Sazuna/UAT_keywords huggingface dataset:
Exomoons and Exorings with the Habitable Worlds Observatory. II. Finding "Endor" with Lunar Eclipses. Giant planets in the habitable zone may host exomoons with conditions conducive to life. In this paper, we describe a method by which the Habitable Worlds Observatory (HWO) could detect such moons: broadband reflected-light lunar eclipses (e.g., the moon passing into the shadow of the planet). We find that an Earth-like moon orbiting a Jovian-size planet at 1 au can outshine its host planet near 1 μm, producing frequent (days timescale) lunar eclipses with depths of order 50%. We determine that single eclipse events out to ∼12 pc may be detectable for Earth-like moons around giant planets, down to 0.9R⊕. Detection of smaller moons, ∼0.5R⊕ (corresponding to about the size of Mars or Ganymede), may be possible, but would generally require multiple events for most systems. These several-hour events provide a clear pathway to detecting habitable moons with HWO, given sufficient stare-time on each system to detect lunar eclipses. The occurrence rate of habitable exomoons remains unconstrained, however, making the ultimate yield uncertain. HWO will be capable of placing the first meaningful constraints on the frequency of habitable exomoons around giant planets; if it is nonnegligible, HWO could also search for life on these worlds, possibly with lunar eclipse spectroscopy.

Keywords: Lunar eclipses, Natural satellites (Extrasolar), Direct imaging
Eccentric Disks with Self-gravity. Can a disk orbiting a central body be eccentric, when the disk feels its own self-gravity and is pressureless? Contradictory answers appear in the literature. We show that, to linear order in eccentricity, such a disk can be eccentric, but only if it has a sharply truncated edge: the surface density Σ must vanish at the edge, and the Σ profile must be sufficiently steep at the point where it vanishes. If either requirement is violated, an eccentric disturbance leaks out of the bulk of the disk, into the low-density edge region, and cannot return. An edge where Σ asymptotes to zero but never vanishes, as is often assumed for astrophysical disks, is insufficiently sharp. Similar results were shown by Hunter &amp; Toomre for galactic warps. We demonstrate these results in three ways: by solving the eigenvalue equation for the eccentricity profile; by solving the initial value problem; and by analyzing a new and simple dispersion relation that is valid for any wavenumber, unlike WKB. As a byproduct, we show that softening the self-gravitational potential is not needed to model a flat disk, and we develop a softening-free algorithm to model the disk's Laplace─Lagrange-like equations. The algorithm is easy to implement and is more accurate than softening-based methods at a given resolution by many orders of magnitude.

Keywords: Planetary rings, Circumstellar disks
What to Make of the Earth's Curiously Intermediate Land Fraction?. Approximately two-thirds of the Earth, the only known inhabited planet, is covered in ocean. Why not 0.01% or 99.99%? It has been previously suggested that this may represent a certain degree of fine-tuning, and thus perhaps observers are a priori more likely to develop on those rare worlds with nearly equal land─ocean ratios, such as our own. In this work, we take the single datum of the Earth and then use Bayesian inference to compare four models for the probability distribution of a planet becoming inhabited by observers as a function of land fraction, f, which we classify as (i) land-centric, (ii) ocean-centric, (iii) equi-centric, and (iv) indifferent. We find that no model is strongly favored over the others, but that (1) the land-centric model is disfavored over all others, and (2) the equi-centric model is favored over all competitors. Further, we show that more extreme models with heavy tail-weighting are strongly disfavored even when conditioned upon the Earth alone. For example, a land-centric model where the median planet has f = 0.82 (or greater) is in strong tension with our existence. Finally, we consider the potential addition of more data via Mars or exoplanets. Should paleo-Mars have once harbored life and had f &lt; 0.20, this would strongly favor the ocean-centric model for life over a land-centric hypothesis. We show that strong evidence for/against the equi-centric model versus its competitors would likely require at least a dozen inhabited exoplanets, offering a well-motivated sample size for future experiments.

Keywords: Astrobiology, Exoplanets
Transformer-based Neural Network for Transient Detection without Image Subtraction. We introduce a transformer-based neural network for the accurate classification of real and bogus transient detections in astronomical images. This network advances beyond the conventional convolutional neural network methods, widely used in image processing tasks, by adopting an architecture better suited for detailed pixel-by-pixel comparison. The architecture enables efficient analysis of search and template images only, thus removing the necessity for computationally expensive difference imaging, while maintaining high performance. Our primary evaluation was conducted using the autoScan dataset from the Dark Energy Survey (DES), where the network achieved a classification accuracy of 97.4% and diminishing performance utility for difference image as the size of the training set grew. Further experiments with DES data confirmed that the network can operate at a similar level even when the input images are not centered on the supernova candidate. These findings highlight the network's effectiveness in enhancing both accuracy and efficiency of supernova detection in large-scale astronomical surveys.

Keywords: Transient detection
Exoplanet Synchronization in the Habitable Zone: Learning from Venus' Retrograde Rotation. The rotation of a planet in the habitable zone (HZ) of a solar-type star may be reversed by a smooth process associated with the formation of its atmosphere and the emergence of torques stronger than and opposite to the normal tidal torques. Our understanding of Venus' rotational dynamics is revisited to look at what might happen to exoplanets in the HZ of a solar-type star. Current theories are used to construct a simplified model of the joint contribution of the gravitational tidal torque and the atmospheric torque. It shows that the reversal of a planet's rotation is not an exceptional fact and may have happened many times amongst the known HZ exoplanets.

Keywords: Extrasolar rocky planets, Tidal friction, Venus, Atmospheric tides, Planetary science, Habitable zone, Astronomical location
Martian Ionospheric Cold Hydrogen Ion Escape at Solar Maximum: First Observations. The water escape from Mars to space could be in the form of hydrogen and oxygen ions as driven by solar wind─Mars interactions. Although oxygen ion escape has been extensively investigated, the H+ escape rate was measured only at solar minimum. To determine the impacts of solar activity on the ionospheric H+ escape rate, we report the observational results from the Tianwen-1 spacecraft at solar maximum. The cold dense ionospheric ion outflows through the magnetotail have an equal energy acceleration process, consistent with the characteristics of ambipolar electric field acceleration. The escape rate of planetary cold H+ through the magnetotail is estimated to be ∼2 × 1023 s−1, a value substantially lower than the neutral hydrogen escape rate, and the H/O ratio (∼0.3) of the tailward escaping ions (H+, O+ and O 2+ ) is below the stoichiometric ratio of water. These results indicate the ionospheric H+ outflow plays a minimal role for the water loss on Mars across solar cycles. To assess the contribution of H+ escape to total hydrogen loss, future analysis must target the pickup H+ escape rate within the magnetosheath.

Keywords: Mars, Solar-planetary interactions
The Exotic Black Hole─Neutron Star Binaries in Our Galaxy. It has been suggested that there are ∼105 black hole─neutron star (BH─NS) binaries in our Galaxy. However, despite the effort of intensive radio search for decades, none of these binaries has been found to date. These binaries are regarded as a holy grail of astronomy because they can greatly improve our understanding about relativistic systems of compact objects and fundamental physics. In this article, we propose the existence of exotic BH─NS binaries that can open a new way in searching the missing BH─NS binaries in our Galaxy. By considering the possible dark matter density spikes formed around the primordial black holes in the BH─NS binaries, we show that extremely high temperature (∼106 K) could be maintained on the surface of the neutron stars due to effective dark matter capture. This interesting feature can also help reveal the nature of dark matter and possibly further improve the upper limit of dark matter scattering cross section well below 10−47 cm2.

Keywords: Neutron stars, Dark matter
Spin and Obliquity Distributions of Low-mass Planets Shaped by Dynamical Instability. Exoplanetary systems hosting multiple low-mass planets are thought to have experienced dynamical instability, during which planet─planet collisions and mergers occur; these collisions can impart a substantial amount of angular momentum to the merger remnants, changing the obliquities of the resulting planets significantly. In this work, we carry out a series of N-body experiments to investigate the spin magnitude (∣S∣) and obliquity (θSL) distributions of low-mass exoplanets that have gone through planetary collisions. In our fiducial super-Earth (with m = 3M⊕, R = 1.3R⊕) and mini-Neptune systems (with m = 9M⊕, R = 2.5R⊕), the collision products follow a nearly uniform distribution in  cosθSL , and the spin magnitude distribution is approximately linear in ∣S∣. Parameter studies and theoretical analysis show that increasing planetary radii or masses, or decreasing the initial planet─planet mutual inclinations, tend to polarize the obliquity distribution toward alignment or antialignment (i.e., excess probability near  cosθSL=±1 ). Experiments with initially two-planet and three-planet systems produce qualitatively similar outcomes, suggesting that the trends in this study may generalize to systems with higher planetary multiplicities.

Keywords: Exoplanet astronomy, N-body simulations, Exoplanet dynamics
Statistical and Temporal Analysis of Multicomponent Burst Clusters from the Repeating FRB 20190520B. Fast radio bursts (FRBs) are bright, millisecond-duration extragalactic radio transients that probe extreme astrophysical environments. Many FRBs exhibit multicomponent structures, which encode information about their emission mechanisms or progenitor systems and thus provide important clues to their origins. In this work, we systematically analyze the burst morphology of FRB 20190520B and compare component distributions across four active FRBs observed with FAST: FRB 20121102A, FRB 20190520B, FRB 20201124A, and FRB 20240114A. We find that multicomponent burst clusters show spectral properties similar to single-peak bursts, and no periodicity is detected in their temporal behavior. The component-count distributions follow a power law, revealing scale-free behavior consistent with self-organized criticality processes. Multicomponent clusters account for 12%─30% of all detected bursts, regardless of source activity, providing new insights into burst-to-burst variability and the physical processes driving FRB emission.

Keywords: Radio bursts, Radio transient sources
A Method for Gamma-Ray Energy Spectrum Inversion and Correction. Accurate spectral analysis of high-energy astrophysical sources often relies on comparing observed data to incident spectral models convolved with the instrument response. However, for gamma-ray bursts and other high-energy transient events observed at high count rates, significant distortions (e.g., pile-up, dead time, and large signal trailing) are introduced, complicating this analysis. We present a method framework to address the model dependence problem, especially to solve the problem of energy spectrum distortion caused by instrument signal pile-up due to high counting rate and high-rate effects, applicable to X-ray, gamma-ray, and particle detectors. Our approach combines physics-based Monte Carlo (MC) simulations with a model-independent spectral inversion technique. The MC simulations quantify instrumental effects and enable correction of the distorted spectrum. Subsequently, the inversion step reconstructs the incident spectrum using an inverse response matrix approach, conceptually equivalent to deconvolving the detector response. The inversion employs a convolutional neural network, selected for its numerical stability and effective handling of complex detector responses. Validation using simulations across diverse input spectra demonstrates high fidelity. Specifically, for 27 different parameter sets of the brightest gamma-ray bursts, goodness-of-fit tests confirm the reconstructed spectra are in excellent statistical agreement with the input spectra and residuals are typically within ±2σ. This method enables precise analysis of intense transients and other high-flux events, overcoming limitations imposed by instrumental effects in traditional analyses.

Keywords: Convolutional neural networks, Gamma-ray bursts, Deconvolution
Do Little Red Dots Vary?. Little red dots (LRDs), high-redshift, compact, red objects with V-shaped spectra, are one of the most exciting and perplexing discoveries made by the James Webb Space Telescope (JWST). While the simplest explanation for LRDs is that they are high-redshift active galactic nuclei (AGN), due to their compactness and frequent association with broad-line emission, the lack of corresponding X-ray emission and observed variability casts doubt on this picture. Here, we simulate LRD light curves using both traditional models for sub-Eddington AGN variability derived empirically from lower-redshift AGN observations and moderately super-Eddington AGN disk models from radiation magnetohydrodynamic simulations to examine the reason for the lack of variability. We find that even though most LRDs have only been observed two to four times in a given wave band, we should still be detecting significantly more variability if traditional sub-Eddington AGN variability models can be applied to LRDs. Instead, our super-Eddington model light curves are consistent with the lack of observed LRD variability. In addition, the ongoing high-cadence NEXUS campaign will detect changes in magnitude ∆m &gt; 1 for traditional sub-Eddington models, but will only observe significant continuum variability for the lowest-mass LRDs for our super-Eddington AGN models. Even if LRDs lack continuum variability, we find that the ongoing spectroscopic JWST campaign TWINKLE should observe broad emission line variability as long as soft X-ray irradiation manages to reach the broad-line region from the inner disk. Our models show that super-Eddington accretion can easily explain the lack of continuum variability in LRDs.

Keywords: Radiative magnetohydrodynamics, High energy astrophysics, Active galaxies, James Webb Space Telescope, Active galactic nuclei
The Dark Energy Bedrock All-sky Supernova Program: Cross Calibration, Simulations, and Cosmology Forecasts. Type Ia supernovae (SNe Ia) have been essential for probing the nature of dark energy; however, most SN analyses rely on the same low-redshift sample, which may lead to shared systematics. In a companion paper, we introduce the Dark Energy Bedrock All-Sky Supernova (DEBASS) program, which has already collected more than 500 low-redshift SNe Ia on the Dark Energy Camera, and present an initial release of 77 SNe Ia within the Dark Energy Survey (DES) footprint observed between 2021 and 2024. Here, we examine the systematics, including photometric calibration and selection effects. We find agreement at the 10 mmag level among the tertiary standard stars of DEBASS, DES, and Pan-STARRS1. Our simulations reproduce the observed distributions of DEBASS SN light-curve properties, and we measure a bias-corrected Hubble residual scatter of 0.08 mag, which, while small, is found in 10% of our simulations. We compare the DEBASS SN distances to the Foundation sample and find consistency with a median residual offset of 0.016 ± 0.019 mag. Selection effects have negligible impacts on distances, but a different photometric calibration solution shifts the median residual −0.015 ± 0.019 mag, highlighting calibration sensitivity. Using conservative simulations, we forecast that replacing historical low-redshift samples with the full DEBASS sample will improve the statistical uncertainties on dark energy parameters w0 and wa by 30% and 24%, respectively, enhance the dark energy Figure of Merit by up to 60%, and enable a measurement of fσ8 at the 25% level.

Keywords: Cosmology, Observational cosmology, Type Ia supernovae
ALMA and JWST Imaging of z &gt; 6 Quasars: No Spatial Position Offset Observed between Quasars and Their Host Galaxies. We present a study determining the spatial offset between the position of the supermassive black hole (as traced through their broad line regions) and the host galaxy in six z &gt; 6 quasars. We determined the host galaxy's position from ≲ 0.″10  (≲600 pc) resolution Atacama Large Millimeter/submillimeter Array (ALMA) [C II] 158 μm and corresponding dust continuum imaging. We determined the quasar's position from ≲400 pc resolution James Webb Space Telescope Near-Infrared Camera (JWST NIRCam) imaging. We estimated the observational uncertainties on the quasar's position using astrometric data from the Global Astrometric Interferometer for Astrophysics of field stars within the NIRCam images. We find that all six quasars are found within the central ∼400 pc of their host galaxy dust continuum and [C II] emission. Apparent offsets seen in rest-frame optical JWST observations are not detected in our ALMA data, suggesting they likely result from dust obscuration rather than a true physical separation between the SMBH and its host galaxy. Kinematic modeling of these data further reveals that none of the galaxies show evidence for recent merger activity, and most of the galaxies can be accurately modeled using a simple disk model. The lack of an offset supports theoretical models that predict that positional offset within these galaxies is either short-lived or intrinsically rare.

Keywords: Supermassive black holes, Disk galaxies, Quasars, Active galactic nuclei, Galaxy evolution
Neural-network Chemical Emulator for First-star Formation: Robust Iterative Predictions Over a Wide Density Range. We present a neural-network emulator for the thermal and chemical evolution in Population III star formation. The emulator accurately reproduces the thermochemical evolution over a wide density range spanning 21 orders of magnitude (10−3─1018 cm−3), tracking six primordial species: H, H2, e−, H+, H−, and H 2+ . To handle the broad dynamic range, we partition the density range into five subregions and train separate deep operator networks (DeepONets) in each region. When applied to randomly sampled thermochemical states, the emulator achieves relative errors below 10% in over 90% of cases for both temperature and chemical abundances (except for the rare species H 2+ ). The emulator is roughly 10 times faster on a CPU and more than 1000 times faster for batched predictions on a GPU, compared with conventional numerical integration. Furthermore, to ensure robust predictions under many iterations, we introduce a novel timescale-based update method, where a short-time-step update of each variable is computed by rescaling the predicted change over a longer time step equal to its characteristic variation timescale. In one-zone collapse calculations, the results from the timescale-based method agree well with traditional numerical integration, even with many iterations at a time step as short as 10−4 of the free-fall time. This proof-of-concept study suggests the potential for neural network-based chemical emulators to accelerate hydrodynamic simulations of star formation.

Keywords: Population III stars, Neural networks, Chemical abundances, Star formation, Chemical reaction network models
SN 2024gy: Multiepoch Spectroscopic Features Suggestive of Delayed Detonation in a Type Ia Supernova. We present photometric and spectroscopic observations of SN 2024gy, a Type Ia supernova (SN Ia) exhibiting high-velocity features (HVFs) in its early-time spectra. This SN reaches a peak B-band magnitude of −19.25 ± 0.29 mag and subsequently declines by ∆m15(B) ≍ 1.12 mag, consistent with the luminosity─width relation characteristic of normal SNe Ia. Based on the peak thermal luminosity of (1.2 ± 0.3) × 1043 erg s−1, we estimate that 0.57 ± 0.14 M⊙ of 56Ni was synthesized during the explosion. Our dense early spectral monitoring revealed significant velocity disparities within the ejecta. Notably, absorption features from the Ca II near-infrared triplet were observed at velocities exceeding 25,000 km s−1, while the Si II λ6355 line velocity at the same epoch was significantly lower at ∼16,000 km s−1. This velocity disparity likely reflects distinct ionization states of intermediate-mass elements in the outermost layers. The prominent Ca II HVFs may originate from ionization suppression within the highest-velocity ejecta, potentially indicative of minimal hydrogen mixing in a delayed-detonation explosion scenario. Additionally, the Ni/Fe ratio derived from the nebular spectrum of SN 2024gy provides further support for this model.

Keywords: Type Ia supernovae
Parker Solar Probe Observations of Suprathermal and Energetic Particles during Orbits 18 and 19. The Parker Solar Probe Integrated Science Investigation of the Sun (IS⊙IS) instrument suite measured a variety of suprathermal and energetic particle events during orbits 18 and 19. We provide an overview of key features of the observations to provide guidance critical to making progress on complicated, integrated data sets like those provided by IS⊙IS. In this work, we analyze and describe observations of particle acceleration signatures associated with coronal mass ejection (CME)─driven shocks and solar flares from 2023 November to 2024 March as measured by the IS⊙IS/Energetic Particle Instrument-Low Energy and Energetic Particle Instrument-High Energy particle detectors. We present energy spectra for protons through Fe ions from ∼10 keV nuc−1 to &gt;10 MeV nuc−1, abundance ratios, and time series analyses for seven solar energetic particle (SEP) events with respect to the magnetic field and plasma context provided by the FIELDS and Solar Wind Electrons Alphas and Protons instruments, respectively. For SEP events in orbits 18 and 19, we find that acceleration driven by multiple CMEs in succession have larger variability in 4He/H and Fe/O ratios than singular CMEs, that flare-associated SEP events preferentially accelerate higher mass-to-charge ratio particles, and that shock upstream transients may be present in CME-driven interplanetary shocks.

Keywords: Solar coronal mass ejections, Solar particle emission, Astronomy data analysis