Sazuna/UAT_keywords huggingface dataset:
VLT/ERIS Observations of the V960 Mon System: A Dust-embedded Substellar Object Formed by Gravitational Instability?. V960 Mon is an FU Orionis object that shows strong evidence of a gravitationally unstable spiral arm that is fragmenting into several dust clumps. We report the discovery of a new substellar companion candidate around this young star, identified in high-contrast  L' -band imaging with Very Large Telescope/Enhanced Resolution Imager and Spectrograph. The object is detected at a projected separation of 0 .″ 898 ± 0 .″ 01 with a contrast of (8.39 ± 0.07) × 10−3. The candidate lies close to the clumps previously detected in the submillimeter (at 1.3 mm) and is co-located with extended polarized IR signal from scattered stellar irradiation, suggesting it is deeply embedded. The object is undetected in the SPHERE H-band total intensity, placing an upper mass limit of ∼38 MJup from the contrast curve. Using evolutionary models at an assumed age of 1 Myr, we estimate a mass of ∼660 MJup from the L' brightness; however, this value likely includes a significant contribution from a disk around the companion. The discrepancy between near- and mid-infrared results again suggests the source is deeply embedded in dust. This candidate may represent an actively accreting, disk-bearing substellar object in a young, gravitationally unstable environment.

Keywords: High contrast techniques, Planetary-disk interactions, Exoplanets, Astronomy image processing, Protostars, Adaptive optics, Exoplanet astronomy, Direct imaging, Protoplanetary disks, Star formation, Exoplanet detection methods, Planet formation
Hydrogen Loss on Venus Driven by Photochemistry. Venus has experienced substantial H loss through hydrodynamic outflow in its early history, transforming from a warm and wet state to the current arid and scorching state. While Venus continues to lose H today, no consensus has been reached regarding the present dominant escape mechanisms. Recently, photochemical escape via HCO+ dissociative recombination (DR) has been proposed as a prevailing process that had previously been overlooked. However, due to uncertainties in the underlying H2 abundance and the solar cycle variations of the input radiative energy, it is essential to explore how these factors influence the modeled H escape flux under different conditions. By combining a photochemical model with a Monte Carlo test particle model, we demonstrate that the H escape flux increases with the underlying H2 concentration over a possible range of 1 × 106–2 × 108 cm‑2 s‑1, but varies nonmonotonically with solar activity due to the competition between photochemical production and collisional hindrance. While our results confirm the dominant role of HCO+ DR, we find that the ion-neutral reaction  OH++O→O2++H  makes an additional contribution, which could reach more than 30% of total H escape. Our findings provide valuable insights into the foundational understanding of photochemically driven H escape because the same mechanism should function in a much broader context.

Keywords: Atmospheric evolution, Upper atmosphere, Planetary atmospheres, Venus, Solar system terrestrial planets
Partial Differentiation of Callisto as Possible Evidence for Pebble Accretion. "Planetesimal or pebble" is one of the most fundamental open questions in planet formation theory. Similarly, "satellitesimal or pebble" remains unsettled regarding the formation of the Galilean satellites. I focus on a unique characteristic of Callisto—its interior is estimated to be only partially differentiated based on gravitational field measurements. I robustly demonstrate that such a state is not achievable through satellitesimal accretion, which inevitably leads to significant differentiation, but can be maintained with pebble accretion. Pebbles can release their impact energy at the surface of the satellite, allowing efficient radiative cooling, and their impact velocities can be reduced by aerodynamic drag from the circumplanetary gas disk. If future missions such as JUpiter ICy moons Explorer confirm that Callisto is indeed only partially differentiated, it could provide the first observed evidence for the pebble accretion mechanism—not only in the context of satellite formation but also in the broader framework of planet formation.

Keywords: Solar system formation, Ganymede, Callisto, Planetary science, Galilean satellites, Planet formation
On the Universality of the Split Monopole Black Hole Magnetosphere. Black holes (BHs) can acquire magnetic flux from their progenitor, through merger with a magnetized star, or via prolonged accretion. We study the evolution of BH magnetospheres using axisymmetric general relativistic magnetohydrodynamic simulations. We show that all initial magnetic field configurations, regardless of complexity, ultimately evolve into a split monopole. The magnetospheric evolution proceeds in two phases. In the first phase, pressure equilibrates on fast Alfvénic timescales (∼60 gravitational light-crossing times), and the flux on the BH event horizon drops sharply. The second phase proceeds in pressure balance, in which the magnetic flux decays via magnetic reconnection in current sheets, governing the dynamics on slower resistive timescales. We present an analytic model for the second phase, quantitatively describing the evolution of flux and current sheet dynamics. Additionally, we show that in the split monopole configuration, magnetic flux decays exponentially, with higher BH spin leading to slower decay. Our results enable a quantitative prediction of the timescales and spatial structure of these evolving magnetospheres, essential for understanding electromagnetic counterparts to gravitational wave events and reconnection-powered flares from accreting BHs.

Keywords: Magnetohydrodynamics, High energy astrophysics, Relativity, Plasma astrophysics, Compact objects, Magnetic fields
EP240801a/XRF 240801B: An X-Ray Flash Detected by the Einstein Probe and the Implications of Its Multiband Afterglow. We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on 2024 August 1 by the Einstein Probe (EP) satellite with a weak contemporaneous signal also detected by the Fermi Gamma-ray Burst Monitor (GBM). Optical spectroscopy of the afterglow, obtained by Gran Telescopio Canarias and Keck, identified the redshift of z = 1.6734. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates that the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP Wide-field X-ray Telescope and Fermi/GBM data yields an isotropic energy  Eγ,iso=(5.57‑0.50+0.54)×1051erg , a peak energy  Epeak=14.90‑4.71+7.08keV , and a fluence ratio S(25–50 keV)/S (50–100keV)=1.67‑0.46+0.74 , classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early R-band behavior and EP Follow-up X-ray Telescope observations suggest multiple components in the afterglow. Three models are considered: a two-component jet model, a forward-reverse shock model, and a forward shock model with energy injection. All three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs.

Keywords: X-ray transient sources, Gamma-ray bursts
JWST/MIRI Reveals the True Number Density of Massive Galaxies in the Early Universe. Early JWST studies reporting an unexpected abundance of massive galaxies at z ∼ 5─8 challenge galaxy formation models in the ΛCDM framework. Previous stellar mass (M⋆) estimates suffered from large uncertainties due to the lack of rest-frame near-infrared data. Using deep JWST/NIRCam and Mid-Infrared Instrument (MIRI) photometry from Public Release IMaging for Extragalactic Research, we systematically analyze massive galaxies at z ∼ 3─8, leveraging rest-frame ≳1 μm constraints. We find MIRI is critical for robust M⋆ measurements for massive galaxies at z &gt; 5: excluding MIRI overestimates M⋆ by ∼0.4 dex on average for M⋆ &gt; 1010M⊙ galaxies, with no significant effects at lower masses. This reduces number densities of M⋆ &gt; 1010M⊙ (1010.3M⊙) galaxies by ∼36% (55%). MIRI inclusion also reduces "Little Red Dot" (LRD) contamination in massive galaxy samples, lowering the LRD fraction from ∼32% to ∼13% at M⋆ &gt; 1010.3M⊙. Assuming pure stellar origins, LRDs exhibit M⋆ ∼ 109─10.5M⊙ with MIRI constraints, rarely exceeding 1010.5M⊙. Within standard ΛCDM, our results indicate a moderate increase in the baryon-to-star conversion efficiency (ϵ) toward higher redshifts and masses at z &gt; 3. For the most massive z ∼ 8 galaxies, ϵ ∼ 0.3, compared to ϵ ≲ 0.2 for typical galaxies at z &lt; 3. This result is consistent with models where high gas densities and short free-fall times suppress stellar feedback in massive high-z halos.

Keywords: Cosmology, Early universe, Galaxy formation, High-redshift galaxies
Acceleration of Solar Eruptions via Enhanced Torus Instability Driven by Small-scale Flux Emergence. Despite decades of research, the fundamental processes involved in the initiation and acceleration of solar eruptions remain not fully understood, making them long-standing and challenging problems in solar physics. Recent high-resolution observations by the Goode Solar Telescope have revealed small-scale magnetic flux emergence in localized regions of solar active areas prior to eruptions. Although much smaller in size than the entire active region, these emerging fluxes reached strengths of up to 2000 G. To investigate their impact, we performed data-constrained magnetohydrodynamic simulations. We find that while the small-scale emerging flux does not significantly alter the preeruption evolution, it dramatically accelerates the eruption during the main phase by enhancing the growth of torus instability, which emerges in the nonlinear stage. This enhancement occurs independently of the decay index profile. Our analysis indicates that even subtle differences in the preeruption evolution can strongly influence the subsequent dynamics, suggesting that small-scale emerging flux can play a critical role in accelerating solar eruptions.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar flares, Solar coronal mass ejections, Active solar corona, Magnetohydrodynamical simulations
Breaking the Mass Inclination Degeneracy of Radial Velocity Measurements via Monitoring von Zeipel–Lidov–Kozai Cycles: Implications in the HD 41004 System. We investigate the dynamical stability of the S-type planet in the compact binary HD 41004. Using N-body simulations, we find that the planet could be dynamically stable at a mutual inclination angle of up to ∼75°. The von Zeipel–Lidov–Kozai (vZLK) mechanism becomes active when the mutual inclination is greater than 39 .° 2. High-inclination orbits exhibit coupled oscillations in eccentricity and inclination, along with apsidal precession. Synthetic radial velocity (RV) modeling shows that these secular variations produce measurable signatures across a broad range of timescales, from full vZLK cycles to observationally accessible decades. For instance, a high mutual inclination at 75° can induce RV drifts exceeding 5 m s‑1 per planetary orbit (∼1.9 m s‑1 yr‑1) in circular binary configurations. The presence of eccentric vZLK further accelerates these drifts, enhancing the detectability. Long-term RV observations of this system offer a unique pathway to dynamically constrain the orbital inclination and thus determine the true mass of HD 41004 Ab. The degeneracy of mass inclination is well known when using RV measurements alone. Our results highlight that HD 41004 Ab and potentially other S-type planets in compact binaries are promising targets for breaking such a degeneracy by studying the dynamics induced by the vZLK mechanism through long-term high-precision RV monitoring.

Keywords: Exoplanet dynamics, Binary stars, Exoplanets, Celestial mechanics, Radial velocity, N-body simulations
Magnetic Field Monitoring of Four Massive A–F Supergiants. We report magnetic field measurements spanning about 15 yr of four massive (7.5–15 M⊙) supergiant stars: α Per (HD 20902, F5Iab), α Lep (HD 36673A, F0Ib), η Leo (HD 87737, A0Ib) and 13 Mon (HD 46300, A1Ib). For each star, spectropolarimetric observations were collected using ESPaDOnS at the Canada–France–Hawaii Telescope. The observed spectra were coadded, normalized, and then processed using least-squares deconvolution to yield mean Stokes I and V profiles. Each spectrum was analyzed to infer the false-alarm probability of signal detection, and the longitudinal magnetic field was measured. This process yielded persistent detection of magnetic fields in all four stars. The median 1σ longitudinal field uncertainty of the Zeeman detections was 0.6 G. The maximum unsigned longitudinal magnetic fields measured from the detections are rather weak, ranging from 0.34 ± 0.19 G for α Lep to 2.61 ± 0.55 G for 13 Mon. The Zeeman signatures show different levels of complexity; those of the two hotter stars are relatively simple, while those of the two cooler stars are more complex. The stars also exhibited different levels of variability of their Zeeman signatures and longitudinal fields. We report periodic variability of the longitudinal field and (complex) Stokes V profiles of α Per with a period of either 50.75 days or 90 days. The (simple) Stokes V profiles of 13 Mon, and probably those of η Leo, show global polarity changes once during the period of observation, but the data are insufficient to place strong constraints on the variability timescales. *This work is based on observations obtained at the Canada–France–Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. The observations at the CFHT were performed with care and respect from the summit of Maunakea, which is a significant cultural and historic site.

Keywords: Stellar magnetic fields
The Cosmic Evolution and Spatial Distribution of Multiphase Gas Associated with QSOs. We investigate the multiphase gas surrounding QSOs traced by 33 absorption lines (e.g., Lyα, C IV, Fe II, Mg II, etc.) in the stacked spectra of background sources, using the Early Data Release from the Dark Energy Spectroscopic Instrument. Our analysis reveals that the equivalent width (W) of metal absorption lines decreases with increasing redshift, following an overall trend described by W ∝ (1 + z)‑4.0±2.7. Different species that trace multiphases of QSO-associated gas exhibit distinct evolutionary patterns. Additionally, the W of these absorption lines decreases with distance (D) from QSOs, which can be effectively characterized by a two-halo model. Compared to the projected two point correlation function of galaxies at similar redshifts, low-ionization ions exhibit similar clustering scales, while high-ionization ions show a significantly more extended spatial distribution. We also find that WFeII/WMgII increases toward lower redshifts, which can be attributed to evolving star formation histories and/or changes in initial mass function for galaxies. By leveraging multiple absorption tracers, we conduct the first comprehensive investigation of diffuse, multiphase gas from the circumgalactic medium to cosmological scales, offering new insights into baryon cycles and the transport of metals throughout cosmic time.

Keywords: Intergalactic medium, Cosmic abundances, Quasar absorption line spectroscopy, Circumgalactic medium
Indication for a Compact Object Next to a LIGO–Virgo Binary Black Hole Merger. The astrophysical origin of binary black hole (BBH) mergers remains uncertain, although many events have been observed by the LIGO–Virgo–KAGRA network. Such mergers are potentially originated in the vicinity of massive black holes (MBHs). GW190814, due to its secondary mass and mass ratio being beyond the expectations of isolated stellar evolution theories, is a promising event that has occurred in an active galactic nucleus (AGN) disk. In this model, a compact object resides in the vicinity of a merging BBH. Here we report multiple pieces of evidence suggesting that GW190814 is a BBH merging near a compact object. The orbital motion of BBHs around a third body produces a line-of-sight acceleration (LSA) and induces a varying Doppler shift. Using a waveform template that considers LSA, we perform Bayesian inference on a few BBH events with a high signal-to-noise ratio in the gravitational-wave (GW) transient catalog. Compared to the model for isolated BBH mergers, we obtain significantly higher network signal-to-noise ratios for GW190814 with the inclusion of LSA, constraining the LSA to  a=0.0015‑0.0008+0.0008cs‑1  at a 90% confidence level. Additionally, the Bayes factor for the LSA case over the isolated case is 58/1, indicating that the LSA model is strongly preferred by the GW data. We conclude that this is the first indication showing merging BBHs are located near a third compact object.

Keywords: Gravitational wave astronomy, Gravitational waves, Gravitational wave sources
GRB 221009A: Observations with LST-1 of CTAO and Implications for Structured Jets in Long Gamma-Ray Bursts. GRB 221009A is the brightest gamma-ray burst (GRB) observed to date. Extensive observations of its afterglow emission across the electromagnetic spectrum were performed, providing the first strong evidence of a jet with a nontrivial angular structure in a long GRB. We carried out an extensive observation campaign in very-high-energy (VHE) gamma rays with the first Large-Sized Telescope of the future Cherenkov Telescope Array Observatory starting on 2022 October 10, about 1 day after the burst. A dedicated analysis of the GRB 221009A data is performed to account for the different moonlight conditions under which data were recorded. We find an excess of gamma-like events with a statistical significance of 4.1σ during the observations taken 1.33 days after the burst, followed by background-compatible results for the later days. The results are compared with various models of afterglows from structured jets that are consistent with the published multiwavelength data but entail significant quantitative and qualitative differences in the VHE emission after 1 day. We disfavor models that imply VHE flux at 1 day considerably above 10−11 erg cm−2 s−1. Our late-time VHE observations can help disentangle the degeneracy among the models and provide valuable new insight into the structure of GRB jets.

Keywords: Gamma-ray bursts, Non-thermal radiation sources, Transient sources
Silicate Sundogs: Probing the Effects of Grain Directionality in Exoplanet Observations. Crystalline ice in Earth's atmosphere can produce spectacular phenomena due to orientation-dependent attenuation, such as sundogs and halos, providing diagnostics of the external processes acting on the aerosol grains. Crystalline mineral aerosols, such as quartz (SiO2) and enstatite/forsterite (MgSiO3/Mg2SiO4), have long been predicted to form in hot Jupiter atmospheres, with JWST's Mid-Infrared Instrument Low Resolution Spectrometer (MIRI LRS) verifying the existence of crystalline quartz observationally. Due to the strong horizontal winds (∼1─5 km s−1) and small aerosol grains (&lt;1 μm) found in hot Jupiter atmospheres, we show that aerosols could be mechanically aligned with the winds. We then derive direction-dependent optical properties of quartz, enstatite, and forsterite and model transmission and emission spectra assuming random and mechanically aligned orientations, finding that the orientation of all three crystalline aerosols can impart ≥100 ppm differences in observed spectra (8─12 μm). We run retrievals on JWST/MIRI LRS transmission and emission data of WASP-17b, and find that directionality alone cannot physically explain the transmission data, pointing towards polymorphs or insufficient laboratory data, and find weak hints of directionality (1.0─1.3σ) in the emission data. This work demonstrates the power of JWST/MIRI LRS in detecting aerosol directionality with future observations, and a technique by which to probe how aerosols interact with atmospheric dynamical processes. To foster the exploration of aerosols in exoplanet data, the open-source code POSEIDON has been updated (v1.3.1) to include 144 new direction- and temperature-dependent aerosols with precomputed optical properties, alongside new aerosol models.

Keywords: Hot Jupiters, Silicate grains, Atmospheric clouds, Exoplanets
A Deep Search for Ethylene Glycol and Glycolonitrile in the V883 Ori Protoplanetary Disk. Ethylene glycol ( (CH2OH)2 ; hereafter EG) and glycolonitrile ( HOCH2CN ; hereafter GN) are considered molecular precursors of nucleic acids. EG is a sugar alcohol and the reduced form of glycolaldehyde (CH2(OH)CHO; hereafter GA). GN is considered a key precursor of adenine formation (nucleotide) and can be a precursor of glycine (amino acid). Detections of such prebiotic molecules in the interstellar medium are increasingly common. How much of this complexity endures to the planet formation stage, and thus is already present when planets form, remains largely unknown. Here we report Atacama Large Millimeter/submillimeter Array observations in which we tentatively detect EG and GN in the protoplanetary disk around the outbursting protostar V883 Ori. The observed EG emission is best reproduced by a column density of  3.63‑0.12+0.11×1016cm‑2  and a temperature of at least 300 K. The observed GN emission is best reproduced by a column density of  3.37‑0.09+0.09×1016cm‑2  and a temperature of  88‑1.2+1.2  K. Comparing the abundance of EG and GN relative to methanol in V883 Ori with other objects, V883 Ori falls between hot cores and comets in terms of increasing complexity. This suggests that the buildup of prebiotic molecules continues past the hot core phase into the epoch of planet formation. Nascent planets in such environments may inherit essential building blocks for life, enhancing their potential habitability. Further observations of this protoplanetary disk at higher spectral resolution are required to resolve blended lines and to confirm these tentative detections.

Keywords: FU Orionis stars, Millimeter-wave spectroscopy, Pre-biotic astrochemistry, Protoplanetary disks, Complex organic molecules, Interferometry
The Intracluster Light Analysis of the Most Evolved Systems of Galaxies: Fossil Groups. We present the analysis of the intracluster light (ICL) in three fossil groups, RX J085640.72+055347.36, RX J1136+0713, and RX J1410+4145, at z ∼ 0.1. We used two optical broadband filters, F435W and F606W, observed with the Hubble Space Telescope, and spectroscopic data obtained with the Gemini Multi-Object Spectrograph to generate the ICL maps and measure the ICL fraction using CICLE, an algorithm developed to disentangle the ICL from the light of galaxies. We found ICL fractions of 9.9%─14.4%, 3.8%─6.1%, and 4.7%─10.7% for RXJ0856, RXJ1136, and RXJ1410, respectively. This behavior is not consistent with the presence of the ICL fraction excess previously observed in merging clusters, and is also inconsistent with the constant ICL fraction distribution characteristic of relaxed systems, although the values found are within the typical range expected for the latter. Instead, they show a significantly increasing trend with wavelengths over ∼3800─5500 Å, indicating that fossil groups are indeed old and undisturbed systems, even compared with regular relaxed clusters.

Keywords: Redshift surveys, Galaxy groups, Spectroscopy