Sazuna/UAT_keywords huggingface dataset:
Evidence for an Accretion Bridge in the DX Cha Circumbinary System from VLTI/MATISSE Observations. DX Cha (HD 104237) is a spectroscopic binary consisting of a Herbig A7.5Ve─A8Ve primary star and a K3-type companion. Here we report on new 3.55 μm interferometric observations of this source with the Multi Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) at the Very Large Telescope Interferometer. To model the four MATISSE observations obtained between 2020 and 2023, we constructed a time-dependent interferometric model of the system, using the oimodeler software. The model consists of an asymmetric ring and two point sources on a Keplerian orbit. Our best-fit model consists of a circumbinary ring with a diameter of 0.86 au (8.1 mas), featuring a strong azimuthal asymmetry. We found that the position angle of the asymmetry changes tens of degrees between the MATISSE epochs. The ring is relatively narrow, with a full width at half-maximum of ∼0.13 au (1.23 mas). The presence of circumstellar dust emission so close to the binary is unexpected, as previous hydrodynamic simulations predicted an inner disk cavity with a diameter of ∼4 au (∼37.5 mas). Thus, we argue that the narrow envelope of material we detected is probably not a gravitationally stable circumbinary ring but may be part of tidal accretion streamers channeling material from the inner edge of the disk toward the stars. *Based on observations collected at the European Southern Observatory under ESO programmes 0104.C-0782(D), 106.21Q8.003, 108.22HB.001, and 110.23X2.002.

Keywords: Astronomical models, Binary stars, Protoplanetary disks, Circumstellar disks, Interferometry
Dynamical Models of the Milky Way in Action Space with LAMOST DR8 and Gaia EDR3. This work explores dynamical models of the Milky Way (MW) by analyzing a sample of 86,109 K giant stars selected through cross-matching the LAMOST DR8 and Gaia EDR3 surveys. Our earlier torus models of Q. Wang et al. did not include Gaia data, making them incompatible with the new sample's proper motion distributions. Here, we refine the construction of action-based, self-consistent models to constrain the three-dimensional velocity distribution of K giants over a larger parameter space, drawing on a series of existing MW models. This approach produces several new MW models. Our best-fit model for the local kinematics near the Sun indicates an MW virial mass of 1.35 × 1012 M⊙, a local stellar density of 0.0696 M⊙ pc‑3, and a local dark matter density of 0.0115 M⊙ pc‑3. Our main conclusion supports a thicker and more extended thick disk, alongside a cooler thin disk, compared to the best-fitting model of Q. Wang et al. Near the Sun, our model aligns well with observations, but it is less satisfactory at distances far from the Galactic center, perhaps implying unidentified structures. Further high-precision observations will be critical for understanding the dynamics in these outer Galactic regions and will require a more realistic model.

Keywords: Milky Way dynamics
DESIVAST: Catalogs of Low-redshift Voids Using Data from the DESI Data Release 1 Bright Galaxy Survey. We present three separate void catalogs created using a volume-limited sample of the DESI Data Release 1 Bright Galaxy Survey. We use the algorithms VoidFinder and V2 to construct void catalogs out to a redshift of z = 0.24. Excluding voids affected by the boundaries of the survey, we obtain 1489 voids with VoidFinder, 389 with V2 using REVOLVER pruning, and 297 with V2 using VIDE pruning. Comparing our catalogs with overlapping Sloan Digital Sky Survey void catalogs, we find generally consistent void properties but significant differences in the void volume overlap, which we attribute to differences in the galaxy selection and survey masks. These catalogs are suitable for studying the variation in galaxy properties with cosmic environment and for cosmological studies.

Keywords: Observational cosmology, Voids, Redshift surveys
Beyond the Goldilocks Zone: Identifying Critical Features in Massive Black Hole Formation. Most galaxies, including the Milky Way, host a supermassive black hole (SMBH) at the center. These SMBHs can be observed out to high redshifts (z ≥ 6) if the accretion rate is sufficiently large. However, we do not fully understand the mechanism through which these black holes form at early times. The heavy (or direct collapse) seeding mechanism has emerged as a probable contender in which the core of an atomic cooling halo directly collapses into a dense stellar cluster that could host supermassive stars that proceed to form a black hole seed of mass ∼ 105 M⊙. We use the Renaissance Simulations to investigate the properties of 35 direct collapse black hole (DCBH) candidate host halos at z = 15–24 and compare them to noncandidate halos. We aim to understand what features differentiate halos capable of hosting a DCBH from the general halo population with the use of statistical analysis and machine learning methods. We examine 18 halo, central, and environmental properties. We find that DCBH candidacy is more dependent on a halo's core internal properties than on exterior factors such as Lyman–Werner (LW) flux and distance to the closest galaxy; our analysis selects density and radial mass influx as the most important features (outside candidacy establishing features). Our results concur with the recent suggestion that DCBH host halos neither need to lie within a "Goldilocks zone" nor have a significant amount of LW flux to suppress cooling. This paper presents insight to the dynamics possibly occurring in potential DCBH host halos and seeks to provide guidance to DCBH subgrid formation models.

Keywords: Supermassive black holes, High-redshift galaxies
Planetary Formation Constrained by Collisions between Millimeter-sized Lunar Particles and Lunar Surface from Chang'E-4 Mission. Exploring low-velocity collisions is crucial for unraveling intricate processes in planetary formation, particularly the bouncing barrier that impedes the aggregation of dust into sizable planetesimals. Observational data on extraterrestrial collision processes remain limited. Here, we quantify collision parameters for millimeter-sized lunar particles impacting the porous lunar surface at speeds ranging from 2.3 to 76.8 cm s‑1 under lunar gravity, leveraging Chang'E-4 imagery. This study represents the first tangible acquisition of extraterrestrial collision data. Our findings reveal that speeds exceeding 7.0 ± 2.6 cm s‑1 result in bouncing, yielding coefficients of restitution ranging from 0.51 to 0.80. In contrast to particle–particle collisions, interactions between lunar particles and the porous lunar surface exhibit a heightened sticking threshold speed, facilitating particles to overcome the bouncing barrier. Diminished coefficients of restitution expedite collapses, significantly reducing dust cloud collapse times. This implies that porous particles foster favorable conditions for overcoming the bouncing barrier and promoting growth. Our results unveil the conducive conditions enabling extraterrestrial samples to overcome the bouncing barrier, advancing our comprehension of planetary formation and providing crucial observational constraints for relevant theories.

Keywords: Planetary science, Planetary system evolution, Planet formation, Solar system evolution
An X-Ray View of the Cataclysmic Variable V902 Mon: Discovery of an X-Ray Eclipse. V902 Mon is one of a few eclipsing intermediate polars (IPs) and shows deep eclipses in the optical lightcurves. The presence of a strong Fe Kα fluorescence line in its X-ray spectrum and its low X-ray flux compared to other IPs suggests significant absorption, most likely from an accretion disk. In an observation carried out using the Nuclear Spectroscopic Telescope Array (NuSTAR), we confirm the presence of an X-ray eclipse in the energy-resolved lightcurves, coincident with the optical AAVSO/CV-band lightcurves. Broadband X-ray spectral analysis using NuSTAR and XMM-Newton observations confirm a strong absorption NH ∼ 1023 cm‑2 local to the source, along with a high equivalent width of about 0.7 keV for an Fe Kα fluorescence line. We interpret this using a model similar to an accretion disk corona source, which has a very high inclination, and the compact object is heavily obscured by the body of the accretion disk. We propose that the primary X-rays from the accretion column in V902 Mon are hidden from our direct view at all times by the accretion disk. In this scenario, the observed scattered X-rays indicate substantial absorption of direct X-rays by the accretion disk. Additionally, a strong Fe fluorescence line suggests reprocessing of the radiation by a more extended region, such as the pre-shock region, which could be located a few white dwarf radii above the orbital plane.

Keywords: Eclipsing binary stars, Cataclysmic variable stars, Astronomy data analysis
The Long-lived Broadband Afterglow of Short Gamma-Ray Burst 231117A and the Growing Radio-detected Short Gamma-Ray Burst Population. We present multiwavelength observations of the Swift short γ-ray burst GRB 231117A, localized to an underlying galaxy at redshift z = 0.257 at a small projected offset (∼2 kpc). We uncover long-lived X-ray Chandra X-ray Observatory and radio/millimeter (VLA, MeerKAT, and ALMA) afterglow emission, detected to ∼37 days and ∼20 days (rest frame), respectively. We measure a wide jet (∼10 4) and relatively high circumburst density (∼0.07 cm‑3) compared to the short GRB population. Our data cannot be easily fit with a standard forward shock model, but they are generally well fit with the incorporation of a refreshed forward shock and a reverse shock at &lt;1 day. We incorporate GRB 231117A into a larger sample of 132 X-ray detected events, 71 of which were radio-observed (17 cm-band detections), for a systematic study of the distributions of redshifts, jet and afterglow properties, galactocentric offsets, and local environments of events with and without detected radio afterglows. Compared to the entire short GRB population, the majority of radio-detected GRBs are at relatively low redshifts (z &lt; 0.6) and have high circumburst densities (&gt;10‑2 cm‑3), consistent with their smaller (&lt;8 kpc) projected galactocentric offsets. We additionally find that 70% of short GRBs with opening angle measurements were radio-detected, indicating the importance of radio afterglows in jet measurements, especially in the cases of wide (&gt;10°) jets where observational evidence of collimation may only be detectable at radio wavelengths. Owing to improved observing strategies and the emergence of sensitive radio facilities, the number of radio-detected short GRBs has quadrupled in the past decade.

Keywords: Gamma-ray bursts, High energy astrophysics, Millimeter astronomy, Relativistic jets, Time domain astronomy, Radio astronomy
The Proxima Centauri Campaign—First Constraints on Millimeter Flare Rates from ALMA. Proxima Centauri (Cen) has been the subject of many flaring studies due to its proximity and potential to host habitable planets. The discovery of millimeter flares from this M dwarf with Atacama Large Millimeter/submillimeter Array (ALMA) has opened a new window into the flaring process and the space-weather environments of exoplanets like Proxima b. Using a total of ~50 hr of ALMA observations of Proxima Cen at 1.3 mm (233 GHz), we add a new piece to the stellar flaring picture and report the first cumulative flare frequency distribution (FFD) at millimeter wavelengths of any M dwarf. We detect 463 flares ranging from energies 1024 to 1027 erg. The brightest and most energetic flare in our sample reached a flux density of 119 ± 7 mJy, increasing by a factor of 1000× the quiescent flux, and reaching an energy of 1027 erg in the ALMA bandpass, with t1/2 ≍ 16 s. From a log─log linear regression fit to the FFD, we obtain a power-law index of αFFD = 2.92 ± 0.02, much steeper than αFFD values (~2) observed at X-ray to optical wavelengths. If millimeter flare rates are predictive of flare rates at extreme-UV wavelengths, the contribution of small flares to the radiation environment of Proxima b may be much higher than expected based on the shallower power-law slopes observed at optical wavelengths.

Keywords: Observational astronomy, M dwarf stars, Flare stars, Stellar activity, Submillimeter astronomy, Radio astronomy
3D Simulations of Semiconvection in Spheres: Turbulent Mixing and Layer Formation. Semiconvection occurs in regions of stars and planets that are unstable to overturning convection according to the Schwarzschild criterion, but stable according to the Ledoux criterion. Previous simulations in Cartesian boxes have advanced our understanding of the semiconvective instability, layer formation, and transport properties. However, much less is known about semiconvection in spherical geometry and under the influence of rotation or magnetic fields. We present 3D simulations of semiconvection in the full sphere (including r = 0) and accounting for rotation. We find that the formation and evolution of semiconvective layers in nonrotating spheres occurs in a similar way to that in nonrotating Cartesian boxes, in the sense that the critical density ratio at which layers are expected to form is approximately the same in both geometries. Layers rapidly merge once they form, ultimately leading to a fully mixed convective sphere. The transport properties measured through the Nusselt numbers and the buoyancy flux ratio are also similar to results from previous studies in boxes. When rotation is added to the system, layer formation and evolution proceed in a similar fashion to the nonrotating runs. However, rotation hampers the radial transport of heat and composition, and, as a result, the time that it takes for the sphere to become fully mixed gets longer as the flow becomes more rotationally constrained. We also find that semiconvective layers exhibit spherical mixing in nonrotating cases, whereas in rotating cases the mixing becomes more cylindrical. We discuss what is needed for future work to build more realistic models.

Keywords: Stellar interiors, Stellar convective zones, Planetary interior, Astrophysical fluid dynamics
The Role of Magnetic and Rotation Axis Alignment in Driving Fast Radio Burst Phenomenology. We propose a scenario that can describe a broad range of fast radio burst (FRB) phenomenology, from nonrepeating bursts to highly prolific repeaters. Coherent radio waves in these bursts are produced in the polar cap region of a magnetar, where magnetic field lines are open. The angle between the rotation and magnetic axes, relative to the angular size of the polar cap region, partially determines the repetition rate and polarization properties of FRBs. We discuss how many of the properties of repeating FRBs—such as their lack of periodicity, energetics, small polarization angle (PA) swing, spectro–temporal correlation, and inferred low source density— are explained by this scenario. The systematic PA swing and the periodic modulation of long-duration bursts from nonrepeaters are also natural outcomes. We derive a lower limit of about 400 on the Lorentz factor of FRB sources applying this scenario to bursts with a linear polarization degree greater than 95%.

Keywords: Neutron stars, Magnetars, Radio transient sources
Rare Event Classification with Weighted Logistic Regression for Identifying Repeating Fast Radio Bursts. An important task in the study of fast radio bursts (FRBs) remains the automatic classification of repeating and nonrepeating sources based on their morphological properties. We propose a statistical model that considers a modified logistic regression to classify FRB sources. The classical logistic regression model is modified to accommodate the small proportion of repeaters in the data, a feature that is likely due to the sampling procedure and duration and is not a characteristic of the population of FRB sources. The weighted logistic regression hinges on the choice of a tuning parameter that represents the true proportion τ of repeating FRB sources in the entire population. The proposed method has a sound statistical foundation, direct interpretability, and operates with only five parameters, enabling quicker retraining with added data. Using the CHIME/FRB Collaboration sample of repeating and nonrepeating FRBs and numerical experiments, we achieve a classification accuracy for repeaters of nearly 75% or higher when τ is set in the range of 50%–60%. This implies a tentative high proportion of repeaters, which is surprising, but is also in agreement with recent estimates of τ that are obtained using other methods.

Keywords: Regression, Classification, Astrostatistics techniques, Linear regression, Astrostatistics distributions, Nonlinear regression, Radio transient sources, Sampling distribution
Investigating Coronal Mass Ejections through Multispacecraft Measurements: STEREO-A and L1 in 2022─2023. The angular width of coronal mass ejections (CMEs) and the variations of CME properties for various crossings through the structure remain insufficiently studied and inadequately understood, primarily due to the rarity of multispacecraft measurements. From 2022 January to 2023 August, STEREO-A was in relative proximity to the Sun─Earth first Lagrangian (L1) point, with the STEREO-A─L1 angular separation reducing from 35∘ to 0∘, corresponding to a time with an increasing activity of solar cycle 25 approaching its maximum. This provides a unique time period to obtain multispacecraft measurements of CMEs and to analyze their properties as observed by Wind/ACE and STEREO-A. Among 49 total CMEs measured by either spacecraft over the 20 months, only 15 were simultaneously detected at both spacecraft, indicating that only 31% of CMEs impacted both within a longitudinal separation of 0∘─35∘. While 80%─100% of CMEs were observed by both spacecraft within 10∘, this percentage rapidly dropped to approximately 30% beyond 10∘, and near 30∘, it fell further to 10%. These findings suggest that the average CME angular width near 1 au is likely between 20∘and 35∘, smaller than previously suggested. Furthermore, the analysis of these 15 events reveals that average CME properties like magnetic field strength and proton speed are largely consistent regardless of angular separation. However, correlations and rms error analyses highlight significant variability in CME properties even within separations of 10∘─20∘, when examining their internal variations in detail. This study raises numerous questions about our knowledge of CME properties.

Keywords: Ejecta, Interplanetary physics, Solar coronal mass ejections
Lyα Processing of Solid-state Ethanolamine: Potential Precursors to Sugar and Peptide Derivatives. Ethanolamine (EA), a key component of phospholipids, has recently been detected in the interstellar medium within molecular clouds. To understand this observation, laboratory studies of its formation and destruction are essential and should be complemented by astrochemical models. This study investigates the photostability of EA ice under Lyα (10.2 eV) irradiation at 10 K, and explores its potential role in the formation of simple and complex organic molecules (COMs) in molecular clouds. The UV-destruction cross section of EA was estimated to be (4.7 ± 0.3) × 10‑18 cm2, providing insight into its half-life of 6.5 × 107 yr in dense interstellar clouds. Fourier transform infrared spectroscopy and quadrupole mass spectrometry were used to identify various photoproducts, with their formation pathways discussed. Ethylene glycol and serine were tentatively detected during the warming-up process following irradiation, suggesting that EA could contribute to the formation of prebiotic molecules such as sugars, peptides, and their derivatives. High-mass signals detected in the mass spectrometer suggest the presence of several COMs, and further analysis of residues at room temperature is planned for future work. The results suggest that EA could contribute to the formation of prebiotic molecules in space, with implications for the origin of life.

Keywords: Mass spectrometry, Infrared spectroscopy, Ice spectroscopy, Astrochemistry, Astrobiology, Astrophysical processes, Interdisciplinary astronomy, Complex organic molecules
Foreground Removal and Angular Power Spectrum Estimation of 21 cm Signal Using Harmonic Space ILC Method. Mapping the distribution of neutral atomic hydrogen (H I) in the Universe through its 21 cm emission line provides a powerful cosmological probe to map the large-scale structures and shed light on various cosmological phenomena. The baryon acoustic oscillations at low redshifts can potentially be probed by sensitive H I intensity mapping experiments and constrain the properties of dark energy. However, the 21 cm signal detection faces formidable challenges owing to the dominance of various astrophysical foregrounds, which can be several orders of magnitude stronger. Our current work introduces a novel and model-independent internal linear combination (ILC) method in harmonic space using the principal components of the 21 cm signal for accurate foreground removal and power spectrum estimation. We estimate the principal components by incorporating prior knowledge of the theoretical 21 cm covariance matrix. We test our methodology by detailed simulations of radio observations, incorporating synchrotron emission, free–free radiation, extragalactic point sources, and thermal noise. We estimate the full-sky 21 cm angular power spectrum after application of a mask on the full-sky cleaned 21 cm signal by using the mode–mode coupling matrix. These full-sky estimates of angular spectra can be directly used to measure the cosmological parameters. For the first time, we demonstrate the effectiveness of a foreground-model-independent ILC method in harmonic space to reconstruct the 21 cm signal.

Keywords: Large-scale structure of the universe, Observational cosmology, Astronomy data analysis, H I line emission
Empirical SED Templates for Star Clusters Observed with HST and JWST: No Strong PAH or IR Dust Emission after 5 Myr. JWST observations, when combined with Hubble Space Telescope (HST) data, promise to improve age estimates of star clusters in nearby spiral galaxies. However, feedback from young cluster stars pushes out the natal gas and dust, making cluster formation and evolution a challenge to model. Here, we use JWST+ HST observations of the nearby spiral galaxy NGC 628 to produce spectral energy distribution (SED) templates of compact star clusters spanning 275 nm through 21 μm. These preliminary SEDs capture the cluster stars and associated gas and dust within radii of ≈0 12–0 67 (corresponding to ≈6–33 pc at the distance of NGC 628). One important finding is that the SEDs of 1, 2, 3, and 4 Myr clusters can be differentiated in the infrared. Another is that, in 80%–90% of the cases we study, the polycyclic aromatic hydrocarbon (PAH) and Hα emission track one another, with the dust responsible for the 3.3 μm PAH emission largely removed by 4 Myr, consistent with pre-supernova stellar feedback acting quickly on the surrounding gas and dust. Nearly embedded cluster candidates have infrared SEDs that are quite similar to optically visible 1–3 Myr clusters. In nearly all cases, we find there is a young star cluster within a few tenths of an arcsec (10–30 pc) of the nearly embedded cluster, suggesting the formation of the cluster was triggered by its presence. The resulting age estimates from the empirical templates are compatible both with dynamical estimates based on CO superbubble expansion velocities, as well as the TODDLERS models, which track spherical evolution of homogeneous gas clouds around young stellar clusters.

Keywords: Polycyclic aromatic hydrocarbons, Spiral galaxies, Young star clusters, HST photometry, James Webb Space Telescope, Spectral energy distribution, H II regions, Superbubbles