One of the advantages of the Super-COSMOS machine is that it scans the plates with a direction parallel to the longtitudinal axis of the spectra. Thus, our spectra are parallel to a coordinate axis. The success of the DETSP procedure is that it detects all the spectra at the same common-wavelength zero-point at 5400 Å. This zero-point (0.000 mm) corresponds to our pixel scale (1-128) at 10 pixels.
After the spectral detection, a new procedure starts, responsible for the extraction of spectra (EXTSP). The spectral length contains 128 pixels. These are: the zero-point plus 118 pixels on the right of zero-point plus 9 pixels in the left of zero-point. For a better signal-to-noise ratio, the actual extraction of the spectrum is performed by means of rectangular weighted "slit'' sliding on data (Balestra et al. ). Its width and shape are either fixed or determined by the average fit on the transversal sections of the spectrum.
The new zero-point defined by DETSP at 5400 Å had to be added to the dispersion curve of the objective prism P1 (Nandy et al. ). The parallel displacement in mm of zero-point gives new distance measurements for various features. The results are shown in Fig. 2 and Table 2.
The extracted spectra are stored in a two-dimensional file , where n=426 is the number of detected spectra. Every row of this file is an independent normalized spectrum with length 128 pixels (Fig. 3).
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