The object extraction EXTRACT/MOS is done with an optimum extraction scheme using different weights for the individual rows (following Horne, 1986, PASP 98, 609). With this command also the sky is subtracted. In addition the sky frame is needed to compute the optimum weights. The object postions are taken from the table .tbl. Cosmics are removed by assigning weight zero to the affected pixels. The procedure is iterative. If the number of iterations is set to a negative number, a spectrum computed with equal weights is returned. The extracted spectra are stored in a 2-D frame, each line corresponding to one extracted object. In addition, the errors for the extracted spectra are returned, one line per spectrum, in the upper part of the same frame.
The command REB1D/MOS splits the 2-dimensional frame (produced by EXTRACT/MOS) up into 1-dimensional frames, one for each object. A root name is given and the rebinned frames are named by appending their row number to the root name. The extracted frames are rebinned to constant wavelength steps using the dispersion relation which has been obtained near the center row of the extracted objects.
If you prefer to avoid the resampling noise you can apply the
dispersion relation to each pixel of an extracted frame (table option)
without rebinning to constant wavelength steps with the command
APPLY/MOS. This command produces for each extracted object a table
with the columns :FLUX, :FLUX_ERROR, :WAVELENGTH and :BIN.