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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 4 August

Earth and Planetary Astrophysics

First multi-opposition recoveries of large-orbit LSST TNOs

Chantal Hemmann, Brett Gladman, Justine Obidowski et al. (+2 more)

We report 2026 CFHT second-opposition recovery observations of three large-orbit Trans-Neptunian Objects (TNOs) discovered by the Vera C. Rubin Telescope's Legacy Survey of Space and Time (LSST) during preliminary observations in 2025. Due to their potential scientific interest, we selected three TNOs whose nominal semimajor axis could be larger than 100~au according to their short-arc ($\leq0.2$-yr) LSST observations. These three targets (2025 LS2, 2025 ME278, 2025 MX348) had discovery opposition orbits of varying observation quality (in terms of the duration and distribution of observations). In two cases, the 2026 CFHT recoveries showed that the semimajor axis dropped by a factor of $\simeq$3-10, and that the object appears to be a (common) plutino in the 3:2 mean-motion resonance with Neptune. We discuss how and why the estimated orbital elements evolved, and re-caution the community to be skeptical of unusual TNO orbits until they have multi-opposition recoveries.
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All authors Chantal Hemmann, Brett Gladman, Justine Obidowski, Jean-Marc Petit, JJ Kavelaars

Instrumentation and Methods for Astrophysics

CCAT: The 410 GHz camera module for FYST - design and testing of the MKID focal plane

Scott C. Chapman, Jordan Wheeler, Anthony Huber et al. (+16 more)

Prime-Cam, the primary first-light instrument for the Fred Young Submillimeter Telescope (FYST) developed by the Cerro Chajnantor Atacama Telescope (CCAT) Collaboration, will accommodate seven modules. Here we describe the off-central 410 GHz imager/polarimeter. The 410 GHz instrument is a camera module for CCAT funded by the Canadian Foundation for Innovation, being developed as a collaboration between Dalhousie University, University of British Columbia (UBC), National Research Council (NRC) - Herzberg, and Duke University. With atmospheric loading in the 410 GHz window being significantly higher than at 350 GHz (but substantially lower than 850 GHz), we assess four MKID test devices with varying inductor volume for performance at 410 GHz. We propose a design for an array of ~6,700 horn-coupled TiN MKIDs optimized for use at 410 GHz, with a planned ~20,000 MKIDs over three arrays, exploring mapping speed versus detector number. We test the four MKID devices optically and assess optimal Qi/Qc and responsivity for the 410 GHz atmospheric window atop Cerro Chajnantor. The detectors will be designed in frequency to be efficiently readout with a second generation, two octave readout (based on the Xilinx RFSoC board), with over 4000 detectors per board.
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All authors Scott C. Chapman, Jordan Wheeler, Anthony Huber, Jason Austermann, James A. Beall, James Burgoyne, Max Chapman, Jesslyn Devina, Douglas Henke, Johannes Hubmayr, Dylan Lockyer, Michael Niemack, Tilak M. Patel, Colin Ross, Douglas Scott, Adrian Sinclair, Eve Vavagiakis, Michael R. Vissers, Ruixuan Xie

Astrophysics of Galaxies

Effect of non-spherical projectiles on the structure of porous dust aggregates formed by coagulation

Lucas Kolanz and Davide Lazzati

Cosmic dust is ubiquitous in the universe, yet the structure and geometry of individual grains remain poorly understood. The existence of non-spherical, fluffy, and even fractal grain structures is predicted by numerical simulation and supported by observations of linear polarization of starlight. However, it has proven challenging to go beyond a qualitative investigation of such crucial grain characteristics. We present soft-sphere discrete element simulations of dust coagulation with sequential collisions using non-spherical projectiles of various sizes. We study the internal structure and geometry of the resulting aggregates under three growth conditions: a constant final aggregate size, a constant number of projectiles, and a constant projectile size. In most cases we allow for projectile internal restructuring, but we also test the effect of enforcing a constant projectile structure after impact. We find that aggregates' porosity and fractal dimension depend both on the size and number of projectiles, and that their asymmetry and stretch parameters depend more on the number of projectiles than on projectile size. Overall, the grain porosity increases with both the number of projectiles and the size of the individual projectiles. Comparison with constraints from interstellar polarization indicates that none of our sufficiently large aggregates have structures capable of reproducing the observed polarization of starlight in the interstellar medium. We conclude that cosmic dust undergoes additional processing after coagulation to acquire structures consistent with observations.
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Earth and Planetary Astrophysics

Callisto from JWST: CO2-rich terrain on the leading hemisphere and global patterns of H2O ice

Maria Camarca, Katherine de Kleer, Richard J. Cartwright et al. (+5 more)

We present maps of H2O, CO2, and a 4.57 um spectral feature across Callisto's surface observed using the James Webb Space Telescope (JWST). H2O ice was mapped by measuring band parameters of the 3.1 um Fresnel peak across the leading and trailing hemispheres under a simplified assumption of crystalline ice. We update the CO2 solid-phase, CO2 gas, and 4.57 um feature band depth maps originally presented in Cartwright et al. (2024) with a new JWST observation of Callisto centered on Valhalla, the largest multi-ring impact basin in the solar system. Our H2O ice map shows that the Fresnel peak on the trailing hemisphere exhibits a bullseye pattern that is weaker at low latitudes, and on the leading hemisphere its strength is associated with impacts. This dichotomy is possibly related to the Jovian magnetospheric plasma impinging on the trailing hemisphere. Our solid-phase CO2 map reveals an enhancement in the vicinity of the Lofn/Heimdall impact craters, a region that may be the largest reservoir of non-radiolytic CO2 on Callisto's surface. The gas-phase CO2 exhibits a patchy spatial distribution and does not clearly correlate with solid CO2.
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All authors Maria Camarca, Katherine de Kleer, Richard J. Cartwright, Geronimo L. Villanueva, Bryan J. Holler, Zachariah Milby, Kevin P. Hand, Lorenz Roth

Earth and Planetary Astrophysics

Searching for Habitable Exoplanets with Relative Astrometry (SHERA). I. The Case for Searching for Planets in Binary Star Systems

Jessie L. Christiansen, Eric E. Mamajek, Gautam Vasisht et al. (+14 more)

Discovering Earth-like planets orbiting Sun-like stars was identified as a priority science goal of the Astronomy 2020 Decadal Survey. It is confounded by many factors, one of which is the high multiplicity of Sun-like stars in the local neighborhood - half of nearby Sun-like stars are in binary or higher-order stellar systems, which are less amenable to the detection of small planets with almost all of the currently productive exoplanet detection techniques. Here we describe the SHERA (Searching for Habitable Exoplanets with Relative Astrometry) NASA Small Explorer mission concept. SHERA utilizes diffractive-pupil technology on a small, simple optical space telescope to achieve microarcsecond precision relative astrometry on 14 Sun-like stars in seven nearby multi-star systems, combining the pupil and stellar binarity to provide a precise reference in the image plane. With this precision, SHERA would enable: (i) a search for rocky planets in the habitable zones of the closest Sun-like stars; (ii) an investigation of the impact of binary star formation on small, widely separated planets; and (iii) the performance of crucial precursor observations on a number of high-priority targets of NASA's future missions to characterize Earth-like planets, such as the Habitable Worlds Observatory. When combined with radial velocity measurements, SHERA relative astrometry will also enable exploration of the three-dimensional orbital structure of planets in binary systems.
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All authors Jessie L. Christiansen, Eric E. Mamajek, Gautam Vasisht, Catherine A. Clark, William Roberson, Eric L. Nielsen, Kaitlin M. Kratter, Juliette Becker, Eduardo Bendek, Ruslan Belikov, Alex Davis, Louis Desdoigts, Alyssa Jankowski, Michael R. Meyer, Benjamin J. S. Pope, Armen Tokadjian, Peter Tuthill

Earth and Planetary Astrophysics

Generating eccentricity from envelope stripping in the Radius Valley

Brad M. S. Hansen

We demonstrate that the stripping of planetary envelopes can result in the excitation of planetary orbital eccentricity if the stripped gas remains in the system long enough to interact gravitationally and absorb angular momentum from the planetary orbit. We estimate that envelope mass fractions of a few percent can excite eccentricities of order 0.1 for single planets. This process can potentially explain the elevated eccentricities observed for planets whose radii lie in, or near, the radius valley. In multiple planet systems, the stripped gas can mediate angular momentum exchange between neighbouring planets, causing the separation to expand. Using data from the Kepler satellite, we find that planet pairs, whose members straddle the radius valley, do appear to be systematically wider than those in which both members are sub-Neptunes. These results support the idea that planets in, or just below, the radius valley are the stripped cores of planets that have lost mass, because the elevated eccentricities represent evidence that the gas remained in the system long enough to absorb additional angular momentum from the planet.
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Earth and Planetary Astrophysics

Joint dynamical-geophysical evidence for a limit cycle in the Galilean moons

Amirhossein Bagheri, Steven Vance, Jim Fuller et al. (+5 more)

Io, Europa, and Ganymede orbit in the Laplace mean-motion resonance, where their orbital and thermochemical evolution are strongly coupled [1-5]. Forced eccentricities sustain tidal dissipation, powering Io's volcanism and maintaining Europa's subsurface ocean [6-8]. Tidal heating depends on the moons' eccentricities, semimajor axes, and interior properties. Orbital evolution depends on how satellite dissipation affects the resonant dynamics [4, 8]. This coupled evolution has not been treated in a self-consistent framework constrained by modern observations. Here, we combine modern astrometric and geophysical measurements of migration rates, surface heat fluxes, tidal response, and moment of inertia [9-13] with an orbital-thermochemical evolution model to constrain the long-term evolution and present state of the moons. We show that the joint observations select an ongoing late-time limit cycle, likely established $\sim$0.8-2.0 Gyr ago through feedback between thermal and orbital evolution. The present-day state recurs within this oscillatory branch, whose cycles repeat every $\sim$95-150 Myr. Io presently experiences high dissipation and migrates inward, whereas Europa and Ganymede continue to migrate outward. Europa is predicted to undergo episodes of inward migration during the cycle. During the cycles, Io's mean melt fraction varies substantially ($\sim$10-30%), while Europa's ice-shell thickness varies by $\sim$3-15 km. The predicted structures of Europa and Io will be assessed by future missions including Europa Clipper, JUICE, and IVO [14-17].
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All authors Amirhossein Bagheri, Steven Vance, Jim Fuller, Brianna Fernandez, Mohit Melwani-Daswani, Hauke Hussmann, Gregor Steinbruegge, Francis Nimmo

Instrumentation and Methods for Astrophysics

The Constant Evolution of the Neil Gehrels Swift Observatory: Two Decades of Operational Innovation for Time-Domain and Multi-Messenger Astrophysics

Jamie A. Kennea

The Neil Gehrels Swift Observatory has, for more than twenty years, served as NASA's premier rapid-response, multi-wavelength facility for the study of gamma-ray bursts (GRBs) and the transient sky. While Swift's hardware has remained essentially unchanged since its 2004 launch, its operational capabilities have evolved continuously, driven by a philosophy of “always be developing.” Hosted entirely at The Pennsylvania State University, with co-located flight and science operations, Swift has repeatedly reinvented how a NASA mission can be commanded, transforming itself from a GRB-chasing autonomous robotic telescope into a flexible, automated platform for time-domain and multi-messenger astrophysics (TDAMM). We review the key operational innovations that have enabled this evolution: the development of automated target-of-opportunity (TOO) uploads in response to the early loss of active X-ray Telescope cooling; onboard tiling of large error regions; the ManyPoint flight-software capability for executing hundreds of pointings; the Gamma-ray Urgent Archiver for Novel Opportunities (GUANO); and the “Urgency 0” continuous-commanding mode that has reduced TOO response latencies from hours to seconds. We illustrate the scientific impact of these capabilities through Swift's gravitational-wave and neutrino follow-up campaigns, including GW170817/AT2017gfo and IceCube-170922A, and through real-time “early-warning” slewing toward predicted compact-binary mergers. Finally, we discuss the heritage Swift is creating for future TDAMM missions, and the ongoing efforts to extend Swift's life, both through attitude-based scheduling that minimizes the spacecraft's atmospheric drag cross-section and through a commercial orbit-boost mission.
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Solar and Stellar Astrophysics

Custom Colors: A Module for Computing Synthetic Photometry On-the-Fly in Stellar Evolution Calculations, Integrated with MESA and Usable with Other Stellar Evolution Codes

Niall Miller, Meridith Joyce and Philip Mocz

Stellar evolution simulations predict physical quantities such as luminosity, whereas broadband photometric observations measure flux in specific bandpasses; converting the predicted stellar state to magnitudes requires interpolating a stellar atmosphere model at the surface parameters, convolving the resulting spectral energy distribution (SED) with filter transmission curves, and applying a photometric zero-point correction. We introduce Custom Colors, which performs this conversion from the stellar model. It is integrated into MESA as MESA Custom Colors, and available as the Python package SED_Model for external applications. At each timestep, the module interpolates a user-specified atmosphere grid at the current T_eff, log g, [M/H], applies geometric dilution at a user-specified distance, convolves the SED with each requested filter transmission curve, and appends observer-frame magnitudes to standard MESA output files. We demonstrate the module across six diverse use cases: TP-AGB evolution, nonlinear RR Lyrae pulsation, starspot-modified photospheres, white dwarf cooling, blue-loop evolution, and rotational spot modulation based on an external YREC SPOTS grid. These cases draw on Kurucz/ATLAS9, BT-Settl, and Koester DA atmosphere grids and filter systems including Roman WFI, LSST ugrizy, Gaia, and extended Johnson UBVRIJHKLMN. Two of these demonstrations compare the module directly with observational data: a 0.6M_dot DA white dwarf cooling track follows the broad Gaia DR3 cooling locus from M_G ~ 8.5 to 15mag without intermediate color transformation, and an RSP model recovers the Kepler light curve of FN Lyr (KIC6936115) to 1.1% in period and 0.2% in amplitude.
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Solar and Stellar Astrophysics

A comparison of best fits obtained in white dwarf asteroseismology using the WDEC and the LPCODE

Agnès Bischoff-Kim

We perform the asteroseismic fitting of 4 DAVs using a grid of WDEC models with chemical pro- files that closely mimic those of the LPCODE models and compare them with published asteroseis- mic fitting results using the LPCODE (Romero et al. 2017). These 4 objects are KIC 11911480, J113655.17+040952.6, KIC 4552982, and GD1212. The similarities in the results in those controlled experiments point to a consistency in the models. Given similar input, the LPCODE and the WDEC make similar models and calculate similar periods. We further perform the asteroseismic fitting of the same 4 DAVs by relaxing the constraints on the chemical profiles. We explore the effects of different methods for weighing the modes when calculating the goodness of fit of the models, as well as the effect of only including a subset of the known period spectrum. Such numerical experiments can help place recent and future efforts in pipeline fitting of numerous DAVs and DBVs using the WDEC on firmer footing (Hall et al. 2023).
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Earth and Planetary Astrophysics

JWST Transmission Spectroscopy of TOI-3235 b: Challenges in Constraining Giant Planet Atmospheres Around M Dwarfs Amid Stellar Contamination

Zoe Ko, Néstor Espinoza, Andrés Jordán et al. (+7 more)

Giant planets orbiting low-mass M dwarfs challenge current planet formation theories, which predict that such planets are unlikely to form. Characterizing their atmospheres can provide key insight into their origins, but analysis is complicated by stellar contamination in transmission spectra. We present a JWST/NIRSpec PRISM transmission spectrum of TOI-3235 b, a 604 K, 0.665 Jupiter-mass giant planet orbiting a 0.39 Solar-mass M dwarf. We apply a hierarchical retrieval framework incorporating an atmospheric model, a parametric stellar contamination model, and a Gaussian process (GP) to capture residual structure not explained by these deterministic components. We find that the inferred atmospheric properties are model-dependent: retrievals that treat stellar contamination deterministically yield a constrained CH4 abundance corresponding to a sub-solar metallicity that would challenge standard expectations from both core accretion and gravitational instability, along with potentially elevated CO and CO2 abundances that would require chemical disequilibrium. However, residual wavelength-correlated structure suggests the deterministic model is incomplete. Including a GP to marginalize over this structure broadens the atmospheric posterior distributions, preventing robust constraints on the atmospheric composition and highlighting the challenge of characterizing giant planet atmospheres around M dwarfs. We demonstrate that an eclipse observation could clarify these model-dependent ambiguities: detected emission features would constrain the planet's metallicity and test formation scenarios, while a featureless spectrum would confirm stellar contamination dominates the transmission spectrum, providing an empirical M dwarf contamination spectrum.
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All authors Zoe Ko, Néstor Espinoza, Andrés Jordán, Daniel Bayliss, Edward M. Bryant, Martin Schlecker, Melissa J. Hobson, Rafael Brahm, Remo Burn, Thomas Henning

Astrophysics of Galaxies

Phosphorous in the moderately metal-poor bulge globular clusters NGC 6539 and NGC 6569

Morgan S. Camargo, Beatriz Barbuy, Heitor Ernandes et al. (+10 more)

The distinct stellar populations of the Galactic bulge can be disentangled through detailed analysis of their chemical abundances and kinematical properties. Recent studies have suggested that globular clusters located in the Galactic bulge with metallicities around $\rm [Fe/H] \approx -0.7$, may represent some of the oldest systems in the Milky Way, potentially tracing the early spheroidal bulge. The coincidence of a metallicity peak at $\rm [Fe/H] \approx -0.7$ in both field stars and globular clusters, together with the presence of phosphorus-rich (P-rich) stars, may provide important clues to the nature of the first generations of stars formed in the Galaxy. In this work, we investigate the odd-Z elements Na, Al and particularly P in the bulge globular clusters NGC~6539 ($\rm[Fe/H] \sim -0.75$) and NGC~6569 ($\rm [Fe/H] \sim -0.85$) using APOGEE spectra. We also examine the clusters Tonantzintla-1 and NGC~6316, which exhibit evidence of phosphorus enhancement. Our analysis confirms that NGC~6539 is a cluster of interest, with one clearly P-rich star, whereas NGC~6569 shows a lower level of P-enhancement. This again suggests that there might have been an early bulge building block with the metallicity of $\rm[Fe/H] \sim-0.75$, of which NGC~6539 would be part of. The observed abundance patterns indicate that the production of Na and Al is consistent with nucleosynthesis in massive stars. However, the origin of the phosphorus enrichment remains uncertain, suggesting that additional nucleosynthetic channels may be required to explain the observed abundances. These findings provide new constraints on the chemical evolution of the Galactic bulge and the nature of its earliest stellar populations.
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All authors Morgan S. Camargo, Beatriz Barbuy, Heitor Ernandes, Amâncio C. S. Friaça, Cristina Chiappini, Bernardo P. L. Ferreira, Stefano O. Souza, Sergio Ortolani, Domenico Nardiello, Eduardo Bica, José G. Fernández-Trincado, Nicolas Barrera, Doug Geisler

Solar and Stellar Astrophysics

A survey of ultra-compact high-state AM CVn binaries with ZTF and Gaia: New discoveries and observational constraints on Galactic space density

Ilkham Galiullin, Antonio C. Rodriguez, Kareem El-Badry et al. (+9 more)

Ultra-compact AM CVn binaries in the high-state of stable mass transfer ($\dot{M}\gtrsim10^{-9}M_\odot/\rm{yr}$) are expected to be among the loudest persistent sources for upcoming space-based GW observatories. These systems typically have orbital periods $P_{\rm{orb}}\lesssim30$ minutes. We present a systematic search for high-state AM CVn binaries in the Milky Way by targeting a region within the Gaia color-magnitude diagram, combined with ZTF time-domain photometry. We focus on variable targets within that sample with 5-30 minute periods. Our survey discovered three new high-state AM CVn binaries (ZTF J1840-1742, ZTF J2007-0527 and ZTF J2111+3158) with orbital periods of 16.86, 18.63, and 16.71 minutes, and recovered three known systems. We obtain high-speed photometry and phase-resolved spectroscopy to confirm their nature. Their spectra show helium emission lines with no detectable hydrogen. In two targets, the lines are double-peaked, and Doppler tomograms confirm an accretion disk. We estimate mass accretion rates of $\sim10^{-9}M_\odot/\rm{yr}$, and $3\sigma$ X-ray luminosity upper limits of $\sim10^{33}\rm{erg/s}$. Based on this sample, we infer a local space density of high-state AM CVn population in the Milky Way of $\sim(1.0-2.7)\times10^{-8}\rm{pc}^{-3}$ (for disk scale heights $h_z=300-200$ pc), representing 2-5% of the total Galactic AM CVn density. Their birth rate, $\sim(2.4-4.3)\times10^{-4}\rm{yr}^{-1}$ (for $h_z=300-200$ pc), is consistent with the total AM CVn birth rate, implying most systems entering the high-state phase survive and evolve to longer orbital periods. This local space density suggests LISA and TianQin will detect about 36% and 19% of the total Galactic population, respectively, during their nominal 4-yr missions ($S/N\ge5$). The Vera C. Rubin Observatory's LSST will detect about 34-44% of these systems over its 10-yr survey ($m_r\lesssim26.9$ mag).
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All authors Ilkham Galiullin, Antonio C. Rodriguez, Kareem El-Badry, Valery Suleimanov, Vladislav Dodon, Askar Sibgatullin, Warren R. Brown, Kevin Burdge, Jan van Roestel, Edo Berger, V. Ashley Villar, Ilaria Caiazzo

Astrophysics of Galaxies

Chemo-dynamical stratification of the Galactic disc using Gaia-ESO open clusters

Casmir O. Obasi, M. Gómez, J. G. Fernández-Trincado et al. (+5 more)

Understanding how the Milky Way disc assembled and evolved requires tracing the coupled evolution of stellar chemistry and orbital structure over time. Open clusters, as coeval stellar populations with well-constrained ages, distances, and chemical properties, provide powerful benchmarks for this purpose. We aim to characterise the age-dependent chemo-dynamical structure of the Galactic disc and to investigate how open clusters populate dynamical phase space as a function of age. We analysed a sample of Galactic open clusters using homogeneous chemical abundances from the Gaia-ESO Survey together with Gaia DR3 phase-space information. Combining cluster ages with orbital parameters and actions, we examined how clusters populate dynamical phase space over the last ~4 Gyr. We find that clusters with similar chemical properties occupy coherent regions of action space, while their orbital structure shows a clear dependence on age. Radial excursions and orbital eccentricities broaden systematically toward older ages, indicating increasingly diverse orbital configurations in the older cluster population. The dispersion in the [Fe/H]-Rg relation also increases with age, consistent with a combination of secular redistribution, survival bias, and dynamically distinct outer-disc populations. In addition, older clusters reach larger vertical amplitudes and vertical actions, revealing a coupled but anisotropic evolution between in-plane and vertical orbital structure. Open clusters provide precise, age-resolved tracers of the chemo-dynamical structure of the Galactic disc. Our results reveal systematic age-dependent variations in the orbital and chemical properties of the cluster population, consistent with the combined effects of secular evolution, orbital redistribution, and environmentally dependent cluster survival over the last few Gyr.
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All authors Casmir O. Obasi, M. Gómez, J. G. Fernández-Trincado, D. Minniti, B. Dias, B. Barbuy, M. V. Alonso, L. D. Baravalle

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

Amnesia in the Axion Misalignment Landscape

Kierthika Chathirathas, Cem Eröncel, Mathieu Kaltschmidt et al. (+2 more)

Pre-inflationary axion cosmologies admit a broad range of initial velocities and angles that generate a landscape of misalignment histories, whose nonlinear fate and small-scale structure remain uncertain. We use lattice simulations to follow the QCD axion in the kinetic misalignment scenario through the QCD crossover into the non-relativistic regime, towards matter-radiation equality. In the meV mass range, this landscape contains a continuum of ”summit-landing" solutions sensitive to both the initial angle and velocity. Nonlinear fragmentation reduces the comoving axion number and modifies the relation between the misalignment history and present relic abundance. For sufficiently large axion masses, strong self-interactions drive the small-scale spectrum towards the attractor found for post-inflationary axions, so that distinct early histories can lead to similar late-time structures.
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All authors Kierthika Chathirathas, Cem Eröncel, Mathieu Kaltschmidt, Javier Redondo, Kenichi Saikawa

Astrophysics of Galaxies

Resolving dense photodissociation regions: the structure of photochemical fronts in three-dimensional gas distributions

Brandt A. L. Gaches, Thomas G. Bisbas, Lothar Brendel et al. (+1 more)

For decades, the Orion Bar has been the prototypical photodissociation region. Viewed nearly edge-on, it offers a unique window into the stratified chemical structure of the atomic-to-molecular transition of the interstellar medium. Understanding its photochemistry is essential to interpreting key observations originating from dense photo-dissociation regions. ALMA and JWST observations reveal that H2 photodissociation front overlaps with the C+ recombination front and exhibits a complex spatial morphology. Despite considerable theoretical effort, existing modeling approaches based on simplified geometrical assumptions have difficulties reproducing the spatial emission structure. Our aim is to investigate the response of photochemistry in realistic three-dimensional density distributions, using the Orion Bar as a representative application. We present the first fully three-dimensional high-resolution model of an Orion Bar analogue that resolves the relevant photochemical fronts using the upgraded steady-state 3D-PDR photo-dissociation region code, which allows for the treatment of plane-irradiatation and for the solution of the non-LTE H2 rovibrational levels. We find that the H2 dissociation front is characterized by a complex surface that overlaps with the C+ recombination front. Our 3D model can reproduce the complex morphology of H2 emission seen in observations, in particular the arc- and filament-like features, and provides a physical explanation of its chemistry. The overlapping H2 dissociation and C+ recombination fronts and the spatial emission morphology can be explained due to the three-dimensional gas distribution, resulting in shadowing and shielding by dense substructures. Our results mark a turning point for astrochemistry, where three-dimensional steady-state models can deliver fundamentally new insights into the chemistry of the interstellar medium. (Abridged)
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All authors Brandt A. L. Gaches, Thomas G. Bisbas, Lothar Brendel, Zhengping Zhu

Earth and Planetary Astrophysics

A new window in time: a mid-infrared slit spectroscopy mode for precision time-series astronomy with JWST/MIRI

Achrene Dyrek, Taylor J. Bell, Pierre-Olivier Lagage et al. (+7 more)

The Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) provides Low Resolution Spectroscopy (LRS) over 5-12 um at a resolving power of R ~ 100. To date, all MIRI LRS time-series observations (TSOs) have been carried out in slitless mode, since long-duration pointing stability within the narrow 4.7” x 0.51” slit could not previously be guaranteed, leading to the possibility of degraded TSOs due to jitter. Commissioning activities established the telescope jitter to be less than 1 milliarcsecond (mas), four times less than the initial requirement. It was, therefore, worth assessing the suitability of the MIRI LRS slit as a TSO mode for precision time-domain science; this is the aim of the Cycle 3 program (PID 6219, PI: A. Dyrek). We observed a transit of the exoplanet HAT-P-12b over ~10 hours and compared the results to archival slitless observations of the same target (PID 1281, PI: P.-O. Lagage). Two independent data reductions of the transit spectra of both slit and slitless configurations are consistent within 1 sigma, validating the feasibility of the new mode. A joint fit of the slit and slitless observations confirms the presence of a spectral feature near 7.5 um. Using measured JWST pointing variations, we estimated slit-loss variations to be smaller than 40 ppm at 10 um. The drawback of the slitless mode is a higher background. Compellingly, the slit background is ~ 38 times lower on average than in slitless mode, improving sensitivity for faint targets (Jmag ~ 13-15). We also identified time-correlated noise unique to the slit dataset at long wavelengths, which requires further investigation. This new capability of TSOs in slit mode, which will be supported in Cycle 7 (in 2028), opens a new avenue for precision time-series astronomy for faint targets with JWST/MIRI.
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All authors Achrene Dyrek, Taylor J. Bell, Pierre-Olivier Lagage, Sarah Kendrew, Gareb Fernandez-Rodriguez, Thomas Greene, Giuseppe Morello, Michiel Min, Mael Voyer, Hannu Parviainen

Instrumentation and Methods for Astrophysics

Breaking the brightness barrier: JWST/NIRCam DHS spectroscopy for high-precision time-series observations

Achrene Dyrek, John Stansberry, Louis E. Bergeron et al. (+12 more)

Many of the most scientifically compelling exoplanets orbit bright nearby stars that exceed the brightness limits of existing JWST spectroscopic observing modes. To address this limitation, a new NIRCam Short Wavelength Grism Time-Series mode has been developed by combining the Dispersed Hartmann Sensor (DHS) with a new on-board multistripe detector readout capability. The DHS disperses the incoming light through multiple pupil sub-apertures, reducing the incident flux and providing slitless spectroscopy between approximately 1.0 and 2.3 um. The multistripe readout mode further increases the accessible brightness range (K ~ 2.5 - 5.7 mag, depending on the spectral type of the object), with the previous limit being K ~ 5.7 mag at 1.5 um, by reading only the detector regions containing the DHS spectra, reducing the detector frame time with the standard RAPID readout mode from 10.74 s to 1.36 s over even less when using smaller substripe sizes. Together with the simultaneous long-wavelength grism observations, the new mode provides spectroscopic continuous coverage from approximately 1.0 to 5.0 um for targets as bright as K ~ 2.5 mag. We present the first results of on-orbit commissioning of this new observing mode with the final stage consisting of observations of a full transit of the exoplanet WASP-18b, which allowed us to demonstrate the feasibility of using NIRCam DHS for high-precision time-series observations. The commissioning presented in this paper marks the first deployment of the multistripe detector readout on JWST. Beyond NIRCam DHS, this new capability will be extended to other spectroscopic modes, including NIRISS SOSS and NIRSpec PRISM. Bright nearby stars host many of the highest-priority targets for exoplanet atmospheric characterization, making multistripe an important new capability for maximizing the scientific return of JWST.
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All authors Achrene Dyrek, John Stansberry, Louis E. Bergeron, Everett Schlawin, Nestor Espinoza, Brian Brooks, Mario Gennaro, Martha L. Boyer, Russell Ryan, Bryan Hilbert, Munazza K. Alam, Aarynn L. Carter, Norbert Pirzkal, Julien H. Girard, Anton M. Koekemoer

High Energy Astrophysical Phenomena

Profile Reconstruction from Temporally Stable Emission Components for Timing PSR J1713+0747

Shaswata Chowdhury, M. A. Krishnakumar, Sharika Dhakappa et al. (+26 more)

The assumption of long-term pulse-profile stability underpins high-precision pulsar timing and forms the basis of pulsar timing array experiments. However, several millisecond pulsars exhibit temporal profile variability that can introduce systematic biases in pulse time of arrival measurements and compromise timing precision. We present a profile-domain analysis of PSR J1713+0747 at low radio frequencies, in the 300-500 MHz band, using upgraded GMRT observations for the Indian Pulsar Timing Array experiment. We model frequency-resolved pulse profiles using a Bayesian Gaussian decomposition framework in which individual Gaussian components are associated with persistent emission regions through informative phase priors that permit modest temporal variations. By tracking the evolution of the decomposed components across observing epochs and frequency sub-bands, we identify central Gaussian components that remain precisely localized despite changes in the integrated pulse morphology. We then reconstruct pulse profiles with realistic noise using these central components and perform timing analysis. Our approach provides a physically motivated framework for mitigating pulse-profile variability and offers a generic methodology for recovering robust timing information from pulsars exhibiting profile evolution.
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All authors Shaswata Chowdhury, M. A. Krishnakumar, Sharika Dhakappa, Vidit Singh, Debabrata Deb, Jyotijwal Debnath, Kaustubh Rai, Pratik Tarafdar, Abhimanyu Susobhanan, Churchil Dwivedi, Bhal Chandra Joshi, Shantanu Desai, Neelam Dhanda Batra, Jaikhomba Singha, Himanshu Grover, Manjari Bagchi, Mayuresh Surnis, Avinash Kumar Paladi, Aman Srivastava, Arul Pandian B., Suruj Jyoti Das, Jibin Jose, Kuldeep Meena, Sushovan Mondal, K Nobleson, Keitaro Takahashi, Hemanga Tahbildar, Kunjal Vara, Zenia Zuraiq

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

Consistent Thermal Resummation and Phase Transitions with 2PI Methods

Amitayus Banik and Kimmo Kainulainen

We apply the two-particle irreducible (2PI) formalism as a framework for a consistent thermal resummation in studies of cosmological phase transitions. Considering a model with two mixing real scalar fields, we work within the Hartree approximation and renormalize the 2PI effective action, while introducing a connection to physical parameters. This yields the Hartree-resummed finite-temperature effective potential, which is valid for all temperatures and avoids the limitations of conventional methods based on the high-temperature approximation. With this potential, we study one- and two-step transitions within the model, and compare our results with those obtained using resummation schemes widely employed in the literature. Finally, we evaluate the gravitational wave spectrum generated from first-order phase transitions, demonstrating the impact of the choice of resummation scheme on the predicted spectrum.
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Astrophysics of Galaxies

Implications of Broad [O III] 4364 and UV Line Emission in Two Little Red Dots at z ~ 7 - 8

Casey Papovich, Kaila Ronayne, Weida Hu et al. (+17 more)

We present deep, NIRSpec G140M and G395M spectroscopy of Little Red Dots (LRDs) at z = 6.68 and z = 8.35. Both LRDs show broad Balmer and [O III] $\lambda$4364 emission. The broad [O III] $\lambda$4364 lines have FWHM ~1000 km/s, about 1/3 that of the H$\beta$ lines. Assuming gas temperatures T ~ 15,000 - 25,000 K, the [O III] $\lambda$4364/[O III] $\lambda$5008 ratios of the broad lines yield high gas densities, log n/cm^-3 = 6.3 to 7.9, 3-10$\times$ higher than those in broad-line regions of low-redshift quasars. If the broad-lines trace virial motions, it is evidence for metal-enhanced gas clouds, ~1-10~pc from the LRD engine. Both LRDs show narrow [C III] $\lambda$1907 + C III] $\lambda$1909, and O III] $\lambda\lambda$1661,1666. The C III] ratios yield narrow-line gas densities, log n/cm^-3 = 4.2-5.2, similar to those in other star-forming galaxies. The line equivalent widths, EW(O III]), EW(C III]), are at, or exceed, limits expected for stellar populations, likely requiring an additional ionizing source. The LRDs also have [O III] $\lambda$4364/H$\gamma$ ratios that favor ionization from an accretion disk, possibly combined with stars. Both LRDs show nitrogen enhancement based on detections of N III] $\lambda$1746 or N IV] $\lambda$1486, which may imply rapid, recent star-formation. These results favor a scenario where the LRD gas envelopes are highly stratified, having high-density clouds with a non-unity covering factors and a complex geometry, such that ionizing radiation from the LRD accretion disk, combined with that from star-forming regions, produce the nebular emission features.
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All authors Casey Papovich, Kaila Ronayne, Weida Hu, Dale D. Kocevski, Pablo Arrabal Haro, Taylor A. Hutchison, Steven L. Finkelstein, Erini Lambrides, Rebecca L. Larson, Bren E. Backhaus, Micaela B. Bagley, Nikko J. Cleri, Mark Dickinson, Ray Garner III, Jeyhan Kartaltepe, Vasily Kokorev, Grace M. Olivier, Anthony J. Taylor, Jonathan R. Trump, Jiayang Yang

High Energy Astrophysical Phenomena

From Multimessenger Inference to Simulations: A Ranked Ensemble of Finite-Temperature Equations of State

Max Jacobi, Giulia Huez, Sebastiano Bernuzzi et al. (+1 more)

We construct a set of microphysical, finite-temperature equations of state (EOSs) for numerical simulations of neutron star mergers and core-collapse supernovae that is consistent with modern constraints from nuclear theory and multimessenger astronomy and systematically spans the posterior distribution of allowed EOSs. The EOSs are based on a simplified Skyrme functional whose inputs are nuclear matter saturation properties, extended to supra-saturation densities through the speed of sound at a set of reference densities. The models are assigned continuous likelihood weights from chiral effective field theory and perturbative quantum chromodynamics calculations, the gravitational wave signal GW170817, the complete set of NICER mass-radius measurements, and the Shapiro-delay mass measurement of the radio pulsar J0348. From the resulting catalogue of 5.2 million EOSs, the posterior yields $R_{1.4} = 11.8^{+0.8}_{-0.7}$ km, $\Lambda_{1.4} = 334^{+193}_{-113}$, and $M_{\rm max}^{\rm TOV} = 2.18^{+0.22}_{-0.14}\,M_\odot$ (medians with 90% credible intervals). From this posterior we select a ranked 12-member ensemble, headed by a fiducial, central EOS, whose members are individually plausible while jointly bracketing the posterior spread of neutron-star observables. For all ensemble members we generate general-purpose finite-temperature tables with the SROEOS code, each accompanied by nucleon effective-mass variants that bracket the ensemble's thermal-sector uncertainty, to be made publicly available upon publication.
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All authors Max Jacobi, Giulia Huez, Sebastiano Bernuzzi, David Radice

Astrophysics of Galaxies

Column-Density Estimation from the Equivalent Widths of Absorption Doublets

Avshalom Badash and Doron Kushnir

Na I D absorption is widely used to estimate the dust extinction toward Galactic and extragalactic sources, but the inferred column densities are unreliable once the lines saturate. We present an analytical framework for estimating column densities from the equivalent widths ($EW$s) of absorption-line doublets. The method requires only that the two doublet members be measured separately – the velocity structure need not be resolved – so a resolving power $\lambda/\Delta\lambda\gtrsim10^{3}$ suffices for Na I D, two orders of magnitude below velocity-resolved methods. For the Gaussian curve of growth, the classical inversion reduces to a universal saturation correction depending only on the doublet ratio, $R=EW_2/EW_1$: at fixed $R$, the inferred column density is linear in the measured $EW$. The formulation yields the exact Gaussian inversion, $N_{\tilde\kappa}$, which provides the Doppler parameter; a closed-form second-order approximation; and a strict lower bound, $N_{\rm min}$, valid for an arbitrary velocity structure. We recommend reporting $N_{\rm min}$: an optimal, assumption-free lower bound, within a few per cent of $N_{\tilde\kappa}$ for $R\gtrsim1.4$ and at most a factor $3.5$ below it at $R=1.1$. The ratio $N_{\tilde\kappa}/N_{\rm 2nd}$ provides a per-object saturation diagnostic. We validate the framework against published profile-fitting Na I D column densities toward Type Ia supernovae, using only the integrated $EW$s. An explicit closed-form formula converts the two $EW$s into an extinction estimate through the observed $\log N(\mathrm{Na\,I})$–$A_V$ relation. A public implementation with full uncertainty propagation accompanies the paper.
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Astrophysics of Galaxies

Predicting the Kinematics of the Cold Circumgalactic Medium from its Morphology using Convolutional Neural Networks

Connor Jennings, Earl P. Bellinger, Imad Pasha et al. (+2 more)

We present a novel approach to predicting plane-of-sky velocities of cold gas clouds in the circumgalactic medium (CGM) of galaxies. The method uses a convolutional neural network (CNN) trained on simulated emission maps derived from the TNG50 cosmological simulation, with forward modeled noise properties consistent with upcoming observational facilities. Using 182 Milky Way/Andromeda analog galaxies, we generate emission maps in H$\alpha$ using $\texttt{Cloudy}$ models, as well as line-of-sight averaged 2D velocity maps. Using a UNet architecture, we train the CNN to take emission maps as input and return plane-of-sky velocity maps as output, which cannot be observationally constrained using traditional methods. Qualitatively, the model is generally able to infer the true overall flow direction. We quantify the effects of Gaussian noise on the network's training and predictive power. At depths expected to be probed by forthcoming telescopes such as MOTHRA, the network has a typical RMS error for the plane-of-sky velocity direction of $0.3-0.5 v_{vir}$. This implies that 2D emission maps of sufficient depths will be able to estimate two additional phase space dimensions of cold CGM gas, enabling targeted followup and a better understanding of overall CGM flows.
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All authors Connor Jennings, Earl P. Bellinger, Imad Pasha, Pieter van Dokkum, Pratik J. Gandhi

Earth and Planetary Astrophysics

Self-consistent 1D modelling of Jupiter's upper atmosphere as an exoplanet analogue

Nils-Martin Robeling, Sudeshna Boro Saikia, Gwenaëlle Van Looveren et al. (+5 more)

Jupiter's upper atmosphere provides a real-world laboratory for validating first-principles models of giant gaseous exoplanets and for constraining the key physical processes that govern them. We extended the 1D first-principles thermo-chemical planetary upper atmosphere model Kompot to simulate hydrogen-rich atmospheres of giant exoplanets and benchmarked it against the archetype giant planet Jupiter. We modelled a longitudinal and latitudinal average thermal and chemical profile of Jupiter's upper atmosphere by solving the equations of energy balance, photochemical kinetics, hydrodynamics, and vertical transport in a 1D radial atmospheric grid. The thermal properties of the upper atmosphere were determined by a balance between heating from solar X-ray and ultraviolet (XUV), and infrared (IR) radiation, thermal conduction, Joule heating, and radiative cooling due to H3+ and CH4. The model results were compared with Jupiter observations from Galileo, JUNO, and other instruments. The simulation results were also used as input in the radiative transfer module of the TauREx code to simulate Jupiter's infrared transmission spectrum. Our model reproduces Jupiter's observed upper-atmospheric thermal structure and observed CH4 volume mixing ratios. The chemical abundances of other gases also exhibit strong agreement with observations and existing photochemical models. Heating and cooling results show that Joule heating is the dominant heating source throughout most of the upper atmosphere. The transmission spectrum indicates the rich presence of CH4 in the near- and mid-IR wavelength ranges. Our physically consistent model framework for Jupiter's upper atmosphere provides a validated baseline for future self-consistent simulations of the thermal and chemical structure of a diverse population of hydrogen-rich exoplanet atmospheres.
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All authors Nils-Martin Robeling, Sudeshna Boro Saikia, Gwenaëlle Van Looveren, Ivan Stanković, Simon Schleich, Colin P. Johnstone, Manuel Güdel, Kristina Kislyakova

Astrophysics of Galaxies

The Most Dangerous Seed: Nonlinear Optimal Perturbations in Rayleigh-Taylor Instability

Suoqing Ji and Bin Shi

Long-term instabilities in astrophysical fluids are inherently nonlinear, where even small-amplitude perturbations can trigger dramatic instability. However, owing to the complex interactions among non-normal modes, the perturbation structures responsible for the greatest growth remain poorly understood. In this paper, we employ the nonlinear optimization method known as the conditional nonlinear optimal perturbation (CNOP) to identify the most dangerous initial velocity perturbation, i.e., the perturbation that maximizes the kinetic energy growth in the two-dimensional compressible Rayleigh-Taylor instability in astrophysical hydrodynamics. Compared with random perturbations, the optimal perturbation forms a coherent wave-packet structure localized around the density interface. We investigate its dependence on spatial resolution and optimization time horizon through two sets of numerical experiments. For a fixed optimization time, increasing the spatial resolution produces a more sharply localized wave packet, whereas for a fixed spatial resolution, increasing the optimization time causes the wave packet to become progressively more dispersed. Furthermore, we analyze the optimal perturbations in Fourier space using the fast Fourier transform (FFT), which provides a clearer characterization of the spectral distribution. Higher-resolution simulations concentrate most of the perturbation energy into only a few dominant modes, while longer optimization times distribute the energy over a broader range of modes. These results indicate that short optimization time horizons involve relatively weak modal interactions and remain closer to the linear regime, whereas longer optimization times enhance nonlinear modal interactions, broaden the spectral distribution, and reduce the predictive capability of linear stability theory.
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Cosmology and Nongalactic Astrophysics

Cosmological constraints and standard sirens forecasts for non-dynamical dark energy in Horndeski gravity

Marcello Miranda, Ruchika, Ivan De Martino et al. (+2 more)

We investigate an analytically tractable sector of the Extended Cuscuton model, a non-dynamical dark-energy realization within the framework of viable Horndeski gravity. We focus on four benchmark submodels and constrain them with current background probes, namely cosmic chronometers, Type-Ia supernovae, and BAO, while imposing theoretical viability, Lunar Laser Ranging, and Big Bang Nucleosynthesis bounds. We then forecast third-generation bright-standard-siren constraints with Einstein Telescope and Cosmic Explorer networks, considering prompt-emission, afterglow, and kilonova counterparts. Current data already restrict the viable parameter space to small departures from $\Lambda$CDM and do not remove the calibration-driven offset between the CC+SN and CC+BAO determinations of $H_0$. In principle, future bright sirens substantially sharpen the constraints, especially for kilonova catalogues and extended detector networks. Across the forecast configurations, the relative uncertainty on $H_0$ remains below $13.18\%$ and can reach $0.21\%$ in the most constraining cases, while $\Omega_\Lambda$ is recovered at the percent level in the best cases. These results show that third-generation standard sirens can provide a precise complementary test of non-dynamical dark energy beyond $\Lambda$CDM.
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All authors Marcello Miranda, Ruchika, Ivan De Martino, Daniele Vernieri, Salvatore Capozziello

Astrophysics of Galaxies

The most extreme high-z radio quasars in the eRASS:1 X-ray survey

L. Ighina, L. Palmieri, L. N. Martínez-Ramírez et al. (+7 more)

We present the selection and identification of high-z radio quasars from a combination of X-ray (eROSITA All-Sky Survey), optical/NIR (DECam Local Volume Exploration), and radio (Rapid ASKAP Continuum Survey) surveys. After building a sample of 68 new high-z quasar candidates, we performed follow-up spectroscopic observations on 46 sources, confirming 39 to have redshifts z>3.5. For the subset of radio quasars at z>4, the 14 new sources identified here represent an increase of $\sim$65% in the known population of objects above the same flux limits in the same area. Using X-ray-to-optical relative intensity, we identified blazars in our sample, which we then used to compare the total number of z>4, X-ray selected blazars to the predictions of a fractional IC/CMB model previously proposed in the literature. Overall we find a relatively good agreement, even considering the potential biases in the redshift distribution from the incompleteness of the spectroscopic follow-up and the blazar classification criteria. The sources presented in this work represent a sample well suited for investigating the evolution of the most extreme systems in the early Universe, including their relativistic jets and accretion properties
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All authors L. Ighina, L. Palmieri, L. N. Martínez-Ramírez, A. Caccianiga, T. Connor, A. Moretti, B. Arsioli, Y. Beletsky, E. Marini, A. Rossi

Earth and Planetary Astrophysics · Cross-listed from physics.pop-ph

The Astronomy of Halakhic Nightfall: Calculating Ts'eit HaKokhavim and Motsa'ei Shabbat

Aster G. Taylor

In Jewish tradition, the boundary between days is not midnight, but nightfall. Nightfall is when one must pray ma'ariv, count the omer, and may engage in activity after Shabbat. While there are slightly different definitions of nightfall for Shabbat restrictions (Motsa'ei Shabbat) versus other purposes (Ts'eit HaKokhavim), most minhagim define nightfall to be when three stars of some specified size and proximity are visible in the sky. This definition presents some difficulty. Not only are these conditions difficult to define, they are further complicated by weather, cloud cover, and light pollution. Observant Jews therefore usually approximate these times by defining nightfall to be when the sun has reached a certain distance below the horizon. Although these approximations have been effective, modern astronomy enables us to calculate precisely when these conditions are met. This work applies these techniques to calculate the time of Ts'eit HaKokhavim and Motsa'ei Shabbat evaluates the accuracy of the approximations, and explores the effects of light pollution on these times. While Ts'eit HaKokhavim is reasonably well-approximated by standard methods, the conditions for Motsa'ei Shabbat generally occur after the time predicted by the approximations. Light pollution does not shift Ts'eit HaKokhavim by more than a minute but significantly changes Motsa'ei Shabbat. In fact, light pollution causes the conditions of Motsa'ei Shabbat to never be met on at least some nights in every population center. Finally, I provide a tool (halakhic-nightfall.streamlit.app) for calculating Ts'eit HaKokhavim and Motsa'ei Shabbat at an arbitrary time and location on Earth.
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Instrumentation and Methods for Astrophysics

Charged Clouds of Ionized Gas Emerge from Tribocharging Grains

Patrick Hock, Jens Teiser and Gerhard Wurm

If two solid particles collide, charge is exchanged. However, this transfer is not restricted to the surface of the particle. Ions are also dispersed into the environment. They form a charge cloud around the particle. In this way, all particle-laden atmospheres from volcanic plumes on Earth over exoplanet atmospheres to protoplanetary disks might be subject to gas-phase ionization by means of particle collisions. In laboratory experiments, we quantify the amount of ions produced in a collision of glass beads with 2.8 mm diameter. We extract the ions by applying an external electrostatic field and measuring the generated current. The ions are detected at all the pressures studied, i.e. from 0.3 mbar to 100 mbar. However, the ionization rate peaks at about 1 mbar. Scaled to individual bouncing collisions, charge as high as 1 pC of each polarity was detected. This implies collisions of grains can be a significant source of ions in various atmospheres.
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