Effect of CCD Photometric Calibration on Precise Measurement of Stellar Images

In the highly precise CCD measurement of a stellar image for its position and photometry, some researchers use CCD photometric calibration but the others do not. Whether we need to do this calibration or not in the future precise measurement of some stellar images? In order to answer this question, we have taken some real images and done this calibration correction by using a linear photometric response model. The experimental results have revealed that the photometric calibration corrections for a faint star (~16 mag) have nearly 0.2 mag and 0.02 pixel in its photometry and in its position, respectively. These corrections for a bright star (~10 mag), however, decrease to about 0.02 mag and 0.002 pixel in its photometry and its position, respectively. Obviously, we should be carefully concerned with a faint stellar image for its highly precise measurement, especially for its photometry.