  Neuhaeuser et al. (2005) presented direct imaging evidence for a sub-stellar
companion to the young T Tauri star GQ Lup. Common proper motion was highly
significant, but no orbital motion was detected. Faint luminosity, low gravity,
and a late-M/early-L spectral type indicated that the companion is either a
planet or a brown dwarf. We have monitored GQ Lup and its companion in order to
detect orbital and parallactic motion and variability in its brightness. We
also search for closer and fainter companions. We have taken six more images
with the VLT Adaptive Optics instrument NACO from May 2005 to Feb 2007, always
with the same calibration binary from Hipparcos for both astrometric and
photometric calibration. By adding up all the images taken so far, we search
for additional companions. The position of GQ Lup A and its companion compared
to a nearby non-moving background object varies as expected for parallactic
motion by about one pixel (2 \pi with parallax \pi). We could not find evidence
for variability of the GQ Lup companion in the K-band (standard deviation being
\pm 0.08 mag), which may be due to large error bars. No additional companions
are found with deep imaging. There is now exceedingly high significance for
common proper motion of GQ Lup A and its companion. In addition, we see for the
first time an indication for orbital motion (about 2 to 3 mas/yr decrease in
separation, but no significant change in the position angle), consistent with a
near edge-on or highly eccentric orbit. We measured the parallax for GQ Lup A
to be \pi = 6.4 \pm 1.9 mas (i.e. 156 \pm 50 pc) and for the GQ Lup companion
to be 7.2 \pm 2.1 mas (i.e. 139 \pm 45 pc), both consistent with being in the
Lupus I cloud and bound to each other.
