Sazuna/UAT_keywords huggingface dataset:
Detection and Timing of Gamma-Ray Pulsations from the 707 Hz Pulsar J0952-0607. The Low-Frequency Array radio telescope discovered the 707 Hz binary millisecond pulsar (MSP) J0952-0607 in a targeted radio pulsation search of an unidentified Fermi gamma-ray source. This source shows a weak energy flux of F  γ  = 2.6 × 10-12 erg cm-2 s-1 in the energy range between 100 MeV and 100 GeV. Here we report the detection of pulsed gamma-ray emission from PSR J0952-0607 in a very sensitive gamma-ray pulsation search. The pulsar’s rotational, binary, and astrometric properties are measured over 7 years of Fermi-Large Area Telescope data. For this we take into account the uncertainty on the shape of the gamma-ray pulse profile. We present an updated radio-timing solution now spanning more than 2 years and show results from optical modeling of the black-widow-type companion based on new multiband photometric data taken with HiPERCAM on the Gran Telescopio Canarias on La Palma and ULTRACAM on the New Technology Telescope at ESO La Silla (based on observations collected at the European Southern Observatory, Chile; programme 0101.D-0925, PI: Clark, C. J.). PSR J0952-0607 is now the fastest-spinning pulsar for which the intrinsic spin-down rate has been reliably constrained ({\dot{P}}int}≲ 4.6× {10}-21 {{s}} {{{s}}}-1). The inferred surface magnetic field strength of {B}surf}≲ 8.2× {10}7 {{G}} is among the 10 lowest of all known pulsars. This discovery is another example of an extremely fast spinning black-widow pulsar hiding within an unidentified Fermi gamma-ray source. In the future such systems might help to pin down the maximum spin frequency and the minimum surface magnetic field strength of MSPs.

Keywords: Gamma-ray sources, Millisecond pulsars
The Eruption of Outer Spine-like Loops Leading to a Double-stage Circular-ribbon Flare. Circular-ribbon flares occur in a confined magnetic structure, but can also be associated with coronal mass ejections (CMEs) when a filament embedded under the fan erupts. Here we study an M8.7 circular-ribbon flare (SOL2014-12-17T04:51), which is accompanied by a CME yet without a clear indication of filament eruption. Using a nonlinear force-free field model, we find that the outer spine-like loops form a magnetic flux rope (FR1) rooted at the edge of the fan, and that there is another flux rope (FR2) at the main magnetic polarity inversion line (PIL) under a fan-like flux rope FR3. We divide the event evolution into two stages by combining modeling results with EUV observations. The onset stage is featured with bidirectional jets that occurred between a filament and FR1, immediately followed by an upward motion of the latter. During this first stage, the inner/outer spine-related ribbons and the circular ribbon begin to brighten up. After about 10 minutes, another ejection stems from the main PIL region. In this second stage, all ribbons are significantly enhanced, and the twist of FR2 footpoints is decreased. We discuss these results in favor of a scenario where the initial reconnection between the filament and FR1 activates the latter to reconnect with FR3 with opposite twist. This produces larger scale erupting loops and consequently causes a weakening of FR3, which induces another eruption of FR2 from below. This event thus represents a new type of eruptive circular-ribbon flare caused by unstable outer spine-like loops.

Keywords: Solar activity, Solar flares, Solar magnetic fields
EVR-CB-001: An Evolving, Progenitor, White Dwarf Compact Binary Discovered with the Evryscope. We present EVR-CB-001, the discovery of a compact binary with an extremely low-mass (0.21 ± 0.05M ⊙) helium core white dwarf progenitor (pre-He WD) and an unseen low-mass (0.32 ± 0.06M ⊙) helium white dwarf (He WD) companion. He WDs are thought to evolve from the remnant helium-rich core of a main-sequence star stripped during the giant phase by a close companion. Low-mass He WDs are exotic objects (only about 0.2% of WDs are thought to be less than 0.3 M ⊙), and are expected to be found in compact binaries. Pre-He WDs are even rarer, and occupy the intermediate phase after the core is stripped, but before the star becomes a fully degenerate WD and with a larger radius (≈0.2R ⊙) than a typical WD. The primary component of EVR-CB-001 (the pre-He WD) was originally thought to be a hot subdwarf (sdB) star from its blue color and under-luminous magnitude, characteristic of sdBs. The mass, temperature (T eff = 18,500 ± 500 K), and surface gravity ({log}(g)=4.96+/- 0.04) solutions from this work are lower than values for typical hot subdwarfs. The primary is likely to be a post-red-giant branch, pre-He WD contracting into a He WD, and at a stage that places it nearest to sdBs on color-magnitude and T eff-log(g) diagrams. EVR-CB-001 is expected to evolve into a fully double degenerate, compact system that should spin down and potentially evolve into a single hot subdwarf star. Single hot subdwarfs are observed, but progenitor systems have been elusive.

Keywords: White dwarf stars, B subdwarf stars, Compact binary stars, Compact objects, Stellar remnants
Modeling Mg II During Solar Flares. I. Partial Frequency Redistribution, Opacity, and Coronal Irradiation. The Interface Region Imaging Spectrograph has routinely observed the flaring Mg II near-ultraviolet (NUV) spectrum, offering excellent diagnostic potential and a window into the location of energy deposition. A number of studies have forward-modeled both the general properties of these lines and specific flare observations. Generally these have forward-modeled radiation via post-processing of snapshots from hydrodynamic flare simulations through radiation transfer codes. There has, however, not been a study of how the physics included in these radiation transport codes affects the solution. A baseline setup for forward-modeling Mg II in flares is presented and contrasted with approaches that add or remove complexity. It is shown for Mg II that (1) partial frequency distribution (PRD) is still required during flare simulations despite the increased densities; (2) using full angle-dependent PRD affects the solution but takes significantly longer to process a snapshot; (3) including Mg I in non-LTE (NLTE) results in negligible differences to the Mg II lines but does affect the NUV quasi-continuum; (4) only hydrogen and Mg II need to be included in NLTE; (5) ideally the nonequilibrium hydrogen populations, with nonthermal collisional rates, should be used rather than the statistical equilibrium populations; (6) an atom consisting of only the ground state, h and k upper levels, and continuum level is insufficient to model the resonance lines; and (7) irradiation from a hot, dense flaring transition region can affect the formation of Mg II. We discuss modifications to the RH code allowing straightforward inclusion of the transition region and coronal irradiation in flares.

Keywords: Solar flares, Near ultraviolet astronomy, Solar flare spectra, Computational methods, Radiative transfer simulations, Solar chromosphere, Active solar chromosphere
Into the Darkness: Classical and Type II Cepheids in the Zona Galactica Incognita. The far side of the Milky Way’s disk is one of the most concealed parts of the known universe due to extremely high interstellar extinction and point-source density toward low Galactic latitudes. Large time-domain photometric surveys operating in the near-infrared hold great potential for the exploration of these vast uncharted areas of our Galaxy. We conducted a census of distant classical and type II Cepheids along the southern Galactic midplane using near-infrared photometry from the VISTA Variables in the Vía Láctea survey. We performed a machine-learned classification of the Cepheids based on their infrared light curves using a convolutional neural network. We have discovered 640 distant classical Cepheids with up to ∼40 mag of visual extinction and over 500 type II Cepheids, most of them located in the inner bulge. Intrinsic color indices of individual Cepheids were predicted from sparse photometric data using a neural network, allowing their use as accurate reddening tracers. They revealed a steep, spatially varying near-infrared extinction curve toward the inner bulge. Type II Cepheids in the Galactic bulge were also employed to measure robust mean selective-to-absolute extinction ratios. They trace a centrally concentrated spatial distribution of the old bulge population with a slight elongation, consistent with earlier results from RR Lyrae stars. Likewise, the classical Cepheids were utilized to trace the Galactic warp and various substructures of the Galactic disk and uncover significant vertical and radial age gradients of the thin disk population at the far side of the Milky Way.

Keywords: Surveys, Population II Cepheid variable stars, Galactic bulge, Milky Way disk, Delta Cepheid variable stars, Interstellar extinction, Catalogs
Inverse Compton Cascades in Pair-producing Gaps: Effects of Triplet Pair Production. Inverse Compton-pair cascades are initiated when gamma-rays are absorbed on an ambient soft photon field to produce relativistic pairs, which in turn up-scatter the same soft photons to produce more gamma-rays. If the Compton scatterings take place in the deep Klein-Nishina regime, then triplet pair production (e{γ }b\to {{ee}}+{e}-) becomes relevant and may even regulate the development of the cascade. We investigate the properties of pair-Compton cascades with triplet pair production in accelerating gaps, i.e., regions with an unscreened electric field. Using the method of transport equations for the particle evolution, we compute the growth rate of the pair cascade as a function of the accelerating electric field in the presence of blackbody and power-law ambient photon fields. Informed by the numerical results, we derive simple analytical expressions for the peak growth rate and the corresponding electric field. We show that for certain parameters, which can be realized in the vicinity of accreting supermassive black holes at the centers of active galactic nuclei, the pair cascade may well be regulated by inverse Compton scattering in the deep Klein-Nishina regime and triplet pair production. We present indicative examples of the escaping gamma-ray radiation from the gap, and discuss our results in application to the TeV observations of radio galaxy M87.

Keywords: Active galaxies, Non-thermal radiation sources
Sculpting Eccentric Debris Disks with Eccentric Gas Rings. Many debris disks seen in scattered light have shapes that imply their dust grains trace highly eccentric, apsidally aligned orbits. Apsidal alignment is surprising, especially for dust. Even when born from an apse-aligned ring of parent bodies, dust grains have their periastra dispersed in all directions by stellar radiation pressure. The periastra cannot be reoriented by planets within the short dust lifetimes at the bottom of the collisional cascade. We propose that what realigns dust orbits is drag exerted by second-generation gas. Gas is largely immune to radiation pressure, and when released by photodesorption or collisions within an eccentric ring of parent bodies should occupy a similarly eccentric, apse-aligned ring. Dust grains launched onto misaligned orbits cross the eccentric gas ring supersonically and can become dragged into alignment within collisional lifetimes. The resultant dust configurations, viewed nearly but not exactly edge-on, with periastra pointing away from the observer, appear moth-like, with kinked wings and even doubled pairs of wings, explaining otherwise mysterious features in HD 61005 (“The Moth”) and HD 32297, including their central bulbs when we account for strong forward scattering from irregularly shaped particles. Around these systems we predict gas at Kuiper-belt-like distances to move on highly elliptical streamlines that owe their elongation, ultimately, to highly eccentric planets. Unresolved issues and an alternative explanation for apsidal alignment are outlined.

Keywords: Exoplanet dynamics, Exoplanets, Exozodiacal dust, Circumstellar grains, Circumstellar disks, Debris disks, Circumstellar gas
Time-reversed Gamma-Ray Burst Light-curve Characteristics as Transitions between Subluminal and Superluminal Motion. We introduce a simple model to explain the time-reversed and stretched residuals in gamma-ray burst (GRB) pulse light curves. In this model an impactor wave in an expanding GRB jet accelerates from subluminal to superluminal velocities, or decelerates from superluminal to subluminal velocities. The impactor wave interacts with the surrounding medium to produce Cerenkov and/or other collisional radiation when traveling faster than the speed of light in this medium, and other mechanisms (such as thermalized Compton or synchrotron shock radiation) when traveling slower than the speed of light. These transitions create both a time-forward and a time-reversed set of light-curve features through the process of relativistic image doubling. The model can account for a variety of unexplained yet observed GRB pulse behaviors, including the amount of stretching observed in time-reversed GRB pulse residuals and the relationship between stretching factor and pulse asymmetry. The model is applicable to all GRB classes since similar pulse behaviors are observed in long/intermediate GRBs, short GRBs, and X-ray flares. The free model parameters are the impactor’s Lorentz factor when moving subluminally, its Lorentz factor when moving superluminally, and the speed of light in the impacted medium.

Keywords: Gamma-ray bursts, Relativistic jets, Astronomy data analysis, Non-thermal radiation sources, Time series analysis
The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations. Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk’s mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ∼7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet-disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules.

Keywords: Very Large Array, Millimeter astronomy, T Tauri stars, Dust continuum emission, Protoplanetary disks, Planet formation
The Analogous Structure of Accretion Flows in Supermassive and Stellar Mass Black Holes: New Insights from Faded Changing-look Quasars. Despite their factor of ∼108 difference in black hole mass, several lines of evidence suggest possible similarities between black hole accretion flows in active galactic nuclei (AGN) and Galactic X-ray binaries. However, it is still unclear whether the geometry of the disk-corona system in X-ray binaries directly scales up to AGN and whether this analogy still holds in different accretion states. We test this AGN/X-ray binary analogy by comparing the observed correlations between the UV-to-X-ray spectral index (α OX) and Eddington ratio in AGN to those predicted from observations of X-ray binary outbursts. This approach probes the geometry of their disk-corona systems as they transition between different accretion states. We use new Chandra X-ray and ground-based rest-UV observations of faded “changing-look” quasars to extend this comparison to lower Eddington ratios of &lt;10-2, where observations of X-ray binaries predict a softening of α OX in AGN. We find that the observed correlations between the α OX and Eddington ratio of AGN displays a remarkable similarity to accretion state transitions in prototypical X-ray binary outbursts, including an inversion of this correlation at a critical Eddington ratio of ∼10-2. Our results suggest that the structures of black hole accretion flows directly scale across a factor of ∼108 in black hole mass and across different accretion states, enabling us to apply theoretical models of X-ray binaries to explain AGN phenomenology.

Keywords: Supermassive black holes, X-ray binary stars, Active galactic nuclei, Quasars
Evidence for Inside-out Galaxy Growth and Quenching of a z ∼ 2 Compact Galaxy From High-resolution Molecular Gas Imaging. We present high spatial resolution imaging of the CO(1-0) line from the Karl G. Jansky Very Large Array of COSMOS 27289, a massive, compact star-forming galaxy (SFG) at z = 2.234. This galaxy was selected because of its structural similarity to z ∼ 2 passive galaxies. Our previous observations showed that it is very gas poor with respect to typical SFGs at these redshifts, consistent with a rapid transition to quiescence as the molecular gas is depleted. The new data show that both the molecular gas fraction, {f}{{{H}}2}\equiv {M}{{{H}}2}/{M}star}, and the molecular gas depletion time, {t}dep}\equiv {M}{{{H}}2}/SFR, are lower in the central 1-2 kpc of the galaxy and rise at larger radii ∼2-4 kpc. These observations are consistent with a scenario in which COSMOS 27289 will imminently cease star formation in the inner regions before the outskirts, i.e., inside-out quenching, the first time this phenomenon has been seen via observations of molecular gas in the high-redshift universe. We find good qualitative and quantitative agreement with a hydrodynamical simulation of galaxy quenching, in which the central suppression of molecular gas arises due to rapid gas consumption and outflows that evacuate the central regions of gas. Our results provide independent evidence for inside-out quenching of star formation as a plausible formation mechanism for z ∼ 2 quiescent galaxies.

Keywords: Molecular gas, Compact galaxies, Galaxy structure, Galaxy quenching, High-redshift galaxies
High-resolution Optical Spectroscopy of Stars in the Sylgr Stellar Stream. We observe two metal-poor main-sequence stars that are members of the recently discovered Sylgr stellar stream. We present radial velocities, stellar parameters, and abundances for 13 elements derived from high-resolution optical spectra collected using the Magellan Inamori Kyocera Echelle spectrograph. The two stars have identical compositions (within 0.13 dex or 1.2σ) among all elements detected. Both stars are very metal-poor ([Fe/H] = -2.92 ± 0.06). Neither star is highly enhanced in C ([C/Fe] &lt; +1.0). Both stars are enhanced in the α elements Mg, Si, and Ca ([α/Fe] = +0.32 ± 0.06), and the ratios among Na, Al, and all Fe-group elements are typical for other stars in the halo and ultra-faint and dwarf spheroidal galaxies at this metallicity. Sr is mildly enhanced ([Sr/Fe] = +0.22 ± 0.11), but Ba is not enhanced ([Ba/Fe] &lt; -0.4), indicating that these stars do not contain high levels of neutron-capture elements. The Li abundances match those found in metal-poor unevolved field stars and globular clusters (GCs) (log ɛ(Li) = 2.05 ± 0.07), which implies that environment is not a dominant factor in determining the Li content of metal-poor stars. The chemical compositions of these two stars cannot distinguish whether the progenitor of the Sylgr stream was a dwarf galaxy or a GC. If the progenitor was a dwarf galaxy, the stream may originate from a dense region such as a nuclear star cluster. If the progenitor was a GC, it would be the most metal-poor GC known. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Globular star clusters, Nucleosynthesis, Stellar abundances, Dwarf galaxies, Population II stars
Mutual Neutralization in Li<SUP>+</SUP>-D<SUP>-</SUP> Collisions: A Combined Experimental and Theoretical Study. We present a combined experimental and theoretical study of the mutual neutralization (MN) process in collisions of lithium ions (Li+) with deuterium anions (D-) at collision energies below 1 eV. We employ a merged-beam apparatus to determine total and state-to-state MN cross sections. We perform nuclear dynamics calculations using the multichannel Landau-Zener model based on accurate ab initio molecular data. We obtain an excellent agreement between the experimental and theoretical results over the energy range covered in this work. We show that the basis sets used in the ab initio calculations have a limited influence on the total cross section, but strongly impacts the results obtained for the partial cross sections or the reaction branching ratios. This demonstrates the important role of high-precision measurements to validate the theoretical approaches used to study gas-phase reactive processes. Finally, we compute MN rate coefficients for Li+ + H- and Li+ + D-, and discuss their significance for astrochemistry models.

Keywords: Early universe, Stellar abundances, Laboratory astrophysics, Reaction rates, Collision physics, Stellar atmospheres
Infrared Interferometric Three-dimensional Diagnosis of the Atmospheric Dynamics of the AGB Star R Dor with VLTI/AMBER. The mechanism of mass loss in late evolutionary stages of low- and intermediate-mass stars is not yet well understood. Therefore, it is crucial to study the dynamics of the region within a few R ⋆, where the wind acceleration is considered to take place. We present a three-dimensional diagnosis of the atmospheric dynamics of the closest asymptotic giant branch star R Dor from the low photospheric layers to the extended outer atmosphere, for the first time for a star other than the Sun. The images reconstructed with a spatial resolution of 6.8 mas—seven times finer than the star’s angular diameter of 51.2 mas in the continuum—using the AMBER instrument at the Very Large Telescope Interferometer show a large, bright region over the surface of the star and an extended atmosphere. The velocity-field maps over the star’s surface and atmosphere obtained from the Mg and H2O lines near 2.3 μm forming at atmospheric heights below ∼1.5 R ⋆ show little systematic motion beyond the measurement uncertainty of 1.7 km s-1. In marked contrast, the velocity-field map obtained from the CO first overtone lines reveals systematic outward motion at 7-15 km s-1 in the extended outer atmosphere at a height of ∼1.8 R ⋆. Given the detection of dust formation at ∼1.5 R ⋆, the strong acceleration of material between ∼1.5 and 1.8 R ⋆ may be caused by the radiation pressure on dust grains. However, we cannot yet exclude the possibility that the outward motion may be intermittent, caused by ballistic motion due to convection and/or pulsation. Based on AMBER observations made with the Very Large Telescope and Very Large Telescope Interferometer of the European Southern Observatory. Program ID: 092.D-0456(A), 092.D-0465(A/B).

Keywords: Optical interferometry, Starspots, Stellar mass loss, Asymptotic giant branch stars, Stellar atmospheres