Showing new listings for Wednesday, 24 September 2025

[olozhika]

Showing new listings for Wednesday, 24 September 2025

Auto update Star Formation & Molecular Cloud papers at about 2:30am UTC (10:30am Beijing time) every weekday.

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']

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

Today: 27papers

Automatic Classification of Magnetic Chirality of Solar Filaments from H-Alpha Observations

• Authors: Alexis Chalmers, Azim Ahmadzadeh

• Subjects: Subjects:
  Solar and Stellar Astrophysics (astro-ph.SR); Artificial Intelligence (cs.AI)

• Arxiv link: https://arxiv.org/abs/2509.18214

• Pdf link: https://arxiv.org/pdf/2509.18214

• Abstract
  In this study, we classify the magnetic chirality of solar filaments from H-Alpha observations using state-of-the-art image classification models. We establish the first reproducible baseline for solar filament chirality classification on the MAGFiLO dataset. The MAGFiLO dataset contains over 10,000 manually-annotated filaments from GONG H-Alpha observations, making it the largest dataset for filament detection and classification to date. Prior studies relied on much smaller datasets, which limited their generalizability and comparability. We fine-tuned several pre-trained, image classification architectures, including ResNet, WideResNet, ResNeXt, and ConvNeXt, and also applied data augmentation and per-class loss weights to optimize the models. Our best model, ConvNeXtBase, achieves a per-class accuracy of 0.69 for left chirality filaments and $0.73$ for right chirality filaments.

The Streaming Instability in 3D: Conditions for Strong Clumping

• Authors: Jeonghoon Lim, Jacob B. Simon, Rixin Li, Olivia Brouillette, David G. Rea, Wladimir Lyra

• Subjects: Subjects:
  Earth and Planetary Astrophysics (astro-ph.EP)

• Arxiv link: https://arxiv.org/abs/2509.18270

• Pdf link: https://arxiv.org/pdf/2509.18270

• Abstract
  The streaming instability (SI) is a leading mechanism for planetesimal formation, driving the aerodynamic concentration of solids in protoplanetary disks. The SI triggers strong clumping (i.e., strong enough for clumps to collapse) when the solid-to-gas column density ratio, $Z$, exceeds a threshold, $\Zcrit$. This threshold depends on the dimensionless stopping time, $\tau_s$. Although the strong-clumping threshold has been explored over the last decade, it has been determined largely through 2D axisymmetric simulations. In this work, we perform a suite of 3D, vertically stratified simulations to establish a clumping threshold across $10^{-3} \leq \tau_s \leq 1.0$. Additionally, we study SI-driven concentration that is unique to 3D. We find that $\Zcrit$ is as low as $\approx 0.002$ at $\tau_s=0.1$ and exceeds $\approx 0.03$ at $\tau_s=10^{-3}$. Compared to 2D, our 3D results yield lower $\Zcrit$ for $\tau_s > 0.02$, but higher for $\tau_s \leq 0.02$, with a sharp transition between $\tau_s = 0.02$ and 0.03. This transition correlates with midplane density ratio ($\epsilon$): $\epsilon < 1$ where 3D gives lower thresholds, and $\epsilon > 1$ where 3D gives higher thresholds. We also find a filaments-in-filaments structure when $\epsilon < 1$, which enhances clumping compared to 2D. By contrast, when $\epsilon > 1$ and $\tau_s \leq 0.03$, dust filaments in 3D do not drift inward, suppressing filament mergers and strong clumping. In 2D, filaments drift inward regardless of $\epsilon$, triggering strong clumping easier in this regime. Our results underscore the necessity of 3D simulations for accurately capturing SI-driven concentration and building the strong-clumping threshold.

Crank-rocker optical fiber mode scrambler prototype for the GMT-Consortium Large Earth Finder (G-CLEF)

• Authors: Matthew C. H. Leung, Colby Jurgenson, Andrew Szentgyorgyi, William Podgorski, Mark Mueller, Yahel Sofer Rimalt, Joseph Zajac, Cem Onyuksel, Daniel Durusky, Peter Doherty

• Subjects: Subjects:
  Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2509.18306

• Pdf link: https://arxiv.org/pdf/2509.18306

• Abstract
  When coherent light propagates through a multimode optical fiber, the modes interfere at the fiber exit boundary, producing a high-contrast speckle interference pattern called modal noise. This non-uniform interference pattern introduces systematic errors in fiber-fed precision radial velocity (RV) spectrographs which are detrimental to exoplanet mass measurement. Modal noise can be mitigated by a device called a fiber mode scrambler or fiber agitator, which dynamically perturbs the fiber to change the interference pattern over time, smoothing it over long exposures. In this paper, we present a prototype optical fiber mode scrambler based on a four-bar linkage crank-rocker mechanism, developed for the GMT-Consortium Large Earth Finder (G-CLEF). G-CLEF is a fiber-fed, high-resolution, precision RV spectrograph for the Magellan Clay Telescope and Giant Magellan Telescope (GMT). To support this effort, we developed a fiber testing setup capable of imaging the near-field and far-field output of fibers and measuring focal ratio degradation. We designed, built, and tested the mode scrambler, using our setup, on step-index multimode optical fibers with various shapes, including octagonal, square, and rectangular core cross-sections. We developed custom software utilizing alpha shapes to identify the boundary of an arbitrarily shaped fiber and to compute a signal-to-noise ratio metric for quantifying modal noise. We investigated the effects of different mode scrambler parameters, such as agitation frequency, on mitigating modal noise. Our results offer valuable insights into optimizing fiber mode scrambling for precision RV spectrographs.

Piecing together formic acid isomerism in dark clouds. Detection of cis-formic acid in TMC-1 and astrochemical modeling

• Authors: G. Molpeceres, M. Agúndez, M. Mallo, C. Cabezas, M. Sanz-Novo, V.M. Rivilla, J. García de la Concepción, I. Jiménez-Serra, J. Cernicharo

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

• Arxiv link: https://arxiv.org/abs/2509.18315

• Pdf link: https://arxiv.org/pdf/2509.18315

• Abstract
  The presence of molecular isomers in interstellar environments has become a topic of growing interest within the astrochemical community. Contrary to predictions based on thermodynamic equilibrium, recent observations reveal a diverse array of high-energy isomers and conformers. One of the most iconic molecular isomers detected in space, formic acid (HCOOH, FA), has been the focus of extensive theoretical research aimed at understanding its speciation into cis and trans conformers in dark clouds and photodissociation regions. In this work, we report the detection of c-FA, the higher-energy conformer, using ultrasensitive observations of TMC-1. This detection adds to previous findings in the Barnard-5 and L483 dark clouds. The derived trans-to-cis isomer ratio in TMC-1, 17.5, closely matches those observed in other sources, suggesting that the same chemical processes are at play across these environments. To investigate this, we conducted detailed astrochemical gas-grain models tailored to formic acid isomerism to explain the observed ratios. Our models successfully reproduce the observed trans/cis ratios and indicate that the presence of cis-formic acid can be attributed to the release of c-FA from grains, followed by isomerization driven by the excess energy released during the desorption process, a process that we name as isomerization upon desorption. The models also show that the isomerization of t-FA to c-FA in the gas phase is negligible at 10 K, meaning the observed ratios are a direct consequence of the formation pathways of both isomers on the surface of dust grains. However, at higher temperatures, quantum tunneling mediated direct isomerization in the gas becomes significant, and the ratios converge toward the thermodynamic equilibrium value.

The Timescales of Embedded Star Formation as Observed in STARFORGE

• Authors: Tobin M. Wainer, Julianne J. Dalcanton, Michael Y. Grudić, Stella S. R. Offner, Adam Smercina, Benjamin F. Williams, L. Clifton Johnson, J. Peltonen, Eric W. Koch, Kartik R. Neralwar

• Subjects: Subjects:
  Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2509.18322

• Pdf link: https://arxiv.org/pdf/2509.18322

• Abstract
  Star formation occurs within dusty molecular clouds that are then disrupted by stellar feedback. However, the timing and physical mechanisms that govern the transition from deeply embedded to exposed stars remain uncertain. Using the STARFORGE simulations, we analyze the evolution of ``embeddedness'', identifying what drives emergence. We find the transition from embedded to exposed is fast for individual stars, within 1.3 Myr after the star reaches its maximum mass. This rapid transition is dominated by massive stars, which accrete while remaining highly obscured until their feedback eventually balances, then overcomes, the local accretion. For these massive stars, their maximum mass is reached simultaneously with their emergence. Once these stars are revealed, their localized, pre-supernova feedback then impacts the cloud, driving gas clearance. Because massive stars dominate the luminosity, their fast, local evolution dominates the light emergence from the dust. We calculate the dependence of these processes on the mass of the cloud and find that emergence always depends on when massive stars form, which scales with the cloud's free-fall time. We also examine the evolution of dust emission and H$\alpha$ luminosity. We find that dust dominates the luminosity for roughly 2 Myrs before stellar luminosity becomes more luminous. These results suggest that deeply embedded star-forming clusters tend to be rare compared to those partially exposed. Thus, because the initial embedding of the most luminous stars is highly local, the emergence of stars is a faster, earlier, more local event than the overall disruption of the cloud by gas expulsion.

Simulations of multiple dust ring formation in a subsolar-metallicity protoplanetary disk

• Authors: Ryoki Matsukoba, Eduard I. Vorobyov, Takashi Hosokawa

• Subjects: Subjects:
  Earth and Planetary Astrophysics (astro-ph.EP)

• Arxiv link: https://arxiv.org/abs/2509.18449

• Pdf link: https://arxiv.org/pdf/2509.18449

• Abstract
  Super-Earths exist around subsolar-metallicity host stars with a frequency comparable to that around solar-metallicity stars, suggesting efficient assembly of dust grains even in metal-deficient environments. In this study, we propose a pathway for the formation of multiple dust rings that will promote planetesimal formation in a subsolar-metallicity disk. We investigate the long-term evolution of a circumstellar disk with 0.1 $Z_{\odot}$ over 750 kyr from its formation stage using two-dimensional thin-disk hydrodynamic simulations. The motion of dust grains is solved separately from the gas, incorporating dust growth and self-consistent radial drift. The disk is initially gravitationally unstable and undergoes intense fragmentation. By 300 kyr, it tends toward a stable state, leaving a single gravitationally bound clump. This clump generates tightly wound spiral arms through its orbital motion. After the clump dissipates at $\sim$410 kyr, the spiral arms transition into axisymmetric substructures under the influence of viscosity. These axisymmetric substructures create local gas pressure bumps that halt the inward radial drift of dust grains, resulting in the formation of multiple-ring-shaped dust distributions. We observe several rings within $\simeq$200 au of the central star, with separations between them on the order of $\sim$10 au, and dust surface density contrasts with inter-ring gaps by factors of $\sim$10-100. We also demonstrate that turbulent viscosities at observationally suggested levels are essential for converting spiral arms into axisymmetric substructures. We speculate that the physical conditions in the dust rings may be conducive to the development of streaming instability and planetesimal formation.

Design overview of the fiber feed for the Hobby-Eberly telescope's HRS

• Authors: Devika K Divakar, Phillip MacQueen, Joseph Strubhar

• Subjects: Subjects:
  Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2509.18450

• Pdf link: https://arxiv.org/pdf/2509.18450

• Abstract
  We present the redesign of the fiber feed for the High Resolution Spectrograph (HRS) at the Hobby Eberly Telescope (HET). The upgrade incorporates a static atmospheric dispersion corrector (ADC) using Ohara i-line glasses (BAL15Y and S-FPL51Y), carefully selected for high internal transmission (> 99%), and optimized to improve throughput and image quality across the 360 - 1000 nm band. The ADC consists of two identical Amici prisms, fixed at an orientation optimized for the HET's nominal zenith angle (35\textdegree), correcting dispersion over the HET zenith range of 26.5\textdegree to 43.5\textdegree. Relay optics were optimized to improve blue end sensitivity and maintain substantially sub-fiber-core RMS spot radii across the full field of view. Simulations, including atmospheric dispersion modeling in ZEMAX show residual dispersion $\le$ 0.42" considering the entire range of wavelengths and zenith distances, with transmission efficiency of 91 to 94%. We also discuss how the mechanical design integrates all optical elements, including the ADC, in a rigid, modular input head assembly mounted in the HET Prime Focus Instrument Package (PFIP). This optimized fiber feed enhances coupling efficiency, improves S/N in the blue, and enables higher radial velocity precision , maintaining HET - HRS as a leading facility for high - resolution spectroscopy.

Tidally-Controlled Fragmentation around Black Holes, Massive Clumps, Protostars, and the Galactic Center

• Authors: Guang-Xing Li

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

• Arxiv link: https://arxiv.org/abs/2509.18495

• Pdf link: https://arxiv.org/pdf/2509.18495

• Abstract
  Gravity plays important roles at multiple scales in the universe. An important, yet often neglected, role of gravity is its ability in driving anisotropic fragmentation through tides. When tides dominate, fragmentation becomes anisotropic, and the Jeans length along the short axis, $l_{\rm tidal, Jeans}$, is approximately $\sigma_{\rm v}/\sqrt{G \rho_{\rm mean}}$, determined by the external tides through the mean density $\rho_{\rm mean}$. We compare predictions of $l_{\rm tidal, Jeans}$ against observational results in massive star-forming clumps, the Circumnuclear Disk (CND) around the supermassive black hole Sgr A* at the center of the Galaxy, the Central Molecular Zone in the Galactic Center, a hub-filament system, and a streamer around a young star. We find that the observed widths of these filamentary structures match theoretical predictions from tidally-controlled Jeans fragmentation. The formation of filaments can potentially shield cold gas against radiation pressure and photoevaporation, as well as hydrodynamical interaction with the ambient medium, potentially enabling the cold gas to survive. Thus, tidal forces are major players regulating gas transport around massive objects.

Kinematics of the interstellar medium using Gaia: A catalogue of 102 YSO-MC associations within 3.5 kpc from the Sun with 3D velocities

• Authors: Ji-Xuan Zhou, Guang-Xing Li, Bing-Qiu Chen

• Subjects: Subjects:
  Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2509.18496

• Pdf link: https://arxiv.org/pdf/2509.18496

• Abstract
  Kinematic information is crucial for understanding the evolution of complex systems, such as interstellar gas. Obtaining full 3D kinematic information is a crucial final step for modeling and interpretation. Molecular clouds are nurseries where stars are born. Stars at a very early stage, like young stellar objects (YSOs), inherit the spatial and kinematic structure of the gas patches they originate from. In this paper, we combine measurements of radial velocities towards the gas and the kinematic information of YSOs from Gaia DR3 to derive 3D velocities of a sample of YSO (Young Stellar Object)-MC (Molecular Cloud) complexes at d$\lesssim$3.5kpc from the Sun. We find that the molecular interstellar medium traced by the YSO-MC complexes generally follows Galactic rotation, with an additional peculiar velocity of 8.6 km s$^{-1}$. The random motion of these complexes in the Galactic XY plane is more energetic than motion along the Z direction. A catalogue containing the 3D velocities of the YSO-MC complexes at different reference frames is available, and the distances and 3D velocities of well-known molecular clouds are presented. Our results set the foundation for exploring the interplay between the Galaxy, the molecular ISM, and star formation. Data available at this https URL.

A recent re-acceleration of the Local Bubble revealed by kinematics of young star associations

• Authors: Guang-Ya Zeng, Guang-Xing Li, Bing-Qiu Chen, Ji-Xuan Zhou, Martin G.H. Krause

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

• Arxiv link: https://arxiv.org/abs/2509.18525

• Pdf link: https://arxiv.org/pdf/2509.18525

• Abstract
  The low-density region of the interstellar medium (ISM) where the Sun is located is known as the Local Bubble, a cavity filled with high-temperature and low-density plasma that may be created by a series of supernova (SN) explosions over the past 14 Myr. However, the effects of these SN explosions on the formation and evolution of the Local Bubble, as well as on nearby star formation, remain not fully understood. To study the expansion history of the Local Bubble, we use the kinematic data of the young stars obtained by cross-matching the pre-main-sequence (PMS) star catalog of \citet{Zari2018} with the high-precision astrometric and photometric data from the {\it Gaia} DR3 database. We perform a three-dimensional spatial clustering analysis on these young stars to identify star associations. We discover three unique star associations that exhibit a wiggle-like velocity pattern. The distances of these star associations are 108.5308, 141.5284, and 176.0318 pc, respectively. Their radial velocities in the Local Standard of Rest (LSR) are 10.0622, 5.4982, and 9.0581 km/s, showing a pattern of decreasing and then increasing. This velocity pattern, as predicted by \citet{Krause&Diehl2014}, is caused by a recent re-acceleration affected by the SN explosion, reinforcing the picture of the Local Bubble as an evolving entity.

Mass dependence of overshooting beneath convective envelopes

• Authors: J. Pratt, I. Baraffe, M.-G. Dethero, M. Stuck, D.G. Vlaykov, T. Goffrey

• Subjects: Subjects:
  Solar and Stellar Astrophysics (astro-ph.SR); Fluid Dynamics (physics.flu-dyn)

• Arxiv link: https://arxiv.org/abs/2509.18543

• Pdf link: https://arxiv.org/pdf/2509.18543

• Abstract
  Although the dependence of convective core overshooting on mass has attracted much attention, no corresponding work exists for overshooting below a convective envelope. We aim to quantify this relationship for pre-main sequence stars of intermediate mass ranging from $1.2 M_{\mathsf{sun}}$ to $6 M_{\mathsf{sun}}$. These stars have a similar thermal and density structure, making this a suitable choice to isolate the effect of changing mass. We produce a series of two-dimensional global simulations of stars using MUSIC, a fully compressible, time-implicit hydrodynamics code. The stars that we select for this study are near the end of the pre-main sequence and are convectively unstable above 80% of their stellar radius; they thus have a convective envelope that is shallower than the current sun. For this series of stellar models, a simple scaling with luminosity, with a scaling exponent of 1/4, accounts for the increasing overshooting with stellar mass. This result has interesting similarities with the scaling found by Baraffe et al. [2023] for a range of intermediate mass and massive stars at the zero-age main sequence (ZAMS) that have convective cores.

Silicate Precursor Silane detected in Cold Low-Metallicity Brown Dwarf

• Authors: Jacqueline K. Faherty, Aaron M. Meisner, Ben Burningham, Channon Visscher, Michael Line, Genaro Suarez, Jonathan Gagne, Sherelyn Alejandro Merchan, Austin James Rothermich, Adam J. Burgasser, Adam C. Schneider, Dan Caselden, J. Davy Kirkpatrick, Marc Jason Kuchner, Daniella Carolina Bardalez Gagliuffi, Peter Eisenhardt, Christopher R. Gelino, Eileen C. Gonzales, Federico Marocco, Sandy Leggett, Nicolas Lodieu, Sarah L. Casewell, Pascal Tremblin, Michael Cushing, Maria Rosa Zapatero Osorio, Victor J. S. Bejar, Bartosz Gauza, Edward Wright, Mark W. Phillips, Jun-Yan Zhang, Eduardo L. Martin

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

• Arxiv link: https://arxiv.org/abs/2509.18635

• Pdf link: https://arxiv.org/pdf/2509.18635

• Abstract
  Within 20 pc of the Sun there are currently 29 known cold brown dwarfs, sources with measured distances and an estimated effective temperature between that of Jupiter (170K) and ~500K. These sources are almost all isolated and are the closest laboratories we have for detailed atmospheric studies of giant planets formed outside the solar system. Here we report JWST observations of one such source, WISEA J153429.75-104303.3 (W1534), which we confirm is a substellar mass member of the Galactic halo with a metallicity <0.01xsolar. Its spectrum reveals methane (CH4), water (H2O), and silane (SiH4) gas. Although SiH4 is expected to serve as a key reservoir for the cloud-forming element Si in gas giant worlds, it eluded detection until now because it is removed from observable atmospheres by the formation of silicate clouds at depth. These condensates are favored with increasing metallicity, explaining why SiH4 remains undetected on well studied, metal-rich solar system worlds like Jupiter and Saturn. On the metal-poor world W1534, we detect a clear signature of SiH4 centered at ~4.55 microns with an abundance of 19+/-2 parts per billion (ppb). Our chemical modelling suggests that this SiH4 abundance may be quenched at ~kilobar levels just above the silicate cloud layers, whereupon vertical atmospheric mixing can transport SiH4 to the observable photosphere. The formation and detection of SiH4 demonstrates key coupled relationships between composition, cloud formation, and atmospheric mixing in cold brown dwarf and planetary atmospheres.

Properties of Chromospheric Fibrils Around a Quiescent Filament

• Authors: Qifan Dong, Xiaoli Yan, Zhike Xue, Jincheng Wang, Zhe Xu, Liheng Yang, Yian Zhou, Xinsheng Zhang, Zongyin Wu, Guotang Wu

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

• Arxiv link: https://arxiv.org/abs/2509.18646

• Pdf link: https://arxiv.org/pdf/2509.18646

• Abstract
  Fibrils are dynamic plasma structures in the solar chromosphere. Studying these structures is critical for understanding solar atmospheric heating and mass transportation. The purpose of this study is to obtain the characteristics of fibrils surrounding the filament. By employing high-resolution H-alpha data obtained from the New Vacuum Solar Telescope (NVST), we undertake a detailed analysis of the properties of 63 fibrils situated in the vicinity of the filament. Comparing the fibrils on both sides of the filament demonstrates that these fibrils have similar physical properties except for their orientation. The properties of fibrils are statistically measured, including lifetimes of 150-650 s, widths of 320-850 km, maximum lengths of 3-8.5 Mm, projection velocities of 7-29 km/s, and decelerations of 45-474 m/s2. The dominant oscillation period of fibrils is predominantly concentrated in the range of 4.8-6.6 minutes (2.5-3.5 mHz). Transverse oscillations are identified in a subset of fibrils, with periodicities of 269-289 s and phase speeds of 13.7-25.8 km/s, indicating the presence of kink-mode magnetohydrodynamic (MHD) waves.

Listening to the long ringdown: A novel way to pinpoint the EOS in neutron-star cores

• Authors: Christian Ecker, Tyler Gorda, Aleksi Kurkela, Luciano Rezzolla

• Subjects: Subjects:
  High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)

• Arxiv link: https://arxiv.org/abs/2509.18665

• Pdf link: https://arxiv.org/pdf/2509.18665

• Abstract
  Gravitational waves (GWs) from binary neutron star (BNS) merger remnants complement constraints from the inspiral phase, mass-radius measurements, and microscopic theory by providing information about the neutron-star equation of state (EOS) at extreme densities. We perform general-relativistic simulations of BNS mergers using EOS models that span the uncertain high-density regime. We find a robust correlation between the ratio of energy and angular momentum lost during the late-time post-merger GW signal - the long ringdown - and the EOS at the highest densities in neutron star cores. Applying this correlation to post-merger GW signals reduces EOS uncertainty at several times saturation density, where no direct constraints currently exist.

A multi-object approach for studying exoplanet atmospheres using high-resolution spectrographs

• Authors: Manjunath Bestha, Athira Unni, T. Sivarani, Dhanush S R, Lokesh Manickavasaham, Parvathy M, Devika K Divakar, Arun Surya

• Subjects: Subjects:
  Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)

• Arxiv link: https://arxiv.org/abs/2509.18721

• Pdf link: https://arxiv.org/pdf/2509.18721

• Abstract
  Atmospheric characterization of exoplanets has traditionally relied on Low-Resolution Transmission Spectroscopy (LRTS), obtained from both space- and ground-based facilities, as well as on High-Resolution Transmission Spectroscopy (HRTS). Although HRTS can resolve individual spectral lines, it is subject to normalization degeneracies that limit the accurate retrieval of key atmospheric parameters such as pressure, abundance, and cloud opacity. A promising strategy to mitigate this issue is to combine ground-based HRTS with space-based LRTS. However, this approach depends on two separate datasets, thereby requiring two independent observations. In this study, we explore the feasibility of Multi-Object High-Resolution Transmission Spectroscopy (Mo-HRTS) as a means to constrain atmospheric parameters in retrievals using a single dataset. Through simulations based on existing spectrograph specifications for a well-studied target, we demonstrate that low-resolution broadband transmission spectra can be extracted from Mo-HRTS data.

SDSS-IV MaNGA: Data-Model Discrepancy in Temperature-sensitive Line Ratios for Star-forming Galaxies

• Authors: Ziming Peng, Renbin Yan, Xihan Ji, Zesen Lin, Man-Yin Leo Lee

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

• Arxiv link: https://arxiv.org/abs/2509.18770

• Pdf link: https://arxiv.org/pdf/2509.18770

• Abstract
  Gas-phase metallicity is a fundamental parameter that helps constrain the star-forming history and chemical evolution of a galaxy. Measuring electron temperature through auroral-to-strong line ratios is a direct approach to deriving metallicity. However, there is a longstanding discrepancy between metallicity measured through the direct method and that based on the photoionization models. This paper aims to verify and understand the discrepancies. We bin ~ 1.5 million spaxels from SDSS-IV MaNGA according to metallicity and ionization parameters derived from theoretical strong-line calibrations. We stack the spectra of spaxels within each bin and measure the flux of strong lines and faint auroral lines. Auroral lines for [OII], [SII], [OIII], and [SIII] are detected in the stacked spectra of most bins, and the [NII] auroral line is detected in fewer bins. We apply an empirical method to correct dust attenuation, which makes more realistic corrections for low ionization lines. We derive electron temperatures for these five ionic species and measure the oxygen and sulfur abundances using the direct method. We present the resulting abundance measurements and compare them with those model-calibrated strong-line abundances. The chemical abundances measured with the direct method are lower than those derived from the photoionization model, with a median of 0.09 dex. This discrepancy is smaller compared to the results based on other metallicity calibrations previously reported. However, we notice that the direct method could not account for the variation in ionization parameters, indicating that the precise calibration of metallicity using the direct method has yet to be fully realized. We report significant discrepancies between data and the photoionization model, which illustrates that the one-dimensional photoionization model is incapable of representing the complexity of real situations.

Constraining Axion-Like Particle mediated Dark Matter with Observational Constraints: A Statistical and Machine Learning Approach

• Authors: Prashant Thakur, Aravind Taridalu, Ishfaq Ahmad Rather, Tanech Klangburam, Chakrit Pongkitivanichkul

• Subjects: Subjects:
  High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

• Arxiv link: https://arxiv.org/abs/2509.18863

• Pdf link: https://arxiv.org/pdf/2509.18863

• Abstract
  We present a comprehensive investigation into the phenomenological consequences of axion-like particle (ALP) mediated dark matter (DM) on neutron star (NS) structure. Using a relativistic mean-field framework with non-linear mesonic self-interactions constrained by nuclear data and astrophysical observations, we explore the DM parameter space spanning $m_\chi \in [0, 1000]\mathrm{GeV}$ and $q_f \in [0, 0.06]\mathrm{GeV}$, generating over 30,000 equations of state (EoSs). Two representative hadronic EoSs are employed, a stiff (EoS1) and a soft (EoS18), with explicit inclusion of the crustal EoS. A multi-tiered statistical filtering scheme, combining voting, likelihood, and kernel density estimation scores, is applied using constraints from radio and X-ray pulsars, GW170817, and the low-mass compact object HESS J1731-347. We find that models satisfying the PSR J0614$-$3329 radius bound automatically comply with HESS, positioning ALP-mediated DM as a viable explanation for low-mass compact objects while still supporting $2,M_\odot$ NSs. For the stiff EoS, we obtain $m_\chi \gtrsim 43~\mathrm{GeV}$, with score-weighted posteriors favoring $q_f = 0.034^{+0.020}{-0.012}$ and a broad allowed DM mass range $m\chi \in [101, 949]~\mathrm{GeV}$ (median $\sim 466$ GeV). The soft EoS yields no strict lower bound, though large $m_\chi$--$q_f$ combinations are disfavored. A high-precision supervised regression model built with AutoGluon achieves $R^2 &gt; 0.998$ for inferring DM parameters from NS observables. Feature analysis reveals $m_\chi$ is constrained by structural ratios such as $R_{1.6}/R_{1.4}$, whereas $q_f$ is set mainly by the tidal deformability $\Lambda_{1.4}$.

Ultra-Wideband Polarimetry of the April 2021 Profile Change Event in PSR J1713+0747

• Authors: Rami F. Mandow, Andrew Zic, J. R. Dawson, Shuangqiang Wang, Malgorzata Curylo, Shi Dai, Valentina Di Marco, George Hobbs, Vivek Gupta, Agastya Kapur, M. Kerr, Marcus E. Lower, Saurav Mishra, Daniel Reardon, Christopher J. Russell, Ryan M. Shannon, Lei Zhang, Xingjiang Zhu

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

• Arxiv link: https://arxiv.org/abs/2509.18972

• Pdf link: https://arxiv.org/pdf/2509.18972

• Abstract
  The millisecond pulsar PSR J1713+0747 is a high-priority target for pulsar timing array experiments due to its long-term timing stability, and bright, narrow pulse profile. In April 2021, PSR~J1713$+$0747 underwent a significant profile change event, observed by several telescopes worldwide. Using the broad-bandwidth and polarimetric fidelity of the Ultra-Wideband Low-frequency receiver on Murriyang, CSIRO's Parkes radio telescope, we investigated the long-term spectro-polarimetric behaviour of this profile change in detail. We highlight the broad-bandwidth nature of the event, which exhibits frequency dependence that is inconsistent with cold-plasma propagation effects. We also find that spectral and temporal variations are stronger in one of the orthogonal polarisation modes than the other, and observe mild variations ($\sim 3$ - $5,\sigma$ significance) in circular polarisation above 1400 MHz following the event. However, the linear polarisation position angle remained remarkably stable in the profile leading edge throughout the event. With over three years of data post-event, we find that the profile has not yet recovered back to its original state, indicating a long-term asymptotic recovery, or a potential reconfiguration of the pulsar's magnetic field. These findings favour a magnetospheric origin of the profile change event over a line-of-sight propagation effect in the interstellar medium.

Formation of thiocarbonic acid (H2CS3) - the sulfur counterpart of carbonic acid (H2CO3) - in interstellar analog ices

• Authors: Lina Coulaud, Jia Wang, Ashanie Herath, Andrew M. Turner, Mason Mcanally, Ryan C. Fortenberry, Ralf I. Kaiser

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

• Arxiv link: https://arxiv.org/abs/2509.19065

• Pdf link: https://arxiv.org/pdf/2509.19065

• Abstract
  The first experimental formation of thiocarbonic acid (H2CS3) is presented in this work from low-temperature interstellar ice analogs composed of hydrogen sulfide (H2S) and carbon disulfide (CS2) exposed to electron irradiation simulating the impact of galactic cosmic rays (GCRs) on interstellar ices. The recent attention brought to sulfur-bearing molecules, as well as the recent detection of carbonic acid (H2CO3) in the interstellar medium (ISM), invites the study of the interstellar detection of the sulfur counterpart, thiocarbonic acid. However, the interstellar formation pathways of thiocarbonic acid have remained elusive. In this work, thiocarbonic acid was identified in the gas phase during the temperature programmed desorption (TPD) using isomer-selective single photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS), suggesting that the hitherto astronomically unobserved thiocarbonic acid represents a promising candidate for future astronomical searches. The formation of H2CS3 isomers was investigated through additional isotopically labeled experiments and the formation mechanisms through quantum chemical studies. These findings unravel a key reaction pathway to thiocarbonic acid and represent a first step toward its possible formation and detection in the ISM, shedding light on the missing sulfur problem.

Linking Young Stellar Object Morphology to Evolutionary Stages with Self-Organizing Maps

• Authors: David Hernandez, Odysseas Dionatos, Marc Audard, Gábor Marton, Julia Roquette, Ilknur Gezer, Máté Madarász, Kai L. Polsterer

• Subjects: Subjects:
  Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

• Arxiv link: https://arxiv.org/abs/2509.19069

• Pdf link: https://arxiv.org/pdf/2509.19069

• Abstract
  Studies in the past few decades have investigated young stellar object evolution based on their spectral energy distribution (SED). The SED is heavily influenced not only by evolutionary stage, but also the morphology of the young star. This work is part of the NEMESIS project which is aiming to revisit star formation with the aid of machine learning techniques and provides the framework for this work. In a first effort towards a novel spectro-morphological classification we analyzed young stellar object morphologies and linked them to the currently used observational classes. Thereby we aim to lay the foundation for a spectro-morphological classification, and apply the insights learned in this study in a future, revisited classification scheme. We obtained archival high-resolution survey images from VISTA for approximately 10,000 literature young stellar object candidates towards the Orion star formation complex (OSFC). Utilizing a Self-Organizing map (SOM) algorithm, an unsupervised machine learning method, we created a grid of morphological prototypes from near- and mid-infrared images. Furthermore, we determined which prototypes are most representative of the different observational classes, derived from the infrared spectral index, via Bayesian inference. We present our grids of morphological prototypes of young stellar objects in the near-infrared, which were created purely from observational data. They are thus non-dependent on theoretical models. In addition, we show maps that indicate the probability for a prototype belonging to any of the observational classes. We find that SOMs created from near-infrared images are a useful tool, with limitations, to identify characteristic morphologies of young stellar objects in different evolutionary stages. This first step lays the foundation for a spectro-morphological classification of young stellar objects to be developed in the future.

Early Planet Formation in Embedded Disks (eDisk). XX: Constraining the Chemical Tracers of Young Protostellar Sources

• Authors: Rajeeb Sharma, Jes K. Jørgensen, Merel L. R. van 't Hoff, Jeong-Eun Lee, Yuri Aikawa, Sacha Gavino, Yao-Lun Yang, Nagayoshi Ohashi, John J. Tobin, Patrick M. Koch, Zhi-Yun Li, Leslie W. Looney, Mayank Narang, Suchitra Narayanan, Travis J. Thieme

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

• Arxiv link: https://arxiv.org/abs/2509.19158

• Pdf link: https://arxiv.org/pdf/2509.19158

• Abstract
  Recent studies indicate that the formation of planets in protoplanetary disks begins early in the embedded Class 0/I phases of protostellar evolution. The physical and chemical makeup of the embedded phase can provide valuable insights into the process of star and planet formation. This study aims to provide a thorough overview of the various morphologies for molecular emissions observed on disk scales toward nearby embedded sources. We present high angular resolution (0.1", 15 au) molecular line emissions for $^{12}$CO, $^{13}$CO, C$^{18}$O, SO, SiO, DCN, CH$_3$OH, H$_2$CO, and c-C$_3$H$_2$ towards 19 nearby protostellar sources in the context of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program "Early Planet Formation in Embedded Disks (eDisk)". Emissions in $^{12}$CO are seen towards all sources and primarily trace outflowing materials. A few sources also show high-velocity jets in SiO emission and high-velocity channel maps of $^{12}$CO. The $^{13}$CO and C$^{18}$O emissions are well-known tracers of high-density regions and trace the inner envelope and disk regions with clear signs of rotation seen at continuum scales. The large-scale emissions of $^{13}$CO also delineate the outflow cavity walls where the outflowing and infalling materials interact with each other, and exposure to UV radiation leads to the formation of hydrocarbons such as c-C$_3$H$_2$. Both DCN and CH$_3$OH, when detected, show compact emissions from the inner envelope and disk regions that peak at the position of the protostar. The CH$_3$OH emissions are contained within the region of DCN emissions, which suggests that CH$_3$OH traces the hot core regions. Likewise, a few sources also display emissions in CH$_3$OH towards the outflow. Both SO and H$_2$CO show complex morphology among the sources, suggesting that they are formed through multiple processes in protostellar systems.

A Scatter of Light from a Polarized World

• Authors: Sloane J. Wiktorowicz, Pushkar Kopparla, Jiazheng Li, Yuk L. Yung

• Subjects: Subjects:
  Earth and Planetary Astrophysics (astro-ph.EP)

• Arxiv link: https://arxiv.org/abs/2509.19172

• Pdf link: https://arxiv.org/pdf/2509.19172

• Abstract
  Many known exoplanets harbor clouds, which lead to degeneracies in spectroscopic models between particle composition and size. Polarimetry, however, provides independent assessment. Here we report the $7.2 \sigma$ discovery of linearly polarized, scattered light from the hot Jupiter HD 189733b in $B$ band (390 to 475 nm) peaking near quarter phase with $\Delta p = 40.9 \pm 7.1$ ppm. Polarization measurements, obtained with the POLISH2 polarimeter at both Gemini North and the Lick Observatory 3-m, are best explained by silicate (SiO$2$ or MgSiO$3$) particles with effective radius $r\text{eff}=0.038^{+0.047}{-0.023}$ $\mu$m ($90%$ confidence). This is broadly consistent with results from both Hubble transmission spectroscopy and JWST secondary eclipse spectroscopy suggesting small, SiO$_2$ scattering particles. It is difficult to reconcile large polarization and moderate Hubble secondary eclipse depth via pure Rayleigh, silicate, or MnS scatterers. The measured polarization of HD 189733b is detected with such high confidence that we place a $2\sigma$ lower limit on its $B$ band geometric albedo of $A_g &gt; 0.26$ with a preferred value of $A_g = 0.6$. This is larger than the prior estimate of $A_g = 0.226 \pm 0.091$ from Hubble secondary eclipse photometry, and it presents HD 189733b as one of the most reflective known exoplanets in $B$ band. It also validates Rayleigh scattering from the exoplanet, as opposed to starspot contamination, as the cause of HD 189733's blue optical slope in transmission spectroscopy. Assuming other known exoplanets harbor atmospheres like HD 189733b, we model dozens to be detectable with at least $5 \sigma$ confidence after one week of Gemini time each.

Internal dynamics and structure of Cepheus OB4. The asymmetric expansion of Berkeley 59

• Authors: Bruno Wiesneth, Koraljka Muzic, Victor Almendros-Abad

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

• Arxiv link: https://arxiv.org/abs/2509.19175

• Pdf link: https://arxiv.org/pdf/2509.19175

• Abstract
  Accurate measurements of young stellar cluster internal dynamics provide crucial insights into their formation. With Gaia, we are now able to trace stellar motions and study the dynamics of star clusters with unprecedented precision, but this requires a reliable list of probable members. We examine a 2 deg-radius region in Cepheus OB4, centered on the young cluster Berkeley 59, to build a reliable candidate member list, enabling the study of the cluster's structure, kinematics, and stellar population. We compiled a catalog of optical and near-infrared photometry, along with precise positions and proper motions from Gaia DR3, for sources in the Cepheus OB4 field. Membership probabilities were determined using a probabilistic random forest algorithm and further refined by requiring HR diagram positions consistent with a young age. From a list of 1030 probable members, we estimate a distance of 1009+-12 pc to Berkeley 59. Masses, extinction, and ages were derived by fitting the spectral energy distributions to atmospheric and evolutionary models, while internal dynamics was analyzed using proper motions relative to the cluster's mean motion. Berkeley 59 exhibits an asymmetric expansion pattern with velocity increasing outward and a preferred motion toward the north. The IMF between 0.4 and 7 MSun follows a single power law (dN/dM \propto M**-alpha), with the slope alpha=2.3+-0.3, consistent with Salpeter's slope and previous studies in the region. The region's median age, estimated from the HR diagram, is 2.9 Myr. The velocity dispersion of Berkeley 59 exceeds the virial velocity dispersion derived from its total mass (650+-30 MSun) and half-mass radius (1.71+-0.13 pc). The 2D motions of a stellar group located about 1 deg north of Berkeley 59 provide further support for the previously proposed triggered star formation scenario. (Abridged)

Lyman-$α$ Escape through Anisotropic Media

• Authors: Silvia Almada Monter, Max Gronke, Seok-Jun Chang

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

• Arxiv link: https://arxiv.org/abs/2509.19184

• Pdf link: https://arxiv.org/pdf/2509.19184

• Abstract
  The escape of Lyman-$\alpha$ (Ly$\alpha$) radiation encodes valuable information on the neutral interstellar medium and is often used as a proxy for the escape of ionizing photons. Yet, the theory of Ly$\alpha$ transfer through anisotropic gas distributions remains underdeveloped. We present Monte Carlo radiative transfer simulations of Ly$\alpha$ propagation through porous, inhomogeneous neutral gas, systematically exploring the effects of channel geometry, outflows, dust, and lognormally distributed column densities. We find that Ly$\alpha$ photons do not preferentially escape through the lowest-column-density pathways, but instead traverse channels of substantial optical depth, leading to suppressed central flux and the absence of strongly beamed escape. Subdividing channels has little impact, indicating that geometry and covering fraction are more important than porosity. Channels containing moderate amounts of neutral hydrogen alter escape in characteristic ways, including the appearance of quadruple-peaked spectra, which can be captured by a simple flux-channel relation. Outflows reshape the spectra by facilitating escape through dense media, redshifting photons and blending central features, while dust modulates the visibility of small channels by suppressing flux at line center; in both cases, we develop an analytical model that predicts the resulting central fluxes. Extending to lognormal column density fields, we show that Ly$\alpha$ photons probe a broad range of optical depths, producing skewed spectra that can be approximated by weighted sums of homogeneous models. Our results have direct implications for using Ly$\alpha$ as a tracer of gas properties and ionizing photon escape; for instance, spectra suggestive of high column densities may nonetheless allow LyC leakage through narrow channels.

Recalibration of the H$α$ surface brightness-radius relation for planetary nebulae using Gaia DR3: new distances and the Milky Way oxygen radial gradient

• Authors: Oscar Cavichia, Hektor Monteiro, Adalberto R. da Cunha-Silva, Walter J. Maciel, André F. S. Cardoso

• Subjects: Subjects:
  Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

• Arxiv link: https://arxiv.org/abs/2509.19239

• Pdf link: https://arxiv.org/pdf/2509.19239

• Abstract
  The spatial distribution of chemical elements in the Galactic disk provides key constraints on models of galaxy evolution. However, studies using planetary nebulae (PNe) as tracers have been historically limited by large uncertainties in their distances. To overcome the long-standing distance uncertainties, we recalibrated the H$\alpha$ surface brightness-radius relation (Frew et al. 2016) with Gaia DR3 parallaxes, deriving statistical distances for 1,200 PNe and Bayesian distances for 419 objects with reliable parallaxes. Adopting Bayesian values preferentially, we determined the O/H radial gradient for 230 disk PNe. We tested three models: a single linear gradient, a segmented fit with one break, and a segmented fit with two breaks. Although model selection is statistically inconclusive, segmented fits indicate a change in slope near the solar radius ($R \sim 8$ kpc), with a flatter or slightly positive gradient inward and a steeper negative gradient outward. This feature may reflect changes in star formation efficiency driven by the Galactic bar or the corotation resonance of the spiral arms. Comparison with other tracers - Cepheids, red giants, and open clusters - shows qualitative consistency. The two-dimensional O/H distribution in the Galactic plane supports the adopted distances and reveals modest azimuthal asymmetry, with enhanced abundances near the bar at positive longitudes, and a bimodal abundance structure between the inner and outer solar regions. Our results provide new constraints on the chemical evolution of the Milky Way, the impact of non-axisymmetric structures, and the possible existence of distinct radial abundance regimes across the Galactic disk.

3D Macro Physics and Light Odd-Z Element Production in O-C Shell Mergers: Implications for $^{40}\mathrm{K}$ production and radiogenic heating inventories of rocky exoplanets

• Authors: Joshua Issa, Falk Herwig, Stephen J. Mojzsis, Marco Pignatari

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

• Arxiv link: https://arxiv.org/abs/2509.19240

• Pdf link: https://arxiv.org/pdf/2509.19240

• Abstract
  The light odd-Z elements P, Cl, K, and Sc are underproduced in galactic chemical evolution models compared to spectroscopic observations of stars in the Milky Way. The most promising solution to this puzzle is that some massive stars experience O-C shell mergers boosting their yields through dynamic, convective-reactive nucleosynthesis. We report how convective macro physics based on 3D $4\pi$ hydrodynamic simulations impacts production in the O shell by post-processing the $\mathrm{M_{ZAMS}}=15~\mathrm{M_\odot}$ $Z=0.02$ model from the NuGrid dataset. We explore a mixing downturn, boosted velocities, reduced ingestion rate, and convective quenching. Across 24 mixing cases, the pre-explosive yields for [P/Fe], [Cl/Fe], [K/Fe], and [Sc/Fe] are modified by $[-0.33,0.23]\mathrm{dex}$, $[-0.84,0.64]\mathrm{dex}$, $[-0.78,1.48]\mathrm{dex}$, and $[-0.36,1.29]\mathrm{dex}$, respectively. Cases with a convective downturn with the fastest ingestion rate have the largest enhancement, and production is non-monotonic with boosted velocities. Which reactions are most important for the convective-reactive element production pathways depends on the mixing. We parameterize production of $^{40}\mathrm{K}$ ($t_{1/2} = 1.248~\mathrm{Gyr}$), an important radiogenic heat source for younger ($2{-}3~\mathrm{Gyr}$) rocky planets and find a yield variation exceeding three orders of magnitude. This range of initial abundances for $^{40}\mathrm{K}$ implies the early geodynamic behaviour of silicate mantles in rocky planets can differ greatly from that of Earth. These results underscore the importance of investigating the 3D macro physics of shell merger convection through hydrodynamic simulations to develop a predictive understanding of the origin and variability of the light odd-Z elements and the $^{40}\mathrm{K}/\mathrm{K}$ ratio in planet host stars.

Jittering jets promote dust formation in core-collapse supernovae

• Authors: Noam Soker (Technion, Israel)

• Subjects: Subjects:
  High Energy Astrophysical Phenomena (astro-ph.HE)

• Arxiv link: https://arxiv.org/abs/2509.19264

• Pdf link: https://arxiv.org/pdf/2509.19264

• Abstract
  I find that the dust morphologies in some core-collapse supernova (CCSN) remnants (CCSNRs) possess jet-shaped morphologies, and propose that the properties of the jets that explode the CCSNe and their interaction with the core and envelope (if it exists) are among the factors that determine the amount of dust formed and its morphology. I find that some of the dust-rich structures in the CCSNRs Cassiopeia A and the Crab Nebula are distributed in point-symmetric morphologies, and that the dust in SN 1987A follows the bipolar morphology of the inner ejecta. Earlier studies attributed these morphologies in these CCSNRs to shaping by jets in the framework of the jittering jets explosion mechanism (JJEM). These dust morphologies suggest, in the framework of the JJEM, that exploding jets enhance dust formation in CCSNRs. This study adds to the variety of processes that CCSN exploding jets are involved in and to the establishment of the JJEM as the explosion mechanism of CCSNe.

by olozhika (Xing Yuchen).

2025-09-24