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Physics Astrophysics Instrumentation and Methods for Astrophysics

astro-ph.IM Watch Instrumentation and Methods for Astrophysics

Saturday 3 October

Instrumentation and Methods for Astrophysics

The LOFAR Decametre Sky Survey (LoDeSS) I. Survey description and first data release

C.M. Cordun, C. Groeneveld, H. W. Edler et al. (+12 more)

The decametre radio sky ($\sim 10$-$30$ MHz) remains largely unexplored due to strong ionospheric distortions and severe radio-frequency interference. Despite its scientific potential, including access to steep-spectrum synchrotron emission from aged electron populations and coherent radio emission from planetary and stellar magnetospheres, sub-arcminute imaging at these frequencies has only recently become feasible with instruments such as the Low Frequency Array (LOFAR). In this work, we present the first data release (DR1) of the LOFAR decametre Sky Survey (LoDeSS), which maps the northern sky above a declination of $20^\circ$ between 15 and 30 MHz. LoDeSS reaches an angular resolution of $\sim45^{\prime\prime}$ and typical noise levels of $\sim11.5$ mJy beam$^{-1}$ at a central frequency of 23 MHz. Observations were obtained with the LOFAR Low Band Antenna (LBA) system using a multi-beam strategy, with typical integration times of $\sim5$ h per pointing. They were carried out at night to reduce the impact of ionospherically reflected radio-frequency interference. Data quality varies across fields as a result of the ionospheric conditions and the fraction of data flagged due to radio-frequency interference. This first release covers $\sim15\%$ of the full survey area and consists of fields originally selected around exoplanet candidates for radio auroral emission. The products released to the community include primary-beam-corrected images in Stokes I and V, and a source catalogue for fields with reliable flux density scales. This release demonstrates that LOFAR enables sensitive, wide-field imaging in the decametre regime with unprecedented resolution, opening new opportunities for studies of pulsars, exoplanetary systems, galaxy clusters, and other low-frequency phenomena.
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All authors C.M. Cordun, C. Groeneveld, H. W. Edler, H. K. Vedantham, F. de Gasperin, R. J. van Weeren, J. R. Callingham, E. Osinga, F. F. S. van der Tak, M. J. Hardcastle, M. Brüggen, A. Botteon, H. Röttgering, T. W. Shimwell, M. Iacobelli

Instrumentation and Methods for Astrophysics

Xenia: A Table-Driven Code for Astrophysical Multi-Fluid Hydrodynamics

Lei Xing

Models of escaping planetary atmospheres require neutral and ion species with distinct velocities and thermal pressures, coupled by photoionization, recombination, radiation, and collisions. Implementing and extending such coupled models is often hindered when species definitions and stiff interactions are embedded in solver-specific kernels. We present Xenia, a table-driven code for astrophysical multi-fluid hydrodynamics designed to lower this barrier. Species, coupling channels, chemistry, heating and cooling, and radiation channels are declared in Python, compiled to symbolic tapes, and passed through a versioned interface to shared C/Kokkos kernels; changing a problem therefore changes data rather than kernel code. For ionized configurations, electrons provide a pressure-only quasi-neutral closure: electron density follows from ion populations, electron mass and momentum are not advanced, and only electron pressure is transported. Stiff coupling is treated by operator splitting into a radial radiation scan, hyperbolic transport, and a cell-local implicit source solve. The same symbolic tapes yield an analytic finite-difference-free Jacobian for a direct dense LU solve. The public v0.1 release is validated with acoustic convergence, dustybox drag relaxation, conservation and closure contracts, two-fluid cloud-shock coupling, curvilinear geometry bookkeeping, three escape chains, and 394 passing tests. Conservation and positivity are not claimed to match mature production codes; radiation uses a radial Beer-Lambert prefix product rather than a general solver; escape chains are reproducibility checks rather than new science predictions; and backend evidence is limited to functional deployment and equivalence fingerprints. Xenia is released under GPLv2 at https://github.com/YFG-tec/xenia.
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Instrumentation and Methods for Astrophysics

Vector field dark matter search with Sagnac interferometer

Yuki Inoue, Quynh Lan Nguyen and Ippei Obata

We present the first calculation showing that a material-asymmetric Sagnac speed meter can improve quantum-noise-limited sensitivity to $B-L$ vector dark matter by nearly two orders of magnitude over a Fabry–Perot Michelson position meter at the low-mass end of the band. We introduce material contrast into a dual-ring interferometer to probe composition-dependent $B-L$ forces and compare the two configurations at equal incident power, input-mirror transmissivity, and cavity round-trip length. For sapphire mirrors and a one-week benchmark, the quantum-noise-only median expected $95\%$ CL upper limit reaches $1.2\times10^{-27}$ at $m_A=4.1\times10^{-14}\,\mathrm{eV}/c^2$ ($10\,\mathrm{Hz}$), a factor-$57$ improvement. This band-edge forecast assumes negligible classical noise; sensitivity at $10\,\mathrm{Hz}$ is not established for a realizable suspension and isolation system. The material-induced displacement is essentially identical in both configurations, with the gain arising from reduced low-frequency quantum backaction. These results identify speed-meter readout as a promising route to lower-mass vector-dark-matter searches.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

Cross-Modal Solar Image Synthesis: Adapting the Surya Foundation Model from He I 10830 Å to EUV Translation and Coronal Hole Segmentation

Marco Marena, Andrés Muñoz Jaramillo, Qin Li et al. (+8 more)

The long observational record of He I 10830 Å offers a means to investigate solar morphology before modern extreme-ultraviolet (EUV) imaging. We adapt the Surya solar foundation model to predict Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) 94, 193, and 304 Å images and a coronal hole (CH) probability map from full-disk helium observations. A convolutional input adapter, low-rank backbone updates, and dedicated output decoders learn from temporally paired, geometrically registered observations, with Spatial Possibilistic Clustering Algorithm (SPOCA) catalog polygons providing CH supervision. On observations held out from downstream fine-tuning, the selected dedicated models achieve disk-restricted correlation coefficients (CCs) of 0.8196, 0.8885, and 0.8398 for the three AIA channels, respectively; the CH model achieves an intersection over union (IoU) of 0.4360. The predictions recover broad solar structure, although local agreement varies substantially by channel. An optional residual refiner addresses spatial detail, and its application on pre-SDO dates improves the correlation of synthetic AIA 304 with Solar and Heliospheric Observatory/Extreme-ultraviolet Imaging Telescope (SOHO/EIT) 304 references from 0.6511 to 0.7085. Together, these results support the feasibility of helium-conditioned EUV morphological proxies and motivate their use in historical reconstruction, within the scope of the downstream test and cross-instrument evaluation.
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All authors Marco Marena, Andrés Muñoz Jaramillo, Qin Li, Haodi Jiang, Jinghao Cao, Wen He, Ziyang Zhang, Chenxi Yuan, Chao Wang, Haimin Wang, Bo Shen

Instrumentation and Methods for Astrophysics

An RFSoC-Based 100 GbE Spectrometer/Correlator for the Baryon Mapping Experiment: Digital Backend Design and On-Sky Validation

Liju Philip, Paul O'Connor, Benjamin Saliwanchik et al. (+2 more)

We describe the implementation and on-sky commissioning of a two-input spectrometer/correlator built on a Xilinx ZCU208 Radio Frequency System-on-Chip (RFSoC) and deployed on the Baryon Mapping eXperiment (BMX) interferometric array at Brookhaven National Laboratory. The system combines direct RF sampling, FPGA-based correlation, and 100 Gigabit Ethernet (GbE) visibility transport. Two inputs are digitized directly at 1050 MHz without analog downconversion and channelized into 2048 frequency channels. The correlator forms two autocorrelations and the real and imaginary parts of the cross-correlation, accumulates them in on-chip memory, and transmits the spectra as UDP packets at a fixed firmware-controlled rate. Two independent campaigns using 500 ms and 100 ms accumulation times produced 958,918 consecutive accumulations with no lost, duplicated, or malformed packets. A Cauchy-Schwarz bound is satisfied across all 1.96e9 channel-samples, confirming correct field identification and scaling. On-sky validation includes compact-source transits in six GNSS bands with the expected fringes, coherent detection of the Cygnus A zenith transit at the predicted time, and a Galactic HI plane crossing detected independently in autocorrelation on both dishes. The correlator is parameterizable in input count, with arithmetic scaling quadratically. For extension to BMX's full eight-input dual-polarization system, an occupancy model validated against the deployed firmware indicates that visibility buffering fits when moved to UltraRAM, while multi-tile synchronization, logic utilization, and timing closure remain to be demonstrated in an eight-input implementation.
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All authors Liju Philip, Paul O'Connor, Benjamin Saliwanchik, Anže Slosar, Emi Tamura

Instrumentation and Methods for Astrophysics

The Robots are Coming: Artificial Intelligence Searching for Extraterrestrial Intelligence

Steve Croft

Breakthrough Listen, humanity's most ambitious search for technosignatures, or evidence of extraterrestrial technology, is carrying out surveys across the sky and across the electromagnetic spectrum, in images, spectra, time series, catalogs, and alerts. Classical techniques still play a major role in the search, but the recent rapid growth in the capabilities of artificial intelligence is enabling new and more powerful algorithms and approaches to be deployed across enormous datasets. Surveys designed to look for technosignatures are still a major focus for the Breakthrough Listen program, but excitingly, the new strategies also enable comprehensive mining of archives and of general-purpose real-time data streams. We outline how artificial intelligence and machine learning are being used to scale up the search, including with the newly-commissioned Vera C. Rubin Observatory, in addition to radio telescopes around the planet. The chances of a detection have never been better.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

Stellar parameters and abundances for 3.2 million DESI DR1 spectra using machine learning

Nagaraj Vernekar, Michael Hayden and Sara Lucatello

We present a machine-learning pipeline for determining stellar parameters and chemical abundances from spectra observed by the Dark Energy Spectroscopic Instrument (DESI). Building on the model-driven Payne framework, we train an artificial neural network on ~370,000 synthetic spectra spanning FGK stars, and fit the network directly to the flux-calibrated, un-normalised spectral energy distribution (SED) of each star, rather than to a continuum-normalised spectrum as done by DESI's official Stellar Parameter (SP) pipeline. Internal accuracy tests show a median interpolation error of less than 0.3% for 90% of a synthetic verification sample, and the full fitting workflow recovers input labels to high accuracy even at low signal-to-noise ratio (S/N). Validating our method on cross-matched samples of 6719 APOGEE and 3455 GALAH stars observed by DESI with S/N > 20, we recover Teff and logg with smaller systematic offsets than the DESI SP pipeline, an improvement we attribute to fitting the full SED shape rather than a normalised spectrum. We further recover 12 elemental abundances (Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Ni, Ba, and Y) to an accuracy that matches or exceeds SP where a comparison is possible, and provide four abundances, Mn, V, Ba, and Y, that SP does not report at all. Applying this pipeline to the DESI Data Release 1 stellar sample, we deliver a catalogue of stellar parameters and abundances for 3.2 million stars.
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Friday 2 October

Instrumentation and Methods for Astrophysics

An Assessment of the Triangulation Capabilities of a Multi-Site All-Sky Infrared Camera Array

Abraham Loeb, Alex Delacroix, Ezra Kelderman et al. (+2 more)

The Galileo Project operates three autonomous multi-camera observing sites near Las Vegas, Nevada, separated by baselines of $2$ and $10\,$km, with the goal of characterizing the populations of natural and human-made objects that cross the sky and thereby isolating any event that fits none of them. Each site carries an array of eight long-wave infrared (LWIR) cameras arranged in a fixed dome-like structure, an IR-Dalek, providing $360^{\circ}$ azimuthal coverage. We report the commissioning of the three arrays and present the triangulation pipeline built on them. Because our targets are not assumed to follow any particular trajectory, we depart from the parametric fits standard in meteor work and estimate the instantaneous three-dimensional position at each time step as the point that minimizes the weighted sum of squared distances to the simultaneous lines of sight, weighting each camera by its own pointing uncertainty and by its range to the object. We describe the intrinsic and extrinsic calibration procedure, which uses Automatic Dependent Surveillance-Broadcast (ADS-B) aircraft as reference sources in the absence of stars or fixed landmarks in the LWIR field of view, and the multi-sensor track association scheme that decides which detections belong to the same object. Using one week of data (2026 May 24-30; $1{,}650$ camera-hours, $2.1\times10^{8}$ detections and $5.3\times10^{6}$ tracks), we validate the recovered positions, speeds and accelerations against ADS-B records, recovering distances to within $5$% for $99$% of the aircraft solved from three sites and for $83$% of those solved from a single site pair and speeds to within $5$% for $78$% and $63$% of them respectively. We characterize the identification completeness of the array, which is set by apparent size: the $50$% identification threshold falls at $1.8$ pixels of apparent wingspan.
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All authors Abraham Loeb, Alex Delacroix, Ezra Kelderman, Eric Masson, Regina Sarmiento

Instrumentation and Methods for Astrophysics

Shared Geometry Is Not Shared Physics: A Layerwise Test of the Platonic Representation Hypothesis in Astronomy

Kshitij Duraphe, Aravind Kannappan, Dun Li Chan et al. (+4 more)

In this paper we investigate whether geometrically aligned astronomical representations are also scientifically interchangeable. We analyze every layer's representation from 36 pretrained models using cross-matched optical images, infrared images, and spectra. All 139 analyzed model-survey comparisons show significant local-neighborhood alignment somewhere in the network after accounting for the search over depth. However, alignment does not generally increase with network depth and can be stronger for the changes between consecutive computational blocks than for the block outputs themselves. We find that geometry-selected stages under-perform label-selected stages in every image-transfer comparison; moreover, every final HSC-COSMOS-Web model pair is aligned while every redshift transfer has negative R^2. Models can therefore recover a similar cross-survey geometry among astronomical objects without recovering a survey-invariant linear encoding of the physical properties tested here.
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All authors Kshitij Duraphe, Aravind Kannappan, Dun Li Chan, Okiki Famutimi, Yaswant Sai Ejjagiri, Michael J. Smith, John F. Wu

Instrumentation and Methods for Astrophysics

LoFreq-SETI: A Low-Frequency Technosignature Search Pipeline for the LWA Swarm

Craig A. Taylor, Lillian Ekness and Chenoa Tremblay

The search for extraterrestrial intelligence (SETI) is conducted across the electromagnetic spectrum to understand the prevalence and distribution of intelligent life in the universe. At radio frequencies, this effort focuses on searching for "technosignatures", observable indicators of technological activity consistent with our understanding of an advanced civilization. Historically, the microwave regime from 1-10 GHz has been the primary frequency range searched for these technosignatures, but recent SETI experiments utilizing low-frequency radio telescopes, such as the Low Frequency Array (LOFAR), Murchison Widefield Array, and MeerKAT radio telescope have explored the insufficiently studied frequency range below 1 GHz. However, the lowest radio frequencies ($<$100 MHz) have been even less explored for technosignatures, despite significant human communication signals occupying this band. The Long Wavelength Array (LWA) is a low-frequency (3-88 MHz) interferometer array telescope collaboration comprised of dipole 'stations' distributed across the Southwestern United States, and the LWA Swarm is the aperture synthesis telescope consisting of interconnected LWA stations operating as a long baseline interferometer. Here we present a narrowband technosignature pipeline using the Breakthrough Listen Interesting Signal Search algorithm for raw beamformed single-station LWA data and outline its planned extension to correlated visibilities from the LWA Swarm. We demonstrate the pipeline on a limited selection of fast radio burst observations to evaluate the data processing and spatial coincidence filtering for a future observing campaign of exoplanet systems.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

A forest of emission lines observed by Sunrise III/SUSI above the solar limb

J. S. Castellanos Durán, F. A. Iglesias, S. K. Solanki et al. (+31 more)

We present off-limb spectroscopy using low-straylight data from the Sunrise Spectropolarimeter and Imager (SUSI) onboard the Sunrise III stratospheric solar observatory. A spatial scan with SUSI's slit almost parallel to the local limb reached from within the solar disc to 6.5 Mm off-limb. The wavelength range spanned from 407.6 to 410.25 nm. We detected a total of 174 spectral lines in emission off-limb, a 2.5-fold increase over previous reports. Surprisingly, 122 of these lines begin to appear in emission already on the disc, although close to the limb. In addition, one-fifth of relatively prominent emission lines are due to rare-earth and heavy elements and molecules, where the absorption lines of these transitions are typically weak on-disc.
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All authors J. S. Castellanos Durán, F. A. Iglesias, S. K. Solanki, A. Lagg, I. Milic, H. N. Smitha, D. Vukadinović, T. L. Riethmüller, A. Gandorfer, A. Feller, J. Blanco Rodríguez, D. Orozco Suárez, Y. Katsukawa, J. Hölken, J. C. del Toro Iniesta, S. Rao, M. Sánchez Toledo, K. Singh, P. Bernasconi, T. Berkefeld, A. Alvarez-Herrero, M. Kubo, V. Martínez Pillet, B. Grauf, M. Carpenter, A. Bell, H. Strecker, A. L. Siu-Tapia, P. Santamarina Guerrero, Y. Kawabata, T. Matsumoto, R. T. Ishikawa, E. Harnes, T. Oba

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

AEGIS: Differentiable Mars Climate Model with Neural Closures

Sameera S Kashyap, Victor Cruz, Angel Yepez et al. (+1 more)

General circulation models (GCMs) are the primary tool for simulating planetary atmospheres. They play a vital role in understanding Mars's atmosphere, as forecasting its unique weather is mission-critical for operations such as entry, descent, and landing. Mars poses unusual challenges for these models, as observations are sparse compared to Earth. In addition, a thin \co{} atmosphere alongside a radiatively active dust cycle creates a volatile atmosphere with large diurnal temperature swings and no true terrestrial analog for validation. Existing Mars GCMs, including the LMD PCM, the NASA Ames Mars GCM, and PlanetWRF, are mature and physically detailed but are implemented in legacy Fortran with finite-difference or finite-volume solvers, and they do not expose gradients for calibration or machine learning. Here we present AEGIS, a modular differentiable Mars climate model that couples Mars's unique atmospheric physics to the Dinosaur dynamical core, with interfaces for neural closures. We showcase stable ten-Mars-year simulations that reproduce the seasonal \co{} cycle while conserving the total \co{} inventory, capture realistic large-scale surface-temperature structure, and produce surface pressure that follows Mars Orbiter Laser Altimeter (MOLA) topography. Gradients through coupled trajectories agree with finite differences and support physical calibration and neural training. We compare with conventional GCMs, highlighting the framework's computational efficiency and differentiability.
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All authors Sameera S Kashyap, Victor Cruz, Angel Yepez, Razvan Marinescu

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Measuring the Age and Initial Composition of Interstellar Objects

Aster G. Barry-Taylor

Measuring the age and composition of interstellar objects is necessary to understand their origins. However, existing methods for measuring the age are either imprecise or require an unusually bright target, while the composition is confounded by the effects of Galactic cosmic rays, which drive chemical reactions in the cometary matrix. As the Vera C. Rubin Observatory expands the census of interstellar objects, measuring these properties will be critical to understanding the overall population. In this work, I derive a new methodology for simultaneously estimating the age and initial composition of an interstellar object from time-series observations of the coma. Measurements of both the composition and its gradient versus depth into the nucleus are shown to fully constrain both properties in most circumstances. A simple model using only CO and CO$_2$ is discussed and used to demonstrate the properties of this inference process. When applied to 3I/ATLAS, this simple model indicates that this object is at least 0.6 Gyr old and has an initial CO/CO$_2$ ratio of 1.5, supporting a formation outside the CO ice line. Further refinement of the chemical network and improved observational strategies will improve the precision and accuracy of these measurements, enabling a deeper understanding of the interstellar object population and extrasolar planet formation.
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Instrumentation and Methods for Astrophysics

The Nancy Grace Roman Space Telescope Wide Field Instrument: Characterization of the Brighter-Fatter Effect in a Roman H4RG-10 Detector using the Talbot Effect

Jennie Paine, Ami Choi, Christopher Merchant et al. (+14 more)

The Nancy Grace Roman Space Telescope will conduct several community-driven surveys using its Wide Field Instrument (WFI), which contains 18 Teledyne H4RG-10 near-infrared detectors in the focal plane. Roman's wide area survey to measure weak gravitational lensing places particularly stringent requirements on point spread function (PSF) precision for the WFI. The brighter-fatter effect (BFE) is a nonlinear detector effect caused by the deflection of new charge away from pixels with previously accumulated charge during an exposure. As a result, the PSF measured at the detector depends on the charge contrast between pixels, and therefore the effective PSF for astronomical sources is a function of flux contrast and integration time. We present characterization of the BFE observed in a non-flight H4RG by projecting a grid of bright point sources onto the detector using the Talbot Illuminator at the NASA Goddard Space Flight Center Detector Characterization Lab. We find that the effective area of a pixel decreases by $(-2.18\pm0.04) \times 10^{-6}$ per electron of charge contrast with its neighbors, corresponding to a measurable increase in the effective PSF size over the course of an exposure. Despite charge migration, the total signal detected in the vicinity of a bright source is roughly conserved. We also analyze flat field statistics for the same detector to measure the total inter-pixel nonlinearity (IPNL), which is dominated by BFE. We present a method to correct BFE in H4RG images using the flat field IPNL results, adapted from an extant optical correction technique. The correction reduces the observed BFE by about a factor of 25 as measured by the effective pixel area change, but there is remaining nonlinearity in the corrected data. We discuss possible sources of residual nonlinearity and suggest avenues to investigate optimal BFE correction in Roman survey images.
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All authors Jennie Paine, Ami Choi, Christopher Merchant, Timothy D. Brandt, Jeffrey Kruk, Joshua E. Schlieder, Edward J. Wollack, Analia Cillis, Jahmour J. Givans, Robert Hill, Christopher Hirata, Dana R. Louie, Gregory Mosby, Anna Porredon, Bernard J. Rauscher, Maxime J. Rizzo, Rujula Yete

Instrumentation and Methods for Astrophysics

Tracing the evolution of galaxy environments with manifold learning

Ana Sofía M. Uzsoy, Claire Lamman, Peixin Zhu et al. (+1 more)

We present SONDE (SOrted Neighbor Distance Embedding): a scalable manifold learning approach to create a nuanced, continuous, low-dimensional representation of the geometry of galaxies' local environments. SONDE is a variation on Isomap that uses similarity distances between galaxy neighborhoods to create an embedding space, within which galaxies cluster according to their neighborhood geometries. We additionally present a novel method to project different datasets into the same embedding space, enabling comparisons of environmental embeddings across redshifts. We demonstrate this method on the TNG100 simulations at $z = 0 - 5$ and show that the embedding values evolve with redshift and correlate with galaxies' physical properties. We train a neural network to predict physical properties based on environmental features and show that our first embedding dimension outperforms a standard environmental quantifier, the number of neighbors, while the top three dimensions encode as much environmental information as a ten-bin radial profile. Our results are consistent with known density correlations, including galaxy halo mass, central vs. satellite status, and quenching. SONDE provides a straightforward way to encode subtleties of galaxy environments that could have significant implications for future analysis of galaxy-environment interactions.
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All authors Ana Sofía M. Uzsoy, Claire Lamman, Peixin Zhu, Melanie Weber

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.CO

Map-based asymmetric beam treatment: application of real-space beam patterns in CMB data analysis

Artem Basyrov

Real telescope beams are asymmetric, breaking the simple $B_{\ell}$ factorisation in harmonic space and coupling modes across $\ell$ and $m$. We develop a map-domain treatment in which beam convolution is a local, scan-dependent operation applied directly to the time-ordered data (TOD), accommodating the full beam shape and giving a direct handle on intensity-to-polarisation ($I \rightarrow P$) leakage. A noiseless validation against spherical-harmonic convolution reproduces the input temperature and $B$-mode power spectra up to $\ell \simeq 1000$, well beyond the range of primordial $B$-mode science. We outline how the operation maps onto a sparse linear BeamOperator for modular map-making.
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Instrumentation and Methods for Astrophysics

Design, Fabrication, and Free-Space Characterization of a Two-Photon-Polymerized Nano-printed Photonic Lantern

Kyra Watts, Natasha Popenoe, Benjamin Gerard et al. (+6 more)

Photonic lanterns provide an interface between multimode optical fields and arrays of single-mode waveguides, making them promising components for modal filtering, wavefront sensing, and high-contrast astronomical instrumentation. We present the design, simulation, two-photon-polymerization fabrication, and free-space characterization of a compact photonic lantern optimized for operation at $ 1050~\mathrm{nm} $. The device was designed to transform a multimode input into five nominally single-mode output waveguides. Eigenmode-expansion simulations in Ansys Lumerical MODE were used to optimize the lantern geometry while minimizing insertion loss and output-channel power nonuniformity. The optimized structure was fabricated using a Nanoscribe Photonic Professional GT2 two-photon-polymerization system and developed as a standalone polymer-waveguide component. The fabricated lantern was characterized using a free-space optical setup consisting of a $ 635~\mathrm{nm} $ laser for preliminary characterization, collimation and focusing optics, and camera-based imaging of the transmitted fields. Measurements were used to assess optical throughput, output intensity distribution, and light-guiding performance. Differences between simulated and measured results may arise from the wavelength mismatch, fabrication tolerances, material and surface-scattering losses, alignment errors, and deviations from the idealized material and geometric parameters used in simulation. These results demonstrate a compact, additively manufactured photonic-lantern platform and establish a pathway toward free-space-coupled astrophotonic systems for future high-contrast exoplanet-imaging instrumentation.
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All authors Kyra Watts, Natasha Popenoe, Benjamin Gerard, Paul Pax, Dominic Sanchez, David Feng, C. Cole Dunn, Cari Johnston, Xiaoxing Xia

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.CO

A novel, fast, and accurate code for cosmological loop calculations

Tjark Harder, Luca Amendola, Thiago S. Pereira et al. (+1 more)

We introduce neckar, a public code for the one-loop matter and galaxy power spectrum, as well as correlation function, in the Eulerian Effective Field Theory of Large-Scale Structure (EFTofLSS). It is based on the FFTLog expansion, and is designed for fast and accurate parameter inference from large-scale structure data, making it a powerful tool for high-dimensional Bayesian analyses of current and upcoming galaxy surveys. neckar combines several numerical and analytical improvements, including the separation between pre-computable and cosmology-dependent contributions, a semi-analytic treatment of the Alcock-Paczynski effect for power spectrum multipoles, and an implementation of the symmetry-based bootstrap kernels, allowing straightforward applications to a broader class of cosmological models. The code also incorporates an improved infrared resummation scheme that corrects previous implementation inaccuracies, and which led to errors of the order of 1% for the quadrupole, and of 10% for the hexadecapole at scales $k \gtrsim 0.1 h \textrm{Mpc}^{-1}$, as well as an asymptotic treatment that extends the range of accurate predictions into mildly non-linear scales $k \sim 0.4 h \textrm{Mpc}^{-1}$. This leads to relevant corrections in the correlation function around the BAO peak. Taken altogether, these improvements render neckar up to two orders of magnitude faster than similar existing codes without relying on emulators, and at the same time improving numerical accuracy. The code is written in C and is distributed with a Python wrapper for convenience.
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All authors Tjark Harder, Luca Amendola, Thiago S. Pereira, Miguel Quartin

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.SR

Plato benchmark stars I. The initial benchmark sample

T. Merle, P. F. L. Maxted, O. L. Creevey et al. (+23 more)

The ESA PLATO mission aims to detect and characterise Earth-size exoplanets orbiting bright, late-type stars using high-precision photometry and asteroseismology. Precise stellar parameters of host stars are essential for exoplanet characterisation and model benchmarking. This work defines the PLATO benchmark stars (PBS) catalogue, a comprehensive sample of well-characterised stars designed to support all mission phases. We compiled data from eclipsing and spectroscopic binaries, interferometry, asteroseismology, and large spectroscopic and photometric surveys. Fundamental and atmospheric stellar properties (mass, radius, luminosity, age, effective temperature, surface gravity, density, and limb darkening) were assigned quality levels (B1, B2, B3) reflecting their degree of model dependence. Homogenized ancillary parameters (including Gaia DR3 bias-corrected parallaxes, metallicities, bolometric fluxes, extinction, rotation periods, and X-ray fluxes for M dwarfs) are also provided. The PBS catalogue contains 1090 FGKM main-sequence and subgiant stars, divided into three quality tiers based on model-independent (B1) parameters: gold (15 stars with B1 mass, radius, and luminosity), silver (195 with B1 mass and radius), and bronze (416 with at least one B1 property). The remaining stars feature well-characterised model-dependent (B2) or empirical (B3) properties. About 40% of the sample lies within the PLATO fields of view (285 in LOPN1 and 143 in LOPS2). The PBS sample represents the largest catalogue of benchmark stars assembled to date, providing a key resource for validating automated pipelines, testing evolutionary models, and cross-survey calibration. The catalogue is available online at https://astro.ulb.ac.be/pbs and will be updated regularly.
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All authors T. Merle, P. F. L. Maxted, O. L. Creevey, U. Heiter, D. B. Palakkatharappi, K. G. Hełminiak, C. C. Aguilera Gómez, M. Bazot, S. Cassisi, N. Ebrahimkutty, R. E. Giribaldi, P. Jofré, F. Kiefer, M. N. Lund, N. Miller, T. Morel, D. Mourard, N. Nardetto, J.-D. do Nascimento, Jr., T. Olander, G. N. Pawar, A. Rebassa-Mansergas, R. Raddi, B. Rojas-Ayala, J. Southworth

Instrumentation and Methods for Astrophysics

Robust Bayesian non-linear pulsar timing and noise analysis using a sequential data-tempered ensemble sampler

Abhimanyu Susobhanan

We develop a sequential ensemble MCMC scheme for Bayesian pulsar timing and noise analysis that uses data size as the tempering parameter. The method enables gradual and reliable convergence from potentially uninformed initial points by iteratively increasing the data size, thereby increasing sensitivity and progressively narrowing the target distribution until the posterior of the full dataset is reached. The initial iterations use sub-datasets that can be orders of magnitude smaller than the full dataset, substantially reducing computational cost, which is further lowered by employing approximate lower-rank models justified by the reduced sensitivity of these sub-datasets. Bayesian inference is performed using the final MCMC chain sampled from the true target distribution after applying appropriate burn-in. We demonstrate the method using the NANOGrav 12.5-year data of PSR B1855+09, showing progressive convergence to the target posterior and that most of the computational time is spent sampling the true target distribution rather than in the preceding tempered iterations.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

Performance of AutoRegressive Planet Search methodology on simulated PLATO lightcurves

Eric D. Feigelson, Marco Montalto, Geert Jan Talens et al. (+4 more)

AIM. This study examines the PLATO mission sensitivity to small transiting planets (radii between 0.5 and 2.0 R$_\oplus$) using Autoregressive Planet Search (ARPS) methodology based on simulated lightcurves. Methods. Several thousand simulations of PLATO-like lightcurves from magnetically active stars expected from the PLATO Long Observation Phase South 2 (LOPS2) field with injected transiting planets smaller than 2.0 R$_\oplus$ radius are examined. The lightcurves are analyzed with ARPS that uses autoregressive modeling for filtering of nonplanetary signals and the Transit Comb Filter periodogram for planetary transit detection. False alarms of nonexistent periodic signals are reduced by thresholds on two ARPS parameters, peak periodogram power, and transit duration. Results. When applied to PLATO's simulated first three months observations of bright stars (P1 and P2 samples), at least 50% of Earth-size planets are recovered for periods shorter than 40 d. In two years of LOPS2 observation, 25% are recovered for periods less than 240 d. Methodological implications on detrending, periodograms, False Alarms, vetting, and catalog evaluation are discussed. The utility of a positive predicted value heat map after detection and vetting is demonstrated. Conclusions: While the ARPS planet detection procedure is not entirely well-suited for PLATO analysis, this study provides methodological insight into the sensitivity and reliability of small transiting planet detection.
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All authors Eric D. Feigelson, Marco Montalto, Geert Jan Talens, Suzanne Aigrain, Luca Malavolta, Valerio Nascimbeni, Tiziano Zingales

Instrumentation and Methods for Astrophysics

Do Astronomical Foundation Models Know When They Will Fail?

Vaidehi Bulusu, Mehul Goyal, Md Rabius Sany Apu et al. (+2 more)

Astronomical foundation models are increasingly used as reusable representations across surveys, but it is unclear when the same object remains consistently represented across instruments or whether a model can warn us before transfer fails. We present a conformal framework for auditing cross-survey representations using cross-matched Legacy Survey–HSC, HSC–JWST, and SDSS–HSC objects. Astronomy-specific AstroPT embeddings show lower translation errors and tighter conformal regions than general-purpose visual backbones at comparable coverage, while different model families fail on different objects. We then use adaptive conformal prediction to test whether the source embedding contains information about its own future error. Using a ridge difficulty model fitted to source embeddings, we find that this warning signal is consistent across the tested backbones for Legacy$\rightarrow$HSC, backbone-dependent for HSC$\rightarrow$JWST, and largely absent for SDSS$\rightarrow$HSC. When informative, adaptation improves coverage for the hardest objects. Matched-control analysis further reveals silent failures not explained by magnitude, apparent size, or nearest-neighbor distance. Hence, we show that conformal uncertainty provides a realistic way to identify when astronomical representations transfer reliably and when they fail without warning.
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All authors Vaidehi Bulusu, Mehul Goyal, Md Rabius Sany Apu, Michael J. Smith, Shashwat Sourav

Thursday 1 October

Instrumentation and Methods for Astrophysics

Learning Approximate Isometric Embeddings for Efficient Template Placement

Alexandra Wernersson, Jessica Irwin, Melissa Lopez et al. (+1 more)

The sphere covering problem has broad applications in science however, exact solutions are computationally infeasible on curved, high-dimensional manifolds because distances must be evaluated using a position-dependent metric. We present $\texttt{isobank}$, a normalizing flow that learns an approximately isometric coordinate transformation, such that Euclidean distances in the latent space approximate metric-induced proper distances in the physical parameter space. This enables template placement using Euclidean distance checks in the latent space, avoiding repeated metric evaluations during placement. We evaluate $\texttt{isobank}$ in the context of gravitational wave template bank construction, where the sphere covering problem corresponds to the template placement problem. On a five-dimensional eccentric binary parameter space, $\texttt{isobank}$ reaches 97% coverage at a maximum mismatch of $\mu=0.03$ with 23% fewer templates than the state-of-the-art stochastic placement code $\texttt{mbank}$, which reaches 94% coverage. Coverage is measured on independent injections drawn uniformly over the masses, spins and eccentricity, using the exact waveform match rather than the metric approximation. Training the flow takes about 2.5h and placing the bank under 1h on 32 CPU cores. $\texttt{isobank}$ is publicly available on Github https://github.com/Alexandra-Wernersson/isobank
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All authors Alexandra Wernersson, Jessica Irwin, Melissa Lopez, Sarah Caudill

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.EP

TOI-1408: the limb darkening models, photometric and Doppler noises, and the exoplanetary system

Roman V. Baluev

We perform a self-consistent analysis of Doppler and photometric TESS and ground-based transit observations available for TOI-1408, known to host a system with two planets orbiting near 2:1 mean-motion commensurability and a distant companion. In general we confirm its orbital configuration derived in previous studies, however we found that the likelihood function contains multiple local maxima spread over a wider parametric domain, thus making some model uncertainties significantly larger than deemed before. In particular, the planet b radius still appears poorly constrained (from $\sim 1.2$~$R_{\rm Jup}$ to $\sim 3.5$~$R_{\rm Jup}$) because of the near-tangential transit geometry. We also show that the derived model is very prior-dependent regarding the astrophysical (spectrum-derived) constraints on the stellar mass $M_\star$ and radius $R_\star$. While such estimations may potentially contribute a significant information to the fit, their prior distribution must be accurately specified to be useful. Presently so accurate characterization (e.g. the correlation between $M_\star$ and $R_\star$) is not available in the literature.
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Instrumentation and Methods for Astrophysics · Cross-listed from cs.AI

FlashSinkhorn 2: Block-Sparse Entropic Optimal Transport

Felix X.-F. Ye, Yu Chin Fabian Lim, Naigang Wang et al. (+1 more)

Streaming GPU solvers for entropic optimal transport (EOT), such as FlashSinkhorn, avoid storing the dense kernel but still evaluate all $n\times m$ point pairs in every Sinkhorn iteration. We present FlashSinkhorn~2 (FS2), a solver for squared-Euclidean cost on low-dimensional point clouds that solves large discrete EOT problems to a prescribed marginal residual on a single GPU by coupling two stages. A coarse stage solves on cell centroids, lifts the potentials to every point and, when a sampled marginal check rejects the lift, continues on the centroids, replacing most point-level updates. A block-sparse fine stage then removes the centroid error that coarse updates cannot. Its Morton-ordered blocks support screening and fused tensor-core execution, and a threshold set by the block masses bounds each omitted tile's contribution to every row and column. On synthetic benchmarks, FS2 reaches the target residual on all 32 problems and GeomLoss multiscale on 10. On one A100, FS2 solves discrete EOT between two $1.34\times10^8$-particle measures from a cosmological $N$-body simulation, at an entropic blur equal to the mean interparticle distance, to an all-particle marginal residual below 0.01 in under 2.5 hours. To our knowledge, it is the largest discrete EOT problem solved to this accuracy within hours. For reproducibility, we release an open-source implementation at https://github.com/ot-triton-lab/flash-sinkhorn
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All authors Felix X.-F. Ye, Yu Chin Fabian Lim, Naigang Wang, Davis Wertheimer

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.CO

Point spread function requirements for dark matter subhalo detection with the Habitable Worlds Observatory

Georgios N. Vassilakis, Susan F. Redmond, Jason D. Rhodes et al. (+2 more)

Different theories of dark matter predict different populations and morphologies of galactic subhaloes below about $10^8M_{\odot}$. The planned angular resolution and optical stability of the Habitable Worlds Observatory (HWO) should enable it to detect subtle subhalo perturbations in strongly lensed galaxy images. We simulate 2000-second exposures with its High Resolution Imager (HRI) under the fiducial Exploratory Analytic Case 1 (EAC1) design, assuming known source structure and omitting lens-galaxy light. Pre-selecting the top 50 of 965 lenses (5.2%) using only arc signal-to-noise and relative gradient power lowers the median mass threshold for 10% aperture coverage roughly tenfold relative to the full ensemble. The top 12 (1.2%) reach a median of $6.6\times10^7M_{\odot}$ for the same coverage. At their most sensitive positions, the top 50 and top 12 reach median thresholds of $3\times10^7M_{\odot}$ and $1.5\times10^7M_{\odot}$, respectively. Non-linear fits support the Fisher forecasts at the tested masses and positions. For these 12 lenses, increasing the physical wavefront error from 35 to 65 nm RMS raises the median thresholds by only 0.1 dex when the point spread function (PSF) is modelled correctly. Deliberately mismodelling the 35-nm reference PSF removes detectable positions, although false detections remain rare. Under our illustrative retention criteria, loss of sensitive area sets a median tolerated wavefront mismatch of 5 nm RMS (range 2–10 nm). Selective HWO follow-up of lenses discovered by Euclid or Roman could therefore transform our understanding of the nature of dark matter, provided that the PSF is characterized accurately enough to preserve this sensitivity.
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All authors Georgios N. Vassilakis, Susan F. Redmond, Jason D. Rhodes, Richard J. Massey, Qiuhan He

Instrumentation and Methods for Astrophysics

Optimizing spectral-matching component separation for measuring CMB B-mode polarization with a satellite mission

Hoang Viet Tran, Guillaume Patanchon, Michele Citran et al. (+1 more)

The measurement of primordial CMB B-mode polarization is fundamentally limited by our ability to separate this faint signal from bright and complex Galactic foregrounds. Spectral Matching Independent Component Analysis (SMICA) offers a flexible, semi-blind approach to this foreground-cleaning problem. However, its standard implementation relies on a physically unrealistic assumption of non-spatially varying foreground emission, reducing the efficiency of the method. In this work, we develop two complementary strategies to address this limitation at the component-separation level. First, we augment SMICA with effective foreground components beyond the physical dust and synchrotron degrees of freedom. Second, we extend SMICA to operate independently on subsets of the sky, better capturing local variations in the foreground emission. Beyond component separation, we further explore a likelihood-level marginalization procedure using internally reconstructed foreground templates. We demonstrate the performance of the pipeline on simulated LiteBIRD-like observations, using foreground models of increasing complexity based on $\texttt{d1s1}$ and $\texttt{d10s5}$. Combining our component-separation improvements with template marginalization brings the recovered tensor-to-scalar ratio $r$ to effectively unbiased levels, with statistical uncertainties on the order of $10^{-3}$ or below.
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All authors Hoang Viet Tran, Guillaume Patanchon, Michele Citran, Benjamin Beringue

Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.HE

Testing internal dynamics in neutron stars with radio pulsar timing

Reginald Christian Bernardo

Rotational variations in pulsars reflect either internal angular momentum exchange via equal and opposite torques (stationary spin noise) or independent torques causing diffusive changes in total angular momentum (nonstationary spin noise). We compare two models of a radio-emitting crust and interior superfluid to test the stationarity of angular velocity fluctuations through observed pulsar phases. We present results for three isolated pulsars with measurable timing noise, demonstrating distinct inference outcomes. For PSR J1359-6038, the data mildly favor independent torques over equal-and-opposite torques, with an odds ratio of seven hundred to one. For PSR B1937+21, the analysis shows no clear preference between the models. For Vela in a pre-glitch interval, excess scatter and unexplained residual structure limit the interpretation.
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Instrumentation and Methods for Astrophysics

Comment on: "The Preprint Evolution: The Rise of Unreviewed Drafts on arXiv and its Implications for Astronomy"

Noam Soker

I argue against the proposal of arXiv:2609.35787 to divide arXiv astrophysics submissions into two streams: peer-reviewed papers and pre-review discussion drafts. I contend that such a division would threaten open scientific discussion and could lead to increasingly restrictive categories based on journal impact factor or mainstream versus non-mainstream papers. Instead, readers who want only peer-reviewed work can use AI or other tools to filter papers, while others can continue monitoring the broader literature. I emphasize three benefits of posting papers on arXiv before journal acceptance. First, public posting lets researchers beyond the referee provide feedback, including identifying possible errors, missing references, and overlooked prior work, improving manuscripts beyond what a single referee may catch. Second, arXiv can help address weaknesses in the traditional anonymous peer-review system, such as lengthy delays, inconsistent reports, or unjustified rejection. Public posting establishes a transparent record of priority and allows the community to access results immediately. Finally, I propose that astrophysics journals require authors to post their papers on arXiv for at least a week before acceptance, making arXiv the central component of the astrophysical publication process.
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Instrumentation and Methods for Astrophysics

A comprehensive simulation framework for multi-modal kilonova observations from all-sky surveys

Felipe Fontinele Nunes, Andrew Toivonen, Farhana Taiyebah et al. (+5 more)

Current all-sky surveys such as Vera Rubin's Legacy Survey of Space and Time and the Zwicky Transient Facility (ZTF) promise a wealth of scientific gains that are contained in the millions of astrophysical transient candidates produced each night. Kilonovae, one such transient of interest, will be challenging to identify in the alert stream and will require efficient artificial intelligence models to parse the large, real-time influx of data. In order to build these large models, comprehensive multimodal datasets are necessary for training. Due to a lack of numerous kilonova observations, we propose $\texttt{kilonova-multimodal-emulator}$ – a simulation pipeline for realistic, multimodal kilonova observations comprised of photometry, spectra, and images. We demonstrate this pipeline for ZTF-type observations, based on historical cadence and limiting magnitude information from the Bright Transient Survey (BTS) and using the latest radiative transfer kilonova models to produce a comprehensive dataset meant for the training of large artificial intelligence model.
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All authors Felipe Fontinele Nunes, Andrew Toivonen, Farhana Taiyebah, Leonard Lupin-Jimenez, Skylar Callis, Malhar Kulkarni, Soumi De, Michael W. Coughlin