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Recipe for Slit Nodding Observations Reduction
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| XSHOOTER Pipeline:
Recipe for Slit Nodding Observations Reduction |
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For more details see the pipeline user manual at the pipelines page.
Description: The raw frames consist of a series of couples with object positions A and B on the slit. The recipe first sums all frames at the same nod position. Then it performs for each nodded pair a number of common data reduction steps, that are described here for the pair A, B. The frame A-B is computed to subtract the sky contribution at the first order. In order to detect both the positive cosmic ray hits (from A) and negative ones (from B) in A-B, the frames |A-B| and sign(A-B) are computed so that A-B = sign(A-B) x |A-B|. The cosmic ray hits are corrected using the Van Dokkum algorithm (van Dokkum 2001, PASP 113, 1420) on |A-B|, and the resulting frame is multiplied by the sign(A-B) frame. The frame A-B is flat-fielded and rectified, i.e. transformed from pixel-pixel space to wavelength-slit space. Then the spectra are localized (the positive frame is used to derive the localization of A, and its opposite to derive the position of B). The rectified B-A is taken as the opposite of A-B and shifted by an integer amount of pixels along the slit. These operations are repeated for each nod pair of (co-added) frames. Next all the |
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