From common proper motion and signatures of youth, researchers have identified about 30 members of a putative TW Hydrae Association. Only four of these had parallactic distances from Hipparcos. We have measured parallaxes and proper motions for 14 primary members. We combine these with literature values of radial velocities to show that the Galactic space motions of the stars, with the exception of TWA 9 and 22, are parallel and do not indicate convergence at a common formation point sometime in the last few million years. The space motions of TWA 9 and 22 do not agree with the others and indicate that they are not TWA members. The median parallax is 18 mas or 56?pc. We further analyze the stars' absolute magnitudes on pre-main-sequence evolutionary tracks and find a range of ages with a median of 10.1?Myr and no correlation between age and Galactic location. The TWA stars may have formed from an extended and filamentary molecular cloud but are not necessarily precisely coeval.
展开▼
机译：通过青年的正常正常运动和签名，研究人员确定了推定的TW Hydrae协会的大约30名成员。其中只有四个与Hipparcos的视差距离。我们已经测量了14个主要成员的视差和适当的运动。我们将这些与径向速度的文献值相结合，以表明恒星的银河空间运动（TWA 9和22除外）是平行的，并且并不表示在过去几百万年的某个时间某个共同的形成点会聚。 TWA 9和TWA 22的空间运动与其他运动不一致，表明它们不是TWA成员。中值视差为18 mas或56？pc。我们进一步分析了主序前演化轨道上的恒星绝对大小，并发现了一个年龄范围，中位数为10.1？Myr，年龄与银河位置之间没有相关性。 TWA星可能是由延伸的丝状分子云形成的，但不一定精确地同时形成。
展开▼
