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Arxiv_Daily_Notice/2026-01-16-Arxiv-Daily-Paper.md

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+# Showing new listings for Friday, 16 January 2026
+Auto update Star Formation & Molecular Cloud papers at about 2:30am UTC (10:30am Beijing time) every weekday.
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+
+阅读 `Usage.md`了解如何使用此repo实现个性化的Arxiv论文推送
+
+See `Usage.md` for instructions on how to personalize the repo. 
+
+
+Keyword list: ['star formation', 'star-forming', 'molecular cloud', 'interstellar medium', 'cloud', 'clump', 'core', 'filament', 'atomic gas', 'N-PDF']
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+
+Excluded: ['galaxies', 'galaxy cluster', ' AGN ', 'standard candle', 'X-ray binar', 'solar corona']
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+
+### Today: 6papers 
+#### The influence of magnetic fields in Cloud-Cloud Collisions
+ - **Authors:** Theotokis Georgatos, AnthonyP.Whitworth
+ - **Subjects:** Subjects:
+Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
+ - **Arxiv link:** https://arxiv.org/abs/2601.09794
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.09794
+
+ - **Abstract**
+ Cloud-cloud collisions are expected to trigger star formation by compressing gas into dense, gravitationally unstable regions. However, the role of magnetic fields in this process is unclear. We use SPH to model head-on collisions between two uniform density clouds, each with mass $500 \,$M$_{\odot}$, initial radius 2 pc, and embedded in a uniform magnetic field parallel to the collision velocity. As in the nonmagnetic case, the resulting shock-compressed layer fragments into a network of filaments. If the collision is sufficiently slow, the filaments are dragged into radial orientations by non-homologous gravitational contraction, resulting in a $\textit{Hub Filament}$ morphology, which spawns a centrally concentrated monolithic cluster with a broad mass function shaped by competitive accretion and dynamical ejections. If the collision is faster, a $\textit{Spiders Web}$ of intersecting filaments forms, and star-systems condense out in small subclusters, often at the filament intersections; due to their smaller mass reservoirs, and the lower probability of dynamical ejection, the mass function of star-systems formed in these subclusters is narrower. Magnetic fields affect this dichotomy quantitatively by delaying collapse and fragmentation. As a result, the velocity threshold separating $\textit{Hub Filament}$ and $\textit{Spiders Web}$ morphologies is shifted upward in magnetised runs, thereby enlarging the parameter space in which $\textit{Hub Filament}$ morphologies form, and enhancing the likelihood of producing centrally concentrated clusters. Consequently, magnetic fields regulate both the morphology and timing of star formation in cloud-cloud collisions: they broaden filaments, delay the onset of star formation, and promote the formation of $\textit{Hub Filament}$ morphologies, monolithic clusters and high-mass star-systems.
+#### HR-GO II: chemical abundances of low-$E$ retrograde dynamically-tagged-groups: Revealing Thamnos as a very metal-poor substructure
+ - **Authors:** Renjing Xie, Zhen Yuan, Haining Li, Tadafumi Matsuno, Nicolas F. Martin, Ruizhi Zhang, Zhiqiang Yan, Federico Sestito, Guillaume F. Thomas, Projjwal Banerjee, Ruizheng Jiang, Linda Lombardo, David S. Aguado, Kohei Hattori, Gang Zhao
+ - **Subjects:** Subjects:
+Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
+ - **Arxiv link:** https://arxiv.org/abs/2601.09796
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.09796
+
+ - **Abstract**
+ Milky Way halo substructures identified in dynamical space are known to suffer from contamination from the Milky Way in-situ stars, which makes their accreted origins uncertain. We present detailed chemical abundances of 35 stars belonging to two sets of dynamically tagged groups, Rg8 and Rg9, to investigate their accreted nature. Both groups are composed of stars with low orbital energy and very retrograde orbits. We find that Rg8 and Rg9 are chemically indistinguishable across all elements, from C to Eu, strongly indicating that they belong to the same structure. The iron-abundance distribution of this low-$E$ retrograde group has a prominent peak at [Fe/H] $\approx-2.1$, revealing that its main population is very metal-poor, and a secondary peak at [Fe/H] $\approx-1.5$, very likely due to contamination from Milky Way in-situ stars. These groups also heavily overlap with the Thamnos substructure in dynamical space, and we thus use them to investigate the chemical properties of Thamnos. The dominant, low-metallicity population provides strong evidence for the ex-situ origin of Thamnos, as well as its very metal-poor nature. We do not see any evidence of an $\alpha$ knee in our sample, which is consistent with previous studies. Comparison with the Cetus-Palca stream in the chemical space shows similar abundance distributions, and thus it suggests that the Thamnos progenitor dwarf galaxy had a truncated star formation history due to its early merger with the Milky Way.
+#### The formation of periodic three-body orbits for Newtonian systems
+ - **Authors:** Simon Portegies Zwart, Arjen Doelman, Jelmer Sein
+ - **Subjects:** Subjects:
+Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM); Mathematical Physics (math-ph)
+ - **Arxiv link:** https://arxiv.org/abs/2601.09843
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.09843
+
+ - **Abstract**
+ Braids are periodic solutions to the general N-body problem in gravitational dynamics. These solutions seem special and unique, but they may result from rather usual encounters between four bodies. We aim at understanding the existence of braids in the Galaxy by reverse engineering the interactions in which they formed. We simulate self-gravitating systems of N particles, starting with the constructing of a specific braid, and bombard it with a single object. We study how frequently the bombarded braid dissolves in four singles, a triple and a single, a binary and 2 singles, or 2 binaries. The relative proportion of those events gives us insight into how easy it is to generate a braid through the reverse process. It turns out that braids are easily generated from encounters between 2 binaries, or a triple with a single object, independent on the braid's stability. We find that 3 of the explored braids are linearly stable against small perturbations, whereas one is unstable and short-lived. The shortest-lived braid appears the least stable and the most chaotic. nonplanar encounters also lead to braid formation, which, in our experiments, themselves are planar. The parameter space in azimuth and polar angle that lead to braid formation via binary-binary or triple-single encounters is anisotropic, and the distribution has a low fractal dimension. Since a substantial fraction of ~9% of our calculations lead to periodic 3-body systems, braids may be more common than expected. They could form in multi-body interactions. We do not expect many to exist for time, but they may be common as transients, as they survive for tens to hundreds of periodic orbits. We argue that braids are common in relatively shallow-potential background fields, such as the Oort cloud or the Galactic halo. If composed of compact objects, they potentially form interesting targets for gravitational wave detectors.
+#### sponchpop II: Population Synthesis to Investigate Volatile Sulfur as a Fingerprint of Gas Giant Formation Histories
+ - **Authors:** Anna Sommerville-Thomas, Mihkel Kama, Oliver Shottle, Jason Ran
+ - **Subjects:** Subjects:
+Earth and Planetary Astrophysics (astro-ph.EP)
+ - **Arxiv link:** https://arxiv.org/abs/2601.10508
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.10508
+
+ - **Abstract**
+ Planet population synthesis is an integral tool for linking exoplanets to their formation environments. Most planet population synthesis studies have focused on the carbon-to-oxygen ratio (C/O) in gas or solids, yet more insight into planet formation may be afforded by considering a wider suite of elements. Sulfur is one such key element. It has been assumed to be entirely refractory in population synthesis models, restricting it to being a tracer of accreted rocky solids. However, sulfur also has a volatile reservoir dominant at the onset of star and planet formation. We investigate sulfur's wider potential as a formation history tracer by implementing the first multi-phase treatment of S in a planet population synthesis model. We present the planet formation module of \textsc{sponchpop} and its first predicted planet growth tracks and populations. We explore the diversity of planet compositions in terms of their sulfur budget, including both refractory and volatile components, and apply a novel gas-grain conversion of sulfur to study how formation trajectories of giant planets relate to final core and envelope compositions. We show that planets inherit a wide range of core and envelope sulfur content related to accretion history while considering late-stage planetesimal infall, providing a new diagnostic tool for planet formation. The diverse sulfur content of planet cores suggests some rocky planets may be born sulfur-poor, with implications for their geochemistry and habitability. Enhanced sulfur abundances in gas-giant atmospheres can be attributed to formation beyond the H2S iceline, such as the giants in our Solar System.
+#### High-fidelity stellar extinction with Gaia and APOGEE -- I. The method and a new extinction curve
+ - **Authors:** Jie Yu, Luca Casagrande, John A. Taylor, Ioana Ciucă, Giacomo Cordoni, Ronald Drimmel, Shourya Khanna, Hiep Nguyen, Tomasz Różański, Dennis Stello, Haibo Yuan, Zhen Yuan
+ - **Subjects:** Subjects:
+Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
+ - **Arxiv link:** https://arxiv.org/abs/2601.10595
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.10595
+
+ - **Abstract**
+ The scarcity of high-fidelity extinction measurements remains a bottleneck in deriving accurate stellar properties from Gaia parallaxes. In this work, we aim to derive precision extinction estimates for APOGEE DR19 stars, establishing a new benchmark for Galactic stellar population studies. We first determine reddening by comparing observed colorsr, etrieved from photometric surveys or standardized synthetic magnitudes from Gaia BP/RP spectra, to intrinsic colors predicted via an XGBoost model. The model is trained on minimally reddened stars to infer intrinsic colors and their associated uncertainties, using APOGEE stellar parameters (Teff, logg, [Fe/H], and [alpha/Fe]). The derived reddening values are then converted into extinctions using an anchor ratio of A_BP / A_RP = 1.694 +/- 0.004, derived from red-clump-like stars. Here, we provide extinction measurements in 39 filters across 10 photometric systems and introduce a new empirical extinction curve optimized for broadband passbands. Our extinction estimates (Av) outperform existing results (Bayestar19, StarHorse, SEDEX), achieving a typical precision of 0.03 mag in Av. Notably, we identify systematic deviations of up to 30% between monochromatic and passband-integrated extinction ratios at wavelengths greater than 700 nm. This result highlights the necessity of adopting passband-specific coefficients when correcting extinction to derive stellar parameters. As the foundation for a forthcoming series of papers, these benchmark measurements will be used to (1) revise asteroseismic scaling relations, (2) calibrate differential reddening in open clusters, and (3) reconcile heterogeneous dust maps into a unified, all-sky extinction scheme.
+#### HII regions in NGC 628: the view of two catalogs
+ - **Authors:** Ksenia I. Smirnova, Dmitri S. Wiebe
+ - **Subjects:** Subjects:
+Astrophysics of Galaxies (astro-ph.GA)
+ - **Arxiv link:** https://arxiv.org/abs/2601.10642
+
+ - **Pdf link:** https://arxiv.org/pdf/2601.10642
+
+ - **Abstract**
+ The study is devoted to comparing the parameters of the interstellar medium of HII regions in the Kongiu and Groves catalogs for the galaxy NGC 628. The article analyzes the characteristics of star-forming regions, including a comparison of radiation fluxes in the ranges of 7.7 $\mu$m and 21 $\mu$m and in the H$\alpha$, H$\beta$, OIII and CO lines, calculating the kinematic parameters (FWHM) for the lines, and analyzing the spatial distribution of regions for both catalogs. The results of the study showed that the regions from the Groves catalog demonstrate higher line widths compared to the Kongiu catalog. Signs of possible misidentified classification of some regions from the Groves catalog were revealed: there is a possibility that some of them are not HII regions, but shock ionization regions.
+
+
+by olozhika (Xing Yuchen). 
+
+
+2026-01-16