Sazuna/UAT_keywords huggingface dataset:
Magnetic Thomson Transport in High-opacity Domains. X-ray radiation from neutron stars manifests itself in a variety of settings. Isolated pulsars and magnetars both exhibit quasi-thermal persistent soft X-ray emission from their surfaces. Transient magnetospheric bursts from magnetars and pulsed signals from accreting neutron stars mostly appear in harder X-rays. The emission zones pertinent to these signals are all highly Thomson optically thick, so that their radiation anisotropy and polarization can be modeled using sophisticated simulations of scattering transport from extended emission regions. Validation of such codes and their efficient construction is enhanced by a deep understanding of scattering transport in high-opacity domains. This paper presents a new analysis of the polarized magnetic Thomson radiative transfer in the asymptotic limit of high opacity. The integrodifferential equations for photon scattering transport that result from a phase matrix construction are reduced to a compact pair of equations. This pair is then solved numerically for two key parameters that describe the photon anisotropy and polarization configuration of high Thomson opacity environs. Empirical approximations for these parameters as functions of the ratio of the photon and cyclotron frequencies are presented. Implementation of these semi-analytic transport solutions as interior boundary conditions is shown to speed up scattering simulations. The solutions also enable the specification of the anisotropic radiation pressure. The analysis is directly applicable to the atmospheres of magnetars and moderate-field pulsars, and to the accretion columns of magnetized X-ray binaries, and can be adapted to address other neutron star settings.

Keywords: Neutron stars, Magnetars, Magnetic fields
Superoutbursts and Positive Superhumps Occurred during the Standstill of a Z Cam-type Dwarf Nova. Dwarf novae (DNe) are semidetached binaries, where a white dwarf accretes material from a cool main-sequence companion via an accretion disk, and are known for their intermittent outbursts, making them key systems for studying accretion physics. The accumulation of large survey data sets has challenged traditional models, which assumed that the disk remains hot and cannot produce superoutbursts during the standstill of a Z Camelopardalis (Z Cam)-type DN and that superoutbursts require a mass ratio of q = M2/M1 ≤ 0.25–0.33. Here we report the detection of superoutbursts and positive superhumps (PSHs) during a standstill in the Z Cam-type star AT Cnc with a mass ratio larger than 0.33. Notably, the PSHs evolve gradually before the superoutburst begins, suggesting that an eccentric, precessing disk forms first, with the superoutburst occurring as the disk radius continues to expand. These findings provide the first detailed observational evidence of superoutbursts and PSHs occurring during standstill, offering important new insights into the classification of DNe and the underlying mechanisms of outbursts.

Keywords: Binary stars, Dwarf novae, Z Camelopardalis stars, SU Ursae Majoris stars, Cataclysmic variable stars
Simulation-based Prediction of Black Hole X-Ray Spectra and Spectral Variability. Data derived from general relativistic magnetohydrodynamic simulations of accretion onto black holes can be used as input to a postprocessing scheme that predicts the radiated spectrum. Combining a relativistic Compton scattering radiation transfer solution in the corona with detailed local atmosphere solutions incorporating local ionization and thermal balance within the disk photosphere, it is possible to study both spectral formation and intrinsic spectral variability in the radiation from relativistic accretion disks. With this method, we find that radiatively efficient systems with black holes of 10M⊙ accreting at ≈0.01 in Eddington units produce spectra very similar to those observed in the hard states of X-ray binaries. The spectral shape above 10 keV is well described by a power law with an exponential cutoff. Intrinsic turbulent variations lead to order-unity changes in bolometric luminosity, variations in the logarithmic spectral slope ∼0.1, and factor of 2 alterations in the cutoff energy on timescales ∼50 (MBH/10M⊙) ms. Within the corona, the range of gas temperature spans more than 1 order of magnitude. The wide distribution of temperatures is central to defining the spectrum: the logarithmic spectral slope is harder by ∼0.3 and the cutoff energy larger by a factor ∼10–30 than if the coronal temperature everywhere were its mass-weighted mean.

Keywords: X-ray binary stars, Stellar mass black holes, Astrophysical black holes, Relativistic disks
Identification and Analysis of Galactic Bars in DESI Legacy Imaging Surveys. We present a comprehensive study of bar structures in the local universe using data from the DESI Legacy Imaging Surveys. Through isophotal analysis of 232,142 galaxies, we identify bars and classify them into strong and weak categories based on normalized bar length, using a threshold of 0.4. We find a total bar fraction of 42.9%, rising to 62.0% in disk galaxies, with strong barred galaxies accounting for 30.0%. For barred galaxies in our sample, deprojected bar lengths are measured both in absolute terms and normalized by galaxy size. Most bars are found to have absolute lengths of 3–7 kpc, and normalized bar lengths concentrated around a median value of 0.4. Bar ellipticity mainly ranges from 0.2 to 0.6, with a median value of 0.3. Our analysis reveals a bimodal distribution of bar fractions with respect to galaxy color, with weak bars in our classification being more prevalent in intermediate-color systems. With respect to stellar mass, strong bars also present a bimodal distribution, while weak bars are distributed uniformly. Normalized bar length remains relatively stable across stellar masses, while absolute bar length positively correlates with stellar mass. Cross-validation with visual classifications from Galaxy Zoo DESI catalog confirms a bar identification accuracy of 93%. These results validate our automated method for bar identification and measurement, demonstrating its reliability. Our findings underscore the importance of bars in galaxy evolution and highlight the potential of upcoming wide-field surveys to deepen our understanding of barred galaxies.

Keywords: Galaxy structure, Barred spiral galaxies, Galaxy evolution, Galaxies
SDSS-IV MaNGA: Spatial Evolution of Gas-phase Metallicity Changes Induced by Galaxy Interactions. Gas-phase metallicity in interacting and merging galaxies offers key insights into their star formation processes and evolutionary histories. This study investigates the spatial evolution of gas-phase metallicity (i.e., oxygen abundance, 12 + log(O/H)) in these galaxies using integral field unit data from the SDSS-IV MaNGA survey, focusing on changes in metallicity gradients across different stages of interactions—from early encounters to final coalescence. By comparing interacting and merging galaxies with isolated counterparts, we identify characteristic trends in how interactions influence metallicity gradients over time. Our analysis reveals that metallicity gradients typically flatten shortly after the first pericenter passage, likely due to radial gas mixing, with later stages showing either metallicity enrichment or dilution depending on the intensity of the interaction and star formation activity. These changes can result in gradients that are either flatter or steeper than the initial profiles. Notably, we observe steeper metallicity gradients in interacting galaxies at certain merger stages, which is inconsistent with predictions from some galaxy simulations. This discrepancy emphasizes the complexity of galaxy interactions. Overall, our findings provide valuable insights into how galaxy interactions reshape metallicity distribution, enhancing our understanding of the processes driving galaxy evolution during mergers.

Keywords: Interacting galaxies, Metallicity, Galaxy evolution, Interstellar medium
Filament Mass Losses Forced by Magnetic Reconnection in the Solar Corona. Recent observations of the solar atmosphere in cool extreme-ultraviolet lines have reported the prevalence of coronal rain falling from coronal cloud filaments that are associated with the magnetic dips of coronal X-point structures. These filaments mysteriously appear as clouds of mass in the corona that subsequently shrink and disappear due to mass losses that drain as coronal rain along arced field lines. Using a two-and-a-half-dimensional magnetohydrodynamic model, we investigated evaporation-condensation as the formation mechanism of the subset of coronal cloud filaments that form above coronal X-points. Our simulation included the effects of field-aligned thermal conduction and optically thin radiation, and used the state-of-the-art transition region adaptive conduction (TRAC) method to model the formation, maintenance, and mass loss of a filament above a coronal X-point. This paper presents a physical model that demonstrates magnetic reconnection as a filament loss mechanism, producing hybrid filament/coronal rain via mass losses through the X-point. A detailed analysis of how the mass of the filament forces the field to reconnect is also presented, revealing three phases that characterize the evolution of the reconnecting current sheet and associated mass losses. We conclude that the formation of certain coronal cloud filaments and subsequent mass losses via coronal rain can be explained by the evaporation-condensation model combined with filament mass losses forced by magnetic reconnection. We also report that rebound shocks generated by the impact of coronal rain condensations on the chromosphere together with retractive upflows can cause upward-propagating condensations to form through a dynamic thermal runaway process.

Keywords: Magnetohydrodynamics, Solar magnetic reconnection, Solar prominences, Solar filaments, Solar magnetic fields, Solar corona
A Multifrequency Census of 100 Pulsars below 100 MHz with LWA: A Systematic Study of Flux Density, Spectra, Timing, Dispersion, Polarization, and Its Variation from a Decade of Observations. We present a census of 100 pulsars, the largest below 100 MHz, including 94 normal pulsars and six millisecond pulsars, with the Long Wavelength Array (LWA). Pulse profiles are detected across a range of frequencies from 26–88 MHz, including new narrowband profiles facilitating profile evolution studies, and breaks in pulsar spectra at low frequencies. We report mean flux density, spectral index, curvature, and low-frequency turnover-frequency measurements for 97 pulsars, including new measurements for 61 sources. Multifrequency profile widths are presented for all pulsars, including component spacing for 27 pulsars with two components. Polarized emission is detected from 27 of the sources (the largest sample at these frequencies) in multiple frequency bands, with one new detection. We also provide new timing solutions for five recently discovered pulsars. Low-frequency observations with the LWA are especially sensitive to propagation effects arising in the interstellar medium. We have made the most sensitive measurements of pulsar dispersion measures (DMs) and rotation measures, with median uncertainties of 2.9 × 10‑4 pc cm‑3 and 0.01 rad m‑2, respectively, and can track their variations over almost a decade, along with other frequency-dependent effects. This allows for stringent limits on average magnetic fields, with no variations detected above ∼20 nG. Finally, the census yields some interesting phenomena in individual sources, including the detection of frequency- and time-dependent DM variations in B2217+47, and the detection of highly circularly polarized emission from J0051+0423.

Keywords: Pulsar timing method, Solar wind, Pulsars, Interstellar medium, Interstellar scattering
Can Neutron Star Tidal Effects Obscure Deviations from General Relativity?. One of the main goals of gravitational-wave astrophysics is to study gravity in the strong-field regime and constrain deviations from general relativity (GR). Any such deviation affects not only binary dynamics and gravitational-wave emission but also the structure and tidal properties of compact objects. In the case of neutron stars, masses, radii, and tidal deformabilities can all differ significantly between different theories of gravity. Currently, the measurement uncertainties in neutron star radii and tidal deformabilities are quite large. However, much less is known about how the large uncertainty in the nuclear equation of state (EOS) might affect tests of GR using binary neutron star mergers. Conversely, using the wrong theory of gravity might lead to incorrect constraints on the nuclear EOS. Here, we study this problem within scalar–tensor (ST) theory. We apply the recently derived ℓ = 2 tidal Love numbers in this theory to parameter estimation of GW170817. Correspondingly, we test if physics beyond GR could bias measurements of the nuclear EOS and neutron star radii. We find that parameter inference for both the GR and ST cases returns consistent component masses and tidal deformabilities. The radius and the EOS posteriors, however, differ between the two theories, but neither is excluded by current observational limits. This indicates that measurements of the nuclear EOS may be biased and that deviations from GR could go undetected when analyzing current binary neutron star mergers.

Keywords: Neutron stars, Gravitation, Non-standard theories of gravity, Gravitational wave astronomy, Gravitational waves
BASS. XLV. Quantifying Active Galactic Nuclei Selection Effects in the Chandra COSMOS-legacy Survey with BASS. Deep extragalactic X-ray surveys, such as the Chandra COSMOS-Legacy field (CCLS), are prone to be biased against active galactic nuclei (AGN) with high column densities due to their lower count rates at a given luminosity. To quantify this selection effect, we forward model nearby (z ∼ 0.05) AGN from the BAT AGN Spectroscopic Survey (BASS) with well-characterized (≳1000 cts) broadband X-ray spectra (0.5─195 keV) to simulate the CCLS absorption distribution. We utilize the BASS low-redshift analogs with similar luminosities to the CCLS (  ∼ 1042−45 erg s), which are much less affected by obscuration and low-count statistics, as the seed for our simulations and follow the spectral fitting of the CCLS. Our simulations reveal that Chandra would fail to detect the majority (53.3%; 563/1056) of obscured (NH ≥ 1022 cm−2) simulated BASS AGN given the observed redshift and luminosity distribution of the CCLS. Even for detected sources with sufficient counts (≥30) for spectral modeling, the level of obscuration is significantly overestimated. This bias is most extreme for objects whose best fit indicates a high-column density AGN (NH ≥ 1024 cm−2), since the majority (66.7%; 18/27) of these are actually unobscured sources (NH &lt; 1022 cm−2). This implies that previous studies may have significantly overestimated the increase in the obscured fraction with redshift and the fraction of luminous obscured AGN. Our findings highlight the importance of directly considering obscuration biases and forward modeling in X-ray surveys, as well as the need for higher-sensitivity X-ray missions such as the Advanced X-ray Imaging Satellite (AXIS), and the importance of multiwavelength indicators to estimate obscuration in distant supermassive black holes.

Keywords: Seyfert galaxies, Active galaxies, X-ray active galactic nuclei, X-ray surveys
Observations and Radiative Transfer Simulations of the Carbon-rich AGB Star V Oph with VLTI/MATISSE. Carbon-rich asymptotic giant branch (AGB) stars are among the most important contributors of enriched materials to the interstellar medium due to their strong stellar winds. To fully characterize mass loss on the AGB, it is necessary to determine the distributions of dust and gas around the stars, where the dust begins to condense from the gas, and how this extended atmospheric structure evolves over the pulsational period of the star. We present an analysis of L-band (2.8─4.2 μm) interferometric observations of the carbon-rich AGB star V Oph made with the MATISSE instrument at the Very Large Telescope Interferometer at the maximum and minimum of the star's visual light curve. Using the radiative transfer software RADMC-3D, we model the circumstellar dust shell, and find stellar radii of 395 and 495R⊙ at the two phases, and dust radii of 790 and 742.5R⊙ at the two epochs, respectively. By adding C2H2 and HCN gas to the RADMC-3D models, we are able to fit the visibility spectra well, with some deviations at the 3.11 μm feature. Reasons for this deviation and interpretation of the best fitting models are discussed in the text, and we discuss motivations for follow-up imaging observations of V Oph. *Based on ESO Program ID 105.208BT, PI: Gioia Rau.

Keywords: Asymptotic giant branch stars, Stellar winds, Stellar evolution, Stellar mass loss
Polarization Estimation for Radio Pulsars. A number of polarization estimators have been developed for a variety of astrophysical applications to compensate measurements of linear polarization for a bias contributed by the instrumental noise. Most derivations of the estimators assume that the amplitude and orientation of the polarization vector are constant. This assumption generally is not valid for the radio emission from pulsars that fluctuates from pulse to pulse. The radio emission from pulsars, fast radio bursts, and magnetars can be elliptically polarized, and estimators of the total polarization and absolute value of the circular polarization are used in their observations. However, these estimators have not been formally developed to a level that is commensurate with those of linear polarization. Estimators are derived for circular, linear, and total polarization when the amplitude of the polarization vector is a constant or a random variable. Hybrid estimators are proposed for general application to pulsar polarization observations. They are shown to be more effective at removing instrumental noise than their commonly used counterparts.

Keywords: Radio pulsars
The Effect of Radiation and Supernovae Feedback on LyC Escape in Local Star-forming Galaxies. Feedback is widely recognized as an essential condition for Lyman continuum (LyC) escape in star-forming galaxies. However, the mechanisms by which galactic outflows clear neutral gas and dust remain unclear. In this paper, we model the Mg II 2796 Å, 2804 Å absorption and emission lines in 29 galaxies taken from the Low-z LyC Survey to investigate the impact of (radiation and mechanical) feedback on LyC escape. Using constraints on Mg+ and photoionization models, we map the outflows' neutral hydrogen content and predict   with a multiphase wind model. We measure mass-, momentum, and energy loading factors for the neutral winds, which carry up to 10% of the momentum and 1% of the energy in star formation rate (SFR)-based deposition rates. We use spectral energy distribution template fitting to determine the relative ages of stellar populations, allowing us to identify radiation feedback dominant systems. We then examine feedback related properties (stellar age, loading factors, etc.) under conditions that optimize feedback efficiency, specifically high-SFR surface density and compactness. Our findings indicate that the strongest leakers are radiation feedback dominant, lack deep Mg II absorption features, but have extended broad components in higher-ionization lines like [O III] 5007 Å, as observed by Amorín et al. In contrast, galaxies experiencing supernovae feedback typically exhibit weaker   and show evidence of outflows in both Mg II and higher-ionization lines. We attribute these findings to enhanced LyC escape facilitated by turbulence and cloud fragmentation in intense radiation fields, prolonged in low-metallicity environments experiencing delayed supernova feedback.

Keywords: Galactic winds, Neutral hydrogen clouds, Ultraviolet astronomy, Interstellar medium, Circumgalactic medium, Reionization
The Life and Times of Star-forming Cores: An Analysis of Dense Gas in the STARFORGE Simulations. Dense gas in molecular clouds is an important signature of ongoing and future star formation. We identify and track dense cores in the STARFORGE simulations, following the core evolution from birth through dispersal by stellar feedback for typical Milky Way cloud conditions. Only ∼8% of cores host protostars, and most disperse before forming stars. The median starless and protostellar core lifetimes are ∼0.5–0.6 Myr and ∼0.8–1.1 Myr, respectively, where the protostellar phase lasts   Myr. While core evolution is stochastic, we find that virial ratios and line widths decline in prestellar cores, coincident with turbulent decay. Collapse occurs over ∼0.1 Myr, once the central density exceeds ≳106 cm‑3. Starless cores, only, follow line-width–size and mass–size relations, σ ∝ R0.3 and M ∝ R1. The core median mass, radius, and velocity dispersion scale weakly with the cloud magnetic field strength. We cluster the core properties and find that protostellar cores have &gt;80% likelihood of belonging to three particular groups that are characterized by high central densities, compact radii, and lower virial parameters. Overall, core evolution appears to be universally set by the interplay of gravity and magnetized turbulence, while stellar feedback dictates protostellar core properties and sets the protostellar phase lifetime.

Keywords: Star formation, Stellar feedback, Magnetohydrodynamical simulations
Graph-based Recursive Relations for Computing and Analyzing r-process Abundances. We develop recursive relations among abundances in an r-process network evolving neutron captures, photodisintegrations and beta decays through the use of the matrix-tree and matrix-forest theorems. Since these theorems are based on results from graph theory, we term the relations the GrRproc (Graphical R-process) relations. We validate the relations by using them to compute r-process abundances in network calculations in different astrophysical environments. We also illustrate how they can be used to follow complex reaction flows quantitatively in an evolving r-process network through the concept of contribution paths. Such contribution paths show how particular reactions govern the evolution of abundance features during the nucleosynthesis and, consequently, can clarify the role of key nuclear data and astrophysical environments in that evolution. The Python open-source package that implements the tool is freely available.

Keywords: Astronomy software, Nucleosynthesis, R-process, Nuclear astrophysics, Astrophysical processes, Astronomical simulations