A new window in time: a mid-infrared slit spectroscopy mode for precision time-series astronomy with JWST/MIRI
Abstract
The Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) provides Low Resolution Spectroscopy (LRS) over 5-12 um at a resolving power of R ~ 100. To date, all MIRI LRS time-series observations (TSOs) have been carried out in slitless mode, since long-duration pointing stability within the narrow 4.7'' x 0.51'' slit could not previously be guaranteed, leading to the possibility of degraded TSOs due to jitter. Commissioning activities established the telescope jitter to be less than 1 milliarcsecond (mas), four times less than the initial requirement. It was, therefore, worth assessing the suitability of the MIRI LRS slit as a TSO mode for precision time-domain science; this is the aim of the Cycle 3 program (PID 6219, PI: A. Dyrek). We observed a transit of the exoplanet HAT-P-12b over ~10 hours and compared the results to archival slitless observations of the same target (PID 1281, PI: P.-O. Lagage). Two independent data reductions of the transit spectra of both slit and slitless configurations are consistent within 1 sigma, validating the feasibility of the new mode. A joint fit of the slit and slitless observations confirms the presence of a spectral feature near 7.5 um. Using measured JWST pointing variations, we estimated slit-loss variations to be smaller than 40 ppm at 10 um. The drawback of the slitless mode is a higher background. Compellingly, the slit background is ~ 38 times lower on average than in slitless mode, improving sensitivity for faint targets (Jmag ~ 13-15). We also identified time-correlated noise unique to the slit dataset at long wavelengths, which requires further investigation. This new capability of TSOs in slit mode, which will be supported in Cycle 7 (in 2028), opens a new avenue for precision time-series astronomy for faint targets with JWST/MIRI.
Versions
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BibTeX
@misc{dyrek2026window,
title = {{A new window in time: a mid-infrared slit spectroscopy mode for precision time-series astronomy with JWST/MIRI}},
author = {Achrene Dyrek and Taylor J. Bell and Pierre-Olivier Lagage and Sarah Kendrew and Gareb Fernandez-Rodriguez and Thomas Greene and Giuseppe Morello and Michiel Min and Mael Voyer and Hannu Parviainen},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.04110},
eprint = {2608.04110},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.04110},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A new window in time: a mid-infrared slit spectroscopy mode for precision time-series astronomy with JWST/MIRI
AU - Achrene Dyrek
AU - Taylor J. Bell
AU - Pierre-Olivier Lagage
AU - Sarah Kendrew
AU - Gareb Fernandez-Rodriguez
AU - Thomas Greene
AU - Giuseppe Morello
AU - Michiel Min
AU - Mael Voyer
AU - Hannu Parviainen
PY - 2026
DA - 2026/08/04
PB - arXiv
DO - 10.48550/arxiv.2608.04110
UR - https://arxiv.org/abs/2608.04110
AB - The Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) provides Low Resolution Spectroscopy (LRS) over 5-12 um at a resolving power of R ~ 100. To date, all MIRI LRS time-series observations (TSOs) have been carried out in slitless mode, since long-duration pointing stability within the narrow 4.7'' x 0.51'' slit could not previously be guaranteed, leading to the possibility of degraded TSOs due to jitter. Commissioning activities established the telescope jitter to be less than 1 milliarcsecond (mas), four times less than the initial requirement. It was, therefore, worth assessing the suitability of the MIRI LRS slit as a TSO mode for precision time-domain science; this is the aim of the Cycle 3 program (PID 6219, PI: A. Dyrek). We observed a transit of the exoplanet HAT-P-12b over ~10 hours and compared the results to archival slitless observations of the same target (PID 1281, PI: P.-O. Lagage). Two independent data reductions of the transit spectra of both slit and slitless configurations are consistent within 1 sigma, validating the feasibility of the new mode. A joint fit of the slit and slitless observations confirms the presence of a spectral feature near 7.5 um. Using measured JWST pointing variations, we estimated slit-loss variations to be smaller than 40 ppm at 10 um. The drawback of the slitless mode is a higher background. Compellingly, the slit background is ~ 38 times lower on average than in slitless mode, improving sensitivity for faint targets (Jmag ~ 13-15). We also identified time-correlated noise unique to the slit dataset at long wavelengths, which requires further investigation. This new capability of TSOs in slit mode, which will be supported in Cycle 7 (in 2028), opens a new avenue for precision time-series astronomy for faint targets with JWST/MIRI.
ER -