2005AJ....129.2294M

To search for thermal emission from substellar companions, we have obtained Z-band images of 15 weak-lined T Tauri stars in the Taurus-Auriga and Ophiuchus star-forming regions using the Planetary Camera 2 on the Hubble Space Telescope. We found 18 faint nearby objects at separations larger than 4" but none at smaller separations. For 11 of these we have enough color information to suggest that they are not substellar members of the star-forming regions. The remaining seven faint nearby objects are candidate substellar objects. Our detection limit for companions with separations larger than about 1" is apparent Z=19.5 mag, corresponding to substellar objects in the mass range 3M_J-15M_Jfor the age range of our targets, 1.2-25 Myr. Our detection limit degrades for smaller separations and is 4-6 mag poorer at a separation of 0".2, corresponding to a projected separation of 30 AU. Inside 0".2 our sensitivity is insufficient to detect substellar companions. To complement the imaging program, extensive spectroscopic observations were obtained with the Center for Astrophysics Digital Speedometers. Four of our targets proved to be spectroscopic binaries, one of them double-lined. We report orbital solutions for these four stars. Our radial velocities support the membership of all our targets to their respective star-forming regions, except for HD 283759, which must be rejected as a member.