Home
LibraryD. Gasman (MPIA Heidelberg), I. Argyriou (KU Leuven), D.R. Law (STScI), S. Juillard (Univ. of Arizona, Nat. Astron. Obs. Japan), V. Christiaens (Univ. Paris-Saclay, KU Leuven, Univ. Liege), O. Absil (Univ. Liege), A. Glasse (Roayl Obs. Edinburgh), K.D. Gordon (STScI), P.J. Kavanagh (Maynooth Univ.), J.E. Morrison (Univ. Arizona), P. Patapis (ETH Zürich), G.C. Sloan (STScI, UNC Chapel Hill)
2026, A&A, submitted
Context. 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.
Aims. 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 like the MRS, is to reconstruct a spectral cube
from the detector images. Theoretically, detector-extracted spectra could
reach higher S/N, and better handle bad pixels.
Methods. We apply 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 are used in a detector-based optimal
extraction algorithm building on past approaches, where the contributions
per pixel are weighted by their noise properties and contribution to the
total illumination. Furthermore, the PSF models are used to subtract the
PSF of a bright central source from the detector, both by direct
subtraction, and a principal component analysis (PCA) approach.
Results. 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 match more involved cube processing,
where the extraction aperture is smaller and the background subtraction is
performed more optimally. We are also able to subtract the PSF down to
percent and 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.
Conclusions. The novel approach greatly improves on the current standard
pipeline reduction, but is only able to match the performance of more
optimised cube processing. 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.
Last modified 21 September, 2026. © Gregory C. Sloan and others.