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E. L. N. Jensen (Swarthmore College)
In 1978, Herbig first noted that the K7 star TW Hya had earmarks of a T Tauri star---variability, strong H\alpha emission, and high Li abundance---but was not associated with any dark cloud. Subsequent work added further evidence for its youth (excess infrared and submillimeter continuum emission, molecular line emission, strong and variable x-ray emission), culminating in a Hipparcos parallax measurement that places it unambiguously above the main sequence at an age of ~107 years. Further studies have shown that a number of other young stars are present near TW Hya, but the origin of these stars, dubbed the TW Hya Association, remains unclear. In addition, other pre--main-sequence stars have been discovered far from known regions of star formation. Were these stars formed in situ, or are they escapees from known star-forming regions? How common are such stars, and thus how unusual is the TW Hya Association? I will review the past work that has brought us to this point in our understanding of this group of stars and of isolated young stars in general. In particular, I will focus on the observational challenges that face us in trying to find stars in the 107--108 yr age range, and on the potential benefits for our understanding of star and planet formation when we do.
The author(s) of this abstract have provided an email address for comments about the abstract: ejensen1@swarthmore.edu