Earth and Planetary Astrophysics
Atmospheric Circulation of High-Obliquity Mini-Neptunes
Yanhong Lai, Xianyu Tan and Yubo Su
With the operation of JWST, atmospheric characterization has now extended to low-mass
exoplanets. In compact multiplanetary systems, secular
spin-orbital resonance may preserve high obliquities and asynchronous rotation even for tidally-despinning, low-mass
planets, potentially leading to unique atmospheric circulation patterns. To understand the impact on the atmospheric circulation and to identify the potential atmospheric observational signatures of such high-obliquity
planets, we simulate the three dimensional circulation of a representative mini-Neptune K2-290 b, whose obliquity may reach about 67 degrees. Whether synchronously rotating or not, the
planet's slow rotation, moderate temperature and radius result in a global Weak-Temperature-Gradient (WTG) behavior with moderate horizontal temperature contrasts. Under synchronous rotation, broad eastward superrotating jets efficiently redistribute heat. Circulation in an asynchronous rotation exhibits a seasonal cycle driven by high obliquity, along with quasi-periodic oscillations in winds and temperatures with a period of about 70 orbital periods. These oscillations, driven by wave-mean flow interactions, extend from low to mid-latitudes due to the slow planetary rotation. Higher atmospheric
metallicity strengthens radiative forcing, increasing temperature contrasts and jet speeds. Clouds have minimal impact under synchronous rotation but weaken jets under nonsynchronous rotation by reducing temperature contrasts. In all cases, both thermal emission and transmission spectra exhibit moderate observational signals at a level of 100 ppm, and high-obliquity effects contribute differences at the 10 ppm level. Our results are also applicable to a range of potential high-obliquity
exoplanets, which reside in the WTG regime and likely exhibit nearly homogeneous horizontal temperature patterns.
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High Energy Astrophysical Phenomena
Radio streaks in the Lighthouse Nebula discovered with MeerKAT – Particles escaping from the tail and illuminating the ambient magnetic field
Pierrick Martin, Mickael Coriat, Barbara Olmi et al. (+6 more)
Bow-shock
pulsar wind nebulae are valuable sources for investigating the dynamics of relativistic
pulsar winds and the mechanisms by which they produce
cosmic-ray
leptons at the highest energies. The Lighthouse Nebula is one such object, famous for the high velocity of its
pulsar and its long, misaligned X-ray jet, which may provide a specific escape channel for the most energetic particles. We aim to understand how the bulk of non-thermal particles is released into the ISM. We focus on GHz
radio observations, which probe lower-energy particles that are dominant in number and long-lived, thus providing a picture of how escape proceeds over long timescales. We analysed MeerKAT and ASKAP observations at 1.28GHz and 0.94GHz, respectively. MeerKAT observations reveal a highly structured synchrotron nebula downstream of the
pulsar PSRJ1101-6101. A cometary tail extends beyond 5pc from the
pulsar, while we detect multiple two-sided transverse emission streaks for the first time. We detect no
radio counterpart of the misaligned X-ray jet, but the spectral index map shows an apparent asymmetry, with the steepest values near the base of the jet. We interpret the
radio streaks as the occasional, charge-independent release of energetic
leptons from the tail into the surrounding medium, resulting from dynamical instabilities and reconfiguration in the downstream flow. Most of the particle content of the nebula is discharged into the ambient medium within several pc. Escaped particles light up the ambient
magnetic field, which appears to have a coherence length of at least a few pc. The length and persistence of the streaks indicate a low level of
magnetic turbulence, possibly slightly enhanced with respect to average
cosmic-ray transport conditions in the
Galaxy. This may result from self-generated
turbulence caused by a resonant streaming instability or from past activity of the progenitor
star.
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All authors Pierrick Martin, Mickael Coriat, Barbara Olmi, Elena Amato, Niccolò Bucciantini, Sanja Lazarević, Miroslav D. Filipović, Alexandre Marcowith, Sarah Recchia
Astrophysics of Galaxies
Gas distributions inside and around haloes in the alternative dark matter simulations AIDA-TNG
Chi Zhang, Enrico Garaldi, Giulia Despali et al. (+3 more)
The nature of Dark Matter (DM) is one of the greatest mysteries of modern astrophysics. While the standard Cold DM (CDM) model successfully explains observations on most astrophysical scales, DM particles have not yet been detected, leaving room for a plethora of different models. In order to identify their observable signatures, we use the AIDA-TNG cosmological simulation suite to predict the distributions of gas and neutral hydrogen (HI) in the CDM, Self-Interacting DM (SIDM), velocity-dependent SIDM (vSIDM), and Warm DM (WDM) models. We find that the DM models investigated have very limited impact on the median gas and HI profiles of
haloes. Nevertheless, for the most massive
haloes ($M_{\rm vir}\sim10^{14}\,\mathrm{M}_\odot$), we find that DM self-interactions can reduce the central potential, thereby lowering gravitational heating and the central gas temperature. We find that, in all models, the
halo-to-
halo variation in the HI profiles is explained by AGN feedback, and that the specific characteristics of the DM model are largely subdominant. Nevertheless, we detect some systematic difference in the case of SIDM, with more HI surviving close to the centre with respect to other models. We provide fitting functions for the gas and HI profiles. We investigate the
galaxy-Ly$\alpha$ cross-correlation function (\galacc) for different
halo masses,
redshifts and observational strategies. We find that at $z=0$ vSIDM can be distinguished from CDM in
haloes with $10^{12}\lesssim M_{\rm vir}\lesssim10^{13}\,{\rm M}_\odot$, while SIDM1 can be distinguished from CDM in
haloes with $M_{\rm vir}\gtrsim10^{13}\,{\rm M}_\odot$. We estimate that statistically-robust detection requires sampling $\sim160$
haloes with $\sim20$ sightlines each, a task that can be achieved with current and future facilities like WEAVE, 4MOST, PFS, ELT and WST.
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All authors Chi Zhang, Enrico Garaldi, Giulia Despali, Matteo Viel, Lauro Moscardini, Mark Vogelsberger
Astrophysics of Galaxies
Ancient relic moderately metal-rich bulge cluster Tonantzintla 2
Sergio Ortolani, Stefano O. Souza, Domenico Nardiello et al. (+6 more)
The assembly history of the
Galactic bulge is intimately tied to the formation of the proto-Milky Way, yet reconstructing this early phase is difficult because mergers and secular
evolution have erased most of its original structure. Among present-day
stellar systems, only globular clusters retain the ancient signatures needed to trace these
primordial building blocks. Here we present the most detailed characterization to date of Tonantzintla 2, a
prime candidate for a relic of the Milky Way's
primordial bulge. It is a moderately metal-rich globular cluster projected onto the bulge that has remained largely unexplored despite its potential to constrain the early formation of the inner Milky Way. We derive its fundamental parameters using proper motion-corrected Hubble Space
Telescope WFC3 and ACS photometry. By applying an isochrone fitting to very clean data, we obtain an age of 13.58 Gyr, a reddening E(B-V) = 1.44, a
metallicity [M/H]=-0.68, and a heliocentric distance of d = 7.38 kpc. A complementary chemical-abundance analysis of seven member
stars from APOGEE high-resolution spectroscopy reveals an enrichment pattern consistent with an in-situ origin. Tonantzintla 2 is among the oldest globular clusters studied in the literature, and the oldest so far analyzed in the
Galactic bulge. Its age places a stringent constraint on the onset of the bulge formation, implying that
star formation in the inner
Galaxy began within ~0.2 Gyr of the Big Bang and that Tonantzintla 2 represents an exceptional relic of the Milky Way's earliest chemical enrichment.
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All authors Sergio Ortolani, Stefano O. Souza, Domenico Nardiello, Beatriz Barbuy, Eduardo Bica, Bernardo P. L. Ferreira, Cristina Chiappini, José Fernandez-Trincado, Heitor Ernandes
Solar and Stellar Astrophysics
Different Transient Phenomena at the Edges of Traveling Foreshocks
Primoz Kajdic, Xóchitl Blanco-Cano, Diana Rojas-Castllo et al. (+1 more)
Past kinetic simulations and spacecraft observations have shown that traveling foreshocks (TFs) are bounded by either foreshock compressional boundaries (FCBs) or foreshock bubbles (FBs). Here we present four TFs with a different kind of structure appearing at one of their edges. Two of them, observed by the Cluster mission, are bounded by a hot flow anomaly (HFA). In one case, the HFA was observed only by the spacecraft closest to the bow shock, while the other three probes observed an FCB. In addition, two other TFs were observed by the MMS spacecraft to be delimited by a structure that we call HFA-like FCB. In the spacecraft data, these structures present signatures similar to those of HFAs: dips in
magnetic field magnitude and
solar wind density, decelerated and deflected
plasma flow and increased temperature. However, a detailed inspection of these events reveals the absence of heating of the SW beam. Instead, the beam almost disappears inside these events and the
plasma moments are strongly influenced by the suprathermal particles. We suggest that HFA-like FCBs are related to the
evolution and structure of the directional discontinuities of the interplanetary
magnetic field whose thickness is larger than the gyroradious of suprathermal ions. We also show that individual TFs may appear together with several different types of transient upstream mesoscale structures, which brings up a question about their combined effect on regions downstream of the bow shock.
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All authors Primoz Kajdic, Xóchitl Blanco-Cano, Diana Rojas-Castllo, Nojan Omidi
High Energy Astrophysical Phenomena
Multi-epoch VLBI observations of the blazar 3C 66A: Spatial twisting and temporal oscillation of the parsec-scale jet
Paloma Thevenet, Jeonguk Kim, Guang-Yao Zhao et al. (+2 more)
Previous VLBI kinematic studies of the blazar 3C 66A have unveiled complex jet kinematic behaviors. Using follow-up high-resolution VLBI observations and archival data, we investigate the morphology and the variations in orientation and core flux density of the 3C 66A jet to gain a deeper insights into its kinematic behavior and physical origins. We performed KVN and VERA array (KaVA) observations at 22/43 GHz over three epochs in 2014 and collected 109 sets of Very Long Baseline Array (VLBA) archival data at 43 GHz between 1996 - 2025. We imaged the parsec-scale jet and parameterized it using circular Gaussian fittings to the UV visibilities. Finally, we derived the inner jet PA and the core flux densities for the VLBA data. The jet presents a twisted morphology in the KaVA maps. The PA of the fitted Gaussian components is in the range between 170 deg and 195 deg. Our kinematic analysis using the VLBA data indicates that the PA oscillates with an amplitude of 7.77 pm 0.79 deg and a period of 10.94 pm 0.22 years, presented for the first time in this work. This oscillation is topped by a continuous clockwise shift of the PA by -0.83 pm 0.07 deg/year. We also identified a strong core flux variability with possible periodicity and a 2 sigma correlation between the core flux density and the inner jet PA change. We discuss possible physical models that could explain the observed features for this object; in particular, a supermassive black hole binary (SMBHB) system, Lense Thirring (LT) effect, and jet or disk instabilities. The oscillation and continuous shift of the PA and the possible
radio flux periodicity, together with the optical flux periodicity of approximately 2 years that had previously been confirmed in several independent studies, favor a jet precession scenario driven by orbital motion and disk-orbit misalignment in a SMBHB system.
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All authors Paloma Thevenet, Jeonguk Kim, Guang-Yao Zhao, Bong Won Sohn, Suk-Jin Yoon
High Energy Astrophysical Phenomena
XFit: Global Optimization and Degeneracy Mapping in X-ray Spectral Modeling
Austin MacMaster, Adam Rogers, Jason Fiege et al. (+2 more)
The standard approach to modeling X-ray spectral data relies on local optimization methods, such as the Levenberg-Marquardt
algorithm. While effective for simple models and speedy spectral fitting, these local optimizers are prone to becoming trapped in local minima, particularly in high-dimensional or degenerate parameter spaces, and typically require extensive user intervention. In this work, we introduce XFit, a global optimization method for fitting X-ray data, which makes extensive use of the Ferret evolutionary
algorithm. XFit enables automated exploration of complex parameter spaces, efficient mapping of confidence intervals, and identification of degenerate solutions that may be overlooked by local methods. We demonstrate the performance of XFit using two representative X-ray sources: the Central Compact Object in Cassiopeia A and the
supernova remnant G41.1-0.3. These examples span both low- and high-dimensional models, allowing us to illustrate the advantages of global optimization. In both cases, XFit produces solutions that are consistent with or improve upon those found with traditional methods, while also revealing alternative fits or degenerate solutions within statistically acceptable confidence levels. The automated mapping of parameter space offered by XFit makes it a powerful complement to existing spectral fitting tools, particularly as models and data quality become increasingly complex. Future work will expand the application of XFit to broader
datasets and more physically motivated models.
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All authors Austin MacMaster, Adam Rogers, Jason Fiege, Rebecca Man, Samar Safi-Harb
Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics
Gravitational wave detectors from an experimental perspective
Marina Trad-Nery, Margherita Turconi and Walid Chaibi
This chapter introduces the fundamental principles of gravitational wave detectors in a simple and comprehensive manner. Because these instruments aim for extremely high sensitivity, it is essential to understand their various noise sources, how such noise couples to the detector output, and the strategies used to mitigate them. These noises contributions are computed in the frame of the Virgo detector and a sensitivity curve is calculated. Although a simplified layout of a gravitational wave detector is considered, it takes into account the most dominant effects and yields in a sensitivity estimate close to the what is observed in real detectors.
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Astrophysics of Galaxies
Galactic Large-scale Filaments Resident in Asymmetric Environments: Clues from Cross-filament Profiles of Density and Temperature
Keyun Su, Ke Wang, Fengwei Xu et al. (+1 more)
Large-scale filaments ubiquitously exist in the
Galactic interstellar medium, and their radial profiles offer insights into their formation mechanisms. We present a statistical analysis of molecular hydrogen column density ($\rm N(H_2)$) and
dust temperature ($\rm T_d$) radial profiles for 35
Galactic large-scale filaments. We divided their spines into 315 segments, extracted the radial profiles of each segment using $\rm N(H_2)$ and $\rm T_d$ maps derived from $Herschel$ Hi-GAL data, and estimated the asymmetry degree within the radial profiles ($\alpha_{\rm asy}$), as well as the length proportion of segments with asymmetric profiles across the entire filament ($f_{\rm asy}$). We found that
Galactic large-scale filaments reside in surroundings distinctly asymmetric and varied in $\rm N(H_2)$, and mild asymmetric yet stable in $\rm T_d$. Different filament morphology types do not show significant differences in $\alpha_{\rm asy}$ or $f_{\rm asy}$. A bent filament shape does not necessarily correspond to an asymmetric radial profile, whereas a straight filament shape may be associated with a symmetric profile. Segments with asymmetric surroundings in $\rm N(H_2)$ may not simultaneously appear asymmetric in $\rm T_d$, and vice versa. We found three filaments with 4-44% of their spine show asymmetric $\rm N(H_2)$ and $\rm T_d$ radial profiles in inverse trends, likely caused by nearby HII region. HII regions of similar scale to large filaments can induce asymmetric radial profiles within them, indicating their influence on filament
evolution. However, they are unlikely to independently trigger the formation of an entire
Galactic large-scale filament, in contrast to their role in small-scale filament formation.
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All authors Keyun Su, Ke Wang, Fengwei Xu, N. K. Bhadari
Cosmology and Nongalactic Astrophysics
First Observational Evidence for Split Infall Flow of Cosmic Filaments into Clusters
Ji Yao, Huanyuan Shan, Pengjie Zhang et al. (+5 more)
Velocity fields in the
cosmic web are fundamental to structure formation but remain difficult to observe directly beyond the linear regime. Here we present observational evidence that
galaxy filaments connecting pairs of
galaxy clusters undergo a split infall, with opposite velocity flows toward the two clusters. Using spectroscopic
galaxies from the Sloan Digital Sky Survey, we isolate the internal filament velocity field by subtracting its rigid-body background motion and Hubble flow, and detect this effect at greater than $5\sigma$ significance across a wide range of cluster and filament selections. The measured velocity profile exhibits a sign reversal near the filament midpoint and a maximum infall amplitude of $\sim30$ km/s ($\sim20$ km/s projected onto the line-of-sight) for clusters of mass $\sim10^{14.3}M_\odot$, substantially lower than expected for infall from an average
cosmic environment. Multiple results on density-velocity correlation, mass-dependency, and validation with simulation indicate that filaments dynamically respond to competing gravitational potentials rather than acting as passive mass transport channels. Our results establish a new observational window on quasi-linear velocity fields in the
cosmic web and provide a promising probe of mass measurement, testing
gravity and velocity reconstruction with upcoming wide-field spectroscopic surveys.
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All authors Ji Yao, Huanyuan Shan, Pengjie Zhang, Xiaohu Yang, Jiale Zhou, Jiaxin Han, Peng Wang, Haojie Xu
High Energy Astrophysical Phenomena
Exploring the role of accretion shocks in galaxy clusters as sources of ultrahigh-energy cosmic rays
A.D. Supanitsky and S.E. Nuza
Recently, the Pierre Auger Observatory has found strong evidence supporting the extragalactic origin of the most energetic
cosmic rays. Despite several observed excesses in the distribution of arrival directions for the highest energy
cosmic rays, the sources remain unidentified.
Accretion shocks in
galaxy clusters have been proposed as potential sources in the past. These immense shock waves, which can have radii on the order of megaparsecs, are generated by the infall of material from the intergalactic medium into the gravitational potential wells of
galaxy clusters. In this work, we investigate the possibility that ultrahigh-energy
cosmic rays are accelerated in these regions. Nearby massive
galaxy clusters, including Virgo, are treated as a discrete component of the cluster mass distribution. Less massive
galaxy clusters, as well as distant massive ones, are assumed to follow a continuous distribution in agreement with cluster mass statistics. We fit the flux at Earth and the composition profile measured by the Pierre Auger Observatory, assuming the injection of different
nuclear species by these sources, to determine the values of the model parameters. Our results indicate that
cosmic ray acceleration in cluster
accretion shocks may account for at least a fraction of the observed UHECR flux at energies below the suppression scale. At higher energies, direct acceleration from the thermal pool would be feasible only if local fluctuations create favorable conditions, such as
magnetic fields about an order of magnitude stronger than those typically expected in cluster
accretion shocks, or for particular shock normal-
magnetic field configurations.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Assessing astrophysical foreground subtraction in DECIGO using compact binary populations inferred from the first part of the LIGO-Virgo-KAGRA's fourth observation run
Takahiro S. Yamamoto
Detecting the
stochastic gravitational wave background (SGWB) from our Universe under the inflationary era is one of the primary scientific objectives of DECi-hertz Interferometer Gravitational wave Observatory (DECIGO), a space-borne gravitational wave detector sensitive in the 0.1Hz frequency band. This frequency band is dominated by the gravitational waves from inspiraling compact object binaries. Subtracting these signals is necessary to search for the
primordial SGWB. In this paper, we assess the feasibility of the subtraction of such binary signals by employing the population model inferred from the latest gravitational wave event catalogue of the LIGO-Virgo-KAGRA Collaboration. We find that the projection scheme, which was originally proposed by Cutler & Harms (2005), is necessary to reduce the binary signals to the level where DECIGO can detect the
primordial background.
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High Energy Astrophysical Phenomena
Resolution Dependence in Magnetohydrodynamic Simulations of Neutrino-Driven Core-Collapse Supernovae
Vishnu Varma and Bernhard Müller
We investigate the role of resolution and initial
magnetic field strength on core-collapse
supernovae in simulations of a non-rotating $13 \mathrm{M_\odot}$ progenitor. Specifically, we study the effect on shock revival, explosion dynamics, and the properties of the compact remnant. We run four models with different numerical grid resolutions with an initial central dipole field strength of $\mathord{\approx}10^{12}\, \mathrm{G}$. Two of those resolutions are also run with a weaker central
magnetic field of $\mathord{\approx}10^{10}\, \mathrm{G}$ . The shock revival time for all models is largely independent of resolution and initial
magnetic field strength, but we find higher explosion energies when the initial magnetism is stronger and at higher resolutions. We find that models with strong
magnetic fields have lower
neutrino luminosity and energies, due to a proto-
neutron star (PNS) that is deformed by the strong
magnetic fields. At higher resolutions,
magnetic fields are amplified more efficiently in the gain region and in the PNS via the small-scale dynamo. Although the strong
magnetic fields do not directly drive the explosion, they have a subsidiary impact on the explosion mechanism and compensate for the reduced
neutrino heating. Stronger
magnetic energies in the PNS also affect energy and angular momentum redistribution, leading to more extended and vigorous PNS convection zones at higher resolutions.
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Earth and Planetary Astrophysics
Possible favored Great Oxidation Event scenario on exoplanets around M-Stars with the example of TRAPPIST-1e
Adam Y. Jaziri, Nathalie Carrasco and Benjamin Charnay
The Great Oxidation Event (GOE), which marked the transition from an anoxic to an oxygenated atmosphere, occurred 2.4 billion years ago on Earth, several hundreds of millions of years after the emergence of oxygenic photosynthesis. This long delay implies that specific conditions in terms of biomass productivity and burial were necessary to trigger the GOE. It could be a limiting factor for the development of oxygenated atmospheres on inhabited
exoplanets. In this study, we explore the specificities of a terrestrial
planet in the habitable zone of an M
dwarf for a GOE. Using a 1D coupled photochemical-
climate model, we simulate the atmospheric
evolution of TRAPPIST-1 e, an Earth-like
exoplanet, exploring the effect of oxygen sources (biotic or abiotic). Our results show that the
stellar energy distribution promotes O3 production at lower O2 concentrations compared to Earth, and the ozone layer on TRAPPIST-1 e forms more efficiently. This lowers the threshold for atmospheric oxidation, suggesting that the GOE on TRAPPIST-1 e would occur quickly after the rise of oxygenic photosynthesis, up to 1Gyrs earlier than on Earth, and would reach O2 enabling oxygenic respiration and thus the development of animals. We may question whether this is a general behavior around several M-
stars. Furthermore, we discuss how the overproduction of ozone could make O3 detection possible using the James Webb Space
Telescope, providing a potential method to observe oxygenation signatures on
exoplanets in the near future. Previous studies predicted that for an Earth-like atmosphere O3 would require over 150 transits for detection, but our results show that significantly fewer transits could be needed.
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Instrumentation and Methods for Astrophysics
Photoexcitation spectroscopy of highly charged ions for application to astronomy using a compact electron beam ion trap (EBIT) at the synchrotron radiation facility SPring-8
Leo Hirata, Yuki Amano, Moto Togawa et al. (+6 more)
In the past few decades, X-ray astronomy satellites equipped with grating spectrometers and microcalorimeters have enabled high-resolution spectroscopic observations of astrophysical objects. The need for accurate atomic data has arose as we attempt detailed analysis of the high-resolution spectra they provide. This is because current spectral models, which heavily rely on theoretical calculations, entail non-negligible uncertainties. We employ a
plasma spectroscopy device called electron beam ion trap (EBIT) to experimentally obtain precise atomic data. An EBIT with a design that allows combined operation with synchrotron radiation facilities was developed based on the Heidelberg Compact EBIT and installed at ISAS/JAXA for this purpose. We conducted a spectroscopic experiment using the JAXA-EBIT at the synchrotron radiation facility SPring-8, and successfully obtained high-resolution spectra of the L$\alpha$ resonance transition of Ne-like Fe$^{16+}$ ions, 3C, as well as the K$\alpha$ resonance transition of He-like O$^{6+}$ ions. We also measured another Ne-like Fe$^{16+}$ L$\alpha$ resonance transition, 3G, and constrained an upper limit of the oscillator strength ratio of 3G to 3C, using our experimental results. The experimental values obtained in this study will be applied to observational studies of astrophysical objects as a part of the
plasma spectral modeling.
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All authors Leo Hirata, Yuki Amano, Moto Togawa, Hiroyuki A. Sakaue, Nobuyuki Nakamura, Makoto Sawada, Hiromasa Suzuki, Masaki Oura, Hiroya Yamaguchi
Astrophysics of Galaxies
The Most Luminous H$\beta$ Reverberation Mapping of E1821+643 Indicates the Lower Boundary of the Radius-Luminosity Relation
Sha-Sha Li, Hai-Cheng Feng, Jiancheng Wu et al. (+5 more)
The radius-luminosity ($R_{\rm BLR}$-$L_{5100}$) relation is fundamental to active
galactic nucleus (AGN) studies, enabling supermassive black hole (SMBH) mass estimates and AGN-based cosmology applications. However, its high-luminosity end remains poorly calibrated due to insufficient reliable reverberation mapping (RM) data. We present a four-year RM campaign of the luminous
quasar E1821+643 using the Lijiang 2.4-m
telescope, supplemented by archival multi-wavelength data. E1821+643 is the most luminous AGN with an \hb\ RM measurement to date. The measured time lag of $83.2_{-18.7}^{+17.5}$ days is a factor of 5.6 shorter than predicted by the canonical $R_{\rm BLR}$-$L_{5100}$ relation. By compiling the full \hb\ RM sample, we find that such deviation defines a lower envelope ($0.2R_{\rm BLR}$) of measured lags across the entire luminosity range, while the upper envelope lies near $2R_{\rm BLR}$, implying that the scatter for individual AGNs can reach 1 dex. Spectral decomposition reveals two distinct \hb\ components: a core component with a lag of $267.0_{-17.6}^{+16.6}$ days closer to the $R_{\rm BLR}$-$L_{5100}$ relation, and a redshifted tail with a much shorter lag of $-49.0_{-34.5}^{+50.5}$ days. The short-lag component not only accounts for the significantly shortened overall lag, but also leads to an opposite interpretation of the intrinsic BLR kinematics. These effects can introduce systematic uncertainties in black hole mass estimates by factors of up to tens. Our findings demonstrate that shortened lags in high-
accretion-rate AGNs arise from multi-component BLR structures, posing substantial challenges to single-epoch mass estimates and impacting SMBH demographics and cosmological applications.
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All authors Sha-Sha Li, Hai-Cheng Feng, Jiancheng Wu, J. M. Bai, H. T. Liu, Kai-Xing Lu, Mouyuan Sun, Jian-Guo Wang
High Energy Astrophysical Phenomena
Revisiting a Quasar Microlensing Event Towards AGN~J1249+3449
Mario Cazzolla, Francesco De Paolis, Antonio Franco et al. (+1 more)
The gravitational wave event GW190521 seems to be the only BH merger event possibly correlated with an electromagnetic counterpart, which appeared about 34 days after the GW event. This work aims to confirm that the electromagnetic bump towards the Active
Galactic Nucleus (AGN) J1249+3449 can be explained within the framework of the gravitational microlensing phenomenon. In particular, considering the data of the Zwicky Transient Facility (ZTF), what emerges from a detailed analysis of the observed light curve using three fitting models (Point Source Point Lens, Finite Source Point Lens, Uniform Source Binary Lens) is that the optical bump can be explained as a microlensing event caused by a lens with mass {$\sim\,$0.1 $M_{\odot}$}, lying in the host
galaxy of the AGN in question.}
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All authors Mario Cazzolla, Francesco De Paolis, Antonio Franco, Achille Nucita
Astrophysics of Galaxies
Chemical study of two starless cores in the B213/L1495 filament
L. Moral-Almansa, A. Fuente, M. Rodríguez-Baras et al. (+7 more)
The chemical
evolution of pre-
stellar cores during their transition to a protostellar stage is not yet fully understood. Detailed chemical characterizations of these sources are needed to better define their chemistry during
star formation. Our goal is to characterize the chemistry of the starless cores C2 and C16 in the B213/L1495 filament of the Taurus Molecular Cloud, and to understand how it relates to the environmental conditions and the evolutionary state of the cores. We made use of two complete spectral surveys at 7 mm of these sources, carried out using the Yebes 40-m
telescope. Derived molecular abundances were compared with those of other sources in different evolutionary stages and with values computed by chemical models. Including isotopologs, 22 molecules were detected in B213-C2, and 25 in B213-C16. The derived rotational temperatures have values of between $\sim$ 5 K and $\sim$ 9 K. A comparison of the two sources shows lower abundances in C2, except for l-C$_{3}$H and HOCO$^{+}$, which have similar values in both cores. Model results indicate that both cores are best fit assuming early-time chemistry, and point to C2 being in a more advanced evolutionary stage, as it presents a higher molecular hydrogen density and sulfur depletion, and a lower
cosmic-ray ionization rate. Our chemical modeling successfully accounts for the abundances of most molecules, including complex organic molecules and long cyanopolynes (HC$_{5}$N, HC$_{7}$N), but fails to reproduce those of the carbon chains CCS and C$_{3}$O. Chemical differences between C2 and C16 could stem from the evolutionary stage of the cores, with C2 being closer to the pre-
stellar phase. Both cores are better fit assuming early-time chemistry of t $\sim$ 0.1 Myr. The more intense UV radiation in the northern region of B213 could account for the high abundances of l-C$_{3}$H and HOCO$^{+}$ in C2.
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All authors L. Moral-Almansa, A. Fuente, M. Rodríguez-Baras, T. Alonso-Albi, G. Esplugues, D. Navarro-Almaida, P. Riviére-Marichalar, B. Tercero, A. Asensio Ramos, C. Westendorp Plaza
Instrumentation and Methods for Astrophysics
150 years of ground-based solar instrumentation at Meudon observatory (1876-2026)
Jean-Marie Malherbe
The Sun has been observed through a
telescope for four centuries. However, its study made a prodigious leap at the end of the nineteenth century with the appearance of photography and spectroscopy, then at the beginning of the following century with the invention of the coronagraph and monochromatic filters, and finally in the second half of the twentieth century with the advent of large ground-based
telescopes and space exploration. This article retraces the main stages of
solar instrumental developments in Meudon, from its foundation by Jules Janssen in 1876 to the present day, limited to ground-based or balloon instrumentation, designed in Meudon and installed there or in other places (Nan{\c c}ay, Pic du Midi, Canary Islands). The Meudon astronomers played a pioneering role in the history of
solar physics through the experimentation of innovative techniques. After the golden age of inventions, came the time of large instruments, studied in Meudon but often installed in more favourable sites, and that of space, in a framework of international collaboration, but this is not discussed here.
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Solar and Stellar Astrophysics
Dynamical Mass Loss at the End of TP-AGB stars
Yingzhen Cui, Song Wang, Xiangcun Meng et al. (+3 more)
The thermally pulsating asymptotic
giant branch (TP-AGB) phase plays a key role in the
evolution of low- to intermediate-mass
stars, driving mass loss that influences their final stages and contributes to
galactic chemical enrichment. However, the mechanisms behind mass loss, particularly at the end of AGB, are still not well understood. We aim to investigate the relationship between
stellar parameters and envelope dynamics during the TP-AGB phase, evaluating whether dynamical instabilities in the envelope can act as a possible mass-loss mechanism. We use hydrodynamics method in MESA to simulate the dynamical pulsations and resulting mass loss during the TP-AGB phase of a
star evolved from a 1.5 Msun zero-age main sequence. Our simulations reproduce the dynamical pulsation behavior of
stars during the TP-AGB phase, demonstrating that the envelope mass is a key factor governing pulsational properties. As the envelope mass decreases, both the pulsation period and radial amplitude increase, consistent with observational trends. For 1.5 Msun model, once the envelope mass declines to approximately 0.25 Msun, the model enters a regime of violent pulsations, potentially ejecting the remaining envelope within a few hundred years. We suggest that the instability can act as the dominant mass-loss mechanism in the end of the TP-AGB phase, marking a rapid transitional stage toward the post-AGB phase.
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All authors Yingzhen Cui, Song Wang, Xiangcun Meng, Jifeng Liu, Shuguo Ma, Weitao Zhao
Solar and Stellar Astrophysics
Inferring photospheric horizontal flows from multiple observations with SUVEL models
Quan Xie, Jiajia Liu, Robert Erdélyi et al. (+1 more)
Photospheric horizontal velocity fields play essential roles in the formation and
evolution of numerous
solar activities. Various methods for estimating the horizontal velocity field have been proposed in the past. Aiming at the highest available (and future) spatial resolution (10 km/pixel) observations, a new method the Shallow U-net models (SUVEL) based on realistic numerical simulation and machine learning techniques was recently developed to track the photospheric horizontal velocity fields. Although SUVEL has been tested on numerical simulation data, its performance on
solar observational data remained unclear. In this work, we apply SUVEL to the photospheric intensity observations from four ground-based
solar telescopes (DKIST, GST, NVST, and SST) with the largest available apertures, and compare the results obtained from SUVEL with the
Fourier local correlation tracking method (FLCT). Average correlation indices between granular regions and velocity fields inferred by SUVEL (FLCT) are 0.63, 0.81, 0.80, and 0.87 (0.00, 0.11, 0.16, and 0.10) for DKIST, GST, NVST, and SST observations. Higher correlation indices between the velocity fields tracked by SUVEL and granular patterns than FLCT reveal the superior performance of SUVEL, validating its reliability with respect to
solar observational data.
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All authors Quan Xie, Jiajia Liu, Robert Erdélyi, Yuming Wang
Instrumentation and Methods for Astrophysics · Cross-listed from physics.flu-dyn
AI-based separation of turbulence from coherent background flows in decaying hydrodynamic turbulence
Ji-Hoon Ha and Elena S. Volnova
Separating turbulent fluctuations from coherent large-scale background flows is a longstanding challenge in the analysis of numerical simulations and astronomical observations. Traditional approaches commonly rely on decomposition-based techniques such as
Fourier or wavelet filtering, which assume that a meaningful separation can be achieved through scale selection. In realistic flows, however, coherent motions and
turbulence often overlap across a broad range of scales and interact nonlinearly, making a unique separation inherently ambiguous. In this work, we investigate the robustness of an AI-based
turbulence-background separation approach using two-dimensional incompressible Navier-Stokes simulations of decaying hydrodynamic
turbulence. The simulations are initialized with a coherent background flow and divergence-free turbulent perturbations with a Kolmogorov-like spectrum and evolve without external forcing, providing a controlled physical testbed. A neural network trained exclusively on static synthetic images is applied to simulation snapshots at different evolutionary stages. The model recovers turbulent fluctuations during early and intermediate stages when partial scale separation is present. At later stages, where nonlinear interactions increasingly mix coherent and turbulent structures, the separation becomes less distinct; nevertheless, the recovered fields remain visually and spectrally consistent with the expected turbulent behavior. Quantitative comparisons with a
Fourier filtering baseline show that the AI-based approach achieves comparable reconstruction accuracy while not requiring an explicit spectral cutoff scale. These results suggest that AI models trained on static data can provide a flexible diagnostic tool for
turbulence-background separation in time-evolving flows, with potential applications to astrophysical
datasets.
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Astrophysics of Galaxies
In-depth analysis of bar formation mechanisms of disk galaxies in halos of different concentrations
T. Worrakitpoonpon
We use $N$-body simulations to investigate the distinct bar formation processes in disks residing in
halos of various concentrations. In a highly concentrated
halo, the bar development is limited by the dominant multi-arm modes as a result of the swing amplification in the early stage. Only after the multi-arm modes decay, the bar growth proceeds mechanically owing to the particle trapping in continuation of that bar seed. In this scheme, the corotation resonance of the bar modes does not come into play at all, justified by a low amount of disk-
halo angular momentum transfer and a modestly decreasing bar pattern speed. On the other hand, although reducing the
halo concentration suggests the reduction of the preferred swing-amplified modes to be bi-symmetric, the bar formation in a lowly concentrated
halo does not involve the swing amplification at all. Rather, the fast-growing linearly unstable bar modes of a single uniform frequency is solely the governing factor, attributed to a mild shearing. The bar modes trigger the corotation resonance since the beginning and such resonance is maintained until the end, which leads to a high amount of angular momentum transfer and a fast slowdown. For the intermediate
halo concentration, the kinematical analyses of multiple non-axisymmetric modes suggests that the linear modes, the swing amplification, and the particle trapping are all present in the
evolution chronology. To specify bars formed in the different
halo concentrations, full analyses of the isophotal shape, the radial
Fourier amplitude, and the resonance diagram can be of use.
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Astrophysics of Galaxies
JWST Spectroscopic Census of ALMA Faint Submillimeter Galaxies in the Hubble Ultra Deep Field
Tomokazu Kiyota, Masami Ouchi, Daisuke Iono et al. (+6 more)
We present a JWST/NIRSpec rest-frame optical spectroscopic census of ALMA 1-mm continuum sources in the Hubble Ultra Deep Field (UDF) identified by the deep ALMA UDF and ASPECS programs. Our sample is composed of the ALMA flux-limited ($S_{1\,\mathrm{mm}}\gtrsim 0.1\,\mathrm{mJy}$) sources observed with medium-resolution NIRSpec spectroscopy from JADES and SMILES, 16 faint submillimeter
galaxies (SMGs) at spectroscopic
redshifts of $z\sim 1$-$4$. These SMGs show bright longer-wavelength optical lines (H$\alpha$, [N II]$\lambda\lambda6548,6583$, and [S II]$\lambda\lambda6717,6731$) and faint shorter-wavelength optical lines (H$\beta$ and [O III]$\lambda\lambda4959,5007$) with a large nebular attenuation, $E(B-V)\sim0.3$-$1.8$. We test the SMGs using BPT diagnostics and Chandra X-ray fluxes, and find that most SMGs are classified as AGNs; the AGN fraction is $\sim80\%$ for the SMGs at $M_*>10^{10.5} M_\odot$. We find only one SMG ($<10\%$) with a broad Balmer line, indicating that the SMGs are predominantly obscured AGNs. With the optical lines, we estimate the
metallicities of the SMGs to be moderately high, $\sim0.4$-$2 Z_\odot$, exceeding the model-predicted
dust-growth critical
metallicity ($\sim0.1$-$0.2Z_\odot$), which naturally explains the dusty nature of the SMGs. Interestingly, the SMGs fall in the mass-
metallicity relation and the
star-formation main sequence, showing no significant differences from other high-$z$
galaxies. Similarly, we find electron densities of $n_e\sim10^2$-$10^3\,\mathrm{cm}^{-3}$ for the SMGs that are comparable with other high-$z$
galaxies. Together with the high SMG fraction ($\sim 100\%$) at the massive end ($M_*>10^{10.5} M_\odot$), these results indicate that the SMGs are mostly not special, but typical massive
star-forming
galaxies at high
redshift.
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All authors Tomokazu Kiyota, Masami Ouchi, Daisuke Iono, Seiji Fujimoto, Kotaro Kohno, Yoshihiro Ueda, Kimihiko Nakajima, Moka Nishigaki, Hidenobu Yajima
High Energy Astrophysical Phenomena
Neuro-Parametric Spectral Classification of Black Hole and Neutron Star X-ray Binary Systems
Akash Garg, Aman Kumar, Ajit Kembhavi et al. (+5 more)
We perform the classification of black hole and
neutron star X-ray binary systems using deep neural networks applied to archival RXTE X-ray spectral data. We first construct two neural network models: one trained using only spectral flux values and another trained using both fluxes and their associated errors. Both models achieve high classification accuracies of ~90-94 %. To gain physical interpretability of these networks, we fit all spectra with a simple phenomenological model consisting of a thermal disk component and a power-law. From this analysis, we identify the blackbody temperature, power-law index, the ratio of blackbody to power-law flux, the reduced $\chi^2$, and the variance of the data as key parameters that likely contribute to the classification. We validate this inference by designing an additional neural network trained exclusively on this reduced parameter set, without using the spectral data directly. This parameter-based model achieves a classification accuracy comparable to that of the spectral models. Our results show that deep neural networks can not only classify compact objects in X-ray binaries with high accuracy but can also be interpreted in terms of physically meaningful spectral parameters derived from conventional X-ray spectral analysis. This framework offers a promising, mission-agnostic approach for compact object classification in current and future X-ray surveys.
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All authors Akash Garg, Aman Kumar, Ajit Kembhavi, Ranjeev Misra, Aniruddha Kembhavi, N. S. Philip, Rohan Pattnaik, Shreya Watwe
Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
Sub-ion scale current sheets in kinetic Alfvén wave turbulence
Johan Sharma, Ch Akshath Kumar, Kirit D. Makwana et al. (+2 more)
3D kinetic particle-in-
cell (PIC) simulations are performed using the kinetic Alfvén wave (KAW) eigenvector relations from a two-fluid model as initial conditions, in order to study turbulent fluctuations and intermittent structures at sub-ion and electron scales. Simulations with different ion-to-electron mass ratios are set up to investigate the role of electron scales in the formation of intermittent structures. We analyze the current sheet structures that develop in these simulations. Two
algorithms, namely Breadth-First Search (BFS) and Density-Based Spatial Clustering of Applications with Noise (DBSCAN), are employed to determine the thickness, length, and width of the current sheets, and both methods are found to yield consistent results. The average current sheet thickness scales inversely with the square root of the ion-to-electron mass ratio, with values close to the electron skin depth ($d_e$), indicating the presence of electron-scale current sheets in the simulations. The widths and lengths of the current sheets show a weaker scaling with the mass ratio. The scale-dependent kurtosis reveals enhanced intermittency at electron scales, consistent with magnetosheath observations. Distributions of scale-dependent properties of the current sheets also align with the electron skin depth of the different simulations and they lie within ranges observed in kinetic scale
solar wind
turbulence. This study reveals the nature of sub-ion-scale current sheets in KAW
turbulence and their role in dissipation.
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All authors Johan Sharma, Ch Akshath Kumar, Kirit D. Makwana, Tulasi N Parashar, Sruti Satyasmita
Earth and Planetary Astrophysics
Effects of Stellar X-ray Photoevaporation on Planetesimal Formation via the Streaming Instability
Xuchu Ying, Beibei Liu, Haifeng Yang et al. (+7 more)
The formation of planetesimals via the streaming instability (SI) is a crucial step in
planet formation, yet its triggering conditions and efficiency are highly sensitive to both disk properties and specific evolutionary processes. We aim to study the planetesimal formation via the SI, driven by the
stellar X-ray photoevaporation during the late stages of disk dispersal, and quantify its dependence on key disk and
stellar parameters. We use the DustPy code to simulate the
dust dynamics including coagulation, fragmentation, and radial drift in a viscously accreting disk undergoing
stellar X-ray photoevaporation.
Stellar X-rays drive the disk dispersal, opening a cavity at a few au orbital distance and inducing the formation of an associated local pressure maximum. This pressure maximum acts as a trap for radially drifting
dust, therefore enhancing the
dust density to the critical level required to initiate the streaming instability and the subsequent collapse into planetesimals. The fiducial model produces 31.4 M_\oplus of planetesimals with an initial
dust to final planetesimal conversion efficiency of 20.4%. This pathway is most efficient in larger disks with higher
metallicities, lower viscosities, higher
dust fragmentation threshold velocities, and/or around
stars with higher X-ray luminosities. This work demonstrates that
stellar X-ray photoevaporation is a robust and feasible mechanism for triggering planetesimal formation via the SI during the final clearing phase of protoplanetary disk
evolution.
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All authors Xuchu Ying, Beibei Liu, Haifeng Yang, Joanna Drazkowska, Sebastian M. Stammler, Zhaohuan Zhu, Linn E.J. Eriksson, Hongping Deng, Bin Liu, Ping Chen
High Energy Astrophysical Phenomena
Mia Kumamoto and Catherine Welch
Neutrino interactions play a central role in transport and
flavor evolution in the ejecta of binary
neutron star mergers. Simulations suggest that
neutron star mergers may produce
magnetic fields as strong as $10^{17}$ G, but computational difficulties have hampered the inclusion of
magnetic field effects in
neutrino interaction rates. In this paper we give approximate interaction rates for
neutrinos in the presence of strong
magnetic fields, including the effects of Landau quantization and anomalous
magnetic moments with errors of order $\sqrt{T/M}$. We also comment on a
neutrino production channel from individual
neutrons that can produce low-energy $\nu \bar{\nu}$ pairs even at low density.
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