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MASTER_FLATs L(ower) and U(pper CCD), with the echelle orders slightly inclined from left to right. The central white boxes (100x300 pixels wide) mark the windows used for the statistical analysis. The large-scale fringes appear very prominently on both CCDs. The closeups obviously are too small to catch these structures but there is also a lot of small-scale structure. |
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Closeup of masters L and U, with the pixels from the analysis boxes extracted. Horizontal axis is dispersion (X), vertical axis is slit coordinate, Y. 3 (2) orders are fully visible. The inclined dark strip is part of the slit function. The L frame shows strong interference patterns of typical size 10 px, plus more extended structure. The U frame shows only faint extended structure. |
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Difference frames of the first two raw frames used
for creating the MASTER_FLATs. Differences in pixel intensity are
purely statistical (photon noise). The black interorder areas have
been masked to avoid contribution to the statistical analysis. Orientation of all raw frames is rotated by 90 degrees. |
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X-derivative frames. The first raw frame of the stack has been shifted in X by 1 px and subtracted. The result frames (for U and L areas) show any structure in X (dispersion) direction enhanced. The L frame has strong fringes, plus an absorption line in the middle order. The U frame shows some faint extended structure. Gain fluctuations are randomized. Interorder space is masked to not contribute to the resulting std dev. |
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Y-derivative frames. The first raw frame of the stack has been shifted in Y by 1 px and subtracted. The result frames (for U and L areas) show the Y-structure enhanced. Both L and U frames show the slit function very clearly. The L frame shows strong fringing in addition. The U frame has faint extended structure in the same way as the X-derivative. Interorder space is masked. |