2003/12/01 by Inseok Song, B. Zuckerman, M. S. Bessell · 7 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #Astro and Planetary Science
paper · pdf · doi:10.1086/379194
openalex publication_date 2003/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We have identified five new members of the TW Hydrae association (TWA), 11 new members of the β Pic moving group, and 11 new Tucana/Horologium association members. These are the three youngest (≲30 Myr) known kinematic stellar groups near the Earth. Newly identified β 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 β 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 s -1 . A couple of mid-M spectral type β Pic members show emission features [He I λ5876+λ6678) and Na D λ5890+λ5896)] seen among earlier spectral type stars in the TWA and β Pic groups. To derive the distances of the non- Hipparcos members of these groups, we have constructed a V-K versus M K 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 ( L X / L bol ~ 10 -3 ). One newly identified TWA member, SSS 101727-5354, is estimated to be only 22 pc away from Earth. Its extreme youth, late spectral type (~M5), and proximity to Earth make SSS 101727-5354 perhaps the best target for direct imaging detection of cooling planets.