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Physics Astrophysics Instrumentation and Methods for Astrophysics

astro-ph.IM Watch Instrumentation and Methods for Astrophysics

Tuesday 15 September

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

Determining elemental composition in laboratory meteorite ablation spectra through radiative transfer modeling

Adriana Pisarčíková, Jiří Borovička and Pavol Matlovič

Laboratory simulations of meteor ablation provide a critical quantitative link between the chemical composition of meteoroids and their observed spectral features. In this work, we analyzed high-resolution Echelle spectra (wavelength range 380-780 nm) of 22 diverse meteorites from the dataset presented in our previous work (Matlovič et al., 2024), representing the largest collection of laboratory meteor analogs to date. Using a radiative transfer model assuming local thermodynamic equilibrium (LTE) and accounting for self-absorption in optically thick plasma, we derived plasma parameters and elemental abundances for both major (Fe, Mg, Cr, Mn, Si, Na, Ni, Li, and K) and minor (Co, Cu, and V) species. Comparison with known bulk meteorite compositions allowed us to validate the modeling approach and assess chemical biases resulting from laboratory-induced ablation. Our analysis suggested plasma temperatures between 5220 and 5810 K and revealed systematic discrepancies in the elemental abundances compared to the original chemical composition. Specifically, we observed a significant enhancement of volatile species (Na, K) relative to Fe, accompanied by a depletion of the moderately volatile element Mg, while refractory elements (Al, Ca, Ti) remained undetected in the plasma radiation. These trends are consistent with the equilibrium vaporization model and demonstrate that under the simulated entry conditions ($\sim$12 km/s at $\sim$80 km altitude), the ablation process is dominated by incomplete and fractional vaporization. We conclude that while laboratory spectra of plasma from ablated meteorites do not fully reflect the original bulk composition, radiative transfer modeling effectively characterizes the state of the radiating plasma, offering a more robust approach for interpreting compositional properties from meteor observations.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.comp-ph

Adding slow magnetoacoustic mode to the HLL-type multi-state approximate Riemann solution

Fan Zhang, Stefaan Poedts and Andrea Lani

Multi-state HLL-type approximate Riemann solutions of ideal magnetohydrodynamics (MHD) typically assume that the medium within the Riemann fan is incompressible, and thus the slow magnetoacoustic mode cannot be included in their space-time wave configurations for the approximated states. We propose a new strategy to design multi-state HLL-type approximate solutions, allowing for the medium within the Riemann fan to be compressible. In particular, for the complete seven-wave configuration of the MHD Riemann problem, we first estimate the slow magnetoacoustic speeds and a longitudinal flow speed between the slow modes, and then follow the conservation laws and Rankine-Hugoniot jump relations across the fast, Alfvén, and slow waves, to calculate all the intermediate states within the Riemann fan. Moreover, we discuss the solutions when certain wave modes degenerate, ensuring well-posedness and smooth transitions between complete and degenerate wave configurations. Numerical simulations using a Finite Volume (FV) solver show that the proposed approximate Riemann solution is less diffusive than the classic HLLD scheme, particularly for slow mode waves. For example, in a 1D test case with a strong longitudinal magnetic field, the new scheme needs one order of magnitude fewer grid cells compared to the classic HLLD scheme to resolve all wave modes.
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Instrumentation and Methods for Astrophysics

Optimal exposure time for satellite imaging? A trade-off between residual tip-tilt and registration accuracy

Florian Cheyssial, Laurent M. Mugnier and Cyril Petit

Adaptive-Optics assisted astronomical imaging and satellite imaging from the ground share many commonalities but have also specificities. In particular satellites are non-stationary objects in terms of both shape and flux, encouraging relatively short exposure times. Besides, very short exposures freeze the turbulence and preserve high spatial frequency information in speckles, but at the cost of a low image SNR, which complicates the post-processing. Conversely, long exposures lead to speckle-less images where some high frequency information is lost. In this communication, we propose a method for determining the exposure time that optimizes the image quality after post-processing. In particular, we focus on the reduction of the jitter effects – induced by atmospheric tip-tilt residues, vibrations and object non stationarity – which may dramatically reduce the image quality when imaging satellites. Our model takes into account the object type and flux, the residual aberrations power spectral density and the noise level.
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Instrumentation and Methods for Astrophysics

Hardware-efficient neural networks for FPGA-based radio triggering of extensive air showers

Vesselin Dimitrov, Alperen Aksoy, Ilja Bekman et al. (+7 more)

We present a hardware-efficient hybrid trigger for FPGA-based radio detection of extensive air showers. The hybrid design consists of a lightweight denoiser that cleans raw ADC traces and a compact classifier that operates on the denoised output, enabling robust near-threshold pulse detection in high-interference environments. Both neural networks are trained quantization-aware. Signals are generated from detector-folded CoREAS/CORSIKA simulations and embedded into measured noise to form a realistic benchmark. The trigger reaches an AUC of 0.992 while fitting comfortably within the resource budget of a Zynq-7000 Z-7020, with microsecond-scale latency and sub-watt power consumption. RTL validation confirms agreement between the fixed-point hardware and the quantized software model, demonstrating that neural denoising combined with classification provides reliable, low-cost radio triggering in noisy environments.
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All authors Vesselin Dimitrov, Alperen Aksoy, Ilja Bekman, Markus Cristinziani, Eric-Teunis de Boone, Qader Dorosti, Chimezie Eguzo, Stefan Heidbrink, Stefan van Waasen, Andre Zambanini

Instrumentation and Methods for Astrophysics

Design of an atmospheric dispersion corrector and double scrambler for improved fiber coupling and illumination uniformity for the HET HRS

Devika K Divakar, Joseph Strubhar, Andrew Pinckney et al. (+1 more)

The Hobby–Eberly Telescope High Resolution Spectrograph (HET–HRS) is undergoing a major instrument upgrade to improve its performance over the 360–1000 nm wavelength range. As part of this effort, a new fiber-feed system has been developed to increase throughput and enhance illumination stability. This paper presents the optical and opto-mechanical designs of the upgraded HRS Input Head Module Package and lens-based Double Scramblers. The Input Head incorporates a static Atmospheric Dispersion Corrector (ADC) and relay optics optimized for the HET operational zenith-angle range, reducing the residual atmospheric dispersion to less than 0.42 arcsec while improving wavelength-dependent fiber coupling. Separate Double Scrambler designs were developed for the 260 \textmu m and 320 \textmu m science fibers to exchange the near-field and far-field illumination distributions. Geometrical image analyses demonstrate stable near-field and far-field illumination, reduced coupling losses, and acceptable angular acceptance across both fiber geometries. The opto-mechanical designs supporting the Input Head and Double Scrambler are also presented to provide the alignment accuracy and mechanical stability required for the upgraded fiber-feed system. These results establish the proposed architecture as a practical solution for improving the optical performance and illumination stability of HET–HRS.
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All authors Devika K Divakar, Joseph Strubhar, Andrew Pinckney, Phillip MacQueen

Monday 14 September

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

FOSSIL: A future mission for CMB spectral distortion measurements

N. Aghanim, B. Maffei, J. Aumont et al. (+96 more)

We present FOSSIL, a proposed space mission which is designed to deliver unprecedented absolute spectroscopic measurements of the sky intensity over a broad frequency range (50GHz to 2THz) to accurately measure chemical-potential mu-type, Compton y-type, and Compton relativistic y-type CMB spectral distortions. FOSSIL will reach monopole sensitivities representing a gain of roughly three orders of magnitude over COBE/FIRAS. These capabilities will allow us to constrain primordial density fluctuations on scales k~(10 to 10^4)Mpc^-1, test inflationary models, probe dark matter annihilation/decay/interactions, constrain primordial black hole seed scenarios, and pin down feedback models in galaxy evolution and structure formation by measuring the cosmic thermal energy content. Furthermore, its 130 spectral channels will enable legacy astrophysics, including precise characterisation of the Cosmic Infrared Background, line intensity mapping during cosmic noon, and detailed Galactic dust mapping.
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All authors N. Aghanim, B. Maffei, J. Aumont, A. Beelen, B. Borgo, E. Bozzo, J. Chluba, X. Coulon, S. Couturier, F. Cuttaia, B. Cyr, P. De Bernardis, C. De Jabrun, J.-J. Diaz-Garcia, D. Eckert, G. Fabbian, L. Ferrari, F. Finelli, T. Gascard, J. E. Gudmundsson, A. Kogut, G. Lagache, M. Loquet Le Gall, S. Martin, A. I. Silva Martins, A. Monfardini, C. O'Sullivan, L. Pagano, D. Paoletti, G. Pisano, M. Remazeilles, V. Reveret, J. A. Rubino-Martin, V. Sauvage, G. Savini, L. Spencer, A. Tartari, L. Terenzi, N. Trappe, D. Watts, B. Winter, E. Baker, E. S. Battistelli, R. Battye, J. L. Bernal, A. Besnard, F. R. Bouchet, M. Braglia, C. Burigana, M. Calvo, S. Caminade, M. Citran, D. Clements, W. Coulton, E. Courau, G. De Zotti, E. Di Valentino, H. Dole, G. Domenech, S. Evangelista, S. Farrens, M. Frailis, K. A. Glasscock, V. Hervier, E. Kovetz, H. Liu, T. Louis, F. Madec, A. S. Maniyar, C. J. A. P. Martins, S. Masi, L. Maurin, F. Moll, L. Morelli, S. K. Naess, A. Nicola, F. Pace, N. Ponthieu, V. Poulin, E. Prele, N. Sanchez, W. Qin, L. Rodriguez, D. Scott, F. Simon, J. Singal, T. Slatyer, E. M. Teixeira, L. Thiele, M. Tristram, T. Trombetti, L. Vacher, S. Vinzl, A. Zacchei, E. Allys, K. Aryan, J. M. Casas Gonzales, O. Lahav, C. Sidiropoulos

Instrumentation and Methods for Astrophysics

RAMA: A new agile AO bench for the telescope FEELINGS

Matteo Pasinetti, Rodrigo Andres Munoz Gomez, Benjamin Andres Gonzalez Barraza et al. (+16 more)

The ground-based observation of extended objects such as satellites suffer from severe atmospheric propagation constraints. Specifically, high tracking velocities and low-elevation lines of sight generate non-stationary turbulence alongside strong scintillation. Developing robust wavefront control strategies is therefore critical to maintain stable observations. In this context, we present RAMA, an adaptive optics (AO) testbench deployed on ONERA's 60\,cm FEELINGS telescope. Designed as a pathfinder for future systems like the PROVIDENCE ground station, RAMA evaluates a visible, non-modulated Pyramid Wavefront Sensor (PWFS). The hardware baseline also includes two pupil-conjugated deformable mirrors (DM97 and DM192) driven by the DAO Real-Time Computer (RTC). Inheriting the modular and evolving philosophy of the PAPYRUS project, the bench provides a flexible environment to test new components on-sky and allows for direct comparisons between classical controllers and advanced, data-driven strategies. By implementing Convolutional Neural Networks (CNN) for phase reconstruction and Reinforcement Learning (RL) for loop control, RAMA aims to overcome the specific limitations associated with scintillation and extended-object observations. This paper details the opto-mechanical design, numerical simulations of the bench expected wavefont control performance, preliminary laboratory closed-loop results and the first on-sky optical coupling with the telescope.
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All authors Matteo Pasinetti, Rodrigo Andres Munoz Gomez, Benjamin Andres Gonzalez Barraza, Francisco Oyarzun, Sylvain Cetre, Jean-François Sauvage, Axel Vincent-Randonnier, Julien Charton, Marie Laslandes, Roméo Roudeix, Nicolas Védrenne, Cyril Petit, Pierre-Louis Mayeur, Esteban Vera Rojas, Andrew Reeves, Perrine Lognoné, Morgan Gray, Thierry Fusco, Benoit Neichel

Instrumentation and Methods for Astrophysics

Commissioning the AIP's ultrafast laser Inscription facility: defining the parameter space for type-I waveguide fabrication

Rima Islam, Aline N. Dinkelaker, Abani Shankar Nayak et al. (+2 more)

Astrophotonics offers a compact, stable alternative to bulk optics in traditional astronomical instrumentation, spanning high-precision spectroscopy to high-contrast interferometry. However, the strict requirements for throughput, accuracy, precision, and stability require tailored manufacturing processes that go beyond standard telecommunications technology. This work presents the iterative experimental and statistical methods used to determine the optimal laser-writing conditions for passive waveguides in silica glass using a femtosecond laser inscription setup. We systematically explored the parameter space by varying pulse energy, repetition rate, translation speed, and scan numbers to identify the optimal conditions for Type-1 waveguides, characterized by a positive refractive-index modification in their cores. We report on the refinement of these parameters to manufacture single-mode, high-throughput waveguides that operate in the astronomical J-band (1300-1400 nm). A key focus of this optimization is to match the mode field diameter (MFD) to the SMF28 fibre and minimize insertion losses. This development is critical for astrophotonics devices, such as photonic reformatters, beam combiners, and pupil remappers, as well as post-fabrication correction of phase errors in photonic components fabricated using traditional photolithographic methods. Some of these components will be used for future on-sky validation at the Calar Alto Observatory and the CHARA array.
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All authors Rima Islam, Aline N. Dinkelaker, Abani Shankar Nayak, Kalaga Madhav, Martin Roth

Instrumentation and Methods for Astrophysics

Optomechanical design of an ADC and image rotator for the HJST Coudé Spectrograph at McDonald Observatory

Devika K Divakar, Phillip MacQueen, Andrew Pinckney et al. (+1 more)

High-resolution spectroscopic observations require stable slit illumination and mitigation of atmospheric refraction effects that degrade throughput and spectral fidelity. We present the optical and mechanical design of a Rotational Atmospheric Dispersion Corrector (RADC) for the coudé Tull Spectrograph on the Harlan J. Smith 2.7 m Telescope. Atmospheric dispersion introduces wavelength-dependent image displacement that increases with zenith distance and reaches approximately 4 arcsec across the 350 - 1000 nm wavelength range at a zenith angle of 65{\deg}, leading to wavelength-dependent slit losses and non-uniform slit illumination. The RADC employs a pair of counter-rotating Amici prisms to provide continuous correction over the operational zenith-angle range while maintaining image quality and compatibility with the existing coudé pre-slit optics. The optical and mechanical design of the deployable ADC subsystem, its integration within the limited relay envelope, and its expected impact on throughput and slit illumination stability are presented. In addition, we discuss a K-mirror image rotator as a potential future upgrade for observations of extended and non-point-like targets, where maintaining a fixed slit position angle on the sky may be desirable during long integrations. Preliminary optical studies of the image-rotation concept and its integration considerations within the HJST coudé relay are briefly summarized. Together, these developments support enhanced observing capabilities for high-resolution spectroscopy on the HJST.
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All authors Devika K Divakar, Phillip MacQueen, Andrew Pinckney, Joseph Strubhar

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Bridging the chirp-mass gap: searching for gravitational waves from inspiraling subsolar-mass ultra-compact binaries using LIGO O4ab data

Andrew L. Miller

Gravitational-wave searches for subsolar-mass compact binaries have left a gap between the planetary-mass regime accessible to long-duration searches and the higher masses probed by conventional compact-binary analyses. We close this gap by searching for the inspiral of ultra-compact binaries with chirp masses $10^{-2}$–$10^{-1}\,M_\odot$ in LIGO O4ab data. Using the statistically robust BinaryGFH-v2 method, a time-frequency technique to search for rapidly evolving inspirals lasting minutes to hours, we cover this previously challenging parameter space with a computational cost of only $\sim 350$ CPU-hours, and find no significant candidates. We thus set 90% confidence upper limits on the binary merger-rate density, providing the first gravitational-wave constraints across this chirp-mass range. Assuming that primordial-black-hole binaries formed in the early Universe with no binary suppression ($f_{\rm sup}=1$), these results provide the first gravitational-wave constraints on the primordial-black-hole \dmh fraction in this mass range, yielding upper limits with $f_{\rm PBH}<1$ for equal-mass binaries with component masses $10^{-2}$–$10^{-1}\,M_\odot$ and asymmetric binaries with secondary masses $m_2=3\times10^{-4}$–$10^{-2}\,M_\odot$ for a primary mass $m_1=2.5\,M_\odot$.
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Instrumentation and Methods for Astrophysics · Cross-listed from astro-ph.CO

Peering Beyond the Veil of Last Scattering: A View of the Universe with CMB Spectral Distortions

Bryce Cyr, Nabila Aghanim, Ethan Baker et al. (+37 more)

The frequency spectrum of the cosmic microwave background is the most precise blackbody ever measured in nature, with deviations constrained at the level of almost one part per million from the COBE satellite. Nevertheless, departures away from a perfect blackbody are present in standard $\Lambda$CDM cosmology, lurking just beneath the surface of our current observational bounds. These spectral distortions provide invaluable information on our thermal history in both the post- and pre-recombination epochs, allowing us to peer beyond last scattering and into the primordial Universe. Here, we present an overview of the underlying physics responsible for generating CMB spectral distortions at all epochs. As an illustration of this rich physics, we review a comprehensive set of mechanisms capable of generating distortions both within and beyond the standard $\Lambda$CDM paradigm. We also discuss the information that can be gleaned by going beyond the monopole (sky-averaged) spectrum and exploiting the spatial information present in anisotropic spectral distortions. To supplement our discussion of the diverse science of spectral distortions, we provide an overview of the upcoming and proposed experimental landscape. We highlight that the combination of the TMS, COSMO, and BISOU experiments will provide the first discovery of a monopole $y$-type distortion within the coming decade. From space, the proposed FOSSIL experiment is forecasted to improve upon the original COBE/FIRAS measurement by roughly three orders of magnitude in sensitivity, bringing with it the detection of the $\Lambda$CDM $\mu$-type distortion sourced by the dissipation of small scale acoustic modes in the pre-recombination plasma. With transformational measurements on the horizon, CMB spectral distortions offer a uniquely sensitive probe of the thermal history of the Universe at redshifts $z \lesssim 2 \times 10^6$.
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All authors Bryce Cyr, Nabila Aghanim, Ethan Baker, Elia Stefano Battistelli, Richard Battye, José Luis Bernal, Jens Chluba, Xavier Coulon, William Coulton, Paolo de Bernardis, Eleonora Di Valentino, Guillem Domènech, Sara Evangelista, Giulio Fabbian, Fabio Finelli, J. Colin Hill, Rishi Khatri, Alan Kogut, Guilaine Lagache, Hongwan Liu, Bruno Maffei, Fereshteh Majidi, Abhishek S. Maniyar, C. J. A. P. Martins, Silvia Masi, Jeff McMahon, Daniela Paoletti, Vivian Poulin, Wenzer Qin, Mathieu Remazeilles, José Alberto Rubiño-Martín, Alina Sabyr, Mayuri Sathyanarayana Rao, Carlos Sierra, Jack Singal, Tracy R. Slatyer, Elsa M. Teixeira, Leander Thiele, Léo Vacher, Duncan Watts

Instrumentation and Methods for Astrophysics

MUSHY: Multimodal Flow-Based Amortized Bayesian Inference for Spectroscopic Data Fusion

Jeff Shen

We are in an era of unprecedented spectroscopic data availability, with surveys such as APOGEE, GALAH, and DESI observing millions of stars. However, data are heterogeneous and to date, efforts to exploit synergies between surveys have been limited. In particular, there is a lack of principled methods that combine spectroscopic data from different surveys to improve inference of physical parameters. In this work we present a new method, MUSHY, for spectroscopic data fusion. MUSHY is an amortized Bayesian inference method, using a rectified flow model with multimodal inputs to learn a posterior distribution over physical parameters. Using synthetic spectra generated via ATLAS12/SYNTHE, including realistic instrumental effects and noise, we demonstrate that MUSHY can precisely infer physical parameters with well-calibrated posteriors from any combination of surveys, with multimodal inputs providing stronger constraints on the posterior than single-survey data alone. This work paves the way for principled combination of spectroscopic data from heterogeneous sources.
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Instrumentation and Methods for Astrophysics

Disentangling 3D Magnetic Field Geometry from Turbulence: A Polarization-Based Classification Method

Sophia Kressy and Fabian Heitsch

We develop a decision tree classifier that recovers 3D magnetic field geometry from synthetic polarization and position angle maps of a magnetized, turbulent field. We test the classifier for a series of geometries: Uniform, Wavy, Helical, and Hourglass. The classifier is calibrated across a range of Alfvénic Mach numbers and injected Stokes Q,U noise levels for each geometry. Our models show the median and skewness of the polarization fraction, as well as the position angle circular variance, vary systematically with both geometry and the Alfvénic Mach number. We find that the 3D geometry can be isolated by using a variety of polarization and position angle metrics to break degeneracies. The classifier recovers most geometries well for sub-Alfvénic cases (Alfvénic Mach Number < 1). For Alfvénic Mach Number > 1, polarization and position angle statistics converge across all geometries and the classifier fails to recover the magnetic field structure.
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Instrumentation and Methods for Astrophysics

Automatic astrometric calibration of low-cost all-sky cameras

J. R. González Fernández, Laura Hermosa Muñoz, María Fernández Alonso et al. (+1 more)

All-sky cameras support weather monitoring, amateur astronomy, fireball and space-debris detection, and measurements of light pollution. These applications require reliable astrometric calibration despite imperfect camera alignment and variable observing conditions. We present an open-source procedure that combines a compact fisheye model, an exact rotation to account for camera tilt, and automatic star matching. It can initialise a calibration from a single frame given the observing site coordinates and observation time. We evaluate the procedure on nine cloud-free, moonless frames, obtained with a Raspberry Pi camera and a 1.55 mm lens. Fitting on eight frames and evaluating on the ninth in turn gives a median residual of 0.70 px (95% interval 0.64-0.80 px) across 4172 matches, reduced to 0.60 px by two optional decentering parameters. All nine single-frame calibrations pass the quality criteria and predict positions on other frames with a median residual of 0.78 px, taking about six seconds per calibration. We also apply the clear-sky calibration to 73 frames with varying lunar illumination or cloud cover, obtaining comparable residuals for accepted matches on moonlit frames (0.62 px). These results support reusing a calibration while the camera geometry remains unchanged and enough stars remain visible for reliable matching. The procedure is available as the Python package ascal.
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All authors J. R. González Fernández, Laura Hermosa Muñoz, María Fernández Alonso, Lucía González Cuesta

Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics

Setup and performance of focal-plane characterization benches for high precision astrometry

Fabrice Pancher, Sebastien Soler, Fabien Malbet et al. (+7 more)

Detecting Earth-like exoplanets requires micro-arcsecond astrometry, which relies on a precisely calibrated focal plane equipped with high-resolution detectors. Accurate calibration depends on characterizing detector imperfections and systematic effects. Optical benches have been developed to assess the sensor's behavior: an integrating-sphere setup for electro-optical parameters, an interferometric bench for pixel-level geometry, and a star-field projection system for intrinsic distortion. This work presents the characterization benches built for a 46-Megapixels (MP) imaging sensor, based on the same technology as the four 220-MP detectors foreseen for the final focal-plane, and the performance metrics obtained from these setups in the context of NASA's HWO and ESA's M-class missions. Upgrades will bring the test environment closer to operational conditions: a second 46-MP sensor will be added for multi-detector tests, plus an adjustable-angle fringeprojection system and improved alignment.
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All authors Fabrice Pancher, Sebastien Soler, Fabien Malbet, Hugo Rousset, Manon Lizzana, Alain Leger, Thierry Lépine, Florence Ardellier-Desages, Jerôme Amiaux, Pierre-Olivier Lagage

Instrumentation and Methods for Astrophysics

Calibrations for high precision differential astrometry onboard Theia and HWO

Manon Lizzana, Fabien Malbet, Hugo Rousset et al. (+3 more)

Future space astrometry missions such as Theia and an astrometric mode of the Habitable Worlds Observatory (HWO) require detector calibration and instrumental characterization at an unprecedented level to achieve sub-micro-arcsecond precision. This work presents three complementary developments addressing these requirements. First, we report an independent characterization of the GIGAPYX-4600 back-side illuminated CMOS detector, evaluating its linearity, readout noise, dark current, pixel response non-uniformity, defective pixel fraction, and inter-pixel capacitance. The results demonstrate excellent detector performance and confirm its suitability as a candidate for future gigapixel focal planes. Second, we develop an interferometric calibration method based on Young's fringes to measure pixel centroid displacements, enabling the characterization of inter-pixel response variations with an approach compatible with onboard implementation. The method is investigated through numerical simulations and an experimental testbed using the GIGAPYX-4600 detector. Finally, we introduce an astro-calibration framework that jointly estimates stellar astrometric parameters, telescope attitude, plate scale, and optical distortion through a global iterative optimization. Although this calibration approach is still under development, simulations and laboratory activities are underway to validate its performance. Together, these developments contribute to the technological and calibration framework required for the next generation of high-precision astrometric space missions.
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All authors Manon Lizzana, Fabien Malbet, Hugo Rousset, Sébastien Soler, Fabrice Pancher, Éric Thiébaut

Instrumentation and Methods for Astrophysics

Gnuastro: removing extended/diffuse outliers while coadding

Mohammad Akhlaghi, Héctor Vives Arias, Pablo Renard et al. (+2 more)

Deep astronomical images are produced by the coadding (also called "stacking") of several individual exposures. However, individual exposures are often plagued with many artifacts which will reduce the quality of the deep image if not properly removed. Most are removed during reduction/calibration, but the more diffuse may stay. To address this problem, the following new operators were introduced to the Arithmetic program in Gnuastro 0.23: 'madclip-maskfilled', 'sigclip-maskfilled' and 'collapse-*clip-fill-*'. They are able to mask many such outliers successfully by using all the exposures to find outlying pixels in each exposure and exploiting their contiguity. This research note is reproducible with Maneage, on the Git commit bf3815a.
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All authors Mohammad Akhlaghi, Héctor Vives Arias, Pablo Renard, Héctor Vázquez Ramió, Raúl Infante-Sainz

2609.15529 · 14 Sep · To appear in RNAAS. Reproducible source on Codeberg (https://codeberg.org/gnuastro/papers/src/branch/maskfilled), that is archived on Software Heritage (swh:1:dir:84092a4318c15846b51fe6124dac5ba47fd191b2) with supplements on Zenodo (https://doi.org/10.5281/zenodo.22676761)

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

Detecting transiting exoplanets in simulated PLATO data: A comparison of light curve filter and transit search algorithms

Geert Jan Talens, Leigh C. Smith, Luca Malavolta et al. (+3 more)

Aims: Our goal is to test and compare transit search methodologies, and provide recommendations as to the best practices to be implemented by the upcoming ESA PLATO mission, in order to achieve its goal of detecting Earth-like planets in the habitable zones of Sun-like stars. Methods: We generate simulated two-year PLATO light curves with injected planets with sizes 0.5–2.0 $R_\oplus$, and compare the performance of the CETRA, umbra, and nuance transit search methods. CETRA and umbra require pre-filtered light curves and we test the biweight, Huber spline, Lowess, and YSD-Lowess filters. nuance uses a Gaussian process to model the stellar variability at all proposed transit parameters. Results: nuance achieves the best performance, recovering 61.2% signals using a simple harmonic oscillator Gaussian process kernel, and it performs especially well for both hot and fast-rotating stars. However, when multiple Huber spline filter windows are considered, both CETRA and umbra can match nuance's performance. CETRA matches nuance with four windows, recovering 61.3% of signals. umbra matches nuance with two windows, recovering 61.7% of signals. Recovery rates exceeding nuance are possible by using more windows. The computational cost of running nuance is so high that running CETRA or umbra on multiple windows is preferred. Conclusions: The PLATO pipeline should use the Huber spline with a range of window sizes as its primary light curve filter. CETRA should be updated to use the warped least-squares templates implemented in umbra. The use of nuance should be considered for hot, rapidly rotating stars.
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All authors Geert Jan Talens, Leigh C. Smith, Luca Malavolta, Lionel Garcia, Simon Hodgkin, Suzanne Aigrain

Instrumentation and Methods for Astrophysics

PYRA and MYTHRA: new statistical analysis for image reconstruction

Julien Drevon, Margaux Abello, Florentin Millour et al. (+2 more)

Image reconstruction in optical interferometry remains a challenging inverse problem due to sparse Fourier sampling and the strong dependence of the reconstructed images on user-defined parameters. We present PYRA (Python for MiRA) and MYTHRA (Mean Astrophysical Images with PYRA), two tools designed to improve the robustness and reproducibility of interferometric imaging. PYRA automatically generates large ensembles of MiRA reconstructions by exploring a wide range of reconstruction parameters, while MYTHRA statistically analyzes the resulting images to identify the most consistent solutions and derive a final averaged image with associated uncertainty estimates. The methodology is validated using the blind datasets of the 2024 Interferometric Imaging Contest, where our reconstruction strategy achieved the best overall score. We further apply the method to VLTI/MATISSE observations of the triple AGB system {\pi}1 Gru and the A[e] supergiant 3 Pup. These results demonstrate that statistical analysis of large reconstruction ensembles provides a powerful framework for assessing image reliability and reducing reconstruction artifacts in optical interferometry.
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All authors Julien Drevon, Margaux Abello, Florentin Millour, Anthony Meilland, Armando Domiciano de Souza

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Deterministic denoising of long-duration gravitational-wave signal candidates with $\alpha$-(de)blending

Przemysław Figura and Michał Bejger

We present a deterministic machine-learning method for denoising candidate signals from all-sky searches for continuous gravitational waves from rotating neutron stars. Using the time-domain $F$-statistic search pipeline, we post-process the resulting $F(f,\dot{f})$ candidate patterns with iterative $\alpha$-(de)blending, a deterministic diffusion-type generative model implemented as a U-Net, well suited to the non-Gaussian, correlated noise of the $F$-statistic output. Two models, trained on data based on simulated 6- and 12-day time-domain segments with software-injected signals similar to the LVK hardware injections, are tested by comparing deblended images to the library of expected signal patterns via the Structural Similarity Index Measure. In general the method recovers the correct sky-position-dependent pattern for signal-to-noise ratios $\rho \gtrsim 4$, moderately below typical all-sky detection thresholds, with recovery depending strongly on pattern morphology, demonstrating that deterministic diffusion-based denoising may serve as a consistency/veto tool ahead of the semi-coherent coincidence stage. We also discuss limitations and possible improvements of the method.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Testing the equivalence principle with lunar laser ranging residuals from different planetary and lunar ephemerides

Jun Ke, Jie Luo, Qin Li et al. (+2 more)

Lunar laser ranging (LLR) provides a sensitive test of the equivalence principle (EP) through a possible synodic perturbation in the Earth–Moon distance. In this work, we develop an independent LLR data-reduction framework and investigate this signature in the post-fit O–C residuals obtained with the EPM21, INPOP21, and DE430 planetary and lunar ephemerides. The same observation model and parameter-adjustment procedure are applied to the three ephemerides, allowing their residual-based results to be compared within a consistent framework. To account for the nonuniform distribution of LLR observations over the synodic angle $D$, the residuals are fitted with cosine and sine harmonics up to the third order. Signal-injection tests are also performed to quantify the attenuation of a possible $\cos D$ signal during the parameter adjustment. After correcting for signal attenuation, solar radiation pressure, and the thermal response of the lunar retroreflectors, the preferred EPM21, INPOP21, and DE430 solutions yield $\Delta(m_g/m_i)_{\rm EM}=(0.900\pm3.183)\times10^{-14}$, $(0.496\pm3.624)\times10^{-14}$, and $(2.669\pm7.048)\times10^{-14}$, respectively. The EPM21 and INPOP21 results are based on observations from 1970 to 2024, whereas the DE430 solution was obtained using observations up to 2016. All three estimates are consistent with zero within their uncertainties. This work demonstrates that residual-based analysis can provide an independent and transparent EP test, while also offering guidance for assessing sampling and ephemeris-dependent effects in future high-precision LLR studies.
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All authors Jun Ke, Jie Luo, Qin Li, Yu-Jie Tan, Cheng-Gang Shao

Instrumentation and Methods for Astrophysics

FOSSIL: Thermo-mechanical architecture

Valentin Sauvage, Clémence de Jabrun, Sylvain Martin et al. (+13 more)

FOSSIL (FTS fOr CMB Spectral diStortIon expLoration) is a proposed ESA M8 mission tailored to measure the spectral distortions of the Cosmic Microwave Background (CMB) with a sensitivity three orders of magnitude beyond the COBE/FIRAS legacy measurement. Achieving this sensitivity demands an extraordinarily challenging cryogenic architecture: the scientific instrument must be maintained at the lowest achievable temperature (4.5 K), while the detector focal plane assembly operates at 50 mK. This paper presents the thermal architecture of the FOSSIL payload and instrument, from the spacecraft service module at 293 K down to the sub-kelvin detector stage. The thermal design draws on heritage from the Planck and ARIEL missions and relies on a staged passive cooling chain comprising a multi-layer insulation blanket, three V-groove radiators (operating at approximately 130 K, 90 K, and 50 K), and a 25 K actively cooled shield fed by an ESA-provided 4 K cryocooler chain. Sub-kelvin temperatures are achieved via a multi-stage adiabatic demagnetisation refrigerator (ADR) system developed for NewAthena/X-IFU, providing continuous cooling at 1.8 K and 350 mK, and 50 mK with an 80% duty cycle. The Focal Plane Assembly (FPA), which houses four Kinetic Inductance Detector (KID) arrays at 50 mK, is thermally isolated from the 4.5~K bench via a carbon-fibre reinforced polymer (CFRP) hexapod structure with staged heat interception. We present the steady-state thermal budget across all stages, demonstrating comfortable margins at every temperature level, and discuss key thermal design drivers on the Blackbody Internal Reference (BBIR).
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All authors Valentin Sauvage, Clémence de Jabrun, Sylvain Martin, Bruno Maffei, Nabila Aghanim, Anaïs Besnard, Bruno Borgo, Ivan Charles, Xavier Coulon, Sandrine Couturier, Francesco Cuttaia, Jean-Marc Duval, Morgane Loquet Le Gall, Giorgio Savini, Luca Terenzi, Berend Winter

Instrumentation and Methods for Astrophysics

Nii-MALA: A Fast Metropolis-Adjusted Langevin Sampler with Radial Velocity Benchmarks

Jian Jiao, Sheng Jin, Wenxin Jiang et al. (+1 more)

Markov chain Monte Carlo is widely used for model assessment and parameter fitting in astronomy and astrophysics, leading to numerous ready-to-use packages implementing various sampling techniques. For large-scale analyses involving many individual targets, computational efficiency becomes paramount, as it dictates the overall runtime. We introduce Nii-MALA, a high-performance C implementation of the Metropolis-Adjusted Langevin Algorithm, which leverages Message Passing Interface for parallelization and incorporates automatic differentiation backends for gradient evaluation. The code offers flexible control via a configuration file, allowing users to specify the proposal step sizes for all model parameters across parallel chains. We validate its effectiveness on 15- and 30-dimensional Gaussian distributions and a bimodal distribution, and further benchmark it against several other codes using radial velocity data from 51 Pegasi b. Our benchmarks confirm the efficiency of Langevin sampling over random-walk sampling in obtaining the effective sample size, particularly as the dimensionality of the target function increases. This algorithmic advantage can be effectively leveraged when paired with an efficient automatic differentiation library. However, for complex functions commonly encountered in astronomy—such as radial velocity orbital fitting—the derivative-dependent Langevin sampler shows lower efficiency than parallel tempering or alternative sampling approaches, as revealed by effective sample size analysis.
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All authors Jian Jiao, Sheng Jin, Wenxin Jiang, Dong-Hong Wu

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

The driving mode of turbulence in disc galaxy simulations with adaptive mesh refinement

James Watt, Christoph Federrath, Thorsten Tepper-Garcia et al. (+2 more)

Turbulence is a key ingredient in controlling the structure of the interstellar medium (ISM) and star formation, yet we still lack a detailed understanding of its drivers in galaxies. Previous idealised simulations of turbulence employ a stochastic forcing field to drive turbulence. The geometry of this forcing field - whether it is predominantly solenoidal or compressive - is a key parameter governing how turbulence shapes the ISM density distribution and regulates the star formation rate. The turbulence driving parameter ($b$) quantifies the relative contribution of compressive versus solenoidal driving.. Therefore, accurate knowledge of the driving parameter is essential for understanding and predicting star formation, and for sub-grid modelling of ISM physics and the star formation rate. In this work, we introduce an algorithm to measure the turbulence driving parameter in adaptive mesh refinement (AMR) simulations of galaxies. We focus our analysis on a synthetic Large Magellanic Cloud (LMC), present-day analogue with a total mass $M \approx 10^{11}\,\mathrm{M}_\odot$. We find that turbulence is driven primarily solenoidally ($b<0.4$) within the inner $\sim4\,\mathrm{kpc}$ of the galaxy, and becomes increasingly compressive with $b>0.4$ towards the outskirts, $R\gtrsim4.5\,\mathrm{kpc}$. The volume-weighted median across the disc, $b\simeq0.4$, is consistent with the natural mixture of driving modes. We further find that $b$ is weakly correlated with the strength of shear, in that solenoidal driving tends to be associated with regions of higher shear, as expected for the more central parts of galaxies. These trends persist over $\sim\!2\,\mathrm{Gyr}$ of the galaxy's evolution.
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All authors James Watt, Christoph Federrath, Thorsten Tepper-Garcia, Oscar Agertz, Joss Bland-Hawthorn

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

Field-Level Baryon Acoustic Oscillation Reconstruction of the DESI DR1 Luminous Red Galaxies with Linear Field Transformer (LiFT)

Liam Parker, Uroš Seljak, Adrian E. Bayer et al. (+2 more)

We present the first application of neural field-level baryon-acoustic oscillation (BAO) reconstruction to real spectroscopic survey data. We develop Linear Field Transformer (LiFT), a 3D vision transformer that takes as input the observed galaxy field, its standard reconstruction, and a set of context channels encoding local line of sight, survey coverage, and redshift, and learns to correct standard reconstruction toward the linear density field. We construct a forward-modeling pipeline to produce mock lightcones similar to the DESI Data Release 1 (DR1) luminous red galaxy (LRG) sample, and train LiFT on these. We validate LiFT on held-out simulations, as well as on additional mocks which differ in gravity solver, halo finder, HOD, cosmology, and fiber-assignment history, as well as on mocks analyzed with a distorted distance-redshift relation; ultimately, we find unbiased dilation parameters with consistently tighter constraints than standard reconstruction. Applied to the DESI DR1 LRGs, LiFT improves errors on $\alpha_{\rm iso}$ by 13%, 24%, and 30% and on $\alpha_{\rm AP}$ by 5%, 22%, and 30% relative to the DESI DR1 standard reconstruction analysis in the LRG1, LRG2, and LRG3 bins respectively; meanwhile, our DR1 central values remain consistent with DR1 and DR2. This equates to a factor of 1.2, 1.7 and 2.0 increase in Figure of Merit (or effective survey volume) if one were to only use standard reconstruction. Ultimately, these results establish LiFT as a validated, survey-ready tool for current and upcoming galaxy surveys.
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All authors Liam Parker, Uroš Seljak, Adrian E. Bayer, Richard Feder, David Valcin

Sunday 13 September

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

Euclid: Data Release 1 (DR1) – Fornax-7, an ultra-faint companion to the Fornax dwarf spheroidal galaxy? A remote star cluster or dwarf satellite of the Fornax dSph

T. Saifollahi, A. Lançon, A. M. N. Ferguson et al. (+165 more)

We report the discovery of an ultra-faint stellar system in the vicinity of the Fornax dwarf spheroidal (dSph) galaxy in Euclid DR1. This system, which we designate Fornax-7, is located $1.1$ deg from the centre of the Fornax dSph at about $145$ kpc, corresponding to a projected distance of $\sim 2.8$ kpc assuming the distance of the Fornax dSph. We characterise Fornax-7 using constraints from its colour-magnitude diagram (CMD), luminosity function (LF), and integrated optical colours from ground-based data. These observables are modelled jointly through a forward-modelling framework to constrain its distance modulus, stellar population properties, and total stellar mass. Assuming a low metallicity of $-2.2 \leq {\rm [M/H]} \leq -2.0$, similar to known ultra-faint systems around the Milky Way and the LMC, we derive a distance modulus consistent with that of the Fornax dSph. We estimate an age of $(10.4\pm1.9)$ Gyr and infer a stellar mass of $170^{+50}_{-62}$ solar masses. Relaxing the metallicity constraint and allowing for a wider range that covers the metallicity of the known old Fornax globular clusters (GCs), we find a metal-poor population but with a higher metallicity ${\rm [M/H]}=-1.4\pm0.3$, while the age, distance modulus, and mass remain mostly the same. These results suggest a likely physical association with the Fornax dSph. Fornax-7 may represent either an extremely remote star cluster associated with Fornax, a dwarf satellite of Fornax (i.e., a "satellite of a satellite"), or an independent ultra-faint satellite in the outer halo of the Milky Way. In all cases, it constitutes an exceptional system probing the lowest-mass regime of galaxy and star cluster formation, and the structure of dwarf galaxy haloes. Deeper photometric and spectroscopic follow-up observations are required to confirm both the nature of the system and its dynamical connection to Fornax.
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All authors T. Saifollahi, A. Lançon, A. M. N. Ferguson, P. Boldrini, M. Gatto, J. M. Howell, N. F. Martin, A. C. Robin, F. Annibali, M. Baes, E. Balbinot, G. Battaglia, M. Bellazzini, Michele Cantiello, M.-R. L. Cioni, C. Crociati, V. Dornan, P.-A. Duc, A. Genina, C. M. Gutierrez, R. Habas, P. Jablonka, S. S. Larsen, M. Libralato, F. R. Marleau, D. Martínez-Delgado, S. Martocchia, D. Massari, F. Niederhofer, J. D. Sakowska, M. Urbano, L. R. Bedin, M. Griggio, A. Mohandasan, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, S. Kermiche, A. Kiessling, B. Kubik, K. Kuijken, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, M. Meneghetti, E. Merlin, G. Meylan, P. Monaco, A. Mora, M. Moresco, C. Moretti, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, W. J. Percival, V. Pettorino, A. Pezzotta, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, I. Risso, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, M. Schirmer, P. Schneider, A. Secroun, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, A. Tsyganov, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, A. Zacchei, F. M. Zerbi, I. A. Zinchenko, E. Zucca, J. García-Bellido, K. Tanidis

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

Decoding RR Lyrae light curves with deep learning for accurate absolute magnitude estimation

Shunxuan He, Huiwen Wu, Yang Huang et al. (+6 more)

RR Lyrae stars are essential standard candles for distance measurements in the Milky Way and nearby galaxies. Traditional estimates rely on the Period–Absolute Magnitude–Metallicity relation but are limited by uncertainties in metallicity determinations. We present a deep learning approach that directly predicts absolute magnitudes from RRab and RRc light curves, eliminating the need for metallicity estimates. Our model achieves validation precisions of 0.053 mag and 0.036 mag (approximately 2.5% and 1.7% in distance) for individual RRab and RRc stars, respectively. Tests on globular clusters yield typical distance precisions of 1.0% for RRab and 1.7% for RRc stars. For the benchmark systems, combining the RRab- and RRc-based models yields distance moduli of 18.498 $\pm$ 0.001$_{\text{stat}}$ $\pm$ 0.018$_{\text{sys}}$ mag for the Large Magellanic Cloud and 19.564 $\pm$ 0.003$_{\text{stat}}$ $\pm$ 0.019$_{\text{sys}}$ mag for the Sculptor dwarf spheroidal galaxy. These measurements are in excellent agreement with previous results, achieve a distance precision of approximately 1%, and represent a 1.8-fold improvement over traditional RR Lyrae calibration relations. Our approach showcases the ability of AI to directly extract key physical parameters from complex, information-rich light curves, resolve degeneracies, and scale to broader applications.
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All authors Shunxuan He, Huiwen Wu, Yang Huang, Deyi Zhang, Guirong Xue, Jifeng Liu, Xiaodian Chen, Xinyu Qi, Xiaoyu Tang

Instrumentation and Methods for Astrophysics · Cross-listed from math.OC

Convex Pursuit-Evasion Games for Spacecraft Proximity Operations on Circular and Elliptical Orbits

Omer Burak Iskender

Inspecting or servicing a non-cooperative spacecraft is a two-player game: the target can thrust to defeat the inspector's plan. Hamilton-Jacobi-Isaacs reachability answers such games exactly but its cost grows exponentially with state dimension, while learning-based controllers scale yet certify nothing. Convex formulations are the usual escape, typically cast as convex-concave saddle-point problems. That framing fails in the terminal-distance orbital game: with effort regularization, the payoff is convex in both controls, so no pure open-loop saddle point need exist. In its place we derive two exact one-sided guarantees read from the players' terminal reachable sets via support functions: an escape certificate proving the target can hold a guaranteed standoff, and a security strategy bounding the miss distance the inspector can force. Together they bracket the engagement without assuming player rationality, and over two hundred perturbed trials the escape certificate separated capture from escape without error. A projected extragradient method supplies a strategy pair in about 25 ms, certified in place by best-response gaps. The construction carries unchanged to elliptical reference orbits via Yamanaka-Ankersen dynamics, where the orbital phase moves miss distance by nearly a factor of two, reproduced by nonlinear Keplerian propagation. Under receding-horizon play the inspector captures in half of ten representative engagements. Angles-only navigation error, keep-out zones, multiple pursuers, and closed-loop play are treated as extensions.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Parameter Estimation of Ringdown Quasinormal Modes with Autoencoder

Momoka Iida, Hayato Motohashi and Hirotaka Takahashi

Ringdown gravitational waves from binary black hole mergers can be modeled as superpositions of quasinormal modes (QNMs), whose frequencies and excitation factors encode properties of the remnant Kerr black hole. Reliable extraction of multiple QNM components is challenging because of mode overlap and noise. We develop an autoencoder-based framework for multi-component QNM analysis, in which the latent space is trained to represent the physical parameters of individual modes, enabling waveform denoising and parameter estimation within a common framework. Using controlled model waveforms constructed as finite sums of Kerr QNMs with recently established high-precision frequencies and excitation factors, including their nontrivial spin dependence near resonant excitation, we assess the method across partitioned spin intervals. The model achieves good in-domain waveform reconstruction and parameter recovery for the two longest-lived components of eight-component input waveforms, while its performance degrades when the validation spins lie far outside the training range. In a selected spin interval, the framework also recovers the 32 parameters of an eight-component waveform with good overall agreement. These results demonstrate the feasibility of physics-informed autoencoder-based inference for a prescribed multi-component ringdown waveform family and motivate further tests with progressively more realistic signals.
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Saturday 12 September

Instrumentation and Methods for Astrophysics

A compact time-domain reduced order quadrature for gravitational wave inspirals with non-stationary noise

Benjamin Zhang, Kris Pardo and Bence Bécsy

We develop the first time-domain reduced order quadrature for gravitational waves in the early inspiral period, motivated by the need for dataset compression in the presence of gaps, uneven sampling, and dense covariance matrices. A single reduced basis with 1290 elements can represent inspirals from supermassive black hole binary sources with chirp masses between $10^7-10^{10}$ $M_\odot$, but in the presence of non-stationary noise $\sim 1290^2$ reduced order quadrature weights must be stored. We are able to reduce the stored weights by a factor of two by partitioning our parameter space by GW frequency, with relative waveform/likelihood accuracies remaining below $10^{-5}$/$10^{-3}$ after partition. Finally, we point out that heterodyning can be combined with reduced order methods with no loss in accuracy. Our reduced order quadrature makes inspiral searches in the time domain feasible for both pulsar timing arrays and relative stellar astrometry.
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