Sazuna/UAT_keywords huggingface dataset:
SN 2024afav: A Superluminous Supernova with Multiple Light-curve Bumps and Spectroscopic Signatures of Circumstellar Interaction. We present a comprehensive optical and near-infrared (NIR) spectroscopic study of SN 2024afav, a hydrogen-poor superluminous supernova (SLSN-I) that peaks at ≍−20.7 mag and exhibits an unusual multibumped light curve. Our spectroscopic observations, spanning phases of −14 to +160 days, reveal several unusual features: (i) a narrow (1800 km s−1) and blueshifted (11,000 km s−1) absorption from Hα starting at +20 days; (ii) persistent optical and NIR He I lines at all available phases, showing double absorption structure in NIR spectra at +23 days, with a high-velocity component at a similar velocity to Hα; (iii) early appearance of nebular [O III] emission starting at ≍+50 days; and (iv) a strong [O II] + [Ca II] 7300 Å emission complex starting at ≍+110 days. These unusual features, and their onset at the time of the light-curve bumps, provide compelling evidence of circumstellar interaction between the SN ejecta and a nearby hydrogen-rich shell, as well as the presence of helium in both the outer layers of the progenitor star and the circumstellar medium. A comparison of SN 2024afav to other SLSNe-I showing bumpy light curves and similar spectral properties (PTF 10hgi, SN 2017egm, SN 2019hge) points to a rare subgroup of SLSNe-I in which circumstellar medium interaction provides an important modulation to the energy input.

Keywords: High resolution spectroscopy, Optical observation, Core-collapse supernovae, Helium-rich stars, Transient sources, Circumstellar shells, Spectroscopy, Supernovae, Near infrared astronomy
Evolutionary Tracks and Spectral Properties of Quasi-stars and Their Correlation with Little Red Dots. JWST has revealed a population of red, compact, high-redshift (z ∼ 3─10) objects referred to as "Little Red Dots" (LRDs). These objects exhibit unusual spectral features reminiscent of stellar spectra with blackbody-like spectral energy distributions, large hydrogen Balmer breaks, Balmer line absorption, and classical stellar absorption features such as calcium H&K and the calcium triplet. Following the recent suggestion that these may be actively accreting direct-collapse black holes in the process of assembly, i.e., quasi-stars, we present evolutionary models of quasi-stars using our recently released, publicly available MESA-QUEST modeling framework. We compute a grid of models spanning a range of black hole masses and predict the luminosities, temperatures, surface gravities, and lifetimes of these objects. We find that these models lie along a Hayashi track once they hit their "late stage," which constitutes the majority of their lives (∼20 Myr). We present scaling relations for estimating the mass of a quasi-star as a function of the bolometric luminosity, as well as the bolometric luminosity as a function of the effective temperature for the Hayashi track. The short lifetimes in tandem with the observed number density of LRDs imply the possibility that every supermassive black hole detected at these epochs was once a quasi-star. We compare synthetic spectra of our quasi-star models to observations of LRDs, and show that these models are broadly capable of reproducing the continuum spectra of observed LRDs. These results indicate that quasi-stars are promising candidates for the origin of supermassive black holes via direct collapse in the early Universe.

Keywords: Supermassive black holes, Black holes, Stellar evolutionary models, Active galactic nuclei, Galaxies
Intruder Alert: Breaking Resonant Chains with Planetesimal Flybys. The orbital architectures of compact "Kepler-multi" (KM) exoplanet systems record their complicated dynamical histories. The "breaking-the-chains" hypothesis proposes that compact systems typically form in chains of mean-motion resonances and subsequently break out on a ∼100 Myr timescale. We investigate a scenario for breaking the chains through intermittent flybys of planetesimals originating from a distant reservoir. Using N-body simulations and semianalytical calculations, we find that the probability of escaping resonance through flybys depends mainly on the product of the typical planetesimal mass and the square root of the number of flybys, or "root-cumulative mass" (RCM); an RCM ≳ 50 M⊕ is required to disrupt &gt;50% of compact KM chains. We perform long-term integrations to find the fraction of chains rendered unstable by flybys; we find that an RCM ∼ 50─100 M⊕ reproduces the late-time (≳100 Myr) occurrence rate of resonant KM systems. This mechanism operates in systems with both a sufficiently massive reservoir and an efficient mechanism for planetesimal injection. Consequently, we predict an anticorrelation between resonant inner systems and dynamically active outer configurations.

Keywords: Exoplanet dynamics, Planetesimals, N-body simulations, Orbital resonances
Discovery of a Dwarf Planet Candidate in an Extremely Wide Orbit: 2017 OF201. We report the discovery of a dwarf planet candidate, 2017 OF201, currently located at a distance of 90 au. Its orbit is extremely wide and extends to the inner Oort cloud, with a semimajor axis of 830 au and a perihelion of 45 au, precisely determined from 24 observations over 20 yr. Assuming a typical albedo of 0.13, we estimate a diameter ∼700 km, making it the second-largest known object in this dynamical population and a dwarf planet candidate with the widest orbit. Its high eccentricity suggests that an unseen population of similar objects would total ∼1% of Earth's mass. Notably, the longitude of perihelion of 2017 OF201 lies outside the clustering observed in extreme trans-Neptunian objects, posing a challenge to the proposed dynamical evidence for the hypothetical Planet Nine.

Keywords: Solar system planets, Solar system, Dwarf planets, Scattered disk objects, Detached objects, Trans-Neptunian objects
Molecular Hydrogen Controls the Temperatures of Flares on TRAPPIST-1. Early JWST observations of TRAPPIST-1 have revealed an unexpected puzzle: energetic white-light flares (E &gt; 1030 erg) reach temperatures of only ∼3500─4000 K, nearly 3 times cooler than typical solar flares, which peak around 9000─10,000 K. Here we explain this difference by identifying the physical mechanism that regulates flare temperatures on late M dwarfs. The key factor is that in the cool, dense atmosphere of TRAPPIST-1, magnetic heating is strongly moderated by the dissociation of molecular hydrogen (H2) into atomic hydrogen. This "H2 dissociation thermostat" acts as an efficient energy sink, preventing flare regions from heating above ∼4000 K. Our chemical equilibrium and heat capacity calculations show that this effect depends sensitively on stellar atmospheric pressure and the local abundance of H2. In hotter stars, from early M dwarfs to solar-type stars, the scarcity of molecular hydrogen renders this mechanism ineffective; instead, atomic hydrogen ionization limits flare temperatures near ∼9000 K.

Keywords: Starspots, Stellar flares, Stellar activity
Ancient Relic Moderately Metal-rich Bulge Cluster Tonantzintla 2. The assembly history of the Galactic bulge is intimately tied to the formation of the proto─Milky Way, yet reconstructing this early phase is difficult because mergers and secular evolution have erased most of its original structure. Among present-day stellar systems, only globular clusters retain the ancient signatures needed to trace these primordial building blocks. Here we present the most detailed characterization to date of Tonantzintla 2, a prime candidate for a relic of the Milky Way's primordial bulge. It is a moderately metal-rich globular cluster projected onto the bulge that has remained largely unexplored despite its potential to constrain the early formation of the inner Milky Way. We derive its fundamental parameters using proper-motion-corrected Hubble Space Telescope WFC3 and Advanced Camera for Surveys photometry. By applying an isochrone fitting to very clean data, we obtain an age of 13.58 −1.0+0.72  Gyr, a reddening E(B ─ V) = 1.44 ± 0.02, a metallicity [M/H] = −0.68 −0.05+0.04 , and a heliocentric distance of d⊙ = 7.38 0.080.13  kpc. A complementary chemical-abundance analysis of seven member stars from APOGEE high-resolution spectroscopy reveals an enrichment pattern consistent with an in situ origin. Tonantzintla 2 is among the oldest globular clusters studied in the literature, and the oldest so far analyzed in the Galactic bulge. Its age places a stringent constraint on the onset of the bulge formation, implying that star formation in the inner Galaxy began within ∼0.2 Gyr of the Big Bang and that Tonantzintla 2 represents an exceptional relic of the Milky Way's earliest chemical enrichment.

Keywords: Globular star clusters, Galaxy ages
The Effect of a Nonuniversal Extinction Curve on the Wesenheit Function and Cepheid Distances. The Wesenheit function is widely used to reduce the effects of interstellar reddening in distance measurements. Its construction, however, relies on the assumption of a universal extinction curve and on fixed values of the total-to-selective extinction ratio, RV. Recent studies have shown that RV varies significantly across the Milky Way and between different galaxies, raising concerns about systematic biases in Wesenheit magnitudes and period─Wesenheit relations. In this work, we discuss the impact of nonuniversal extinction on Wesenheit indices by combining the RV-dependent extinction curve with a grid of stellar atmosphere models. We compute the integrated extinction in optical and near-infrared passbands, derive RV-dependent R coefficients for multiple Wesenheit indices, and examine how changes in RV propagate into Wesenheit magnitudes and Cepheid distances in our Galaxy. We find that the R coefficients in the Wesenheit functions vary strongly with RV. For classical Cepheids in the Milky Way disk, variations of RV within the typical observed range (2.6─3.6) can lead to substantial differences in the Wesenheit function, reaching ± 0.7 mag from the mean for the Gaia-based Wesenheit index WG and resulting in distance errors of almost 40%. Near-infrared Wesenheit indices are much less sensitive to RV changes. Our results clearly show that accounting for variable RV is essential when applying period─Wesenheit relations, particularly in the optical regime, or that near- or mid-infrared-based distances should be used. While we present this effect for classical Cepheids, it applies to all pulsating stars for which period─Wesenheit relations are used to infer distances.

Keywords: Magnitude, Pulsating variable stars, Reddening law, Interstellar reddening, Cepheid distance, Interstellar extinction, Stellar distance
Type IIb Supernova Progenitors in 3D: Variability and Episodic Mass Loss Revealed by Radiation Hydrodynamics Simulations. We present the first 3D radiation hydrodynamics simulations of partially stripped ( Mcore∼10M⊙ , Menv ∼ 0.1─1M⊙) yellow supergiant (L ∼ 105L⊙, Teff ≍ 5000─8000 K) envelopes, constructed with Athena++. These envelope models represent the progenitors of type IIb supernovae (SNe IIb), which have lost a substantial fraction of their H-rich envelope before undergoing core collapse. The luminosity-to-mass ratio is high in these extended envelopes, and convection is strongly driven by hydrogen and helium opacity peaks. This surface convection, coupled with changes in the opacity, sustains large-amplitude low-azimuthal-order radial pulsations, creating order-of-magnitude variability in the stellar luminosity on a timescale of tens of days. If persistent prior to the SN, these variations will be detectable with dedicated monitoring of SN IIb progenitor candidates in nearby galaxies and within deep all-sky time-domain surveys, such as the Vera Rubin Observatory's Legacy Survey of Space and Time. Supersonic fluid motions across the outer layers of the star lead to both successful and failed mass-ejection events, which shape the circumstellar environment and drive episodic mass loss (∼10−6─10−5 M⊙ yr−1, in outbursts). The resulting 3D gas distribution in the outer atmosphere, responsible for early-time SN shock-breakout and shock-cooling emission, shows orders-of-magnitude fluctuations in both space and time at any given radial location. This intrinsically complex halo of bound and unbound material complicates predictions for early SN IIb light curves relative to spherically symmetric models. However, it does provide a natural, self-consistent explanation for the presence and diversity of dense circumstellar material observed or inferred around pulsating evolved stars.

Keywords: Hydrodynamical simulations, Radiative magnetohydrodynamics, Stellar convection envelopes, Stellar pulsations, Stellar phenomena, Type II supernovae, Massive stars, Pulsating variable stars, Yellow hypergiant stars, Stellar mass loss, Supernovae
The NANOGrav 15 yr Dataset: Targeted Searches for Supermassive Black Hole Binaries. We present the first targeted searches for continuous gravitational waves (CWs) from 114 active galactic nuclei that may host supermassive black hole binaries, using the NANOGrav 15 yr dataset. By incorporating electromagnetic priors on sky location, distance, redshift, and CW frequency, our strain and chirp-mass upper limits are typically improved by a factor of ∼2 (median 2.2) relative to all-sky limits at the same frequency. Bayesian comparisons against a model including only a Hellings─Downs-correlated background disfavors a CW signal for all targets, with a mean Bayes factor of 0.73 ± 0.32. Two targets have Bayes factors slightly above unity, but coherence tests, random-targeting experiments, and a conservative accounting of the 114-target trials factor all indicate that they are consistent with noise. We use these two candidates as worked examples to illustrate an end-to-end targeted CW search analysis and a suite of follow-up tests that future promising candidates would need to pass. We find that the electromagnetic interpretations of both candidates are ambiguous, and we update the constraints on a putative binary in 3C 66B, ruling out part of its previously allowed parameter space. Ultimately, our results demonstrate the current sensitivity of targeted pulsar timing array searches for CWs and define a road map for future multimessenger CW detections.

Keywords: Gravitational waves
The Maximum Particle Energy Gain during Magnetic Reconnection. The factors that control the maximum energy attained by protons and electrons during magnetic reconnection are investigated analytically and using large-scale simulations with the kglobal model. Previous work revealed that a strong ambient guide field strongly impacts particle energy gain during reconnection, suppressing energy gain from Fermi reflection by increasing the radius of curvature of reconnected field lines. However, previous simulations have also shown that the maximum energy gain increases with the system size. The physical basis for this result has not been explored. We perform simulations that vary the effective system size over a large range to isolate the processes determining the maximum energy gain. The maximum energy  Wmax  is regulated by the number of magnetic-island mergers that occur, as multiple flux ropes that form at early time repeatedly merge until the largest approaches the system scale. Fermi reflection in these repeated mergers dominates particle energy gain. The number of mergers is linked to the effective system size—larger systems produce a larger number of flux ropes and more mergers. That  Wmax  is linked to the number of flux-rope mergers has implications for understanding why particle-in-cell simulations only produce power-law distributions of energetic particles with a limited range in energy.

Keywords: Space plasmas, Solar magnetic reconnection, Plasma physics, Solar magnetic fields, Magnetic fields
A Global View of Jupiter's Upper Atmosphere Through H<inline-formula> <mml:math><mml:msubsup><mml:mrow></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math> </inline-formula>. Planetary upper atmospheres couple the deep atmosphere to the space environment. The dynamics and energetics of this rarefied, partially ionized region govern atmospheric evolution. At Jupiter, decades of past plasma measurements have revealed a variable and enigmatic ionosphere inconsistent with photochemical predictions and unusual global structures imprinted by the planet's powerful magnetic field. Upper-atmospheric temperatures have been measured sporadically and thus are unable to fully characterize the energy transfer mechanism responsible for its unexpectedly hot thermosphere. Observations to date have been too limited spatially, or too insensitive, to uncover the driving mechanisms behind the strong variability and magnetically organized features found in Jupiter's upper atmosphere. Here, we present high spatial resolution global maps of ion densities and temperatures constructed from &gt;175,000 Keck/NIRSPEC spectra collected over 4 yr. Irregular ionospheric emission features, first seen more than 25 yr ago, are shown to be persistent and due to local ion density modifications. Global temperatures decrease steadily from auroral to equatorial latitudes and are remarkably stable, with equatorial deviations of &lt;10% night to night. Thus, despite appearing stochastic in previous observations, Jupiter's upper atmosphere exhibits predominantly spatial rather than temporal variability, yielding a steady global structure generated by local plasma dynamics. These results illustrate how neutral winds and magnetic fields can create globally persistent plasma structures on hydrogen-dominated worlds and provide an explanation for decades of puzzling Jovian upper-atmospheric observations.

Keywords: Planetary ionospheres, Upper atmosphere, Infrared spectroscopy, Jupiter, Aurorae, Ground-based astronomy, Spectroscopy
Surprisingly Similar: The Mass Function of Gaia Neutron Stars and Firstborn Double Neutron Stars. The mass distribution of neutron stars (NSs) encodes information about their formation and binary evolution. We compare the masses of two distinct populations: (I) the recently identified Gaia NSs in wide orbits with solar-like companions and (II) the assumed firstborn recycled pulsar in Galactic double NS systems. Naively, one would expect their masses to differ due to both the presumed differences in their evolutionary histories, as well as astrophysical selection effects that can filter out configurations that would merge or be disrupted. Yet we find that their mass distributions are strikingly similar. Using a two-component Gaussian model, we find that both populations exhibit a narrow component centred near 1.3 M⊙, accompanied by a broader, higher-mass component that extends the distribution toward larger masses. The highest density regions of their fitted parameter posteriors coincide by over 91.6%. Statistical tests further confirm the agreement between these distributions with a Jensen─Shannon divergence JS &lt; 0.08 and an Earth mover's distance of W &lt; 0.063 M⊙ at 90% credibility. This finding seems to imply that both mass functions reflect the natal mass distribution of firstborn NSs in binary systems, supporting the hypothesis that NSs can be born with high masses. Consequently and perhaps surprisingly, binary evolutionary processes need not impart features on the NS mass distribution.

Keywords: Neutron stars, Binary stars, Stellar mass functions, Compact objects, Stellar remnants, Stellar evolution
Secular Evolution of PSR J2021+4026: Long-term γ-Ray Flux and Spin-down Variability beyond State Transitions. PSR J2021+4026 is a remarkable γ-ray pulsar exhibiting repeated transitions between high γ-ray flux (HGF) and low γ-ray flux (LGF) states. With 17 yr Fermi Large Area Telescope monitoring, we reveal persistent secular evolution and enhanced spin-down rate variability within individual emission states—beneath the quasiperiodic state transitions. After removing discrete jumps, the jump-corrected flux δFγ shows a three-phase evolution: rise ( +2.02−0.15+0.17%yr−1 ), decline ( −3.72−0.47+0.34%yr−1 ), and rapid rise ( +14.9−4.4+6.4%yr−1 ), with all rates quoted relative to the long-term mean flux &lt;Fγ&gt; = 7.8 × 10−10 erg cm−2 s−1. Moreover, the flux of the LGF state is gradually approaching the stable HGF level at a rate of +0.72% ± 0.11% yr−1. These results demonstrate that secular flux evolution in PSR J2021+4026 operates largely independently of discrete state transitions, yet jointly with them drives the system toward a stable high-flux equilibrium.

Keywords: Neutron stars, Gamma-ray sources
A 2 au Resolution View by ALMA of the Planet-hosting WISPIT 2 Disk. We present deep, high-spatial-resolution interferometric observations of 0.88 mm continuum emission from the TYC 5709-354-1 system, hereafter WISPIT 2, obtained with the goal of detecting circumplanetary emission in the vicinity of the newly discovered WISPIT 2b planet. Observations with the most extended baseline configuration offered by the Atacama Large Millimeter/submillimeter Array, achieving an angular resolution of 25 × 17 mas (3.3 × 2.2 au), revealed a single, narrow ring with a deprojected radius of 144.4 au and width of 7.2 au, and no evidence of circumplanetary emission within the cavity. Injection and recovery tests demonstrate that these observations can rule out pointlike emission at the location of WISPIT 2b brighter than ≍ 45 μJy at the 3σ level. While these data can rule out PDS 70 c-like circumplanetary emission, the upper limit is consistent with empirical mass─flux relationships extrapolated from the stellar regime. Visibility modeling of the continuum ring confirms that WISPIT 2b lies significantly interior to the millimeter dust ring, raising doubts about the ability of WISPIT 2b to be the only driver of the dust structure. Possible solutions include either another lower-mass companion, residing between WISPIT 2b and the cavity edge, likely in the gap seen by SPHERE at ∼130 au, or that WISPIT 2b is either substantially more massive than estimates based on IR photometry (∼15 MJup) or on a moderately eccentric orbit. The combination of observations sensitive to the gas and dust distributions on larger spatial scales and dedicated hydrodynamical modeling will help differentiate between scenarios.

Keywords: Radio interferometry, Protoplanetary disks, Planet formation
Water Production of Interstellar Comet 3I/ATLAS from SOHO/SWAN Observations after Perihelion. The Solar Wind Anisotropies all-sky hydrogen Lyman-alpha camera on the Solar and Heliosphere Observatory observed the hydrogen coma of interstellar comet 3I/ATLAS, also called C/2025 N1 (ATLAS), beginning on 2025 November 6, 9 days after perihelion. Water production rates were calculated from each image of 3I/ATLAS using the methodology of J. T. T. Mäkinen and M. R. Combi, and fluorescence rates and g-factors were calculated using the daily solar Lyman-alpha fluxes from the LASP database (https://lasp.colorado.edu/lisird/data) corrected for solar rotation and for the comet's heliocentric velocity. The method has been used for over 90 comet apparitions. A water production rate of 3.17 × 1029 s−1 was found on November 6 when the comet was at a heliocentric distance of 1.40 au and at a sufficient solar elongation angle. It decreased over time after that, down to 1─2 × 1028 s−1 around 40 days postperihelion (December 9).

Keywords: Ultraviolet astronomy, Free floating planets, Comet volatiles , Interstellar objects