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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 3 March

Solar and Stellar Astrophysics

A fast method for deriving relative small-scale magnetic field variations from high-resolution spectroscopy

Paul I. Cristofari, Steven H. Saar, Aline A. Vidotto et al. (+1 more)

Observational constraints on stellar magnetic fields are essential to both stellar and planetary physics. Recent studies revealed the diversity and evolution of large-scale magnetic fields in low-mass stars. These large-scale fields only account for a small fraction of the observed unsigned magnetic flux. Most of the surface magnetic flux if accounted for by small (spatial) scale magnetic fields, which exhibit clear temporal evolution of time scales of years. We aim at developing new techniques to extract small-scale magnetic field estimates from time series of observed spectra. Our ultimate goal is to study the temporal evolution of small-scale magnetic fields which will provide insight into the magnetic properties of low-mass stars and their magnetic cycles. We implement a process to capture relative pixel variations caused by changes in magnetic field strengths, relying on synthetic spectra computed with ZeeTurbo. This approach provides extremely fast and reliable estimates of relative magnetic field strength variations from series of high-resolution spectra, mitigating the impact of systematics between models and observations. We assess the performance of the proposed method through its application to simulated data and publicly available spectra. In addition, we implement a model-driven process to derive relative temperature variations and explore the influence magnetic fields have on these measurements. Our results are in excellent agreement with previous magnetic field estimates. The method provides robust constraints and proves to be relatively insensitive to small changes in the assumed atmospheric parameters and broadening. We find that magnetic field variations have the potential of introducing biases in relative temperature estimates, in particular for domains containing a large number of magnetically-sensitive transitions.
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All authors Paul I. Cristofari, Steven H. Saar, Aline A. Vidotto, Stefano Bellotti

High Energy Astrophysical Phenomena

Probing Axions with Relativistic Jet Polarimetry

Dashon Michel Jones, Richard Anantua, Razieh Emami et al. (+1 more)

The prospect of identifying axion signals due to axion-photon coupling induced changes to the polarization has now become a reality in view of near-horizon polarimetric observations by the Event Horizon Telescope (EHT). Axion-like particles (ALPs), motivated as dark matter candidates by the strong CP problem, induce frequency-independent birefringence in linearly polarized radiation, producing observable rotations of the electric vector position angle. While previous studies have focused exclusively on axion signatures in near-horizon accretion disk emission, the relativistic jet of M87 – extending from 10 gravitational radii to kiloparsec scales – remains unexplored as an axion probe despite offering extended path lengths through the putative dark matter distribution. In this study, we investigate the effects of an axion cloud around the jet in M87 on the Stokes maps of relativistic jets using a stationary, axisymmetric, self-similar model for the jet and a coherent, homogeneous soliton core in M87's galactic center for the axion background. At 230 GHz, for representative couplings in range $g_{a \gamma} \sim 5 \times 10^{-15} - 5 \times 10^{-14} GeV^{-1}$, we find that axion masses in the $10^{-21} eV $ range produce degree-level to multi-degree EVPA rotations, in some cases exceeding typical EHT measurement uncertainties, whereas masses in the $10^{-22} eV$ range yield predominantly sub-degree rotations. We identify a suite of morphological diagnostics that together constitute a framework for distinguishing axion-induced birefringence from plasma Faraday rotation in resolved jet polarimetry.
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All authors Dashon Michel Jones, Richard Anantua, Razieh Emami, Nate Lujan

High Energy Astrophysical Phenomena

A broadband search for coherent radio emission in cataclysmic variables

Margaret E. Ridder, Paul E. Barrett, Craig O. Heinke et al. (+1 more)

Radio observations of cataclysmic variables have revealed a variety of behavior. From some systems, we see bright unpolarized radio flares occurring during dwarf nova outbursts, consistent with synchrotron emission from jets. In others, we see highly polarized emission, restricted in frequency, superimposed on a flat-spectrum continuum, suggesting a coherent emission process. Here, we present spectro-temporal analysis of 2–4 GHz and 8–12 GHz VLA observations of 6 cataclysmic variables. Our results show both broad- and narrow-band, highly polarized, variable radio emission. We suggest that this emission is consistent with electron-cyclotron maser emission or plasma radiation. This could be from an isolated emission region in the case of the narrow-band emission, or a region with varying magnetic field strength or density in the case of the broad-band emission. In one target, V2400 Oph, we see largely unpolarized emission changing on minute timescales, that may coincide with interactions between the white dwarf's magnetosphere and diamagnetic blobs.
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All authors Margaret E. Ridder, Paul E. Barrett, Craig O. Heinke, Gregory R. Sivakoff

Solar and Stellar Astrophysics

The Periastron Passage of T Tauri South B as Viewed by ALMA: Millimeter Flux Variations and Dust Heating Triggered by Orbital Motion

Tracy L. Beck, Stephane Guilloteau, Gail Schaefer et al. (+3 more)

We present 225 and 350 GHz imaging of the iconic T Tauri system using the Atacama Large Millimeter submillimeter Array (ALMA). T Tauri is a hierarchical triple system, and the close binary T Tau Sa/Sb underwent periastron passage in March 2023. The ALMA images were obtained in epochs spanning November 2019 through June 2023, and therefore covered the time frame of the recent periastron passage. We clearly resolve the Sa-Sb binary in two epochs of high-resolution measurements with ALMA. We find increases in millimeter flux from heating of the Sa disk and the wider distribution of dust in the environment of the binary. This heating is likely in response to increased stellar accretion activity triggered by orbital motion during the dynamic periastron passage of T Tau Sb around Sa. Resolved, extended millimeter emission is also found to change morphology and increase in flux in the immediate environment of the Sa-Sb binary after periastron passage. This may suggest an increase in nonthermal emission from magnetic interaction, gravitational disruption of the circumstellar disks as the stars passed through periastron, or both of these phenomena. We also detected structures in the compact (24 au radius), thermal dust disk around T Tau N. In particular, we identify a crescent-shaped emission excess just outside a shallow gap at 12 au radius that appears to move at Keplerian speed. Future measurement of dust spectral indices can clarify the origin of increased and variable millimeter emission in the environment of the T Tau S binary.
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All authors Tracy L. Beck, Stephane Guilloteau, Gail Schaefer, Edwige Chapillon, Anne Dutrey, Emmanuel Di Folco

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Ultra slow-turn inflation

Ana Achúcarro, Perseas Christodoulidis, Jinn-Ouk Gong et al. (+1 more)

In standard multi-field models, tachyonic isocurvature perturbations generally indicate the presence of an instability. We revisit the stability of some known counterexamples and show that, in a certain class of models that we call ultra slow-turn, an exponentially decreasing turn rate can shut off this potential instability. We argue that the stability of a given model can be correctly inferred by the total entropy perturbation, even if the effective mass squared of the isocurvature perturbation is negative. Several recent supergravity- or string-inspired models such as fibre inflation, SL(2,$\mathbb{Z}$) attractors and modular inflation fall into the ultra slow-turn class.
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All authors Ana Achúcarro, Perseas Christodoulidis, Jinn-Ouk Gong, Oksana Iarygina

Instrumentation and Methods for Astrophysics · Cross-listed from physics.data-an

Data Unfolding: From Problem Formulation to Result Assessment

Nikolay D. Gagunashvili

Experimental data in particle and nuclear physics, particle astrophysics, and radiation protection dosimetry are collected using experimental facilities that consist of a complex system of sensors, electronics, and software. Measured spectra or cross sections are considered as Probability Density Functions (PDFs) that deviate from true PDFs due to resolution, bias, and efficiency effects. Unfolding is viewed as a procedure for estimating an unknown true PDF. Reliable estimates of the true PDF are necessary for testing theoretical models, comparing results from different experiments, and combining results from various research endeavors. Both external and internal quality assessment methods can be applied for this purpose. In some cases, external criteria exist to evaluate deconvolution quality. A typical example is the deconvolution of a blurred image, where the sharpness of the restored image serves as an indicator of quality. However, defining such external criteria can be challenging, particularly when a measurement has not been performed previously. This paper discusses various internal criteria for assessing the quality of the results independently of external information, as well as factors that influence the quality of the unfolded distribution.
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Cosmology and Nongalactic Astrophysics

Testing gravitational wave polarizations with LISA

Shingo Akama, Maxence Corman, Paola C. M. Delgado et al. (+16 more)

In this paper we quantify the ability of the Laser Interferometer Space Antenna (LISA) to test the presence of non-tensorial polarizations as well as modifications to the tensor ones in gravitational waves emitted from massive black hole binaries. We employ the Parametrized Post-Einsteinian (PPE) formalism to model deviations from General Relativity (GR) for tensor, vector, and scalar polarizations. Our PPE parametrization is inspired by post-Newtonian waveforms from four modified gravity theories: Horndeski, Einstein-aether, Rosen's bimetric, and Lightman-Lee. We consistently implement these modifications across the inspiral, merger, and ringdown phases, ensuring proper waveform alignment and tapering. Subsequently, we perform Fisher forecasts to derive expected constraints on deviations from General Relativity and map these constraints to the parameter spaces of the four gravity theories. For tensor polarizations, LISA achieves constraints on amplitude modifications ranging between $\sim 10^{-4}-10^{-2}$ precision level, depending on the frequency evolution of the modifications, for systems with $10^5-10^7 {\, \rm M}_\odot$ at $z = 1$. We find that LISA can distinguish breathing and longitudinal scalar polarizations only for relatively light binaries with $M \lesssim 10^4 {\, \rm M}_\odot$, beyond which these modes become degenerate in the detector response. Importantly, constraints on vector polarizations are approximately 2-3 times more precise than for scalar polarizations. For both vector and scalar modes, amplitude measurements reach precisions ranging between $\sim 10^{-8}-10^{-2}$, depending on the frequency evolution of the modifications, for systems with $10^5-10^7 {\, \rm M}_\odot$ at $z = 1$. These results demonstrate LISA's potential to probe gravity in the strong-field regime via gravitational wave polarizations.
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All authors Shingo Akama, Maxence Corman, Paola C. M. Delgado, Alice Garoffolo, Macarena Lagos, Alberto Mangiagli, Sylvain Marsat, Manuel Piarulli, Gianmassimo Tasinato, Jann Zosso, Giuseppe Gaetano Luciano, Nils A. Nilsson, Leandros Perivolaropoulos, Kristen Schumacher Aloh, Benjamin Sutton, Roxane Theriault, Amresh Verma, Yiqi Xie, Mian Zhu

High Energy Astrophysical Phenomena

Multi-wavelength insights into the pulsar wind nebula candidate near 1LHAASO J0343+5254u: an obscured merging galaxy cluster?

H. W. Edler, M. Arias, A. Botteon et al. (+1 more)

The advent of the Large High Altitude Air Shower Observatory (LHAASO) accelerated the detection of TeV and PeV gamma-ray sources. Some of these are associated with pulsar wind nebulae (PWNe) and other Galactic objects, while others are yet to be connected to sources at other wavelengths. Recently, the discovery of an extended X-ray source within the unidentified PeV source 1LHAASO J0343+5254u was reported, this source was claimed as a candidate PWN based on its X-ray spectrum. We will revisit the interpretation of the extended X-ray source based on multi-wavelength observations. We present new LOFAR continuum radio imaging at observing frequencies of 54 and 144 MHz, an alternative X-ray modeling and archival near-infrared (NIR) data. We discover several radio sources with morphologies and spectra suggestive of a radio halo, a radio relic and tailed radio galaxies, all of which are typically found in (merging) galaxy clusters. Furthermore, we show that the X-ray data can be modeled as thermal emission from the intracluster medium (ICM), with our best-fitting thermal ICM model being slightly preferred to a non-thermal power-law fit. We further find a 9.7$\sigma$ over-density in red NIR sources in the surrounding region, among them possible hosts of the tailed radio sources. Our results favor an interpretation of the X-ray source as a massive, merging galaxy cluster located in a highly extinct region of the Galactic plane, unrelated to 1LHAASO J0343+5254u. Future observations in the hard X-ray regime will be able to conclusively settle the discussion on the nature of the X-ray emission.
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All authors H. W. Edler, M. Arias, A. Botteon, C. G. Bassa

Astrophysics of Galaxies

Estimating the dynamical masses of dwarf galaxies in the presence of binary-star contamination

José María Arroyo-Polonio, Giuseppina Battaglia and Guillaume F. Thomas

Ultra-faint dwarf galaxies (UFDs) show extreme dynamical mass-to-light ratios of approximately 100-5000 in solar units within the half-light radius, making them critical tests for cosmological models. However, it is a concern whether the line-of-sight (l.o.s.) velocity component of the orbital motion of undetected binary stars is significantly inflating the observed l.o.s. velocity dispersions and, consequently, UFDs dynamical mass estimates. We correct the current estimates of these quantities for UFDs to account for the presence of undetected binaries with single-epoch data. We use the latest binary population models in the solar neighborhood to compute the expected velocity distribution of binary stars. We then convolve this distribution with a Gaussian to model the l.o.s. velocity distribution of UFDs in a mixture model, in which the binary fraction is a free parameter. We apply this methodology to observed UFDs whose dynamical masses are potentially inflated by binaries. In order to generalize to the multi-epoch data case, we compute the velocity distribution of undetected binaries by applying the same cuts to the models as one would apply to the observed data to remove binaries. We find that estimated dynamical masses of UFDs decrease by a factor of 1.5 to 3 once undetected binaries are accounted for. These corrections significantly affect considerations about DM models based on these systems, even challenging the classification of Leo IV, Unions I and Sagittarius II as galaxies. We find that a dedicated multi-epoch campaign spanning one year could substantially mitigate the impact of binaries. Finally, we find that the expected level of binary-star contamination in DM halo density profile inferences from dynamical models of classical dwarf spheroidal galaxies is negligible.
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Astrophysics of Galaxies

MOSS II: Mid frequency radio catalog of Saraswati core region

Robert Kincaid, Edwin Retana-Montenegro, Bruno Slaus et al. (+6 more)

The MeerKAT Observations of the Saraswati Supercluster (MOSS) is an ongoing project attempting to study the radio and optical properties of the core region of the Saraswati supercluster which will eventually entail a full survey of the entire supercluster region. We have used MeerKAT L-band (1.28 GHz) images at an angular resolution of 8 arcsec from previous deep (central RMS noise of 11 - 16 uJy beam-1) pilot observations of the core region (z ~ 0.28) of the Saraswati supercluster containing the two most massive galaxy clusters: Abell 2631 and ZwCl2341. These cluster fields cover an area of 1.6 deg2 and the radio catalogs produced from each cluster region contain 1999 and 2611 sources (5sigma limit) for Abell 2631 and ZwCL2341, respectively. For each catalogue, we investigated the noise properties, astrometry, flux density scale accuracy, spectral properties, etc of the radio sources. The catalogs were then corrected for various observational biases before derivation of the radio source counts. In agreement with previous studies, we find that at the sub-mJy level our counts show the characteristic flattening, indicating the increased dominance of the star-forming galaxy (SFG) population over the active galactic nuclei (AGN). Furthermore, in this sub-mJy regime the counts lie slightly higher (a 'bump' feature) compared to other deep MeerKAT data and recent radio-sky simulations. We suggest that this feature could be attributed to an enhanced population of intermediate SFG and/or AGNs associated with these galaxy cluster fields. In addition cosmic variance could represent an important source of uncertainty in the source counts.
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All authors Robert Kincaid, Edwin Retana-Montenegro, Bruno Slaus, Viral Parekh, Pascale Jablonka, Sameer Salunkhe, Shishir Sankhyayan, Vernesa Smolčic, Marco Bondi

Instrumentation and Methods for Astrophysics

Nemesis: A Multi-Scale, Multi-Physics Algorithm for Astrophysics

Erwan Hochart and Simon Portegies Zwart

In this work, an updated version of the multi-scale, multi-physics algorithm, Nemesis which makes use of the Astrophysical Multipurpose Software Environment (AMUSE). The algorithm is formally introduced and validated. A suite of simulations is run to assess its performance in simulating star clusters containing planetary systems, its ability to capture the von Zeipel-Lidov-Kozai effect, and its computational scalability. Nemesis is found to yield indistinguishable results in both the global and local scales when compared with the direct N-body code Ph4. The same conclusion is found when analysing its ability to capture the von Zeipel-Lidov-Kozai effect. When analysing its computational performance, the wall-clock time scales roughly as $t_{\rm sim \propto 1/ \sqrt{\delta t_{\rm nem}}$ where $\delta t_{\rm nem}$ represents the time synchronisation between the global and local scales. When changing the number of planetary systems, the wall-clock time remains unchanged as long as the number of available cores exceeds the number of systems. Beyond this, it's found that at worst, the computational time increases linearly with the number of excess systems. The method introduced here can find it's use in numerous domains of astronomy thanks to its flexibility and modularity, from simulating protoplanetary disks in star clusters to binary black holes in the galactic center.
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High Energy Astrophysical Phenomena

ATLAS100 – I. A volume-limited sample of supernovae and related transients within 100 Mpc

Shubham Srivastav, Stephen J. Smartt, Thomas Moore et al. (+29 more)

We present ATLAS100 – a sample of 1729 supernovae and other explosive optical transients within $\sim 100$ Mpc observed by the ATLAS survey over a span of 5.75 years from 2017 September 21 to 2023 June 21. The volume-limited sample includes transients associated with galaxies with a spectroscopic redshift of $z \leq 0.025$, and spectroscopically classified transients within this redshift threshold where a host redshift was not available in existing catalogues. Our host galaxy list is constructed from aggregating all available galaxy redshift and distance catalogues. We carefully select all transients within a projected radius of 50\,kpc of these hosts. The ATLAS100 transient sample has a host galaxy redshift completeness fraction of $83$ per cent, consistent with expectations for the redshift completeness of local galaxy catalogues. Within this volume, the spectroscopic classifications are 87 per cent complete and we reclassify many ambiguous transients with joint light curve and spectroscopic considerations. Here, we release the catalogue together with compiled, binned and cleaned ATLAS photometry for all transients. We fit the light curve data to derive peak luminosity and characteristic timescales. We explore the sample characteristics, demographics and discuss completeness and purity of the sample.
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All authors Shubham Srivastav, Stephen J. Smartt, Thomas Moore, Kenneth W. Smith, David R. Young, Michael D. Fulton, Charlotte R. Angus, Matt Nicholl, Heloise F. Stevance, Ting-Wan Chen, Andrea Pastorello, Julian Sommer, Fiorenzo Stoppa, Jack W. Tweddle, Joseph P. Anderson, Mark E. Huber, Armin Rest, Lauren Rhodes, Luke J. Shingles, Aysha Aamer, Alejandro Clocchiatti, Alexander J. Cooper, Nicolas Erasmus, James H. Gillanders, Dylan Magill, Giuliano Pignata, Paige Ramsden, Brian P. Schmidt, Xinyue Sheng, Joshua G. Weston, Larry Denneau, John L. Tonry

Astrophysics of Galaxies

An Origin of Radially Aligned Filaments in Hub-Filament Systems

Shingo Nozaki and Shu-ichiro Inutsuka

Recent observations have identified hub-filament systems (HFSs) as the primary formation sites of massive stars and star clusters. Some HFSs are characterized by multiple filaments aligned radially toward a central high-density hub. However, the physical origin of radially aligned filaments remains unknown. Here, we propose a new formation mechanism of HFSs driven by the interaction of a fast magnetohydrodynamic shock with a molecular cloud characterized by an hourglass-shaped magnetic field and density inhomogeneity. Our three-dimensional magnetohydrodynamic simulations show that the shock propagation leads to the formation of radially aligned filamentary structures with line masses slightly above the thermally critical line mass and lengths of $1$-$3\,\rm{pc}$, and widths of $0.06$-$0.08\,\rm{pc}$. High-density filamentary gas ($n_{\rm{H_2}} \sim 10^4 \, \rm{cm^{-3}}$) selectively exhibits inward velocities of $1-4\, \rm{km \, s^{-1}}$ that increase toward the hub center, while the ambient low-density inter-filament gas retains low velocities regardless of the radius. Mass accretion onto the hub is channeled through dense filaments. The filament formation is driven by oblique shocks generated at the bent magnetic field lines. The resulting post-shock amplification of the tangential magnetic field induces a magnetically guided inflow. The shock-interface interaction amplifies density perturbations, resembling Richtmyer–Meshkov instability modes, which promotes the fragmentation of the shocked layer into multiple filaments. The process studied in this Letter explains both the morphology of radially aligned filaments and the selective mass accretion observed in HFSs. In our simulation, the resulting star formation efficiency is $\sim4\%$, suggesting that the shock-driven evolution limits the SFE to only a few percent.
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Earth and Planetary Astrophysics

Dynamics of the TWA 7 planetary system and possibility of an additional planet

A. Lacquement, H. Beust, G. Duchêne et al. (+1 more)

The debris disk surrounding the young star TWA 7 exhibits morphological features that tightly constrain its planetary architecture. JWST/MIRI observations have recently revealed a directly imaged outer planet at large separation. The disk also displays a sharply defined inner edge near 23 au and an extended asymmetric structure that may trace a horseshoe-like distribution of material indicative of gravitational interactions between planets and planetesimals. We investigate whether the observed disk morphology and the possible co-orbital material can be explained by the combined gravitational influence of the known outer planet and an undetected inner companion. We aim to identify planetary configurations consistent with both the disk structure and the long-term stability of the system. We combined N-body simulations and secular perturbation theory to explore how an undetected inner planet could shape the inner edge of the disk while maintaining the dynamical coldness required for stable co-orbital structures around the outer planet. The analytical framework quantifies the secular coupling between the two planets and delineates dynamically viable configurations. The inner edge of the disk near 23 au can be reproduced by a sub-Jovian planet orbiting between 13 and 23 au. Secular interactions further restrict this companion to nearly circular orbits, as higher eccentricities would excite the outer planet and destabilize the co-orbital material. Together, these constraints confine the system to a narrow region of parameter space. The TWA 7 system appears dynamically cold, with all components, including the planets and the debris disk, sharing nearly circular and coplanar orbits. Such a quiescent configuration likely reflects the weak dynamical stirring, making it a promising laboratory to study the early interplay between planet formation, co-orbital dynamics, and debris-disk evolution.
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All authors A. Lacquement, H. Beust, G. Duchêne, A.-M. Lagrange

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Effects of isovector spin-orbit interaction on the charge-weak form factor difference in $^{48}$Ca, $^{208}$Pb, $^{90}$Zr and $^{62}$Ni

Tong-Gang Yue, Zhen Zhang and Lie-Wen Chen

The nucleon spin-orbit interaction is a cornerstone of nuclear structure theory, yet its isospin dependence remains insufficiently constrained within modern nuclear energy density functional (EDF) theory. It was recently shown that, within the framework of extended Skyrme EDFs, the charge-weak form factor difference $\Delta F_{\rm CW}$ in $^{48}$Ca exhibits remarkable sensitivity to the effective isovector spin-orbit (IVSO) interaction, whereas $\Delta F_{\rm CW}$ in $^{208}$Pb is much less sensitive to this channel. Extending this analysis to other nuclei, we find that $^{90}$Zr, with its ten spin-orbit unpaired $1\mathrm{g}_{9/2}$ neutrons, displays a $\Delta F_{\rm CW}$ sensitivity to the IVSO strength similar to that of $^{48}$Ca, arising from modifications to the central mean-field potential rather than the one-body spin-orbit potential. In contrast, $^{62}$Ni, like $^{208}$Pb, remains largely insensitive to the IVSO interaction. This structure-driven distinction suggests an experimental strategy: future parity-violating electron scattering measurements, e.g., the MREX experiment at the MESA facility, on $^{48}$Ca and $^{90}$Zr would help constrain the effective IVSO strength, while measurements on $^{208}$Pb and $^{62}$Ni can provide a cleaner probe of the density dependence of the symmetry energy with reduced IVSO sensitivity.
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Astrophysics of Galaxies

Search for quasar pairs with Gaia astrometric data IV. Confirmation of 17 dual quasars and 143 projected quasars

Zhuojun Deng, Qihang Chen, Liang Jing et al. (+2 more)

Dual quasars separated at the kiloparsec scale are widely regarded as precursors to binary supermassive black holes and offer a key insight into the dynamical evolution of galaxy mergers. Our series of studies focuses on searching for dual quasars by using a selection strategy of zero proper motion and zero parallax to isolate candidate quasars near known ones and by follow-up spectroscopy of the candidates. This paper, the fourth in the series, reports the spectroscopic confirmations of our quasar pair candidates based on the spectroscopic data of the SDSS and DESI DR1. We newly identified 17 dual quasars and 143 projected quasars. The redshifts of the 17 dual quasars range from 0.573 to 2.758, with a median of 1.512. One notable system, J0023+0417, exhibits nearly identical spectral features in the two members and shows evidence of a potential foreground galaxy, making it a high-confidence strong gravitational lensing system. The redshifts of the 143 projected quasars are from 0.301 to 4.030, with a median of 1.596. Among them, four have projected distances below 30 kpc, offering valuable opportunities to probe the circumgalactic medium (CGM) of the foreground host galaxy through absorption lines.
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All authors Zhuojun Deng, Qihang Chen, Liang Jing, Xingyu Zhu, Jianghua Wu

Solar and Stellar Astrophysics

Component masses in stellar and substellar binaries from Gaia astrometry and photometry

C.A.L. Bailer-Jones and L. Kreidberg

The masses of stars and planets can be measured dynamically in binary systems. For an unresolved binary, time series astrometry yields some orbital parameters, but it cannot provide the component masses, because we observe only the motion of the system's photocentre. However, as a star's luminosity is related to its mass, the observable photometry of both components together provides information on the system mass. Here we develop a method to determine the individual component masses of an unresolved binary using the astrometric orbit together with three-band photometry from Gaia. We use a mass-flux relation fitted from stellar isochrone models for each Gaia band to infer the unknown flux ratio. This enables our method to distinguish between near equal-mass, near equal-brightness stellar binaries and star-planet binaries, which otherwise have identical astrometric signatures. Using a likelihood approach, we sample the posterior probability distribution over the stellar parameters, marginalizing over system age and metallicity to get the individual masses. We apply this to 20 000 systems with a main sequence primary within 300 pc of the Sun using data from the Gaia data release 3 non-single star catalogue. Primary masses can be determined with a precision (one-sigma posterior width) of 10-20% in 90% of cases. Secondary masses, which extend down to planetary-mass objects, are less precise, although half are more than 25% precise. Interestingly, adding either infrared photometry or spectroscopic orbits from Gaia does not change the mass estimates much (less than 4% and 1% respectively). Interstellar extinction likewise has little impact for this sample. This work shows that reasonably precise masses can be obtained for stars and substellar objects using just the Gaia astrometry and photometry without need for extensive follow-up.
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High Energy Astrophysical Phenomena

The Evolution of X-ray Spectra in Tidal Disruption Events

Wei Chen and Erlin Qiao

The study of the evolution of X-ray spectra in tidal disruption events (TDEs) is an important approach for understanding the physical processes occurring near a supermassive black hole. Observations show that the X-ray spectra of TDEs are very soft at the peak after the outburst, followed by a spectral hardening on a timescale of years. Theoretically, TDEs are suggested to undergo super-Eddington accretion at the time around the outburst. In this paper, we constructed a new disc-corona model to explain the observed X-ray spectral hardening in TDEs. In our model, there is a transition radius $r_{\text{tr}}$. For $r< r_{\text{tr}}$, the accretion flow exists in the form of a slim disc, the emission of which is dominated by soft X-rays. While for $r>r_{\text{tr}}$, the accretion flow exists in the form of a traditionally sandwiched disc-corona, in which a harder X-ray spectrum is produced. Our calculations show that $r_{\text{tr}}$ decreases with decreasing mass accretion rate $\dot {M}$, which intrinsically can predict the hardening of the X-ray spectra since the relative contribution of the outer disc-corona to the inner slim disc to the X-ray spectrum increases with decreasing $\dot {M}$. Our model has been applied to explain the observed X-ray spectral hardening in TDE candidate AT 2019azh, in which $\dot {M}$ is assumed to decrease proportionally to $t^{-5/3}$. Potential applications of the model in explaining the X-ray spectral evolution in upcoming rich TDE observations are also expected.
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Earth and Planetary Astrophysics

Reproducing the stellar-mass dependence of the giant planet occurrence rate with pebble accretion models

Heather F Johnston, Olja Panic, Sabine Reffert et al. (+2 more)

The stellar mass dependence of the unbiased giant planet occurrence rate may be the best statistical tool to constrain the formation of such planets. This rate rises and falls as a function of stellar mass, peaking around stars of $\sim 1.7{-}2 \Ms$. In this work, we carry out a population synthesis study, using pebble-driven core accretion model of planet formation, to investigate the planet formation conditions that may be responsible for this stellar-mass dependence. We use the inferred giant planet occurrence rated of three combined homogenised radial velocity surveys (EXPRESS, PPPS, and Lick giant star survey) to constrain the models. We find that we can produce a synthetic giant planet population with closely aligned occurrence and properties when we base our model on observationally-supported assumptions that accretion rates are higher and disk lifetimes are shorter around more massive stars, we can produce a synthetic giant planet population with closely aligned properties to the observed distribution. We also find that in this scenario, the runaway gas accretion occurs at a larger orbital distance and earlier times as the stellar mass increases.
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All authors Heather F Johnston, Olja Panic, Sabine Reffert, Beibei Liu, Xinghao Ma

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Magnetic monopoles and high frequency gravitational waves from quasi-stable strings

Rinku Maji and Qaisar Shafi

The spontaneous breaking of $SO(10)$ via flipped $SU(5)$ to the Standard Model yields a novel scenario in which the superheavy topologically stable GUT monopole carrying a single unit ($2\pi/e$) of Dirac magnetic charge emerges from the merger of a confined but topologically distinct monopole-antimonopole pair that are pulled together by a string. The $SO(10)$ breaking via the subgroup $SU(4)_c\times SU(2)_L\times SU(2)_R$, following a similar reasoning, produces a topologically stable monopole that carries two units ($4\pi/e$) of Dirac charge. We explore the cosmological consequences of this scenario by assuming that the monopoles and strings experience a limited number of inflationary $e$-foldings, before re-entering the horizon and ultimately forming a network of quasi-stable strings bounded by monopole-antimonopole pairs. We identify regions of the parameter space that yield an observable number density of the GUT monopole from the collapse of the appropriate string segments. The gravitational waves emitted by these quasi-stable cosmic strings lie in the Hz to kHz range, which can be tested in a number of proposed and ongoing experiments.
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High Energy Astrophysical Phenomena

Tilted, warped, and eccentric disks

P. Chris Fragile, Adam Ingram, Gibwa Musoke et al. (+1 more)

We review some of the interesting consequences that tilts, warps, and eccentricities can introduce into the dynamics, thermodynamics, and observational appearance of accreting systems, with an emphasis on disks around black holes and compact stars. We begin with a review of the two types of precession that are associated with eccentric and tilted orbits in general relativity and Newtonian gravity. We then discuss the types of accretion systems that may manifest tilted or eccentric disks. In separate sections we discuss first tilted and then eccentric disks, each section covering relevant and interesting observational, theoretical, and numerical results. Next, we explore potential connections between the phenomenology of quasi-periodic oscillations and either tilted or eccentric disks. Finally, we present some concluding thoughts and discuss future directions this research might take.
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All authors P. Chris Fragile, Adam Ingram, Gibwa Musoke, Gordon I. Ogilvie

Astrophysics of Galaxies

New morpho-kinematic classification: The two-dimensional spatial distribution of stellar specific angular momentum in late-type galaxies

Juan Manuel Pacheco-Arias, Philippe Amram, Benoît Epinat et al. (+1 more)

The two-dimensional spatial distribution of stellar specific angular momentum (sAM) within galaxies has never been previously analysed. We investigate its morpho-kinematics and its relation to total stellar sAM (jstar) and stellar mass (Mstar) for 30 spiral and irregular galaxies from the GHASP survey. We constructed high-resolution stellar sAM surface density (sAMSD) maps by combining 3.4 micron WISE photometry with Halpha velocity fields and HI rotation curves. Their structure was quantified using non-parametric morphological indicators (concentration, asymmetry, smoothness) plus two additional coefficients measuring similarity to an axisymmetric Freeman disc and the strength of bisymmetric substructures in sAMSD space. Each galaxy was assigned to one of five new morpho-kinematic classes based on its dominant sAMSD feature: jstar-ring, jstar-spiral, jstar-bar, jstar-clump, and jstar-irregular. This defines a classification scheme that combines directly morphology and dynamics. For 14 galaxies, the classical morphological type differs from the sAMSD-based category. As expected, jstar correlates strongly with Mstar. We also find correlations between jstar and star formation rate, and between jstar and total HI mass. The mean jstar and Mstar for the different jstar types occupy distinct regions along the Fall relation, with significant internal scatter. The link between the two-dimensional sAMSD distribution and global jstar, together with the location of each type in the jstar-Mstar plane, suggests a possible morpho-kinematic evolutionary sequence for late-type galaxies. The mechanisms reshaping galaxies in sAMSD space appear to be related to disc stability: in low-mass systems, angular momentum redistribution may arise from feedback, dynamical friction, shocks, and resonances, whereas in massive spirals it is likely driven by quasi-stationary rotating density waves.
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All authors Juan Manuel Pacheco-Arias, Philippe Amram, Benoît Epinat, Wilfried Mercier

Instrumentation and Methods for Astrophysics · Cross-listed from nlin.CD

Data-Driven Prediction of Chaotic Transition in Periapsis Poincaré Maps

Shanshan Pan, Taiki Urashi, Mai Bando et al. (+3 more)

Chaotic trajectories in multi-body dynamical systems play a crucial role in designing low-energy trajectories in astrodynamics. However, predicting these trajectories is inherently difficult, as small errors in initial conditions can grow exponentially, making long-term predictions unreliable. This study introduces a novel methodology using Dynamic Mode Decomposition (DMD) to predict chaotic transitions in the periapsis Poincaré map of the circular restricted three-body problem (CRTBP). Unlike standard DMD approaches that model continuous equations of motion, the proposed method approximates deformations in a low-dimensional Poincaré map, enabling trajectory prediction and revealing transition structures. Two approaches are developed: the Local Deformation Map-based DMD (LDMD) and the Global Deformation Map-based DMD (GDMD). LDMD constructs discrete maps to track local deformations of periapsis sets, while GDMD captures global deformations using widely distributed data. A key advantage of this framework is that it approximates nonlinear chaotic transport using a linear operator, which enables fast prediction of periapsis evolution via matrix powers and direct access to geometric structures. To validate the proposed method, the deformation map is applied to design ballistic transfer trajectories to the Moon using a targeting strategy, demonstrating its practical relevance in astrodynamics. This work highlights the potential of data-driven modeling to bridge chaotic dynamics with systematic trajectory design.
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All authors Shanshan Pan, Taiki Urashi, Mai Bando, Yasuhiro Yoshimura, Hongru Chen, Toshiya Hanada

Instrumentation and Methods for Astrophysics

A signal dedispersion algorithm for imaging-based transient searches

Cristian Di Pietrantonio, Marcin Sokolowski, Christopher Harris et al. (+2 more)

Dedispersion is the computational process of correcting for the frequency-dependent time delay affecting a radio signal that propagates through the interstellar and intergalactic media. It is a crucial component of transient search pipelines that maximises the signal-to-noise ratio, especially when targeting highly dispersed signals: for instance, pulsar emissions making their way through a dense cloud of ionised gas, and fast radio bursts travelling cosmological distances. This paper introduces Streaming high Time-Resolution Imaging DEdispersion (STRIDE), a novel dedispersion algorithm to generate per-pixel dedispersed time series from high time and frequency resolution interferometric images. Unlike straightforward approaches to image dedispersion, STRIDE does not involve expensive manipulation of the input data layout, such as explicitly building dynamic spectra or shifting images. Furthermore, it is the first dedispersion algorithm to partition a dispersive sweep over the time dimension, in addition to frequency. As a consequence, images corresponding to the entire time span of the target dispersive delay are not required all at once. Instead, the algorithm works with an arbitrarily-sized subset of images at a time, adopting an incremental, streaming-based approach to dedispersion. In evaluating STRIDE on the presented test case, it is shown that the minimum memory requirement is reduced by 97.9%, going from 684.5 GB to 14.4 GB. As current and future generations of widefield interferometers increasingly turn to imaging techniques for detection and localisation of radio transients, STRIDE positions itself as a strong alternative to traditional dedispersion methodologies. It arguably is the only viable option for imaging-based searches with low-frequency instruments such as the Murchison Widefield Array (MWA) and low-frequency Square Kilometre Array (SKA-Low).
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All authors Cristian Di Pietrantonio, Marcin Sokolowski, Christopher Harris, Danny C. Price, Randall Wayth

Solar and Stellar Astrophysics

Wind Accretion in Massive Binaries Experiencing High Mass Loss Rates: II. Eccentricity

Bhawna Mukhija and Amit Kashi

We perform numerical simulations to investigate high-power wind accretion in massive binary systems undergoing enhanced mass-loss episodes. The primary star is taken in the mass range $M_{1} = 60$–$90\,\mathrm{M_{\odot}}$, while the companion is a $30\,\mathrm{M_{\odot}}$ hot star. We model binary orbits with eccentricities of $e = 0$–$0.6$ and orbital periods of $P=455$–$1155$ days. We initiate strong eruptive events for the primary with mass-loss rates of $\dot{M}_{\rm w} = 10^{-2}$ – $10^{-1}\,\rm{M_{\odot}~{yr}^{-1}}$, lasting for $1.5$ years. A fraction of the ejected wind material is accreted by the companion, with the accretion efficiency determined by the orbital separation, eccentricity, and stellar mass ratio. We analyze the resulting accretion rates and provide an analytical relation describing their dependence on the stellar mass ratio, mass-loss rate, and orbital parameters. We find that although the accretion modifies the stellar parameters of the secondary, the companion remains in thermal equilibrium and does not undergo significant radial expansion. We further include wind mass loss from the companion during wind accretion and find a substantial reduction in accretion efficiency compared to no wind scenario. For longer orbital periods, the models yield negative accretion rates, implying that any captured material is expelled or prevented from settling onto the accretor. These results provide new insight into the role of eccentric orbits and extreme mass-loss events in shaping the mass-transfer processes in massive binaries.
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Astrophysics of Galaxies

Spatial Property of Multiple Metallic Populations in the Tidal Stream of {\omega} Centauri

Shiru Zheng, Baitian Tang, Long Wang et al. (+4 more)

{\omega} Centauri, the remnant nucleus of an accreted dwarf galaxy, is a unique laboratory for studying complex stellar populations. The recently discovered Fimbulthul stream provides a fossil record of its ongoing tidal dissolution. In this work, we investigate the spatial distributions of metal-rich and metal-poor populations within {\omega} Centauri and its stream to constrain the cluster's formation history. Using synthetic photometry from Gaia DR3 XP spectra, we classify stars via a Support Vector Classifier (SVC). The spatial distributions are then compared to a scaling N-body simulation performed with the PeTar code. Our analysis reveals no significant radial gradient in population ratios within the cluster, though the metal-rich stars may be slightly more extended. The population ratio in the tidal stream is consistent with that of the present-day cluster, albeit with large uncertainties. Our simulation indicates that any initial radial gradient must have been shallow, with a maximum fraction difference less than 0.15. Both observational and dynamical results suggest that the metal-rich population is not formed centrally concentrated. By combining our results and existing literature, we propose a new formation scenario for {\omega} Centauri.
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All authors Shiru Zheng, Baitian Tang, Long Wang, Jose G. Fernandez-Trincado, Ruoyun Huang, Xia Li, XiaoDong Li

Earth and Planetary Astrophysics · Cross-listed from cs.RO

Emerging trends in Cislunar Space for Lunar Science Exploration and Space Robotics aiding Human Spaceflight Safety

Arsalan Muhammad, Yue Wang, Hai Huang et al. (+1 more)

In recent years, the Moon has emerged as an unparalleled extraterrestrial testbed for advancing cuttingedge technological and scientific research critical to enabling sustained human presence on its surface and supporting future interplanetary exploration. This study identifies and investigates two pivotal research domains with substantial transformative potential for accelerating humanity interplanetary aspirations. First is Lunar Science Exploration with Artificial Intelligence and Space Robotics which focusses on AI and Space Robotics redefining the frontiers of space exploration. Second being Space Robotics aid in manned spaceflight to the Moon serving as critical assets for pre-deployment infrastructure development, In-Situ Resource Utilization, surface operations support, and astronaut safety assurance. By integrating autonomy, machine learning, and realtime sensor fusion, space robotics not only augment human capabilities but also serve as force multipliers in achieving sustainable lunar exploration, paving the way for future crewed missions to Mars and beyond.
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All authors Arsalan Muhammad, Yue Wang, Hai Huang, Hao Wang

Cosmology and Nongalactic Astrophysics

Luminosity-Dependent Variations in the Secondary Maximum of Type Ia Supernovae and Their Connection to Host Galaxy Morphology

Jagriti Gaba, Rahul Kumar Thakur, Dinkar Verma et al. (+2 more)

Type Ia supernovae (SNe Ia) are considered standardizable candles and are therefore important probes of the universe's expansion history and cosmic distances. In comparison to the optical and IR photometric observations, NIR light curves of SNe Ia are more uniform and are less affected by dust extinction; hence, they can provide more precise distance estimates. This study examines the relationship between the luminosity-dependent behavior of the NIR secondary maximum ($t_2$) and the decline rate parameter ($\Delta m_{15}$) in the B Band. We analyzed 54 SNe Ia using linear, piecewise linear regression, and non-linear models along with non-parametric statistical techniques to examine the correlation between $t_2$ and $\Delta m_{15}$. Our results show that the secondary maximum timing varies among SNe Ia but exhibits a luminosity-dependent structure, with significant differences between SNe hosted in late and early-type galaxies. Two separate groups belonging to different host morphologies have been identified through our analysis, one containing brighter SNe and the other containing fainter SNe. These findings have important implications for improving the calibration of SNe Ia for cosmological applications.
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All authors Jagriti Gaba, Rahul Kumar Thakur, Dinkar Verma, Naresh Sharma, Shashikant Gupta

Cosmology and Nongalactic Astrophysics

The many boundaries of the stratified dark matter halo

Jiaxin Han

We review the physics of halo collapse giving rise to various halo boundaries, as well as their identification, observation, and applications. The classical halo is typically defined as a monolithic, virialized object enclosed within its virial radius – a definition which, however, does not account for ongoing halo growth. Continuous accretion causes the orbits of infalling particles to shrink over time, confining newly accreted material in a growing layer outside the virialized region. Several novel halo boundaries, such as the splashback and depletion radii, have recently been proposed to characterize this growth layer from different perspectives. Along with the turnaround radius, which operates on an even larger scale to enclose the entire infall region, these multiple boundaries comprise an extended view of a dark matter halo as a stratified structure. Theoretical models can largely explain the existence of various boundaries, while challenges remain in providing unified and quantitative predictions of their properties. The multiple boundaries open new avenues for observing halo growth and may substantially improve our understanding and modeling of cosmic structure formation. We provide a python package, SpheriC, implementing the key spherical collapse models.
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Solar and Stellar Astrophysics

Gaia DR3 high radial velocity stars: Genuine fast-moving objects or outliers?

D. Katz, A. Gómez, E. Caffau et al. (+39 more)

The third Gaia data release includes 33.8 million radial velocity measurements, extending to a magnitude of G_RVS = 14. To reach this magnitude limit, spectra were processed down to a signal-to-noise ratio (S/N) of 2. In this very low S/N regime, noise-induced peaks in the cross-correlation function can result in spurious radial velocity determinations. Quality filters were applied to the dataset to mitigate such artefacts as much as possible prior to publication. Nevertheless, the high radial velocity (HRV) stars – defined here as those with radial velocities below -500 or above +500 km/s – are so sparsely populated that even a few hundred spurious measurements can lead to significant contamination. The objectives of the present study are as follows: (i) to confirm or refute the radial velocity values of the order of one hundred Gaia DR3 HRV stars, (ii) to evaluate the rate of spurious radial velocities in the Gaia DR3 catalogue as a function of S/N and radial velocity, and (iii) to examine the properties of the genuine HRV stars. A total of 134 Gaia DR3 HRV stars were observed using the SOPHIE and UVES spectrographs. (abridged) Ground-based measurements confirm the Gaia DR3 radial velocities of 104 out of our 134 targets, and they refute those of the remaining 30. The combination of these data with the spectroscopic surveys mentioned above enabled an assessment of the rate of spurious measurements as a function of S/N and across three intervals of absolute value of the radial velocity. (abridged) The majority of these stars follow retrograde orbits. Their location in the energy-vertical component of the angular momentum diagram coincides with the region where several structures associated with past merging events have been identified: Sequoia, Arjuna and I'itoi, Antaeus, ED-2, and ED-3. It is likely that most of these HRV stars were accreted.
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All authors D. Katz, A. Gómez, E. Caffau, P. Bonifacio, C. Hottier, O. Vanel, C. Soubiran, P. Panuzzo, D. Chosson, P. Sartoretti, R. Lallement, P. Di Matteo, M. Haywood, N. Robichon, S. Baker, A. Barbier, D. Bashi, K. Benson, R. Blomme, N. Brouillet, L. Casamiquella, L. Chemin, M. Cropper, Y. Damerdji, C. Dolding, S. Faigler, Y. Frémat, E. Gosset, A. Guerrier, R. Haigron, H.E. Huckle, N. Leclerc, A. Lobel, O. Marchal, T. Mazeh, A. Mints, F. Royer, G. M. Seabroke, M. Smith, O. Snaith, F. Thévenin, K. Weingrill