Sazuna/UAT_keywords huggingface dataset:
Inactive Longitude and Superflare in the Active Single-lined Pre-main-sequence Binary V2279 Cyg. Young, solar-like stars in the pre-main-sequence (PMS) stage exhibit vigorous magnetic activity that significantly influences their circumstellar environments and the processes of planetary formation and evolution. In binary systems, tidal forces and magnetic interactions can further shape the magnetic geometry. We report a longitudinal preference of starspots, chromospheric activities, and flares in the active single-lined spectroscopic PMS binary system V2279 Cyg, based on long-term photometric observations from Kepler and TESS alongside spectroscopic data from LAMOST. The system is classified as a weak-line T Tauri binary, with component masses estimated at 0.86 M⊙ and 0.27 M⊙. V2279 Cyg's nearly circular orbit is synchronized with its 4.126 day rotational period. Observations reveal large starspot regions clustered near the far-side hemisphere. Spectroscopic data show strong, double-peak Hα emission, the strength of which is highly correlated with starspot distribution, indicating the presence of an active longitude on the primary star. We also mapped the prominence structure corotating with the primary star, suggesting a dense structure close to the near-side hemisphere. Furthermore, we identify an inactive longitude of flares during the 4 yr Kepler observations, where the frequency of flare activity is significantly reduced after the superior conjunction, marking the first such identification in active binary systems. Additionally, a white light superflare, releasing energy of 2.5 × 1037 erg, was detected in TESS observations. These findings provide valuable insights into the magnetic field geometry and dynamo processes in PMS binaries, underscoring the critical role of tidal interactions in shaping magnetic activities.

Keywords: Binary stars, Stellar activity, Flare stars, Pre-main sequence stars, Magnetic fields
Microscopic Current Sheets and Fast Tearing Modes in Plasma Turbulence. Since the seminal work by W. H. Matthaeus &amp; S. L. Lamkin, a large amount of evidence has been collected over the years that magnetic reconnection can disrupt current sheets formed in turbulence. The details about how this happens, however, are not clear, yet. The observation of plasmoids suggests that tearing-type modes are involved, but their nature of spontaneous linear instabilities developing on a static (or at most steady) magnetic equilibrium poses strong constraints on their growth rate versus the timescale of the current sheet evolution. None of the tearing-based scenarios, which to date are most credited in literature, seems to fulfill both this constraint and other consistency requirements on the equilibrium profile. In revising them and the main hypotheses, which any tearing-based theory for 2D turbulent reconnection must satisfy, we propose a possible explanation—supported by numerical calculations—for why tearing modes may be relevant. This explanation is grounded on the microscopic thickness that current sheets attain in turbulence, which makes the growth rates of tearing modes large enough for the instability to possibly develop. At the same time, this implies that theoretical growth rates obtained from a boundary layer analysis cannot be applied in this case. We discuss a few implications of these elements in solar wind turbulence and in comparison with alternative models for tearing-based turbulent reconnection that are available in literature.

Keywords: Space plasmas, Solar wind, Plasma astrophysics, Plasma physics
Compact Ionized Gas Region Surrounded by Porous Neutral Gas in a Dusty Lyman Break Galaxy at Redshift z = 8.312. Porous interstellar medium (ISM) structure in galaxies at the epoch of reionization gives us a hint to understand what types of galaxies contribute to reionization. Although recent studies have pointed out the positive correlation between high ionizing photon escape fractions and high [O III] 88 μm/[C II] 158 μm ratios found in UV-luminous star-forming galaxies at z &gt; 6 with the Atacama Large Millimeter/submillimeter Array, previous studies have paid little attention to the neutral gas porosity that allows ionizing photons to escape. Here we present a detailed analysis of a z = 8.312 Lyman break galaxy, MACS0416_Y1 with a high L[O III] 88 μm/L[C II] 158 μm ratio (≍9) and dust continuum detection. We construct a multiphase ISM model incorporating the neutral gas covering fraction (covPDR). The best-fit model reveals a covPDR ≍ 25%, indicating that ≍75% of the ionized gas region is exposed to intercloud space. We confirm that our conclusions hold even when varying star formation history, stellar age, gas/stellar metallicity, and carbon-to-oxygen abundance ratio. This finding meets one of the necessary conditions for galaxies to have a nonzero escape fraction of ionizing photons and supports recent studies that galaxies with a high [O III] 88 μm/[C II] 158 μm ratio, such as MACS0416_Y1, could contribute to cosmic reionization. Furthermore, the modeled H II region with the best-fitting parameters has a typical size (D = 0.90 pc) and gas density ( lognH,c/cm−3=2.7 ) that are comparable to local compact H II regions. This suggests that the H II regions in MACS0416_Y1 are in an early evolutionary stage.

Keywords: Lyman-break galaxies, Galaxy evolution, Interstellar medium
Expansion Signatures in 35 H II Regions Traced by SOFIA [C II] Emission. We analyze the expansion signatures of 35 H II regions mapped in [C II] 158 μm emission by the Stratospheric Observatory for Infrared Astronomy. The [C II] emission primarily traces photodissociation regions (PDRs) at the transition between ionized and neutral gas. The brightness and narrow line width of [C II] allow us to measure PDR expansion. Bubble-shaped regions often exhibit expansion, while irregular-shaped ones are less likely to. Of the 35 H II regions, 12 (∼34%) exhibit clear expansion in position–velocity diagrams, making them expansion candidates (ECs), with an average expansion velocity of ∼12.2 km s‑1. The remaining 23 regions show no clear expansion signatures, though they may still be expanding below detection limits. Blueshifted expansion is more common (eight ECs solely blueshifted, one redshifted, three both), with mean velocities of ∼10.9 km s‑1 (blueshifted) and ∼13.2 km s‑1 (redshifted). A comparison of our observations to spherical expansion models supports expansion in eight of 12 ECs. Estimated dynamical ages are 10–100 times shorter than the ionizing star lifetimes, in agreement with the results of previous studies. Of the 35 regions, 14 (∼40%) appear as [C II] bubbles; nine of the 12 ECs are bubble-shaped. Thermal pressure likely drives expansion in M43, while stellar winds dominate in M17, M42, RCW 120, and RCW 79. For other ECs, available data do not allow a definitive conclusion. Larger samples and more information about ionizing sources are needed to refine our understanding of H II region feedback and evolution.

Keywords: Star forming regions, H II regions, Interstellar medium, Stellar wind bubbles
The First Photometric Evidence of a Transient/Variable Source at z &gt; 5 with JWST. The James Webb Space Telescope (JWST) discovered 79 transients out to z ∼ 4.8 through the JADES Transient Survey (JTS), but the JTS did not find any z &gt; 5 transients. We present the first photometric evidence of a z &gt; 5 transient/variable source with JWST. The source, AT 2023adya, resides in a zspec = 5.274 galaxy in GOODS-N, which dimmed from mF356W = 26.05 ± 0.02 mag to 26.24 ± 0.02 mag in the rest-frame optical over approximately 2 rest-frame months, producing a clear residual signal in the difference image (mF356W = 28.01 ± 0.17 mag; SNvar = 6.09) at the galaxy center. Shorter-wavelength bands (F090W/F115W) show no rest-frame UV brightness change. Based on its rest-frame V-band absolute magnitude (MV = −18.48 mag), AT 2023adya could be any core-collapse supernova (SN) subtype or an SN Ia. However, due to low SN Ia rates at high redshift, the SN Ia scenario is unlikely. Alternatively, AT 2023adya may be a variable active galactic nucleus (AGN). The NIRCam/Grism spectrum shows no broad Hα emission line (FWHM = 130 ± 26 km s−1), but we cannot exclude the existence of a faint broad line and therefore cannot exclude the AGN scenario. AT 2023adya is unlikely to be a tidal disruption event (TDE) because the TDE models matching the observed brightness changes have low event rates. Although it is not possible to determine AT 2023adya's nature based on the two-epoch single-band photometry alone, this discovery pushes the transient/variable science frontier past z = 5 and toward the Epoch of Reionization.

Keywords: Transient sources, Transient detection
Polka-dotted Stars: A Hierarchical Model for Mapping Stellar Surfaces Using Occultation Light Curves and the Case of TOI-3884. We present StarryStarryProcess, a novel hierarchical Bayesian framework for mapping stellar surfaces using exoplanet transit light curves. While previous methods relied solely on stellar rotational light curves—which contain limited information about spot properties—our approach leverages planetary transits as probes of stellar surfaces. When a planet crosses a spot during transit, it creates a distinctive change in the light curve that directly reveals spot properties. Our model integrates planetary transit modeling with stellar variability analysis by combining the spherical harmonic surface map representation from starry, the probabilistic approach to spot properties of StarryProcess, and a comprehensive transit model that accounts for spot-crossing events during transits. We demonstrate through synthetic data experiments that our model successfully recovers spot distributions, stellar orientation, and spot physical properties. We extend the framework to handle evolving stellar surfaces through time-dependent modeling. Applying our method to TESS observations of TOI-3884, we find evidence for high-latitude spot concentrations and significant spin–orbit misalignment. The transit-based approach overcomes fundamental limitations of previous models by providing constraints on spot properties that would remain hidden in the null space of rotational light curves alone. This methodology enables more accurate exoplanet characterization by disentangling stellar activity due to starspots from planetary signals while simultaneously providing insights into stellar magnetic activity patterns. The whole paper is reproducible and can be found by clicking the GitHub icon ✎.

Keywords: Surface variability, Astrostatistics techniques, Stellar magnetic fields, Astrostatistics, Exoplanet astronomy
On Type 1 Active Galactic Nuclei with Double-peaked [O III]. II. Properties of Long-term Optical Variability. Double-peaked [O III] profiles could potentially indicate kiloparsec-scale dual active galactic nuclei (AGNs). We analyze long-term optical light curves of 35 type 1 AGNs with such features from our recent catalog in Zheng et al. These light curves are obtained from the Catalina Sky Survey and modeled using a damped random walk process. A control sample of 210 normal type 1 AGNs, matched in redshift, intrinsic luminosity, and black hole mass, is also studied. If the double-peaked [O III] is caused by two type 1 AGNs (dual type 1 AGN), then the combined variability from the two AGNs would be expected to differ from that of a single type 1 AGN. However, there is no statistically significant difference in the variability timescale τ and intrinsic variability amplitude σ between these double-peaked AGNs and the control sample of 210 normal type 1 AGNs. Crucially, computer simulations reveal that dual AGN systems systematically produce lower variability amplitudes than single AGNs, which is inconsistent with the observed variability properties of our double-peaked [O III] sample. Moreover, simulations suggest that the fraction of dual type 1 AGNs is ∼3%, indicating that double-peaked [O III] may not be a reliable indicator of dual type 1 AGNs in these systems. However, this does not rule out the possibility that some objects may still host dual AGNs involving other combinations, such as type 1+type 2 AGNs. Future studies with larger samples and higher-quality light curves will help clarify the true nature of these systems.

Keywords: Light curves, Active galaxies, Active galactic nuclei, Emission line galaxies
The Impact of Foregrounds on Dark Ages Measurements with the Highly Redshifted 21 cm Line. Studies of the cosmic dark ages (30 ≲ z ≲ 150) using the highly redshifted 21 cm line of neutral hydrogen offer unparalleled amounts of cosmological information, and recent years have seen the refinement of concepts for such experiments (e.g., CoDEX and FarView), nominally feasible with technology and resources in the next one to two decades. This work studies how the "foreground wedge"—a term in the 21 cm cosmology literature referring to the contamination of power spectrum modes through the combination of smooth-spectrum foreground emission and the frequency-dependent point-spread function of a radio interferometer—manifests at these very high redshifts. We find the effect is more significant than at epoch of reionization redshifts targeted by current ground-based experiments, with foreground avoidance techniques (which discard all k modes falling within the wedge) typically losing 1 order of magnitude of sensitivity. Given the extreme faintness of the 21 cm signal from the cosmic dark ages and the very high sky temperatures (the dominant source of noise) at low radio frequencies, we conclude that some level of foreground subtraction will be necessary to enable dark ages 21 cm cosmology with experiments of the scale believed to be achievable in the near term.

Keywords: Cosmology, Early universe, Radio interferometry
Imprints of Different Types of Low-angular-momentum Accretion Flow Solutions in General Relativistic Hydrodynamic Simulations. Depending on the astrophysical source and its environment, the accretion flows can exhibit a variety of behaviors and characteristics in accordance with the type of solutions. We study low-angular-momentum accretion flows onto black holes using 2D general relativistic hydrodynamic simulations to find imprints of different types of accretion solutions. Such flows, relevant to X-ray binaries and wind-fed low-luminosity active galactic nuclei, often lack sufficient angular momentum to form standard accretion disks. We initialize simulations with semianalytical transonic solutions defined by specific energy ( E0 ) and angular momentum (λ0), allowing a systematic classification of flow types with: (i) an outer sonic point, (ii) an inner sonic point, and (iii) both, exhibiting shock transitions. Only solutions with two sonic points produce hot, thermally driven bipolar jets/outflows with Lorentz factors up to γ ∼ 2, despite the absence of magnetic fields. Using a general relativistic radiation transfer calculation, we compute broadband spectra and images at X-ray (1 keV) from bremsstrahlung emission. Radiative properties depend strongly on the type of accretion solution. Solutions with inner sonic points produce the brightest and most extended X-ray emission, while outer-point solutions produce compact, fainter signals. These multidimensional models are thus essential for predicting radiative signatures and will enable the development of semianalytical tools for interpreting X-ray binaries and possibly Sgr A* in weak magnetic field regimes.

Keywords: Accretion, Black hole physics, X-ray binary stars, High energy astrophysics
Constraining Star Formation in M87 Using Deep Hubble Space Telescope UV Data. We analyzed the deepest Hubble Space Telescope F275W ultraviolet (UV) imaging of M87 to obtain the most robust constraints on its star formation rate (SFR) and star formation history (SFH). After removing the galaxy continuum and globular clusters, we detected an excess of UV point sources near the center. By comparing their colors to young stellar source (YSS) colors generated by stochastically simulated star formation (SF) for various SFRs and SFHs, we ruled out their origin as a UV-upturn population and identified them as YSS. We found an extremely low SFR of ∼2 × 10−5 M⊙ yr−1 in M87, with evidence of a weak starburst ∼125 Myr ago that formed ∼1000 M⊙ of stars. Unlike other cool-core clusters where SF is stronger and directly linked to cooling gas, we found no spatial correlation between YSS and Hα filaments. Comparing SF activity with M87's active galactic nucleus (AGN) outburst history suggests that recent AGN feedback events (≲12 Myr ago) neither triggered nor were associated with any detectable SF; however, earlier outbursts may have triggered weak starbursts. We detected UV filaments cospatial with Hα filaments with similar lengths and widths, though they are obscured by dust near the center. These filaments are likely powered by metal-line emission from collisional ionization, suggesting ongoing low-level precipitation of the intracluster medium. Our results indicate that AGN feedback has quenched SF significantly in M87 for at least 200 Myr, even though some precipitation persists. Additionally, we identified a hotspot created by the counterjet, with the spectral index also constrained.

Keywords: Radio hot spots, Interstellar filaments, Young star clusters, Active galactic nuclei, Star formation, Radio active galactic nuclei
Complete Survey of r-process Conditions: The (Un)robustness of the r-process(es). Heavy elements are synthesized by the r-process in neutron star mergers and potentially in rare supernovae linked to strong magnetic fields. Expensive hydrodynamic simulations of these extreme environments are usually postprocessed to calculate the nucleosynthesis. In contrast, here we follow a site-independent approach based on three key parameters: electron fraction, entropy, and expansion timescale. Our model reproduces the results based on hydrodynamic simulations. Moreover, the 120,000 astrophysical conditions analyzed allow us to systematically and generally explore the astrophysical conditions of the r-process, also beyond those found in current simulations. Our results show that a wide range of conditions produce very similar abundance patterns explaining the observed robustness of the r-process between the second and third peak. Furthermore, we cannot find a single condition that produces the full solar r-process pattern from first to third peak. Instead, a superposition of at least two or three conditions or components is required to reproduce the typical r-process pattern as observed in the solar system and very old stars. The different final abundances are grouped into eight nucleosynthesis clusters, which can be used to select representative conditions for comparisons to observations and investigations of the nuclear physics input.

Keywords: R-process, Chemical abundances, Nucleosynthesis
Rossby Number Regime, Convection Suppression, and Dynamo-generated Magnetism in Inflated Hot Jupiters. Hot Jupiters (HJs) are commonly thought to host the strongest dynamo-generated magnetic fields among exoplanets, up to 1 order of magnitude larger than Jupiter. Thus, they have often been regarded as the most promising exoplanets to display magnetic star─planet interaction signals and magnetically driven coherent radio emission, which unfortunately remains elusive, despite many diversified observational campaigns. In this work, we investigate the evolution of the internal convection and dynamo properties of HJs via one-dimensional models. We explore the dependency on orbital distance, planetary and stellar masses, and types of heat injection. We employ one-dimensional evolutionary models to obtain internal convective structures. Specifically, we obtain the Rossby number Ro as a function of planetary depth and orbital period, after showing that tidal synchronization is likely valid for all HJs. When the heat is applied uniformly, the convective layers of almost all HJs remain in the fast rotator regime, Ro ≲ 0.1, except possibly the most massive planets with large orbital distances (but still tidally locked). We recover magnetic field strengths for inflated HJs by applying well-known scaling laws for fast rotators. When strong heat sources are applied mostly in the outer envelope and outside the dynamo region, as realistic ohmic models predict, convection in the dynamo region often breaks down. Consequently, the heat flux and the derived surface magnetic fields can be greatly reduced to or below Jovian values, contrary to what is commonly assumed, thus negatively affecting estimates for coherent radio emission, and possibly explaining the failure in detecting it so far.

Keywords: Magnetospheric radio emissions, Hot Jupiters, Exoplanet evolution, Exoplanet structure, Star-planet interactions, Planetary cores, Planetary structure
Turbulence Inhibits Planetesimal Formation in Class 0/I Disks Subject to Infall. There is growing evidence that planet formation begins early, within the ≲1 Myr Class 0/I phase, when infall dominates disk dynamics. Our goal is to determine if Class 0/I disks reach the conditions needed to form planetesimals (∼100 km planet building blocks) by the streaming instability (SI). We focus on a recent suggestion that early infall causes an "inflationary" phase in which dust grains are advected outward. We modified the DustPy code to build a 1D disk that includes dust evolution, infall, and heating and cooling sources. We ran six models and examined the implications for the SI, taking into account recent works on how the SI responds to external turbulence. In line with other works, we find that grains are advected outward, which leads to an "advection-condensation-drift" loop that greatly enhances the dust density at the water snowline. However, we do not see this process at the silicate line. Instead, we find a new pile up at the edge of the expanding disk. However, despite these localized enhancements, even a modest amount of turbulence (α = 10−3) leaves planetesimal formation far out of reach. The midplane dust-to-gas ratio is at least an order of magnitude below the SI threshold, even taking into account recent results on how dust coagulation boosts the SI. For planetesimals to form in the Class 0/I phase may require a way to transport angular momentum without turbulence (e.g., disk winds) or a non-SI mechanism to form planetesimals.

Keywords: Exoplanet formation, Protoplanetary disks, Planet formation