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Proper motion and X-ray selected search for new members of the young TW Hya association
We have searched for new members of the TW Hya association (TWA) amongunidentified ROSAT X-ray sources by identifying them in proper motioncatalogues and selecting those that would be consistent with kinematicalmembership to the TWA. Spectroscopic follow-up observations of 19 membercandidates revealed the detection of moderate lithium absorption linesfor the following three stars: GSC 7206 845, TYC 7216-55, and TYC7247-12. The isochronal ages of the latter TYC stars are estimated to be 20 Myr while the other one has 100 Myr age based on akinematic distance estimate that assumes TWA membership. However, themoderately Li-rich stars are not likely to be new pre-main sequencemembers of TWA partly because of the discrepant radial velocities.Infrared follow-up imaging in the H-band for the 3 stars shows companioncandidates near two of them. While one system (TYC 7216-55) is probablya near-equal-magnitude stellar binary, our follow-up H-band spectrum ofthe faint companion candidate near GSC 7206 845 shows that it is insteada background K-type star rather than a companion.Based on observations obtained in ESO programs 66.C-0540, 66.C-0138B,and 68.C-0009 on La Silla, Chile, as well as with ROSAT and theUniversity of Hawaii Institute for Astronomy 2.2m telescope on MaunaKea.
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