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Fig. 3


Step-wise analysis of order eight of the UVES observations obtained during the night of June 17, 2007. First panel: aligned spectra (after step 1). Second panel: residuals after subtracting the mean value from each column. Third panel: residuals after applying a high-pass box-filter with a width of 40 pixels (roughly 40 km s−1). Fourth panel: after subsequent removal of four principal components (step 5). Fifth panel: after dividing each column from the fourth panel by the standard deviation in each column (step 6). This weighs down columns that intrinsically have a lowersignal-to-noise. The strong vertical structures in the third panel are telluric water lines. These are effectively removed by the principal component analysis.

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