adsabs/SciX_UAT_keywords huggingface dataset:
Magnetoacoustic Waves in a Magnetic Slab Embedded in an Asymmetric Magnetic Environment. II. Thin and Wide Slabs, Hot and Cold Plasmas

Wave propagation in magnetically structured atmospheres is a thoroughly studied, yet practically inexhaustible, well of investigations in the field of solar magneto-seismology. A simple but powerful example is the examination of wave behavior in a magnetic slab. Our previous study used an analytical approach to derive the general dispersion relation for magnetoacoustic waves in a magnetic slab of homogeneous plasma, which was enclosed in an asymmetric magnetic environment. In the present study, we focus on the analysis of wave propagation in various limiting cases applicable to solar and space plasma physics or astrophysics. The thin- and wide-slab approximations, as well as the limits of low and high plasma β values, are considered. Utilizing the fact that in a weakly asymmetric slab the dispersion relation can be decoupled, the behavior of quasi-sausage and quasi-kink modes is studied in further analytical and numerical detail, and their avoided crossings are described. The results highlight how asymmetry influences the wave properties, e.g., the phase speed of eigenmodes, depending on the ratios of external to internal densities and magnetic fields on the two sides. Notably, the phase speeds of surface modes will converge to different values for the quasi-sausage and quasi-kink modes in the wide-slab limit, and cutoff frequencies are introduced with respect to both surface and body modes, in thin as well as wide slabs, beyond which the solutions become leaky. These obtained properties of MHD wave behavior could be measured with suitable high-resolution instruments in the future.

Keywords: solar atmosphere; solar prominences; solar filaments; magnetohydrodynamics; solar oscillations; solar coronal seismology; solar coronal waves; solar magnetic bright points; plasma astrophysics
A Readily Implemented Atmosphere Sustainability Constraint for Terrestrial Exoplanets Orbiting Magnetically Active Stars

With more than 4300 confirmed exoplanets and counting, the next milestone in exoplanet research is to determine which of these newly found worlds could harbor life. Coronal mass ejections (CMEs), spawned by magnetically active, superflare-triggering dwarf stars, pose a direct threat to the habitability of terrestrial exoplanets, as they can deprive them of their atmospheres. Here we develop a readily implementable atmosphere sustainability constraint for terrestrial exoplanets orbiting active dwarfs, relying on the magnetospheric compression caused by CME impacts. Our constraint focuses on an understanding of CMEs propagation in our own Sun-heliosphere system that, applied to a given exoplanet requires as key input the observed bolometric energy of flares emitted by its host star. Application of our constraint to six famous exoplanets, Kepler-438b, Proxima Centauri b, and Trappist-1d, -1e, -1f, and -1g, within or in the immediate proximity of their stellar host's habitable zones showed that only for Kepler-438b might atmospheric sustainability against stellar CMEs be likely. This seems to align with some recent studies that, however, may require far more demanding computational resources and observational inputs. Our physically intuitive constraint can be readily and en masse applied, as is or generalized, to large-scale exoplanet surveys to detect planets that warrant further scrutiny for atmospheres and, perhaps, possible biosignatures at higher priority by current and future instrumentation.

Keywords: exoplanets; habitable zone; solar flares; solar coronal mass ejections; stellar coronal mass ejections; stellar flares
A Unified Model for Bipolar Outflows from Young Stars: Apparent Magnetic Jet Acceleration

We explore a new, efficient mechanism that can power toroidally magnetized jets up to two to three times their original terminal velocity after they enter a self-similar phase of magnetic acceleration. Underneath the elongated outflow lobe formed by a magnetized bubble, a wide-angle free wind, through the interplay with its ambient toroid, is compressed and accelerated around its axial jet. The extremely magnetic bubble can inflate over its original size, depending on the initial Alfvén Mach number M A of the launched flow. The shape-independent slope ∂v r /∂r = 2/3t is a salient feature of the self-similarity in the acceleration phase. Peculiar kinematic signatures are observable in the PV diagrams and can combine with other morphological signatures as probes for density-collimated jets arising in toroidally dominated magnetized winds. The apparent second acceleration is powered by the decrease of the toroidal magnetic field but operates far beyond the scales of the primary magnetocentrifugal launch region and the free asymptotic terminal state. Rich implications may connect the jets arising from the youngest protostellar outflows such as HH 211 and HH 212 and similar systems with parsec-scale jets across the mass and evolutionary spectra.

Keywords: magnetohydrodynamical simulations; astronomical simulations; magnetohydrodynamics; star formation; stellar wind bubbles; stellar winds; jets; relativistic jets; radio jets; stellar jets; stellar-interstellar interactions
A Study in Frequency-dependent Effects on Precision Pulsar Timing Parameters with the Pulsar Signal Simulator

In this paper we introduce a new PYTHON package, the PULSAR SIGNAL SIMULATOR, or PSRSIGSIM, which is designed to simulate a pulsar signal from emission at the pulsar, through the interstellar medium, to observation by a radio telescope, and digitization in a standard data format. We use PSRSIGSIM to simulate observations of three millisecond pulsars, PSRs J1744-1134, B1855+09, and B1953+29, to explore the covariances between frequency-dependent parameters, such as variations in the dispersion measure (DM), pulse profile evolution with frequency, and pulse scatter broadening. We show that PSRSIGSIM can produce realistic simulated data and can accurately recover the parameters injected into the data. We also find that while there are covariances when fitting DM variations and frequency-dependent parameters, they have little effect on timing precision. Our simulations also show that time-variable scattering delays decrease the accuracy and increase the variability of the recovered DM and frequency-dependent parameters. Despite this, our simulations also show that the time-variable scattering delays have little impact on the rms of the timing residuals. This suggests that the variability seen in recovered DMs, when time-variable scattering delays are present, is due to a covariance between the two parameters, with the DM modeling out the additional scattering delays.

Keywords: millisecond pulsars; interstellar medium; open source software; gravitational waves; astronomical simulations
A Collision Mechanism for the Removal of Earth's Trojan Asteroids

Due to their strong resonances with their host planet, Trojan asteroids can remain in stable orbits for billions of years. As a result, they are powerful probes for constraining the dynamical and chemical history of the solar system. Although we have detected thousands of Jupiter Trojans and dozens of Neptune Trojans, there are currently no known long-term stable Earth Trojans (ETs). Dynamical simulations show that the parameter space for stable ETs is substantial, so their apparent absence poses a mystery. This work uses a large ensemble of N-body simulations to explore how the Trojan population dynamically responds if Earth suffers large collisions, such as those thought to have occurred to form the Moon and/or to have given Earth its late veneer. We show that such collisions can be highly disruptive to the primordial Trojan population, and could have eliminated it altogether. More specifically, if Earth acquired the final 1% of its mass through ${ \mathcal O }(10)$ collisions, then only ~1% of the previously bound Trojan population would remain.

Keywords: solar system; earth trojans; planetary science; trojan asteroids; near-earth objects
ABYSS. I. Targeting Strategy for the APOGEE and BOSS Young Star Survey in SDSS-V

The fifth iteration of the Sloan Digital Sky Survey is set to obtain optical and near-infrared spectra of ~5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE and BOSS Young Star Survey (ABYSS) will observe ~105 stars with ages <30 Myr that have been selected using a set of homogeneous selection functions that make use of different tracers of youth. The ABYSS targeting strategy we describe in this paper is aimed to provide the largest spectroscopic census of young stars to date. It consists of eight different types of selection criteria that take the position on the H-R diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of ~200,000 sources (of which a half are expected to be observed) provides representative coverage of the young Galaxy, including both nearby diffuse associations as well as more distant massive complexes, reaching toward the inner Galaxy and the Galactic center.

Keywords: spectroscopy; young stellar objects; pre-main sequence
Very Long Baseline Astrometry of PSR J1012+5307 and its Implications on Alternative Theories of Gravity

PSR J1012+5307, a millisecond pulsar in orbit with a helium white dwarf (WD), has been timed with high precision for about 25 yr. One of the main objectives of this long-term timing is to use the large asymmetry in gravitational binding energy between the neutron star and the WD to test gravitational theories. Such tests, however, will be eventually limited by the accuracy of the distance to the pulsar. Here, we present very long baseline interferometry (VLBI) astrometry results spanning approximately 2.5 yr for PSR J1012+5307, obtained with the Very Long Baseline Array as part of the $\mathrm{MSPSR}\pi $ project. These provide the first proper motion and absolute position for PSR J1012+5307 measured in a quasi-inertial reference frame. From the VLBI results, we measure a distance of ${0.83}_{-0.02}^{+0.06}$ kpc (all the estimates presented in the abstract are at 68% confidence) for PSR J1012+5307, which is the most precise obtained to date. Using the new distance, we improve the uncertainty of measurements of the unmodeled contributions to orbital period decay, which, combined with three other pulsars, places new constraints on the coupling constant for dipole gravitational radiation ${\kappa }_{D}=(-1.7\pm 1.7)\times {10}^{-4}$ and the fractional time derivative of Newton's gravitational constant $\dot{G}/G=-{1.8}_{-4.7}^{+5.6}\times {10}^{-13}\,{\mathrm{yr}}^{-1}$ in the local universe. As the uncertainties of the observed decays of orbital period for the four leading pulsar-WD systems become negligible in ≈10 yr, the uncertainties for $\dot{G}/G$ and κD will be improved to ≤1.5 × 10-13 yr-1 and ≤1.0 × 10-4, respectively, predominantly limited by the distance uncertainties.

Keywords: neutron stars; gravitation; parallax; galactic radio sources; astrometry; binary pulsars; pulsar timing method
Architectures of Compact Super-Earth Systems Shaped by Instabilities

Compact nonresonant systems of sub-Jovian planets are the most common outcome of the planet formation process. Despite exhibiting broad overall diversity, these planets also display dramatic signatures of intrasystem uniformity in their masses, radii, and orbital spacings. Although the details of their formation and early evolution are poorly known, sub-Jovian planets are expected to emerge from their natal nebulae as multiresonant chains, owing to planet-disk interactions. Within the context of this scenario, the architectures of observed exoplanet systems can be broadly replicated if resonances are disrupted through postnebular dynamical instabilities. Here, we generate an ad hoc sample of resonant chains and use a suite of N-body simulations to show that instabilities can not only reproduce the observed period ratio distribution, but that the resulting collisions also modify the mass uniformity in a way that is consistent with the data. Furthermore, we demonstrate that primordial mass uniformity, motivated by the sample of resonant chains coupled with dynamical sculpting, naturally generates uniformity in orbital period spacing similar to what is observed. Finally, we find that almost all collisions lead to perfect mergers, but some form of postinstability damping is likely needed to fully account for the present-day dynamically cold architectures of sub-Jovian exoplanets.

Keywords: exoplanet dynamics; exoplanet astronomy; orbital resonances; exoplanet formation
Dust Outburst Dynamics and Hazard Assessment for Close Spacecraft-Comet Encounters

Using the gas drag by sublimating cometary surface ices for the acceleration of dust particles and deceleration by the gravity field of the nucleus combined with basic laws of mechanics, the sizes, velocities, and number densities of escaping particles are calculated and evaluated with respect to the hazard assessment of comet-spacecraft flybys and encounters. We find good agreement between our analytical method and the more elaborate and precise DSMC calculations, but, being simpler, our method can more easily be used to explore a wide range of cometary conditions and can be more easily scaled to specific comets with different nucleus sizes, masses, and gravity potentials and various gas and dust production rates. Our analytical method is applied to outbursts expanding into a cone of ~60°, where the gas density falls off with height from the surface rather than radial distance from the center of a uniformly outgassing nucleus. In this scenario, larger dust particles can be ejected and attain ballistic trajectories, go into orbit, or escape from the nucleus, thus being potentially more hazardous to a spacecraft. Sample calculations are carried out for potential dust outbursts for the highly active Centaur/Comet 29P/Schwassmann-Wachmann 1 for various assumed active areas and dust particle size distributions. Particle velocity ranges for ballistic trajectories, orbiting particles, and particles escaping into the coma are presented. These calculations are used to estimate the coma particle number densities during outbursts to get an assessment of the hazards and required mitigation for a flyby or orbiting space mission.

Keywords: comae; space probes
The Intracluster Light and Its Link with the Dynamical State of the Host Group/Cluster: The Role of the Halo Concentration

We investigate the role of halo concentration in the formation of intracluster light (ICL) in galaxy groups and clusters, as predicted by a state-of-the-art semianalytic model of galaxy formation, coupled with a set of high-resolution dark-matter-only simulations. The analysis focuses on how the fraction of ICL correlates with halo mass, concentration, and fraction of early-type galaxies (ETGs) in a large sample of groups and clusters with $13.0\leqslant \mathrm{log}{M}_{\mathrm{halo}}\leqslant 15.0$ . The fraction of ICL follows a normal distribution, a consequence of the stochastic nature of the physical processes responsible for the formation of the diffuse light. The fractional budget of ICL depends on both halo mass (very weakly) until group scales, and concentration (remarkably). More interestingly, the ICL fraction is higher in more concentrated objects, a result of the stronger tidal forces acting in the innermost regions of the halos where the concentration is the quantity playing the most relevant role. Our model predictions do not show any dependence between the ICL and ETGs fractions, and so we instead suggest the concentration rather than the mass, as recently claimed, to be the main driver of the ICL formation. The diffuse light starts to form in groups via stellar stripping and mergers and later assembled in more-massive objects. However, the formation and assembly keep going on group/cluster scales at lower redshift through the same processes, mainly via stellar stripping in the vicinity of the central regions where tidal forces are stronger.

Keywords: galaxy formation
Investigations of Flaring Plasma Parameters during an M-class Flare Using the Differential Evolution Method and XSM/Chandrayaan-2 Observations

We employ the differential evolution (DE) method to analyze observations from the Solar X-Ray Monitor on board the Chandrayaan-2 spacecraft. DE belongs to the family of evolutionary algorithms that find solutions using mechanisms inspired by biological processes. This approach enables us to simultaneously calculate the distribution of the differential emission measure and elemental abundances through an iterative process. We establish a model for the emission sources of flaring plasma, incorporating temperature, emission measure, and abundances of eight elements: Mg, Al, Si, S, Ar, Ca, Fe, and Ni, for an M3.9 GOES-class solar flare that occurred on 2021 May 7 (SOL2021-05-07T19:04). Our analysis covers various phases of the flare, determining the evolution of temperature, emission measure, and elemental abundances. Additionally, utilizing data from the Spectrometer Telescope for Imaging X-rays on board the Solar Orbiter, we investigate the evolution of hard X-ray source morphology, source volume, electron density, and thermal behavior of the flaring plasma throughout the event. The results reveal notable variations in elemental abundances between photospheric and coronal values during different flare phases. This emphasizes the significance of elemental abundance information in comprehending X-ray emissions during solar flares.

Keywords: the sun; solar x-ray flares; solar abundances; solar corona
In Situ Measurement of Curvature of Magnetic Field in Turbulent Space Plasmas: A Statistical Study

Using in situ data, accumulated in the turbulent magnetosheath by the Magnetospheric Multiscale Mission, we report a statistical study of magnetic field curvature and discuss its role in the turbulent space plasmas. Consistent with previous simulation results, the probability distribution function of the curvature is shown to have distinct power-law tails for both high and low value limits. We find that the magnetic-field-line curvature is intermittently distributed in space. High curvature values reside near weak magnetic-field regions, while low curvature values are correlated with small magnitude of the force acting normal to the field lines. A simple statistical treatment provides an explanation for the observed curvature distribution. This novel statistical characterization of magnetic curvature in space plasma provides a starting point for assessing, in a turbulence context, the applicability and impact of particle energization processes, such as curvature drift, that rely on this fundamental quantity.

Keywords: space plasmas; plasma physics; magnetohydrodynamics
Analytic Approach to the Late Stages of Giant Planet Formation

This paper constructs an analytic description for the late stages of giant planet formation. During this phase of evolution, the planet gains the majority of its final mass through gas accretion at a rapid rate. This work determines the density and velocity fields for material falling onto the central planet and its circumplanetary disk, and finds the corresponding column density of this infalling envelope. We derive a steady-state solution for the surface density of the disk as a function of its viscosity (including the limiting case where no disk accretion occurs). Planetary magnetic fields truncate the inner edge of the disk and determine the boundary conditions for mass accretion onto the planet from both direct infall and from the disk. The properties of the forming planet and its circumplanetary disk are determined, including the luminosity contributions from infall onto the planet and disk surfaces, and from disk viscosity. The radiative signature of the planet formation process is explored using a quasi-spherical treatment of the emergent spectral energy distributions. The analytic solutions developed herein show how the protoplanet properties (envelope density distribution, velocity field, column density, disk surface density, luminosity, and radiative signatures) vary with input parameters (instantaneous mass, orbital location, accretion rate, and planetary magnetic field strength).

Keywords: planet formation; protoplanetary disks; planetary system formation; solar system formation
Secondary Proton Beam Instability in a Turbulent Solar Wind at 50 R ⊙

We investigate a secondary proton beam instability coexisting with the ambient solar wind turbulence at 50 R ☉. Three-dimensional hybrid numerical simulations (particle ions and a quasi-neutralizing electron fluid) are carried out with the plasma parameters in the observed range. In the turbulent background, the particle distribution function, in particular the slope of the "bump-on-tail" responsible for the instability, is time-dependent and inhomogeneous. The presence of the turbulence substantially reduces the growth rate and saturation level of the instability. We derive magnetic power spectra from the observational data and perform a statistical analysis to evaluate the average turbulence intensity at 50 R ☉. This information is used to link the observed frequency spectrum to the wavenumber spectrum in the simulations. We verify that Taylor's frozen-in hypothesis is valid for this purpose to a sufficient extent. To reproduce the typical magnetic power spectrum of the instability observed concurrently with the background turbulence, an artificial spacecraft probe is run through the simulation box. The thermal-ion instabilities are often seen as power elevations in the kinetic range of scales above an extrapolation of the turbulence spectrum from larger scales. We show that the elevated power in the simulations is much higher than the background level. Therefore, the turbulence at the average intensity does not obscure the secondary proton beam instability, as opposed to the solar wind at 1 au, in which the ambient turbulence typically obscures thermal-ion instabilities.

Keywords: space plasmas; interplanetary turbulence; solar wind
The Many-faceted Light Curves of Young Disk-bearing Stars in Taurus as Seen by K2

We present a comprehensive study of the variability properties of young disk-bearing stars in the Taurus star-forming region, paralleling our previous investigation in ρ Oph and Upper Sco. A sample of 99 confirmed Taurus association members is placed in the diagnostic Q - M plane of flux asymmetry (M) and (Q), which guides our assignment of variability classes. We find a similar proportion of flux-symmetric variables in Taurus, but more bursters and fewer dippers relative to Upper Sco. The regions also differ in that the amplitudes for periodic and sources are larger in Taurus relative to the more evolved Upper Sco star/disk systems. The relationship between photometric variability patterns at optical wavelengths, which arise in the inner disk and at the stellar surface, are assessed relative to available disk inclination measurements.

Keywords: young stellar objects; classical t tauri stars; pre-main sequence stars; stellar accretion; circumstellar disks; protoplanetary disks; variable stars; time domain astronomy
Spectrum and Morphology of the Very-high-energy Source HAWC J2019+368

The MGRO J2019+37 region is one of the brightest sources in the sky at TeV energies. It was detected in the second HAWC catalog as 2HWC J2019+367 and here we present a detailed study of this region using data from HAWC. This analysis resolves the region into two sources: HAWC J2019+368 and HAWC J2016+371. We associate HAWC J2016+371 with the evolved supernova remnant CTB 87, although its low significance in this analysis prevents a detailed study at this time. An investigation of the morphology (including possible energy-dependent morphology) and spectrum for HAWC J2019+368 is the focus of this work. We associate HAWC J2019+368 with PSR J2021+3651 and its X-ray pulsar wind nebula, the Dragonfly nebula. Modeling the spectrum measured by HAWC and Suzaku reveals a ∼7 kyr pulsar and nebula system producing the observed emission at X-ray and γ-ray energies.

Keywords: gamma-ray sources; pulsars