2005A&A...435L..13N

We present a companion of the ≤2Myr young classical T Tauri star GQ Lup in the Lupus star forming region at 140±50pc from imaging, astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO, we detected an object 6mag fainter than GQ Lup located 0.7'' west of it. Compared to images obtained 2 to 5 years earlier with Subaru/CIAO and HST/PC, this object shares the proper motion of GQ Lup by 5 and 7σ, respectively, hence it is a co-moving companion. Its K-L' color is consistent with a spectral type early to mid L. Our NACO K-band spectrum yields spectral type M9-L4 with H₂O and CO absorption, consistent with the new GAIA-Dusty template spectrum for logg≃2 to 3 and T_eff≃2000K with ∼2R_jup radius at ∼140pc, hence few Jupiter masses. Using the theoretical models from Wuchterl & Tscharnuter (2003A&A...398.1081W), Burrows et al. (1997ApJ...491..856B), and Baraffe et al. (2002A&A...382..563B), the mass lies between 1 and 42 Jupiter masses.