Astrometric and spectroscopic confirmation of a brown dwarf companion to GSC 08047-00232. VLT/NACO deep imaging and spectroscopic observations

G. Chauvin (1) , A.-M. Lagrange (1) , F. Lacombe , C. Dumas , D. Mouillet (1) , B. Zuckerman , E. Gendron , I. Song , J.-L. Beuzit (1) , P. Lowrance , T. Fusco

1 LAOG - Laboratoire d'Astrophysique de Grenoble

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 3.1 σ. On the contrary, the candidate companion to HIP 6856 is probably a background object with a significance of 4.3 σ. 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 4 σ. Recent VLT/NACO spectroscopic measurements of GSC 08047-00232 finally confirm the substellar nature of this young brown dwarf with a derived spectral type M 9.5±1. GSC 08047-00232 B, with an estimated mass of 25±10 MJup and an effective temperature of 2100±200 K, is presently the third substellar companion identified among young, nearby associations. Based on observations obtained at the VLT in ESO with programs 70.C-0677 and 072.C-0644.

G. Chauvin, A.-M. Lagrange, F. Lacombe, C. Dumas, D. Mouillet, et al.. Astrometric and spectroscopic confirmation of a brown dwarf companion to GSC 08047-00232. VLT/NACO deep imaging and spectroscopic observations. Astronomy and Astrophysics - A&A, 2005, 430, pp.1027-1033. ⟨10.1051/0004-6361:20041353⟩. ⟨hal-00398116⟩