Sazuna/UAT_keywords huggingface dataset:
An Improved Method for Coupling Hydrodynamics with Astrophysical Reaction Networks. Reacting astrophysical flows can be challenging to model, because of the difficulty in accurately coupling hydrodynamics and reactions. This can be particularly acute during explosive burning or at high temperatures where nuclear statistical equilibrium is established. We develop a new approach, based on the ideas of spectral deferred corrections (SDC) coupling of explicit hydrodynamics and stiff reaction sources as an alternative to operator splitting, that is simpler than the more comprehensive SDC approach we demonstrated previously. We apply the new method to a double-detonation problem with a moderately sized astrophysical nuclear reaction network and explore the time step size and reaction network tolerances, to show that the simplified-SDC approach provides improved coupling with decreased computational expense compared to traditional Strang operator splitting. This is all done in the framework of the Castro hydrodynamics code, and all algorithm implementations are freely available.

Keywords: Hydrodynamical simulations, Computational methods, Nucleosynthesis
Parker Solar Probe Observations of Near-f <SUB>Ce</SUB> Harmonic Emissions in the Near-Sun Solar Wind and Their Dependence on the Magnetic Field Direction. Wave emissions at frequencies near electron gyrofrequency harmonics are observed at small heliocentric distances below about 40 R ⊙ and are known to occur in regions with quiescent magnetic fields. We show the close connection of these waves to the large-scale properties of the magnetic field. Near electron gyrofrequency harmonic emissions occur only when the ambient magnetic field points to a narrow range of directions bounded by polar and azimuthal angular ranges in the RTN coordinate system of correspondingly 80° ≲ θ  B  ≲ 100° and 10° ≲ ϕ  B  ≲ 30°. We show that the amplitudes of wave emissions are highest when both angles are close to the center of their respective angular interval favorable to wave emissions. The intensity of wave emissions correlates with the magnetic field angular changes at both large and small timescales. Wave emissions intervals correlate with intervals of decreases in the amplitudes of broadband magnetic fluctuations at low frequencies of 10-100 Hz. We discuss possible generation mechanisms of the waves.

Keywords: Space plasmas, Solar wind, Plasma physics
Mitigating Bias in CMB B-modes from Foreground Cleaning Using a Moment Expansion. One of the primary challenges facing upcoming cosmic microwave background (CMB) polarization experiments aiming to measure the inflationary B-mode signal is the removal of polarized foregrounds. The thermal dust foreground is often modeled as a single modified blackbody; however, overly simplistic foreground models can bias measurements of the tensor-to-scalar ratio r. As CMB polarization experiments become increasingly sensitive, thermal dust emission models must account for greater complexity in the dust foreground while making minimal assumptions about the underlying distribution of dust properties within a beam. We use Planck dust temperature data to estimate the typical variation in dust properties along the line of sight and examine the impact of these variations on the bias in r if a single modified blackbody model is assumed. We then assess the ability of the moment method to capture the effects of spatial averaging and to reduce bias in the tensor-to-scalar ratio for different possible toy models of dust emission. We find that the expected bias due to temperature variations along the line of sight is significant compared to the target sensitivities of future CMB experiments, and that the use of the moment method could reduce bias as well as shed light into the distribution of dust physical parameters.

Keywords: Interstellar dust, Cosmic microwave background radiation
The Mass Scale of High-redshift Galaxies: Virial Mass Estimates Calibrated with Stellar Dynamical Models from LEGA-C. Dynamical models for 673 galaxies at z = 0.6-1.0 with spatially resolved (long-slit) stellar kinematic data from LEGA-C are used to calibrate virial mass estimates defined as ${M}_{\mathrm{vir}}=K\sigma {{\prime} }_{\star ,\mathrm{int}}^{2}R$ , with K a scaling factor, $\sigma {{\prime} }_{\star ,\mathrm{int}}$ the spatially integrated stellar velocity second moment from the LEGA-C survey, and R the effective radius measured from a Sérsic profile fit to Hubble Space Telescope imaging. The sample is representative for M ⋆ &gt; 3 × 1010 M ☉ and includes all types of galaxies, irrespective of morphology and color. We demonstrate that using R = R sma (the semimajor axis length of the ellipse that encloses 50% of the light) in combination with an inclination correction on $\sigma {{\prime} }_{\star ,\mathrm{int}}$ produces an unbiased M vir. We confirm the importance of projection effects on $\sigma {{\prime} }_{\star ,\mathrm{int}}$ by showing the existence of a similar residual trend between virial mass estimates and inclination for the nearby early-type galaxies in the ATLAS3D survey. Also, as previously shown, when using a Sérsic profile-based R estimate, a Sérsic index-dependent correction to account for nonhomology in the radial profiles is required. With respect to analogous dynamical models for low-redshift galaxies from the ATLAS3D survey we find a systematic offset of 0.1 dex in the calibrated virial constant for LEGA-C, which may be due to physical differences between the galaxy samples or an unknown systematic error. Either way, with our work we establish a common mass scale for galaxies across 8 Gyr of cosmic time with a systematic uncertainty of at most 0.1 dex.

Keywords: Galaxy masses, Galaxy dynamics, Galaxy evolution, Scaling relations
High-frequency Radio Imaging of 3CR 403.1 with the Sardinia Radio Telescope. We present multifrequency observations of the radio source 3CR 403.1, a nearby (z = 0.055), extended (~0.5 Mpc) radio galaxy hosted in a small galaxy group. Using new high-frequency radio observations from the Sardinia Radio Telescope (SRT), augmented with archival low-frequency radio observations, we investigated radio spectral and polarimetric properties of 3CR 403.1. From the MHz-to-GHz spectral analysis, we computed the equipartition magnetic field in the lobes to be B eq = 2.4 μG and the age of the source to be ~100 Myr. From the spectral analysis of the diffuse X-ray emission we measured the temperature and density of the intracluster medium (ICM). From the SRT observations, we discovered two regions where the radio flux density is below the background value. We computed the Comptonization parameter both from the radio and from the X-ray observations to test whether the Sunyaev-Zel'dovich effect is occurring here and found a significant tension between the two estimates. If the negative signal is considered as real, then we speculate that the discrepancy between the two values could be partially caused by the presence of a nonthermal bath of mildly relativistic ghost electrons. From the polarimetric radio images, we find a net asymmetry of the Faraday rotation between the two prominent extended structures of 3CR 403.1 and constrain the magnetic field strength in the ICM to be 1.8-3.5 μG. The position of 3CR 403.1 in the magnetic field-gas density plane is consistent with the trend reported in the literature between central magnetic field and central gas density.

Keywords: Galaxy clusters, Radio jets, Active galactic nuclei, Intergalactic medium, Extragalactic astronomy
ELUCID. VII. Using Constrained Hydro Simulations to Explore the Gas Component of the Cosmic Web. Using reconstructed initial conditions in the Sloan Digital Sky Survey (SDSS) survey volume, we carry out constrained hydrodynamic simulations in three regions representing different types of the cosmic web: the Coma cluster of galaxies; the SDSS Great Wall; and a large low-density region at z ~ 0.05. These simulations, which include star formation and stellar feedback but no active galactic nucleus formation and feedback, are used to investigate the properties and evolution of intergalactic and intracluster media. About half of the warm-hot intergalactic gas is associated with filaments in the local cosmic web. Gas in the outskirts of massive filaments and halos can be heated significantly by accretion shocks generated by mergers of filaments and halos, respectively, and there is a tight correlation between the gas temperature and the strength of the local tidal field. The simulations also predict some discontinuities associated with shock fronts and contact edges, which can be tested using observations of the thermal Sunyaev-Zel'dovich effect and X-rays. A large fraction of the sky is covered by Lyα and O VI absorption systems, and most of the O VI systems and low-column-density H I systems are associated with filaments in the cosmic web. The constrained simulations, which follow the formation and heating history of the observed cosmic web, provide an important avenue to interpret observational data. With full information about the origin and location of the cosmic gas to be observed, such simulations can also be used to develop observational strategies.

Keywords: Hydrodynamical simulations, X-ray photometry, Quasar absorption line spectroscopy, Large-scale structure of the universe, Sunyaev-Zeldovich effect, Coma Cluster, Voids, Cosmic web, Intergalactic medium, Warm-hot intergalactic medium, Intracluster medium, Intergalactic filaments
Hard X-Ray Polarization Catalog for a Five-year Sample of Gamma-Ray Bursts Using AstroSat CZT Imager. The Cadmium Zinc Telluride Imager (CZTI) on board AstroSat has been regularly detecting gamma-ray bursts (GRBs) since its launch in 2015. Its sensitivity to polarization measurements at energies above 100 keV allows CZTI to attempt spectropolarimetric studies of GRBs. Here, we present the first catalog of GRB polarization measurements made by CZTI during its first five years of operation. This includes the time-integrated polarization measurements of the prompt emission of 20 GRBs in the energy range 100-600 keV. The sample includes the bright GRBs that were detected within an angle range of 0°-60° and 120°-180° where the instrument has useful polarization sensitivity and is less prone to systematics. We implement a few new modifications in the analysis to enhance the polarimetric sensitivity of the instrument. The majority of the GRBs in the sample are found to possess less/null polarization across the total bursts' duration in contrast to a small fraction of five GRBs that exhibit high polarization. The low polarization across the bursts might be due either to the burst being intrinsically weakly polarized or to a varying polarization angle within the burst even when it is highly polarized. In comparison to POLAR measurements, CZTI has detected a larger number of cases with high polarization. This may be a consequence of the higher energy window of CZTI observations, which results in the sampling of a shorter duration of burst emissions than POLAR, thereby probing emissions with less temporal variation in polarization properties.

Keywords: X-ray astronomy, Gamma-ray bursts, Spectropolarimetry, Astronomical instrumentation, Polarimetry
The Isotopic Abundances of Galactic Cosmic Rays with Atomic Number 29 ≤ Z ≤ 38. The Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer spacecraft has been operating successfully in a halo orbit about the L1 Lagrange point since late 1997. We report here the isotopic composition of the Galactic cosmic ray (GCR) elements with 29 ≤ Z ≤ 38 derived from more than 20 years of CRIS data. Using a model of cosmic-ray transport in the Galaxy and the solar system (SS), we have derived from these observations the isotopic composition of the accelerated material at the GCR source (GCRS). Comparison of the isotopic fractions of these elements in the GCRS with corresponding fractions in the solar system gives no indication of GCRS enrichment in r-process isotopes. Since a large fraction of core-collapse supernovae (CCSNe) occur in OB associations, the fact that GCRs do not contain enhanced abundances of r-process nuclides indicates that CCSNe are not the principal source of lighter (Z ≤ 38) r-process nuclides in the solar system. This conclusion supports recent work that points to binary neutron-star mergers, rather than supernovae, as the principal source of galactic r-process isotopes.

Keywords: Galactic cosmic rays, Interstellar medium, Particle astrophysics
New Class of Laboratory Astrophysics Experiments: Application to Radiative Accretion Processes around Neutron Stars. Extreme radiative phenomena, where the radiation energy density and flux strongly influence the medium, are common in the universe. Nevertheless, because of limited or nonexistent observational and experimental data, the validity of theoretical and numerical models for some of these radiation-dominated regimes remains to be assessed. Here, we present the theoretical framework of a new class of laboratory astrophysics experiments that can take advantage of existing high-power laser facilities to study supersonic radiation-dominated waves. Based on an extension of Lie symmetry theory we show that the stringent constraints imposed on the experiments by current scaling theories can in fact be relaxed, and that astrophysical phenomena can be studied in the laboratory even if the ratio of radiation energy density to thermal energy and systems' microphysics are different. The validity of this approach holds until the hydrodynamic response of the studied system starts to play a role. These equivalence symmetries concepts are demonstrated using a combination of simulations for conditions relevant to Type I X-ray burst and of equivalent laboratory experiments. These results constitute the starting point of a new general approach expanding the catalog of astrophysical systems that can be studied in the laboratory.

Keywords: Neutron stars, Accretion, Laboratory astrophysics, Scaling relations, X-ray sources
Nonlinear Color-Metallicity Relations of Globular Clusters. XI. Nonlinearity Effect Revealed by NGC 5128 (Centaurus A) and NGC 4594 (Sombrero) Galaxies. Metallicity distributions (MDs) of globular clusters (GCs) provide crucial clues for the assembly and star formation history of their host galaxies. GC colors, when GCs are old, have been used as a proxy of GC metallicities. Bimodal GC color distributions (CDs) observed in most early-type galaxies have been interpreted as bimodal MDs for decades, suggesting the presence of merely two GC subpopulations within single galaxies. However, the conventional view has been challenged by a new theory that nonlinear metallicity-to-color conversion can cause bimodal CDs from unimodal MDs. The unimodal MDs seem natural given that MDs involved many thousand protogalaxies. The new theory has been tested and corroborated by various observational and theoretical studies. Here we examine the nonlinear nature of GC color-metallicity relations (CMRs) using photometric and spectroscopic GC data of NGC 5128 (Centaurus A) and NGC 4594 (Sombrero), in comparison with stellar population simulations. We find that, with a slight offset in color, the overall shapes of observed and modeled CMRs agree well for all available colors. Diverse color-depending morphologies of GC CDs of the two galaxies are well reproduced based on their observed spectroscopic MDs via our CMR models. The results corroborate the nonlinear CMR interpretation of the GC color bimodality, shedding further light on theories of galaxy formation.

Keywords: Globular star clusters, Stellar populations, Galaxy evolution
No Self-shadowing Instability in 2D Radiation Hydrodynamical Models of Irradiated Protoplanetary Disks. Theoretical models of protoplanetary disks including stellar irradiation often show a spontaneous amplification of scale height perturbations, produced by the enhanced absorption of starlight in enlarged regions. In turn, such regions cast shadows on adjacent zones that consequently cool down and shrink, eventually leading to an alternating pattern of overheated and shadowed regions. Previous investigations have proposed this to be a real self-sustained process, the so-called self-shadowing or thermal wave instability, which could naturally form frequently observed disk structures such as rings and gaps, and even potentially enhance the formation of planetesimals. All of these, however, have assumed in one way or another vertical hydrostatic equilibrium and instantaneous radiative diffusion throughout the disk. In this work we present the first study of the stability of accretion disks to self-shadowing that relaxes these assumptions, relying instead on radiation hydrodynamical simulations. We first construct hydrostatic disk configurations by means of an iterative procedure and show that the formation of a pattern of enlarged and shadowed regions is a direct consequence of assuming instantaneous radiative diffusion. We then let these solutions evolve in time, which leads to a fast damping of the initial shadowing features in layers close to the disk surface. These thermally relaxed layers grow toward the midplane until all temperature extrema in the radial direction are erased in the entire disk. Our results suggest that radiative cooling and gas advection at the disk surface prevent a self-shadowing instability from forming, by damping temperature perturbations before these reach lower, optically thick regions.

Keywords: Hydrodynamical simulations, Radiative transfer simulations, Protoplanetary disks, Planet formation
Searching for Quasi-periodic Oscillations in Astrophysical Transients Using Gaussian Processes. Analyses of quasi-periodic oscillations (QPOs) are important to understanding the dynamic behavior in many astrophysical objects during transient events like gamma-ray bursts, solar flares, magnetar flares, and fast radio bursts. Astrophysicists often search for QPOs with frequency-domain methods such as (Lomb-Scargle) periodograms, which generally assume power-law models plus some excess around the QPO frequency. Time-series data can alternatively be investigated directly in the time domain using Gaussian process (GP) regression. While GP regression is computationally expensive in the general case, the properties of astrophysical data and models allow fast likelihood strategies. Heteroscedasticity and nonstationarity in data have been shown to cause bias in periodogram-based analyses. GPs can take account of these properties. Using GPs, we model QPOs as a stochastic process on top of a deterministic flare shape. Using Bayesian inference, we demonstrate how to infer GP hyperparameters and assign them physical meaning, such as the QPO frequency. We also perform model selection between QPOs and alternative models such as red noise and show that this can be used to reliably find QPOs. This method is easily applicable to a variety of different astrophysical data sets. We demonstrate the use of this method on a range of short transients: a gamma-ray burst, a magnetar flare, a magnetar giant flare, and simulated solar flare data.

Keywords: Gamma-ray bursts, Bayesian statistics, Solar flares, Model selection, Astrostatistics techniques, Astrostatistics, X-ray transient sources, Magnetars, Gamma-ray transient sources, Time series analysis
The Great Dimming of Betelgeuse: A Surface Mass Ejection and Its Consequences. The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801), underwent a historic optical dimming during 2020 January 27-February 13. Many imaging and spectroscopic observations across the electromagnetic spectrum were obtained prior to, during, and subsequent to this dimming event. These observations of Betelgeuse reveal that a substantial surface mass ejection (SME) occurred and moved out through the extended atmosphere of the supergiant. A photospheric shock occurred in 2019 January-March, progressed through the extended atmosphere of the star during the following 11 months and led to dust production in the atmosphere. Resulting from the substantial mass outflow, the stellar photosphere was left with lower temperatures and the chromosphere with a lower density. The mass ejected could represent a significant fraction of the total annual mass-loss rate from the star suggesting that episodic mass-loss events can contribute an amount comparable to that of the stellar wind. Following the SME, Betelgeuse was left with a cooler average photosphere, an unusual short photometric oscillation, reduced velocity excursions, and the disappearance of the ~400 day pulsation in the optical and radial velocity for more than two years following the Great Dimming.

Keywords: M supergiant stars, Red supergiant stars, Stellar chromospheres, Stellar mass loss, Stellar atmospheres
COCONUT, a Novel Fast-converging MHD Model for Solar Corona Simulations: I. Benchmarking and Optimization of Polytropic Solutions. We present a novel global 3D coronal MHD model called COCONUT, polytropic in its first stage and based on a time-implicit backward Euler scheme. Our model boosts run-time performance in comparison with contemporary MHD-solvers based on explicit schemes, which is particularly important when later employed in an operational setting for space-weather forecasting. It is data-driven in the sense that we use synoptic maps as inner boundary inputs for our potential-field initialization as well as an inner boundary condition in the further MHD time evolution. The coronal model is developed as part of the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) and will replace the currently employed, more simplistic, empirical Wang-Sheeley-Arge (WSA) model. At 21.5 R ⊙ where the solar wind is already supersonic, it is coupled to EUHFORIA's heliospheric model. We validate and benchmark our coronal simulation results with the explicit-scheme Wind-Predict model and find good agreement for idealized limit cases as well as real magnetograms, while obtaining a computational time reduction of up to a factor 3 for simple idealized cases, and up to 35 for realistic configurations, and we demonstrate that the time gained increases with the spatial resolution of the input synoptic map. We also use observations to constrain the model and show that it recovers relevant features such as the position and shape of the streamers (by comparison with eclipse white-light images), the coronal holes (by comparison with EUV images), and the current sheet (by comparison with WSA model at 0.1 au).

Keywords: Space weather, Magnetohydrodynamics, Solar wind, Solar corona
Search for the Gravitational-wave Background from Cosmic Strings with the Parkes Pulsar Timing Array Second Data Release. We perform a direct search for an isotropic stochastic gravitational-wave background (SGWB) produced by cosmic strings in the Parkes Pulsar Timing Array (PPTA) Data Release 2 (DR2). We find no evidence for such an SGWB, and therefore place a 95% confidence level upper limit on the cosmic string tension, G μ, as a function of the reconnection probability, p, which can be less than 1 in the string-theory-inspired models or pure Yang–Mills theory. The upper bound on the cosmic string tension is G μ ≲ 5.1 × 10‑10 for p = 1, which is about five orders of magnitude tighter than the bound derived from the null search of individual gravitational-wave bursts from cosmic string cusps in the PPTA DR2, and comparable to previous bounds derived from the null search of the SGWB from cosmic strings.

Keywords: Millisecond pulsars