Scattered Light Features
Testing on the ground and during commissioning has uncovered a number of ways that unwanted light can find its way onto the detectors, causing various flavors of scattered light. Because these different flavors manifest themselves differently, they have been given names to identify the observed effects; thus, claws, the light saber, dragon's breath, glow sticks, and short streaks have entered the JWST lexicon.
Some of these problems are caused by light from very bright stars offset from the field of view that enters an instrument by a "rogue path" instead of reflections off the primary and secondary mirrors. Others are due to bright stars just outside the detector field of view. In the case of the glow sticks in MIRI, the origin of the light is emission from the observatory itself.
As more is learned from analysis of commissioning data as well as in real operations, it is likely that careful pre-planning may be able to avoid or at least minimize some of the effects, but they may be observed in early data until such time that they can be fully characterized and planned around. The individual instrument articles, listed below, report on these features in each instrument's data, as appropriate. If any of these effects show up on your data, contact the JWST Help Desk as your experience will help us better define and ultimately mitigate them as much as possible.
- NIRISS Instrument Features and Caveats
- NIRCam Instrument Features and Caveats
- NIRSpec Instrument Features and Caveats
- MIRI Instrument Features and Caveats