WFC3/UVIS Shutter Characterization

A series of internal flat field images and standard star observations were obtained to check the shutter performance. The series of images were similar to the ones taken during SMOV so that the performance of the shutter could be compared with the performance during SMOV in 2009, and check if the behavior of shutter mechanism has changed in the meantime. The flat field images show that the intensity of the flat field lamp has decreased by about 1.6 +/0.2% over the past 6 years. Our observations are consistent with the earlier finding that the variation in exposure time across the detector due to shutter shading is less than 0.1%. The standard star observations show that there is no noticeable difference in the present performance of the shutter mechanism compared to its performance during SMOV.