WFPC2 Flatfields with Reduced Noise

We examine the noise contributed by the WFPC2 flatfields during normal calibration, and provide new low-noise flats for 41 filters. Highly exposed science images (>20,000 electrons per pixel) will show significant noise reduction if these new flats are used; this is especially true for images on the PC1 chip. For some ultraviolet filters a significant improvement occurs even for much lower exposure levels. Potential photometric issues are also discussed. The new flats are available in the HST data archive as “correction” images which observers can multiply into calibrated science data (i.e. data which have already calibrated with the normal flatfields) to obtain the noise reduction. These corrections may be incorporated in the normal pipeline flatfields at some future date for selected filters.