txdump phot.dat OTIME,MAG “LID ==1”,MAG “LID ==2” > obj1phot.dat
Normalizing the flats:
The “response” function within the “twodspec” spectroscopy tool, “longslit”. Response allows us to fit a spline across the flat data and normalize it accordingly.
Then, the most appropriate flat field available for each scientific spectrum is extracted from a region covering exactly the same pixels covered by the scientific spectrum, collapsed to a 1D spectrum along the dispersion direction, and normalized to one. The region that does not contain a significant fringing pattern is then flattened exactly to 1, to avoid adding extra noise to the scientific spectra. Finally, this specially prepared 1D spectroscopic flat is aligned to the scientific spectra and scaled until the residuals of the fringing pattern were minimized, using the IRAF “telluric” task, and applied to scientific spectra to correct them for fringing.