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Hubble Space Telescope
New COS/FUV Flat-Field and Flux-Calibration at LP3

A new COS FUV flat-field reference file has been derived for use with Lifetime Position 3 (LP3) data and delivered for use in the archive. This new reference file provides a correction for low-order detector response variations (L-flat) observed on both the FUVA and FUVB detectors. At COS/FUV LP3, the low-order detector response variations are different for the three gratings, while at LP2, a single L-flat was derived for all gratings. Therefore, at LP3 each grating has its own L-flat correction in the new reference file. The magnitude of these variations is up to ~9% for FUVA and ~3% for FUVB, with structure changing most for each grating at the edges of the detectors.

Additionally, a new flux calibration has been derived for all COS/FUV gratings and cenwaves at LP3, except for G130M/1055 and G130M/1096 which remain at LP2.

Together, the new flat-field and flux calibrations bring the absolute flux calibration of all COS/FUV modes at LP3 to within 5%.

Users who have COS FUV data obtained after February 9th, 2015 are advised to re-retrieve their data from the archive to get the most up-to-date calibrations. The flat-field and flux calibration reference files should be applied simultaneously to calibrate LP3 data.