adsabs/SciX_UAT_keywords huggingface dataset:
On Calculating Diffusion Coefficients Numerically in Synthetic Turbulence Using Particle Pushers

Numerical simulations of test particle transport in the presence of synthetic turbulence with known properties still provide the most reliable estimations of the diffusion coefficients of charged particles in turbulent space plasmas available. The development and implementation of such simulations, however, are far from straightforward. The present study provides a comprehensive treatment of the development and testing of such a simulation code, detailing the simulation of synthetic turbulence and diffusion coefficients, as well as various numerical tests to validate code output. Furthermore, a novel test for such codes is proposed, namely, the transport of charged particles in pure slab turbulence, which proves sensitive to numerical factors prior tests remain insensitive to.

Keywords: magnetic fields; computational methods; cosmic rays
Double-decker Pair of Flux Ropes Formed by Two Successive Tether-cutting Eruptions

Double-decker filaments and their eruptions have been widely observed in recent years, but their physical formation mechanism is still unclear. Using high spatiotemporal resolution, multi-wavelength observations taken by the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we show the formation of a double-decker pair of flux rope system by two successive tether-cutting eruptions in a bipolar active region. Due to the combined effect of photospheric shearing and convergence motions around the active region's polarity inversion line (PIL), the arms of two overlapping inverse-S-shaped short filaments reconnected at their intersection, which created a simultaneous upward-moving magnetic flux rope (MFR) and a downward-moving post-flare-loop (PFL) system striding the PIL. Meanwhile, four bright flare ribbons appeared at the footpoints of the newly formed MFR and the PFL. As the MFR rose, two elongated flare ribbons connected by a relatively larger PFL appeared on either side of the PIL. After a few minutes, another MFR formed in the same way at the same location and then erupted in the same direction as the first one. Detailed observational results suggest that the eruption of the first MFR might experienced a short pause before its successful eruption, while the second MFR was a failed eruption. This implies that the two newly formed MFRs might reach a new equilibrium at relatively higher heights for a while, which can be regarded as a transient double-decker flux rope system. The observations can well be explained by the tether-cutting model, and we propose that two successive confined tether-cutting eruptions can naturally produce a double-decker flux rope system, especially when the background coronal magnetic field has a saddle-like distribution of magnetic decay index profile in height.

Keywords: solar activity; solar flares; solar filaments; solar magnetic reconnection; solar filament eruptions
The First Ka-band (26.1–35 GHz) Blind Line Survey toward Orion KL

We conducted a Ka-band (26.1–35 GHz) line survey toward Orion KL using the TianMa 65 m Radio Telescope (TMRT). It is the first blind line survey in the Ka band and achieves a sensitivity at the mK level (1–3 mK at a spectral resolution of ∼1 km s‑1). In total, 592 Gaussian features are extracted. Among them, 257 radio recombination lines (RRLs) are identified. The maximum Δn of RRLs of H, He, and C are 20, 15, and 5, respectively. Through stacking, we have detected the β lines of ion RRLs (RRLs of C+ with the possible contribution of other ions like O+) for the first time, and a tentative signal of the γ lines of ion RRLs can also be seen on the stacked spectrum. Besides this, 318 other line features were assigned to 37 molecular species, and 10 of these species were not detected in the Q-band survey of TMRT. The vibrationally excited states of nine species were also detected. The emission of most species can be modeled under LTE. A number of transitions of E-CH3OH (J 2 ‑ J 1) display maser effects, which are confirmed by our modeling, and besides the bumping peak at J ∼ 6, there is another peak at J ∼ 13. Methylcyanoacetylene (CH3C3N) is detected in Orion KL for the first time. This work emphasizes that the Ka band, which was long ignored for spectral line surveys, is very useful for surveying RRLs and molecular lines simultaneously.

Keywords: single-dish antennas; millimeter astronomy; radio spectroscopy; star formation; young stellar objects; ob stars; molecular clouds; interstellar line emission; interstellar molecules; recombination
Active Galactic Nuclei and Host Galaxies in COSMOS-Web. I. NIRCam Images, Point-spread-function Models and Initial Results on X-Ray-selected Broad-line AGNs at 0.35 ≲ z ≲ 3.5

We present detailed and comprehensive data reduction and point-spread-function (PSF) model construction for all public JWST NIRCam imaging data from the COSMOS-Web treasury program (up to 2023 June, totaling 0.28 deg2). We show that the NIRCam PSF has significant short-timescale temporal variations and random spatial variations in all four filters (F115W, F150W, F277W, and F444W). Combining NIRCam with archival Hubble Space Telescope imaging, we perform multiwavelength active galactic nucleus (AGN)+host image decomposition to study the properties of 143 X-ray-selected (L bol = 1043.6–47.2 erg s‑1) broad-line AGNs at 0.35 ≲ z ≲ 3.5. Leveraging the superb resolution, wavelength coverage, and sensitivity of NIRCam, we successfully detect host stellar emission after decomposing the central AGN point source in 142 objects. ∼2/3 AGNs are in star-forming galaxies based on the UVJ diagram, suggesting that there is no instantaneous negative AGN feedback. X-ray-selected broad-line AGN hosts follow a similar stellar mass–size relation as inactive galaxies, albeit with slightly smaller galaxy sizes. We find that although major mergers are rare (∼7%–22%) among the sample, more subtle nonaxisymmetric features from stellar bars, spiral arms, and minor mergers are ubiquitous, highlighting the importance of secular processes and minor mergers in triggering AGN activity. For a subsample of 30 AGNs at 1 < z < 2.5 with black hole mass measurements from single epoch spectra, they follow a similar black hole mass-stellar mass relation as local inactive early-type galaxies but reside preferentially near the upper envelope of nearby AGNs. We caution that selection biases and the intrinsic differences of AGN populations at different redshifts may significantly affect their location on the black hole mass-stellar mass plane.

Keywords: agn host galaxies; active galactic nuclei; galaxy structure; supermassive black holes; galaxy evolution; sky surveys
Discovery of a Compact X-Ray Object with a 614 s Periodicity in the Direction of the Galactic Center

We report on analysis of X-ray, optical, and radio observations of the previously overlooked X-ray source 2CXO J174517.0-321356 located just 3.°2 away from the Galactic center. Timing analysis of X-ray observations of the source with XMM-Newton reveals periodic pulsations with periods of 1228 and 614 s, with the latter being tentatively considered fundamental. On the other hand, an observation of the object with NuSTAR reveals a hard thermal-bremsstrahlung spectrum. Inspection of the archival Very Large Telescope image reveals, however, no obvious optical counterpart down to R > 25 mag. Observations made with ATCA showed a possible faint radio counterpart with a positive spectral index (α > 0.51) between 1 and 3 GHz, but follow-up ATCA and Very Large Array observations at frequencies between 4.5-10 GHz and 3-22 GHz, respectively, could not detect it. Given the properties in these three bands, we argue that the most likely origin of the X-ray source is emission from a new intermediate polar close to the Galactic center. Alternatively, and less likely, it is an ultracompact X-ray binary, which is one of the most compact X-ray binaries.

Keywords: white dwarf stars; neutron stars; x-ray binary stars
The Galaxy Environment of Extremely Massive Quasars. I. An Overdensity of Hα Emitters at z = 1.47

We measure a strong excess in the galaxy number density around PG 1630+377, an extremely massive (MBH ≃ 109.7M⊙) quasar at z = 1.475, using near-infrared narrowband imaging. We identify 79 narrow H-band excess objects in a 525 arcmin2 area including the vicinity and surroundings of the quasar. These sources are likely Hα line emitting, star-forming galaxies at z ≈ 1.47. We detect a δ = 6.6 ± 2.7 overdensity of narrow H-band excess objects located at a projected distance ≈2.1 Mpc northeast of the quasar, which is the densest region in the target area. The overdensity is present in BzK color-selected galaxies, while a previously reported overdensity in the immediate vicinity of PG 1630+377 is not, and yet appears as a group-like structure. These megaparsec-scale environments are estimated to merge into a ≃1014.7M⊙ cluster at present. Our results support the view that extremely massive black holes form and grow in group-scale environments and later incorporate into a galaxy cluster.

Keywords: galaxy groups; protoclusters; supermassive black holes; quasars
The CARMA-NRO Orion Survey: Protostellar Outflows, Energetics, and Filamentary Alignment

We identify 45 protostellar outflows in CO maps of the Orion A giant molecular cloud from the Combined Array for Research in Millimeter-wave Astronomy-Nobeyama Radio Observatory Orion survey. Our sample includes 11 newly detected outflows. We measure the mass and energetics of the outflows, including material at low velocities, by correcting for cloud contributions. The total momentum and kinetic energy injection rates of outflows are comparable to the turbulent dissipation rate of the cloud. We also compare the outflow position angles to the orientation of C18O filaments. We find that the full sample of outflows is consistent with being randomly oriented with respect to the filaments. A subsample of the most reliable measurements shows a moderately perpendicular outflow-filament alignment that may reflect accretion of mass across filaments and onto the protostellar cores.

Keywords: star formation; giant molecular clouds; stellar feedback; protostars; interstellar medium; interstellar filaments
First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole

We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a "variability noise budget" in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse (u, v)-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of ~50 μas, consistent with the expected "shadow" of a 4 × 106 M ⊙ black hole in the Galactic center located at a distance of 8 kpc.

Keywords: aperture synthesis; black holes; galactic center; radio astronomy; very long baseline interferometry; high angular resolution
The Sun Remains Relatively Refractory Depleted: Elemental Abundances for 17,412 Gaia RVS Solar Analogs and 50 Planet Hosts

The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R = 11,200) using TheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R > 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies.

Keywords: stellar abundances; solar system formation; solar abundances
33 New Stellar Angular Diameters from the NPOI, and Nearly 180 NPOI Diameters as an Ensemble

We present new angular diameter measurements for 33 stars from the Navy Precision Optical Interferometer, reaching uncertainties on the limb-darkened diameter of 2% or less for 21 targets. We also determined the physical radius, bolometric flux, luminosity, and effective temperature for each star. Our sample is a mix of giant, subgiant, and dwarf stars, and span spectral classes from mid-A to to mid-K. We combined these 33 stars with samples from previous publications to analyze how the NPOI diameters compare to those obtained using other means, namely (V - K) color, the JMMC Stellar Diameters Catalog, and Gaia predictions.

Keywords: fundamental parameters of stars; high angular resolution; optical interferometry
Revisiting the Color-Color Selection: Submillimeter and AGN Properties of NUV-r-J Selected Quiescent Galaxies

We examine the robustness of the color-color selection of quiescent galaxies (QGs) against contamination of dusty star-forming galaxies using the latest submillimeter data. We selected 18,304 QG candidates out to z ∼ 3 using the commonly adopted NUV-r-J selection based on the high-quality multiwavelength COSMOS2015 catalog. Using extremely deep 450 and 850 μm catalogs from the latest JCMT SCUBA-2 Large Programs, S2COSMOS and STUDIES, as well as the Atacama Large Millimeter/submillimeter Array submillimeter, VLA 3 GHz, and Spitzer MIPS 24 μm catalogs, we identified luminous, dusty, star-forming galaxies among the QG candidates. We also conducted stacking analyses in the SCUBA-2 450 and 850 μm images to look for less-luminous dusty galaxies among the QG candidates. By cross matching to the 24 μm and 3 GHz data, we were able to identify a subgroup of "IR-radio-bright" QGs that possess strong 450 and 850 μm stacking signals. The potential contamination of these luminous and less-luminous dusty galaxies accounts for approximately 10% of the color-selected QG candidates. In addition, there exists a spatial correlation between the luminous star-forming galaxies and the QGs at a ≲60 kpc scale. Finally, we found a high QG fraction among radio active galactic nuclei (AGNs) at z < 1.5. Our data show a strong correlation between QGs and radio AGNs, which may suggest a connection between the quenching process and the radio-mode AGN feedback.

Keywords: galaxy formation; high-redshift galaxies; quenched galaxies; early-type galaxies; observational astronomy; active galactic nuclei; agn host galaxies; submillimeter astronomy; astrostatistics; galaxy evolution; galaxy quenching; extragalactic astronomy
X-Ray Intraday Variability of the TeV Blazar PKS 2155-304 with Suzaku during 2005-2014

We have examined 13 pointed observations of the TeV-emitting high synchrotron peak blazar PKS 2155-304, taken by the Suzaku satellite throughout its operational period. We found that the blazar showed large-amplitude intraday variabilities in the soft (0.8-1.5 keV) and the hard (1.5-8.0 keV) bands in the light curves. Spectral variability on intraday timescales is estimated using the hardness ratio. The blazar usually becomes harder when brighter and vice versa, following the typical behavior of high synchrotron peak blazars. The power spectral density analyses of 11 out of 13 light curves in the total energy (0.8-8.0 keV) are found to be dominated by red noise, with power-law spectral indices that span a large range, from -2.81 to -0.88. Discrete correlation function analyses of all the 13 light curves between the soft and the hard bands show that they are well correlated and peak at, or very close to, zero lag. This indicates that the emissions in soft and hard bands are probably cospatial and emitted from the same population of leptons. Considering fluxes versus variability timescales, we found no correlation on intraday timescales, implying that X-ray emission from PKS 2155-304 is not dominated by simple changes in the Doppler factor. We briefly discuss the most likely emission mechanisms responsible for the observed flux and spectral variabilities and place constraints on magnetic field strength and Lorentz factors of the electrons emitting the X-rays in the most likely scenario.

Keywords: blazars; timing variation methods; x-ray astronomy
The Galactic Center Lobe as an H II Region

The Galactic center lobe (GCL) is an object ∼1° across that is located north of the Galactic center. In the mid-infrared (MIR) the GCL appears as two 8.0 μm filaments between which there is strong 24 μm and radio continuum emission. Due to its morphology and location in the sky, previous authors have argued that the GCL is located in the Galactic center region, created by outflows from star formation or by activity of the central black hole Sagittarius A*. In an associated paper, low-frequency radio emission indicates that the GCL must instead lie foreground to the Galactic center. If the GCL is foreground to the Galactic center, it is likely to be a type of object common throughout the Galactic disk; we here investigate whether its properties are similar to those of Galactic H II regions. We find that the GCL's MIR morphology, MIR flux densities, dust temperatures, and radio recombination line properties as traced by the Green Bank Telescope Diffuse Ionized Gas Survey are consistent with those of known Galactic H II regions, although the derived electron temperature is low. We search for the ionizing source(s) of the possible H II region and identify a stellar cluster candidate (Camargo #1092/Ryu & Lee #532) and a cluster of young stellar objects (the SPICY cluster G359.3+0.3) whose members have Gaia parallaxes distances of 1.7 ± 0.4 kpc. Taken together, the results of our companion paper and those shown here suggest that the GCL has properties consistent with those of an H II region located ∼2 kpc from the Sun.

Keywords: h ii regions; interstellar line emission; interstellar medium; infrared photometry; galactic center
Unveiling the True Nature of Plasma Dynamics from the Reference Frame of a Superpenumbral Fibril

The magnetic geometry of the solar atmosphere, combined with projection effects, makes it difficult to accurately map the propagation of ubiquitous waves in fibrillar structures. These waves are of interest due to their ability to carry energy into the chromosphere and deposit it through damping and dissipation mechanisms. To this end, the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope was employed to capture high-resolution Hα spectral scans of a sunspot, with the transverse oscillations of a prominent superpenumbral fibril examined in depth. The oscillations are reprojected from the helioprojective Cartesian frame to a new frame of reference oriented along the average fibril axis through nonlinear force-free field extrapolations. The fibril was found to be carrying an elliptically polarized, propagating kink oscillation with a period of 430 s and a phase velocity of 69 ± 4 km s‑1. The oscillation is damped as it propagates away from the sunspot with a damping length of approximately 9.2 Mm, resulting in the energy flux decreasing at a rate on the order of 460 W m‑2/Mm. The Hα line width is examined and found to increase with distance from the sunspot, a potential sign of a temperature increase. Different linear and nonlinear mechanisms are investigated for the damping of the wave energy flux, but a first-order approximation of their combined effects is insufficient to recreate the observed damping length by a factor of at least 3. It is anticipated that the reprojection methodology demonstrated in this study will aid with future studies of transverse waves within fibrillar structures.

Keywords: solar fibrils; solar oscillations; solar chromosphere; solar atmosphere
Lyapunov and Clearing Timescales in Planetary Chaotic Zones

Debris disks in planetary systems are known to possess gaps "opened" by planets in their close-to-coorbital neighborhoods; the gaps are free from low-mass material such as planetesimals. We consider the escape process of the initially zero-eccentric particles from the gap zone in a scenario consisting of two basic consequent stages: (1) the particle orbit's eccentricity is inflated, while its specific energy is relatively constant, and (2) the particle orbit's semimajor axis is inflated, while its specific angular momentum is relatively constant. During the first stage, the chaotic transport (diffusion) proceeds along the "staircase" of (p + 1):p (with integer p ≫ 1) overlapping particle-planet resonances, and during the second stage, it proceeds along the p:1 particle-planet resonance staircase. A specialized two-dimensional area-preserving map (a "tokamap" version) is derived to describe the first stage, while a multiharmonic Kepler map theory is used to describe the second stage. We derive the μ (mass parameter) scaling for the clearing timescale in the planetary chaotic zone. At small μ, it turns out to be inverse-quadratic in μ. The μ scaling for the Lyapunov timescale inside the gap is also derived. The derived scalings are in qualitative agreement with available numerical-experimental data.

Keywords: orbital motion; orbital resonances; exoplanet systems; exoplanets; dynamical evolution; exoplanet dynamics; celestial mechanics; three-body problem