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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 12 January

Astrophysics of Galaxies

Broad line regions behind haze: Intrinsic shape of Br$\gamma$ line and its origin in a type-1 Seyfert galaxy

Keiichi Wada, Tohru Nagao, Taro Shimizu et al. (+3 more)

The broad-line region (BLR) of active galactic nuclei (AGN) is an essential component, yet its small size keeps its origin, structure, and kinematics uncertain. Infrared interferometry with VLTI/GRAVITY is now resolving BLR-scale emission, with data for NGC 3783 consistent with a rotating, geometrically thick configuration. However, the processes shaping the spectra remain poorly constrained, and the cloud models are tuned phenomenologically rather than derived from first-principles predictions. We address this by coupling three-dimensional radiation-hydrodynamic (RHD) simulations of gas around a supermassive black hole with radiative-transfer calculations using Cloudy, comparing the results to the SINFONI Br$\gamma$ profile of NGC 3783. We find that Br$\gamma$ arises from ionized gas in the surface of the rotating thin disk, with electron temperatures of approximately $T_e \approx 10^4$ K and number densities of $n_e \approx 10^8-10^{11}$ cm$^{-3}$. However, the intrinsic line profile produced by the RHD kinematics is narrower than observed and displays substructure. An approximate treatment of the electron scattering suggests that scattering in surrounding diffuse ionized gas significantly broadens and smooths the intrinsic Br$\gamma$ profile, making it consistent with the observed profile. This scattering medium has an electron temperature of $10^4 - 10^5$ K, and a number density of $n \lesssim 10^8$ cm$^{-3}$. Although a best-fit viewing angle of $\approx 15$ deg is suggested, the scattered line is notably less sensitive to inclination than the intrinsic line. The observed BLR profiles may be understood as the intrinsic emission viewed through an electron-scattering haze, such that some spectral detail is plausibly redistributed rather than seen directly.
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All authors Keiichi Wada, Tohru Nagao, Taro Shimizu, Daryl Joe D. Santos, Jinyi Shangguan, Richard Davies

Astrophysics of Galaxies

The stellar initial mass function of nearby young moving groups

Rafael Bertolotto-Stefanelli, Juan José Downes, Genaro Suárez et al. (+3 more)

The solar neighbourhood is populated by nearby, young moving groups (NYMGs) of stars that are candidates to be remnants of individual stellar clusters and associations, currently dispersing in the galactic disc. To derive the initial mass function (IMF) of a large sample of NYMGs, we developed and applied an algorithm that uses photometry and astrometry from Gaia DR3 to detect NYMGs in a kinematic space. We inferred individual masses from the photometry of both the detected and the previously known candidates. We estimated the IMFs for 33 groups, 30 of them for the first time, in an average mass range $0.1<m/M_\odot<5$ with some groups going as low as $0.02~M_{\odot}$ and as high as $10~M_{\odot}$. We parameterized these IMFs using a log-normal for $m<1~M_\odot$ and a power-law for $m>1~M_\odot$. We detected 4166 source candidate members of 44 known groups, including 2545 new candidates. We recovered 44-54% of the literature candidates and estimated a contamination rate from old field stars of 16-24%. The candidates of the detected groups distribute along young isochrones, which suggests that they are potential members of NYMGs. Parameterizations of both the average of the 33 IMFs based on our detections ($m_c=0.25\pm0.17~M_{\odot}$, $\sigma_c=0.45\pm0.17$, and $\alpha=-2.26\pm0.09$) and the one based on the known candidates from the literature ($m_c=0.22\pm0.14~M_{\odot}$, $\sigma_c=0.45\pm0.17$, and $\alpha=-2.45\pm0.06$) are in agreement with the IMF parameterization of the solar neighbourhood and young stellar associations. Our parameterization of the average IMF together with the distribution of the detected group members along young isochrones provide strong evidence suggesting that the NYMGs are remnants of individual stellar associations and clusters and that there are no systematic biases in our detection and in the literature in the range $0.1<m/M_{\odot}<10$.
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All authors Rafael Bertolotto-Stefanelli, Juan José Downes, Genaro Suárez, Cecilia Mateu, Jonathan Gagné, Carlos Román Zúñiga

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

Chiroptical effect induced by gravitational waves

Haorong Wu and Xilong Fan

We propose the gravitational analog of the chiroptical effect for the first time, demonstrating that gravitational waves (GWs) can induce a reversal of photon chirality through the exchange of angular momentum, namely the spin-2-gravitation chiroptical effect. By analyzing the interaction between photon spin angular momentum (SAM) and GWs, we derive the selection rules governing this exchange, which are strictly dictated by the spin-1 and spin-2 nature of the electromagnetic and gravitational fields, respectively. We find that the gravitational chiroptical effect reflects the local nature of SAM which prevents the accumulation of gravitational perturbations over spatial phase windings, and offers a theoretically rigorous tool to probe the chiral structure of GWs. This mechanism provides a novel observational pathway to constrain modified gravity theories, measure the asymmetric properties of compact binaries, and explore parity-violating physics in the early universe.
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High Energy Astrophysical Phenomena

Does the radio-active phase of XTE~J1810$-$197 recur following the same evolutionary pattern?

Zhipeng Huang, Zhen Yan, Zhiqiang Shen et al. (+12 more)

Magnetars are the most strongly magnetized compact objects known in the Universe and are regarded as one of the primary engines powering a variety of enigmatic, high-energy transients. However, our understanding of magnetars remains highly limited, constrained by observational sample size and radiative variability. XTE~J1810$-$197, which re-entered a radio-active phase in 2018, is one of only six known radio-pulsating magnetars. Leveraging the distinctive capability for simultaneous dual-frequency observations, we utilized the Shanghai Tianma Radio Telescope (TMRT) to monitor this magnetar continuously at both 2.25 and 8.60~GHz, capturing its entire evolution from radio activation to quenching. This enabled precise characterization of the evolution in its integrated profile, spin frequency, flux density, and spectral index ($\alpha$, defined by $S \propto f^{\alpha}$). The first time derivative of its spin frequency $\dot{\nu}$ passed through four distinct phases – rapid decrease, violent oscillation, steady decline, and stable recovery – before returning to its pre-outburst value concomitant with the cessation of radio emission. Remarkably, both the amplitudes and the characteristic time-scales of these $\dot{\nu}$ variations match those observed during the previous outburst that began in 2003, providing the first demonstration that post-outburst rotational evolution and radiative behavior in a magnetar are repeatable. A twisted-magnetosphere model can qualitatively account for this repeatability as well as for the progressive narrowing and abrupt disappearance of the radio pulse radiation, thereby receiving strong observational support.
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All authors Zhipeng Huang, Zhen Yan, Zhiqiang Shen, Hao Tong, Mingyu Ge, Zhifu Gao, Yajun Wu, Rongbing Zhao, Jie Liu, Rui Wang, Xiaowei Wang, Fan Yang, Chuyuan Zhang, Zhenlong Liao, Yangyang Lin

Astrophysics of Galaxies

A Study Revealing Physical Attributes of Supernova Remnant in G321.3-3.9

Shaobo Zhang, Xianhuan Lei, Hui Zhu et al. (+5 more)

We present a radio analysis of the recently identified supernova remnant G321.3-3.9 using archival multi-wavelength data spanning 88-2304 MHz. The source exhibits an elliptical shell-like morphology (1.3 deg x 1.7 deg) and a relatively flat non-thermal spectral index of alpha = -0.40 +/- 0.03. The distance is estimated using both the Sigma-D relation (1.6-2.9 kpc) and tentative associations with HI structures, the latter suggesting a near-side solution of 2.5-3.3 kpc, though the physical connection remains uncertain.
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All authors Shaobo Zhang, Xianhuan Lei, Hui Zhu, Xueying Hu, Xiaohong Cui, Wenwu Tian, Haiyan Zhang, Dan Wu

Astrophysics of Galaxies

First Submillimeter Lights from Dome A: Tracing the Carbon Cycle in the Feedback of Massive Stars

Yan Gong, Jiaqiang Zhong, Yuan Ren et al. (+38 more)

The cycling of carbon between its ionized, atomic, and molecular phases shapes the chemical compositions and physical conditions of the interstellar medium (ISM). However, ground-based studies of the full carbon cycle have been limited by atmospheric absorption. Dome~A, the most promising site for submillimeter astronomy, has long resisted successful submillimeter astronomical observations. Using the 60~cm Antarctic Terahertz Explorer, we present the first successful CO ($4-3$) and [CI] ($^3P_1 - ^3P_0$) mapping observations of two archetypal triggered massive star-formation regions at Dome~A. These data, together with archival [CII], provide the first complete characterization of all three carbon phases in these environments. We find elevated C$^{0}$/CO abundance ratios in high-extinction regions, plausibly driven by deep penetration of intense radiation fields from massive stars into a clumpy ISM. These findings mark a major milestone for submillimeter astronomy at Dome~A and offer valuable insights into the impact of massive star feedback on the surrounding ISM.
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All authors Yan Gong, Jiaqiang Zhong, Yuan Ren, Yilong Zhang, Daizhong Liu, Yiping Ao, Qijun Yao, Wen Zhang, Wei Miao, Zhenhui Lin, Wenying Duan, Dong Liu, Kangmin Zhou, Jie Liu, Zheng Wang, Junda Jin, Kun Zhang, Feng Wu, Jinpeng Li, Boliang Liu, Xuan Zhang, Zhengheng Luo, Jiameng Wang, Huiqian Hao, Xingming Lu, Shaoming Xie, Jia Quan, Yanjie Liu, Jingtao Liang, Xianjin Deng, Jun Jiang, Li Li, Liang Guo, Tuo Ji, Peng Jiang, Yi Zhang, Chenggang Shu, Sudeep Neupane, Ruiqing Mao, Shengcai Shi, Jing Li

Earth and Planetary Astrophysics

Limit cycles and the climate history of Mars

Jacob Haqq-Misra

Evidence for fluvial features and standing liquid water indicate that Mars was a warmer and wetter place in its past; however, climate models have historically been unable to produce conditions to yield a warm early Mars under the faint young sun. Some models invoke thick greenhouse atmospheres to produce continuously warm conditions, but others have argued that available geologic evidence is more consistent with short-duration and transient warming events on an otherwise cold Mars. One possibility of harmonizing these perspectives is that early Mars experienced climate limit cycles that caused the climate to oscillate between short periods of warmth and prolonged periods of glaciation, due to modulation of greenhouse warming by the carbonate-silicate cycle. This study suggests that episodic limit cycling during the Noachian and Hesperian periods provides a hypothetical explanation for the timing and formation of fluvial features on Mars. A schematic time-forward trajectory of the full history of Mars is calculated using an energy balance climate model, which includes an active carbonate-silicate cycle, instellation changes due to the sun's main sequence evolution, variations in the obliquity of Mars, and supplemental warming from additional greenhouse gases beyond carbon dioxide alone. These calculations demonstrate the viability of a climate history for Mars involving episodic limit cycling to enable the formation of the valley networks at 4.1-3.5 Ga and delta features at 3.3-3.0 Ga, interspersed with cold stable climates and ending in the late Amazonian in a carbon dioxide condensation regime. This schematic climate trajectory provides a plausible narrative that remains consistent with available geologic data, and further exploration of warming mechanisms for the climate of Mars should consider the possibility of episodic transient events driven by carbonate-silicate limit cycling.
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Solar and Stellar Astrophysics

Slow White Dwarf Mergers as a New Galactic Source of Trans-Iron Elements

Umberto Battino, Claudia Lederer-Woods, Claudia Travaglio et al. (+2 more)

The astrophysical origins of the heaviest stable elements that we observe today in the Solar System are still not fully understood. Recent studies have demonstrated that H-accreting white dwarfs (WDs) in a binary sys- tem exploding as type Ia supernovae could be an efficient p-process source beyond iron. However, both observational evidence and stellar models challenge the required frequency of these events. In this work, we calculate the evolution and nucleosynthesis in slowly merging carbon-oxygen WDs. As our models approach the Chandrasekhar mass during the merger phase, the 22Ne(a,n)25Mg neutron source reaction is activated in the external layers of the primary WD, where the carbon-rich material accreted from the secondary WD is burned via the 12C+12C reaction, which provides the necessary {\alpha}-particles via the 12C(12C,{\alpha})20Ne channel. The resulting neutron capture abundance distribution closely resembles a weak s-process one and peaks at Zr, which is overpro- duced by a factor of 30 compared to solar. The mass of the most external layers enriched in first-peak s-process elements crucially depends on the 12C+12C re- action rate, ranging between 0.05 Msun and ~0.1 Msun. These results indicate that slow white dwarf mergers can efficiently produce the lightest p-process iso- topes (such as 74Se, 78Kr, 84Sr, 92Mo and 94Mo) via {\gamma}-induced reactions if they explode via a delayed detonation mechanism, or eject the unburned external layers highly enriched in first peak s-process elements in the case of a pure deflagration. In both cases, we propose for the first time that slow WD mergers in binary systems may be a new relevant source for elements heavier than iron.
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All authors Umberto Battino, Claudia Lederer-Woods, Claudia Travaglio, Friedrich Konrad Röpke, Brad Gibson

Instrumentation and Methods for Astrophysics

The Potential Impact of Neuromorphic Computing on Radio Telescope Observatories

Nicholas J. Pritchard, Richard Dodson and Andreas Wicenec

Radio astronomy relies on bespoke, experimental and innovative computing solutions. This will continue as next-generation telescopes such as the Square Kilometre Array (SKA) and next-generation Very Large Array (ngVLA) take shape. Under increasingly demanding power consumption, and increasingly challenging radio environments, science goals may become intractable with conventional von Neumann computing due to related power requirements. Neuromorphic computing offers a compelling alternative, and combined with a desire for data-driven methods, Spiking Neural Networks (SNNs) are a promising real-time power-efficient alternative. Radio Frequency Interference (RFI) detection is an attractive use-case for SNNs where recent exploration holds promise. This work presents a comprehensive analysis of the potential impact of deploying varying neuromorphic approaches across key stages in radio astronomy processing pipelines for several existing and near-term instruments. Our analysis paves a realistic path from near-term FPGA deployment of SNNs in existing instruments, allowing the addition of advanced data-driven RFI detection for no capital cost, to neuromorphic ASICs for future instruments, finding that commercially available solutions could reduce the power budget for key processing elements by up to three orders of magnitude, transforming the operational budget of the observatory. High-data-rate spectrographic processing could be a well-suited target for the neuromorphic computing industry, as we cast radio telescopes as the world's largest in-sensor compute challenge.
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Astrophysics of Galaxies

The Hierarchical Structure of the Open Cluster NGC 752

Delong Jia, Heng Yu, Zhengyi Shao et al. (+1 more)

The structure of open clusters provides key insights into their evolution and the dynamics of the Milky Way. Using Gaia DR3 data, we applied a hierarchical clustering algorithm to the open cluster NGC 752 based on the kinematical information and identified four substructures corresponding to different stages of disintegration. The cluster exhibits a pronounced signature of mass segregation. Its outer members show a clear expansion trend with a velocities of 0.25 $\rm{km~s^{-1}}$ in the plane of the sky. In addition, the system shows a projected rotational pattern with an angular velocity of approximately 0.03 $\rm{rad~Myr^{-1}}$. We also identified a correlation between the escape times of disturbed members and the epochs at which the cluster crossed the Galactic disk, highlighting the role of Galactic tidal forces in accelerating cluster dissolution. We conclude that hierarchical clustering based on projection bounding energy is effective for studying the internal structure of star clusters, but it has limitations when dealing with unconstrained structures such as tidal tails.
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All authors Delong Jia, Heng Yu, Zhengyi Shao, Lu Li

Cosmology and Nongalactic Astrophysics

More power on large scales

Jeremy Mould

The high value of the cosmic microwave dipole may be telling us that dark matter is macroscopic rather than a fundamental particle. The possible presence of a significant dark matter component in the form of primordial black holes suggests that dark halo formation simulations should be commenced well before redshift z = 100. Unlike standard CDM candidates, PBHs behave as dense, non-relativistic matter from their inception in the radiation-dominated era. This allows them to seed gravitational potential wells and begin clustering earlier. We find that starting N-body simulations at redshifts even before matter-radiation equality yield galaxy bulk flow velocities that are systematically larger than those predicted by standard LCDM models. The early, high-mass concentrations established by PBHs lead to a more rapid and efficient gravitational acceleration of surrounding baryonic and dark matter, generating larger peculiar velocities that remain coherent over scales of hundreds of Mpc. Furthermore, a sub-population of PBHs in the 10^-20 to 10^-17 solar mass range would lose a non-negligible fraction of their mass via Hawking radiation over cosmological timescales. This evaporation process converts matter into radiation, so a time-varying matter density parameter, Omega_m', is introduced, which behaves like a boosted radiation term in the Friedmann equation. This dynamic term acts to reduce the Hubble tension. A higher effective Omega_r in the early universe reduces the sound horizon at the epoch of recombination. PBH mass loss also influences fits to the equation of state parameter, w, at low redshift. The naive N-body modelling presented here suggests investigation with tried and tested cosmology codes should be carried out, by introducing mass losing PBHs and starting the evolution as early as practicable.
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Sunday 11 January

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

Ghost-free non-local $F(R)$ Gravity Compatible with ACT

Shin'ichi Nojiri, S.D. Odintsov and V.K. Oikonomou

We confront the ghost-free non-local $F(R)$ gravity theories with the latest Atacama Cosmology Telescope (ACT) constraints on the spectral index of the scalar perturbations and the updated constraints of Planck/BICEP on the tensor-to-scalar ratio. After reviewing how the ghost-free non-local version of $F(R)$ gravity can be obtained, we show that the de Sitter solution can be obtained in this framework. Also, we show that the resulting theory can be cast in terms of an $F(R,\phi)$ theory of gravity. We analyze two models of non-local $F(R)$ gravity, one power-law and the $R^2$ model, and we show that both models can be compatible with the ACT and updated Planck/BICEP constraints.
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Solar and Stellar Astrophysics

On the 3D time evolution of the dust size distribution in protostellar envelopes

Maxime Lombart, Ugo Lebreuilly and Anaëlle Maury

Dust plays a fundamental role during protostellar collapse, disk and planet formation. Recent observations suggest that efficient dust growth may begin early, in the protostellar envelopes, potentially even before the formation of the disk. Three-dimensional models of protostellar evolution, addressing multi-size dust growth, gas and dust dynamics and magnetohydrodynamics, are required to characterize the dust evolution in the embedded stages of star formation. We aim to establish a new framework for dust evolution models, following in 3D the dust size distribution both in time and space, in MHD models describing the formation and evolution of star-disk systems, at low numerical cost. We present our work coupling the COALA dust evolution module into the code RAMSES, performing the first 3D MHD simulation of protostellar collapse including simultaneously polydisperse dust growth modeled by the Smoluchowski equation as well as dust dynamics in the terminal velocity approximation. Ice-coated micron-sized grains can rapidly grow in the envelope and survive by not entering the fragmentation regime. The evolution of the dust size distribution is highly anisotropic due to the turbulent nature of the collapse and the development of favorable locations such as outflow cavity walls, which enhance locally the dust-to-gas ratio. We analyzed the first 3D non-ideal MHD simulations that self-consistently account for the dust dynamics and growth during the protostellar stage. Very early in the lifetime of a young embedded protostar, micron-sized grains can grow, and locally the dust size distribution deviates significantly from the MRN initial shape. This new numerical method opens the perspective to treat simultaneously gas/dust dynamics and dust growth in 3D simulations at a low numerical cost for several astrophysical environments.
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Earth and Planetary Astrophysics

Magma Ocean Waves and Thermal Variability on Lava Worlds

Mohammad Farhat and Eugene Chiang

Lava worlds are rocky planets with dayside skins made molten by stellar irradiation. Tidal heating on these shortest-period planets is more than skin deep. We show how orbital eccentricities of just a few percent (within current observed bounds and maintained secularly by exterior companions) can create deep magma oceans. “Lava tidal waves” slosh across these oceans; we compute the multi-modal response of the ocean to tidal forcing, subject to a coastline at the day-night terminator and a parameterized viscous drag. Wave interference produces a dayside heat map that is spatially irregular and highly time-variable; hotspots can wander both east and west of the substellar point, and thermal light curves can vary and spike aperiodically, from orbit to orbit and within an orbit. Heat deposited by tides is removed in steady state by a combination of fluid, mushy, and solid-state convection in the mantle. For Earth-sized planets with sub-day periods, the entire mantle may be tidally liquified.
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Cosmology and Nongalactic Astrophysics

A New Consistency Test for the $\Lambda$CDM Model using Radial and Transverse BAO Measurements

Xing-Han A. Zhao and Zheng Cai

We present a calibration-free consistency test of spatially flat $\Lambda$CDM based on baryon acoustic oscillation (BAO) distance measurements. The method forms ratios of BAO distances including the Hubble distance, the comoving angular diameter distance, and the volume-averaged distance, so that the sound horizon scale cancels, and then maps each observed ratio to an effective flat-$\Lambda$CDM matter density parameter, ${\Omega}_{\rm M}^{\Lambda}$, defined as the value of $\Omega_{\rm M}$ that reproduces the measured ratio within $\Lambda$CDM. Flat $\Lambda$CDM predicts that ${\Omega}_{\rm M}^{\Lambda}$ should be independent of redshift and of the particular ratio used. For ratios involving the integrated distances, we associate them with well-defined effective line-of-sight redshift intervals based on the integral mean value theorem. We apply the test to BAO measurements from the Dark Energy Spectroscopic Instrument (DESI) Data Release~1 and Data Release~2, propagating the full published BAO covariance matrices into all derived ratios and ${\Omega}_{\rm M}^{\Lambda}$ constraints. Within current uncertainties, the inferred ${\Omega}_{\rm M}^{\Lambda}$ values are broadly consistent with a redshift-independent constant, providing an internal consistency check of flat $\Lambda$CDM that can be strengthened straightforwardly as BAO measurements improve.
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High Energy Astrophysical Phenomena

The Structure of Poloidal Fields Embedded in Thin Disks

Yossef Zenati, Ethan T. Vishniac and Amir Jafari

Many accreting systems are modeled as geometrically thin disks. Simulations of accretion disks cannot be extended to this regime, although local models can address the behavior of narrow annuli. A global model needs to account for the interactions between a large-scale poloidal field, accreted from the environment, and the disk. The disk magnetosphere can be modeled subject to the boundary conditions imposed by the disk. These depend on the structure of the magnetic field as it crosses the disk and the degree to which the disk can support a bend in the field lines. Building on earlier work we derive a set of equations describing a stationary disk with an embedded poloidal field. We derive a modified induction equation that incorporates tensorial turbulent diffusivities and a helicity-regulated $\alpha$-effect. We quantify how helicity conservation introduces a nonlinear backreaction on the large-scale dynamo, dynamically coupling turbulent diffusion and $\alpha$-quenching. We discuss the challenges encountered in finding a unique solution under stationary flows $E_\phi =0$, which balances the inflow of $B_z$ due to accretion, the outflow due to radial diffusion of $B_z$, and the vertical movement of $B_r$ due to turbulent diffusion and buoyancy. The vertical profiles of both the azimuthal diffusion coefficient $D_{ijk}$ and the helicity-driven $\alpha_{ij}$ demonstrate that changes in the radial gradient can restructure the magnetic field geometry. The ability of disks to sustain large bending angles in the poloidal field implies that angular momentum flux through the magnetosphere can dominate over internal transport even for weak fields. Competing factors can result in non-unique solutions, necessitating extra constraints and diagnostics that highlight the role of isotropic turbulence and helicity regulation in magnetized disk environments.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Oscillatory Freeze from Inertial Holographic Dark Energy

Swapnil Kumar Singh

We study a generalized holographic dark energy model in which the infrared cutoff depends on the Hubble parameter and its first two time derivatives. The inclusion of the $\ddot H$ term introduces a finite relaxation timescale for the horizon degrees of freedom, which can be interpreted as an effective entropic inertia of the holographic vacuum energy. The resulting background dynamics admit late–time solutions in which the cosmic expansion gradually halts. In the underdamped regime, the Hubble parameter undergoes exponentially damped oscillations and asymptotically approaches $H\to0$. The scale factor grows monotonically but by a finite amount, while curvature invariants decay exponentially, leading to an asymptotically Minkowski spacetime without future singularities. We confront the full nonlinear background evolution with cosmic chronometer measurements of the Hubble parameter and find good agreement with current late–time expansion data, with a reduced chi–squared $\chi^2/\nu\simeq0.52$. At observable redshifts, oscillatory features are strongly suppressed and remain consistent with existing constraints.
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High Energy Astrophysical Phenomena

Magnetic winds in resistive compact binary discs

Marc Van den Bossche, Geoffroy Lesur and Guillaume Dubus

Dwarf Novae and low-mass X-ray binaries are eruptive binary systems comprised of a Roche-lobe overflowing solar-type star and an accreting compact object. Their recurrence time can be explained by a low-accreting phase, the quiescence, during which the angular momentum transport parameter is inferred to be $\alpha \approx 0.01$ by the Disc Instability Model. Non-magnetics mechanisms, such as spiral wave transport, only achieve angular momentum transport an order of magnitude too low, at best, because these discs are so thin in quiescence. During this phase, the Magneto-rotational Instability is known to be suppressed by the increased resistivity of the weakly ionised plasma. Studying these thin magnetised discs is a numerical challenge because of the wide range of scales to be resolved. Thanks to the new GPU-accelerated code Idefix, we produce global 3D MHD simulations of a very thin disc $(H/R = 0.01)$ for the first time. We explore the possibility that an MHD wind arises and increases accretion in low magnetic Reynolds number $(\mathrm{Rm}\approx100)$ and realistic plasma parameter ($\beta \approx 1000$) regimes. We observe that the MRI is only quenched in the resistive disc bulk but survives in the disc atmosphere. This drives strong accretion and wind launching. We quantify the efficiency of the resulting wind and measure its global effect on the disc. We explore the effect of the initial disc magnetisation and compare the accretion/ejection regime with and without resistivity.
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Earth and Planetary Astrophysics

Rings around irregular bodies. II. Numerical simulations of the 1/3 spin-orbit resonance confinement and applications to Chariklo

Heikki Salo and Bruno Sicardy

Rings have been found around Chariklo, Haumea and Quaoar, three small objects of the Solar System. All these rings are observed near the second-order spin-orbit resonances (SORs) 1/3 or 5/7 with the central body, suggesting an active confinement mechanism by these resonances. Our goal is to understand how collisional rings can be confined near second-order SORs in spite of the fact that they force self-intersecting streamlines.We use full 3D numerical simulations that treat rings of inelastically colliding particles orbiting non-axisymmetric central bodies, characterized by a dimensionless mass anomaly parameter mu. While most of our simulations ignore self-gravity, a few runs include gravitational interactions between particles, providing preliminary results on the effect of self-gravity on the ring confinement. The 1/3 SOR can confine ring material, by transferring the forced resonant mode into free Lindblad modes. We derive a criterion ensuring that the 1/3 SOR counteracts viscous spreading. Assuming meter-sized ring particles, and tau~1, this requires a threshold value mu > 1e-3 in Chariklo's case. The confinement is not permanent as a slow outward leakage of particles is observed in our simulations. This leakage can be halted by an outside moonlet with a mass of ~1e-7 - 1e-6 relative to Chariklo, corresponding to subkilometer-sized objects. With self-gravity, the ring viscosity nu increases by a factor of few in low-tau rings due to gravitational encounters. For large tau, self-gravity wakes enhance nu by a factor of ~100 compared to a non-gravitating ring, requiring ~10-fold larger mu since the threshold value increases proportional to square-root of nu.
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Astrophysics of Galaxies

Nitrogen abundances in star-forming galaxies 2.2 Gyr after the Big Bang are not elevated

D. Schaerer, Y.I. Izotov, R. Marques-Chaves et al. (+22 more)

Using deep medium-resolution JWST rest-optical spectra of a sample of typical star-forming galaxies (Lyman break galaxies and Lyman-$\alpha$ emitters) from the LyC22 survey at $z \sim 3$, we determined the nebular abundances of N, O, and Ne relative to H for a subsample of 25 objects with the direct method, based on auroral [OIII]4363 line detections. Our measurements increases the number of accurate N/O determinations at $z \sim 2-4$ using a homogeneous approach. We found a mean value of $\log({\rm N/O})=-1.29^{+0.25}_{-0.21} $ over a metallicity range 12+log(O/H)=7.5 to 8.44. The observed N/O ratio and scatter are indistinguishable from that observed in low-z galaxies and HII regions over the same metallicity range, showing thus no redshift evolution of N/O for typical galaxies over a significant fraction of cosmic time. We also show that typical $z \sim 3$ galaxies show a similar offset in the BPT diagram as galaxies from the low-z Lyman Continuum Survey (LzLCS), when compared to the average of SDSS galaxies, and show that this offset is not due to enhanced nitrogen abundances. Our results establish a basis for future studies of the evolution of N and O at higher redshifts.
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All authors D. Schaerer, Y.I. Izotov, R. Marques-Chaves, C. C. Steidel, N. Reddy, A. E. Shapley, S. Mascia, J. Chisholm, S. R. Flury, N. Guseva, T. Heckman, A. Henry, A.K. Inoue, I. Jung, H. Kusakabe, K. Mawatari, P. Oesch, G. Oestlin, L. Pentericci, N. Roy, A. Saldana-Lopez, R. Sato, E. Vanzella, A. Verhamme, B. Wang

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

Probing Compact Binary Coalescences in the Decihertz GW Band with IndIGO-D

Abhishek Sharma, Divya Tahelyani, Anand S. Sengupta et al. (+1 more)

We present an astrophysical science-case study of IndIGO-D, a decihertz gravitational-wave mission concept, focusing on compact binary sources across the 0.1-10 Hz band bridging LISA and next-generation ground-based interferometers. For these science projections, we consider three spacecraft forming an L-shaped interferometer in a heliocentric orbit, with two orthogonal 1000 km arms sharing a common vertex. We calculate the time-dependent antenna response of this geometry, including modulation produced by the orbital motion of the constellation. We treat the strain-sensitivity curve supplied by the IndIGO-D collaboration as an input. For the assumed sensitivity, we estimate a BNS detection rate of $\sim76$-$767\,{\rm yr}^{-1}$. We compute horizon distances for different source classes and find that intermediate-mass black-hole binaries with masses $10^2$-$10^3\,M_\odot$ are detectable throughout their formation history, complementing the reach of LISA and terrestrial detectors. Binary neutron star systems are observable to a horizon redshift of $z\lesssim0.3$, allowing continuous multi-band coverage with Voyager-class interferometers from the decihertz regime to merger. A Bayesian parameter-estimation study of a GW170817-like binary shows that the sky localization area improves from $\sim21\,{\rm deg}^2$ at one month, $\sim1\,{\rm deg}^2$ at one week, down to $0.3\,{\rm deg}^2$ at six hours pre-merger. These sky areas are readily tiled by the Rubin Observatory, whose $9.6\,{\rm deg}^2$ field of view and r-band depth enable high-cadence, repeated coverage of GW170817-like kilonovae at this distance and beyond. IndIGO-D bridges the gap between millihertz and terrestrial observations, enabling early warnings on timescales from months to hours and enhancing the prospects for multi-band and multi-messenger discoveries. (abridged)
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All authors Abhishek Sharma, Divya Tahelyani, Anand S. Sengupta, Sanjit Mitra

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

Viable f(R) Scenarios Unifying Inflation with Realistic Dynamical Dark Energy

S.D. Odintsov, V.K. Oikonomou and G.S. Sharov

Two $F(R)$ gravity models are tested on the basis of their viability during all stages of cosmological evolution. It is shown that these models can describe both the early-time inflationary epoch and the dark energy epoch. The models are confronted with the latest observational data, including the Pantheon+ catalogue with Type Ia supernovae, the Dark Energy Spectroscopic Instrument measurements of baryon acoustic oscillations, the Hubble parameter estimations and data from cosmic microwave background radiation. Investigation of the viability conditions for these models, in particular, the condition $\frac{dF}{dR}>0$ required a deep analysis. Both models appeared to be viable during the early-time era, but for the late-time evolution the viability conditions are not fulfilled in definite domains in the parameter spaces of these models. However the best fitted parameters, determined in confrontation with the mentioned observational data, lie far from the forbidden domains for both models. These $F(R)$ gravity models describe the observations with the large advantage over the $\Lambda$-Cold-Dark-Matter model, not only in $\chi^2$ statistics, but also with Akaike and Bayesian information criteria. This success of the two $F(R)$ gravity scenarios is connected with their capability to mimic dynamical dark energy, similarly to models with variable equation of state, that is necessary for describing the latest Pantheon+ and DESI observational data.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Strong Einstein-Hilbert Gravity Inflation and ACT Phenomenology

V.K. Oikonomou, Eleni I. Manouri and Georgios Konstantellos

In this work we study rescaled effective single scalar field theories, and we confront these with the ACT constraint on the spectral index of the scalar primordial perturbations and the updated BICEP/Planck constraint on the tensor-to-scalar ratio. Rescaled scalar theories of gravity may be the result of an effective $f(R,\phi)$ gravity at strong curvature regimes, which may result on a rescaling of the Einstein-Hilbert term of the form $\sim \alpha R$. It turns out that canonical scalar field theories with stronger gravity compared to standard Einstein-Hilbert gravity can be compatible with the ACT and updated Planck/BICEP constraints, with stronger gravity meaning that the rescaling parameter $\alpha$ takes values smaller than unity.
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Astrophysics of Galaxies

The Isaac Newton Telescope Monitoring Survey of Local Group Dwarf Galaxies-VIII. A Census of Long-Period Variable Stars across the Andromeda Dwarf Satellite System

Hedieh Abdollahi, Atefeh Javadi, Jacco Th. van Loon et al. (+6 more)

We present a comprehensive catalog, in the Sloan $i$ and Harris $V$ filters, of long-period variable (LPV) stars in the spheroidal dwarf satellites of the Andromeda galaxy, based on a dedicated survey for variable stars in Local Group dwarf systems. Using photometric time-series data obtained with the Wide Field Camera (WFC) on the 2.5 m Isaac Newton Telescope (INT), we identify approximately 2800 LPV candidates across 17 Andromeda satellites, spanning a broad range in luminosity and variability amplitude. This study is accompanied by a public data release that includes two comprehensive catalogs, a catalog of the complete stellar populations for each galaxy and a separate catalog listing all identified LPV candidates. Both are available through CDS/VizieR and provide a valuable resource for investigating quenching timescales, stellar mass distributions, and the effects of mass-loss and dust production in dwarf galaxies. We derive updated structural parameters, including newly measured half-light radii, and determine distance moduli using the Tip of the Red Giant Branch (TRGB) method with Sobel-filter edge detection, yielding values between $23.38\pm0.06$ and $25.35\pm0.06$ mag.
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All authors Hedieh Abdollahi, Atefeh Javadi, Jacco Th. van Loon, Iain McDonald, Mahdi Abdollahi, Elham Saremi, Habib G. Khosroshahi, László Molnár, Hamidreza Mahani

Earth and Planetary Astrophysics · Cross-listed from gr-qc

Numerical Study of Polytropes with n=1 and Differential Rotation

T.L. Razinkova, A.V. Yudin and S.I. Blinnikov

The solution space of differentially rotating polytropes with n=1 has been studied numerically. The existence of three different types of configurations: from spheroids to thick tori, hockey puck-like bodies and spheroids surrounded by a torus, separate from or merging with the central body has been proved. It has been shown that the last two types appear only at moderate degrees of rotation differentiality, sigma~2. Rigid-body or weakly differential rotation, as well as strongly differential, have not led to any "exotic" types of configurations. Many calculated configurations have had extremely large values of parameter tau, which has raised the question of their stability with respect to fragmentation.
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Solar and Stellar Astrophysics

Turbulent Properties of Interplanetary Coronal Mass Ejections Observed by Solar Orbiter in the Inner Heliosphere

Jyoti Sheoran, Supratik Banerjee, Vaibhav Pant et al. (+2 more)

We investigate the turbulent properties of 12 interplanetary coronal mass ejections (ICMEs) observed by Solar Orbiter between 0.29 and 1.0 AU. We analyze fluctuation power, spectral indices, break scales, and correlations between magnetic and velocity fluctuations (v-b) to quantify differences between ICME substructures (sheath and magnetic ejecta (ME)) and the surrounding solar wind. The ICME sheath is consistently the most turbulent region at all distances. In the solar wind, Alfvénicity influences inertial-range scaling, resulting in either single power laws near f^-3/2 or f^-5/3, or a coexistence of both, whereas ICME substructures consistently exhibit Kolmogorov-like f^-5/3 spectra. Alfvénicity is reduced within ICMEs, particularly in the ejecta, indicating more balanced Alfvénic fluctuations than in the solar wind. Spectral breaks shift to higher frequencies in ICME regions, with average break frequencies of 0.53 +/- 0.35 Hz (solar wind), 1.87 +/- 1.46 Hz (sheath), and 1.46 +/- 1.28 Hz (ME), reflecting differences in underlying microphysical scales. Our findings highlight distinct turbulence regimes in ICMEs compared to the solar wind and support the use of fluctuation power, spectral breaks, and v-b correlations as effective diagnostics for identifying ICME boundaries.
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All authors Jyoti Sheoran, Supratik Banerjee, Vaibhav Pant, Dipankar Banerjee, M. Saleem Khan

Instrumentation and Methods for Astrophysics

Computing Natural Magnitudes in the Photometric Systems of Astronomical Plates using Gaia DR3 SEDs

Maryam Raouph and Andreas Schrimpf

Context. Accurate photometric calibration of astronomical photographic plates remains a fundamental challenge in astronomy, especially when bridging historical photographic data with modern observations due to the mismatch of spectral sensitivities of photographic plates and passbands of modern calibration catalogs. Aims. We intend to derive consistent natural magnitudes for celestial sources within the intrinsic photometric systems of astronomical photographic plates by using Gaia Data Release 3 (DR3) blue photometer (BP) and red photometer (RP) low-resolution spectral data and to show its superiority to former methods. Methods. We compiled spectral characteristic data for emulsions and filters applied in photometric observations using glass plates. The collected color sensitivities, modified by atmospheric reddening depending on the air mass, are then used to compute accurate natural magnitudes and fluxes of objects in the photographic plates through synthetic photometry, utilizing a catalog of Gaia spectral energy distributions (SEDs) over the wavelength range 330 nm to 1050 nm (XP spectra). This process uses GaiaXPy, a Python library designed to handle Gaia DR3 spectral data. These natural magnitudes are then compared with results from the color term method used to compile the data in existing photoplate archives. Results. Comparing the synthetic magnitudes with those existing in the Archives of Photographic PLates for Astronomical USE (APPLAUSE), we were able to reveal systematic errors of the existing data in the range of +/-0.3 mag and higher. In addition, the presented method allows for an accommodation of stars with similar color index but of different luminosity classes as well as an effective correction of atmospheric reddening at higher air masses, approximately 0.2 mag.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Probing Dark Matter annihilation in the Galactic Centre with TRIDENT

Yingwei Wang, Xinhui Chu, Andrew Cheek et al. (+7 more)

We determine the future sensitivity of the TRIDENT neutrino telescope to dark matter annihilation in the Galactic Centre. By applying the full detector design and assuming an NFW halo profile, we show that TRIDENT will probe annihilation cross-section down to $\langle\sigma v\rangle\approx5\times10^{-27}\,{\rm cm}^3\,{\rm s}^{-1}$ for $10\,{\rm TeV}$ dark matter, falling below the thermal freeze-out benchmark. The analysis is carried out with all-flavour neutrino interactions, where we demonstrate that cascade events, primarily due to $\nu_{e,\tau}$, show greater sensitivity to a dark matter signal compared to the more commonly studied track events. Furthermore, we highlight the impact of a previously overlooked background, Galactic neutrinos produced from interactions between hadronic cosmic rays and interstellar gas. We find dark matter sensitivities are more strongly degraded in the high energy region above $\sim 10\, {\rm TeV}$, with a maximal weakening of approximately a factor of 2. This effect remains smaller than the uncertainty associated with the dark matter density profile but can nonetheless mimic a positive annihilation signal. We contextualise these results with a concrete particle model and show that TRIDENT will be able to probe the most interesting untested parts of parameter space.
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All authors Yingwei Wang, Xinhui Chu, Andrew Cheek, Iwan Morton-Blake, Qichao Chang, Gwenael Giacinti, Samy Kaci, Xin Xiang, Donglian Xu, Fuyudi Zhang

Astrophysics of Galaxies

Joint Optical-HI mock catalogues and prospects for upcoming HI surveys

Sauraj Bharti and J. S. Bagla

Atomic hydrogen (HI) regulates star formation as cold gas fuels star formation. It represents a key phase in the baryon cycle. Redshifted $21$ cm line emission serves as a key tracer for investigating HI in the interstellar medium (ISM) and circumgalactic medium (CGM) in distant galaxies, and enables the study of galaxy evolution. Direct detections of HI are currently limited to $z \leq 0.4$ due to the inherently weak $21$ cm emission line. Ongoing and upcoming large radio surveys aim to detect $21$ cm emission from galaxies up to $z \gtrsim 1$. We present a novel approach for creating optical-HI joint mock catalogues for upcoming SKA precursor surveys: MIGHTEE-HI, LADUMA and WALLABY. Incorporation of optical properties along with HI makes these mock catalogues a powerful tool for making predictions for surveys and provides a benchmark for exploring the HI science (e.g., conditional HIMF and optical-to-HI scaling relations) expected from these surveys. As a case study, we show the use of the joint catalogues for predicting the expected outcome of stacking detection for average HI mass in galaxies that are below the threshold for direct detection. We show that combining stacking observations with only the number of direct detections puts a strong constraint on the HI mass function. We also show that this can be done separately for parts of the color-magnitude diagram for galaxies, enabling a fine grained study of galaxy evolution. This may be used to set priors for the full determination of the HI mass function.
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Earth and Planetary Astrophysics

SPHEREx Re-Observation of Interstellar Object 3I/ATLAS in December 2025: Detection of Increased Post-Perihelion Activity, Refractory Coma Dust, and New Coma Gas Species

C.M. Lisse, Y.P. Bach, S.A. Bryan et al. (+13 more)

In December-2025, the NASA SPHEREx spacecraft re-observed ISO 3I/ATLAS post-perihelion, finding a much more active object compared to August-2025 SPHEREx pre-perihelion observations, with marked evidence for development into an cometary body fully sublimating all its ices. The new imaging spectrophotometry was dominated by spatially resolved features due to light scattered by dust, along with thermal emission, plus gas-line emissions from CN (0.93 um), H2O (2.7 um), organic C-H (3.2 to 3.6 um), CO2 (4.25 to 4.27 um), and CO (4.6 to 4.8 um). The CO2 gas-coma continues to be extended out to a 3 arcmin radius. The continuum spectral signature of H2O-ice absorption had mostly disappeared, replaced by scattered-light plus thermal-emission from organo-silicaceous dust grains while the H2O gas-emission is 40x times brighter. The CO- and CO2-gas comae were circularly symmetric, while the other comae appear morphologically similar to the dust-coma with its pear-shaped, solar-pointing, large icy dust grains dust tail. The new appearance of CN and C-H features suggests that these carbon-rich ice species were contained either in H2O phases or were trapped under them.
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All authors C.M. Lisse, Y.P. Bach, S.A. Bryan, P. M. Korngut, B.P. Crill, A.J. Cukierman, O. Doré, A. Cooray, B. Fabinsky, A.L. Faisst, H. Hui, G.J. Melnick, C.H. Nguyen, Z. Rustamkulov, V. Tolls, M.W. Werner