2000A&A...360L..39N

We present optical and infrared spectra as well as the proper motion of an H=12mag object 2'' off the ∼5mag brighter spectroscopic binary star CoD-33 ° 7795 (=TWA-5), a member of the TW Hya association of T Tauri stars at ∼55pc. It was suggested as companion candidate by Lowrance et al. (1999ApJ...512L..69L) and Webb et al. (1999ApJ...512L..63W), but neither a spectrum nor the proper motion of the faint object were available before. Our spectra taken with FORS2 and ISAAC at the ESO-VLT reveal that the companion candidate has spectral type M8.5 to M9. It shows strong Hα emission and weak Na I absorption, both indicative of a young age. The faint object is clearly detected and resolved in our optical and infrared images, with a FWHM of 0.18'' in the FORS2 image. The faint object's proper motion, based on two year epoch difference, is consistent with the proper motion of CoD-33 ° 7795 by 5 Gaussian σ significance. From three different theoretical pre-main sequence models, we estimate the companion mass to be between ∼15 and 40M_jup, assuming the distance and age of the primary. A slight offset between the VLT and HST images with an epoch difference of two years can be interpreted as orbital motion. The probability for chance alignment of such a late-type object that close to CoD-33 ° 7795 with the correct proper motion is below 7x10^–9. Hence, the faint object is physically associated with CoD-33 ° 7795, the 4th brown dwarf companion around a normal star confirmed by both spectrum and proper motion, the first around a pre-main sequence star.