Sazuna/UAT_keywords huggingface dataset:
The DECam MAGIC Survey: A Wide-field Photometric Metallicity Study of the Sculptor Dwarf Spheroidal Galaxy. The metallicity distribution function (MDF) and internal chemical variations of a galaxy are fundamental to understand its formation and assembly history. In this work, we analyze photometric metallicities for 3883 stars over 7 half-light radii (rh) in the Sculptor (Scl) dwarf spheroidal (dSph) galaxy, using new narrowband imaging data from the Mapping the Ancient Galaxy in CaHK (MAGIC) survey conducted with the Dark Energy Camera (DECam) at the 4 m Blanco Telescope. This work demonstrates the scientific potential of MAGIC using the Scl dSph galaxy, one of the most well-studied satellites of the Milky Way. Our sample ranges from [Fe/H] ≍ ─4.0 to [Fe/H] ≍ ─0.6, includes six new extremely metal-poor candidates ([Fe/H] ≤ ─3.0), and is almost 3 times larger than the largest spectroscopic metallicity data set in the Scl dSph. Our spatially unbiased sample of metallicities provides a more accurate representation of the MDF, revealing a more metal-rich peak than observed in the most recent spectroscopic sample. It also reveals a break in the metallicity gradient, with a strong change in the slope: from −3.26 ± 0.18 dex deg−1 for stars inside ∼1 rh to −0.55 ± 0.26 dex deg−1 for the outer part of the Scl dSph. Our study demonstrates that combining photometric metallicity analysis with the wide field of view of DECam offers an efficient and unbiased approach for studying the stellar populations of dwarf galaxies in the Local Group.

Keywords: Dwarf galaxies, Metallicity, Dwarf spheroidal galaxies
In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main-sequence and Post-main-sequence Systems. Tidal interactions are one of the primary drivers of orbital evolution for massive planets with short orbital periods. Tidal dissipation within host stars can cause the orbits of such planets to decay. However, the mechanisms of tidal dissipation are difficult to probe. Generally, tidal dissipation is parameterized by the modified stellar tidal quality factor, or  Q*' , but the lack of observational evidence of orbital decay to confirm dissipation theories has resulted in orders of magnitude of uncertainty in  Q*' . We present a new transit timing analysis of 54 systems with varying stellar evolutionary states in an attempt to search for orbital decay across multiple stages of stellar evolution. For each system, we obtained mid-transit times from new TESS data and evaluated potential departures from a linear ephemeris using the Bayesian information criterion. We then determined tidal quality factors using widely tested theoretical relations. Of the systems studied, 25 showed evidence of a decrease in orbital period over time and eight showed evidence of a decrease that was inconsistent with zero by three standard deviations: CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, and XO-3. However, the significance of some of these detections may be influenced by unreliable transit time measurements. Similarly, we see that the lower limit on  Q*'  for evolved systems is marginally lower than it is for the sample of all systems, though both limits are orders of magnitude below the expected theoretical values for both samples. These new constraints on transit times and  Q*'  values will help to narrow the search for orbital decay in the future and place important constraints on current theories of star─planet interactions.

Keywords: Exoplanet dynamics, Transits, Exoplanets, Hot Jupiters, Transit timing variation method, Tidal interaction
JWST/NIRCam Imaging of the Bipolar Planetary Nebula NGC 6537: The (Infra)red Spider, Revealed. We present James Webb Space Telescope (JWST) Near-Infrared Camera (NIRCam) Brα, H2, [Fe II], and polycyclic aromatic hydrocarbon (PAH) imaging of the molecule-rich, high-excitation bipolar planetary nebula (PN) NGC 6537 (the Red Spider), complemented by new Atacama Large Millimeter/submillimeter Array (ALMA) and Chandra X-ray Observatory (Chandra) observations and archival Hubble Space Telescope (HST) images. The resulting multiwavelength view of the Red Spider establishes the detailed lobe─torus structure of the nebula and the mass-loss history of its progenitor star. The extinction-penetrating JWST/NIRCam Brα and PAH and ALMA 3 mm continuum imaging exposes the complexity of the ionized inner nebula. JWST/NIRCam H2 imaging traces the full, ∼1.1 pc extent of the bubble-like lobes formed by fast (∼300─400 km s−1) polar outflows, while ALMA 13CO(1─0) mapping reveals a point-symmetric, slowly (∼10 km s−1) expanding equatorial torus of radius ∼ 0.13 pc. In striking contrast, the [Fe II] image displays an extended S-shaped emission morphology that traces collisions between an active, collimated wind and slower-moving material along the lobe rims. No X-rays are detected from the nebula or its central star in deep Chandra/HRC-I imaging. However, the combined HST and JWST imaging reveals a near-IR excess at the central star indicative of emission from hot (∼1000 K) circumstellar dust. We propose that interactions between the nebular progenitor star and a close companion are responsible for the ejection of NGC 6537's molecular torus, the formation of a circumbinary dust disk, and the launching of fast, wandering, collimated outflows that have inflated the polar lobe bubbles traced by near-IR H2 emission and are presently generating the [Fe II]-emitting shocks.

Keywords: Stellar jets, Stellar winds, Planetary nebulae
Do Young Suns Produce Frequent, Massive CMEs? Results from Five-year Dedicated Optical Observations of EK Draconis and V889 Hercules. We report results from a five-year (132-night) dedicated observational campaign targeting two nearby young solar-type stars, EK Draconis (∼50─125 Myr age) and V889 Hercules (∼30 Myr age), using the 3.8 m Seimei Telescope and Transiting Exoplanet Survey Satellite. The aim is to observationally constrain statistical properties of flaring radiation/heating, as well as coronal mass ejections (CMEs), through high time-cadence Hα spectroscopy. We obtained an unprecedented sample of 15 Hα superflares, including two blueshifted absorption, two blueshifted emission, one redshifted emission, and nine line broadening events. We obtain the following results: (1) larger flares exhibit broader Hα line widths, up to 14.1±2.4 Å, indicating higher chromospheric heating than solar flares; (2) the long-lasting redshifted event at ∼100 km s−1 may indicate dense postflare loops; (3) Hα blueshifted absorptions/emissions provide evidence of massive filament/prominence eruptions, the core structures of CMEs. One newly identified event showed an unexpected rapid decrease in velocity; (4) the lower limit of the CME/eruption association rate with superflares is 27 −16+25 %, yielding occurrence rates of 0.21±0.12 and &lt;0.32 −0.32+0.46  events per day for EK Draconis and V889 Hercules, respectively; and (5) we derived the first direct estimate of the lower limit of the mass-loss rate driven by super-CMEs (≳1033 erg) for EK Dra as 4 × (10−13─10−12) M⊙ yr−1, comparable to the stellar wind mass loss at a similar age. This study provides critical observational constraints on the radiation and plasma environment around young solar-type stars and the early Sun, which can drive planetary space weather and stellar mass/angular momentum loss.

Keywords: Solar analogs, G dwarf stars, Flare stars, Stellar mass loss, Stellar flares, Optical flares, Stellar coronal mass ejections
Voyager 1 Observations of Galactic Cosmic-Ray Isotopes in the Very Local Interstellar Medium: Evidence for Primary <SUP>2</SUP>H and B. We present the first measurements of the energy spectra of the isotopes of Galactic cosmic rays (GCRs) with nuclear charge Z = 1─14 in the very local interstellar medium (VLISM). We also update our previously published energy spectra of GCR elements in the VLISM from Z = 1─28 for a new longer time period of observations, 2013 January 1 through 2021 December 31. The observations are from the Cosmic Ray Subsystem on the Voyager 1 (V1) spacecraft and cover the Z-dependent energy range from ∼3 to 661 MeV nuc−1. The data are fit to eight models using the GCR propagation code GALPROP, which differ by having four options for fragmentation and two options for production cross sections. The models are all plain diffusion models with injection spectra as power laws in rigidity, where the propagation parameters and the injection power-law index are the same for all species, and derived self-consistently and independently for each model. The VLISM energy spectra generated by the models agree reasonably well with the observed VLISM energy spectra for the elements with Z = 1─28 and with the isotopes with Z = 1─14. However, to achieve reasonable fits to the 2H and B energy spectra, it was necessary to add a primary source of 2H and B.

Keywords: Galactic cosmic rays, Interstellar medium
A Dedicated System for Coordinated Radio and Optical Monitoring of the Space Weather of Young, Solar-type Stars. Low-frequency radio emission in the form of type II and III bursts is a direct indicator of plasma motion in the solar corona and interplanetary medium. However, detecting equivalent events on solar analogs requires thousands of observing hours and complementary multiwavelength observations to constrain the origin of the radio emission. To address this, we have begun the Study of Space Weather Around Young Suns (SWAYS), a multiwavelength program for monitoring space weather around young, solar-type stars. This program currently focuses on five solar-type stars spanning 100─800 Myr in age. It includes a dedicated observing scheme from the recently upgraded Owens Valley Radio Observatory (OVRO) Long Wavelength Array (LWA) operating at 13─86 MHz to search for stellar analogs of solar type II and III bursts. We have built the optical photometry instrument Flarescope to operate simultaneously with OVRO-LWA observations to investigate whether radio bursts are accompanied by magnetic reconnection events. We analyze the performance based on a 1 hr observation of π1 UMa, which shows that Flarescope can reach submillimagnitude precision through nondifferential photometry on π1 UMa in 60 s integration times when diffusing the light with engineered diffusers. A small field of OVRO-LWA cross-correlated data centered on π1 UMa reaches a noise level of 740 mJy at 10 s integration time, consistent with confusion noise. With this precision, we should be able to detect large optical flares and related radio bursts that may indicate accompanying coronal mass ejections and energetic particle events. In this paper, we present the design, framework, and performance of the SWAYS program.

Keywords: Interferometers, Transient sources, Stellar activity, Astronomical instrumentation, Optical flares, Photometer, Telescopes, Radio transient sources
Very High-energy Gamma-Ray and Neutrino Emission from Hadronic Interaction in Compact Binary Millisecond Pulsars. Black widow and redback systems are millisecond pulsars in compact orbits with ultra-light and low-mass companions, respectively, collectively known as "spider pulsars." In such systems, an intrabinary shock can form between the pulsar and the companion winds, serving as a site for particle acceleration and associated nonthermal emission. Assuming that protons can be extracted from the neutron star surface and accelerated at the intrabinary shock and/or within the pulsar wind, we model the very high-energy gamma-ray and neutrino emissions (0.1─103 TeV) produced through interactions with the companion wind and the companion star. We first calculate the high-energy emissions using an optimistic combination of parameters to maximize the gamma-ray and neutrino fluxes. We find that, for energetic spider pulsars with a spin-down power ≳1035 erg s−1 and a magnetic field of ∼103 G in the companion region, the gamma-ray emission could be detectable as point sources by the Cherenkov Telescope Array and the Large High Altitude Air Shower Observatory, while the neutrino emission could be detectable by the future TRIDENT detector. Finally, we build a synthetic population of these systems, compute the cumulative neutrino flux expected from spider pulsars, and compare it with the Galactic neutrino diffuse emission measured by IceCube. We find that, under realistic assumptions on the fraction of the spin-down power converted into protons, the contribution of spiders to the diffuse Galactic neutrino flux is negligible.

Keywords: Gamma-ray sources, Neutrino astronomy, High energy astrophysics, Millisecond pulsars
The Interstellar Medium in I Zw 18 Seen with JWST/MIRI. II. Warm Molecular Hydrogen and Warm Dust. We present JWST/MIRI spectra from the Medium-resolution Spectrometer of I Zw 18, a nearby dwarf galaxy with a metallicity of ∼3% Solar. Here, we investigate warm molecular hydrogen, H2, observed in spectra extracted in ∼120 pc apertures centered on eleven regions of interest. We detect seven H2 rotational lines, some of which are among the weakest ever measured. The H2 population diagrams are fit with local-thermodynamic-equilibrium models and models of photodissociation regions. We also fit the ortho-/para-H2 ratios (OPRs); in three of the six regions for which it was possible to fit the OPR, we find values significantly greater than 3, the maximum value for local thermodynamic equilibrium. To our knowledge, although predicted theoretically, this is the first time that OPR significantly &gt;3 has been measured in interstellar gas. We find that an OPR tends to increase with decreasing H2 column density, consistent with the expected effects of self-shielding in advancing photodissociation fronts. The population diagrams are consistent with H nucleon densities of ∼105 cm−3, and an interstellar radiation field scaling factor, G0, of ∼103. This warm, dense H2 gas coexists with the same highly ionized gas that emits [O IV] and [Ne V]. Emission from T ≳ 50 K dust is detected, including an as-yet-unidentified dust emission feature near 14 μm; possible identification of Al2O3 is discussed. The continuum emission from several regions requires that a considerable fraction of the refractory elements be incorporated in dust. Despite stacking spectra in the SE where H2 is found, no significant emission from polycyclic aromatic hydrocarbons is detected.

Keywords: Dwarf irregular galaxies, Blue compact dwarf galaxies, Infrared spectroscopy, Interstellar medium
Peculiar Disk Substructures Associated with the Young Eruptive Star EX Lupi. Young eruptive stars such as EXors undergo dramatic accretion outbursts characterized by sudden optical brightenings, yet the underlying physical mechanism remains uncertain. We present high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 and 4 continuum observations of EX Lupi, the prototypical EXor-type variable, reconstructed using super-resolution imaging with sparse modeling. Our images reveal, for the first time, two distinct substructures: a compact, crescent-shaped inner arc within 10 au of the star, and a narrow outer ring at 30 au. The inner arc is strongly elongated and casts a shadow observed in Very Large Telescope/SPHERE near-infrared scattered light. The outer ring exhibits a radial width comparable to the local pressure scale height, consistent with moderately efficient dust trapping. Geometric and thermal analysis of the disk surface, based on combined ALMA and SPHERE data, indicates that the disk is moderately flared with an average disk temperature consistent with that of classical T Tauri disks. The observed substructures suggest dynamical perturbations—plausibly induced by a massive companion—that may modulate accretion rates through gravitational interaction with the inner arc. These findings provide morphological evidence linking disk substructure to episodic accretion in the structurally mature disk.

Keywords: Astronomy image processing, Planetary-disk interactions, Protoplanetary disks, High angular resolution
Planetary Albedo Is Limited by the Above-cloud Atmosphere: Implications for Sub-Neptune Climates. Energy limits that delineate the "habitable zone" for exoplanets depend on a given exoplanet's net planetary albedo (or "Bond albedo"). We here demonstrate that the planetary albedo of an observed exoplanet is limited by the above-cloud atmosphere—the region of the atmosphere that is probed in remote observation. We derive an analytic model to explore how the maximum planetary albedo depends on the above-cloud optical depth and scattering versus absorbing properties, even in the limit of a perfectly reflective gray cloud layer. We apply this framework to sub-Neptune K2-18b, for which a high planetary albedo has recently been invoked to argue for the possibility of maintaining a liquid-water ocean surface, despite K2-18b receiving an energy flux from its host star that places it inside of its estimated "habitable zone" inner edge. We use a numerical multiple-scattering line-by-line radiative transfer model to retrieve the albedo of K2-18b based on the observational constraints from the above-cloud atmosphere. Our results demonstrate that K2-18b's observed transmission spectrum already restricts its possible planetary albedo to values below the threshold required to be potentially habitable, with the data favoring a median planetary albedo of 0.17─0.18. Our results thus reveal that currently characterizable sub-Neptunes are likely to be magma-ocean or gas-dwarf worlds. The methods that we present are generally applicable to constrain the planetary albedo of any exoplanet with measurements of its observable atmosphere, enabling the quantification of potential exoplanet habitability with current observational capabilities.

Keywords: Exoplanets, Exoplanet astronomy, Radiative transfer, Planetary climates, Planetary science, Albedo, Habitable planets, Exoplanet atmospheres
A Unified Three-dimensional Magnetohydrodynamic Model of the Solar Corona, Solar Wind, and Global Heliosphere with Turbulence Transport. We present results from a unified three-dimensional magnetohydrodynamic model of the solar corona, solar wind, and global heliosphere that incorporates turbulence transport. The fully three-dimensional model is based on Reynolds-averaged mean-flow equations coupled with transport equations for turbulence energy, cross helicity, energy difference, and correlation length scale. The computational domain extends from the coronal base to the local interstellar medium and is divided into four regions: (1) the corona, 1─30 R⊙; (2) the solar wind, 30 R⊙─5 au; (3) the distant solar wind, 5─40 au; and (4) the global heliosphere, 40─1200 au. Representative boundary conditions are imposed at the coronal base and in the interstellar medium. Steady-state solutions are obtained sequentially using time relaxation in each of the four regions. The model accounts for Reynolds stresses, eddy viscosity, turbulent heating, electron heat conduction, Coulomb collisions between thermal protons and electrons, and—beyond 5 au—the effects of pickup protons. In this study, we add an evolution equation for the energy difference and revise the correlation length scale equation to include additional terms associated with cross helicity and eddy viscosity. We show that a region of enhanced turbulence energy forms ahead of the hydrogen wall in the outer heliosheath, and that pickup protons have a negligible influence on the angular momentum flux carried by the solar wind. We compare our simulation results with in situ observations from the Parker Solar Probe, WIND, Ulysses, and New Horizons. The simulation results show overall agreement with the observed plasma, magnetic field, and turbulence quantities.

Keywords: Magnetohydrodynamics, Heliosphere, Interplanetary turbulence, Solar wind, Solar corona, Heliosheath
Binary Stars Approaching Supermassive Black Holes: Hydrodynamics of Stellar Collisions, Mass Fallback, and Partial Tidal Disruption Events. When binaries are injected into low-angular-momentum orbits around a central supermassive black hole (SMBH), various outcomes can occur, including binary tidal breakup, double stellar disruptions, and stellar collision. We use hydrodynamical simulations to study stellar collisions triggered by binary─SMBH encounters, examining both head-on and grazing collisions in deep (βb = 5) and gentle (βb = 0.6) encounters, where βb is the ratio of the binary tidal disruption radius to the binary pericenter distance to the SMBH. Head-on collisions consistently result in appreciable mass loss (∼5%) and a single merger remnant. Grazing collisions have varied outcomes. In gentle encounters, multiple collisions typically form a single remnant with minimal mass loss (≲1%). For deep encounters, the result depends on the specific collision parameters and stellar structure: γ = 5/3 polytropic stars in our simulation produced two disturbed remnants, while solar-type stars (modeled with MESA) in our deep-grazing run formed a single merger remnant in a low-velocity collision. All merger remnants feature extended envelopes, making them susceptible to partial tidal disruptions when they return to the SMBH. The morphology and orbital energy distribution of collision-induced debris differ significantly from those of tidal disruption event (TDE) debris of single stars. Approximately half of the collision-generated debris falls back onto the SMBH, exhibiting a distinct time evolution of the fallback rate. We suggest that such mass loss and fallback can generate electromagnetic flares that mimic weak TDEs.

Keywords: Tidal disruption, Binary stars, Black holes, Stellar dynamics
Search for Type IL Gamma-Ray Bursts: Criterion, Results, Verification, and Physical Implication. As an interesting subclass of gamma-ray bursts (GRBs), Type IL GRBs (such as GRB 211211A and GRB 230307A) features a long-duration prompt emission but originating from a compact binary merger. The "long duration" emission of Type IL GRBs are dominantly composed of the main burst, rather than the extended emission, differentiating them from the traditional "long-short" GRB (e.g., GRB 060614). A previous study has reported several Type IL GRBs by visual inspection of their light curves. In this work, we established a detailed criterion to identify Type IL GRBs by light curve and then systematically searched the archival Fermi/Gamma-ray Burst Monitor data with this criterion, resulting in a sample of five type IL GRBs from 2014 January 1 to 2024 January 1, i.e., GRB 230307A, GRB 211211A, GRB 200914A, GRB 200311A, and GRB 170228A. Apart from the light-curve pattern, we find that the temporal and spectral properties of these five GRBs also support this classification. Interestingly, we find that the energy ratio between extended emission and main emission is almost constant (∼0.7, with small scattering) for these GRBs, which have strong implications on the mechanism of Type IL burst. We discuss theoretical models to interpret the progenitor, central engine, and extended emission of these Type IL bursts.

Keywords: Gamma-ray bursts