A candidate substellar companion to CD -33 degrees 7795 (TWA 5)

We present the discovery of a candidate substellar object in a survey of yo ung stars in the solar vicinity using the sensitivity and spatial resolutio n afforded by the NICMOS coronagraph on the Hubble Space Telescope. The H = 12.1 mag object was discovered approximately 2" from the TW Hydrae associa tion member CD -33 degrees 7795 (TWA 5), and the photometry implies a spect ral type M8-M8.5, with a temperature of similar to 2600 K. We estimate that the probability of a chance alignment with a background object of this nat ure is less than 2 x 10(-5) and therefore postulate that the object (TWA 5B ) is physically associated at a projected separation of 100 AU, Given the l ikely youth of the primary (similar to 10 Myr), current brown dwarf cooling models predict a mass of approximate to 20M(Jup) for TWA 5B.