Sazuna/UAT_keywords huggingface dataset:
Boundary Treatment for the Subsonic/Alfvénic Inner Boundary at 2.5 R <SUB>⊙</SUB> in a Time-dependent 3D Magnetohydrodynamics Solar Wind Simulation Model. A new magnetohydrodynamics (MHD) simulation model of the global solar corona and solar wind is presented. The model covers the range of heliocentric distance from 2.5 solar radii, so that coronal mass ejections at the earliest phase near the Sun can be treated in the future. This model is constructed by introducing a characteristics-based boundary treatment to an existing heliosphere 3D MHD model. In tailoring a set of characteristic equations for this new model, we assume that the coronal magnetic field is open to interplanetary space and that the solar coronal plasma is flowing outward everywhere at 2.5 solar radii. The characteristic equations for the subsonic/Alfvénic inner boundary surface are satisfied by altering the plasma density and/or temperature to maintain a polytropic relationship. In this article, the details of the characteristics-based boundary treatment for the middle of the corona (named CharM) are provided. The quasi-steady states of the solar wind derived from simulations with various choices of a parameter in the boundary treatments are compared and examined. Although further improvements are needed, we apply the new boundary treatment to simulations for three Carrington rotation periods from the minimum to maximum phase of the solar activity cycle, and show that an optimal choice yields a reasonable quasi-steady state of the transonic/Alfvénic solar wind matching the specified subsonic/Alfvénic plasma speed at 2.5 R ⊙.

Keywords: Solar wind, Solar corona, Magnetohydrodynamical simulations
A Self-gravity Module for the PLUTO Code. We present a novel implementation of an iterative solver for the solution of Poisson's equation in the PLUTO code for astrophysical fluid dynamics. Our solver relies on a relaxation method in which convergence is sought as the steady-state solution of a parabolic equation, whose time discretization is governed by the Runge-Kutta-Legendre (RKL) method. Our findings indicate that the RKL-based Poisson solver, which is both fully parallel and rapidly convergent, has the potential to serve as a practical alternative to conventional iterative solvers such as the Gauss-Seidel and successive overrelaxation methods. Additionally, it can mitigate some of the drawbacks of these traditional techniques. We incorporate our algorithm into a multigrid solver to provide a simple and efficient gravity solver that can be used to obtain the gravitational potentials in self-gravitational hydrodynamics. We test our implementation against a broad range of standard self-gravitating astrophysical problems designed to examine different aspects of the code. We demonstrate that the results match excellently with analytical predictions (when available), and the findings of similar previous studies.

Keywords: Gravitation, Hydrodynamical simulations, Computational methods
The GFCAT: A Catalog of Ultraviolet Variables Observed by GALEX with Subminute Resolution. We have performed the first systematic search of the full Galaxy Evolution Explorer (GALEX) data archive for astrophysical variability on timescales of seconds to minutes by rebinning data across the whole mission to 30 s time resolution. The result is the GALEX Flare Catalog (GFCAT), which describes 1426 ultraviolet variable sources, including stellar flares, eclipsing binaries, δ Scuti and RR Lyrae variables, and active galactic nuclei. Many of these sources have never previously been identified as variable. We have also assembled a table of observations of ultraviolet flares and accompanying statistics and measurements, including energies, and of candidate eclipsing stars. This effort was enabled by a significantly enhanced version of the gPhoton software for analyzing time-domain GALEX data; this "gPhoton2" package is available to support follow-on efforts.

Keywords: Delta Scuti variable stars, Astronomy software, Space telescopes, Flare stars, Ultraviolet astronomy, RR Lyrae variable stars, Active galactic nuclei, Time domain astronomy, Eclipsing binary stars, Catalogs
Implementation of Chemistry in the Athena++ Code. Chemistry plays a key role in many aspects of astrophysical fluids. Atoms and molecules are agents for heating and cooling, determine the ionization fraction, serve as observational tracers, and build the molecular foundation of life. We present the implementation of a chemistry module in the publicly available magnetohydrodynamic code Athena++. We implement several chemical networks and heating and cooling processes suitable for simulating the interstellar medium (ISM). A general chemical network framework in the KIDA format is also included, allowing users to easily implement their own chemistry. Radiation transfer and cosmic-ray ionization are coupled with chemistry and solved with the simple six-ray approximation. The chemical and thermal processes are evolved as a system of coupled ordinary differential equations with an implicit solver from the CVODE library. We perform and present a series of tests to ensure the numerical accuracy and convergence of the code. Many tests combine chemistry with gas dynamics, including comparisons with analytic solutions, 1D problems of the photodissociation regions and shocks, and realistic 3D simulations of the turbulent ISM. We release the code with the new public version of Athena++, aiming to provide a robust and flexible code for the astrochemical simulation community.

Keywords: Magnetohydrodynamical simulations, Interstellar medium, Astrochemistry
Two-stage Hierarchical Framework for Solar Flare Prediction. Solar flares, often accompanied by coronal mass ejections and other solar phenomena, are one of the most important sources affecting space weather. It is important to investigate the forecast approach of solar flares to mitigate their destructive effect on the Earth. Statistical analysis, associated with data from 2010 to 2017 in Space-weather HMI Active Region Patches (SHARPs) collected by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager, reveals that there is a distribution divergence between the two types of active regions (ARs) of solar flares. A two-stage hierarchical prediction framework is formulated to better utilize this intrinsic distribution information. Specially, we pick up the ARs where at least one solar flare event occurs within the next 48 hr as flaring ARs through balanced random forest and naive Bayesian methods and then predict the events from flaring ARs by a cascade module of learning models. The empirical evaluation of SHARPs data from 2016 to 2019 verifies the promising performance of our framework, e.g., 0.727 for the true skill statistic.

Keywords: Solar flares, Astronomy data analysis
Noise Reduction Methods for Large-scale Intensity-mapping Measurements with Infrared Detector Arrays. Intensity-mapping observations measure galaxy clustering fluctuations from spectral-spatial maps, requiring stable noise properties on large angular scales. We have developed specialized readouts and analysis methods for achieving large-scale noise stability with Teledyne 2048 × 2048 H2RG infrared detector arrays. We designed and fabricated a room-temperature low-noise ASIC Video8 amplifier to sample each of the 32 detector outputs continuously in sample-up-the-ramp mode with interleaved measurements of a stable reference voltage that remove current offsets and 1/f noise from the amplifier. The amplifier addresses rows in an order different from their physical arrangement on the array, modulating temporal 1/f noise in the H2RG to high spatial frequencies. Finally, we remove constant signal offsets in each of the 32 channels using reference pixels. These methods will be employed in the upcoming SPHEREx orbital mission that will carry out intensity-mapping observations in near-infrared spectral maps in deep fields located near the ecliptic poles. We also developed a noise model for the H2RG and Video8 to optimize the choice of parameters. Our analysis indicates that these methods hold residual 1/f noise near the level of SPHEREx photon noise on angular scales smaller than ~30'.

Keywords: Observational cosmology, Astronomical instrumentation, Cosmic background radiation, Near infrared astronomy
The Calibration of the 35-40 GHz Solar Radio Spectrometer with the New Moon and a Noise Source. Calibrating solar radio flux has always been a concern in the solar community. Previously, fluxes were calibrated by matching load or the new Moon for relative calibration, and at times with the assistance of other stations' data. Moreover, the frequency coverage seldom exceeded 26 GHz. This paper reports the upgraded and calibrated Chashan Broadband Solar millimeter spectrometer (CBS) working from 35 to 40 GHz at the Chashan Solar Observatory (CSO). Initially, the calibration of the solar radiation brightness temperature is accomplished using the new Moon as the definitive source. Subsequently, the 35-40 GHz standard flux is achieved by establishing the correlation between the solar radio flux, brightness temperature, and frequency. Finally, the calibration of the solar radio flux is implemented by utilizing a constant temperature-controlled noise source as a reference. The calibration in 2023 February and March reveals that the solar brightness temperature is 11,636 K at 37.25 GHz with a standard deviation (STD) of 652 K. The solar radio flux's intensity is ~3000-4000 solar flux units (SFU) in the range of 35-40 GHz with a consistency bias of ±5.3%. The system sensitivity is about ~5-8 SFU by a rough evaluation, a noise factor of about 200 K, and the coefficient of variation of the system transmission slope of 6.5% @ 12 hr at 37.25 GHz. It is expected that the upgraded CBS will capture more activity during the upcoming solar cycle.

Keywords: Calibration, Astronomical techniques
Kinematics of the Local Spiral Structure Revealed by Young Stars in Gaia DR3. Using young open clusters and O-B2-type stars in Gaia Data Release 3, we investigate the kinematics of the local spiral structure. In general, the young sources in the outer spiral arms may present larger peculiar motions than those in the inner spiral arms. The young open clusters appear to have smaller peculiar motions than the O-B2-type stars, and the sources in both the Perseus and Local Arms may show an inward motion toward the Galactic center and rotate slower than Galactic rotation. Meanwhile, the sources in the Carina Arm may move in the opposite direction from the Sun to the Galactic center and rotate marginally faster than Galactic rotation. In addition, using young open clusters and O-B2-type stars, we have improved the distance estimations of kinematic methods for several regions near the Sun.

Keywords: Open star clusters, OB stars, Galaxy kinematics
Optical Constants of Martian Dust Analogs at UV-Visible-Near-infrared Wavelengths. We present an advanced light-scattering model to retrieve the optical constants of three Martian dust analogs: Johnson Space Center regolith simulant, Enhanced Mojave Mars Simulant, and Mars Global Simulant. The samples are prepared to have narrow particle-size distributions within the geometric-optics domain. We carry out laboratory measurements to obtain the particle-size distributions, shapes, and diffuse reflectance spectra of the Martian analogs deposited on a surface. Our model framework includes a ray-optics code to compute scattering properties for individual particles, and a radiative-transfer treatment to simulate the surface. The irregular shapes of the dust particles are taken into account in the model. We compare our derived imaginary parts of the refractive indices with those in the literature and find that they are much smaller than the ones that are commonly used for Martian dust. A sensitivity study shows that the retrieved optical constants are sensitive to the particle shape, which needs to be accounted for in applications that use different shapes. Finally, the derived values are validated by using them to reproduce the reflectance spectrum of the Martian surface regolith as observed by the Nadir and Occultation for Mars Discovery instrument on board the ExoMars mission.

Keywords: Mars, Planetary surfaces, Computational methods
The Panchromatic Hubble Andromeda Treasury. XXI. The Legacy Resolved Stellar Photometry Catalog. We present the final legacy version of stellar photometry for the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We have reprocessed all of the Hubble Space Telescope Wide Field Camera 3 and Advanced Camera for Surveys near-ultraviolet (F275W, F336W), optical (F475W, F814W), and near-infrared (F110W, F160W) imaging from the PHAT survey using an improved method that optimized the survey depth and chip-gap coverage by including all overlapping exposures in all bands in the photometry. An additional improvement was gained through the use of charge transfer efficiency (CTE)-corrected input images, which provide more complete star finding as well as more reliable photometry for the NUV bands, which had no CTE correction in the previous version of the PHAT photometry. While this method requires significantly more computing resources and time than earlier versions where the photometry was performed on individual pointings, it results in smaller systematic instrumental completeness variations as demonstrated by cleaner maps in stellar density, and it results in optimal constraints on stellar fluxes in all bands from the survey data. Our resulting catalog has 138 million stars, 18% more than the previous catalog, with lower density regions gaining as much as 40% more stars. The new catalog produces nearly seamless population maps that show relatively well-mixed distributions for populations associated with ages older than 1-2 Gyr and highly structured distributions for the younger populations.

Keywords: Stellar populations, Andromeda Galaxy, HST photometry, Multi-color photometry
Deciphering the Morphological Origins of X-shaped Radio Galaxies: Numerical Modeling of Backflow versus Jet Reorientation. X-shaped radio galaxies (XRGs) develop when certain extragalactic jets deviate from their propagation path. An asymmetric ambient medium (backflow model) or complex active galactic nucleus activity (jet-reorientation model) enforcing the jet direction to deviate may cause these structures. In this context, the present investigation focuses on the modeling of XRGs by performing 3D relativistic magnetohydrodynamic simulations. We implement different jet-propagation models applying an initially identical jet-ambient medium configuration to understand distinctive features. This study, the first of its kind, demonstrates that all adopted models produce XRGs with notable properties, thereby challenging the notion of a universal model. Jet reorientation naturally explains several contentious properties of XRGs, including wing alignment along the ambient medium's primary axis, development of collimated lobes, and the formation of noticeably longer wings than active lobes. These XRGs disrupt the cluster medium by generating isotropic shocks and channeling more energy than in the backflow scenario. Our synthetic thermal X-ray maps of the cluster medium reveal four clear elongated cavities associated with the wing-lobe alignment, regardless of projection effects, but they affect their age estimation. We show that the depth and geometric alignment of the evolved cavities may qualify as promising characteristics of XRGs, which may be used to disentangle different formation scenarios.

Keywords: Galaxy clusters, Relativistic jets, X-ray sources, Shocks, Magnetohydrodynamical simulations
Aliphatics and Aromatics in the Universe: The Pre-JWST Era. The so-called "unidentified infrared emission" (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 μm ubiquitously seen in a wide variety of astrophysical regions are generally attributed to polycyclic aromatic hydrocarbon (PAH) molecules. Astronomical PAHs often have an aliphatic component (e.g., aliphatic sidegroups like methyl -CH3 may be attached as functional groups to PAHs) as revealed by the detection in many UIE sources of the aliphatic C-H stretching feature at 3.4 μm. With its unprecedented sensitivity and spatial resolution, and high spectral resolution, the James Webb Space Telescope (JWST) holds great promise for revolutionizing the studies of aliphatics and aromatics in the Universe. To facilitate analyzing JWST observations, we present a theoretical framework for determining the aliphatic fractions (η ali) of PAHs (the fractions of C atoms in aliphatic units) from the emission intensity ratios of the 3.4 μm aliphatic C-H feature to the 3.3 μm aromatic C-H feature. To demonstrate the effectiveness of this framework, we compile the 3.3 and 3.4 μm UIE data obtained in the pre-JWST era for an as-complete-as-possible sample, and then apply the framework to these pre-JWST data. We derive a median aliphatic fraction of &lt;η ali&gt; ≈ 5.4%, and find that the aliphatic fractions are the highest in protoplanetary nebulae illuminated by cool stars lacking ultraviolet radiation. Nevertheless, the "hardness" of stellar photons is not the only factor affecting the PAH aliphaticity, and other factors such as the starlight intensity may also play an important role.

Keywords: Interstellar molecules, Polycyclic aromatic hydrocarbons, Interstellar medium, Astrochemistry
Grids of Wolf-Rayet Stars Using MESA with the k - ω Model: From 25 to 120 M <SUB>⊙</SUB> at Z = 0.02. To explore overshoot mixing and rotational mixing beyond the convective core during the core He-burning phase in massive stars, we computed a grid of stellar models, both rotating and nonrotating, with the k - ω model at Z = 0.02, covering a mass range of 25-120 M ⊙. The rotating models start with a rotation rate of v ini/v crit = 0.4 at the zero-age main sequence, and the evolution is computed until the end of the central carbon-burning phase. Models with the k - ω model provide larger convective cores and a broadening of the main-sequence width. The diffusive-overshoot models with f ov = 0.027 are, on average, closer to the k - ω models for massive stars at Z = 0.02, particularly for the stars with masses greater than 40 M ⊙. The final masses of the Wolf-Rayet (WR) stars range from 9.5-17.5 M ⊙ and 10-23 M ⊙ for the rotating and nonrotating models, respectively. In the rotating models, the C/N ratio decreases slowly below 0.1 outside the convective core, resulting in a flatter element transition region. In addition, the lifetimes of the WNC phase are 1-4 × 104 yr, which is about 1 order of magnitude longer than that in the nonrotating models. The masses of the WNC stars are dominated by internal mixing processes and the maximum masses of the He-burning convective cores during the core He-burning phase are in the range of 15-35 M ⊙. The expected WNC/WR ratios are 0.059 and 0.004 for the rotating and nonrotating models, respectively.

Keywords: Stellar convective zones, Stellar structures, Massive stars, Stellar rotation, Stellar evolution
CHIANTI-An Atomic Database for Emission Lines. XVII. Version 10.1: Revised Ionization and Recombination Rates and Other Updates. The CHIANTI atomic database provides sets of assessed data that are used for simulating spectral observations of astrophysical plasmas. This article describes updates that will be released as version 10.1 of the database. A key component of CHIANTI is the provision of ionization and recombination rates that are used to compute the ionization balance of a plasma over a range of temperatures. Parameters for calculating the ionization rates of all stages of ions from H through Zn were compiled and inserted into the CHIANTI database in 2009. These were based on all measurements that were available at the time and supplemented with distorted wave calculations. Since then, there have been a number of new laboratory measurements for ions that produce spectral lines that are commonly observed. Parameters have been fit to these new measurements to provide improved ability to reproduce the ionization cross sections and rate coefficients, and these are added to the database. CHIANTI 10.1 also includes new recombination rates for the phosphorus isoelectronic sequence, and the updated ionization and recombination rates have been used to calculate a new ionization equilibrium file. In addition, CHIANTI 10.1 has new electron collision and radiative data sets for eight ions in the nitrogen and oxygen isoelectronic sequences and updated energy level and wavelength data for six other ions. *Released on 2023 July 17.

Keywords: Ultraviolet spectroscopy, Atomic data, Solar ultraviolet emission, Solar x-ray emission
Improvement of Pan-STARRS Photometric Calibration with LAMOST and Gaia. In this work, we perform the recalibration of Pan-STARRS1 (PS1) photometry by correcting for position-dependent systematic errors using the spectroscopy-based stellar color regression (SCR) method, the photometry-based SCR method, and the Gaia BP/RP synthetic photometry method. We confirm the significant large-scale and small-scale spatial variation of the magnitude offsets for all the grizy filters. We show that the PS1 photometric calibration precisions in the grizy filters are around 5-7 mmag when averaged over 14' regions. We note a much larger calibration error up to 0.04 mag in the Galactic plane, which is probably caused by the systematic errors of the PS1 magnitudes in crowded fields. The results of the three methods are consistent with each other within 1-2 mmag or better for all the filters. We provide 2D maps and a Python package to correct for position-dependent magnitude offsets of PS1, which can be used for high-precision investigations and as a reference to calibrate other surveys.

Keywords: Stellar photometry, Calibration, Astronomy data analysis
A Small-scale Structure Model of a Jet Based on Observations of Microvariability. We developed a multiregion radiation model for the evolution of flux and spectral index with time. In this model, each perturbation component in the jet produces an independent flare. The model can be used to study the decomposition of microvariability, the structural scale of the perturbed components, and the physical parameters of the acceleration processes. Based on the shock acceleration model for a relativistic jet, the influence of the acceleration parameters on multiband flare parameters is calculated. We present the results of multiband optical microvariability of the blazar BL Lacertae observed during 89 nights in the period from 2009 to 2021, and use them as a sample for model fitting. The results show that both the amplitude and duration of flares decomposed from the microvariability light curves conform to a log-normal distribution. The time delays between the optical bands follow a normal distribution and amount to several minutes, which corroborate with both predictions from the theoretical model and the calculation of the discrete correlation function. Using the spectral index evolution and the simultaneous fitting of the multiband variability curves, we obtain the acceleration and radiation parameters to constrain and distinguish the origins of different flares. Based on the flare decomposition, we can effectively reproduce the time-domain evolution trends of the optical variations and energy spectrum, and explain the various redder-when-brighter and bluer-when-brighter behaviors.

Keywords: Blazars, Jets, BL Lacertae objects