Sazuna/UAT_keywords huggingface dataset:
A Novel Approach to Identifying Substructures through Analysis of Metallicity Distribution Functions. We present a new method for identifying Galactic halo substructures accreted from dwarf galaxies by combining metallicity distribution functions (MDFs) with orbital parameters. Using apogalactic distance─orbital phase space, we assume that the MDF peak of a substructure reflects its progenitor's chemical signature. We test this approach with two Galactic potentials (St ä ckel and McMillan) and find consistent results. Our sample consists of retrograde halo stars with low orbital inclinations and intermediate eccentricities (0.5 &lt; e ≤ 0.7), drawn from Sloan Digital Sky Survey and Large sky Area Multi-Object Fiber Spectroscopic Telescope spectroscopy combined with Gaia DR3 astrometry. We identify four distinct low-inclination retrograde substructures (LRS 1, LRS 2, LRS 3, LRS 4) with MDF peaks at [Fe/H] = −1.5, −1.7, −1.9, and −2.1, respectively; LRS 3 is newly discovered. Further analysis reveals an additional stream (LRS 2B) with [Fe/H] = −2.3 embedded within LRS 2; the remaining LRS 2 stars (LRS 2A) are associated with Sequoia. LRS 1 is likely linked to Thamnos 2 and Arjuna, and LRS 4 is likely linked to I'itoi. Comparison with the ED-2 stream suggests that LRS 2B is chemically distinct, but high-resolution spectroscopy is required to confirm whether they originate from separate progenitors. Our MDF-based approach demonstrates the utility of chemodynamical space for uncovering halo substructures, while highlighting caveats such as metallicity gradients and redshift evolution of the mass─metallicity relation, which may blur the mapping between MDF peaks and progenitors.

Keywords: Stellar kinematics, Stellar abundances, Stellar populations, Surveys, Stellar dynamics, Milky Way stellar halo, Milky Way Galaxy
Active Galactic Nucleus Star Dynamics Under the Influence of Outflow–Ambient Interactions. Stars with outflows interacting with ambient gas experience accelerations arising from the gravitational feedback induced by the interaction structure. In this work, three-dimensional local shearing box simulations are performed to investigate the dynamical evolution of a star with outflows embedded in the outer regions of an active galactic nucleus (AGN) disk. Two types of stellar wind are considered, isotropic winds and axisymmetric jets, along with variations in the radial pressure gradient profile. The results show that antifriction enables AGN stars to acquire angular momentum from the ambient gas, resulting in outward migration away from the disk center. The formation and stability of the headwind structure, which is crucial for maintaining antifriction, are sensitive to both the strength of the stellar outflow and the radial pressure gradient of the disk gas. Once the headwind structure is disrupted, the antifriction effect ceases to operate effectively. A case study is also presented, focusing on a stellar-mass black hole (sBH) in an AGN disk. It is shown that jet material launched along the z-axis is confined to the trailing side of the object's motion by high gas inflow velocities, thereby activating antifriction and inducing outward migration. If such an sBH migrates inward initially, the interplay between inward and outward migration may trap it at an equilibrium radius, potentially facilitating the formation and merger of black hole binaries.

Keywords: Stellar dynamics, Stellar mass black holes, Stellar mass loss, Stellar winds, Active galactic nuclei, Dynamical friction
A Tale of Two Sightlines: Comparison of Hydrocarbon Dust Absorption Bands toward Cygnus OB2-12 and the Galactic Center. Infrared spectra of hydrocarbon dust absorption bands toward the bright hypergiant Cygnus OB2-12 are compared to published spectra of the Quintuplet Cluster, a sightline to the Galactic center. The Cyg OB2-12 data include a new ground-based 2.86‑3.70 μm spectrum and a previously published, but here further analyzed, spectrum of the 5.50–7.34 μm region. Higher-spectral-resolution data for the Cyg OB2-12 sightline in the 3 μm region allows a detailed comparison of the 3.4 μm aliphatic bands to those observed toward the Quintuplet. Despite differences in interstellar environments along each sightline, strong similarities are observed in the central wavelengths and relative strengths for bands at ∼3.3, 3.4, 5.85, 6.2, and 6.85 μm. Analysis of these bands, produced by aromatic, aliphatic, olefinic, hydrogenated, and oxygenated components, shows that carbonaceous dust is a significant component of the diffuse interstellar medium (ISM), second in abundance only to silicates, and is primarily aromatic in nature. The grains producing these bands likely consist of large aromatic carbon cores with thin aliphatic mantles composed of hydrogenated amorphous carbon. Laboratory analog spectra reproduce the observed aliphatic absorption bands well, supporting the presence of such mantles. We present evidence that the carriers of both the 3.4 μm aliphatic and the 3.3 μm aromatic bands reside exclusively in the diffuse ISM, and that the 3.3 μm bands observed in the diffuse ISM differ from the 3.25 μm band seen in dense clouds, implying chemically distinct carriers.

Keywords: Interstellar dust processes
SN 2019tsf: Evidence for Extended Hydrogen-poor CSM in the Three-peaked Light Curve of Stripped Envelope of a Type Ib Supernova. We present multiband ATLAS and ZTF photometry for SN 2019tsf, a Type Ib stripped-envelope supernova (SESN). The slow spectral evolution could be associated with an uncommon explosion mechanism specific to this SN. Possible explanations include fallback accretion onto a compact remnant or a long-lived central engine, both of which could provide extended energy injection responsible for the late-time rebrightening and unusual spectral features. The rebrightening observations represent the latest photometric measurements of a multipeaked Type Ib SN. As late-time photometry and spectroscopy suggest no hydrogen, the potential circumstellar material (CSM) must be H-poor. The absence of a nebular phase and the lack of narrow emission lines in the late-time spectra (&gt;142 days) of the SNe suggest that any CSM interaction is likely asymmetric and enveloped by the SN ejecta. However, an extended CSM structure is evident through a follow-up radio campaign with the Karl G. Jansky Very Large Array (VLA), indicating a source of bright optically thick radio emission at late times, which is highly unusual among H-poor SESNe. We attribute this phenomenology to an interaction of the supernova ejecta with asymmetric CSM, potentially disk-like, and we present several models that may explain the origin of this rare Type Ib supernova. We propose a warped disk model in which a tertiary companion—commonly present around massive stars—perturbs the progenitor's CSM, producing density enhancements that may explain the observed multipeaked SN 2019tsf light curve. This SN 2019tsf is a unique SN Type Ib among the recently discovered class of SNe that undergo mass transfer at the moment of explosion.

Keywords: Magnetars, Type Ib supernovae
Diffusion of Relativistic Charged Particles and Field Lines in Isotropic Turbulence. I. Numerical Simulations. The transport of nonthermal particles across a large-scale magnetic field in the presence of magnetized turbulence has been a long-standing issue in high-energy astrophysics. Of particular interest is the dependence of the parallel and perpendicular mean free paths λ∥and λ⊥on rigidity  R . We have revisited this important issue with a view to applications from the transport of Galactic cosmic rays (CRs) to acceleration at astrophysical shocks. We have run test particle simulations of CR transport in synthetic, isotropic Kolmogorov turbulence at unprecedentedly low reduced rigidities of rg/Lc ≃ 10‑4, corresponding to  R≃10TV  for a turbulent magnetic field of Brms = 4 μG and correlation length of Lc = 30 pc. Extracting the (asymptotic) parallel and perpendicular mean free paths λ∥and λ⊥, we have found  λ∥∝(rg/Lc)1/3  as expected for a Kolmogorov turbulence spectrum. In contrast, λ⊥has a faster dependence on rg/Lc for 10‑2 ≲ rg/Lc ≲ 1, but for rg/Lc ≪ 10‑2,  λ⊥∝(rg/Lc)1/3 . Our results have important implications for the transport of Galactic CRs.

Keywords: Milky Way magnetic fields, Interstellar plasma, Galactic cosmic rays, Magnetic fields, Cosmic rays
Diffusion of Relativistic Charged Particles and Field Lines in Isotropic Turbulence. II. Analytical Models. The transport of high-energy particles in the presence of small-scale, turbulent magnetic fields is a long-standing issue in astrophysics. Analytical theories on transport perpendicular to the large-scale magnetic field disagree with numerical simulations at rigidities where the particles' gyroradii are slightly smaller than the correlation length of turbulence. At the same time, extending the numerical simulations to lower rigidities has proven computationally prohibitive. We present an analytical model for the perpendicular transport, based on (1) initial particle transport along field lines, (2) the transport of field lines, and (3) the eventual decorrelation of particles from field lines. Transport parallel to the large-scale field is governed by pitch-angle scattering, and so for times larger than the inverse pitch-angle diffusion coefficient, particles spatially diffuse in the parallel direction. Our results suggest that perpendicular diffusion occurs when particles have displaced in the perpendicular direction by a few correlation lengths of turbulence. We have tested the analytical theory by running a large suite of test particle simulations at unprecedentedly low rigidities, making extensive use of graphical processing units. Our numerical results exhibit a nonstandard rigidity dependence for the perpendicular diffusion coefficient at intermediate rigidities. At the lowest rigidities, the standard rigidity dependence is recovered. The simulated diffusion coefficients are nicely reproduced by our analytical model. We have traced the nonstandard rigidity dependence to a subdiffusive phase in the field line transport. Our study confirms our understanding of the escape of cosmic rays from the Galactic halo and its rigidity dependence. It also rejects speculations about different rigidity dependencies of the parallel and perpendicular diffusion coefficients at very low rigidities that were invoked to explain nonstandard gamma-ray spectra from the Galactic center. Other possible applications concern particle acceleration at perpendicular shocks.

Keywords: Milky Way magnetic fields, Interstellar plasma, Galactic cosmic rays, Magnetic fields, Cosmic rays
Chondrule Dust Rim Growth: Influence of Restructuring Using Molecular Dynamics Simulations. We investigate the influence of disruptive collisions on chondrule rim growth, emphasizing the role of kinetic energy in determining the outcomes of these interactions. We establish a threshold of approximately 10 cm s‑1 for the "hit-and-stick" collision regime, beyond which significant changes occur in the structure of rimmed chondrules. Our findings highlight that at low collision energies (KE &lt; 10‑12 J), minimal structural alteration takes place, while higher energies (KE up to 10‑10 J) lead to compaction of the rim, reducing both its thickness and porosity. Collisions with energies exceeding 10‑8 J result in the complete disruption of the rim, with particles being expelled from it. These results are correlated with the turbulence levels within the disk, as kinetic energy scales with the relative velocities of colliding particles. Leveraging machine learning models trained on our collision data, we predict changes in rim characteristics and employ these predictions in a Monte Carlo simulation to explore rim growth dynamics. Our simulations reveal that rim development is sustained in low-turbulence environments (α ≤ 10‑5), while intermediate turbulence levels (α = 10‑3–10‑4) lead to erosion, preventing further rim accumulation in high-turbulence contexts.

Keywords: Planetary system formation, Chondrules
Stars Born in the Wind: M82's Outflow and Halo Star Formation. Starburst galaxies, such as M82, launch kiloparsec-scale galactic outflows that interact with the circumgalactic medium (CGM) in complex ways. Apart from enriching the CGM with metals and energy, these outflows may trigger star formation in the halo—either by driving shocks into the CGM or transporting cold, star-forming gas. To investigate such processes, we analyze the star formation history (SFH) of the Southern Arcs—arc-like stellar features located ∼5 kpc from M82's star-forming disk along the minor axis—using Hubble Space Telescope Wide Field Camera 3 photometry. From resolved stellar populations, we derive SFHs over the last ∼500 Myr, finding that ∼85% of the stellar mass formed between ∼150 and ∼70 Myr ago, followed by a brief pause, with the remaining ∼15% forming since ∼30 Myr ago. The two stellar populations are cospatial on scales of at least ∼200 pc. The timing of the ∼100 Myr burst aligns with star formation in the M82 disk and the age distribution of its star clusters, suggesting a causal link between the disk starburst and halo star formation. We explore two mechanisms that could explain these observations. In the first, shocks driven by the interaction between hot outflowing gas and cooler CGM material compress dense clouds, triggering collapse and star formation. In the second, stars form directly within massive, cool clouds associated with the outflow. As these clouds move ballistically through the halo, subsequent interactions with tidal debris may trigger additional star formation, producing the observed episodic structure.

Keywords: Star formation, Starburst galaxies, Galaxy winds, Circumgalactic medium
Three-dimensional Polarimetric Structure of Jets from Radio Galaxy MRC 0600─399 in A3376. MRC 0600─399, in the merging galaxy cluster A3376, is one of the unique head─tail radio galaxies that have abruptly bending structures, the origin of which is still under discussion. A previous study suggested that the interaction between the jets and the magnetic fields on the cold front has produced such an outstanding feature; however, it is still not known how the jet propagates such a long distance while keeping its sharp shape. In this study, we performed a polarization analysis of MRC 0600─399 and a nearby radio source using MeerKAT L-band data. To interpret the Faraday structure, we constructed a pseudo-3D visualization map of the reconstructed 3D cube of the Faraday dispersion function. MRC 0600─399 has a complicated Faraday depth structure, and some of the Faraday depth features are in good agreement with the 2D structure on the celestial sphere. For the northern jet of MRC 0600─399, the Faraday depth values show a clear gap at the tip region. Based on the polarization analysis and comparison with other observations, we concluded that the synchrotron radiation from the tip region of the northern jet originates from the magnetic field on the cold front.

Keywords: Relativistic jets, Radio galaxies, Tailed radio galaxies, Radio continuum emission, Radio interferometry, Polarimetry, Extragalactic magnetic fields
High-resolution Simulations of the Interaction between the Nova/Supernova Ejecta and the Accretion Disk. Many nova and Type Ia supernova (SN Ia) explosion scenarios involve accretion disks. However, direct numerical simulations of these explosive phenomena have barely addressed the question of the impact of ejecta‑disk collision on the midterm evolution of such explosions. This is particularly critical for a better understanding of classical and recurrent novae, where each nova cycle depends on the imprint left by the precedent explosion. In this work, we describe and analyze a set of high-resolution simulations of the ejecta‑disk interaction. We show that, depending on the initial configuration of the binary system, the disk is partially or, more often, totally destroyed, which will impact the next nova explosion cycle. In the case of SNe Ia, the much larger kinetic energy carried by the ejecta always provokes complete destruction of the accretion disk. We also discuss the alterations induced in the geometry of the ejecta by the shielding effect of the disk, which has been shown to cause reduced contamination of the companion star up to a factor ∼1.5–2 in key nuclei produced during the nova outburst. In the framework of recurrent nova simulations, we report for the first time on the formation of a cavity in the ejecta after its interaction with the disk. We also describe the onset and development of several hydrodynamic instabilities such as Kelvin–Helmholtz and Richtmyer–Meshkov.

Keywords: Hydrodynamical simulations, Hydrodynamics, Type Ia supernovae, Recurrent novae, Stellar accretion disks, Classical novae
Massive Double White Dwarf Binary Mergers from the Moon: Extending the Reach of Multimessenger Astrophysics. We explore the potential of lunar-based gravitational-wave detectors to broaden the multimessenger astrophysics landscape by detecting mergers of massive (M1, M2 &gt; 1M⊙) double white dwarf (WD) binaries. These systems are potential progenitors of Type Ia supernovae and could serve as independent probes of cosmic expansion. We examine two proposed lunar gravitational-wave detector concepts operating in the subhertz band (0.1─1 Hz): the Gravitational-Wave Lunar Observatory for Cosmology (a proxy for suspended test mass detectors) and the Lunar Gravitational-Wave Antenna (a proxy for seismic array detectors). We estimate that these detectors could reach distances of up to ∼1 Gpc for the most massive mergers. We show that lunar detectors could observe up to dozens of massive WD mergers annually, including those originating from globular clusters. Lunar detectors would constrain the masses of these WDs with an unprecedented accuracy of one part in a million. Furthermore, these detectors would provide early warnings weeks before mergers, including sky-localization of square arcminute resolution, enabling a new era of coordinated multimessenger follow-up of electromagnetic transients—whether they evolve into Type Ia supernovae or accretion-induced collapse events.

Keywords: Gravitational wave detectors, White dwarf stars, Gravitational wave sources, Type Ia supernovae, Gravitational waves
A Galactic Interloper: A Study of the Camelopardis OB1 Association's Clusters and Its Visitor from the Perseus Arm. Within the molecular clouds of the Camelopardis OB1 (Cam OB1) association exists a region previously noted as one subgroup. However, bulk clustering from Gaia astrometry has recently shown three distinctive kinematically coherent groups, all found in a similar location in the sky (137 ⪅ l ⪅ 145 and ‑2 ⪅ b ⪅ 5) and at a similar distance (∼1 kpc). In this work, we derive from first principles the three proposed clusters in this region, refine the membership list and cluster ages, and, for the first time, examine the 3D structure, motion, and origin of the clusters. Using clustering of Gaia data in 3D position + 2D velocity space, supplemented by available fifth-generation Sloan Digital Sky Survey radial velocities, we find clusters of ages 10, 15.8, and 20 Myr with members numbering 140, 469, and 184, respectively. All three clusters overlap currently in 3D space. Tracing their previous locations, based on present-day motions, shows that each cluster originated in its own distinct region and exhibited no influence on each other's formation. Two of the clusters trace their origin to different areas within the Cam OB1 association, with the oldest cluster tracing its origins to the near edge of the Perseus Arm, in the direction of the Perseus OB1 or Cassiopeia OB6 associations. Overall, this work illustrates how different stellar groups, even those originating in a different spiral arm, can visit and pass through each other as they travel through the Galaxy.

Keywords: Stellar ages, Stellar kinematics, Galaxy structure, Stellar associations, Star clusters
Early Planet Formation in Embedded Disks (eDisk). XXII. Keplerian Disk, Disk Structures, and Jets/Outflows in the Class 0 Protostar IRAS 04166+2706. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class 0 protostar IRAS 04166+2706, obtained as part of the ALMA Large Program Early Planet Formation in Embedded Disks. These observations were made in the 1.3 mm dust continuum and molecular lines at angular resolutions of  ∼0.″05  (∼8 au) and  ∼0.″16  (∼25 au), respectively. The continuum emission shows a disklike structure with a radius of ∼22 au. Kinematical analysis of 13CO (2─1), C18O (2─1), H2CO (30,3─20,2), CH3OH (42─31) emission demonstrates that these molecular lines trace the infalling-rotating envelope and possibly a Keplerian disk, enabling us to estimate the protostar mass to be 0.15 M⊙ &lt; M⋆ &lt; 0.39 M⊙. The dusty disk is found to exhibit a brightness asymmetry along its minor axis in the continuum emission, probably caused by a flared distribution of the dust and the high optical depth of the dust emission. In addition, the 12CO (2─1) and SiO (5─4) emissions show knotty and wiggling motions in the jets. Our high-angular-resolution observations revealed the most recent mass ejection events, which have occurred within the last ∼25 yr.

Keywords: Protostars, Stellar jets
Nebular Spectra of Kilonovae with Detailed Recombination Rates. I. Light r-process Composition. To investigate spectra of kilonovae in the nonlocal thermal equilibrium phase (t ≳ 1 week), we perform atomic calculations for dielectronic recombination (DR) rates for the light r-process elements Se (Z = 34), Rb (Z = 37), Sr (Z = 38), Y (Z = 39), and Zr (Z = 40) using the HULLAC code. For the different elements, our results for the DR rate coefficients for recombining from the ionization states of II to I, III to II, and IV to III vary between 2 × 10‑12–5 × 10‑11 cm3 s‑1, 10‑13–5 × 10‑11 cm3 s‑1, and 2 × 10‑15–10‑11 cm3 s‑1, respectively, at a temperature of T = 10,000 K. Using this new atomic data (DR), we study the impact on kilonova model spectra at phases of t = 10 days and t = 25 days after the merger using the spectral synthesis code SUMO. Compared to models using the previous treatment of recombination as a constant rate, the new models show significant changes in ionization and temperature, and, correspondingly, in emergent spectra. With the new rates, we find that Zr (Z = 40) plays a yet more dominant role in kilonova spectra for light r-process compositions. Furthermore, we show that previously predicted mid-infrared (e.g., [Se III] 4.55 μm) and optical (e.g., Rb I 7802, 7949 Å) lines weaken in the new model. Instead, [Se I] 5.03 μm emerges as a signature. These results demonstrate the importance of considering the detailed microphysics for modelling and interpreting the late-time kilonova spectra.

Keywords: Neutron stars, Atomic physics, Transient sources, Time domain astronomy, Radiative transfer