Sazuna/UAT_keywords huggingface dataset:
A 7 day Multiwavelength Flare Campaign on AU Mic. II. Electron Densities and Kinetic Energies from High-frequency Radio Flares. M dwarfs are the most common type of star in the solar neighborhood, and many exhibit frequent and highly energetic flares. To better understand these events across the electromagnetic spectrum, a campaign observed AU Mic (dM1e) over 7 days from the X-ray to radio regimes. Here, we present high-time-resolution light curves from the Karl G. Jansky Very Large Array (VLA) Ku band (12─18 GHz) and the Australia Telescope Compact Array (ATCA) K band (16─25 GHz), which observe gyrosynchrotron radiation and directly probe the action of accelerated electrons within flaring loops. Observations reveal 16 VLA and three ATCA flares of varying shapes and sizes, from a short (30 s) spiky burst to a long-duration (∼5 hr) decaying exponential. The Ku-band spectral index is found to often evolve during flares. Both rising and falling spectra are observed in the Ku band, indicating optically thick and thin flares, respectively. Estimations from optically thick radiation indicate higher loop-top magnetic field strengths (∼1 kG) and sustained electron densities (∼106 cm−3) than previous observations of large M dwarf flares. We estimate the total kinetic energies of gyrating electrons in optically thin flares to be between 1032 and 1034 erg when the local magnetic field strength is between 500 and 700 G. These energies are able to explain the combined radiated energies from multiwavelength observations. Overall, values are more aligned with modern radiative-hydrodynamic simulations of M dwarf flares, and future modeling efforts will better constrain findings.

Keywords: M dwarf stars, Red dwarf flare stars, Stellar activity, Stellar flares, Radio sources
The Tip of Red Giant Branch Distances to Nearby Dwarf Galaxies WLM and Sextans A with JWST. Distance measurements to extragalactic systems that are both accurate and precise are cornerstones of modern astrophysics, underpinning the calibration of standard candles and the determination of the Hubble constant. Dwarf galaxies, such as Wolf–Lundmark–Melotte (WLM) and Sextans A, provide valuable laboratories for testing distance scales across different stellar populations. In this work, we utilize the high sensitivity and spatial resolution of the James Webb Space Telescope to measure the distances to WLM and Sextans A using the tip of the red giant branch (TRGB) method. Adopting the TRGB absolute magnitude calibrated by NGC 4258, we determine distance moduli of μ0,WLM = 24.977 ± 0.018(stat) ± 0.056(sys) mag for WLM and μ0,SexA = 25.740 ± 0.011(stat) ± 0.057(sys) mag for Sextans A. Our results are consistent within a 3% distance uncertainty with previous measurements based on TRGB, Cepheids, and J-Region Asymptotic Giant Branch methods. With improved distance measurements in the future, these two galaxies have the potential to serve as additional anchor points for TRGB calibration and reduce the TRGB-based distance uncertainty to below 2%.

Keywords: Red giant tip, Dwarf galaxies, Standard candles, Distance indicators, Hubble constant, Red giant stars
Thermally Induced Electromagnetic Fluctuations by Protons and Alpha Particles in the Solar Wind. We present an initial study on the contribution of alpha particles, alongside electrons and protons, to the generation of thermally induced electromagnetic fluctuations (TIEFs) in space plasmas, such as the solar wind. The inclusion of alpha particles is anticipated to influence the regulation of the quasi-stable region in the beta-anisotropy diagram for both ion species, as well as the amplitude of the fluctuations. For this analysis, we filtered 30 yr of solar wind data at 1 au, focusing on conditions close to isotropy for protons and alpha particles, given that the observational distribution peaks near this state. The filtered data are displayed and organized in the (β∥p, β∥α) plane, where β∥ denotes the ratio of parallel plasma pressure to magnetic pressure for protons (p) and alpha particles (α). In this plane, we analyze the ratio of alpha particle to proton density, nα/np, the squared perpendicular magnetic fluctuations, and compressibility. Furthermore, we compare these magnetic fluctuations with the total fluctuating magnetic energy density derived from a generalized fluctuation–dissipation theorem, highlighting a clear similarity. We also present Fourier spectra for a subset of the data and the corresponding theoretical curve predicted by TIEFs. This study suggests that TIEFs may play a significant role in explaining the unexpected fluctuations observed in space plasmas. Additionally, it provides preliminary evidence that the inclusion of additional ion species could serve as a quantitative test for the theoretical models proposed to describe these fluctuations.

Keywords: Space plasmas, Solar wind, Plasma astrophysics, Plasma physics
Spatial Scales of Electron Density Fluctuations in the Martian Ionosphere. In recent Martian ionospheric studies, the spatial scales of electron density irregularities have been computed using magnetic field measurements by treating these fluctuations as electromagnetic. As Mars lacks an intrinsic magnetic field, estimation of spatial scales in the parallel and perpendicular directions of the ambient magnetic field is not straightforward. In the present study, the magnetic field averaged over a longer time window is used to get the direction of the ambient magnetic field. The process of averaging removes the short-time fluctuations and retains only the slowly varying part, which can be treated as an ambient magnetic field. This approach is applied to long-term (2014–2023) magnetic field measurements from the fluxgate magnetometer on board the Mars Atmosphere and Volatile EvolutioN (or MAVEN) spacecraft to investigate separately the dominant spatial scales in the parallel and perpendicular directions. The spatial scales parallel and perpendicular to the ambient magnetic field dominantly lie in the range of λ∣∣ = 150–350 km and λ⊥= 50–80 km, respectively. However, the tendency of λ∣∣ &gt; λ⊥ weakens in the region of the strong crustal magnetic field. Irregularities with density fluctuations of more than 25% are prevalent in the dawn and dusk sectors at an altitude of 140–180 km. Spatial scales of λ⊥ &lt; 70 km are more probable at an altitude above 200 km in the Martian ionosphere. Information about the spatial scales of electron density fluctuations is crucial for understanding their impact on the radio wave propagation in the Martian ionosphere, as well as the underlying processes responsible for their generation.

Keywords: Planetary magnetospheres
Quasi-thermal Photosphere Emission from Structured Jets of Gamma-Ray Bursts. The prompt emission of gamma-ray bursts (GRBs) is supposed to be released from the relativistic jet launched from the central engine. Apart from the nonthermal nature of spectra in the majority of GRBs, there is evidence for the presence of quasi-thermal components in the prompt emission of a few GRBs according to observations by the Fermi satellite. On the other hand, the GRB jet has been revealed as structured in recent research. The theoretical spectra of photosphere emissions observed by an off-axis observer and the dependence of the spectra on the viewing angle under the assumption of structured jets remain unexplored. In this paper, we numerically calculate the instantaneous photosphere spectra by different viewing angles from a structured jet, from which relevant temporal and spectral characteristics are derived. Moreover, we address the necessity of proper treatment of the outflow boundary in the photosphere emission scenario. Furthermore, our calculations suggest that the Einstein Probe and Space-based Multi-band Astronomical Variable Object Monitor will have the capability to detect short GRBs similar to GRB 170817A up to a luminosity distance of 200 Mpc if the off-axis viewing angle is less than 10°.

Keywords: Gamma-ray bursts
The Origin of the Cluster of Local Interstellar Clouds. The interstellar medium within ≈15 pc of the Sun consists of a complex of 15 diffuse, partially ionized clouds. Located within the Local Bubble, these clouds, known as the Cluster of Local Interstellar Clouds (CLIC), constitute the interstellar environment impinging upon our heliosphere. While each individual cloud can be modeled with a distinct velocity vector, the complex demonstrates a coherent bulk motion suggestive of a common origin. Here, we examine two theories for the origin of the CLIC: that it formed due to an ionization front associated with nearby Strömgren spheres and/or due to a nearby supernova explosion that occurred within the pre-evacuated cavity of the Local Bubble. Tracing back the trajectory of the clouds, we disfavor a purely Strömgren sphere origin, given the CLIC's position interior to the surface of the most significant nearby Strömgren sphere and its motion transverse to the sphere's trajectory. Turning to a supernova origin, we model the formation of the CLIC assuming individual clouds have been swept up over time due to the expansion of a supernova remnant in its pressure-driven snowplow phase. We find that the 3D spatial-dynamical properties of the CLIC can be explained by the most recent supernova that exploded in the nearby Upper Centaurus Lupus cluster ≈1.2 Myr ago and propagated into an ambient density of n ≈ 0.04 cm‑3. Our model predicts that the formation of the individual CLIC clouds occurred progressively over the past 1 Myr and offers a natural explanation for the observed distribution, column density, temperature, and magnetic field structure of the complex.

Keywords: Supernova remnants, Interstellar dynamics, Diffuse interstellar clouds
ChronoFlow: A Data-driven Model for Gyrochronology. Gyrochronology is a technique for constraining stellar ages using rotation periods, which change over a star's main-sequence (MS) lifetime due to magnetic braking. This technique shows promise for MS FGKM stars, where other methods are imprecise. However, the observed dispersion in rotation rates for similar coeval stars has historically been difficult to characterize. To properly understand this complexity, we have assembled the largest standardized data catalog of rotators in open clusters to date, consisting of ≈ 7600 stars across 30 open clusters/associations spanning ages of 1.5 Myr to 4 Gyr. We have also developed ChronoFlow: a flexible data-driven model that accurately captures observed rotational dispersion. We show that ChronoFlow can be used to accurately forward-model rotational evolution, and to infer both cluster and individual stellar ages. We recover cluster ages with a statistical uncertainty of 0.06 dex (≈15%), and individual stellar ages with a statistical uncertainty of 0.7 dex. Additionally, we conducted robust systematic tests to analyze the impact of extinction models, cluster membership, and calibration ages. These contribute an additional 0.06 dex of uncertainty in cluster age estimates, resulting in a total error budget of 0.08 dex. We apply ChronoFlow to estimate ages for M34, NGC 2516, NGC 6709, and the Theia 456 stellar stream. Our results show that ChronoFlow can precisely estimate the ages of coeval stellar populations, and constrain ages for individual stars. Furthermore, its predictions may be used to inform physical spin-down models. ChronoFlow is publicly available online (https://github.com/philvanlane/chronoflow).

Keywords: Nonparametric inference, Bayesian statistics, Stellar ages, Neural networks, Astrostatistics, Dwarf stars, Main sequence stars, Open star clusters, Stellar rotation, Catalogs
Cosmic Himalayas: The Highest Quasar Density Peak Identified in a 10,000 deg<SUP>2</SUP> Sky with Spatial Discrepancies between Galaxies, Quasars, and IGM H I. We report the identification of a quasar overdensity in the BOSSJ0210 field, dubbed the Cosmic Himalayas, consisting of 11 quasars at z = 2.16‑2.20, the densest overdensity of quasars (17σ) in the ∼10,000 deg2 of the Sloan Digital Sky Survey (SDSS). We present the spatial distributions of galaxies and quasars and a H I absorption map of the intergalactic medium (IGM). On the map of 465 galaxies selected from the MAMMOTH-Subaru survey, we find two galaxy density peaks that do not fall on the quasar overdensity but instead exist at the northwest and southeast sides, approximately 25 h‑1 comoving Mpc (cMpc) apart from the quasar overdensity. With a spatial resolution of 15 h‑1 cMpc in projection, we produce a three-dimensional H I tomography map by the IGM Lyα forest in the spectra of 23 SDSS/eBOSS quasars behind the quasar overdensity. Surprisingly, the quasar overdensity coincides with neither an absorption peak nor a transmission peak of IGM H I but lies near the border separating opaque and transparent volumes, with the more luminous quasars located in an environment with less IGM H I. Hence, remarkably, the overdensity region traced by the 11 quasars, albeit all in coherently active states, has no clear coincidence with peaks of galaxies or H I absorption densities. Current physical scenarios with mixtures of H I overdensities and quasar photoionization cannot fully interpret the emergence of the Cosmic Himalayas, suggesting this peculiar structure is an excellent laboratory to unveil the interplay between galaxies, quasars, and the IGM.

Keywords: Large-scale structure of the universe, Quasars, Intergalactic medium, Lyman-alpha galaxies, High-redshift galaxies
The Use of Binary Black Holes Merging in Active Galactic Nuclei Disks for Hubble Constant Measurements. We study the impact of environmental effects on the measurement of the Hubble constant (H0) from gravitational-wave (GW) observations of binary black hole mergers residing in active galactic nuclei (AGNs) near the central supermassive black hole. Using the potential hierarchical triple merger candidate GW190514–GW190521 in AGN J124942.3+344929 with its potential electromagnetic counterpart ZTF19abanrhr as a multimessenger case study, we demonstrate that environmental effects can be negligible for mergers at approximately tens to hundreds of Schwarzschild radii from the supermassive black hole. We find  H0=40.9‑8.9+19.3kms‑1Mpc‑1  (median and 68% credible interval) under a flat prior and flat ΛCDM cosmology. Incorporating GW170817 prior information improves constraints to  H0=68.8‑6.0+7.7kms‑1Mpc‑1 . We suggest that, in general, AGN environments could serve as viable laboratories for cosmological studies from GW observations where environmental effects remain below detection thresholds.

Keywords: Hubble constant, Active galactic nuclei, Gravitational wave sources
Origin of the Multiphase Interstellar Medium: The Effects of Turbulence and Magnetic Field. The interstellar medium (ISM) consists of multiphase gas, including the warm neutral medium (WNM), the unstable neutral medium (UNM), and the cold neutral medium (CNM). While significant attention has been devoted to understanding the WNM and CNM, the formation of a substantial fraction of the UNM, with temperatures ranging from a few hundred to a few thousand Kelvin, remains less well understood. In this study, we present 3D hydrodynamical and magnetohydrodynamic simulations of the turbulent multiphase ISM to investigate the roles of turbulence and magnetic fields in regulating the multiphase ISM. Our results confirm that turbulence is crucial in redistributing energy and producing the UNM. The turbulent mixing effect smooths the phase diagram, flattens the pressure–density relationship, and increases the fraction of gas in the UNM. We find magnetic fields not only contribute to sustaining the UNM but also influence the dynamics and distribution of gas across all phases. Magnetic fields introduce anisotropy to the turbulent cascade, reducing the efficiency of turbulent mixing in the direction perpendicular to the magnetic field. We find the anisotropy results in a less flat phase diagram compared to hydrodynamical cases. Furthermore, the inclusion of magnetic fields shallows the second-order velocity structure functions across multiple ISM phases, suggesting that more small-scale fluctuations are driven. These fluctuations contribute to the formation of the UNM by altering the energy cascade and thermodynamic properties of the gas. Our findings suggest that the combined effects of turbulence and magnetic fields are important in regulating the multiphase ISM.

Keywords: Interstellar magnetic fields, Neutral hydrogen clouds, Interstellar medium, Magnetohydrodynamical simulations
From Pretransit to Posteclipse: Investigating the Impact of 3D Temperature, Chemistry, and Dynamics on High-resolution Emission Spectra of the Ultrahot Jupiter WASP-76b. High-resolution spectroscopy has provided a wealth of information about the climate and composition of ultrahot Jupiters (UHJs). However, the 3D structure of their atmospheres makes observations more challenging to interpret, necessitating 3D forward-modeling studies. In this work, we model phase-dependent thermal emission spectra of the archetype UHJ WASP-76b to understand how the line strengths and Doppler shifts of Fe, CO, H2O, and OH evolve throughout the orbit. We postprocess outputs of the SPARC/MITgcm global circulation model with the 3D Monte Carlo radiative transfer code gCMCRT to simulate emission spectra at 36 orbital phases. We then cross correlate the spectra with different templates to obtain cross-correlation function and Kp–Vsys maps. For each species, our models produce consistently negative Kp offsets in pre- and posteclipse, which are driven by planet rotation. The size of these offsets is similar to the equatorial rotation velocity of the planet. Furthermore, we demonstrate how the weak vertical temperature gradient on the nightside of UHJs mutes the absorption features of CO and H2O, which significantly hampers their detectability in pre- and posttransit. We also show that the Kp and Vsys offsets in pre- and posttransit are not always a measure of the line-of-sight velocities in the atmosphere. This is because the cross-correlation signal is a blend of dayside emission and nightside absorption features. Finally, we highlight that the observational uncertainty in the known orbital velocity of UHJs can be multiple kilometers per second, which makes it hard for certain targets to meaningfully report absolute Kp offsets.

Keywords: High resolution spectroscopy, Hot Jupiters, Exoplanet atmospheric dynamics, Exoplanet atmospheres, Doppler shift
Fe XVIII and Fe XX Forbidden Lines Observed by Solar Orbiter/SPICE. The first simultaneous observations of the Fe XVIII 974.86 Å and Fe XX 721.56 Å forbidden lines from the Spectral Imaging of the Coronal Environment (SPICE) spectrograph on Solar Orbiter are presented. The lines were observed from the postflare loops of an M2.5 class solar flare that peaked at 23:49 UT on 2024 March 23. The Fe XX/Fe XVIII ratio is used to derive a temperature spacetime map for the flaring period, with values ranging from 8 to 20 MK. The map reveals repeated episodes of heating at the SPICE slit location over a 30 minute period. For one location with the brightest emission, the plasma cooled from 10 to 8 MK in 5 minutes, which is longer than the expected conductive cooling time of 170 s, suggesting continued background heating during the cooling period. Doppler shifts of between 0 and +10 km s‑1 were obtained with precisions of 1–4 km s‑1, but the accuracies are lower due to uncertainties over the absolute wavelength calibration; hence, we cannot conclude there are plasma flows in the flare loops. The widths of the two lines were found to be close to the instrumental widths with no evidence of nonthermal broadening although this result is limited by the instrument resolution. The Fe XVIII and Fe XX lines have high signal-to-noise with only a 5 s exposure time, demonstrating that the lines will be valuable for high-cadence flare studies with SPICE.

Keywords: Solar flares, Solar flare spectra, Solar extreme ultraviolet emission
Empirical Parametric Model for Venus Plasma Boundaries Based on Venus Express Data. Venus's induced magnetosphere is characterized by regions with different plasma and magnetic field properties, which are separated by plasma boundaries. These boundaries' locations and shapes vary with upstream solar wind conditions, and these variations have been characterized by several previous studies. In this study, we developed quantitative parametric models of the bow shock and ion composition boundary (ICB), which allow us to determine the location and shape of the boundaries given a set of upstream conditions. To quantitatively model these boundaries, we used a database of boundary crossings derived from plasma and magnetic field measurements by Venus Express. We modeled the bow shock as a conic section curve, which depends on the interplanetary magnetic field (IMF) magnitude and the solar wind proton flux. Furthermore, we considered the shock normal angle, the angle between the IMF and the local shock normal vector, to describe a quasi-perpendicular/quasi-parallel shock asymmetry. We modeled the dayside ICB as a half sphere that depends solely on the solar EUV flux and the solar wind proton flux. These parametric models are compared with models that average over upstream conditions; our bow shock parametric model improves the prediction accuracy by 16% and the ICB parametric model by 6%.

Keywords: Plasma physics, Solar wind, Planetary bow shocks, Venus, Interplanetary magnetic fields
A Morphological Study of AGN-host Dwarf Galaxies. The study of morphology in galaxies offers a convenient and quantitative method to measure the shapes and characteristics of galaxy light distribution that reflect the evolutionary history. For active galactic nucleus (AGN)-host dwarf galaxies, however, there is a lack of detailed studies of their morphologies. In this work, we compile a relatively large sample (∼400 members) of local AGN-host dwarf (M⋆ ≤ 109.5M⊙ and z &lt; 0.055) galaxies selected via various methods. We use the grz bands images from DESI DR10 and the Python package statmorph to measure nonparametric coefficients. We also carry out visual inspection with the assistance of deep learning to classify these galaxies into early-type galaxies (ETGs), late-type galaxies (LTGs), and mergers, and find that about 37%, 44%, and 13% of the total sample sources are ETGs, LTGs, and mergers, respectively. In comparison to normal dwarf galaxies, AGN-host dwarfs have a higher probability to be LTGs, and a lower merger rate, indicating that mergers/interactions are not the primary driver of AGN activities. Among the subsamples selected with different methods, the Baldwin, Phillips &amp; Terlevich sample has the highest fraction of ETGs, the variability sample consists of the largest fraction of LTGs, and the mid-IR sample contains the most mergers.

Keywords: AGN host galaxies, Dwarf galaxies, Galaxy classification systems