Removal of Interference Fringes in Images from the YNAO 2.4m Telescope and the Impacts on Photometry

Interference fringes are obviously present in some CCD images obtained by the YFOSC camera on the 2.4m telescope at the Lijiang station of the Yunnan Observatory. This is especially the case for images taken with long-wavelength bandpasses, such as the Johnson I bandpass. As an experiment to remove interference fringes we created a "supersky" image by stacking a series of CCD images of the open cluster NGC 2324 observed by the telescope in the I bandpass. After subtracted by the "supersky", which contains the pattern of the interference fringes, the observed CCD images of the cluster become greatly improved in quality, and the photometric precisions of faint stars in the images are about twice better than without the "supersky" subtraction.