Sazuna/UAT_keywords huggingface dataset:
Hot Springs and Dust Reservoirs: JWST Reveals the Dusty, Molecular Aftermath of Extragalactic Stellar Mergers. We present James Webb Space Telescope (JWST) observations of four luminous red novae (LRNe): dusty, extragalactic transients from stellar mergers following common-envelope evolution (CEE) in massive binary stars. Our targets—AT 2021blu, AT 2021biy, AT 2018bwo, and M31-LRN-2015—span a broad range in progenitor primary masses (≍3─24 M⊙) and post-merger ages (≍1100─3700 days). All four were observed with the Mid-Infrared Instrument from 5 to 25 μm; AT 2021blu and AT 2021biy additionally have 5─12 μm spectra from the Low-Resolution Spectrometer. These spectra show strong features of oxygen-rich molecules, including water vapor, supporting the recent association of water fountain sources with CEE. Radiative transfer modeling of the spectral energy distributions yields dust masses of ≍4.2 × 10−5, 3 × 10−4, 7.5 × 10−5, and 7.7 × 10−4 M⊙, respectively—corresponding to ≍10%, 60%, 6%, and 12% of median dust masses in core-collapse supernovae (CCSNe) at similar phases. Accounting for their occurrence rates, we estimate that LRNe can contribute ∼25% as much dust as CCSNe to the cosmic dust budget. Furthermore, the lower expansion velocities of LRNe may reduce dust destruction by reverse shocks compared to CCSNe, potentially increasing this contribution. In addition to dust masses, we use our JWST observations to measure late-time properties such as the luminosities, temperatures, radii, and dust-to-gas ratios of the merger remnants. Our results highlight the need for broader infrared studies of LRNe to quantify their contribution to the cosmic dust budget, study the evolution of oxygen-rich molecules, and probe the final fates of CEE.

Keywords: Water vapor, Infrared spectroscopy, Stellar mergers, Astrophysical dust processes, James Webb Space Telescope, Circumstellar dust, Infrared photometry
The Effect of Tidal Heating and Volatile Budgets on the Outgassed Atmosphere of 55 Cancri e. 55 Cancri e (55 Cnc e) is an ∼8 Gyr rocky world (1.95 R⊕ and 8.8 M⊕) orbiting a K-type star. JWST observations suggest a carbon-dominated atmosphere (CO2 and CO) over a global magma ocean (&gt;3000 K). We suggest that any CO2-dominated atmosphere, with trace amounts of H2O and O2, likely arises from outgassing of its initial volatile reservoir. As solidification drives the magma ocean and atmosphere away from solution equilibrium, tidal and greenhouse heating can prolong outgassing. Early atmosphere outgassing reflects rapid degassing of the volatile-saturated melt during postformation cooling. Without tidal heating, an initial 5 wt% water mass fraction ( FH2O ) or 3 wt% CO2 mass fraction ( FCO2 ) can sustain outgassing for at least ∼10 Myr. With both at 10 wt%, greenhouse warming alone can prolong outgassing up to ∼30 Myr. Our model shows that tidal heating can reduce the volatile threshold required to maintain a high surface temperature (∼3200 K at e = 0.005) and delay outgassing of additional volatiles to the present day. However, higher tidal heating presents a trade-off between prolonging tenuous outgassing and enlarging the overall size of the secondary atmosphere. Tidally enhanced outgassing may produce minor pressure variations that could contribute to the observed phase-curve variability. Additionally, our model shows that tidal heating strongly controls outgassing in the planet's young-to-midlife stage, then shifts toward a volatile inventory dependence at mature ages. Using 55 Cnc e, we present a framework to prioritize atmosphere detections on rocky ultrashort period magma ocean planets, linking age-dependent tidal heating and volatile inventory to the formation and size of secondary atmospheres.

Keywords: Extrasolar rocky planets, Exoplanet atmospheric composition , Land-atmosphere interactions, Solid body tides, Planetary atmospheres, Exoplanet tides, Eccentricity, Tides, Exoplanet atmospheres, Exoplanet atmospheric evolution
Chaotic Motion of Ions in Finite-amplitude Low-frequency Alfvén Waves. Finite-amplitude low-frequency Alfvén waves (AWs) are ubiquitous in space plasmas, where they play a key role in the transport and dissipation of energy, particularly in the heating of ions in the solar corona and solar wind. In this study, we investigate the nonlinear interaction between ions and obliquely propagating AWs. When the wave amplitude and propagation angle lie within specific ranges, ion motion becomes chaotic. We quantify this behavior using the maximum Lyapunov exponent (λm) and define a new parameter, the chaos ratio (CR), to describe the fraction of chaotic particles across different initial states. The global chaos threshold is determined as the contour CR = 0.01. Analysis of magnetic moment variations reveals that the physical origin of chaos is pitch-angle scattering induced by wave-driven field-line curvature (WFLC), which disrupts adiabatic invariance and leads to stochastic ion energization. The onset condition for chaos can be expressed by an effective relative curvature radius, Peff. &lt; 25. This analytical criterion delineates the boundary of the chaotic region in the (kx, kz, Bw) parameter space and agrees well with numerical results. The identified WFLC mechanism provides a new physical pathway for converting macroscale Alfvénic disturbances into microscopic ion heating. This analysis offers a simplified model that illustrates a plausible ion energization mechanism in Alfvénic turbulent plasmas, including those associated with solar wind switchbacks and coronal fluctuations. These results highlight a universal chaotic process that may underlie stochastic heating in heliospheric and astrophysical plasmas.

Keywords: Solar coronal heating, Solar wind, Alfven waves
HST Study of the Proper Motion of HST-1 in the Jet of M87. The radio galaxy M87 is well known for its jet, which features a series of bright knots observable from radio to X-ray wavelengths. The most famous of these, HST-1, exhibits superluminal motion, and our analysis of Chandra data reveals a correlation between the X-ray flux of HST-1 and its separation from the core. This correlation likely arises from moving shocks in the jet, allowing measurement of the internal structure of HST-1 in the X-ray band. To follow up on these results, we use observations from the Hubble Space Telescope Advanced Camera for Surveys (ACS) High-Resolution Channel/Wide-Field Channel/Solar-Blind Channel and the Wide Field Camera 3 (WFC3)'s UVIS to analyze the image and flux variability of HST-1. Our analysis includes 245 ACS and 120 WFC3 observations from 2002─2022, with a total exposure time of ∼345 ks. We study the brightness profile of the optical jet and measure the relative separation between the core and HST-1 for comparison to the X-ray. We find that the X-ray and the UV/optical emission could arise from physically distinct regions. The measured proper motion of the knot HST-1 is 1.04 ± 0.04c from 2002─2005 and around 2.1 ± 0.05c from 2005─2022. We discuss the acceleration of the jet and the flaring synchrotron emission from HST-1 from optical to X-rays.

Keywords: Hubble Space Telescope, Relativistic jets, Active galactic nuclei
Reconstructing the Assembly of Massive Galaxies. III. Quiescent Galaxies Lose Angular Momentum as They Evolve in a Mass-dependent Fashion. We study the evolution of stellar kinematics of a sample of 952 massive quiescent galaxies with M* &gt; 1010.5 M⊙ at 0.6 &lt; z &lt; 1. Utilizing spatially integrated spectroscopy from the LEGA-C survey, we focus on the relationship between the observed integrated stellar velocity dispersion ( σstar' ) and the morphological axial ratio (q), and its variation with the stellar age and mass of quiescent galaxies. For the youngest quiescent galaxies, regardless of stellar mass,  σstar'  decreases with increasing q, a trend that is consistent with a system having significant rotation and hence suggests that massive galaxies still retain a significant amount of angular momentum in the aftermath of quenching. As they continue to evolve, the variation of the  σstar' -q relationship depends on stellar mass. For quiescent galaxies with M* &lt; 1011.3M⊙,  σstar'  decreases with q in all stellar-age bins, suggesting that the quiescent populations of this mass regime retain significant rotation even a long time after quenching. In contrast, for more massive quiescent galaxies with M* &gt; 1011.3M⊙, the relationship between  σstar'  and q becomes significantly flattened with increasing stellar age. This indicates that, as the very massive galaxy populations continue to evolve after quenching, angular momentum gradually reduces, which eventually transforms them into velocity-dispersion supported systems. We suggest that incoherent, continuous merging and accretion events onto the galaxies are the main drivers of the observed mass-dependent, postquenching dynamical evolution because more massive galaxies are more likely to undergo such interactions. We are witnessing the early formation epoch of fast and slow rotators at z ∼ 0.8, when the Universe was only half of its current age.

Keywords: Galaxy formation, Galaxy structure, High-redshift galaxies, Galaxy evolution
A Portrait of the Cosmic Reionization History in the Context of the Early Dark Energy Model. Recent JWST observations of Lyα emission at z ∼ 11─6 indicate a rapid reionization of the intergalactic medium within the first ∼700 Myr. The required Lyman continuum (LyC) photon budget may naturally arise from the unexpectedly high galaxy number densities revealed by JWST, reducing the need for scenarios invoking very high LyC escape fractions (fesc ≳ 0.2) or dominant contributions from ultrafaint galaxies (MUV &gt; −15) in the standard ΛCDM framework. In this work, we model the reionization history under the early dark energy (EDE) paradigm—originally proposed to ease the Hubble tension—which also explains the observed overabundance of high-z galaxies without extreme star formation efficiencies. The EDE model yields reionization histories consistent with current constraints while requiring only moderate LyC escape fractions and UV luminosity densities (fesc ∼ 0.05─0.1, MUV ≲ −17 to −15). Our results suggest that, once key astrophysical parameters are better constrained, the reionization history could serve as an independent and complementary probe of EDE cosmologies.

Keywords: Reionization, Galaxy abundances, High-redshift galaxies, Dark energy
Upper Limits on Microhertz Gravitational Waves from Supermassive Black Hole Binaries Using PSR J1909─3744 Data from the Second IPTA Data Release. We present the results of a search for gravitational waves (GWs) from individual sources using high-cadence observations of PSR J1909−3744 obtained during an intensive observing campaign with the International Pulsar Timing Array second data release between 2010 July and 2012 November. The observations, conducted at three different radio frequencies with the Nançay Radio Telescope and Parkes Telescope and five frequencies with the Green Bank Telescope, enabled precise corrections for dispersion measure effects and scattering variations. After these corrections, the timing residuals showed an unmodeled periodic noise component with an amplitude of 340 ns. Our analysis yields upper limits on the GW strain from individual sources, constraining it to be below 1.9 × 10−14 at 71 nHz and 2.3 × 10−13 at 1 μHz for average sky locations, while for optimal source locations, the limits improve to 6.2 × 10−15 and 8.9 × 10−14 at the same frequencies, respectively. Our new limits are about a factor of 1.52 more stringent than those of B. B. P. Perera et al. (2018) based on an earlier EPTA data.

Keywords: Gravitational wave detectors, Pulsar timing method, Millisecond pulsars, Gravitational wave astronomy, Radio astronomy
Coronal Mass Ejection Transit Time Prediction Based on Spatiotemporal Modeling Using 3D Convolutional Neural Networks. Coronal mass ejections (CMEs) are intense solar eruptions that, once reaching Earth, pose catastrophic risks to the near-Earth space environment. Thus, improving CME transit time forecast accuracy to mitigate damage to ground-based facilities is critical for space weather forecasting. In this study, we constructed a 3D convolutional neural network (3D CNN) framework that learns from Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph white-light image sequences to predict CME transit times. Our main contributions are threefold. (1) Unlike prior work, we first integrate the temporal dimension and use 3D CNN for joint spatiotemporal modeling of CME sequences to predict transit times. (2) To address the uneven sequence-length variations across events and to optimize data set usage, we propose a method that samples multiple fixed-length subsequences for each event and applies mean pooling to their features, which enhances model performance and generalization. (3) To enhance interpretability, we apply gradient-weighted class activation mapping across all convolutional layers to reveal each layer's attention focus. The results show that shallow layers focus on the CME body and evolve over time, while deeper layers show stronger responses in the background and weaker responses to the CME body. On an independent test set, the model achieves a mean absolute error (MAE) of 11.04 hr; in the transit time range with the most samples, MAE is 6.37 hr, comparable to prior studies. These results confirm 3D CNN's effectiveness in modeling CME spatiotemporal evolution and predicting transit times, offering a promising path for physically interpretable, data-driven space weather forecasting.

Keywords: Solar-terrestrial interactions, Convolutional neural networks, Solar coronal mass ejections
Parallaxes, Proper Motions, and Near-infrared Photometry for 173 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program. We present near-infrared parallax and proper motion astrometry for 74 L dwarfs and 99 T dwarfs, as single objects or in binary systems, obtained with the ASTROCAM astrometric imager on the USNO, Flagstaff Station 1.55 m telescope over two observing periods. For all 173 objects, the median number of observational epochs was 62 with a median time frame of 5.25 yr, resulting in median uncertainties of σ(πabs) = 1.51 mas, σ(μabs) = 1.02 mas yr−1, and σ( Vtan ) = 1.01 km s−1. Our observations provide the first parallax/proper-motion results for 16 objects and the highest-precision parallaxes/proper motions for an additional 116 objects. A serendipitous overlap of 40 objects with Gaia DR3 astrometry allows for direct comparison and confirmation of our results, along with an investigation on the effects of resolved binarity on astrometric results. We also provide a uniform set of J-, H-, KS-band photometry in the UKIRT/MKO system, most of it being from new observations. We use these results to examine objects included in this study of special-interest populations, consisting of binaries, wide companions, young objects, subdwarfs, and brown dwarf spectral standards.

Keywords: Brown dwarfs, Trigonometric parallax, Astrometry, Proper motions, Late-type dwarf stars
Calibrating Mid-infrared Emission Features as Diagnostics of Star Formation in Infrared-luminous Galaxies via Radiative Transfer Modeling. Luminous infrared (IR) galaxies are key sites of obscured stellar mass assembly at z &gt; 0.5. Their star formation rates (SFRs) are often estimated using the luminosities of the 6.2 and 11.2 μm polycyclic aromatic hydrocarbon (PAH) features or those of the [Ne II] and [Ne III] fine-structure lines, as they are minimally affected by obscuration. It is uncertain whether the calibration of these features as SFR tracers depends on the starburst bolometric luminosity or the level of active galactic nucleus (AGN) activity. We here investigate the relationship between the luminosities of PAH and neon lines with SFR for highly luminous objects using radiative transfer modeling and archival observations of 42 local ultraluminous (≥1012L⊙) IR galaxies (ULIRGs). We find that PAH and [Ne II] features arise mainly in star-forming regions, with small contributions from the AGN or host, but that the [Ne III] line has a mixed contribution from both star formation and AGN activity. We present relations between LPAH and L[Ne II], and both starburst luminosity and SFR. We find relations for lower-luminosity (LIR ≃ 1010─1012L⊙) systems underestimate the SFRs in local ULIRGs by up to ∼1 dex. The 6.2 and 11.2 μm PAH features, and the [Ne II] line, are thus good tracers of SFR in ULIRGs. We do not find that a more luminous AGN affects the relationship between SFR and PAH or neon luminosity but that it can make PAH emission harder to discern. Our results and derived relations are relevant to studies of star-forming and composite galaxies at z &lt; 3 with the James Webb Space Telescope.

Keywords: Star formation, Polycyclic aromatic hydrocarbons, Ultraluminous infrared galaxies, Infrared galaxies
Simulations of Electron Beam Interactions in Brown Dwarf Atmospheres. Over two decades ago, the first detection of electron cyclotron maser instability radio emission from a brown dwarf confirmed the presence of aurorally precipitating electrons on these objects. This detection established that brown dwarfs can exhibit magnetic activity that is planetary and auroral, rather than stellar in nature. This discovery motivated ongoing observational searches for the corresponding optical, ultraviolet, and infrared auroral emission expected based on solar system analogs. The continuing nondetection of such auroral emission indicates that important differences exist between auroral processes on brown dwarfs and solar system planets. In this work, we implement a Monte Carlo simulation of monoenergetic electron beams interacting with brown dwarf atmospheres as a step toward understanding the physics of brown dwarf auroral emission. We detail the algorithm and underlying assumptions and validate against previously published Jovian results. Our results agree well with the literature, with some discrepancies from our updated interaction cross sections. We demonstrate the applicability of our simulation across the range of surface gravities and effective temperatures of radio-emitting brown dwarfs. We present an analytic parameterization of interaction rates based on our finding that atmospheric column density governs the interaction profiles. We apply this parameterization to calculate the total volumetric interaction rates and energy deposition rate for representative electron beam energy spectra enabling future predictions for spectra of aurorally emitting brown dwarfs. Simulations of high-energy electron interactions with substellar hydrogen-dominated atmospheres will guide observational searches for multiwavelength auroral features beyond the solar system.

Keywords: Planetary magnetospheres, Brown dwarfs, Aurorae
Observational Evidence Linking Loop Length and Thermal─Nonthermal Peak Timing in Solar Flares. We investigate how the magnetic loop length of solar flares relates to the timing between their thermal and nonthermal emission signatures. Our study analyzes a sample of 96 C-, M-, and X-class flares observed between 2013 and 2015 with soft X-rays, hard X-rays, and extreme UV. For each event, we determine the time delay ∆t between the hard X-ray and soft X-ray peak, and estimate the flare loop length L from UV footpoints assuming a semicircular geometry. In every case, longer flare loops are consistently associated with larger timing delays. Across the full sample, we find a strong correlation R = 0.88 between L and ∆t. We also quantify how closely each flare follows the Neupert effect using a coefficient RN, defined as the Pearson correlation between the time derivative of the soft X-ray flux and the hard X-ray light curve. Applying correlation thresholds of RN ≥ 0.5 and RN ≥ 0.8 yields subsets of 87 and 46 events, respectively. In both cases, the linear relationship between loop length and peak delay remains clearly expressed. For the RN ≥ 0.5 subset, the correlation is R = 0.87, while the more selective subset with RN ≥ 0.8 displays an even stronger correlation of R = 0.91. These results show that the overall trend persists across increasingly stringent correlation thresholds. The results provide direct observational confirmation that magnetic loop geometry plays a key role in governing the temporal evolution of energy transport in solar flares.

Keywords: Solar flares
Correlations between Dust Extinction Features across All Wavelength Scales: From Diffuse Interstellar Bands to R(V). Understanding variations in the dust extinction curve is imperative for using dust as a tracer of local structure in the interstellar medium, understanding dust chemistry, and performing extinction corrections. However, the extinction curve is complicated and exhibits features across a wide range of wavelength scales, from narrow atomic lines and diffuse interstellar bands (DIBs), to intermediate-scale and very broad structures (ISSs and VBSs), and the overall slope of the optical extinction curve, parameterized by R(V). Robust, population-level studies of variations in these features are only now possible with large, all-sky, spectroscopic surveys. However, these features are often studied independently because they require drastically different spectral resolution. In this work, we couple features with disparate wavelength scales by cross-matching precision catalogs of DIB measurements from APOGEE (7 DIBs) and Gaia RVS (1 DIB) with low-resolution extinction-curve measurements from Gaia XP. Using this combination, we demonstrate meaningful correlations between the strengths of extinction-curve features across all wavelength scales. We present a model that partially explains the excess scatter in DIB strength versus extinction and we show variation in line shapes of two DIBs as a function of R(V). We find that most DIBs studied in this work increase in strength with increasing R(V) and/or increasing ISS strength, though we found one DIB that anomalously decreases in strength with increasing R(V). Using the behavior of the ensemble of APOGEE DIBs, we present this as the first evidence of systematic chemical composition variation accompanying R(V) variation.

Keywords: Diffuse interstellar bands, Interstellar dust extinction, Interstellar absorption, Interstellar medium, Spectroscopy
Looking at Infrared Background Radiation Anisotropies with Spitzer. II. Small Scale Anisotropies and their Implications for New and Upcoming Space Surveys. Spitzer-based source-subtracted cosmic infrared background (CIB) fluctuations at arcminute-to-degree scales indicate the presence of new populations, whereas subarcminute power arises from known z ≲ 6 galaxies. We reconstruct the evolution of the near-IR CIB anisotropies on subarcminute scales by known galaxy populations. This method is based on, and significantly advanced over, the empirical reconstruction by Helgason et al. which is combined with the halo model connecting galaxies to their host dark matter halos. The modeled CIB fluctuations from known galaxies produce the majority of the observed small-scale signal down to statistical uncertainties of &lt;10% and we constrain the evolution of the halo mass regime hosting such galaxies. Thus, the large-scale CIB fluctuations from new populations are produced by sources with negligible small-scale power. This appears to conflict with the presented intra-halo light models, but is accounted for if the new sources are at high z. Our analysis spanning several Spitzer datasets allows us to narrow the estimated contributions of remaining known galaxies to the CIB anisotropies to be probed potentially from surveys by new and upcoming space missions such as Euclid, SPHEREx, and Roman. Of these, the Roman surveys have the best prospects for measuring the source-subtracted CIB and probing the nature of the underlying new populations at λ &lt; 2 μm, followed by Euclid's surveys, while for SPHEREx the source-subtracted CIB signal from them appears significantly overwhelmed by the CIB from remaining known galaxies.

Keywords: Star formation, Cosmic background radiation, Large-scale structure of the universe