As its name suggests, the Single-Object Slit-less Spectroscopy (SOSS) mode of NIRISS is slit-less and thus the spectrum of a target star may be contaminated by partly overlapping spectra of nearby stars. For a given target, the details of this potential contamination are a function of the Aperture Position Angle (APA) at which the observations are taken. This tool simulates SOSS observations of a given target and produces an estimate of the level of contamination as a function of the APA of the observation; it may be used to plan observations at the optimal APA. The tool also computes the JWST accessibility windows of the target, along with the corresponding accessible PAs for NIRISS observations.
Important! Before September 26, 2017, there was an inconsistency in the definition of the APA used for this tool and and that used in APT. This has now been fixed, i.e. the APA here and in APT are the same. If you had used this tool prior to 2017 September 26 to plan observations, please re-do your calculations. Sorry for the inconvenience.