adsabs/SciX_UAT_keywords huggingface dataset:
CME Arrival Modeling with Machine Learning

Space weather phenomena have long captured the attention of the scientific community, and along with recent technological developments, the awareness that such phenomena can interfere with human activities on Earth has grown considerably. Coronal mass ejections (CMEs) are among the main drivers of space weather. Therefore, developing tools to provide information on their arrival at Earth's nearby space has become increasingly important. Liu et al. developed a tool, called CME Arrival Time Prediction Using Machine Learning Algorithms (CAT-PUMA), to obtain fast and accurate predictions of CME transit time. This present work aims at the expansion of the CAT-PUMA concept, employing supervised learning to obtain vital information about the arrival of CMEs at Earth. In this study, we report the results of our work following the implementation of supervised regression and classification models in the CAT-PUMA framework. We conducted a comparison of various machine learning models in the context of predicting the transit time of CMEs and classifying CMEs as either Earth impacting or non-impacting. In this way, we are able to provide information on the possibility of a CME reaching Earth relying on CME features and solar wind parameters measured at take-off. This application thus provides quantitative indications about the geoeffectiveness of these space weather events. While machine-learning models can demonstrate fairly strong performance in regression and classification tasks, it is not always straightforward to extrapolate their practical potential and real-world applicability. To address this challenge, we employed model interpretation techniques, specifically Shap values, to gain quantitative insights into the limitations that affect these models.

Keywords: solar coronal mass ejections; space weather
Implementation of an Efficient Bayesian Search for Gravitational-wave Bursts with Memory in Pulsar Timing Array Data

The standard Bayesian technique for searching pulsar timing data for gravitational-wave bursts with memory (BWMs) using Markov Chain Monte Carlo (MCMC) sampling is very computationally expensive to perform. In this paper, we explain the implementation of an efficient Bayesian technique for searching for BWMs. This technique makes use of the fact that the signal model for Earth-term BWMs (BWMs passing over the Earth) is fully factorizable. We estimate that this implementation reduces the computational complexity by a factor of 100. We also demonstrate that this technique gives upper limits consistent with published results using the standard Bayesian technique, and may be used to perform all of the same analyses of BWMs that standard MCMC techniques can perform.

Keywords: gravitational waves; general relativity; gravitational wave detectors; gravitational wave astronomy
An Electron-scattering Time Delay in Black Hole Accretion Disks

Universal to black hole X-ray binaries, the high-frequency soft lag gets longer during the hard-to-intermediate state transition, evolving from ≲1 to ~10 ms. The soft lag production mechanism is thermal disk reprocessing of nonthermal coronal irradiation. X-ray reverberation models account for the light-travel time delay external to the disk, but assume instantaneous reprocessing of the irradiation inside the electron-scattering-dominated disk atmosphere. We model this neglected scattering time delay as a random walk within an α-disk atmosphere, with approximate opacities. To explain soft lag trends, we consider a limiting case of the scattering time delay that we dub the thermalization time delay, t th; this is the time for irradiation to scatter its way down to the effective photosphere, where it gets thermalized, and then scatter its way back out. We demonstrate that t th plausibly evolves from being inconsequential for low mass accretion rates $\dot{m}$ ṁ characteristic of the hard state, to rivaling or exceeding the light-travel time delay for $\dot{m}$ ṁ characteristic of the intermediate state. However, our crude model confines t th to a narrow annulus near peak accretion power dissipation, so cannot yet explain in detail the anomalously long-duration soft lags associated with larger disk radii. We call for time-dependent models with accurate opacities to assess the potential relevance of a scattering delay.

Keywords: stellar mass black holes; x-ray binary stars; reverberation mapping
The Water-ice Feature in Near-infrared Disk-scattered Light around HD 142527: Micron-sized Icy Grains Lifted up to the Disk Surface?

We study the 3 μm scattering feature of water ice detected in the outer disk of HD 142527 by performing radiative transfer simulations. We show that an ice mass abundance at the outer disk surface of HD 142527 is much lower than estimated in a previous study. It is even lower than inferred from far-infrared ice observations, implying ice disruption at the disk surface. Next, we demonstrate that a polarization fraction of disk-scattered light varies across the ice-band wavelengths depending on ice grain properties; hence, polarimetric spectra would be another tool for characterizing water-ice properties. Finally, we argue that the observed reddish disk-scattered light is due to grains a few microns in size. To explain the presence of such grains at the disk surface, we need a mechanism that can efficiently oppose dust settling. If we assume turbulent mixing, our estimate requires α ≳ 2 × 10-3, where α is a nondimensional parameter describing the vertical diffusion coefficient of grains. Future observations probing gas kinematics would be helpful to elucidate vertical grain dynamics in the outer disk of HD 142527.

Keywords: protoplanetary disks; near infrared astronomy; spectropolarimetry
Energizing Star Formation: The Cosmic-Ray Ionization Rate in NGC 253 Derived from ALCHEMI Measurements of H3O+ and SO

The cosmic-ray ionization rate (CRIR) is a key parameter in understanding the physical and chemical processes in the interstellar medium. Cosmic rays are a significant source of energy in star formation regions, impacting the physical and chemical processes that drive the formation of stars. Previous studies of the circum-molecular zone of the starburst galaxy NGC 253 have found evidence for a high CRIR value: 103-106 times the average CRIR within the Milky Way. This is a broad constraint, and one goal of this study is to determine this value with much higher precision. We exploit ALMA observations toward the central molecular zone of NGC 253 to measure the CRIR. We first demonstrate that the abundance ratio of H3O+ and SO is strongly sensitive to the CRIR. We then combine chemical and radiative transfer models with nested sampling to infer the gas properties and CRIR of several star-forming regions in NGC 253 from emission from their transitions. We find that each of the four regions modeled has a CRIR in the range (1-80) × 10-14 s-1 and that this result adequately fits the abundances of other species that are believed to be sensitive to cosmic rays, including C2H, HCO+, HOC+, and CO. From shock and photon-dominated/X-ray dominated region models, we further find that neither UV-/X-ray-driven nor shock-dominated chemistry is a viable single alternative as none of these processes can adequately fit the abundances of all of these species.

Keywords: starburst galaxies; interstellar medium; active galaxies; interstellar abundances
Moderate-resolution K-band Spectroscopy of Substellar Companion κ Andromedae b

We present moderate-resolution (R ∼ 4000) K-band spectra of the "super-Jupiter," κ Andromedae b. The data were taken with the OSIRIS integral field spectrograph at Keck Observatory. The spectra reveal resolved molecular lines from H2O and CO, and are compared to a custom PHOENIX atmosphere model grid appropriate for young planetary-mass objects. We fit the data using a Markov chain Monte Carlo forward-modeling method. Using a combination of our moderate-resolution spectrum and low-resolution, broadband data from the literature, we derive an effective temperature of Teff = 1950-2150 K, a surface gravity of $\mathrm{log}g=3.5\mbox{--}4.5$ , and a metallicity of [M/H] = -0.2-0.0. These values are consistent with previous estimates from atmospheric modeling and the currently favored young age of the system (<50 Myr). We derive a C/O ratio of ${0.70}_{-0.24}^{+0.09}$ for the source, broadly consistent with the solar C/O ratio. This, coupled with the slightly subsolar metallicity, implies a composition consistent with that of the host star, and is suggestive of formation by a rapid process. The subsolar metallicity of κ Andromedae b is also consistent with predictions of formation via gravitational instability. Further constraints on formation of the companion will require measurement of the C/O ratio of κ Andromedae A. We also measure the radial velocity of κ Andromedae b for the first time, with a value of -1.4 ± 0.9 km s-1 relative to the host star. We find that the derived radial velocity is consistent with the estimated high eccentricity of κ Andromedae b.

Keywords: direct imaging; exoplanet atmospheres; high resolution spectroscopy; exoplanet formation; radial velocity
Velocity Response of the Observed Explosive Events in the Lower Solar Atmosphere. I. Formation of the Flowing Cool-loop System

We observe plasma flows in cool loops using the Slit-Jaw Imager on board the Interface Region Imaging Spectrometer (IRIS). Huang et al. observed unusually broadened Si IV 1403 Šline profiles at the footpoints of such loops that were attributed to signatures of explosive events (EEs). We have chosen one such unidirectional flowing cool-loop system observed by IRIS where one of the footpoints is associated with significantly broadened Si IV line profiles. The line-profile broadening indirectly indicates the occurrence of numerous EEs below the transition region (TR), while it directly infers a large velocity enhancement/perturbation, further causing the plasma flows in the observed loop system. The observed features are implemented in a model atmosphere in which a low-lying bipolar magnetic field system is perturbed in the chromosphere by a velocity pulse with a maximum amplitude of 200 km s-1. The data-driven 2D numerical simulation shows that the plasma motions evolve in a similar manner as observed by IRIS in the form of flowing plasma filling the skeleton of a cool-loop system. We compare the spatio-temporal evolution of the cool-loop system in the framework of our model with the observations, and conclude that their formation is mostly associated with the velocity response of the transient energy release above their footpoints in the chromosphere/TR. Our observations and modeling results suggest that the velocity responses most likely associated to the EEs could be one of the main candidates for the dynamics and energetics of the flowing cool-loop systems in the lower solar atmosphere.

Keywords: solar chromosphere; solar atmosphere; solar coronal loops
The Pre-He White Dwarfs in Eclipsing Binaries. I. WASP 0131+28

We report the first BV light curves and high-resolution spectra of the post-mass transfer binary star WASP 0131+28 to study the absolute properties of extremely low-mass white dwarfs. From the observed spectra, the double-lined radial velocities were derived, and the effective temperature and rotational velocity of the brighter, more massive primary were found to be ${T}_{\mathrm{eff},1}={\rm{10,000}}\pm 200$ K and ${v}_{1}\sin i$ = 55 ± 10 km s-1, respectively. The combined analysis of the Transiting Exoplanet Survey Satellite (TESS) archive data and ours yielded the accurate fundamental parameters of the program target. The masses were derived to about 1.0% accuracy and the radii to 0.6%, or better. The secondary component's parameters of ${M}_{2}=0.200\pm 0.002$ ${M}_{\odot }$ , ${R}_{2}=0.528\pm 0.003$ ${R}_{\odot }$ , ${T}_{\mathrm{eff},2}$ = 11,186 ± 235 K, and ${L}_{2}=3.9\pm 0.3$ ${L}_{\odot }$ are in excellent agreement with the evolutionary sequence for a helium-core white dwarf of mass 0.203 ${M}_{\odot }$ , and indicates that this star is halfway through the constant luminosity phase. The results presented in this article demonstrate that WASP 0131+28 is an EL CVn eclipsing binary in a thin disk, which is formed from the stable Roche-lobe overflow channel and composed of a main-sequence dwarf with a spectral type A0 and a pre-He white dwarf.

Keywords: ccd photometry; spectroscopy; white dwarf stars; eclipsing binary stars; stellar evolution; fundamental parameters of stars
Using Stellar Rotation to Identify Tidally Stripped Members of the Praesepe Open Cluster

As an open cluster orbits the Milky Way, gravitational fields distort it, stripping stars from the core and forming tidal tails. Recent work has identified tidal tails of the Praesepe cluster; we explore rotation periods as a way to confirm these candidate members. In open clusters, the rotation period distribution evolves over time due to magnetic braking. Since tidally stripped stars originally formed within the cluster, they should follow the same period distribution as in the cluster core. We analyze 96 candidate members observed by NASA's Transiting Exoplanet Survey Satellite mission. We measure reliable rotation periods for 32 stars, while 64 light curves are noise-dominated. The 32 newly identified rotators are consistent with the period distribution in the core, and with past membership in Praesepe. We therefore suggest that for nearby open clusters, stellar rotation offers a quick and inexpensive method for confirming past members dispersed into tidal tails.

Keywords: milky way dynamics; open star clusters; stellar dynamics; stellar rotation
Updated Proper Motions for Local Group Dwarf Galaxies Using Gaia Early Data Release 3

Updated systemic proper motion estimates for 58 Milky Way satellite galaxies, based on Gaia Early Data Release 3 (EDR3), are provided. This sample is identical to that studied by McConnachie & Venn and the methodology is essentially unchanged from the original paper. The superiority of Gaia EDR3 compared to Gaia Data Release 2 means that Boötes 4, Cetus 3, Pegasus 3 and Virgo 1 have detectable systemic proper motions for the first time. For the entire galaxy sample, the median random uncertainties in the systemic proper motions are approximately a factor of two better than the previous estimates using Gaia DR2. Relevant systematic errors, which are also a factor of two smaller, dominate over random uncertainties for 25 out of the 58 objects in the sample.

Keywords: dwarf galaxies; local group; proper motions; galaxy dynamics
Formation of Gaps in Self-gravitating Debris Disks by Secular Resonance in a Single-planet System. I. A Simplified Model

Spatially resolved images of debris disks frequently reveal complex morphologies such as gaps, spirals, and warps. Most existing models for explaining such morphologies focus on the role of massive perturbers (i.e., planets, stellar companions), ignoring the gravitational effects of the disk itself. Here we investigate the secular interaction between an eccentric planet and a massive, external debris disk using a simple analytical model. Our framework accounts for both the gravitational coupling between the disk and the planet, as well as the disk self-gravity—with the limitation that it ignores the non-axisymmetric component of the disk (self-)gravity. We find generally that even when the disk is less massive than the planet, the system may feature secular resonances within the disk (contrary to what may be naively expected), where planetesimal eccentricities get significantly excited. Given this outcome, we propose that double-ringed debris disks, such as those around HD 107146 and HD 92945, could be the result of secular resonances with a yet-undetected planet interior to the disk. We characterize the dependence of the properties of the secular resonances (i.e., locations, timescales, and widths) on the planet and disk parameters, finding that the mechanism is robust provided the disk is massive enough. As an example, we apply our results to HD 107146 and find that this mechanism readily produces ∼20 au wide non-axisymmetric gaps. Our results may be used to set constraints on the total mass of double-ringed debris disks. We demonstrate this for HD 206893, for which we infer a disk mass of ≈170M⊕ by considering perturbations from the known brown dwarf companion.

Keywords: exoplanet dynamics; circumstellar disks; debris disks
The Nature of Ultra-diffuse Galaxies in Distant Massive Galaxy Clusters: A370 in the Hubble Frontier Fields

We report the discovery of ultra-diffuse galaxies (UDGs) in Abell 370 (A370; z = 0.375). We find 46 UDGs in A370 from the images of the Hubble Frontier Fields. Most UDGs are low-luminosity red sequence galaxies, while a few of them are blue UDGs. We estimate the abundance of UDGs in A370, N(UDG) = 644 ± 104. Combining these results with those of Abell S1063 (z = 0.348) and Abell 2744 (z = 0.308), we derive a mean radial number density profile of UDGs in the three clusters. The number density profiles of UDGs and bright galaxies show a discrepancy in the central region of the clusters: the profile of UDGs shows a flattening as clustercentric distance decreases, while that of bright galaxies shows a continuous increase. This implies that UDGs are prone to disruption in the central region of the clusters. The relation between the abundance of UDGs and virial masses of their host systems is described by a power law with an index of nearly one: $N({\rm{UDG}})\propto {M}_{200}^{0.99\pm 0.05}$ for M200 > 1013 M⊙. We estimate approximately dynamical masses of UDGs using the fundamental manifold method and find that most UDGs have dwarf-like masses (M200 < 1011M⊙). This implies that most UDGs have a dwarf-like origin and a small number of them could be failed L* galaxies. These results suggest that multiple origins may contribute to the formation and evolution of UDGs in massive galaxy clusters.

Keywords: low surface brightness galaxies; dwarf galaxies; galaxy clusters
Nonlinear Simulation of Ionospheric Irregularities at Mars

Motivated by the observations and linear theory analysis of ionospheric irregularities at Mars, we performed numerical simulations of the nonlinear evolution of the electromagnetic gradient drift instability in the Martian ionospheric dynamo region. The seeding source of ionospheric irregularities is perturbation zonal neutral wind. We found that the perturbation electric fields induced by the gradient drift instability can convect lower density plasma into higher density plasma at higher altitudes. Then, the associated perturbation magnetic field and electric field can cause the velocity shear of the plasma, which induced the Kelvin-Helmholtz instability at higher altitude. The Kelvin-Helmholtz instabilities furthermore lead to smaller-scale irregularities in plasma density, magnetic field, and electric field in the Martial ionosphere. Key points: (1) Nonlinear simulation of small-scale ionospheric irregularities at Mars was present. (2) Ionospheric irregularities at Mars can be seeded by the perturbation neutral winds. (3) Model results are comparable to linear theory analysis and satellite observations.

Keywords: mars; plasma physics
Mirror Acceleration of Cosmic Rays in a High-β Medium

In a weakly compressible high-β medium, pitch-angle scattering and the associated scattering acceleration of cosmic rays (CRs) by anisotropic Alfvén and slow modes of magnetohydrodynamic (MHD) turbulence is inefficient. To tap the energy from magnetic compressions for efficient particle acceleration, a diffusion mechanism that can effectively confine particles in space without causing their trapping or pitch-angle isotropization is needed. We find that the mirror diffusion in MHD turbulence recently identified in Lazarian & Xu satisfies all the above conditions and serves as a promising diffusion mechanism for efficient acceleration of CRs via their stochastic nonresonant interactions with magnetic compressions/expansions. The resulting mirror acceleration is dominated by the slow-mode eddies with their lifetime comparable to the mirror diffusion time of CRs. Consequently, we find that the acceleration time of mirror acceleration is independent of the spatial diffusion coefficient of CRs. The mirror acceleration brings new life for the particle acceleration in a weakly compressible/incompressible medium and has important implications for studying CR reacceleration in the high-β intracluster medium.

Keywords: magnetohydrodynamics; cosmic rays; intracluster medium
Morphological Types of DM Halos in Milky Way-like Galaxies in the TNG50 Simulation: Simple, Twisted, or Stretched

We present a comprehensive analysis of the shape of dark matter (DM) halos in a sample of 25 Milky Way-like galaxies in TNG50 simulation. Using an enclosed volume iterative method, we infer an oblate-to-triaxial shape for the DM halo with median T ≃ 0.24. We group DM halos into three different categories. Simple halos (32% of the population) establish principal axes whose ordering in magnitude does not change with radius and whose orientations are almost fixed throughout the halo. Twisted halos (32%) experience levels of gradual rotations throughout their radial profiles. Finally, stretched halos (36%) demonstrate a stretching in the lengths of their principal axes where the ordering of different eigenvalues changes with radius. Subsequently, the halo experiences a "rotation" of ∼90° where the stretching occurs. Visualizing the 3D ellipsoid of each halo, for the first time, we report signs of a reorienting ellipsoid in twisted and stretched halos. We examine the impact of baryonic physics on DM halo shape through a comparison to dark matter only (DMO) simulations. This suggests a triaxial (prolate) halo. We analyze the impacts of substructure on DM halo shape in both hydrodynamical and DMO simulations and confirm that they are subdominant. We study the distribution of satellites in our sample. In simple and twisted halos, the angle between satellites' angular momentum and the galaxy's angular momentum grows with radius. However, stretched halos show a flat distribution of angles. Overlaying our theoretical outcome on the observational results presented in the literature establishes a fair agreement.

Keywords: galaxy classification systems; cold dark matter; hydrodynamical simulations
Test for Echo: X-Ray Reflection Variability in the Seyfert-2 Active Galactic Nucleus NGC 4388

We report on a study of the narrow Fe Kα line and reflection spectrum in the well-known Seyfert-2 active galactic nucleus (AGN), NGC 4388. X-ray spectra summed from two extensive NICER monitoring campaigns, separated by years, show strong evidence of variation in the direct continuum and reflected emission, but only small variations in the obscuring gas. Fits to the spectra from individual NICER observations find a strong, positive correlation between the power-law photon index, Γ, and direct flux that is commonly observed in unobscured AGN. A search for a reverberation lag between the direct and reflected spectra—dominated by the narrow Fe Kα emission line—measures a timescale of $t={16.37}_{-0.38}^{+0.46}$ days, or a characteristic radius of $r={1.374}_{-0.032}^{+0.039}\,\times {10}^{-2}$ pc $={\,3.4}_{-0.1}^{+0.1}\times {10}^{4}\,{GM}/{c}^{2}$ . Only one cycle of this tentative lag is observed, but it is driven by a particularly sharp drop in the direct continuum that leads to the subsequent disappearance of the otherwise prominent Fe Kα line. Physically motivated fits to high-resolution Chandra spectra of NGC 4388 measure a line production radius of $r={2.9}_{-0.7}^{+1.2}\,\times {10}^{4}\,{GM}/{c}^{2}$ , formally consistent with the tentative lag. The line profile also prefers a Compton-thick reflector, indicating an origin in the disk and/or thick clumps within a wind. We discuss the strengths and weaknesses of our analysis and methods for testing our results in future observations, and we note the potential for X-ray reverberation lags to constrain black hole masses in obscured Seyferts wherein the optical broad line region is not visible.

Keywords: black holes; x-ray active galactic nuclei; active galactic nuclei