Evidence for a co-moving sub-stellar companion of GQ Lup

Abstract

We present a companion of the ≤2 Myr young classical T Tauri star GQ Lup in the Lupus star forming region at 140 ±50 pc from imaging, astrometry, and spectroscopy. With direct K-band imaging using VLT/NACO, we detected an object 6 mag 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 1σ, 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 H 2O and CO absorption, consistent with the new GAIA-Dusty template spectrum for log g ≃ 2 to 3 and Teff ≃ 2000 K with ∼2 Ajup radius at ∼140 pc, hence few Jupiter masses. Using the theoretical models from Wuchterl & Tscharnuter (2003), Burrows et al. (1997), and Baraffe et al. (2002), the mass lies between 1 and 42 Jupiter masses. © ESO 2005.