adsabs/SciX_UAT_keywords huggingface dataset:
Two Rings and a Marginally Resolved, 5 au Disk around LkCa 15 Identified via Near-infrared Sparse Aperture Masking Interferometry

Sparse aperture masking interferometry (SAM) is a high-resolution observing technique that allows for imaging at and beyond a telescope's diffraction limit. The technique is ideal for searching for stellar companions at small separations from their host star; however, previous analyses of SAM observations of young stars surrounded by dusty disks have had difficulties disentangling planet and extended disk emission. We analyze VLT/SPHERE-IRDIS SAM observations of the transition disk LkCa 15, model the extended disk emission, probe for planets at small separations, and improve contrast limits for planets. We fit geometrical models directly to the interferometric observables and recover previously observed extended disk emission. We use dynamic nested sampling to estimate uncertainties on our model parameters and to calculate evidences to perform model comparison. We compare our extended disk emission models against point-source models to robustly conclude that the system is dominated by extended emission within 50 au. We report detections of two previously observed asymmetric rings at ~17 and ~45 au. The peak brightness location of each model ring is consistent with the previous observations. We also, for the first time with imaging, robustly recover an elliptical Gaussian inner disk, previously inferred via SED fitting. This inner disk has an FWHM of 5 au and a similar inclination and orientation to the outer rings. Finally, we recover no clear evidence for candidate planets. By modeling the extended disk emission, we are able to place a lower limit on the near-infrared companion contrast of at least 1000.

Keywords: protoplanetary disks; exoplanet detection methods; planet formation
Modeling of Transverse Oscillations Driven by p-modes in Short Coronal Loops

Recent observations have revealed two types of decayless transverse oscillations in short coronal loops: one with short periods scaling with loop lengths, and the other with longer periods that exhibit a peak at around 5 minutes in the period distribution. To understand such a difference in period, we work in the framework of ideal MHD and model a short coronal loop embedded in an atmosphere with density stratification from the chromosphere to the corona. An inclined p-mode-like driver with a period of 5 minutes is launched at one loop footpoint. It is discovered that two types of decayless transverse oscillations can be excited in the loop. We interpret the 5 minutes periodicity as being directly driven by the footpoint driver, while the others, with periods of several tens of seconds, are regarded as kink eigenmodes of different harmonics. Therefore, our simulation shows that both types of decayless oscillations found in observations can be excited by p-modes in one short coronal loop. This study extends our understanding of ubiquitous decayless transverse oscillations in the corona. Furthermore, it suggests that p-modes could be an important energy source for coronal heating by driving decayless transverse oscillations.

Keywords: magnetohydrodynamics; solar atmosphere; solar oscillations; solar coronal loops; solar coronal waves; magnetohydrodynamical simulations
Dynamics of Four Triple Systems

Orbital motions in four hierarchical stellar systems discovered by speckle interferometry are studied. Their inner orbits are relatively well constrained, while the long outer orbits are less certain. The eccentric and misaligned inner orbits in the early-type hierarchies ϵ Cha (B9V, central star of the 5 Myr old association, P = 6.4 yr, e = 0.73) and I 385 (A0V, P ~ 300 yr, e ~ 0.8) suggest past dynamical interactions. Their nearly equal masses could be explained by a dynamical decay of a 2+2 quadruple progenitor consisting of four similar stars. However, there is no evidence of the associated recoil, so similar masses could be just a consequence of accretion from the same core. The other two hiearchies, HIP 32475 (F0IV, inner period 12.2 yr) and HIP 42910 (K7V, inner period 6.8 yr), have smaller masses and are double twins where both inner and outer mass ratios are close to one. A double twin could either result from a merger of one inner pair in a 2+2 quadruple or can be formed by a successive fragmentation followed by accretion.

Keywords: multiple stars; binary stars
Bernstein-Greene-Kruskal Ion Modes in Dusty Space Plasmas Application in Saturn's Magnetosphere

Frequent observations of ion beams moving out from Saturn's plasma environment hints at the generation of ion Bernstein-Greene-Kruskal (BGK) modes. As the plasma environments of Saturn and its moon Enceladus are characterized by the ubiquitous presence of massive negatively charged dust particles, the existing BGK theory for electron-ion plasma models cannot address this scenario. This manuscript develops a theoretical model for studying ion BGK modes in dusty plasmas. The analysis reveals that the presence of dust in the plasma enhances the stability of BGK modes. As the dust density increases, the effect of other parameters on stability, such as the electron temperature, becomes negligible. The model is developed by assuming that electrons and ions follow a kappa distribution, featuring a long tail trend in the superthermal component, in agreement with observations. Different scenarios with either electrons or ions obeying a Maxwell or kappa distribution function have been considered. A thorough analysis of the trapped ion distribution function considering various combinations indicates that a plasma where electrons are in thermal equilibrium and ions follow kappa distribution is the least favorable system for the generation of BGK modes.

Keywords: saturn
The Substructures in the Anticenter Region of the Milky Way

We investigated the observational properties of Triangulum-Andromeda (TriAnd), Monoceros Ring (MRi), and Anti-Center Stream (ACS) in the anticenter region using K giants, M giants, and RGB stars from LAMOST and SDSS survey. The Friends of Friends algorithm was applied to select member stars of these structures. We found a new spur of TriAnd at l ~ 133° based on member stars selected in this work and compiled from the literature. The distributions of radial velocity and proper motion of its member stars indicate that TriAnd is gradually moving away from the Sun. The comparisons of [Fe/H] and [α/Fe] between TriAnd and thick-disk/halo stars reveal that TriAnd is likely to originate from the thick disk. MRi and ACS are adjacent in space with a boundary around latitude 30°, and there is no significant difference between the two structures in velocity, proper motions, and orbits. We suggested that MRi and ACS probably have a common origin. We made projections of the four structures in three-dimensional space for the exploration of the movements between the Sagittarius (Sgr) stellar stream and MRi, and found that a new spur was formed by the Sgr stream members in the velocity distribution as it passed through the MRi region.

Keywords: stellar streams; galaxy structure
Signatures of Cross-sectional Width Modulation in Solar Spicules due to Field-aligned Flows

We report the first observational detection of frequency modulation in the cross-sectional width of spicule structures due to field-aligned plasma flows. Cross-sectional width variations were estimated for the least superimposed off-limb spicules observed in high-resolution Hα imaging spectroscopy data. Analysis of estimated cross-sectional widths suggest periodic oscillations, concurrent with 2D numerical modeling for a jet structure in a stratified solar atmosphere. Spectral analysis for both observed and simulated cross-sectional widths indicate frequency modulation as noticeable shifts in estimated periodicities during rise and fall phases of field-aligned plasma flows in the jet structure. Furthermore, the presence of the first overtone in a dynamic/spicular waveguide is also evident in both the observed and the simulated jet structures. These harmonics can be an important tool for future chromospheric magnetoseismology investigations and applications to dynamic waveguides (like spicules).

Keywords: the sun; solar spicules; solar chromosphere
Flaring-associated Complex Dynamics in Two M Dwarfs Revealed by Fast, Time-resolved Spectroscopy

Habitability of an exoplanet is believed to be profoundly affected by activities of the host stars, although the related coronal mass ejections (CMEs) are still rarely detected in solar-like and late-type stars. We here report an observational study on the flares of two M dwarfs triggered by the high-cadence survey performed by the Ground-based Wide Angle Camera system. In both events, the fast, time-resolved spectroscopy enables us to identify symmetric broad Hα emission with not only a nearly zero bulk velocity, but also a large projected maximum velocity as high as ~700-800 km s-1. This broadening could be resulted from either the Stark (pressure) effect or a flaring-associated CME at the stellar limb. In the context of the CME scenario, the CME mass is estimated to be ~4 × 1018 and 2 × 1019 g. In addition, our spectral analysis reveals a temporal variation of the line center of the narrow Hα emission in both events. The variation amplitudes are at tens of kilometers per second, which could be ascribed to the chromospheric evaporation in one event, and to a binary scenario in the other one. With the total flaring energy determined from our photometric monitor, we show a reinforced trend in which the larger the flaring energy, the higher the CME mass is.

Keywords: stellar flares; optical flares; late-type dwarf stars; solar coronal mass ejections; time domain astronomy; spectroscopy
Broadband VLA Spectral-line Survey of a Sample of Ionized Jet Candidates

The study of the interaction between ionized jets, molecular outflows, and their environments is critical to understanding high-mass star formation, especially because jets and outflows are thought to be key in the transfer of angular momentum outward from accretion disks. We report a low spectral resolution Karl G. Jansky Very Large Array (VLA) survey for OH, NH3, CH3OH, and hydrogen radio recombination lines, toward a sample of 58 high-mass star-forming regions that contain numerous ionized jet candidates. The observations are from a survey designed to detect radio continuum; the novel aspect of this work is to search for spectral lines in broadband VLA data (we provide the script developed in this work to facilitate exploration of other data sets). We report detection of 25 GHz CH3OH transitions toward 10 sources; 5 of them also show NH3 emission. We found that most of the sources detected in CH3OH and NH3 have been classified as ionized jets or jet candidates and that the emission lines are coincident with, or very near (≲0.1 pc), these sources; hence, these molecular lines could be used as probes of the environment near the launching site of jets/outflows. No radio recombination lines were detected, but we found that the rms noise of stacked spectra decreases following the radiometer equation. Therefore, detecting radio recombination lines in a sample of brighter free-free continuum sources should be possible. This work demonstrates the potential of broadband VLA continuum observations as low resolution spectral-line scans.

Keywords: astrophysical masers; interstellar medium; interstellar emissions; interstellar molecules
Accelerating Polyhedral Discrete Element Method with CUDA

This paper presents an efficient CUDA-based implementation of a nonspherical discrete element method where irregular particles are described by using polyhedrons. Two strategies are employed to exploit the parallelism of the numerical method. One is to perform contact detection based on the contact pair level instead of the traditional particle level. The second is to reduce the computational burden of each kernel function by allocating thread blocks reasonably. Contact detection between potential contact pairs is the most complicated, time-consuming, and essential process for the polyhedral discrete element method. The linear bounding volume hierarchies are introduced to fix this issue. The hierarchies of the bounding volume tree are organized in a spatially coherent way. Such a structure can minimize branch divergence and is very suitable for parallel implementation with GPU. Two numerical examples are presented to show the performance of the code. It is found from the scenario of two sphere collision that improving the mesh resolution of polyhedral particles can reduce the computational error while slowing down the computational speed correspondingly. A trade-off must be made between accuracy and efficiency. The other example of self-gravitating aggregation demonstrates the code is convergent, stable, and highly efficient. Particularly, with a mainstream GPU, the proposed method easily performs hundreds of times faster than the serial CPU code that does the same function.

Keywords: astronomical simulations; n-body problem
Tracer Particles for Core-collapse Supernova Nucleosynthesis: The Advantages of Moving Backward

After decades, the theoretical study of core-collapse supernova explosions is moving from parameterized, spherically symmetric models to increasingly realistic multidimensional simulations. However, obtaining nucleosynthesis yields based on such multidimensional core-collapse supernova simulations is not straightforward. Frequently, tracer particles are employed. Tracer particles may be tracked in situ during the simulation, but often they are reconstructed in a post-processing step based on the information saved during the hydrodynamic simulation. Reconstruction can be done in a number of ways, and here we compare the approaches of backward and forward integration of the equations of motion to the results based on inline particle trajectories. We find that both methods agree reasonably well with the inline results for isotopes for which a large number of particles contribute. However, for rarer isotopes that are produced only by a small number of particle trajectories, deviations can be large. For our setup, we find that backward integration leads to better agreement with the inline particles by more accurately reproducing the conditions following freeze-out from nuclear statistical equilibrium, because the establishment of nuclear statistical equilibrium erases the need for detailed trajectories at earlier times. Based on our results, if inline tracers are unavailable, we recommend backward reconstruction to the point when nuclear statistical equilibrium was last applied, with an interval between simulation snapshots of at most 1 ms for nucleosynthesis post-processing.

Keywords: nuclear astrophysics; supernova dynamics; nucleosynthesis
Broad-line Region of the Quasar PG 2130+099 from a Two-year Reverberation Mapping Campaign with High Cadence

As one of the most interesting Seyfert 1 galaxies, PG 2130+099 has been the target of several reverberation mapping (RM) campaigns over the years. However, its measured broad Hβ line responses have been inconsistent, with time lags of ∼200 days, ∼25 days, and ∼10 days being reported for different epochs while its optical luminosity changed no more than 40%. To investigate this issue, we conducted a new RM-campaign with homogenous and high cadence (about ∼3 days) for two years during 2017-2019 to measure the kinematics and structure of the ionized gas. We successfully detected time lags of broad Hβ, He II, He I, and Fe II lines with respect to the varying 5100 Å continuum, revealing a stratified structure that is likely virialized with Keplerian kinematics in the first year of observations, but an inflow kinematics of the broad-line region from the second year. With a central black hole mass of ${0.97}_{-0.18}^{+0.15}\times {10}^{7}{M}_{\odot }$ , PG 2130+099 has an accretion rate of ${10}^{2.1\pm 0.5}{L}_{\mathrm{Edd}}{c}^{-2}$ , where LEdd is the Eddington luminosity and c is speed of light, implying that it is a super-Eddington accretor and likely possesses a slim, rather than thin, accretion disk. The fast changes of the ionization structures of the three broad lines remain puzzling.

Keywords: supermassive black holes; seyfert galaxies; active galactic nuclei; quasars; reverberation mapping; time domain astronomy
Electron-to-ion Bulk Speed Ratio as a Parameter Reflecting the Occurrence of Strong Electron-dominated Current Sheets in the Solar Wind

Current sheets (CSs) are preferred sites of magnetic reconnection and energy dissipation in astrophysical plasmas. Electric currents in them may be carried by both electrons and ions. In our prior theoretical studies of the CS formation in turbulent plasmas, we utilized fully kinetic and hybrid code simulations with ions considered as particles and electrons-as a massless fluid. We found that electron-dominated CSs in which electrons become the main carriers of the electric current and contributors to energy dissipation may form inside or nearby ion-dominated CSs. These structures represent a distinguished type of CSs and should not be mixed up with so-called electron-scale CSs. Current simulations show that such CSs are characterized by the electron-to-ion bulk speed ratio (u e /u i ) increases that can be seen at ion scales according to theoretical predictions and high-resolution observations from the Magnetospheric Multiscale mission. Therefore, applying the u e /u i parameter to the solar wind data may allow locating the strongest electron-dominated CSs with an ordinary spacecraft resolution of 1-3 s. This study shows that, indeed, electron-dominated CSs observed during a period of quiet solar wind conditions at 1 au impact the surrounding plasma, which may be reflected in sharp changes of u e /u i . Electron-dominated CSs are found to be localized in the vicinity of ion-dominated CSs identified via changes in the magnetic field and plasma parameters, displaying the same clustering. We conclude that u e /u i may be used as one of the key parameters for statistical studies of CSs in the solar wind and analyzing the role of electrons in them.

Keywords: heliosphere
A Model-insensitive Baryon Acoustic Oscillation Feature in the 21 cm Signal from Reionization

We examine the impact of baryon-dark matter relative velocities on intergalactic small-scale structure and the 21 cm signal during reionization. Streaming velocities reduced clumping in the intergalactic medium on mass scales of ∼104-108 M⊙. This effect produced a distinct baryon acoustic oscillation (BAO) feature in the 21 cm power spectrum at wavenumbers k ∼ 0.1 h/Mpc, near which forthcoming surveys will be most sensitive. In contrast to the highly uncertain impact of streaming velocities on star formation, the effect on clumping is better constrained because it is set mainly by cosmology and straightforward gas dynamics. We quantify the latter using coupled radiation-hydrodynamic simulations that capture the Jeans scale of pre-reionization gas. The clumping factor of ionized gas is reduced by 5%-10% in regions with rms streaming velocities. The suppression peaks ≈5 Myr after a region is reionized, but disappears within 200 Myr due to pressure smoothing. We model the corresponding impact on the 21 cm signal and find that the BAO feature is most likely to appear at ≈10% ionization. During this phase, the feature may appear at the 1% (5%) level at k ∼ 0.1 (0.06) h/Mpc with an amplitude that varies by a factor of <10 across a range of reionization histories. We also provide a model for the signal originating from streaming velocity's impact on ionizing sources, which can vary by 4 orders of magnitude depending on highly uncertain source properties. We find that the clumping signal probably dominates the source one unless Population III star formation in 106-108 M⊙ halos contributed significantly to the first 10% of reionization.

Keywords: reionization; observational cosmology; intergalactic medium
Constraints on the Alfvénicity of Switchbacks

Switchbacks (SBs) are localized structures in the solar wind containing deflections of the magnetic field direction relative to the background solar wind magnetic field. The amplitudes of the magnetic field deflection angles (θ) for different SBs vary from ~40° to ~160°-170°. Alignment of the perturbations of the magnetic field (Δ B ) and the bulk solar wind velocity (Δ V ) is observed inside SBs so that Δ V ~ Δ B when the background magnetic field is directed toward the Sun (if the background solar wind magnetic field direction is anti-sunward then Δ V ~ - Δ B , supporting anti-sunward propagation in the background solar wind frame). This causes spiky enhancements of the radial bulk velocity inside SBs. We have investigated the deviations of SB perturbations from Alfvénicity by evaluating the distribution of the parameter α, defined as the ratio of the parallel to Δ B component of Δ V to Δ V A = Δ B /4π n i m i inside SBs, i.e., α = V ∣∣/∣Δ V A∣ (α = ∣Δ V ∣/∣Δ V A∣ when Δ V ~ Δ B ), which quantifies the deviation of the perturbation from an Alfvénic one. Based on Parker Solar Probe (PSP) observations, we show that α inside SBs has systematically lower values than it has in the pristine solar wind: α inside SBs observed during PSP Encounter 1 were distributed in a range from ~0.2 to ~0.9. The upper limit on α is constrained by the requirement that the jump in velocity across the switchback boundary be less than the local Alfvén speed. This prevents the onset of shear flow instabilities. The consequence of this limitation is that the perturbation of the proton bulk velocity in SBs with θ > π/3 cannot reach α = 1 (the Alfvénicity condition) and the highest possible α for an SB with θ = π is 0.5. These results have consequences for the interpretation of switchbacks as large amplitude Alfvén waves.

Keywords: solar wind
Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z > 6.5 Universe

The Reionization Era Bright Emission Line Survey (REBELS) is a cycle-7 ALMA Large Program (LP) that is identifying and performing a first characterization of many of the most luminous star-forming galaxies known in the z > 6.5 universe. REBELS is providing this probe by systematically scanning 40 of the brightest UV-selected galaxies identified over a 7 deg2 area for bright [C II]158 μm and [O III]88 μm lines and dust-continuum emission. Selection of the 40 REBELS targets was done by combining our own and other photometric selections, each of which is subject to extensive vetting using three completely independent sets of photometry and template-fitting codes. Building on the observational strategy deployed in two pilot programs, we are increasing the number of massive interstellar medium (ISM) reservoirs known at z > 6.5 by ~4-5× to >30. In this manuscript, we motivate the observational strategy deployed in the REBELS program and present initial results. Based on the first-year observations, 18 highly significant ≥ 7σ [C II]158 μm lines have already been discovered, the bulk of which (13/18) also show ≥3.3σ dust-continuum emission. These newly discovered lines more than triple the number of bright ISM-cooling lines known in the z > 6.5 universe, such that the number of ALMA-derived redshifts at z > 6.5 rival Lyα discoveries. An analysis of the completeness of our search results versus star formation rate (SFR) suggests an ~79% efficiency in scanning for [C II]158 μm when the SFRUV+IR is >28 M ⊙ yr-1. These new LP results further demonstrate ALMA's efficiency as a "redshift machine," particularly in the Epoch of Reionization.

Keywords: high-redshift galaxies; dust continuum emission; far infrared astronomy; far infrared interferometry