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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 17 December

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

GRHayL: a modern, infrastructure-agnostic, extensible library for GRMHD simulations

Samuel Cupp, Leonardo R. Werneck, Terrence Pierre Jacques et al. (+2 more)

Interpreting multimessenger signals from neutron stars and black holes requires reliable general relativistic magnetohydrodynamics (GRMHD) simulations across rapidly evolving high-performance computing platforms, yet key algorithms are routinely rewritten within infrastructure-specific numerical relativity codes, hindering verification and reuse. We present the General Relativistic Hydrodynamics Library (GRHayL), a modular, infrastructure-agnostic GR(M)HD library providing conservative-to-primitive recovery, reconstruction, flux/source and induction operators, equations of state, and neutrino leakage through an intuitive interface. GRHayL refactors and extends the mature IllinoisGRMHD code into reusable point- and stencilwise kernels, enabling rapid development and cross-code validation in diverse frameworks, while easing adoption of new microphysics and future accelerators. We implement the same kernels in the Einstein Toolkit (Carpet and Carpetx) and BlackHoles@Home, demonstrating portability with minimal duplication. Validation combines continuous-integration unit tests with cross-infrastructure comparisons of analytic GRMHD Riemann problems, dynamical Tolman-Oppenheimer-Volkoff evolutions, and binary neutron star mergers, showing comparable or improved behavior over legacy IllinoisGRMHD and established Einstein Toolkit codes.
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All authors Samuel Cupp, Leonardo R. Werneck, Terrence Pierre Jacques, Samuel Tootle, Zachariah B. Etienne

Earth and Planetary Astrophysics

A JWST Transmission Spectrum of the Temperate Sub-Neptune TOI-732 c

Frances E. Rigby, Nikku Madhusudhan, Subhajit Sarkar et al. (+3 more)

In recent years, JWST has facilitated detections of carbon-bearing molecules in the atmospheres of temperate sub-Neptunes orbiting M dwarfs, ushering in a new era in the characterization of this intriguing planetary regime. We report the transmission spectrum of the temperate sub-Neptune TOI-732 c, observed with JWST NIRISS, NIRSpec G395H and MIRI LRS between 0.9-12 $\mu$m. The observations provide evidence for methane (CH$_4$) in a H$_2$-rich atmosphere, at a volume mixing ratio of $\sim$1%, and non-detection of NH$_3$ and HCN, along with nominal constraints on other prominent molecules H$_2$O, CO and CO$_2$, which are typically expected in H$_2$-rich atmospheres. We conduct a comprehensive survey of 250 chemical species and find moderate to strong evidence (up to $\ln B\sim 5.9$, $3.9\sigma$) for additional absorption due to one or more complex molecules including higher-order hydrocarbons and/or sulfur-bearing molecules. The spectral features are strongly degenerate among these molecules and with methane, which we find at $\ln B=3.2-8.8$ (up to $3.0-4.6$$\sigma$) significance. Two complex molecules are preferred with at least moderate evidence ($\ln B \gtrsim 2.5$) in both the near- and mid-infrared, while several others show such evidence in at least one of the two wavelength ranges. The preferred molecules are found in trace quantities on Earth, with no significant sources identified in other planetary atmospheres, requiring future work to assess their physical plausibility in this planet. Future observations are required to resolve the degeneracies and place more robust constraints on these species. We highlight the need for further theoretical and experimental work to robustly characterize the atmospheric and internal composition of TOI-732 c and similar sub-Neptunes.
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All authors Frances E. Rigby, Nikku Madhusudhan, Subhajit Sarkar, Lorenzo Pica-Ciamarra, Måns Holmberg, Julianne I. Moses

Instrumentation and Methods for Astrophysics

Galaxies as stochastic systems: why the next breakthrough in galaxy evolution requires one hundred million spectra

Sandro Tacchella, Vasily Belokurov, Harry T. J. Bevins et al. (+4 more)

Each galaxy is observed only once along its life, making galaxy evolution fundamentally an inverse statistical problem: time-dependent physics must be inferred from ensembles of single-epoch snapshots. To move beyond descriptive scaling relations toward physical regulation mechanisms of star formation, quenching, chemical enrichment and black hole growth, galaxies must be treated as realizations of a stochastic process whose hyper-parameters (e.g., correlation timescales, burstiness, duty cycles) are inferred hierarchically. This demands both depth and scale: continuum S/N sufficient for absorption-line ages and chemistry, and samples far larger than those in SDSS, DESI, 4MOST or MOONS, which provide either depth or size but not both across $0<z<3$. Once the relevant axes of mass, redshift, environment, structure and evolutionary phase are populated, the requirement naturally rises from $10^7$ to $\sim10^8$ galaxies. This is the regime where stochastic hyper-parameters can be well constrained and where comparisons to simulations and cosmological forward models become limited by theory rather than observations. We outline the science enabled by such a programme and the corresponding requirements for a future ESO wide-field spectroscopic facility capable of delivering tens to hundreds of millions of rest-UV-optical spectra over $0\lesssim z\lesssim3$.
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All authors Sandro Tacchella, Vasily Belokurov, Harry T. J. Bevins, Roberto Maiolino, Hiranya V. Peiris, Lucia Pozzetti, Mark T. Sargent

Instrumentation and Methods for Astrophysics

What Builds and Quenches the Most Massive Galaxies in the Early Universe?

Mengyuan Xiao, Longji Bing, Guilaine Lagache et al. (+4 more)

The first few billion years of cosmic history witnessed the rapid emergence of the most massive galaxies, yet their true space density, baryon assembly pathways, and early quenching mechanisms remain poorly constrained. Current surveys lack the wide-field, rest-frame FIR sensitivity needed to obtain a complete census of massive systems and to trace their cold gas, dust, and diffuse emission on galactic and circumgalactic scales. A next-generation facility with a very large aperture, wide field of view, and high mapping speed is essential to carry out deep, degree-scale rest-frame FIR surveys. Such capabilities are required to determine how common massive galaxies are, how they assemble their baryons, and what physical processes drive their early transformation and quenching.
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All authors Mengyuan Xiao, Longji Bing, Guilaine Lagache, Miroslava Dessauges-Zavadsky, Olivier Ilbert, Benjamin Magnelli, Pascal A. Oesch

Cosmology and Nongalactic Astrophysics

The Simons Observatory: forecasted constraints on primordial gravitational waves with the expanded array of Small Aperture Telescopes

The Simons Observatory Collaboration: I. Abril-Cabezas, S. Adachi, P. Ade et al. (+478 more)

We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned extension of the survey duration to 2035, this expansion will significantly enhance SO's search for a $B$-mode signal in the polarisation of the cosmic microwave background, a potential signature of gravitational waves produced in the very early Universe. Assuming a $1/f$ noise model with knee multipole $\ell_{\rm knee} = 50$ and a moderately complex model for Galactic foregrounds, we forecast a $1\sigma$ (or 68% confidence level) constraint on the tensor-to-scalar ratio $r$ of $\sigma_r = 1.2\times10^{-3}$, assuming no primordial $B$-modes are present. This forecast assumes that 70% of the $B$-mode lensing signal can ultimately be removed using high resolution observations from the SO Large Aperture Telescope (LAT) and overlapping large-scale structure surveys. For more optimistic assumptions regarding foregrounds and noise, and assuming the same level of delensing, this forecast constraint improves to $\sigma_r = 7\times10^{-4}$. These forecasts represent a major improvement in SO's constraining power, being a factor of around 2.5 times better than what could be achieved with the originally planned campaign, which assumed the existing three SATs would conduct a five-year survey.
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All authors The Simons Observatory Collaboration: I. Abril-Cabezas, S. Adachi, P. Ade, A. E. Adler, P. Agrawal, J. Aguirre, S. Aiola, T. Alford, A. Ali, D. Alonso, M. A. Alvarez, R. An, M. Aravena, K. Arnold, P. Ashton, F. Astori, Z. Atkins, J. Austermann, S. Azzoni, C. Baccigalupi, D. Baker, R. Balafendiev, A. Baleato Lizancos, D. Barron, P. Barry, J. Bartlett, A. Basyrov, N. Battaglia, E. S. Battistelli, R. Battye, A. Bayer, A. Bazarko, J. A. Beall, R. Bean, D. Beck, S. Beckman, J. Begin, A. Beheshti, B. Beringue, T. Bhandarkar, S. Bhimani, F. Bianchini, E. Biermann, M. Billi, S. Biquard, B. Bixler, L. Bizzarri, S. Boada, D. Boettger, B. Bolliet, J. R. Bond, J. Borrill, J. Borrow, C. Braithwaite, T. L. R. Brien, M. L. Brown, S. M. Bruno, S. Bryan, R. Bustos, H. Cai, E. Calabrese, V. Calafut, F. M. Carl, A. Carones, J. Carron, A. Challinor, E. Chamberlain, P. Chanial, N. Chen, K. Cheung, B. Chiang, Y. Chinone, J. Chluba, H. S. Cho, S. K. Choi, M. Chu, J. Clancy, S. E. Clark, P. Clarke, J. Cleary, D. L. Clements, J. Connors, C. Contaldi, G. Coppi, L. Corbett, N. F. Cothard, W. Coulton, D. Crichton, K. D. Crowley, K. T. Crowley, A. Cukierman, J. M. D'Ewart, K. Dachlythra, O. Darwish, R. Datta, S. Day-Weiss, T. de Haan, S. Desai, M. Devlin, L. Di Mascolo, S. Dicker, K. Ding, C. Doux, P. Dow, S. Doyle, C. J. Duell, S. M. Duff, A. J. Duivenvoorden, J. Dunkley, M. Duparc, D. Dutcher, R. Dünner, M. Edenton, H. El Bouhargani, C. Embil Villagra, J. Errard, G. Fabbian, V. Fanfani, F. Farhadi Khouzani, G. S. Farren, J. Fergusson, S. Ferraro, R. Flauger, M. Forconi, A. Foster, K. Freese, J. C. Frisch, A. Frolov, G. Fuller, N. Galitzki, P. A. Gallardo, G. Galloni, J. T. Galvez Ghersi, K. Ganga, X. Garrido, E. Gawiser, M. Gerbino, R. Gerras, S. Giardiello, A. Gill, V. Gilles, U. Giri, E. Gleave, V. Gluscevic, N. Goeckner-Wald, S. Goldstein, J. E. Golec, S. Gordon, M. Gralla, S. Gratton, D. Green, J. C. Groh, C. Groppi, S. Grubb, Y. Guan, N. Gupta, J. E. Gu{\dh}mundsson, B. Hadzhiyska, S. Hagstotz, P. Hargrave, S. Haridas, K. Harrington, I. Harrison, M. Hasegawa, M. Hasselfield, V. Haynes, M. Hazumi, A. He, E. Healy, S. W. Henderson, B. S. Hensley, E. Hertig, C. Hervías-Caimapo, M. Higuchi, C. A. Hill, J. C. Hill, M. Hilton, A. D. Hincks, G. Hinshaw, R. Hložek, A. Y. Q. Ho, S. Ho, S. P. Ho, T. D. Hoang, J. Hoh, J. Holder, J. Hood, E. Hornecker, A. L. Hornsby, S. C. Hotinli, Z. Huang, Z. B. Huber, J. Hubmayr, K. Huffenberger, A. Hughes, J. P. Hughes, A. Idicherian Lonappan, M. Ikape, K. Inaba, K. Irwin, J. Iuliano, A. H. Jaffe, B. Jain, D. Jain, H. T. Jense, O. Jeong, A. Johnson, B. R. Johnson, M. Johnson, M. E. Jones, N. Joshi, B. Jost, W. Kabalan, V. Kabra, D. Kaneko, J. Kania, E. D. Karpel, Y. Kasai, N. Katayama, B. Keating, B. Keller, R. Keskitalo, A. A. Khatua, J. Kim, T. Kisner, K. Kiuchi, K. Knowles, A. M. Kofman, Y. Koizumi, B. J. Koopman, A. Kosowsky, R. Kou, N. Krachmalnicoff, D. Kramer, A. Krishak, A. Krolewski, A. Kusaka, A. Kusiak, Y. Kvasiuk, P. La Plante, A. La Posta, A. Laguë, A. Lai, J. Lashner, M. Lattanzi, A. Lee, E. Lee, J. Leech, L. Legrand, C. Lessler, J. S. Leung, A. Lewis, Y. Li, Z. Li, M. Limon, L. Lin, E. Linder, M. Link, J. Liu, Y. Liu, J. Lloyd, J. Lonergan, T. Louis, T. Lucas, M. Ludlam, M. Lungu, M. Lyons, N. MacCrann, A. MacInnis, M. Madhavacheril, D. Mak, F. Maldonado, M. Mallaby-Kay, A. Manduca, A. Mangu, H. Mani, A. S. Maniyar, G. A. Marques, P. Masson, J. Mates, J. Mathewson, T. Matsumura, P. Mauskopf, A. May, N. McCallum, H. McCarrick, F. McCarthy, M. McCulloch, J. McMahon, P. D. Meerburg, Y. Mehta, J. Melin, E. Meulbroek, J. Meyers, A. Middleton, Y. Miki, A. Miller, M. Mirmelstein, Y. Mizozoe, B. Mohammadian, G. Montefalcone, K. Moodley, J. Moore, T. Morris, M. Morshed, T. Morton, E. Moser, T. Mroczkowski, M. Murata, J. Myers, M. Münchmeyer, S. Naess, H. Nakata, T. Namikawa, M. Nashimoto, F. Nati, P. Natoli, M. Negrello, S. K. Nerval, L. Newburgh, D. V. Nguyen, A. Nicola, M. D. Niemack, H. Nishino, Y. Nishinomiya, A. Novelli, S. O'Neill, N. Okumoto, A. Orlando, J. Orlowski-Scherer, L. Pagano, L. A. Page, S. Pandey, A. Papageorgiou, I. Paraskevakos, B. Partridge, D. Patel, R. Patki, S. Paulino Korte, M. Peel, K. Perez Sarmiento, F. Perrotta, P. Phakathi, L. Piccirillo, E. Pierpaoli, T. Pinsonneault-Marotte, G. Pisano, J. Pitocco, D. Poletti, C. Popik, B. Prasad, R. Puddu, G. Puglisi, F. J. Qu, F. Rahman, M. J. Randall, C. Ranucci, C. Raum, R. Reeves, C. L. Reichardt, M. Remazeilles, X. Ren, Y. Rephaeli, D. Riechers, B. Reid Guachalla, A. Rizzieri, J. Robe, M. F. Robertson, N. Robertson, K. Rogers, F. Rojas, A. Romero, E. Rosenberg, A. Rotti, S. Rowe, A. Roy, S. Sadeh, N. Sailer, K. Sakaguri, T. Sakuma, Y. Sakurai, M. Salatino, G. H. Sanders, D. Sasaki, M. Sathyanarayana Rao, T. P. Satterthwaite, L. Saunders, L. Scalcinati, E. Schaan, B. Schmitt, M. Schmittfull, N. Sehgal, J. Seibert, Y. Seino, U. Seljak, S. Shaikh, E. Shaw, P. Shellard, B. Sherwin, M. Shimon, J. E. Shroyer, C. Sierra, J. Sievers, C. Sifón, P. Sikhosana, M. Silva-Feaver, S. M. Simon, A. Sinclair, K. Smith, W. Sohn, X. Song, R. F. Sonka, T. Souverin, J. Spisak, S. T. Staggs, G. Stein, J. R. Stevens, R. Stompor, E. Storer, R. Sudiwala, Y. Sueno, J. Sugiyama, P. Suman, K. M. Surrao, S. Sutariya, A. Suzuki, J. Suzuki, O. Tajima, R. Takaku, S. Takakura, A. Takeuchi, I. Tansieri, A. C. Taylor, G. Teply, T. Terasaki, A. Thomas, D. B. Thomas, R. Thornton, P. Timbie, H. Trac, T. Tsan, E. Tsang King Sang, C. Tucker, J. Ullom, L. Vacher, L. Vale, A. van Engelen, J. Van Lanen, J. van Marrewijk, D. D. Van Winkle, C. Vargas, E. M. Vavagiakis, I. Veenendaal, C. Vergès, A. Villarrubia Aguilar, M. Vissers, M. Viña, K. Wagoner, S. Walker, L. Walters, Y. Wang, B. Westbrook, J. Williams, P. Williams, J. Wilson, H. Winch, E. J. Wollack, K. Wolz, J. Wong, Z. Xu, K. Yamada, E. Young, B. Yu, C. Yu, G. Zagatti, M. Zannoni, W. Zhang, K. Zheng, N. Zhu, A. Zonca, I. Zubeldia

Instrumentation and Methods for Astrophysics

Accretion and Ejection Physics at High Time Resolution

F. M. Vincentelli, P. Casella, A. Veledina et al. (+18 more)

Accretion onto compact objects is one of the most fundamental phenomena in the astrophysics, powering some of the most luminous objects in the sky. Along with this, accretion has also a key impact on the evolution of the Universe, through the launch of powerful outflows that affect the surrounding medium. In the last years sub-second optical-infrared observations of accreting X-ray binaries have opened a new window in the study of inflow-outflow connection, discovering a wide range of previously unkown phenomena. Here we review the key open questions in accretion and ejection physics and discuss how a dedicated facility, equipped with photon-counting detectors and high spectral resolution from the UV to the mid-infrared, can enable transformative advances in our understanding of accretion processes.
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All authors F. M. Vincentelli, P. Casella, A. Veledina, A. Ambrifi, M. C. Baglio, D. Buckley, N. Castro Segura, Y. Cavecchi, D. de Martino, M. del Santo, P. Gandhi, G. Iliano, R. La Paca, C. Malacaria, A. Marino, K. O'Brien, N. Rea, A. Sanna, S. Scaringi, T. Shahbaz, L. Zampieri

Instrumentation and Methods for Astrophysics

Nova Explosions in 2040

Alessandro Ederoclite, Domitilla De Martino, Paul Groot et al. (+7 more)

Novae are thermonuclear explosions on the surface of accreting white dwarfs and are key laboratories for studying explosive nucleosynthesis, particle acceleration, shock physics, and binary evolution. Despite major progress driven by wide-field time-domain surveys and multi-wavelength facilities, our understanding of nova explosions remains limited by incomplete temporal coverage, heterogeneous spectroscopic follow-up, and poorly constrained ejecta properties. In this white paper we outline the open scientific questions that will define nova research in the 2040s, focusing on the mass, composition, geometry, and dynamics of the ejecta, the role of the underlying binary system, and the connection between nuclear burning, shocks, and emission across the electromagnetic spectrum. We argue that decisive progress requires rapid-response, high-cadence, multi-wavelength observations, anchored by systematic high-resolution optical and near-infrared spectroscopy from eruption to quiescence. Finally, we identify key technological requirements needed to enable transformative advances in the physics of nova explosions over the coming decades.
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All authors Alessandro Ederoclite, Domitilla De Martino, Paul Groot, Elena Mason, Gloria Sala, Martín Guerrero, Thomas Kupfer, Anna Francesca Pala, Simone Scaringi, Noel Castro Segura

Instrumentation and Methods for Astrophysics

Sailing to the next safe harbour in our trip to the early Universe: The massive star population of metal-poor galaxies

N. Castro, M. Garcia, A. Herrero et al. (+5 more)

Very metal-poor massive stars in the Local Group are our best proxies for the Universe's first stars, making them essential for modeling reionization and early galactic chemical evolution. Studying such stars in our Local Universe is key to extrapolating our knowledge to more distant regions, where individual massive stars cannot be resolved but are dynamically and chemically shaping their environments. The MUSE integral field spectrograph has transformed massive star studies in the Milky Way and Magellanic Clouds, but resolving star-forming galaxies containing very metal-poor stars is at the limit of the current field of view and sensitivity. Therefore, only small dedicated efforts of selected regions are studied, providing us with snapshots of low-metallicity massive stars rather than a comprehensive picture. This scarcity is a major bottleneck for understanding and sufficiently modelling the evolution and feedback of massive stars across cosmic time. We therefore envision a new generation of panoramic integral-field spectrographs and high multiplex multi-object spectrographs mounted on dedicated large optical telescopes. Such facilities will not only allow to resolve very-metal-pool galaxies, but further enable the systematic exploration of the massive stellar content across the entire Local Group, thereby reaching a new era in massive star studies and understanding.
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All authors N. Castro, M. Garcia, A. Herrero, A. A. C. Sander, A. F. McLeod, M. M. Roth, I. Negueruela, J. S. Vink

Instrumentation and Methods for Astrophysics

Asteroseismology of white dwarfs in the 2040s

Murat Uzundag, Ingrid Pelisoli, Stephane Charpinet et al. (+6 more)

White dwarfs, the final evolutionary stage of the vast majority of stars, serve as critical tools for cosmochronology, studies of planetary system evolution, and laboratories for non-standard physics, including exotic cooling channels and weakly interacting particles, as well as crystallization processes. Beyond surface properties accessible via spectroscopy and model atmospheres, global pulsations exhibited by white dwarfs during various evolutionary phases provide a direct window into their deep interiors. Asteroseismology, the comparison of observed pulsation periods with theoretical models, enables us to infer internal chemical stratification, total mass, rotation profiles, and magnetic field strengths. Despite major advances from space missions providing uninterrupted, high-precision photometry, key challenges remain: many predicted pulsators remain quiet, while others oscillate outside theoretical instability strips, highlighting gaps in our understanding of mode excitation, diffusion, and convective mixing. Determining the masses of white dwarfs, particularly for massive and hydrogen-deficient stars, remains uncertain, with discrepancies between spectroscopic, asteroseismic, astrometric, and photometric methods. In the coming decades, large-scale surveys combining high-precision space-based photometry with coordinated ground-based spectroscopic follow-up will dramatically increase both the number and quality of pulsating white dwarf observations.
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All authors Murat Uzundag, Ingrid Pelisoli, Stephane Charpinet, Alejandro H. Corsico, Leandro G. Althaus, V. Van Grootel, Suzanna Randall, Thomas Kupfer, Roberto Raddi

Instrumentation and Methods for Astrophysics

Milky Way disc & Bulge in situ populations: ESO white paper - Expanding horizons call

M. Bergemann, G. Kordopatis, G. Casali et al. (+11 more)

The formation and evolution of the Milky Way's disc, bar, and bulge remain fundamentally limited by the lack of a contiguous, Galaxy-wide, high-precision chemo-dynamical map. Key open questions - including the survival or destruction of the primitive discs, the origin of the bulge's multi-component structure, the role of mergers and secular processes, and the coupling between stellar chemistry, dynamics, and the Galactic potential - cannot be fully resolved with current or planned facilities. Existing spectroscopic surveys provide either high resolution for small samples or wide coverage at insufficient resolution and depth, and none can obtain homogeneous abundances, precise 3D kinematics, and reliable ages for the millions of stars required, particularly in the obscured midplane, the far side of the bar, or the outer, low-density disc. A new wide-field, massively multiplexed, large-aperture spectroscopic facility, capable of both high- and low-resolution spectroscopy over tens of thousands of square degrees, is therefore essential. Such a facility would deliver the statistical power, sensitivity, and completeness needed to reconstruct the Galaxy's assembly history, constrain its gravitational potential, and establish the Milky Way as the definitive benchmark for galaxy evolution.
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All authors M. Bergemann, G. Kordopatis, G. Casali, S. Khoperskov, P. McMillan, L. Marques, I. Minchev, E. Poggio, M. Schultheis, C. Viscasillas Vázquez, H.-F. Wang, V. Grisoni, V. Hill, R. Smiljanic

Instrumentation and Methods for Astrophysics

An Improved Machine Learning Approach for Radio Frequency Interference Mitigation in FAST-SETI Survey Archival Data

Li-Li Zhao, Xiao-Hang Luan, Xin Chao et al. (+6 more)

The search for extraterrestrial intelligence (SETI) commensal surveys aim to scan the sky to detect technosignatures from extraterrestrial life. A major challenge in SETI is the effective mitigation of radio frequency interference (RFI), a critical step that is particularly vital for the highly sensitive Five-hundred-meter Aperture Spherical radio Telescope (FAST). While initial RFI mitigation (e.g., removal of persistent and drifting narrowband RFI) are essential, residual RFI often persists, posing significant challenges due to its complex and various nature. In this paper, we propose and apply an improved machine learning approach, the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, to identify and mitigate residual RFI in FAST-SETI commensal survey archival data from July 2019. After initial RFI mitigation, we successfully identify and remove 36977 residual RFIs (accounting for $\sim$ 77.87%) within approximately 1.678 seconds using the DBSCAN algorithm. This result shows that we have achieved a 7.44% higher removal rate than previous machine learning methods, along with a 24.85% reduction in execution time. We finally find interesting candidate signals consistent with previous studies, and retain one candidate signal following further analysis. Therefore, DBSCAN algorithm can mitigate more residual RFI with higher computational efficiency while preserving the candidate signals that we are interested in.
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All authors Li-Li Zhao, Xiao-Hang Luan, Xin Chao, Yu-Chen Wang, Jian-Kang Li, Zhen-Zhao Tao, Tong-Jie Zhang, Hong-Feng Wang, Dan Werthimer

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Observable Gravitational Wave Strain at Second Order

Guillem Domènech, Shi Pi and Ao Wang

There is currently no rigorous definition of gravitational wave strain at second order in cosmological perturbation theory. The usual association of gravitational waves with transverse and traceless fluctuations of the metric on spatial hypersurfaces becomes ambiguous at second order, as it inherently depends on the spacetime slicing. While this poses no practical issues in linearized gravity, it presents a fundamental problem for secondary gravitational waves, especially notorious for gravitational waves induced by primordial fluctuations. We compute, for the first time, the observable gravitational wave strain at second order, as measured by geodesic observers that emit and receive electromagnetic signals, thereby settling the debate on gauge ambiguities. Working in a gauge invariant fashion, we find that the measured gravitational wave strain coincides with the transverse-traceless components in the Newton gauge.
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Earth and Planetary Astrophysics

Structure of Jupiter's High-Latitude Storms: Folded Filamentary Regions Revealed by Juno

L.N. Fletcher, Z. Zhang, S. Brown et al. (+17 more)

Sprawling, turbulent cloud formations dominate the meteorology of Jupiter's mid-to-high latitudes, known as Folded Filamentary Regions (FFRs). A multi-wavelength characterisation by Juno reveals the spatial distribution, vertical structure, and energetics of the FFRs. The cloud tops display multiple lobes of stratiform aerosols, separated by darker, cloud-free lanes, and embedded with smaller eddies and high-altitude cumulus clouds. These cyclonic FFRs are microwave-bright in shallow-sounding wavelengths ($p<5$ bars) and microwave-dark in deep-sounding wavelengths ($p>10$ bars), with the transition potentially associated with the water condensation layer (6-7 bars). Associating microwave contrasts with temperature anomalies, this implies despinning of cyclonic eddies above/below their mid-planes. Despite deep roots (being detectable in wavelengths sounding $\sim100$ bars), they are “pancake vortices” with horizontal extents at least an order of magnitude larger than their depth. In the northern hemisphere, FFRs are most common in cyclonic belts poleward of $40^\circ$N (all latitudes are planetocentric), particularly a North Polar Filamentary Belt (NPFB) near $66-70^\circ$N that defines the transition from organised belts/zones to the chaotic polar domain. This distribution explains the high lightning rates from $45-80^\circ$N, peaking in a belt poleward of $52.3^\circ$N, which may trace the availability of water for moist convection. Many observed lightning flashes can be associated to specific FFRs containing bright storms, but some FFRs display no activity, suggesting quiescent periods during storm evolution. Analogies to Earth's oceanic eddies suggest that cyclones deform isentropic surfaces at their midplanes, raising deep water-rich layers upwards to promote moist convection, release latent heat, and inject clouds into the upper troposphere.
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All authors L.N. Fletcher, Z. Zhang, S. Brown, F.A. Oyafuso, J.H. Rogers, M.H. Wong, A. Mura, G. Eichstädt, G.S. Orton, S. Brueshaber, R. Sankar, C. Li, S.M. Levin, F. Biagiotti, T. Guillot, A. P. Ingersoll, D. Grassi, C.J. Hansen, S. Bolton, J.H. Waite

Astrophysics of Galaxies

The Milky Way in motion: gauging stellar trajectories that shape the Galactic thin disc

M. L. L. Dantas, R. Smiljanic, R. S. de Souza et al. (+2 more)

As stars traverse the Milky Way, their orbits evolve through perturbations that alter their orbital radii. These changes arise from two mechanisms: churning, which modifies angular momentum, and blurring, which induces eccentric orbits without major angular momentum change. To assess whether churning or blurring dominates the dynamical evolution of Gaia-ESO stars, we refine Galactic chemical-evolution models by constructing finer grids that span a wider age range. Using a generalised additive model (GAM), we estimate stellar birth radii beyond the limits of binned metallicity models and compare them with dynamical parameters derived from Gaia parallaxes and proper motions, and Galpy. Our metallicity-stratified sample, grouped through hierarchical clustering of 21 chemical abundances, reveals clear migratory signatures: metal-rich stars formed in the inner disc preferentially move outwards, while more metal-poor stars formed at larger radii tend to migrate inwards. About 75% of stars show signs of churning, while the remainder are largely undisturbed or shaped by blurring. These patterns vary among chemical groups, likely reflecting interactions with the Galactic bar and spiral arms.
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All authors M. L. L. Dantas, R. Smiljanic, R. S. de Souza, P. B. Tissera, L. Magrini

Instrumentation and Methods for Astrophysics

National Mapping and Testing of Astronomical Sites in Ethiopia (NMTASE)

SSGI Collbaration: Shambel Sahlu, Nebiyu Suleyman, Gemechu M. Kumssa et al. (+8 more)

This work aims to choose potential astronomical sites that can be candidates for a new astronomical optical observatory in Ethiopia, in addition to the Entoto Observatory and Lalibela sites. For our primary investigation, the six basic criteria, namely the altitude of the mountains, artificial light pollution, cloud coverage, humidity, wind speed, and wind direction, were taken into account. Consequently, using the multi-criteria statistical Decision analysis (MCDSA) techniques, 21 high-potential places are selected and presented for further investigation out of 367 mountains. Among these 21 selected places, three sites, Bauhit, Meseraia, and T'at'a are the most suitable places for optical astronomy in Ethiopia. Those selected mountains are mapped and presented to study the future of the astronomical seeing effect. This study may contribute to the protection of those potential astronomical sites and their dark skies and the development of astrotourism for the sustainable development of modern astronomy in Ethiopia and in the East African region.
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All authors SSGI Collbaration: Shambel Sahlu, Nebiyu Suleyman, Gemechu M. Kumssa, Solomon T. Belay, Feraol F. Dirirsa, Esubalew Mulugeta, Melesse Getnet, Mirjana Povic, Seblu H. Negu, Betelehem Bilata, Jerusalem Tamrat

Astrophysics of Galaxies

The longest known tails of ram-pressure-stripped star-forming galaxies are caused by an intracluster medium shock in Abell 1367

H. W. Edler, M. Hoeft, S. Bhagat et al. (+10 more)

The environment plays an important role in shaping the evolution of cluster galaxies through mechanisms such as ram pressure stripping (RPS), whose effect may be enhanced in merging clusters. We investigate a complex of three galaxies UGC 6697, CGCG 097-073, and CGCG 097-079, that are currently undergoing extreme RPS, as evident from their multi-wavelength-detected tails. The galaxies are members of the nearby ($d=92$ Mpc) merging cluster Abell 1367 and are located in proximity to an intracluster medium (ICM) shock that is traced by X-ray observations and the presence of a radio relic. We analyzed LOFAR and MeerKAT observations at frequencies of 54, 144, 817, and 1270 MHz to perform a detailed spectral analysis of the tails. We found that all three tails are significantly more extended than in previous radio studies, with lengths of $\geq70$ kpc. For UGC 6697, we detected a tail of 300 kpc, making it the longest known RPS tail of a star-forming galaxy at any wavelength. The length and spectral variations of the tail cannot be explained purely by the spectral aging of stripped cosmic rays. We construct a model of the tail that includes compression and re-acceleration due to the encounter with the nearby ICM shock, which can plausibly account for the extreme RPS as well as the length and spectral variation of the tail. We further discover a radio plume at the leading edge of UGC 6697 that connects to a narrow filament. These sources exhibit extremely steep ($\alpha\approx-1.7$) and highly curved spectra. We speculate that this emission arises from cosmic rays re-energized by UGC 6697's rapid infall that propagate along magnetic filaments in the cluster center. Our findings represent direct evidence of a cluster merger shock impacting the evolution of member galaxies. Furthermore, we report the first tentative detection of particle acceleration at the leading edge of an infalling galaxy.
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All authors H. W. Edler, M. Hoeft, S. Bhagat, A. Basu, A. Drabent, K. Rajpurohit, M. Sun, F. de Gasperin, A. Botteon, M. Brüggen, A. Ignesti, I. D. Roberts, R. van Weeren

Instrumentation and Methods for Astrophysics

Towards ALMA2040: An update from the European community and invitation to contribute

Stefano Facchini, Jacqueline Hodge, Jes Jørgensen et al. (+27 more)

Over the last 15 years, the Atacama Large Millimeter/submillimeter Array (ALMA) has revolutionized astrophysics by providing unprecedented resolution and sensitivity in observing the cold universe, including the formation of stars, planets, and galaxies. With groundbreaking discoveries ranging from the first detailed images of protoplanetary disks to the kinematics of galaxies in the Epoch of Reionization, ALMA has showcased the vast discovery potential of the (sub-)mm wavelength regime. However, in another 15 years from now–in the 2040s–the science landscape will have changed dramatically as new major observational facilities will have started their operations or have come towards advanced maturity in their scientific outcome (e.g., JWST, Rubin Observatory, ELT, Euclid, Gaia, Plato, Ariel, Roman Space Telescope, SPHEREx, LiteBIRD, LISA, SKA and others). At the same time, ALMA's current Wideband Sensitivity Upgrade will have been in place for ~10 years, and ALMA itself will have been operational for 30 years. To fully exploit this era, the community needs a next-generation facility operating at (sub-)mm wavelengths with capabilities far beyond those possible within ALMA's current infrastructure. To this end, ALMA2040 is a community-driven initiative to define the key scientific questions of the 2040s and translate them into a technical vision for a next-generation transformational (sub-)millimeter facility. Our goal with this document is to summarize the current status of the effort, synthesize outcomes from the 2025 workshops, outline next steps toward a reference design concept, and invite broad participation from the global mm/sub-mm community to help shape this future facility. In the following we provide details on the process and scope. We invite everyone who wishes to join the effort and/or contribute to the dedicated White Papers planned for 2026.
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All authors Stefano Facchini, Jacqueline Hodge, Jes Jørgensen, Eva Schinnerer, Gie Han Tan, Tom Bakx, Andrey Baryshev, Maite Beltran, Leindert Boogaard, Roberto Decarli, María Díaz Trigo, Jan Forbrich, Peter Huggard, Elizabeth Humphreys, Violette Impellizeri, Karri Koljonen, Kuo Liu, Luca Matrà, Miguel Pereira Santella, Arianna Piccialli, Gergö Popping, Miguel Querejeta, Miriam Rengel, Francesca Rizzo, Lucie Rowland, Hannah Stacey, Wouter Vlemmings, Catherine Walsh, Sven Wedemeyer, Martina Wiedner

Solar and Stellar Astrophysics

Eruption-Related Ultraviolet Irradiance Enhancements Associated with Flares

Luke Majury, Marie Dominique, Ryan Milligan et al. (+3 more)

Large solar flares (GOES M-class or higher) are usually associated with eruptions of material. However, when considering flare irradiance enhancements and dynamics such as chromospheric evaporation, potential contributions from erupted material have historically been neglected. We analyse nine eruptive M- and X-class flares from 2024 to early 2025, quantifying the relative contributions of erupted material to irradiance enhancements during the events. SDO/AIA images from four different channels had ribbon and eruption irradiance contributions separated using a semi-automated masking method. The sample-averaged percentages of excess radiated energy by erupted material over the impulsive phase were $10^{+4}_{-4}\%$, $24^{+14}_{-14}\%$, $21^{+14}_{-10}\%$ and $13^{+6}_{-9}\%$ for the $131\,$Å, $171\,$Å, $304\,$Å and $1600\,$Å channels, respectively. For three events that were studied in further detail, HXR imaging showed little to no signatures of nonthermal heating within the eruptions. Our results suggest that erupted material can be a significant contributor to UV irradiance enhancements during flares, with possible heating mechanisms including nonthermal particle heating, Ohmic heating, or dissipation of MHD waves. Future work may clarify the heating mechanism and evaluate the impact of eruptions on spectral variability, particularly in Sun-as-a-star and stellar flare observations.
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All authors Luke Majury, Marie Dominique, Ryan Milligan, Dana-Camelia Talpeanu, Ingolf Dammasch, David Berghmans

Astrophysics of Galaxies

The impact of bars on the properties of HII regions in the TIMER survey

Laura Sánchez-Menguiano, Dimitri A. Gadotti, Almudena Zurita et al. (+10 more)

In this study we perform a comparative analysis of the properties of the HII regions located in different areas of barred galaxies, with the aim of investigating the impact of bars on the physical properties of the ionised gas. Based on integral field spectroscopy data for 17 barred galaxies covering approximately the central 6x6 kpc, we detect a total of 2200 HII regions, of which 331 are located within the nuclear disc (also known as circumnuclear regions), 661 in the bar region, and 1208 in the disc. Among the physical properties of the HII regions, we explore the O/H and N/O abundances, H$\alpha$ luminosity, dust extinction, electron density, and H$\alpha$ equivalent width. We find clear differences in the properties of the HII regions between the nuclear disc, the bar and the disc, that could be explained by an enhancement in the molecular gas concentration in the central parts driven by bar-induced gas flows. As this gas is channelled towards the galaxy centre, the most extreme values in the analysed properties are found for the circumnuclear HII regions. Unlike the bar strength, galaxy mass does seem to affect the properties of the HII regions, with massive galaxies presenting higher values in most of the properties, possibly due to the increased amount of gas in these systems. This study provides evidence that the bar-driven redistribution of material within the galaxy inner parts causes significant differences in the HII region properties depending on their location within the galaxies.
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All authors Laura Sánchez-Menguiano, Dimitri A. Gadotti, Almudena Zurita, Estrella Florido, Isabel Pérez, Paula Coelho, Jesús Falcón-Barroso, Taehyun Kim, Adriana de Lorenzo-Cáceres, Alejandra Z. Lugo-Aranda, Justus Neumann, Camila de Sá-Freitas, Patricia Sánchez-Blázquez

Solar and Stellar Astrophysics

RR Lyrae stars with variable mean magnitudes

Gergely Hajdu, Johanna Jurcsik, Márcio Catelan et al. (+6 more)

Context. A number of RR Lyrae stars show variable mean magnitudes in the OGLE survey light curves of the Galactic bulge. Hitherto this phenomenon was not studied, as it was generally assumed to be related to problems with the photometry. Aims. We investigate whether the mean magnitude variability of RR Lyrae variables is due to genuine astrophysical phenomena. Methods. We make use of the extended, and in many cases overlapping, light curves from multiple microlensing surveys, to study RR Lyrae stars with apparent mean-magnitude variations. A modified Fourier-series based fitting method is introduced to analyze the light curves showing mean-magnitude variations. Data from infrared surveys are also used to construct spectral energy distributions (SEDs). Results. 72 stars are presented where the mean-magnitude variations are most probably of genuine astrophysical origin, and not the result of problems with the photometry. The ratio of variation between the V and I bands is compatible with variable extinction by dust in most cases, but no infrared excess is detected in the SEDs. The occurrence rate of the phenomenon, after correcting for selection effects, is $\sim0.9\%$ among RR Lyrae variables in the OGLE bulge fields.
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All authors Gergely Hajdu, Johanna Jurcsik, Márcio Catelan, Grzegorz Pietrzyński, Vincent Hocdé, Igor Soszyński, Andrzej Udalski, Chung-Uk Lee, Dong-Jin Kim

Cosmology and Nongalactic Astrophysics

Note on bulk viscosity as an alternative to dark energy

P. P. Avelino, A. R. Gomes and D. A. Tamayo

Bulk viscosity, which characterizes the irreversible dissipative resistance of a fluid to volume changes, has been proposed as a potential mechanism for explaining both early- and late-time accelerated expansion of the Universe. In this work, we investigate two distinct physical scenarios for the origin of bulk viscosity: (1) nonminimal interactions between two fluids, and (2) elastic collisions in an ideal gas. In both cases, we demonstrate that while the associated energy-momentum exchange can significantly influence fluid dynamics, overall energy-momentum conservation precludes such exchange from having any direct gravitational effect in the context of General Relativity. In case (1), we show that the standard bulk viscous energy-momentum tensor can be obtained for the two-fluid system only at the cost of the violation of all classical energy conditions: null, weak, dominant, and strong. In case (2), we consider a single fluid composed of point particles undergoing instantaneous, energy- and momentum-conserving collisions, and find that the proper pressure remains strictly non-negative, with the equation-of-state parameter confined to the interval $[0,1/3]$. In both scenarios, achieving a sufficiently negative effective pressure to drive cosmic acceleration requires assumptions that compromise the physical viability of the model. Our results highlight some of the key physical challenges involved in modeling dark energy through bulk viscous effects.
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Cosmology and Nongalactic Astrophysics

The art of simulating the early Universe. Part II. Non-canonical cases & gravitational waves

Jorge Baeza-Ballesteros, Daniel G. Figueroa, Adrien Florio et al. (+7 more)

We present a discussion on lattice techniques for the simulation of non-canonical field theory circumstances, complementing our previous monograph (arXiv:2006.15122) on canonical cases. We begin by reviewing basic aspects of lattice field theory, including symplectic and non-symplectic evolution algorithms. We then introduce lattice implementations of non-canonical interactions, considering scalars with a non-minimal coupling to gravity, $\phi^2R$, non-minimal scalar kinetic theories, $\mathcal{G}_{ab}(\lbrace\phi_c\rbrace)\partial_\mu\phi^a\partial^\mu\phi^b$, and axion-like particle (ALP) interactions with Abelian gauge fields, $\phi F_{\mu\nu}\tilde F^{\mu\nu}$. Next, we discuss methods to set up special field configurations, including the creation of cosmic defect networks towards scaling (e.g. cosmic strings and domain walls), field configurations based on arbitrary power spectra or spatial profiles, and probabilistic methods as required e.g. for thermal configurations. We further extend the notion of non-canonical theories, discussing the discretization of scalar field dynamics in $d + 1$ dimensions, with $d \neq 3$. Unrelated to non-canonical aspects, we also discuss implementation(s) of gravitational wave (GW) dynamics on the lattice. This document represents the theoretical basis for the non-canonical field theory aspects (interactions, initial conditions, dimensionality) and GW dynamics implemented in ${\mathcal C}$osmo${\mathcal L}$attice v2.0, to be released in 2026.
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All authors Jorge Baeza-Ballesteros, Daniel G. Figueroa, Adrien Florio, Joanes Lizarraga, Nicolás Loayza, Kenneth Marschall, Toby Opferkuch, Ben A. Stefanek, Francisco Torrentí, Ander Urio

Instrumentation and Methods for Astrophysics

Benchmarking Dimensionality Reduction Methods for High-Dimensional ALMA Image Cubes

Haley N. Scolati, Ryan A. Loomis, Anthony J. Remijan et al. (+1 more)

High-dimensional astronomical data cubes provide a wealth of spectral and structural information that can be used to study astrophysical and chemical processes. The complexity and sheer size of these datasets pose significant challenges in their efficient analysis, visualization, and interpretation. In specific astronomical use cases, a number of dimensionality reduction techniques, including traditional linear (e.g. principal component analysis) and modern nonlinear methods (e.g. convolutional autoencoders) have been used to tackle this high-dimensional problem. In this study, we assess the strengths, weaknesses, and nuances of various methods in their ability to capture and preserve astronomically-relevant features at lower dimensions. We provide recommendations to guide users in identifying and incorporating these treatments to their data, and provide insights into the computational scalability of these methods for observatory level data processing. This benchmark study uses publicly available archival ALMA data from a diverse sampling of source morphologies and observing setups to assess the performance and trade-offs between computational cost, image reconstruction accuracy, and scalability. Finally, we discuss the generalizability of these techniques in regard to data segmentation and labeling algorithms and how they can be exploited for advanced data product generation and streamlined archival analysis as we prepare to enter the era of the ALMA Wideband Sensitivity Upgrade.
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All authors Haley N. Scolati, Ryan A. Loomis, Anthony J. Remijan, Kin Long Kelvin Lee

High Energy Astrophysical Phenomena

Hadronic Clues in Quasars Caught by Fermi-LAT

Antonio Galván, Nissim Fraija, Edilberto Aguilar-Ruiz et al. (+3 more)

This work explores whether hadronic processes could be responsible for the high-energy emission seen in quasars identified by the Large Area Telescope (LAT) instrument aboard the Fermi satellite. In contrast to purely leptonic models, this work investigates whether hadronic mechanisms can explain the observed gamma-ray spectra by analyzing the spectral energy distributions (SEDs) of a chosen sample of FSRQs (Flat-Spectrum Radio Quasars). By incorporating both hadronic and leptonic components into their multi-wavelength modeling, we evaluate the model's feasibility to simultaneously describe the data collected by Fermi-LAT and neutrinos detected by IceCube. According to the results, a hadronic contribution would be required to explain the SED of quasars detected by Fermi-LAT. However, their contribution to the neutrino flux detected by IceCube remains understated.
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All authors Antonio Galván, Nissim Fraija, Edilberto Aguilar-Ruiz, Hermes León Vargas, Maria G. Dainotti, Jose Antonio de Diego

Cosmology and Nongalactic Astrophysics

Comparing cosmic shear nulling methods for Stage-IV surveys

Naomi Clare Robertson and Alex Hall

We present an analysis comparing nulling strategies for reducing the impact of baryon feedback on cosmic shear measurements. We consider three different approaches which aim to `null' the high-$k$ modes using transformations applied to the data vector: the Bernardeau-Nishimichi-Taruya (BNT) transform which operates on the lensing field, a new implementation of an LU factorisation of the discretized Limber integral (LUnul) which operates on the lensing two-point statistics, and finally a method which uses a correlated LSS tracers to suppress contributions from lower redshifts (cross-correlation). We compare these methods to un-nulled (or standard) cosmic shear at the data vector level and assess whether these methods are able to reduce the bias on cosmological constraints using a Fisher forecast. We find that the nulling techniques considered can have a large impact on reducing the bias on $S_8$ and Dark Energy parameters. The cross-correlation method is effective at reducing biases in $S_8$, but requires additional information from galaxy clustering. The LUnul method is the most aggressive of the methods and hence reduces biases most efficiently as $k_{\rm max}$ is increased, although this improvement in accuracy comes at the cost of precision. The BNT approach preserves more information than LUnul, and has a more rigorous theoretical grounding. We demonstrate that all three of these methods are effective at mitigating bias, and can be readily applied in forthcoming lensing analyses.
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Instrumentation and Methods for Astrophysics

Spectroscopic Alerts for the Time-Domain Era

Alejandra Melo, Paula Sanchez-Saez, Valentin D. Ivanov et al. (+13 more)

Time-domain astronomy is entering an era of unprecedented discovery driven by wide-field, high-cadence surveys such as LSST, Roman, Euclid, SKA, and PLATO. While some of these facilities will generate enormous photometric alert streams, the physical interpretation of variability and transients often requires spectroscopy, which encodes changes in ionisation state, kinematics, and accretion that are inaccessible to photometry alone. A critical gap is therefore emerging: next-generation surveys may produce up to $\sim10^9$ alerts per year, whereas global spectroscopic follow-up is limited to only $\sim10^4$–$10^5$ transient spectra annually. We present the concept of spectroscopic alerts: real-time notifications triggered by significant spectral evolution, enabling spectroscopy to act as a discovery channel rather than solely as follow-up. We outline the key science cases enabled by this capability and describe the instrumental and operational requirements of a wide-field, highly multiplexed spectroscopic facility capable of delivering real-time spectral discovery for 2040s time-domain and multi-messenger astronomy.
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All authors Alejandra Melo, Paula Sanchez-Saez, Valentin D. Ivanov, Richard I. Anderson, Amelia Bayo, Avraham Binnenfeld, Sofia Bisero, Dragana Ilić, Andjelka B. Kovačević, Fatemeh Zahra Majidi, Jaroslav Merc, Anna Pala, Swayamtrupta Panda, Sarath Satheesh-Sheeba, Fabian Schüssler, Susanna D. Vergani

Solar and Stellar Astrophysics

Extensive Observational Evidence for Massive Star Stellar Wind Variability at Low Metallicities: implications for mass-loss rate determination

Timothy N. Parsons, Raman K. Prinja, Derck L. Massa et al. (+1 more)

Mass-loss from massive stars is fundamental to stellar and galactic evolution and enrichment of the interstellar medium. Reliable determination of mass-loss rate is dependent upon unravelling details of massive star outflows, including optical depth structure of the stellar wind. That parameter introduces significant uncertainty due to the nearly ubiquitous presence of large-scale optically thick wind structure. We utilize suitable available ultraviolet spectra of 20 Large and Small Magellanic Cloud (LMC, SMC) OB stars to extend existing Galactic results quantifying uncertainty inherent in individual observations to lower metallicity environments. This is achieved by measuring standard deviations of mean optical depths of multiple observations of suitable wind-formed absorption profiles as a proportion of their mean optical depths. We confirm earlier findings that wind structure is prevalent at low metallicities and demonstrate that quantifying the consequent uncertainty is to some extent possible, despite the near-complete absence of time series UV spectroscopic observations in those environments. We find that the uncertainty inherent in any single observation of stellar wind optical depth at low metallicity is of similar magnitude to that already identified at Galactic metallicity (up to 45% for cooler OB stars). We further demonstrate how the effect of varying narrow absorption components in wind-formed UV spectral profiles is unlikely to be properly accounted for in existing mass-loss models. We present further evidence of a binary companion to the SMC O-type giant star AzV 75. The importance of obtaining high cadence multi-epoch, or genuine time series, UV spectroscopic observations at low metallicities is highlighted.
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All authors Timothy N. Parsons, Raman K. Prinja, Derck L. Massa, Alex W. Fullerton

Astrophysics of Galaxies

First reverberation mapping of a Bowen fluorescence line

Martin W. Ochmann, Edward M. Cackett, Lukas Diehl et al. (+3 more)

Reverberation mapping (RM) is a powerful tool to determine the extent, structure, and kinematics of the broad-line region (BLR) of active galactic nuclei (AGN). So far, RM of the BLR has only been performed for recombination lines responding to the varying ionizing continuum. We tested whether OI 8446, attributed to Bowen fluorescence driven by Ly$\beta$ pumping, varied on short (day- to week-long) timescales during a 2016 HST/STIS campaign of NGC 4593, and examined how it relates to other emission lines and the ionizing UV continuum. We quantified the variability of OI 8446 by calculating its rms amplitude. We then extracted integrated light curves of OI 8446 and other UV and optical emission lines, and compared them with each other and with the UV continuum light curve using correlation analyses. In addition, we used archival near-infrared spectra to assess the dominant excitation mechanism of OI 8446. We detect, for the first time, variability in OI 8446 on day timescales. The fractional rms amplitude is $\sim 4$% over the 4-week campaign. The OI 8446 light curve reverberates with a delay of $\sim 2.5$ days relative to Ly$\alpha$, used as a proxy for Ly$\beta$, detected at a false-alarm probability of 0.6% (significance of $\sim 2.8\sigma$) under our adopted null hypothesis. It closely tracks H$\alpha$ with only a minor additional delay of $\sim0.3$ days, placing its emission region at essentially the same distance as the Balmer-line weighted BLR. Line ratios indicate that Ly$\beta$ pumping is the dominant excitation mechanism for O I 8446. Our results establish OI 8446 as the first Bowen-fluorescence line reverberation-mapped, responding directly to variations in Ly$\beta$ flux. We propose that in future campaigns targeting AGN with larger BLRs, O I could enable dual-driver RM using both the continuum and the pumping line as drivers.
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All authors Martin W. Ochmann, Edward M. Cackett, Lukas Diehl, Keith Horne, Malte A. Probst, Wolfram Kollatschny

Solar and Stellar Astrophysics

A Machine-Learning Approach for Identifying CME-Associated Stellar Flares in TESS Observations

Yu Shi, Hong-Peng Lu, Li-Yun Zhang et al. (+2 more)

Coronal mass ejections (CMEs) are major drivers of stellar space weather and can strongly influence the habitability of exoplanets. However, compared to the frequent occurrence of white-light flares, confirmed stellar CMEs remain extremely rare. Whether such flares are commonly accompanied by CMEs is a key question for solar-stellar comparative studies. Using Sun-as-a-star soft X-ray flare light curves observed by the GOES XRS 1–8~Å\ channel, we compiled a sample of 1,766 M-class and larger solar flares and extracted features with both deep convolutional neural networks and manual methods. Five machine-learning classifiers were trained to distinguish eruptive from confined flares, with the random forest model achieving the best performance (true skill statistic; TSS = 0.31). This TSS value indicates that the model possesses a moderate ability to discriminate between eruptive and confined flares. Normalized white-light and GOES XRS flare light curves show broadly consistent temporal evolution, reflecting their shared energy-release history and supporting a probabilistic transfer of the model to white-light flare data. We applied the best-performing RF model to 41,405 TESS-detected flares on FGKM-type main-sequence stars, predicting that approximately 47% of events show CME-like morphological characteristics, with the model-implied intrinsic association fraction lying in the range 35%–60%. Intriguingly, the CME occurrence rate decreases with increasing flare energy, indicating that the most energetic flares may be more strongly confined by overlying magnetic fields. These results provide new insight into flare-CME connections in diverse stellar environments and have important implications for assessing the impact of stellar eruptive activity on exoplanetary atmospheres.
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All authors Yu Shi, Hong-Peng Lu, Li-Yun Zhang, Tian-Hao Su, Chao Tan

Instrumentation and Methods for Astrophysics

A Characterization of JWST MIRI Detector Persistence and Implications for High-Contrast Imaging

Alisha Vasan, Mary Anne Limbach, Andrew Vanderburg et al. (+2 more)

The JWST MIRI detector exhibits a flux deficit persistence, but its timescales and impacts remain largely uncharacterized, particularly at the longest imaging wavelengths. In this study, we analyze full-field MIRI imager observations at 21 $\mu$m (F2100W) to quantify detector persistence following a saturation event by a bright (K = 5.65 mag) nearby (8.12 $\pm$ 0.04 pc) mid M-dwarf star, IRAS 21500+5903. Unlike typical persistence that appears as excess flux, this effect presents as a flux deficit in pixels previously illuminated by the saturating or near saturating source. We measure persistence at two post-saturation epochs: shortly after saturation (11.6 minutes) and an hour later (1.39 hours). Immediately after the saturation event, we detect a persistence level of $1.69 \pm 0.10$%. By fitting a Bayesian exponential decay model to the two epochs, we estimate that persistence decreases to one-tenth of its initial value after $5.16^{+1.49}_{-0.94}$ hours. We examine the implications of persistence for MIRI high-contrast imaging using the imager (not coronagraphy). Specifically, we discuss how MIRI detector persistence can produce false-positive exoplanet signals in direct imaging surveys, as well as degrade PSF subtraction, particularly at small inner working angles. We also outline mitigation strategies to avoid these impacts in future observations.
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All authors Alisha Vasan, Mary Anne Limbach, Andrew Vanderburg, Rachel Bowens-Rubin, Kevin B. Stevenson