOGEE-2, and GALAH DR3. We present evidence for radial expansion of the two groups from a common center. Unlike previous work, our study suggests that evidence of stellar group expansion is confined only to OBP-near and Briceño-1, whereas the rest of the groups in the complex show more complicated motions. Interestingly, the stars in the two groups lie at the center of a dust shell, as revealed via an extant 3D dust map. The exact mechanism that produces such coherent motions remains unclear, while the observed radial expansion and dust shell suggest that massive stellar feedback could have influenced the star formation history of these groups.

Keywords: Stellar ages, Stellar feedback, Star forming regions, Stellar dynamics, Stellar associations
Confirmation of a Second Propeller: A High-inclination Twin of AE Aquarii. For decades, AE Aquarii (AE Aqr) has been the only cataclysmic variable star known to contain a magnetic propeller: a persistent outflow whose expulsion from the binary is powered by the spin-down of the rapidly rotating, magnetized white dwarf. In 2020, LAMOST J024048.51+195226.9 (J0240) was identified as a candidate eclipsing AE Aqr object, and we present three epochs of time-series spectroscopy that strongly support this hypothesis. We show that, during the photometric flares noted by Thorstensen, the Balmer and He I emission lines reach velocities of ~3000 km s-1, well in excess of what is observed in normal cataclysmic variables. This is, however, consistent with the high-velocity emission seen in flares from AE Aqr. Additionally, we confirm beyond doubt that J0240 is a deeply eclipsing system. The flaring continuum, He I and much of the Balmer emission likely originate close to the WD because they disappear during the eclipse that is centered on inferior conjunction of the secondary star. The fraction of the Balmer emission remaining visible during eclipse is likely produced in the extended outflow. Most enticingly of all, this outflow produces a narrow P Cygni absorption component for nearly half of the orbit, and we demonstrate that this scenario closely matches the outflow kinematics predicted by Wynn et al. While an important piece of evidence for the magnetic-propeller hypothesis-a rapid WD spin period-remains elusive, our spectra provide compelling support for the existence of a propeller-driven outflow viewed nearly edge-on, enabling a new means of rigorously testing theories of the propeller phenomenon.

Keywords: White dwarf stars, Cataclysmic variable stars, Magnetic stars, DQ Herculis stars
Stars with Photometrically Young Gaia Luminosities Around the Solar System (SPYGLASS). I. Mapping Young Stellar Structures and Their Star Formation Histories. Young stellar associations hold a star formation record that can persist for millions of years, revealing the progression of star formation long after the dispersal of the natal cloud. To identify nearby young stellar populations that trace this progression, we have designed a comprehensive framework for the identification of young stars and use it to identify ~3 × 104 candidate young stars within a distance of 333 pc using Gaia DR2. Applying the HDBSCAN clustering algorithm to this sample, we identify 27 top-level groups, nearly half of which have little to no presence in previous literature. Ten of these groups have visible substructure, including notable young associations such as Orion, Perseus, Taurus, and Sco-Cen. We provide a complete subclustering analysis of all groups with substructure, using age estimates to reveal each region's star formation history. The patterns we reveal include an apparent star formation origin for Sco-Cen along a semicircular arc, as well as clear evidence for sequential star formation moving away from that arc with a propagation speed of ~4 km s-1 (~4 pc Myr-1). We also identify earlier bursts of star formation in Perseus and Taurus that predate current, kinematically identical active star-forming events, suggesting that the mechanisms that collect gas can spark multiple generations of star formation, punctuated by gas dispersal and cloud regrowth. The large spatial scales and long temporal scales on which we observe star formation offer a bridge between the processes within individual molecular clouds and the broad forces guiding star formation at galactic scales.

Keywords: Stellar ages, Young star clusters, OB associations, Young stellar objects, Pre-main sequence stars, Star formation, Stellar associations