If flux calibration is not being performed it is sometimes desirable to remove the blaze function from the extracted spectrum to assist in fitting line profiles etc. during data analysis.
A task is provided for this purpose which operates by fitting polynomials to the flat-field orders. The fits may be automatically or interactively clipped and the resulting blaze spectrum is normalised such that its median intensity is unity. The normalised blaze is then divided into the extracted spectrum.
It is important to remember that this operation must be performed upon the extracted spectrum before any scrunching takes place. After a blaze function has been applied to the extracted order, the function is reset to unity to ensure that the order(s) cannot be re-flattened in error. If the blaze is to be re-applied then the correct procedure is to first re-extract the order(s) concerned and then re-fit the blaze.
A typical interactive plot appears below.
Martin Clayton