Solar and Stellar Astrophysics
Evidence for elemental diffusion in the eclipsing binary star AI Phoenicis
Pierre F. L. Maxted, Nicholas Storm, Andreas J. Korn et al. (+7 more)
AI Phe is an eclipsing binary
star with an orbital period of 24.6 days for which the surface
gravity and effective temperature are known from direct measurements to very high precision and accuracy. We have obtained high-quality spectroscopy of the K0IV
star during the total eclipse of the F7V companion, and also obtained spectra with a very high signal-to-noise ratio for this
star and its F7V companion using the spectral disentangling technique. We have used these spectra to measure the abundances of iron and magnesium for both
stars. We compare the values of [Fe/H] and [Mg/H] for the F7V
star and the K0IV
star to
stars in M67, an open cluster of similar age and
metallicity to AI Phe. We find that our [Fe/H] and [Mg/H] measurements clearly show the signature of elemental
diffusion in the F7V
star. This suggests that AI Phe can be used to test models of single
stars that include
diffusion and mixing of elements.
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All authors Pierre F. L. Maxted, Nicholas Storm, Andreas J. Korn, Marília Carlos, Matthew R. Gent, Sviatoslav B. Borisov, Paula Jofré, Maria Bergemann, Hans-Günter Ludwig, Nicola J. Miller
High Energy Astrophysical Phenomena
The Complete Catalog of Gamma-Ray Transients Observed by GRBAlpha & VZLUSAT-2 CubeSat Missions
Marianna Dafcikova, Jakub Ripa, Andras Pal et al. (+45 more)
We present the largest sample of gamma-ray transients observed by any CubeSat mission so far. Observations were acquired by a 1U CubeSat GRBAlpha, the smallest astrophysical space observatory, and a 3U CubeSat VZLUSAT-2. Both missions were technological pathfinders and carried a novel CsI scintillator-based detector read-out by silicon photomultipliers. They operated on Sun-synchronous low Earth orbits below 550 km for about four years; GRBAlpha between March 2021 and June 2025 while VZLUSAT-2 between January 2022 and November 2025. Despite being technological experiments, they observed over 300 gamma-ray transients including gamma-ray bursts (GRBs),
solar flares, soft gamma repeaters and one outburst from an X-ray binary. Among these are the two brightest GRBs ever observed, GRB 221009A and GRB 230307A, without saturation and GRBs at
redshifts up to z=4.2. GRBAlpha also contributed to the InterPlanetary Network. Regular monitoring of transients was demonstrated by a detection rate of two transients or one GRB a week and the shortest time between two subsequent detections of only 42 minutes. We show that a constellation of nanosatellites around the Earth would observe at least 60% of
Fermi/GBM GRBs with 5$\sigma$ significance and over 90% at 3$\sigma$ level. GRBAlpha and VZLUSAT-2 prove that routine monitoring of the gamma-ray sky can also be done by low-cost and quickly developed nanosatellite missions.
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All authors Marianna Dafcikova, Jakub Ripa, Andras Pal, Norbert Werner, Michaela Duriskova, Yasushi Fukazawa, Martin Kolar, Laszlo Meszaros, Filip Munz, Masanori Ohno, Lea Szakszonova, Hiromitsu Takahashi, Masato Yokota, Jean-Paul Breuer, Hsiang-Kuang Chang, Balazs Csak, Vladimir Daniel, Juraj Dudas, Marcel Frajt, Gabor Galgoczi, Peter Hanak, Filip Hroch, Chin-Ping Hu, Jan Hudec, Nikola Husarikova, Yuto Ichinohe, Jakub Kapus, Miroslav Kasal, Martin Koleda, Robert Laszlo, Chih-Hsun Lin, Tsung-Che Liu, Tsunefumi Mizuno, Kazuhiro Nakazawa, Hirokazu Odaka, Michal Pazderka, Ales Povalac, Maksim Rezenov, Martin Sabol, Kaustubha Sen, Miroslav Smelko, Petr Svoboda, Martin Topinka, Che-Chih Tsao, Tomas Urbanec, Ivo Vertat, Tomas Vitek, Chih-En Wu
Cosmology and Nongalactic Astrophysics
Comparing explicit likelihood and likelihood-free simulation-based inference for weak lensing cosmic shear
Simone Vinciguerra, Nicolas Martinet and Marco Gatti
Simulation-based inference (SBI) has become a major tool for extracting cosmological information from weak-
lensing (WL) surveys, particularly from non-Gaussian observables. We compare its two main paradigms: explicit likelihood inference (ELI), based on a Gaussian likelihood built from an emulator and covariance
matrix, and likelihood-free inference (LFI), which learns the likelihood directly from simulations using neural density
estimators. Using Gaussian random field mocks representative of the non-tomographic final Euclid data release, we analyse shear two-point correlation functions (shear-2PCFs), compressed with linear or non-linear methods, together with a fundamentally different map-level convolutional neural network (CNN) statistic, focusing on $\Omega_{\rm m}$ and $S_8$. We deploy posterior calibration diagnostics developed for LFI, including the test of accuracy with random points (TARP), showing that ELI becomes strongly miscalibrated under emulation inaccuracies or likelihood non-Gaussianity, whereas LFI remains well calibrated. These effects drive substantial disagreement between ELI and LFI, which largely vanishes once addressed. We further show that the compression scheme can significantly degrade ELI while leaving LFI largely unaffected. Although shear-2PCFs should capture all the information in Gaussian fields, finite compression and non-Gaussian likelihoods cause ELI constraints to differ by up to a factor of two from those inferred with the CNN, while the discrepancy drops to $\approx 30\%$ for LFI, underscoring the robustness of the deep-learning probe. Overall, our results indicate that in our simple setup, which neglects systematic biases, LFI provides a more robust and better-calibrated framework, while highlighting accurate non-Gaussian likelihood modelling and posterior calibration diagnostics as essential for future ELI analyses.
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Solar and Stellar Astrophysics
Probabilistic Stellar Age Estimation for Gaia XP Stars with NGBoost
Xiaokun Hou, Wenbo Wu, Gang Zhao et al. (+2 more)
Stellar age is a fundamental quantity for
Galactic archaeology, but reliable age estimation for large
stellar samples remains challenging. In this work, we develop an uncertainty aware NGBoost framework for
stellar age estimation using
Gaia XP-derived atmospheric parameters and chemical abundances. Different from the standard NGBoost model, we modify the loss function by incorporating the uncertainties of the training age labels. We further use a Monte Carlo strategy to quantify the influence of input-feature uncertainties on the predicted ages. The resulting model provides age estimates together with uncertainty estimates. Applying this framework to
Gaia XP
stars, we construct a
stellar age catalog containing 15,175,107
stars.
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All authors Xiaokun Hou, Wenbo Wu, Gang Zhao, Haining Li, Jingkun Zhao
Instrumentation and Methods for Astrophysics
gevolution 2.0: GPU-accelerated relativistic N-body simulations for cosmology
Julian Adamek and Øyvind Christiansen
High-performance computing is increasingly dominated by hardware acceleration using Graphics Processing Units (GPUs). To take advantage of this long-term trend, we implement a major overhaul of the parallelisation approach in the relativistic particle-mesh N-body code gevolution. The new version 2.0 of gevolution employs three layers of parallelisation: MPI for scalability on a distributed
memory system, shared
memory parallelisation on each MPI rank using OpenMP, and offloading all compute intensive tasks to GPUs using CUDA. The code also includes many new features that have been developed over the past years. We provide an overview of the code structure and show key performance
benchmarks. The public release of gevolution 2.0 can be found at https://github.com/gevolution-code/gevolution-2.0. We also release a GPU-ready version of the LATfield2 library which provides the parallelisation backend, available at https://github.com/gevolution-code/LATfield2.
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Solar and Stellar Astrophysics
Solar, Heliospheric and Ionospheric Physics: Pathfinders, Precursors and SKAO Perspective
Pietro Zucca, Rohit Sharma, Divya Oberoi et al. (+5 more)
The
Solar, Heliospheric and Ionospheric (SHI) Physics Science Working Group of the Square Kilometre Array Observatory (SKAO) addresses the full chain of
plasma processes linking the
solar corona to the terrestrial environment. This overview chapter synthesises 16 topical contributions to Advancing Astrophysics with the SKA-II, spanning the quiet and active
solar atmosphere, eruptive phenomena, heliospheric
turbulence and
solar-wind diagnostics, ionospheric science,
stellar-
solar connections, and the observational frameworks required to deliver these science goals. The primary focus is on the capabilities of Array Assembly 4 (AA4), the design baseline for both SKA-LOW (50-350,MHz) and SKA-MID (0.35-15.4,GHz), which together provide continuous spectral coverage, sub-arcsecond angular resolution, full-Stokes polarimetry, and sensitivity gains of an order of magnitude over existing facilities. From resolving fine-scale coronal heating events to mapping coronal mass ejection
magnetic fields and characterising multi-scale heliospheric
turbulence, SKAO will deliver transformative advances in
solar and space-weather science. We frame these contributions as a single end-to-end Sun-to-Earth system. We identify cross-cutting themes and gaps not fully addressed by individual chapters and outline the staged roadmap from early operations through to the full AA4 capability.
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All authors Pietro Zucca, Rohit Sharma, Divya Oberoi, Eduard Kontar, John Morgan, Peter Gallagher, Sven Wedemeyer, Biagio Forte
Cosmology and Nongalactic Astrophysics
Magnetically assisted primordial scalar perturbations: Scalar-Induced Gravitational Waves
Arko Bhaumik, Theodoros Papanikolaou and Anish Ghoshal
Primordial magnetic fields (PMFs) provide a well-motivated source of cosmological perturbations through their anisotropic stress and may leave observable imprints in both the scalar and tensor sectors. In this work, we study scalar metric perturbations sourced by a PMF evolving through a finite post-inflationary epoch characterized by a constant equation-of-state (EoS) parameter $w$. Working in a gauge-invariant framework, we derive the sourced
evolution equation for the Bardeen gravitational potential in a general constant-$w$ background. Our analysis indicates faster (slower) growth of PMF-sourced scalar perturbations on superhorizon scales for a stiffer $w>1/3$ (softer $w<1/3$) background compared to the marginal radiation-dominated scenario with $w=1/3$. We then derive the scalar-induced gravitational wave (SIGW) background induced at second order by the magnetically generated scalar perturbations. Our analysis indicates a narrow viable parametric region for a kination-like post-inflationary era and a nearly scale-invariant PMF that may give rise to a PMF-sourced SIGW signal dominating over the direct PMF-generated tensor background. Simultaneously, the induced tensor modes are found to be perturbatively small compared to the
magnetic sector, which, in turn, exerts negligible backreaction on the background. Interestingly enough, for an inflationary scale $H_{\rm inf}\sim10^3-10^9$ GeV and duration of reheating in $e$-folds $N_{\rm reh}\sim8-10$, the dominant PMF-sourced SIGW signal may be detectable by next-generation terrestrial and space-based interferometric GW detectors spanning the mHz$-$kHz frequency range.
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Astrophysics of Galaxies
Spatio-kinematical structure of the Galactic Nuclear Stellar Disk revealed in VLBI astrometry of circumstellar masers
Hiroshi Imai, Kohei Kurahara, Huib J. van Langevelde et al. (+2 more)
SKA-VLBI astrometry will enable us to measure up to thousands of three dimensional motions of OH masers associated with circumstellar envelopes (CSEs) of OH/IR
stars in the
Nuclear Stellar Disk (NSD) and sites of high mass
star formation in the Central Molecular Zone (CMZ) of the
Galactic Center (GC). It is expected that the spatio-kinematical distribution of those OH masers should indicate the existence of a ring structure in the NSD, which has formed as a result of outward propagation of
star-formation activities in the GC. This is likely visualized clearly by a group of OH/IR
stars, some of which should have
stellar pulsation periods of >400 days and the corresponding ages of <500 Myr, and some sites of ongoing
star formation. These OH/IR
stars should host 1612-MHz OH masers, some of which should become targets of huge-sample VLBI astrometry, in moderate accuracy, in SKA-MID Band 2 (~1.6 GHz). The data of maser source proper motions will exhibit a stream motion in the
stellar ring structure. Furthermore, the information of accurate distances (error <100 pc) of the maser sources are necessary to directly find the major-axis direction of a possible elliptical ring of
stars at ~8 kpc. These distances may be yielded through trigonometric parallaxes measurable in SKA-MID Band 5a (5–7 GHz) and/or photometric parallaxes derived from the pulsation period–luminosity relation of long period variable
stars hosting the maser sources.
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All authors Hiroshi Imai, Kohei Kurahara, Huib J. van Langevelde, Maria J. Rioja, Richard Dodson
High Energy Astrophysical Phenomena
Black hole spin-mass correlation and vector resonant relaxation in gaseous star clusters: the origin of GW231123?
Zacharias Roupas
During the formation of a
star cluster a
spin-mass correlation of
stellar black holes is generated as they grow via
accretion of the residual gas. Moreover, the black hole
spin tends to be anti-aligned with its orbital angular momentum in the cluster. We show that GW231123, reported by the LIGO-Virgo-KAGRA (LVK) collaboration, lies on our predicted high-mass, high-
spin plateau of the
spin-mass correlation with positive
Bayesian evidence over the LVK prior. Furthermore, vector resonant relaxation (VRR)
equilibrium is favored over the isotropic LVK prior in reproducing the distribution of the relative
spin tilt. The joint Bayes factor suggests strong evidence for the favored cluster models. GW231123 is thus consistent with our proposed channel that generates correlated black hole masses and
spins, and drives the
spins' orientations.
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Solar and Stellar Astrophysics
Fast and periodic propagating disturbances along coronal loops detected with EUI on board Solar Orbiter
A. Dolliou, S. Mandal, K. Barczynski et al. (+9 more)
Recent high-resolution observations from the
Solar Orbiter mission can help detect the indirect signatures of heating at the smallest scales. In this work we measure the properties and investigate the physical origin of propagating disturbances (PDs) in the intensity at the smallest resolvable scales with
Solar Orbiter/EUI along coronal loops. We used two sequences of EUI/HRIEUV at high spatial (down to 125 km per pixel) and temporal resolutions (5 s of cadence). We placed slits along 13 active region (AR) coronal loops. We measured the plane-of-sky (PoS) velocities and the intensity perturbation damping along the slits of PDs. We also measured the periodicity of PDs in one slit by using a
Fourier analysis. We report the detection of PDs that have high PoS velocities ranging between 500 and 2000 km/s (which we call "fast" PDs). They are only visible in the upper part of the coronal loops. The intensity increase associated with these fast PDs is on the order of 4% to 8% of the HRIEUV intensity, and we measured little to no damping of their intensity with distance. We also measured a peak in the
Fourier power spectra at 2 min above the 95% confidence limit that is associated with fast PDs. The fast PDs are detected in the same coronal loops as PDs with a lower PoS velocity (70 to 90 kms/s), which we refer to as "slow" PDs. Unlike the fast PDs, these slow PDs are only visible in the lower part of the coronal loop, and they show clear intensity damping. Slow PDs show properties consistent with slow magneto-acoustic modes or upflows. On the other hand, fast PDs cannot be explained by slow magneto-acoustic modes. Instead, they show properties consistent with fast flows induced by
magnetic reconnection, current sheet generated by propagating transverse oscillations, and fast magnetohydrodynamics modes or Alfvén waves.
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All authors A. Dolliou, S. Mandal, K. Barczynski, T. Van Doorsselaere, D. Berghmans, C. Froment, F. Auchère, P. Antolin, H. Eklund, Y. Zhu, E. Kraaikamp, C. Verbeeck
Astrophysics of Galaxies
Revealing a multi-zone circumnuclear dust response in UGC~11487 through phase-resolved WISE W1–W2 diagnostics
I.O. Izviekova, O.V. Kompaniiets and I.B. Vavilova
Mid-infrared (MIR)
flares provide a direct probe of
dust reprocessing in obscured
tidal disruption event (TDE) candidates when the primary optical or ultraviolet
flare is weak, missed, or strongly attenuated. We present a phase-resolved analysis of the WISE/NEOWISE W1-W2
evolution of the MIR-selected TDE candidate UGC 11487/WTP14adeqka over 2014-2024. We combine timing, colour, and flux diagnostics with phenomenological modelling, hydrodynamically motivated clumpy
dust-echo calculations, and an aperture-matched ultraviolet-to-
radio spectral energy distribution of the host. The decade-long
flare shows a delayed and broader W2 response, colour hysteresis, and cooling from approximately 900 K to 500-600 K. Positive-fluence centroids yield a preferred delay of $224 +/- 45$ d, corresponding to $0.188 +/- 0.038$ pc. The effective infrared luminosity peaks at approximately $3 x 10^{43}$ erg s$^{-1}$, and the integrated infrared energy is $(2.9-3.8) x 10^{51}$ erg. A single self-similar MIR response is strongly disfavoured, with Delta BIC = 281.7, while the preferred compact description is a two-component phenomenological model. Representative hydro-clumpy calculations reproduce the empirical diagnostics in a structured, multi-zone
dust-response scenario. The host is a moderately
star-forming isolated barred disc without a dominant persistent active
galactic nucleus component. These results support an obscured TDE-like
accretion transient reprocessed by structured circumnuclear
dust and show that phase-resolved WISE diagnostics can recover characteristic sub-parsec response scales in obscured
accretion-powered
nuclear transients.
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Instrumentation and Methods for Astrophysics
DESTINY: a new binding-energy-resolved astrochemical framework. Self-Consistent Competitiveness using Branched Absorbing Markov Chains
Maria Groyne, Cedric Baijot and Michaël De Becker
Under cryogenic interstellar conditions, the amorphous structure of interstellar ice results in binding-energy distributions (BEDs) per species. However, only few studies attempted their inclusion in astrochemical models. This paper introduces DESTINY, a deterministic astrochemical framework designed to incorporate BEDs while self-consistently accounting for the competition among activated surface processes. The framework is currently constrained to a monolayer. Surface processes initiated by surface species are reformulated using a trial-frequency-capped formalism represented through branched absorbing Markov chains. The ordinary differential equations (ODE) system is redefined based on normalized effective probabilities. Preliminary results based on a reduced surface network are discussed. To isolate the effects of the probabilistic reformulation from those induced by BED discretizations, DESTINY is benchmarked against Nautilus, a single-BE rate-equation based open source code. In the single-BE limit, DESTINY reproduces the behavior of Nautilus for most species. The largest deviations are obtained for CH$_{x = [2,4]}$ ; these are traced to a different treatment of the H$_2$ encounter effect, impacting both H$_2$ surface exploration and desorption efficiencies within the DESTINY framework. Introducing BEDs redistributes species among adsorption sites of different depths, altering the balance between
diffusion, desorption, and reactions. Significant effects are found for H, H$_2$, NH$_x$, NO, CH$_x$, CO and H$_x$CO. Preliminary results showed that the self-consistent treatment of the H$_2$ encounter effect coupled with the explicit treatment of BEDs can substantially modify grain-surface chemistry. Further framework extensions are expected in the near future.
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Cosmology and Nongalactic Astrophysics
Intracluster light and dark matter halo shapes reflect common assembly, not mutual coupling: shape correspondence in CDM but not SIDM
G. Martin, N. A. Hatch, W. Cui et al. (+8 more)
The intracluster light (ICL) has been proposed as a luminous tracer of the dark matter (DM)
halo shape in
galaxy clusters, with recent observational studies and $\Lambda$CDM simulations suggesting close
alignment between the two components. We test whether this correspondence holds in a self-interacting dark matter (SIDM) cosmology using matched CDM and SIDM ($\sigma_\mathrm{DM}/m = 0.1$ and $0.5\;\mathrm{cm^{2}\,g^{-1}}$) hydrodynamical cluster simulations from TheThreeHundred project. We measure 3D axis ratios and major-axis orientations as a function of radius for both the DM
halo and the
stellar (BCG+ICL) distribution, and quantify the spatial correspondence using the Weighted Overlap Coefficient. In the SIDM simulations, DM
haloes become significantly rounder in their inner regions with increasing DM cross-section, while the
stellar distribution retains the same elongated morphology in both CDM and SIDM. This decoupling is robust across two baryonic physics models and two resolution levels, and is detected at $>5\sigma$ for $\sigma_\mathrm{DM}/m = 0.5\;\mathrm{cm^{2}\,g^{-1}}$. It arises because the
stellar shape is governed by the
accretion geometry of tidally stripped satellites along the large-scale structure, which is identical in CDM and SIDM, whereas, in SIDM,
halo shapes respond additionally to local self-interactions. The ICL-DM shape correspondence demonstrated in CDM therefore breaks down in an SIDM universe.
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All authors G. Martin, N. A. Hatch, W. Cui, A. Fernandez, Y. M. Bahé, M. S. Fischer, M. Montes, F. R. Pearce, C. G. Sabiu, G. Yepes, J. Yoo
Astrophysics of Galaxies
Testing [O II] $\lambda3727$ as a Star Formation Rate Tracer in Quasar Host Galaxies
Xiaotong Feng, Xue-Bing Wu, Yuming Fu et al. (+3 more)
The [O II] $\lambda3727$ emission line is a widely used
star formation rate (SFR) tracer. However, its application to type I
quasars is not straightforward, because the line can be affected by
dust extinction,
metallicity and contamination from the AGN narrow-line region (NLR). We test the reliability of [O II] SFRs using a sample of 202 SDSS and PG
quasars, by comparing [O II] SFRs and reference far-infrared (FIR) SFRs derived from multiwavelength SED decomposition. We measure [O II], [O III], and narrow Balmer emission lines by spectral fitting. Then, we calculate [O II] SFRs after correcting
dust extinction and
metallicity. We then compare these SFRs with the FIR SFRs, both with and without subtracting the AGN contribution estimated from [O III]. After this correction, the median offset between [O II] and FIR SFRs is $-0.20\pm0.72$ dex for the full analysis sample and $-0.17\pm0.69$ dex for sources with S/N $>5$ in both [O II] and [O III]. Without subtracting the AGN contribution, the corresponding offsets are $0.00\pm0.69$ and $0.12\pm0.66$ dex. We conclude that [O II] is useful as a statistical SFR tracer for
quasar host
galaxies, but individual objects still require careful treatment of AGN contamination, extinction,
metallicity, aperture effects, and
redshift-dependent systematics.
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All authors Xiaotong Feng, Xue-Bing Wu, Yuming Fu, Yuxuan Pang, Rui Zhu, Huimei Wang
Solar and Stellar Astrophysics
Binary White Dwarfs as Gravitational Wave Sources for LISA
Sreeta Roy, Surajit Kalita, Tomasz Bulik et al. (+1 more)
Gravitational waves (GWs) have proven to be a powerful probe of compact binary populations. In the millihertz frequency range accessible to
Laser Interferometer Space
Antenna LISA, binary white
dwarfs (BWDs) are expected to constitute a dominant source, forming both individually resolvable signals and an unresolved
Galactic background. In this work, we construct a Milky Way like population model and calculate the GW background from unresolved
Galactic BWD in the LISA sensitivity range, with particular emphasis on exploring and constraining uncertainties in binary
stellar evolution. We employ COMPAS binary population synthesis framework to generate synthetic populations of BWD in the Milky Way. Various physically motivated
evolution prescriptions and initial model parameters are used to study diverse population of BWDs. From these populations, we construct the GW background and investigate the dependence of the background spectrum on the assumptions on binary analysis. We discuss the possibility of constraints on binary
evolution that LISA GW observations may yield. We find that the shape and amplitude of the background are sensitive to key binary
evolution parameters like common envelope
evolution and mass-transfer efficiencies. Variations in these assumptions lead to measurable differences in the predicted background spectrum. Our results demonstrate that LISA observations of the unresolved BWD background have the potential to constrain binary
evolution models. This highlights the importance of GW background modelling as a complementary tool for studying the formation and
evolution of compact binaries in the Milky Way.
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All authors Sreeta Roy, Surajit Kalita, Tomasz Bulik, Dorota Gondek-Rosińska
Astrophysics of Galaxies
Structural and dynamical properties of Tidal dwarf galaxies in the tails and bridge of the Guitar galaxy Arp 105
Jyoti Prakash and Kanak Saha
We present a multi-wavelength (far-ultraviolet to infrared) analysis of two
tidal dwarf galaxy (TDG) candidates and a
tidal bridge in the interacting system Arp 105 at $z = 0.029$ in the Abell 1185 cluster. Far-ultraviolet observations obtained with the Ultraviolet Imaging
Telescope onboard AstroSat reveal strong FUV emission from the
tidal galaxies Arp~105N and Arp~105S, indicating recent
star formation. In Arp~105N, strong nebular emission lines and large equivalent widths $EW(H\alpha)=77.6\pm1.3$ $\overset{\circ}{\mathrm {A}}$ and $EW(H\beta)=15.8\pm1.7$ $\overset{\circ}{\mathrm {A}}$ imply a dominant starburst age of $\sim$6 - 10~Myr under an instantaneous-burst assumption, while the FUV emission suggests
star formation sustained over the past $\sim100 - 200$~Myr. The relatively high
metallicity, $\sim2/3,Z_\odot$ (based on the strong-line method), is consistent with expectations for a
tidal dwarf galaxy formed from material inherited from the host
galaxy. Together, these results suggest that Arp~105N hosts a composite
stellar population, consisting of older
stars stripped from the host
galaxy and younger
stars formed in situ. Spectral energy distribution modeling yields
stellar masses of $5.75\times10^{9}$, $0.8\times10^{9}$, and $6.8\times10^{9},\rm M_\odot$ for Arp~105N, Arp~105S, and the
tidal bridge, respectively. Based on the dynamical mass estimate from VLA HI measurements for Arp~105N and based on CFHT H$\alpha$ kinematics for A105S, they have a dynamical-to-baryonic mass ratio of $\sim1.95$ and $\sim1.30$, respectively, indicating a deficiency of dark matter. Further observations, particularly integral field spectroscopy and high-resolution 21~cm observations, may provide better constraints into the kinematics and improve understanding of TDG formation.
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Astrophysics of Galaxies
The stability of radially anisotropic rotating stellar systems with a central density cusp
Pierfrancesco Di Cintio and Anna Lisa Varri
We investigate the interplay between radial velocity anisotropy and internal rotation in self-gravitating systems characterised by initial spherical
symmetry and a moderate density cusp. We study the stability properties of such configurations to disentangle the impact of anisotropy, rotation, and density structure on the formation of triaxial
stellar systems. We perform a set of collisionless $N$-body simulations starting from initial
equilibria with a phase space distribution function of the class introduced by Osipkov and Merritt, modified to impose a net global angular momentum with the Lynden-Bell daemon protocol. We analyse the growth of the density and phase space distribution modes, as well as the axial ratios and triaxiality index of the final configurations. We find that internal rotation has a mitigating effect on the strength of the radial orbit instability in radially anisotropic models with \mbox{Fridman-Polyachenko-Shukhman} anisotropy index close to the consistency limit, while it slightly enhances the onset of the instability in marginally stable models. From the analysis of the growth rate of the density modes, we also find that an inner bar, which for maximally rotating initial conditions declines after its initial growth, is formed even in systems with initial profiles with a central density cusp.
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Astrophysics of Galaxies
Far-Infrared Star Formation Rates of Quasar Host Galaxies from Multiwavelength Spectral Energy Distribution Decomposition
Xiaotong Feng, Xue-Bing Wu, Yuming Fu et al. (+3 more)
Reliable
star formation rates (SFRs) are essential for studying the connection between black hole growth and
quasar host
galaxies. We study the far-infrared (FIR) SFRs and the host
galaxy properties of 202 SDSS and PG
quasars at $0.02<z\lesssim0.8$, spanning $\log({\rm SFR}_{\rm FIR}/M_\odot\,{\rm yr}^{-1})\simeq-0.45$–$2.76$, using multiwavelength spectral energy distribution (SED) decomposition. The photometry covers wavelengths from the optical to the FIR and is supplemented by JCMT/SCUBA-2 observations at 450 and 850 $\mu$m. We model the SEDs with CIGALE and AGNfitter and adopt multiple cold
dust templates to quantify systematic uncertainties. The median model-dependent scatter among the five FIR SFR estimates is $0.14$ dex, and AGNfitter gives FIR SFRs lower than the mean CIGALE estimate by a median of $0.09$ dex. For the 58
quasars with SCUBA-2 coverage, including SCUBA-2 data changes the adopted FIR SFR by only $\sim$0.01 dex on average but can affect individual sources with limited Herschel coverage or
radio-loud emission. Within our FIR-constrained sample, many
quasar hosts lie on or above the
star-forming main sequence, but the
redshift-dependent FIR selection of the SDSS subsample limits conclusions about the full
quasar-host population. We find no clear correlation between the main-sequence (MS) offset and the direct Eddington ratio, while the offset is positively related to the infrared-based $L_{\rm tor}/L_{\rm Edd}$ proxy. The minimum radiation field intensity in the
dust model, $U_{\rm min}$, increases with bolometric luminosity and
dust temperature. WISE W2 (4.6 $\mu$m) and W3 (12 $\mu$m) combined with Herschel bands can also provide useful empirical indicators of $f_{\rm AGN}$.
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All authors Xiaotong Feng, Xue-Bing Wu, Yuming Fu, Yuxuan Pang, Rui Zhu, Huimei Wang
Astrophysics of Galaxies
Two Peas in a Pod: The First Confirmed Dual Active Galactic Nucleus within a Green Pea Galaxy System
Konstantinos Kouroumpatzakis, Peter G. Boorman, Jiří Svoboda et al. (+5 more)
The growth of
galaxies in the early Universe is thought to be dominated by compact, intensely
star-forming systems, yet the corresponding growth of supermassive black holes (SMBHs) within such environments remains poorly constrained. Green Pea
galaxies are nearby analogs of rapidly assembling
galaxies in the early Universe owing to their compact morphologies, intense
star formation, low
metallicities, and extreme ionization conditions. Although
galaxy interactions are thought to trigger episodes of rapid SMBH growth, direct observations of simultaneous
accretion onto multiple SMBHs in compact, intensely
star-forming
galaxies are lacking. Here we report the discovery of the first confirmed dual active
galactic nucleus (AGN) in a Green Pea system, SDSS J162209.41+352107.5. Chandra imaging resolves two luminous hard X-ray sources separated by 8.4 kpc in projection, demonstrating simultaneous
accretion onto two SMBHs. Follow-up Keck spectroscopy confirms that the two optical
nuclei share a common
redshift and independently exhibit broad Balmer emission and high-ionization AGN emission lines. Unlike most known dual AGN, which are typically found in massive mergers, J162209.41+352107.5 is a compact low-mass system analogous to
galaxies thought to dominate early phases of
galaxy assembly. These findings demonstrate that efficient growth of multiple SMBHs can occur in such environments and establish Green Pea
galaxies as nearby laboratories for investigating the interplay between
galaxy interactions,
star formation, and black-hole growth under conditions analogous to those prevalent in the young Universe.
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All authors Konstantinos Kouroumpatzakis, Peter G. Boorman, Jiří Svoboda, Ryan Pfeifle, Abhijeet Borkar, Maitrayee Gupta, Daniel Stern, Andreas Zezas
Astrophysics of Galaxies
Feature-driven anomaly flagging in obscured active galactic nucleus light curves with autoencoders
Natale De Bonis, Demetra De Cicco, Stefano Cavuoti et al. (+5 more)
Active
galactic nuclei (AGN) are among the most complex classes of astrophysical objects, displaying a wide range of variability and observational properties. Identifying unusual AGN is crucial for understanding the physical mechanisms behind their emission better and for discovering potentially new subclasses or rare behaviors. With the increasing volume of data from next-generation surveys, machine-learning-based anomaly detection offers a promising approach to flagging and investigating such outliers systematically. We explore the use of unsupervised
algorithms with a feature-driven approach to flag anomalous AGN, further explored by a human expert. The main focus is on obscured AGN, which tend to be harder to characterize. The
algorithm we used was an AutoEncoder, which we trained on features extracted from the light curves rather than working with the light curves directly. The unsupervised nature of the method allows the detection of anomalies without relying on labeled data. To properly characterize the feature space and the detection process, we used the SHAP method. Our method flagged $11.18\%$ of the AGN we studied as anomalous. We focused in particular on anomalous obscured AGN and identified a refined subset of features that yields a comparable performance to the full set. Together with an in-depth analysis of the anomalies, this provides insight into how the AutoEncoder assigns anomalous status and which features are most indicative of astrophysically interesting behaviors or phenomena.
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All authors Natale De Bonis, Demetra De Cicco, Stefano Cavuoti, Ylenia Marruccia, Dragana Ilić, Andjelka B. Kovacević, Giuseppe Riccio, Simone Vaccaro
Cosmology and Nongalactic Astrophysics
Repulsive ultralight dark matter from Hosotani mechanism
Philippe Brax and Patrick Valageas
We build an ultralight dark matter model with repulsive self-interactions, starting from a 5D action that only includes a $U(1)$ gauge field and several massive and charged free
fermions. The dark matter scalar field corresponds to the fifth component of the gauge field, after compactification to 4D. Although the single-
fermion case only leads to attractive self-interactions, two
fermions can already give rise to repulsive self-interactions, thanks to a Scherk-Schwarz twist around the fifth dimension. We check the observational and theoretical self-consistency of this scenario, from the inflation stage to the current time. We find that large ranges of model parameters are allowed. For scalar masses below $10^{-12}$ eV the self-interactions are negligible and the model behaves as fuzzy dark matter. For higher masses the repulsive self-interactions govern the formation of
solitons of astrophysical size. Larger sizes require a large initial misalignment or small masses in the fuzzy dark matter regime.
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Solar and Stellar Astrophysics
Sloshing Oscillations in coronal loops excited by successive M- and C-Class flares
Hitesh Paliwal, S. Krishna Prasad and M. V. Sunil Krishna
Slow magnetoacoustic waves in hot coronal loops have remained a topic of considerable interest and debate over the past two decades. The periodic back-and-forth motion of
plasma within a coronal loop, often initiated by a
flare, is commonly referred to as sloshing oscillation. In the present study, we report unprecedented observations of sloshing oscillations in coronal loops excited by successive M- and C-class
flares, using data from the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO). A total of fifteen oscillation events were identified within seven distinct coronal loops, providing the rare opportunity to evaluate the influence of
flare strength on the characteristics of the oscillations. Based on the appearance of the oscillations, their properties were extracted mainly from the AIA 131 and 94 Å channels. Additionally, we estimate the deprojected length of each loop by assuming a semi-circular geometry. Our results indicate considerable changes in the properties of oscillations from one
flare to another, suggesting the role of individual
flares in shaping the local physical conditions. The
plasma temperature estimated from the loop length and oscillation period ranges from 9 to 31 MK. Additionally, we find that the damping times are not always longer in the colder 94 Å channel as previously observed. By combining the results obtained from all events, we study the inter-dependences between various parameters, including oscillation period, damping time, loop length, and
plasma temperature, and discuss these results in the context of the theory of slow waves.
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Solar and Stellar Astrophysics
Dual-Perspective Microwave and Hard X-ray Constraints of Asymmetric Nonthermal Loops in an X-class Flare
Ruifei Huang, Yao Chen, Victor Melnikov et al. (+9 more)
We report dual-perspective microwave and HXR observations of an X-class
flare on 2024 May 15, taking advantage of the unique geometry of a front-side view from the Earth and a back-side perspective from the
Solar Orbiter (SolO). Using spatially resolved imaging spectroscopy from Siberian Radioheliograph (SRH) together with Chashan Broadband
Solar millimeter spectrometer (CBSmm) and STIX data, we identify a set of nonthermal flaring loops in an asymmetric
magnetic field, with microwave sources located near the loop top and HXR sources associated with the southern footpoint. Compared with HXR, the microwave emission shows an opposite ascending trend, an increasing time lag in time profile, and a distinctive “SHH” spectral pattern, which we attribute to energy-dependent trapping and precipitation of energetic electrons in an asymmetric
magnetic configuration. Flux pulsations and their spectral and polarization signatures are consistent with intermittent particle acceleration rather than MHD wave modulation. Microwave
magnetic diagnostics, corroborated by non-linear force free field (NLFFF) extrapolation, provide key constraints on the three-dimensional
magnetic configuration. The dual-perspective flux profile comparison and consistent QPP signatures across wavelengths together support a self-consistent picture of energy-dependent electron trapping, precipitation, and transport in these asymmetric loops.
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All authors Ruifei Huang, Yao Chen, Victor Melnikov, Alexey Kuznetsov, Zhao Wu, Dmitriy Smirnov, Sergey Anfinogentov, Feiyu Yu, Xiangliang Kong, Ze Zhong, Mingzhe Guo, Hao Ning
Instrumentation and Methods for Astrophysics
The IRT Telescope on board the THESEUS mission
Diego Gotz, Aline Meuris, Eric Doumayrou et al. (+28 more)
We present the Infra-Red
Telescope (IRT), which is part of the payload of the THESEUS mission, one on the three phase A candidate missions for the M7 slot of ESA (launch date 2037). The IRT is a 0.7 m class
telescope with an off-axis Korsch optical design, with imaging capabilities in the 0.7-1.8 microns range over a 15 x 15 arc min field of view. The IRT also provides slit-less low resolution spectroscopy (R~400) over a limited field of view of 2 x 2 arc min, in the 0.8-1.6 microns range. The goal of the IRT is to identify the near infrared counterparts to the Gamma-Ray Bursts (GRBs) detected by the two other
telescopes on board THESEUS (the XGIS and the SXI), and to measure on board its photometric
redshift in near real-time. The position and the
redshift will be transmitted immediately to ground to allow for deeper follow-up by the large
telescopes (ELT, VLT, ...). If the source is bright enough, spectroscopy will be performed to characterize the GRB environment.
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All authors Diego Gotz, Aline Meuris, Eric Doumayrou, Dehbia Lattab, Frederic Pinsard, Samuel Ronayette, Thierry Tourrette, Herni Triou, Bortolino Saggin, Marco Giovanni Corti, Stefano Covino, Fabrizio Fornasiero, Luca Oggioni, Luca Terenzi, Stephane Basa, Enrico Bozzo, Ludovic Genolet, Lauro Conti, Mariachiara Celato, Paul Hedderman, Shaymaa Hussein, Christoph Tenzer, Karine Mercier, Lander Ruiz de Ocenda, Jean-Michel Le Duigou, Adrien Fort, Florent Robinet, Andras Peter Joo, Rebeka Kiss, Bendeguz Koncz, L. Viktor Toth
High Energy Astrophysical Phenomena
Time-dependent Accretion Disks in Tidal Disruption Events: Long-term Light Curves
Chenlei Guo and Erlin Qiao
The time-dependent
accretion disk has been applied to explain the light curves observed in
tidal disruption events (TDEs). Radiation pressure instability is expected to be an important factor that can shape the
evolution of the
accretion disk. In this paper, we upgrade the time-dependent disk model in Guo $\&$ Qiao by incorporating an index $\mu$ (with the stress tensor $\propto p^{\mu}p^{1-\mu}_{\rm{gas}}$, where $p=p_{\rm{gas}} + p_{\rm{rad}}$) for the modified viscosity, and a parameter $f_{\rm{w}}$ for the strength of the wind. Meanwhile, we adopt a more realistic fallback rate to inject into the disk. After systematically testing the effects of the newly incorporated parameters, we find that $f_{\rm{w}}$ can affect the time when the instability occurs, while $\mu$ can influence the occurrence and variation magnitude of the radiation pressure instability. When $\mu<0.4$, the radiation pressure instability is completely removed from the disk, and the light curves evolve stably without large-scale magnitude variation. When $\mu>0.4$, the light curves can show oscillations caused by the instability, or drop steeply when the instability occurs and become flat in the late-time
evolution, which mainly occurs when the viscous viscosity parameter $\alpha$ is small or the impact parameter $\beta$ is small. Since the drop magnitude can be modulated by $\mu$, we apply these `decay-to-flatten' light curves to some optical/UV observations in TDEs with different magnitudes of decline. Finally, we discuss the potential application of our model to some special TDEs that show oscillations in the light curves.
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Solar and Stellar Astrophysics
CW Cas: A solar-type contact binary system with an unseen third companion in a hierarchical quadruple system
Azizbek Matekov, Liying Zhu, Linjia Li et al. (+11 more)
We present a comprehensive multiband photometric and spectroscopic study of the G-type binary CW Cas whose parameters have not been well determined. Our double-lined spectroscopic radial velocity curve of this system yields a reliable mass ratio of $q = 1.88(9)$. By combining $BVR_{c}I_{c}$ bands, TESS light curves and radial velocity curves, we found that CW Cas is a W-subtype shallow contact binary with a fill-out factor of 15%. The components have masses of $0.98(6)M_{\odot}$ and $0.52(4)M_{\odot}$, separated by $2.25(5)R_{\odot}$. A notable asymmetry in the maxima of the light curves was detected and explained by a dark spot located on the surface of at least one component. Comparison of light curves from different years revealed that these dark spot activities exhibit cyclic variations with an approximate period of 1250 days. Orbital period analysis via O-C diagram spanning 125 years shows a long-term decrease superimposed with periodic oscillation caused by the light-travel-time effect (LTTE) due to a third body. This tertiary component has an orbital period of $P_{3} = 99.4(6)$ years and a minimal mass of $M_{3}=0.91(1)M_{\odot}$. The absence of detectable signatures for this massive object in either spectroscopic or photometric
datasets implies it must be a compact object such as a white
dwarf or
neutron star. Furthermore, a visual companion was identified based on
Gaia DR3 astrometric data, suggesting that CW Cas is part of a hierarchical quadruple system. As such, CW Cas represents a valuable laboratory for probing 2+1+1 hierarchical multiple system hosting compact object.
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All authors Azizbek Matekov, Liying Zhu, Linjia Li, Fangbin Meng, Nianping Liu, ShengBang Qian, Ergang Zhao, Mikhail Kovalev, Jiangjiao Wang, Yufei Chen, Aktam Hafizov, Soonthornthum Boonrucksar, Somsawat Rattanasoon, Shuhrat Ehgamberdiev
Earth and Planetary Astrophysics
Probing disk dynamics and dust evolution through shadows in protoplanetary disks: A case study of the HD 142527 disk
Yuya Fukuhara, Ryuta Orihara, Satoshi Okuzumi et al. (+1 more)
Planet formation begins with
dust growth and planetesimal formation within protoplanetary disks surrounding young
stars. To understand these processes, it is essential to estimate
dust grain sizes from disk observations. In this study, we develop a new method to constrain grain size based on the estimation of cooling timescales. Our approach applies to transitional disks that possess an inclined inner disk casting shadows on the outer disk, whose temperature variations serve as a tracer of
dust properties. By constructing a three-dimensional model of the disk surface using near-infrared scattering light images and comparing it with submillimeter
dust continuum maps, we estimate the spatial offset between the irradiated and shadowed regions to derive the cooling timescale. We then build an analytic model that calculates the cooling timescale at the
dust thermal emission height with an assumed turbulent
diffusion intensity to infer the
dust surface density and
dust grain size. Applying this method to the protoplanetary disk around HD~142527, we find that the disk's northern shadowed region cools on a timescale of a few percent of the orbital period and that the maximum grain size consistent with the observations is approximately 0.1-1 mm. We also find that the conditions required for the vertical shear instability, which needs a short cooling timescale, are satisfied, allowing
turbulence with an intensity consistent with near-infrared observations. This study demonstrates that estimating cooling timescales is an effective tool for constraining
dust grain size. Our approach can be generally applied to other transition disks with inner-disk-induced shadows.
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All authors Yuya Fukuhara, Ryuta Orihara, Satoshi Okuzumi, Takayuki Muto
Instrumentation and Methods for Astrophysics
Optimal mode-sorting coronagraphy: limits of single-moded measurements for the Habitable Worlds Observatory
Yinzi Xin, Sebastiaan Haffert and Rico Landman
Conventional coronagraph architectures struggle to reach the theoretical limit of
exoplanet detection at close working angles. Spatial mode-sorting is capable of reaching the theoretical limit, which previous work has calculated for a completely unresolved
star whose signal lies entirely in the fundamental piston mode of the
telescope. More recently, we have calculated optimized nulling modes as a function of the size of the
star and
planet parameters, with the goal of improving coronagraphic performance at ~l/D working angles given partially resolved
stars and complex
telescope apertures. In this work, we further explore the limits of a coronagraph involving the measurement of a single spatial mode, with potential applications for the infrared arm of the Habitable Worlds Observatory. We present the achievable single-channel 1 l/D
planet throughput as a function of the single-channel
stellar suppression (for a 0.03 l/D diameter
star), and show that the ability to measure a single optimized spatial mode can allow us to reach at least ~80% of the theoretical information limit.
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Astrophysics of Galaxies
On the Separation Between the Brightest Cluster Galaxy and the Intracluster Light
Emanuele Contini and Sukyoung K. Yi
We present a model-based framework to define an aperture separation between the brightest cluster
galaxy (BCG) and the intracluster light (ICL). Using the intrinsic BCG and ICL components predicted by the semi-analytic model FEGA25, we determine, for each
halo, the aperture radius that minimizes the bias in the recovered ICL mass. The optimal radius is obtained by balancing the BCG
stellar mass lying outside the aperture with the ICL mass enclosed within it. At $z=0$, the optimal aperture in physical units increases with
halo mass approximately as $r_{\rm cut}\propto M_{\rm halo}^{0.28}$, close to the expected virial scaling. When expressed in units of the virial radius, the aperture becomes nearly independent of
halo mass, with $r_{\rm cut}/R_{\rm vir}\simeq 0.045$ at $10^{14}M_\odot$. Applying the resulting aperture prescriptions, we recover the intrinsic BCG mass to better than 8% (lowest percentile), while the ICL mass is recovered with median values very close to unity, and an average scatter of $\pm 3\%$. Extending the analysis to $z=1$ and $z=2$, we find that the mass trends remain similar, with the slope and intercept of $r_{\rm cut}/R_{\rm vir}$ that stay stable. Robustness tests show that the inferred aperture is most sensitive to the ICL concentration and BCG size, but the main trends are preserved. Our results provide a physically motivated aperture definition for connecting observational BCG–ICL measurements to intrinsic model components.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Massive Compact Stars Beyond the General Relativity Limit in Finslerian Gravity: A Possible Explanation for the GW190814 Secondary
Praveen J, Rajesh Kumar, Sadaf Fatima et al. (+1 more)
The existence of an upper mass limit for compact
stars is one of the fundamental predictions of general relativity (GR), with important implications for the outcome of compact binary mergers and the nature of the proposed
neutron star black hole mass gap. The LIGO Virgo collaboration announced the discovery of a compact binary merger, GW190814, containing a compact
star with mass 2.5 to 2.67 $M_\odot$ [R. Abbott et al.(2020) ApJ Lett., 896, L44], which provided an exciting new stimulus to the ongoing debate on whether a gap exists between the maximum mass of NS and the minimum mass of black hole. Such GW detection has also challenged conventional
stellar models and renewed interest in exploring whether modified theories of
gravity can accommodate such ultra-massive compact objects without invoking black hole formation. The present work investigated the structure and physical properties of compact
stars within the framework of Finslerian
gravity, employing the Heintzmann IIa gravitational potentials and showed that the our model can substantially enhance the maximum mass of compact
stars upto $2.67 M_{\odot}$, thereby offering a plausible explanation for massive compact objects such as the secondary component of GW190814. In addition, the moment of inertia is found to increase, indicating stronger rotational support and a redistribution of the internal mass profile. The analysis focuses on key astrophysical observables, including the mass radius and moment of inertia mass relations, and a detailed comparison with the GR counterpart is performed. Assuming a linear equation of state, we construct a class of physically viable anisotropic
stellar models and analyze their behavior under the influence of Finslerian corrections. The physical viability of the model is rigorously tested through stability criteria.
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All authors Praveen J, Rajesh Kumar, Sadaf Fatima, S K Narasimhamurthy