Sazuna/UAT_keywords huggingface dataset:
Preferential Energization of Solar Wind Ions Below the Alfvénic Surface. Understanding how solar wind ions are heated and accelerated remains a central question in heliophysics. Observations consistently show that alpha particles are hotter and faster than protons, particularly close to the Sun. This suggests that kinetic processes play a dominant role in shaping ion distributions. Theoretical models have proposed that much of this preferential energization occurs near the Alfvén critical surface, a spatially varying boundary where the solar wind transitions from magnetically dominated to thermally dominated flow. With in situ measurements from Parker Solar Probe (PSP), it is possible to explore this question near the Sun directly. In this study, we analyze PSP observations from near-perihelion encounters to statistically compare the thermodynamic properties of protons and alpha particles across the Alfvén surface. We find that ion temperature anisotropies, differential flows, and heating signatures are coherently organized by the local Alfvén Mach number (MA). In the sub-Alfvénic regime, alpha particles exhibit strong perpendicular temperature heating and elevated alpha-to-proton temperature ratio, which decline across the Alfvénic transition. Meanwhile, proton heating peaks near MA ∼ 1, consistent with anisotropic wave–particle energization. These findings highlight the Alfvén surface as a key boundary for ion energization and momentum exchange, and establish MA as a fundamental organizing parameter in the kinetic evolution of solar wind ions in the inner heliosphere.

Keywords: Space plasmas, Heliosphere, The Sun, Solar wind, Solar system evolution, Alfven waves
Observational Evidence of Dust Evolution in Supernova Remnants: Size Redistribution toward Larger Grains in the Early Sedov Phase. Recent observations have revealed that dust is widespread and abundant in galaxies up to z ≃ 8, significantly influencing their appearance and spectral properties. In the early Universe, dust is thought to form primarily in supernova (SN) ejecta, but also undergoes destruction from the reverse shock. Studying dust in local supernova remnants (SNRs) of different sizes and ages thus provides key constraints on dust formation and evolution during the cosmic dawn. Using the newly released 3D RV map, we derived local RV ≡ AV/E(B ‑ V) values for dust in 14 Galactic SNRs in the early Sedov phase and their surrounding interstellar medium (ISM). For the first time, we detect a moderately strong positive correlation between the difference in SNR and ISM RV (ΔRV) and SNR radius (RSNR), with a Spearman coefficient of rs = 0.62 ± 0.14. This trend offers direct observational evidence for a redistribution of dust grain sizes toward larger grains during SN shock processing, consistent with theoretical models. Our findings provide essential observational constraints on dust size evolution in SNRs and important implications for understanding the rapid enrichment and survival of dust in the early Universe.

Keywords: Supernova remnants, Interstellar dust, Dust destruction, Reddening law
A Two-stage Kick Scenario for the Peculiar Low-mass X-Ray Binary GX 1+4. The low-mass X-ray binary (LMXB) GX 1+4 stands out with its unique properties. Despite being an old system, it hosts a strongly magnetized neutron star (NS), a trait usually linked to younger systems. Its exceptionally long orbital period (1160 days) and low eccentricity (0.101) imply that the NS formed with minimal mass loss and a weak natal kick. These features collectively point toward the NS having formed through the accretion-induced collapse (AIC) of a white dwarf. However, GX 1+4's unusually high peculiar velocity (∼189.36 km s‑1) defies standard AIC explanations. To address this discrepancy, we propose a two-stage kick scenario within the AIC framework: an initial natal kick followed by a delayed electromagnetic "rocket effect" kick. Our Monte Carlo simulations indicate that while the natal kick (≲100 km s‑1) can generate a wide range of orbital eccentricities, the subsequent rocket kick (∼240–480 km s‑1) explains both the high systemic velocity and low eccentricity. This two-stage kick mechanism naturally reproduces the observed characteristics of GX 1+4, provided that the NS's initially buried magnetic field reemerges after the acceleration process ends. Our study represents the first attempt to quantitatively constrain the kick velocities in GX 1+4 and underscores the importance of possible rocket kicks in forming such peculiar LMXB systems.

Keywords: Neutron stars, Low-mass x-ray binary stars, Supernovae
RIOJA. JWST and ALMA Unveil the Inhomogeneous and Complex Interstellar Medium Structure in a Star-forming Galaxy at z = 6.81. We report the discovery of a complex density-stratified interstellar medium (ISM) in the star-forming galaxy COS-2987 at z = 6.81, revealed by the unprecedented synergy between James Webb Space Telescope (JWST)/NIRSpec integral field spectroscopy and Atacama Large Millimeter/submillimeter Array (ALMA) observations. These observations detect key emission lines, including [O II] λλ 3727, 3730, [O III] 4364, [O III] λλ 4960, 5008, and [O III] 88 μm, as well as Hα and Hβ. JWST spectroscopy alone indicates ISM properties that are typical for galaxies at z ∼ 7. These include low dust extinction (AV ≍ 0.14 mag), moderate electron density (ne ≍ 500 cm−3), and low gas-phase metallicity (∼10%). However, the strong far-infrared [O III] 88 μm emission detected by ALMA cannot be explained by a single-component ionized medium with uniform electron density and temperature. Instead, a two-component ISM model—comprising compact, high-temperature, and high-density gas components (Te ≍ 26,000 K; ne ≍ 600 cm−3) and an extended, cooler, and lower-density component (Te ≍ 8000 K; ne ≍ 50 cm−3)—successfully reproduces the observed line ratios of [O III] 88 μm/[O III] 5008 Å and [O III] 4364/[O III] 5008 Å, with a volume ratio of 1 : 300 between the two components. Our results demonstrate that JWST alone probes only a fraction of the ISM and highlight the critical importance of combining JWST and ALMA to reveal the density-stratified ISM of early galaxies.

Keywords: Galaxy formation, Galaxy evolution, Interstellar medium
Quantifying the Distribution of Europium in the Milky Way Disk: Its Connection to Planetary Habitability and the Source of the r-process. The astrophysical site of the r-process remains one of the most pressing questions in stellar nuclear synthesis. Although multiple theoretical sites have been proposed, with some observational counterparts available, the current Galactic distribution cannot be reproduced from a single consistent injection site. To disentangle the prospective sites of r-process production, the distribution of r-process elements in the Galaxy today must be scrutinized. In this study, we find that the intrinsic star-to-star distribution of the r-process element europium (Eu) at a fixed metallicity and temperature has a small intrinsic [Eu/H] scatter of 0.025 dex. In addition to a small dispersion, we demonstrate an anticorrelation between [Eu/α] and [α/H] consistent with r-process production being metallicity-dependent in core-collapse supernova and/or being produced in double neutron star mergers with a delay time distribution greater than t‑1. Furthermore, using Eu as a proxy for the radioactive r-process elements U and Th, and assuming that rocky planetary abundances reflect their parent star's composition, we show how these elements play a key role in the evolution of the magnetic dynamo on Earth-mass planets. Specifically, we find that only above [α/H] &gt; ‑0.25 do most stars' planetary systems meet the threshold abundance of [Eu/α] &lt; +0.06 to support a persistent magnetic dynamo, supporting the notion of a "habitable metallicity range" in the Galactic disk.

Keywords: Geomagnetic fields, Nucleosynthesis, R-process, Exoplanet evolution, Milky Way disk, Astrobiology
The Light Echo of a High-redshift Quasar Mapped with Lyα Tomography. Ultraviolet (UV) radiation from accreting black holes ionizes the intergalactic gas around early quasars, carving out highly ionized bubbles in their surroundings. Any changes in a quasar's luminosity are therefore predicted to produce outward-propagating ionization gradients, affecting the Lyα absorption opacity near the quasar's systemic redshift. This "proximity effect" is well-documented in rest-UV quasar spectra but only provides a one-dimensional probe along our line of sight. Here we present deep spectroscopic observations with the James Webb Space Telescope (JWST) of galaxies in the background of a superluminous quasar at zQSO ≈ 6.3, which reveal the quasar's "light echo" with Lyα tomography in the transverse direction. This transverse proximity effect is detected for the first time toward multiple galaxy sightlines, allowing us to map the extent and geometry of the quasar's ionization cone. We obtain constraints on the orientation and inclination of the cone, as well as an upper limit on the obscured solid angle fraction of fobsc &lt; 91%. Additionally, we find a timescale of the quasar's UV radiation of  tQSO=105.6‑0.3+0.1  yr, which is significantly shorter than would be required to build up the central supermassive black hole (SMBH) with conventional growth models, but is consistent with independent measurements of the quasars' duty cycle. Our inferred obscured fraction disfavors a scenario where short quasar lifetimes can be explained exclusively by geometric obscuration, and instead supports the idea that radiatively inefficient accretion or growth in initially heavily enshrouded cocoons plays a pivotal role in early SMBH growth. Our results pave the way for novel studies of quasars' ionizing geometries and radiative histories at early cosmic times.

Keywords: Supermassive black holes, Early universe, Quasars
Einstein Probe Discovery of EP J182730.0‑095633: A New Black Hole X-Ray Binary Candidate in Faint Outburst?. Black hole X-ray binaries (candidates) currently identified in our Galaxy are mainly transient sources, with the majority discovered through the detection of their X-ray outbursts. Among these, only four were found during faint outbursts exhibiting peak X-ray luminosities LX ≲ 1036 erg s‑1, likely due to the previous lack of sensitive, wide-field monitoring instruments in the X-ray band. In this Letter, we present the discovery of an intriguing X-ray transient, EP J182730.0‑095633, via the Einstein Probe (EP) and subsequent multiwavelength follow-up studies. This transient, located on the Galactic plane, experienced a faint and brief X-ray outburst lasting about 20 days. Its X-ray spectrum is nonthermal and consistent with a power-law model with a nearly constant photon index of Γ ∼ 2 throughout the outburst. A long-lasting mHz quasiperiodic oscillation signal was detected in its X-ray light curve, centered around a frequency of ∼0.04 Hz. A transient near-infrared source was identified as its counterpart, although no optical emission was detectable, likely due to significant extinction. A radio counterpart was also observed, displaying an inverted radio spectrum with α ∼ 0.45. The X-ray spectral and temporal characteristics, along with the multiwavelength properties, indicate that the source is a faint low-mass X-ray binary, with the compact object likely being a black hole. This work demonstrates the potential of the EP in discovering new X-ray binaries by capturing faint-level X-ray outbursts.

Keywords: Low-mass x-ray binary stars, X-ray transient sources, Black holes
A New Subclass of Carbon-enhanced Metal-poor Stars at Extremely Low Metallicity. We report the discovery of a new subclass of carbon-enhanced metal-poor (CEMP) stars, characterized by high absolute carbon abundances (A(C) &gt; 7.39) and extremely low metallicity ([Fe/H] ≤ –3.1) but notably lacking enhancements in neutron-capture elements, thus falling under the CEMP-no category. This population emerged from a detailed analysis of low-resolution spectroscopic data obtained from the Sloan Digital Sky Survey and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, where the observed frequency trends with the decreasing metallicity of CEMP-s (s-process-enhanced) and CEMP-no (no neutron-capture enhanced) stars deviated from established expectations. In contrast to earlier findings, we observe a rise in high-A(C) stars below [Fe/H] = ‑3.1, which we interpret as a distinct group not accounted for in traditional CEMP classifications. Following the Yoon–Beers group classification, we define these stars as Group IV. Statistical modeling confirms their presence as a separate peak in the A(C) distribution, and available radial velocity data suggest that about 30% of Group IV stars may be binaries, indicating possible binary-related formation mechanisms. This discovery challenges the current CEMP-no star formation pathways and implies the existence of alternative or hybrid enrichment scenarios in the early Universe. High-resolution spectroscopic follow-up of Group IV candidates will be crucial for identifying their progenitors and understanding their evolutionary implications.

Keywords: Surveys, Stellar abundances, CEMP stars, Milky Way stellar halo
JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLAS. 3I/ATLAS is the third confirmed interstellar object to visit our solar system and only the second to display a clear coma. Infrared spectroscopy with the James Webb Space Telescope (JWST) provides the opportunity to measure its coma composition and determine the primary activity drivers. We report the first results from our JWST NIRSpec campaign for 3I/ATLAS, at an inbound heliocentric distance of rH = 3.32 au. The spectral images (spanning 0.6─5.3 μm) reveal a CO2-dominated coma, with enhanced outgassing in the sunward direction and the presence of H2O, CO, water ice, dust, and a tentative detection of OCS. The coma CO2/H2O mixing ratio of 7.6 ± 0.3 is among the highest ever observed in a comet, and is 4.5σ above the trend as a function of rH for long-period and Jupiter-family comets (excluding the outlier C/2016 R2). Our observations are compatible with an intrinsically CO2-rich nucleus, which may indicate that 3I/ATLAS contains ices exposed to higher levels of radiation than solar system comets or that it formed close to the CO2 ice line in its parent protoplanetary disk. A relatively low coma H2O gas abundance may also be implied, for example, due to inhibited heat penetration into the nucleus, which could suppress the H2O sublimation rate relative to CO2 and CO.

Keywords: Small Solar System bodies, Infrared spectroscopy, Comet nuclei, Ice spectroscopy, Molecular spectroscopy, Astrochemistry, Interstellar objects, Protoplanetary disks, Planetesimals, Comet volatiles
Astrometric Methods for Detecting Exomoons Orbiting Imaged Exoplanets: Prospects for Detecting Moons Orbiting a Giant Planet in α Centauri A's Habitable Zone. Nearby giant exoplanets offer an opportunity to search for moons (exomoons) orbiting them. Here, we present a simulation framework for investigating the possibilities of detecting exomoons via their astrometric signal in planet-to-star relative astrometry. We focus our simulations on α Centauri A, orbited by a hypothetical giant planet consistent with candidate detections in Very Large Telescope and James Webb Space Telescope observations. We consider a variety of observatory architectures capable of searching for exomoons, including upcoming facilities and also a hypothetical dedicated facility—e.g., a purpose-built space telescope with diameter = 3 m, central observing wavelength of 500 nm, and contrast-limited performance of ∼10‑9 in 1 hr observations. We find that such a facility would be capable of detecting ∼Earth-mass moons in a 5 yr campaign, assuming a Saturn-mass planet. More generally, we simulate expected detection limits for a variety of levels of astrometric precision. We find that moons as small as ∼0.2 M⊕ on orbital periods of 4‑30 days can be detected with astrometric precision of 0.1 mas and observing cadence of 1 hr over a 5 yr campaign. Additionally, we find that a 39 m ground-based telescope can detect Earth-sized exomoons orbiting the same hypothetical planet with a more modest observing cadence of 1 day. We discuss these results as motivation for a dedicated space observatory as well as a more detailed study of the physical parameters of a greater variety of star–planet–moon systems.

Keywords: Exoplanet astronomy, Natural satellites (Extrasolar), Space astrometry
Coexistence of Longitudinal and Transverse Oscillations in Polar Plumes Observed with Solar Orbiter/Extreme Ultraviolet Imager. Magnetohydrodynamic waves play a key role in heating the solar corona and driving the solar wind. Recent observations have shown the presence of slow magnetoacoustic and Alfvénic waves in polar plumes and interplumes. However, a complete understanding of wave dynamics in the polar regions has long been limited by the lack of simultaneous high-resolution observations. In this study, we utilize a high-spatial-resolution (210 km per pixel) and high-cadence (5 s) data set from the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter, acquired on 2021 September 14. Our findings reveal the simultaneous presence of slow magnetoacoustic and Alfvénic waves within the same polar plumes. For the slow magnetoacoustic waves, the amplitudes of the propagating disturbances are 1.4%–3.2% of the background intensity, with periodicities of 9 minutes, and the projected speeds of these disturbances range between 115 and 125 km s‑1. The corresponding electron temperatures in plumes range between 0.58 and 0.69 MK. The damping lengths of these propagating disturbances for five plumes are ≈2.4–7.1 Mm. The propagating disturbances are also detected in the fine-scale substructures within the plumes. Alfvénic waves, on the other hand, are detected with average displacement amplitude, periodicity, and velocity amplitude of 165 ± 82 km, 93 ± 39 s, and 12 ± 7 km s‑1, respectively. The ranges for the displacement amplitude, period, and velocity amplitude are 50–600 km, 50–250 s, and 3–32 km s‑1, respectively. These results mark the first demonstration of the ability of Solar Orbiter/EUI to simultaneously detect both slow magnetoacoustic and Alfvénic wave modes extending up to 20 Mm in polar plumes.

Keywords: The Sun, Solar coronal waves, Solar corona
A Carbon-rich Disk Surrounding a Planetary-mass Companion. During the final assembly of gas giant planets, circumplanetary disks (CPDs) of gas and dust form due to the conservation of angular momentum, providing material to be accreted onto the planet and the ingredients for moons. The composition of these disks has remained elusive, as their faint nature and short separations from their host stars have limited our ability to access them. Now, with the spatial and spectral resolution of the JWST/MIRI Medium-Resolution Spectrograph, we can observe and characterize this reservoir for wide-orbit planetary-mass companions for the first time. We present the mid-infrared spectrum from the CPD surrounding the young companion CT Cha b. The data show a carbon-rich chemistry with seven carbon-bearing molecules (up to C6H6) and one isotopolog detected and indicate a high gaseous C/O &gt; 1 that is in contrast with the elemental abundance ratios typically measured in directly imaged gas giant atmospheres. This carbon-rich chemistry is also in stark contrast to the spectrum of the disk surrounding the host star, CT Cha A, which shows no carbon-bearing molecules. This difference in disk chemistry between the host disk and its companion indicates rapid, divergent chemical evolution on ∼million-year timescales. Nonetheless, the chemical properties of the CPD follow trends observed in isolated objects, where disks transition from an oxygen-rich to carbon-rich composition with decreasing host mass. Our results provide the first direct insight into the chemical and physical properties of material being accreted onto a gas giant analog and into its potential moon system.

Keywords: Exoplanet formation, High contrast spectroscopy, Protoplanetary disks, Infrared spectroscopy
Modeling Tails of Escaping Gas in Exoplanet Atmospheres with Harmonica. Exoplanets that reside close to their host stars, and therefore receive substantial amounts of X-ray and ultraviolet radiation, are prone to suffer from strong atmospheric escape. This can lead to the creation of an envelope of escaping gas along the planet's orbital trajectory, often referred to as a tail. When transiting in front of their host star, these tails can not only produce larger depths in the transit light curves but also introduce significant asymmetries between ingress and egress. Using the publicly available software Harmonica, we present a method to model the light curves of transiting planets surrounded by extended envelopes of escaping gas and subsequently infer the shape and size of the latter. We apply this method to the JWST NIRISS/SOSS observations of HAT-P-18 b, which show pronounced helium tail features in the spectroscopic light curve of the metastable helium triplet at 10830 Å. Our model reveals that, in order to fit the observed light curve of HAT-P-18 b, the planet must possess a trailing helium tail of  15.79‑1.05+1.14  planetary radii. We carry out injection-recovery tests to validate the effectiveness of the proposed methodology. We demonstrate that, with sufficient precision, we would be able to fit a multilayer envelope to the data, which would provide insight into the relative radial variations in the opacity profile.

Keywords: Exoplanet atmospheres, Transits, Exoplanets, James Webb Space Telescope
Survival of 2D Turbulence in the Local Interstellar Medium. The evolution of 2D turbulence in the partially ionized local interstellar medium is investigated using 2D MHD simulations coupled with a neutral hydrogen gas via charge exchange. While it has been discussed that Alfvén and compressible waves are damped in a partially ionized plasma due to plasma-neutral drag effects, little is known about how (quasi-)2D turbulence (or magnetic flux ropes) interacts with a neutral gas. We expect that quasi-2D turbulence is unaffected by such an interaction since there is no associated velocity fluctuation, and our nonlinear simulation reveals that magnetic fluctuations in a partially ionized plasma are undamped, whereas the magnetic, kinetic plasma, and neutral spectra are modified to a −7/3 spectrum. The modified spectra can be explained by a Kolmogorov-type scaling law in which the turbulence cascade occurs through magnetic reconnection, as observed in the simulation. Our result suggests that magnetic fluctuations perpendicular to the background magnetic field cascade down to smaller scales without damping, whereas Alfvénic turbulence is damped at the characteristic scale associated with the plasma-neutral drag, and LISM turbulence will be magnetically rather than kinetically dominated. We note that the possible dominance of quasi-2D turbulence in the local interstellar medium can be crucial to the diffusive transport of cosmic rays.

Keywords: Interplanetary turbulence, Space plasmas, Interstellar medium