8.3 Dark Frames

Dark frames are long exposures that are taken with no light incident on the CCDs. They are used to detect CCD counts (the dark current) caused by thermal processes at the interfaces between the silicon and oxide layers, as well as charged particle and secondary radiation events. Estimated dark current and cosmic ray event rates are given in Dark Backgrounds and Cosmic Rays, respectively. Observers are cautioned that the calibration provided by the pipeline may not use the most up-to-date dark frames until several weeks after the observation is taken. The time delay is the time it takes for coeval dark frames to be taken, archived, and processed into dark reference files, and delivered for use in the pipeline and OTFC. Use of optimal darks can be important due to the new hot pixels continually being generated. Each week of observations typically has one applicable (optimum) dark reference file.