MIRI Imaging TSOs

JWST MIRI currently has limited support for time-series observations (TSOs) with the imager.

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The MIRI imager has limited support for high precision imaging photometry in time-series observations (TSOs). Available capabilities and limitations for such observations are described below.

Sensitivity and saturation

See also: MIRI SensitivityMIRI Bright Source Limits

Sensitivities and saturation limits are available in the description of MIRI Predicted Performance.

Users should always refer to the Exposure Time Calculator (ETC) for the most accurate signal-to-noise calculations.


See also: MIRI Imaging Dithering

Contrary to regular imaging observations, TSOs should be carried out without dithering to maintain target position on the same pixels throughout the observation.

Words in bold are GUI menus/
panels or data software packages; 
bold italics are buttons in GUI
tools or package parameters.

Imaging observations with Dither set to None are currently available as a standard option only for the SUB64 subarray. Non-dithered imaging for the FULL array and other subarrays are a limited access option in the Astronomer's Proposal Tool (APT) that can only be selected by checking the Allow Restricted box in the Proposal Information form. Note that use of limited access options requires justification in the proposal text.

Filters and subarrays

See also: MIRI Filters and DispersersMIRI Detector Subarrays

All filters available for general MIRI imaging observations can be selected for TSOs.

Target acquisition

See also: MIRI Imaging Target AcquisitionJWST Pointing Performance

Target acquisition with the MIRI imager, whilst recommended for TSOs, is not currently supported. Placement accuracy of the target in the field will be determined by the telescope's blind pointing capability.

Exposure time limitations

See also: JWST Exposure Time Calculator Overview

Regular (non-TSO) MIRI imager observations have an exposure time limit of 10,000 s for a single exposure. For TSOs, this limitation can be waived to allow observations of long time-variable phenomena in a single exposure, which is optimal for stability and photometric precision. Selecting Time Series Observation in the Special Requirements pane in APT enables this waiver. 

Imaging TSOs in APT

See also: MIRI Imaging TSOs

MIRI imaging observing proposals for TSOs should use the standard MIRI imaging template, then select the Time Series Observation and No Parallel special requirements to enable the optimal TSO functionality. This will waive the exposure time limit.

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