A second substellar companion in the Gliese 86 system^*

A brown dwarf in an extrasolar planetary system

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
² Universität Heidelberg, Institut für Theoretische Astrophysik, Tiergartenstr. 15, 69121 Heidelberg, Germany
³ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁴ University of California Berkeley/Center for Adaptive Optics, 601 Campbell Hall, Berkeley, CA 94720, USA
⁵ DSM/DANIA/Service d'Astrophysique, CEA/Saclay, 91191 Gif-sur-Yvette, France
⁶ Institut für Astronomie, Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria

Corresponding author: S. G. Els, sels@kso.tls-tautenburg.de

Received: 1 February 2001
Accepted: 22 February 2001

Abstract

We report observations using the ESO adaptive optics system ADONIS of the known extrasolar planetary system Gliese 86. This star has a known planet in a 15.8 day orbit and exhibits an additional, large, long-period, radial velocity drift ([CITE]). The coronographic images reveal a faint () object at a projected distance of and . 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 [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 can be inferred from the models by [CITE]. Dusty model atmospheres appear not to be compatible with the IR colors.