adsabs/SciX_UAT_keywords huggingface dataset:
WawHelioGlow: A Model of the Heliospheric Backscatter Glow. I. Model Definition

The helioglow is the fluorescence of interstellar atoms inside the heliosphere, where they are excited by the solar EUV emission. So far, the helioglow of interstellar H and He has been detected. The helioglow features a characteristic distribution in the sky, which can be used to derive the properties of both interstellar neutral (ISN) gas and the solar wind. This requires a simulation model capable of catching with sufficient realism the essential coupling relations between the solar and interstellar factors. The solar factors include the solar wind flux and its variation with time and heliolatitude, as well as the heliolatitude and time variation of the solar EUV output. The ISN gas inside the heliosphere features a complex distribution function, which varies with time and location. The paper presents the first version of a WawHelioGlow simulation model for the helioglow flux using an optically thin, single-scattering approximation. The helioglow computations are based on a sophisticated kinetic treatment of the distribution functions of interstellar H and He provided by the (n)WTPM model. The model takes into account the heliolatitudinal and spectral variations of the solar EUV output from observations. We present a formulation of the model and the treatment of the solar spectral flux. The accompanying Paper II illustrates details of the line-of-sight evolution of the elements of the model and a brief comparison of results of the WawHelioGlow code with selected sky maps of the hydrogen helioglow, obtained by the SWAN instrument on board the Solar and Heliospheric Observatory mission.

Keywords: heliosphere; solar extreme ultraviolet emission; interstellar medium; solar wind; interstellar atomic gas; astronomical models; solar neighborhood; the sun
Statistical Significance of Mission Parameters on the Deflection Efficiency of Kinetic Impacts: Applications for the Next-generation Kinetic Impactor

Understanding how to deflect an incoming asteroid is of great importance and a focus of research undertaken internationally by the planetary defense community. Deflection of an asteroid by a kinetic impactor is one such mitigation method that has a high degree of technological maturity. In 2022, NASA's planetary defense mission, the Double Asteroid Redirection Test (DART), will provide the first full-scale technology demonstration of a kinetic impactor. However, the DART mission is just a single test of one kinetic impactor design, prompting the question: Is it possible to optimize the design of a kinetic impactor to make it the most efficient deflector that it can be? In this paper, we use high-fidelity hydrodynamic simulations to examine the effect of five mission parameters (impactor mass, impact velocity, impactor composition, impactor geometry, and target strength) on three observables related to deflection efficiency (crater morphology, ejecta distribution, and momentum transfer) resulting from kinetic impacts. We find that the most significant mission parameters for determining postimpact factors are the impact velocity, impactor mass, and target strength. The impactor geometry and impactor composition emerge as statistically nonsignificant. Overall, we find that the ogive impactor geometry results in the highest variance in predicting the momentum enhancement factor (β), and that generally, impactors with smaller volumes and flat leading edges (plates and rings) produce smaller craters and less ejecta mass compared to impactors with larger volumes and sharper leading edges (spheres, ogives, and cones).

Keywords: impact phenomena; planetary science
Simulating Hydrodynamics in Cosmology with CRK-HACC

We introduce CRK-HACC, an extension of the Hardware/Hybrid Accelerated Cosmology Code (HACC), to resolve gas hydrodynamics in large-scale structure formation simulations of the universe. The new framework couples the HACC gravitational N-body solver with a modern smoothed-particle hydrodynamics (SPH) approach called conservative reproducing kernel SPH (CRKSPH). CRKSPH utilizes smoothing functions that exactly interpolate linear fields while manifestly preserving conservation laws (momentum, mass, and energy). The CRKSPH method has been incorporated to accurately model baryonic effects in cosmology simulations-an important addition targeting the generation of precise synthetic sky predictions for upcoming observational surveys. CRK-HACC inherits the codesign strategies of the HACC solver and is built to run on modern GPU-accelerated supercomputers. In this work, we summarize the primary solver components and present a number of standard validation tests to demonstrate code accuracy, including idealized hydrodynamic and cosmological setups, as well as self-similarity measurements.

Keywords: computational methods; hydrodynamical simulations; large-scale structure of the universe; cosmology
The Coherent Magnetic Field of the Milky Way

We present a suite of models of the coherent magnetic field of the Galaxy based on new divergence-free parametric functions describing the global structure of the field. The model parameters are fit to the latest full-sky Faraday rotation measures (RMs) of extragalactic sources and polarized synchrotron intensity (PI) maps from the Wilkinson Microwave Anisotropy Probe and Planck. We employ multiple models for the density of thermal and cosmic-ray electrons in the Galaxy, needed to predict the sky maps of RMs and PI for a given Galactic magnetic field (GMF) model. The robustness of the inferred properties of the GMF is gauged by studying many combinations of parametric field models and electron density models. We determine the pitch angle of the local magnetic field (11° ± 1°), explore the evidence for a grand-design spiral coherent magnetic field (inconclusive), determine the strength of the toroidal and poloidal magnetic halo fields below and above the disk (magnitudes the same for both hemispheres within ≈10%), set constraints on the half-height of the cosmic-ray diffusion volume (≥2.9 kpc), investigate the compatibility of RM- and PI-derived magnetic field strengths (compatible under certain assumptions), and check if the toroidal halo field could be created by the shear of the poloidal halo field due to the differential rotation of the Galaxy (possibly). A set of eight models is identified to help quantify the present uncertainties in the coherent GMF spanning different functional forms, data products, and auxiliary input. We present the corresponding sky maps of rates for axion–photon conversion in the Galaxy and deflections of ultrahigh-energy cosmic rays.

Keywords: milky way magnetic fields; galaxy magnetic fields; milky way galaxy physics; cosmic rays; cosmic ray astronomy
Machine Learning-based Prediction of Sunspots using Fourier Transform Analysis of the Time Series

The study of solar activity holds special importance since the changes in our star's behavior affect both the Earth's atmosphere and the conditions of the interplanetary environment. They can interfere with air navigation, space flight, satellites, radar, high-frequency communications, and overhead power lines, and can even negatively influence human health. We present here a machine learning-based prediction of the evolution of the current sunspot cycle (solar cycle 25). First, we analyze the Fourier Transform of the total time series (from 1749 to 2022) to find periodicities with which to lag this series and then add attributes (predictors) to the forecasting models to obtain the most accurate result possible. Consequently, we build a trained model of the series considering different starting points (from 1749 to 1940, with 1 yr steps), applying Random Forests, Support Vector Machines, Gaussian Processes, and Linear Regression. We find that the model with the lowest error in the test phase (cycle 24) arises with Random Forest and with 1915 as the start year of the time series (yielding a Root Mean Squared Error of 9.59 sunspots). Finally, for cycle 25 this model predicts that the maximum number of sunspots (90) will occur in 2025 March.

Keywords: sunspots; solar activity; time series analysis; random forests; linear regression; gaussian processes regression; support vector machine
Void Probability Function of Simulated Surveys of High-redshift Lyα Emitters

We calculate the void probability function (VPF) in simulations of Lyα emitters (LAEs) across a wide redshift range (z = 3.1, 4.5, 5.7, 6.6). The VPF measures the zero-point correlation function (i.e., places devoid of galaxies) and naturally connects to higher-order correlation functions while being computationally simple to calculate. We explore the Poissonian and systematic errors on the VPF, specify its accuracy as a function of average source density and the volume probed, and provide the appropriate size scales to measure the VPF. At small radii, the accuracy of the VPF is limited by galaxy density, while at large radii, the VPF is limited by the number of independent volumes probed. We also offer guidelines for understanding and quantifying the error in the VPF. We approximate the error in the VPF by using independent subvolumes of the catalogs, after finding that jackknife statistics underestimate the uncertainty. We use the VPF to probe the strength of higher-order correlation functions by measuring and examining the hierarchical scaling between the correlation functions using the count-in-cells method. The negative binomial model (NBM) has been shown to best describe the scaling between the two-point correlation function and the VPF for low-redshift galaxy observations. We further test the fit of the NBM by directly deriving the volume-averaged two-point correlation function from the VPF and vice versa. We find the NBM best describes the $z=3.1,4.5,5.7$ simulated LAEs, with a 1σ deviation from the model in the z = 6.6 catalog. This suggests that LAEs show higher-order clustering terms similar to those of normal low-redshift galaxies.

Keywords: large-scale structure of the universe; astronomical simulations; high-redshift galaxies
Identifying Galaxy Mergers in Simulated CEERS NIRCam Images Using Random Forests

Identifying merging galaxies is an important-but difficult-step in galaxy evolution studies. We present random forest (RF) classifications of galaxy mergers from simulated JWST images based on various standard morphological parameters. We describe (a) constructing the simulated images from IllustrisTNG and the Santa Cruz SAM and modifying them to mimic future CEERS observations and nearly noiseless observations, (b) measuring morphological parameters from these images, and (c) constructing and training the RFs using the merger history information for the simulated galaxies available from IllustrisTNG. The RFs correctly classify ~60% of non-merging and merging galaxies across 0.5 < z < 4.0. Rest-frame asymmetry parameters appear more important for lower-redshift merger classifications, while rest-frame bulge and clump parameters appear more important for higher-redshift classifications. Adjusting the classification probability threshold does not improve the performance of the forests. Finally, the shape and slope of the resulting merger fraction and merger rate derived from the RF classifications match with theoretical Illustris predictions but are underestimated by a factor of ~0.5.

Keywords: random forests; galaxy mergers; astronomical simulations; james webb space telescope
Unraveling the Observational Signatures of Cloud-Cloud Collision and Hub-filament Systems in W31

To understand the formation process of massive stars, we present a multiscale and multiwavelength study of the W31 complex hosting two extended H II regions (i.e., G10.30-0.15 (hereafter, W31-N) and G10.15-0.34 (hereafter, W31-S)) powered by a cluster of O-type stars. Several Class I protostars and a total of 49 ATLASGAL 870 μm dust clumps (at d = 3.55 kpc) are found toward the H II regions where some of the clumps are associated with the molecular outflow activity. These results confirm the existence of a single physical system hosting the early phases of star formation. The Herschel 250 μm continuum map shows the presence of a hub-filament system (HFS) toward both W31-N and W31-S. The central hubs harbor H II regions and they are depicted with extended structures (with T d ~ 25-32 K) in the Herschel temperature map. In the direction of W31-S, an analysis of the NANTEN2 12CO(J = 1-0) and SEDIGISM 13CO(J = 2-1) line data supports the presence of two cloud components around 8 and 16 km s-1, and their connection in velocity space. A spatial complementary distribution between the two cloud components is also investigated toward W31-S, where the signposts of star formation, including massive O-type stars, are concentrated. These findings favor the applicability of cloud-cloud collision (CCC) around ~2 Myr ago in W31-S. Overall, our observational findings support the theoretical scenario of CCC in W31, which explains the formation of massive stars and the existence of HFSs.

Keywords: star formation; star forming regions; h ii regions; interstellar medium; molecular clouds; dust continuum emission; interstellar emissions; pre-main sequence stars; young stellar objects
Origin of Nitrogen Isotopic Variations in the Rocky Bodies of the Solar System

Noncarbonaceous (NC; inner solar system) meteorites have lower 15N/14N ratios than carbonaceous (CC; outer solar system) meteorites. Whether this is evidence of a primordial heterogeneity of N reservoirs in the protosolar disk remains unclear. In this study, I consider the N isotopic compositions of meteorite (chondrite, achondrite, and iron meteorite) parent bodies as a function of their growth zones. Despite the 15N/14N ratios of CC meteorites being generally higher than NC meteorites, there is a substantial overlap between them. Late-stage mixing of isotopically distinct reservoirs cannot explain this overlap. 15N/14N ratios of meteorites, independent of the growth zones, are correlated with the accretion ages of their parent bodies. A common correlation of the 15N/14N ratios of NC and CC chondrites with their peak metamorphic temperatures suggests that N isotopic compositions of meteorites were likely set by a universal time-dependent process-thermal evolution of their parent bodies by radiogenic heating. Therefore, heterogeneous N isotopic compositions of meteorites do not allude to isotopically heterogeneous primitive N reservoirs in the protosolar disk. Rather, it is likely that the N isotopic compositions of meteorites are a direct reflection of a differential response of labile 15N-rich and refractory 15N-poor components in common organic precursors to variable degrees of parent body processing. Consequently, the isotopic ratios of N, and other highly volatile elements like C and H, in meteorites do not reflect the isotopic compositions of primitive volatile reservoirs in the protosolar disk and thus cannot be used independently to cosmolocate volatile reservoirs in the disk.

Keywords: meteorites; iron meteorites; chondrites; planetesimals; protoplanetary disks; planet formation
AGN STORM 2. IV. Swift X-Ray and Ultraviolet/Optical Monitoring of Mrk 817

The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, τ(λ), that increase with increasing wavelength roughly following τ(λ) ∝ λ 4/3, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve-the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum.

Keywords: active galactic nuclei; supermassive black holes; reverberation mapping; seyfert galaxies; accretion
The Potential of Asteroseismology to Resolve the Blue Supergiant Problem

Despite major progress in our understanding of massive stars, concerning discrepancies still remain between observations and theory. Most notable are the numerous stars observed beyond the theoretical main sequence, an evolutionary phase expected to be short lived and hence sparsely populated. This is the "Blue Supergiant Problem." Stellar models with abnormal internal structures can provide long-lived solutions for this problem: core hydrogen-burning stars with oversized cores may explain the hotter ones, and core helium-burning stars with undersized cores may explain the cooler ones. Such stars may result from enhanced or suppressed mixing in single stars or, more likely, as the products of binary interaction and stellar mergers. Here we investigate the potential of asteroseismology to uncover the nature of blue supergiants. We construct stellar models for the above scenarios and show that they predict g-mode period spacings that differ by an order of magnitude: ∼200 min versus ∼20 min for long-lived core H and He burning stars, respectively. For the classical scenario of H-shell-burning stars rapidly crossing the HG, we furthermore predict changes of the order of 10‑2 μHz yr‑1 in high-frequency modes; this effect would be in principle observable from ∼5 yr of asteroseismic monitoring if these modes can be identified. This raises the possibility of revealing the internal structure of blue supergiants and thus determining whether these stars are indeed binary merger products. These asteroseismic diagnostics may be measurable through long time-series observations from the ongoing TESS mission and upcoming PLATO mission, thereby laying a path toward resolving the blue supergiant problem.

Keywords: asteroseismology; stellar evolution; binary stars; massive stars; b supergiant stars
Tracing the Accretion Geometry of H1743-322 with Type C Quasiperiodic Oscillations in Multiple Outbursts

We present a systematic analysis of type C quasiperiodic oscillation (QPO) observations of H1743-322 throughout the Rossi X-ray Timing Explorer era. We find that, while different outbursts have significant flux differences, they show consistent positive correlations between the QPO fractional rms amplitude and nonthermal fraction of the emission, which indicate an independence of the intrinsic QPO rms on individual outburst brightnesses in H1743-322. However, the dependence of the QPO rms on frequency is different between the outburst rise and decay phases, where the QPO fractional rms of the decay phase is significantly lower than that of the rise phase at low frequencies. The spectral analysis also reveals different ranges of coronal temperature between the two outburst stages. A semiquantitative analysis shows that the Lense-Thirring precession model could be responsible for the QPO rms differences, requiring a variable coronal geometric shape. However, the variable-Comptonization model could also account for the findings. The fact that the rms differences and the hysteresis traces in the hardness-intensity diagram accompany each other indicates a connection between the two phenomena. By correlating the findings with QPO phase lags and the quasi-simultaneous radio flux previously published, we propose there could be corona-jet transitions in H1743-322 similar to those that have been recently reported in GRS 1915+105.

Keywords: accretion; black hole physics; x-ray binary stars; stellar mass black holes
The Relaxation of Reconnected Open Magnetic Field Lines in the Earth's Magnetosphere

Magnetic reconnection is a fundamental and important physical process that can release magnetic energy and change magnetic topology. A statistic study of reconnected magnetic field lines has been carried out by Cluster spacecraft 1 during 58 current sheet crossing events. We calculated the values of $| {B}_{n}/B| $ at different distances from reconnection site to describe the loosing process of magnetic field lines. Our results suggest that current sheets in ion diffusion regions have small values of $| {B}_{n}/B| $ . As the distance from reconnection site increases, the reconnected magnetic field lines relax, and subsequently have relatively large values of $| {B}_{n}/B| $ . However, such large values of $| {B}_{n}/B| $ are found to be closely related to open magnetic field lines that connect the Earth's magnetosphere and the solar wind.

Keywords: geomagnetic fields; earth (planet); solar-terrestrial interactions; solar wind; planetary magnetospheres
As a Matter of Tension: Kinetic Energy Spectra in MHD Turbulence

While magnetized turbulence is ubiquitous in many astrophysical and terrestrial systems, our understanding of even the simplest physical description of this phenomena, ideal magnetohydrodynamic (MHD) turbulence, remains substantially incomplete. In this work, we highlight the shortcomings of existing theoretical and phenomenological descriptions of MHD turbulence that focus on the joint (kinetic and magnetic) energy fluxes and spectra by demonstrating that treating these quantities separately enables fundamental insights into the dynamics of MHD turbulence. This is accomplished through the analysis of the scale-wise energy transfer over time within an implicit large eddy simulation of subsonic, super-Alfvénic MHD turbulence. Our key finding is that the kinetic energy spectrum develops a scaling of approximately k-4/3 in the stationary regime as magnetic tension mediates large-scale kinetic to magnetic energy conversion and significantly suppresses the kinetic energy cascade. This motivates a reevaluation of existing MHD turbulence theories with respect to a more differentiated modeling of the energy fluxes.

Keywords: magnetohydrodynamical simulations; magnetic fields; theoretical techniques; plasma astrophysics; magnetohydrodynamics
Faraday Dispersion Function of Disk Galaxies with Axisymmetric Global Magnetic Fields. I.

Faraday tomography is a novel method to probe the three-dimensional structure of magnetic fields of polarized radio sources. In this paper, we investigate the intrinsic Faraday dispersion function (FDF) of disk galaxies extending a simple analytic model of galactic magnetic fields developed in Ideguchi et al. The model consists of axisymmetric coherent fields and turbulent fields, and we consider the effects of inclination, the relative amplitude of coherent and turbulent magnetic fields, and the pitch angle of coherent fields. Our simple model makes it easy to obtain a physical interpretation of FDFs and helps us understand observational results. We find that FDFs generally have two peaks when galaxies are observed with nonzero inclination and the gap between the two peaks, their relative heights, and their widths are dependent on the model parameters. In particular, the gap is strongly dependent on the inclination angle and typically varies by a factor of two when we consider the inclination of 10°-60°, while the relative height varies by less than 20%. These findings provide us with the important lesson that the presence of two peaks in intrinsic FDFs does not necessarily imply the presence of two separate radio sources within a beam and they allow us to estimate the galactic parameters.

Keywords: galaxy magnetic fields; milky way magnetic fields; galaxy properties