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A. Steinhauer, C. P. Deliyannis (Indiana U.)
We present WIYN/Hydra high signal-to-noise (about 200), high resolution (about 20,000) lithium (Li) observations of over 200 A, F, and early G stars in the young star cluster M35 with the goal of elucidating our understanding of the physical mechanism(s) that forms the lithium gap in F stars. M35 is a very rich open cluster whose age, while somewhat uncertain, is certainly older than the Pleiades, possibly by as much as 100 Myr. This makes it an interesting cluster for testing the physical origin of the lithium gap. The Li gap is a severe depletion of lithium in F stars that occurs during the main sequence, in stark contradiction to the predictions of standard (no rotation, mass loss, diffusion, magnetic fields) stellar evolution theory; thus there is additional physics at work. Mass loss, diffusion, and slow mixing induced by rotation or waves have all been proposed as the cause of the Li gap. While each mechanism produces a gap, their timing differs: to explain the Hyades Li data, mass loss and diffusion act later, closer to the age of the Hyades (1 Gyr), whereas rotationally-induced mixing acts earlier, closer to the age of the Pleiades (100 Myr), which shows no lithium gap, or at best just a hint of one. We discuss our M35 Li data in the context of these predictions. This work is supported by NSF Grant AST-9812735.