Sazuna/UAT_keywords huggingface dataset:
An Eccentric Planet Orbiting the Polar V808 Aurigae. We analyze 15 yr of eclipse timings of the polar V808 Aur. The rapid ingress/egress of the white dwarf and bright accretion region provide timings as precise as a few tenths of a second for rapid cadence photometric data. We find that between 2015 and 2018, the eclipse timings deviated from a linear ephemeris by more than 30 s. The rapid timing change is consistent with the periastron passage of a planet in an eccentric orbit about the polar. The best-fit orbital period is 11 ± 1 yr and we estimate a projected mass of $M\sin (i)=6.8\pm 0.7$ Jupiter masses. We also show that the eclipse timings are correlated with the brightness of the polar with a slope of 1.1 s mag‑1. This is likely due to the change in the geometry of the accretion curtains as a function of the mass transfer rate in the polar. While an eccentric planet offers an excellent explanation to the available eclipse data for V808 Aur, proposed planetary systems in other eclipsing polars have often struggled to accurately predict future eclipse timings.

Keywords: Stellar magnetic fields, Exoplanet detection methods, Cataclysmic variable stars, AM Herculis stars, Eclipsing binary minima timing method
The Lorentz Force at Work: Multiphase Magnetohydrodynamics throughout a Flare Lifespan. The hour-long, gradual phase of solar flares is well observed across the electromagnetic spectrum, demonstrating many multiphase aspects, where cold condensations form within the heated post-flare system, but a complete 3D model is lacking. Using a state-of-the-art 3D magnetohydrodynamic simulation, we identify the key role played by the Lorentz force through the entire flare lifespan, and show that slow variations in the post-flare magnetic field achieve the bulk of the energy release. Synthetic images in multiple passbands closely match flare observations, and we quantify the role of conductive, radiative, and Lorentz force work contributions from flare onset to decay. This highlights how the non-force-free nature of the magnetic topology is crucial to trigger Rayleigh–Taylor dynamics, observed as waving coronal rays in extreme ultraviolet observations. Our C-class solar flare reproduces multiphase aspects such as post-flare coronal rain. In agreement with observations, we find strands of cooler plasma forming spontaneously by catastrophic cooling, leading to cool plasma draining down the post-flare loops. As there is force balance between magnetic pressure and tension and the plasma pressure in gradual-phase flare loops, this has potential for coronal seismology to decipher the magnetic field strength variation from observations.

Keywords: Solar physics, Solar flares, Magnetohydrodynamics
Spectroscopic Constraints on the Mid-infrared Attenuation Curve. I. Attenuation Model Using Polycyclic Aromatic Hydrocarbon Emission. We introduce a novel model to spectroscopically constrain the mid-infrared (MIR) extinction/attenuation curve from 3–17 μm, using polycyclic aromatic hydrocarbon (PAH) emission drawn from an AKARI–Spitzer extragalactic cross-archival data set. Currently proposed MIR extinction curves vary significantly in their slopes toward the near-infrared, and the variation in the strengths and shapes of the 9.7 μm and 18 μm silicate absorption features make MIR spectral modeling and interpretation challenging, particularly for heavily obscured galaxies. By adopting the basic premise that PAH bands have relatively consistent intrinsic ratios within dusty starbursting galaxies, we can, for the first time, empirically determine the overall shape of the MIR attenuation curve by measuring the differential attenuation at specific PAH wavelengths. Our attenuation model shows PAH emission in most (ultra)luminous infrared galaxies is unambiguously subjected to attenuation, and we find strong evidence that PAH bands undergo differential attenuation as obscuration increases. Compared to preexisting results, the MIR attenuation curve derived from the model favors relatively gray continuum absorption from 3–8 μm and silicate features with intermediate strength at 9.7 μm but with stronger than typical 18 μm opacity.

Keywords: Starburst galaxies, Polycyclic aromatic hydrocarbons, Interstellar dust extinction, Ultraluminous infrared galaxies, Luminous infrared galaxies
Dependence of Lunar Pickup Ion Flux on Source Location: ARTEMIS Observations. The Moon is enveloped in an exosphere, which is comprised of a variety of neutral atoms and molecules. Once exospheric neutrals are ionized by photons, protons, or electrons from the Sun, the resulting ions are accelerated by the electromagnetic fields of their surroundings and can thereby travel away from their source locations. These ions are the so-called pickup ions and are frequently observed by the two Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. In this study, we identify 115 events from an 11 yr period of ARTEMIS observations, which contain a total of 11,987 samples for our statistics. By using analytical ion trajectory calculations, we trace the source location of each pickup ion observation. Most pickup ion trajectories originate near the subsolar point, consistent with the efficiency of sputtering. We find that the flux of pickup ions strongly anticorrelates with the source altitude, providing indirect evidence of decreasing exospheric ion flux with increasing altitude. We also find that the flux of pickup ions does not show a significant relationship with the crustal magnetic field intensity. This implies that a depression of sputtering efficiency or the trapping of near-surface freshly born ions by a crustal magnetic anomaly may not reduce the subsequent pickup ion flux as effectively as expected. In summary, the present paper provides a statistical view of lunar pickup ion fluxes in association with the altitude, local time, and local crustal magnetic field of their source locations.

Keywords: Solar wind, The Moon, Space plasmas, Lunar science
Joint r-process Enrichment by Supernovae with a Metallicity Threshold and Neutron Star Mergers. The enrichment history of r-process elements has been imprinted on the stellar abundances that change in accordance with increasing metallicity in galaxies. Close examination of the [Eu/Fe] feature caused by stars in nearby galaxies, including the Large Magellanic Cloud (LMC), shows its perplexity. The decreasing trend of the [Eu/Fe] feature is followed by a nearly constant value; this trend is generally attributed to an onset of the delayed Fe release from Type Ia supernovae (SNe Ia), which is the same interpretation of the [α/Fe] feature. However, this feature appears in the LMC at [Fe/H] of approximately ‑0.7, which is significantly higher than that for the [α/Fe] case (≈‑2). This result potentially indicates the presence of an overlooked property of the r-process site that remains unseen in the study of the Milky Way. Here, we propose that this [Eu/Fe]-knee feature is created by a fade-out of core-collapse SNe producing r-process elements; these elements along with neutron star mergers (NSMs) promote the r-process enrichment under the condition for this specific SNe such that their occurrence is limited to a low-metallicity environment. This metallicity threshold for the occurrence rate of r-process SNe at a subsolar is nearly identical to that for long gamma-ray bursts whose origin may be connected to fast-rotating massive stars. Moreover, we reason that the contribution of Eu from NSMs is crucial to maintain a high [Eu/Fe] at an early stage in dwarf galaxies by a balance with Fe from SNe Ia; both enrichments via NSMs and SNe Ia proceed with similar delay time distributions.

Keywords: Galaxy chemical evolution, Core-collapse supernovae, Stellar abundances, Galactic archaeology, R-process, Large Magellanic Cloud
Dynamics of Star Cluster Formation: Mergers in Gas-rich Environments. We perform high-resolution simulations of forming star clusters as they merge inside giant molecular clouds (GMCs) using hydrodynamics coupled to N-body dynamics to simultaneously model both the gas and stars. We zoom in to previously run GMC simulations and resolve clusters into their stellar and gas components while including the surrounding GMC environment. We find that GMC gas is important in facilitating the growth of clusters in their embedded phase by promoting cluster mergers. Mergers induce asymmetric expansion of the stellar component of the clusters in our simulations. As well, mergers induce angular momentum in the clusters' stellar and gas components. We find that mergers can lead to an increase in the amount of dense gas present in clusters if a background gas distribution is present. We predict that this can lead to new star formation that can change the overall distribution of cluster stars in velocity space. Our results suggest that subcluster mergers in the presence of background gas can imprint dynamical signatures that can be used to constrain cluster formation histories.

Keywords: Stellar kinematics, Star formation, Stellar dynamics, Star clusters
Tackling the Challenges in the 21 cm Global Spectrum Experiment: The Impact of Ionosphere and Beam Distortion. The H I 21 cm global signal from the Cosmic Dawn and the Epoch of Reionization (EoR) offers critical insights into the evolution of our Universe. Yet, its detection presents significant challenges, due to its extremely low signal-to-contamination ratio and complex instrumental systematics. In this paper, we examine the effects of the ionosphere and antenna beam on data analysis. The ionosphere, an ionized plasma layer in the Earth's atmosphere, refracts, absorbs, and emits radio waves in the relevant frequency range. This interaction results in additional spectral distortion of the observed signal, complicating the process of foreground subtraction. Additionally, chromatic variations in the beam can also introduce further contamination into the global spectrum measurement. Notably, the ionospheric effect, being dependent on the direction of incoming light, interacts with the instrumental beam, adding another layer of complexity. To address this, we evaluate three different fitting templates of foreground: the logarithmic polynomial, the physically motivated Experiment to Detect the Global EoR Signature (EDGES) template, and a singular value decomposition (SVD)-based template. Our findings indicate that the EDGES and SVD templates generally surpass logarithmic polynomials in performance. Recognizing the significance of beam chromaticity, we further investigate specific beam distortion models and their impacts on the signal extraction process.

Keywords: Cosmology, Reionization, Earth ionosphere
The Population of Massive Stars in Active Galactic Nuclei Disks. Gravitational instability in the outskirts of active galactic nuclei (AGN) disks leads to disk fragmentation and formation of ∼300 M ⊙ supermassive stars with potentially long lifetimes. Alternatively, stars can be captured ex situ and grow from gas accretion in the AGN disk. However, the number density distribution throughout the disk is limited by thermal feedback as their luminosities provide the dominant heating source. We derive equilibrium stellar surface density profiles under two limiting contexts: in the case where the stellar lifetimes are prolonged, due to the recycling of hydrogen-rich disk gas, only the fraction of gas converted into heat is removed from the disk accretion flow. Alternatively, if stellar composition recycling is inefficient and stars can evolve off the main sequence, the disk accretion rate is quenched toward smaller radii resembling a classical starburst disk, albeit the effective removal rate depends not only on the stellar lifetime, but also the mass of stellar remnants. For AGNs with central supermassive black hole masses of ∼106–108 M ⊙ accreting at ∼0.1 Eddington efficiency, we estimate a total number of 103–105 massive stars and the rate of stellar mergers to be 10‑3 to 1 yr‑1. We initiate the detailed study of the interaction between a swarm of massive stars through hydro and N-body simulations to provide better prescriptions of dynamical processes in AGN disks, and to constrain more accurate estimates of the stellar population.

Keywords: Stellar mergers, Massive stars, Galaxy accretion disks, Active galactic nuclei, Stellar evolution
Charting the Galactic Acceleration Field. II. A Global Mass Model of the Milky Way from the STREAMFINDER Atlas of Stellar Streams Detected in Gaia DR3. We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to −β  h  = −3 yield an inner power-law slope of $-{\gamma }_{h}=-({0.97}_{-0.21}^{+0.17}\,)$ , a scale radius of ${r}_{0,h}={14.7}_{-1.0}^{+4.7}\,\mathrm{kpc}$ , a halo density flattening q  m,h  = 0.75 ± 0.03, and a local dark matter density of ρ  h,☉ = 0.0114 ± 0.0007 M ☉ pc−3. Freeing β yields $\beta ={2.53}_{-0.16}^{+0.42}$ , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of ${4.20}_{-0.53}^{+0.44}\times {10}^{10}\,{M}_{\odot }$ , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are ${2.17}_{-0.08}^{+0.18}$ and ${1.62}_{-0.13}^{+0.72}\,\mathrm{kpc}$ , respectively, while their scale heights are ${0.347}_{-0.010}^{+0.007}$ and ${0.86}_{-0.02}^{+0.03}\,\mathrm{kpc}$ , respectively. The virial mass of the favored model is ${M}_{200}={1.09}_{-0.14}^{+0.19}\times {10}^{12}\,{M}_{\odot }$ , while the mass inside of 50 kpc is M  R&lt;50 = 0.46 ± 0.03 × 1012 M ☉. We introduce the Large Magellanic Cloud (LMC) into the derived potential models, and fit the Orphan stream therein, finding a mass for the LMC that is consistent with recent estimates. Some salient highlights include the nearby trailing arm of ω Cen, and a nearby very metal-poor stream that was once a satellite of the Sagittarius dwarf galaxy. Finally, we unambiguously detect a hot component around the GD-1 stream, consistent with it having been tidally preprocessed within its own dark matter subhalo.

Keywords: Galaxy structure, Dark matter, Stellar streams
Effects of Earth's Oblateness on Black Hole Imaging through Earth–Space and Space–Space Very Long Baseline Interferometry. Earth-based very long baseline interferometry (VLBI) has made rapid advances in imaging black holes. However, due to the limitations imposed on terrestrial VLBI by the Earth's finite size and turbulent atmosphere, it is imperative to have a space-based component in future VLBI missions. This paper investigates the effect of the Earth's oblateness, also known as the J 2 effect, on orbiters in Earth–space and space–space VLBI. The paper provides an extensive discussion on how the J 2 effect can directly impact orbit selection for black hole observations and how, through informed choices of orbital parameters, the effect can be used to a mission's advantage, a fact that has not been addressed in previous space VLBI investigations. We provide a comprehensive study of how the orbital parameters of several current space VLBI proposals will vary specifically due to the J 2 effect. For black hole accretion flow targets of interest, we demonstrate how the J 2 effect leads to a modest increase in shorter-baseline coverage, filling gaps in the (u, v) plane. Subsequently, we construct a simple analytical formalism that allows isolation of the impact of the J 2 effect on the (u, v) plane without requiring computationally intensive orbit propagation simulations. By directly constructing (u, v) coverage using J 2-affected and J 2-invariant equations of motion, we obtain distinct coverage patterns for M87* and Sgr A* that show extremely dense coverage on short baselines as well as long-term orbital stability on longer baselines.

Keywords: Artificial satellites, Very long baseline interferometry, Astrophysical black holes, Space observatories
Measurement of Interstellar Magnetization by Synchrotron Polarization Variance. Since synchrotron polarization fluctuations are related to the fundamental properties of the magnetic field, we propose the polarization intensity variance to measure the Galactic interstellar medium (ISM) magnetization. We confirm the method's applicability by comparing it with the polarization angle dispersion and its reliability by measuring the underlying Alfvénic Mach number of magnetohydrodynamic turbulence. With the finding of the power-law relation of ${ \mathcal A }\propto {M}_{{\rm{A}}}^{2}$ between polarization intensity variance ${ \mathcal A }$ and Alfvénic Mach number M A, we apply the new technique to the Canadian Galactic Plane Survey data, achieving the Alfvénic Mach number of the Galactic ISM. Our results show that the low-latitude Galactic ISM is dominated by sub-Alfénic turbulence, with M A approximately between 0.5 and 1.0.

Keywords: Interplanetary turbulence, Interstellar emissions, Radiative magnetohydrodynamics, Interstellar medium
Sp1149. II. Spectroscopy of H II Regions near the Critical Curve of MACS J1149 and Cluster Lens Models. Galaxy-cluster gravitational lenses enable the study of faint galaxies even at large lookback times, and, recently, time-delay constraints on the Hubble constant. There have been few tests, however, of lens model predictions adjacent to the critical curve (≲8″) where the magnification is greatest. In a companion paper, we use the GLAFIC lens model to constrain the Balmer L─σ relation for H II regions in a galaxy at redshift z = 1.49 strongly lensed by the MACS J1149 galaxy cluster. Here we perform a detailed comparison between the predictions of 10 cluster lens models that employ multiple modeling assumptions with our measurements of 11 magnified, giant H II regions. We find that that the models predict magnifications an average factor of 6.2 smaller, a ∼2σ tension, than that inferred from the H II regions under the assumption that they follow the low-redshift L─σ relation. To evaluate the possibility that the lens model magnifications are strongly biased, we next consider the flux ratios among knots in three images of Sp1149, and find that these are consistent with model predictions. Moreover, while the mass-sheet degeneracy could in principle account for a factor of ∼6 discrepancy in magnification, the value of H 0 inferred from SN Refsdal's time delay would become implausibly small. We conclude that the lens models are not likely to be highly biased, and that instead the H II regions in Sp1149 are substantially more luminous than the low-redshift Balmer L─σ relation predicts.

Keywords: Galaxy clusters, Strong gravitational lensing, Gravitational lensing, Galaxy spectroscopy, H II regions, High-redshift galaxies, Galaxies
Revisiting High-energy Polarization from Leptonic and Hadronic Blazar Scenarios. X-ray and MeV polarization can be powerful diagnostics for leptonic and hadronic blazar models. Previous predictions are mostly based on a one-zone framework. However, recent IXPE observations of Mrk 421 and 501 strongly favor a multizone framework. Thus, the leptonic and hadronic polarization predictions need to be revisited. Here we identify two generic radiation transfer effects, namely, double depolarization and energy stratification, that can have an impact on the leptonic and hadronic polarization. We show how they are generalized from previously known multizone effects of the primary electron synchrotron radiation. Under our generic multizone model, the leptonic polarization degree is expected to be much lower than the one-zone prediction, unlikely detectable in most cases. The hadronic polarization degree can reach a value as high as the primary electron synchrotron polarization during simultaneous multiwavelength flares, consistent with the one-zone prediction. Therefore, IXPE and future X-ray and MeV polarimeters such as eXTP, COSI, and AMEGO-X, have good chances to detect hadronic polarization during flares. However, the hadronic polarization cannot be well constrained during the quiescent state. Nonetheless, if some blazar jets possess relatively stable large-scale magnetic structures, as suggested by radio observations, a nontrivial polarization degree may show up for the hadronic model after a very long exposure time (≳1 yr).

Keywords: Blazars, Relativistic jets, Polarimetry, High energy astrophysics
The Deeper Studies of IC 2488 and IC 2714. In this paper, we use two methods, an algorithm of the density-based spatial clustering of applications with noise combined with the Gaussian mixture model, and the maximum likelihood method, to study two open clusters: IC 2488 and IC 2714 with Gaia Data Release 3 data. We compare the two methods in terms of cluster star number, isochrone fitting, cluster mass, and radius. The comparison shows that the selections of cluster stars by the two methods are consistent. The parameters obtained by the two methods are very close. But there are slight differences between the two methods for faint stars in IC 2714. The maximum likelihood method selects more faint stars outside of the main-sequence stripe. We conclude that the maximum likelihood method is more likely affected by field stars.

Keywords: Open star clusters, Clustering
Reduced Water Loss due to Photochemistry on Terrestrial Planets in the Runaway Greenhouse Phase around Pre-main-sequence M Dwarfs. Terrestrial planets currently in the habitable zone around M dwarfs are estimated to have been in runaway greenhouse conditions for up to ∼1 Gyr due to the long-term pre-main-sequence phase of M dwarfs. These planets likely lose a significant portion of water during the pre-main-sequence phase owing to H2O photolysis followed by hydrogen and oxygen loss to space. However, the effects of H2O reproduction reactions and UV shielding by chemical products that reduce photolysis-induced water loss have yet to be estimated. Here, we apply a 1D photochemical model to a H2O-dominated atmosphere of an Earth-like planet around a pre-main-sequence M dwarf to estimate these effects. We find that water loss is suppressed by efficient H2O reproduction reactions and by UV shielding due to O2. The water loss rate decreases by several to several hundred times compared to that in previous studies, with the assumption that the water loss rate is limited by stellar X-ray and extreme-ultraviolet flux or hydrogen diffusion through the atmosphere. Our results imply that terrestrial planets currently in the habitable zone around M dwarfs are more likely to retain surface water than previously estimated.

Keywords: M dwarf stars, Atmospheric evolution, Water vapor, Planetary atmospheres, Exoplanet evolution, Astrobiology, Planetary science, Solar-terrestrial interactions, Habitable planets, Exoplanet atmospheres, Exoplanet atmospheric evolution