Program: GN-2005B-Q-30

We propose GMOS spectroscopy of low mass stars in two very young open clusters with nuclear turn-off ages of about 15Myr. We will determine the luminosity at which lithium remains unburned, yielding precise, almost model-independent "lithium depletion boundary " (LDB) ages. These would be the first clusters younger than 35Myr to have absolute ages measured in this way, and would enable us to: 1. Constrain uncertain physics (particularly core convective overshoot) in the very high-mass stars of the same clusters, by demanding that their LDB and nuclear turn-off ages agree. 2. Investigate convective efficiency in youthful low-mass stars by demanding agreement between LDB ages and isochronal fits to low-mass stars descending their Hayashi tracks. 3. Subsequently use these clusters to follow the evolution of angular momentum, the dispersal of dust and debris discs, and the decay of magnetic activity among young stars over this critical, yet poorly studied, time interval.