16587

Throughout the lifetime of WFC3 comma a growing number of blobs (small comma circular regions with slightly decreased sensitivity) have appeared in WFC3-IR images. Dark-Earth flats (observations of the dark side of the Earth) can be used to monitor the number and positions of blobs that appear in IR images due to dust on the channel select mechanism (CSM). These flats provide a high enough background level due to the dark-Earth airglow (virgul1000 DN - virgul3500 DN per pixel in each virgul25 second SPARS25 sample for F153M) which make the blobs easier to detect. By limiting the exposure time to 102.9 seconds comma we avoid saturating the detector and yet will obtain several 25-sec samples to select from comma in case some are contaminated by city lights. In addition to monitoring the number and positions of these blobs on the IR detector comma this program will allow us to monitor the repeatability of WFC3.s channel select mechanism movements to ensure it does not exhibit anomalous behavior. More information can be found in WFC3 ISR 2018-06.