Flat Fields for Simulated Mid- Infrared JWST Images

Self-calibration flat fields are compared to super-sky flat fields for simulated JWST images in this report which is a continuation of the investigation presented in Casertano & Holfeltz 2002. Self-calibration flats derived from 10 or 100 dithered exposures with a com-bined exposure time of 100 ksec typically result in flat fields which are good to approxi-mately 1 % at 2 microns and 0.03 % at 20 microns. Super-sky flats derived from 10-100 chopped or dithered exposures totalling 100 ksec exposure time yield flats good to 1.6 % at 2 microns and 0.04 % at 20 microns. Dithering the science data was found to be crucial in obtaining satisfactory calibrations, regardless of the provenance of the applied flat field. Both methods come within 20 % of the results expected for a perfect flat field without espe-cially aggressive observation planning, as long as proper dithering is used