Sazuna/UAT_keywords huggingface dataset:
The Error Estimation of Transverse Coronal Loop Oscillation Parameters Based on Least Chi-squares Fitting. Transverse oscillations of coronal loops not only influence coronal dynamics, but also provide a new perspective for coronal detection. To enhance their exploitation and utilization, accurately estimating the oscillation parameters is crucial. The least chi-squares fitting is a widely employed method for this estimation. However, due to the highly nonlinear nature of the fitting process, there is no established theory to provide the exact error of the fitted parameters. In this study, we systematically investigated the accuracy and precision of the fitted parameters of transverse coronal oscillations through a series of forward simulations. Our investigation indicates that the accuracy and precision of fitted oscillation parameters are influenced not only by the standard deviation of the measurement error, but also by the temporal resolution and the characteristics of the signal itself. Based on these findings, we conducted additional forward simulations to estimate the influences on the real observation examples. The results clearly show that (1) the fitted damping timescale should be overestimated in a significant number of transverse coronal loop oscillations, and (2) errors estimated by the general method may be biased. In response, we have developed a forward simulation-based schema to achieve a self-consistent error estimation for the fitted oscillation parameters. These contributions not only offer valuable insights into the error estimation of fitted transverse coronal oscillation parameters, but also establish a robust foundation for obtaining accurate and precise transverse oscillation parameters of the corona.

Keywords: Solar coronal seismology, Solar coronal waves, Active solar corona
GRB 221009A: The B.O.A.T. Burst that Shines in Gamma Rays. We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest gamma-ray burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded, by 1 s, the low-energy (&lt;10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a bad time interval of 64 s caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 s suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event.

Keywords: Gamma-ray astronomy, Gamma-ray bursts, High energy astrophysics
The FAST H I 21 cm Absorption Blind Survey. II. Statistical Exploration for Associated and Intervening Systems. We present an extragalactic H I 21 cm absorption lines catalog from a blind search at z ≤ 0.35, using drift-scan data collected in 1325.6 hr by the ongoing Commensal Radio Astronomy Fast Survey and FAST All Sky H I Survey, which spans a sky area of 6072.0 deg2 and covers 84,533 radio sources with a flux density greater than 12 mJy. Fourteen previously identified H I absorbers and 20 newly discovered H I absorbers were detected, comprising 15 associated systems, 10 intervening systems, and nine systems with undetermined classifications. Through spectral stacking, the mean peak optical path, mean velocity-integrated optical path, mean FWHM, and mean H I column density are measured to be 0.47 and 0.30; 27.19 and 4.36 km s‑1; 42.61 and 9.33 km s‑1; 0.49 and 0.08 Ts × 1020 cm‑2 K‑1, for the associated and intervening samples, respectively. Statistical analysis also reveals that associated systems tend to be hosted by red (g ‑ r &gt; 0.7) galaxies at lower redshifts, whereas galaxies hosting intervening H I absorption are typically found at higher redshifts and are of a bluer (g ‑ r ≤ 0.7) type. A noticeable difference is observed in the positions of foregrounds, backgrounds of intervening systems, and high-redshift and low-redshift associated systems on the Wide-field Infrared Survey Explorer color–color diagram. All identified foreground sources in our sample have W1 – W2 magnitudes below 0.8, suggesting no active galactic nuclei (AGNs). In contrast, backgrounds of intervening systems tend to have W1 – W2 magnitudes above 0.8, indicating AGN presence. For associated absorption, most low-redshift (z ≤ 0.5) systems show W1 – W2 values below 0.8, while higher-redshift associated absorption (z &gt; 0.5) displays a broader range of W1 ‑ W2 values.

Keywords: Interstellar line absorption, Extragalactic radio sources, Galaxy spectroscopy, Galaxy evolution
The S-PLUS Ultra-short Survey: Photometric Recalibration with the Best Star Database. We present an independent validation and comprehensive recalibration of S-PLUS Ultra-short Survey (USS) DR1 12-band photometry using about 30,000–70,000 standard stars from the Best Star (BEST) database. We identify the spatial variation of zero-point offsets, up to 30–40 mmag for blue filters (u, J0378, and J0395) and 10 mmag for others, predominantly due to the higher uncertainties of the technique employed in the original USS calibration. Moreover, we detect large- and medium-scale CCD position-dependent systematic errors, up to 50 mmag, primarily caused by different aperture and flat-field corrections. We then recalibrate the USS DR1 photometry by correcting the systematic shifts for each tile using second-order two-dimensional polynomial fitting combined with a numerical stellar flat-field correction method. The recalibrated results from the XP spectrum based synthetic photometry and the stellar color regression standards are consistent within 6 mmag in the USS zero-points, demonstrating both the typical precision of the recalibrated USS photometry and a sixfold improvement in USS zero-point precision. Further validation using the Sloan Digital Sky Survey and Pan-STARRS1, as well as LAMOST DR10 and Gaia photometry, also confirms this precision for the recalibrated USS photometry. Our results clearly demonstrate the capability and efficiency of the BEST database in improving calibration precision to the millimagnitude level for wide-field photometric surveys. The recalibrated USS DR1 photometry is publicly available on ChinaVO at doi:10.12149/101503.

Keywords: Stellar photometry, Calibration, Astronomy data analysis
Extracting Cleaned Swift/UVOT Ultraviolet Grism Spectra with the uvotpy Package. The Ultraviolet/Optical Telescope (UVOT) on board the Neil Gehrels Swift Observatory is capable of imaging with seven lenticular filters and of taking slitless spectra with two grisms. Both image and grism data have been widely used to study gamma-ray bursts (GRBs), supernovae, and other ultraviolet (UV)/optical transients, and proved UVOT is a powerful instrument in time-domain astronomy. However, the second-order contamination, for blue sources, strongly limits the red end of UV grism spectra. This, in turn, reduces the valid wavelength range to only about 33% of the total. To explore the broadband spectral energy distribution of GRBs at the early stage, a larger valid wavelength range is required. Hence, based on the uvotpy (https://github.com/PaulKuin/uvotpy) package, we propose a method to remove the second-order contamination from UV grism spectra (nominal mode) up to ∼4000 Å, i.e., about 70% of the full wavelength range. The 1σ systematic uncertainty of this method is ∼11.2%. In addition, if a source is red enough, the red end of the valid range could reach ∼5000 Å. The source code is available on GitHub at https://github.com/HaoZhou0810/cluvotpy.

Keywords: Ultraviolet astronomy, Astronomy data reduction
Weak-lensing Characterization of the Dark Matter in 29 Merging Clusters that Exhibit Radio Relics. We present a multiwavelength analysis of 29 merging galaxy clusters that exhibit radio relics. For each merging system, we perform a weak-lensing analysis on Subaru optical imaging. We generate high-resolution mass maps of the dark matter distributions, which are critical for discerning the merging constituents. Combining the weak-lensing detections with X-ray emission, radio emission, and galaxy redshifts, we discuss the formation of radio relics from the past collision. For each cluster, we obtain mass estimates by fitting a multicomponent Navarro–Frenk–White model with and without a concentration–mass relation. We compare the mass estimates of each subcluster to their velocity dispersion measurements and find that they preferentially lie below the expected velocity dispersion scaling relation, especially at the low-mass end (∼1014 M⊙). We show that the majority of the clusters that exhibit radio relics are in major mergers with a mass ratio below 1:4. We investigate the position of the mass peak relative to the galaxy luminosity peak, number density peak, and brightest cluster galaxy (BCG) locations and find that the BCG tends to better trace the mass peak position. Finally, we update a golden sample of eight galaxy clusters that have the simplest geometries and can provide the cleanest picture of the past merger, which we recommend for further investigation to constrain the nature of dark matter and the acceleration process that leads to radio relics.

Keywords: Weak gravitational lensing, Galaxy clusters, Dark matter distribution, Large-scale structure of the universe, Gravitational lensing, Shocks, Intracluster medium
Stunted Outbursts and Z Cam─like Behaviors in the Long-term Light Curves of Novalike Cataclysmic Variables. A program of long-term ground-based photometric monitoring of 134 old novae and novalike cataclysmic variables (CVs) has been concluded. In this paper, we display, analyze, and discuss the light curves of 33 of these targets, which have shown "stunted" outbursts (StOBs) during the years 1990─2014. Because our light curves have long time baselines and strong homogeneity, most of our analysis centers on the aggregate properties of StOBs to take advantage of the strengths of our data sets, as opposed to more detailed analysis of individual systems. The StOBs amplitudes exhibit a range of ∼0.14─1.35 mag, with a peak near ∼0.55 mag and durations in the range of ∼5─50 days. We have provided additional targets including FY Per, X Ser, CT Ser, and BK Lyn. A few Z Cam stars were also monitored, providing a photometric comparison of Z Cam and StOB stars at a common cadence and sampling. We refine the properties of the small StOBs and better characterize their relationship to somewhat similar photometric features in Z Cam─type dwarf novae as well as IW And─type and AH Pic─type phenomena. We also compare our ground-based photometry of four CVs displaying StOBs with results from published Kepler mission photometry. The dense spacing and high precision of the Kepler data reveal faint excursions (dips) that are numerous for some CVs, while the ground-based data cover a wider range of CV types. Ultimately, we find that our data provide evidence for both accretion disk instabilities and rapid mass transfer modulation episodes as probable StOB contributing mechanisms.

Keywords: Optical bursts, Novae, Z Camelopardalis stars, Nova-like variable stars, Cataclysmic variable stars
A Catalog of 12,766 Carbon-enhanced Metal-poor Stars from LAMOST Data Release 8. Metal-poor stars are a rare and ancient type of star; carbon-enhanced metal-poor (CEMP) stars are a subset of these celestial bodies that show an enrichment of carbon relative to iron. They are believed to be formed from gas polluted by the first generation of stars after the Big Bang and are important objects for studying the early Universe, galaxy evolution, and nucleosynthesis. Due to their rarity, the search for metal-poor stars and CEMP stars is a valuable task. This study investigates the search for CEMP stars based on the low-resolution stellar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 8 (DR8), and proposes a deep learning scheme. From the LAMOST DR8 spectral library, this work discovered 12,766 CEMP star candidates. For ease of reference and use, we provide the estimated parameters Teff,   [Fe/H], and [C/H] for them.

Keywords: Catalogs, CEMP stars, Astronomy data analysis, Chemical abundances
GRB Redshift Classifier to Follow up High-redshift GRBs Using Supervised Machine Learning. Gamma-ray bursts (GRBs) are intense, short-lived bursts of gamma-ray radiation observed up to a high redshift (z ∼ 10) due to their luminosities. Thus, they can serve as cosmological tools to probe the early Universe. However, we need a large sample of high-z GRBs, currently limited due to the difficulty in securing time at the large aperture telescopes. Thus, it is painstaking to determine quickly whether a GRB is high-z or low-z, which hampers the possibility of performing rapid follow-up observations. Previous efforts to distinguish between high- and low-z GRBs using GRB properties and machine learning (ML) have resulted in limited sensitivity. In this study, we aim to improve this classification by employing an ensemble ML method on 251 GRBs with measured redshifts and plateaus observed by the Neil Gehrels Swift Observatory. Incorporating the plateau phase with the prompt emission, we have employed an ensemble of classification methods to unprecedentedly enhance the sensitivity. Additionally, we investigate the effectiveness of various classification methods using different redshift thresholds, zthreshold = zt at zt = 2.0, 2.5, 3.0, and 3.5. We achieve a sensitivity of 87% and 89% with a balanced sampling for both zt = 3.0 and zt = 3.5, respectively, representing a 9% and 11% increase in the sensitivity over random forest used alone. Overall, the best results are at zt = 3.5, where the difference between the sensitivity of the training set and the test set is the smallest. This enhancement of the proposed method paves the way for new and intriguing follow-up observations of high-z GRBs.

Keywords: Gamma-ray bursts, Support vector machine
Deep Learning–based Pseudocontinuum Fitting of C IV Emission-line Regions for High-quality Absorption-line Measurement. Intrinsic associated absorption lines (AALs) in quasar spectra play a crucial role in providing insights into the chemical and physical properties of quasar outflows, host galaxies, and their surrounding interstellar medium. Affected by the complexity of the overlap of absorption lines with emission profiles, there are still many challenges to effectively measure the AALs of massive quasar data, which significantly limits the benefits of spectroscopic surveys. In this study, we first constructed a reliable sample of 3000 spectra containing only narrow absorption lines, 3000 spectra with broad absorption lines, and 3000 spectra with no detected absorption lines, based on the spectroscopic data from the Sloan Digital Sky Survey. We then implemented a deep learning model capable of automatically extracting pseudocontinuum profiles of C IV emission lines. The model proposed was validated by comparing its generated pseudocontinuum with those from the methods presented by W.-R. Huang et al., A. M. Quider et al., and G. Zhu &amp; B. Ménard, as well as by measuring and comparing the C IV AAL parameters based on different approaches, thereby demonstrating the model's reliability. This dramatically simplifies massive data processing and improves the convenience of scientific studies related to quasars.

Keywords: Active galaxies, Astronomy data reduction, Quasar absorption line spectroscopy, Quasars
COSMIC-S: A Photometric Catalog of Observed Stars in the Small Magellanic Cloud. The Dark Energy Camera (DECam) is a wide-field instrument mounted on the 4 m V. Blanco Telescope (Cerro Tololo Inter-American Observatory). Its impressive technical characteristics make it one of the most suitable ground-based telescopes for the production of accurate stellar photometry, even toward crowded regions such as the Magellanic Clouds. We analyzed DECam images acquired from 2018 February to 2020 January toward the Small Magellanic Cloud. We performed a point-spread function photometry by using the SExtractor and PSFEx tools and producing a comprehensive photometric catalog in the Sloan Digital Sky Survey system, considering the gri filters. Then, we present COSMIC-S, a photometric catalog consisting of 10,971,906 sources, including gri magnitudes with a mean error &lt;σm&gt; ≃ 0.04 mag. A total of 2,456,434 sources have good photometry in all three bands. The catalog appears virtually complete to m ≃ 22, with a limiting magnitude m ≃ 25. We derived the color–magnitude and color–color diagrams in order to prove the goodness of the catalog.

Keywords: Stellar photometry, Small Magellanic Cloud, Catalogs
An End-to-end Ensemble Machine Learning Approach for Predicting High-impact Solar Energetic Particle Events Using Multimodal Data. Solar energetic particle (SEP) events, in particular high-energy-range SEP events, pose significant risks to space missions, astronauts, and technological infrastructure. Accurate prediction of these high-impact events is crucial for mitigating potential hazards. In this study, we present an end-to-end ensemble machine learning (ML) framework for the prediction of high-impact ∼100 MeV SEP events. Our approach leverages diverse data modalities sourced from the Solar and Heliospheric Observatory and the Geostationary Operational Environmental Satellite integrating extracted active region polygons from solar extreme ultraviolet (EUV) imagery, time-series proton flux measurements, sunspot activity data, and detailed active region characteristics. To quantify the predictive contribution of each data modality (e.g., EUV or time series), we independently evaluate them using a range of ML models to assess their performance in forecasting SEP events. Finally, to enhance the SEP predictive performance, we train an ensemble learning model that combines all the models trained on individual data modalities, leveraging the strengths of each data modality. Our proposed ensemble approach shows promising performance, achieving a recall of 0.80 and 0.75 in balanced and imbalanced settings, respectively, underscoring the effectiveness of multimodal data integration for robust SEP event prediction and enhanced forecasting capabilities.

Keywords: Solar energetic particles, Space weather
Collision-energy-sensitive State Selectivity and Line Ratios in Charge Exchange between N<SUP>5+</SUP> and He. Astrophysical charge-exchange modeling depends on an accurate database of state-resolved and velocity-dependent cross sections. The cross sections, resolved by the quantum state with principal n and orbital angular momentum ℓ, are pivotal in determining X-ray and extreme ultraviolet (EUV) emissions following charge exchange between highly charged ions and neutrals. However, the current cross-sectional data are primarily theoretically derived and have undergone limited experimental validation. Using high-resolution cold-target recoil-ion momentum spectroscopy, we conduct an experimental study on state-selective cross sections of charge exchange between 5.36 and 75 keV u‑1 N5+ ions and He. Evidently, at low collision energies electrons are mainly captured in the n = 3 state of N4+ ions, and higher n capture competitively comes into play as the increase of collision energy. The relative cross sections are reported for state-selective electron capture into 2s, 2p, 3s, 3p, 3d, 4ℓ, 5ℓ, and n ≥ 6 Rydberg series of N4+(1s2nl) ions. The ℓ distributions commonly used in astrophysical literature are evaluated by comparing them to the measured ℓ-resolved state-selective cross sections for the dominant n = 3 capture, which allows us to experimentally derive the collision-energy-dependent EUV line ratios.

Keywords: Atomic physics, Collision physics, Atomic spectroscopy, Atomic data benchmarking, Charge exchange recombination
New Theoretical Fe II Templates for Bright Quasars. We present a set of new theoretical Fe II templates for bright quasars covering a wavelength range of 1000–10000 Å based on the recent atomic database available in the C23.00 version of the photoionization code CLOUDY. We compute a grid of models for a range of incident photon flux, gas density, and multiple microturbulence velocities. We examine the equivalent widths and the ratios of Fe II emission over various wave bands and compare them with observations. Our key results are as follows: (1) The flux generated from the shielded side of the cloud is insufficient to describe the measured Fe II emission. (2) Despite using the newest atomic data, we still confirm the long-standing problem that the predicted Fe II UV/optical ratio is significantly larger than that observed in the active galactic nuclei spectra. (3) The Fe II UV/optical ratio is not significantly affected by the variations in the microturbulence and the metallicity. (4) The microturbulence can create an additional apparent velocity shift of up to 1000 km s‑1 in the spectra. (5) There is no Fe II template based on a single set of physical parameters that can fit the observed UV to optical Fe II emission spectra. We shortly discuss the most likely effects responsible for the Fe II UV/optical mismatch problem: the assumption of the constant density clouds and the heating mechanism for Fe II emitting clouds.

Keywords: Active galactic nuclei, Photoionization, Atomic physics, Quasars
SILVERRUSH. XIV. Lyα Luminosity Functions and Angular Correlation Functions from 20,000 Lyα Emitters at z ∼ 2.2–7.3 from up to 24 deg<SUP>2</SUP> HSC-SSP and CHORUS Surveys: Linking the Postreionization Epoch to the Heart of Reionization. We present luminosity functions (LFs) and angular correlation functions (ACFs) derived from 18,960 Lyα emitters (LAEs) at z = 2.2‑7.3 over a wide survey area of ≲24 deg2 that are identified in the narrowband data of the HSC-SSP and CHORUS surveys. Confirming the large sample with 241 spectroscopically identified LAEs, we determine Lyα LFs and ACFs in the brighter luminosity range down to 0.5L⋆, and confirm that our measurements are consistent with previous studies but offer significantly reduced statistical uncertainties. The improved precision of our ACFs allows us to clearly detect one-halo terms at some redshifts, and provides large-scale bias measurements that indicate host halo masses of ∼1011M⊙ over z ≃ 2‑7. By comparing our Lyα LF (ACF) measurements with reionization models, we estimate the neutral hydrogen fractions in the intergalactic medium to be xH I &lt; 0.05 (=  ) at z = 5.7 and xH I =   ( ),  , and   at z = 6.6, 7.0, and 7.3, respectively. Our findings suggest that the neutral hydrogen fraction remains relatively low, xH I ≲ 0.2, at z = 5‑7, but increases sharply at z &gt; 7, reaching xH I ∼ 0.9 by z ≃ 8‑9, as indicated by recent JWST studies. The combination of our results from LAE observations with recent JWST observations suggests that the major epoch of reionization occurred at z ∼ 7‑8, likely driven by the emergence of massive sources emitting significant ionizing photons.

Keywords: Galaxy formation, Reionization, Lyman-alpha galaxies, Luminosity function