Sazuna/UAT_keywords huggingface dataset:
Cassiopeia A's Reverse Shock and Its Effects on the Expanding SN Ejecta. Using optical and near-infrared images of the Cassiopeia A (Cas A) supernova remnant covering the time period 1951─2022, together with optical spectra of selected filaments, we present an investigation of Cas A's reverse shock velocity and the effects it has on the remnant's metal-rich ejecta. We find the sequence of optical ejecta brightening and the appearance of new optical ejecta indicating the advancement of the remnant's reverse shock in the remnant's main shell has velocities typically between 1000 and 2000 km s−1, which is ∼1000 km s−1 less than recent measurements made in X-rays. We further find that the reverse shock appears to move much more slowly and is nearly even stationary in the sky frame along the remnant's western limb. However, we do not find the reverse shock to move inward at velocities as large as ∼2000 km s−1 as has been reported. Optical ejecta in Cas A's main emission shell have proper motions indicating outward tangential motions ≃3500─6000 km s−1, with the smaller values preferentially along the remnant's southern regions, which we speculate may be partially the cause of the remnant's faint and more slowly evolving southern sections. Following interaction with the reverse shock, ejecta knots exhibit extended mass ablated trails  ─  in length, leading to extended emission indicating reverse shock induced decelerated velocities as large as ≃1000 km s−1. Such ablated material is most prominently seen in higher ionization line emissions, whereas denser parts of ejecta knots show surprisingly little deceleration. *Based in part on observations 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.

Keywords: Supernova remnants, Interstellar emissions, Filamentary nebulae, Core-collapse supernovae
A Local Dwarf Galaxy Search Using Machine Learning. We present a machine learning search for local, low-mass galaxies (z &lt; 0.02 and 106 M⊙ &lt; M* &lt; 109 M⊙) using combined photometric data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys (hereafter, Legacy Survey) and the Wide-field Infrared Survey Explorer survey. We introduce the spectrally confirmed training sample, discuss evaluation metrics, investigate features, compare different machine learning algorithms, and find that a seven-class neural network classification model is highly effective in separating the signal (local, low-mass galaxies) from various contaminants, reaching a precision of 95% and a recall of 76%. The principal contaminants are nearby sub-L*galaxies at 0.02 &lt; z &lt; 0.05 and nearby massive galaxies at 0.05 &lt; z &lt; 0.2. We find that features encoding surface brightness information are essential to achieving a correct classification. Our final catalog, which we make available, consists of 112,859 local, low-mass galaxy candidates, of which 36,408 have high probability (psignal &gt; 0.95), covering the entire Legacy Survey DR9 footprint. Using DESI-Early Data Release public spectra and data from the Satellites around Galactic Analogs and Exploration of Local Volume Satellites surveys, we find that our model has a precision of ∼100%, 96%, and 97%, respectively, and a recall of ∼51%, 68%, and 53%, respectively. The results of those independent spectral verifications demonstrate the effectiveness and efficiency of our machine learning classification model.

Keywords: Dwarf galaxies, Neural networks
Quantified Estimation of Molecular Detections across Different Classes of Neptunian Atmospheres Using Cross-correlation Spectroscopy: Prospects for Future Extremely Large Telescopes with High-resolution Spectrographs. Neptune-size exoplanets are less studied as characterizing their atmospheres presents challenges due to their relatively small radius and atmospheric scale height. As the most common outcome of planet formation, these planets are crucial for understanding planetary formation, migration theories, atmospheric composition, and potential habitability. Their diverse atmospheres, influenced by equilibrium temperature, composition, and cloud presence, offer unique opportunities to study atmospheric dynamics and chemistry. While low-resolution spectroscopy struggles with atmospheric characterization due to clouds, high-resolution observations provide detailed analysis of the atmospheres by detecting molecular lines beyond the cloud deck. This study investigates four subclasses of Neptune atmospheres: HAT-P-11 b (warm Neptune), HD 63433c (warm sub-Neptune), K2-25 b (temperate Neptune), and TOI-270 d (temperate sub-Neptune), using six ground-based spectrographs: GIANO-B, CARMENES, IGRINS, HISPEC, MODHIS, and ANDES over one and three transits. Our simulation integrates the chemical kinetics model VULCAN with the 1D line-by-line radiative transfer model petitRADTRANS, and estimates detection significance using the ground-based noise simulator SPECTR. We aim to predict how future extremely large telescopes (ELTs) such as TMT (MODHIS) and E-ELT (ANDES) can utilize their higher resolving powers and larger collecting areas to surpass current observatories in detecting molecular bands. We highlight the importance of photochemistry in these atmospheres and demonstrate how ELTs will help further in constraining nitrogen and sulfur chemistry. Finally, we present a comprehensive picture of cloud presence in the atmospheres and its impact on molecular detectability in Neptune-class atmospheres.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Extrasolar gaseous planets, Spectroscopy, Mini Neptunes, Exoplanet atmospheres
X-Ray Spectral Variability of 13 TeV High-energy-peaked Blazars with XMM-Newton. We present a comprehensive study of the X-ray spectral variability observed in 13 TeV photon-emitting high-energy-peaked BL Lacertae objects (HBLs). These data come from 54 XMM-Newton EPIC-pn pointed observations made during its operational period from 2001 June through 2023 July. We performed spectral studies in the energy range of 0.6–10 keV by fitting X-ray spectra of the pointed observations with power-law and log-parabolic (PL and LP) models. We found at a 99% confidence level that 31 of these X-ray spectra were best fitted with a range of LP models with local photon indices (at 1.0 keV), α ≃ 1.75–2.66, and convex curvature parameter β ≃ 0.02–0.25. PL models with photon index Γ ≃ 1.78–2.68 best described the spectra of 14-pointed observations. Nine PN spectra resulted in negative curvature parameters in fitting an LP model, and eight among them were significant (β ≥ 2βerr). We fitted broken power-law models to these eight X-ray spectra and found spectral hardening in the range of ΔΓ ≃ 0.06‑0.54 for these observations. EPIC-MOS spectra were also studied for those eight observations to search for similar trends, and we were able to find them in only two, one observation each of PKS 0548-322 and Mrk 501. This indicates the possibility of the coexistence of an inverse Compton component along with the dominant synchrotron component for these two observations. We also performed correlation studies between various LP spectral parameters and briefly discuss their possible implications.

Keywords: Blazars, X-ray active galactic nuclei, BL Lacertae objects
Experimental Branching Fractions, Transition Probabilities, and Oscillator Strengths of La II. Branching fractions of 86 La II lines in the spectral range of 243.340–626.229 nm have been measured using a grating spectrometer based on the emission spectra of a lanthanum hollow cathode lamp. Combining these branching fractions with previously measured radiative lifetimes using the time-resolved laser-induced fluorescence technique, transition probabilities and oscillator strengths were determined for 86 lines belonging to transitions 5d2–4f5d, 5d6s–4f5d, 4f6s–5d7s, 4f5d–5d7s, 5d6p–5d7s, 4f6s–5d6d, 4f5d–5d6d, 5d6p–5d6d, 6s6p–5d6d, 4f5d–4f2, and 5d6p–4f2. These fundamental atomic parameters are important for deriving chemical abundances from astronomical spectra by the method of equivalent widths or synthetic spectra.

Keywords: Transition probabilities, Atomic spectroscopy, Radiative processes, Atomic physics
Impact of Interacting Parameters on Dark Matter in an Interacting Dark Energy Model. This paper investigates a dark energy model within the Friedmann–Lemaître–Robertson–Walker cosmological framework, considering both interacting and noninteracting scenarios. Introducing an interaction scheme between dark energy and dark matter through a specific ansatz for the dark energy density (ρde), we derive the Hubble parameter H(z) for both cases. To examine the influence of the interaction parameter on dark matter, we use a combination of observational data sets, including cosmic chronometers, Type Ia supernovae, and baryon acoustic oscillation measurements from the Dark Energy Spectroscopic Instrument Year 1 and Sloan Digital Sky Survey IV. We estimate the posterior distribution of each model parameter using the Markov Chain Monte Carlo method. In our analysis, we treat rd as a free parameter, allowing late-time data sets to constrain each model's parameters, including H0, rd, and  . Our analysis shows that the interaction parameter affects dark matter. Additionally, we plot H(z), μ(z), ΔH(z), and Δμ(z) with cosmographic parameters to examine the behavior of the late-time expansion of the Universe. Further, the Om(z) diagnostic is applied to distinguish interacting and noninteracting scenarios from the standard ΛCDM model. Finally, statistical metrics are used to compare different models, evaluate their goodness of fit, and determine the best-fit scenario.

Keywords: Cosmic microwave background radiation
Barium Abundances from the LAMOST Medium-Resolution Survey Stellar Spectra. Based on a template-matching method, we estimate the barium (Ba) abundances for stellar spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Medium-Resolution Spectroscopic Survey (MRS). The Ba abundances of 198,011 stars have been determined from MRS spectra with signal-to-noise ratios (S/N) &gt; 40 combined with the stellar atmospheric parameters from the LAMOST Low-Resolution Spectroscopic Survey DR9 by the LAMOST Stellar Parameter Pipeline. The uncertainties in the Ba abundances from the LAMOST MRS spectra are less than 0.3 dex when S/N exceeds 40, which align closely with the results based on the high-resolution UVES spectra from the Gaia-ESO survey obtained by spectral synthesis. Further analysis of Ba abundances from repeated observations of the same stars reveals that random errors related to spectral quality remain below 0.3 dex at the same S/N, with a systematic overestimation for the low-S/N spectra. This extensive sample of stellar Ba abundances will enhance studies of the s-, i-, and r-processes, and deepen our understanding of the chemical-evolution history of the Milky Way.

Keywords: Stellar abundances, Sky surveys, Catalogs
Open-source Flux Transport (OFT). I. HipFT–High-performance Flux Transport. Global solar photospheric magnetic maps play a critical role in solar and heliospheric physics research. Routine magnetograph measurements of the field occur only along the Sun–Earth line, leaving the far side of the Sun unobserved. Surface flux transport (SFT) models attempt to mitigate this by modeling the surface evolution of the field. While such models have long been established in the community (with several releasing public full-Sun maps), none are open source. The Open-source Flux Transport (OFT) model seeks to fill this gap by providing an open and user-extensible SFT model that also builds on the knowledge of previous models with updated numerical and data acquisition/assimilation methods along with additional user-defined features. In this first of a series of papers on OFT, we introduce its computational core: the High-performance Flux Transport (HipFT) code (https://github.com/predsci/hipft). HipFT implements advection, diffusion, and data assimilation in a modular design that supports a variety of flow models and options. It can compute multiple realizations in a single run across model parameters to create ensembles of maps for uncertainty quantification and is high-performance through the use of multi-CPU and multi-GPU parallelism. HipFT is designed to enable users to write extensions easily, enhancing its flexibility and adaptability. We describe HipFT's model features, validations of its numerical methods, performance of its parallel and GPU-accelerated code implementation, analysis/postprocessing options, and example use cases.

Keywords: Computational astronomy, Open source software, Solar magnetic flux emergence, Solar differential rotation, Solar photosphere, Astronomy software, Astronomy data analysis, Solar surface, Computational methods, Solar magnetic fields, Solar meridional circulation, GPU computing
synax: A Differentiable and GPU-accelerated Synchrotron Simulation Package. We introduce synax (https://github.com/dkn16/Synax), a novel library for automatically differentiable simulation of Galactic synchrotron emission. Built on the JAX framework, synax leverages JAX's capabilities, including batch acceleration, just-in-time compilation, and hardware-specific optimizations (CPU, GPU, TPU). Crucially, synax uses JAX's automatic differentiation (AD) mechanism, enabling precise computation of analytical derivatives with respect to any model parameters. This facilitates powerful inference algorithms, such as Hamiltonian Monte Carlo (HMC) and gradient-based optimization, which enables inference over models that would otherwise be computationally prohibitive. In its initial release, synax supports synchrotron intensity and polarization calculations down to GHz frequencies, alongside several models of the Galactic magnetic field (GMF), cosmic-ray spectra, and thermal electron density fields. When running synax on the CPU we obtain identical performance to hammurabi, a state-of-the-art synchrotron simulation package, while on the GPU synax brings a 20-fold enhancement in efficiency. We further demonstrate the potential of AD in enabling full posterior inference using gradient-based inference algorithms. Using synax with HMC to perform inference over a four-parameter test model, we attain a twofold improvement compared to standard random walk Metropolis─Hastings (RWMH). When applied to a more complex 16-parameter model, HMC is still able to obtain accurate posterior expectations, while RWMH fails to converge. We also showcase the application of synax to optimizing the GMF based on the Haslam 408 MHz map, achieving residuals with a standard deviation below 1 K.

Keywords: Galaxy magnetic fields, Radio astronomy, Interstellar synchrotron emission, Astronomical simulations
A Formalism for Calibrating the Instrumental Polarization of Radio Interferometric Arrays at Meter Wavelengths Using Unpolarized Sky: A Demonstration Using MWA Observations. Calibration of instrumental polarization is critical for measuring polarized radio emissions from astrophysical sources to extract the magnetic field information in astrophysical, heliospheric, and terrestrial plasmas. At meter wavelengths, calibration of radio polarimetric observations is particularly challenging because of the scarcity of bright polarized sources due to significant Faraday depolarization. Here, we present a novel formalism for polarization calibration using an unpolarized sky model. The formalism is specifically designed for wide-field, low-frequency instruments like the Murchison Widefield Array (MWA), the LOw Frequency ARray (LOFAR), New Extension in Nançay Upgrading LOFAR, Owens Valley Radio Observatory Long Wavelength Array, low-frequency telescope of the Square Kilometre Array Observatory, etc. By leveraging the apparent polarization of the unpolarized sky induced by the polarized primary beam of the radio telescope, this method avoids dependence on bright polarized calibrators. It is also immune to ionospheric Faraday rotation. The validation of the approach via MWA observations confirms the accuracy of the method. This formalism provides a robust framework for low-frequency polarization calibration. It addresses the longstanding calibration challenges and advances the field of low-frequency polarimetry by enabling polarization studies of astrophysical radio sources.

Keywords: Spectropolarimetry, Polarimetry, Calibration, Astronomical techniques, Radio interferometry, Radio astronomy, Astronomical methods
Pulsation Properties of Blazhko and Non-Blazhko RRab Stars. In this study, we conduct a comparative analysis of the properties of Blazhko and non-Blazhko RRab stars. We identified 1054 non-Blazhko and 785 Blazhko RRab stars in the photometric data observed by the K2 mission, which, combined with those 37 stars observed in the original Kepler field, constituted our study sample. Using the Fourier decomposition method, we calculated the pulsation parameters, including phase differences and amplitude ratios, for these RRab stars, revealing significant discrepancies in the pulsation parameters between Blazhko and non-Blazhko RRab stars. However, distinguishing between Blazhko and non-Blazhko RRab stars based on Fourier parameters remains challenging due to the significant overlap in their distributions. By crossmatching our sample with the low-resolution spectra of LAMOST Data Release (DR) 12, we identified 147 Blazhko and 111 non-Blazhko RRab stars, which exhibit similar metallicity distributions. Furthermore, crossmatching with Gaia DR3 data yielded 766 Blazhko and 950 non-Blazhko RRab stars, showing differences in color indices but not in absolute magnitudes. Our findings suggest that the Blazhko effect is linked to pulsation parameters and colors rather than metallicities or absolute magnitude.

Keywords: RRab variable stars, RR Lyrae variable stars
Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. II. Statistical Properties from the First Data Release. We present the identification of changing-look active galactic nuclei (CL-AGNs) from the Dark Energy Spectroscopic Instrument First Data Release and Sloan Digital Sky Survey Data Release 16 at z ≤ 0.9. To confirm the CL-AGNs, we utilize spectral flux calibration assessment via an [O III]-based calibration, pseudophotometry examination, and visual inspection. This rigorous selection process allows us to compile a statistical catalog of 561 CL-AGNs, encompassing 527 Hβ, 149 Hα, and 129 Mg II CL behaviors. In this sample, we find (1) a 283:278 ratio of turn-on to turn-off CL-AGNs. (2) The median Eddington ratio for CL-AGNs in the dim state is approximately λEdd ∼ 0.01. (3) A strong correlation between the change in the luminosity of the broad emission lines (BELs) and variation in the continuum luminosity, with Mg II and Hβ displaying similar responses during CL phases. (4) The Baldwin–Phillips–Terlevich diagram for CL-AGNs shows no statistical difference from the general AGN catalog. (5) Five CL-AGNs are associated with asymmetrical mid-infrared flares, possibly linked to tidal disruption events. Given the large CL-AGN sample and the stochastic sampling of spectra, we propose that some CL phenomena are inherently due to typical AGN variability during low accretion rates, particularly for CL phenomenon only occurring on one BEL. Finally, we introduce a monotonically dimming CL phase for objects characterized by a gradual decline over decades in the light curve and the complete disappearance of entire BELs in faint spectra, indicative of a real transition in the accretion disk.

Keywords: Accretion, Supermassive black holes, Active galaxies, Active galactic nuclei, Catalogs
Minute-cadence Observations of the Galactic Plane with the Wide Field Survey Telescope (WFST): Overview, Methodology, and Early Results. As the time-domain survey telescope of the highest survey power in the Northern Hemisphere currently, the Wide Field Survey Telescope (WFST) is scheduled to hourly/daily/semiweekly scan the Northern sky up to ∼23 mag in four optical (ugri) bands. Unlike the observation cadences in forthcoming regular survey missions, WFST performed "staring" observations toward the Galactic plane in a cadence of ≈1 minute for a total on-source time of about 13 hr during the commissioning and pilot observation phases. Such an observation cadence is well applied in producing densely sampled light curves and hunting for stars exhibiting fast stellar variabilities. Here we introduce the primary methodologies in detecting variability, periodicity, and stellar flares among half a million sources from the minute-cadence observations, and present the WFST g/r-band light curves generated from periodic variable stars and flaring stars. Benefiting from the high photometric precisions and deep detection limits of WFST, the observations have captured several rare variable stars, such as a variable hot white dwarf (WD) and an ellipsoidal WD binary candidate. By surveying the almost unexplored parameter spaces for variables, WFST will lead to new opportunities in discovering unique variable stars in the Northern sky.

Keywords: Short period variable stars, Sky surveys, Optical flares
Spectroscopic Evolution in Ice Analogs of Trans-Neptunian Objects Exposed to Ionizing Radiation. I. Visible Reflectance Spectra and Colors. Trans-Neptunian objects (TNOs) exhibit a color diversity containing a wealth of clues for understanding complex compositions and the formation history of our solar system. The origin of this wide color distribution is still uncertain, but it is likely due to surface ice exposed to ionizing radiation at various levels. Here, we present the spectroscopic evolution of visible reflectance, spectral slopes, and colors from TNO surface ice analogs processed by Galactic cosmic-ray proxy. This study provides compelling evidence that irradiated carbon-containing molecular ices show notable reddening in their visible reflectance spectra. The spectral slopes of processed water ices are neutral and independent of the radiation dose, whereas those of ammonia decrease with the increasing radiation dose. When the carbon-containing molecules are mixed with water and ammonia, the reddening process is found to be neutralized. The irradiation experiments at different temperatures demonstrate that the irradiation temperature could control the reddening efficiency of ices containing carbon and oxygen. For example, the color slopes of pure methanol and carbon dioxide ices significantly increase when the irradiation temperature is 40 K, but there is almost no change at 10 K. This indicates that the color diversity of TNOs can be influenced not only by different levels of radiation exposure but also by varying irradiation temperatures. The data in the current study provide new insights into the influence of initial composition, radiation dose, and irradiation temperature on the color diversity of TNOs, which supply important information for cataloging their surface compositions.

Keywords: Ice spectroscopy, Surface ices, Trans-Neptunian objects