3.2.1 Preliminary Reduction

• setinstrument specphot: Sets up ccdred parameters.
• zerocombine: Average all of the bias frames separately for each night of observing.
• ccdproc: Apply zero correction to all frames using the appropriate zero image for each individual night. The trim section and bias section are specified during this process. Also, any bad CCD columns can be removed at this time using the fixpix parameter once you have constructed a bad pixel map.

• flatcombine: Average together the flat field images taken for each mask separately. Scale by the exposure time if necessary.

• apflatten: This routine flattens the flat field for each mask leaving an image which represents the pixel-to-pixel gain variations in the CCD. Presently you have to load this from the noao.twodspec.apextract package. The resulting flat-field no longer has spatial (slit-function) information, but this is appropriate for quartz exposures. During this task, the apertures must be defined and traced. Make certain that you explicitly set the "width" parameter to the width of the full slit using the colon command (i.e., :width=30) once within this task, or the trace will not work correctly. Each aperture must be fit with an appropriate polynomial to remove the overall shape of the quartz lamp flat. We suggest function=spline3 and order=90 with nit=3 for flattening the spectra.

• ccdproc: Apply the flat field correction to each individual mask image (object images as well as the comparison lamp images) being sure that the flattened image corresponds to the same mask as the object and comparison images it is being applied to.

• setjd *.imh Set the jd in all the image headers; this will be used in refspec below.