Filter Ghosts

source: email from Tom Brown

Ambient Test UV25S01 - UVIS Ghosts

The test obtained images using the Xenon lamp and three filters: F225W, F280N, and F606W, which together give a fair representation of the full range of ghost behavior seen in the January test (when we inspected all of the UVIS filters). As written, the current test obtained a pair of unsaturated and saturated images in these 3 filters at 8 field points:
(-1600,-1600) 800x800 subarray unsaturated, 800x800 subarray saturated
(-1600,+1600) 800x800 subarray unsaturated, 800x800 subarray saturated
(+1600,-1600) 800x800 subarray unsaturated, 800x800 subarray saturated
(+1600,+1600) 800x800 subarray unsaturated, 800x800 subarray saturated
(0,+200) 200x200 subarray unsaturated, full frame saturated
(0,-200) 200x200 subarray unsaturated, full frame saturated
(0,+1000) 800x800 subarray unsaturated, 800x800 subarray saturated
(0,-1000) 800x800 subarray unsaturated, 800x800 subarray saturated

Because the ghosts appeared to be unchanged from the January tests, the last two positions were canceled during the current test.

Looking at the images, the ghosts appear to be the same, both qualitatively and quantitatively, as seen in the January tests (see WFC3 ISR 2004-04). The F225W shows a series of strong donut ghosts that move relative to the source and have a total strength of approximately 15%. The F280N shows ring-like ghosts in some positions (total strength of 5-10%), while in other positions the dominant feature is strong scattered light around the source. The F606W shows both faint donut ghosts from the window (3 ghosts at 0.1% each) and a handful of point-like ghosts (at strengths approaching 0.1% each) with a total ghost strength of approximately 0.6%.