Sazuna/UAT_keywords huggingface dataset:
Empirical Prediction of Plasma Emission Measure Distributions and X-Ray/Extreme-ultraviolet Spectra of Late-type Stars. High-energy emission spectra from the outer atmospheres of late-type stars represent an important feature of the stellar activity in several contexts, such as the photoevaporation and photochemistry of planetary atmospheres or the modeling of irradiated circumstellar disks in young objects. An accurate determination of these spectra in the EUV and soft X-ray (XUV) band requires high-resolution spectroscopy, which is rarely feasible with current instrumentation. We employed a relatively large set of plasma emission measure distributions (EMDs) as a function of temperature, derived from far-ultraviolet and X-ray emission line spectra acquired with the Hubble Space Telescope and Chandra or XMM-Newton, in order to devise a relatively simple recipe for predicting EMDs and XUV spectra of stars of different spectral types, activity levels, and plasma metallicities. We show that the EMDs in the range of temperatures between 104 and 107.5 K can be described using the stellar surface X-ray flux as a control parameter, but this parameterization also depends on the spectral type. In particular, we find that M-type stars show slightly lower emission measure at temperatures below ∼105 K and higher emission measures for T ≳ 106.5 K with respect to FGK stars with similar surface X-ray fluxes. We evaluated the uncertainties in the broadband EUV and X-ray fluxes derived from synthetic EMDs and spectra, considering in the error budget also the limited knowledge on the chemical abundances in stellar outer atmospheres.

Keywords: Late-type stars, Stellar chromospheres, Extreme ultraviolet astronomy, Stellar coronae, X-ray stars
Bistability, Oscillations, and Multistability on Hycean Planets. Hycean planets are hypothetical exoplanets characterized by H2O oceans and H2-rich atmospheres. These planets are high-priority targets for biosignature searches, as they combine abundant surface liquid water with easy-to-characterize H2-rich atmospheres. Perhaps their most unusual climate feature is convective inhibition, which can dramatically alter a planet's temperature structure. However, so far, hycean planets have mostly been investigated using 1D models that do not account for convective inhibition, and its effects are still poorly understood. This work develops pen-and-paper theory to analyze the effects of moist convective inhibition on hycean planets. The theory is tested and verified against a 1D radiative─convective model. We show that hycean planets near the onset of convective inhibition can exhibit either bistability or oscillations, due to the inhibition layer's trapping of heat and moisture. Meanwhile, hot hycean planets exhibit multistability, in which the inhibition layer and surface climate show multiple stable equilibria due to the lack of constraints on the water cycle inside the inhibition layer. The water cycle inside the inhibition layer is influenced by numerous processes that are challenging to resolve in 1D, including turbulent diffusion, convective overshoot, and large-scale circulations. Our results demonstrate that hycean planets have unexpectedly rich climate dynamics. Meanwhile, previous claims about hycean planets should be treated with caution until confirmed with more self-consistent 1D and 3D models; this includes the claim that K2-18b might be habitable, as well as the proposal to infer H2O oceans on sub-Neptunes from JWST measurements of chemical species in their upper atmospheres.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheric variability, Habitable planets, Exoplanet atmospheres, Exoplanet atmospheric structure
Abundance of Heavy r-process Elements in CEMP-rs Stars: The Role of the i-process. Carbon-enhanced metal-poor (CEMP) stars are ancient stars enriched in carbon and heavy elements. Some of these stars exhibit enhanced s-process and/or r-process elements, and hence are classified as CEMP-s, CEMP-rs, or CEMP-r. This classification is challenging due to the limited availability of heavy element abundances, particularly among r-process elements. Heavy r-process elements such as terbium, holmium, thulium, ytterbium, lutetium, tantalum, and iridium have rarely been measured because their sensitive lines are located in the ultraviolet. However, they provide sensitive diagnostics of the s-, r-, and i- nucleosynthetic processes. In this work, we aim to obtain a secure classification of CEMP-s and -rs stars and investigate whether the i-process can account for the measured abundance patterns in CEMP-rs stars. We derive the abundance profiles, notably for 12 heavy r-elements, including, in some cases, tantalum, using high-resolution UVES spectra of 17 CEMP-s and -rs stars. Based on indicators such as the [s/r] abundance ratio or the model-independent "abundance distance", nine stars are confirmed as CEMP-rs and six as CEMP-s. The classification of two objects remains uncertain. The i-process satisfactorily reproduces the abundance patterns of CEMP-rs stars. However, larger samples are needed to confirm trends with metallicity and clarify how CEMP-rs stars differ from CEMP-s stars.

Keywords: Stellar nucleosynthesis, Asymptotic giant branch stars, Binary stars, Chemical abundances
Widespread Hot Molecular Gas Heated by Shear-induced Turbulence in the Galactic Center. We observed NH3 metastable inversion lines from (3, 3) to (18, 18) toward G0.66-0.13 in the Galactic center with the Shanghai Tianma 65 m radio telescope and Yebes 40 m telescope. Highly excited lines of NH3 (17, 17) and (18, 18) were detected in emission for the first time in the interstellar medium, with upper energy levels up to 3100 K. Mapping observations reveal widespread hot molecular gas traced by NH3 (13, 13) toward G0.66-0.13. The rotation temperatures of hot gas traced by NH3 exceed 400 K, which amounts to 5% of the total NH3 in the Galactic center. Hot gas (&gt;400 K) and warm gas (100─140 K) are found in distinct clumps, with the hot gas located at the interfacing regions between different warm clouds. The theory of intermittency in turbulence reproduces the complex temperature structure in the central molecular zone (CMZ), especially the hot gas observed here. The results presented here demonstrate that turbulence heating dominates the heating of the molecular gas in the CMZ, while the turbulence is induced by the shear motion of molecular clouds under the gravitational potential of the nuclear star clusters and the supermassive black hole. Our results suggest that shear-induced turbulence heating could be a widespread factor influencing galactic evolution.

Keywords: Galactic center, Interstellar medium
Probing Spectral Line Asymmetries due to the Propagating Transverse Waves in the Solar Corona. Decades-long studies of asymmetric spectral lines in the solar corona suggest mass and energy transport from lower atmospheric layers to the corona. While slow magnetoacoustic waves and plasma flows are recognized as drivers of these spectral line asymmetries, the role of transverse MHD waves remains largely unexplored. Previous simulations have shown that unidirectionally propagating kink waves, in the presence of perpendicular density inhomogeneities, can produce a turbulence-like phenomenon called "uniturbulence." However, the spectroscopic signatures of this effect have not been investigated until now. Due to varying Doppler shifts from the plasma elements with different emissions, we expect to observe signatures of both blueward and redward asymmetries. Past instruments like the EUV Imaging Spectrometer may have missed these signatures due to resolution limitations, but current instruments like DKIST offer a better opportunity for detection. We conducted 3D MHD simulations of transverse waves in a polar plume with density inhomogeneities and performed forward modeling for the Fe XIII emission line at 10749 Å. Our findings show that transverse waves and uniturbulence induce alternating red and blueward asymmetries, with magnitudes reaching up to 20% of peak intensity and secondary peak velocities between 30 and 40 km s−1, remaining under 100 km s−1. These asymmetries propagate with the transverse waves, and even at DKIST resolution, similar signatures can be detected. Our study suggests that spectral line asymmetries can serve as a diagnostic tool for detecting transverse-wave-induced uniturbulence.

Keywords: Magnetohydrodynamics, Solar coronal waves, Solar corona
The Relation between AGN and Host Galaxy Properties in the JWST Era. II. The Merger-driven Evolution of Seyferts at Cosmic Noon. In Paper I, we exploited the unsurpassed resolution and depth of JWST/NIRCam imagery to investigate the relationship between active galactic nuclei (AGN) and host-galaxy properties in the JWST era, finding a correlation between the level of spatial disturbance (as measured by shape asymmetry, AS) and obscuration (NH). Here in Paper II, we report an expansion of our X-ray and infrared analysis of Seyfert-luminosity host galaxies with four additional metrics to the single-metric morphology analysis of Paper I, as well as new samples of inactive control galaxies. This expanded study of one of the largest and most complete, multiwavelength samples of AGN detected at 0.6 &lt; z &lt; 3.8 in the GOODS-South and -North fields, confirms that mergers surprisingly play a significant role in obscured, subquasar AGN host galaxies. Additionally, the pattern of morphological disturbances observed amongst the X-ray- and mid-IR-selected AGN suggests that these represent different phases of AGN evolution tied to a major-merger timeline, as opposed to distinct populations of AGN. These results indicate that mergers are important in triggering subquasar AGN at these redshifts.

Keywords: AGN host galaxies
A Comprehensive Photometric Selection of "Little Red Dots" in MIRI Fields: An Infrared-Bright Little Red Dot at z = 3.1386 with Warm Dust Emission. JWST has revealed a population of compact "Little Red Dots" (LRDs) at z ≳ 4, with red rest-frame optical and blue UV colors. These objects are likely compact dusty starbursts or heavily reddened AGNs, playing a pivotal role in early black hole growth, dust production, and stellar assembly. We introduce a new photometric selection to identify LRDs over a broad range in redshifts and rest-frame UV to near-IR (NIR) colors enabling a more complete census of the population. This method identifies 248 LRDs with F444W &lt; 27 mag over 263 arcmin2 in the JADES, PRIMER-COSMOS, and PRIMER-UDS fields with MIRI coverage, increasing the number density by 1.7× compared to previous samples, suggesting that previous censuses were underestimated. Most LRDs are detected in MIRI/F770W but only 7% (17) are detected in F1800W. We use MIRI-based rest-frame [1 ─ 3 μm] colors to trace dust emission. F1800W-detected LRDs have a median [1 ─ 3 μm] = 1.5 mag, with a broad scatter indicative of diverse dust emission properties. About 20% exhibit colors [1 ─ 3 μm] &lt; 1 mag consistent with negligible dust emission, but the majority show significant dust emission at 3 μm ( f3μmdust≲0.8 ) from the galaxy's interstellar medium or a hot-dust-deficient active galactic nucleus torus. The correlation between bluer UV to NIR colors and stronger IR emission suggests that the bluest LRDs may resemble unobscured QSOs. We report an LRD at zspec = 3.1386, detected by MIRI, Spitzer/MIPS, and Herschel/PACS. Its IR spectral energy distribution rises steeply at λrest &gt; 6 μm and peaks near ∼40 μm, providing the first direct evidence of warm dust emission (T = 50─100 K) in an LRD.

Keywords: AGN host galaxies, High-redshift galaxies, Infrared excess galaxies, Compact galaxies
Dissociation and Cooling Dynamics of 2-cyanoindene Monocations: Survival of Small PAHs in Harsh Interstellar Radiation Fields. The molecule, 2-cyanoindene, C10H7N (2CNI) is the only cyanosubstituted polycyclic aromatic hydrocarbon (PAH) detected in space, for which the hydrocarbon counterpart, indene, has also been observed in the same astrochemical environment—the molecular cloud TMC-1. In this study, based on experiments in two different laboratories, the collision and radiation-driven dissociation and cooling dynamics of the 2-cyanoindene monocations are investigated using one of the electrostatic ion-beam storage rings of the DESIREE facility, and the DESIRS beamline at the SOLEIL synchrotron radiation facility. The storage ring experiments quantify the balance between fragmentation and radiative cooling of the stored cations, while the synchrotron experiments characterize dissociation channels from the vacuum ultraviolet-induced dissociative photoionization of the neutrals. Recurrent fluorescence is shown to play an important role in the radiative stabilization of 2CNI+. The results from both sets of experiments are combined to obtain a self-consistent set of microcanonical rate coefficients for dissociation and radiative cooling that completely describe the near-dissociation threshold dynamics of 2CNI+ across the microseconds-seconds time range. This timescale is suitable for incorporation into astrochemical models of PAH growth and destruction lifecycles. This study extends its findings to different astrochemical environments by simulating the extent of fragmentation and the cascade emission spectra of 2CNI+ under varying interstellar radiation fields. These results indicate that radiative cooling enhances the resilience of 2-cyanoindene to harsh radiation conditions, suggesting that small cyano-PAHs may survive longer than previously assumed in a wider range of astrochemical environments, extending beyond cold, dark molecular clouds.

Keywords: Laboratory astrophysics, Polycyclic aromatic hydrocarbons
A High-resolution Study of the Cold Neutral Medium in and around 30 Doradus. With the aim of evaluating the roles of the cold neutral medium (CNM) in the cloud-scale baryon cycle, we perform a high-resolution study of the CNM in and around the extreme star-forming region 30 Doradus (30 Dor). For our study, we use Galactic Australian Square Kilometre Array Pathfinder H I Survey data and produce H I emission and absorption cubes on 7 pc scales. To examine the CNM structures toward 30 Dor, we decompose the H I absorption cube into 862 Gaussian components and find that these components are distributed at four velocity ranges (B1, B2, B3, and B4, respectively): 200─230 km s−1, 230─260 km s−1, 260─277 km s−1, and 277─300 km s−1. We derive line-of-sight average spin temperatures and opacity-corrected total H I column densities and show that the B1─B4 structures have systematically different properties, indicating that they are physically distinct. As for the nature of the observed CNM structures, we find that B2 is associated with the main dense structure where ionized, atomic, and molecular gases are concentrated. B3 and B4 trace inflows whose combined mass flux rate of 0.14 M⊙ yr−1 is comparable to the current star formation rate, while B1 probes outflows with a much lower mass flux rate of 0.007 M⊙ yr−1. Interestingly, the H I column densities in B1─B4 are nearly uniform with a factor of 2 spatial variations, implying the presence of H I shielding layers for H2 formation.

Keywords: Interstellar molecules, Interstellar phases, Radio astronomy, Interstellar atomic gas, Molecular clouds, Large Magellanic Cloud, Photodissociation regions, Interstellar absorption, Cold neutral medium, Interstellar medium, H II regions
Large Magnetic Flux Rope Formation in an X2.1 Flare Observed on 2011 September 6. Solar active region 11283 produced an X2.1 flare associated with a solar eruption on 2011 September 6. Observations revealed a preflare sigmoidal structure and a circular flare ribbon surrounding the typical two-ribbon structure, along with remote brightenings located at a considerable distance from the main flare site. To interpret these observations in terms of the dynamics of the three-dimensional coronal magnetic field, we conducted data-constrained magnetohydrodynamic simulations. Using a nonlinear force-free field as the initial condition, we reconstructed a realistic preflare magnetic environment, capturing a sheared sigmoid above the polarity inversion line surmounted by a fan─spine structure. Our simulations revealed that reconnection between the sigmoidal field, the adjacent fan─dome field lines, and the neighboring large loops facilitated the transfer of magnetic twist and led to the formation of a large magnetic flux rope (MFR). This transfer and propagation of twist are clearly visible throughout the MFR. As reconnection progresses, the entire fan─spine structure expands along with the evolving MFR. A notable outcome of the simulation is that the footpoints of the newly formed MFR align closely with the observed circular flare ribbon and the remote brightening region. Our findings suggest that a large MFR formed during the X2.1 flare, providing a coherent explanation for the observed phenomena.

Keywords: Solar flares, Solar magnetic fields, Magnetohydrodynamical simulations
Forming Double Neutron Stars Using Detailed Binary Evolution Models with POSYDON: Comparison to the Galactic Systems. With over two dozen detections in the Milky Way, double neutron stars (DNSs) provide a unique window into massive binary evolution. We use the POSYDON binary population synthesis code to model DNS populations and compare them to the observed Galactic sample. By tracing their origins to underlying single and binary star physics, we place constraints on the detailed evolutionary stages leading to DNS formation. Our study reveals a bifurcation within the well-known common envelope (CE) formation channel for DNSs, which naturally explains an observed split in the orbital periods of the Galactic systems. The two subchannels are defined by whether the donor star has a helium core (Case B mass transfer) or a carbon-oxygen core (Case C) at the onset of the CE, with only the helium core systems eventually merging due to gravitational-wave-modulated orbital decay. We find that across different treatments of the CE phase, the formation of DNSs through both subchannels requires either a generous core definition of ≃30% H-fraction or a high CE ejection efficiency of αCE ≳ 1.2. By testing different supernova kick velocity models, we find that galactic DNSs are best reproduced using a prescription that favors low velocity kicks (≲50 km s−1), in agreement with previous studies. Furthermore, our models indicate that merging DNSs are born from a stripped progenitor with a median pre-supernova envelope mass ∼0.2M⊙. Our results highlight the value of detailed evolutionary models for improving our understanding of exotic binary star formation.

Keywords: Neutron stars, Close binary stars, Compact binary stars, Gravitational wave sources, Binary pulsars
Gas Accretion from a Neighbouring Galaxy Fuels the Low-luminosity Active Galactic Nucleus in NGC 4278. How a seemingly "dead" host galaxy provides fuel for its active galactic nucleus (AGN) remains an unresolved problem. Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we present a new high-sensitivity atomic-hydrogen (H I) observation toward the nearby elliptical galaxy NGC 4278 and its adjacent region. From the observation, we found that external gas accretion from a neighbouring galaxy fuels the low-luminosity AGN in NGC 4278 through tidal interactions. The accreted gas entering NGC 4278 exhibits a rotating gas disk. Moreover, the accreted galaxy has been gas poor and has an H I to stellar mass ratio of about 0.02. Due to the process of gas accretion, it is likely that relativistic jets are generated in the AGN of NGC 4278. The emission of TeV gamma rays in NGC 4278 is likely to be associated with the newly accreted H I gas.

Keywords: Gamma-ray astronomy, Low-luminosity active galactic nuclei, Intergalactic medium
Interpretations of the 10% Polarization Observed in the Early Forward Shock Afterglow of GRB 091208B. The ∼10% optical polarization observed at the early stage of GRB 091208B comes from the forward shock emission, which is higher than the conventionally predicted value. Polarizations of the forward shock radiation would depend on the observational geometry and the postshock magnetic field structure. This magnetic field could arise either from the compression of a preexisting magnetic field (i.e., the magnetic field in the outer medium) or from the shock-generated instabilities. In this paper, we use a synchrotron radiation model to fit the light curve and polarization observations of GRB 091208B. Two scenarios are considered: one is the case of a slightly off-axis observer, and the other is with a large-scale ordered magnetic field component in the burst environment. We found both scenarios could interpret the observations of GRB 091208B. For the slightly off-axis observation scenario, the observational angle is restricted to be within the range of (1.02, 1.05) times the jet half-opening angle. For the large-scale ordered magnetic field component scenario, the ratio between the ordered component and the random component is constrained to be around 1.

Keywords: Starlight polarization, Gamma-ray bursts, Magnetic fields
The Effect of a Self-bound Equation of State on the Structure of Rotating Compact Stars. This paper investigates how a self-bound equation of state (EOS), which describes strange quark stars, affects the rotational properties of compact stars, focusing on deviations from universal relations governing gravitational mass and radius changes due to rotation. The analysis reveals significant deviations in stars with higher surface-to-center total energy-density ratios,  ϵsϵc+c2Pc , challenging the established universal relations. For Newtonian stars, hydrostatic equilibrium ensures that the difference between the gravitational potential at the center, Φc, and at the poles, Φp, remains constant within sequences of rotating neutron stars characterized by the same central and polar specific enthalpy (Φc − Φp = − hc + hp). Combined with the scaling  Φ∝Re2 , where Re denotes the equatorial radius, this condition naturally leads to a quasi-universal behavior in the rotational change of radius within these sequences. Similarly, in general relativistic stars, the hydrostatic equilibrium maintains that  ΦpGR−ΦcGR  remains unchanged within these sequences, where ΦGR is one of the metric potentials. Inspired by this theoretical framework, a toy model has been developed to capture the dependence of gravitational mass and radius deviations on the surface-to-central total energy density ratio. Subsequently, an improved set of empirical universal relations has been proposed for accurately modeling rapidly rotating compact stars with self-bound EOSs.

Keywords: Neutron stars, Relativistic stars, Millisecond pulsars, Pulsars, Newtonian gravitation, General relativity, Compact objects, Stellar rotation