adsabs/SciX_UAT_keywords huggingface dataset:
Wave Emission of Nonthermal Electron Beams Generated by Magnetic Reconnection

Magnetic reconnection in solar flares can efficiently generate nonthermal electron beams. The energetic electrons can, in turn, cause radio waves through microscopic plasma instabilities as they propagate through the ambient plasma along the magnetic field lines. We aim at investigating the wave emission caused by fast-moving electron beams with characteristic nonthermal electron velocity distribution functions (EVDFs) generated by kinetic magnetic reconnection: two-stream EVDFs along the separatrices and in the diffusion region, and perpendicular crescent-shaped EVDFs closer to the diffusion region. For this purpose, we utilized 2.5D fully kinetic Particle-In-Cell code simulations in this study. We found the following: (1) the two-stream EVDFs plus the background ions are unstable to electron/ion (streaming) instabilities, which cause ion-acoustic waves and Langmuir waves due to the net current. This can lead to multiple-harmonic plasma emission in the diffusion region and the separatrices of reconnection. (2) The perpendicular crescent-shaped EVDFs can cause multiple-harmonic electromagnetic electron cyclotron waves through the electron cyclotron maser instabilities in the diffusion region of reconnection. Our results are applicable to diagnose the plasma parameters, which are associated to magnetic reconnection in solar flares by means of radio wave observations.

Keywords: solar radio emission; solar electromagnetic emission; non-thermal radiation sources; astronomical radiation sources
Electron Density Dependence of Extreme Ultraviolet Line Intensity Ratios in Ar XIV

We report the electron density dependence of extreme ultraviolet line intensity ratios in Ar XIV studied using a well-defined electron beam ion trap plasma. The purpose of this study is to examine the potential of the Ar XIV lines in diagnosing the electron density of solar corona active regions with a temperature higher than 3 MK. The experimentally obtained dependence is in good agreement with collisional-radiative model calculations, which ensures the usability of the Ar XIV lines.

Keywords: atomic data benchmarking; solar extreme ultraviolet emission
Three-component Kinematics of Multiple Stellar Populations in Globular Clusters with Gaia and VLT

The internal dynamics of multiple stellar populations in globular clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity dispersion, could be related to the initial configuration of the system. In recent work, we provided the first study of the kinematics of different stellar populations in NGC 0104 over a large field of view in the plane of the sky, exploiting Gaia Data Release 2 (DR2) proper motions combined with multi-band ground-based photometry. In this paper, we combine Gaia DR2 proper motions with Very Large Telescope radial velocities to investigate the kinematics along the line of sight and in the plane of the sky of multiple populations in seven GCs, namely NGC 0104, NGC 0288, NGC 5904, NGC 6121, NGC 6254, NGC 6752, and NGC 6838. Among the analyzed clusters, only NGC 0104 and NGC 5904 show significant rotation. Separating our sample into two groups of first- and second-population stars (1P and 2P) we find that overall these two populations exhibit a similar rotation pattern in NGC 0104. However, some hints of different rotation are observed in the external regions of this cluster. Interestingly, 1P and 2P stars in NGC 5904 show different rotation curves, with distinct phases and such differences are significant at the ∼2.5σ level. The analysis of the velocity-dispersion profiles of multiple populations confirms that 2P stars of NGC 0104 show stronger anisotropy than the 1P.

Keywords: globular star clusters; stellar kinematics; proper motions; stellar populations
Computing Helioseismic Sensitivity Kernels for the Sun's Large-scale Internal Flows Using Global-scale Wave-propagation Simulations

Helioseismic waves observable at the solar surface can be used to probe the properties of the Sun's interior. By measuring helioseismic travel times between different location on the surface, flows and other interior properties can be inferred using so-called sensitivity kernels that relate the amount of travel-time shift with variations in interior properties. In particular, sensitivity kernels for flows have been developed in the past, using either ray or Born approximation, and have been used to infer solar interior flows such as the meridional circulation, which is of particular interest for understanding the structure and dynamics of the Sun. Here we introduce a new method for deriving three-dimensional sensitivity kernels for large-scale horizontal flows in the solar interior. We perform global-Sun wave-propagation simulations through 784 small flow perturbations placed individually in the interior of a simulated Sun, and measure the shifts in helioseismic travel times caused by these perturbations. Each measurement corresponds to a linear equation connecting the flow perturbation velocities and the sensitivity kernels. By solving the resulting large set of coupled linear equations, we derive three-dimensional sensitivity kernels for horizontal flows, which have a longitudinal component (parallel to the wave's travel direction) and a transverse component (perpendicular to the wave's travel direction). The kernels exhibit a "banana" shape, similar to kernels derived using Born-approximation methods, and show that transverse components are not negligible in inversions for interior flows.

Keywords: helioseismology; solar interior; solar oscillations; computational methods
Dynamical Modulation of Solar Flare Electron Acceleration due to Plasmoid-shock Interactions in the Looptop Region

A fast-mode shock can form in the front of reconnection outflows and has been suggested as a promising site for particle acceleration in solar flares. Recent developments in the study of magnetic reconnection have shown that numerous plasmoids can be produced in a large-scale current layer. Here we investigate the dynamical modulation of electron acceleration in the looptop region when plasmoids intermittently arrive at the shock by combining magnetohydrodynamics simulations with a particle kinetic model. As plasmoids interact with the shock, the looptop region exhibits various compressible structures that modulate the production of energetic electrons. The energetic electron population varies rapidly in both time and space. The number of 5-10 keV electrons correlates well with the compression area, while that of >50 keV electrons shows good correlation with the strong compression area but only moderate correlation with shock parameters. We further examine the impacts of the first plasmoid, which marks the transition from a quasi-steady shock front to a distorted and dynamical shock. The number of energetic electrons is reduced by ∼20% at 15-25 keV and nearly 40% for 25-50 keV, while the number of 5-10 keV electrons increases. In addition, the electron energy spectrum above 10 keV evolves softer with time. We also find that double or even multiple distinct sources can develop in the looptop region when the plasmoids move across the shock. Our simulations have strong implications to the interpretation of nonthermal looptop sources, as well as the commonly observed fast temporal variations in flare emissions, including the quasi-periodic pulsations.

Keywords: solar flares; non-thermal radiation sources; solar magnetic reconnection; solar particle emission; shocks
Wide Twin Binaries are Extremely Eccentric: Evidence of Twin Binary Formation in Circumbinary Disks

The Gaia mission recently revealed an excess population of equal-mass "twin" wide binaries, with mass ratio q ≳ 0.95, extending to separations of at least 1000 au. The origin of this population is an enigma: Twin binaries are thought to form via correlated accretion in circumbinary disks, but the typical observed protostellar disks have radii of ~100 au, far smaller than the separations of the widest twins. Here, we infer the eccentricity distribution of wide twins from the distribution of their v-r angles, i.e., the angle between the components' separation and relative velocity vectors. We find that wide twins must be on extremely eccentric orbits. For the excess-twin population at 400-1000 au, we infer a near-delta-function excess of high-eccentricity systems, with eccentricity 0.95 ≲ e ≤ 1. These high eccentricities for wide twins imply pericenter distances of order 10 au and suggest that their orbits were scattered via dynamical interactions in their birth environments, consistent with a scenario in which twins are born in circumbinary disks and subsequently widened. These results further establish twin wide binaries as a distinct population and imply that wide twins can be used as a probe of the dynamical history of stellar populations.

Keywords: binary stars; wide binary stars; eccentricity; circumstellar disks
Taking a Long Look: A Two-decade Reverberation Mapping Study of High-luminosity Quasars

Reverberation mapping (RM) of active galactic nuclei (AGNs) has been used over the past three decades to determine AGN broad-line region (BLR) sizes and central black hole masses, and their relations with the AGN luminosity. Until recently, the sample of objects with RM data was limited to low-luminosity AGNs (Lopt ≲ 1046 erg s-1) and low redshifts (z ≲ 0.5). Here we present results from an RM project of some of the most luminous and highest-redshift quasars that have been mapped to date. The study is based on almost 20 years of photometric monitoring of 11 quasars, 6 of which were monitored spectrophotometrically for 13 yr. This is the longest RM project carried out so far on this type of AGNs. We successfully measure a time lag between the C IV λ 1549 broad emission line and the quasar continuum in three objects, and measure a C III] λ 1909 lag in one quasar. Together with recently published data on C IV RM, the BLR size is found to scale as the square root of the UV luminosity over eight orders of magnitude in AGN luminosity. There is a significant scatter in the relation, part of which may be intrinsic to the AGNs. Although the C IV line is probably less well suited than Balmer lines for determination of the mass of the black hole, virial masses are tentatively computed, and in spite of a large scatter, we find that the mass of the black hole scales as the square root of the UV luminosity.

Keywords: active galactic nuclei; active galaxies; galaxy nuclei; high-luminosity active galactic nuclei; low-luminosity active galactic nuclei; quasars
Nonthermal Acceleration of Electrons, Positrons, and Protons at a Nonrelativistic Quasi-parallel Collisionless Shock

Energetic positrons have been observed in the interstellar medium, and high-energy positrons with relativistic energies up to approximately 1 TeV have been detected in Galactic cosmic rays. We conducted a study on the acceleration of particles, specifically positrons, in a nonrelativistic quasi-parallel collisionless shock induced by a plasma consisting of protons, electrons, and positrons. The positron-to-proton number density ratio in the plasma is 0.1. We focused on a representative shock with a sonic Mach number of 17.1 and an Alfvénic Mach number of 16.8 in the rest frame of the shock. To investigate the acceleration mechanisms of particles including positrons in the shock, we utilized 1D particle-in-cell simulations. It was found that all three species of particles in the shock can be accelerated and exhibit power-law spectra. At the shock front, a significant portion of incoming upstream particles are reflected and undergo significant energy increases, and these reflected particles can be efficiently injected into the process of diffusive shock acceleration (DSA). Moveover, the reflected positrons can be further accelerated by an electric field parallel to the magnetic field when they move along the magnetic field upstream of the shock. As a result, positrons can be preferentially accelerated to be injected in the DSA process compared to electrons.

Keywords: shocks; interplanetary particle acceleration
Strong Lens Models for 37 Clusters of Galaxies from the SDSS Giant Arcs Survey

We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging, with ground-based imaging and spectroscopy from Magellan, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 < z < 0.66 with a median redshift of z = 0.45, and sample a wide range of dynamical masses, 1.5 < M200 < 35 × 1014 M_{⊙}, as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 1"3 < θE < 23"1 for a source at z = 2, with a median θE = 10"8. The reduced HST images and lens model outputs are made available to the scientific community as high-level data products with this publication.

Keywords: galaxy clusters; strong gravitational lensing; gravitational lensing; dark matter; star forming regions; observational astronomy; high-redshift galaxies; spectroscopy
NICER, NuSTAR, and Insight-HXMT Views to Black Hole X-Ray Binary SLX 1746–331

We study the spectral and temporal properties of the black hole (BH) X-ray transient binary SLX 1746–331 during the 2023 outburst with NICER, NuSTAR, and Insight-HXMT observations. Through the joint fitting of the spectra from NICER, NuSTAR, and Insight-HXMT, the spin and inclination angles are measured for the first time as 0.85 ± 0.03 and 53° ± 0.°5, respectively. Accordingly, the mass of the compact star is updated from the previous lower limit of 3.3 ± 2.1M ⊙ to 5.5 ± 3.6M ⊙, which is consistent with 5.2 ± 4.5M ⊙ measured with an empirical mass–luminosity correlation of BH samples. With more NICER observations covering the later decay of the outburst, we confirm that the entire outburst was dominated by the disk emissions, and the thermal spectrum follows $F\propto {T}_{\mathrm{in}}^{3.974\pm 0.003}$ , until a luminosity of over 2 magnitudes lower than the maximum of the outburst.

Keywords: x-ray binary stars
Pre-supernova Alert System for Super-Kamiokande

In 2020, the Super-Kamiokande (SK) experiment moved to a new stage (SK-Gd) in which gadolinium (Gd) sulfate octahydrate was added to the water in the detector, enhancing the efficiency to detect thermal neutrons and consequently improving the sensitivity to low energy electron anti-neutrinos from inverse beta decay (IBD) interactions. SK-Gd has the potential to provide early alerts of incipient core-collapse supernovae through detection of electron anti-neutrinos from thermal and nuclear processes responsible for the cooling of massive stars before the gravitational collapse of their cores. These pre-supernova neutrinos emitted during the silicon burning phase can exceed the energy threshold for IBD reactions. We present the sensitivity of SK-Gd to pre-supernova stars and the techniques used for the development of a pre-supernova alarm based on the detection of these neutrinos in SK, as well as prospects for future SK-Gd phases with higher concentrations of Gd. For the current SK-Gd phase, high-confidence alerts for Betelgeuse could be issued up to 9 hr in advance of the core collapse itself.

Keywords: neutrino astronomy; supernova neutrinos; particle astrophysics; particle physics; silicon burning; core-collapse supernovae
GJ 367b Is a Dark, Hot, Airless Sub-Earth

We present the mid-infrared (5–12 μm) phase curve of GJ 367b observed by the Mid-Infrared Instrument on the James Webb Space Telescope (JWST). GJ 367b is a hot (T eq = 1370 K), extremely dense (10.2 ± 1.3 g cm‑3) sub-Earth orbiting an M dwarf on a 0.32 day orbit. We measure an eclipse depth of 79 ± 4 ppm, a nightside planet-to-star flux ratio of 4 ± 8 ppm, and a relative phase amplitude of 0.97 ± 0.10, all fully consistent with a zero-albedo planet with no heat recirculation. Such a scenario is also consistent with the phase offset of 11°E ± 5° to within 2.2σ. The emission spectrum is likewise consistent with a blackbody with no heat redistribution and a low albedo of A B ≈ 0.1, with the exception of one anomalous wavelength bin that we attribute to unexplained systematics. The emission spectrum puts few constraints on the surface composition but rules out a CO2 atmosphere ≳1 bar, an outgassed atmosphere ≳10 mbar (under heavily reducing conditions), or an outgassed atmosphere ≳0.01 mbar (under heavily oxidizing conditions). The lack of day–night heat recirculation implies that 1 bar atmospheres are ruled out for a wide range of compositions, while 0.1 bar atmospheres are consistent with the data. Taken together with the fact that most of the dayside should be molten, our JWST observations suggest that the planet must have lost the vast majority of its initial inventory of volatiles.

Keywords: exoplanet atmospheres; exoplanet surface composition; james webb space telescope; extrasolar rocky planets
Quasi-periodic Energy Release and Jets at the Base of Solar Coronal Plumes

Coronal plumes are long, ray-like, open structures that have been considered as possible sources of the solar wind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observations revealed blueshifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flows and/or propagating slow-mode waves, but these interpretations (flows versus waves) remain under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called plumelets, which account for most of the plume emission. Here we present high-resolution observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Interface Region Imaging Spectrograph that revealed numerous, quasi-periodic, tiny jets (so-called jetlets) associated with transient brightening, flows, and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at stressed 3D null points. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of ~3-5 minutes, which is remarkably consistent with the photospheric/chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. The jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of the switchbacks recently detected by the Parker Solar Probe.

Keywords: jets; solar magnetic reconnection; solar wind; solar coronal plumes
Regional Investigations of Polygonal Impact Craters on the Moon and Vesta

Studies suggest that fracture systems are the driving mechanism for the formation of polygonal impact craters (PICs) on planetary bodies including the Moon and Vesta. We used the Java Mission-planning and Analysis for Remote Sensing crater application to investigate PICs on regional scales for both the Moon and Vesta to further understand how surface and subsurface fracture systems play a role in PIC formation. We measured the number of straight rim segments (sides) for each PIC, measured the angle between each of the straight rim segments and calculated the mean angle for each crater and the mean angle for the body to conduct a further analysis with other planetary bodies. The comparison with other planetary bodies helps to identify how PIC formation may vary based on a body's surface composition. From this study, it appears that surface fractures are not the main driving mechanism for PIC formation within our study regions and instead subsurface fractures may be the more dominant factor.

Keywords: lunar craters; asteroid satellites; vesta; lunar impacts
Revealing the Interior Structure of Icy Moons with a Bayesian Approach to Magnetic Induction Measurements

Some icy moons and small bodies in the solar system are believed to host subsurface liquid water oceans. The interaction of these saline, electrically conductive oceans with time-varying external magnetic fields generates induced magnetic fields. Magnetometry observations of these induced fields in turn enable the detection and characterization of these oceans. We present a framework for characterizing the interiors of icy moons using multifrequency induction and Bayesian inference applied to magnetometry measurements anticipated from the upcoming Europa Clipper mission. Using simulated data from the Europa Clipper Magnetometer, our approach can accurately retrieve a wide range of plausible internal structures for Europa. In particular, the ocean conductivity is recovered to within ±50% for all internal structure scenarios considered, and the ocean thickness can be retrieved to within ±25 km for five out of seven scenarios. Characterization of the ice shell thickness to ±50% is possible for six of seven scenarios. Our recovery of the ice shell thickness is highly contingent on accurate modeling of magnetic fields arising from the interaction of Europa with the ambient magnetospheric plasma, while the ocean thickness is more modestly affected and the ocean conductivity retrieval is largely unchanged. Furthermore, we find that the addition of a priori constraints (e.g., static gravity measurements) can yield improved ocean characterization compared to magnetometry alone, suggesting that multi-instrument techniques can play a key role in revealing the interiors of Europa and other ocean worlds.

Keywords: europa; galilean satellites; magnetic fields; planetary interior; markov chain monte carlo
Influence of Neutrino-Nuclear Reactions on the Abundance of 74Se

The p-nuclei are supposed to be produced in different astrophysical processes, such as rapid-proton capture, photonuclear reaction, and neutrino-induced reaction. To date, their abundance cannot be reasonably explained. In the present work, the cross sections of the 74Ge (ν e , e -) 74As reaction are calculated with the theoretical and experimental B(GT) values, respectively. The abundance ratios between 74Se and 74Ge produced from the neutrino process (ν-process) are estimated based on the simple hypothesis for core-collapse supernova explosions. The results show that the upper limit of the 74Se and 74Ge abundance ratio resulting from the ν-process is about 36% of the value in the solar system.

Keywords: core-collapse supernovae; explosive nucleosynthesis; supernova neutrinos; p-process