Fig. 1
![thumbnail](/articles/aa/full_html/2011/06/aa16231-10/aa16231-10-fig1.jpg)
Upper panel: the range of airmass covered during the run. Mid and bottom panels: the variation around the median values of the position of the centroid of the stellar psf on the detector. The positions of those images that were discarded because of pointing jumps whose amplitude is larger than the plotted range are not shown for the sake of clarity.
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