observations three months earlier (Feb 2006 and 2007) and two more observations three months later (July/Aug 2005 and 2006), when GQ Lup is still visible at the end or start of the night, respectively, so that we can use the data not only for proper motion and photometric monitoring, but also for trying to determine the absolute or relative parallaxes of GQ Lup A and its companion.

For the astrometric calibration, we observed the Hipparcos binary star HIP 73357 in each run. See the online appendix for more information and Table 1 for the results.

[llccc|rr|rr]{}\
Epoch & Date of & No. (a) & FWHM & Re- & &\
year & observation & images & \[mas\] & mark & value & abs. err. & change & rel. err. & value & abs. err. & change & rel. err.\
2004.48 & 25 Jun 2004 & 27 & 64 & (b) & $13.23  \pm 0.05 $ & (b) & $0.14 \pm 0.25$ & (b)\
2005.40 & 27 May 2005 & 18 & 74 & & $13.240 \pm 0.050$ & $0     \pm 0.001$ & $0.21 \pm 0.33$ & $0     \pm 0.007$\
2005.60 & 7/8 Aug 2005 & 15 & 63 & (c) & 