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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 22 June

Earth and Planetary Astrophysics

Characterising transiting exoplanets at long orbital period: lessons learned for PLATO from 10 years of monitoring the HIP41378 system

Alexandre Santerne, Salomé Grouffal and Stéphane Udry

The upcoming launch of the PLATO mission will open a new area of exoplanetary research by probing transiting exoplanets at long orbital periods around bright stars. These planets will be amenable to follow-up observations, especially with the ESO telescopes as the first PLATO field is in the southern sky. In this paper we listed the lessons we learned by monitoring the bright HIP41378 multi-planetary system over one decade via both radial-velocity and transit observations. These lessons are important for the follow-up strategy of PLATO transiting exoplanets.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Detector orientation matters: Consequences for gravitational-wave background detectability

Nelson Christensen, Joseph D.Romano, Mairi Sakellariadou et al. (+1 more)

Cross-correlation searches for gravitational-wave backgrounds depend on the geometrical configuration (physical separation and relative orientation) of the detectors comprising the network. Applying standard techniques to a few simple examples, we illustrate how the relative orientation of a pair of Earth-based L-shaped laser interferometers can drastically impact the detectability of both isotropic and anisotropic gravitational-wave backgrounds.
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All authors Nelson Christensen, Joseph D.Romano, Mairi Sakellariadou, Jishnu Suresh

Instrumentation and Methods for Astrophysics · Cross-listed from stat.CO

First analytical coverage bounds of a fully specified nested sampling algorithm

Johannes Buchner

Nested sampling is a Monte Carlo algorithm for posterior estimation and Bayesian model comparison. It maintains a population of $K$ live points sampled from the prior, and at each iteration discards the lowest-likelihood point and replaces it with a new sample drawn from the prior restricted to exceed the discarded likelihood. Achieving this likelihood-restricted prior sampling efficiently and reliably is the central computational challenge. For low-to-moderate dimensional problems, MLFriends is a general and robust region-based approach that constructs a proposal region by bootstrap aggregation over the current live points and rejects proposals outside this region. We present a self-contained mathematical formulation of MLFriends and derive, under a homogeneous Binomial point process model for the live points, heuristic bounds on the expected fraction of the likelihood-restricted prior not covered by the proposal region. These bounds decay as $(\frac{1}{3}Km)^{-3/2}$, where $m$ is the number of bootstrap rounds, and are negligibly small for practical parameter choices. We show heuristically that the resulting bias in the marginal likelihood estimate is negligible compared to the inherent statistical variance of a nested sampling run. While a fully rigorous treatment remains an open problem, these results provide the first analytical characterisation of a fully specified and practically implementable nested sampling algorithm, without assuming an idealised or asymptotic sampling procedure.
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Instrumentation and Methods for Astrophysics · Cross-listed from stat.CO

Mode Collapse in Nested Sampling

Johannes Buchner

Nested Sampling is a Monte Carlo algorithm enabling posterior estimation and Bayesian model comparison, and is especially robust in multi-modal posteriors. This is because nested sampling maintains a population of live points sampled from the entire prior. In each iteration, the population is advanced above a likelihood threshold, potentially discarding modes ruled out by the data. However, the Monte Carlo nature of point replenishment can also accidentally discard a mode. We draw a connection to the neutral Moran process in genetics, and quantify the occurrence probability of this failure mode of nested sampling with a simple symmetric random walk model on the live point occupancy. We find a simple rule for setting the minimum number of live points so that mode die-out is made unlikely.
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Solar and Stellar Astrophysics

Influence of mass-transfer stability on the formation of post-common-envelope binaries

Yanxu Shi, Hongwei Ge, Zhenwei Li et al. (+9 more)

Post-common-envelope binaries are the natural laboratories for constraining the physics of common envelope evolution, which is one of the most uncertain phases in binary stellar evolution. Traditional binary population synthesis models, adopting mass transfer stability criteria based on polytropic stellar models, systematically overpredict the number of post-common-envelope binaries with solar-type main-sequence companions. In this work, we present an updated binary population synthesis model using the rapid binary evolution code Binary Star Evolution, incorporating a physically motivated mass transfer stability criterion and a self-consistent envelope binding energy prescription. We compile a comprehensive sample of classic white dwarf + main sequence post-common-envelope binaries with well-measured parameters, hosting both M-dwarf and A/F/G/K- stars. We find that the enhanced mass transfer stability is an additional mechanism responsible for the observed dearth of post-common-envelope binaries with solar-type main sequence companions; neither magnetic braking nor selection effects alone can fully account for this deficit, and a combination of all three processes is most likely required. Models with inefficient common envelope evolution ($\alpha_{\rm CE}=0.25$) provide the best overall match to the observed population. These results highlight the critical role of MT stability in shaping the observed post-common-envelope binaries population and provide new constraints on common envelope evolution.
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All authors Yanxu Shi, Hongwei Ge, Zhenwei Li, Diogo Belloni, Rizhong Zheng, Dengkai Jiang, Hailiang Chen, A. Santos-Garcia, Santiago Torres Gil, Alberto Rebassa-Mansergas, Xuefei Chen, Zhanwen Han

High Energy Astrophysical Phenomena

Are most detected tidal disruption events partial?

Megha Sharma, Daniel J. Price, Alexander Heger et al. (+1 more)

During a tidal disruption event (TDE), a star loses mass due to the tidal gravitational forces of the black hole. In a partial tidal disruption event, a stellar remnant is left behind. Several dozen TDEs have been detected so far, including repeating partial events. We use the Phantom smoothed particle hydrodynamics code to model the disruption of a 1 Msun star around a 10^6 Msun black hole for impact parameters resulting in less than equal to 50 % mass loss. We only consider zero energy orbits. Our simulations show that the mass fallback rate can exceed the Eddington limit for beta greater than or equal to 0.8, allowing debris to obscure the accretion disc by forming a reprocessing layer, similar to full TDEs. The mass fallback rate is shallower than t^{-5/3}, tracking closer to t^{-9/4}. Assuming thermal emission from the debris, that shock heating is trapped, that electron scattering dominates the opacity, and a color correction f_{col} of 1.7, we find temperatures of ~10^4 K, optical bolometric luminosities of ~ 10^{42-44} erg/s and blackbody radii ranging from 10-100 au for our simulations. We compare our values with observations and find support for the previous argument that some TDEs classified as full disruptions might actually be partial. Moreover, our results explain the detected optical/UV TDEs. We also find that our zero energy partial TDEs have properties similar to the repeating partial TDEs such as ASSASN-19dj, ASSASN-14ko, ASSASN-18ul, ASSASN-22ci, AT2020vdq and AT2022dbl. In the beta=0.8, isentropic simulation where radiation is assumed to escape, we find X-ray luminosities of ~ 10^{44-45} erg/s and radii lower than the inner most stable circular orbit.
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All authors Megha Sharma, Daniel J. Price, Alexander Heger, Katie Auchettle

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Diffuse Supernova Neutrinos with Secret Neutrino Interactions

Praveen Bharadwaj, Utpal Chattopadhyay, Dilip Kumar Ghosh et al. (+1 more)

The Diffuse Supernova Neutrino Background (DSNB), an isotropic flux arising from the cumulative neutrino emission of all stellar core-collapse events throughout cosmic history, is expected to be detected by next-generation neutrino observatories. As DSNB neutrinos propagate over cosmological distances through the cosmic neutrino background (C$\nu$B), they may undergo non-standard neutrino self-interactions ($\nu$SI), leaving distinct spectral imprints on the observed flux. In this work, we investigate the impact of scalar ($\phi$)-mediated $\nu$SI on the DSNB within a full three-flavor framework that retains the complete PMNS structure. We consider four representative flavor-diagonal coupling structures–universal, $e$-, $\mu$-, and $\tau$-specific. The resonant scattering $\nu_i\nu_k\to\phi\to\nu_j\nu_l$ off the lightest, relativistic C$\nu$B state produces broad spectral depletion whose pattern depends on the coupling structure and the neutrino mass ordering, generating distinctive signatures across the six flavor fluxes. We compute the resulting event spectra at JUNO, Hyper-Kamiokande with gadolinium loading, and DUNE, and derive projected $3\sigma$ sensitivities in the $(m_{\phi},~g)$ parameter plane. We find that these experiments can probe couplings as low as $g\sim10^{-8}$ for $m_\phi\sim100$–$300$ eV, surpassing existing bounds by up to a few orders of magnitude in the sub-100 eV mass range. Moreover, unlike the flavor-blind cosmological and supernova bounds, the DSNB sensitivity is flavor-discriminating, offering a unique opportunity to identify the underlying flavor structure of $\nu$SI in the event of a detection.
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All authors Praveen Bharadwaj, Utpal Chattopadhyay, Dilip Kumar Ghosh, Arnab Sarker

Solar and Stellar Astrophysics

X-shooter spectroscopy of giant stars in the nuclear star cluster

L. Origlia, C. Fanelli, A. Mucciarelli et al. (+5 more)

Near-IR spectra of a homogeneous sample of 15 red giants in the Galactic nuclear star cluster, within 1.5 pc of SgrA*, have been acquired with X-shooter at the Very Large Telescope. From these spectra line-of-sight radial velocities and chemical abundances of iron, carbon, oxygen and other alpha and light elements have been derived. By combining radial velocities from this study and proper motions from the literature we computed the orbits of these stars, finding that they have been confined within 12 pc from SgrA* for their entire lifetime, thus strongly suggesting an in-situ formation and evolution. Iron abundances between half and twice solar, about solar-scaled values within +/-0.1 dex for {\alpha} elements, Ti and V, some enhancement of [Na/Fe], [K/Fe] and [Al/Fe] and some depletion of [C/Fe] with respect to the solar ratios have been measured. The inferred chemical abundance distributions are consistent with a formation from a gas enriched by both type II and type I SNe over a prolonged timescale, closely matching those of the metal-rich populations of the inner bulge field and other complex stellar systems like Terzan 5 and Liller 1.
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All authors L. Origlia, C. Fanelli, A. Mucciarelli, R. M. Rich, M. Schultheis, N. Ryde, B. Thorsbro, T. Fritz

High Energy Astrophysical Phenomena

Testing the Generalization and Domain Stability of Compact Feature Representations for Photometric Supernova Classification

Anurag Garg

Photometric classification of supernovae increasingly requires models that are not only accurate within a single survey but also robust to changes in cadence, noise properties, filter coverage, and survey domain. We investigate the generalization and domain stability of a compact 16-feature representation for Type Ia supernova classification. The feature set consists of physically interpretable descriptors of brightness, color, variability, and temporal evolution. Using the Supernova Photometric Classification Challenge (SPCC) dataset as the reference domain, we confirm that a compact XGBoost classifier achieves strong within-survey performance, reaching an F1 score of 0.844 and a PR-AUC of 0.928 on a held-out test set. We then evaluate robustness under alternative classifiers, repeated resampling, feature perturbations, missing-band proxies, shortened temporal coverage, and cross-survey transfer to PLAsTiCC. The compact representation remains stable under resampling and moderate perturbations, but direct SPCC$\rightarrow$PLAsTiCC transfer produces a substantial performance degradation. Class-conditional centroid analysis shows that the SPCC and PLAsTiCC Type Ia populations occupy different regions of the compact feature space. The cross-survey Ia centroid shift exceeds the Ia/non-Ia separation within either survey, indicating that the transfer gap is driven primarily by feature-space domain shift rather than classifier instability. These results show that compact physically interpretable features are robust within a survey and useful for diagnostic analysis, but are not automatically survey-invariant. Cross-survey deployment therefore requires feature harmonization, domain adaptation, or restriction to a smaller set of survey-stable features.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.AI

AI Scientists as Engines of Discovery: A Case for Development within Reformed Institutions

Raul Jimenez, Boris Bolliet, Francisco Villaescusa-Navarro et al. (+7 more)

Agentic artificial intelligence (AI) systems are beginning to assist, accelerate, and partially automate scientific discovery, performing tasks that span literature synthesis, code generation, data analysis, hypothesis proposal, and model criticism. We argue that this transition is qualitative rather than incremental, and that suitably designed multi-agent systems may evolve from passive computational tools into “AI scientists” that can expand the hypothesis-generating and verification capacity of science. Such systems must be developed and deployed within a scientific ecosystem fit for purpose: institutions must be redesigned for verification, accountability, interpretability, and dual-use safety. We sketch how multi-agent architectures, illustrated by the prototype framework Denario, accelerate the discovery cycle and traverse model spaces beyond human reach; examine what this implies for authorship, peer review, and the enduring role of human scientists; and close with recommendations for governing AI as an epistemic actor rather than a mere instrument.
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All authors Raul Jimenez, Boris Bolliet, Francisco Villaescusa-Navarro, Rabih Zbib, Benjamin Wandelt, David N. Spergel, Thomas Meier, Jessica Montgomery, Hana Aliee, Licia Verde

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Remarks on atmospheric effect of D-foam in light of muon puzzle

Chengyi Li

In our recent paper~[1], we used a stringy model for quantum space-time foam to suggest that the so-induced subluminal Lorentz violation~(LV) for photons would not lead to experimentally unacceptable changes in the developments of particle showers initiated by cosmic $\gamma$-rays in the Earth's atmosphere, in contrast to other approaches to LV. The result indicated, nonetheless, at the same time that the foam can mildly modify the electromagnetic cascades under certain conditions, by suppressing pair creation on nuclei by primary photons. In this addendum, we consider how this modification affects the detection of extensive air shower~(EAS) initiated by an ultrahigh-energy cosmic-ray particle~(viz., a primary hadron), like proton with $E \sim 10^{19}~\textrm{eV}$, given that secondary photon subshowers following $\pi^{0}$ decays could be similarly influenced. We argue that fewer electrons would reach the detector and hence the energy of the primary particle may be underestimated due to foam effects, enhancing in such a way the muon content in EASs. This opens up the possibility of interpreting the alleged “excess” of muons, as reported by Auger and Telescope Array collaborations recently and many other experiments on high-energy cosmic rays, with a quantum-gravitational effect. Future observations are anticipated to confirm whether this anomaly really exists.
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Astrophysics of Galaxies

Observations of a Possible Transient Magnetically Arrested Accretion State in a Nearby Quasar: OQ208

Brian Punsly, Cormac Reynolds, Paola Marziani et al. (+12 more)

OQ208 is a nearby, partially obscured quasar (z=0.077) that is a young, bright, parsec scale radio source. We assemble archival and new high frequency VLBA and VLA observations and optical spectra to form a data-set spanning 39 years. Radio light curves covering 58 years were also compiled. We utilize new spectrophotmetry to calibrate previous spectroscopy using forbidden narrow lines that are expected to be stable on much longer time scales. VLBA and VLA observations of a light-year scale bright nuclear flare at 15.4~GHz and 22~GHz reveal a rise (fade) beginning in mid-1996 (early-2000). Quasi-contemporaneously, from 2/7/1997-6/3/2000, the H$\alpha$ broad line equivalent widths (EWs) and fluxes dropped dramatically. In the context of the tendency of radio loud quasars to have a depressed extreme ultraviolet (EUV) continuum (the main source of ionizing flux for H$\alpha$) relative to radio quiet quasars at matched UV luminosity (the EUV deficit of radio loud quasars), this may not be a coincidence. Analytic models previously developed to explain the relationship between jet power and the EUV deficit are consistent with (but not direct observational proof of) the small EWs being a consequence of transient magnetically arrested accretion states from $\sim1997-2001$. The 22 GHz VLBA nucleus gradually fades, in 2023 the flux density is $<5\%$ of its value in 2000. The environs of the nucleus also fade at 22 GHz, but in a time delayed fashion.
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All authors Brian Punsly, Cormac Reynolds, Paola Marziani, Gary J. Hill, Alexander B. Pushkarev, Carlo Stanghellini, Frank Schinzel, Christopher O'Dea, Gregory R. Zeimann, Andrew Biggs, Jian-Min Wang, Pu Du, Alberto Floris, Mauro D'Onofrio, Levi Malmstrom

Solar and Stellar Astrophysics

Surface brightness-color relations for red giant branch stars: Observational constraints on metallicity effects using the ARD method

Jianping Xiong, Xiaodian Chen, Jiao Li et al. (+5 more)

Aims: We aim to quantify the metallicity dependence of the SBCR for red giant branch (RGB) stars and to test the robustness of the relation using asteroseismic radii, Gaia distances, and atmospheric parameters from APOGEE. Methods: We selected more than 2,000 RGB stars from APOKASC-3 to calibrate and validate the SBCR. Johnson V magnitudes were synthesized from Gaia XP spectra and homogenized to widely used SBCR photometric systems, while K_s photometry was taken from 2MASS. Angular diameters derived from asteroseismic radii and Gaia distances (ARD) were used to construct the SBCR. We explored three fitting strategies: metallicity-free, metallicity-binned, and global metallicity-dependent relations. Results: Over the range V-K_s=2-3, the SBCR shows only a weak metallicity dependence. A change of 1 dex in [Fe/H] modifies the predicted angular diameter by less than 1%, well below the intrinsic scatter of the calibration (~0.05 mag). This result is consistent with theoretical expectations. Comparison with the interferometric sample reveals a systematic offset of ~1.5% toward smaller angular diameters in our SBCR predictions, with a mild color dependence. Conclusions: The metallicity effect on the SBCR is small in the color range explored here, but it becomes relevant for sub-percent distance measurements. Our results show that large RGB samples with asteroseismic radii and Gaia distances provide a powerful observational route for SBCR calibration, with clear potential for extension to cooler and redder giants as the precision and parameter coverage of the input data improve.
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All authors Jianping Xiong, Xiaodian Chen, Jiao Li, Qiyuan Cheng, Xiaobin Zhang, Chao Liu, Zhanwen Han, Xuefei Chen

Astrophysics of Galaxies

Highly filamentary H{\,\small I} gas in the circumgalactic medium and intragalactic medium around NGC 4631

C. Zhang, Tie Liu, Xiaofeng Mai et al. (+1 more)

Neutral hydrogen (H{\,\small I}) in the circumgalactic medium (CGM) and intergalactic medium (IGM) traces baryon cycling and galaxy evolution, yet fine filamentary substructures in diffuse CGM/IGM H{\,\small I} remain poorly constrained observationally. We combine FAST FEASTS single-dish and VLA THINGS interferometric H{\,\small I} data of the NGC 4631 group to report the first robust detection of kpc-scale filamentary structures in the CGM/IGM, with widths of $0.5$-$3.3\ \mathrm{kpc}$ and lengths of $6.1$-$49.8\ \mathrm{kpc}$. These features confirm that low-density CGM/IGM gas hosts velocity coherent substructure. From position-velocity kinematic analysis, we identify three filament classes (U-shaped, linear, and wavy), implying diverse formation mechanisms. Our results establish a structural bridge connecting pc-scale interstellar filaments, kpc-scale CGM/IGM filaments, and Mpc-scale cosmic-web filaments, providing key observational support for multiscale gaseous coupling in cosmic ecosystem.
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All authors C. Zhang, Tie Liu, Xiaofeng Mai, Jing Wang

Astrophysics of Galaxies

Black Hole Occupation Fraction: Dependence on Black Hole Mass Threshold, Environment, Resolution and Redshift

Emanuele Contini, J.K. Jang, Jinsu Rhee et al. (+2 more)

We take advantage of the state-of-the-art semi-analytic model FEGA25 \citep{contini2025}, run on merger trees extracted from three dark matter-only cosmological simulations, to study the relation between the black hole (BH) occupation fraction, $f_{\rm BH,occ}$, and galaxy stellar mass as a function of BH mass threshold, galaxy type, simulated volume, numerical resolution, sampled galaxy population, and redshift. FEGA25 includes an improved treatment of active galactic nucleus feedback and does not impose a pre-existing BH seed population: BHs grow naturally through quasar and radio modes. Starting from the prerequisite that FEGA25 reproduces the observed BH mass function from at least $z=2$ to the present day, our analysis leads to several results. We find that $f_{\rm BH,occ}$ increases with stellar mass, but that its normalization and shape depend strongly on the adopted BH mass threshold and on the relative contribution of central and satellite galaxies. The relative behavior of central and satellite galaxies depends on the simulation box and BH mass threshold, while the global relation should be interpreted as a population-weighted quantity. We also find significant box-to-box variations, reflecting the combined impact of numerical resolution, simulated volume, and sampled galaxy population. The redshift evolution is not universal: YS50 and the NewCluster zoom-in simulation show a trend qualitatively similar to that reported by \citet{tremmel2024}, whereas larger-volume boxes show the opposite behavior. Finally, comparison with other studies shows that the inferred occupation fraction is highly sensitive to BH mass threshold, simulated volume, numerical resolution, and sampled galaxy population.
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All authors Emanuele Contini, J.K. Jang, Jinsu Rhee, Changjo Seo, Sukyoung K. Yi

Sunday 21 June

Instrumentation and Methods for Astrophysics

Carruthers Data Processing Pipeline: Radiometric Responsivity Calibration

Alex Zhang, Heather Filippini, Gonzalo Cucho-Padin et al. (+5 more)

The Carruthers Geocorona Observatory is NASA's first mission dedicated to investigating the fundamental nature of Earth's exosphere and its dynamic response to space weather. Its primary payload, the GeoCoronal Imager, consists of two co-aligned broadband photometric imagers that support simultaneous, common-volume sensing of ultraviolet emission at 121.6 nm (Lyman-alpha) by exospheric hydrogen atoms. Accurate exospheric parameter retrieval from these images requires accurate knowledge of the instrument's optical responsivity, which enables conversion of measured exospheric signal rates into the scientifically relevant quantity of emission radiance. The Carruthers mission achieves absolute sensitivity calibration through the acquisition of photometric measurements of stars and subsequent inversion of the observed fluxes to retrieve the wavelength-dependent responsivity across the passband for each imaging configuration. The retrieval algorithm performance is enhanced by its incorporation of an objective, algorithm-driven ranking criterion to systematically select target calibration stars from a stellar spectral library. The end-to-end workflow, from the stellar selection criterion to the passband inversion, is validated using synthetically generated stellar measurements. These validation tests establish that our optical responsivity retrieval approach has high recovery fidelity, achieving error rates of <5% at the Lyman-alpha wavelength for all primary science imaging modes.
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All authors Alex Zhang, Heather Filippini, Gonzalo Cucho-Padin, Lara Waldrop, John Clarke, Pratik Joshi, Parisa Karimi, Martin M. Sirk

High Energy Astrophysical Phenomena

Finite-volume scheme for first-order viscoresistive relativistic magnetohydrodynamics

Ruben Lier, Jay Armas and Oliver Porth

We present a numerical implementation of dissipative relativistic magnetohydrodynamics based on Bemfica-Disconzi-Noronha-Kovtun (BDNK) theory, in which first-order corrections render the equations causal without introducing additional dynamical variables. We show how these corrections can be incorporated in a finite-volume scheme describing the coupled dissipation of energy, momentum, and magnetic field, with the latter treated as a one-form charge. While a minimal set of BDNK terms can convert diffusive equations into telegrapher-type equations, we find that in the ultra-relativistic limit an additional correction is required for the system to behave in a stable and causal manner. With this set of equations, we develop an efficient method for primitive-variable recovery and validate the implementation through an analytical benchmark and various two-dimensional simulations.
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High Energy Astrophysical Phenomena

Polarization Angle Geodesics in PSRs B1133+16 and B2016+28

M. M. McKinnon

Recent models of pulsar polarization predict that the position and ellipticity angles of the polarization vector can trace portions of a small or great circle on the Poincare sphere. A great circle can arise from a transition in dominance of orthogonal polarization modes, where the relative intensity of the modes changes with pulse longitude. A small circle may be caused by a rotation of the vector, where the phase difference between the modes changes with pulse longitude or wavelength. Observations of PSRs B1133+16 and B2016+28 are reanalyzed to search for these polarization features within their pulse profiles. The polarization angles observed in part of PSR B1133+16 are shown to follow a great circle on the Poincare sphere. The angles observed across the pulse of PSR B2016+28 follow an arc that resembles a portion of a great circle that has been altered by the pulsar's rotation. The observations are interpreted within the context of three different polarization models. All three models produce similar results for both pulsars and indicate that the observed geodesics are caused by mode transitions. The arc observed in PSR B2016+28 can also be interpreted as a vector rotation, provided the modes are elliptically polarized. The observations and accompanying analysis show that mode transitions are not restricted to the equatorial plane of the Poincare sphere and that arcs and partial circles may be more common than previously recognized.
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Solar and Stellar Astrophysics

Comparative Study of Two Luminous Red Novae I. Progenitor Modeling and Dust Formation

M. Wavasseur, N. Blagorodnova, M. A. Gómez-Muñoz et al. (+1 more)

Luminous red novae are astrophysical transients associated with unstable mass transfer in interacting binaries and are commonly interpreted as outcomes of common-envelope evolution, possibly ending in merger. These interactions can liberate large amounts of gas, part of which may later condense into dust. We study the luminous red novae AT2021biy and AT2021blu to constrain their binary progenitors, estimate the mass ejected during the outbursts, and infer the dust mass from the infrared evolution of their remnants. We computed two grids of binary stellar-evolution tracks with the MESA binary module, constrained by pre-outburst photometry. We applied mass-transfer instability criteria to select progenitors able to merge on timescales compatible with archival observations. From these models, we estimated the gas mass lost during the mass-transfer phase and lower and upper bounds on the envelope mass that could be ejected during common-envelope evolution using the available orbital energy. We compared these ejecta-mass estimates with values inferred from light-curve models. Finally, we modeled mid-infrared NEOWISE data to derive dust masses up to ~3 years post-outburst, providing an additional lower limit on the total ejecta mass. We constrained the donor masses to Md = 18-23 Msun for AT2021biy and Md = 14 +/- 0.5 Msun for AT2021blu. Lower limits on the ejected envelope mass are 0.03-2.98 Msun for AT2021biy and 0.02-0.1 Msun for AT2021blu. Comparison with light-curve models favors intermediate mass ratios, q = 3-10 for AT2021biy and q = 5-15 for AT2021blu. The inferred dust masses are 1-5 orders of magnitude below the estimated ejected envelope masses, implying that only a small fraction of the gas condenses into dust. Their evolution is consistent with shock interaction and suggests pre-existing circumstellar material, in line with the pre-outburst mass loss predicted by our MESA models.
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All authors M. Wavasseur, N. Blagorodnova, M. A. Gómez-Muñoz, O. R. Pols

Cosmology and Nongalactic Astrophysics

Understanding the non-Gaussian nature of Galactic foreground emissions towards small scales

Fazlu Rahman, Pravabati Chingangbam, Kevin Huffenberger et al. (+4 more)

We present a unified, multi-scale study of non-Gaussianity of Galactic foreground emissions using Minkowski Functionals and generalized skewness-kurtosis parameters, focusing on the characterization of small-scale non-Gaussianity and its underlying physical origin. We find that all foreground components studied exhibit a remarkably universal non-Gaussian nature dominated by excess kurtosis, whose shape remains stable across angular scales despite large differences in emission physics. Focusing on thermal dust, we perform a detailed comparison between observed maps (GNILC and Planck 545 GHz) and dust model realizations (PySM and filament-based models) to assess the performance of state-of-the-art models in reproducing the observed non-Gaussian properties. At the global level, GNILC and PySM display closely matched kurtosis behavior over the angular scales where the GNILC reconstruction is reliable, while the filament-based model produces substantially weaker skewness and kurtosis signals. For PySM, however, a patch-based analysis reveals statistically significant regional variations, indicating that while the model reproduces the overall non-Gaussian amplitude and scale dependence, it does not fully capture the spatial variability of the observed kurtosis signal. Using simple PDF-based toy models, we demonstrate that the universal kurtosis signature arises from the combination of heavy-tailed one-point statistics and steep large-scale spatial correlations, while its detailed amplitude and scale dependence depend on the underlying foreground physics. These results identify excess kurtosis as a robust statistical fingerprint of Galactic foregrounds and provide a practical framework for validating small-scale foreground models for future CMB analyses.
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All authors Fazlu Rahman, Pravabati Chingangbam, Kevin Huffenberger, Tuhin Ghosh, Dmitri Pogosyan, Tarun Souradeep, Changbom Park

Cosmology and Nongalactic Astrophysics

Radio spectral properties and aging of two tailed radio galaxies in a galaxy group at z=0.35

Paula Vulić, Vernesa Smolčić, Alexis Finoguenov et al. (+3 more)

We present a study of two tailed radio galaxies in the core of a massive, dynamically young galaxy group - an early group-group merger. Using VLA (3 GHz and 1.4 GHz), MeerKAT (1.35 GHz), and GMRT (610 and 325 MHz) observations, we investigate their radio spectral properties, spectral and dynamical ages. Radio morphologies show clear evidence of interaction with the intragroup medium (IGM). One galaxy is a wide-angle tail (WAT) source, while the other is most likely a head-tail (HT) galaxy. Both galaxies exhibit high radio luminosities, and we find spectral indices of $\alpha=0.8\pm 0.1$ (WAT) and $\alpha=0.6\pm 0.2$ (HT). Spectral index analysis reveals spectral steepening with distance from the core in both galaxies, with localized flattening in the WAT lobes and hotspots along the northern jet, and indications of such flattening in the middle of the HT tail. Spectral ages derived using Jaffe-Perola model are $33.80\substack{+7.63 \\ -7.23}$ Myr (WAT) and $20.86\substack{+10.07 \\ -17.17}$ Myr (HT), significantly lower than dynamical ages of $420\pm60$ to $700\pm100$ Myr (WAT) and $140\pm20$ Myr (and possibly up to $280\pm40$ Myr, for HT), yielding dynamical-to-spectral age ratios of $\sim12-20$ and $\sim7$ (and up to $\sim14$), respectively. The discrepancy may be reduced by using more complex dynamical age models, incorporating interactions with the IGM, which requires deeper X-ray observations of the group. Spectral age estimates may be affected by mixing of electron populations, and could be better constrained with future deep, high-resolution broad-band radio observations at both MHz and frequencies above 3 GHz. The combination of extended radio structures, spectral signatures of radiative aging with localized re-acceleration, and activity timescales up to hundreds of Myr indicates that galaxies are actively interacting with, and likely depositing energy into their environment.
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All authors Paula Vulić, Vernesa Smolčić, Alexis Finoguenov, Ghassem Gozaliasl, Hiddo Algera, Ivan Delvecchio

Astrophysics of Galaxies

On the Tully-Fisher Relation for Active Galaxies – I: Evidence of Larger Scatter

Justin H. Robinson, Mitchell Revalski, Misty C. Bentz et al. (+12 more)

We present an investigation of the Tully-Fisher (TF) relation solely for galaxies hosting an active galactic nucleus (AGN). Using 22 galaxies with primary, z-independent distances, we find that active galaxies exhibit significantly larger scatter about all TF relations compared to each respective calibration for (largely) inactive galaxies. The larger scatter persists despite removal of the AGN contamination from the photometry of the Type 1 AGNs via 1) careful surface brightness decompositions or 2) employing SEDs to constrain the light contribution of the AGN. These results suggest that the influence of an AGN on its host galaxy's surface brightness may extend beyond the nucleus. We also calculate the percentage difference between TF and primary distances, and find that TF-based distances are biased towards overestimation of the primary distances to active galaxies by anywhere from 5-10 percent for the optical/near-infrared and approximately 15 percent for distances predicted from inverting the Baryonic TF (BTF) relation. As TF-based distances (especially the I-band) are relied on heavily for analysis and modeling of the local peculiar velocity (Vpec) field, we suggest that active galaxies be removed from future Vpec modeling samples.
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All authors Justin H. Robinson, Mitchell Revalski, Misty C. Bentz, D. Michael Crenshaw, Hélène M. Courtois, Veronica Lahue, Julian Falcone, Rachael L. Merritt, Ishita Chintala, Thomas Kay, Mira Menon, Naveen Ali, Bradley Clemons, Atul Gautam, Thomas Gregoire

Instrumentation and Methods for Astrophysics · Cross-listed from stat.ME

OASIS: Observation-Aware Simulation-Based Inference via Distributional Matching

Arya Farahi, Conghao Zhou and Ritwik Vashistha

We introduce OASIS, a simulation-based inference framework for scientific settings where observations are distorted by measurement error, selection effects, and other survey-specific transformations. In many real applications, simulators generate latent, noiseless quantities, while the data are observed only after passing through a complex observational pipeline. Standard simulation-based inference methods often ignore this distinction, comparing observations to idealized simulator outputs or relying on low-dimensional summaries that can miss important structure. OASIS addresses this mismatch by explicitly embedding the observation model into the simulator and performing inference directly at the level of observed-data distributions. The method constructs a pseudo-posterior by reweighting prior samples according to a maximum mean discrepancy (MMD) loss between the empirical distributions of the observed data and forward-simulated observations, thereby avoiding both handcrafted summaries and learned neural surrogates. We provide theoretical guarantees for Monte Carlo consistency, convergence of the empirical pseudo-posterior to its population counterpart, and posterior concentration on the MMD-identified parameter set, with consistency for the true parameter under correct specification and identifiability. In controlled errors-in-variables regression experiments, OASIS delivers robust parameter recovery and well-calibrated uncertainty under heterogeneous and non-Gaussian measurement noise. We then demonstrate the method on a realistic cosmological application involving galaxy cluster observations across multiple wavelengths, in which latent physical properties are linked to observables through nonlinear scaling relations, heteroscedastic errors, selection functions, and incomplete coverage.
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Astrophysics of Galaxies

Migration Traps as Variability Attractors. I. Optical/UV Signatures of Embedded Stellar-Mass Black Holes in Active Galactic Nucleus Disks

Jing-Tong Xing, Tong Liu, Mouyuan Sun et al. (+5 more)

We investigate whether embedded stellar-mass black holes (sBHs) in active galactic nucleus (AGN) disks can leave observable optical/UV variability signatures through migration-trap-driven magnetic heating. This mechanism operates when sBHs migrating toward torque-balance radii pile up near migration traps, triggering localized, stochastic magnetic reconnection that heats the disk atmosphere. It is potentially important because it provides a physical source of non-coronal disk heating and directly links optical/UV continuum variability to otherwise hidden compact-object populations. By coupling a one-dimensional sBH population synthesis model with a corona-heated accretion-disk reprocessing variability framework, we show that migration traps concentrate sBHs at preferred radii and generate localized, stochastic reconnection heating. The resulting heating is self-regulated: sBH pile-ups enhance the reconnection rate, while gap opening reduces the local gas density and partially suppresses the reconnection power. This heating produces excess short-timescale optical/UV variability, flattened short-term structure functions, and deviations from the standard $\tau\propto\lambda^{4/3}$ lag-wavelength relation, which describes the time delay between variability at different wavelengths for a standard thin accretion disk. These signatures are strongest at low-to-moderate Eddington ratios, and related observations could provide indirect evidence for embedded compact-object populations in AGN disks.
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All authors Jing-Tong Xing, Tong Liu, Mouyuan Sun, Ya-Ping Li, Shuying Zhou, Zhen-Yi Cai, Da-Bin Lin, Jian-Min Wang

Earth and Planetary Astrophysics

Parameterizing slantwise convection in icy moon oceans

Yaoxuan Zeng and Malte F. Jansen

Convection in icy moon oceans is strongly influenced by rotation, organizing into slantwise columnar structures aligned with the planetary rotation axis. They generate significant meridional heat transport, which can affect the ice shell topography, a primary observable of these moons. However, global ocean simulations cannot resolve convection under realistic icy moon conditions, and traditional convection schemes cannot represent slantwise convection. Here, we develop a slantwise convection scheme and implement it in a global ocean model. We perform benchmark tests in a global spherical shell by comparing parameterized fluxes with convection-resolving simulations. The scheme reproduces the meridional heat transport inside the tangent cylinder, where slantwise convection dominates. The resulting meridional heat transport significantly modifies the surface heat flux, producing variations comparable to the imposed bottom heating magnitude. Although the simulations with parameterized convection cannot fully reproduce the temperature structure, likely due to an inability to reproduce the temperature gradients near the boundaries, they capture the bulk interior vertical temperature gradient. The new scheme allows unresolved slantwise convection to be represented in global ocean simulations for icy moons. It is also applicable to other rapidly rotating oceans with small natural Rossby number ($\mathrm{Ro}^* \ll 1$), including deep ocean worlds on exoplanets.
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High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

Characterization of Numerical Dissipation in Simulations of Magnetohydrodynamic Turbulence

Yuyang Hua, Zhonghai Zhao and Bin Qiao

Comprehensive characterization of numerical dissipation is essential for high-fidelity simulations of magnetohydrodynamic (MHD) turbulence. In this work, we present an a posteriori framework for directly estimating numerical dissipation in MHD turbulence from simulation data without invoking a priori assumptions. Implemented in the open-source Python package PyMHD, the framework is applied to simulations of Alfvénic turbulence, turbulent small-scale dynamos, and MRI-driven turbulence, yielding a systematic characterization of the anisotropy and spectral properties of numerical dissipation across these regimes. The results indicate that numerical dissipation primarily dissipates energy transferred by the turbulent cascade at small scales, consistent with the conventional interpretation. However, its spectral properties are distinct from those of physical viscosity and resistivity, such that it cannot simply be represented by effective dissipation coefficients. In addition, numerical dissipation inherits the anisotropy of the underlying turbulence, and can even exhibit anomalous anti-dissipative behavior under certain circumstances. Moreover, this framework enables identification of the conditions under which physical dissipation dominates numerical dissipation across all scales, thereby providing practical guidance for achieving high-fidelity simulations of astrophysical MHD turbulence.
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Solar and Stellar Astrophysics

FAUST XXXI. Grain properties and variability of three sources in GSS 30

Q. Yang, H. Baobab Liu, S. Feng et al. (+55 more)

To advance our understanding of dust properties in class 0/I young stellar objects, it is crucial to resolve their structures at multiple wavelengths and investigate how grain growth and environmental effects shape their spectral properties. We present 0.5 arcsec resolution ALMA observations of the GSS 30 complex at 1.2-3.0 mm from the FAUST large programme, achieving a linear resolution of 69 au. We analyse the dust continuum emission and perform modelling to constrain dust properties and disk structures. For IRS3, the spectral index increases radially from 2.0 at the centre to 2.5 at the disk edge, while decreasing to 1.6-1.8 along the outflow direction. The asymmetric low-alpha region towards the northeastern blueshifted lobe may result from cold outer envelope dust obscuring warmer inner regions. SED fitting suggests maximum grain sizes of tens of microns and a dust mass of 650-1510 M_earth. IRS1 is associated with an extended north-eastern structure, which may represent an outflow-disk complex, a trailing structure linked to a circumbinary disk, or a gas streamer accreting onto IRS1. The central IRS1 shows alpha < 0.8, consistent with marginally optically thick free-free emission. IRS2 displays brightness variations over 420 s, and multi-epoch comparison suggests a flare lasting tens of minutes, likely caused by magnetic activity in the protostar. Our results highlight the importance of environmental effects, including dust obscuration and streamer structures, in shaping the observed properties of young disks, and reveal millimetre variability associated with possible protostellar magnetic flares.
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All authors Q. Yang, H. Baobab Liu, S. Feng, C. J. Chandler, F. Fontani, N. Sakai, Y. Oya, T. Hanawa, C. Codella, C. Ceccarelli, I. Jiménez-Serra, L. Cacciapuoti, E. Bianchi, M. Bouvier, M. De Simone, A. Isella, D. Johnstone, L. Loinard, G. Sabatini, Y. Shirley, Y. Aikawa, M. J. Maureira, P. Caselli, F. Menard, N. Balucani, E. Caux, S. Charnley, N. Cuello, F. Dulieu, L. Evans, D. Fedele, T. Hama, E. Herbst, T. Hirota, B. Lefloch, A. López-Sepulcre, L. T. Maud, A. Miotello, G. Moellenbrock, H. Nomura, Y. Oba, S. Ohashi, Y. Okoda, J. Pineda, L. Podio, A. Rimola, T. Sakai, D. Segura-Cox, B. Svoboda, L. Testi, C. Vastel, S. Viti, N. Watanabe, Y. Watanabe, Y. Zhang, Z. E. Zhang, F. O. Alves, S. Yamamoto

Earth and Planetary Astrophysics

Magnetic field strengths of hot giant exoplanets consistent with Solar System values

Julia V. Seidel, Vivien Parmentier, Bibiana Prinoth et al. (+29 more)

Magnetic fields are ubiquitous in the universe. They play a key role in shaping the activity of stars, the habitability of rocky planets, and the long-term retention of planetary atmospheres. Theoretical scaling laws are largely constrained by the limited set of stars and Solar System planets, leading to a wide range of possible values for hot giant planets outside of the Solar System from fractions of the Jovian field to orders of magnitude larger. Ultra-hot Jupiters, with their highly ionised atmospheres, provide a new avenue to probe magnetic effects, as their atmospheric circulation could be directly sensitive to atmospheric magnetic field strength. Using high-spectral resolution observations targeting the iron lines of ultra-hot Jupiters we measure the Doppler shift and thus the wind speed of seven transiting ultra-hot Jupiters. We find a clear decrease of wind speed with increasing planetary temperature, a trend inconsistent with purely hydrodynamic mechanisms but naturally reproduced by magnetic drag. From this relation we estimate the possible strength of magnetic fields of hot giant planets to at most a few gauss - comparable to the Jovian equatorial field. Our results support the idea that magnetic fields affect the atmospheric circulation of ultra-hot Jupiters and could provide a crucial benchmark for scaling laws used to predict magnetic fields in exoplanets, from hot Jupiters to rocky Earths with additional implications for future direct observations.
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All authors Julia V. Seidel, Vivien Parmentier, Bibiana Prinoth, Thea Hood, Nishil Mehta, Valentin De Lia, Konstantin Batygin, Tristan Guillot, Ragnar Van den Broeck, Hayley Beltz, Brian Thorsbro, Florian Debras, Daniel D. B. Koll, Thaddeus D. Komacek, Emily Rauscher, Lorenzo Pino, Matteo Brogi, Joost P. Wardenier, Jacob L. Bean, Björn Benneke, Jean-Michel L. B. Désert, Pablo Drake, Siddharth Gandhi, Mark Hammond, David Kasper, Michael R. Line, Elspeth K. H. Lee, Stefan Pelletier, Andreas Seifahrt, Adrien Simonnin, Peter C. B. Smith, Kevin B. Stevenson

High Energy Astrophysical Phenomena

Unified Mass-Scaled QPO Signatures of Kerr Sen Black Holes from Stellar Mass to Supermassive Sources

Orhan Donmez and G. Mustafa

In this study, we numerically investigate Bondi-Hoyle-Lyttleton (BHL) accretion around Kerr-Sen black holes and examine how the charge-related deformation of the spacetime affects the shock-cone morphology, the variation of the mass accretion rate, and the quasi-periodic oscillation (QPO)-like temporal behavior. The relativistic BHL flow is solved numerically in the equatorial plane for two different black hole spin parameters, a = 0.9 M and a = 0.5 M. From the numerically computed mass accretion rate signal, we calculate the power spectral density (PSD) and perform multi-component Lorentzian fits to identify the dominant QPO-like modes excited around the black hole. The results show that the Kerr-Sen deformation shifts the characteristic frequencies, changes the coherence properties of the oscillation modes, and produces near-resonant harmonic structures close to 3:2 and 2:1. By using inverse mass scaling, the numerically computed frequencies are compared with observed QPOs from stellar-mass, intermediate-mass, and supermassive black hole systems. In particular, reasonable agreement between the numerical simulation results and observations is found for the sources GRS 1915+105, IGR J17091-3624, M82 X-1, NGC 5408 X-1, RE J1034+396, 1H 0707-495, and ESO 113-G010. This comparative analysis indicates that Kerr-Sen black hole shock-cone oscillations may provide a unified framework for interpreting timing features over a broad range of black hole masses and may additionally contribute to constraining the mass and spin parameters of sources whose properties are not yet fully established observationally. These findings further imply that combined hydrodynamical and timing diagnostics constitute a promising approach for assessing the extent to which deviations associated with the Kerr-Sen geometry can be empirically distinguished from those of the Kerr spacetime.
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Cosmology and Nongalactic Astrophysics

Tracing Large-scale Structure with the MeerKLASS On-the-Fly Survey: Angular Clustering of Radio Sources at 816 MHz

Sourabh Paul, Suman Chatterjee, Keith Grainge et al. (+8 more)

We present the first measurement of the angular two-point correlation function \(w(\theta)\) of radio sources from the MeerKAT Large Area Synoptic Survey (MeerKLASS) UHF on-the-fly (OTF) continuum Data Release~1. DR1 provides interferometric Stokes-\(I\) imaging at a reference frequency of 816\,MHz over \(\sim 800~\mathrm{deg}^2\) within the DESI footprint. We detect a positive clustering signal over \(0.02^\circ \lesssim \theta \lesssim 10^\circ\). The measurement is stable to reasonable variations of the depth mask and flux threshold on intermediate and large scales. Modelling the intermediate-scale signal (\(0.112^\circ\le\theta\le 1.36^\circ\)) with a fixed-slope power law (\(\gamma=1.8\)) yields \(A(1^\circ)=(1.434\pm0.475)\times10^{-3}\), corresponding to \(\log_{10}A=-2.843^{+0.124}_{-0.175}\). We infer an effective large-scale bias by fitting \(\Lambda\)CDM projected-matter templates \(w_{\rm DM}(\theta)\) computed with CAMB and Limber projection, including an integral-constraint correction evaluated from random–random weights. Using two bracketing T-RECS redshift-distribution priors, we obtain \(b_{\rm eff}=1.998\pm0.350\) (AGN prior) and \(b_{\rm eff}=1.530\pm0.265\) (TOTAL prior), demonstrating that the dominant modelling uncertainty arises from \(N(z)\). As a derived summary we Limber-invert the power-law amplitude to obtain \(r_0=6.18\pm1.13\) and \(5.59\pm1.02~h^{-1}\mathrm{Mpc}\) for the AGN and TOTAL priors, respectively. These results establish MeerKLASS UHF DR1 as a new wide-area, intermediate-frequency dataset for radio-continuum clustering. As MeerKLASS expands and overlapping optical/IR spectroscopy provides improved redshift calibration, future releases will enable population-split clustering and bias evolution measurements with substantially reduced modelling uncertainty.
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All authors Sourabh Paul, Suman Chatterjee, Keith Grainge, Laura Wolz, Aishrila Mazumder, Steven Cunnington, Sarvesh Mangla, Joseph J. Mohr, Mario G. Santos, Oleg Smirnov, Cyril Tasse