2001A&A...370L...1E

We report observations using the ESO adaptive optics system ADONIS of the known extrasolar planetary system Gliese 86. This star has a known 4M_Jupsini planet in a 15.8 day orbit and exhibits an additional, large, long-period, radial velocity drift (Queloz et al., 2000A&A...354...99Q). The coronographic images reveal a faint (J=14.7, H=14.4, K=13.7) object at a projected distance of r=1.72''±0.02 and PA=119±1°. Gliese 86 and the discovered object share the same proper motion, as confirmed by independent measurements at three different epochs indicating that this system is gravitationally bound. From the infrared colors and magnitudes we infer an approximate spectral type for Gliese 86B at the transition from L to T dwarfs, also called ``early T dwarf'' assuming the classification by Leggett et al. (2000ApJ...536L..35L). Although present brown dwarf evolutionary models do not cover the mass and age range probed by this objects, an upper limit of the mass of about M_GJ86B≤70M_Jup can be inferred from the models by Baraffe et al. (1998A&A...337..403B). Dusty model atmospheres appear not to be compatible with the IR colors.