Sazuna/UAT_keywords huggingface dataset:
The Emerging Class of Double-faced White Dwarfs. We report our findings on a spectroscopic survey of seven unresolved DA+DB binary white dwarf candidates. We have discovered extreme spectroscopic variations in one of these candidates, SDSS J084716.21+484220.40. Previous analysis failed to reproduce the optical spectrum using a single object with a homogeneous atmosphere. Our time-resolved spectroscopy reveals a double-faced white dwarf that switches between a DBA and DA spectral type over 6.5 or 8.9 hr due to varying surface abundances. We also provide time-series spectroscopy of the magnetic DBA, SDSS J085618.94+161103.6 (LB 8915), and confirm an inhomogeneous atmosphere. We employ an atmosphere model with hydrogen caps and a helium belt that yields excellent fits to our time-resolved spectra. We use the oblique rotator model to derive the system geometry for both targets. With the addition of these two objects, the emerging class of double-faced white dwarfs now consists of seven members. We summarize the properties of this new class of objects, and discuss how magnetism impacts the convective processes and leads to the formation of double-faced white dwarfs. We identify cooler versions of white dwarfs with inhomogeneous atmospheres among the cool magnetic DA white dwarf sample, where the Hα line is shallower than expected based on pure hydrogen atmosphere models.

Keywords: White dwarf stars, Stellar atmospheres, Stellar magnetic fields, Variable stars
Dust Coagulation Assisted by Streaming Instability in Protoplanetary Disks. The streaming instability is a promising mechanism for planetesimal formation. The instability can rapidly form dense clumps that collapse self-gravitationally, which is efficient for large dust grains with Stokes number of the order of 0.1. However, dust growth models predict that collisional fragmentation prevents dust grains from growing to such sizes. We perform local simulations of the streaming instability and measure characteristic collision velocities and collision rates of dust grains based on their trajectories in moderate clumping. The collision velocities are of the order of 0.1% of the sound speed or lower, implying that dust grains can overcome the fragmentation barrier via clumping. We also find that the collision rates are appreciably high regardless of the low collision velocities. Corresponding timescales are of the order of 10 Keplerian periods or shorter, suggesting that dust grains can overcome the drift barrier as well. This streaming-instability-assisted coagulation greatly relaxes the conditions for planetesimal formation as recently implied.

Keywords: Protoplanetary disks, Planet formation, Planetesimals
RAMBO. I. Project Introduction and First Results with uGMRT. Magnetic hot stars can emit both coherent and incoherent nonthermal radio emission. Understanding the nature of these emissions and their connection to stellar rotation and magnetic field characteristics remains incomplete. The RAdio Magnetospheres of B and O stars (RAMBO) project aims to address this gap by systematically detecting and characterizing gyrosynchrotron and cyclotron maser radio emission in rapidly rotating magnetic hot stars. Using the upgraded Giant Metrewave Radio Telescope, we present the first detection of radio emission from HD 55522 at 650 MHz, confirming it as a new radio-bright magnetic hot star. This supports the predictions of the Centrifugal Breakout model, furthering its application in understanding particle acceleration mechanisms in centrifugal magnetospheres of hot stars. Additionally, we report nondetections for four other targets, improving sensitivity limits by a factor of a few compared to previous observations. These findings demonstrate the potential of RAMBO to uncover the complexities of radio emission in massive stars and highlight the need for broader, multiwavelength observations to probe magnetospheric physics comprehensively. The sensitivity of the Square Kilometre Array will enable significant advancements.

Keywords: Early-type stars, Magnetospheric radio emissions, Galactic radio sources, Massive stars, Stellar magnetic fields, Non-thermal radiation sources, Stellar rotation
Constraining First-order Phase Transition inside Neutron Stars with Application of Bayesian Techniques on PSR J0437–4715 NICER Data. Understanding the existence of phases of exotic matter and phase transitions within the cores of neutron stars is crucial to advancing our knowledge of cold dense matter physics. Recent multimessenger observations, including gravitational waves from neutron star mergers and precise X-ray data from NASA's Neutron Star Interior Composition Explorer (NICER) mission, have significantly constrained the neutron star equation of state (EOS). This study investigates the effects of phase transitions in neutron stars, focusing on NICER's latest observation of PSR J0437‑4715. We employ Bayesian inference techniques to evaluate the presence of first-order phase transitions using a piecewise polytropic EOS model. Our analysis incorporates data from multiple NICER sources to refine constraints on key phase transition parameters, including critical density and transition depth. We find that including data from PSR J0437‑4715 improves the evidence of phase transitions and tightens the EOS constraints, especially at higher densities. However, Bayes factor analysis only indicates a slight preference for models without phase transitions, and the current observational precision is insufficient to draw definitive conclusions. In particular, this polytropic model identifies the critical phase transition mass of neutron stars as being close to 1.4 solar masses, which coincides with the approximate mass range of PSR J0437–4715. This work emphasizes the importance of precise measurements of PSR J0437‑4715 for deepening our understanding of neutron star interiors and exploring potential new physics at extreme densities.

Keywords: Neutron stars, Bayesian statistics, X-ray stars
The BoRG-JWST Survey: Program Overview and First Confirmations of Luminous Reionization-era Galaxies from Pure-parallel Observations. We present the BoRG-JWST survey, a combination of two JWST Cycle 1 programs aimed at obtaining NIRSpec spectroscopy of representative, UV-bright 7 &lt; z &lt; 10 galaxy candidates across 22 independent sight lines selected from Hubble/WFC3 pure-parallel observations. We confirm the high-z nature of 12 out of 21 observed primary targets through low-resolution prism observations, with the rest revealing themselves unsurprisingly to be z ∼ 1–3 interlopers, brown dwarfs, or yielding inconclusive results. From the Multi Shutter Array (MSA) observations, we confirm an additional nine filler sources at z &gt; 5, highlighting the large abundance of high-redshift galaxies even in individual WFC3 pointings. The primary sample spans the absolute magnitude range ‑20.4 mag &lt; MUV &lt; ‑22.4 mag and harbors UV continuum slopes of β ≃ ‑2.5 to ‑2.0, representing some of the most luminous z &gt; 7 sources currently known and comparable to the brightest NIRCam sources at z &gt; 10. Prominent [O III]+Hβ lines are found across the full sample, while a stack of sources reveals a plethora of other rest-optical lines and additional rest-UV C III] 1909 Å emission. Despite their luminosities, none of the low-resolution spectra display evidence for type 1 active galactic nucleus activity based on a search for broad-line emission. Lastly, we present a spectroscopic data release of 188 confirmed 0.5 ≲ z ≲ 5.0 sources from filler MSA observations, highlighting the legacy value of the survey and a representative benchmark for comparisons to deep field observations.

Keywords: Reionization, High-redshift galaxies, Galaxy evolution, James Webb Space Telescope
The JWST-NIRCam View of Sagittarius C. I. Massive Star Formation and Protostellar Outflows. We present James Webb Space Telescope (JWST) Near Infrared Camera observations of the massive star-forming molecular cloud Sagittarius C (Sgr C) in the Central Molecular Zone (CMZ). In conjunction with ancillary mid-IR and far-IR data, we characterize the two most massive protostars in Sgr C via spectral energy distribution (SED) fitting, estimating that they each have current masses of m * ∼ 20 M ⊙ and surrounding envelope masses of ∼100 M ⊙. We report a census of lower-mass protostars in Sgr C via a search for infrared counterparts to millimeter continuum dust cores found with the Atacama Large Millimeter/submillimeter Array (ALMA). We identify 88 molecular hydrogen outflow knot candidates originating from outflows from protostars in Sgr C, the first such unambiguous detections in the infrared in the CMZ. About a quarter of these are associated with flows from the two massive protostars in Sgr C; these extend for over 1 pc and are associated with outflows detected in ALMA SiO line data. An additional ∼40 features likely trace shocks in outflows powered by lower-mass protostars throughout the cloud. We report the discovery of a new star-forming region hosting two prominent bow shocks and several other line-emitting features driven by at least two protostars. We infer that one of these is forming a high-mass star given an SED-derived mass of m * ∼ 9 M ⊙ and associated massive (∼90 M ⊙) millimeter core and water maser. Finally, we identify a population of miscellaneous molecular hydrogen objects that do not appear to be associated with protostellar outflows.

Keywords: Galactic center, Millimeter astronomy, Stellar jets, Massive stars, Stellar bow shocks, Star formation, Spectral energy distribution, H II regions, Near infrared astronomy
The JWST-NIRCam View of Sagittarius C. II. Evidence for Magnetically Dominated H II Regions in the Central Molecular Zone. We present JWST-NIRCam narrowband, 4.05 μm Br α images of the Sgr C H II region, located in the central molecular zone (CMZ) of the Galaxy. Unlike any H II region in the solar vicinity, the Sgr C plasma is dominated by filamentary structure in both Br α and the radio continuum. Some bright filaments, which form a fractured arc with a radius of about 1.85 pc centered on the Sgr C star-forming molecular clump, likely trace ionization fronts. The brightest filaments form a "π-shaped" structure in the center of the H II region. Fainter filaments radiate away from the surface of the Sgr C molecular cloud. The filaments are emitting optically thin free─free emission, as revealed by spectral index measurements from 1.28 GHz (MeerKAT) to 97 GHz (Atacama Large Millimeter/submillimeter Array). But, the negative in-band 1 to 2 GHz spectral index in the MeerKAT data alone reveals the presence of a nonthermal component across the entire Sgr C H II region. We argue that the plasma flow in Sgr C is controlled by magnetic fields, which confine the plasma to ropelike filaments or sheets. This results in the measured nonthermal component of low-frequency radio emission plasma, as well as a plasma β (thermal pressure divided by magnetic pressure) below 1, even in the densest regions. We speculate that all mature H II regions in the CMZ, and galactic nuclei in general, evolve in a magnetically dominated, low plasma β regime.

Keywords: Emission nebulae
Discovery of a Pulsar Wind Nebula Candidate Associated with the Galactic PeVatron 1LHAASO J0343+5254u. The astronomical origins of the most energetic galactic cosmic rays and gamma rays are still uncertain. X-ray follow-up of candidate "PeVatrons"—systems producing cosmic rays with energies exceeding 1 PeV—can constrain their spatial origin, identify likely counterparts, and test particle emission models. Using ∼120 ks of XMM-Newton observations, we report the discovery of a candidate pulsar wind nebula, a possible counterpart for the LHAASO PeVatron J0343+5254u. This extended source has a power-law X-ray spectrum with spectral index ΓX = 1.9—softer at greater distance from the center—and asymmetric spatial extension out to  . We conduct leptonic modeling of the X-ray and gamma-ray radiation from this complex system, showing that a fully leptonic model with elevated IR photon fields can explain the multiwavelength emission from this source, similar to other very high-energy pulsar wind nebulas; excess gamma-ray emissivity not explained by a leptonic model may be due to hadronic interactions in nearby molecular cloud regions, which might also produce detectable astroparticle flux.

Keywords: X-ray astronomy, High energy astrophysics, Pulsar wind nebulae, X-ray sources, Nebulae, Ultra-high-energy cosmic radiation
Detection of Molecular Clouds in the PeVatron Candidate Source LHAASO J0341+5258 by the Nobeyama 45-m Radio Telescope. We report a new CO observation survey of LHAASO J0341+5258, using the Nobeyama Radio Observatory 45-m telescope. LHAASO J0341+5258 is one of the unidentified ultra-high-energy (UHE; E &gt; 100 TeV) gamma-ray sources detected by LHAASO. Our CO observations were conducted in 2024 February and March, with a total observation time of 36 hr, covering the LHAASO source (∼0 3─0 5 in radius) and its surrounding area (1° × 1 5). Within the LHAASO source extent, we identified five compact (&lt;2 pc) molecular clouds at nearby distances (&lt;1─4 kpc). These clouds can serve as proton─proton collision targets, producing hadronic gamma rays via neutral pion decays. Based on the hydrogen densities (700─5000 cm−3) estimated from our CO observations and archived H I data from the Dominion Radio Astrophysical Observatory survey, we derive the total proton energy of Wp (E &gt; 1 TeV) ∼ 1045 erg to account for the gamma-ray flux. One of the molecular clouds appears to be likely associated with an asymptotic giant branch (AGB) star with an extended CO tail, which may indicate some particle acceleration activities. However, the estimated maximum particle energy below 100 TeV makes the AGB-like star unlikely to be a PeVatron site. We conclude that the UHE emission observed in LHAASO J0341+5258 could be due to hadronic interactions between the newly discovered molecular clouds and TeV─PeV protons originating from a distant SNR or due to leptonic emission from a pulsar wind nebula candidate, which is reported in our companion X-ray observation paper.

Keywords: Cosmic rays, Gamma-rays, Molecular clouds
Spectral Analysis of the X-Ray Flares in the 2023 Outburst of the New Black Binary Transient Swift J1727.8–1613 Observed with Insight-HXMT. The new black hole transient Swift J1727.8–1613 exhibited a series of X-ray flares during its 2023 outburst extensively observed with Insight-HXMT. We analyze the spectra of the flaring period using a series of models consisting of a multicolor disk and several different nonthermal components, and several consistent conclusions are obtained among these models. First, Swift J1727.8–1613 was in the transition process from the hard intermediate state to the very high state (VHS) during the first flaring period (MJD 60197–60204), and afterward, it exhibited typical VHS parameter characteristics, such as the high temperature of the disk inner radius and a steep power-law spectrum with a photon index of 2.6. Second, the flares in the VHS are characterized by a rapid increase in the flux of the accretion disk, accompanied by a simultaneous rapid expansion of the inner radius, which could be apparent if the accretion disk hardening factor varies significantly. The strong power-law component during the VHS is likely produced by the synchrotron self-Compton process in the relativistic jets, which is in agreement with the observed weak reflection component and lack of correlation with the disk component.

Keywords: Stellar accretion disks, X-ray binary stars, Astronomy data analysis, Stellar x-ray flares
Is the Central Compact Object in HESS J1731-347 a Hybrid Star with a Quark Core? An Analysis with the Constant Speed of Sound Parameterization. In this work, we investigate the possibility of the compact object in HESS J1731-347 with   and   to be a hybrid star with quark matter in the inner core. The observation of this low-mass compact star dictates the use of a softer equation of state, which, on the contrary, cannot explain the massive compact stars. This poses a new challenge for astrophysicists in their search for the equation of state of compact objects. The hybrid equations of state are constructed using the IUFSU parameterization based on the relativistic mean field theory for the hadronic part and the generic constant speed of sound (CSS) parameterization for the phase transition to quark matter. The CSS framework is characterized by three key parameters, namely the transition density (ρtr), the energy jumps (Δɛ), and the speed of sound (Cs). Here, our primary aim is to investigate the influence of individual CSS parameters on the formation of an object of small mass and radius compatible with HESS J1731-347 parameters. We have also examined the effect of hadronic parameters such as effective mass, symmetry energy, and the slope of the symmetry energy at saturation densities on the formation of this compact object. Finally, our analysis suggests that, within a 1σ credible level, HESS J1731-347 aligns with the scenario of a stable hybrid star with early deconfinement and higher energy gap.

Keywords: Neutron stars, Nuclear astrophysics, Compact objects
Reprocessing from Highly Ionized Gas in the Soft Spectral State of V4641 Sgr with NuSTAR. V4641 Sgr is a low-mass black hole X-ray binary system with somewhat puzzling spectral characteristics during its soft state. Recent high-resolution spectroscopic studies of V4641 Sgr have revealed strong ionized emission-line features in both the optical and X-ray bands, including P-Cygni signatures, and an unusually low soft-state luminosity, indicating that the central engine is obscured. Here, we present an analysis of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of V4641 Sgr taken during its recent outburst in 2021, when the source was in the soft state. We identify highly ionized Fe K emission lines—consistent with a combination of the near-neutral 6.4 keV Fe Kα line and the H-like and He-like Fe Kα and Fe Kβ transitions found at 6.7–7 keV and ∼8 keV—and find no evidence for strong relativistic broadening. The line fluxes correlate linearly with the observed disk continuum flux, implying a direct connection between the central engine and the reprocessing region. Most interestingly, all five spectra also show a persistent highly ionized Fe K continuum edge feature at ∼9 keV with a stable optical depth, which is likely smeared, implying a localized reprocessing zone. We find tentative supporting evidence for obscuration of the inner accretion disk based on its unusually low intrinsic luminosity, although the NuSTAR spectra do not require obscuration from cold, optically thick gas.

Keywords: Accretion, Black hole physics, X-ray astronomy, Atomic physics, Low-mass x-ray binary stars
A [C II] 158 μm Survey of Damped Lyα Absorber Galaxies at z ∼ 4: Observations of Dense and Metal-enriched Neutral Gas within the Circumgalactic Medium of Star-forming Galaxies. We present a survey undertaken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the galaxies associated with a representative sample of 16 damped Lyα absorbers (DLAs) at z ≈ 4.1–4.5, using the [C II] 158 μm ([C II]) line. We detect seven [C II]-emitting galaxies in the fields of five DLAs, all of which have absorption metallicity [M/H] &gt; ‑1.5. We find that the detectability of these H I-selected galaxies with ALMA is a strong function of DLA metallicity, with a detection rate of  % for DLAs with [M/H] &gt; ‑1.5 and 0+18% for DLAs with [M/H] &lt; ‑1.5. The identified DLA galaxies have far-IR properties similar to those of typical star-forming galaxies at z ∼ 4, with estimated obscured star formation rates ranging from ≲6 M⊙ yr‑1 to 110 M⊙ yr‑1. High-metallicity DLAs therefore provide an efficient way to identify and study samples of high-redshift, star-forming galaxies, without preselecting the galaxies by their emission properties. The agreement between the velocities of the metal absorption lines of the DLA and the [C II] emission line of the DLA galaxy indicates that the metals within the DLA originated in the galaxy. With observed impact parameters between 14 and 59 kpc, this indicates that star-forming galaxies at z ∼ 4 have a substantial reservoir of dense, cold, neutral gas within their circumgalactic medium that has been enriched with metals from the galaxy.

Keywords: Interstellar atomic gas, Quasar absorption line spectroscopy, Damped Lyman-alpha systems, Neutral hydrogen clouds, Interstellar medium, Circumgalactic medium, Submillimeter astronomy, High-redshift galaxies
A Tale of Two Black Holes: Multiband Gravitational-wave Measurement of Recoil Kicks. The nonlinear dynamics of General Relativity leave their imprint on remnants of black hole mergers in the form of a recoil "kick." The kick has profound astrophysical implications across the black hole mass spectrum, from stellar-mass to supermassive black holes. However, a direct measurement of the kick would require observing the binary from different orientations. Therefore, the kick is primarily inferred by constraining the premerger parameters, mainly the spin orientations and mass ratio of the black holes and fitting them with postmerger parameters. In this study, we demonstrate the prospects for such measurements of black hole kicks in a multiband gravitational-wave network consisting of space mission LISA, the current Earth-based detector network, and a third-generation detector. For two distinct cases of remnant black hole kick (68, 1006 km s‑1) emerging from near identical premerger configuration of GW190521—the first confirmed intermediate-mass black hole—we find that the multiband network will recover with a 90% credible level of the projection of the kick vector relative to the orbital plane within tens of km s‑1 accuracy. Such precise measurement of the kick offers a new set of multimessenger follow-ups and unprecedented tests of astrophysical formation channels.

Keywords: Gravitational wave astronomy
AT 2020nov: Evidence for Disk Reprocessing in a Rare Tidal Disruption Event. We present a detailed analysis of AT 2020nov, a tidal disruption event (TDE) in the center of its host galaxy, located at a redshift of z = 0.083. AT 2020nov exhibits unique features, including double-peaked Balmer emission lines, a broad UV/optical flare, and a peak log luminosity in the extreme-ultraviolet (EUV) estimated at  . A late-time X-ray flare was also observed, reaching an absorbed luminosity of 1.67 × 1043 erg s‑1 approximately 300 days after the UV/optical peak. Multiwavelength coverage, spanning optical, UV, X-ray, and mid-infrared (MIR) bands, reveals a complex spectral energy distribution (SED) that includes MIR flaring indicative of dust echoes, suggesting a dust covering fraction consistent with typical TDEs. Spectral modeling indicates the presence of an extended, quiescent disk around the central supermassive black hole with a radius of  . The multicomponent SED model, which includes a significant EUV component, suggests that the primary emission from the TDE is reprocessed by this extended disk, producing the observed optical and MIR features. The lack of strong active galactic nuclei signatures in the host galaxy, combined with the quiescent disk structure, highlights AT 2020nov as a rare example of a TDE occurring in a galaxy with a dormant but extended preexisting accretion structure.

Keywords: Accretion, Tidal disruption, Galaxy accretion disks, Black holes