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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 25 April

Instrumentation and Methods for Astrophysics

gateau: an observation simulator for ground-based submillimeter astronomy with integral field units and kinetic inductance detectors

A. Moerman, N. Soshnin, S. A. Brackenhoff et al. (+7 more)

Submillimeter (submm) integral field units (IFUs) utilising kinetic inductance detectors (KIDs) are a promising instrument architecture for the study of galaxies, galaxy clusters, and the large-scale structure of the Universe. In order to design successful experiments targeting these science cases, several aspects such as instrument design, observation and calibration strategies, and data reduction pipelines must be collectively developed, tested, and optimised. This can be achieved through end-to-end simulations of the experiment, allowing for quantitative assessment of the aforementioned aspects. To this end, we have developed gateau, a modular, flexible, and efficient simulator for submm IFU observations of astronomical sources. The simulator consists of a Python interface, powered by a C/C++ backend that uses CUDA for GPU-acceleration, and is publicly available and fully open-source. gateau simulates observations by taking user input such as an astronomical source, a set of atmospheric screens, a scan pattern, and telescope and instrument parameters. It then propagates the source signal to the detectors. A physically motivated photon-noise model is used to add a white noise component to the received power. Detector noise is added as temporally correlated pink noise. The output is stored in the form of time-ordered datasets. We validated gateau against observations with DESHIMA 2.0, a superconducting, ultra-wideband spectrometer utilising KIDs and on-chip filterbank technology. We show that we can reproduce real observations of the atmosphere and Uranus with gateau simulations. Lastly, we present a use case to show how gateau can simulate long observations in timespans orders of magnitude smaller than the observation time itself, highlighting its applicability and efficiency.
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All authors A. Moerman, N. Soshnin, S. A. Brackenhoff, S. O. Dabironezare, K. Karatsu, L. H. Marting, S. A. H. de Rooij, M. Roos, B. R. Brandl, A. Endo

Astrophysics of Galaxies

The functional form of galaxy and halo luminosity and mass functions

Amelia Ford, Harry Desmond, Deaglan J Bartlett et al. (+1 more)

The galaxy luminosity and stellar mass function (LF, SMF), and halo mass function (HMF), are fundamental quantities in astrophysics and crucial inputs to a range of astrophysical and cosmological analyses. They are typically parametrised by fitting functions that have been chosen "by eye" to match observed or simulated data. We apply symbolic regression – specifically the Exhaustive Symbolic Regression (ESR) algorithm – to automate the search for optimal LF, SMF and HMF functional forms. ESR scores all functions up to a maximum complexity composed of a user-defined basis set of operators using the description length, an approximation to the Bayesian evidence that balances accuracy with complexity. We find many functions outperforming the Schechter and double Schechter functions for the LF and SMF, and that outperform the Press–Schechter and Warren/Tinker functions for the HMF. By additionally imposing "physicality checks" on functions' extrapolation and integration properties, we identify the optimal, low-complexity functional forms in terms of accuracy, simplicity and behaviour beyond the data range. As well as providing drop-in replacements for literature LF, SMF and HMF fitting functions, and identifying robust behaviour across well-fitting functions, we present a framework with which symbolic regression may be used to automate the discovery of optimal functions for any astrophysical dataset.
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All authors Amelia Ford, Harry Desmond, Deaglan J Bartlett, Pedro G Ferreira

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Effect of total dose proton irradiation on the performance of Kinetic Inductance Detectors for far-Infrared space observatory

A. Besnard, G. Conenna, V. Sauvage et al. (+5 more)

Kinetic Inductance Detectors (KIDs) are a promising technology for future space missions, where exposure to high-energy particles may affect detector performance. In this work, we irradiated two types of KID arrays, absorber coupled and antenna coupled, with high-energy protons at 120 mK. We used a total dose equivalent to approximately 10 years of operation at the L2 Lagrange point. A comparison between pre-irradiation and post-irradiation measurements (24 hours after a 5.7 krad total dose) was done, while keeping the detectors at 120 mK. We find that there is no significant change in the quasi-particle lifetime {\tau}_qp and the dark responsivity d{\theta}/dPdark, but we do observe an increase in the noise and NEP that is tentatively attributed to limitations in the post radiation data analysis.
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All authors A. Besnard, G. Conenna, V. Sauvage, K. Karatsu, S.J.C. Yates, J.J.A Baselmans, B. Maffei, L. Ferrari

Cosmology and Nongalactic Astrophysics

Parametric Resonance in $\phi^4$ Preheating: An Exact Numerical Study

Hrisikesh Thakur and Malay K. Nandy

Preheating after inflation proceeds through parametric resonance, leading to efficient particle production in scalar field models. In this work, we investigate the structure of parametric resonance in the $\phi^4$ chaotic inflationary model during the preheating phase by performing a fully numerical analysis of the coupled dynamical equations governing the inflaton field and the mode function of the produced particles, thereby avoiding the approximations commonly employed in earlier studies. Our results reveal resonance patterns that differ significantly from those obtained with approximate analytical treatments. In the weak coupling regime, short-wavelength modes rapidly settle into oscillations with nearly constant amplitude, while the corresponding occupation numbers approach saturation. However, the long-wavelength modes exhibit gradual amplitude growth, with occupation numbers transitioning into a non-linear oscillatory regime. As the coupling strength increases, the dynamics becomes increasingly nonlinear, leading to the emergence of stochastic behavior. In the strong coupling regime, short-wavelength modes display a step-like (staircase) evolution in the occupation number, indicative of intermittent bursts of particle production. However, the long-wavelength modes exhibit a more gradual, monotonic growth with small superimposed fluctuations. These findings highlight the rich, coupling-dependent, structure of parametric resonance in the quartic inflationary model and underscore the importance of exact numerical treatment in accurately capturing preheating dynamics.
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Instrumentation and Methods for Astrophysics

Successful irradiation campaign on PRIMA/PRIMAger KIDs detectors with DRACuLA

Valentin Sauvage, Anaïs Besnard, Giulia Conenna et al. (+4 more)

DRACuLA (Detector irRAdiation Cryogenic faciLity for Astrophysics) is a mobile dilution refrigerator platform developed at the Institut d'Astrophysique Spatiale (IAS) to expose sub-Kelvin detectors to particle beams at their nominal operating temperature, in the range 50-300 mK. We report on its design, beam-line integration at the Particle Therapy Research Center (PARTREC) in Groningen, and the operational performance achieved during the September 2025 irradiation campaign on Kinetic Inductance Detector (KID) arrays developed by SRON for the PRIMA mission. The detector samples were maintained at 120 mK throughout a 12-hour proton irradiation run at 184 MeV. The scientific results of this campaign are reported in the companion paper by Besnard et al.
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All authors Valentin Sauvage, Anaïs Besnard, Giulia Conenna, Kenichi Karatsu, Stephen J.C. Yates, Lorenza Ferrari, Bruno Maffei

High Energy Astrophysical Phenomena

The line modulations of H-like Fe, Ca, Ar, and S observed with $XRISM$/Resolve in Cyg X-3

Tomohiro Hakamata, Hirokazu Odaka, Ryota Tomaru et al. (+13 more)

Cygnus X-3, hosting a Wolf-Rayet (WR) star whose dense wind produces various spectral lines due to photoionization by X-rays from a compact object, provides an ideal laboratory for studying wind dynamics and density structure. We measured the orbital modulations of the Fe, Ca, Ar, and S Ly$\alpha$ lines observed with the X-ray microcalorimeter (Resolve) onboard the $XRISM$, taking account of both emission and absorption lines of the Ly$\alpha$ complexes. The modulations of Doppler shifts of the Fe, Ca, Ar, and S Ly$\alpha$ lines showed amplitudes of 500 km s$^{-1}$ and phase offsets of 0.04, 0.09, 0.11, and 0.17, respectively, in units of an orbital period (4.8 hours) relative to the orbital motion of the compact object. This result indicated that H-like Fe most closely follows the compact object's motion. The line widths ranged from 400 to 1000 km s$^{-1}$. The intensities of both emission and absorption lines reached their minima around orbital phase 0.0 and their maxima around phase 0.5. The absorption peaks, however, did not align exactly with phase 0.5, suggesting the inhomogeneous structures such as an accretion wake and/or a bow shock. We compared the observed modulations with calculations based on a stellar wind model, accelerated by ultraviolet radiation from the WR star. One of the calculations qualitatively reproduced the observed trend that H-like Fe ions were concentrated near the compact object, whereas H-like S was distributed across the binary system, with H-like Ca and Ar showing intermediate spatial distributions. From this comparison, we estimated that a mass-loss rate of the stellar wind was approximately $5 \times 10^{-6}$-$1 \times 10^{-5}\ M_{\odot}\ {\rm yr}^{-1}$.
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All authors Tomohiro Hakamata, Hirokazu Odaka, Ryota Tomaru, Hironori Matsumoto, Taiki Kawamuro, Ralf Ballhausen, Tim Kallman, Daiki Miura, Hiroya Yamaguchi, Teruaki Enoto, Natalie Hell, Shunji Kitamoto, Hiroshi Nakajima, Shin Watanabe, Shinya Yamada, Kazutaka Yamaoka

Astrophysics of Galaxies

A graph-based Neural Network surrogate model for accelerating semi-analytical model of galaxy formation and evolution

Xuejie Li, Zhongxu Zhai, Xiaohu Yang et al. (+2 more)

Understanding how galaxy populations emerge and evolve from the growth of dark matter structure is a central challenge in galaxy formation theory. Semi-analytic models (SAMs) provide an efficient framework to address this problem, but exploring large ensembles of merger trees across broad parameter spaces remains computationally demanding. We develop a conditional graph neural network surrogate model that combines merger tree information with SAM parameters to predict galaxy properties across cosmic time. Using merger trees of dark matter halos from the Uchuu simulation and the Galacticus SAM, the model predicts stellar mass, luminosity, angular momentum, gas metal mass, and specific star formation rate across the wide redshift range of 0 <= z <= 5. For instance, the model can predict stellar mass at 0 <= z <= 3 with a scatter of 0.19-0.28 dex and coefficient of determination R^2 of 0.946-0.973 (R^2 close to 1 indicates prediction closely matching the truth). The results show that a single graph based model can reproduce these galaxy properties with good accuracy over multiple SAM realizations, merger trees and redshifts. This catalog-level model provides a practical route for accelerating SAM based studies of galaxy formation to enable a more detailed investigation of the model parameter space. The inference code, trained models, and example data products are publicly available at https://github.com/MutongCat/sam2galaxy-gnn.
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All authors Xuejie Li, Zhongxu Zhai, Xiaohu Yang, Andrew Benson, Yun Wang

Instrumentation and Methods for Astrophysics

PEEPSS: Photonic-Enabled ExoPlanet Spectroscopic Sensor for the Habitable Worlds Observatory

Genevieve Markees, Stephen S. Eikenberry, Rodrigo Amezcua-Correa et al. (+5 more)

The next few years will be critical for technology development for Habitable Worlds Observatory (HWO) in its mission to search for and characterize extrasolar planets. To achieve its stated goals with contrasts of one part in ten billion, HWO will require outstanding stability and precision, particularly in measuring and controlling the wavefront of the light propagate through the telescope and coronagraph system. We present simulations for the Photonic-Enabled ExoPlanet Spectroscopic Sensor (PEEPSS), which uses a set of photonic lanterns to efficiently couple light from the "dark hole" in the coronograph focal plane (where the exoplanets are expected to lie) into single-mode fibers and the main spectrograph. PEEPSS uses rejected host star light from the region interior to the dark hole to aid in the wavefront sensing; this has the advantage of doing the sensing in the coronograph focal plane, eliminating non-common-path errors between the wavefront sensing and science channels. The photonics lanterns allow us to combine our science channel and wavefront sensor into a single system. PEEPSS will be particularly advantageous provide in the near-infrared (NIR) bandpass, which is of particular interest for HWO. Because the limiting inner working angle (IWA) of a coronagraph scales as wavelength over diameter, exoplanet imaging in the NIR becomes a major challenge as the IWA can exceed the exoplanet orbital radius. PEEPSS will enable NIR coronagraphic observations at smaller IWA than other approaches, increasing the observational parameter space HWO can probe in the search for exoplanets.
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All authors Genevieve Markees, Stephen S. Eikenberry, Rodrigo Amezcua-Correa, Miguel Bandres, Rebecca Jensen-Clem, Sergio Leon-Saval, Laurent Pueyo, Raphaël Pourcelot

Astrophysics of Galaxies

The Dependence of the Mean Spectral Energy Distributions on the Accretion Rate for Quasars with $z < 0.75$ from the Sloan Digital Sky Survey

Yan-Song Ma, Yu-Meng Guan, Jian-Xia Jiang et al. (+4 more)

We construct mean spectral energy distributions (SEDs) for a substantial sample of 56,969 Sloan Digital Sky Survey DR16 quasars with $z < 0.75$, utilizing multiwavelength data from the mid-infrared (MIR) to ultraviolet (UV). These SEDs are built on eigenvector 1 parameters – the relative optical $\rm Fe~ II$ strength ($R_{\rm Fe~II}$) and the H$\beta$ line width ($\rm H\beta$) – that capture the principal spectral variance of quasar spectra. From three $R_{\rm Fe~II}$-dependent mean SEDs we find that quasars with a larger $R_{\rm Fe~II}$ exhibit redder UV and optical and redder MIR and near-infrared (NIR) continua, indicating more dust emission. We also split our sample directly into Eddington ratio $L_{\rm Bol} /L_{\rm Edd}$ (or dimensionless accretion rate $\dot{\mathscr{M}}$) bins to construct different mean SEDs and find that the continua become increasingly red with increasing $L_{\rm Bol} /L_{\rm Edd}$ (or $\dot{\mathscr{M}}$) in the MIR, NIR, and UV bands. This demonstrates that the shapes of Type 1 AGN SEDs depend on the accretion rate. However, the optical continuum shows the opposite trend (becoming harder and bluer), indicating the complexity of the optical emission region. From $\rm FWHM_{H\beta}$-dependent mean SEDs we find that quasars with a larger $\rm FWHM_{H\beta}$ show redder optical and NIR continua and bluer UV and MIR continua. The bluer MIR continuum suggests that a larger angle between of the line of sight and the torus plane results in weaker torus emission in the MIR.
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All authors Yan-Song Ma, Yu-Meng Guan, Jian-Xia Jiang, Shao-Jun Li, Xiang-Wei Ning, Yi Tang, Wei-Hao Bian

Astrophysics of Galaxies

Hessian-based photometric substructure as an evolutionary tracer of OB cluster candidates in M31

Yuan Liang, Chao-Wei Tsai and Jingwen Wu

Using Hubble Space Telescope images from the PHAT and PHAST surveys, we construct an updated catalogue of 747 OB cluster (OBC) candidates. We introduce a dimensionless structural metric, the trace coefficient of variation ($CV_{\rm tr}$), derived from the Hessian matrix in four HST bands, to quantify the internal photometric substructure of partially resolved OBC candidates. Cross-matching with the subset of M31 clusters that have independent colour–magnitude diagram (CMD) age estimates yields 247 objects in common. We find statistically significant anti-correlations between $CV_{\rm tr}$ and age in the UV and blue bands, suggesting a progressive smoothing of the light distribution as clusters evolve. Bootstrap resampling confirms the robustness of these trends. Forward modelling of synthetic clusters analysed with the same pipeline recovers a monotonic $CV_{\rm tr}$–age relation under simplified but physically motivated assumptions. These results show that second-order photometric structure contains measurable evolutionary information within the CMD-calibrated regime ($\sim10$–300~Myr).
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High Energy Astrophysical Phenomena

UHECR doublets and their conditional association with nearby radio galaxies

Victor Barbosa Martins

The origin of ultra-high-energy cosmic rays (UHECRs) remains a fundamental question in astroparticle physics. While localized 3 $\sigma$ correlations with active galactic nuclei and starburst galaxies have been reported using time-integrated analyses, we propose and implement a spatiotemporal multiplet search method utilizing a pre-defined fixed window of 3 degrees and 15 days, a kinematic filter designed to isolate high-rigidity particles and keep chance coincidences low. Applying this method to 16 years of Pierre Auger Observatory data, we identify 28 UHECR multiplets (doublets) above 32 EeV. We backtrack these trajectories using three Galactic magnetic field models across eight distinct nuclear species. Testing the backtracked directions against the ten nearest bright radio galaxies yields an overall post-trial significance of 5.8 $\sigma$, conditioned on the individual best-fit associations. Specifically, we find a 4.5 $\sigma$ conditional post-trial significance for the joint association of 8 of these multiplets with the Fornax A region alone. These results point to radio galaxies, with a strong contribution from Fornax A, as long-term accelerators of heavy (Z > 3) UHECRs, possibly within the mildly relativistic backflows of their extended radio lobes, detected at Earth primarily as independent secondary fragments above 32 EeV.
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Astrophysics of Galaxies

Analysis of a Septuple Open Cluster System and Its Extended Family in Gaia DR3

Muhammad Akmal Husain, Ferdinand, Mochamad Ikbal Arifyanto et al. (+1 more)

A rare multiple open cluster system has been analyzed using Gaia DR3 astrometry and photometry data. Using Agglomerative Hierarchical clustering and Bayesian-HDBSCAN, we identify a compact core consisting of seven known open clusters and two additional components, including a new candidate, forming a nine-member association. Membership probabilities are refined through statistical modeling, combining GUMM, Bayesian-KDE, and Bayesian-XDGMM for tidal tails identification. Backward orbital integrations confirm coherent motions over 20-30 million years, suggesting a common origin from the same massive molecular cloud. This system offers a unique laboratory for investigating cluster multiplicity, dynamical evolution, and Galactic structure.
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All authors Muhammad Akmal Husain, Ferdinand, Mochamad Ikbal Arifyanto, Muhammad Irfan Hakim

Solar and Stellar Astrophysics

Multi-Viewpoint Observation of a Failed Prominence Eruption on the Sun

Tingyu Gou, Katharine K. Reeves, Peter R. Young et al. (+5 more)

Solar eruptions are sudden ejections of coronal mass and magnetic fields accompanied by intense energy release. The eruptive structure does not always erupt successfully, but sometimes fails to escape the Sun after initiation. The failure of an eruption, however, provides an invaluable opportunity for understanding the intricate mechanism of eruptions. We present a comprehensive observation of a failed prominence eruption on the Sun, taking advantage of multi-viewpoint and multi-messenger imaging. Simultaneous off-limb and on-disk observation gives evidence of magnetic reconnection processes occurring at different sites during the flare. Particularly, in addition to the standard flare reconnection behind the eruption, strong external reconnection occurs on the erupting flux rope, evidenced by a wealth of signatures via multi-wavelength imaging and spectroscopy. The two reconnection processes may play contrasting roles in the flux rope's acceleration and compete in altering the magnetic flux in the rope. As the high rate of external reconnection proceeds, the flux rope and embedded prominence decelerate noticeably and fail to erupt into the heliosphere, under strong magnetic confinement of overlying fields. Our results illustrate a well-defined physical picture for solar eruptive activities and provide insight into the lack of coronal mass ejections found in other solar-type stars.
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All authors Tingyu Gou, Katharine K. Reeves, Peter R. Young, Astrid M. Veronig, Xingyao Chen, Sijie Yu, Bin Chen, Bin Zhuang

Friday 24 April

Astrophysics of Galaxies

Itô tracers: continuous-trajectory Lagrangian particles for Eulerian hydrodynamics

Eric R. Moseley, R. Teyssier and Tom Abel

Lagrangian tracer particles have long been used to track the history of individual gas parcels in hydrodynamical codes. Particles advected by the cell-centered velocity carry no representation of underlying numerical diffusion, and thus exhibit systematic bias. The Monte-Carlo (MC) tracer resolves this with discrete probabilistic cell-to-cell, flux-based jumps, at the cost of trajectories that are discontinuous in time. We introduce the Itô tracer, a continuous-time Lagrangian particle with moments matched to the advection, diffusion, and dispersion of the gas. A subgrid-scale variant (SGS-Itô) replaces the numerical diffusion with a Smagorinsky–Lilly turbulent diffusivity, illustrating that the form of the diffusion matters less than its magnitude. We validate these methods with a 1D square-pulse advection test and 3D decaying turbulence at $\sigma_{\rm rms} = 15\,c_{\rm s}$. We compare the different tracer particle methods using several statistical tests. Itô tracers largely reproduce or improve upon MC tracers statistics across column-density maps, joint density histograms, log-density-ratio PDFs, and density power spectra. In the turbulence test, Itô tracers improve the correlation between tracers and gas over the MC tracers by >3%, and reduce the width of the log-density ratio PDF by nearly 50%. Relative to classical tracers, these improvements are $\gtrsim$30% and 230%, respectively. Because Itô tracers follow a stochastic differential equation, the method maps onto other continuous-trajectory Lagrangian processes (e.g. dust grains, charged particles, cosmic rays), admits variance-reduction techniques, higher-order integrators, and GPU-friendly implementations – all of which are unavailable to discrete-jump schemes.
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Earth and Planetary Astrophysics · Cross-listed from eess.SY

Integrated Lander-Propulsion-GNC Framework for Autonomous Lunar Powered Descent

Emre Aklan, Fatih Seker, Bekir Gencalioglu et al. (+5 more)

This paper presents an integrated lander-propulsion-GNC framework for autonomous lunar powered descent. The BUG VTVL test vehicle serves as the reference platform, with the YUNT V0 throttleable bipropellant engine providing variable thrust across a wide operating envelope, integrated with a real-time successive convexification guidance solver. The vehicle design accounts for structural configuration, landing stability, center-of-mass migration, and inertia evolution, while the propulsion architecture defines the throttle ratio, dead-zone behavior, and gimbal authority that constrain the guidance problem. A successive convexification algorithm addresses all nonconvexities; thrust lower bounds, mass depletion coupling, and thruster dead-zone behavior are all handled within a unified second-order cone program solvable in near-real time. Parametric analysis reveals a fundamental coupling between throttle ratio, pointing authority, and surface gravity. Monte Carlo simulations validate guidance robustness, achieving sub-50-meter landing precision under realistic perturbations.
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All authors Emre Aklan, Fatih Seker, Bekir Gencalioglu, Mehmet Batuhan Kaya, Yigit Serceoglu, Furkan Yavuz, Omer Burak Iskender, Burak Yaglioglu

Solar and Stellar Astrophysics

Current Unsolved Problems in Planetary Nebulae Research

Sun Kwok, Bruce Balick, You-Hua Chu et al. (+5 more)

While there has been significant progress in our understanding of the origin and evolu-tion of planetary nebulae in the last 50 years, there remain several unsolved problems. These include the true 3D morphological structure of the nebulae, origin of multipolar nebulae, the dust and molecular distribution relative to the optical nebulosity, large-scale structures outside of the main nebulae, the relevance of binarity to planetary nebulae evolution, and a precise definition of the planetary nebula phenomenon. The long-standing problem of elemental abundance discrepancy still remains unsolved. In this paper, we summarize current observations related to these problems and present possible future directions to tackle them.
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All authors Sun Kwok, Bruce Balick, You-Hua Chu, Bruce J. Hrivnak, Alberto López, Quentin Parker, Raghvendra Sahai, Albert Zijlstra

Instrumentation and Methods for Astrophysics

KilonovaSCORER: Prior-Predictive Scoring of Kilonovae for Real-Time Multimessenger Follow-Up

P. Darc and C. D. Kilpatrick

Real-time ranking of optical transient candidates during gravitational-wave (GW) and multimessenger follow-up is challenging when only sparse early-time, multi-band photometry is available.We present KilonovaSCORER, an open-source framework for scoring and ranking in this regime. It quantifies the consistency of each candidate with a physically motivated kilonova model grid in absolute magnitude space using two complementary per-observation metrics, $P_{\mathrm{tail},\mathrm{KNe}}$ and $P_{\mathrm{near},\mathrm{KNe}}$. These are aggregated into a cumulative ranking score via inverse-variance weighting in logit space, naturally accounting for heterogeneous observational uncertainties across bands and epochs. A sequential Approximate Bayesian Computation (ABC) diagnostic tracks photometric consistency across epochs, penalizing candidates whose temporal evolution is incompatible with kilonova expectations. We validate the framework on AT\,2017gfo and SN\,2025ulz, and test it against supernova simulations under a realistic Rubin/LSST Target-of-Opportunity strategy. The framework recovers kilonova candidates with high confidence while ruling out supernova contaminants within five days of the gravitational-wave trigger. In our LSST ToO simulations, median cumulative scores for thermonuclear and core-collapse supernova contaminants fall to zero by $3$–$4$\,d post-trigger, whereas kilonova medians remain $\gtrsim 0.4$. KilonovaSCORER supports real-time workflows for ToO teams and LSST alert brokers, integrates with follow-up coordination platforms such as the Tool for Rapid Object Vetting and Examination, and is publicly available at https://github.com/phelipedarc/KilonovaSCORER/tree/main.
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Earth and Planetary Astrophysics

A Machine Learning Approach to Meteor Classification

Samantha Hemmelgarn, Nicholas Moskovitz and Denis Vida

We use machine learning to develop a framework for classifying meteoroids based on 13 directly observed parameters from the Global Meteor Network. This method adds depth to the $K_{b}$ parameter, which uses only three parameters. We employ a semi-qualitative approach using 28,177 meteor events observed in 2023 by the Lowell Observatory Cameras for All-Sky Meteor Surveillance (LO-CAMS) network to evaluate multiple normalization, dimensionality-reduction, and clustering algorithms. We find that a combination of Factor Analysis (FA) and a Gaussian Mixture Model (GMM) results in clusters most consistent with traditional models. Three FA-derived factors corresponding to meteoroid kinematics, activation thresholds, and size/geometry effects describe the underlying structure of meteoroid behavior. The activation factor emerged as the most discriminating factor distinguishing whether a meteor is of asteroidal or cometary origin. Resulting 3, 6, and 11 cluster models reveal progressively finer compositional structure, from broad physical regimes to detailed subdivisions within cometary and asteroidal populations. From these results, we introduce a physically motivated hardness classification scheme: $H_{\mathrm{class}}$. $H_{\mathrm{class}}$ is a data-driven extension of $K_{b}$ which physically interprets clusters in terms of the densest iron meteoroids down to the softest cometary material. Application to nine well-studied meteor showers and analysis of clusters in orbital space aids in the physical interpretation of $H_{\mathrm{class}}$ groups. The $H_{\mathrm{class}}$ model is supported by an analytical FA-GMM formulation that enables application to future datasets. Our results demonstrate that machine learning methods can extract compositional information from modern optical meteor datasets at scale and offers a new framework for interpreting meteoroid populations.
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Solar and Stellar Astrophysics

The POKEMON Speckle Survey of Nearby M dwarfs. IV. Distance-Limited Catalog (POKEMON-DLC)

Catherine A. Clark, Zafar Rustamkulov, Gerard T. van Belle et al. (+5 more)

The Solar Neighborhood is dominated by stars smaller, colder, and fainter than the Sun: the M dwarfs. If we are to understand the context in which the Sun formed and evolved, then we must investigate the system architectures of our low-mass neighbors. We have therefore carried out the Pervasive Overview of Kompanions of Every M Dwarf in Our Neighborhood (POKEMON) speckle survey of nearby M-dwarf primaries. We created the survey with the goal of observing a volume-limited (north of -30 degrees) sample of M-dwarf primaries through M9 out to 15 pc at diffraction-limited resolution. Pre-Gaia parallax measurements yielded a catalog of 454 nearby M-dwarf primaries. However, the precise astrometry from Gaia indicated that there are additional low-mass sources within 15 pc. Here we present the POKEMON-Distance Limited Catalog (POKEMON-DLC), a supplemental catalog that consists of speckle observations for the 66 additional M-dwarf primaries identified by Gaia, increasing the number of ultracool dwarf (later than M6.5) primaries in the POKEMON catalog by a factor of 1.6. In our observations we detect four likely bound companions. After carrying out a literature search for additional companions, we update the projected separation distribution and find a peak at 7.91 au ({\sigma}log(a) = 1.1, SElog(a) = 0.10). We also update the M-dwarf stellar multiplicity and companion rates, and find values of 22.7 p/m 1.8% and 27.5 p/m 2.0%, respectively. These results emphasize the utility of Gaia for identifying low-mass, nearby sources, and we find that ensuing characterization of these sources by SPHEREx will continue to clarify the nature of the Solar Neighborhood.
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All authors Catherine A. Clark, Zafar Rustamkulov, Gerard T. van Belle, Mark E. Everett, Colin Littlefield, Sarah J. Deveny, David R. Ciardi, Kaspar von Braun

High Energy Astrophysical Phenomena

Probable Detection of a Cooler Gas Component in the Perseus Cluster with XRISM

Julian Meunier, Brian R. McNamara, Aurora Simionescu et al. (+36 more)

We present an analysis of the temperature structure of the Perseus cluster atmosphere using XRISM Resolve observations. The average temperature rises from 3.3 keV near the nucleus of NGC 1275 to 8 keV at 10 arcmin (210 kpc), which is consistent with Chandra and XMM measurements. The velocity and velocity dispersion profiles are broadly consistent with those in arXiv:2509.04421. While the gas at altitudes beyond $\sim60$ kpc can be modeled as a single temperature plasma, we find evidence for more than one gas phase in the inner $\sim60$ kpc. The hotter gas component, traced primarily by the Fe He$\alpha$ line, has a velocity dispersion of $\lesssim140$ km s$^{-1}$. We detect a cooler, $\sim1.87-2.43$ keV, gas component with a velocity dispersion of $\sim300-400$ km s$^{-1}$ and a bulk velocity of $\sim 21-213$ km s$^{-1}$ with respect to the central galaxy. These ranges reflect large systematic uncertainties associated with modeling spatial-spectral mixing and the bright central point source. Potential low energy gain variations may add additional uncertainties. The cooler component is identified by broad wings in prominent emission lines, most notably S Ly$\alpha$ and Fe He$\alpha$. This cooler component's Mach number $\sim0.73-0.96$ and non-thermal pressure fraction of $\sim22.9-33.7\%$ are much higher than found for the hotter gas. The cooler gas may be associated with merging halos along the line of sight which formed the cool, sloshing spiral and/or cooling gas being disturbed by the radio jets and lobes.
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All authors Julian Meunier, Brian R. McNamara, Aurora Simionescu, François Mernier, Irina Zhuravleva, Congyao Zhang, Annie Heinrich, Julie Hlavacek-Larrondo, Frederick S. Porter, Benjamin Vigneron, John ZuHone, Elena Bellomi, Ian Drury, Megan E. Eckart, Ryuichi Fujimoto, Yutaka Fujita, Liyi Gu, Isamu Hatsukade, Yuto Ichinohe, Yoshiaki Kanemaru, Takao Kitaguchi, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Hironori Matsumoto, Kyoko Matsushita, Kostas Migkas, Ikuyuki Mitsuishi, Koji Mori, Hiroshi Nakajima, Hirofumi Noda, Anna Ogorzalek, Naomi Ota, Lior Shefler, Nhut Truong, Ayşegül Tümer, Nagomi Uchida, Yuusuke Uchida, Shutaro Ueda

Cosmology and Nongalactic Astrophysics

Cosmological evolution of interacting dark energy with a CPL equation of state

Gerald Neumann, Nelson Videla and Dorian Araya

This paper examines interacting dark energy models within the Chevallier-Polarski-Linder (CPL) parametrization, emphasizing both theoretical structure and observational viability. Two commonly adopted interaction terms are considered: $Q = \beta H \rho_{de}$ and $Q = \beta H \rho_c$. We derive exact analytic solutions that describe how the dark sector evolves. These solutions involve incomplete gamma functions and reveal a non-trivial mathematical structure that is often missed in numerical analyses. We perform a Bayesian analysis using current cosmological observations, including the Hubble parameter (OHD), Type Ia supernovae (SNIa), baryon acoustic oscillations (BAO), and cosmic microwave background (CMB) data. Relative to the non-interacting CPL scenario, the interacting model with $Q = \beta H \rho_{de}$ yields a modestly improved fit, as indicated by the Akaike Information Criterion (AIC). However, the Bayesian Information Criterion (BIC) penalizes increased model complexity, leading to a continued preference for $\Lambda$CDM. In contrast, the interaction model that depends on dark matter density does not provide observational support. The preferred interacting scenario indicates that the dark energy equation of state evolves dynamically, transitioning from an effective phantom regime at high redshift to quintessence-like behavior at late times. Further analysis indicates the potential for a transient phase of cosmic acceleration in the future. These findings suggest that interacting dark energy models within the CPL framework enrich the standard cosmological model by introducing more diverse phenomenology while maintaining consistency with current observations.
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Cosmology and Nongalactic Astrophysics

Gravitational Scattering of Oort Cloud Objects by Dark Matter: Constraints on the Primordial Black Hole Fraction

Sohrab Rahvar

Planetary systems can act as long-term gravitational detectors for dark matter. We investigate the gravitational scattering of Oort cloud objects by primordial black holes (PBHs) using celestial kinematics in the impulsive approximation. By evaluating the energy transfer during these encounters, we compute the rates at which stellar-mass PBHs eject icy planetesimals or inject them into Earth-crossing orbits, demonstrating a linear scaling $\Gamma \propto m_{\mathrm{PBH}}$. Comparing these theoretical rates with four independent observables—Oort cloud survival limits, dynamically new long-period comet fluxes, and pristine terrestrial and lunar impact records—we derive stringent upper limits on the PBH dark matter fraction, $f_{\mathrm{PBH}}$. Our most robust combined constraint yields $f_{\mathrm{PBH}} \lesssim 0.65 (m_{\mathrm{PBH}}/M_\odot)^{-1}$, which excludes PBHs as the dominant dark matter component in the intermediate-to-high mass window of $10^2 M_\odot \lesssim m_{\mathrm{PBH}} \lesssim 10^5 M_\odot$. Furthermore, the solar motion through the Galactic halo induces a “dark matter wind,” generating a pronounced dipole anisotropy in the arrival directions of PBH-injected comets. This geometrical signature, manifesting as a $\sim 2.7:1$ hemispherical asymmetry (and a $\sim 40:1$ polar contrast) between the anti-apex and apex directions, provides a robust, testable discriminant against isotropic stellar perturbations. This distinct signature could be statistically detected with the discovery of $\mathcal{O}(10^2)$ new long-period comets by upcoming surveys such as the Legacy Survey of Space and Time (LSST) at the Rubin Observatory.
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Earth and Planetary Astrophysics

Characterization of the Volatile Properties of 133P/Elst-Pizarro and Other Main-Belt Comets with JWST and Ground-Based Observations

Henry H. Hsieh, John W. Noonan, Michael S. P. Kelley et al. (+10 more)

We report results from an analysis of the volatile composition and evolution of main-belt comet (MBC) 133P/Elst-Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P's orbit, finding Q(H2O)=(1.9+/-0.6)x10^25 molecules/s on UT 2024 June 12 (at a true anomaly of nu=8 deg and heliocentric distance of rh=2.674 au), and Q(H2O)=(1.4+/-0.4)x10^25 molecules/s on UT 2024 October 14 (at nu=37.4 deg and rh=2.747 au). These measurements nominally represent a decline of ~25% in Q(H2O) between the visits, although they are also consistent with no change within uncertainties. We do not detect CO, CO2, or CH3OH, placing 133P's hypervolatile depletion (Q(CO2)/Q(H_2O)<0.009) at a similar level found for previously observed MBCs. We find log(Afrho/Q(H2O)) values for the three MBCs for which water vapor outgassing has been successfully detected that are consistent within uncertainties with an average value of log(Afrho/Q(H2O))=-24.6+/-0.2. Lastly, we find no clear correlations of water production rates with nucleus size, semimajor axis, or heliocentric distance among MBCs observed by JWST so far, but would particularly encourage future JWST observations of additional MBCs interior to the 5A:2J MMR with Jupiter and at high inclinations, as well as multiple observations of MBCs during single active apparitions to further investigate areas of interest identified from the current sample of JWST-observed MBCs.
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All authors Henry H. Hsieh, John W. Noonan, Michael S. P. Kelley, Dennis Bodewits, Jana Pittichova, Audrey Thirouin, Marco Micheli, Scott S. Sheppard, Colin O. Chandler, Theodore Kareta, Colin Snodgrass, Richard E. Cannon, Brian P. Murphy

Earth and Planetary Astrophysics

Emerging Diversity Among the Main-Belt Comets: Insights from JWST and Ground-Based Observations of 457P/Lemmon-PANSTARRS

John W. Noonan, Henry H. Hsieh, Michael S. P. Kelley et al. (+10 more)

We present JWST NIRSpec and NIRCam observations of 457P/Lemmon-PANSTARRS, a main-belt comet that displayed activity around its 2020 perihelion and that was observed to regain activity during its 2024 perihelion by a ground-based observing campaign. The previous successful measurements of water production from two main-belt comets by the JWST NIRSpec instrument confirmed the hypothesis that H2O reservoirs are responsible for activity in dynamically stable main-belt comets. However, the main-belt comets observed with JWST thus far, 238P/Read and 358P/PANSTARRS, occupy orbits in the outer main-belt, with main-belt comets with smaller semi-major axes not yet sensitively tested for H2O. We find that despite clearly displaying dust activity in both ground-based and JWST imaging over a broad period, there were no corresponding H2O, CO, CO2, or CH3OH emissions within sensitive upper limits; notable given 457P is the first main-belt comet with a semi-major axis within the 5:2 mean-motion resonance with Jupiter. We show that we were sensitive to production rates of gas predicted by the dust/gas ratios of 238P and 358P, and hypothesize that 457P may be more depleted than its companions; Q(H2O) must be less than 2x10^24 molecules/s, or 0.035 kg/s. Further surveying of main-belt comets across the parameter space of semi-major axis and eccentricity will shed light on whether 457P represents an edge member of a spectrum or a distinct subclass of main-belt comets.
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All authors John W. Noonan, Henry H. Hsieh, Michael S. P. Kelley, Dennis Bodewits, Jana Pittichova, Audrey Thirouin, Marco Micheli, Scott S. Sheppard, Colin O. Chandler, Theodore Kareta, Colin Snodgrass, Richard E. Cannon, Brian P. Murphy

Solar and Stellar Astrophysics

Dynamical masses of young stellar objects with the VLBA: DYNAMO-VLBA: Radio binary stars in Orion

Sergio A. Dzib, Jazmín Ordóñez-Toro, Laurent Loinard et al. (+9 more)

We present results from a multi-epoch Very Long Baseline Array (VLBA) survey conducted as part of the DYNAMO-VLBA project, aimed at measuring the dynamical masses of young stellar systems in the Orion complex. Our observations include 19 radio sources associated with 15 binary or multiple young systems. For four visual binaries in which both components were detected, the derived Keplerian orbits yield model-independent stellar masses; in particular, Brun~656 and HD~294300 show excellent agreement between VLBA-based and spectral-energy-distribution-based estimates, providing valuable benchmarks for pre-main-sequence evolutionary models. The component NU Ori C is confirmed as an intermediate-mass ($\sim$7\,M$_\odot$) star with nonthermal radio emission, offering rare evidence of magnetic activity near the boundary with the high-mass regime. Several additional sources exhibit astrometric accelerations or periodic residuals, revealing unseen companions and extending dynamical constraints to systems with only one radio-emitting component. These results highlight the capability of very long baseline interferometry astrometry to obtain precise and model-independent masses of young binaries, providing critical empirical anchors for stellar evolution models and new insights into the origin of magnetism in intermediate-mass stars.
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All authors Sergio A. Dzib, Jazmín Ordóñez-Toro, Laurent Loinard, Marina Kounkel, Gisela Ortiz-Leon, Phillip A. B. Galli, Luis F. Rodríguez, Amy J. Mioduszewski, Josep M. Masqué, Eoin O'Kelly, Jan Forbrich, Karla Moo-Herrera

High Energy Astrophysical Phenomena

Quantitative modelling of type Ia supernovae spectral time series III: Implications for type Ia supernovae standardisation in cosmology

M. R. Magee

The physics driving type Ia supernovae (SNe~Ia) standardisation in cosmology remains poorly-understood. Recent advances however mean that it is now possible to systematically analyse the explosion properties of large numbers of cosmological SNe~Ia. To that end we use riddler, a machine learning based framework for rapidly modelling SNe~Ia based on realistic explosion simulations, to perform quantitative spectral modelling of the Zwicky Transient Facility SN~Ia DR2 sample and determine their best-fitting explosion mechanism(s). We find that approximately two thirds of our sample is best reproduced by sub-Chandrasekhar mass explosions. Analysing their light curve and host galaxy properties, we find that Chandrasekhar mass explosions are not favoured for the fastest-evolving SNe~Ia, while sub-Chandrasekhar mass explosions are favoured for the reddest SNe~Ia. Due to the differences in their environments, selecting SNe~Ia in massive, passive galaxies could produce a homogeneous sample of violent merger SNe~Ia. We show that standardising each explosion mechanism independently reduces scatter in distance estimates and previously claimed environmental and non-linear light curve shape corrections may be due to changes in the relative populations of different explosion mechanisms. Although a step forward towards understanding SNe~Ia physics in cosmology, we highlight a number of limitations affecting our conclusions, including sample biases and small numbers. We therefore cannot assess the statistical significance of our results and they should be treated with caution. Larger and more uniformly observed samples will be key to determining the significance of any trends hinted at here.
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High Energy Astrophysical Phenomena

Quantitative modelling of type Ia supernovae spectral time series II: Exploring the diversity of thermonuclear explosion scenarios

M. R. Magee

Observations of type Ia supernovae (SNe Ia) have led to suggestions of multiple progenitor and explosion scenarios. Distinguishing between scenarios and tying specific SNe Ia to individual scenarios however has so far been challenging. Constraints on the explosion physics are often achieved through empirical modelling of SNe Ia spectra and qualitative assessments of the level of agreement. While this approach has provided useful insights, it cannot be scaled up to large numbers of SNe Ia in a robust and systematic way. As a machine learning based framework for automated and quantitative fitting of SNe Ia, riddler is designed to overcome these limitations. Neural networks are used as radiative transfer emulators and, in conjunction with nested sampling, emulated spectra are fit to observations of SNe Ia to determine the best-fitting input parameters and explosion scenario. In this work, we present recent improvements to riddler, including a significantly expanded training dataset covering pure deflagrations, delayed detonations, double detonations, gravitationally confined detonations, and violent mergers. We show that despite the increased complexity and variety of our training data, riddler is able to accurately recover the input parameters and explosion scenario of spectra unseen during training. Using riddler, we fit observations of three SNe Ia covering different sub-classes: SN 2011fe, SN 2005hk, and SN 2018byg. We detail a number of limitations and assumptions that should be considered when applying similar approaches. Nevertheless, the benefits of this approach and riddler will result in automated fitting playing an increasingly important role in the coming years.
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Astrophysics of Galaxies

Supermassive stars with embedded stellar black hole cores: dense assembling star clusters as faint multiple Little Red Dot systems

Antti Rantala

Numerical simulations have established that star clusters with densities comparable to the high redshift ($z>6$-$10$) James Webb Space Telescope (JWST) proto globular clusters may build up extremely massive (EMSs; $m_\mathrm{\star}>1000 M_\odot$) or even supermassive stars (SMSs; $m_\mathrm{\star}>10000 M_\odot$) and potentially intermediate mass black holes (IMBHs) through runaway stellar collisions. Using direct simulations of assembling star clusters including post-Newtonian black hole dynamics and stellar evolution, we demonstrate that in such dense environments ($\Sigma_\mathrm{h} \gtrsim 10^6 M_\odot$pc$^\mathrm{-2}$) stellar BHs ($m_\bullet \lesssim 60 M_\odot$), driven by rapid mass segregation and relaxation effects within the sphere of influence of the EMSs/SMSs, may strongly interact with the extremely massive stars and become embedded within their gaseous layers. We suggest that this quasi-star (QS) like embedded BH phase is a natural outcome of the runaway formation of EMSs/SMSs in the densest star clusters. The QS phase may be $1$-$2$ orders of magnitude longer in duration than the lifetime of the SMS, enabling an extended growth period by stellar collisions, and allows the formation of embedded gravitational wave sources if the QS captures more than a single stellar BH. The star cluster assembly region sizes ($\sim100$ pc), QS masses ($\gtrsim 10^4 M_\odot$) and their proximity to young, massive blue star forming clumps are consistent with the faint population of multiple little red dots (LRDs) recently discovered by the JWST.
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High Energy Astrophysical Phenomena

Discovery of ultra-fast outflows with v$_{\rm out}>0.3 \rm c$ in local bright active galactic nuclei

Laura Borrelli, Matteo Guainazzi, Giorgio Lanzuisi et al. (+5 more)

Ultra-fast outflows (UFOs) are mildly relativistic (outflow velocity $v_{out}>0.1c$) nuclear winds detected as blueshifted absorption lines from highly ionized, dense gas in the X-ray spectra of active galactic nuclei. The AGN feedback mechanism is believed to be powered by these outflows, which can inject a large amount of energy and momentum into the surrounding interstellar medium, shaping the coevolution of the AGNs and their host galaxies. We performed a systematic search and rigorous statistical assessment of the presence of UFOs in the 7-12 keV band, in a sample of bright local AGNs. This study also aims to understand whether the presence and characteristics of UFOs depend on the state of the sources, by studying the relations between the incidence of UFOs and the accretion properties of AGNs. We collected X-ray spectroscopic flux-limited XMM data of 33 observations of local (z<0.2) type 1 AGNs. We modeled their spectra in the 2-12 keV band using a combination of direct-continuum and reflection components and searched for absorption features. This represents the first systematic search for UFOs up to 12 keV. We performed Monte Carlo simulations to assess the statistical significance of the detected lines. We report strong detections of UFOs in six sources of the sample at the >95% confidence level via MC simulations, corresponding to a fraction of 18% in our sample. From the observed energies of each absorption line, we evaluated the respective wind velocities, which in some cases exceed 40% of the speed of light. The velocity distribution found in this work is therefore shifted to higher energies than those found in previous searches for UFOs in local sources, which were limited to 10 keV. Moreover, our analysis shows no correlation between the accretion properties of the SMBHs and the presence of winds. Furthermore, our study highlights the temporal variability of UFOs.
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All authors Laura Borrelli, Matteo Guainazzi, Giorgio Lanzuisi, Enrico Piconcelli, Laura Pentericci, Alfredo Luminari, Jiri Svoboda, Abhijeet Borkar

Astrophysics of Galaxies

Cluster-green galaxy correlations: where do these galaxies live?

Selene Levis, Facundo Rodriguez, Héctor J. Martínez et al. (+2 more)

Green valley (GV) galaxies are thought to represent a transitional population between star-forming and quiescent systems. However, their spatial distribution relative to galaxy systems remains unclear, particularly in relation to the large-scale environmental influence on galaxy quenching. We aim to determine whether GV galaxies preferentially inhabit specific environments within galaxy systems. We analyse the spatial distribution of GV galaxies using the cluster-galaxy cross-correlation function (CCF), based on the hydrodynamical simulation Illustris TNG300-1 (TNG) and observational data from the Sloan Digital Sky Survey (SDSS). Galaxy systems with $\log(M_{200}/M_{\odot}) \geq 13.5$ are used as cluster centres, while galaxies classified as blue, green, or red serve as tracers for the correlation analysis. In TNG, GV galaxies show an increasing relative fraction with cluster-centric distance, peaking in the outskirts, particularly for low-mass galaxies and haloes, and in some cases the GV fraction exceeds that of red galaxies. SDSS data reveal qualitatively similar trends, with the GV fraction remaining below that of red galaxies at all scales. Mock catalogues built from TNG and matched to SDSS selection functions reproduce the observational signal, indicating that projection effects drive the differences between datasets. GV galaxies preferentially reside in the outskirts of galaxy systems as satellites bound to the central halo, supporting a scenario in which they are transitioning objects influenced by environmental quenching.
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All authors Selene Levis, Facundo Rodriguez, Héctor J. Martínez, Valeria Coenda, Hernán Muriel