LONG-TERM VARIATION OF THE SHUTTER DELAY TIME OF Y4KCAM OF THE CTIO 1.0 M TELESCOPE

We investigate the long-term spatial drift of the center and the temporal variation of the shutter delay time map of Y4KCam mounted on the CTIO 1.0~m telescope. We have collected shutter delay time maps over eight years as a part of our long-term survey program. We find that the center of the shutter delay time map can drift up to 450 $\mu$m, equivalent to $\approx$ 30 pixels, on the CCD. This effect can result in a small amount of error in integration time without the proper shutter delay time correction, but it does not appear to cause any significant problems in photometric measurements. We obtain a mean shutter delay time of 69.1 $\pm$ 0.8 ms and find no temporal variation of the shutter delay time of Y4KCam over eight years, indicative of the mechanical stability of the shutter. We suggest that using a master shutter delay time correction frame would be sufficient to achieve high precision photometry, which does not exceed photometric errors $\approx$ 1.7 mmag across the CCD frame for exposure times longer than 1 s.