Fringe science: Defringing CCD images with neon lamp flat fields

摘要

Fringing in CCD images is troublesome from the aspect of photometric quality and image flatness in the final reduced product. Additionally, defringing during calibration requires the inefficient use of time during the night to collect and produce a "supersky" fringe frame. The fringe pattern observed in a CCD image for a given near-IR filter is dominated by small thickness variations across the detector, with a second-order effect caused by the wavelength extent of the emission lines within the bandpass that produce the interference pattern. We show that essentially any set of emission lines that generally match the wavelength coverage of the night-sky emission lines within a bandpass will produce an identical fringe pattern.We present an easy, inexpensive, and efficient method that uses a neon lamp as a flat-field source and produces high-S/N fringe frames to use for defringing an image during the calibration process.