Astrophys. J., 599, 342-350 (2003/December-2)
New members of the TW Hydrae association, β Pictoris moving group, and Tucana/Horologium association.
SONG I., ZUCKERMAN B. and BESSELL M.S.
Abstract (from CDS):
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. 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 MKcolor-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∼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.
Galaxy: Open Clusters and Associations: Individual: Name: TW Hydrae - open clusters and associations: individual (β Pictoris, Tucana) - Stars: Evolution - Stars: Kinematics - Stars: Pre-Main-Sequence
Table 1: TWA NN (Nos 21-25) added.
erratum vol. 603, p. 804 (2004)
Table 1: TWA numbers should have been applied only to TWA members, not to beta Pictoris moving group and Tucana-Horologium association stars.
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