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Physics Astrophysics

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Astrophysics of Galaxies

Atomic hydrogen in $z=0$ galaxies in the COLIBRE simulations

Kyle A. Oman, Ruby J. Wright, Andrea Gebek et al. (+12 more)

We present an overview of the properties of atomic hydrogen (HI) in galaxies at redshift $z=0$ in the COLIBRE cosmological galaxy formation simulations. COLIBRE directly simulates the multi-phase interstellar medium (ISM) and includes new methods to follow radiative cooling to $\approx 10\,\rm{K}$, non-equilibrium chemistry coupled to dust, and dust formation, growth & destruction. We focus on the $(200\,\rm{cMpc})^3$ volume with resolution elements of $2\times 10^{6}\,\rm{M}_{\odot}$. No HI properties informed the calibration of model parameters and yet we find very good agreement with the observed $M_{\star}$-$M_{\rm{HI}}$ relation, the HI mass and velocity width functions, the HI mass-size relation, and (baryonic) Tully-Fisher relations, albeit with some mismatches at the extremes of the galaxy population. HI surface density profiles are realistic, except at large radii around massive ($M_{\star}\gtrsim 10^{10}\,\rm{M}_{\odot}$) galaxies where we find a population of possibly spurious circumgalactic HI clouds, whose abundances and masses decrease, however, with increasing mass resolution). Using smaller simulations to vary some of the uncertain model parameters, we find that the main scaling relations are at most mildly affected, although this may not extend to detailed HI morphokinematics. Convergence across mass resolution levels a factor of $8$ higher and lower is good: the median HI mass and HI `occupation fraction' as a function of halo mass, and the HI mass function, are remarkably stable, although the highest resolution model overproduces HI sources by a factor of $\approx2$ at $M_{\rm{HI}}\gtrsim 3\times 10^{9}\,\rm{M}_{\odot}$. Upturns in the low-mass and low-velocity slopes of the HI mass and velocity width functions with potentially subtle observational signatures are predicted.
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All authors Kyle A. Oman, Ruby J. Wright, Andrea Gebek, Diego Dado, Katherine E. Harborne, Evgenii Chaikin, Carlos S. Frenk, Filip Huško, Claudia D. P. Lagos, Aaron D. Ludlow, Sylvia Ploeckinger, Alexander J. Richings, Matthieu Schaller, Joop Schaye, James W. Trayford

Cosmology and Nongalactic Astrophysics

Validation of harmonic-space likelihood methods for LiteBIRD B-mode polarisation analysis

G. Galloni, P. Campeti, C. Gimeno-Amo et al. (+112 more)

The LiteBIRD satellite mission aims to measure the tensor-to-scalar ratio $r$ with unprecedented sensitivity through observations of the cosmic microwave background (CMB) $B$-mode polarisation. Robust constraints on $r$ require accurate likelihood modelling across a wide range of angular scales. In this work, we validate harmonic-space likelihood methods against pixel-based benchmarks using 20\,000 end-to-end simulations that include CMB, instrumental noise, and Galactic foreground residuals processed through a realistic component-separation pipeline. We compare a debiased pixel-based likelihood, which serves as our benchmark on large scales ($\ell\leq32$), with an offset Hamimeche & Lewis (oHL) likelihood applicable across the full multipole range. We systematically explore the space of analysis settings, identifying the number of simulations used for covariance estimation and the choice of beam window function as the most critical factors. Over the full multipole range considered ($\ell\leq128$), where the benchmark combines the pixel-based likelihood at $\ell\leq32$ with a harmonic one at smaller scales, the 68% upper bound on $r$ from the oHL likelihood is $19$–$29\%$ larger than the benchmark one, depending on the beam window function. This demonstrates its viability as a computationally efficient baseline for LiteBIRD data analysis and cosmological inference from the polarisation $B$-mode field.
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All authors G. Galloni, P. Campeti, C. Gimeno-Amo, A. Carones, A. Rizzieri, Y. Chinone, N. Krachmalnicoff, E. Martínez-González, L. Pagano, D. Adak, E. Allys, A. Anand, K. Aryan, J. Aumont, C. Baccigalupi, A. J. Banday, R. B. Barreiro, N. Bartolo, A. Basyrov, M. Bersanelli, A. Besnard, F. Bouchet, N. Brancadori, T. Brinckmann, F. J. Casas, L. Castelló Gomar, L. Colombo, F. Columbro, A. Coppolecchia, M. Cruz, F. Cuttaia, P. de Bernardis, E. de la Hoz, M. De Lucia, S. Della Torre, C. Demay, P. Diego-Palazuelos, J. J. Díaz García, F. Finelli, C. Franceschet, U. Fuskeland, M. Galloway, K. Ganga, M. Gerbino, T. Ghigna, S. Giardiello, E. Gjerløw, M. Gomes, A. Gruppuso, S. E. Harper, M. Hazumi, S. Henrot-Versillé, L. T. Hergt, E. Hivon, K. Ikuma, H. Ishino, K. Kohri, L. Lamagna, M. Lattanzi, C. Leloup, M. Lembo, F. Levrier, A. I. Lonappan, M. López-Caniego, D. Maino, V. Maranchery, S. Masi, S. Matarrese, S. Micheli, M. Migliaccio, M. Monelli, L. Montier, G. Morgante, M. Morshed, L. Mousset, M. Najafi, T. Namikawa, P. Natoli, I. Obata, A. Occhiuzzi, A. Paiella, D. Paoletti, S. Paradiso, G. Pascual-Cisneros, F. Piacentini, G. Piccirilli, M. Pinchera, G. Polenta, L. Porcelli, M. Reinecke, M. Remazeilles, A. Ritacco, J. A. Rubiño-Martín, M. Ruiz-Granda, Y. Sakurai, L. Salvati, J. Sanghavi, D. Scott, D. Shenoy, M. Shiraishi, G. Signorelli, S. Stellati, R. M. Sullivan, K. Tassis, L. Terenzi, M. Tomasi, H. Tran, L. Vacher, B. van Tent, P. Vielva, S. Vinzl, D. J. Watts, I. K. Wehus, G. Weymann-Despres, for the LiteBIRD Collaboration

Cosmology and Nongalactic Astrophysics

CosmoForge II. An exact treatment of arbitrary linear filters in quadratic maximum-likelihood power spectrum estimation

Giacomo Galloni

Ground-based cosmic microwave background (CMB) experiments filter their time-ordered data to remove $1/f$ noise and ground pickup, which removes or mixes the large angular scales where primordial $B$ modes peak. A common remedy is a pseudo-$C_\ell$ estimator with harmonic $B$-purification and a transfer function measured from simulations. Another applies it after a matrix-based $E/B$ purification of the maps. We extend the quadratic maximum-likelihood (QML) estimator of CosmoForge to filtered maps, treating the filter exactly: a linear filter conjugates the estimator's ingredients without altering its structure. The same holds for the pixel-based likelihood of CosmoForge, which gives the smallest error bar achievable on the same maps. We compare all methods in a simplified setup under several map-level filters through the error bars on bandpowers and on the tensor-to-scalar ratio $r$. QML sits $2$ to $4\%$ above the pixel-likelihood bound on $\sigma (r)$ in every filter state. At low noise, the pure pseudo-$C_\ell$ $\sigma (r)$ is $1.21$ times QML's without filtering, $3.0$ times under a scan filter along stripes of constant declination, and $3.7$ times under one from a toy constant-elevation scan. The matrix-purified pseudo-$C_\ell$ $\sigma (r)$ is at most $1.03$ times QML's except under the constant-elevation filters, where it reaches $1.10$. These factors shrink towards unity at higher noise. The pure pseudo-$C_\ell$ gap comes from apodisation and from harmonic $E/B$ separation; pixel-space separation closes it, except under the constant-elevation filters, which attenuate modes rather than remove them and widen the gap. QML stays within a few per cent of the optimal error bars without the tuning and simulated transfer functions of the pseudo-$C_\ell$ pipelines. Thus, CosmoForge provides a robust framework for power-spectrum estimation and inference on filtered maps. (Abridged)
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High Energy Astrophysical Phenomena

A0538-66: A transient ultraluminous X-ray source with a relativistic outflow, 69ms pulsations, and anomalous optical activity

Lorenzo Ducci, Sandro Mereghetti, Ciro Pinto et al. (+8 more)

A0538-66 is a peculiar Be/X-ray binary in the Large Magellanic Cloud, hosting the fastest spinning neutron star of its class (~69ms) and showing the brightest optical bursts of any system of this type. We report four XMM-Newton observations obtained near periastron in 2025, together with MAXI and REM monitoring, and a reanalysis of archival RXTE data. On 30 September 2025 the source reached L_X~1.5E39 erg/s (0.2-10 keV), the highest level since 1980, and in February, May, and August 2026, MAXI detected similarly bright outbursts. During the XMM-Newton observation taken on 30 September 2025, we detected the pulsations, measuring P_spin=69.25878(2) ms and dP_spin/dt=6.58(9)E-10 s/s; the pulsed fraction was low (~3% in 1-10 keV), increased with energy, and the soft and hard pulse profiles were shifted by half a cycle. A new detection in RXTE data of 3 December 1998 gives a faster spin period of P_spin=68.88813(28) ms. The XMM-Newton/RGS spectra show emission lines from photoionised plasma at rest and blueshifted absorption lines that imply an outflow at ~0.12c. This indicates a highly super-Eddington accretion rate and an intrinsic L_X~1.5E39 erg/s, and it makes A0538-66 a transient ultra-luminous X-ray pulsar, a class of which only a few objects are known so far. Since 2023 the optical bursts observed by REM have become longer and brighter, resembling those of the 1980s, but most of them lack a luminous X-ray counterpart (L_X>1E37 erg/s). We interpret these results in terms of a radiation pressure dominated accretion disc whose geometrically thick inner regions intermittently screen the innermost emitting regions.
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All authors Lorenzo Ducci, Sandro Mereghetti, Ciro Pinto, Matteo Bachetti, Motoki Nakajima, Rahul Sharma, Stefano Covino, Michela Rigoselli, Caterina Tresoldi, Tatehiro Mihara, Mutsumi Sugizaki

Earth and Planetary Astrophysics

Physical characterization of Earth's quasi-satellite 2025 PN7

Grigori Fedorets, Zuri Gray, Mikael Granvik et al. (+1 more)

A hypothetical origin as lunar ejecta for Earth's quasi-satellites (QS) has gained initial support in recent years, but there is scarce photometric and/or spectroscopic data to support the premise due to the rare observational windows to obtain such data for these small objects. One of the key pieces of evidence supporting the lunar-origin hypothesis, the lunar-like, very red reflectance spectrum of QS (469219) Kamo'oalewa, was recently found to be flawed. We present reflectance spectroscopy of Earth's QS 2025~PN$_7$ obtained with FORS2 at UT1-Antu of the ESO Very Large Telescope. This is only the second QS that has ever been characterized, the first being (469219) Kamo'oalewa, the sample-return target of the Tianwen-2 mission. Our results indicate that 2025~PN$_7$ exhibits a near-solar, flat visual spectrum, most consistent with the B-type in the Bus-DeMeo taxonomy. Our results therefore still support an asteroid-belt origin for most of Earth's QSs. The lunar-ejecta hypothesis can only be formally rejected with a larger sample of spectroscopically characterized QSs.
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All authors Grigori Fedorets, Zuri Gray, Mikael Granvik, Eric MacLennan

Solar and Stellar Astrophysics

Revisiting the Role of Global Magnetic Variables in Coronal Heating of Solar Active RegionsDavid H. Brooks

David H. Brooks, Harry P. Warren and Johnathan R. Stauffer

Reconnection-based models of coronal heating predict that magnetic complexity—non-potential configurations, currents, shear—should enhance coronal emission independently of total magnetic flux. Previous work, however, found no evidence that complexity contributes independently to coronal heating (Fisher et al. 1998). We revisit this question using SDO/HMI vector magnetograms and SDO/AIA EUV imaging. HMI Space-weather Active Region Patches (SHARPs) provide 16 magnetic parameters characterizing field strength, gradients, currents, helicity, and non-potentiality. We measure spatially-integrated transition region and coronal emission using AIA 304A, 193A, 94A, and isolated Fe XVIII emission for 137 active regions, sampling plasma at ~0.09MK, ~1.4MK, and ~7.1MK. Partial correlation analysis isolates the contribution of each complexity parameter after controlling for total unsigned vertical magnetic flux. Unsigned flux (Phi_M) explains 72–82% of variance in emission, following power laws (I ~ Phi_M^alpha, where alpha=0.61-1.19) consistent with prior soft X-ray results. Partial correlations reveal weak positive contributions (r = 0.2-0.3) to transition region (304A) emission from some vertical current and field parameters, but little evidence that other active-region-averaged measures of magnetic complexity enhance coronal emission. The exception is total photospheric magnetic free energy density (rho_tot), which shows a positive partial correlation (r = 0.49, p < 0.001) with Fe XVIII emission, but negative, or non-existent, partial correlations with other AIA filters. These results suggest quasi-steady coronal heating scales with magnetic flux, while rho_tot may contribute to high temperature coronal heating. At lower temperatures, regions with more stored energy than expected for their flux produce less EUV emission than expected.
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Earth and Planetary Astrophysics

Radiation limits on amino acid preservation and chiral measurement at Oxia Planum

Dimitra Atri

Amino acid enantiomeric excess (EE) is a potential biosignature, but its measurement requires sufficient surviving material as well as preserved chirality. We derive a criterion that separates abundance-limited from racemization-limited preservation and apply it to the Mars Organic Molecule Analyzer (MOMA) on the ExoMars Rosalind Franklin rover. The model combines cosmic-ray and radiogenic doses with laboratory destruction kinetics and assumed ratios of interconversion to destruction rates. For an initially homochiral population of 1000~ppmw, the surviving EE is 58% or 25% when the total abundance reaches 1~ppmw for rate ratios of 0.04 or 0.10, respectively. This abundance criterion does not ensure that both enantiomers can be quantified. Applying provisional estimates of 1~ppmw per enantiomer and 10% EE, serine at 2~m requires initial concentrations of 340 and 960~ppmw after cosmic-ray exposures of $10^{7}$ and $10^{8}$~yr, respectively, under transferred fused-silica–perchlorate kinetics and a 1.57-MGy radiogenic dose. These concentrations exceed measured meteoritic serine abundances, but do not predict the initial Oxia inventory. For organics retained in a closed host since deposition 3.9~Ga ago, the modeled radiogenic dose is 1.6–5.6~MGy across the adopted compositions. In the lower-dose case, drilling to 2~m reduces the total dose by only a factor of 1.5 after $10^{7}$~yr. The boundaries depend on mineral kinetics and organic residence time; they distinguish preserved chirality from a measurable excess.
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Solar and Stellar Astrophysics

A breath of fresh air: Oxygen enhancement from silicate sublimation during early protostellar evolution

F.J. Ballieux, M.K. McClure, Ł. Tychoniec et al. (+5 more)

Recently, an analog to the t = 0 moment of our Solar System's meteoritic record was identified for the first time around the Class I protostar HOPS-315. Crystalline silicates were found to recondense from SiO gas that cools as it advects upward from a hot thermostat region in the inner midplane. This t=0 moment may be associated with the formation of the first planetesimals in this disk. We explore whether HOPS-68, a Class I protostar with similar properties and system geometries, is engaged in such refractory recondensation as well. A detection of cooler gas-phase SiO in absorption above a hot disk midplane would allow us to achieve this goal, thanks to a previous detection of crystalline silicates. HOPS-68 was observed with the JWST MIRI and NIRSpec, showing multiple bands of molecular absorption. We use local thermal equilibrium slab models to measure the temperature, column density, velocity, and radial location of these bands. The molecular absorption bands of gaseous SiO, H2O, CO2, and 13CO trace a warm molecular inversion layer (300-500 K) at mid-altitudes above the hot disk midplane from 0.3-16 AU, which is consistently blue-shifted with respect to the system velocity by 33-53 km/s. Atacama Large Millimeter/submillimeter Array (ALMA) observations of HOPS-68 kinematically resolve an SiO-rich jet and wind. We confirm that HOPS-68, like HOPS-315, is undergoing an epoch analogous to the t=0 moment in the Solar System's planet formation timeline. The detected warm molecular layer traces the base of a disk wind, which carries sublimated material from the thermostat region near 2 AU up into the outer disk. As for HOPS-315, the molecular layer in the inner few AU of HOPS-68 is enhanced in bulk oxygen as a result of this sublimation. Since HOPS-68 is less evolved than HOPS-315, this may indicate a prolonged epoch in protostellar evolution in which such oxygen enhancement occurs.
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All authors F.J. Ballieux, M.K. McClure, Ł. Tychoniec, L. Francis, A. Egliene, E.A. Bergin, M.R. Van 't Hoff, E.F. Van Dishoeck

Earth and Planetary Astrophysics

Rattling Resonant Chains with Dynamical Tides and Parametric Resonance Passage

Mohammad Farhat and Eugene Chiang

Close-in sub-Neptunes are born in mean-motion resonant chains that break apart on a timescale of $\sim$100 Myr. If the chains are first ”rattled” — have their free eccentricities excited to a few percent — then breaking occurs on the required timescale. We propose that chains are rattled by internal oscillations tidally driven by the star in the innermost planet. Unlike other proposals, there is no need to invoke any reservoir of planetesimals or external perturbers — the chain unravels from within. We develop a Hamiltonian theory (and an accompanying toy model) which predicts a parametric instability whereby chain librations exponentially amplify when the tidal forcing frequency equals the sum of the internal mode frequency and the chain libration frequency. We also introduce a new eigenmode solver for rotating planets, $\texttt{MAQAM}$, that in combination with the evolutionary code $\texttt{ORCHARD}$ enables us to track the frequency evolution of pressure, gravity, and inertial modes in cooling sub-Neptunes. Inertial modes in the gas envelope and fluid mantle can evolve to become momentarily parametrically resonant. Passage through a single parametric resonance can raise the free eccentricities in the chain to a few percent within a few tens of Myrs.
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Earth and Planetary Astrophysics

Size, atmospheric, and ring constraints on the large Kuiper belt object (55565) Aya from a stellar occultation

Ko Arimatsu, Hidekazu Hanayama, Satoshi Takita et al. (+3 more)

We aim to constrain the projected size, geometric albedo, possible atmosphere, and possible ring material of the mid-sized trans-Neptunian object (55565) Aya from the stellar occultation of 2024 May 10 (UT). We observed the event from three Japanese sites with high-cadence optical imaging. We combined one positive occultation chord with an informative prior on the shadow centre derived from orbital and astrometric uncertainties, and inferred the body radius with Bayesian Markov chain Monte Carlo modelling. We constrained a possible atmosphere by fitting refraction models for pure CH$_4$, N$_2$, and CO atmospheres to multi-band light curves, and searched for ring-like extinction signatures in unbinned and binned high-time-resolution photometry. We derive an equivalent radius, i.e., the radius of the circle fitted to the projected shadow, of $r=401^{+28}_{-40}$ km for Aya, corresponding to a geometric albedo of $p_V=0.101^{+0.023}_{-0.013}$. This estimate is insensitive to the adopted ephemeris solution and is consistent with an ephemeris-independent analysis that makes no assumption about the position of the shadow centre. We obtain 3$\sigma$ upper limits on the atmospheric surface pressure of $p_0=60$, 90, and 80 nbar for pure CH$_4$, N$_2$, and CO compositions, respectively. No significant ring-like extinction is detected over projected distances of about 430-8060 km sampled by the three stations, and our most sensitive data exclude dense narrow features with apparent opacity $p'\gtrsim0.1$ and radial widths of a few kilometres or larger over $\sim3r$-$14r$. This is the first stellar occultation by Aya ever observed. In addition to constraining Aya's size and albedo and finding no ring-like extinction, we place a stringent atmospheric upper limit that supports diversity in atmospheric states among similarly sized trans-Neptunian objects.
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All authors Ko Arimatsu, Hidekazu Hanayama, Satoshi Takita, Fumi Yoshida, Tsutomu Hayamizu, Jun-ichi Watanabe

Cosmology and Nongalactic Astrophysics

Mapping Dark Matter in Merging Clusters with Weak Lensing for CSST: Morphology and Filament Recovery

Xinyue Chen, Ran Li, Qiao Wang et al. (+6 more)

Weak gravitational lensing offers a direct probe of the projected dark matter distribution in cluster-scale structures and the surrounding cosmic web. We investigate the capability of the China Space Station Telescope (CSST) to recover non-spherical dark matter morphologies using mock reduced-shear maps generated from cosmological N-body simulations. We apply the deep-learning-based MIU2Net mass-reconstruction framework to CSST-like wide- and deep-field source densities, focusing on two representative systems: filament-connected halo pairs and elongated halos. MIU2Net accurately recovers halo centers, elongated mass distributions, and the filamentary structures connecting halo pairs in both survey configurations. Halo centers are localized within about 0.1 h^(-1) Mpc, and elongated-halo shapes and orientations are reliably recovered. Filament paths are stable against shape noise, with mean normalized instability parameters I_F, defined as the mean deviation from the true filament locus in units of R_200, decreasing from 0.041 to 0.037 in the low-redshift bin and from 0.051 to 0.045 in the high-redshift bin from the wide to deep field. The recovered filament shapes remain consistent with the true maps at the percent level. Compared with conventional Kaiser-Squires reconstruction, MIU2Net better preserves low-contrast anisotropic structures while suppressing small-scale noise. These results demonstrate that CSST weak-lensing data, combined with machine-learning-based mass reconstruction, will enable statistical studies of cluster assembly, anisotropic matter accretion, and the connection between massive halos and the filamentary cosmic web.
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All authors Xinyue Chen, Ran Li, Qiao Wang, Hengjie Lin, Liang Gao, Xiangkun Liu, Huanyuan Shan, Ji Yao, Ming Li

Earth and Planetary Astrophysics

Tracing the Influence of Distant companions on Exoplanetary Systems (TIDES) I. Highly Eccentric and Misaligned Binary Companions to Hot Jupiters

Marvin Morgan, Jerry W. Xuan, Brendan P. Bowler et al. (+9 more)

The origin of hot Jupiters remains an open question. A significant fraction reside in binary or multiple star systems, suggesting that stellar companions may play an important role in shaping their present-day architectures. However, the orbits of the vast majority of these stellar companions remain poorly constrained, leaving their role in hot Jupiter evolution an open question. We present the Tracing the Influence of Distant companions on Exoplanetary Systems (TIDES) survey, a campaign to map the orbits of stellar companions in systems hosting hot Jupiters to assess the extent to which binaries play a role in hot Jupiter formation and migration. Here, we introduce our survey design and new orbital fits for the first six systems in our sample—$\tau$ Boo, WASP-2, WASP-11, WASP-76, HAT-P-14, and HAT-P-16—by combining previous observations of the stellar companions together with new Keck/NIRC2 imaging and Keck/KPIC relative radial velocities. Among these six systems, the four with the most precisely constrained orbits exhibit high eccentricities ($e \geq 0.8$), and three of these systems also display significant planet–binary misalignments ($\Delta i \geq 20^\circ$). This suggests the orbital properties of stellar companions to hot Jupiter host stars are qualitatively different than field binaries and binaries hosting inner transiting small planets. These orbital architectures are consistent with stellar companions shaping the evolution of hot Jupiters, either through high-eccentricity migration or by participating in an earlier episode of dynamical evolution that ultimately led to hot Jupiter formation. Continued orbital monitoring of the full sample will reveal whether outer stellar companions play a causal role in the evolution of hot Jupiters.
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All authors Marvin Morgan, Jerry W. Xuan, Brendan P. Bowler, Kyle Franson, Michael C. Liu, Konstantin Batygin, Heather A. Knutson, Björn Benneke, Julianne Cronin, Luke Finnerty, Chih-Chun Hsu, Aniket Sanghi

Astrophysics of Galaxies

Phase Separation of HI in the Draco Nebula: CNM formation Triggered by Colliding WNM Flows

Yuhi Naruse, Hiroaki Yamamoto, Yamato Matsuzuki et al. (+3 more)

We investigate the thermal phase structures and kinematics of atomic hydrogen (H I) gas in the Draco nebula to clarify how infalling H I evolves toward cold atomic and molecular clouds. Using the DHIGLS H I 21 cm data, we apply the Regularized Optimization for Hyper-Spectral Analysis (ROHSA) algorithm to decompose the emission into spatially coherent Gaussian components, and classify them as warm neutral medium (WNM), lukewarm neutral medium (LNM), and cold neutral medium (CNM). We identify two kinematically distinct WNM components: WNM1 near $-3$ km s$^{-1}$ and WNM2 near $-30$ km s$^{-1}$. The LNM forms a broad velocity bridge between two WNMs, whereas the CNM is concentrated within a narrower intermediate velocity range. CO emission is also confined to this interval and is associated with CNM-rich regions. The H I mass fractions are $\sim 41\%$, $\sim 23\%$, $\sim 17\%$, and $\sim 19\%$ for WNM1, WNM2, LNM, and CNM, respectively, with the LNM and CNM together accounting for $\sim 36\%$ of the total H I mass. No comparably independent WNM component is recovered at intermediate velocities, although a weak broad component may remain unresolved. The observed phase structures are consistent with a dynamically compressed multiphase interaction layer in which compression increases the gas density, shortens the radiative cooling time, and drives the evolution from WNM through thermally unstable gas toward the CNM. The present interaction may both create new CNM, and further compress or grow pre-existing dense structures. Our results provide the missing link between previous evidence for dynamical interaction and molecular cloud formation in Draco, and identify CNM formation as a key step in transforming gas accreting toward the Galactic disk into cold atomic and molecular clouds.
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All authors Yuhi Naruse, Hiroaki Yamamoto, Yamato Matsuzuki, Rin Yamada, Atsushi Nishimura, Toshikazu Onishi

High Energy Astrophysical Phenomena

IC 1297: The Most Distant Known X-ray Planetary Nebula and One of the Most Luminous

H. Yuan, Q. A. Parker and M. A. Guerrero

We present the first targeted Einstein Probe (EP) X-ray observations of any planetary nebula (PN). Using the onboard Follow-up X-ray Telescope (FXT), we detect X-ray emission within the central region of IC 1297. The spectral analysis yields a plasma temperature of $kT = 0.086^{+0.054}_{-0.058}$ keV ($T\sim1.0 \times 10^{6}$ K), characteristic of shocked wind bubbles in PNe, whereas there is no evidence that its Wolf-Rayet central star emits X-rays. The absorption-corrected X-ray luminosity in the 0.3–2.0 keV energy band is $L_{\mathrm{X}} = 2.8 \times 10^{32}$ erg s$^{-1}$, also consistent with a hot bubble. At an adopted distance of $\sim3.8$ kpc, IC 1297 is the most distant X-ray emitting PN found to date, opening up a new observational window on hot-bubble formation and evolution. It is also among the most luminous known X-ray-emitting PNe. Our results demonstrate the capability of the EP FXT for detecting and characterizing faint, extended X-ray sources in the soft X-ray band for distant PNe, extending the known spectral properties of detectable X-ray emitting PNe. We also compiled the X-ray properties of all 41 known Galactic XPNe, finding a clear correlation between distance and X-ray luminosity that reflects an observational bias toward detecting the brightest sources at large distances. The compilation also shows a separation in X-ray luminosity between hot bubbles powered by H-rich and [WR]-type central stars, with the latter reaching luminosities up to an order of magnitude higher. The ten most luminous XPNe all host [WR]/PG 1159 central stars.
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Earth and Planetary Astrophysics

Dynamically Coupled Three-dimensional Cloud-Chemistry in Rapidly Rotating Irradiated Atmospheres: an Application to the Compact White Dwarf-Brown Dwarf system ZTFJ0038+2030

Yanhong Lai, Xianyu Tan, Daphne Broski-Laing et al. (+7 more)

Clouds and disequilibrium chemistry shape the observable properties of substellar and planetary atmospheres, and JWST time-resolved spectroscopy now enables direct tests of their three-dimensional structures. We present an update to the 3D atmospheric framework ADAM, coupling the dynamical core to a miniature kinetic chemistry scheme (mini-chem) and a saturation-relaxation tracer cloud module. Using this framework, we investigate the atmosphere of the brown dwarf orbiting the white dwarf ZTFJ0038+2030 in a 10-hour orbit. The brown dwarf receives stellar irradiation comparable to its internal heat flux, placing the atmosphere in a regime where the circulation is characterized by a standing Matsuno–Gill wave response and equatorial superrotation. Rapid rotation confines these structures closer to the equator, producing more symmetric broadband light curves with smaller hotspot offsets than canonical hot Jupiters, in agreement with recent JWST observations of this system. Although most species are globally homogenized, rapid rotation limits global-scale horizontal mixing and allows circulation-driven vertical transport to maintain strong CO and CO$_2$ inhomogeneities in the photosphere. These chemical inhomogeneities produce asymmetric phase curves in the CO and CO$_2$ absorption bands, which could qualitatively explain the observed CO$_2$ light-curve asymmetry. When clouds are included, Na$_2$S clouds dominate the photosphere and weaken the large-scale circulation, lowering photospheric CO and CO$_2$ abundances, while MgSiO$_3$ and Fe clouds rain out at deeper levels. Because the dominant Na$_2$S clouds reside mostly above the quench region, cloud-driven convection has limited impact on the quenched abundances, which are instead regulated mainly by large-scale circulation.
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All authors Yanhong Lai, Xianyu Tan, Daphne Broski-Laing, Yifan Zhou, Sarah L. Casewell, Jenni R. French, Elspeth K. H. Lee, Joshua D. Lothringer, Vivien Parmentier, Shang-Min Tsai

Earth and Planetary Astrophysics

Experimental evidence for physical alteration of fine regolith on near-Sun asteroids

Jooyeon Geem, Mikael Granvik, Georgios Tsirvoulis et al. (+5 more)

The surfaces of airless bodies evolve through processes such as (micro)meteoroid impacts and thermal fatigue, which modify physical properties such as grain size, porosity, and mineral texture. These properties provide clues to surface evolution and are necessary for interpreting telescopic observations. Near-Sun asteroids (NSAs), which reach heliocentric distances of $\lesssim$0.2 au, are notable targets, as their surfaces are likely modified by intense solar radiation. However, experimental studies of how radiative heating modifies the physical properties of carbonaceous asteroid surfaces remain scarce compared with studies of thermally induced compositional and spectral changes. We investigate these modifications experimentally. Near-Sun conditions at heliocentric distances $0.09<r<0.19$ au are simulated using the Space and High-Irradiance Near-Sun Simulator. CM-type carbonaceous chondrite simulants are irradiated under vacuum. Brightness is monitored in situ with a video camera during heating, and morphological changes are examined using a stage microscope and a scanning electron microscope (SEM). The irradiated samples show initial darkening followed by brightening, consolidation, and morphological modifications from sub-micrometer to millimeter scales. The observed brightness modifications are more consistent with changes in the absorption properties of the sample than with variations in surface roughness. SEM imaging of the heated samples shows structures similar to those formed by sintering, which are completely absent in unheated samples. These results suggest that sintering is a likely candidate for the mechanism responsible for the observed consolidation and morphological changes. This work provides experimental evidence to help constrain the surface evolution of NSAs in general, and supports sintering as a possible mechanism proposed for (3200) Phaethon in particular.
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All authors Jooyeon Geem, Mikael Granvik, Georgios Tsirvoulis, Leonard Schirner, Marianna L. Kemell, Antti Penttila, Axel Hagermann, Athanasia Toliou

High Energy Astrophysical Phenomena

The Promise of Gravitational-Wave Astronomy

Parameswaran Ajith

We review the promise of upcoming gravitational-wave (GW) observations in addressing some of the important open questions in astrophysics and cosmology. A decade after the first direct detection of GWs, the field is entering a transformative phase driven by progressive detector upgrades and the anticipated advent of space-based and next-generation ground-based observatories. These instruments will not only push the distance horizon of GW observations to cosmological redshifts, but will dramatically extend the accessible frequency band, opening entirely new source classes that lie beyond the reach of current detectors. The source landscape is rich enough that surprises are likely. This review surveys our current understanding across this landscape and offers some perspective on the discoveries that upcoming GW observations are poised to deliver.
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High Energy Astrophysical Phenomena

Observational evidence of black hole event horizon from ultra-compact X-ray binaries

Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng et al. (+1 more)

The event horizon is the most crucial feature that distinguishes black hole (BH) from all other objects in the universe. However, since no radiation can escape from the event horizon, its direct observational evidence remains lacking. Although both are compact objects, the event horizon leads to differences in the radiative behavior between black hole and neutron star (NS) X-ray binaries. Historically efforts to probe the existence of event horizons revealed that the BH X-ray binaries are fainter than NSs with similar orbital periods in their quiescent states. Here, we use a special class of X-ray binaries namely the ultra-compact X-ray binaries (UCXBs), to reveal the existence of the event horizon near stellar-mass black holes. In short-period UCXBs, gravitational radiation dominates the orbital angular momentum loss, allowing us to accurately determine their accretion rates. Based on five UCXBs with orbital periods shorter than 40 min, located in globular clusters, and identified accretors (NS or BH), we obtained their accretion rates. Combining their accretion rates and X-ray luminosities, we calculated the X-ray radiative efficiencies of NS and BH. The radiative efficiency of BH is about two to three orders of magnitude lower than that of NS systems, indicating the accretion energy is swallowed by the BH, thereby indirectly probe the presence of the event horizon.
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All authors Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng, Mouyuan Sun

Astrophysics of Galaxies

Non-equilibrium chemistry and radiation hydrodynamics in metal-poor and metal-rich interstellar gas

Shyam H. Menon, Piyush Sharda, Blakesley Burkhart et al. (+1 more)

We present a flexible implementation of non-equilibrium chemical networks with the $\texttt{KROME}$ framework, coupled to a nonlocal variable Eddington tensor-closed radiation transport scheme ($\texttt{VETTAM}$). Our fiducial network is designed to explicitly capture the formation pathways of important molecular species such as CO, OH, and $\rm H_2O$, intermediaries like $\rm H_3^+$, and the destruction of these species through photon and cosmic-ray dissociation. We validate our scheme through benchmark tests, and demonstrate its success in 1D and 3D problems covering a broad range of metallicities ($0 \leq Z \lesssim \rm Z_{\odot}$) and densities ($n \lesssim 10^{17} \, \rm cm^{-3}$). We confirm earlier works that suggest that OH and $\rm H_2O$ are the key molecular species in dense gas ($n \gtrsim 10^{5} \, \rm cm^{-3}$) for $Z\lesssim 0.01 \rm Z_{\odot}$, dominate the cooling at these densities, and demonstrate that our scheme can reproduce their abundances with similar accuracy as dedicated static photo-dissociation region (PDR) codes. We also find that the dominant fine-structure coolant in dense ($n \gtrsim 10^3 \, \, \rm cm^{-3}$) PDRs transitions from CI to CII to OI at increasingly lower $Z$. Finally, we find that in turbulent media, rapid mixing at PDR interfaces renders the chemical species out of equilibrium, and show that this could potentially alleviate the long-standing problem of (static) PDR models producing excess CI in the diffuse ISM over UV absorption-line measurements. We conclude by presenting and comparing with alternative implementations of reduced but faster chemical networks in our scheme, discussing the problem-dependent performance-accuracy tradeoffs and future prospects.
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All authors Shyam H. Menon, Piyush Sharda, Blakesley Burkhart, Tommaso Grassi

Astrophysics of Galaxies

Mergers may not be the main channel for galaxy stellar mass growth at redshift $z\gtrsim5$: Predictions from cosmological hierarchical models and simulations

Hao Fu, Mohammadreza Ayromlou, Francesco Shankar et al. (+13 more)

Mergers are a crucial channel of galaxy growth, but their role relative to star formation remains uncertain at high redshift. Here we investigate merger rates and merger-driven stellar mass assembly for galaxies with stellar mass $M_\star \gtrsim 10^8 \, {\rm M_{\odot}}$ at $z\simeq 5-11$, by combining complementary theoretical approaches within $\Lambda$CDM. These include the DECODE semi-empirical model, the TNG100 and EAGLE hydrodynamical simulations, and the L-Galaxies semi-analytical model, together with the Millennium and TNG100-Dark simulations used to examine dark matter subhalo statistics and merger timescales. This compares models with different treatments of baryonic physics and galaxy-halo connections. We find that dark matter-only simulations predict merger timescales $\sim 30\%$ longer than those inferred from cosmological simulations including baryons. Galaxy major merger ($M_{\rm \star,sat} / M_{\rm \star,cen} > 0.25$) rates are high at cosmic dawn and increase towards earlier epochs, reaching $\sim 1/{\rm Gyr}$ at $z\sim 5$ and peaking at $\sim 3/{\rm Gyr}$ at $z\sim 8$. Despite these high rates, mergers contribute only $\lesssim 10\%$ of the total cosmic stellar mass density evolution. The ex-situ stellar mass fraction ranges from a few percent to $\sim 20\%$ for all galaxies at $z\gtrsim 5$, across different models and simulations. Their broad agreement implies that stellar mass assembly at cosmic dawn is dominated by in-situ star formation rather than mergers. These findings suggest that the high pair fractions identified by JWST may not directly trace efficient ex-situ stellar mass growth, highlighting the need for physically motivated merger timescales to interpret galaxy assembly in the early Universe.
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All authors Hao Fu, Mohammadreza Ayromlou, Francesco Shankar, Lars Hernquist, Andrea Lapi, Daniel Roberts, Feng Yuan, Maulik Bhatt, Evgenii Chaikin, Simona Gallerani, Luca Graziani, Antonio La Marca, George Mountrichas, Yingjie Peng, Haocheng Wang, Kai Wang

Earth and Planetary Astrophysics

Elastic Properties of Titan Tholins Revealed by Brillouin Spectroscopy

Mark A. Johnson, Jose R. Montes-Bojorquez, Adis Husic et al. (+7 more)

Titan tholins, complex organic solids synthesized by simulating photochemical processes in Titan's atmosphere, are widely regarded as analogs to organic surface materials on the Saturnian moon. Their mechanical properties are critical for understanding the evolution of Titan's geomorphology and crustal layering. Here, we report the first direct experimental determination of the complete set of aggregate elastic moduli of tholins using Brillouin spectroscopy. Measurements conducted on tholin powder samples yielded a bulk modulus of 11 (2) GPa and a shear modulus of 3.9 (5) GPa, from which we derive a Young's modulus of 11 (1) GPa and a Poisson's ratio of 0.34 (3). Thin-film samples synthesized under slightly different conditions yield similar results. Compared with other Titan-relevant organic compounds, tholins exhibit the highest elastic stiffness measured to date, exceeding even H2O ice in both bulk and shear moduli. These results support the interpretation that complex organics contribute significantly to the mechanical stability and transport behavior of Titan's equatorial dune sediments. Measurements following prolonged atmospheric exposure reveal persistent stiffening of tholins that remains after vacuum treatment, likely associated with minor chemical modification and physical reorganization, highlighting the importance of controlled sample handling for future laboratory investigations. This study also demonstrates the effectiveness of Brillouin spectroscopy as a non-destructive technique for characterizing planetary organic materials and provides new constraints relevant to future seismic and geophysical investigations by the Dragonfly mission.
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All authors Mark A. Johnson, Jose R. Montes-Bojorquez, Adis Husic, Xinting Yu, Wenhao Su, Jia-Sen Hu, Ryan Blase, Edward Patrick, Alan Whittington, Jin S. Zhang

Astrophysics of Galaxies

A radio counterpart of the local little-red-dot J092359+415736

Tao An, Ruqiu Lin and Ailing Wang

Little red dots (LRDs) are compact red sources at z>~4. Broad lines suggest accreting black holes, yet radio and X-ray measurements are usually weak. Local LRDs allow multi-frequency, multi-epoch radio studies that are inaccessible at high redshift. We search archival radio images for a counterpart to the local LRD J092359+415736 at z~0.323, quantify its long-term radio variability, and identify the plausible origin of the radio emission. Flux densities at the optical position are measured in FIRST, LoTSS, RACS, VAST, and VLASS products spanning 0.144-3.0 GHz and 1994-2024. A compact 144 MHz counterpart is detected at 42sigma in LoTSS, coincident with the Gaia position, and is recovered in FIRST, RACS, VAST, and VLASS. LoTSS and ASKAP give a spectral index alpha ~ -0.30 +/- 0.11. The source varies on multiple timescales: FIRST at 1.4 GHz (1994) is a factor of ~2.6 below ASKAP (2021-2024) and below the extrapolated LoTSS-ASKAP spectrum, indicating long-term brightening over 26 yr; the 3 GHz flux density rises by 2.3sigma between VLASS epochs 2.2 and 3.2. A star-formation-only origin would require ~200 Msun/yr, against an unobscured H-alpha upper limit of 3.3 Msun/yr, implying an extreme obscured starburst. Ordinary radio supernovae and tidal disruption events are strongly disfavoured by the luminosity and 30-yr recovery, while refractive scintillation would itself require an ultracompact nuclear emitter. The persistent radio counterpart is best explained by accretion onto the central black hole. Among the three radio-detected local LRDs, this source is intermediate in luminosity and the only one with reported multi-year variability, adding a temporal dimension to the radio diversity of the class.
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Astrophysics of Galaxies

Sulphur-bearing molecule survey towards prestellar and starless cores in the Perseus molecular cloud

J. Ferrer Asensio, S. Scibelli, A. Pokorny-Yadav et al. (+7 more)

Sulphur is drastically depleted from the gas phase in dense starless and prestellar cores, creating the long-standing "missing sulphur problem". Observations of sulphur-bearing molecules are crucial to understanding sulphur chemistry, core-environment relationships, and the physical evolution of star-forming regions. We present a survey of four sulphur-bearing molecules, HCS+, OCS, H2CS, and SO, towards 15 starless and prestellar cores in the Perseus molecular cloud using the Yebes 40m telescope. The HCS+ 1-0, OCS 3-2 and 4-3, H2CS 1_{0,1}-0_{0,0}, and SO 3_2-2_2 transitions were observed, fitted with Gaussian profiles, and column densities were calculated assuming local thermodynamic equilibrium (LTE). We also compare these with observations of CS, CCS, and CCCS from a previous study. HCS+, OCS, H2CS, and SO are detected in 100%, 93%, 100%, and 73% of the sample, respectively. Derived column densities are (2.2-17.0)x10^11 cm^-2 for HCS+, (1.9-25.0)x10^12 cm^-2 for OCS, (1.0-15.0)x10^12 cm^-2 for H2CS, and (0.3-17.0)x10^13 cm^-2 for SO, spanning over an order of magnitude. HCS+ and SO abundances strongly correlate (inversely and directly, respectively) with core volume density, reinforcing their early- and late-type status. Correlations indicate a differentiation between carbon and oxygen chemistry for sulphur-bearing molecules, with CS showing the strongest correlations as expected. Cores in protostellar outflow paths do not show consistently higher abundances. The chemical age (SO/CS) correlates with physical age (volume density), except for Per752, an outlier likely linked to an enhanced cosmic ray ionization rate. These results provide a robust observational baseline constraining chemical models of sulphur chemistry in early star formation.
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All authors J. Ferrer Asensio, S. Scibelli, A. Pokorny-Yadav, L. Steffes, B. Kulterer, Y. Shirley, A. Megías, I. Jiménez-Serra, A. Fuente, G. Esplugues

Monday 12 October

Instrumentation and Methods for Astrophysics

Unveiling photometric transients with the ILMT and their follow-up using DOT

Priyanshi Kumari, Bhavya Ailawadhi, Talat Akhunov et al. (+10 more)

The two 4-m class telescopes at the Devasthal site in India are complementary: the 4-m International Liquid Mirror Telescope (ILMT) is dedicated to the discovery of new transient phenomena, which can be followed up using the 3.6-m Devasthal Optical Telescope (DOT) for their optical characterisation. The ILMT continuously surveys a $22.3^\prime \times 22.3^\prime$ wide strip of the zenith sky. A dedicated transient detection and classification pipeline, PyLMT, based on optimised image subtraction and convolutional neural network (CNN) techniques, enables the discovery of numerous photometric transients with the ILMT. However, these transient discoveries still require spectroscopic confirmation to determine their types, for which spectra obtained with the DOT are essential. Here, we present a selection of photometric transients, specifically supernova candidates. We investigate their photometric and spectroscopic properties using ILMT light curves, supplemented with ZTF data and DOT spectroscopic observations.
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All authors Priyanshi Kumari, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Gokul Singh Mehra, Kuntal Misra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav

Solar and Stellar Astrophysics

What Does 2D Coronal Seismology Measure?

Zihao Yang, Yuhong Fan, Giuliana de Toma et al. (+2 more)

Two-dimensional (2D) coronal seismology based on coronagraphic imaging spectroscopy has emerged as a promising method for mapping the coronal magnetic field, but the physical meaning of its inferred quantities under optically thin line-of-sight (LOS) integration remains uncertain. We investigate this problem by synthesizing coronagraphic observables from a global wave-driven magnetohydrodynamic model with a long LOS extent and a structured corona, and by applying the same analysis procedures used for observations. We compare the diagnosed density, wave propagation direction, phase speed, and magnetic-field strength with different LOS-weighted reference quantities from the model. We find that the measured density and the wave propagation direction are both well represented by LOS emissivity-weighted quantities. In contrast, the phase speed is not controlled by emissivity weighting alone: the LOS distribution of wave velocity amplitude also plays an important role. As a result, the inferred magnetic field is better represented by combining the emissivity-weighted density with an amplitude-dependent effective speed. Emissivity weighting nevertheless remains a reasonable approximation, and a useful baseline, over much of the field of view, especially where the LOS does not cross strongly structured plasma-sheet-like regions. These results clarify the physical interpretation of 2D coronal seismology and provide guidance for future coronal magnetic-field tomography and model-constrained applications.
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All authors Zihao Yang, Yuhong Fan, Giuliana de Toma, Sarah Gibson, Matthias Rempel

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

Internal Nucleon Properties and the Equation of State of Ultra-Dense Matter

Bikram Keshari Pradhan, Jérôme Margueron, Guy Chanfray et al. (+1 more)

The question of the link between the nucleon properties and the equation of state of ultra-dense matter, both being composed of quarks and gluons, is investigated by adopting a soliton model to describe internal nucleon properties and a direct mapping between nucleon and quark matter to obtain the equation of state of ultra-dense matter. We compare $\pi+\omega$ and $\pi+\omega+\rho$ soliton models and analyze the presence of a pressure singularity at the nucleon center due to the $\rho$ field. This singularity impacts the equation of state in ultra-dense matter. Only the pressure derived from the canonical energy-momentum tensor has a singularity, while the Belinfante pseudo-gauge transformation of the energy-momentum tensor generates an internal pressure without a singularity. We then investigate predictions for the equation of state of ultra-dense matter based on different prescriptions for the nucleon pressure. It is shown that none of the prescriptions agree with the thermodynamical pressure defined in uniform matter. The mismatch between any equation of state and the thermodynamical one questions the simplicity of the direct mapping between finite-size nucleon properties and uniform matter as well as the role of the nucleon surface in the internal energy density and the pressure.
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All authors Bikram Keshari Pradhan, Jérôme Margueron, Guy Chanfray, Hubert Hansen

Solar and Stellar Astrophysics

Henrietta Leavitt's classical Cepheid relation

Daniel Majaess

The Leavitt & Pickering (1912) mean period-magnitude relation for SMC Cepheids exhibits correlated residuals relative to modern Gaia $B_G$ and Johnson $V$ photometry ($r_{\delta V/\delta L12}\approx0.76$). Therefore dispersion inherent to Leavitt's photographic photometry relation is not solely random scatter ($\sigma_{L12,B_G,V}=0.22\pm0.03,0.25\pm0.04,0.20\pm0^{m}.03$), and is potentially consistent with the partial encoding of combined effects from the elongated SMC, classical Cepheid instability strip, differential reddening, etc. OGLE data indicate that $\gtrsim870$ SMC variables identified by Leavitt (1908, Table 2) are classical Cepheids ($\gtrsim 90$ %), and the preliminary unphased Table 2 photometry likewise features correlated residuals relative to contemporary observations ($r_{\delta B_G/\delta L08-T2}\approx0.54$). Table 6 data in Leavitt (1908, $n=16$) define a highly linear Leavitt law over an extensive baseline ($r\approx-0.98$), but constitute a smaller sample than the later 1912 work ($n=25$).
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Instrumentation and Methods for Astrophysics

Simulation and Deep Learning Inversion for Full-sky Energetic Neutral Atom Imaging at the Heliospheric Boundary

Weining Wang, Rong Lin, Jiansen He et al. (+11 more)

The distribution of energetic neutral atom (ENA) differential flux density at the heliospheric boundary is the key to revealing the interaction mechanism between the solar wind and the interstellar medium. The Helios ENA Rapid Mapper (HERMA) is a pre-research project for a new ENA detection concept and technical principle, which is designed to provide technical support for refined detection with its advantages of wide energy range coverage and high spatial resolution. To verify the high spatiotemporal resolution rapid imaging capability of the HERMA, this study restored the particle response characteristics of the HERMA (spatial modulation grid + 256-pixel linear array silicon detector) based on Geant4 simulation, and we compared the performance of the traditional inversion algorithm with the convolutional neural network (CNN) inversion algorithm using INCA data as the benchmark. The results show that under different sampling times, the source distribution inverted by the CNN algorithm has a higher degree of agreement with the ideally expected distribution, and the CNN algorithm exhibits better stability and accuracy than the traditional algorithm under the conditions of low signal-to-noise ratio and short staring time. This study provides core technical support for the engineering verification and on-orbit application of the HERMA instrument, fills the technical gap in wide-energy-range and high-resolution ENA detection, and helps to deepen the research on the interaction mechanism between the solar wind and the interstellar medium at the heliospheric boundary.
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All authors Weining Wang, Rong Lin, Jiansen He, Hong Zou, Yongfu Wang, Jiali Chen, Yuguang Ye, Weihong Shi, Wei Zhang, Xi Lu, Die Duan, Tianhang Chen, Linghua Wang, Qiugang Zong

Astrophysics of Galaxies

Intermittency in the Multiphase ISM — II. Non-Gaussian Dust Polarization and Foreground Variance

Yue Hu

Interstellar turbulence produces non-Gaussian polarized Galactic dust emission whose higher-order statistics depend on thermal phase and turbulent forcing. We synthesize optically thin dust polarization from three thermally multiphase diffuse interstellar medium (ISM) simulations with compressive, mixed, and solenoidal forcing. We characterize the resulting non-Gaussian structure in the warm, unstable, and cold phases using $E$- and $B$-mode spectra, one-point distributions, scale-dependent increments, and Minkowski functionals. Both $E$ and $B$ modes are intermittent. Warm-phase emission remains closest to Gaussian, whereas cold gas shows flatter intermediate-scale spectra, broader non-Gaussian tails, and the strongest departures from Gaussian morphology. Compressive forcing generally produces the strongest projected intermittency, particularly in the cold phase and total emission, while mixed and solenoidal forcing show weaker signatures. These higher-order structures also enhance spatial fluctuations in polarized dust power: Gaussian fields matched to the same two-point covariance underestimate the region-to-region scatter by factors of up to $\sim2.6$. Our results show that thermal phase and turbulent forcing regulate not only the mean polarized dust spectrum but also the field-to-field distribution of foreground power, with implications for modeling Galactic foreground in CMB polarization measurements.
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Earth and Planetary Astrophysics

Ultraviolet Reflected-Light Spectroscopy of Modern Earth Analogs with Starshade Observations

Zahra Ahmed, Stuart Shaklan, Mario Damiano et al. (+3 more)

Characterizing rocky, habitable zone planets in reflected light is a key science objective for future direct imaging missions, and the ultraviolet (UV) is uniquely suited for supporting the characterization of Earth-like atmospheres. The Hartley-Huggins ozone band at $0.25 ~\mu\mathrm{m}$ remains detectable at low spectral resolution down to $0.1\%$ PAL $\mathrm{O}_2$, providing a sensitive proxy for oxygen-bearing chemistry even for Proterozoic-like atmospheres where the visible and near-infrared $\mathrm{O}_2$ features become inaccessible. This work uses an end-to-end framework for UV starshade spectroscopy of modern Earth analogs that integrates high-fidelity observation simulation, conservative post-processing, and Bayesian spectral retrieval to quantify ozone detection significance. The framework is applied across 108 simulated scenes spanning a range of planet phase angles, system inclinations, and exozodiacal dust densities. The results establish that robust ozone detection with UV-only, $R=7$ reflected light spectroscopy requires a photometric $\mathrm{SNR} \sim 30$. UV starshade observations with the Habitable Worlds Observatory achieve this threshold within 3-day integrations for solar-type systems at 10 parsecs with inclinations up to $60^\circ$ at favorable phases ($\leq 90^\circ$). Above this SNR threshold, ozone detections are robust to systematic bias from imperfect exozodi calibration within $\sim30\%$, and the median retrieved ozone abundance remains accurate to within one order of magnitude of the true value.
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All authors Zahra Ahmed, Stuart Shaklan, Mario Damiano, Armen Tokadjian, Edward W. Schwieterman, Simone D'Amico