A young binary brown dwarf in the R-CrA star formation region

¹ Max-Planck Institut für extraterrestrische Physik, Giessenachstraße 1, 85748 Garching bei München, Germany e-mail: hbouy@mpe.mpg.de
² European Southern Observatory, Karl Schwarzschildstraße 2, 85748 Garching bei München, Germany
³ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, 414 rue de la piscine, 38400 Saint-Martin-d'Hères, France e-mail: Xavier.Delfosse@obs.ujf-grenoble.fr
⁴ Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: brandner@mpia.de
⁵ Instituto de Astrofisica de Canarias, 38200 La Laguna, Spain e-mail: ege@ll.iac.es
⁶ Centre de Recherche Astronomique de Lyon (UML 5574), École Normale Supérieure, 69364 Lyon Cedex 07, France e-mail: [fallard;ibaraffe]@ens-lyon.fr
⁷ Canada-France-Hawaii Telescope Corporation, PO Box 1597, Kamuela 96743, USA e-mail: forveille@cfht.hawaii.edu
⁸ Institut d'Astrophysique de Paris, 98bis, Bd Arago, 75014 Paris, France e-mail: demarco@iap.fr

Received: 30 December 2003
Accepted: 29 April 2004

Abstract

We present imaging and spectroscopic observations with HST (WFPC2, ACS/HRC and STIS), VLT (FORS2) and Keck (HIRES) of the dM 8 ultra-cool dwarf DENIS-P J185950.9-370632, located in the R-CrA region. The presence of lithium absorption at 670.8 nm and the strong Hα emission indicate a young age and a sub-stellar mass. Our diffraction-limited images resolve a companion at the separation limit of HST/ACS (~006). The 2.1 mJy flux in the LW2 filter (5.0-8.5 μm) of the Infrared Space Observatory [CITE] likely corresponds to an infrared excess, suggesting the presence of circumstellar material. Proper motion and photometric measurements, as well as the Hα activity, confirm membership in the R-CrA star forming region. If confirmed by further observations, DENIS-P J185950.9-370632 would be the first accreting sub-stellar multiple system observed to date.