Sazuna/UAT_keywords huggingface dataset:
Statistical Analysis of Circular-ribbon Flares. Circular-ribbon flares (CFs) are a special type of solar flares owing to their particular magnetic topology. In this paper, we conducted a comprehensive statistical analysis of 134 CFs from 2011 September to 2017 June, including 4 B-class, 82 C-class, 40 M-class, and 8 X-class flares. The flares were observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory spacecraft. The physical properties of CFs are derived, including the location, area (A CF), equivalent radius (r CF) assuming a semispherical fan dome, lifetime (τ CF), and peak soft X-ray (SXR) flux in 1-8 Å. It is found that all CFs are located in active regions, with the latitudes between -30° and 30°. The distributions of areas and lifetimes could be fitted with a lognormal function. There is a positive correlation between the lifetime and area. The peak SXR flux in 1-8 Å is well in accord with a power-law distribution with an index of -1.42. For the 134 CFs, 57% of them are accompanied by remote brightenings or ribbons. A positive correlation exists between the total length (L RB) and average distance (D RB) of remote brightenings. About 47% and 51% of the 134 CFs are related to type III radio bursts and jets, respectively. The association rates are independent of flare energies. About 38% of CFs are related to minifilament eruptions, and the association rates increase with flare classes. Only 28% of CFs are related to coronal mass ejections (CMEs), meaning that a majority of them are confined rather than eruptive events. There is a positive correlation between the CME speed and peak SXR flux in 1-8 Å, and faster CMEs tend to be wider.

Keywords: The Sun, Active sun, Solar physics
Kepler Pixel Project: Background RR Lyrae Stars in the Primary Kepler Mission Field of View. In this paper, we describe a project we initiated to investigate individual pixels in downloaded Kepler apertures in order to find objects in the background of the main targets with variable brightness. In the first paper of this series, we discovered and investigated 547 short-period eclipsing binaries. Here we present the independent discovery of 26 new RR Lyrae stars in the Kepler background pixels obtained during the primary mission and provide continuous and precise photometry for these objects. Twenty-one of these stars were already noted by the Gaia or the Pan-STARRS survey. This new population of dominantly faint and distant RR Lyrae stars increases by 50% and complements nicely the 52 already known main target RR Lyrae stars in the original Kepler field. Despite their faintness, the four-year quasi-uninterrupted light curves of these stars allow an unprecedented view of these faint halo objects. We present an analysis of the light curves of the new RR Lyrae sample, verify their classification using Fourier parameters, and discuss the properties of these newly found pulsating variable stars. Most notably, this is the first time that such faint RR Lyrae stars have been investigated with the help of a photometric data set with outstanding cadence and precision. Interestingly, these objects share the properties of their brighter siblings in terms of subclass characteristics, additional mode content, and modulation occurrence rates.

Keywords: Stellar photometry, Horizontal branch stars, Pulsating variable stars, Stellar pulsations, Light curves, RR Lyrae variable stars, Time domain astronomy, Pulsation modes, Space telescopes, Double-mode variable stars, Time series analysis
An Insight-HXMT Dedicated 33 day Observation of SGR J1935+2154. I. Burst Catalog. Magnetars are neutron stars with an extreme magnetic field and sometimes manifest as soft gamma-ray repeaters (SGRs). SGR J1935+2154 is one of the most prolific bursters and the first confirmed source of a fast radio burst (FRB; i.e., FRB 200428). Encouraged by the discovery of the first X-ray counterpart of FRBs, the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) implemented a dedicated 33-day-long Target of Opportunity observation of SGR J1935+2154 since 2020 April 28. With the HE, ME, and LE telescopes, Insight-HXMT provides a thorough monitoring of burst activity evolution of SGR J1935+2154, in a very broad energy range (1-250 keV) with high temporal resolution and high sensitivity, resulting in a unique valuable data set for detailed studies of SGR J1935+2154. In this work, we conduct a comprehensive analysis of this observation, including detailed burst search, identification, and temporal analyses. After carefully removing false triggers, we find a total of 75 bursts from SGR J1935+2154, out of which 70 are single pulsed. The maximum burst rate is about 56 bursts day-1. Both the burst duration and the waiting time between two successive bursts follow lognormal distributions, consistent with previous studies. We also find that bursts with longer duration (some are multipulsed) tend to occur during the period with relatively high burst rate. There is no correlation between the waiting time and the fluence or duration of either the former or latter burst. It also seems that there is no correlation between burst duration and hardness ratio, in contrast to some previous reports. In addition, we do not find any X-ray burst associated with any reported radio bursts except for FRB 200428.

Keywords: Magnetars
An Insight-HXMT Dedicated 33 day Observation of SGR J1935+2154. II. Burst Spectral Catalog. Since 2020 April 28, Insight-HXMT has implemented a dedicated observation on the magnetar SGR J1935+2154. Thanks to the wide energy band (1-250 keV) and high sensitivity of Insight-HXMT, we obtained 75 bursts from SGR J1935+2154 during a month-long activity episode after the emission of FRB 200428. Here we report the detailed time-integrated spectral analysis of these bursts and the statistical distribution of the spectral parameters. We find that for ~15% (11/75) of SGR J1935+2154 bursts, the CPL model is preferred, and most of them occurred in the later part of this active epoch. In the cumulative fluence distribution, we find that the fluence of bursts in our sample is about an order of magnitude weaker than that of Fermi/GBM, but it follows the same power-law distribution. Finally, we find a burst with similar peak energy to the time-integrated spectrum of the X-ray burst associated with FRB 200428 (FRB 200428-Associated Burst), but the low energy index is harder.

Keywords: Magnetars
Generalized Fluid Models of the Braginskii Type. Several generalizations of the well-known fluid model of Braginskii (1965) are considered. We use the Landau collisional operator and the moment method of Grad. We focus on the 21-moment model that is analogous to the Braginskii model, and we also consider a 22-moment model. Both models are formulated for general multispecies plasmas with arbitrary masses and temperatures, where all of the fluid moments are described by their evolution equations. The 21-moment model contains two "heat flux vectors" (third- and fifth-order moments) and two "viscosity tensors" (second- and fourth-order moments). The Braginskii model is then obtained as a particular case of a one ion-electron plasma with similar temperatures, with decoupled heat fluxes and viscosity tensors expressed in a quasistatic approximation. We provide all of the numerical values of the Braginskii model in a fully analytic form (together with the fourth- and fifth-order moments). For multispecies plasmas, the model makes the calculation of the transport coefficients straightforward. Formulation in fluid moments (instead of Hermite moments) is also suitable for implementation into existing numerical codes. It is emphasized that it is the quasistatic approximation that makes some Braginskii coefficients divergent in a weakly collisional regime. Importantly, we show that the heat fluxes and viscosity tensors are coupled even in the linear approximation, and that the fully contracted (scalar) perturbations of the fourth-order moment, which are accounted for in the 22-moment model, modify the energy exchange rates. We also provide several appendices, which can be useful as a guide for deriving the Braginskii model with the moment method of Grad.

Keywords: Collision physics, Space plasmas, Plasma physics
The R-process Alliance: A Nearly Complete R-process Abundance Template Derived from Ultraviolet Spectroscopy of the R-process-enhanced Metal-poor Star HD 222925. We present a nearly complete rapid neutron-capture process (r-process) chemical inventory of the metal-poor ([Fe/H] = -1.46 ± 0.10) r-process-enhanced ([Eu/Fe] = +1.32 ± 0.08) halo star HD 222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 ≤ Z ≤ 90, including elements rarely detected in r-process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The r-process elements from Ba to Pb, including all elements at the third r-process peak, exhibit remarkable agreement with the solar r-process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends from Ga to Se, Nb through Cd, and In through Te. The r-process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the r-process. The lanthanide fraction, log X La = -1.39 ± 0.09, is typical for r-process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar r-process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. These observations are primarily associated with program GO-15657. Data from programs GO-7348, GO-8197, GO-9804, GO-12554, GO-14161, and GO-14765 are also used. This paper also includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Nucleosynthesis, Stellar abundances, R-process, Spectral line identification, Ultraviolet astronomy
New Fe I Level Energies and Line Identifications from Stellar Spectra. III. Initial Results from UV, Optical, and Infrared Spectra. The spectrum of neutral iron is critical to astrophysics, yet furnace laboratory experiments cannot reach high-lying Fe I levels. Instead, Peterson &amp; Kurucz and Peterson et al. adopted ultraviolet (UV) and optical spectra of warm stars to identify and assign energies for 124 Fe I levels with 1900 detectable Fe I lines, and to derive astrophysical gf values for over 1000 of these. An energy value was assumed for each unknown Fe I level, and confirmed if the wavelengths predicted in updated Kurucz Fe I calculations matched the wavelengths of four or more unidentified lines in the observed spectra. Nearly all these identifications were for LS levels, those characterized by spin-orbit coupling, whose lines fall primarily at UV and optical wavelengths. This work contributes nearly 100 new Fe I level identifications. Thirty-nine LS levels are identified largely by incorporating published positions of unidentified laboratory Fe I lines with wavelengths &lt;2000 Å. Adding infrared (IR) spectra provided 60 Fe I jK levels, where a single outer electron orbits a compact core. Their weak IR lines are searchable, because their mutual energies obey tight relationships. For each new Fe I level, this work again makes publicly available its identification, its energy, and a list of its potentially detectable lines with theoretical gf values, totalling &gt;16,000 lines. For over 2000 of these, this work provides astrophysical gf values adjusted semiempirically to fit the stellar spectra. The potential impact of this work on modeling UV and IR stellar spectra is noted.

Keywords: Line positions, Stellar ages, Stellar abundances, Spectral line identification, Experimental techniques, Stellar colors, Atomic data benchmarking, Transition probabilities
A Compound Poisson Generator Approach to Point-source Inference in Astrophysics. The identification and description of point sources is one of the oldest problems in astronomy, yet even today the correct statistical treatment for point sources remains one of the field's hardest problems. For dim or crowded sources, likelihood-based inference methods are required to estimate the uncertainty on the characteristics of the source population. In this work, a new parametric likelihood is constructed for this problem using compound Poisson generator (CPG) functionals that incorporate instrumental effects from first principles. We demonstrate that the CPG approach exhibits a number of advantages over non-Poissonian template fitting (NPTF)-an existing method-in a series of test scenarios in the context of X-ray astronomy. These demonstrations show that the effect of the point-spread function, effective area, and choice of point-source spatial distribution cannot, generally, be factorized as they are in NPTF, while the new CPG construction is validated in these scenarios. Separately, an examination of the diffuse-flux emission limit is used to show that most simple choices of priors on the standard parameterization of the population model can result in unexpected biases: when a model comprising both a point-source population and diffuse component is applied to this limit, nearly all observed flux will be assigned to either the population or to the diffuse component. A new parameterization is presented for these priors that properly estimates the uncertainties in this limit. In this choice of priors, CPG correctly identifies that the fraction of flux assigned to the population model cannot be constrained by the data.

Keywords: Bayesian statistics, X-ray point sources, Spatial point processes, X-ray telescopes, Parametric hypothesis tests, Prior distribution, Astrostatistics strategies
NuSTAR Observations of 52 Compton-thick Active Galactic Nuclei Selected by the Swift/Burst Alert Telescope All-sky Hard X-Ray Survey. We present systematic broadband X-ray spectral analysis of 52 Compton-thick ( $24\leqslant \mathrm{log}{N}_{{\rm{H}}}^{\mathrm{LOS}}/{\mathrm{cm}}^{-2}$ ) active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight ${N}_{{\rm{H}}}^{\mathrm{LOS}}$ obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction ${N}_{{\rm{H}}}^{\mathrm{Equ}}$ of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor C 22 obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio ( $\mathrm{log}{R}_{\mathrm{Edd}}\leqslant -1.0$ ), whereas C 22 inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio ( $-1.0\leqslant \mathrm{log}{R}_{\mathrm{Edd}}$ ). The average value of the Compton-thick torus covering factor C 24 obtained from the XClumpy model is ${36}_{-4}^{+4}$ %. This value is larger than that of Ricci et al. ( ${C}_{24}\simeq {27}_{-4}^{+4}$ %) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.

Keywords: Supermassive black holes, High energy astrophysics, Seyfert galaxies, X-ray active galactic nuclei, Active galactic nuclei, Astrophysical black holes
Dependence of Narrow-line Region Sizes on [O III] Luminosity in Low-redshift Active Galactic Nuclei with Double-peaked Broad Balmer Emission Lines. In this paper, simple but interesting results are reported on the upper limits of narrow-line region (NLR) sizes of a small sample of 38 low-redshift (z &lt; 0.1) active galactic nuclei (AGN) with double-peaked broad emission lines (double-peaked BLAGN), in order to check whether the NLR sizes in type-1 AGN (broad line) and type-2 AGN (narrow line) obey a similar empirical dependence on [O III] luminosity. In order to correct the inclination effects on projected NLR sizes of type-1 AGN, the accretion disk origin is commonly applied to describe the double-peaked broad Hα line, leading to the determined inclination angles of central disk-like broad-line regions of 38 double-peaked BLAGN. Then, considering the fixed Sloan Digital Sky Survey (SDSS) fiber radius, the upper limits of the NLR sizes of the 38 double-peaked BLAGN can be estimated. Meanwhile, a strong linear correlation between continuum luminosity and [O III] luminosity is applied to confirm that the [O III] emissions of the 38 double-peaked BLAGN are totally covered in the SDSS fibers. Considering the reddening-corrected measured [O III] luminosity, the upper limits of the NLR sizes of the 38 double-peaked BLAGN are within a 99.9999% confidence interval of the expected results from the empirical relation between NLR size and [O III] luminosity in type-2 AGN. In the current understanding, there are no challenges to the unified model of AGN through the space properties of NLRs.

Keywords: Active galaxies, Active galactic nuclei, Emission line galaxies, Quasars
Chemical Cartography with APOGEE: Mapping Disk Populations with a 2-process Model and Residual Abundances. We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] versus [Mg/H] with a 2-process model, which decomposes abundance patterns into a "prompt" component tracing core-collapse supernovae and a "delayed" component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals Δ[X/H] from this two-parameter fit. The rms residuals range from ~0.01-0.03 dex for the most precisely measured APOGEE abundances to ~0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow for the comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3-13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15-17 kpc), 0.05-0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4-1 dex) of multiple elements in ω Cen. The residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.

Keywords: Stellar populations, Milky Way disk, Galaxy chemical evolution
The US Naval Observatory VLBI Spectroscopic Catalog. Despite their importance for astrometry and navigation, the active galactic nuclei (AGNs) that comprise the International Celestial Reference Frame (ICRF) are relatively poorly understood, with key information such as their spectroscopic redshifts, AGN spectral type, and emission-/absorption-line properties generally missing from the literature. Using an updated, publicly available, state-of-the-art spectroscopic fitting code optimized for the spectra of AGNs from low to high redshift, we present a catalog of emission-line and spectral continuum parameters for 1014 unique ICRF3 objects with single-fiber spectra from the Sloan Digital Sky Survey DR16. We additionally present black hole virial mass scaling relationships that use Hα-, Hβ-, Mg II-, and C IV-based line widths, all consistent with each other, which can be used in studies of radio-loud objects across a wide range of redshifts, and we use these scaling relationships to provide derived properties such as black hole masses and bolometric luminosities for the catalog. We briefly comment on these properties for the ICRF objects, as well as their overall spectroscopic characteristics.

Keywords: Black hole physics, Active galaxies, Catalogs, Quasars
Three-month Monitoring of the Variability toward W51 IRS2 with Ammonia, Water, and Methanol Transitions. A four-epoch monitoring program spanning ~three months (from 2020 January 8 to April 7) for ammonia, water, and methanol transitions toward the high-mass star-forming region W51 IRS2 was conducted using the Shanghai 65 m Tianma Radio Telescope with its K-band (18-26.5 GHz) receiver. In total, 33 ammonia transitions and 16 methanol transitions were detected toward the target at least once during this monitoring program. Among them, 14 ammonia and 4 methanol transitions show maser emission characteristics. Rapid variabilities (including both increases and decreases) in the ammonia and methanol transitions were detected from both maser and thermal emissions during the three months of the monitoring. In addition, H2O masers with obvious variability were also detected. The results of the rotation diagram analysis for the ammonia and methanol quasi-thermal transitions show the variations in their rotational temperatures during the monitoring. The derived temperatures from the transitions with larger upper energies (E  u /κ) generally decreased over the whole monitoring period, from January 8 to April 7, but those with smaller E  u /κ first increased from January 8 to April 1, then rapidly decreased from April 1 to April 7. These findings support the suggestion that an inside-out heatwave propagation in W51 IRS2 was involved with the accretion burst over a short duration (only on the order of months) and caused the drastic variability behaviors of the different line transitions during high-mass star formation.

Keywords: Interstellar line emission, Galactic center, Molecular spectroscopy, Molecular clouds, Star formation, Interstellar masers