Instrumentation and Methods for Astrophysics
CCAT: Optical Design of the 410 GHz Prime-Cam Module
Tilak M. Patel, Tanner Buck, Anthony Huber et al. (+7 more)
Prime-Cam is a first-generation instrument for the Fred Young Submillimeter
Telescope (FYST), enabling wide-field, multi-frequency observations for cosmology, line-intensity mapping, and
galaxy studies. We present an optical performance study for a candidate 410 GHz broadband module designed to field approximately 21,000 polarisation-sensitive kinetic inductance detectors (KIDs). The three-lens silicon design was adapted from the SO LATR design and used for the existing 280 and 350 GHz
Prime-Cam instrument modules, as well as this study. At 410 GHz, a shorter wavelength places tighter demands on wavefront quality and beam shape. Using Ansys Zemax OpticStudio and Huygens PSF analysis, we evaluate candidate module positions, compare 350 and 410 GHz performance, and assess field-dependent Strehl ratio, ellipticity, and encircled-energy behaviour. A preliminary tolerancing study, using inverse increment and Monte Carlo methods, tests sensitivity to selected
alignment perturbations.
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All authors Tilak M. Patel, Tanner Buck, Anthony Huber, Eve M. Vavagiakis, James Burgoyne, Scott Chapman, Ben Keller, Jenna E. Moore, Michael D. Niemack, CCAT Collaboration
Earth and Planetary Astrophysics
Rotation, spectral type, and albedo of the potentially hazardous asteroid (153814) 2001 WN$_{\text 5}$ Prior to the 2028 June close approach
Jin Beniyama, Alexey V. Sergeyev, Konstantinos Odysseas Xenos et al. (+6 more)
The potentially hazardous asteroid (153814) 2001 WN$_5$ will pass inside the lunar distance on June 26, 2028, offering a rare opportunity to characterize a kilometer-scale near-Earth asteroid at high angular resolution. We aim to constrain the rotation state, shape, visible colors,
geometric albedo, and taxonomy of 2001 WN$_5$ before its 2028 close approach. We combined new photometry from the 1.54 m Danish
Telescope (DK154) with archival and survey observations from the Transiting
Exoplanet Survey Satellite (TESS), Dark Energy Camera (DECam), Zwicky Transient Facility (ZTF), and the Asteroid Terrestrial-impact Last Alert System (ATLAS). These data were used to refine the rotation period, investigate the
spin-shape solution space, derive visible colors, and estimate the
geometric albedo from phase curve slopes. The available lightcurves do not uniquely constrain the sidereal rotation period, but the preferred pole solutions lie in the southern hemisphere in ecliptic coordinates. Visible colors from multiple independent
datasets are consistent with the C-complex, while the TESS phase curve slopes give $p_{\rm V} = 0.13\pm0.04$, consistent with previous thermal-infrared albedo estimates. Combining the visible colors, albedo, and published near-infrared spectra, we classify 2001 WN$_5$ as most likely a B-type asteroid. The effective diameter is estimated to be $D = 0.81 \pm 0.13$ km using the $H$-$G$ model, while the linear model yields a slightly smaller value of $0.74 \pm 0.11$ km. During the 2028 encounter, 2001 WN$_5$ should reach an apparent diameter of about 0.5~arcsec, making it an excellent target for coordinated photometric, spectroscopic, and high-angular-resolution observations. Observations during the 2026-2027 apparition will be essential for improving its
spin and shape model before its 2028 close approach.
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All authors Jin Beniyama, Alexey V. Sergeyev, Konstantinos Odysseas Xenos, Benoit Carry, Petr Pravec, Petr Fatka, Peter Kušnírák, Larry Denneau, Vasilij Shevchenko
Instrumentation and Methods for Astrophysics
Foundation Models for Astrophysics
Xiaosheng Zhao and Yuan-Sen Ting
Foundation models are high-capacity networks pretrained once on broad data and then reused across many tasks. This chapter introduces them through the idea of a transferable representation, the internal description a network forms during training, which, rather than the fitted task, is what carries over to new problems. We develop the idea from first principles for an astronomical reader, starting from why a representation matters and what makes one useful, and then surveying the architectures, self-supervised objectives, scaling, adaptation, and cross-modal learning that produce one. A theme throughout is the distinction between these methods and the goal they serve. The presence of a
transformer, a self-supervised objective, and large-scale pretraining does not by itself make a model a foundation model, since the defining property is that the learned representation transfers, as tested by its ability to work on new tasks with little or no task-specific training data (few-shot and zero-shot learning). We then consider astronomy, where data are abundant but labels are scarce and simulations often stand in for ground truth. Here we offer a cautious reading of the current literature, in which many models adopt the architecture of foundation models while clear demonstrations of transfer across instruments, populations, and tasks remain comparatively rare. This is to be expected, since robust transfer beyond
language is still uncommon even in
vision and the wider physical sciences, and whether further scaling or a different account of representation will close the gap remains an open question. We close by placing the goal within the broader aim of machine intelligence and outlining the evidence that would mark real progress.
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Astrophysics of Galaxies
Radial abundance gradients of 18 elements in Galactic open clusters from infrared MWM spectra A detailed analysis of 655 giants in 133 clusters
S. Bijavara Seshashayana, H. Jönsson, V. D'Orazi et al. (+3 more)
Open clusters are powerful tools for studying the Milky Way. While large spectroscopic surveys now provide spectra for many cluster members, automated pipelines and heterogeneous membership selections can introduce systematics and inflate apparent cluster scatter. Therefore, a homogeneous re-analysis with careful membership control and an explicit treatment of departures from Local Thermodynamic
Equilibrium is valuable for establishing robust abundance gradients. The aim is to derive precise
Galactic radial abundance gradients for multiple elements using open cluster
giants, and to investigate how these gradients depend on cluster age. We re-analysed high-resolution infrared APOGEE Milky Way Mapper spectra from DR19 of the Sloan Digital Sky Survey for 655 open cluster members selected from
Gaia data that satisfied strict quality cuts on signal-to-noise ratio.
Stellar parameters and 18 elemental abundances were obtained using spectrum fitting with the Python version of Spectroscopy Made Easy, applying Non-Local Thermodynamic
Equilibrium corrections for several key atomic species. Further quality control of the results was made by visual inspection of all fitted synthetic spectra. The
metallicity of the clusters decreases with Galactocentric radius, following a global slope close to -0.06 dex/kpc. Beyond 10-11 kpc, there is modest flattening. In addition to the elements analysed in the \cite{otto2026} study, we derive open-cluster gradients for V, Cu, Zn and Yb using APOGEE spectra.
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All authors S. Bijavara Seshashayana, H. Jönsson, V. D'Orazi, K. Cunha, P. Frinchaboy, J. M. Otto
Solar and Stellar Astrophysics
You're Gonna Need a Bigger Core: Calibrating Massive Star Models against Galactic OB-type Stars
Thibault Lechien, Selma E. de Mink, Stephen Justham et al. (+3 more)
The
evolution of massive
stars above 8 M$_\odot$ depends critically on the amount of mixing above the convective core during the main sequence. However, current models typically extrapolate results from lower-mass
stars, where constraints from asteroseismology and eclipsing binary systems are more readily available. A new opportunity to study the
evolution of massive
stars and their distribution in the Hertzsprung–Russell diagram arises by combining the IACOB spectroscopic sample of over 900
Galactic OB-type
stars with
Gaia distances. We use this homogeneously analyzed sample to place population-level constraints on main-sequence
evolution. We analyze the data by forward modeling
stellar evolution tracks with MESA and applying
Bayesian inference. This enables us to 1) determine a physically-motivated, data-driven location of the terminal-age main sequence, 2) constrain convective boundary mixing and resulting core masses, and 3) provide a set of massive
star models calibrated against modern data. We explore how boundary mixing depends on mass and find that it is well described by a constant overshooting parameter in the mass range of 12 to 40 M$_\odot$, with $\alpha_{\mathrm{ov}} = 0.33 \pm 0.02$, or $f_{\mathrm{ov}} = 0.028 \pm 0.003$ in the step and exponential overshooting schemes respectively. We find evidence against a continuation of the trend to increase with mass that is found at lower masses. Instead, the data does not exclude a decreasing trend at the high mass end. We find that the resulting helium core masses are 10 to 40% larger than other commonly used overshooting prescriptions. Combining our findings with existing observational constraints for low- and intermediate-mass
stars, we propose a new mass-dependent overshooting prescription for a wide range of masses. Our calibration and model set are particularly useful for population and spectral synthesis applications.
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All authors Thibault Lechien, Selma E. de Mink, Stephen Justham, Abel de Burgos, Ruggero Valli, Sergio Simón-Díaz
Cosmology and Nongalactic Astrophysics
Effective reheating in Gauss–Bonnet inflation with $\mu(\phi,X)$ coupling
Ali Seidabadi, Sara Saghafi and Kourosh Nozari
We study effective reheating in a scalar–Gauss–Bonnet inflationary model with a phase-space-dependent coupling $\mu(\phi,X)$, in which a compact field-space feature is combined with a bounded kinetic gate. The modified inflationary background determines the pivot-scale quantities and the effective energy density at the end of inflation. These quantities are then used to derive the reheating duration $N_{\rm re}$ and temperature $T_{\rm re}$ through the thermal-history matching relation. We first perform two fixed-pivot reference scans by varying the overall Gauss–Bonnet strength $\lambda_{\rm GB}$ and the kinetic parameter $g_{_X}$ separately. For the reference parameter choices, increasing either parameter increases $N_{\rm re}$ and decreases $T_{\rm re}$ for the selected reheating equations of state. Additional
benchmark calculations clarify how these variations depend on the dynamical regime of the model. In the $\lambda_{\rm GB}$ scan, the increase in $N_{\rm re}$ and the decrease in $T_{\rm re}$ persist, although both variations become strongly suppressed when the coupling is more localized or when the end of inflation is controlled more strongly by the E-model potential. In the $g_{_X}$ scan, stronger field-space localization and kinetic saturation can instead lead to a slight decrease in $N_{\rm re}$ and an increase in $T_{\rm re}$ as $g_{_X}$ is increased. When the bounded kinetic contribution is considered together with a weaker overall Gauss–Bonnet interaction, the resulting changes in the reheating quantities become nearly negligible. The fixed-pivot predictions of the representative and alternative
benchmarks are compared with CMB constraints.These reheating constraints are then discussed for four representative values of the effective equation-of-state parameter, $\overline{w}_{\rm re}=-1/3,0,2/3,$ and $1$.
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Cosmology and Nongalactic Astrophysics
Axion Inflation: Perturbative control in the strong backreaction regime
Valerie Domcke, Alexandros Papageorgiou, Marco Peloso et al. (+1 more)
We study the strong backreaction regime in
axion inflation, in which the friction from Abelian gauge fields generated via the pseudo-scalar interaction $\frac{\beta}{4 M_p} \phi F {\tilde F}$ is comparable to Hubble friction. The non-linear dynamics associated with the gauge fields render this regime phenomenologically particularly interesting, but also notoriously difficult to study with perturbative methods. Quantifying the perturbative control through the direct impact on the spectral backreaction using (i) a first-order gradient-expansion formalism including
axion gradients, and (ii) a one-loop in-in calculation, we discover an extended mild backreaction regime at large couplings $\beta$, with a relatively large, nearly constant particle production parameter $\xi$. In passing, we point out that CMB non-Gaussianity bounds impose a general upper limit on the product of
axion gauge field coupling and Hubble parameter during inflation, $\beta H/M_p < 1.4\cdot 10^{-3}$, independently of the choice of the
axion potential.
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All authors Valerie Domcke, Alexandros Papageorgiou, Marco Peloso, Stefan Sandner
Earth and Planetary Astrophysics
The Length of Martian Crater Rays and Their Relation to Lunar Cold Spots
Trevor P. Erwin, Brandon C. Johnson, David Minton et al. (+1 more)
Impact-generated crater rays are well-documented on the Moon, with most appearing as high-albedo streaks extending radially from a crater's center. On Mars, however, crater rays are significantly rarer and discernible only through thermal imaging due to their lower thermal inertia compared to surrounding terrain. This study presents the first comparative analysis between the lengths of Martian and lunar crater rays, including lunar albedo rays and cold spots, which are ray-like thermal anomalies associated with many of the youngest lunar craters. Our findings indicate that both Martian crater rays and lunar cold spots extend significantly farther than lunar albedo rays, with lengths an order of magnitude greater for craters of equivalent diameter. Furthermore, we propose a connection between the formation mechanisms of Martian crater rays and lunar cold spots based on their thermal properties. By integrating thermal rays into existing ejecta models, we refine the understanding of crater-ray formation and suggest that Martian crater rays and lunar cold spots may share a similar formation mechanism via secondary cratering processes. Advancing knowledge of these features has implications for impact dynamics and surface
evolution across planetary bodies.
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All authors Trevor P. Erwin, Brandon C. Johnson, David Minton, Alexandria V. Johnson
Cosmology and Nongalactic Astrophysics
Response to: "Isotropic deceleration and near-zero baseline acceleration in Pantheon+ supernovae: new arguments in the dark energy debate”
Animesh Sah, Mohamed Rameez and Subir Sarkar
Ray et al. [1] have claimed that the acceleration of the Hubble expansion rate inferred from Type Ia
supernovae in the Pantheon+ catalogue "is equally strong in the CMB dipole ($q_m = + 1.45$) and anti-dipole hemispheres ($+ 1.55$), directly contradicting the SRS26 anisotropy argument". Here SRS26 refers to our analysis [2] which showed that "locally $q_0$ has a strong dipole anisotropy aligned approximately with the bulk flow, and only a small monopole component remains at distances exceeding a few hundred Mpc". We find that these authors confused Equatorial with
Galactic coordinates, thereby getting the CMB dipole direction wrong. Hence their conclusion is baseless.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
The $g$-mode frequencies in cold neutron stars and nuclear saturation parameters
Hajime Sotani and Hajime Togashi
Oscillation frequencies excited in
neutron stars are crucial for extracting their interior properties. In addition to the fundamental and pressure modes, the
gravity ($g$-) modes can be excited even in zero-temperature
stellar models due to the composition gradient. In this study, we systematically study the $g$-mode frequencies, focusing on the nucleonic equation of state. Then, we can derive an empirical relation for the 1st $g$-mode frequencies as a function of the
stellar compactness and the combination of the
nuclear saturation parameters, $\eta_0 \equiv L/K_0$, where $K_0$ and $L$ denote the incompressibility of symmetric
nuclear matter and the density dependence of the
nuclear symmetry energy, respectively. If an observed 1st $g$-mode frequency significantly deviates from our empirical relation, it may indicate the emergence of additional degrees of freedom or new compositions inside the
star.
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Cosmology and Nongalactic Astrophysics
Isotropic universes with a preferred direction
Jose Beltrán Jiménez and Shinji Tsujikawa
We present a class of cosmological scenarios in which a preferred spatial direction in the matter sector coexists with an exactly homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker (FLRW) geometry. The Cosmological Principle is realized on shell, with the vector-field equations enforcing a vanishing momentum density and suitable interactions eliminating the anisotropic stress. Consequently, the construction yields an entire FLRW branch without tuning the matter-field initial conditions. The preferred direction reemerges in perturbations, producing direction-dependent propagation and mixing among scalar, vector, and tensor modes already at linear order. In particular, the mixing opens a linear channel through which perturbations in the scalar sector can in principle source gravitational waves. Our construction thus reveals a new route by which preferred-direction physics can leave observable cosmological signatures while remaining hidden in the background geometry.
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Solar and Stellar Astrophysics
A catalogue of high angular resolution and contrast polarimetric maps of 45 nearby AGB stars with SPHERE/ZIMPOL
Nekolgne Aymard Badolo, Eric Lagadec, Mamadou N'Diaye et al. (+7 more)
We present the largest catalogue of asymptotic
giant branch (AGB)
stars, 45 targets in total, observed in polarized light at high angular resolution (~ 20 milliarcsec). The main goal of the study is to detect and characterize
dust shells in the close environment of nearby AGB
stars. This work also aims to systematically classify the AGB
star circumstellar morphologies obtained with the SPHERE instrument installed at the Very Large
Telescope (VLT), thanks to its Zurich Imaging Polarimeter (ZIMPOL). We extracted and analyzed polarized intensity maps for 45 AGB
stars, constructed from polarimetric observation data obtained with the SPHERE/ZIMPOL instrument. An ellipse fitting method was applied to characterize the circumstellar envelopes.
Stellar parameters (luminosity, effective temperature, surface
gravity, extinction,
metallicity) were compiled and recalculated when necessary from spectral energy distribution (SED) fitting using the Python SED fitting tool (PySSED) software. These data were then used to train a random forest machine learning model to determine the most discriminating variables for a resolved envelope around a given
star. We constructed polarization maps for all
stars in the sample, revealing a wide diversity of circumstellar morphologies. We detected 16 dusty circumstellar envelopes, including three never observed before. They display a wide range of morphologies, all of them showing a clear departure from spherical
symmetry, indicating interaction with a companion or asymmetric mass ejections. The random forest model identified optimal thresholds for several physical parameters, thus providing robust criteria to anticipate SPHERE's ability to resolve
dust envelopes around AGB
stars. These results facilitate the selection of targets for future observations and contribute to a better understanding of the
evolution mechanisms of circumstellar envelopes.
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All authors Nekolgne Aymard Badolo, Eric Lagadec, Mamadou N'Diaye, Sie Zacharie Kam, Iain McDonald, Alexis Matter, Jean Koulidiati, Lyu Abe, Marcel Carbillet, Thierry Fusco
Solar and Stellar Astrophysics
Statistical insights on the decorrelation lengths of solar wind parameters at L1 point under varying conditions
Yogesh, Aparupa Apsara Baruah, Dibyendu Chakrabarty et al. (+3 more)
Understanding the spatial coherence of
solar wind
plasma and
magnetic field properties is essential for interpreting multi-spacecraft observations and for characterizing the large-scale structure of heliospheric transients. In this study, we quantify the spatial correlation of six key
solar wind parameters - interplanetary
magnetic field components, bulk flow speed,
proton number density, and the alpha-to-
proton abundance ratio - using simultaneous measurements from the ACE and Wind spacecraft as a function of their instantaneous separation distance. The analysis is performed separately for intervals of background
solar wind, Interplanetary Coronal Mass Ejections (ICMEs), and Stream Interaction Regions (SIRs). The decay of the Pearson correlation coefficient with distance is modeled using an exponential function to infer characteristic de-correlation length scales. We find that the bulk
solar wind speed is the most spatially coherent parameter in all regimes, while
plasma composition exhibits the weakest coherence.
Magnetic field coherence shows strong dependence on
solar wind structure: ICMEs display near-unity correlations and the largest
magnetic coherence scales, consistent with organized, flux-rope-like configurations, whereas SIRs exhibit reduced coherence - particularly in the north - south
magnetic field component - reflecting compressed and turbulent
plasma. The background
solar wind exhibits intermediate behavior, with large-scale coherence in bulk
plasma properties but shorter coherence lengths in
magnetic fluctuations. These results provide a quantitative framework for distinguishing
solar wind structures based on their spatial coherence properties and have important implications for multi-point
solar wind studies and space weather applications.
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All authors Yogesh, Aparupa Apsara Baruah, Dibyendu Chakrabarty, Kalyan Bhuyan, Aakash Gupta, Gregory G. Howes
Cosmology and Nongalactic Astrophysics
Axial Bianchi IX meets Gaia data
Thomas Schücker
The aim of the present work is two-fold: {\it(i)} Compute the drift of comoving extragalactic sources in axial Bianchi IX universes, in particular in those satisfying Einstein's equations with positive cosmological constant and comoving
dust. {\it(ii)} Linearize this drift (and for comparison the previously calculated Lemaître-Hubble diagram) simultaneously in small anisotropy and in small positive
curvature. We find that the drift in this linear approximation coincides with the drift in axial Bianchi I universes. This is not true for Lemaître-Hubble diagrams.
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High Energy Astrophysical Phenomena
Magnetic rigidity reveals the PeVatron acceleration region in SS 433
Jie Liao, Wancheng Xu, Lang Cui et al. (+10 more)
PeVatrons are
cosmic accelerators capable of driving particles to petaelectronvolt (PeV) energies. Recently, microquasar jets have emerged as compelling
Galactic PeVatron candidates. This is especially the case for SS 433 as its $>100$ TeV gamma-ray emission is spatially coincident with an atomic cloud. However, the exact region where PeV
protons are accelerated and injected within these jets remains unresolved. Here we report, using archival, multi-frequency VLBA observations, the
magnetic field profile $B(H)$ along the SS 433 inner jet on tens of AU scale, where $H$ is the distance from the central compact object. We find that the field declines as $B(H) \propto H^{-0.50\pm0.12}$, demonstrating that the
magnetic rigidity $B(H)R_{\rm acc}$ grows with $H$ for a conical jet. This implies the Hillas limit ($E_{\rm max} \propto BH$) to lie well beyond a PeV at a few hundred-AU scale, which becomes a highly potential site for accelerating
protons to energies $E_{\rm cut} \simeq 2.6$ PeV inferred from the LHAASO gamma-ray spectrum. These results reveal a hidden PeVatron within the baryonic ejecta of microquasar SS 433, well upstream of the extended TeV-emitting lobes.
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All authors Jie Liao, Wancheng Xu, Lang Cui, Pak-Hin Thomas Tam, Xi Yan, Linuo Yang, Ruo-yu Liu, Liang Chen, Ning Chang, Yong-Feng Huang, Long Ji, Ashutosh Tripathi, Felix Aharonian
Astrophysics of Galaxies
XRISM Resolves the Circum-nuclear Environment of NGC 4945
Peter G. Boorman, Poshak Gandhi, Yoshihiro Ueda et al. (+31 more)
Compton-thick Active
Galactic Nuclei (AGN) represent one of the most elusive phases of massive black hole growth, yet are expected to contribute substantially to the
Cosmic X-ray Background and the integrated growth of massive black holes. NGC 4945 is the closest Compton-thick AGN and amongst the brightest AGN in the hard X-ray sky, making it an important
benchmark for more distant Compton-thick AGN. We present the first high-resolution X-ray spectral analysis of NGC 4945 using XRISM/Resolve. The entire 4-15 keV Resolve spectrum, including a strong Fe K$\alpha$ doublet and weak Compton Shoulder, is well described by a de-coupled dual-obscurer model. The model features a low-covering-factor Compton-thick primary obscurer intersecting the line-of-sight that permits the rapidly variable, direct transmitted coronal continuum to dominate above 10 keV. A Compton-thin secondary reprocessor with a high covering factor dominates the reprocessed emission between $\sim$4-10 keV. Assuming that virial motion accounts for line broadening, the secondary reprocessor can exist at $\sim$0.12 pc, and could help explain the weak high-ionisation optical and infrared emission lines observed in NGC 4945. If such obscuration geometries are common among more distant and/or fainter Compton-thick AGN, our results suggest that simpler coupled X-ray spectral modelling could substantially over-estimate Compton-thick covering factors and under-estimate intrinsic X-ray luminosities.
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All authors Peter G. Boorman, Poshak Gandhi, Yoshihiro Ueda, Bert Vander Meulen, Kanta Fujiwara, Aoi Nakano, Johannes Buchner, Claudio Ricci, Kirpal Nandra, Daniel Stern, Almudena Alonso Herrero, Carolina Andonie, Franz E. Bauer, Stefano Bianchi, Murray Brightman, Francesca Civano, Richard I. Davies, Gulab Dewangan, Georgios Dimopoulos, Ismael García-Bernete, Santiago García-Burillo, Sebastian F. Hönig, Nancy A. Levenson, Andrea Merloni, Yuya Nakatani, Hirofumi Noda, Shoji Ogawa, Chris Packham, Simonetta Puccetti, Cristina Ramos Almeida, Marko Stalevski, Yuichi Terashima, Martin Ward, Satoshi Yamada
Instrumentation and Methods for Astrophysics
Spatial Mapping and Capacitor Trimming Developments to Improve Usable Pixel Yield in PRIMA FIRESS Kilo-Pixel Arrays
Chris Albert, Jonathon Hunacek, Hien Nguyen et al. (+12 more)
The Probe far-Infrared Mission for Astrophysics (PRIMA) will use 8 kilo-pixel kinetic inductance detector (KID) arrays in its spectrometer module. We present an improved resonant frequency to spatial position mapping system designed to preserve each array's mapping after transferring it from the mapping apparatus to the flight housing. Such a mapping is necessary for astronomical observations, and additionally allows us to
laser trim the capacitive elements of KIDs to optimize resonance separation in frequency space. This increases the operating yield by eliminating collided resonances, reduces crosstalk, and reduces the sensitivity to frequency drift over time.
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All authors Chris Albert, Jonathon Hunacek, Hien Nguyen, Ritoban Basu Thakur, Andrew Beyer, Charles Bradford, Peter Day, Pierre Echternach, Byeong Ho Eom, Logan Foote, Marc Foote, Steve Hailey-Dunsheath, Reinier Janssen, Elijah Kane, Henry LeDuc
High Energy Astrophysical Phenomena
Production of High Energy Neutrinos in the Coronae of Ultraluminous X-ray Sources
Norita Kawanaka and Shigeo S. Kimura
We investigate the possibility of high-energy
neutrino production in coronae associated with ultraluminous X-ray sources (ULXs) as super-Eddington accreting black holes. Adopting the disk-wind-fed corona model, we calculate
stochastic proton acceleration and the resulting
neutrino emission from the ULX corona. We first examine whether the corona can be regarded as a collisionless
plasma, which is a prerequisite for efficient non-thermal particle acceleration. We find that the collisionless condition is satisfied only when the mass
accretion rate is lower than ($\sim 5\dot{M}_{\rm Edd}$). In this regime,
protons are accelerated up to energies of a few tens of TeV and produce
neutrinos through both photomeson ($p\gamma$) and hadronuclear ($pp$) interactions. The importance of hadronuclear interactions increases with
accretion rate owing to the enhanced coronal density, resulting in broad
neutrino spectra shaped by both $p\gamma$ and $pp$ processes. We also derive a correlation between
neutrino and X-ray luminosities, ($L_{\nu,{\rm tot}} \propto L_X^{2.4}$), and estimate the
neutrino flux from nearby ULXs. We show that M82 X-1 is among the most promising targets and may be detectable at the 90% confidence level by future
neutrino observatories. These results suggest that super-Eddington accreting black holes constitute a previously unexplored class of high-energy
neutrino sources.
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Solar and Stellar Astrophysics
Towards understanding stellar variability at the sub m/s level: granulation-induced variability across the optical spectrum
Cis Lagae, Ginger Frame, Heather M. Cegla et al. (+5 more)
Detecting the radial velocity signal of Earth-mass
exoplanets requires the characterisation and removal of granulation-induced radial velocity variability from spectroscopic observations. By coupling three-dimensional (3D) hydrodynamic (HD) simulations to a radiative transfer code, we can isolate and study the effect of granulation on
stellar lines. In this study we isolated the impact of granulation on spectral line shapes and shifts for the largest and most diverse synthetic spectral line sample to date. Our aims were twofold. First, we quantified how granulation affects the temporal
evolution of shapes and shifts of 72 unblended spectral lines in two wavelength regions: 5500-5600 Å and 6100-6200 Å, from disc centre to the
stellar limb. Second, we investigated if spectral lines behave coherently in their line shape variability. We find that weak lines show the largest radial-velocity variability due to granulation, up to 40 m/s at disc centre and 50 m/s at the
stellar limb. On the other hand, strong lines exhibit larger variability in equivalent width than weak lines across the
stellar disc. In addition, the equivalent width and line depth of a spectral line are strongly linearly correlated with its radial velocity. While granulation affects all three of these quantities, planetary Doppler shifts only affect radial velocities, opening the door to new granulation-mitigation methods. Lastly, we find that the radial velocity and equivalent width of most spectral lines in our sample evolve coherently in time, with the Fe I and Ca I lines behaving the most similarly. Due to the coherency, line blends will not significantly affect the temporal behaviour of RV and line shape, as induced by granulation. Besides, the coherency between spectral lines offer the opportunity to create disc-integrated spectra of many lines simultaneously, which will be explored in future work.
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All authors Cis Lagae, Ginger Frame, Heather M. Cegla, Veronika Witzke, René Holzreuter, Sergiy Shelyag, Christopher Watson, Alexander Shapiro
Earth and Planetary Astrophysics
Accretion across scales: streamers, surface-layer transport, and rapid replenishment in young protoplanetary discs
Christian Granzow Holm, Michiel Lambrechts, Michael Kuffmeier et al. (+3 more)
Protoplanetary discs evolve around newly-formed
stars through an interplay of infall from surrounding turbulent cloud material,
accretion towards the young
star, and
outflow driven mass-loss. It has been challenging to determine if discs are fed predominantly through infall along the disc midplane, or along the poles, and if
accretion occurs in a steady or burst-like fashion. Here, we present a suite of 3D ideal magnetohydrodynamical simulations of protoplanetary disc formation and
evolution in a dynamic, large-scale molecular cloud environment using the adaptive mesh refinement framework DISPATCH. We focus on nine
stellar systems, where we resolve discs down to a scale of 0.8 au. Across the sample,
stellar accretion proceeds at rates of $\sim$10$^{-5}$ M$_\odot$ yr$^{-1}$ over 10$^{5}$ yr, with significant variability. Discs grow to 100 au scales and remain gravitationally stable in time, with disc-to-
star mass ratios below 10 %. Transient high-density streamers, with 10 kyr infall times, can drive anisotropic mass delivery at rates comparable to the background
accretion flow. Their interaction with discs typically results in a temporary reduction of the disc size by half, and disc mass by 40 %. During later quiescent disc
evolution stages ($t\gtrsim$50 kyr),
accretion predominantly occurs through the midplane and disc surface layers. This is associated with the development of a toroidal
magnetic field morphology, which includes field reversals across both disc surfaces. In this way, the full disc mass reservoir is replenished on 10 kyr-timescales. These findings support that the outer parts of very young discs, when well-ionised and close to the ideal MHD regime, are not yet conducive to
planet formation, due to high replenishment rates, strong
turbulence, and disruptive streamer infall events.
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All authors Christian Granzow Holm, Michiel Lambrechts, Michael Kuffmeier, Anders Johansen, Troels Haugbølle, Åke Nordlund
Cosmology and Nongalactic Astrophysics
A refined method for measuring cosmological distances using variability and proper motions in AGN with VLBI-detected counter-jets
Jeffrey A. Hodgson, Anthony Carr, David Parkinson et al. (+6 more)
In a previous paper, we described a `standard speed-gun' (SSG) distance that uses the speed of light to standardize a ruler under the assumption that the
radio variability seen in blazars is causally limited. The apparent size is then measured with Very Long Baseline Interferometry in order to derive the angular diameter distance. A key limitation of this method is that it requires knowledge of the relativistic Doppler factor. Previously, we estimated the distance to the bright
radio source, 3C 84 at the center of the Perseus cluster assuming a Doppler factor of \delta ~ 1. In this paper, we aim to describe how a detected counter-jet and approaching jet proper motions can be used to remove the need for knowledge of the Doppler factor when measuring cosmological distances in this way. Under the assumption of a disk (or spherical) geometry and parameterizing the relationship between the physical emitting region and the variability timescale via a causality correction factor (kappa), we estimate a refined angular diameter distance to 3C 84 (z=0.0178) with statistical errors. Assuming kappa=1, we derive distances of D_A,disk = 78.9(-9.8+11.0) Mpc (or D_A,sphere = 71.2(-8.8+9.7) Mpc). Comparing these results to literature
benchmarks, we find that the spherical assumption yields a distance consistent with local Type Ia
supernovae calibrated to the SH0ES H0, while a disk-like geometry aligns with expectations from a lower H0 cosmology. Ultimately, this demonstrates that utilizing jet and counter-jet kinematics successfully removes the Doppler-factor dependence from the standard speed-gun method, providing a viable independent distance estimate once the
geometric structure of the jet is resolved.
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All authors Jeffrey A. Hodgson, Anthony Carr, David Parkinson, Matteo Statti, Jaehyeon Myeong, Benjamin L'Huillier, Arman Shafieloo, Ioannis Liodakis, Se Heon Oh
Solar and Stellar Astrophysics
Performance of radio-based detection to operational monitoring M5+ class solar flares
Julia van Ravenswaaij, Ines Wilms, Ivan Ricardo et al. (+1 more)
Early detection of major
solar flares is critical for defense operations due to their potential to disturb radar and
radio systems. Typically, soft X-ray flux is used to monitor and classify
solar flares, but since this flux has to be measured in space, it means that its availability itself is dependent on space weather conditions. For this reason, in this paper, we investigated the feasibility of using ground
radio observations to monitor major (M5+ class)
solar flares. We made use of
datasets from the GOES-16 satellite and the
Radio Solar Telescope Network in the time range between March 2023 and March 2025. An elastic net regularized logistic regression model was trained on this data, optimized through a grid search and with incorporated class weighting for class imbalance. It was found that especially higher frequencies (8800 MHz) had a reasonable ability in monitoring and predicting major
flares (precision and recall for
flare events are 53% and 65%, respectively - implying that roughly one third of
flares were not detected - with signals appearing, on average, 3 to 4 minutes before the M5 threshold is exceeded).
Radio measurements at super high frequencies can thus serve as an alternative method to monitor major
solar flaring activity.
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All authors Julia van Ravenswaaij, Ines Wilms, Ivan Ricardo, Michaela Brchnelova
Instrumentation and Methods for Astrophysics
The Wetterstein Millimeter Telescope: A New German Facility for Astronomy and Geodesy
Alexander Neidhardt, Matthias Kadler, Anne-Kathrin Baczko et al. (+7 more)
The Wetterstein Millimeter
Telescope (WMT) is a planned broadband (1.2-120 GHz)
radio telescope to be established near the Environmental Research Station Schneefernerhaus (UFS) on Germany's highest mountain, the Zugspitze. Developed by a consortium of German research institutes and partners, the WMT is conceived as a multidisciplinary research infrastructure supporting
radio astronomy, geodetic VLBI, satellite communications, space situational awareness, and technology development. The
telescope is designed to operate within international VLBI networks, including the European VLBI Network, the Global mm-VLBI Array, and future ngVLA and SKA-VLBI observations. This contribution summarizes recent progress in the WMT project, including the
evolution of the
antenna design, and highlights the potential of the WMT to support future astronomical and geodetic VLBI.
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All authors Alexander Neidhardt, Matthias Kadler, Anne-Kathrin Baczko, Guido Dietl, Urs Hugentobler, Matthias Schartner, Tobias Ullmann, Till Rehm, Jompoj Wongphechauxsorn, for the WMT consortium
Earth and Planetary Astrophysics
A JWST Study of Stardust. I. Infrared Spectroscopy of Comet 81P/Wild 2 and Overall Composition
Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden et al. (+11 more)
We report observations of comet 81P/Wild 2, target of the Stardust sample return mission, on UT 2023 March 20 and 24 at a heliocentric distance ($r_H$) of 1.85 au using the NIRSpec and MIRI integral field unit spectrographs on board the James Webb Space
Telescope (JWST). This study is the first compositional comparison between JWST remote-sensing spectroscopy of a
solar system object against terrestrial analysis of its returned samples. We securely detected molecular emission from H$_2$O, CH$_4$, C$_2$H$_6$, CH$_3$OH, CO, CO$_2$, $^{13}$CO$_2$, OCS, HCN, and CN and find molecular abundances consistent within $2\sigma$ with those reported during previous perihelion passages. The water ortho-to-para ratio was $2.76\pm0.05$, and the $^{12}$CO$_2$/$^{13}$CO$_2$ ratio was $85\pm4$. Thermal emission from the
nucleus and
dust was detected and modeled, providing an effective
nucleus radius of $1.77\pm0.04$ km and a
dust composition (relative mass fraction of the submicron grains) of $\sim36\%$ amorphous carbon, $\sim25\%$ amorphous Mg:Fe olivine, $\sim23\%$ Mg-rich crystalline olivine, and $\sim15\%$ amorphous Mg:Fe pyroxene. The crystalline mass fraction of the sub-micron grains in the coma was $0.362\pm0.003$. Comparison of the JWST-derived thermal model against the fine-grained materials in Stardust returned samples demonstrates complementarity between the missions, with each most sensitive to a different population of the coma
dust grains.
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All authors Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden, Charles E. Woodward, Dominique Bockelee-Morvan, Michael S. P. Kelley, Steven B. Charnley, Simon J. Clemett, Martin A. Cordiner, Perry A. Gerakines, David E. Harker, Els Peeters, Ella Sciamma-O'Brien, Geronimo L. Villanueva
Earth and Planetary Astrophysics · Cross-listed from math.DS
Laskar's frequency map analysis revisited
Zhicheng Tong and Yong Li
In this paper, we establish the exponential convergence of Laskar's pioneering frequency map analysis, strictly improving upon classical
polynomial bounds. By utilizing appropriately chosen weighting functions, we achieve such exponential rates in the analytic quasi-periodic regime for frequency vectors satisfying Diophantine or Brjuno nonresonance conditions. Furthermore, we extend the theoretical framework beyond the analytic quasi-periodic regime into the analytic almost periodic setting. By employing and generalizing Bourgain's framework, we accommodate a much broader class of anisotropic spatial structures. These results yield the first unified theory of exponential convergence for frequency map analysis, revealing the interplay among analyticity, spatial structures, nonresonance conditions, the choice of weighting functions, and convergence rates. This framework has important implications for applications in fields including celestial mechanics. Moreover, the novel techniques developed herein yield new insights into the study of weighted Birkhoff averages.
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Cosmology and Nongalactic Astrophysics
Testing Scale-Dependent Suppression of Structure Growth in the Linear Regime
Fernanda Oliveira, Miguel A. Sabogal, Felipe Avila et al. (+2 more)
We investigate recent reports of a suppression in the growth rate of
cosmic structures inferred from analyses of the $[f\sigma_8](z)$
dataset. To address this issue, we explore the hypothesis that the
evolution of matter clustering is more accurately described within the framework of scale-dependent modified
gravity. We perform a joint analysis of $[f\sigma_8](z)$,
cosmic chronometer $H(z)$ measurements, luminosity distance data, and CMB observations using Markov Chain Monte Carlo techniques to constrain the parameters of a scale-dependent cosmological model and investigate its impact on the
evolution of $[f\sigma_8](z)$. Our results indicate that the suppression of the growth rate of large-scale structures is more pronounced during the matter-dominated era than in the dark-energy-dominated epoch. We find evidence for scale-dependent growth at a statistical significance of $2.2\, \sigma$. In addition, we constrain the $S_8$ parameter and find it to be consistent with the value inferred from the CMB observations of the Planck Collaboration. Overall, our analysis shows that $k$-dependent growth models provide a viable explanation for the observed clustering of matter without exacerbating the current cosmological tensions.
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All authors Fernanda Oliveira, Miguel A. Sabogal, Felipe Avila, Rafael C. Nunes, Armando Bernui
Earth and Planetary Astrophysics
Ammonium salt formation and abundance in protoplanetary disks
Maxime Ruaud, Jean-Christophe Loison and Uma Gorti
Ammonium salts may represent an important reservoir of volatile species in
Solar system primitive bodies, but the question of how and when these salts can form during the
star formation process remains unknown. In this paper, we use thermo-chemical models to study the formation of ammonium salts during the protoplanetary disk stage. We show that ammonium salts form efficiently in the inner disk midplane (i.e. $r \lesssim 50 $ au), inside the comet forming region. In this region, our model predicts that almost all the available nitrogen is in the form of salts (i.e. mainly in ammonium cyanate) at the surface of grains after evolving for 10 Myrs. For sulfur, we show that almost all the available S is in the form of ammonium hydrosulfide in the inner disk midplane. We show that inside $r\sim 30$ au, ammonium salt formation is enhanced by a
cosmic-ray-driven sink effect that progressively converts gas-phase CO and N$_2$ into carbon dioxide and salts, respectively, at the surface of grains on a timescale $\gtrsim 1$ Myr. This impacts the location of the CO and N$_2$ radial snowlines which both shift closer to the
star as a function of time.
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Earth and Planetary Astrophysics
Dynamo generation reveals redox conditions during formation of differentiated planetesimals
Hannah R. Sanderson, James F. J. Bryson and Claire I. O. Nichols
In the early
Solar System, an isotopic dichotomy existed between non-carbonaceous (NC) and carbonaceous (CC) planetesimals. Depending on the formation location of these planetesimals relative to condensation lines in the protoplanetary disk, NC and CC differentiated planetesimals could have had distinct redox states and water contents. However, the extent of these differences and the resulting
accretion environments of NC and CC planetesimals are debated. Here, we use thermal
evolution and dynamo generation models to explore the effect of planetesimal core size, a proxy for redox state, and mantle water content on planetesimal dynamo generation. We find that combinations of core size and water content consistent with different formation scenarios produce planetesimals with stark contrasts in both
magnetic field strength and duration. By comparing our models to existing paleomagnetic data for NC planetesimals, we suggest these bodies formed with a small amount of water-ice and degassed efficiently during differentiation. Future paleomagnetic measurements could determine whether CC planetesimals degassed as efficiently as NC planetesimals and the number of planetesimal formation regions in the NC reservoir. Overall, we demonstrate that meteorite paleomagnetism combined with dynamo generation models provides novel insight into the
accretion environments of planetesimals and the
evolution of their water contents.
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Instrumentation and Methods for Astrophysics
Pollux UV & FUV polarimeters: first lab results
Adrien Girardot, Ninon Demelier, Coralie Neiner et al. (+6 more)
Pollux is a high-resolution spectropolarimeter proposed by a European consortium for the Habitable Worlds Observatory (HWO). Its design covers a broad spectral range from the far-ultraviolet (FUV) to the near-infrared (97-1\,750 nm), with polarimetric channels relying on \ch{MgF2} birefringent optics in the mid- and near-UV (MUV-NUV), and on an innovative all-reflective polarimeter in the FUV, where no birefringent material is available. To validate these polarimeters, whose required polarimetric precision is $10^{-3}$, a dedicated
vacuum ultraviolet test bench has been developed, with two configurations: one for the MUV-NUV range (120-290 nm) and one for the FUV range (98-120 nm). We present the first laboratory results obtained with this bench. On the MUV-NUV configuration, the full optical chain has been integrated: a first polarised spectrum of the deuterium lamp was acquired, the polarisation generation subsystem was validated against Mueller
matrix predictions, and a first end-to-end polarimetric measurement was performed. On the FUV configuration, the windowless deuterium
plasma source has been characterised, the
alignment strategy of the K-mirror modulator has been implemented, and the mirror-based analyser has been manufactured and tested, showing a polarisation extinction ratio of 10 at 120 nm. These results demonstrate the operation of the bench and pave the way for the characterisation of the polarimetric precision of the Pollux polarimeters, increasing the Technology Readiness Level of UV spectropolarimetry for HWO.
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All authors Adrien Girardot, Ninon Demelier, Coralie Neiner, Jean-Michel Reess, Juan Ignacio Larruquert, Paloma Lopez-Reyes, Anejandro Garcia Canas, Nuria Gutierrez Luna, Ana Iglesias Moreno
High Energy Astrophysical Phenomena
Accretion-induced spin-up: Implications for mass constraints of AMXPs
Xiaoyu Lai
We investigate the influence of the global structure of accreting millisecond X-ray
pulsars (AMXPs) on
accretion-induced
spin-up, using three equations of state (EoS) models representing
neutron stars,
quark stars, and strangeon
stars. By applying the classical
accretion torque formalism, and deriving the
accretion rate and
magnetic field from observations of three AMXPs — XTE J1751-305, SAX J1808.4-3658, and IGR J00291+5934 — we derive mass contours in the plane of luminosity versus
spin-up rate. Our results show that the inferred masses are broadly consistent across the three EoS models, indicating that the method is insensitive to the specific EoS and can serve as an evolutionary channel for constraining the masses of
pulsar-like compact
stars. Notably, we find that SAX J1808.4-3658 and IGR J00291+5934 are constrained to very low masses, while XTE J1751-305 yields a mass consistent with the typical range for
pulsars. Our analysis suggests that future improvements in distance and
spin-up measurements would refine these mass constraints, which could offer crucial evidence to distinguish different EoS models. This paper also presents the idea that using EoS-specific parameters could yield new insights.
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