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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 29 January

Solar and Stellar Astrophysics

Proposal of a Novel Physical Parameter Characterizing Solar Wind Speed in a Wave-Driven Model

Kyogo Tokoro, Munehito Shoda and Shinsuke Imada

Empirical solar wind speed models play an important role in enabling space weather forecasting with low computational cost. Among these, one model called WS model is based on the asymptotic expansion factor. However, it is known that it fails in the case of pseudostreamers. In this study, as a first step toward constructing a solar wind speed empirical model based on physical parameters, we investigated the effect of the radial profile of flux-tube shape on the solar wind speed using one-dimensional numerical simulations. In the simulations, ad hoc Alfvén waves are injected from the photosphere at $r=R_\odot$ as the energy source, and the MHD equations are solved out to the interplanetary space at $r=70R_\odot$ to reproduce solar wind acceleration. As a result, even when the coronal base magnetic field and the asymptotic expansion factor are fixed, the final solar wind speed varies by approximately 300 km s$^{-1}$ depending on changes in the expansion height or non-monotonic expansion. Additionally, across all simulations performed, a better correlation is found with the quantities that reflect the information about the radial profile of flux-tube shape than the asymptotic expansion factor. Our results suggest that, as a physical characteristic parameter of the solar wind speed, an operation that can account for the expansion factor throughout the corona is necessary.
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Earth and Planetary Astrophysics

A Comprehensive Network for the Discovery and Characterization of Interstellar Objects

Oem Trivedi and Abraham Loeb

Interstellar object (ISO) astronomy has rapidly emerged over the past decade as a new frontier in planetary astrophysics, yet current observations remain limited by short visibility windows, inference degeneracies and fragmented follow-up capabilities. We argue that these constraints are structural rather than incidental and motivate a coordinated, end-to-end observational strategy for future ISO studies. We propose the Comprehensive ISO Network (CISON) which combines dual hemisphere wide-field discovery with rapid high resolution characterization and selective escalation to interceptor missions. By coupling this architecture to the differential formulation of the Loeb Scale, ISO classification and risk assessment become predictive rather than reactive. This framework transforms ISO astronomy into a mature, scalable discipline capable of maximizing scientific return and informing planetary defense in the coming decades.
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Solar and Stellar Astrophysics

Strontium-84 Enrichments in Presolar Grains Provide First Evidence of p-process Nucleosynthesis in Core-collapse Supernovae

Ishita Pal, Manavi Jadhav, Danielle Z. Shulaker et al. (+9 more)

This study reports detection of rare p-process isotopes within presolar grains. Presolar grains are relic dust grains from dying stars. These microscopic dust particles are found in primitive solar system materials. Their distinct isotopic compositions record the nucleosynthetic processes in their parent stars and the Galactic chemical environment in which these stars formed. We studied presolar graphite grains of high-density type from the Murchison meteorite and found five grains with subgrains that show enrichments in 84Sr compared to the solar abundance.84Sr is the neutron-deficient isotope of strontium that can be produced in the deep oxygen-rich interior of high-mass stars that end their lives as core-collapse supernovae. The observed 84Sr excesses cannot be produced in low-mass asymptotic giant branch stars, the source of most high-density presolar graphites found in meteorites. High-density graphites with embedded 84Sr excesses are, instead, compatible with a core-collapse supernovae origin. The graphite subgrains condensed from carbon-rich materials in the outer layers of core-collapse supernovae, where 84Sr was destroyed by neutron captures during hydrostatic evolution of the stars and their final explosion. Based on current theoretical stellar models, a few percent of contribution from the inner regions of core-collapse supernovae, which are enriched in p-process nuclides, to the outer carbon-rich regions is the most likely explanation for the observed enrichment of 84Sr in the subgrains of the high-density graphites. In this study, we present the first observational evidence that core-collapse supernovae produce and eject isotopes made by the p-process.
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All authors Ishita Pal, Manavi Jadhav, Danielle Z. Shulaker, Michael R. Savina, Marco Pignatari, Lorenzo Roberti, Heather Bouillion, Maria Lugaro, Christopher J. Dory, Frank Gyngard, Noriko Kita, Sachiko Amari

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

Exact analytic rotating black-hole solutions with primary hair

Pedro G. S. Fernandes

Exact, analytic, asymptotically flat rotating black-hole solutions are exceedingly rare, with only a handful of examples known. Using a Kerr-Schild ansatz, we derive a multitude of exact, analytic, asymptotically flat rotating black-hole solutions within a broad class of Generalized Proca theories. These black holes differ significantly from Kerr black holes, as they possess primary hair and are non-circular, thus breaking a symmetry that vacuum black holes exhibit in General Relativity.
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Solar and Stellar Astrophysics

The Pre-He White Dwarfs in Eclipsing Binaries. V. TIC 399725538

Jae Woo Lee, Kyeongsoo Hong, Min-Ji Jeong et al. (+2 more)

We present echelle spectra of TIC 399725538 obtained in Korea and Thailand to investigate the physical properties and evolutionary scenarios of EL CVn-type binaries. The time-series spectra yielded the radial velocities (RVs) of the primary component and its atmospheric parameters, $T_{\rm eff,A}=7194\pm70$ K and $v_{\rm A}\sin i=68\pm9$ km s$^{-1}$. Joint modeling of our RVs and the archival TESS data provided component masses of $M_{\rm A}=1.930\pm0.054$ $M_\odot$ and $M_{\rm B}=0.211\pm0.005$ $M_\odot$, radii of $R_{\rm A}=1.922\pm0.020$ $R_\odot$ and $R_{\rm B}=0.207\pm0.005$ $R_\odot$, and luminosities of $L_{\rm A}=8.87\pm0.39$ $L_\odot$ and $L_{\rm B}=0.546\pm0.034$ $L_\odot$. The surface gravity and distance derived from this modeling are consistent with the model-independent $\log g_{\rm B}$ obtained from the direct observables and with the Gaia distance. The third light of $l_3=0.136\pm0.003$ comes mainly from two neighboring stars, TIC 399725539 and TIC 399725544. Comparison with stellar models indicates that TIC 399725538 A lies within the instability region of $\delta$ Sct$-$$\gamma$ Dor hybrids, whereas its extremely low-mass companion is markedly underluminous compared to theoretical white dwarf (WD) counterparts. Multifrequency analysis of the binary-subtracted residual lights revealed three significant signals, two of which correspond to aliases at two and four times the dominant frequency $f_1=0.0848$ day$^{-1}$. The $f_1$ frequency is likely a $\gamma$ Dor-type pulsation arising from the brighter A component, though further confirmation is required. Our results demonstrate that TIC 399725538 is a short-period EL CVn system belonging to the thick-disk population, consisting of a main-sequence $\gamma$ Dor pulsator and a helium-core WD precursor formed through stable mass transfer.
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All authors Jae Woo Lee, Kyeongsoo Hong, Min-Ji Jeong, Pakakaew Rittipruk, Jang-Ho Park

Wednesday 28 January

Solar and Stellar Astrophysics

Discovery of a compact hierarchical triple main-sequence star system while searching for binary stars with compact objects

Ataru Tanikawa, Akito Tajitsu, Satoshi Honda et al. (+5 more)

We have discovered a compact hierarchical triple main-sequence star system, which is cataloged as Gaia DR3 1010268155897156864 or TIC 21502513. Hereafter, we call it “G1010”. G1010 consists of a primary (the most massive) star and inner binary that orbit each other. The primary star is a $0.85_{-0.03}^{+0.03}\;{\rm M}_\odot$ main-sequence (MS) star, and the inner binary components are $0.63_{-0.02}^{+0.02}$ and $0.61_{-0.02}^{+0.02}\;{\rm M}_\odot$ MS stars. The outer and inner orbital periods are $277.2_{-1.3}^{+1.6}$ and $\sim 18.26$ days, respectively. G1010 is categorized as a single-lined spectroscopic binary, and its orbital solution indicates that G1010 possibly accompanies a massive compact object, such as a neutron star or massive white dwarf. In order to confirm the presence of a massive compact object, we have performed several-times low signal-to-ratio (SNR) and one-time high SNR spectroscopic observations, and determined the outer orbital parameters. Moreover, we have deeply analyzed the high SNR spectroscopic data, and found that G1010 accompanies not a massive compact object, but an inner binary. We have investigated G1010's light curve in Transiting Exoplanet Survey Satellite (TESS), and concluded that the inner binary is actually an eclipsing binary, not included in TESS Eclipsing Binary Stars. We have obtained the inner orbital parameters from the TESS light curve. G1010 is similar to compact hierarchical triple star systems previously discovered by eclipse timing variation analysis. Our discovery has shown that such triple star systems can be discovered by combination of low- and high-SNR spectroscopic observations with the help of Gaia DR3 and the upcoming Gaia DR4/DR5.
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All authors Ataru Tanikawa, Akito Tajitsu, Satoshi Honda, Hiroyuki Maehara, Bun'ei Sato, Kento Masuda, Masashi Omiya, Hideyuki Izumiura

Cosmology and Nongalactic Astrophysics

Euclid preparation. Decomposing components of the extragalactic background light using multi-band intensity mapping cross-correlations

Euclid Collaboration: Y. Cao, A. R. Cooray, T. Li et al. (+268 more)

The extragalactic background light (EBL) fluctuations in the optical/near-IR encode the cumulative integrated galaxy light (IGL), diffuse intra-halo light (IHL), and high-$z$ sources from the epoch of reionisation (EoR), but they are difficult to disentangle with auto-spectra alone. We aim to decompose the EBL into its principal constituents using multi-band intensity mapping combined with cosmic shear and galaxy clustering. We develop a joint halo-model framework in which IHL follows a mass- and redshift-dependent luminosity scaling, IGL is set by an evolving Schechter luminosity function, and EoR emission is modelled with Pop II/III stellar emissivities and a binned star-formation efficiency. Using mock surveys in a flat $\Lambda$CDM cosmology with ten spectral bands spanning 0.75-5.0$\rm \mu m$ in the NEP deep fields over about 100$\deg^2$ with source detections down to AB=20.5 for masking, and six redshift bins to $z=2.5$, we fit auto- and cross-power spectra using a MCMC method. The combined SPHEREx$\times$Euclid analysis recovers all fiducial parameters within 1$\sigma$ and reduces 1$\sigma$ uncertainties on IHL parameters by 10-35% relative to SPHEREx EBL-only, while EoR star-formation efficiency parameters improve by 20-35%. Cross-correlations reveal a stronger coupling of IHL than IGL to the shear field, enhancing component separation; conversely, the EoR contribution shows negligible correlation with cosmic shear and galaxy clustering, aiding its isolation in the EBL. Relative to the SPHEREx EBL-only case, the inferred IHL fraction as a function of halo mass is significantly tightened over $10^{11}-10^{14} M_{\odot}$, with uncertainties reduced by 5-30%, and the resulting star-formation rate density constraints extend to $z\sim 11$, with uncertainty reductions of 22-31%.
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All authors Euclid Collaboration: Y. Cao, A. R. Cooray, T. Li, Y.-T. Cheng, K. Tanidis, S. H. Lim, D. Scott, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, J.-C. Cuillandre, H. Degaudenzi, G. De Lucia, H. Dole, M. Douspis, F. Dubath, X. Dupac, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, D. Sapone, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespí, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, M. Ballardini, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, L. Gabarra, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, N. Mauri, R. B. Metcalf, P. Monaco, A. A. Nucita, A. Pezzotta, M. Pöntinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, S. Anselmi, M. Archidiacono, E. Aubourg, L. Bazzanini, D. Bertacca, M. Bethermin, A. Blanchard, L. Blot, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, F. Cogato, S. Conseil, O. Cucciati, S. Davini, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, A. Enia, A. Finoguenov, A. Fontana, A. Franco, K. Ganga, T. Gasparetto, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, A. Hall, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, M. Lattanzi, L. Legrand, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, S. J. Liu, M. Magliocchetti, F. Mannucci, C. J. A. P. Martins, L. Maurin, M. Miluzio, C. Moretti, G. Morgante, K. Naidoo, P. Natoli, A. Navarro-Alsina, S. Nesseris, L. Pagano, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, E. Sarpa, C. Scarlata, A. Schneider, D. Sciotti, E. Sellentin, L. C. Smith, J. G. Sorce, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, A. Venhola, D. Vergani, G. Verza, S. Vinciguerra, N. A. Walton, J. R. Weaver, A. H. Wright

Solar and Stellar Astrophysics

The First Quantitative Study of Tail Regrowth of CME-Driven Disconnection in Comet C/2023 P1 Nishimura

Shaheda Begum Shaik, Guillermo Stenborg, Phillip Hess et al. (+3 more)

Comet C/2023 P1 (Nishimura) was observed by the Solar Orbiter Heliospheric Imager (SoloHI), onboard the Solar Orbiter spacecraft, from 2023 September 1 to 14. During this period, the ion tail of the comet exhibited continual fluctuations and four tail disconnection events (TDEs), each coinciding with the passage of a coronal mass ejection (CME). In this work, we report on the ion tail dynamics of the best observed TDE, which occurred on September 11. The SoloHI white-light images reveal an abrupt bending, subsequent kinks, and severing of a downstream portion of the pre-existing ion tail. The onset of disconnection occurred $\sim$6.5 hours after the projected passage of the CME leading edge in the images, consistent with a CME flank encounter. After the disconnection, the ion tail reformed within $\sim$24 hours, with a regrowth rate of $\sim$86$\pm7~\mathrm{km\,s^{-1}}$, indicating the rate at which newly ionized material forms along the magnetic field draped around the comet's coma. After the TDE, the detached tail drifted anti-sunward at an estimated speed of $\sim$295$\pm20~\mathrm{km\,s^{-1}}$, comparable to the local CME flank's speed, suggesting that the severed plasma was most likely carried away from the comet by the CME. This study provides the first direct, quantitative characterization of comet-CME interactions and the subsequent regrowth phase of a cometary TDE. These measurements were achievable by SoloHI's unique inner-heliospheric coverage, thanks to a combination of high photometric sensitivity, short exposure times, and a wide field of view that preserves the fine-scale tail dynamics.
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All authors Shaheda Begum Shaik, Guillermo Stenborg, Phillip Hess, Angelos Vourlidas, Karl Battams, Robin Colaninno

Astrophysics of Galaxies

Disk Wind Feedback from High-mass Protostars. V. Application of Multi-Modal Machine Learning to Characterize Outflow Properties

Duo Xu, Ioana A. Stelea, Joshua S. Speagle et al. (+2 more)

Characterizing protostellar outflows is fundamental to understanding star formation feedback, yet traditional methods are often hindered by projection effects and complex morphologies. We present a multi-modal deep learning framework that jointly leverages spatial and spectral information from CO observations to infer protostellar mass, inclination, and position angle ($PA$). Our model, trained on synthetic ALMA observations generated from 3D magnetohydrodynamic simulations, utilizes a cross-attention fusion mechanism to integrate morphological and kinematic features with probabilistic uncertainty estimation. Our results demonstrate that Vision Transformer architectures significantly outperform convolutional networks, showing remarkable robustness to reduced spatial resolution. Interpretability analysis reveals a physically consistent hierarchy: spatial features dominate across all parameters, whereas spectral profiles provide secondary constraints for mass and inclination. Applied to observational ALMA data, the framework delivers stable mass and $PA$ estimates with exceptionally tightly constrained inclination angles. This study establishes multi-modal deep learning as a powerful, interpretable tool for overcoming projection biases in high-mass star formation studies.
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All authors Duo Xu, Ioana A. Stelea, Joshua S. Speagle, Yichen Zhang, Jonathan C. Tan

High Energy Astrophysical Phenomena

NOCTURNE. I. The radio spectrum of narrow-line Seyfert 1 galaxies

M. Berton, E. Järvelä, S. Chen et al. (+8 more)

The origin of the radio emission in active galactic nuclei (AGN) is still debated. Multiple physical mechanisms can contribute to the spectrum at these frequencies, including relativistic jets, the jet base, outflows, star formation, and synchrotron emission from the hot corona. Recently, new extreme radio variability has been observed in the class of low-mass/high-Eddington AGN known as narrow-line Seyfert 1 (NLS1) galaxies, suggesting that another, more exotic mechanism may also play a role, especially at frequencies above 10 GHz. To investigate this relatively unexplored area of the radio spectrum, we observed a sample of 50 NLS1s with the Karl G. Jansky Very Large Array (JVLA), and 20 of them were observed twice. In this sample, 24 sources were not detected, while the others are typically characterized by a steep spectrum that can be modeled with a power law. We also identified two new candidate jetted NLS1s, including a high-frequency peaker, which is an extremely young relativistic jet. We found no significant variability in the sources observed twice. We conclude that the radio spectrum of NLS1s is typically dominated by optically thin emission, likely from low-power outflows, or by circumnuclear star formation, with a limited contribution from relativistic jets. Further studies at different spatial scales and at other wavelengths are necessary to fully constrain the origin of the radio emission in this class of active galaxies.
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All authors M. Berton, E. Järvelä, S. Chen, L. Crepaldi, I. Varglund, M. Coloma Puga, A. Jimenez-Gallardo, A. Lähteenmäki, S. Panda, C. Piscitelli, A. Tortosa

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

Rethinking Resonance Detectability during Binary Neutron Star Inspiral: Accurate Mismatch Computations for Low-lying Dynamical Tides

Alberto Revilla-Peña, Ruxandra Bondarescu, Andrew P. Lundgren et al. (+1 more)

We compute deviations from observed gravitational wave signals, where the amplitude of the signal is unchanged. As an example, we consider the detectability of low lying dynamical tides in binary neutron star or neutron star black hole mergers. Tidal forces can excite oscillatory modes of one or both of the stars in the binary when the orbital frequency of the binary system sweeps through the resonant mode frequency dissipating energy into the vibrational mode. The orbital energy loss to the vibrational mode extracts energy from the orbital motion, advancing the time to merger. The inspiral then continues with an excess phase and a time advance. Both will cause a mismatch when fitting to a system that has not gone through the resonance. To resolve this effect, we compute the mismatch for current and planned detectors using both a quasi-analytical approach that relies on the computation of moment integrals and an optimized version of the standard numerical match function. We conclude that detectability can occur for time advances of the order of 1 ms with advanced LVK detectors for an excess energy-flux that is a few percent of the gravitational wave emission. Our results contrast with previous work, which model this effect solely as a phase shift of the waveform or by using the difference in the number of cycles induced by the resonant behavior. We show that tidal resonance effects primarily cause a time advance of the merger, rather than a phase difference, and that the single-frequency approximation commonly used in the literature significantly overestimates the detectability of this effect.
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All authors Alberto Revilla-Peña, Ruxandra Bondarescu, Andrew P. Lundgren, Jordi Miralda-Escudé

Earth and Planetary Astrophysics

Thermal emission spectra of the ultra-hot Jupiter WASP-33 b

Qianyi Zou, Meng Zhai, Wei Wang et al. (+12 more)

Observations of exoplanetary atmospheres provide critical insights into their chemical composition, formation and evolution history. Ultra-hot Jupiters serve as excellent targets for atmospheric characterization; studies of these planets may yield key understanding of gas giant's formation and evolution history. We present a thermal emission study of WASP-33 b's dayside atmosphere, based on two secondary eclipse observations with CFHT/WIRCam in two specific narrow band filters, namely the CO and CH4$_{\rm on}$ filters, and archival data with HST/WFC3 and Spitzer. Stellar pulsations of the host star induce some quasi-periodic photometric variations, particularly in the CH4$_{\rm on}$ band, which are modelled and corrected in the high-precision differential light curves. An eclipse depth of $1565.2^{+228.6}_{-237.5}$ ppm and $914.3^{+56.1}_{-57.0}$ ppm is determined for the CO and CH4$_{\rm on}$ bands, respectively. Combined with HST/WFC3 and Spitzer data, our joint retrieval of WASP-33 b's dayside atmosphere reveals a high metallicity ([Fe/H] $= 1.52^{+0.35}_{-0.52}$), high C/O ratio (C/O $= 0.78^{+0.03}_{-0.04}$), and a thermal inversion layer, suggesting a formation history involving metal-rich gas accretion. We confirm the presence of the molecules H$_{2}$O, H$^{-}$ and CO, and report a tentative detection of TiO in the dayside atmosphere of WASP-33 b. Future higher precision observations with JWST may provide better understand constraints on the chemical abundances of oxygen and refractory element abundances to better WASP-33 b's formation and evolutionary pathway.
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All authors Qianyi Zou, Meng Zhai, Wei Wang, Guo Chen, Enric Palle, Fei Yan, HuanYu Teng, Qinglin Ouyang, Yaqing Shi, Li Zhou, Zewen Jiang, Yujuan Liu, Thomas Henning, Nicolas Crouzet, Gang Zhao

Solar and Stellar Astrophysics

A rotation-based census of blue lurker candidates in open clusters

Vikrant V. Jadhav, Khushboo K. Rao and Elisabetta Reggiani

Blue lurkers (BLs) are rejuvenated main-sequence stars hidden among normal main-sequence stars on color-magnitude diagrams of star clusters. In comparison, the blue straggler stars, formed via similar mass transfers or mergers, occupy a distinct space in the color-magnitude diagrams. We compile a list of BL candidates in open clusters using available rotation catalogs. BLs can be identified using either unusually faster rotation compared to similar mass stars, which is a signature of recent accretion, or the presence of a companion, which can only be formed by mass donation, e.g., an extremely low mass white dwarf. Here, we searched for fast-rotating stars on the main sequence of open clusters using Kepler, TESS, and spectroscopic rotation indicators, such as rotation periods and $v\sin i$ measurements. We identified 97 new BL candidates across 35 open clusters, almost tripling the previously known sample of 36. Based on the estimated completeness of $\approx$3%, thousands of BLs are likely hidden within the cluster population. Detailed spectroscopic and time-series analyses will be essential to confirm their mass-transfer histories.
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High Energy Astrophysical Phenomena

Towards precision astrometry of scattered images of compact radio sources: scintillometry theory and prospects

Dylan L. Jow and Delon Shen

Compact radio sources such as pulsars and FRBs undergo scintillation in the interstellar medium (ISM) when scattered images interfere at the observer. “Scintillometry” refers to the range of techniques to extract astrometric information – such as the angular positions of the images and distances to the scattering screen and source – from scintillation observations. Pulsar scintillometry has proven to be a powerful technique, revealing rich and unexpected scattering phenomenology in the ISM and also shedding light on the emission physics of pulsars. FRB scintillometry stands to be a similarly powerful probe of FRB emission, as well as structure on tiny scales in ionized media beyond our galaxy, such as the circumgalactic medium (CGM). However, nascent FRB scintillation studies are far from the sophisticated lensing geometry reconstructions that have been performed for scintillating pulsars. In this paper, we introduce a novel theoretical framework for scintillometry, demonstrating that the full astrometric content of scintillation observations is contained within a single underlying observable: the instantaneous spatial wavefield. We relate the instantaneous spatial wavefield to more familiar concepts from the pulsar scintillometry literature, such as the dynamic spectrum. Using this framework, we discuss prospects and limitations for FRB scintillometry, towards the goal of full astrometric reconstructions of FRB lensing geometries. We show how key degeneracies in two-screen scattering measurements can be ameliorated. In addition, we discuss the possibility of inferring dispersion measure gradients across scintillation screens, which may shed light on the highly unconstrained physics of the cool CGM phase on tiny ($\sim 100\,{\rm au}$) scales.
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Astrophysics of Galaxies

The LEGARE Project. I. Chemical evolution model of the Nuclear Stellar Disc in a Bayesian framework

E. Spitoni, M. Schultheis, F. Matteucci et al. (+5 more)

The Nuclear Stellar Disc (NSD) of the Milky Way is a dense, rotating stellar system in the central 200 pc. The NSD is thought to be primarily fuelled by bar-driven gas inflows from the inner Galactic disc. As part of the LEGARE project, we construct the first chemical evolution models for the NSD using a Bayesian approach tailored to reproduce the observed metallicity distribution functions (MDFs) and compared with the available abundance ratios for Mg, Si, Ca relative to Fe. We adopt a state-of-the-art chemical evolution model in which the gas responsible for the formation of the NSD is assumed to be driven by the Galactic bar-induced inflows. The chemical composition of the accreted material is assumed to reflect that of the Galactic disc at a radius of 4 kpc. A Bayesian MCMC framework is used to fit the MDFs of different samples of NSD stars. If we take the NSD data at face value, without considering a possible contamination from bulge stars, we find that a formation scenario based on the inner disc flowing gas is inconsistent with the low metallicity tail of the observed MDF. This is because the inner disc metallicity, at the epoch of bar formation, was already near solar. On the other hand, models invoking dilution from additional metal-poor inflows successfully reproduce the observations. The best-fit model requires inflow metallicity 5 times lower than the inner disc and a moderate star formation efficiency. The same model successfully reproduces the observed [$\alpha$/Fe] vs. [Fe/H] ratios and predicts a star formation history consistent with the most recent estimates. However, if we assume that the MDF is contaminated by metal poor bulge stars and restricted to [Fe/H] > -0.3 dex, gas dilution is no longer required. In this case, the best-fit model has a very low star formation efficiency and a mild galactic wind.
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All authors E. Spitoni, M. Schultheis, F. Matteucci, N. Ryde, G. Cescutti, A. Saro, M.C. Sormani, B. Thorsbro

Earth and Planetary Astrophysics

Balancing Variety and Sample Size: Optimal Parameter Sampling for Ariel Target Selection

Emilie Panek, Alexander Roman, Katia Matcheva et al. (+2 more)

Targeted astrophysical surveys are limited by the amount of telescope time available, which makes it impossible to observe every single object of interest. In order to maximize the scientific return, we need a well thought strategy for selecting the observational targets, in our case exoplanets. This study evaluates various strategies for selecting exoplanet targets within limited observation windows, focusing specifically on the selection of exoplanet targets for Tier 2 transit spectroscopy with ESA's upcoming Ariel mission. We define three distinct selection criteria – sample size, variance, and leverage – and translate them into objective functions compatible with modern optimization algorithms. Specifically, we test five heuristics for maximizing sample leverage: leverage greedy, simulated annealing, K-means clustering, regular classes, and quantile classes. The performance of these methods is demonstrated through three practical exercises across one, two, and three parameters of diversity. Each criterion represents a unique trade-off between sample size, diversity, and total observation time. While a time-greedy approach maximizes the quantity of planets, it fails to capture diversity. Conversely, variance-greedy selection prioritizes diversity but introduces significant drawbacks: it oversamples rare cases and undersamples typical planets, ultimately reducing the total number of targets observed. Leverage-based selections emerge as the most effective middle ground, successfully balancing sample diversity with a robust sample size. This work supports the broader community effort to ensure that Ariel delivers the most diverse and scientifically valuable sample of exoplanet atmospheres within mission limits.
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All authors Emilie Panek, Alexander Roman, Katia Matcheva, Konstantin T. Matchev, Nicolas B. Cowan

Solar and Stellar Astrophysics

27 years of Spaceborne IR Astronomy: An ISO, Spitzer, WISE and NEOWISE Survey for Large-Amplitude Variability in Young Stellar Objects

Chinmay S. Kulkarni, Thomas Behling, Elisabeth E. Banks et al. (+10 more)

Infrared observations can probe photometric variability across the full evolutionary range of young stellar objects (YSOs), from deeply embedded protostars to pre-main-sequence stars with dusty disks. We present 3-8 micron light curves extending 27 years from 1997 to 2024 obtained with three space-based IR telescopes: ISO, Spitzer and WISE. Although unevenly sampled with large gaps in coverage, these light curves show variability on time scales ranging from days to decades. We focus on the Spitzer-identified YSOs with disks and envelopes that exhibit variations of a factor of two or more in this wavelength range. We identified seven YSOs where the light curves are dominated by bursts of sustained (> 5 yr) high flux, including four that show a steep decay ending the burst and three that are ongoing as of the final observation. We find six YSOs that are undergoing declines, which may be the end of bursts that began before 1997. The most common form of variability, exhibited by 26 YSOs in our sample, show variations over time intervals of years to months but do not exhibit sustained bursts or fades. The Spitzer [3.6]-[4.5] and WISE [3.5]-[4.6] colors either increase or remain constant with increasing brightness, inconsistent with dust extinction as being the primary source of the large-amplitude variability.
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All authors Chinmay S. Kulkarni, Thomas Behling, Elisabeth E. Banks, Jason Jones, Tyler Robbins, Nathanael Burns-Watson, S. Thomas Megeath, Robert Gutermuth, Samuel Federman, Savio B. Oliveira, Wafa Zakri, William J. Fischer, Riwaj Pokhrel

Astrophysics of Galaxies

The Initial Mass Function as the Equilibrium State of a Variational Process: why the IMF cannot be sampled stochastically

Eda Gjergo, Zhiyu Zhang and Pavel Kroupa

The stellar initial mass function (sIMF) is often treated as a stochastic probability distribution, yet such an interpretation implies Poisson noise that is inconsistent with growing observational evidence. In particular, the observed relation between the mass of the most massive star formed in an embedded cluster and the cluster's total stellar mass supports a deterministic sampling process, known as optimal sampling. However, the physical origin of optimal sampling has not been formally established in the literature. In this work, we show that the stellar mass distribution implied by optimal sampling emerges from applying the Maximum Entropy principle to the fragmentation of star-forming clumps, whose structure is set by density-dependent cooling in the optically thin regime. Here, the maximum entropy leads to unbiased distributions. By applying calculus of variations to minimize the entropy functional obtained assuming fragmentation, we recover the power-law form of the sIMF, and we show that any distribution deviating from the sIMF violates the Maximum Entropy principle. This work provides a first-principles foundation for the deterministic nature of star formation. Thus, the sIMF is the distribution resulting from a maximally unbiased system.
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Astrophysics of Galaxies

Radio-Near Infrared Imaging of Dual Active Galactic Nuclei Candidates

Makoto A. Johnstone, Ilsang Yoon, Emmanuel Momjian et al. (+13 more)

We report the results of a pilot study that searched for dual active galactic nuclei (AGN) in local ($z<$0.25) galaxies hosting double-peaked narrow emission lines in their optical spectra. We present high-resolution $L-$band (1.5 GHz or 18 cm) continuum images from the Very Long Baseline Array (VLBA) as well as WFC3/IR F160W images from the Hubble Space Telescope of two candidate dual AGN systems: J0948+6848 and J1223+5409. In both targets, we detected compact non-thermal radio emission that is approximately co-spatial with the near-infrared AGN. Both systems host two high brightness temperature ($>10^{8}$ K) radio sources that indicate the presence of either a parsec-scale-separation dual AGN ($d_{\text{sep}} \sim 90$ pc and $\sim 56$ pc, respectively) or a radio jet. Matched-resolution multi-band radio observations are necessary to further characterize the AGN activity in these systems.
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All authors Makoto A. Johnstone, Ilsang Yoon, Emmanuel Momjian, Loreto Barcos-Muñoz, A.S. Evans, Bjorn Emonts, Eilat Glikman, Dong-Chan Kim, Ji Hoon Kim, Minjin Kim, Mark Lacy, George C. Privon, Devaky Kunneriath, Jaya Nagarajan-Swenson, Núria Torres-Albà, Kara N. Green

Astrophysics of Galaxies

Properties of Polarized Radio Sources in the Wide Chandra Deep Field South from 2 to 4GHz

Samantha Adams, Mark Lacy, Preshanth Jagannathan et al. (+14 more)

We present a study of the linear polarization properties of radio sources within the 10 deg$^2$ Wide Chandra Deep Field South (W-CDFS) in S-band (2-4 GHz). Our W-CDFS image has an angular resolution of 15 arcsec and a 1$\sigma$ RMS in Stokes $I$ of $\approx$50 $\mu$Jy/beam. We detect 1920 distinct source components in Stokes $I$ and 175 in linear polarization. We examine the polarized source counts, Faraday Rotation measures, and fractional polarization of the sources in the survey. We show that sources with a total intensity above $\approx$10mJy have a mean fractional polarization value of $\approx$3% from modeling the polarized counts. We also calculate an estimate for the limit on the fractional polarization level of sources with a total intensity below 1mJy (mostly star-forming galaxies) of $\stackrel{<}{_{\sim}}$3% using stacking. The mean Faraday Rotation we measure is consistent with that due to the Milky Way. We also show that fractional polarization is correlated with in-band spectral index, consistent with a lower mean fractional polarization for the flat-spectrum population. In addition to characterizing the S-band polarization properties of sources in the W-CDFS, this study will be used to validate the shallower, but higher angular resolution S-band polarimetric information that the VLA Sky Survey will provide for the whole sky above Declination -40 degrees over the next few years.
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All authors Samantha Adams, Mark Lacy, Preshanth Jagannathan, Jose Afonso, William Nielsen Brandt, B. M. Gaensler, Evanthia Hatziminaoglou, Anna Kapinska, Josh Marvil, Hugo Messias, Steve Myers, Ray Norris, Kristina Nyland, Wiphu Rujopakarn, Nick Seymour, Mattia Vaccari, Rick White

Astrophysics of Galaxies

Tidal features as tracers of galaxy merger histories: the colours of tidal features in HSC-SSP

A. Desmons, S. Brough, L. Canepa et al. (+1 more)

We measure the radial $g-i$ colour profiles of $\sim$32,000 galaxies drawn from the Hyper Suprime-Cam Subaru Strategic Program optical imaging survey, including 1415 exhibiting tidal features. We compare the colour profiles of galaxies with and without tidal features to extract information about the properties of the mergers that created these features. We find negative colour gradients for both galaxies with and without tidal features and find that tidal feature-hosting red sequence galaxies have redder outskirts than their non-tidal feature hosting counterparts, consistent with the outskirts of these galaxies being dominated by stars accreted from gas-poor minor mergers. We find decreasing mass ratios of tidal features-to-host galaxy with increasing galaxy stellar mass, suggesting that less massive galaxies undergo mergers with companions closer in mass than more massive galaxies. Galaxies exhibiting streams have bluer outskirts than those hosting shells, and shells around red sequence galaxies tend to be more massive and have higher mass ratios to their hosts than streams, consistent with streams being formed from mergers with satellites less massive than those responsible for shells. The agreement between our findings and those of other observational and simulation-based works confirms the validity of our methodology and highlights the value of tidal features colours as a probe into the process through which galaxies evolve.
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All authors A. Desmons, S. Brough, L. Canepa, A. Khalid

Cosmology and Nongalactic Astrophysics

The Lambert $W$ equation of state in light of DESI BAO

Vipin Chandra Dubey, Subhajit Saha and Abdulla Al Mamon

We investigate a unified dark-fluid model whose effective equation of state (EoS) is described by logarithmic and power-law terms involving the Lambert $W$ function. The model parameters are constrained using BAO data, including DESI measurements, together with Pantheon+ Type Ia supernova observations and direct Hubble parameter measurements. The analysis yields $\theta_{1}=0.087\pm 0.011$, $\theta_{2}=-3.35\pm 0.13$, $r_d = 146\pm 2.5$~Mpc, and $H_0 = 67.4 \pm 1.2~\text{km\,s}^{-1}\text{Mpc}^{-1}$. The inferred Hubble constant, $H_{0}$, is consistent with the Planck 2018 measurement and remains in tension with local determinations, thereby reflecting the Hubble tension. We further examine the evolution of deceleration, effective EoS, and jerk parameters, complemented by the $Om(z)$ diagnostic. Our analysis reveals that the model provides a consistent description of late-time cosmic acceleration. Finally, the observational viability of the model is assessed using Akaike and Bayesian information criteria and compared with that of the standard $\Lambda$CDM model.
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Cosmology and Nongalactic Astrophysics

A Universal CMB $B$-Mode Spectrum from Early Causal Tensor Sources

Kylar Greene, Aurora Ireland, Gordan Krnjaic et al. (+1 more)

Many early universe scenarios predict post-inflationary tensor perturbations from causality-limited, sub-horizon sources. While the microphysical details may differ, as long as these sources are bounded in duration and correlation length, their tensor power spectra exhibit a universal scaling behavior at small wavenumber: $P_h(k) \propto k^3$, corresponding to white noise on super-horizon scales at the time of production. If these early causal tensor sources (ECTs) exclusively produce gravitational waves before redshift $z \sim 10^5$, this scaling is realized on all of the scales observed in the cosmic microwave background (CMB), and thus yields a universal multipole distribution for the $B$-mode angular power spectrum. Unlike the scale-invariant distributions of inflationary $B$ modes, ECTs generically predict enhanced power on small scales and suppressed power on large scales, which allows these source classes to be distinguished given measurements over a sufficient range of angular scales. In this paper, we introduce a unified framework for characterizing ECTs and demonstrate how their universal infrared scaling manifests in low-frequency observables, including CMB $B$ modes and stochastic gravitational wave spectral densities. We illustrate this mapping with representative case studies of this universality class involving first-order phase transitions, topological defects, and enhanced scalar perturbations, which source tensor modes at second order in perturbation theory.
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All authors Kylar Greene, Aurora Ireland, Gordan Krnjaic, Yuhsin Tsai

Earth and Planetary Astrophysics

The Third Option: Color Phase Curves to Characterize the Atmospheres of Temperate Rocky Exoplanets

Drake Deming, Andrew Lincowski, Laura Kreidberg et al. (+6 more)

Detecting and characterizing the atmospheres of rocky exoplanets has proven to be challenging for JWST. Transit spectroscopy of the TRAPPIST-1 planets has been impacted by the effects of spots and faculae on the host star. Secondary eclipses have detected hot rocks, but evidence for atmospheres has been difficult to obtain. However, there is a third option that we call color phase curves. This method will apply to synchronously rotating non-transiting planets as well as transiting planets. A color phase curve uses photometry at a long-IR wavelength where the planetary thermal emission is strong (e.g., 21 microns) divided by photometry at a shorter wavelength where the star dominates (e.g., 12 microns). We avoid wavelengths having potentially strong molecular absorption (e.g., 15 microns) to minimize degeneracies in the color phase curve, and we aim to detect and characterize the planetary atmosphere via its longitudinal heat transfer. The ratio of two wavelengths observed nearly simultaneously is designed to isolate thermal emission from the planet, discriminate against the star, and largely cancel instrumental systematic effects. Moreover, we show that invoking mass-radius relations, and using self-consistent physical models, will permit the longitudinal heat transfer to be measured independent of the orbital inclination. Radial velocity surveys are detecting many new exoplanets, including temperate rocky worlds with Earth-like masses. Most of those planets will not transit, but color phase curves have the potential to detect and characterize their atmospheres.
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All authors Drake Deming, Andrew Lincowski, Laura Kreidberg, Miles Currie, Jean-Michel Desert, Guangwei Fu, Jacob Lustig-Yaeger, Victoria Meadows, Ignas Snellen

High Energy Astrophysical Phenomena

Proposal to Search for the CP Violating Electromagnetic Vacuum Angle at the Event Horizon Telescope

Willy Fischler and Tom Banks

We examine the possibility that evidence for a non-zero value of the CP violating $ \frac{e^2 }{32\pi^2}\theta_{EM} \int d^4 x {\vec E}\cdot {\vec B}$ coupling might be extracted from Event Horizon Telescope observations of the black holes SgA* and M87*. The Fischler-Kundu\cite{FK} effect predicts a universal Hall current in the relaxation of charge falling onto the black hole horizon. We argue that this leads to a non-zero value of a certain CP-violating observable ${\cal C}$, defined below. The effect can be masked by parity violating plasma currents. In particular, evidence for polarization flips \cite{flip} in the signals from M87* indicate strong plasma effects in the data. We suggest that time averaging the data over periods including the flip might leave over a residual that would be an indicator of the FK signal. In addition, similarities in the polarization patterns between the two very different black holes, and a part of the signal that is uniform in frequency, might enable us to distinguish the universal topological signal from source and frequency dependent plasma effects. Current data does not appear to be sufficient to perform such a test.
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High Energy Astrophysical Phenomena

Early results in the search for extreme coronal line emitters with the Dark Energy Spectroscopic Instrument

Peter Clark, Joseph Callow, Or Graur et al. (+44 more)

Here we present the results of our search through the Early Data Release (EDR) of the Dark Energy Spectroscopic Instrument (DESI) for extreme coronal line emitters (ECLEs) - a rare classification of galaxies displaying strong, high-ionization iron coronal emission lines within their spectra. With the requirement of a strong X-ray continuum to generate the coronal emission, ECLEs have been linked to both active galactic nuclei (AGNs) and tidal disruption events (TDEs). We focus our search on identifying TDE-linked ECLEs. We identify three such objects within the EDR sample, highlighting DESI's effectiveness for discovering new nuclear transients, and determine a galaxy-normalized TDE-linked ECLE rate of $R_\mathrm{G}=5~^{+5}_{-3}\times10^{-6}~\mathrm{galaxy}^{-1}~\mathrm{yr}^{-1}$ at a median redshift of z = 0.2 - broadly consistent with previous works. Additionally, we also identify more than 200 AGNs displaying coronal emission lines, which serve as the primary astrophysical contaminants in searches for TDE-related events. We also include an outline of the custom python code developed for this search.
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All authors Peter Clark, Joseph Callow, Or Graur, Alexei V. Filippenko, Thomas G. Brink, WeiKang Zheng, Jessica Aguilar, Steven Ahlen, Segev BenZvi, Davide Bianchi, David Brooks, Todd Claybaugh, Andrei Cuceu, Axel de la Macorra, Arjun Dey, Peter Doel, Jaime E. Forero-Romero, Enrique Gaztañaga, Satya Gontcho A Gontcho, Gaston Gutierrez, Victoria Fawcett, Mustapha Ishak, Jorge Jimenez, Dick Joyce, Stephanie Juneau, Theodore Kisner, Anthony Kremin, Martin Landriau, Laurent Le Guillou, Marc Manera, Aaron Meisner, Ramon Miquel, John Moustakas, Seshadri Nadathur, Will J. Percival, Francisco Prada, Ignasi Pérez-Ràfols, Graziano Rossi, Eusebio Sanchez, David Schlegel, Michael Schubnell, Joseph Harry Silber, David Sprayberry, Gregory Tarlé, Benjamin A. Weaver, Rongpu Zhou, Hu Zou

Cosmology and Nongalactic Astrophysics

First constraints on causal sources of primordial gravitational waves from BICEP/Keck, SPTpol, SPT-3G, Planck and WMAP $B$-mode data

Jessica A. Zebrowski, Aurora Ireland, Christian L. Reichardt et al. (+4 more)

Non-inflationary sources of gravitational waves in the early Universe generically predict causality-limited tensor power spectra at low frequencies. We report the first-ever constraints on such sources based on cosmic microwave background (CMB) $B$-mode polarization measurements. Using data from BICEP/Keck, SPTpol, SPT-3G, Planck, and WMAP, we constrain the amplitude of an early causal tensor (ECT) power spectrum parameterized by $r_{ect}$, the ratio of causal tensor power to total scalar power at $k~=~0.01$ Mpc$^{-1}$, and obtain a 95% CL upper limit of $r_{ect}<$ 0.0077. Since $r_{ect}$ can easily be related to the parameters of a given theory, our bound robustly constrains a broad class of well-motivated gravitational wave sources in the early universe, including first-order cosmological phase transitions, enhanced small-scale density perturbations, and various topological defects. Finally, we translate our limit into a bound on the present-day energy density in gravitational waves at ultra-low frequencies otherwise inaccessible to traditional gravitational wave detection strategies, including pulsar timing arrays, interferometers, and resonant cavities.
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All authors Jessica A. Zebrowski, Aurora Ireland, Christian L. Reichardt, Kylar Greene, Gordan Krnjaic, Yuhsin Tsai, François R. Bouchet

Astrophysics of Galaxies

Anomalous narrow line Seyfert I galaxies from SDSS DR17

Arihant Tiwari, Rachana, Vivek M et al. (+1 more)

We present an analysis of 22,656 narrow-line Seyfert 1 galaxies (NLSy1s) from Sloan Digital Sky Survey (SDSS) DR17 ($0.1\leq z\leq 0.9$), identifying a sample of spectroscopically anomalous sources. These anomalies were detected via the spectroscopic quasar anomaly detection (SQuAD) algorithm, which employed principal component analysis and hierarchical k-means clustering. Various physical diagnostic analysis were performed such as the color excess ($E_{(B-V)}$) calculations, Wide-field Infrared Survey Explorer (WISE) color analysis, probing O III, equivalent width as an inclination indicator, the BPT diagram and eigenvector 1 diagram. We detected 620 anomalous NLSy1s classified into two groups i.e. 246, Red NLSy1s, exhibiting host galaxy dominated spectra with a low luminosity active galactic nuclei (AGN) core revealed by the emission line widths. Another set of 374 Blue NLSy1s, strongly luminous galaxies with enhanced AGN activity, bluer continuum as compared to a typical NLSy1 and stronger Fe II emission. Finally, the third group of 257 outliers, identified as Intermediate Seyferts, a class of Seyfert galaxies identified by composite emission profiles, and extremely strong emission lines paired with virtually no continuum. These sources also exhibit rare and high ionization emission lines unseen in any other NLSy1 spectra (e.g. [Ne V]$\lambda3345$, Ne V $\lambda3426$, Ne III $\lambda3869$ etc). We conclude that the differentiating factor between red and blue NLSy1s is not dust obscuration or orientation effect, but intrinsic distinction in AGN activity. The resulting sample is presented as a value-added catalog.
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All authors Arihant Tiwari, Rachana, Vivek M, Suvendu Rakshit

High Energy Astrophysical Phenomena

Turbulent Dynamo Action in Binary Neutron Star Mergers

Eduardo M. Gutiérrez, David Radice, Jacob Fields et al. (+1 more)

We perform general-relativistic magnetohydrodynamics zoom-in simulations of the merger of two neutron stars starting with pulsar-like realistic initial magnetic field. We employ unprecedented grid resolution down to $\Delta x \simeq 2.9~{\rm m}$. We find rapid amplification of the magnetic energy at small scales, and demonstrate the action of a small-scale turbulent dynamo. We find evidence that ordered large-scale magnetic structures emerge already during the early post-merger evolution. These results indicate that strong magnetic fields can be established promptly after merger, with important consequences for the electromagnetic counterparts of binary neutron star mergers.
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All authors Eduardo M. Gutiérrez, David Radice, Jacob Fields, James M. Stone

Astrophysics of Galaxies

Euclid: Early Release Observations – The star-formation history of massive early-type galaxies in the Perseus cluster

S. Martocchia, A. Boselli, J.-C. Cuillandre et al. (+157 more)

The Euclid Early Release Observations (ERO) programme targeted the Perseus galaxy cluster in its central region over 0.7deg$^2$. We combined the exceptional image quality and depth of the ERO-Perseus with FUV and NUV observations from GALEX and AstroSat/UVIT, as well as $ugrizH\alpha$ data from MegaCam at the CFHT, to deliver FUV-to-NIR magnitudes of the 87 brightest galaxies within the Perseus cluster. We reconstructed the star-formation history (SFH) of 59 early-type galaxies (ETGs) within the sample, through the spectral energy distribution (SED) fitting code CIGALE and state-of-the-art stellar population (SP) models to reproduce the galactic UV emission from hot, old, low-mass stars (i.e. the UV upturn). In addition, for the six most massive ETGs in Perseus [stellar masses $\log_{10}(M_{\ast}/M_{\odot}) \geq 10.3$], we analysed their spatially resolved SP through a radial SED fitting. In agreement with our previous work on Virgo ETGs, we found that (i) the majority of ETGs needs the presence of an UV upturn to explain their FUV emission, with temperatures $\langle T_{\rm UV}\rangle$~33800 K; (ii) ETGs have grown their stellar masses quickly, with SF timescales $\tau\lesssim 1500$ Myr. We found that all ETGs in the sample have formed more than about 30% of their stellar masses at z~5, up to ~100%. At z~5, the stellar masses of the most massive nearby ETGs, which have present-day stellar masses $\log_{10}(M_{\ast}/M_{\odot})\gtrsim 10.8$, are then found to be comparable to those of the red quiescent galaxies observed by JWST at similar redshifts (z>4.6). This study can be extended to ETGs in the 14000 deg$^2$ extragalactic sky that will soon be observed by Euclid, in combination with those from other major upcoming surveys (e.g. Rubin/LSST), and UV observations, to ultimately assess whether the nearby massive ETGs represent the progeny of the massive high-z JWST red quiescent galaxies.
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All authors S. Martocchia, A. Boselli, J.-C. Cuillandre, M. Mondelin, M. Bolzonella, C. Tortora, M. Fossati, C. Maraston, P. Amram, M. Baes, S. Boissier, M. Boquien, H. Bouy, F. Durret, C. M. Gutierrez, M. Kluge, Y. Roehlly, T. Saifollahi, M. A. Taylor, D. Thomas, T. E. Woods, G. Zamorani, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, R. Bender, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, H. Degaudenzi, G. De Lucia, F. Dubath, X. Dupac, S. Escoffier, M. Fabricius, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, M. Frailis, E. Franceschi, P. Franzetti, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, H. Kurki-Suonio, A. M. C. Le Brun, D. Le Mignant, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, L. Moscardini, C. Neissner, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, A. Secroun, G. Seidel, S. Serrano, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, J. Steinwagner, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, A. Veropalumbo, Y. Wang, J. Weller, I. A. Zinchenko, E. Zucca, J. García-Bellido, J. Martín-Fleitas, M. Maturi, V. Scottez