background.

Compared to the data reduction for N05, we now use a new, improved IDL routine for the subtraction of the point spread function (PSF) of the bright GQ Lup A, before measuring the companion. The new routine centers the bright star PSF with sub-pixel precision: after rotating the PSF of GQ Lup A around its center 179 times in steps of 2 degrees, we subtract the rotated image from the original image, and then take the median of all resulting images. This gives the final PSF-subtracted image, which we use to measure the companion (for astrometry and photometry).

We re-reduced the GQ Lup data from June 2004 (published in N05) and thereby obtained slightly better (larger) values for separation and brightness, consistent with N05 within the errors. The new values are given in Table 2. The new values for GQ Lup for 2004 use the same calibration results as in N05 for pixel scale and detector orientation (Table 1), since it was not necessary to re-reduce the 2004 calibration binary observation.

Astrometry
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Since GQ Lup has right ascension 15h 49m, we always placed one observation in May (2005 and 2006), when it is visible the whole night, two 