upper mass limit of 35 M$_{\rm Jup}$ (Seifahrt et al. 2007). Thus, the companion to GQ Lup can be regarded as a [*planet candidate*]{} according to the best guess value of its mass, which is at or below the brown dwarf desert ($\sim 30$ M$_{\rm Jup}$; Grether & Lineweaver 2006), proposed as the deviding line between planets and brown dwarfs. Also, it is possible that the true mass is below 13 M$_{\rm Jup}$, a more conservative upper mass limit for planets.

The large error in the luminosity of the companion, which is used for the mass estimate from evolutionary models, is mostly due to a large distance uncertainty, assuming that the object is in Lupus I ($\pm 50$ pc, N05). Hence, a direct parallax measurement would yield a stronger contraint on luminosity and, hence, mass.

To finally confirm that the fainter object near GQ Lup is really a bound companion (rather than, e.g., another member of the Lupus I cloud not orbiting GQ Lup), one would need to see orbital motion.

For both measurements, parallax and orbital motion, we have monitored GQ Lup and its companion from 2005 to 2007 by taking six new images with Adaptive Optics. In Sects. 