A second substellar companion in the Gliese 86 system

Abstract

We report observations using the ESO adaptive optics system ADONIS of the known extrasolar planetary system Gliese 86. This star has a known $4 {M}_{\mathrm{Jup}} \sin i$ planet in a 15.8 day orbit and exhibits an additional, large, long-period, radial velocity drift ([CITE]). The coronographic images reveal a faint ($J=14.7, H=14.4, K=13.7$) object at a projected distance of $r=1{.^{\prime\prime}}72 \pm 0{.^{\prime\prime}}02$ and ${\rm PA}=119\pm 1 ^\circ$. 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 dwarfassuming the classification by [CITE]. 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 ${{M}}_{\mathrm{GJ86B}} \le 70 {M}_{\mathrm{Jup}}$ can be inferred from the models by [CITE]. Dusty model atmospheres appear not to be compatible with the IR colors.