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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 9 June

Solar and Stellar Astrophysics

A systematic survey for hypervelocity runaways from thermonuclear supernovae

Kareem El-Badry, Klaus Werner, Ken J. Shen et al. (+16 more)

The explosion of a white dwarf (WD) in a close binary can launch a surviving runaway star at velocities of $\gtrsim 1000\, \rm km\,s^{-1}$. Such runaways provide a direct probe of thermonuclear supernovae (SNe) in double-degenerate binaries. Several candidate runaways are known, but their evolutionary states and the demographics of the broader population are uncertain. To enable robust population inference, we carry out a systematic survey for hypervelocity runaways with a simple selection function, selecting candidates based on large Gaia-inferred tangential velocities and blue colors. We classify 100% of the resulting 92 candidates using a combination of spectroscopic follow-up and archival data. The search yields ten suspected D$^6$ stars and three LP 40-365 stars. Three D$^6$ stars are new discoveries, including two hot ($T_{\rm eff} > 50,000$ K) objects and one cool ($T_{\rm eff}\approx 7,000$ K) object. We forward-model our survey under several proposed D$^6$ star evolutionary models, coupling each to a Galactic model and the survey selection function. No single model reproduces the observed diversity of D$^6$ stars, which likely reflects a range of remnant masses, ages, and heating mechanisms. Models in which runaway companions are heated by SN shocks alone are too faint and short-lived to explain most of the observed sample, while fully reheated models are too luminous and long-lived. Models with intermediate heating, as occurs in some simulations of violent mergers and partially disrupted remnants, best match the observed magnitude, distance, and kinematic-age distributions. The inferred D$^6$ star birth rate is model dependent, but the models that best match the observed population require rates of only a few percent of the Galactic SN Ia rate, perhaps implying that most SNe Ia result from WD binaries in which both components explode.
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All authors Kareem El-Badry, Klaus Werner, Ken J. Shen, Jay Strader, Antonio C. Rodriguez, Jiwon Jesse Han, Vedant Chandra, Laura Chomiuk, Zachary P. Vanderbosch, Lisa Blomberg, Natsuko Yamaguchi, Pranav Nagarajan, Ilaria Caiazzo, Jan van Roestel, Hila Glanz, Tin Long Sunny Wong, Aakash Bhat, Mark A. Hollands, Boris T. Gänsicke

Earth and Planetary Astrophysics

Revealing the Origin of Desert Dwellers via Stellar Obliquities

Tim Hallatt, James E. Owen and Sarah Millholland

Observations suggest that the hot Neptune desert contains the remnants of destroyed gas giants. Recent theoretical work has shown that gas giant destruction via Roche lobe overflow (RLO) can indeed populate the desert with remnant planets, but only if mass transfer removes most of the planet's orbital angular momentum ("lossy" RLO). Motivated by the fact that stellar accretion naturally gives rise to such lossy RLO, in this Letter we examine how planet-to-star mass and angular momentum transfer manifests in the distribution of stellar obliquities. We find that RLO tilts host stars into spin/orbit alignment (within a few ${\sim}$tens of degrees) regardless of initial conditions. Obliquity damping by RLO can only be reversed by the presence of misaligned companion planets within ${\lesssim}$2 au. While tides and mass transfer usually produce stellar spin up, host stars can also emerge from RLO slowly rotating if systems begin strongly retrograde; retrograde RLO reconciles theory with the anomalously slow rotation of the desert dweller host, LTT 9779. Predicted spin/orbit alignment may differentiate RLO from alternative giant planet destruction mechanisms, in particular hot Jupiter disruption during high eccentricity migration (which tends to produce broadly distributed stellar obliquities). We summarize other population-level predictions that can further distinguish RLO from high eccentricity migration. Our work suggests that follow-up obliquity measurements may reveal the formation pathways of desert dwellers, and potentially open a window into gas giants' exposed interiors.
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High Energy Astrophysical Phenomena

A phase-coherent timing solution for the X-ray dim isolated neutron star eRASSU J131716.9-402647

J. Kurpas, A. M. Pires, A. D. Schwope et al. (+2 more)

Based on its predominantly thermal X-ray emission and long spin period, the isolated neutron star eRASSU J131716.9-402647 is one of the most promising candidates for membership in the still small class of X-ray dim isolated neutron stars (XDINSs). Confirmation of this classification, however, requires a more detailed characterisation of the source's timing and spectral properties. In this work, we present new NICER observations which, together with previous X-ray follow-up, allow us to constrain the timing properties and long-term evolution of eRASSU J131716.9-402647. We obtain a coherent timing solution with a spin period of $P\sim12.8$ s and a period derivative of $\dot{P}\sim9\times 10^{-14}$ s s$^{-1}$, which best-describes the spin evolution of the source. These parameters imply a dipolar magnetic field strength of $3\times10^{13}$ G and a spin-down luminosity of order $10^{30}$ erg s$^{-1}$. Spectral modelling reveals no significant change in the spectral state over the 15 months of observational monitoring and indicates a thermal luminosity that likely exceeds the rotational energy loss. This suggests a thermal evolution that has been significantly influenced by past reheating. The energy dependence of the double-humped pulse profile closely resembles that observed in the XDINS RX J1308.6+2127, with the pulsed fraction increasing towards higher energies. Taken together, these results unambiguously confirm the XDINS nature of eRASSU J131716.9-402647, making it the first newly confirmed XDINS in more than two decades.
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All authors J. Kurpas, A. M. Pires, A. D. Schwope, F. Haberl, S. Sheth

Astrophysics of Galaxies

Reassessing the low-$\alpha$ massive sequence stars in Gaia RVS

G. Nandakumar, G. Kordopatis, M. Schultheis et al. (+4 more)

Recently, a chemically depleted young massive stellar population was identified using the spectroscopic catalogue of Gaia DR3. To explain its characteristics, a recent enhanced star formation event, via a third infall occurring within the last 2 Gyr, has been evoked. In this paper we reassess the low alpha sequence of massive stars identified in the Gaia spectroscopic catalog and investigate their presence in other Milky Way spectroscopic survey catalogs. We select massive sequence stars and RGB stars from the Gaia DR3 catalogue using the same filtering strategy adopted in previous chemical cartography studies. These samples are then cross matched with APOGEE DR17, GALAH DR4, and Gaia CNN to enable a detailed comparison of stellar parameters and alpha abundances. Stellar masses are estimated by projecting their atmospheric parameters and infrared magnitudes onto PARSEC isochrones. For the massive star sample, we find large discrepancies in stellar parameters and calcium abundances between Gaia DR3 and the three external surveys. The external catalogues do not show a low ca sequence but rather resemble those of thin disc RGB stars. Other alpha elements (si in APOGEE and GALAH, and mg in GALAH) also do not show depleted values. In APOGEE, however, massive sequence stars with metallicities above -0.5 dex display lower mg abundances. We attribute this to APOGEE's use of macroturbulence velocities calibrated solely on metallicity. Our analysis does not show any evidence for alpha element depletion in massive sequence stars. Alpha abundances of massive sequence stars derived from the Gaia RVS spectra should therefore be used with caution. Nevertheless, the previously proposed three infall chemical evolution models remain plausible: even without a chemically depleted young massive population, scenarios involving only mild dilution could still account for recent star formation episodes.
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All authors G. Nandakumar, G. Kordopatis, M. Schultheis, N. Ryde, P. A. Palicio, E. Spitoni, F. Matteucci

Solar and Stellar Astrophysics

AutoClassMK: A public neural network for automatic 2D MK classification of normal stars in basic Python

C. Ian Short

We present AutoClassMK, a simple, fully-connected, five-layer double-headed neural network written entirely in Python and Numpy that classifies normal stellar spectra conforming to the libr18 MK atlas in the 2D MK classification system with a high degree of precision and recall. AutoClassMK has the distinction of having transparent basic code with no calls to specialized libraries. In this paper we take care to explicitly describe in detail the ideas and operations that enable the network. Training AutoClassMK required us to develop large, noisy artificial training and test sets by augmenting the libr18 and libr18_27 MK atlases and to simplify the luminosity classification so that every combination of spectral- and luminosity-class is represented in the training set. We then test the network's ability to predict the MK spectral type of noisy augmentations of spectra in the libr18_225 MK atlas. We then implemented the same architecture in PyTorch to gain further insight and to enable execution on CUDA GPU's. All codes and the training and test sets are available from the OpenStars www site: www.ap.smu.ca/OpenStars.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

DarkAgents

Michele Lucente, Silvia Pascoli, Filippo Sala et al. (+1 more)

We present DarkAgents: a multi-agent system that leverages the reasoning and code-generation capabilities of large language models (LLMs), together with deterministic tested human-written code, to build orchestrated pipelines for theoretical astroparticle physics research. While related approaches have been proposed in collider physics and cosmology, DarkAgents targets the specific challenges of this domain, such as model building, complex pipeline computations, multiple constraints and assumption auditing. The framework can be powered by different agentic command-line tools, including Mistral's, Anthropic's, OpenAI's and local LLMs via Ollama. As first implementation, we apply DarkAgents to the study of cosmological first order transitions, starting from a classically scale-invariant particle-physics model and ending with the fit to the NANOGrav nanohertz gravitational-waves spectrum. DarkAgent-PT provides as output i) the best-fit values of model parameters, ii) their existing experimental and observational constraints, iii) an audit report of the assumptions and priors entering both i) and ii), of particular relevance for astroparticle physics. Our test runs identify inconsistencies in some fits in the literature and produce novel ones based on the dissipative bulk-flow GW template. The code is publicly available at https://github.com/PhysicsZandi/DarkAgents.
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All authors Michele Lucente, Silvia Pascoli, Filippo Sala, Matteo Zandi

High Energy Astrophysical Phenomena

Resolving SLX 1744-299 and SLX 1744-300 in the hard X-ray band: implications for their ultracompact nature

Enzo A. Saavedra, Montserrat Armas Padilla and Teo Muñoz-Darias

Persistent, low-luminosity low-mass X-ray binaries (LMXBs) offer a unique opportunity to study accretion in this poorly understood regime, as well as to unveil new members of the ultracompact X-ray binary (UCXB) family, characterised by orbital periods ($P_{\rm orb}$) shorter than $\sim 80$ min. We report on a NuSTAR archival observation that, for the first time above 10 keV, spatially resolves the Galactic Centre pair SLX 1744$-$299 and SLX 1744$-$300. We find SLX 1744$-$300 to be slightly brighter, with a flux ratio of $\sim 1.15$, increasing to $\sim 1.3$ when extrapolated to 0.5$-$10 keV. Both the timing (root-mean-square variability) and spectral properties (well described in both cases by a thermal Comptonisation model) indicate that the systems were in the hard state. The two sources, however, display markedly different behaviour throughout the observation. SLX 1744$-$299 shows a gradual flux decline consistent with a decrease in the mass-accretion rate, whereas SLX 1744$-$300 remains steady but exhibits two short-recurrence Type-I X-ray bursts indicative of mixed H/He burning. Combining our results with previously reported upper limits on the distance, we derive low persistent X-ray luminosities of $L_{\rm X}\lesssim 1.1\times10^{36}$ erg s$^{-1}$ and $L_{\rm X}\lesssim 2.6\times10^{36}$ erg s$^{-1}$ (3$-$78 keV) for SLX 1744$-$299 and SLX 1744$-$300, respectively. The corresponding mass-accretion rates, when compared with the critical values from the disc instability model, favour $P_{\rm orb}\lesssim 90$ min and $P_{\rm orb}\lesssim 105-155$ min. Although both limits are formally compatible with the UCXB regime, the case of SLX 1744$-$299 appears significantly more compelling, also considering the previously reported intermediate-duration burst.
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Solar and Stellar Astrophysics

GASTAG evolutionary tracks and isochrones from coupled 1D and 3D models: Systematic temperature offsets in red giants

Yixiao Zhou, Jiaqi Ying, Yaguang Li et al. (+1 more)

Models of stellar structure and evolution describe the global and internal properties of stars throughout their lifetimes and are indispensable for studies of stellar clusters and Galactic evolution. However, most 1D evolutionary calculations rely on simplified treatment of convection, resulting in inaccurate near-surface structures and non-negligible uncertainties in the predicted fundamental parameters of low-mass stars. In a series of previous works, a novel approach was developed to couple 1D stellar interior models with 3D model atmospheres throughout the evolutionary calculation. This 1D-3D coupling method makes predicted stellar properties effectively independent of the mixing-length parameter. To expand this framework to ensemble studies of stars and age determinations of clusters, we present the GASTAG stellar evolutionary tracks and isochrones constructed using the 1D-3D coupling approach. Comparing effective temperatures from the APOGEE-Kepler catalog with GASTAG predictions, we find the theoretical temperatures are cooler by about 70 K near solar metallicity. Our isochrones are compared with observed color-magnitude diagrams of star clusters spanning from $\rm [Fe/H] = 0.3$ to $-1.9$. In all cases, the synthesized and observed diagrams agree excellently in the main-sequence, turn-off, and subgiant regions, while isochrones predict systematically cooler red giant branches. Taking these independent findings together reveals that the temperature mismatch is most likely due to deficiencies in stellar models. Because GASTAG is constructed using a method that substantially reduces uncertainties associated with surface boundary conditions and the mixing-length parameter, the difference between modeling and observation can be more confidently attributed to other ingredients in the models, such as $\alpha$-element abundances or uncertainties in low-temperature opacities.
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All authors Yixiao Zhou, Jiaqi Ying, Yaguang Li, Luca Casagrande

Astrophysics of Galaxies

The Doppler effect of the Milky Way rotation on LISA

Giorgio Mentasti and Quentin Baghi

The galactic background of gravitational waves (GWs) is expected to be anisotropic due to the spatial distribution and kinematics of sources in the Milky Way. In this work, we model the stellar density and velocity profiles of the Galaxy and compute the resulting GW spectrum as a function of direction. We account for the Doppler shift induced by the peculiar velocities of stars and the observer's motion. Using a Fisher matrix formalism, we forecast the ability of future detectors (e.g., LISA) to distinguish between models that include or neglect these kinematic effects. We find that if one does not take into account the rotation of the galaxy, the inference of the parameters describing the galactic background can suffer observable biases.
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Instrumentation and Methods for Astrophysics

The Ohio SETI Program – The Last Decades

Abel Méndez, Robert S. Dixon and Russell K. Childers

The Ohio State University Radio Observatory (OSURO), known as the Big Ear, played a pivotal role in both radio astronomy and the Search for Extraterrestrial Intelligence (SETI). Following the completion of the Ohio Sky Survey, the facility was repurposed in 1973 as the world's first full-time dedicated SETI observatory and operated continuously until its decommissioning in 1998. During this period, the Ohio SETI Program evolved from an 8-channel hydrogen-line receiver into increasingly sophisticated survey systems. Over three decades, these surveys covered approximately 70% of the radio sky using a largely consistent instrumental configuration, creating one of the most extensive long-term radio astronomy archives ever assembled. The program is best known for the detection of the Wow! Signal in 1977, but it also accumulated an archive of over 40,000 transient narrowband events, revealed unusual concentrations of radio bursts near the Galactic Center, and established one of the longest continuous radio monitoring records in astronomy. Following the closure of the Big Ear, its scientific legacy continued through Project Argus and, more recently, the Arecibo Wow! project. This paper provides an overview of the final decades of the Ohio SETI Program, including its instrumentation, survey strategies, scientific discoveries, and enduring impact on SETI, time-domain radio astronomy, and the preservation of historical astronomical data. Despite its scientific significance, most of the data collected by the Ohio SETI Program remains unexplored, leaving a unique archive available for future research.
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Instrumentation and Methods for Astrophysics

A data-driven method for measuring corner-clipping probabilities in segmented particle detectors

Joaquín de Jesús, Juan Manuel Figueira, Federico Sánchez et al. (+1 more)

The accuracy of particle counting in highly segmented detectors is limited by the corner-clipping effect, in which a single ionizing particle generates signals in adjacent detection elements. This phenomenon introduces a direction-dependent overcounting bias that distorts reconstructed observables and is commonly corrected using Monte-Carlo simulations, thereby inheriting modeling uncertainties. We present a fully data-driven method to directly measure the single-particle corner-clipping probability, exploiting the nanosecond timing resolution of modern detectors to statistically distinguish genuine corner-clipping events from random coincidences, with non-neighboring detection elements serving as an intrinsic control sample. The technique is validated using detailed simulations of the Underground Muon Detector of the Pierre Auger Observatory, reproducing the true angular dependence of the corner-clipping probability with absolute deviations below 0.01. To parameterize the results, we introduce a compact analytical model incorporating detector geometry, minimum detectable path length, and orientation-independent contributions. The proposed methodology and parameterization enable the direct incorporation of data-driven corner-clipping corrections into reconstruction algorithms, mitigating the overcounting bias and ultimately yielding a more accurate determination of the muonic component of extensive air showers. These developments are broadly applicable to any segmented detector with sufficient timing resolution, making them relevant to a wide range of experiments in high-energy and astroparticle physics.
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All authors Joaquín de Jesús, Juan Manuel Figueira, Federico Sánchez, Darko Veberič

Astrophysics of Galaxies

MusE GAs FLOw and Wind (MEGAFLOW) XIV: Background-Galaxy Absorption Reveals Kiloparsec-Scale Structure in the Cool Circumgalactic Medium

Yucheng Guo, Nicolas F. Bouché, Martin Wendt et al. (+9 more)

The properties of the cool ($T\sim10^4$~K) gas in the circumgalactic medium (CGM) are closely linked to the physical mechanisms that create and maintain this multiphase medium. The cool CGM is thought to consist of discrete clouds, whose characteristic size is unknown. Here we present a geometric and direct approach to constrain the coherence scale of these cool structures using stacked MgII absorption lines measured against extended background galaxies and effectively point-like background quasars, whose sizes are a few kpc and $\lesssim 0.01$pc, respectively. When the background-source size is smaller than the coherence scale of the foreground clouds, incomplete covering lowers the detection fraction and causes the median stacked absorption to differ from the mean. For stacked MgII absorption against background galaxies, the mean and median equivalent width (EW) profiles are broadly consistent. For stacked MgII absorption against background quasars, by contrast, the median and mean EW profiles differ significantly, reaching a $\approx10\sigma$ difference beyond 100 kpc. Furthermore, we find that the median and mean EW profiles are broadly consistent for large background galaxies (median half-light radius $\approx 6.6$ kpc), but differ at the $\approx3\sigma$ level for small background galaxies ($\approx 1.5$ kpc). This suggests that the MgII-bearing gas has an effective transverse coherence scale of order a few kiloparsecs, broadly consistent with the $\sim$2–7 kpc range probed by the background galaxies. Using a toy model in which the CGM is populated with discrete cool clouds, we show that the observed differences arise naturally from the combination of partial covering and beam averaging. Our results provide a new geometry-based measure of the small-scale structure of cool CGM gas.
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All authors Yucheng Guo, Nicolas F. Bouché, Martin Wendt, Timothy Heckman, Joop Schaye, Sanchayeeta Borthakur, Johannes Zabl, Maxime Cherrey, Sowgat Muzahid, Ismael Pessa, Ramona Augustin, Daria Kozlova

Astrophysics of Galaxies

High-Resolution ALMA Imaging for a Gravitationally-lensed Quasar at $z=6.5$: Constraining the AGN Contribution to Galactic-Scale Dust Heating

Minghao Yue, Xiaohui Fan, Anna-Christina Eilers et al. (+6 more)

We present high-resolution (beam size $0\farcs076\times0\farcs040$) Atacama Large Millimeter/submillimeter Array (ALMA) observations of the far-infrared $(\lambda_\text{rest}=162.7\mu\rm{m})$ dust continuum of J0439+1634, a gravitationally lensed quasar at $z=6.52$. We perform pixelated lens modeling for the visibility data, finding that J0439+1634 is well-described by a singular isothermal ellipsoid plus an external shear lensing model. The best-fit lensing potential exhibits a naked-cusp configuration, confirming the finding in Fan et al. (2019). The reconstructed source plane continuum emission shows a compact bright core, with size $\lesssim200$ pc and peak brightness $\sim0.6 \text{ Jy arcsec}^{-2}$. The total continuum flux at 245 GHz is $3.36\pm0.02$ mJy. The flux magnification is {$4.63\pm0.03$}, indicating an average source-plane resolution of $0\farcs019$ (equivalent to 104 pc). The spatial resolution around the supermassive black hole reaches $\sim36$ pc. %Using the new lensing model, we re-fit the Hubble Space Telescope image for J0439+1634, and find that the position of the optical quasar is consistent with the brightest pixel in the dust continuum map. Leveraging the exceptional source-plane resolution, we build a radiative transfer model to describe the observed dust emission profile. The best-fit model indicates that heated dust from the active galactic nucleus (AGN) dominates the sub-millimeter emission at $r\lesssim100$ pc and that star-heated dust dominates the outer region of the host galaxy. AGN heating contributes {$\sim13\%$} to the observed sub-mm flux. Therefore, previous far-infrared-based star formation rate measurements for most high-redshift quasars are likely mildly overestimated.
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All authors Minghao Yue, Xiaohui Fan, Anna-Christina Eilers, Jinyi Yang, Feige Wang, Jianwei Lyu, James W. Nightingale, Ann Zabludoff, Ran Wang

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

A Friendly Phantom: Late-time AdS-to-dS transition and cosmological tensions

Özgür Akarsu, Leandros Perivolaropoulos, A. Emrah Yükselci et al. (+1 more)

We present Ph-$\Lambda_{\rm s}$CDM, a phantom-scalar realization within General Relativity of the sign-switching cosmological-constant idea, $\Lambda_{\rm s}$CDM, in which a phantom scalar evolving on a bounded hyperbolic-tangent potential induces a smooth mirror AdS-to-dS transition in the late-time dark-energy density. The wrong-sign kinetic term, usually viewed as pathological, becomes the mechanism lifting the field from a negative- to a positive-energy vacuum-like regime. The construction also shows that the field can become repulsive while its energy density is still negative. The cosmology nevertheless remains controlled: total energy stays positive, the late-time attractor is de Sitter rather than a Big Rip, and the dynamics remain safely infrared. Ph-$\Lambda_{\rm s}$CDM thus offers a concrete late-time mechanism with the potential to address multiple cosmological tensions.
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All authors Özgür Akarsu, Leandros Perivolaropoulos, A. Emrah Yükselci, Alexander Zhuk

Instrumentation and Methods for Astrophysics · Cross-listed from cond-mat.mtrl-sci

In-situ total scattering investigation of crystalline ordering in amorphous ion-beam sputtered thin films for interferometric gravitational wave detectors

Alberto Martinelli, Giulio Favaro, Giacomo Ciani et al. (+9 more)

Amorphous tantala is an important optical material used in a number of high-precision optical applications, including gravitational wave interferometry. In this paper, we study in-situ the structural changes that occur in amorphous ion-beam sputtered coatings during an annealing treatment by means of a synchrotron radiation scattering experiment. The scattering signal is measured as a function of time on a large range of the Q-space. X-Ray diffraction and Rietveld analysis are used to study crystallization during the annealing treatment, whereas pair distribution function analysis allows to inspect the structural changes occurring during the amorphous to crystalline transition. Our findings indicate that several structural rearrangements occur in parallel, namely a first quick establishment of a backbone structure in the cationic substructure appearing on a rather extended range (up to 100 Angstrom), followed by a progressive rearrangement of the oxygen atoms environment which gradually increases the crystallinity of the structure.
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All authors Alberto Martinelli, Giulio Favaro, Giacomo Ciani, Livia Conti, Jean-Pierre Zendri, David Hofman, Massimo Granata, Angela Trapananti, Flavio Travasso, Laura Silenzi, Valeria Milotti, Marco Bazzan

Astrophysics of Galaxies

The Small-scale Structures in the Wind of Messier 82

Yucheng Guo, Timothy Heckman, Sanchayeeta Borthakur et al. (+10 more)

Small-scale multiphase structure plays a central role in galactic-wind evolution, yet the parsec-scale morphology and excitation of the warm ionised gas remain poorly constrained. We present deep HST narrow-band imaging of the southern wind of Messier~82 (M82) in Halpha, [OIII], [SII], and [NII], designed to resolve the warm ionised phase on parsec scales. The Halpha emission is detected to 2.1 kpc above the disk, while the fainter emission lines are detected over smaller radial extents, with [OIII] reaching 1.5kpc. We develop a filament-finding pipeline for the Halpha image and construct a quantitative catalogue of the filamentary structures. The wind forms a highly connected network of strands and knots, dominated by compact filaments with typical projected widths of 5.3pc and lengths of 9.5pc. Both the projected covering fraction and the line-flux contribution of the filamentary component decline with height, showing that the outer wind becomes increasingly dominated by diffuse emission. Optical line-ratio diagnostics indicate that the warm ionised gas occupies an intermediate excitation regime: photoionisation by the central starburst can energetically power the observed Halpha luminosity, while the systematic separation between filamentary and diffuse emission, together with the evolution of the line ratios with vertical distance, suggests an increasing contribution from shocks or other similar heating in the diffuse outer wind. These results show that separating filamentary and diffuse emission in high-resolution imaging provides a powerful way to connect the morphology, excitation, and multiphase structure of galactic winds.
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All authors Yucheng Guo, Timothy Heckman, Sanchayeeta Borthakur, Peixin Zhu, Rosalia O'Brien, Ralph S. Sutherland, Lisa J. Kewley, Lee Armus, D. B. Fisher, Sebastian Lopez, Brant E. Robertson, Evan E. Schneider, Patrick L. Shopbell

Solar and Stellar Astrophysics

MINDS survey of silicates in T Tauri disks: Correlation between dust and gas

J. Varga, Th. Henning, L. B. F. M. Waters et al. (+20 more)

Context. Silicates are key constituents of planet-forming disks and major building blocks of rocky planets. Mid-infrared spectral features of micron-sized silicate grains trace grain growth, mineralogy, and disk chemistry. Aims. We characterized the dust mineralogy in T Tauri disks using James Webb Space Telescope (JWST)/Mid-Infrared Instrument (MIRI) observations and investigated the connections between the dust and molecular gas compositions. Methods. We analyzed JWST/MIRI spectra of 26 disks from the MIRI mid-Infrared Disk Survey (MINDS). Using our DustComp spectral decomposition tool, we inferred the mass fractions of individual dust species. The fits included Mg$_2$SiO$_4$ (forsterite), MgSiO$_3$ (enstatite), and SiO$_2$ (silica), together with amorphous silicates of corresponding stoichiometry. Results. Mg-rich (and Fe-poor) silicates reproduce the data well, with residuals typically within $\pm3\%$. Grain size distributions are skewed toward sizes larger than $2\mu$m, indicating significant growth. The average dust composition is dominated by Mg$_2$SiO$_4$-stoichiometry grains ($\sim60\%$), followed by MgSiO$_3$ ($\sim30\%$) and SiO$_2$ ($\sim10\%$). Crystalline mass fractions are typically in the $5$-$24\%$ range, with a mean of $14\%$. Annealed silica is robustly detected in nine objects, with cristobalite as the main polymorph. We found a correlation between dust and molecular gas composition: disks with strong annealed silica features show stronger CO$_2$ emission, while forsterite-rich disks display stronger H$_2$O emission. Disks with annealed silica features may also have elevated gas-phase C/O ratios. Conclusions. The observed dust-gas correlation may provide the first indication that the molecular gas composition regulates the availability of dust species in the inner disk.
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All authors J. Varga, Th. Henning, L. B. F. M. Waters, I. Kamp, Á. Kóspál, P. Ábrahám, O. Absil, A. M. Arabhavi, D. Gasman, S. L. Grant, M. Güdel, H. Jang, T. Kaeufer, J. Kanwar, N. T. Kurtovic, P.-O. Lagage, G. Perotti, A. Somigliana, L. M. Stapper, B. Tabone, M. Temmink, E. F. van Dishoeck, M. Vlasblom

Solar and Stellar Astrophysics

Spectroscopic analysis of RGB stars in nine open clusters

Saulo de Oliveira Cantanhêde, Alan Alves-Brito, Rodolfo Smiljanic et al. (+4 more)

Stellar clusters are crucial tools for studying the age, spatial distribution, dynamics, kinematics, and chemical composition of different Galactic stellar populations. In this work, we used red giant stars from open clusters to better understand the extra-mixing process through the CNO abundances and $^{12}$C/$^{13}$C, $^{16}$O/$^{17}$O and $^{16}$O/$^{18}$O isotopic ratios determined using high-quality spectra in the visible and near-infrared regions. We analysed the radial velocities and chemical composition of 22 K-type giant stars from nine open clusters (NGC188, NGC2682, NGC3680, NGC5822, IC4756, NGC6633, NGC3532, NGC6281, and NGC5460). High-resolution and high signal-to-noise spectra of stars in the NGC188 cluster were obtained with the ESPaDOnS spectrograph at the CFHT in the visible region. The stars in the other clusters were observed with the CRIRES spectrograph at the VLT. We used IRAF to compute radial velocities and Turbospectrum and MOOG for the chemical analysis. The values obtained for the radial velocities and abundances of the sample are similar to those found in the literature. The results in the visible and infrared support the occurrence and predicted mass dependence of thermohaline mixing on the red giant branch and of rotation-induced mixing on the main sequence. Variations of the initial abundances of $^{17}$O and $^{18}$O may be needed to explain the dispersion of the oxygen isotopic ratios in red giant stars.
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All authors Saulo de Oliveira Cantanhêde, Alan Alves-Brito, Rodolfo Smiljanic, Beatriz Barbuy, Nadège Lagarde, Corinne Charbonnel, Pierre North

Solar and Stellar Astrophysics

Dimming and pulsation shock of the coalesced star V838 Monocerotis

T. Kamiński, C. E. Woodward, T. Liimets et al. (+3 more)

V838 Mon is the remnant of a stellar merger that occurred in 2002. Twenty-four years after the merger, the remnant closely resembles a red supergiant, but its luminosity is sustained by core H burning and continued contraction toward hydrostatic equilibrium. In late 2025, the system entered the deepest dimming event observed since 2006. We characterize the 2026 dimming using multiband photometry and high-resolution spectroscopy spanning from the dimming minimum through the recovery phase. The photometric color evolution during the dimming can be well reproduced by dust extinction with $A_V=1.26$ mag and $R_V=1.8$, consistent with a transiting clump of freshly formed circumstellar dust composed of small silicate or alumina grains. The photospheric effective temperature changed by no more than ~200 K during the event. During the recovery phase, H recombination lines from the Balmer, Paschen, and Brackett series appeared in emission, with anomalous line ratios matching those of pulsating Mira stars near maximum light. These features are interpreted as arising from a sub-photospheric pulsation shock. Simultaneously, low-ionization metal lines appeared blueshifted by 90 km/s relative to the stellar rest frame, tracing shock-affected gas on the near side of the stellar disk. The spectroscopic sequence suggests that the 2026 dimming was itself triggered by a preceding pulsation shock that occurred earlier in 2025. We present the first observational evidence for pulsations in a stellar merger remnant. Twenty-four years after the coalescence, V838 Mon exhibits pulsation shocks qualitatively identical to those of red supergiants and Mira stars, confirming predictions of pulsational instability in post-merger objects. A further dimming event, triggered by the observed shock, is predicted to start in northern summer 2026.
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All authors T. Kamiński, C. E. Woodward, T. Liimets, M. R. Schmidt, A. A. Djupvik, I. Ilyin

High Energy Astrophysical Phenomena

The link between obscured accretion and mildly relativistic precessing jets

Rob Fender and Sara Motta

We have recently shown evidence that the most relativistic jets (with Lorentz factor >2) from stellar-mass black holes in X-ray binary systems may be locked to a fixed axis, likely the spin axis of the black hole. Slower, mildly relativistic jets (with velocities typically ~ 0.3c) are often seen to precess and can be associated with both neutron stars and black holes. In this paper we demonstrate an additional clear link between highly obscured systems and these lower-velocity, precessing jets. We speculate that this link may be due to mass-loading of the jets close to their launch sites, since these obscured systems are likely to be examples of (sometimes persistent, other times transient) super-Eddington accretion. The fastest relativistic jets are now seen to be both locked to a fixed direction, likely the black hole spin axis, and to be launched in low-density environments, while jets launched in dense environments are generally slower and very likely to precess.
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High Energy Astrophysical Phenomena

Time lags as proxy of spectral evolution in gamma-ray bursts

C. Maraventano, F. Daigne, R. Mochkovitch et al. (+3 more)

Positive lags in gamma-ray bursts (GRBs), where hard photons anticipate softer ones, provide a unique window into the temporal evolution of their prompt emission. Negative lags, when hard photons are delayed, are instead more enigmatic to interpret. Disentangling the effects that produce both kinds of lags is critical for identifying the physical mechanisms at work in the prompt and early afterglow phases of GRBs. We investigate the potential of time lags for distinguishing different emission components at different energy bands. Using data from the Fermi Gamma-ray Burst Monitor (GBM) and the LAT Low Energy(LLE) technique, we perform a time-resolved joint spectral analysis in the range 10 keV-100 MeV for two exceptionally bright bursts, GRB 160625B and GRB 190114C. Time lags between the lowest-energy band (10-100 keV) and progressively higher-energy bands up to 30-100 MeV were computed across their distinct emission episodes via the cross-correlation function. For GRB 160625B, the spectra are described by a single component with clear hard-to-soft evolution, and the time lags are always positive. Analysis of the high-energy exponential cutoff, likely originating above the photosphere, yields bulk Lorentz factor estimates of $\Gamma \sim 120-250$. GRB 190114C exhibits negative lags in the 30-100 MeV band, coinciding with a delayed high-energy powerlaw component that dominates the LLE range after ~2.5 s. Comparison with multi-wavelength observations shows some compatibility with the early afterglow, though its origin remains open, leaving room for external shocks or internal dissipation. Time lags are effective diagnostic tools for the spectral evolution of GRBs: positive lags trace the softening of the prompt emission, whereas negative lags indicate the appearance of a new, independent high-energy spectral component.
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All authors C. Maraventano, F. Daigne, R. Mochkovitch, L. Nava, G. Ghirlanda, T. Di Salvo

Earth and Planetary Astrophysics

First detection of HDO ice in a protoplanetary disk

Alexey Potapov, Piyush Kalambkar, Jeroen Bouwman et al. (+4 more)

Protoplanetary disks are the birthplace of planets and planetary systems. Investigating the molecular inventory of disks is key to linking the chemical evolution of the interstellar medium and the makeup of planets and their atmospheres. In particular, tracing the history of the deuterium enrichment of water along the journey from interstellar clouds through protoplanetary disks to planetary systems provides critical insights into the chemical inheritance. We aim to investigate the chemical composition of ices in protoplanetary disks; specifically, the presence of HDO ice that ought to be present, but has not been detected in disks thus far. We analyzed JWST/NIRSpec observations of the 132-1832 edge-on disk located in the Orion Nebula Cluster using the ENIIGMA fitting tool and unique laboratory data. We report on the first detections of HDO ice in a protoplanetary disk. The estimated upper limit for the HDO/H$_2$O ratio for 132-1832 is much higher, compared to HDO/H$_2$O ratios obtained for chondrites, comets, and embedded young stellar objects. In the disk ices, beyond HDO, we detected H$_2$O, CO$_2$, $^{13}$CO$_2$, CO, OCN$^-$, and OCS, species, whose presence has also been detected in other disks. The HDO ice detection may point to the efficient ice processing in the disk and confirm the findings of laboratory experiments on deuterated ices.
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All authors Alexey Potapov, Piyush Kalambkar, Jeroen Bouwman, Christiaan Boersma, Hiroshi Terada, Will R. Rocha, Hendrik Linz

Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG

When Do Autoregressive Sequence Models Forecast Physical Wavefields? A Controlled Study on Synthetic Seismograms

Waleed Esmail, Stuart Russell, Jana Klinge et al. (+2 more)

Long-horizon autoregressive forecasting of oscillatory physical signals, such as seismograms, gravitational-wave strain, and similar wavefields is limited by error accumulation: as a causal model is fed its own outputs over hundreds of steps, small per-step errors compound into phase drift that pointwise metrics fail to detect. We ask when such rollout stays stable, using synthetic three-component seismograms as a physically structured testbed and the SeismoGPT autoregressive forecaster as the model under study. Through controlled architecture ablations evaluated on free rollout with paired significance tests, we isolate the contribution of each design choice. Multi-token prediction is the dominant stabilizer, accounting for almost the entire improvement over a single-token baseline ($+0.042$ median NCC); a horizon-embedding hybrid prediction head and a cross-horizon STFT-magnitude coherence loss each add a small but consistent further gain. Performance depends sharply on a context-ratio threshold near one, roughly the full P-S interval of observed signal, below which rollout generalization collapses. The dominant residual failure is a polarity inversion: a magnitude-based spectral loss reduces its incidence but, by construction, cannot penalize an inverted segment once it occurs, identifying phase-aware objectives as the natural next step. We frame this as a controlled study of rollout stability on oscillatory wavefields, not a benchmark of forecasting architectures.
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All authors Waleed Esmail, Stuart Russell, Jana Klinge, Alexander Kappes, Christine Thomas

Cosmology and Nongalactic Astrophysics

Isochrones in primordial magnetic field evolution

Axel Brandenburg, Mattia Cielo, Oksana Iarygina et al. (+1 more)

In the early universe, a primordial magnetic field undergoes a turbulent decay while its length scale increases due to an inverse cascade. The size of the largest processed eddy scales with the Alfvén speed and grows with time. In a diagram of Alfvén speed vs.\ length scale, all possible solutions must lie on a line through the origin with a slope proportional to the inverse of the present time. In principle, however, such lines can also be defined for earlier times. The lines for earlier times form isochrones that may be observationally accessible, for example through the magnetically driven stochastic gravitational wave background. However, the position and slope of these isochrones is sensitive to the zero point of the time. Here, we show that for any initial magnetic field, a proper time can be determined such that the resulting isochrones at early times are nearly parallel to those at late times, i.e., they have the same slope. We use two-dimensional numerical simulations of decaying MHD turbulence and vary the initial position of the peak of the magnetic energy spectrum. In this case, the evolution is governed by the conservation of anastrophy. A fit to the Alfvén time yields an accurate estimate of the factor by which the decay time is longer than the Alfvén time, while the offset in the fit provides an estimate of the proper time that needs to be added to the nominal time since the beginning of each simulation. We also find that the presence of an initial velocity field of realistic strength helps producing a more straight track from the beginning. The magnetic field parameters lie on universal isochrones even for early times. They provide a testable framework for magnetic fields generated at times as early as the end of inflation, starting with the time of reheating.
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All authors Axel Brandenburg, Mattia Cielo, Oksana Iarygina, Franco Vazza

Astrophysics of Galaxies

Formation of Parallel Stellar Streams through Encounters with Dark Matter Subhalos and Intermediate-Mass Black Holes

Yuka Kaneda, Masao Mori, Yohei Miki et al. (+2 more)

Dark matter subhalos and intermediate-mass black holes wandering in the Milky Way and the Andromeda galaxy are difficult to directly detect through electromagnetic observations, yet knowing their abundance is essential for understanding galaxy formation and evolution. We propose parallel stellar streams as dynamical imprints left on stellar streams by dark perturbers, including starless dark matter subhalos and wandering intermediate-mass black holes. We report that a single stream can split into two parallel structures after an encounter with a dark perturber. This scenario is supported by analytical modelling and N-body simulations. We also discuss how we can distinguish parallel stellar streams from other formation processes based on observables. We extend the theoretical picture of stream-subhalo interactions by showing that encounters with dark perturbers can generate density depletions perpendicular to the stream elongation, leading to parallel stellar stream morphologies beyond conventional gap-like signatures.
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All authors Yuka Kaneda, Masao Mori, Yohei Miki, Takanobu Kirihara, Andreas Burkert

High Energy Astrophysical Phenomena

Pulsar Wind Nebulae (PWNe) – A Review

Jordan Eagle

Pulsar Wind Nebulae (PWNe) are relativistic, magnetic winds comprised of radiating electrons and positrons, powered by an energetic pulsar. The pulsar continuously injects particles into the PWN that are accelerated at the termination shock. As the relativistic particles enter the PWN, they radiate away the energy received at the shock as they interact with the PWN environment, generating synchrotron emission from interactions with the magnetic field of the PWN and Inverse Compton Scattering (ICS) from interactions with the local photon fields. Synchrotron emission is observed from the majority of known PWNe from radio to X-ray energies, and the ICS is observed in the $\gamma$-ray bands, from MeV to TeV energies. The particle acceleration processes at the termination shock and elsewhere within the PWN remain to be understood. Recent progress in theoretical studies have provided the capability to explain broadband observations of several PWNe including their spectral and spatial features. This work reviews some of the most compelling outcomes of recent literature, outlining the outstanding questions that remain to be answered, and how the future prospects of $\gamma$-ray astronomy will be instrumental in advancing the current understanding of PWNe.
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High Energy Astrophysical Phenomena

Fermi-LAT Gamma-ray Emission Discovered from the Composite Supernova Remnant B0453-685 in the Large Magellanic Cloud

Jordan Eagle

A second extragalactic pulsar wind nebula (PWN) is discovered in the MeV-GeV band using the Fermi-LAT. Faint, point-like gamma-ray emission is detected at the location of the composite supernova remnant (SNR) B0453-685 from energies 300MeV-2TeV. The Fermi-LAT data analysis of the new gamma-ray source is presented together with a detailed multi-wavelength investigation to understand the nature of the observed emission. The observational evidence and physical implications from broadband modeling do not support an SNR gamma-ray origin. Semi-analytic radiative evolutionary models are explored to understand the potential for any pulsar or PWN component responsible for the observed gamma-ray emission. The modeling results favor an evolved PWN ($\tau\sim 14,000$ years) that has been impacted by the return of the SNR reverse shock with a possible substantial pulsar component below $5$GeV. The particle acceleration mechanisms and their efficiency within B0453-685 have important implications for the role PWNe play in generating Cosmic Rays (CRs), but constraints on the synchrotron cut-off are required to accurately characterize the underlying particle properties.
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High Energy Astrophysical Phenomena

A Multiwavelength Interpretation of HESS J1857+026 Emission Using the Fermi-LAT, VERITAS, and HAWC Observatories

Jordan Eagle, Yu Chen, Ramiro Torres-Escobedo et al. (+2 more)

We present a new study on the MeV-TeV gamma-ray origin of HESS J1857+026 using data collected from the Fermi-LAT, VERITAS, and HAWC observatories. A spatial and spectral study of HESS J1857+026 including radiative modeling of the MeV-TeV spectrum determines the likely dominant gamma-ray origin as a pulsar wind nebula (PWN) powered by the energetic pulsar PSR J1856+0245. The MeV-TeV spectrum is further characterized through basic evolutionary radiative modeling assuming a PWN origin to constrain the physical properties of the system such as the magnetic field strength and PWN age. The results of the PWN evolutionary model are consistent with the observational constraints of the system, finding an age of the system between t = [16,21]kyr and a magnetic field strength between B = [0.4,1.6]muG. These estimates support an evolved PWN scenario where the observed gamma-ray emission is generated by the relativistic electrons inverse Compton scattering (ICS) off local photon fields, however the low-energy (E < 10GeV) spectral component could be dominated by hadronic emission originating from a supernova remnant (SNR). For a PWN component above 10GeV, we measure the conditions for particle diffusion, finding that the local diffusion (D(50TeV) ~ $10^{28}cm^{-2}s^{-1}$) is suppressed compared to the interstellar medium (ISM) value, in agreement with similar TeV PWNe. By measuring the radial surface brightness profiles of the gamma-ray source across multiple instruments, we demonstrate that the combined MeV-TeV spatial information is a powerful tool to constrain particle diffusion properties.
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All authors Jordan Eagle, Yu Chen, Ramiro Torres-Escobedo, Youyou Li, Ruo-Yu Shang

Astrophysics of Galaxies

Black hole populations and hierarchical growth across the AGN parameter space

Maria Paola Vaccaro, Michela Mapelli, Alessandro Alberto Trani et al. (+1 more)

Active galactic nuclei (AGNs) have been proposed as efficient environments for the formation of binary black holes (BBHs). We present an updated semi-analytical framework for BBH formation and evolution in AGN disks, following the capture, migration, pair-up, gas-driven hardening, binary–single encounters, and merger of stellar-origin black holes. We systematically explore the dependence of the resulting BBH merger population on the main AGN parameters, namely the supermassive black hole mass $M_\bullet$, the Eddington ratio $\lambda_\bullet$, and the disk viscosity parameter $\alpha$, and construct an intrinsic BBH population by weighting the simulations according to observed low-redshift AGN properties. We find that AGN disks can produce repeated mergers and build a high-mass tail extending beyond the pair-instability mass gap and into the intermediate-mass range. Hierarchical growth is more efficient in lower-viscosity disks, with $\alpha=0.01$, while higher-viscosity disks suppress the formation of massive remnants. The merger efficiency generally increases with $\lambda_\bullet$, but its dependence on $M_\bullet$ is non-trivial. The AGN-assisted BBH population is characterized by increasingly unequal mass ratios at high primary mass, a correlation between primary mass and $|\chi_{\rm eff}|$, and an effective-spin distribution that depends strongly on the fraction of binaries born in prograde or retrograde configurations. We find that the AGN channel can reproduce systems broadly consistent with the massive BBH events GW190521 and GW231123. We test several variations of the physical model, including different formalisms for migration torques, gas hardening, and three-body encounters. The general properties of the population are robust across these variations, with the high-mass tail and spin signatures persisting in all cases except when gas hardening is switched off.
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All authors Maria Paola Vaccaro, Michela Mapelli, Alessandro Alberto Trani, Boyuan Liu

Solar and Stellar Astrophysics

Analysis of the young disk around WRAY 15-1880: does it contain a primitive planetary system?

Elisabetta Rigliaco, Raffaele Gratton, Silvano Desidera et al. (+2 more)

Observations of (giant) planets accreting material within their natal environment are crucial to constrain models for their formation. WRAY 15-1880 (aka RX J1842.9-3532) in the Corona Australis (CrA) complex has a prominent pre-transitional disk, and an age of ~2.8+-0.7 Myr, computed by comparison with isochrones using the accurate dynamical mass derived from disk kinematics. Hence, this star is in the late phases of disk evolution and might host accreting planets. We acquire new polarimetric imaging data with VLT-SPHERE and analyze archive observations taken with VLT-SPHERE, VLT-MUSE, and ALMA, finding a candidate Jupiter-like companion within the disk gap from high-contrast imaging. The mass estimates of the candidate companion, derived from various methods, are consistent with an object in the range of 0.3-7.6 MJup. The spectrum of the candidate companion is consistent with a T3 spectral type, in agreement with expectations of an object of a few Jupiter masses. We find an emission blob North-West of the star in the ALMA data rotating solidly with the candidate companion, that can be interpreted as a vortex/dust trap at the m=1 Lindblad resonance of the planet. Accretion on the candidate planet is not detected from the VLT-MUSE archival data. This may be due to insufficient contrast, an observational geometry that is unfavorable for viewing the planet's surface, or it could indicate that we are merely observing irregularities within the disk. Finally, we identify a microjet extending from the star perpendicular to the disk in these data.
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All authors Elisabetta Rigliaco, Raffaele Gratton, Silvano Desidera, Gabriele Columba, Enrico Grippi