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E.E. Mamajek (Steward Observatory, The University of Arizona)
Post-T Tauri stars are low-mass, pre-MS stars which have ceased accreting, and are not necessarily near star-forming molecular clouds. Historically, they have been difficult to identify due to their benign spectroscopic signatures compared to T Tauri stars. The advent of the ROSAT All-Sky Survey and recent astrometric surveys has, however, accelerated the pace of discovery of these young suns. The nearest post-T Tauri stars will be important targets for ground-based adaptive optics imaging, and to missions like SIRTF, SIM, JWST, and TPF, for characterizing dust disks and planetary systems around young solar analogs.
I discuss the results of a spectroscopic survey to identify solar-mass pre-MS stars in the nearest OB subgroups: Lower Cen-Cru and Upper Cen-Lup. I identify 110 stars as likely members based on lithium abundance, proper motions, X-ray luminosities, and surface gravity. I find that ~1% of pre-MS G/K-type stars with mean age ~13 Myr show signs of disk accretion -- a tight constraint on the lifetimes of optically-thick accretion disks around Sun-like stars.
I conducted a 10 \mum imaging survey of post-T Tauri members of the ~30-Myr-old Tucana-Horologium association, with the MIRAC mid-IR camera on Magellan I, in order to find evidence of dusty disks with orbital radii of <3 AU. The results suggest that if typical 30 Myr-old stars have dust disks, their dust grain surface area is less than a few thousand times that of our inner solar system zody disk.
I will also discuss a method to identify the nearest, youngest stars in the ROSAT All-Sky Survey using proper motions. The method is essentially a variation of the cluster parallax method, but generalized to velocity fields with non-zero Oort parameters, appropriate for young field stars in the solar neighborhood.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.