Sazuna/UAT_keywords huggingface dataset:
SIP-IFVM: A Time-evolving Coronal Model with an Extended Magnetic Field Decomposition Strategy. Time-evolving magnetohydrodynamic (MHD) coronal modeling, driven by a series of time-dependent photospheric magnetograms, represents a new generation of coronal simulations. This approach offers more realistic results than traditional steady coronal models constrained by a static magnetogram. However, its practical application is significantly limited by the low computational efficiency and poor numerical stability in solving low-β issues common in coronal simulations. To address this, we propose an extended magnetic field decomposition strategy and successfully implement it in an implicit MHD coronal model. The traditional decomposition strategies split the magnetic field into a time-invariant potential field and a time-dependent component B1. This works well for quasi-steady-state coronal simulations where ∣B1∣ is typically small. However, when the inner-boundary magnetic field evolves, ∣B1∣ can grow significantly, and its discretization errors often lead to nonphysical negative thermal pressure, ultimately causing the simulation to crash. In the extended magnetic field decomposition strategy, we split the magnetic field into a temporally piecewise-constant field and a time-varying component, B1. This effectively keeps ∣B1∣ consistently small throughout the simulations and performs well in solving time-evolving low-β issues, thereby outperforming traditional methods. We incorporate this improved strategy into our implicit MHD coronal model and apply it to simulate the evolution of coronal structures within 0.1 au over two solar-maximum Carrington rotations. The results show that this coronal model effectively captures observational features and performs more than 80 times faster than real-time evolutions using only 192 CPU cores, making it well suited for practical applications in simulating the time-evolving corona.

Keywords: The Sun, Solar corona, Magnetohydrodynamics, Magnetohydrodynamical simulations
The First Insight-HXMT Localization Catalog of Short-duration Gamma-Ray Bursts: The First Six Years. As of 2023 December, the high-energy telescope (HE) of Insight-HXMT has detected 72 short-duration gamma-ray bursts (sGRBs), which may be related to binary compact star mergers. In this work, we locate these sGRBs by adopting an enhanced time-delay localization method based on the Li modified cross-correlation function (Li-CCF), jointly with Insight-HXMT/HE, Gravitational-wave high-energy Electromagnetic Counterpart All-sky Monitor, Fermi/Gamma-ray Burst Monitor (GBM), INTEGRAL/SPI-ACS, and Konus-Wind. The results indicate that joint localization improves accuracy (3σ) by an average of 59% compared to results with GBM alone, and the participation of HXMT improves the joint localization accuracy (3σ) by an average of 47%. The median and minimum of the joint localization area are 229 and 0.2 square degrees, respectively. We also propose a method to effectively locate those bursts (e.g., GRB 200415A) for which HE suffered from data saturation. In addition, we investigate whether the multiple annuli are independent when there is overlapping data through simulations. The results show that as long as the data from both satellites used have not been overlapped at the same time, the localization results (annuli) are independent. Finally, we verify the robustness of the results by comparing the precise localization bursts observed by Swift/Burst Alert Telescope, as well as publishing the high-time-resolution light curves, orbits and localization probability sky maps in Hierarchical Equal Area Isolatitude Pixelization format files on the website https://ihepbox.ihep.ac.cn/ihepbox/index.php/s/LO1eRZ0SBIEiBIg.

Keywords: Gamma-ray bursts
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XIV. Long-duration High-cadence Reverberation Mapping Results for 11 PG Quasars. We report the results of a long-duration high-cadence reverberation mapping campaign of a second batch of 11 PG quasars using the 2.2 m telescope at the Calar Alto Observatory. This follows a similar earlier study of another sample of 15 objects reported by C. Hu et al. (2021). Among the 11 PG quasars, eight objects have the Hβ time lags measured for the first time, while the other three objects were observed in previous campaigns but only had highly uncertain Hβ-lag measurements. Long-term light curves are presented of photometric V-band, spectroscopic 5100 Å continuum, and the Hβ emission line, lasting for ∼3–6 yr with a cadence of ∼6–14 days. Accurate Hβ time lags ranging from ∼20 to 150 days in the rest frame are obtained. The estimated virial masses of the central supermassive black holes range from ∼(3–300) × 107M⊙. Combining these results with those reported in C. Hu et al. (2021), we now have 26 PG quasars, with representative properties, having reliable Hβ time-lag measurements from our long-duration high-cadence campaign. A tentative fit to the relation between the Hβ time lag and the continuum luminosity for these 26 objects gives a slope of 0.53.

Keywords: Supermassive black holes, Quasars, Reverberation mapping, Seyfert galaxies, Active galactic nuclei, Time domain astronomy
Identification of Blue Horizontal-branch Stars Using Synthetic SkyMapper Colors from Gaia XP Spectra. Blue horizontal-branch (BHB) stars are ideal tracers for mapping the structure of the Galactic stellar halo. Traditionally, BHB sample stars are built from large-scale spectroscopic surveys utilizing their spectral features; however, the resulting sample sizes have been quite limited. In this paper, we construct a catalog of BHB stars based on synthetic colors (u ‑ v)0 and (g ‑ i)0 in SkyMapper photometric systems, which are convolved from Gaia XP spectra. A total of 49,733 BHB stars are selected from nearly the entire sky (excluding regions of low Galactic latitudes ∣b∣ ≤ 8∘ with heavy reddening), with a completeness and purity exceeding 90%. Using member stars of globular clusters with precise distance determinations, we carefully calibrate the relationship between the g-band absolute magnitude and (g ‑ i)0, achieving a precision of 0.11 mag, which corresponds to a 5% uncertainty in distance. This relation is applied to derive distances for all BHB stars in the constructed sample. Given the current capabilities of Gaia XP observations, the constructed BHB sample is primarily located within 20 kpc, enabling detailed mapping of the inner stellar halo. To extend this depth to the outer halo or even the edge of our Galaxy, we explore the potential of the Chinese Space Station Telescope (CSST) and its broadband photometry for detecting BHB stars. Using mock data from synthetic spectra, we find that it is feasible to distinguish BHB stars from blue stragglers stars using CSST near-ultraviolet band (u) photometry. Thanks to the deep limiting magnitude of CSST, its data will provide a groundbreaking perspective on our Galaxy, particularly regarding the outer halo, in an unprecedented volume.

Keywords: Horizontal branch stars, Milky Way stellar halo
Intelligent Forecasting for Solar Flares Using Magnetograms from SDO/SHARP, SDO/HMI, and ASO-S/FMG. In this study, we build multiple data sets based on magnetograms provided by the Solar Dynamics Observatory (SDO)/SHARP, SDO/Helioseismic and Magnetic Imager, and the Full-disk vector Magnetograph (FMG) on board the Advanced Space-based Solar Observatory (ASO-S) for ≥M-class flare prediction within 24 hr. We compare the performance of four models for flare forecasting, including a convolutional neural network (CNN), CNN-BiLSTM, vision transformer (ViT), and MViT. We study the impact of magnetograms with single, multiple, and mixed active regions (ARs) on model performance. Furthermore, we investigate the generalization capability of the models by using multisource data collected within the same period, as well as single-source data gathered across different periods. This is the first time that we utilize ASO-S/FMG data for flare forecasting. Finally, we fairly compare the forecasting performance of the MViT model with that of NASA/CCMC under the same prediction time and AR number. The main results are as follows. (1) Transformer-based models outperform CNN-based models, while spatiotemporal models significantly surpass nonspatiotemporal models. (2) The inclusion of a magnetogram with multiple ARs diminishes the forecasting performance of the models, whereas the use of magnetogram data with a single AR for flare prediction yields superior results compared to data with multiple ARs. (3) The MViT model reaches a true skill score of 0.707 when utilizing the FMG data with a single AR, achieving exceptional performance for solar flare forecasting. (4) The MViT model demonstrates better generalization ability across both single-source data and multisource data. (5) The MViT model demonstrates a performance comparable to current state-of-the-art methods (i.e., NASA/CCMC) in flare prediction.

Keywords: Solar activity, Solar active region magnetic fields, Solar flares, Astronomy data analysis
Spectroscopic Study of Ice Analogs of Trans-Neptunian Objects Exposed to Ionizing Radiation. II. Infrared Spectra and Functional Groups. The surfaces of airless trans-Neptunian objects (TNOs) are subject to continuous ionizing radiation from solar winds and Galactic cosmic rays accompanied by alteration of surface compositions. The crust resulting from chemical reactions and products at various radiation levels can influence their spectral gradients and surface colors, which are essentially controlled by the chromophores of complex organic molecules. This study presents comprehensive infrared spectra of TNO-analog ices processed by ionizing radiation, which include water, methane, ammonia, carbon monoxide, carbon dioxide, and methanol along with their binary mixtures. The spectral data suggest that complex organic and inorganic products are synthesized when carbon-bearing ice mixtures are exposed to proxies of Galactic cosmic-ray and solar wind irradiation. A series of functional groups of hydrocarbons, hydroxyl, amine, carbonyl, imine, cyanate, and nitrile are identified, which can be incorporated in complex compounds including alcohols, aldehydes, ketones, carboxylic acids, esters, amines, amides, cyanates, and nitriles along with critical prebiotic molecules such as sugar and amino acids. By combining them with corresponding visible reflectance spectra, these species play a crucial role in revealing the color diversity of TNOs and are also highly relevant to the emergence of life in our solar system. The findings in this study serve as an important starting point to fully unravel the chemical complexity, compositions, and evolutionary processes of objects in the outer solar system and will also provide fundamental support for the interpretation of astronomical observations such as those from the James Webb Space Telescope.

Keywords: Experimental data, Surface ices, Infrared spectroscopy, Trans-Neptunian objects
12 yr Full Solar Cycle Maps from IBEX-Lo Interstellar Neutral Atom Observations (2009–2020). The Interstellar Boundary Explorer (IBEX) mission investigates the very local interstellar medium (VLISM) and its interaction with our heliosphere, partly by sampling interstellar neutral (ISN) atoms. Over 15 yr, IBEX has provided data to study this interaction through varying solar activity phases. Unlike ISN H, He interacts weakly with the heliospheric boundary and solar wind, offering a growing data set to enhance our knowledge of the VLISM and its motion relative to the Sun. We provide count rates and exposure time maps that capture ISN H and He as a function of orbit and spin angle for energy steps (E-Steps) 2 (29 eV) and 3 (55 eV) throughout solar cycle 24 (2009–2020). While E-Step 3 mainly captures ISN He, E-Step 2 rates include both ISN H and He. We show that these maps qualitatively agree with our model predictions. This data set, publicly available, provides an opportunity to study ISN flow and its response to solar activity. Our maps show variations of the primary ISN He intensity with solar activity; a remarkable decrease in the visibility of secondary He during solar maximum; the presence of ISN H signal in the rising phase of solar activity from 2009's minimum, its disappearance during solar maximum, and reappearance toward cycle 25 minimum. This data set further demonstrates a potential ISN data configuration for the upcoming Interstellar Mapping and Acceleration Probe.

Keywords: Space plasmas, Heliosphere, Interstellar atomic gas, Solar wind, Interstellar medium, Solar activity, Interstellar medium wind
A Characteristic Optical Variability Timescale in Jetted Active Galactic Nuclei: A Large Gamma-Ray Emission Sample. The variability mechanisms from jetted active galactic nuclei (AGNs) are still under debate. Here, the damped random walk (DRW) model, implemented through Gaussian processes (GPs), is used to fit the Zwicky Transient Facility long-term optical light curves of 1684 gamma-ray emission jetted AGNs. This analysis yields one of the largest samples with characteristic optical variability timescales for jetted AGNs. A single DRW model from GPs can fit the optical light curve of most jetted AGNs well/potentially well, while there are still some jetted AGNs whose light curve cannot be fitted well by a single DRW model. After the jet power, proxied by gamma-ray luminosity, is introduced as a new parameter, new relationships among intrinsic variability time scales, black hole mass, and jet power are discovered for efficient accretion AGNs ( τin∝MBH0.29‑0.06+0.06Pjet‑0.3‑0.03+0.03  with scatter of approximately 0.09 dex) and for inefficient accretion AGNs ( τin∝MBH0.06‑0.07+0.07Pjet0.37‑0.11+0.11  with scatter of approximately 0.14 dex), respectively. Our results support that the optical variability of jetted AGNs with efficient accretion may originate within the standard accretion disk at UV-emitting radii similar to nonjetted AGNs, and is directly related to the acceleration of shock in the jet and then enhanced through the beaming effect in beamed AGNs. For the jetted AGNs with inefficient accretion, the intrinsic timescale is consistent with the escape timescale of electrons.

Keywords: Blazars, Galaxy accretion disks, Galaxy jets, Active galactic nuclei, Time domain astronomy, Time series analysis
Research on High-precision Fiber Transmission and Compensation for a Solar Radio Heliograph. Solar radio bursts are a major source of space weather hazards. Thus, developing solar observation systems is essential. The heliograph, based on synthetic aperture imaging and a dual interferometer, enables high-resolution solar imaging, offering rich spatial information beyond conventional radio spectrometers. The performance of a synthetic aperture heliograph depends critically on time-frequency synchronization among multiple antennas. On this basis, we have conducted research on fiber time-frequency synchronization. The research allows the long-distance transmission and synchronization of signals generated by the rubidium atomic clock via optical fiber. Analysis and testing demonstrated that the research achieved frequency stability of 7 × 10‑13/1 s and an accuracy of 0.466 ppm. After compensation, the average time difference achieved 4.6 and 5.4 ps for frequency and time standard signal, respectively. These results not only indicate that our scheme meets the requirements of the synthetic aperture heliograph but also demonstrate good applicability and scalability, providing a solid foundation for the future development of solar observation systems.

Keywords: Solar radio telescopes, Aperture synthesis
Homogeneous Stellar Atmospheric Parameters and 22 Elemental Abundances for FGK Stars Derived from LAMOST Low-resolution Spectra with DD-PAYNE. A deep understanding of our Galaxy calls for detailed decomposition of its stellar populations via their chemical fingerprints. This requires precise stellar abundances of many elements for a large number of stars. Here, we present an updated catalog of stellar labels derived from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution spectra in a physics-sensible and rigorous manner with DD-PAYNE, taking labels from high-resolution spectroscopy as a training set. The catalog contains atmospheric parameters for 6.4 million stars released in LAMOST DR9, and abundances for 22 elements, namely, C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, for nearly 3.6 million stars with spectral signal-to-noise ratio (S/N) higher than 20. The [Fe/H] is valid down to ≃ ‑4.0, while elemental abundance ratios [X/Fe] are mostly valid for stars with [Fe/H] ≳ ‑2.0. Measurement errors in these labels are sensitive to and almost inversely proportional with S/N. For stars with S/N &gt; 50, we achieved a typical error of 30 K in Teff, 0.07 dex in  logg , ∼0.05 dex in abundances for most elements with atomic number smaller than Sr, and 0.1–0.2 dex for heavier elements. Homogenization to the label estimates is carried out via dedicated internal and external calibration. In particular, the nonlocal thermal equilibrium effect is corrected for the [Fe/H] estimates, the Teff is calibrated to the infrared flux method scale, and the  logg  is validated with asteroseismic measurements. The elemental abundances are internally calibrated using wide binaries, eliminating systematic trend with effective temperature. The catalog is publicly available.

Keywords: Galaxy chemical evolution, Surveys, Stellar abundances, Chemical abundances, Stellar physics, Spectroscopy, Milky Way evolution
Generalized Fluid Models of the Braginskii Type. II. The Boltzmann Operator. In our previous paper, we employed the Landau collisional operator together with the moment method of Grad and considered various generalizations of the Braginskii model, such as a multifluid formulation of the 21- and 22-moment models valid for general masses and temperatures, where all of the considered moments are described by their evolution equations (with fully nonlinear left-hand sides). Here, we consider the same models; however, we employ the Boltzmann operator and calculate the collisional contributions via expressing them through the Chapman–Cowling collisional integrals. These "integrals" just represent a useful mathematical technique/notation introduced roughly 100 yr ago, which (in the usual semilinear approximation) allows one to postpone specifying the particular collisional process and finish all of the calculations with the Boltzmann operator. We thus consider multifluid 21- and 22-moment models which are valid for a large class of elastic collisional processes describable by the Boltzmann operator. Reduction into the 13-moment approximation recovers the models of Schunk and Burgers. We only focus on the particular cases of hard spheres, Coulomb collisions, purely repulsive inverse power force ∣K∣/rν, and attractive force ‑∣K∣/rν with repulsive rigid core (or potential V(r) = δ(r) ‑ ∣c∣/rn, so that the particles bounce from each other when they meet), but other cases can be found in the literature. In the Appendix, we introduce the Boltzmann operator in a way suitable for newcomers and we discuss a surprisingly simple recipe to calculate the collisional contributions with analytic software.

Keywords: Collisional processes, Space plasmas, Plasma physics
Metallicities of 20 Million Giant Stars Based on Gaia XP Spectra. We design an uncertainty-aware cost-sensitive neural network (UA-CSNet) to estimate metallicities from dereddened and corrected Gaia BP/RP (XP) spectra for giant stars. This method accounts for both stochastic errors in the input spectra and the imbalanced density distribution in [Fe/H] values. With a specialized architecture and training strategy, the UA-CSNet improves the precision of the predicted metallicities, especially for very metal-poor (VMP; [Fe/H] ≤ ‑2.0) stars. With the PASTEL catalog as the training sample, our model can estimate metallicities down to [Fe/H] ∼ ‑4. We compare our estimates with a number of external catalogs and conduct tests using star clusters, finding overall good agreement. We also confirm that our estimates for VMP stars are unaffected by carbon enhancement. Applying the UA-CSNet, we obtain reliable and precise metallicity estimates for approximately 20 million giant stars, including 360,000 VMP stars and 50,000 extremely metal-poor ([Fe/H] ≤ ‑3.0) stars. The resulting catalog is publicly available via the Chinese Virtual Observatory at doi: 10.12149/101604. This work highlights the potential of low-resolution spectra for metallicity estimation and provides a valuable data set for studying the formation and chemodynamical evolution of our Galaxy.

Keywords: Fundamental parameters of stars, Metallicity, Astronomy data analysis, Spectroscopy
Pulscan: Binary Pulsar Detection Using Unmatched Filters on NVIDIA GPUs. The Fourier domain acceleration search (FDAS) and Fourier domain jerk search (FDJS) are proven matched-filtering techniques for detecting binary pulsar signatures in time-domain radio astronomy data sets. Next-generation radio telescopes such as the SPOTLIGHT project at the Giant Metrewave Radio Telescope (GMRT) produce data at rates that mandate real-time processing, as storage of the entire captured data set for subsequent offline processing is infeasible. The computational demands of FDAS and FDJS make them challenging to implement in real-time detection pipelines, requiring costly high-performance computing facilities. To address this, we propose Pulscan, an unmatched-filtering approach that achieves order-of-magnitude improvements in runtime performance compared to FDAS while being able to detect both accelerated and some jerked binary pulsars. We profile the sensitivity of Pulscan using a distribution (N = 10,955) of synthetic binary pulsars (simulated post–radio-frequency interference mitigation) and compare its performance with FDAS and FDJS. Our implementation of Pulscan includes an OpenMP version for multicore CPU acceleration, a version for heterogeneous CPU/GPU environments such as NVIDIA Grace Hopper, and a fully optimized NVIDIA GPU implementation for integration into an AstroAccelerate pipeline, which will be deployed in the SPOTLIGHT project at the GMRT. Our results demonstrate that unmatched filtering in Pulscan can serve as an efficient data reduction step prior to FDAS or FDJS, selecting data sets for further analysis and focusing subsequent computational resources on likely binary pulsar signatures.

Keywords: Millisecond pulsars, Pulsars, Computational methods, GPU computing, Radio astronomy, Binary pulsars, Radio pulsars