2005A&A...430L..49S

We have used archival survey data, most importantly from the SuperCOSMOS Sky Surveys, to derive accurate proper motions and thus confirm the membership of two previously announced isolated brown dwarfs in the nearby, ∼10Myr old TW Hydrae Association (TWA), 2MASSW J1207334-393254 and 2MASSW 1139511-315921 (Gizis, 2002ApJ...575..484G), and to discover a new substellar candidate. This new object, SSSPM J1102-3431, has extremely red optical, optical-to-infrared, and near-infrared colours (R-I=3.2, I-J=3.4, J-K_s=1.15), while low-resolution not only classifies it as a late-type (M8.5) object, but also shows spectral signatures of low gravity as expected for a young brown dwarf. If it is a true TWA member, brown dwarf cooling models predict its mass to be ∼20M_Jup. SSSPM J1102-3431 lies only ∼12-arcmin away from the T Tauri star TW Hya and their proper motions agree to within the errors, and thus it is possible that the two objects form an extremely wide binary system, with a separation of ∼40000AU at d=56pc. We have also obtained improved proper motions for SSS 120727.4-324700 and SSS 101726.7-535428, recent additions to the list of TWA members (Song et al., 2003ApJ...599..342S). The relatively large proper motion of the latter object is consistent with the suggested proximity (d∼22pc) of this lowest-mass stellar representative of the TWA.