the data to the dusty GAIA model atmospheres confirmed the temperature and luminosity of the companion given in N05 and revised its radius to $0.38 \pm 0.05$ R$_{\odot}$, yielding a mass between 10 and 20 M$_{\rm Jup}$. McElwain et al. (2007) then obtained higher-resolution spectra (R $\simeq 2000$) of the GQ Lup companion in the J- and H-bands with the integral field spectrograph OSIRIS at Keck and found a slightly higher temperature (M6-L0) than in N05 (M9-L4), explained by the fact that H$_{2}$ collision-induced absorption is important for low gravity objects according to Kirkpatrick et al. (2006), but not considered in N05.

Higher-resolution spectra in the J-, H-, and K-bands taken with VLT/Sinfoni compared to GAIA-2 models could better constrain the parameters of the companion: the temperature is $2650 \pm 100$ K, the gravity $\log~g = 3.7 \pm 0.5$ dex, and the radius $3.5^{+1.50} _{-1.03}$ R$_{\rm Jup}$ (Seifahrt et al. 2007). Hence, its mass can be as low as few M$_{\rm Jup}$, but also much higher. Comparing its parameters with 2M0535 A & B, where masses have been determined dynamically (an eclipsing double-lined binary brown dwarf in Orion, similar age as GQ Lup, Stassun et al. 2006), could give an 