Non-uniformities in the COS FUV detectors produce fixed-pattern noise in observed spectra. The most prominent of these features, including low-order response variations and the depressions caused by grid-wire shadows, are corrected by the CalCOS pipeline through the FLATFILE reference file. However, smaller scale pixel-to-pixel variations still remain in the spectra.
1D flat fields (P-flats) that correct residual, localized, fixed pattern noise have shown positive results in testing but are not yet ready for full implementation in the pipeline. While final pipeline changes and reference files for this correction are still undergoing investigation and testing, the COS team is making the preliminary files available to all users on a "use at your own risk" basis.
At this time files are available only for the standard modes of the G130M and G160M gratings. Only high S/N observations will benefit from this calibration. For more information on these corrections or about obtaining the files, please contact the help desk at email@example.com.