Sazuna/UAT_keywords huggingface dataset:
Older Ages for 23 Pre-main Sequence Stars in Upper Scorpius Using Dynamical-mass-constrained Stellar Evolutionary Models. We present revised stellar ages for 23 pre-main-sequence (PMS) K- and M-type stars in the Upper Scorpius (Upper Sco) star-forming region, derived using stellar dynamical masses to constrain isochronal ages from five PMS stellar evolutionary models. We find that mass-constrained stellar ages for all model sets are more consistent with the older, ∼8─11 Myr age for Upper Sco derived using earlier-type stars. Additionally, applying the independent mass constraint to isochronal ages tends to (1) increase stellar ages for most model sets, and (2) decrease age scatter for individual sources between model sets. Models that account for global magnetic fields consistently provide the best match to our observations: they change comparatively little when the mass constraint is applied, and produce 9─10 Myr ages under both unconstrained and mass-constrained conditions. Most standard (nonmagnetic) models produce younger ages (3─5 Myr) when unconstrained, but older ages (6─9 Myr) when constrained by dynamical mass. Our results are consistent with recent literature findings that suggest median disk lifetimes may be ≳2× longer than previously thought.

Keywords: Early stellar evolution, Stellar ages, Stellar properties, Stellar evolutionary models, T Tauri stars, Pre-main sequence stars, Protoplanetary disks, Low mass stars, Circumstellar disks
White Dwarf Merger Remnants with Cooling Delays on the Q Branch Lack Strong Magnetism. A population of anomalous ultramassive white dwarfs discovered with Gaia, often referred to as the Q branch, show high (multi-Gyr) cooling delays produced by exotic physical mechanisms. They are believed to be the products of stellar mergers, but the exact origin and formation channel remain unclear. We obtained a spectroscopically complete, volume-limited sample of the Q branch region within 100 pc and found significant differences in atmospheric composition and rotation rates as a function of tangential velocity. In particular, we discover that stellar remnants with the longest cooling delays do not show strong magnetism nor detectable short-period rotational variability, as opposed to what is generally believed for double-degenerate mergers. This indicates that either these white dwarfs arise from a formation channel with no strong magnetism induced, or that the magnetism produced from the merger dissipates over the cooling delay timescales. Our follow-up photometry has also discovered pulsations in the second and third hydrogen-dominated DAQ white dwarfs, one hotter than 15,500 K, possibly extending the boundaries of the DAV instability strip for white dwarfs with thin hydrogen layers.

Keywords: Stellar mergers, White dwarf stars, Stellar astronomy, Atmospheric composition, Magnetic fields, Stellar evolution
Investigation of Magnetic Topology and Triggering Mechanisms of a C-class Flare and Active Region Blowout Jet. Coronal jets are collimated plasma eruptions that are ubiquitous in the solar atmosphere. Believed to be triggered by magnetic reconnection, these jets can contribute to various phenomena, including coronal heating and particle acceleration. Coronal jets are a contemporary area of research, with their onset mechanism meriting further attention. Importantly, a subclass of jets, the blowout jets, is particularly interesting because of their broad spire, suggesting substantial 3D reconnection between open and closed field lines involving 3D null points. Consequently, here we explore the onset of a blowout jet associated with Active Region SPoCA 29093 detected by the Spatial Possibilistic Clustering Algorithm (SPoCA). This AR produced a C1.1-class flare on 2022 November 10, and we investigate it using a data-constrained magnetohydrodynamic simulation initiated with a non-force-free field extrapolation of the photospheric magnetic field. Key elements of the extrapolated field lines are the presence of a 3D null and a magnetic flux rope (MFR) colocated with the jet activity region, the evolution of which is further traced in the simulation. The simulation suggests that magnetic reconnection is responsible for the evolution of the MFR, leading to a near-simultaneous onset of the flare and jet as observed by the Atmospheric Imaging Assembly/Solar Dynamics Observatory. In particular, the simulation shows spontaneous creation and annihilation of 3D null pairs via magnetic reconnection near the jet region. Such spontaneous null pair generation, in principle, can trigger or contribute to coronal jets, opening up a new avenue for further research.

Keywords: Solar flares, Jets, Solar magnetic reconnection, Eruptive phenomena, Magnetohydrodynamical simulations
Elongation of a Solar Filament and its Three-dimensional Numerical Reconstruction for Magnetic Structures. Quiescent filaments are prominent features of the solar atmosphere, and their evolution reflects the coronal magnetic field's response to photospheric magnetic activity. Here, we report on a quiescent filament observed on 2023 September 28─29, aiming to understand how the magnetic configuration shapes its feet and drives its extension. For this purpose, high-resolution spectral data in Hα and Mg II k are used from the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires and the Interface Region Imaging Spectrograph, respectively. To track changes in the filament, we utilise long-term data from the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO) and from the Global Oscillation Network Group (GONG). We analyse the longitudinal magnetic field in the photosphere using the Solar Optical Telescope on board Hinode, as well as SDO/Helioseismic and Magnetic Imager data. In addition to this, we use GONG Hα data to analyze the longitudinal oscillations in the filament. Observations show that parasitic polarities and canceling flux play a key role in forming and reorganizing the filament feet and in lengthening the filament. A 3D MHD reconstruction using vector magnetograms reveals that its magnetic configuration evolves into a full flux rope (FR), whose extension on the second day matches the observed filament growth. The FR is separated from the surrounding nearly potential field by quasi-separatrix layers, which in turn are separated by current layers. They get more organized around the FR as it grows. Moreover, the longitudinal oscillations in the extended filament are attributed to heating from flux cancellation at underlying bright points.

Keywords: Solar magnetic fields, Stellar spectral lines, Quiescent solar prominence
Identifying Compact Chirping SMBHBs in LSST Using Bayesian Analysis. The Legacy Survey of Space and Time (LSST) is expected to observe up to ∼100 million quasars in the next decade. In this work, we show that it is possible to use such data to measure the characteristic frequency evolution of a "chirp" induced by gravitational waves, which can serve as robust evidence for the presence of a compact supermassive black hole binary. Following the LSST specifications, we generate mock lightcurves consisting of (i) a post-Newtonian chirp produced by orbital motion through, e.g., relativistic Doppler boosting, (ii) a damped random walk representing intrinsic quasar variability, and (iii) Gaussian photometric errors, while assuming nonuniform observations with extended gaps over a period of 10 yr. Through a fully Bayesian analysis, we show that we can simultaneously measure the chirp and noise parameters with little degeneracy between the two. For chirp signals with an amplitude of A = 0.5 mag and a range of times to merger (tm = 15─104 yr), we can typically measure a nonzero amplitude and positive frequency derivative with over 5σ credibility. For binaries with tm = 50 yr, we achieve 3σ (5σ) confidence that the signal is chirping for A ≳ 0.1 (A &gt; 0.2). The median runtime of our analysis is 5.6 minutes, with a minimum as low as 35 s, making it scalable to a large number of lightcurves. This implies that LSST could, on its own, establish the presence of a compact supermassive black hole binary, and thus discover gravitational wave sources detectable by LISA and by Pulsar Timing Arrays.

Keywords: Supermassive black holes, Gravitational waves, Time domain astronomy, Quasars
Probing the Diversity of Type Ia Supernova Remnants in 3D Hydrodynamic Simulations with X-Ray Spectral Synthesis. Type Ia supernovae (SNe Ia), thermonuclear explosions of white dwarfs in binary systems, are widely used as standard candles owing to the empirical width─luminosity relation of their light curves. Recent theoretical and observational studies indicate a diversity of progenitor systems and explosion mechanisms. In the supernova remnant (SNR) phase, the diversity in Fe-Kα centroid energies and line luminosities suggests variations in the underlying explosion mechanisms. X-ray spectra of SNRs, which trace shocked ejecta and the surrounding medium, are crucial diagnostics of progenitor systems and explosion physics. Thanks to recent advances in spectroscopy with XRISM, high-resolution X-ray spectroscopy enables 3D diagnostics, including line-of-sight velocities. In this study, we perform 3D hydrodynamic simulations of SNRs from six Type Ia explosion models: two each of pure deflagration, delayed detonation, and double detonation. Each model is evolved for 1000 yr in a uniform medium, consistently accounting for nonequilibrium ionization. Our efficient numerical scheme enables systematic parameter surveys in full 3D. From these models, we synthesize X-ray spectra with ∼1 eV resolution, exceeding XRISM/Resolve's spectral resolution. This work presents the first calculation of X-ray spectra for Type Ia SNRs derived from 3D hydrodynamic simulations that follow the evolution self-consistently from the SN phase into the SNR phase. Our results show intermodel diversity in the X-ray spectra. Asymmetric, red- and blueshifted line profiles arise from the 3D ejecta distributions. These findings demonstrate that 3D SNR modeling can reproduce the observed diversity of Type Ia SNRs and provide qualitative constraints on progenitor systems and explosion mechanisms.

Keywords: X-ray astronomy, Hydrodynamical simulations, Supernova remnants, Type Ia supernovae, Supernovae
New Insight from the James Webb Space Telescope on Variable Active Galactic Nuclei. Variability detected in galaxies is usually attributed to their active galactic nuclei (AGNs). While all AGNs are intrinsically variable, the AGN unification model predicts that Type 2 AGNs rarely vary because their engines are blocked by dust tori. Previous UV to near-IR variability studies largely support this expectation. Here, we present a variability study with the James Webb Space Telescope (JWST) that reveals a more subtle picture. Using NIRCam imaging data from three surveys over ∼140 arcmin2 in the COSMOS field, we found 117 galaxies with ≥4σ variability in the F356W band across an ∼2 yr baseline. Crossmatching with existing JWST spectroscopic data, we identified five of them at z = 0.19─3.69 (F356W corresponding to rest-frame λ ≍ 0.76─2.97 μm), which were all coincidentally observed by an NIRSpec program almost contemporaneously with the last imaging epoch. One additional variable was identified at z = 0.90 using archival Keck telescope data. These six objects form our spectroscopic subsample. Interestingly, two reside in close-pair environments, while two others form a close pair themselves. Most of their light curves can hardly be explained by nuclear transients, and AGN variability is a more plausible cause. However, among these six objects (1) only one shows broad Bracket and Pfund series permitted lines (∆v &gt; 1000 km s−1) indicative of a Type 1 AGN; (2) two show narrow permitted lines (Hα and/or He I λ10830) consistent with Type 2 AGNs, with another one likely Type 2 based on the host galaxy properties; and (3) two others, which form a pair, show no emission lines. Our results add more challenges to the unification model.

Keywords: Active galactic nuclei
Analytic Modeling of Tidally Locked Rocky Planet Atmospheres across Dynamical Regimes. We present a new first-principles analytic approach to interpreting eclipses and phase curves of rocky planets. Observations with JWST have reported nondetections of atmospheres around the majority of hot rocky planets orbiting M dwarfs. However, most of these "bare rock" inferences are based on models that are ill-suited to many currently observable planets, as they were developed for use on cooler, slower-rotating bodies. In particular, these models rely on the weak temperature gradient assumption, in which rotation is neglected and temperature gradients can be simply related to wind speeds. We find that this assumption may not be valid for over 40% of terrestrials observed with JWST, including TRAPPIST-1 b, GJ 367 b, and TOI-2445 b. Our simple new four-box model does not rely on this assumption, and instead allows the heat transport efficiency to be specified or follow scalings derived herein. This method is fast, interpretable, physically motivated, reproduces previous general circulation model results, and can be used as a starting point for more detailed modeling. We observe that the longitudinal temperature structure of tidally locked terrestrials depends strongly on atmospheric circulation. Considering the applicable range of atmospheric dynamical regimes, we find that a given planet's nightside temperature can plausibly vary by hundreds of kelvin (from detectable to undetectable). Furthermore, a planet's dayside energy balance can display complex behavior, with degeneracies between surface pressure and dayside temperature. Illustrating an application to observations, we find that assumptions about atmospheric dynamics and longitudinal temperature structure can bias atmospheric constraints at the order-of-magnitude level.

Keywords: Exoplanet atmospheric composition , Exoplanets, Exoplanet atmospheric dynamics, Planetary climates, Exoplanet atmospheres
On the Active Sites of Mg-bearing Interstellar Dust Grains: An Experimental and Theoretical Model Study of CO<SUB>2</SUB> Activation. Magnesium silicates represent an important component of interstellar dust. While the formation of molecules in the interstellar region is typically thought to take place in icy mantles covering such dust particles, the bare uncovered grains are hardly considered as reactive or catalytically active species. To explore this aspect, we employ gas-phase magnesium oxide clusters as model systems for interstellar dust and investigate their interaction with CO2 using infrared multiple photon dissociation spectroscopy. Our results demonstrate that all studied magnesium oxide clusters (with the exception of Mg2O2,4+) do not form simple CO2 adducts but instead activate CO2 via formation of carbonate-like CO3 groups, irrespective of their charge state, size, and composition. Comparison with existing literature suggests the preferred formation of η3-bound CO3 on cationic clusters and both η3- and η2-bound CO3 groups on anionic clusters. This assignment is confirmed by density functional theory calculations for selected systems. Further structure and charge analysis identify Mg-O-Mg groups as the active sites for CO3 formation, owing to the increased Lewis basicity of the bridging oxygen atom. Given that such active sites are not unique to small magnesium oxide clusters but are also predicted to exist on the surface of magnesium silicate dust particles, our findings imply that bare silicate dust particles might be highly active species for CO2 activation. This activation, leading to an increased binding energy and consequently slower desorption rates, sets the stage for surface reactions with other molecules, suggesting a potentially more significant role of bare dust particles in interstellar chemistry.

Keywords: Interstellar dust, Silicate grains, Reaction catalysts, Very small grains, Carbon dioxide
New Observations of an Extended Hall Interaction Region Downstream of Lunar Crustal Magnetic Fields. The lunar surface exhibits small-scale crustal magnetic fields that can give rise to various interactions when subjected to the incident solar wind plasma. These lunar crustal magnetic fields exhibit scale lengths that are much smaller than the typical convected ion gyroradius within the solar wind, leading to an effective demagnetization of the ions. Thus, these lunar crustal magnetic fields provide a natural environment within which Hall electric fields and various current structures may be generated. This study reports observations from THEMIS─ARTEMIS during a periselene of 14 km to the lunar surface and examines the plasma environment within the vicinity of various crustal magnetic fields. The reported observations suggest a Hall interaction region that extends downstream of prominent regions of crustal magnetization. Within these extended interaction regions we report a Hall electric field of 2─3 mV m−1 and oriented upward and sunward, as well as a northward current carried by southward ExB drifting electrons. Lastly, Hall electric fields were observed above the lunar crustal magnetic fields oriented downward and antisunward, as well as parallel currents directed toward the lunar surface, and were consistently observed when the magnetic footpoint was within the cusp region.

Keywords: Lunar magnetic fields, Space plasmas, Solar wind, The Moon
The NANOGrav 15 yr Dataset: Improved Timing Precision with Very Long Baseline Interferometry Astrometric Priors. Accurate pulsar astrometric estimates are essential to almost all high-precision pulsar timing experiments. Traditional pulsar timing techniques refine these estimates by including them as free parameters when fitting a model to observed pulse time-of-arrival measurements. However, reliable submilliarcsecond astrometric estimations require years of observations. Even then, power from red noise can be inadvertently absorbed into astrometric parameter fits. This effect biases the resulting estimates and reduces the sensitivity to red noise processes, including gravitational waves (GWs). In this work, we seek to mitigate these shortcomings by using pulsar astrometric estimates derived from very long baseline interferometry (VLBI) as priors for the timing fit. First, we used VLBI and timing astrometric estimates of 18 millisecond pulsars to calibrate a rotation between the reference frames used in timing and VLBI, with a precision of ∼0.7 mas. Through this frame tie, we combined timing- and VLBI-based probabilities to obtain a maximum-posterior astrometric solution. We found offsets between our results and the timing-based astrometric solutions, which, if real, would lead to the absorption of spectral power at the frequencies of interest for single-source GW searches. However, we do not find significant power absorption due to astrometric fitting at the low-frequency domain of the GW background.

Keywords: Very long baseline interferometry, Astrometry, Pulsars
Unification Model of Active Galactic Nuclei by Photoionization Equilibrium Calculation Based on Radiative Hydrodynamic Simulations. To investigate the origin of the dependence of the covering factor on the Eddington ratio suggested by X-ray observations, we examined the angular distribution of H I and H II based on two-dimensional radiative hydrodynamic simulations. To calculate the Compton-thin covering factor C22 and Compton-thick covering factor C24 of H I alone, we performed one-dimensional photoionization equilibrium calculations with the XSTAR code based on radiative hydrodynamic simulations. The results obtained are as follows. (1) The Compton-thin covering factor C22 of H I and H II is independent of the Eddington ratio and is approximately 70%, while C22 of H I alone is also independent of the Eddington ratio and is approximately 30%. (2) The Compton-thick covering factor C24 of H I has the same value as C22 of H I. (3) Our C24 is consistent with that obtained from X-ray observations. (4) Our C22 agrees with that obtained from X-ray observations in a high Eddington ratio, while our C22 is smaller than that from X-ray observations in a low Eddington ratio. (5) To explain the difference between C22 obtained from theoretical calculations and that inferred from X-ray observations, a Compton-thin gas is required in regions extending at least 10 pc beyond the current computational regions.

Keywords: Supermassive black holes, Seyfert galaxies, X-ray active galactic nuclei, High energy astrophysics
The Shape-velocity Alignment of Satellites Forged by Tidal Locking and Dynamical Friction. Utilizing the TNG50 simulation, we study two types of alignments for satellites/subhalos: (1) the alignment of their major axes with the galactocentric radial directions (radial alignment), and (2) with the motion directions (orbital alignment). We find that radial alignment is substantially stronger than orbital alignment, with both signals being consistently stronger for subhalos than for satellites. Interestingly, inward- and outward-moving satellites/subhalos show contrasting orbital alignment behaviors, which can be understood in terms of their radial alignment, orbit decay due to dynamical friction, and the effect of tidal stripping. The orbital alignment is stronger in more-massive halos. In the end, we explore the orbital alignment measured by a mock observer, and find that the observed alignment for Milky Way satellites is due to projection effects, as the major axes of satellites lie within their orbital planes, approximately coplanar with the observer.

Keywords: Hydrodynamical simulations, Galaxy kinematics
Eclipsed X-Ray Bursts from Magnetar SGR J1935+2154 and the Fireball Measurements. In theory, burst activity of the magnetar can lead to the formation of fireballs trapped by the magnetic field and corotating with the star. However, smoking-gun observational evidence of the fireball is elusive. We envisage that the fireball emission should occasionally be eclipsed by the magnetar, especially when the burst duration is comparable to the magnetar's spin period. In this work, we first discover a peculiar type of burst whose light curve has a plateau-like feature among the long bursts of the magnetar SGR J1935+2154 detected by GECAM and Fermi/Gamma-ray Burst Monitor. Then, based on these bursts, we identified four burst candidates with eclipse-like characteristics. By fitting their light curves with the eclipse fireball model, the viewing angle of the magnetar relative to its spin axis is estimated to be 17° ± 10°, and the distances from the fireballs to the magnetar are found to be more than 5 times the magnetar's radius, indicating that the fireballs are suspended in the magnetosphere rather than adhering to the magnetar surface. Furthermore, we find that this configuration is well consistent with the implication of the cyclotron resonance scattering feature we found in their spectra. Our results suggest that some intermediate X-ray bursts may originate from magnetic reconnection within the magnetosphere rather than the starquake.

Keywords: Magnetars, Soft gamma-ray repeaters, Astronomy data analysis