If you are reducing GMOS data, you will need to correct the data by Quantum Efficiency.
If you see something like the figures attached, it means that you need to correct the CCD by QE.
The task to use is gqecorr.
If you find the following error running gqecorr :
Oct 14 16:54: DATABASE – 732 apertures read for ARC_S20160813S0074_1 from /Users/mmora/Dropbox/NGC6845/SCIENCE/655/database/
GQECORR ERROR – GMOS + Hamamatsu_new: no coefficients found. Exiting
You need to look for the gmosQEfactors.dat located in …./ifudrgmos/gmos/data
then replace it is the file you can download from the comment below.