The MIRI/MRS Library. III. Detector-based optimal spectral extraction and high-contrast imaging applications
Year: 2026
Type: article
Abstract: The James Webb Space Telescope (JWST) has now been operational for five years, and the associated data reduction pipelines have reached maturity. For the Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS), one can generally get a good-quality spectrum by simply running the standard pipeline, especially for unresolved sources. However, users are starting to look deeper into the data, trying to detect the smallest features in the faintest objects, and find close companions. Following the lower level corrections we derived in Papers I and II in this series, we now introduce a novel way to extract MIRI/MRS spectra: from the detectors directly. Currently the most common way to analyse data from integral field spectrometers, such as the MRS, is to reconstruct a spectral cube from the detector images. Theoretically, detector-extracted spectra could reach higher signal-to-noise ratios (S/Ns), and better handle bad pixels. We applied the charge migration and fringe corrections derived in Papers I and II to generate stable and well-sampled point-spread function (PSF) models using the sub-pixel scan of calibration star 10 Lac observed in PID 3779 during Cycle 2. These PSFs were used in a detector-based optimal extraction algorithm building on past approaches, where the contributions per pixel were weighted by their noise properties and contribution to the total illumination. Furthermore, the PSF models were used to subtract the PSF of a bright central source from the detector, both by direct subtraction, and a principal component analysis (PCA) approach. We find that our optimal setup allows us to get a $>$1.5 times higher S/N on a faint source compared to the standard pipeline cube extraction. However, we approximately matched more involved cube processing, for which the extraction aperture is smaller and the background subtraction was performed more optimally. We were also able to subtract the PSF down to sub-percent levels, allowing us to extract spectra from faint companions. Currently, the high-contrast imaging extraction quality falls short of a cube-based extraction. The novel approach greatly improves on the current standard pipeline reduction, but it is only able to match the performance of more optimised cube processing. We have not yet reached the fundamental noise limits. However, there are clear points of improvement that can be addressed using additional data. We demonstrate that detector-based processing of MIRI/MRS data has great potential for the characterisation of faint sources and close companions.
Source: Astronomy and Astrophysics
Language: English
Subfield: Instrumentation
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Aeronautics and Space Administration, Northrop Grumman, Utah State University, California Institute of Technology, University of Bern, Space Telescope Science Institute, European Space Agency, University of Leicester, University College London, Cardiff University, Enterprise Ireland, Dublin Institute for Advanced Studies, Universiteit Leiden, Rijksuniversiteit Groningen, Universiteit van Amsterdam, Belgian Federal Science Policy Office, Centre National d’Etudes Spatiales, Chalmers Tekniska Högskola, Eidgenössische Technische Hochschule Zürich, Nederlandse Organisatie voor Wetenschappelijk Onderzoek, Ministerio de Economía y Competitividad, Paul Scherrer Institut, Universität zu Köln, Instituto Nacional de Técnica Aeroespacial, Max-Planck-Institut für Astronomie, Ames Research Center, Jet Propulsion Laboratory, Goddard Space Flight Center, Science and Technology Facilities Council, Consejo Superior de Investigaciones Científicas, Research Ireland
OpenAlex ID: W7223357672