2005A&A...430.1027C

We report VLT/NACO imaging observations of the stars GSC 08047-00232 and HIP 6856, probable members of the large Tucana-Horologium association. During our previous ADONIS/SHARPII deep imaging survey, a substellar candidate companion was discovered around each star. Based on VLT/NACO astrometric measurements, we find that GSC 08047-00232 and the faint candidate companion near to it share the same proper motion with a significance of 3.1σ. On the contrary, the candidate companion to HIP 6856 is probably a background object with a significance of 4.3σ. We also detect a new fainter and closer candidate companion to HIP 6856, but which is likely a background object too with a significance of 4σ. Recent VLT/NACO spectroscopic measurements of GSC 08047-00232 finally confirm the substellar nature of this young brown dwarf with a derived spectral type M9.5±1. GSC 08047-00232B, with an estimated mass of 25±10M_Jup and an effective temperature of 2100±200K, is presently the third substellar companion identified among young, nearby associations.