DISCOVERY OF SEVEN T TAURI STARS AND A BROWN DWARF CANDIDATE IN THE NEARBY TW HYDRAE ASSOCIATION

摘要

We report the discovery of five T Tauri star systems, two of which are resolved binaries, in the vicinity of the nearest known region of recent star formation: the TW Hydrae Association. The newly discovered systems display the same signatures of youth (namely high X-ray flux, large Li abundance, and strong chromospheric activity) and the same proper motion as the original five members. These similarities firmly establish the group as a bona fide T Tauri association, .unique in its proximity to Earth and its complete isolation from any known molecular clouds. At an age of ~10 Myr and a distance of ~50 pc, the association members are excellent candidates for future studies of circumstellar disk dissipation and the formation of brown dwarfs and planets, Indeed, as an example, our speckle imaging revealed a faint, very likely companion 2" north of CD -33deg 7795 (TWA 5). Its color and brightness suggest a spectral type of ~M8.5 which, at an agc of ~10~7 yr, implies a mass ~20M_jup.