MIRI WFSS APT Template
Instructions for filling out the Astronomer's Proposal Tool (APT) MIRI WFSS template are provided in this article.
On this page
An observation in the MIRI WFSS mode proceeds as described in MIRI Wide Field Slitless Spectroscopy. Further information and guidance on executing these steps are described below.
Generic parameters
Words in bold are GUI menus/
panels or data software packages;
bold italics are buttons in GUI
tools or package parameters.
Coordinated Parallel observations
See also: JWST Parallel Observations
MIRI WFSS supports coordinated parallel observations with NIRCam. When the Coordinated Parallel box (visible when the Template parameter is set to MIRI Imaging) is checked, MIRI-NIRCam Imaging can be selected. Note that the default option is None Selected.
MIRI Wide Field Slitless Spectroscopy tab
Science (dispersed) exposures
Dither
By default, direct pre- and post-WFSS images are taken as a single exposure, not dithered. The post-WFSS image can, however, be taken with a 3-point dither pattern to image any out-of-field sources that may be partially dispersed into the science field.
The dispersed exposures must use a dither pattern. STScI offers the default imager CYCLING pattern for maximum flexibility in the number of dither points. A minimum of 4 dither points are recommended to provide enough redundancy. It offers 3 different pattern sizes, with CYCLING-LARGE considered the default.
The CYCLING pattern consists of 311 points. This pattern is a random Gaussian pattern designed to be flexible. Observers will be able to choose (1) the starting position in the dither table and (2) the number of dither positions to maximize observational flexibility. For observers who request more than 311 dither positions, the CYCLING pattern will wrap so that the 312th dither position is the same as the 1st position. Each set of 4 consecutive dithers provides complete ½ pixel sampling.
Users are strongly encouraged to check their observation by visualizing it with the Aladin Viewer.
Sequences
Specify:
- Disperser: The only available option is P750L.
- Readout Pattern: FASTR1 (default), SLOWR1, or FASTGRPAVG8.
- Groups/Int
- Integrations/Exp
- Optional ETC ID (optional)
Direct image exposure parameters
See also: MIRI Wide Field Slitless Spectroscopy, MIRI WFSS Recommended Strategies
Direct Images
A typical WFSS observation will obtain direct images of the field both prior to and after the dispersed exposure sequence, the pre- and post-images. At the last dither position of the dispersed exposure sequence, an image is taken of the scene with the same filter as the pre-image; this is called the "post-image." This "post-image" can optionally be executed with two extra dithers to image sources that have partial traces in the dispersed image. The direct pre- and post-WFSS imaging must use the same filter.
Specify:
- Readout Pattern: This is set automatically by the choice made in Sequences.
- Filter: F560W, F770W, F1000W, F1130W, F1280W, F1500W
- Groups/Int
- Integrations/Exp
- Two Extra Dithers: Whether or not to execute two additional dithers for the post-image. Options are YES or NO (default).
- Optional ETC ID
All exposures display
Exposures
This section records the choices made in Sequences and Direct Images and presents the order of the observations: direct imaging, then WFSS, and followed by direct imaging again. It also presents calculated quantities Total Dithers, Total Integrations, and Total Exposure Time.
Other tabs
Mosaic Properties
See also: JWST Mosaic Overview
See also: 
Specifying Mosaics in APT
The MIRI WFSS may be used to obtain data over a larger area using a mosaic strategy.
Special Requirements
A variety of observatory level Special Requirements may be chosen under the Special Requirements tab. Observations requiring a second sequence with a different spectral orient, to aid with contamination issues, should link the observations with the PA Offset Link Special Requirement.
Comments
The Comments field (under the Comments tab) should be used for observing notes.