Sazuna/UAT_keywords huggingface dataset:
Tidally Distorted Stars Are Triaxial Pulsators. Stars in close binaries are tidally distorted, and this has a strong effect on their pulsation modes. We compute the mode frequencies and geometries of tidally distorted stars using perturbation theory, accounting for the effects of the Coriolis force and the coupling between different azimuthal orders m of a multiplet induced by the tidal distortion. For tidally coupled dipole pressure modes, the tidal coupling dominates over the Coriolis force and the resulting pulsations are "triaxial," with each of the three modes in a multiplet "tidally tilted," to be aligned with one of the three principal axes of the star. The observed amplitudes and phases of the dipole modes aligned orthogonal to the spin axis are modulated throughout the orbit, producing doublets in the power spectrum that are spaced by exactly twice the orbital frequency. Quadrupole modes have similar but slightly more complex behavior. This amplitude modulation allows for mode identification, which can potentially enable detailed asteroseismic analyses of tidally tilted pulsators. Pressure modes should exhibit this behavior in stellar binaries close enough to be tidally synchronized, while gravity modes should remain aligned with the star's spin axis. We discuss applications to various types of pulsating stars and the relationship between the tidal tilting of pulsations and the "single-sided" pulsations sometimes observed in very tidally distorted stars.

Keywords: Delta Scuti variable stars, Tidal distortion, Binary stars, Stellar pulsations, Asteroseismology
Exploring the Circumstellar Environment of Tycho's Supernova Remnant. II. Impact on the Broadband Nonthermal Emission. While the environment around Tycho's supernova remnant has long been believed to be close to homogeneous, the latest analysis of Chandra data has identified a substantial deceleration of the forward shock, which poses a major challenge to this picture. R. Kobashi et al. showed that the existence of dense molecular cloud (MC) surrounding a rarefied wind-like circumstellar matter (CSM) can explain this observational finding in terms of the shock-expansion dynamics, supporting the so-called single-degenerate scenario for the progenitor system. We here extend this work to study the nonthermal emission processes and investigate whether such an environment is consistent with the observed multiwavelength spectrum. While the simulated broadband spectrum based on the wind–MC environment is largely consistent with observations, we find that such an environment predicts a harder gamma-ray spectrum than observed due to the relatively low CSM density in the cavity interior of the MC. This difference can be at least partially attributed to the present 1D setup of the model, which does not account for the clumpy and multidimensional structure of the CSM. Our model provides predictions for the long-term evolution of the broadband spectrum, which can be used to further probe Tycho's surrounding environment in the future, a key to resolving the long-standing issue of Type Ia supernova progenitor channels.

Keywords: Molecular clouds, Supernova remnants, Circumstellar matter, Non-thermal radiation sources, Type Ia supernovae, X-ray sources
Detecting the Black Hole Candidate Population in M51's Young Massive Star Clusters: Constraints on Accreting Intermediate-mass Black Holes. Intermediate-mass black holes (102 &lt; MBH &lt; 105M⊙) are an open question in our understanding of black hole evolution and growth. They have long been linked to dense star cluster environments, thanks to cluster dynamics, but there are a limited number of secure detections. We leverage existing X-ray observations from the Chandra X-ray Observatory and optical catalogs from the Hubble Space Telescope (HST) as well as new radio observations from the Karl G. Jansky Very Large Array to search for any evidence of accreting black holes in young massive star clusters in the nearby galaxy M51. We find that of 44 bright (LX &gt; 1038 erg s−1) X-ray point sources in M51, 24 had probable matches to objects including possible associated star clusters in the HST Legacy Extragalactic UV Survey catalog, seven of which were classified as contaminants (background galaxies or foreground stars). We explore the optical properties of the remaining 17 sources, including cluster age and mass estimates, and search for radio counterparts in the 8─12 GHz band. The lack of radio counterparts to X-ray sources we know to be associated with young massive star clusters in M51 suggests that we do not significantly detect hard-state intermediate-mass black holes (IMBHs) ~104 M⊙ or above. However, more sensitive radio facilities, like the Square Kilometre Array and next-generation Very Large Array, may be able to provide evidence for IMBHs with masses down to ~103 M⊙.

Keywords: Intermediate-mass black holes, Young star clusters, Ultraluminous x-ray sources, Compact objects, Star clusters
Geometrical Distances of Extragalactic Binaries through Spectroastrometry. The growing "Hubble tension" has prompted the need for precise measurements of cosmological distances. This paper demonstrates a purely geometric approach for determining the distances to extragalactic binaries through a joint analysis of spectroastrometry (SA), radial velocity (RV), and light-curve (LC) observations. A parameterized model for the binary system is outlined, and simulated SA, RV, and LC data are computed to infer the probability distribution of model parameters based on the mock data. The impacts of data quality and binary parameters on the distance uncertainties are comprehensively analyzed, showcasing the method's potential for high-precision distance measurements. For a typical eclipsing binary in the Large Magellanic Cloud, the distance uncertainty is approximately 6% under reasonable observational conditions. Within a specific range of data quality and input parameters, the distance measurement precision of individual binary star systems is generally better than 10%. As a geometric method based on the simplest dynamics, it is independent of empirical calibration, and the systematics caused by model selections can be tested using nearby binaries with known distances. By measuring multiple binary star systems or monitoring one binary system repeatedly, geometric distance measurements of nearby galaxies can be achieved, providing valuable insights into the Hubble tension and advancing our understanding of the Universe's structure and evolution.

Keywords: Optical interferometry, Distance measure, Binary stars
Evolution of Magnetic Reconnection in an Electron-scale Current Sheet. Recently, a new type of magnetic reconnection, electron-only reconnection—where there is no obvious ion flow and heating—has been observed in various plasma environments. Previous kinetic simulations have shown that electron-only reconnection is a precursor of standard reconnection. In this paper, by performing a 2.5-dimensional particle-in-cell simulation, we investigate the evolution of electron-only magnetic reconnection to standard magnetic reconnection in a current sheet, whose initial width is of the electron inertial length. In the electron-only reconnection stage, electron outflow produces the electron-scale   pileup, and ions are slightly accelerated in the outflow direction by the Hall electric field force. As the reconnection electric field expands and   is piled up to the ion scale, ions start to be further accelerated inside the ion diffusion region and reflected by the   to the outflow direction. With   pileup as the bond, ions gradually transit from being accelerated by the Hall electric field to being coupled in reconnection by the Lorentz force.

Keywords: Space plasmas, Planetary magnetospheres, Plasma physics
Dependence of Metal Enrichment of Nuclear Star Clusters on Galaxy Stellar Mass. Nuclear star clusters (NSCs) are commonly found in the centers of galaxies, but their dominant formation mechanisms remain elusive. We perform a consistent analysis of stellar populations of 97 nearby NSCs, based on spectroscopic data from the Very Large Telescope. The sample covers a galaxy stellar mass range of 107─1011 M⊙ and is more than 3 times larger than any previous study. We identify three galaxy stellar mass regimes with distinct NSC properties. In the low-mass regime of   ≲ 8.5 (Mhost is in units of M⊙), nearly all NSCs have metallicities lower than their circum-NSC host but similar to those of typical red globular clusters (GCs), supporting the GC inspiral─merger scenario of NSC formation. In the high-mass regime of   ≳ 9.5, nearly all NSCs have higher metallicities than their circum-NSC host and red GCs, suggesting significant contributions from in situ star formation. In the intermediate-mass regime, a comparable fraction of NSCs have higher or lower metallicities than their circum-NSC host and red GCs, with no clear dependence on NSC mass, suggesting intermittent in situ star formation. The majority of NSCs with higher metallicities than their host exhibit a negative age─metallicity correlation, providing clear evidence of long-term chemical enrichment. The average metallicity difference between NSC and host peaks broadly around   and declines toward both higher and lower galaxy masses. We find that the efficiency of dynamical-friction-driven inspiral of GCs observed in present-day galaxies can explain the NSC mass at   but falls short of observed ones at higher galaxy mass, reinforcing our conclusions based on stellar population analysis.

Keywords: Globular star clusters, Stellar populations, Galaxy structure, Galaxy nuclei, Metallicity, Star clusters
A Peculiar Feature of the First Ionization Potential Effect Before a Solar Flare Impulsive Phase Observed by MSS-1B, CHASE, and SDO. The impulsive phase of solar flares is often accompanied by the depletion of the elements with low first ionization potential (FIP), whose abundance decreases from the coronal level to the photospheric level, and then recovers back to the coronal level during the decay phase. Recently, we analyzed the soft X-ray spectroscopic data of the 2024 February 16 flare event observed by the Macao Science Satellite-1B/Soft X-ray Detection Units. Surprisingly, however, it is revealed that the depletion of the low-FIP elements occurred well before the flare impulsive phase. The timing of this change provides important clues about the location of magnetic reconnection, shedding light on the mass and energy transfer between different layers of the solar atmosphere. By examining the multiwavelength data from the Solar Dynamics Observatory and CHASE missions, we found that there was no filament 0.4 hr before the flare eruption. However, an erupting filament was detected in association with the flare event. Based on these features, we propose for the first time that the flare/filament eruption for this event was initiated by magnetic reconnection in the solar chromosphere, rather than in the corona as stated in the standard flare model.

Keywords: Solar flares, Solar magnetic reconnection, Sunspots, Solar x-ray emission, Solar abundances, Solar magnetic fields
Dissecting the Interstellar Media of a Wolf–Rayet Galaxy at z = 2.76. We report JWST/NIRSpec observations of a star-forming galaxy at z = 2.76, MACS J1149-WR1. We securely detect two temperature-sensitive auroral lines, [S III] 6312 (7.4σ) and [O II] 7320+7331 doublets (10σ), and tentatively [N II] 5755 (2.3σ) for the first time in an individual galaxy at z &gt; 1. We perform a detailed analysis of its interstellar media (ISM), and derive electron temperatures, various heavy element abundances (O/H, N/O, S/O, and Ar/O) in the hot ionized region, and the neutral fraction in the warm ionized region. MACS J1149-WR1 shows a broad feature at the wavelength of He II 4686, which consists of a broad (∼1000 km s‑1), blueshifted (∼‑110 km s‑1) line component. Taken together with its mildly elevated N/O abundance, we conclude that MACS J1149-WR1 is experiencing a young starburst (≲10 Myr), likely hosting a large number of Wolf–Rayet (W-R) stars. None of its spectral features support the presence of active galactic nuclei, including (i) the absence of broad components and velocity shifts in hydrogen recombination lines, (ii) low [Fe II]1.257 μm/Paβ ratio, and (iii) the absence of high-ionization lines. Our analysis using He I lines reveals a higher electron temperature and a higher attenuation value, indicating that He I may probe a smaller spatial scale than H I, presumably the region dominated by the aforementioned W-R stars. The star formation rates derived from various He I lines broadly agree with those from hydrogen recombination lines. We thus advocate that He I can be an excellent, independent probe of multiphase ISM in the era of JWST.

Keywords: Star formation, Active galaxies, High-redshift galaxies
Persistence and Burn-in in Solar Coronal Magnetic Field Simulations. Simulations of solar phenomena play a vital role in space-weather prediction. A critical computational question for automating research workflows in the context of data-driven solar coronal magnetic field simulations is quantifying a simulation's burn-in time, after which a solar quantity has evolved away from an arbitrary initial condition to a physically more realistic state. A challenge to quantifying simulation burn-in is that the underlying solar processes and data, like many physical phenomena, are non-Markovian and exhibit long memory or persistence and, therefore, their analysis evades standard statistical approaches. In this work, we provide evidence of long memory in the nonperiodic variations of solar quantities (including over timescales significantly shorter than previously identified) and demonstrate that magnetofrictional simulations capture the memory structure present in magnetogram data. We also provide an algorithm for the quantitative assessment of simulation burn-in time that can be applied to nonstationary time series with long memory. Our approach is based on time-delayed mutual information, an information-theoretic quantity, and includes a small-sample bias correction.

Keywords: Bootstrap, Solar physics, Solar magnetic fields, Time series analysis, Magnetohydrodynamical simulations
Fitting Methods for Probability Distribution Functions in Turbulent Star-forming Clouds. We use a suite of 3D simulations of star-forming molecular clouds, with and without stellar feedback and magnetic fields, to investigate the effectiveness of different fitting methods for volume and column density probability distribution functions (PDFs). The first method fits a piecewise lognormal and power-law (PL) function to recover PDF parameters such as the PL slope and transition density. The second method fits a polynomial spline function and examines the first and second derivatives of the spline to determine the PL slope and the functional transition density. The first PL (set by the transition between lognormal and PL function) can also be visualized in the derivatives directly. In general, the two methods produce fits that agree reasonably well for volume density but vary for column density, likely due to the increased statistical noise in the column density PDFs as compared to the volume density PDFs. We test a well-known conversion for estimating volume density PL slopes from column density slopes and find that the spline method produces a better match (χ2 of 3.34 versus χ2 of 5.92), albeit with a significant scatter. Ultimately, we recommend the use of both fitting methods on column density data to mitigate the effects of noise.

Keywords: Giant molecular clouds, Star forming regions, Star formation, Stellar feedback
A Sensitivity Analysis of the Modeling of Polycyclic Aromatic Hydrocarbon Emission in Galaxies. We have conducted a sensitivity analysis on the mid-infrared spectral decomposition of galaxies and the modeling of the polycyclic aromatic hydrocarbon (PAH) emission spectrum with the NASA Ames PAH Infrared Spectroscopic Database (PAHdb) to assess the variance on the average galaxy PAH population properties under a grid of different modeling parameters. We find that the short-low and short-low+long-low Spitzer-IRS decomposition with PAHFIT provides consistent modeling and recovery of the 5–15 μm PAH emission spectrum. For PAHdb modeling, application of a redshift to the calculated spectra to account for anharmonic effects introduces a 15%–20% variance on the derived parameters, while its absence improves the fits by ∼13%. The 4.00-α release of PAHdb achieves the complete modeling of the 6–15 μm PAH spectrum, including the full 6.2 μm band, improving the average fitting uncertainty by a factor of 2. The optimal PAHdb modeling configuration requires selection of pure PAHs without applying a redshift to the bands. Although quantitatively the PAHdb-derived parameters change under different modeling configurations or database versions, their variation follows a linear scaling, with previously reported trends remaining qualitatively valid. PAHdb modeling of JWST observations, and JWST observations smoothed and resampled to the Spitzer-IRS resolution and dispersion have consistent PAHdb derived parameters. Decomposition with different codes, such as PAHFIT and CAFE, produce PAH emission spectra with noticeable variation in the 11–15 μm region, driving a ∼7% difference in the neutral PAH fraction under PAHdb modeling. A new library of galaxy PAH emission templates is delivered to be utilized in galaxy spectral energy distribution modeling.

Keywords: Interstellar dust, Interstellar molecules, Astronomy data modeling, Polycyclic aromatic hydrocarbons, Interstellar medium, Galaxy spectroscopy, Galaxies
Boulder Migration in the Khonsu Region of Comet 67P/Churyumov–Gerasimenko. The European Space Agency's Rosetta mission is the only space mission that has performed long-term monitoring of a comet at close distances. For over two years, Rosetta rendezvoused with comet 67P/Churyumov–Gerasimenko, which revealed diverse evolutionary processes of the cometary nucleus. One of the most striking events is the migration of a ∼30 m boulder in the southern hemisphere region of Khonsu. Previous works found the boulder's ∼140 m displacement occurred during the three months from 2015 August to October, and several triggering mechanisms were proposed, including outburst at the boulder site, seismic vibrations from nearby activities, or surface erosion of the slope beneath the boulder. In this work, we further analyze this impressive event by analyzing imaging data from Rosetta's OSIRIS camera. We constrained the boulder's migration time to within 14 hr and derived a detailed timeline of the boulder migration event and local dust activities. High-resolution thermophysical modeling shows significant dichotomy in the thermal history of the boulder's southern and northern sides, which could have triggered or facilitated its migration via its own volatile activity.

Keywords: Comet surfaces, Comets, Comet volatiles , Coma dust
Empirical Color Correction to MIST and PARSEC Isochrones on Gaia BR ‑ RP and G ‑ RP with Benchmark Open Clusters. Recent literature reports a color deviation between observed Gaia color–magnitude diagrams (CMDs) and theoretical model isochrone predictions, particularly in the very low-mass regime. To assess its impact on cluster age determination via isochrone fitting, we quantified the color deviations for three benchmark clusters, Hyades, Pleiades, and Praesepe, both for the Gaia color (BP ‑ RP) and (G ‑ RP). In general, the (G ‑ RP) color deviations are smaller than the (BP ‑ RP) ones. Empirical color-correction functions based on these benchmarks are derived for the currently available MESA Isochrones and Stellar Tracks and PAdova and TRieste Stellar Evolution Code (PARSEC) 1.2S isochrone models. Applying the correction functions to 31 additional open clusters and 3 moving groups results in a significantly improved alignment between the isochrones and observed CMDs. With our empirical corrections, isochrones provide age estimates consistent with literature values obtained through the spectral lithium depletion boundary method, validating the effectiveness of our approach. The corresponding metallicities with PARSEC 1.2S also show a good agreement with the spectroscopic results. The empirical color-correction function we present in this work offers a tool for a consistent age determination within the full mass range of stellar clusters using the isochrone fitting method.

Keywords: Open star clusters, Stellar colors, Stellar evolutionary tracks, Stellar associations
High-time-cadence Spectroscopy and Photometry of Stellar Flares on M dwarf YZ Canis Minoris with the Seimei Telescope and TESS. I. Discovery of Rapid and Short-duration Prominence Eruptions. M dwarfs show frequent flares and associated coronal mass ejections (CMEs) may significantly impact close-in habitable planets. M dwarf flares sometimes show blue/red asymmetries in the Hα line profile, suggesting prominence eruptions as an early stage of CMEs. However, their high-time-cadence observations are limited. We conducted spectroscopic monitoring observations of the active M dwarf YZ Canis Minoris with an ∼1 minute time cadence using the Seimei telescope, simultaneously with the optical photometric observations by Transiting Exoplanet Survey Satellite. We detected 27 Hα flares with Hα energies ranging from 1.7 × 1029 to 3.8 × 1032 erg and durations from 8 to 319 minutes. Among them, we identified three blue asymmetry and five red asymmetry events based on criteria using the Bayesian information criterion. The maximum velocity of the blueshifted and redshifted components ranges from 200 to 450 km s−1 and 190 to 400 km s−1, respectively. The duration and time evolution show variety, and in particular, we discovered rapid, short-duration blue/red asymmetry events with the duration of 6─8 minutes. Among the eight blue/red asymmetry events, two blue and one red asymmetry events are interpreted as prominence eruptions because of their fast velocity and time evolution. Based on this interpretation, the lower limit of occurrence frequency of prominence eruptions can be estimated to be ∼1.1 events per day. Our discovery of short-duration events suggests that previous studies with low time cadence may have missed these events, potentially leading to an underestimation of the occurrence frequency of prominence eruptions/CMEs.

Keywords: M dwarf stars, Flare stars, Stellar flares, Optical flares, Stellar coronal mass ejections
Shocked POststarburst Galaxy Survey. IV. Outflows in Shocked Poststarburst Galaxies Are Not Responsible for Quenching. Shocked POstarburst Galaxies (SPOGs) exhibit both emission lines suggestive of shock-heated gas and poststarburst-like stellar absorption, resulting in a unique subset for galaxy evolution studies. We have observed 77 galaxies that fulfilled the SPOG criteria selection using the DeVeny Spectrograph on the Lowell Discovery Telescope. Our long-slit minor axis spectra detect Hα and [O III] in some SPOGs out to 6 kpc above the galactic plane. We find extraplanar ionized gas in 31 targets of our sample overall. Using their internal and external kinematics, we argue that 22 galaxies host outflows with ionized gas masses ranging from 102 M ⊙ to 105 M ⊙. The rest are likely extended diffuse ionized gas. A positive correlation exists between active galactic nuclei (AGN) luminosity and the extraplanar gas extent, velocity dispersion, and mass—suggesting that the AGN may indeed drive the outflows detected in AGN hosts. The low masses of the extraplanar gas suggest that these outflows are not depleting each galaxy's gas reserves. The outflows, therefore, are not likely a significant quenching mechanism in these SPOGs.

Keywords: AGN host galaxies, Galactic winds, Galaxy evolution, Galaxy quenching, Post-starburst galaxies