NIRISS APT Templates
A JWST observing program that uses the NIRISS instrument is designed by using the one of the NIRISS templates in the Astronomer's Proposal Tool (APT).
NIRISS offers 4 observing templates: wide field slitless spectroscopy, single object slitless spectroscopy, aperture masking interferometry, and imaging, with imaging between 0.8–5.0 μm, and slitless spectroscopy between 0.86–2.8 μm.
Step-by-step in APT
The step-by-step instructions for using the NIRISS observing templates in the APT are provided in the following articles:
- NIRISS Wide Field Slitless Spectroscopy Template Guide
- NIRISS Single-Object Slitless Spectroscopy APT Template
- NIRISS Aperture Masking Interferometry APT Template
- NIRISS Imaging APT Template
The text below provides context for each of these observing templates.
The NIRISS wide field slitless spectroscopy (WFSS) mode is designed to obtain spectra in the 0.8–2.2 μm wavelength range for every source within the 2.2' × 2.2' field of view of the NIRISS detector. One or more of the NIRISS short-wavelength imaging filters must be used as blocking elements in WFSS observations. The user can select either one of the NIRISS WFSS grisms or both of them. Use of both grisms provides orthogonal spectra of the objects within the field of view. The WFSS observations are taken in full-frame readout. This observing mode does not use subarrays. The NIRISS PSFs are under-sampled across the wavelength range used for WFSS and dithering is essential.
The NIRISS single object slitless spectroscopy (SOSS) mode is designed for exoplanet transits. SOSS allows high cadence time resolved observations and has two available subarray readout patterns, SUBSTRIP256 and SUBSTRIP96. SOSS provides two usable orders of cross-dispersed spectra for a single object in the wavelength range 0.6–2.8 μm at a resolution of R ≈ 700 in the first order when full-frame readout or the default SUBSTRIP256 subarray readout are used. In the SUBSTRIP96 subarray readout, useful data are obtained only for first order and the wavelength range is somewhat reduced. Dithering is not implemented for SOSS mode. Target acquisition (TA) is required if using a subarray, and strongly encouraged for full-frame readout. SOSS data will be processed properly in the JWST calibration pipeline only if a TA was performed.
The NIRISS aperture masking interferometry (AMI) mode offers the highest spatial resolution on JWST and allows high contrast imaging (10-4) at separations of 70–400 mas in four long-wavelength filters (≈ 2.8, 3.8, 4.3, and 4.8 μm). The NIRISS AMI mode uses an 80 × 80 pixel subarray for bright targets. Dithering is not recommended. Target acquisition (TA) is required if using a subarray.
The NIRISS imaging mode offers imaging capability over the wavelength range 0.8–5.0 μm. This mode is currently supported to be used in parallel with NIRCam imaging as the prime science instrument; NIRISS imaging will be considered as a parallel mode to MIRI imaging in future cycles. Only full frame readout is supported.
Creating an APT observation
To create a new NIRISS observation, create or choose an Observation Folder* in the tree editor and click Add in the active GUI window. This will add a generic observation to the folder and open an observation form. The observation can be assigned a unique number and a text label (which does not need to be unique). Select NIRISS from the Instrument drop-down parameter field. This populates the Template drop-down field with the NIRISS templates; select one of them to continue working on the specifics of the observation.
* Bold italics style indicates words that are also parameters or buttons in software tools (like the APT and ETC). Similarly, a bold style represents menu items and panels.
Information on all available options and restrictions for NIRISS templates are available in the proposal parameters NIRISS Templates articles.