MIRI Imaging TSOs

Time-series observations (TSOs) are fully supported for the MIRI imager.

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Sensitivity and saturation

See also: MIRI SensitivityMIRI Bright Source Limits

Sensitivities and saturation limits are available in the description of MIRI Predicted Performance. There is no difference in the sensitivities or saturation limits of the MIRI imager between "regular" and time-series observations.

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


See also: MIRI Imaging Dithering, MIRI TSO Recommended Strategies

Contrary to regular imaging observations, TSOs should be carried out without dithering to maintain target position on the same pixels throughout the observation. TSO Imaging observations should have the Dither option set to None

Filters and subarrays

See also: MIRI Filters and DispersersMIRI Detector Subarrays, MIRI TSO Recommended Strategies

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

Target acquisition

See also: MIRI Imaging Target AcquisitionJWST Pointing Performance, MIRI TSO Recommended Strategies

Target acquisition with the MIRI imager, whilst generally recommended for TSOs, is not currently supported. The pointing accuracy of TSO imaging observations is determined by the telescope blind pointing capability, which has been found to be sufficiently accurate for high-precision photometry. Even for multi-epoch programs, performance is not limited by blind pointing accuracy. Note that accurate proper motions of the targets, which are provided by the user in APT, are very important for accurate target placement. 

Exposure time limitations

See also: JWST Exposure Time Calculator Overview, MIRI TSO Recommended Strategies

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. 

The total number of groups in a single exposure, summed over all integrations, is limited to 196,608 due to onboard storage restrictions; in addition the maximum number of integrations per exposure is 65,535. Many TSOs therefore require multiple exposures to cover the full desired duration. 

Imaging TSOs in APT

See also: MIRI Imaging TSOs, MIRI TSO Recommended Strategies

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. See the MIRI TSO Recommended Strategies page for further recommendations on how to configure MIRI imaging TSOs. 

Notable updates
    Updated TA, dithering sections, added exposure time limitations
Originally published