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

February 2005 • 2005A&A...430.1027C

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

Abstract • 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 M_Jup 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.

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Patrick Lowrance

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