NEW MEMBERS OF THE TW HYDRAE ASSOCIATION, PICTORIS MOVING GROUP, AND TUCANA/HOROLOGIUM ASSOCIATION

We have identified five new members of the TW Hydrae association (TWA), 11 new members of the Pic moving group, and 11 new Tucana/Horologium association members. These are the three youngest (d30 Myr) known kinematic stellar groups near the Earth. Newly identified Pic group members are located mostly in the northern hemisphere, and they have a slightly different U-component of Galactic velocity compared to that of previously known members. Tracing the motion of Pic members backward in time for 12 Myr indicates that they might have formed in a small region with an initial velocity dispersion of 8 km s1. A couple of mid-M spectral type Pic members show emission features [He i 5876+6678) and Na D 5890+5896)] seen among earlier spectral type stars in the TWA and Pic groups. To derive the distances of the non-Hipparcos members of these groups, we have constructed a VK versus MK color-magnitude diagram that is very useful in separating young K/M stars from older main-sequence counterparts and constraining theoretical pre–main-sequence evolutionary tracks. All newly identified K- and M-type members of the three groups show saturated X-ray activity (LX=Lbol 103). One newly identified TWA member, SSS 1017275354, is estimated to be only 22 pc away from Earth. Its extreme youth, late spectral type (M5), and proximity to Earth make SSS 1017275354 perhaps the best target for direct imaging detection of cooling planets