Sazuna/UAT_keywords huggingface dataset:
Toward a Comprehensive Grid of Cepheid Models with MESA. I. Uncertainties of the Evolutionary Tracks of Intermediate-mass Stars. Helium-burning stars, in particular Cepheids, are especially difficult to model, as the choice of free parameters can greatly impact the shape of the blue loops—the part of the evolutionary track at which the instability strip is crossed. Contemporary one-dimensional stellar evolution codes, like Modules for Experiments in Stellar Astrophysics (MESA), come with a large number of free parameters that allow us to model the physical processes in stellar interiors under many assumptions. The uncertainties that arise from this freedom are rarely discussed in the literature despite their impact on the evolution of the model. We calculate a grid of evolutionary models with MESA, varying several controls, like solar mixture of heavy elements, mixing-length theory prescription, nuclear reaction rates, the scheme to determine convective boundaries, atmosphere model, and temporal and spatial resolution, and quantify their impact on age and location of the evolutionary track on the H-R diagram from the main sequence until the end of core helium burning. Our investigation was conducted for a full range of masses and metallicities expected for classical Cepheids. The uncertainties are significant, especially during core helium burning, reaching or exceeding the observational uncertainties of   and   for detached eclipsing binary systems. For ≥9 M ⊙ models, thin convective shells develop and evolve erratically, not allowing the models to converge. A careful inspection of Kippenhahn diagrams and convergence study is advised for a given mass and metallicity, to assess how severe this problem is and to what extent it may affect the evolution.

Keywords: Blue loop, Stellar evolutionary models, Cepheid variable stars, Stellar evolutionary tracks, Stellar evolution
Detecting Quasiperiodic Pulsations in Solar and Stellar Flares with a Neural Network. Quasiperiodic pulsations (QPP) are often detected in solar and stellar flare lightcurves. These events may contain valuable information about the underlying fundamental plasma dynamics as they are not described by the standard flare model. The detection of QPP signals in flare lightcurves is hindered by their intrinsically nonstationary nature, contamination by noise, and the continuously increasing number of flare observations. Hence, the creation of automated techniques for QPP detection is imperative. We implemented the fully convolution network (FCN) architecture to classify the flare lightcurves depending on whether they have exponentially decaying harmonic QPP or not. To train the FCN, 90,000 synthetic flare lightcurves with and without QPP were generated. After training, it showed an accuracy of 87.2% on the synthetic test data and did not experience overfitting. To test the FCN performance on real data, we used the subset of stellar flare lightcurves observed by Kepler, with strong evidence of decaying QPP identified hitherto with other methods. Then, the FCN was applied to find QPP in a larger-scale Kepler flare catalogue comprised of 2274 events, resulting in a 7% QPP detection rate with a probability above 95%. The FCN, implemented in Python, is accessible through a browser application with a user-friendly graphical interface and detailed installation and usage guide. The obtained results demonstrate that the developed FCN performs well and successfully detects exponentially decaying harmonic QPP in real flare data, and can be used as a tool for preliminary sifting of the QPP events of this type in future large-scale observational surveys.

Keywords: Solar flares, Convolutional neural networks, Stellar flares, Solar oscillations, Active solar corona
Updated System of S I Levels Using Fourier Transform Infrared Spectroscopy in the Range from 800 to 11,000 cm<SUP>‑1</SUP>. In this study we report on high-precision laboratory measurements of transition wavenumbers for 172 atomic sulfur lines in the infrared region 800–11,000 cm‑1 using Fourier transform spectroscopy techniques. Our analysis includes 96 lines that have not been previously measured in the laboratory. We also correct several sulfur energy-level measurements reported in earlier studies. These refined measurements are important for a range of scientific disciplines, such as astrophysics, atmospheric chemistry, and combustion plasma physics. We have used the combined list of all observed lines to derive a refined set of sulfur energy levels. For about half of all nonautoionizing levels, the uncertainties have been reduced by a factor between 2 and 23. From the newly measured nonpenetrating (high-l) Rydberg levels we have also obtained the first ionization energy of the S atom, IE = 83,559.170(11) cm‑1, which is more accurate than the currently recommended value by 2 orders of magnitude. Our analysis has led to a significantly more accurate result than the earlier set of Ritz wavelengths with observed intensities reduced to a common uniform scale and an extended list of recommended transition probabilities.

Keywords: High resolution spectroscopy, Atomic spectroscopy, Atomic data, Infrared spectroscopy
The Simons Observatory: Design, Integration, and Testing of the Small Aperture Telescopes. The Simons Observatory (SO) is a cosmic microwave background survey experiment that includes small-aperture telescopes (SATs) observing from an altitude of 5200 m in the Atacama Desert in Chile. The SO SATs will cover six spectral bands between 27 and 280 GHz to search for primordial B-modes to a sensitivity of σ(r) = 0.002, with quantified systematic errors well below this value. Each SAT is a self-contained cryogenic telescope with a 35° field of view, 42 cm diameter optical aperture, 40 K half-wave plate, 1 K refractive optics, and &lt;0.1 K focal plane that holds &gt;12,000 transition edge sensor detectors. We describe the nominal design of the SATs and present details about the integration and testing for one operating at 93 and 145 GHz.

Keywords: Millimeter astronomy, Cosmic microwave background radiation, Ground telescopes, Telescopes
Equations of State, Thermodynamics, and Miscibility Curves for Jovian Planet and Giant Exoplanet Evolutionary Models. The equation of state of hydrogen–helium (H–He) mixtures plays a vital role in the evolution and structure of gas giant planets and exoplanets. Recent equations of state that account for H–He interactions, coupled with H–He immiscibility curves, can now produce more physical evolutionary models, such as accounting for helium rain with greater fidelity than in the past. In this work, we present a set of tools for planetary evolution that provides a Python interface for existing tables of useful thermodynamic quantities, state-of-the-art H–He equations of state, and pressure-dependent H–He immiscibility curves. In particular, for a collection of independent variable choices, we provide scripts to calculate the variety of thermodynamic derivatives used to model convection and energy transport. These include the chemical potential derived from the internal energy, which is a modeling necessity in the presence of composition gradients when entropy is the other primary variable. Finally, an entropy-based convection formalism is presented and fully described that highlights the physical differences between adiabatic and isentropic interior models. This centralized resource is meant to facilitate both giant planet structural and evolutionary modeling and the entry of new research groups into the field of giant planet modeling. All tables of thermodynamic quantities and derivatives are available at https://github.com/Rob685/hhe_eos_misc, along with a unified Python interface. Tutorials demonstrating the interface are also available in the repository.

Keywords: Planetary interior, Solar system gas giant planets, Chemical thermodynamics
The California Legacy Survey. V. Chromospheric Activity Cycles in Main-sequence Stars. We present optical spectroscopy of 710 solar neighborhood stars collected over 20 years to catalog chromospheric activity and search for stellar activity cycles. The California Legacy Survey stars are amenable to exoplanet detection using precise radial velocities, and we present their Ca II H and K time series as a proxy for stellar and chromospheric activity. Using the High Resolution Echelle Spectrometer at Keck Observatory, we measured stellar flux in the cores of the Ca II H and K lines to determine S-values on the Mount Wilson scale and the   metric, which is comparable across a wide range of spectral types. From the 710 stars, with 52,372 observations, 285 stars were sufficiently sampled to search for stellar activity cycles with periods of 2–25 yr, and 138 stars showed stellar cycles of varying length and amplitude. S-values can be used to mitigate stellar activity in the detection and characterization of exoplanets. We used them to probe stellar dynamos and to place the Sun's magnetic activity into context among solar neighborhood stars. Using precise stellar parameters and time-averaged activity measurements, we found tightly constrained cycle periods as a function of stellar temperature between   of ‑4.7 and ‑4.9, a range of activity in which nearly every star has a periodic cycle. These observations present the largest sample of spectroscopically determined stellar activity cycles to date.

Keywords: High resolution spectroscopy, Stellar chromospheres, Stellar activity, Stellar astronomy, Optical telescopes, Main sequence stars, Time series analysis, Stellar evolution
Physical Parameters and Magnetic Activity of M-type Stars Based on the LAMOST DR9, SDSS, and TESS Surveys. We analyze a catalog comprising 781,232 spectra from 641,095 M dwarf stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution spectroscopic data release 9. Based on the equivalent width of the Hα line, we ascertain the activity properties of the stars, identifying a total of 107,134 active stars, with 31,175 exhibiting Hα variations. Furthermore, we establish a positive correlation between starspot activity from Transiting Exoplanet Survey Satellite light curves, and chromospheric activity observed through LAMOST spectra on M dwarf stars. Utilizing LAMOST and Gaia data, we map the two-dimensional distribution of active fractions across all M dwarfs in the Milky Way based on Hα and Hβ lines, confirming a decrease in the active fraction as the distance above the Galactic disk increases. Additionally, we investigate the relationship between chromospheric activity and absolute height above the Galactic disk in various M subtypes. Our findings reveal distinct trends: for M0 to M5 dwarf stars, the active fraction of Hα and Hβ lines rapidly decreases within the 0–300 pc range. In the 300–500 pc range, M0 to M4 dwarf stars exhibit a gradual increase, followed by a decrease in the 500–1000 pc range. Conversely, M5 dwarf stars show no significant gradual increase in the 300–500 pc range and decrease in the 500–1000 pc range. More data will be needed to confirm the phenomenon.

Keywords: M stars, Stellar activity
Intensity-sensitive Quality Assessment of Extended Sources in Astronomical Images. Radio astronomy studies the Universe by observing the radio emissions of celestial bodies. Different methods can be used to recover the sky brightness distribution (SBD), which describes the distribution of celestial sources from recorded data, with the output dependent on the method used. Image quality assessment (IQA) indexes can be used to compare the differences between restored SBDs produced by different image reconstruction techniques to evaluate their effectiveness. However, reconstructed images (for the same SBD) can appear to be very similar, especially when observed by the human visual system (HVS). Hence, current structural similarity methods, inspired by the HVS, are not effective. In the past, we have proposed two methods to assess point-source images, where low amounts of concentrated information are present in larger regions of noise-like data. But for images that include extended source(s), the increase in complexity of the structure makes the IQA methods for point sources oversensitive because the important objects cannot be described by isolated point sources. Therefore, in this article we propose the augmented low-information similarity index (augLISI), an improved version of LISI, to assess images including extended source(s). Experiments have been carried out to illustrate how this new IQA method can help with the development and study of astronomical imaging techniques. Note that although we focus on radio astronomical images herein, these IQA methods are also applicable to other astronomical images and imaging techniques.

Keywords: Extended radiation sources, Radio astronomy, Astronomy image processing
Causal Attention Deep-learning Model for Solar Flare Forecasting. Solar flares originate from the sudden release of energy stored in the magnetic field of the active region on the Sun, but the trigger for flares is still uncertain. Currently, deep-learning-based solar flare prediction models have achieved good results and are widely recognized. However, these models focus more on data correlation rather than causality. An ideal flare prediction model should probe into the causes/triggers of solar flares, and diagnose the precursors of flares rather than just correlation analysis. To extract more informative precursors of flares from magnetograms, while suppressing the interference of confounding factors, a causal attention module is introduced to disentangle causal and confounder features from the input features. To address the problem of imbalanced positive and negative samples in the data set, an adaptive data set split mechanism is proposed. It divides the data set into several balanced subsets of positive and negative samples, and dynamically adjusts the subsets according to the model's prediction results during the training process. The experimental results demonstrate that our proposed model achieves 4.08%, 8.38%, and 2.19% higher accuracy, true skill score, and area under the receiver operating characteristic curve than the baseline model. Additionally, the class-specific heatmaps by using the gradient-weighted class activation mapping method reveal that our proposed model generally focuses on the polarity inverse line of active regions, well in line with theoretical study.

Keywords: Solar physics, Solar flares
The R-process Alliance: Fifth Data Release from the Search for R-process-enhanced Metal-poor Stars in the Galactic Halo with the GTC. Understanding the abundance pattern of metal-poor stars and the production of heavy elements through various nucleosynthesis processes offers crucial insights into the chemical evolution of the Milky Way, revealing primary sites and major sources of rapid neutron-capture process (r-process) material in the Universe. In this fifth data release from the R-Process Alliance (RPA), we present the detailed chemical abundances of 41 faint (down to V = 15.8) and extremely metal-poor (down to [Fe/H] = ‑3.3) halo stars selected from the RPA. We obtained high-resolution spectra for these objects with the HORuS spectrograph on the Gran Telescopio Canarias. We measure the abundances of light, α, Fe-peak, and neutron-capture elements. We report the discovery of five carbon-enhanced metal-poor, one limited-r, three r-I, and four r-II stars, and six Mg-poor stars. We also identify one star of a possible globular cluster origin at an extremely low metallicity at [Fe/H] = ‑3.0. This adds to the growing evidence of a lower-limit metallicity floor for globular cluster abundances. We use the abundances of Fe-peak elements and the α-elements to investigate the contributions from different nucleosynthesis channels in the progenitor supernovae. We find the distribution of [Mg/Eu] as a function of [Fe/H] to have different enrichment levels, indicating different possible pathways and sites of their production. We also reveal differences in the trends of the neutron-capture element abundances of Sr, Ba, and Eu of various r-I and r-II stars from the RPA data releases, which provide constraints on their nucleosynthesis sites and subsequent evolution. * This paper includes data gathered with the 10.4 m Gran Telescopio Canarias located at La Palma, Canary Islands, Spain.

Keywords: High resolution spectroscopy, Nucleosynthesis, Stellar abundances, R-process, Milky Way stellar halo, Nuclear astrophysics, Population II stars, CEMP stars
The Brown Dwarf Kinematics Project (BDKP). VI. Ultracool Dwarf Radial and Rotational Velocities from SDSS/APOGEE High-resolution Spectroscopy. We present precise measurements of radial (RV) and projected rotational ( ) velocities of a sample of 258 M6 to L2 dwarfs with multiepoch, high-resolution (λ/Δλ = 22,500), near-infrared (1.514–1.696 μm) spectroscopic observations reported in the Apache Point Observatory Galactic Evolution Experiment Data Release 17. The spectra were modeled using a Markov Chain Monte Carlo forward-modeling method, which achieved median precisions of σ RV = 0.4 km s‑1 and   = 1.1 km s‑1. One-half of our sample (138 sources) are previously known members of nearby young clusters and moving groups, and we identified three new kinematic members of the Argus or Carina Near moving groups, 2MASS J05402570+2448090, 2MASS J14093200+4138080, and 2MASS J21272531+5553150. Excluding these sources, we find that the majority of our sample have kinematics consistent with the Galactic thin disk, and 11 sources are associated with the intermediate thin/thick disk. The field sample has a velocity dispersion of 38.2 ± 0.3 km s‑1, equivalent to an age of 3.30 ± 0.19 Gyr based on empirical age–velocity dispersion relations, and a median   of 17 km s‑1. For 172 sources with multiepoch observations, we identified 37 as having significant RV variations, and determined preliminary orbit parameters for 26 sources with four or more epochs, nine of which are short-period binary candidates. For 40 sources with photometric variability periods from the literature less than 5 days and   &gt; 20 km s‑1, we find a decline in projected radii ( ) with age congruent with evolutionary models. Finally, we also present multiepoch RV and   measurements for additional 444 candidate ultracool dwarfs.

Keywords: High resolution spectroscopy, Brown dwarfs, Stellar kinematics, Low mass stars, Radial velocity, Stellar rotation
The Impact of Positive AGN Feedback on the Properties of Galaxies in a Semianalytic Model of Galaxy Formation. We introduce the state-of-the-art semianalytic model Formation and Evolution of GAlaxies (FEGA), which incorporates updated prescriptions for key physical processes in galaxy formation. Notably, FEGA features an unprecedented semianalytic modeling of positive active galactic nucleus (AGN) feedback. The model combines the latest prescriptions for gas infall and cooling, a revised star formation recipe that incorporates the extended Kennicutt–Schmidt relation, disk instability, updated supernova feedback, reincorporation of ejected gas, hot gas stripping from satellite galaxies, and the formation of diffuse light. A novel description of AGN feedback is introduced, describing the positive mode as a burst of star formation from a cooling gas fraction. FEGA is rigorously calibrated using a Markov Chain Monte Carlo procedure to match the evolution of the stellar mass function from high redshift to the present. Subsequently, the model is tested against several observed and predicted scaling relations, including the star formation rate (SFR)–mass, black hole–bulge and stellar mass, stellar-to-halo mass, and red fraction–mass relations. Additionally, we test FEGA against other galaxy properties, such as the distribution of specific SFRs, stellar metallicity, and morphology. Our results demonstrate that the inclusion of positive AGN feedback can coexist with its negative counterpart without drastic alterations to other prescriptions. Importantly, this inclusion improves the ability of the model to describe the primary scaling relations observed in galaxies.

Keywords: Galaxy formation, Active galactic nuclei, Galaxy evolution
High-quality Extragalactic Legacy-field Monitoring (HELM) with DECam: Project Overview and First Data Release. High-quality Extragalactic Legacy-field Monitoring (HELM) is a long-term observing program that photometrically monitors several well-studied extragalactic legacy fields with the Dark Energy Camera (DECam) imager on the CTIO 4 m Blanco telescope. Since 2019 February, HELM has been monitoring regions within COSMOS, XMM-LSS, CDF-S, S-CVZ, ELAIS-S1, and SDSS Stripe 82 with few-day cadences in the (u)gri(z) bands, over a collective sky area of ∼38 deg2. The main science goal of HELM is to provide high-quality optical light curves for a large sample of active galactic nuclei (AGNs), and to build decades-long time baselines when combining past and future optical light curves in these legacy fields. These optical images and light curves will facilitate the measurements of AGN reverberation mapping lags, as well as studies of AGN variability and its dependencies on accretion properties. In addition, the time-resolved and coadded DECam photometry will enable a broad range of science applications from galaxy evolution to time-domain science. We describe the design and implementation of the program and present the first data release that includes source catalogs and the first ∼3.5 yr of light curves during 2019A–2022A.

Keywords: Quasars, Surveys, Optical astronomy, Galactic and extragalactic astronomy, Time domain astronomy
Sherpa: An Open-source Python Fitting Package. We present an overview of Sherpa, an open-source Python project, and discuss its development history, broad design concepts, and capabilities. Sherpa contains powerful tools for combining parametric models into complex expressions that can be fit to data using a variety of statistics and optimization methods. It is easily extensible to include user-defined models, statistics, and optimization methods. It provides a high-level user interface for interactive data analysis, such as within a Jupyter notebook, and it can also be used as a library component, providing fitting and modeling capabilities to an application. We include a few examples of Sherpa applications to multiwavelength astronomical data.

Keywords: Astronomy software
Correlation-based Beam Calibration of 21 cm Intensity Mapping. Foreground removal presents a significant obstacle in both current and forthcoming intensity-mapping surveys. While numerous techniques have been developed that show promise in simulated data sets, their efficacy often diminishes when they are applied to real-world data. A primary issue is the frequency-dependent variations in the instrumental response. In this paper, we propose a novel approach utilizing the internal cross correlation among different frequencies to calibrate the beam's frequency fluctuations. Using a simulated data set that incorporates frequency-dependent random fluctuations into the beam model, we illustrate that our method can achieve considerable improvements over traditional techniques. Our results represent a step forward in enhancing the precision and reliability of foreground removal in intensity-mapping surveys.

Keywords: Cosmology, Radio astronomy, Large-scale structure of the universe