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Keyword list: ['star formation', 'star-forming', 'molecular cloud', 'interstellar medium', 'cloud', 'clump', 'core', 'filament', 'atomic gas', 'N-PDF']

Excluded: ['galaxies', 'galaxy cluster', ' AGN ', 'standard candle', 'X-ray binar']

Today: 9papers

Properties of $\mathrm{H_2O}$ masers and their associated sources in Sagittarius B2

• Authors: Nazar Budaiev, Adam Ginsburg, Ciriaco Goddi, Álvaro Sánchez-Monge, Anika Schmiedeke, Desmond Jeff, Peter Schilke, Christopher De Pree

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2506.09115

• Pdf link: https://arxiv.org/pdf/2506.09115

• Abstract We present high-resolution Karl G. Jansky Very Large Array observations of the 22 GHz $\mathrm{H_2O}$ maser line in the extended Sagittarius B2 cloud. We detect 499 $\mathrm{H_2O}$ masers across the observed velocities between -39 and 172 km s$^{-1}$. To investigate the nature of the masers, we analyze their spatial distribution and cross-match with catalogs of HII regions and protostellar cores. 62% of masers are associated with protostellar cores and 32% with HII regions. The nature of the remaining 6% of sources was not established, but is likely associated with protostellar cores. Based on the spatial extent of the groups of masers, we classify them as either outflow-associated or young stellar object (YSO)-associated. We identify 144 unique sites of maser emission: 23 are associated with HII regions and 94 with protostellar cores, of which 33 are associated with protostellar outflows and 18 with YSOs. The outflow-associated $\mathrm{H_2O}$ maser emission is confined to within $<2000$ au of the central continuum source, despite shocked SiO emission extending over tens of thousands of au. The YSO-associated masers show a lack of detections at $5 < V_{rel} < 30$ km s$^{-1}$, which we suggest may be due to maser self-absorption. We show how $\mathrm{H_2O}$ masers trace the large-scale material flow in Sgr B2 N (North) also seen in SiO and mm continuum emission. Finally, we find that protostellar cores with associated $\mathrm{H_2O}$ masers tend to have brighter 3 mm continuum emission on average, although there is no strong correlation between maser brightness and continuum flux.

A Plasma Torus Around a Young Low-Mass Star

• Authors: Luke G. Bouma, Moira M. Jardine

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2506.09116

• Pdf link: https://arxiv.org/pdf/2506.09116

• Abstract A small fraction of red dwarfs younger than 100 million years show structured, periodic optical light curves suggestive of transiting opaque material that corotates with the star. However, the composition, origin, and even the existence of this material are uncertain. The main alternative hypothesis is that these complex periodic variables (CPVs) are explained by complex distributions of bright or dark regions on the stellar surfaces. Here, we present time-series spectroscopy and photometry of a rapidly-rotating ($P$=3.9 hr) CPV, TIC 141146667. The spectra show sinusoidal time-varying H$\alpha$ emission at twice to four times the star's equatorial velocity, providing direct evidence for cool ($\lesssim$10$^4$ K) plasma clumps trapped in corotation around a CPV. These data support the idea that young, rapidly-rotating M dwarfs can sustain warped tori of cool plasma, similar to other rapidly-rotating magnetic stars. Outstanding questions include whether dust clumps in these plasma tori explain CPV light curves, and whether the tori originate from the star or are fed by external sources. Rough estimates suggest $\gtrsim$10% of M dwarfs host similar structures during their early lives.

Spin-orbit misalignment and residual eccentricity are evidence that neutron star-black hole mergers form through triple star evolution

• Authors: Jakob Stegmann, Jakub Klencki

• Subjects: Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2506.09121

• Pdf link: https://arxiv.org/pdf/2506.09121

• Abstract There is growing evidence that a substantial fraction of the neutron star-black holes (NSBHs) detected through gravitational waves merge with non-zero eccentricity or large BH spin-orbit misalignment. This is in tension with the leading formation scenarios to date. Residual eccentricity rules out formation through isolated binary star evolution, while NS natal kicks and the unequal masses of NSBHs inhibit efficient pairing in dense stellar environments. Here, we report that all observed properties-NSBH merger rate, eccentricity, and spin-orbit misalignment-are explained by the high prevalence of massive stellar triples in the field. Modelling their evolution from the ZAMS, we investigate NSBH mergers caused by gravitational perturbations from a tertiary companion. We show that the formation of the NS decisively impacts the triple stability, preferentially leaving behind surviving NSBHs in compact triple architectures. The rich three-body dynamics of compact, unequal-mass triples enables mergers across a wide range of orbital parameters without requiring fine-tuned highly inclined tertiary orbits and provides a natural explanation for an abundance of residual eccentricity and spin-orbit misalignment. We infer a total NSBH merger rate of $R\sim1-23,\rm Gpc^{-3},yr^{-1}$, with more than a few 10% exhibiting eccentricity $e_{20}>0.1$ or large spin-orbit misalignment $\cos\theta_{\rm BH}<0$, consistent with current observations. Tertiary-driven NSBH mergers closely track the cosmic star formation rate due to their short delay times, include a substantial fraction of burst-like highly eccentric systems ($e_{20} > 0.9$), and almost universally retain eccentricities $e_{20}>10^{-3}$, potentially detectable by next-generation detectors. If evidence for eccentric and misaligned events solidifies, our results suggest that triple dynamics is the dominant formation channel of NSBH mergers.

JWST Coronagraphic Images of 14 Her c: a Cold Giant Planet in a Dynamically Hot, Multi-planet System

• Authors: Daniella C. Bardalez Gagliuffi, William O. Balmer, Laurent Pueyo, Timothy D. Brandt, Mark R. Giovinazzi, Sarah Millholland, Brennen Black, Tiger Lu, Malena Rice, James Mang, Caroline Morley, Brianna Lacy, Julien Girard, Elisabeth Matthews, Aarynn Carter, Brendan P. Bowler, Jacqueline K. Faherty, Clemence Fontanive, Emily Rickman

• Subjects: Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2506.09201

• Pdf link: https://arxiv.org/pdf/2506.09201

• Abstract Most observed multi-planet systems are coplanar, in a dynamically "cold" configuration of concentric orbits like our own Solar System. With the James Webb Space Telescope (JWST) we have detected 14 Her c, the first mature and cold exoplanet directly imaged in a dynamically "hot", multi-planet system. With large eccentricities and a nonzero mutual inclination, the present-day architecture of this system points to a turbulent past and ongoing angular momentum exchange between the planetary orbits of 14 Her b and c. The temperature of 14 Her c rivals both the coldest imaged exoplanet and the coldest known brown dwarf. Moreover, its photometry at 4.4 mu is consistent with the presence of carbon disequilibrium chemistry and water ice clouds in its atmosphere. 14 Her c presents a unique laboratory to study giant planet formation, dynamical evolution of multi-planet system architectures, and atmospheric composition and dynamics in extremely cold worlds.

Apparent motion of penumbral grains in a sunspot simulation

• Authors: Michal Sobotka, Markus Schmassmann

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2506.09504

• Pdf link: https://arxiv.org/pdf/2506.09504

• Abstract Context. The bright heads of penumbral filaments, penumbral grains (PGs), are manifestations of hot plasma flows rising to the surface. They are observed to move horizontally toward the sunspot umbra or away from it. Recent analyses of observations indicate that the direction of this motion is related to the inclination of the surrounding magnetic field. Aims. The penumbra of a sunspot simulated by the radiative magnetohydrodynamic code MURaM is analysed to get typical physical conditions in PGs, compare them to those in the surroundings, describe their spatial distribution, and study their evolution. Methods. We use time series of images that map intensity, temperature, magnetic field vector, and velocity vector in horizontal slices at the visible surface, in subsurface layers, and in vertical cuts through the simulation box to track PGs and compare, statistically and in individual cases, the physical quantities inside them with those in the surroundings. Results. The statistical analysis of simulation results provides average values of temperature, magnetic field strength and inclination, vertical velocity, and their changes with radial distance from the spot centre. We find a subtle difference between simulated PGs with opposite directions of motions when comparing the magnetic field inclinations inside and outside the PGs. The case studies, documented by movies, show that the differences of inclinations and the direction of motions may change during the lifetime of some PGs and that the turbulence in the surface layers introduces some randomness in the apparent motions of PGs.

SKA-Low simulations for a cosmic dawn/epoch of reionisation deep field

• Authors: Anna Bonaldi, Philippa Hartley, Simon Purser, Omkar Bait, Eunseong Lee, Robert Braun, Florent Mertens, Andrea Bracco, Wendy Williams, Cath Trott

• Subjects: Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2506.09533

• Pdf link: https://arxiv.org/pdf/2506.09533

• Abstract We present a realistic simulation of an SKA-Low cosmic dawn/epoch of reionisation (CD/EoR) observation, which can be used to further the development of foreground-mitigation approaches. The simulation corresponds to a deep (1000 h) integration pointing over the 106 MHz-196 MHz frequency range. The sky components include the CD/EoR signal, extragalactic foreground emission featuring strong (over 5 Jy at 150 MHz) out-of-field sources and in-field sources down to 1 microJy at 150 MHz, and Galactic emission from the GSM2016 model complemented with small-scales structure beyond its native $\sim 1$ deg resolution from a magneto-hydrodynamic simulation of the interstellar medium. Modeled errors include a partial de-mixing of the out-of-field sources, direction-dependent calibration errors leading to residual ionospheric effects, and direction-independent gain calibration errors, on top of thermal noise. Simulated observations are delivered as visibilities as well as imaging products with natural weighting. The true, uncorrupted, CD/EoR signal is also delivered, to allow an assessment of the efficacy of foreground-mitigation approaches. The codes used to generate these simulations are also delivered, so that new simulated datasets can be produced. This simulation has been the basis for the SKA Science Data Challenge 3a (SDC3a), which addressed foreground removal.

A core-sensitive mixed $f$/$g$ mode of the Sun predicted by wave topology and hydrodynamical simulation

• Authors: Arthur Le Saux, Armand Leclerc, Guillaume Laibe, Pierre Delplace, Antoine Venaille

• Subjects: Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

• Arxiv link: https://arxiv.org/abs/2506.09572

• Pdf link: https://arxiv.org/pdf/2506.09572

• Abstract Helioseismology has revolutionized our understanding of the Sun by analyzing its global oscillation modes. However, the solar core remains elusive, limiting a full understanding of its evolution. In this work, we study a previously unnoticed global oscillation mode of the Sun using a fully compressible, hydrodynamical simulation of the solar interior, and assess that it is a mixed $f$/$g$ mode with a period of about one hour. This is the first global stellar hydrodynamics simulation that successfuly couple compressible and gravity modes. To understand this coupling, we invoke a recent theory on the nature of $f$-modes seen through the prism of wave topology, characterizing their ability to propagate deep into stellar interiors. We demonstrate that the mixed $f$/$g$ mode is highly sensitive to the core's rotation rate, providing a new promising pathway to explore the Sun's core.

Deriving physical parameters of unresolved star clusters. IX. Sky background effects in the aperture photometry

• Authors: Karolis Daugevičius, Rima Stonkutė, Eimantas Kriščiūnas, Erikas Cicėnas, Vladas Vansevičius

• Subjects: Subjects: Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2506.09622

• Pdf link: https://arxiv.org/pdf/2506.09622

• Abstract The aperture photometry method is a powerful tool that enables us to study large star cluster systems efficiently. However, its accuracy depends on various factors, including the stochasticity of the stellar initial mass function and variations in the sky background. Previously, in the eighth paper of this series, we established the best achievable limits of the aperture photometry method for star cluster studies in the local universe. The aim of this study is to determine how the sky background affects the limits and applicability of the aperture photometry method in star cluster analysis. We used a large sample of star cluster models spanning the parameter space of M 31 clusters. To determine how the background affects star cluster photometry, we placed images of simulated clusters into five background fields of different stellar density from the Panchromatic $Hubble$ Andromeda Treasury (PHAT) survey and measured them using aperture photometry. We determined age and mass limits for the M 31 disc star clusters at which photometric uncertainties are low enough to enable the determination of cluster parameters using the aperture photometry method. We demonstrated that for typical-size clusters, optimal aperture diameters are of ~3 half-light radii. We assessed cluster detection completeness in relation to varying sky background densities, based on the M 31 PHAT survey data. Our results suggest that a significant selection bias towards more compact clusters may exist in the PHAT survey. We derived low-mass limits of the cluster mass function (CMF) in the PHAT survey, reaching down to masses of ~500 $M_\odot$ in outer disc areas, ~1500 $M_\odot$ in middle disc or star-forming regions, and ~3000 $M_\odot$ in inner disc regions. Therefore, we stress a necessity of careful accounting for selection effects arising due to sky background variations when studying the CMF.

The ATLAS Virtual Research Assistant

• Authors: H. F. Stevance, K. W. Smith, S. J. Smartt, S. J. Roberts, N. Erasmus, D. R. Young, A. Clocchiatti

• Subjects: Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2506.09778

• Pdf link: https://arxiv.org/pdf/2506.09778

• Abstract We present the Virtual Research Assistant (VRA) of the ATLAS sky survey which performs preliminary eyeballing on our clean transient data stream. The VRA uses Histogram Based Gradient Boosted Decision Tree Classifiers trained on real data to score incoming alerts on two axes: "Real" and "Galactic". The alerts are then ranked using a geometric distance such that the most "Real" and "Extra-galactic" receive high scores; the scores are updated when new light curve data is obtained on subsequent visits. To assess the quality of the training we use the Recall at rank K, which is more informative to our science goal than general metrics such as accuracy or F1-Scores. We also establish benchmarks for our metric based on the pre-VRA eyeballing strategy, to ensure our models provide notable improvements before being added to the ATLAS pipeline. Finally, policies are defined on the ranked list to select the most promising alerts for humans to eyeball and to automatically remove the bogus alerts. In production the VRA method has resulted in a reduction in eyeballing workload by 85% with a loss of follow-up opportunity <0.08%. It also allows us to automatically trigger follow-up observations with the Lesedi telescope, paving the way to automated methods that will be required in the era of LSST.

by olozhika (Xing Yuchen).

2025-06-12