2 & 3, we explain the observations, data reduction and astrometric results.

We also use the data to monitor the brightness of GQ Lup A and its companion and search for photometric variability (see Sect. 4). We note that Seifahrt et al. (2007) found emission lines in the near-infrared spectra of the companion, indicative of accretion, so some variability is expected. We then add up all imaging data thus far available to obtain a very deep and high-dynamic-range image to search for additional, fainter and/or closer companions (see Sect. 5). We note that both Debes & Sigurdsson (2006) and Boss (2006) argued that if the GQ Lup companion is a planet, it should have been moved to its current large separation ($\sim 100$ AU) from an originally closer orbit by an encounter with another more massive proto-planet, which may be detectable. We use the newly determined parameters to re-estimate some physical parameters of the GQ Lup companion in Sect. 6 and summarize our results at the end.

Observations with VLT / NACO
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We observed GQ Lup A and its companion six times from May 2005 until Feb 2007 in order to detect and monitor possible changes in separation, position 