Contamination & Visibility Calculator

This tool estimates spectral contamination and scheduling visibility for supported JWST slitless time-series modes. It places Gaia field sources on the detector at each position angle, simulates overlap with the target spectrum, and reports the expected contamination as a function of position angle. The visibility calculation provides the dates and telescope orientations available for the selected target, instrument, and epoch.

Important limitations

• Field sources come from Gaia DR3. Coordinates are propagated from the Gaia reference epoch to the selected epoch when proper-motion measurements are available. Sources absent from Gaia or lacking a valid Gaia G-band flux are not included.
• Relative source brightness is currently normalized using Gaia G-band flux. This approximation can be inaccurate when the target and contaminant have substantially different optical-to-infrared colors.
• Trace-placement and distortion uncertainties can shift predicted spectral overlap by several detector pixels.

Questions or unexpected results can be reported through the JWST Help Desk.