Sazuna/UAT_keywords huggingface dataset:
A Thick Volatile Atmosphere on the Ultrahot Super-Earth TOI-561 b. Ultrashort-period (USP) exoplanets—with Rp ≤ 2R⊕ and periods ≤1 day—are expected to be stripped of volatile atmospheres by intense host star irradiation, which is corroborated by their nominal bulk densities and previous eclipse observations, consistent with bare-rock surfaces. However, a few USP planets appear anomalously underdense relative to an Earth-like composition, suggesting an exotic interior structure (e.g., coreless) or a volatile-rich secondary atmosphere increasing their apparent radius. Here, we present the first dayside emission spectrum of the low-density (4.3 ± 0.4 g cm−3) USP planet TOI-561 b, which orbits an iron-poor, alpha-rich, ∼10 Gyr old thick-disk star. Our 3─5 μm JWST/NIRSpec observations demonstrate the dayside of TOI-561 b is inconsistent with a bare-rock surface at high statistical significance, suggesting instead a thick volatile envelope that is cooling the dayside to well below the ∼3000 K expected in the bare-rock or thin-atmosphere case. These results reject the popular hypothesis of complete atmospheric desiccation for highly irradiated exoplanets and support predictions that planetary-scale magma oceans can retain substantial reservoirs of volatiles, opening up the geophysical study of ultrahot super-Earths through the lenses of their atmospheres.

Keywords: Exoplanets, Exoplanet atmospheres
Characterization of the Host Binary of the Directly Imaged Exoplanet HD 143811 AB b. HD 143811 AB is the host star to the directly imaged planet HD 143811 AB b, which was recently discovered using data from the Gemini Planet Imager and Keck NIRC2. A member of the Sco-Cen star-forming region with an age of 13 ± 4 Myr, HD 143811 AB is somewhat rare among hosts of directly imaged planets, as it is a close stellar binary, with an ∼18-day period. Accurate values for the orbital and stellar parameters of this binary are needed to understand the formation and evolutionary history of the planet in orbit. We utilize archival high-resolution spectroscopy from FEROS on the MPG/ESO 2.2 m telescope to fit the orbit of the binary, and we combine with unresolved photometry to derive the basic stellar properties of the system. From the orbit, we derive precise values of orbital period of 18.59090 ± 0.00007 days and mass ratio of 0.886 ± 0.003. When combined with stellar evolutionary models, we find masses of both components of  MA=1.30−0.05+0.03  M⊙ and  MB=1.15−0.04+0.03  M⊙. While the current data are consistent with the planet and stellar orbits being coplanar, the 3D orientations of both systems are currently poorly constrained, with additional observations required to more rigorously test for coplanarity.

Keywords: Spectroscopic binary stars, Binary stars, Exoplanets, Planet hosting stars
HD 143811 AB b: A Directly Imaged Planet Orbiting a Spectroscopic Binary in Sco-Cen. We present confirmation of HD 143811 AB b, a substellar companion to spectroscopic binary HD 143811 AB through direct imaging with the Gemini Planet Imager (GPI) and Keck NIRC2. HD 143811 AB was observed as a part of the GPI Exoplanet Survey in 2016 and 2019 and is a member of the Sco-Cen star formation region. The exoplanet is detected ∼430 mas from the host star by GPI. With two GPI epochs and one from Keck/NIRC2 in 2022, we confirm through common proper motion analysis that the object is bound to its host star. We derive an orbit with a semimajor axis of  64−14+32  au and eccentricity  0.23−0.16+0.24 . Spectral analysis of the GPI H-band spectrum and NIRC2 L' photometry provides additional proof that this object is a substellar companion. We compare the spectrum of HD 143811 AB b to PHOENIX stellar models and Exo-Radioactive-Convective Equilibrium Model (REM) exoplanet atmosphere models and find that Exo-REM models provide the best fits to the data. From the Exo-REM models, we derive an effective temperature of  1042−132+178  K for the planet and translate the derived luminosity of the planet to a mass of 5.6 ± 1.1 MJup assuming hot-start evolutionary models. HD 143811 AB b is the first directly imaged planet around a binary that is not on an ultrawide orbit. Future characterization of this object will shed light on the formation of planets around binary star systems.

Keywords: Binary stars, Substellar companion stars, Exoplanets, Exoplanet astronomy, Direct imaging
Cospatial Multiwavelength Observations of an Eruptive Prominence as the Bright Core of a Coronal Mass Ejection. Coronal mass ejections (CMEs), as seen in white-light (WL) coronagraphs, often exhibit a classic three-part structure consisting of a bright front, a dark cavity, and a bright core. With the launch of Solar Orbiter, cospatial imaging of solar eruptions in multiwavelengths of extreme-ultraviolet (EUV) and WL has become available. We present a CME that erupted on 2022 September 23, observed under a uniquely favorable viewing geometry. The CME bright core and its eruptive prominence can be cospatially observed up to a coronal height of 3.5 R⊙ in the middle corona, in WL using COR1 on board STEREO-A and in EUV using the Full Sun Imager on board Solar Orbiter. Cospatial, multiwavelength observations indicate that the CME bright core observed in WL was almost entirely composed of the prominence material, which was heated during the CME eruption. EUV emissions in 174 and 304 Å of the prominence were largely cospatial when the CME propagated to the middle corona, though subtle differences remained. We further discuss the potential temperature in the bright core region and find that the core was heated as it rose, likely reaching temperatures of about 0.1─0.8 MK.

Keywords: Solar prominences, Solar coronal mass ejections
A Compact Multiplanet System of Three Transiting Giant Planets around TIC 118798035. We report the discovery and characterization of three transiting giant planets in the TIC 118798035 system. The three planets were identified as transiting candidates from data of the TESS mission and confirmed with ground-based photometric transit observations along with radial velocity variations obtained with FEROS, HARPS, and ESPRESSO. The three planets present transit timing variations (TTVs). We performed an N-body orbital fitting to the TTVs and radial velocities, finding that TIC 118798035 b is a warm low-density Neptune with a mass of 0.0250 ± 0.0023 MJ, a radius of 0.655 ± 0.018 RJ, and an orbital period of 11.507 days; TIC 118798035 c is a warm Saturn with a mass of 0.403 ± 0.024 MJ, a radius of 0.973 ± 0.023 RJ, and an orbital period of 22.564 days; and TIC 118798035 d is a warm Jupiter with a mass of 0.773 ± 0.052 MJ, a radius of 0.923 ± 0.044 RJ, and an orbital period of 48.925 days. The bulk metallicities of the three planets do not fully follow the mass─metallicity correlation found for the giant planets of the solar system, which hints at a somewhat different formation history for the planets of the TIC 118798035 system.

Keywords: Transits, Exoplanet astronomy, Transit timing variation method, Radial velocity, Extrasolar gaseous giant planets
A Close Look at the Closest Nitrogen-loud Active Galaxy Akn 564. As a typical secondary element, nitrogen is produced mainly by hydrogen burning in intermediate-mass stars, while α-elements such as carbon and oxygen originate from helium burning in more massive stars. Nitrogen abundance ZN and abundance ratio N/α serve as living fossil for investigating galaxy chemical evolution. A peculiar subclass of active galaxies, namely, "nitrogen-loud" active galactic nuclei (AGN), are of particular interest, with exceptionally strong [N III] λ1750 and [N IV] λ1486 broad emission lines (BELs), but then normal in all of the other BELs. Although it is generally believed that both ZN and N/α are extremely high in the broad-line region (BLR), the nature of their host galaxies remains elusive after more than two decades of extensive studies, as all known nitrogen-loud AGN are far away at z &gt; 1.6. Here we identify the prototype NLS1 Akn 564 (z = 0.024) as the first local nitrogen-loud AGN, with [N III] and [N IV] twice as strong as in the composite spectrum of nitrogen-loud AGN. Emission lines commonly used for abundance diagnostics are all detected with high signal-to-noise ratio. The α-elements show a significant difference between the galactic and the inner galactic region, increasing from Zα,H II(5.4 kpc) ≍ 0.3 Z⊙ to Zα,NLR(100 pc) ≍ Zα,BLR(0.01 pc) ≍ 0.6─0.7 Z⊙, while a steep gradient is found for N/α, jumping from (N/α)NLR ≍ 1(N/α)⊙ to (N/α)BLR ≍ 4 (N/α)⊙within ∆r ≲ 100 pc. This finding indicates different star-formation histories at different scales and the AGN activity possibly driven by the stellar processes in the circumnuclear region, which could be investigated in detail by follow-up high spatial resolution 3D spectroscopy.

Keywords: AGN host galaxies, Abundance ratios, Active galaxies, Chemical abundances, Galaxies
A Sudden Fine-scale Bright Kernel Captured by Hi-C Flare in 11 MK Emission during an M1.6-class Solar Flare's Postmaximum Phase. On 2024 April 17, the third successful Hi-C sounding rocket flight, Hi-C Flare, recorded coronal images in Fe XXI 129 Å emission from 11 MK plasma during the postmaximum phase of an M1.6-class solar flare, achieving unprecedented spatial (∼300 km) and temporal (1.3 s) resolutions. The flare started at 21:55 UT, peaked at 22:08 UT, and lasted ∼40 minutes. Hi-C observed for over 5 minutes (22:15:45─22:21:25), starting roughly 8 minutes after flare maximum. A sudden compact bright burst—875 ± 25 km wide, lasting 90 ± 1.3 s, exhibiting a proper motion of ∼ 50 km s−1, and splitting into two toward the end—occurs near the foot of some postflare loops. Its size and brightness are reminiscent of flare-ribbon kernels during a flare's rapid rise phase, kernels marking sites of sudden heating and hot plasma upflow, making its occurrence during the late phase surprising. Such isolated brightenings in a flare's postmaximum phase are rare and have not been previously reported. The kernel was detected in all Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly channels. Its 1600 Å light curve peaked ∼50 s earlier than its 131 Å light curve, similar to that of flare-ribbon kernels, albeit with a smaller delay of ∼25 s, during the impulsive phase of the flare. In SDO/Helioseismic Magnetic Imager magnetograms, the kernel sits in unipolar positive magnetic flux near an embedded clump of negative flux. Although localized magnetic reconnection within the kernel (a microflare) cannot be ruled out for its cause, the observations favor the localized brightening being an isolated, exceptionally late flare-ribbon kernel, resulting from an exceptionally late burst of the flare's coronal reconnection.

Keywords: Solar active region magnetic fields, Solar flares, Solar extreme ultraviolet emission, Solar coronal heating, Solar active regions, Solar corona, Solar activity, Magnetic fields
Suppression of Inverse Magnetic Energy Transfer in Collisionless Marginally Magnetized Plasmas. We investigate the inverse cascade of magnetic energy in decaying, collisionless pair plasmas with moderate to high β values via first-principles numerical simulations and analytical theory. We find that pressure-anisotropy-driven instabilities, in particular the firehose instability, suppress reconnection-driven coalescence of magnetic structures (i.e., inverse transfer) by nullifying magnetic tension. The presence of a magnetic guide field of sufficient strength restores the system's ability to inverse transfer magnetic energy. These results reveal that inverse energy transfer in collisionless plasmas is not guaranteed, but rather depends sensitively on magnetization. In the astrophysical context, this identifies a kinetic mechanism by which Weibel-generated seed fields may fail to merge consistently, potentially limiting their role in cosmic magnetogenesis.

Keywords: Intergalactic medium, Plasma astrophysics, Magnetic fields, Plasma physics
AT2025ulz and S250818k: Deep X-Ray and Radio Limits on Off-axis Afterglow Emission and Prospects for Future Discovery. The first joint electromagentic (EM) and gravitational-wave (GW) detection, known as GW170817, marked a critical juncture in our collective understanding of compact object mergers. However, it has now been 8 yr since this discovery, and the search for a second EM-GW detection has yielded no robust discoveries. Recently, on 2025 August 18, the LIGO─Virgo─KAGRA Collaboration reported a low-significance (high-false-alarm rate) binary neutron star merger candidate S250818k. Rapid optical follow-up revealed a single optical candidate AT2025ulz (z = 0.08484) that initially appeared consistent with kilonova emission. We quickly initiated a set of observations with Swift, XMM-Newton, Chandra, and the Very Large Array to search for nonthermal afterglow emission. Our deep X-ray and radio search rules out that the optical rebrightening of AT2025ulz is related to the afterglow onset, reinforcing its classification as a stripped-envelope supernova (SN 2025ulz). We derive constraints on the afterglow parameters for a hypothetical binary neutron star merger at the distance of AT2025ulz (≍400 Mpc) based on our X-ray and radio limits. We conclude that our observational campaign could exclude a GW170817-like afterglow out to viewing angles of θv ≍ 12 .° 5. We briefly discuss the prospects for the future discovery of off-axis afterglows.

Keywords: Neutron stars, Gamma-ray bursts, Relativistic jets, Gravitational waves, Time domain astronomy, Compact objects
Evolution of the ZTF SLRN-2020 Star-Planet Merger. We model the optical and infrared transient ZTF SLRN-2020, previously associated with a star-planet merger. We consider the scenario in which orbital decay via tidal dissipation led to the merger, and we find that tidal heating within the star was likely unobservable in the archival image of the system taken 12 yr before the merger. The observed dust formation months before the merger is consistent with a planet of mass Mp ≳ 5MJ ejecting material as it skims the stellar surface. This interaction gradually intensifies, leading to significant mass ejection on a dynamical timescale (≍hours) as the planet plunges into the stellar interior. Part of the recombination transient associated with this dynamical mass ejection might be inaccessible to the optical observations because its duration (≍hours) is comparable to the cadence. Correspondingly, the observed duration of the transient (≍100 days) is inconsistent with a single episode of dynamical mass ejection. Instead, the transient could be powered by the recombination of 3.4 × 10−5M⊙ of hydrogen in an outflow, or the contraction of an inflated envelope of mass ≍10−6M⊙ that formed during the merger. The observed ejecta mass 320 days after the peak of the optical transient is ≍1.3 × 10−4M⊙, consistent with the idea that a fraction of the ejecta might be unobservable in the light curve. Energetically, this post-merger ejecta mass suggests a planet at least as massive as Jupiter. Our results suggest that ZTF SLRN-2020 was the result of a merger between a star close to the main sequence and a planet with mass at least several times that of Jupiter.

Keywords: High energy astrophysics, Stellar astronomy, Exoplanets
The First Radio View of a Type Ibn Supernova in SN 2023fyq: Understanding the Mass-loss History in the Last Decade before the Explosion. Supernovae that interact with hydrogen-poor, helium-rich circumstellar material (CSM), known as type Ibn supernovae (SNe Ibn), present a unique opportunity to probe mass-loss processes in massive stars. In this work, we report the first radio detection of an SN Ibn, SN 2023fyq, and characterize the mass-loss history of its stellar progenitor using the radio and X-ray observations obtained over 18 months post-explosion. We find that the radio emission from 58 to 185 days is best modeled by synchrotron radiation attenuated by free─free absorption from a CSM of density ∼10−18 g cm−3 (∼106 ρISM) at a radius of 1016 cm, corresponding to a mass-loss rate of ∼4 × 10−3 M⊙ yr−1 (for a CSM velocity of 1700 km s−1 from optical spectroscopy) from 0.7 to 3 yr before the explosion. This timescale is consistent with the time frame over which pre-explosion optical outbursts were observed. However, our late-time observations at 525 days post-explosion yield nondetections, and the 3σ upper limits (along with an X-ray nondetection) allow us to infer a drop in the progenitor mass-loss rate at 5─10 yr pre-explosion with  Ṁ &lt; 2.5 × 10−3 M⊙ yr−1. These results suggest a shell-like CSM from at most 4 × 1015 to 2 × 1016 cm (∼105R⊙), with a CSM density that is roughly consistent with predictions from a merger model for this object. Future radio observations of a larger sample of SNe Ibn will provide key details on the extent and density of their helium-rich CSM.

Keywords: High energy astrophysics, Radio astronomy, Core-collapse supernovae, Stellar mass loss
A Yin-yang Galaxy Cluster Merger in A1914 Revealed by XRISM. Hierarchical mergers of galaxy clusters play a key role in converting gravitational energy into thermal and kinetic energy in the local Universe. Understanding this process requires the reconstruction of cluster merger geometry, with careful consideration of projection effects. With its unprecedented spectral resolution, XRISM enables the disentanglement of merging cluster components along the line of sight via X-rays for the first time. In this Letter, we focus on the massive cluster A1914, a puzzling case wherein the galaxy and dark matter (DM) distribution appear to be in tension with the X-ray morphology. We present XRISM observations of A1914 focusing on the velocity structure of the intracluster medium. The Resolve full-array spectrum requires two merging components along the line of sight, with bulk velocities offset by ∼1000 km s−1 and velocity dispersions of ∼200 km s−1. The subarray maps of flux ratios, bulk velocity, and velocity dispersion show the two components are offset and overlapping in the plane of the sky, consistent with a major (mass ratio ∼3), near line-of-sight merger with a pericenter distance of ∼200 kpc. We conclude that the two subclusters create an overlapping spiral pattern, referred to as a "yin-yang" merger. This scenario is further supported by tailored hydrodynamical simulations of the A1914 merger, demonstrating that this type of merger can broadly reproduce the observed X-ray morphology, gas temperature map, gas velocity maps, DM distribution, and galaxy velocities. This work demonstrates the power of high-resolution X-ray spectroscopy, provided by XRISM, to resolve complex cluster merger geometries.

Keywords: Galaxy clusters, Intracluster medium, High energy astrophysics
The CO-to-H<SUB>2</SUB> Conversion Factor in the Milky Way's Central Parsec. Carbon monoxide (CO) emission is a widely used tracer of molecular hydrogen (H2) in the interstellar medium, owing to its abundance, low excitation energy, and ease of detection in cold molecular environments, in contrast to H2 itself. While the CO-to-H2 conversion factor is often assumed to be constant across the disks of galaxies, deviations are observed in extreme environments such as the central molecular zone (CMZ) in galactic nuclei. Here we present the first estimate of the CO-to-H2 conversion factor on subkiloparsec scales. We calculate CO-to-H2 conversion in the Milky Way's circumnuclear disk/ring at ∼1 pc radius around the Galactic Center black hole. We derive a conversion factor of αCO ≃ 4.5 ± 2.5 M⊙ (K km s−1 pc2)−1 or X[CO] ≃ (2.1 ± 1.1) ×1020 cm −2(Kkms−1)−1 . This value is consistent with the Galactic disk but higher than the CMZ.

Keywords: Interstellar molecules, Radio spectroscopy, Galactic center, Interstellar medium, Galaxy circumnuclear disk, Galaxies
The JWST Rocky Worlds DDT Program Reveals GJ 3929b to Likely Be a Bare Rock. We report first results from the JWST Rocky Worlds Director's Discretionary Time program. Two secondary eclipses of the terrestrial exoplanet GJ 3929b were recently observed using MIRI photometric imaging at 15 μm. We present a reduction of these data using the updated SPARTA pipeline. We also refine the planet mass, radius, and predicted time of secondary eclipse using a new sector of TESS data and new, high-precision radial velocities from the MAROON-X spectrograph. For the two JWST observations, we recover secondary eclipse depths of 177  −45+47  ppm and 143  −35+34  ppm at times consistent with a nearly circular orbit, as expected from the radial velocity data. A joint fit of the two visits yields a dayside brightness temperature Tp,dayside = 782 ± 79 K for GJ 3929b, which is consistent with the maximum brightness temperature  Tmax=737±14  K for a bare black rock (i.e., assuming zero Bond albedo and no heat redistribution). These results rule out CO2-rich atmospheres thicker than 100 mbar at &gt;3σ, suggesting that GJ 3929b has lost any significant secondary atmosphere. The radial velocity data also indicate two additional nontransiting planets in the system: a previously identified planet in a 15.0 days orbit and a newly identified planet candidate in a 6.1 days orbit.

Keywords: Exoplanet atmospheric composition , Astrometric exoplanet detection, Exoplanets, Exoplanet systems, Exoplanet surface composition, Exoplanet astronomy, Exoplanet surface characteristics, Exoplanet atmospheres, Exoplanet atmospheric structure
The Formation Rate and Luminosity Function of Fast X-Ray Transients from Einstein Probe. Following its launch on 2024 January 9, the Einstein Probe (EP) telescope has detected hundreds of fast X-ray transients (FXTs), yet their physical origins remain elusive. Understanding their luminosity function and formation rate is crucial for elucidating their nature. Recently, the EP team has provided the latest catalog of EP-detected FXTs. Based on this catalog, we present a model-independent nonparametric approach to derive the luminosity function and formation rate of FXTs. Our analysis reveals significant cosmological luminosity evolution, characterized by a scaling relationship of (1 + z)3.58. After accounting for this evolution, we establish that the local luminosity function is best represented by a broken power law, with a break luminosity of (4.17 ± 0.34) × 1046 erg s−1. The formation rate exhibits a broken power law as ρ(z) ∝ (1 + z)−4.25 at z ⪅ 0.9 and ρ(z) ∝ (1 + z)−0.26 at z ⪆ 0.9, yielding a local rate of approximately  153.8−95.1+249.4  Gpc−3 yr−1. This rate is higher than that of long gamma-ray bursts (LGRBs). Our findings indicate that a component of FXTs is associated with LGRBs.

Keywords: X-ray astronomy, X-ray transient sources, Gamma-ray bursts
Evolution of Flare Ribbon Bead-like Structures in a Solar Flare. We present fast-cadence and high-resolution observations of flare ribbons from the Solar Orbiter Extreme Ultraviolet Imager (EUI). Utilizing the short-exposure observations from the EUI High Resolution Imager in the extreme-ultraviolet, we find small-scale blob/bead-like kernel structures propagating within a hook at the end of a flare ribbon, during the impulsive phase of a C9.9-class solar flare. These bead structures are dynamic, with well-resolved spatial separations as low as ≍420─840 km (3─6 pixels) below the observable limit of full-disk solar imagers. We analyze the evolution of the plane-of-sky apparent velocity and separation of the flare ribbon structures, finding evidence for multiple processes occurring simultaneously within the flare ribbon. These processes include quasiperiodic pulsation─like brightenings, slow back-and-forth zigzag motions along the ribbon, rapid apparent motions along the ribbon (600+ km s−1), and stationary blob-like structures. Finally, we conduct fast Fourier transform analysis and analyze the start times of exponential growth in the power spectrum at different spatial scales across the flare ribbon. Our analysis reveals that the ribbon beads form with a key spatial separation of 1.7─1.9 Mm before developing into more complex structures at progressively larger and smaller spatial scales. This observation is consistent with predictions of the tearing mode instability.

Keywords: Solar atmosphere, Solar flares, Solar magnetic reconnection, Solar extreme ultraviolet emission