Sazuna/UAT_keywords huggingface dataset:
Formation of Organic Hazes in CO<SUB>2</SUB>-rich Sub-Neptune Atmospheres within the Graphite Stability Regime. Super-Earths and sub-Neptunes are the most common exoplanets, with a "radius valley" suggesting that super-Earths may form by shedding sub-Neptunes' gaseous envelopes. Exoplanets that lie closer to the super-Earth side of the valley are more likely to have lost a significant fraction of their original H/He envelopes and become enriched in heavier elements, with CO2 gaining in abundance. It remains unclear which types of haze would form in such atmospheres, potentially significantly affecting spectroscopic observations. To investigate this, we performed laboratory simulations of two CO2-rich gas mixtures (with 2000 times solar metallicity at 300 and 500 K). We found that under plasma irradiation organic hazes were produced at both temperatures, with a higher haze production rate at 300 K, probably because condensation occurs more readily at lower temperature. Gas-phase analysis demonstrates the formation of various hydrocarbons, oxygen- and nitrogen-containing species, including reactive gas precursors like C2H4, CH2O, and HCN, for haze formation. The compositional analysis of the haze particles reveals various functional groups and molecular formulas in both samples. The 500 K haze sample has larger average molecular sizes, a higher degree of unsaturation with more double or triple bonds present, and higher nitrogen content incorporated as N–H and C=N bonds, indicating different haze formation pathways. These findings not only improve the haze formation theories in CO2-rich exoplanet atmospheres but also offer important implications for the interpretation of future observational data.

Keywords: Exoplanet atmospheric composition , Mass spectrometry, Exoplanet atmospheres, Laboratory astrophysics, Complex organic molecules
HST Observations of the Cataclysmic Variable Propeller LAMOST J024048.51+195226.9. We present Hubble Space Telescope (HST) far-UV spectra and light curves of the magnetic cataclysmic variable (CV) LAMOST J024048.51+195226.9 (J0240), the second known CV propeller. The five consecutive HST orbits span a full 7.34 hr binary orbital period. We detect a 24.939 ± 0.006 s far-UV modulation, confirming that J0240 contains the fastest spinning white dwarf (WD) in a CV. A high N V/C IV emission line ratio is considered an indicator of a recent episode of thermal-timescale mass transfer. The observed ratio in J0240 is higher than seen in typical magnetic CVs, but far less than observed in the only other confirmed propeller, AE Aquarii (AE Aqr). We also find that J0240 is significantly less luminous than AE Aqr during both low- and high-flux states. Around orbital phase 0.5, the Si IV emission line displays a P-Cygni absorption profile, likely related to the gas accelerated in the propeller. We derive new mass-dependent limits for the surface temperature of the WD of T ≤ 11,000─15,000 K. This temperature is low enough to allow for WD core crystallization, which may be linked to magnetism in WDs, particularly those in CVs.

Keywords: Close binary stars, White dwarf stars, Ultraviolet astronomy, DQ Herculis stars, Eclipsing binary stars, Cataclysmic variable stars, Magnetic fields, Stellar evolution
Methyl Isocyanate Formation from Oxygen Insertion in Methyl Cyanide Ices. In cold molecular clouds, UV photolysis of icy grain mantles generates radicals that lead to new molecule formation. When radical diffusion is limited by low temperatures, oxygen atom addition and insertion reactions, enabled by photolysis of common ice components such as H2O, CO2, CO, and O3, offer an alternative route to chemical complexity through the production of metastable, highly reactive O(1D) atoms. We examine the reactivity of these oxygen atoms generated by UV photolysis of O3 with methyl cyanide (CH3CN). These studies are conducted in an ultra-high vacuum chamber at cryogenic and low-pressure conditions equipped with in situ infrared spectroscopy to monitor destruction and product formation in real time. We conclude that oxygen atoms rapidly insert into CH3CN to produce primarily methyl isocyanate (CH3NCO) in matrix-free ices. Over the range from 10 to 40 K, we observe no temperature dependence to either CH3CN destruction or CH3NCO production. When placing CH3CN:O3 in H2O and CO2 ice matrices, we find that CH3NCO formation remains robust, but that the yield likely decreases due to competing reaction pathways. In the case of the H2O ice, we also observe a shift in product branching ratios toward alternative pathways such as the formation of hydroxyacetonitrile (HOCH2CN). Overall, our results demonstrate that oxygen atom reactivity provides an important channel for generating chemical complexity from nitriles on cold grains where radical mobility is limited.

Keywords: Laboratory astrophysics, Chemical abundances, Complex organic molecules, Astrochemistry
An Equipotential Disk Model with Irradiation for Nova-like Variables. The reflection effect is here incorporated within an earlier analytic binary system light- and velocity-curve model that includes a circumstellar equipotential disk. The modeled disk is semitransparent, to explore the attenuation and reemission of irradiance within the disk, as well as the irradiance of the companion star. The reflection functions defined in R. E. Wilson ensure efficient computation and allow multiple reflection. A capsule summary of the general binary system potential problem provides a foundation for close binary morphological ideas. Chief among these ideas is that many or perhaps most postnovae may be of the double contact morphological type. The location of an outer-disk null point of effective gravity accurately quantifies a limit on disk size. The disk should not extend beyond the outer null point, as the local material would then be unbound to the disk. The disk's inner extent is set by another null point. The inner and outer null locations are computed at each solution iteration, thus obviating any need for the arbitrary cutoffs seen in other postnova disk models. Remarkably, impersonal light-curve solutions find the disk edge quite close to the outer null point for U Scorpii (U Sco). Other reflection-related topics include irradiation heating and measurement of disk interior density and temperature. Analyses find white dwarf masses about 3%–6% lower than in nongravitating disk models that implicitly include disk mass as part of the white dwarf. The results from CI Aquilae and U Sco analyses are tabulated and prospects for further progress are outlined.

Keywords: Stellar rotation, Chandrasekhar limit, Cataclysmic variable stars, Nova-like variable stars
Inside the Stagnation Radius of the Nearest Billion-solar-mass Black Hole. We used the NSF Jansky Very Large Array at a frequency ν = 22 GHz to study the nearest billion-solar-mass black hole (BH), in the early-type galaxy NGC 3115 at a distance of 9.7 Mpc. We localize a faint continuum nucleus, with flux density S22 GHz = 48.2 ± 6.4 μJy, to a FWHM diameter d22 GHz &lt; 59 mas (2.8 pc). We find no evidence for adjacent emission within a stagnation region of radius Rsta ∼ 360 mas (17 pc) identified in a recent hydrodynamic simulation tailored to NGC 3115. Within that region, the simulated gas flow developed into an advection-dominated accretion flow (ADAF). The nucleus' luminosity density L22 GHz = 5.4 × 1017 W Hz−1 is about 60 times that of Sagittarius A⋆. The nucleus' spectral index  α10GHz22GHz=−1.85±0.18  (Sν ∝ να) indicates optically thin synchrotron emission. The spectral energy distribution of the nucleus peaks near νpeak = 9 GHz. Modeling this radio peak as an ADAF implies a BH mass MADAF = (1.2 ± 0.2) × 109 M⊙, consistent with previous estimates of (1─2) × 109 M⊙ from stellar or hot-gas dynamics. Also, the Eddington-scaled accretion rate for NGC 3115,  ṀADAF/ṀEdd=1.2−0.6+1.0×10−8 , is about 4─8 times lower than recent estimates for Sagittarius A⋆.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, Early-type galaxies, Interferometry
Statistical Analysis of Polycyclic Aromatic Hydrocarbons as a Tracer of Anomalous Microwave Emission Using DIRBE Data. We use archival data from the Diffuse Infrared Background Experiment (DIRBE) to map the polycyclic aromatic hydrocarbon (PAH) 3.3 μm emission feature and analyze its correlation with anomalous microwave emission (AME) in 98 compact sources identified by the Planck collaboration. We find that while far-IR thermal dust emission continues to be a better tracer of AME in most of the considered regions, 17% of the AME sources are better correlated with emission from small PAHs as traced by DIRBE. Furthermore, of the 27 sources that were identified as highly significant AME detections in the Planck analysis, 37% prefer PAHs as an AME tracer. Further work is required to understand to what extent local interstellar conditions are affecting PAH emission mechanisms and to reveal the underlying carriers of AME.

Keywords: Dust physics, Polycyclic aromatic hydrocarbons, Interstellar medium
First Detection of Circular Polarization in 4.7 GHz Excited OH Masers. We report the first detection of circular polarization in 4.7 GHz excited OH masers in star-forming regions made using full Stokes measurements with the Green Bank 100 m telescope. The Zeeman shift between the two circular components provides a measure of the magnetic field pervading these maser spots. Three different methods are used to determine the shift in velocity between the RCP and LCP components. We find fields with B ∼ 100 mG using archival molecular parameters that have limited precision and uncertain values. Reservations of using 1.7 and 6.0 GHz OH masers to estimate magnetic fields in star-forming regions are discussed.

Keywords: Interstellar magnetic fields, Hydroxyl masers, Spectropolarimetry, Young stellar objects
X-Ray Halos of Early-type Galaxies with Active Galactic Nucleus Feedback and Accretion from a Circumgalactic Medium: Models and Observations. Knowledge of the X-ray properties of the hot-gas halos of early-type galaxies (ETGs) has significantly advanced in the past years, for large and homogeneously investigated samples. We compare these results with the X-ray properties of an exploratory set of gas evolution models in realistic ETGs, produced with our high-resolution 2D hydrodynamical code MACER that includes active galactic nucleus feedback and accretion from a circumgalactic medium. The model X-ray emission and absorption are integrated along the line of sight, to obtain maps of the surface brightness ΣX and temperature TX. The X-ray diagnostics considered are the luminosity and average temperature for the whole galaxy (LX and &lt;TX&gt;) and within five optical effective radii (LX,5 and &lt;TX,5&gt;) and the circularized profiles ΣX(R) and TX(R). The values for LX, LX,5, &lt;TX&gt;, and &lt;TX,5&gt; compare very well with those observed. The ΣX(R) and TX(R) also present qualitative similarities with those of the representative galaxy NGC 5129 and those of ETGs with the most commonly observed shape for TX(R): ΣX(R) matches the observed profile over many optical effective radii Re, and TX(R) reproduces the characteristic bump that peaks at R = (1 ÷ 3)Re. Inside the peak position, TX(R) declines toward the center, but the explored models are systematically hotter by ≃30%; possible explanations for this discrepancy are discussed. Interestingly, ΣX(R) and TX(R) as large as those observed outside R ≃ Re are reproduced only with significant accretion from a circumgalactic medium, highlighting its importance.

Keywords: X-ray astronomy, Supermassive black holes, Galaxy evolution, Interstellar medium, Early-type galaxies
Bifrost Models of the Quiet Sun. I. Comparison with Solar Observations. Studying the emergence of magnetic fields is essential for understanding the physical mechanisms behind various phenomena in the solar atmosphere. Most importantly, the emerging fields offer valuable insights into how energy and mass are transferred to the upper solar atmosphere. As a result, they have garnered significant attention from both observational and theoretical perspectives. In this article, we present two models of quiet-Sun-like magnetic fields generated by the Bifrost code. We compare these models with observations from the Swedish 1 m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS). By tracking the magnetic features in both the SST and Bifrost data, we determine the similarities and differences between the fields identified in the models and those observed. We conduct a quantitative comparison of various properties, such as flux content, flux densities, horizontal and line-of-sight velocities, lifetimes, sizes, and surface interactions. Additionally, we identify and analyze the properties of the largest emerging bipoles in the SST and Bifrost data. Our findings indicate that the magnetic bipoles in the Bifrost simulations are generally stronger than those observed with the SST. However, a qualitative comparison of the chromospheric and transition region responses to the emerging fields in the Bifrost models, SST, and IRIS observations shows similar heating processes occurring above and around the emerging fields. Finally, we outline our plans for future work aimed at studying the emergence of magnetic fields in the quiet Sun, with a particular focus on the chromosphere and upper atmospheric layers.

Keywords: Solar magnetic flux emergence, Solar photosphere, Radiative magnetohydrodynamics, Solar magnetic fields, Solar transition region, Solar chromosphere
A New Framework for Understanding Systematic Errors in Cluster Lens Modeling. IV. Constraints from the Giant Arc in Abell 370. We aim to improve cluster lens modeling and source reconstruction by utilizing the full information in giant, caustic-crossing arcs lensed by galaxy clusters. Lens models are generally constrained using image positions and assuming point sources, but spatially extended giant arcs provide more constraints; however, they require a more complex model that accounts for the structure of the extended source. We seek to determine whether improvements to the lens model and reconstructed source merit the difficulty of handling the extra constraints. We choose the spatially extended z = 0.725 giant arc in the z = 0.375 Abell 370 galaxy cluster field for our study. We present (1) a series of pixel-based source reconstructions (PBSRs) for cluster mass models exploring the range of uncertainties in our fiducial model, (2) a similar analysis done using a prototype Python de-lensing code for cluster mass models from each of the Hubble Frontier Fields (HFF) modeling teams, (3) an optimized model with PBSR, and (4) and an investigation of how our optimized model affects the cluster mass model locally and globally in the highest-magnification regions. We find that our optimized model (1) is able to correct resolution-limited assumptions in cluster model inputs local to the arc, (2) has significantly smaller arc model residuals than results from the standard HFF models, and (3) affects the critical curves and therefore the information derived from highest-magnification zones most significantly in regions local to the arc.

Keywords: Abell clusters, Strong gravitational lensing, Gravitational lensing, Luminous arcs
Redshift Evolution of the Intrinsic Alignments of Early-type Galaxies and Subhalos in the Horizon Run 5 Simulation. We investigate the redshift evolution of intrinsic alignments (IAs) of the shapes of galaxies and subhalos with the large-scale structures of the Universe using the cosmological hydrodynamic simulation, Horizon Run 5. To this end, early-type galaxies are selected from the simulated galaxy catalogs based on stellar mass and kinematic morphology. The shapes of galaxies and subhalos are computed using the reduced inertia tensor derived from mass-weighted particle positions. We find that the misalignment between galaxies and their corresponding dark matter subhalos decreases over time. We further analyze the two-point correlation between galaxy or subhalo shapes and the large-scale density field traced by their spatial distribution, and quantify the amplitude using the nonlinear alignment model across a wide redshift range from z = 0.625 to z = 2.5. We find that the IA amplitude, ANLA, of galaxies remains largely constant with redshift, whereas that of dark matter subhalos exhibits moderate redshift evolution, with a power-law slope that deviates from zero at a significance level exceeding 3σ. Additionally, ANLA is found to depend on both the stellar mass and kinematic morphology of galaxies. Notably, our results are broadly consistent with existing observational constraints. Our findings are in good agreement with previous results of other cosmological simulations.

Keywords: Cosmology, Hydrodynamical simulations, Large-scale structure of the universe, Gravitational lensing, Galaxies
Modeling Tidal Disruptions with Dynamical Tides. Tidal disruption events (TDEs) occur when stars pass close enough to supermassive black holes to be torn apart by tidal forces. Traditionally, these events are studied with computationally intensive hydrodynamical simulations. In this paper, we present a fast, physically motivated two-stage model for TDEs. In the first stage, we model the star's tidal deformation using linear stellar perturbation theory, treating the star as a collection of driven harmonic oscillators. When the tidal energy exceeds a fraction γ of the star's gravitational binding energy (with  γ∼O(1) ), we transition to the second stage, where we model the disrupted material as free particles. The parameter γ is determined with a one-time calibration to the critical impact parameter obtained in hydrodynamical simulations. This method enables fast computation of the energy distribution dM/dE and fallback rate dM/dT while offering physical insight into the disruption process. We apply our model to MESA-generated profiles of middle-age main-sequence stars. Our code is available on GitHub (https://github.com/ZihanZhou26/PerTDE).

Keywords: Black hole physics, Galaxies, Hydrodynamics
Dynamical Stability of Hypermassive Neutron Stars against Quasi-radial Perturbations. The dynamical stability of differentially rotating neutron stars, including hypermassive neutron stars, is of paramount importance in understanding the fate of the postmerger remnant of binary neutron stars mergers and the formation of a black hole during core-collapse supernovae. We study systematically the dynamical stability of differentially rotating neutron stars within a broad range of masses, rotation rates, and degrees of differential rotation, modeled as polytropes with Γ = 2. We pay particular attention to quasi-toroidal configurations that are outside the parameter space region explored in previous works. We estimate the limits of the region of stability against quasi-radial perturbations by performing an extensive set of numerical simulations. We find that some of the stability criteria proposed in the past are not sufficient or necessary to determine stability if differential rotation is present, and propose a new, more general criterion. We show that there is a large parameter space that allows for quasi-toroidal configurations that will not collapse immediately to a black hole and that can sustain masses up to ∼2.5 times the maximum mass of a nonrotating neutron star.

Keywords: Neutron stars, Relativistic stars
Determining the Magnetic Field in the Atmosphere of a Solar Active Region Observed by the CLASP2.1 Sounding Rocket Experiment. We determine magnetic fields from the photosphere to the upper chromosphere combining data from the Hinode satellite and the CLASP2.1 sounding rocket experiment. CLASP2.1 provided polarization profiles of the Mg II h and k lines, as well as of the Mn I lines around 2800 Å, across various magnetic structures in an active region, containing a plage, a pore, and the edges of a sunspot penumbra. By applying the weak-field approximation to the circular polarization profiles of these spectral lines, we obtain a longitudinal magnetic field map at three different heights in the chromosphere (lower, middle, and upper). This is complemented by data from Hinode (photospheric magnetic field), the Interface Region Imaging Spectrograph, and the Solar Dynamics Observatory (high spatial resolution observations of the chromosphere and corona). We quantify the height expansion of the plage magnetic fields and find that the magnetic fields expand significantly in the middle chromosphere, shaping the moss observed above in the transition region and corona. We identified an area with polarity reversal at the upper chromosphere around the edge of the pore, suggesting the presence of a magnetic discontinuity in the upper chromosphere. Transient and recurrent jetlike events are observed in this region, likely driven by magnetic reconnection. Around the penumbral edge, we find large-scale magnetic fields corresponding to the superpenumbral fibrils seen in the upper chromosphere. In the superpenumbral fibrils, we find Zeeman-induced linear polarization signals, suggesting the presence of a significantly inclined magnetic field, as strong as 1000 G in the upper chromosphere.

Keywords: Spectropolarimetry, Solar magnetic reconnection, Plages, Solar magnetic fields, Solar instruments, Solar chromosphere
The ATLAS Virtual Research Assistant. We present the Virtual Research Assistant (VRA) of the ATLAS sky survey, which performs preliminary eyeballing on our clean transient data stream. The VRA uses histogram-based gradient-boosted decision tree classifiers trained on real data to score incoming alerts on two axes: "Real" and "Galactic." The alerts are then ranked using a geometric distance such that the most "real" and "extragalactic" receive high scores; the scores are updated when new lightcurve data is obtained on subsequent visits. To assess the quality of the training we use the recall at rank K, which is more informative to our science goal than general metrics (e.g., accuracy, F1-scores). We also establish benchmarks for our metric based on the pre-VRA eyeballing strategy, to ensure our models provide notable improvements before being added to the ATLAS pipeline. Then, policies are defined on the ranked list to select the most promising alerts for humans to eyeball and to automatically remove bogus alerts. In production the VRA method has resulted in a reduction in eyeballing workload by 85% with a loss of follow-up opportunity &lt;0.08%. It also allows us to automatically trigger follow-up observations with the Lesedi telescope, paving the way toward automated methods that will be required in the era of LSST. Finally, this is a demonstration that feature-based methods remain extremely relevant in our field, being trainable on only a few thousand samples and highly interpretable; they also offer a direct way to inject expertise into models through feature engineering.

Keywords: Astroinformatics, Sky surveys, Astrostatistics, Transient detection, Interdisciplinary astronomy